review article potential therapies by stem cell-derived...

Review ArticlePotential Therapies by Stem Cell-Derived Exosomes inCNS Diseases Focusing on the Neurogenic Niche

Alejandro Luarte1 Luis Federico Baacutetiz234 Ursula Wyneken1 and Carlos Lafourcade1

1Laboratorio de Neurociencias Facultad de Medicina Universidad de Los Andes Monsenor Alvaro del Portillo 12455Las Condes 7550000 Santiago Chile2Center for Interdisciplinary Studies on the Nervous System (CISNe) Universidad Austral de Chile Valdivia Chile3Program for Cell Biology and Microscopy Universidad Austral de Chile Valdivia Chile4Instituto de Anatomıa Histologıa y Patologıa Facultad de Medicina Universidad Austral de Chile Valdivia Chile

Correspondence should be addressed to Carlos Lafourcade clafourcadeuandescl

Received 12 February 2016 Accepted 27 March 2016

Academic Editor Yanfang Chen

Copyright copy 2016 Alejandro Luarte et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Neurodegenerative disorders are one of the leading causes of death and disability and one of the biggest burdens on health caresystems Novel approaches using various types of stem cells have been proposed to treat common neurodegenerative disorderssuch as Alzheimerrsquos Disease Parkinsonrsquos Disease or stroke Moreover as the secretome of these cells appears to be of greater benefitcompared to the cells themselves the extracellular components responsible for its therapeutic benefit have been explored Stemcells as well as most cells release extracellular vesicles such as exosomes which are nanovesicles able to target specific cell typesand thus tomodify their function by delivering proteins lipids and nucleic acids Exosomes have recently been tested in vivo and invitro as therapeutic conveyors for the treatment of diseases As such they could be engineered to target specific populations of cellswithin the CNS Considering the fact that many degenerative brain diseases have an impact on adult neurogenesis we discuss howthe modulation of the adult neurogenic niches may be a therapeutic target of stem cell-derived exosomes These novel approachesshould be examined in cellular and animal models to provide better more effective and specific therapeutic tools in the future

1 Introduction

Highly prevalent CNS disorders that are associated with neu-rodegeneration include Parkinsonrsquos Disease (PD) AlzheimerrsquosDisease (AD) Huntington Disease (HD) stroke and epi-lepsy The classification of neurodegenerative disorders isespecially challenging as different disorders may share sim-ilar clinical manifestations Still classifications are nowadaysbased on those clinical manifestations andor the site of thebrain that is affected disorders affecting the basal gangliain the forebrain affect movement and these can be dividedinto hypokinetic (eg PD) or hyperkinetic (eg HD) Anexample of a disorder that involves the cerebral cortex thatdevelops into dementia is AD whereas an example of oneinvolving the spinal cord is amyotrophic lateral sclerosis(ALS) [1] A common trait for a considerable number ofthese disorders is through disparate mechanisms the accu-mulation of insoluble proteins either extra- or intracellularly

AD is characterized by the aggregation of 120573-amyloid and themicrotubule associated protein Tau PD by the accumulationof the nerve terminal protein 120572-synuclein ALS by depositionof phosphorylated TDP43 (a transcriptional repressor) andan enzyme that removes superoxide radicals superoxidedismutase 1 (SOD1) and HD by the accumulation of themutant protein huntingtin [2 3] Despite the wealth ofknowledge that has been generated in the past decades areliable cure for neurodegenerative disorders remains elusiveThere are many reasons with varied degrees of difficultybehind this inability to transform experimental informationinto successful medical treatments The complexity of thecentral nervous system (CNS) and the multifactorial natureof these disorders are themost obvious challenges researchershave to tackle when attempting to predict the onset of apathology and to ameliorate the burden of neurologicaldisorders In this review we will describe evidence showing

Hindawi Publishing CorporationStem Cells InternationalVolume 2016 Article ID 5736059 16 pageshttpdxdoiorg10115520165736059

2 Stem Cells International

that stem cell-derived exosomes might be a new treatmentfor several CNS disorders considering a new interplay withneurogenic niches Thus we propose that engineered stemcell-derived exosomes targeted to the neurogenic niche areagents with therapeutic potential

2 Management of CNS DisordersCurrent State

Even when animal models are indispensable and have pro-vided researchers with important and detailed informationon the development and impact of neurological disordersmostmodels are still incapable of faithfully reproducing thesedisorders [4 5] thus providing an incomplete tool to fully testthe advantages of new drugs or treatments Further compli-cations arise when considering that many disorders progressslowly and as mentioned before that seemingly differentdisorders may be happening simultaneously Furthermorea disorder may express an important number of apparentlydisparate debilitating problems (Huntington Disease egis characterized not only by movement disorders but bya wide array of cognitive and behavioral disabilities [6])Considering these adversities a considerable amount of efforthas been placed not only on treating a specific disorder butalso on discovering biomarkers that may facilitate predictingor recognizing neurodegenerative pathologies during theearly stages of its development where treatments are usuallymost effective

The currently used methods to diagnose neurodegener-ative disorders ante-mortem may range from neuropsycho-logical assessments (eg cognitive tests to evaluate memoryloss in patients suffering from Alzheimer disease (AD) [7])to neuroimaging These methods are not always reliable duein part to the difficulty imposed when trying to differentiatethem from other disorders that share common featuresFor instance diagnosis of Parkinsonrsquos Disease (PD) can beconfounded by other diseases that present clinical syndromesof parkinsonism and a study applying recent criteria [8]to diagnose patients with AD was highly successful (95)when considering nondemented patients but this successrate decreased almost by half when considering a populationof patients with other types of dementia [9]These difficultiesare being tackled and they can be divided for organizationalpurposes in attempts to discover reliable biomarkers on theone hand and endeavors to find appropriate therapies on theother hand

21 Common Biomarkers for CNS Diseases Currently usedbiomarkers rely heavily on imaging technologies which canbe used to study from whole brain structures to proteinaggregates Magnetic resonance imaging (MRI) has beenused for example to associate changes in ventricular volumewith cortical senile plaques (SP) and neurofibrillary tangles(NFT) common features of AD thus being proposed asa diagnostic strategy [10] Nevertheless it may be difficultto separate the changes observed in AD patients from thechanges observed in those suffering other types of dementiaor even the elderly people [11 12] Diffusion MRI has proven

successful in identifying PD patients from those sufferingfrom parkinsonism [13] and diffusion-weighed MRI andcomputer tomography (CT) are the most common ways ofdetecting early cases of acute stroke [14 15] Despite thesometimes prohibitive costs positron emission tomography(PET) is a promising option for early diagnostic of a disorderas well as a powerful tool to determine the success of atreatment over time although the injection of radioactivetracers in the blood makes PET a slightly more invasivetechnique Newly developed tracers for PET have expandedthe possibilities of this technique allowing it to detect notonly the activity of the brain through blood flow and glucoseconsumption but also parameters that may signal the devel-opment of a neurological disorder [16] Examples of thesetracers include 18F-DOPA which has been used to diagnosePD and compounds that bind to amyloid plaques such as18F-florbetapir which presents a higher uptake inADpatientsthan controls [17] and has been recently approved by the FDA[18] Magnetic resonance spectroscopy has also been used todiagnose early stages of PD showing an interesting potentialwhen considering the noninvasiveness of this technology andthe lower associated costs [19]

22 Searching for New Noninvasive Biomarkers for CNSDiseases Relevance of Exosomes andMicroRNAs Body fluidsare also promising sources of molecular biomarkers whichcan be divided into three categories molecules (eg 8-hydroxydeoxyguanosine a byproduct of DNA oxidation thatis found at higher levels in the urine of PD patients)proteins (eg protein aggregates) andRNAs (eg noncodingmicroRNAs see below) [20] The advantage of biomarkersobtained from body fluids (ie cerebrospinal fluid CSFblood plasma serum saliva and urine) is the possibilityof searching for a large number of molecules at once forexample by the use of proteomics or genomics at earlierstages than those exposed by imaging Efforts are being madeto measure the higher levels of glial fibrillary acidic protein(GFAP) in blood for example as an earlymarker of traumaticbrain injuries and stroke as well as a way to follow up on aspecific treatment for these patients [21] Having a biomarkerthat can be accessed from a body fluid has the addedadvantage of not relying onmore expensive technology (suchas imaging equipment) and in some instances (eg salivaandurine) of avoiding invasivemethods altogetherThemaindisadvantage of obtaining biomarkers from body fluids is thelow levels of molecules and the heterogeneity of these assuch samples arise from a wide number of tissues Thus tocircumvent this difficulty and to improve the specificity ofthe biomarker small circulating extracellular vesicles termedexosomes have gathered the interest of biomedical researchesThese extracellular nanovesicles can be isolated from allbodily fluids and they carry a complex cargo consisting ofvarious types of RNA (eg ribosomal RNAs long noncodingRNAs and microRNAs) proteins lipids and DNA that inpart depends on the tissue of origin and its ldquohealth or diseaserdquostate [22ndash24] Catalytically active enzymes like PTEN as wellas bioactive lipids such as prostaglandins can be transferedby exosomes to target cells [25 26]

Stem Cells International 3

Exosomes carry a set of common proteins considered asldquoexosome markersrdquo most of them related to their biogenesis[22] In addition they carry molecules that reflect theircellular origin for example membrane and intraluminalproteins In the case of transmembrane proteins they can beused to immunoisolate exosomes of a specific cellular originseparating them fromother exosomes and thus improving thesensitivity of exosomes as biomarkers [27] In line with thatneurodegenerative disorders are characterized by exosomesthat carry themisfolded protein type found in these disorders(eg 120573-amyloid in AD and 120572-synuclein in PD) [28] Of all themolecules carried by exosomes microRNAs (miRNAs) arethe ones that have gathered the most interest in the last yearsThese short (sim22 nucleotides long) noncoding RNAs areconsidered as ldquomaster regulatorsrdquo of translation one miRNAmay repress translation of several (even a hundred) mRNAsOne of the aspects that make miRNAs per se promisingbiomarkers is that they can be found in body fluids thatare easily accessible such as plasma where they appear tobe transported by lipoproteins and exosomes or bound tothe protein argonaute-2 a key component of the silencingcomplex mediated by miRNAs [29] Exosomes provide anenriched source of miRNAs for biomarker profiling [30] andsets of miRNAs obtained from exosomes circulating in theblood have been proposed as biomarkers for cancer diagnos-tics [31 32] More recently miRNAs present in blood-derivedexosomes have been linked to specific neurodegenerativedisorders such as AD PD and brain injury [33 34]

In this context the possibility of extracting high qualitymiRNAs and profiling them using well-established methodshas also contributed to making them a favored area ofstudy in the search for biomarkers [35] Researchers haveattempted to profile the miRNA identity from body fluids ofpatientswith themost commonneurodegenerative disordersand even when the number of miRNAs associated withneurodegenerative disorders is continually increasing thereare important difficulties that need to be considered if someof these molecules are going to be proposed as reliablebiomarkers The methodologies used for these profiles arenot consistent between laboratories and the sample sizes areusually small thus validating the miRNAs associated withneurological disorders has proven difficult [36] Thereforealthough there are increasing reports on the application ofexosome-derivedmiRNAs as biomarkers for various diseasesit is still an ongoing process with a considerable degreeof variability and efforts are constantly made to increasespecificity and sensitivity [37]

3 Need for New Therapies inDebilitating CNS Diseases

Perhaps the most striking advance in the treatment of aneurodegenerative disorder was the discovery made half acentury ago that administration of L-dopa a precursor ofthe neurotransmitter L-dopamine improved many of thesymptoms associated with PD in which dopamine neuronsin the substantia nigra degenerate Thus this treatmentmerely improves symptoms by elevating levels of the neu-rotransmitter but it does not replace or improve survival

of degenerating neurons In spite of this shortcoming thisdrug still remains the main line of treatment for PD patientsthough it may present side effects such as dyskinesias andit is unable to alleviate the nondopaminergic symptoms(eg dementia and psychiatric disorders) that become moreprevalent as the disease progresses [38 39] The successof L-dopa has not been replicated when trying to modifythe neurotransmitter milieu affecting other neurologicaldisorders associated with degeneration of specific neuronalpopulations gamma-aminobutyric acid (GABA) agonistswere unable to improve patients suffering from Huntingtonrsquosdisease and cholinesterase inhibitors have not been suc-cessful in significantly improving the cognitive impairmentsobserved in patients of AD [40] This has led to exploringother alternatives for example related to more efficientdelivery of drugs across the blood-brain barrier with the useof nanotechnology [41] and to the use of vaccines againstprotein aggregates characteristic of AD (tau or 120573-amyloid[42])

4 Stem Cells as a New Treatment forCNS Diseases

Among the innovative therapeutic strategies the use of stemcells has gained particular attentionThese cells are capable ofself-renewal and can be classified according to their capacityto form a specific tissue or cell lineage totipotent cells canform all the cells of the organism pluripotent cells can formthe tissues from the three germinal layers (ie endodermectoderm and mesoderm) and multipotent cells can giverise to a certain lineage of cells According to their originthey can be divided into embryonic or adult (ie postnatal)and in both cases there are advantages and disadvantagesassociated with their use in the clinic The main advantageof embryonic stem cells is their capacity to generate a vastnumber of cell types The main disadvantages of these cellsare the ethical concerns raised by the use of embryos andthe likelihood of triggering an undesired immune responseor the formation of tumors Adult stem cells have a reducedpotential compared to their embryonic counterpart but sincethey can be obtained from the same patient the chancesof an immune response are significantly lower The risk oftumor formation when using these cells is also lower andthe ethical controversies are avoided altogether [43ndash45] Aremarkable accomplishment was the reprogramming of adultsomatic cells to pluripotent ones (induced pluripotent stemcells iPSCs) by transfection of specific transcription factors[46 47] therefore making them more similar to embryonicstem cells but without the degree of immunoreactivity andthe ethical controversies of the latterThese cells are currentlyused to model a wide variety of diseases from muscularto neurological disorders that have an elusive solution Thepossibility that these cells lead to tumorigenic process dueto incomplete reprogramming or the inhibition of tumorsuppressor genes during the reprogramming stages has so farhindered their use in the clinic [48]

Mesenchymal stem cells (MSCs) are multipotent progen-itors with self-renewal capacity that confer neuroprotectionand can be isolated from umbilical cord (UC) bone marrow


(BM) adipose tissue and evenmenstrual fluids among othersources [49] MSCs have several features that make themuseful for CNS disease treatment for instance they canbe isolated by almost noninvasive procedure being easilycultured and expanded (and thus suitable for molecularengineering) MSCs also have low immunogenicity andtumorigenic potential their use has no ethical constraints[50] and several works have confirmed their healing abilitieson the CNS For example MSCs obtained from the bonemarrow improved behavioral outcomes in a rat model ofPD and decreased depressive-like behavior by promotingneuronal growth and survival [51 52] Moreover BDNF-producing humanMSCs transplanted in the brain of a rodentPD model were able to integrate successfully and delivertrophic factors [53]MSCs fromumbilical cord enhance brainangiogenesis after stroke [54] and MSCs from adipose tissueincrease the number of motor neurons and motor outcomesin a mouse model of ALS [55]

Multipotent stem cells can also be found in neurogenicniches of the adult CNS continuously giving rise to neuronsor glial cells This neurogenic process is severely affected inseveral CNS diseases [56 57] thus the idea of regulatingthe neurogenic niche in neurological disorders has recentlyemerged [23 50 56]

5 Importance of Neurogenic Niches in CNSDisorders A Potential Therapeutic Target

In the mammalian brain there are defined regions termedneurogenic niches areas with the proper environment thatare able to support and modulate neurogenesis during adult-hood [58] The first validated and most studied neurogenicniches of the brain are the subventricular zone (SVZ) ofthe lateral ventricles and the subgranular zone (SGZ) ofthe dentate gyrus in the hippocampus [59] Neverthelessother brain regions have been proposed as having putativeneurogenic niches (eg substantia nigra cerebellum andamygdala) though the extent at which this happens in vivoand in humans remains controversial for some of themNeurogenesis has been shown to occur in the spinal cord ofprimates after injury [60] and recent studies have shown thatadult neurogenesis is active in the hippocampus [61] and inthe striatum [62 63]

These findings raise the question as to whether suchprocesses can be manipulated for therapeutic purposes Anumber of experiments have already shown the impactthat some disorders have on these niches and their rolein improving pathological conditions Animal models ofchronic stress show a reduction in the levels of hippocampalneurogenesis and some of the beneficial actions broughtupon by antidepressants have been shown to involve mod-ulation of the neurogenic niche [64ndash66]

In postmortem brain tissue of humans with PD there isa reduction of proliferating cells in the subependymal zone(SVZ) and the SGZ and similar results have been observed inanimalmodels of PD Proteins like 120572-synucleinmay be one ofthemolecules playing an important role in thesemechanismsas their accumulation disrupts adult neurogenesis [67 68]The impact of AD in adult neurogenesis is more elusive as

both the increase and reduction of neurogenic markers havebeen reported on the hippocampus of humans discrepanciesthat may be partially explained by the severity of the disorderat the time the samples were gathered for example tissueobtained from the early stages versus samples collected fromthe later and more severe manifestations of the pathologySimilarly animal models show disparate results that mayalso depend on the model being used age and strain of theanimals among others [57] Neurogenesis is enhanced after astroke episode in humans and in animalmodels and recoveryafter a stroke in animal models is facilitated or diminishedwhether neurogenesis is enhanced or prevented respectively[69 70] Human striatal neurogenesis is gradually reduced inHD as well [62] Figure 1 shows a summary of several animalmodels of CNS diseases (and memory processing) related tothe proper functioning of neurogenic niches

MSCs may act by regulating neurogenic niche functionas has been already shown in the SGZ of the hippocampuswhere implantation of these cells in the DG increased theproliferation of endogenous NSCs as well as their differen-tiation into neurons [80] It was also shown that cisternamagna injections of human UC-MSCs activated endogenoushippocampal neurogenesis and significantly reduced A12057342levels [81] In fact there seems to be enough evidence topropose that the interplay between MSCs and the differentneurogenic niches could be a key factor in the intervention ofseveral CNS pathologies [50] Nevertheless the regenerativeproperties of MSCs when injected are probably indirect asonly a small proportion of the cells transplanted reach theirtarget zone [82] Coherently administration of MSCs afterbrain injury induced recovery with low MSCs engraftmentin the ischemic zone [83] Therefore therapeutic effects arethought to arise from the release of extracellular factors(membrane-bound and soluble) among them extracellularvesicles like exosomes have gained much attention Nextwe will provide a detailed description of the nature of thesevesicles in order to understand their potential as therapeutictools that modulate neurogenic niche function

6 Extracellular Vesicles and Exosomes

Several kinds of extracellular vesicles (EVs) have beendescribed nearly 30 years ago among them are exosomescharacterized by a nanosize of 30ndash100 nm apoptotic bodiesof around 1 120583m and ectosomes of 100 nmndash1120583m a conceptin which microvesicles microparticles and shedding vesicleshave been included [84ndash86] While exosomes originate fromthe endocytic route the rest of the vesicles emerge directlyfrom plasma membrane The molecular components thatgive rise to exosomes are highly conserved among most ofeukaryotic organisms and there is evidence showing thatvirtually all kinds of cells and extracellular fluids (even inprotozoa) contain exosome-like EVs [87 88] It is importantto have in mind that the precise distinction from otherkinds of EVs is to some extent difficult [89] EVs enrichedin exosomes are harvested from extracellular fluids afterseveral centrifugation steps to get rid of floating cells andcellular debris followed by one or two ultracentrifugationsteps that end up with the recovery of a pellet obtained


SVZ SGZ Spinal cord central canal

Huntington [72] stroke [73]

PD [71] epilepsy [74] and MS [75]Memory [76] stress [77]

stroke [73] and epilepsy [74]

MS [78] ALS [79]

Figure 1 Animal models of CNS diseases (and memory processing) potentially linked to neurogenic niche alterations Schematicrepresentation of brain coronal slices and transverse section of spinal cord Neurogenic niches are indicated in red lines and arrows SVZcorresponds to subventricular zone SGZ corresponds to subgranular zone spinal cord central canal niche is also depicted The referencenumber for each pathology associated with the neurogenic niche is indicated References PD [71] Huntington [72] stroke [73] epilepsy(SVZ) [74] MS (SVZ) [75] memory [76] stress [77] stroke (SGZ) [73] epilepsy (SGZ) [74] MS (spinal cord central canal) [78] ALS [79]

at 100000timesg (or more) for at least one hour [90] In thepresent review wewill use an operational definition of the EVfractionwe are calling exosomes that is pellets obtained fromextracellular fluids (depleted of cells and debris) that werecollected after 100000timesg ultracentrifugations for at least onehour Nevertheless all EV types have common propertiesthat allow them tomediate intercellular interactions elicitingseveral kinds of cellular responses in target cells that we willfurther discuss

61 Exosome Biogenesis and Content The concept of exo-somes as extracellular vesicles was first settled with thedescription of multivesicular bodiesrsquo (MVBs) fusion with theplasma membrane during the maturation of reticulocytesto red blood cells where intraluminal vesicles (ILVs) arereleased to the extracellular space [91ndash94] These structuresbecame notorious because of their novel location (outsidethe cell) and their peculiar topologic organization in whichthe lumen is equivalent to the cytosolic portion of thecell and its membrane has the same orientation of theplasma membrane Much effort has been done to eluci-date the mechanism of MVBs biogenesis and the sortingof cargo into ILVs [22 89 95 96] Two main ways fordestining cellular components to ILVs have been describedthe ESCRT (endosomal sorting complex required for trans-port) dependent and ESCRT independent mechanisms TheESCRTmachinery is composed of four complexes (ESCRT-0ESCRT-I ESCRT-II and ESCRT-III) that sequester ubiqui-tinated membrane proteins into an endosomal microdomainand induce an invagination that generates ILVs formationharboring this cargo Sorting mechanisms of soluble proteinsinto exosomes have been related to microautophagy [97] orphysical interactions with sorted transmembrane proteinsbut it is still a less explored field On the other handESCRT independent incorporation of cellular componentsto exosomes is mediated by ceramide induced ILVs budding[98 99] Other proteins are sorted by variations of thecanonical ESCRT dependent model [100 101] In relation tothe incorporation of nucleic acids into ILVs some miRNAs

harboring the GGAG motif in the 31015840 portion bind to sumoy-lated proteins such as hnRNPA2B1 prior to its destinationinto ILVs [102] Another destination motif for miRNA toexosomes was found to be dependent on uridylation also at31015840 end of the nucleic acid [103]

Exosomes contain proteins related to several cellularfunctions such as vesicular transport (Rab GTPases annex-ins and flotillins) heat shock (HCPHSP 70 and 90) MVBsbiogenesis (Alix and TSG 101) integrins and tetraspanins(CD63 CD9 CD81 and CD82) [104 105] cytoskeletalproteins (actin syntenin and moesin) signal transductionproteins (kinase proteins) andmetabolic enzymes (GAPDHLDHA PGK1 aldolase and PKM) [106] Exosome markersare typically enriched in MVBs Thus some markers arecytosolic proteins like HSP70 which mediates microau-tophagy of cytosolic proteins to MVBs [97] and proteinsrelated to exosome biogenesis such as programmed celldeath 6 interacting protein (PDCD6IP) also known asALIX and tumor susceptibility gene 101 protein (TSG101)Besides membrane associated proteins like LAMP-3 (orCD63 enriched in late endosomes and lysosomes) [107]CD81 MHCII (restricted to specific cell types [108]) andCD9 [90] as well as lipid raft enriched proteins such asflotillin-1 [109] and flotillin-2 [110] are considered exosomemarkers In addition there are proteins that have been shownto be absent in different exosome preparations such asproteins from the endoplasmic reticulum for example Gp96calnexin and the Golgi apparatus for example GM130 andfrom mitochondria for example cytochrome C [90 111]In addition exosomal membranes harbor a characteristiclipid profile that resembles a lipid raft composition contain-ing cholesterol ceramide sphingomyelin and phosphatidyl-serine [112]

62 Mechanisms of Interaction of Exosomes with Target CellsA huge volume of data shows that exosomes transfer severalkinds of functional biomolecules that gate a wide spec-trum of changes on cellular processes [25 113ndash117] Severaluptake mechanisms have been proposed for internalizing


a vesicle into a cell most of which are mediated by theendocytic route such as clathrin mediated endocytosis [118]phagocytosis [119] lipid rafts mediated internalization [120]and macropinocytosis [121] and also by direct fusion withthe plasma membrane (although this is supposed to be aminor contribution [122] and also technically difficult toprove [113]) Regardless of the mechanism before vesiclesenter the cell they may dock plasmamembrane componentsamong which we can find integral transmembrane proteinssuch as CD81 or CD9 (which are also exosome markers)integrins like av (CD51) and b3 (CD61) and extracellularmatrix components such as heparan sulfate proteoglycans(HSPGs) [123] After delivery of exosomes into endocyticcompartments low pHwould favor vesicle membrane fusionwith cell membranes [117] thus most exosomal lipids wouldreach the plasmamembrane indirectly as they come from theendocytic route All this explains lipids and transmembraneassociated proteins transfer but what about functional deliv-ery of miRNAs

It has been shown that MVBs tend to be in closeassociation with the RNA-induced silencing complex orRISC a multiprotein complex which incorporates miRNAand mediates the translational repression of a given targetor mRNA degradation [124] Although still not provenendocytosed exosomes could behave as ILVs that fuse withMVBs internal surrounding membrane (called back-fusion[113]) that would allow RNAs in the lumen of ILVs to findthe cytosolic RISC complex and be functional The rest ofthe lumenal content should be also delivered this way to thecytosol

Exosomes may elicit cellular responses by ligand medi-ated transductional pathways Almost a decade after thefirst description of exosomes Raposo et al [125] describedexosomes as carriers of major histocompatibility complexes(like MHCII) loaded with antigenic peptides that were ableto help B lymphocytes during the immune priming of T cellsFurthermore the same group showed that dendritic cell-derived exosomes harboring MHCII loaded with tumoralepitopes could function as a brand new oncogenic treatment[126] Since then several works have tried to use exosomes ascarriers of molecular and even pharmacological factors

7 Therapeutic Potential of StemCell-Derived Exosomes Focusingon the Neurogenic Niche

One of the key limits for a noninvasive systemic therapy ofCNS disorders is the fact that several substances are not ableto cross the blood-brain barrier (BBB) This is a multicellularinterface composed roughly of pericytes astrocytersquos end feetand an astrocyte induced modified epithelium that becomesparacellularly impermeable to certain molecules (eg drugs)and tomost of the cells of the bloodstream [127] In relation tostem cell therapy there is evidence that systemically injectedMSCs are able to cross the BBB and reach the ldquodamaged zonerdquoof the brain although this is to some extent controversialbecause the integrity of the BBB can be compromised byinflammatory conditions [128]

Regarding new potential therapies for CNS disorders oneof the most outstanding results in the field is the fact thatsystemically injected exosomes are able to cross the BBB andachieve the brain parenchyma For instance it was shown thatneurons can be specifically targeted to receive a functionalsiRNAusing previously transfected and engineered exosomes[129]The same groupwas able to show that systemic deliveryof targeted exosomes containing a siRNA against 120572-synucleinreduced the mRNA and protein levels of 120572-synuclein inthe brain [130] In a similar approach to circumvent theBBB constraints it has been shown that intranasally injectedexosomes are able to deliver curcumin to microglia in thebrain parenchyma inducing a clear recovery in an animalmodel of multiple sclerosis termed experimental autoim-mune encephalomyelitis [131]The same administration path-way was used by this group to deliver miR-17 in nanovectorsto inhibit brain tumor progression [132] With respect to aPD model it was found that macrophages-derived exosomesmade to carry the enzyme catalase are able to reach brainparenchyma (also by intranasal administration) and induceneuroprotective changes in mice [133]

With regard to stem cell-based therapy systemic admin-istration of MSCs exosomes can improve some of the neu-rological conditions observed in animal models of strokeand certain neuronal properties can be enhanced or reducedby upregulating or lowering the levels of specific miRNAin MSCs [134] For example bone marrow mesenchymalstem cells (BM-MSCs) treated with ischemic brain extractproduced exosomes with neuroprotective effects in a strokemodel in rats inducing functional recovery mediated bytransfer of miR-133b in these vesicles [135] Similarly Doepp-ner et al found that systemically injected human BM-MSC-derived exosomes were able to improve angiogenesis andneurogenesis inmice Interestingly they found similar resultswith direct use of parental BM-MSCs [136]With these recentresults several questions arise

71 What Are the Advantages of Using Stem Cell-Derived Exo-somes instead of Parent Stem Cells for Therapeutic PurposesExosomes may provide a way to increase the possibilities of acell to reach many other places in the body and due to theirsmall size they expand the ldquointeracting surface of a cellrdquo inrelation to its volume [137] On that virtue exosomes mayincrease the surfacevolumen ratio and amplify ligand gatedsignaling pathways and the transfer of biomolecules fromstem cells to target tissues

There are several considerations about the advan-tagesrisks of exosomes versus stem cell therapy some ofthem already discussed elsewhere [138] Among the risks ofcell therapy with stem cells are negative tumor modulationmalignant transformation and obstruction of small vesselsWith regard to the cell therapy advantages we might find thecontinuous release of exosomes (cell is alive) soluble factorsand the potential differentiation and replacement of damagedcells [138] The advantages of exosome based therapy are lowimmunogenicity [139] no vascular obstructive effect [138]permeability through BBB [131] and the potential to developlarge scale cellular factories of engineered therapeutic vesicles[86]


Following the idea that stem cell therapies are usuallysafe it has been argued that the risk of stem cell-derivedexosome (harboring the same components)mediated therapyis expected to be low [140] Nevertheless exosomes havespecific physicochemical properties and a molecular signa-ture that demands us to be cautious For example parentalexosome producing cells may have very low or undetectablelevels of the abnormally folded prion protein (PrP) scrapie(PrPsc) on its surface but as previously mentioned thesmaller size of exosomes increases the surfacevolumen ratiocompared with the same amount of cells In fact it has beenshown that exosomes released from infected cells containingPrP and PrPsc are infectious [141] Thus although it seemsunlikely stem cell-derived exosomes may encompass toxicfeatures in some conditions that need to be assessed indepth in order to avoid them Recently several companiesare researching the therapeutic use of EVs in regenerativemedicine Some cautions about the potential oncogenic fea-tures of EVs have been thoroughly discussed in the literature[142] and some articles have highlighted the main concernsthat EV-based therapies should accomplish [140]

72 Could We Specify Key Components of Stem Cell-DerivedExosomes That Are Responsible for Their Therapeutic EffectsEach of the exosomal components may provide a peculiarinteracting mechanism Recently Katsuda and Oshiya dis-cussed the contribution of RNAs and proteins as mediatorsof the therapeutic effect of mesenchymal stem cell-derivedEVs [142] This analysis suggests that most of the functionaleffects of exosomes were explained by the presence of RNAsor specific known miRNAs instead of proteins Althoughthat was not an exhaustive search it may reflect the factthat RNAs and miRNAs are the most relevant cargoes inexosomes in terms of the ability of a small number ofmolecules to influence several proteinsenzymes from one ormore cellular pathways on target cells [143] Perhaps one ofthe most compelling evidences on the importance of miRNAexosomal content is a recent result by Collino et al [144]showing that the therapeutic effect of mesenchymal stromalcell-derived exosomes on acute kidney injury was abolishedwhen exosomes were released by cells depleted of Droshaprotein (producing a total downregulation of miRNAs)

Taking all of the above into consideration previouslymentioned evidence suggests that miRNAs are importantcomponents of the signaling mechanisms mediated by exo-somes as several of the functional effects can be repro-duced by a specific miRNA or be reverted with its block-adeinhibition [134 145] In consequence in the search for atherapeutic use of exosomes their miRNA content should bea fundamental factor if not the main to be considered

73 What Are the Advantages of Stem-Cells Exosomes Com-pared to Those Derived from Adult Cells The lack of clinicaltests and rigorous comparisons makes it difficult to assess theadvantage of using exosomes derived from adult cells com-pared to those obtained from stem cells However researchershave speculated that stem cell-derived extracellular vesiclesincluding exosomes may potentially transmit some of the

unique stem cell properties to other stem cells facilitat-ing stemness maintenance differentiation self-renewal andrepair [146ndash148] and that these properties appear to be inde-pendent of the tissue fromwhere the stem cells were obtained[149] Thus stem cell-derived exosomes may recapitulateseveral features of their cells of origin and may facilitatethe horizontal transfer of information that supports stemcell biology In addition stem cell-derived exosomes playa key role in the induction of reparative programs withininjured tissues Exosomes released fromMSCs are a source ofregeneration in several pathological environments and tissuessuch as myocardial infarction [149ndash151] drug-induced liverinjury [152] endotoxin-induced acute lung injury [54 153]and traumatic brain injury [154] In the latter exosomesderived from MSCs improve functional recovery after trau-matic brain injury by promoting endogenous angiogenesisand neurogenesis and by reducing neuroinflammation [154]

This makes stem cell-derived exosomes particularlyattractive compared to adult cell-derived exosomes butmore research will be needed to analyze the benefits anddisadvantages of one over the other

8 Engineering Exosomes to Target Theminto the Neurogenic Niche

Exosomes have been engineered in several ways Most ofthe modifications are aimed at docking the vesicle with thetarget cell using specific ligandreceptor binding strategiesto facilitate endocytosis For example Ohno et al usedexosomes harboring a GE11 peptide fused to the plateletderived growth factor (PDGF) receptor transmembranedomainThe GE11 peptide has high affinity for the epidermalgrowth factor receptor (EGFR) a protein enriched on severalhuman tumors of epithelial origin Strikingly GE11-positiveexosomes that contained the miRNA let-7 were able toinhibit tumor development in vivo [155] Another interestingexperiment was done using modified EVs expressing theneuron-specific rabies viral glycoprotein (RVG) peptide onthe membrane surface to deliver the siRNA targeting theopioid receptor mu into the brain This EV treatment wasshown to serve as a potential therapy for morphine addiction[156] In this case the RVG peptide was fused to LAMP2ba protein that is highly expressed in exosomes using a verysimilar approach to Alvarez-Erviti

Though speculative one might target the neurogenicniche in the CNS in order to increase differentiation of aspecific cell type or region For example the subgranularzone in the hippocampus related to mood disorders couldbe reached by stem cell-derived exosomes to improve neu-rogenesis Therefore assessing specific molecular features ofthe stem cell niche might help improve exosomal targetingAlthough attempts in that line have been undertaken [157]there is still insufficient information in the fieldNeverthelesswe are including a brief proposal of molecules that mightfunction to specifically target exosomes to the niche Oncea specific molecular target for delivery has been identifiedthe next step is to construct a recombinant protein fusinga mimetic peptide (able to bind target proteins) with the


extracellular domain of a highly expressed exosome markersuch as LAMP2 CD63 or flotillin-1

Although the knowledge of specific markers for neu-rogenic niches is scarce there are few enriched proteinsexposing an extracellular domain that would be able todock exosomes to certain cells For example it has beenshown that the neurogenic niche expresses the gap junctionproteins connexin 43 and connexin 26 While connexin 43is also enriched in astrocytes [158] connexin 26 has beenshown to be enriched in the neurogenic niche associatedwith the subependymal layer (SVZ) [159] This enrichmentis useful as it has been shown that Cx 43 mediates exosomedocking and internalization with target cells [160] Thusthe extracellular domain of a tetraspanin (eg CD63) couldbe fused with a mimetic peptide similar to others that areknown to bind connexins [161 162] or even to the smalldomain of Cx26 that retains the ability to interact withcellular hemichannels Another potential source to achievespecificity is to use the extracellular protein tenascin CTenascin C is highly enriched in the SVZ from embryonicand adult mice [163 164] This protein is mainly expressed inastrocytes but in some conditions neurons also can express it[165] Although tenascin C is an extracellular matrix (ECM)protein it might be used as a target to dock exosomesand favor its endocytosis into cells of the niche In fact asimilar phenomenon occurs with other ECM componentssuch as heparan sulfate proteoglycans (HSPGs) that functionas internalizing receptors of cancer cell-derived exosomes[115] Amimetic peptide that specifically binds tenascin C hasalready been developed [166]

There is a paucity of information about enriched proteinsin cells from other neurogenic niches such as SGZ and spinalcord Development of transgenic animals cell sorting [167168] and laser capture microdissection [169] of NSCs fromthe adult brain might help to fill this gap

Several proteins that mediate neurogenic niche mainte-nance and precursor differentiation such as Notch EGFR[170] and NogginBMP [171] have been identified This is apassionate field in neuroscience and there is a high volume ofcomplex data trying to define the key steps on maintenanceof NSCs and differentiation of NPCs into specific CNS celltypes [172ndash174]Thus the right pathway tomodify in the neu-rogenic niche for a therapeutic purpose is highly speculativeHowever as we have already mentioned the miRNA contentof exosomes seems to be themost effectivemolecular cargo toinduce cellular responses potentially appropriate for therapy

81 Engineering Exosomal Cargo What miRNAs Should BeTransferred by Exosomes in Order to Induce Neurogene-sisGliogenesis and Achieve Recovery on CNS Pathologies Anumber of miRNAs have been shown to be important inthe regulation of neurogenesis [175] and gliogenesis [176]In the neurogenic niche there is a continuous productionof NPCs that commit to a glial or neuronal fate by a seriesof complex molecular mechanisms [177] Among the NPCmolecules mediating this process Notch is considered tobe a master regulator of neural stem cells and neuronaldevelopment [178ndash181] In general its activation is relatedto maintenance of stemness in the niche and inhibition

of neurogenesis [182] Notch receptors and ligands (egDelta1) are both transmembrane proteins and thus suitableto develop an exosome targeted therapy A well studieddownstream target of Notch that has been shown to inhibitneurogenesis is the transcription factor hairy and enhancerof split 1 (Hes1) and it is known that traumatic braininjury induces Hes1 downregulation as a way to increaseneurogenesis and adapt to damage In fact downregulationof Hes1 via stereotaxic injection of RNA interference (RNAi)into the hippocampus (targeting SGZ) of rodents results ina significant increase in neuronal production and promotesthe differentiation of NPCs into mature neurons in the DGthus improving cognitive abilities after traumatic brain injury[181] Interestingly several miRNAs have been identified totarget Notch and its signaling related elements like Hes1among them miR-9 is one of the most studied elements forneurogenesis [183] miR-9 as well as miR-124 directly inducesreduction of Hes1 levels and in general promotes neuronaldifferentiation [184] miR-124 is also upregulated in SVZafter stroke suggesting a role in functional recovery [185] Inrelation to themiRNAs that promote glial fate and generationof astrocytes or oligodendrocytes from NPCs expression oflet-7 has been shown to promote glial fate and its inhibitionproduces neuronal commitment [186]

Another relevant miRNA target regulating NPCs dif-ferentiation (also in SVZ) is SIRT1 a protein deacetylaseimplicated in energy metabolism Inhibition of this proteinincreases the production of new oligodendrocyte precursorcells (OPCs) in the brain and attenuates symptoms in mousemodels of demyelinating injuries [75]Thus SIRT1 regulatingmiRNAs such as miR-204-5p [187] might be useful to loadSVZ targeted exosomes and potentially treat MS

It has been recently demonstrated that exogenous miR-NAs can be incorporated into exosomes ofMSCs and be func-tionally delivered to neural progenitor cells and astrocytesmodifying the expression of several genes in recipient cells[188] Thus as postulated in the review given the capacityto target a specific cell type by engineering the appropriatesurface proteins in exosomes engineered MSC-derived exo-somes may provide an efficient route of therapeutic miRNAdelivery to certain cellular components of the neurogenicniche in particular pathological conditions More researchand a deeper understanding of the exosomal surface proteinsnecessary to target a specific cell type are needed to test thisassumption

With all this information we propose in Figure 2 aschematic flowchart to develop a therapy based on the selec-tive delivery of miRNAs mediated by engineered exosomesto target the neurogenic niche MiRNA loading can beachieved by transfecting the exosome producing cells with anoverexpression plasmid [89] or even by direct electroporationof the mature miRNA into the vesicles [129]

9 Exosomes as Diagnostic Tools ofCNS Diseases

It is well known that different kind of cells produces exo-somes with a specific parental molecular signature [192] For


Exosomesources

Targetengineering

Cargoengineering

Exosomeisolation

Delivery

miR-9 [183]miR-124 [185]

let-7 [186]miR-204-5p [187]

Ultracentrifugation [90]

Immunoaffinity [27]

Intranasally [132 133]

Systemic [130 155 191]

MSCs [190]

iPSCs [189]

Notch [181]Cx26 [159]

Tenasin C [164]EGFR [178]

Figure 2 Schematic flowchart to develop a therapy based on the selective delivery of miRNAs mediated by engineered exosomes targetingneurogenic niches Exosome sources box shows the cell culture type in which exosomes will be produced and harvested target engineeringbox shows neurogenic niche-associated proteins that could be targeted with exosomes engineered to harbor a mimetic binding peptidein the outer surface of the vesicle cargo engineering box shows several miRNAs that are known to modulate the fate of NPCs in theneurogenic niche exosome isolation box shows two strategies to isolate the engineered exosomes from culture media ultracentrifugationor immunoprecipitation of vesicles using antibodies against the extracellular domain of an exosome marker protein delivery box showstwo noninvasive CNS interventions intranasal and systemic (by bloodstream) incorporation of engineered exosomes References iPSCs[189] MSCs [190] Cx26 [159] Tenascin C [164] EGFR [178] Notch [181] miR-9 [183] miR-124 [185] miR-204-5p [187] let-7 [186]ultracentrifugation [90] immunoaffinity [27] intranasally [132 133] systemic [130 155 191]

example B cell receptor is selectively expressed on B cell-derived exosomes as CD11c a specific marker of dendriticcells (DC) is present on DC-derived exosomes [106] Simi-larly oligodendrocyte derived exosomes contain the myelinassociated proteins PLPDM20 [193] Coherently exosomecargo depends on the physiologicalpathophysiological stateof the cell that produces it [194] for instance inflammatoryand hypoxic stimuli change the protein and RNA content ofendothelial cell-derived exosomes [195]

In the CNS cultured cells of the highly malignantbrain tumor glioblastoma multiforme grown under hypoxicconditions secrete exosomes enriched in hypoxia-regulatedmRNAs andproteins like caveolin 1 which is also increased inexosomes isolated from the plasma of glioblastoma patientswith a poor prognosis [196] Similarly it was found thatglioblastoma-specific epidermal growth factor receptor vIII(EGFRvIII) is enriched in exosomes isolated from the serumof glioblastoma patients [197 198] In fact exosomes containeach of the toxic protein types associated with neurodegener-ative disorders such as HD PD AD and prion disease [199]Moreover tau phosphorylated atThr-181 a biomarker forADis elevated in exosomes isolated from the cerebrospinal fluidfrom AD patients [200]

Thus exosomes have a great potential as noninvasivediagnostic tools under several CNS pathological conditionsConsidering that several pathologies are related to alterationsof the stemcell niche it is intriguing to knowwhether changesin the molecular signature of specific stem niche derived

exosomes are induced in response to neuropathologicalconditions A good challenge to solve this question is toidentify a specific transmembrane protein that might be usedas a marker to capture peripherally the exosomes derivedfrom CNS stem cell niches Thus with these exosomes itwould be possible to study the physiological state of a niche

10 Conclusion

The challenges faced when trying to improve the condi-tions of those affected by neurological disorders have urgedresearchers to explore new methodologies and to thinkldquooutside of the boxrdquo The use of stem cell transplants fortherapeutic use is a growing field that though in its infancyis showing promising potential to treat neurodegenera-tive disorders though their potential risks (eg allogenicimmune response and the potential of tumor formation)have hindered progress in this field Interest has thereforeshifted for many researchers towards the exosomes liberatedby these cells Besides the compelling possibility of usingthem as biomarkers these nanovesicles present a number ofadvantages that make them uniquely suited as therapeuticagents (1)They are able to cross the blood-brain barrier thusthey can be delivered through minimally invasive methods(eg blood andor intranasal delivery) (2)Their content canbe manipulated to suit specific needs (3) The membraneproteins expressed by exosomes could be engineered to targetthem to precise cell types improving the specificity of a


treatment and thus reducing the incidence of side effects (4)The possibility of targeting exosomes to specific cell typeswould open up the door for treatments targeted at the adultneurogenic niches of the brain These areas of the brain havebeen insofar unexplored as sites for potential treatment buttheir close association to a wide number of different neuro-logical disorders makes their modulation worth consideringwhen seeking for novel therapeutic methods

Stem cells and the exosomes released by them thus opena vast array of new options for the treatment of disablingneurological pathologies that due to the complexity of thebrain and the difficulty of accessing some of its areas stillremain largely incurable despite decades of intense research

Competing Interests

The authors declare no competing interests

Acknowledgments

This work was supported by CONICYT (FONDECYT Pro-gram 1140108 (UW) and FONDECYT Program 1141015(LFB))

References

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[2] J Brettschneider K Del Tredici V M-Y Lee and J QTrojanowski ldquoSpreading of pathology in neurodegenerative dis-eases a focus on human studiesrdquo Nature Reviews Neurosciencevol 16 no 2 pp 109ndash120 2015

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[4] T Hartung ldquoThoughts on limitations of animal modelsrdquoParkinsonism and Related Disorders vol 14 supplement 2 ppS81ndashS83 2008

[5] M Jucker ldquoThe benefits and limitations of animal models fortranslational research in neurodegenerative diseasesrdquo NatureMedicine vol 16 no 11 pp 1210ndash1214 2010

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[7] B Sheehan ldquoAssessment scales in dementiardquo TherapeuticAdvances in Neurological Disorders vol 5 no 6 pp 349ndash3582012

[8] B Dubois H H Feldman C Jacova et al ldquoResearch criteriafor the diagnosis of Alzheimerrsquos disease revising the NINCDS-ADRDA criteriardquo The Lancet Neurology vol 6 no 8 pp 734ndash746 2007

[9] F H Bouwman N A Verwey M Klein et al ldquoNew researchcriteria for the diagnosis of Alzheimerrsquos disease applied in amemory clinic populationrdquo Dementia and Geriatric CognitiveDisorders vol 30 no 1 pp 1ndash7 2010

[10] L C Silbert J F Quinn M M Moore et al ldquoChanges in pre-morbid brain volume predict Alzheimerrsquos disease pathologyrdquoNeurology vol 61 no 4 pp 487ndash492 2003

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[12] J T OrsquoBrien ldquoRole of imaging techniques in the diagnosis ofdementiardquo British Journal of Radiology vol 80 no 2 pp S71ndashS77 2007

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[96] A Savina M Furlan M Vidal and M I Colombo ldquoExosomerelease is regulated by a calcium-dependentmechanism inK562


cellsrdquo The Journal of Biological Chemistry vol 278 no 22 pp20083ndash20090 2003

[97] R Sahu S Kaushik C C Clement et al ldquoMicroautophagy ofcytosolic proteins by late endosomesrdquo Developmental Cell vol20 no 1 pp 131ndash139 2011

[98] K Trajkovic C Hsu S Chiantia et al ldquoCeramide triggersbudding of exosome vesicles into multivesicular endosomesrdquoScience vol 319 no 5867 pp 1244ndash1247 2008

[99] N Kosaka H Iguchi K Hagiwara Y Yoshioka F Takeshitaand T Ochiya ldquoNeutral sphingomyelinase 2 (nSMase2)-dependent exosomal transfer of angiogenic micrornas regulatecancer cell metastasisrdquoThe Journal of Biological Chemistry vol288 no 15 pp 10849ndash10859 2013

[100] M F Baietti Z Zhang E Mortier et al ldquoSyndecanndashsynteninndashALIX regulates the biogenesis of exosomesrdquoNature Cell Biologyvol 14 no 7 pp 677ndash685 2012

[101] J H Hurley and G Odorizzi ldquoGet on the exosome bus withALIXrdquo Nature Cell Biology vol 14 no 7 pp 654ndash655 2012

[102] C Villarroya-Beltri C Gutierrez-Vazquez F Sanchez-Cabo etal ldquoSumoylated hnRNPA2B1 controls the sorting of miRNAsinto exosomes through binding to specific motifsrdquo NatureCommunications vol 4 article 2980 2013

[103] D Koppers-Lalic M Hackenberg I V Bijnsdorp et al ldquoNon-templated nucleotide additions distinguish the small RNA com-position in cells from exosomesrdquo Cell Reports vol 8 no 6 pp1649ndash1658 2014

[104] M Simons and G Raposo ldquoExosomesmdashvesicular carriers forintercellular communicationrdquo Current Opinion in Cell Biologyvol 21 no 4 pp 575ndash581 2009

[105] A R Taylor M B Robinson D J Gifondorwa M Tytell andC E Milligan ldquoRegulation of heat shock protein 70 release inastrocytes role of signaling kinasesrdquo Developmental Neurobiol-ogy vol 67 no 13 pp 1815ndash1829 2007

[106] N Chaput and C Thery ldquoExosomes immune properties andpotential clinical implementationsrdquo Seminars in Immunopathol-ogy pp 1ndash22 2010

[107] M S Pols and J Klumperman ldquoTrafficking and function of thetetraspanin CD63rdquo Experimental Cell Research vol 315 no 9pp 1584ndash1592 2009

[108] J-M Escola M J Kleijmeer W Stoorvogel J M Griffith OYoshie and H J Geuze ldquoSelective enrichment of tetraspanproteins on the internal vesicles of multivesicular endosomesand on exosomes secreted by human B-lymphocytesrdquo TheJournal of Biological Chemistry vol 273 no 32 pp 20121ndash201271998

[109] K Strauss C Goebel H Runz et al ldquoExosome secretion ame-liorates lysosomal storage of cholesterol in Niemann-Pick typeC diseaserdquo Journal of Biological Chemistry vol 285 no 34 pp26279ndash26288 2010

[110] M Grapp A Wrede M Schweizer et al ldquoChoroid plexustranscytosis and exosome shuttling deliver folate into brainparenchymardquoNature Communications vol 4 article 2123 2013

[111] J Lotvall A F Hill F Hochberg et al ldquoMinimal experimentalrequirements for definition of extracellular vesicles and theirfunctions a position statement from the International Societyfor Extracellular Vesiclesrdquo Journal of Extracellular Vesicles vol3 Article ID 26913 2014

[112] J Kowal M Tkach and C Thery ldquoBiogenesis and secretion ofexosomesrdquo Current Opinion in Cell Biology vol 29 no 1 pp116ndash125 2014

[113] A Montecalvo A T Larregina W J Shufesky et al ldquoMech-anism of transfer of functional microRNAs between mousedendritic cells via exosomesrdquo Blood vol 119 no 3 pp 756ndash7662012

[114] D M Pegtel K Cosmopoulos D A Thorley-Lawson et alldquoFunctional delivery of viral miRNAs via exosomesrdquo Proceed-ings of the National Academy of Sciences of the United States ofAmerica vol 107 no 14 pp 6328ndash6333 2010

[115] H C Christianson K J Svensson T H van Kuppevelt J-P Li and M Belting ldquoCancer cell exosomes depend on cell-surface heparan sulfate proteoglycans for their internalizationand functional activityrdquo Proceedings of the National Academyof Sciences of the United States of America vol 110 no 43 pp17380ndash17385 2013

[116] H Valadi K Ekstrom A Bossios M Sjostrand J J Leeand J O Lotvall ldquoExosome-mediated transfer of mRNAs andmicroRNAs is a novel mechanism of genetic exchange betweencellsrdquo Nature Cell Biology vol 9 no 6 pp 654ndash659 2007

[117] I Parolini C Federici C Raggi et al ldquoMicroenvironmental pHis a key factor for exosome traffic in tumor cellsrdquo Journal ofBiological Chemistry vol 284 no 49 pp 34211ndash34222 2009

[118] T Tian Y-L Zhu Y-Y Zhou et al ldquoExosome uptake throughclathrin-mediated endocytosis and macropinocytosis andmediating miR-21 deliveryrdquoThe Journal of Biological Chemistryvol 289 no 32 pp 22258ndash22267 2014

[119] D Feng W-L Zhao Y-Y Ye et al ldquoCellular internalization ofexosomes occurs through phagocytosisrdquo Traffic vol 11 no 5pp 675ndash687 2010

[120] K J Svensson H C Christianson A Wittrup et al ldquoExosomeuptake depends on ERK12-heat shock protein 27 signalingand lipid raft-mediated endocytosis negatively regulated bycaveolin-1rdquo Journal of Biological Chemistry vol 288 no 24 pp17713ndash17724 2013

[121] D Fitzner M Schnaars D van Rossum et al ldquoSelectivetransfer of exosomes from oligodendrocytes to microglia bymacropinocytosisrdquo Journal of Cell Science vol 124 no 3 pp447ndash458 2011

[122] T Tian Y-L Zhu F-H Hu Y-Y Wang N-P Huang and Z-D Xiao ldquoDynamics of exosome internalization and traffickingrdquoJournal of Cellular Physiology vol 228 no 7 pp 1487ndash1495 2013

[123] L A Mulcahy R C Pink and D R F Carter ldquoRoutes andmechanisms of extracellular vesicle uptakerdquo Journal of Extra-cellular Vesicles vol 3 Article ID 24641 2014

[124] D J Gibbings C Ciaudo M Erhardt and O Voinnet ldquoMulti-vesicular bodies associate with components of miRNA effectorcomplexes and modulate miRNA activityrdquo Nature Cell Biologyvol 11 no 9 pp 1143ndash1149 2009

[125] G Raposo H W Nijman W Stoorvogel et al ldquoB lymphocytessecrete antigen-presenting vesiclesrdquo Journal of ExperimentalMedicine vol 183 no 3 pp 1161ndash1172 1996

[126] L Zitvogel A Regnault A Lozier et al ldquoEradication of estab-lished murine tumors using a novel cell-free vaccine dendriticcell-derived exosomesrdquo Nature Medicine vol 4 no 5 pp594ndash600 1998

[127] S Banerjee andMA Bhat ldquoNeuron-glial interactions in blood-brain barrier formationrdquoAnnual Review ofNeuroscience vol 30pp 235ndash258 2007

[128] J S Jackson J P Golding C Chapon W A Jones and KK Bhakoo ldquoHoming of stem cells to sites of inflammatorybrain injury after intracerebral and intravenous administrationa longitudinal imaging studyrdquo Stem Cell Research and Therapyvol 1 article 17 2010


[129] L Alvarez-Erviti Y Seow H Yin C Betts S Lakhal and M JA Wood ldquoDelivery of siRNA to the mouse brain by systemicinjection of targeted exosomesrdquo Nature Biotechnology vol 29no 4 pp 341ndash345 2011

[130] J M Cooper P B O Wiklander J Z Nordin et al ldquoSystemicexosomal siRNA delivery reduced alpha-synuclein aggregatesin brains of transgenic micerdquo Movement Disorders vol 29 no12 pp 1476ndash1485 2014

[131] X Zhuang X Xiang W Grizzle et al ldquoTreatment of braininflammatory diseases by delivering exosome encapsulatedanti-inflammatory drugs from the nasal region to the brainrdquoMolecular Therapy vol 19 no 10 pp 1769ndash1779 2011

[132] X Zhuang Y Teng A Samykutty et al ldquoGrapefruit-derivednanovectors delivering therapeuticmiR17 through an intranasalroute inhibit brain tumor progressionrdquoMolecular Therapy vol24 no 1 pp 96ndash105 2016

[133] M J Haney N L Klyachko Y Zhao et al ldquoExosomes as drugdelivery vehicles for Parkinsonrsquos disease therapyrdquo Journal ofControlled Release vol 207 pp 18ndash30 2015

[134] H Xin Y Li B Buller et al ldquoExosome-mediated transferof miR-133b from multipotent mesenchymal stromal cells toneural cells contributes to neurite outgrowthrdquo STEM CELLSvol 30 no 7 pp 1556ndash1564 2012

[135] H Xin Y Li Z Liu et al ldquoMiR-133b promotes neural plasticityand functional recovery after treatment of stroke with multipo-tent mesenchymal stromal cells in rats via transfer of exosome-enriched extracellular particlesrdquo STEM CELLS vol 31 no 12pp 2737ndash2746 2013

[136] T R Doeppner J Herz A Gorgens et al ldquoExtracellularvesicles improve post-stroke neuroregeneration and preventpostischemic immunosuppressionrdquo Stem Cells TranslationalMedicine vol 4 no 10 pp 1131ndash1143 2015

[137] J B S Haldane ldquoOn being the right sizerdquo Harperrsquos Magazinevol 152 pp 424ndash427 1926

[138] H Xin Y Li and M Chopp ldquoExosomesmiRNAs as mediatingcell-based therapy of strokerdquo Frontiers in Cellular Neurosciencevol 8 p 377 2014

[139] S El Andaloussi I Mager X O Breakefield and M J AWood ldquoExtracellular vesicles biology and emerging therapeu-tic opportunitiesrdquoNature Reviews Drug Discovery vol 12 no 5pp 347ndash357 2013

[140] T Lener M Gioma L Aigner et al ldquoApplying extracellularvesicles based therapeutics in clinical trialsmdashan ISEV positionpaperrdquo Journal of Extracellular Vesicles vol 4 pp 1ndash32 2015

[141] B Fevrier D Vilette F Archer et al ldquoCells release prionsin association with exosomesrdquo Proceedings of the NationalAcademy of Sciences of the United States of America vol 101 no26 pp 9683ndash9688 2004

[142] T Katsuda K Oki and T Ochiya ldquoPotential application ofextracellular vesicles of human adipose tissue-derived mes-enchymal stem cells in Alzheimerrsquos disease therapeuticsrdquoMeth-ods in Molecular Biology vol 1212 pp 171ndash181 2015

[143] H Ling M Fabbri and G A Calin ldquoMicroRNAs and othernon-coding RNAs as targets for anticancer drug developmentrdquoNature ReviewsDrugDiscovery vol 12 no 11 pp 847ndash865 2013

[144] F Collino S Bruno D Incarnato et al ldquoAKI recovery inducedbymesenchymal stromal cell- derived extracellular vesicles car-ryingmicrornasrdquo Journal of the American Society of Nephrologyvol 26 no 10 pp 2349ndash2360 2015

[145] L Zhang S Zhang J Yao et al ldquoMicroenvironment-inducedPTEN loss by exosomal microRNA primes brain metastasisoutgrowthrdquo Nature vol 527 no 7576 pp 100ndash104 2015

[146] M Khan E Nickoloff T Abramova et al ldquoEmbryonic stemcell-derived exosomes promote endogenous repairmechanismsand enhance cardiac function following myocardial infarctionrdquoCirculation Research vol 117 no 1 pp 52ndash64 2015

[147] J Ratajczak K Miekus M Kucia et al ldquoEmbryonic stem cell-derived microvesicles reprogram hematopoietic progenitorsevidence for horizontal transfer of mRNA and protein deliveryrdquoLeukemia vol 20 no 5 pp 847ndash856 2006

[148] F Fatima and M Nawaz ldquoStem cell-derived exosomes roles instromal remodeling tumor progression and cancer immuno-therapyrdquo Chinese Journal of Cancer vol 34 article 46 2015

[149] F Arslan R C Lai M B Smeets et al ldquoMesenchymal stemcell-derived exosomes increase ATP levels decrease oxidativestress and activate PI3KAkt pathway to enhance myocardialviability and prevent adverse remodeling after myocardialischemiareperfusion injuryrdquo Stem Cell Research vol 10 no 3pp 301ndash312 2013

[150] S Bian L Zhang L Duan X Wang Y Min and H YuldquoExtracellular vesicles derived from human bone marrow mes-enchymal stem cells promote angiogenesis in a rat myocardialinfarction modelrdquo Journal of Molecular Medicine vol 92 no 4pp 387ndash397 2014

[151] K Kang R Ma W Cai et al ldquoExosomes secreted from CXCR4overexpressing mesenchymal stem cells promote cardioprotec-tion viaAkt signaling pathway followingmyocardial infarctionrdquoStem Cells International vol 2015 Article ID 659890 14 pages2015

[152] C Y Tan R C Lai W Wong Y Y Dan S-K Lim and H KHo ldquoMesenchymal stem cell-derived exosomes promote hep-atic regeneration in drug-induced liver injury modelsrdquo StemCell Research andTherapy vol 5 article 76 2014

[153] L Li S Jin and Y Zhang ldquoIschemic preconditioning poten-tiates the protective effect of mesenchymal stem cells onendotoxin-induced acute lung injury in mice through secretionof exosomerdquo International Journal of Clinical and ExperimentalMedicine vol 8 no 3 pp 3825ndash3832 2015

[154] B Zhang M Wang A Gong et al ldquoHucMSc-exosomemediated-Wnt4 signaling is required for cutaneous woundhealingrdquo Stem Cells vol 33 no 7 pp 2158ndash2168 2015

[155] S-I Ohno M Takanashi K Sudo et al ldquoSystemically injectedexosomes targeted to EGFR deliver antitumor microrna tobreast cancer cellsrdquo Molecular Therapy vol 21 no 1 pp 185ndash191 2012

[156] Y Liu D Li Z Liu et al ldquoTargeted exosome-mediated deliveryof opioid receptor Mu siRNA for the treatment of morphinerelapserdquo Scientific Reports vol 5 Article ID 17543 2015

[157] C Lee J Hu S Ralls et al ldquoThe molecular profiles of neuralstem cell niche in the adult subventricular zonerdquoPLoSONE vol7 no 11 Article ID e50501 2012

[158] O Chever U Pannasch P Ezan and N Rouach ldquoAstroglialconnexin 43 sustains glutamatergic synaptic efficacyrdquo Philo-sophical Transactions of the Royal Society of London B BiologicalSciences vol 369 Article ID 20130596 2014

[159] F Mercier and G I Hatton ldquoConnexin 26 and basic fibroblastgrowth factor are expressed primarily in the subpial andsubependymal layers in adult brain parenchyma roles in stemcell proliferation and morphological plasticityrdquo Journal ofComparative Neurology vol 431 no 1 pp 88ndash104 2001

[160] A R Soares T Martins-Marques T Ribeiro-Rodrigues et alldquoGap junctional protein Cx43 is involved in the communicationbetween extracellular vesicles and mammalian cellsrdquo ScientificReports vol 5 Article ID 13243 2015


[161] W H Evans and L Leybaert ldquoMimetic peptides as blockers ofconnexin channel-facilitated intercellular communicationrdquoCellCommunication and Adhesion vol 14 no 6 pp 265ndash273 2007

[162] W H Evans and S Boitano ldquoConnexin mimetic peptides spe-cific inhibitors of gap-junctional intercellular communicationrdquoBiochemical Society Transactions vol 29 no 4 pp 606ndash6122001

[163] E Garcion A Halilagic A Faissner and C Ffrench-ConstantldquoGeneration of an environmental niche for neural stem celldevelopment by the extracellular matrix molecule tenascin CrdquoDevelopment vol 131 no 14 pp 3423ndash3432 2004

[164] R Chiquet-Ehrismann G OrendM Chiquet R P Tucker andK S Midwood ldquoTenascins in stem cell nichesrdquoMatrix Biologyvol 37 pp 112ndash123 2014

[165] L Ferhat N Chevassus-Au-Louis M Khrestchatisky Y Ben-Ari andA Represa ldquoSeizures induce tenascin-CmRNAexpres-sion in neuronsrdquo Journal of Neurocytology vol 25 no 9 pp535ndash546 1996

[166] M Y Kim O R Kim Y S Choi et al ldquoSelection and charac-terization of tenascin C targeting peptiderdquoMolecules and Cellsvol 33 no 1 pp 71ndash77 2012

[167] J M Schwarz ldquoUsing fluorescence activated cell sorting toexamine cell-type-specific gene expression in rat brain tissuerdquoJournal of Visualized Experiments vol 2015 no 99 Article IDe52537 2015

[168] B W Okaty K Sugino and S B Nelson ldquoA quantitativecomparison of cell-type-specific microarray gene expressionprofiling methods in the mouse brainrdquo PLoS ONE vol 6 no 1Article ID e16493 2011

[169] A Jovicic R Roshan N Moisoi et al ldquoComprehensive expres-sion analyses of neural cell-type-specific miRNAs identify newdeterminants of the specification and maintenance of neuronalphenotypesrdquo Annals of Internal Medicine vol 158 no 6 pp5127ndash5137 2013

[170] E Pastrana L-C Cheng and F Doetsch ldquoSimultaneous pro-spective purification of adult subventricular zone neural stemcells and their progenyrdquo Proceedings of the National Academyof Sciences of the United States of America vol 106 no 15 pp6387ndash6392 2009

[171] M A Bonaguidi C-Y Peng T McGuire et al ldquoNogginexpands neural stem cells in the adult hippocampusrdquo Journalof Neuroscience vol 28 no 37 pp 9194ndash9204 2008

[172] Y H Evelyn Heng B Zhou L Harris et al ldquoNFIX regulatesproliferation and migration within the murine SVZ neurogenicnicherdquo Cerebral Cortex vol 25 no 10 pp 3758ndash3778 2015

[173] L C Fuentealba S B Rompani J I Parraguez et al ldquoEmbry-onic origin of postnatal neural stem cellsrdquo Cell vol 161 no 7pp 1644ndash1655 2015

[174] A Alvarez-Buylla J M Garcıa-Verdugo and A D TramontinldquoA unified hypothesis on the lineage of neural stem cellsrdquoNatureReviews Neuroscience vol 2 no 4 pp 287ndash293 2001

[175] Q Shen and S Temple ldquoFine control microRNA regulation ofadult neurogenesisrdquoNature Neuroscience vol 12 no 4 pp 369ndash370 2009

[176] K Zheng H Li Y Zhu Q Zhu and M Qiu ldquoMicroRNAsare essential for the developmental switch from neurogenesisto gliogenesis in the developing spinal cordrdquo The Journal ofNeuroscience vol 30 no 24 pp 8245ndash8250 2010

[177] R Kageyama T Ohtsuka H Shimojo and I ImayoshildquoDynamic Notch signaling in neural progenitor cells and arevised view of lateral inhibitionrdquo Nature Neuroscience vol 11no 11 pp 1247ndash1251 2008

[178] A Aguirre M E Rubio and V Gallo ldquoNotch and EGFRpathway interaction regulates neural stem cell number and self-renewalrdquo Nature vol 467 no 7313 pp 323ndash327 2010

[179] R Kopan and M X G Ilagan ldquoThe canonical notch signalingpathway unfolding the activationmechanismrdquoCell vol 137 no2 pp 216ndash233 2009

[180] C Andreu-Agullo J M Morante-Redolat A C Delgadoand I Farinas ldquoVascular niche factor PEDF modulates notch-dependent stemness in the adult subependymal zonerdquo NatureNeuroscience vol 12 no 12 pp 1514ndash1523 2009

[181] Z Zhang R Yan Q Zhang et al ldquoHes1 a Notch signalingdownstream target regulates adult hippocampal neurogenesisfollowing traumatic brain injuryrdquo Brain Research vol 1583 no1 pp 65ndash78 2014

[182] I Imayoshi M Sakamoto M Yamaguchi K Mori and RKageyama ldquoEssential roles of Notch signaling in maintenanceof neural stem cells in developing and adult brainsrdquo Journal ofNeuroscience vol 30 no 9 pp 3489ndash3498 2010

[183] M Coolen S Katz and L Bally-Cuif ldquomiR-9 a versatileregulator of neurogenesisrdquo Frontiers in Cellular Neurosciencevol 7 article 220 2013

[184] CWangN Yao C-L Lu D Li andXMa ldquoMousemicroRNA-124 regulates the expression of Hes1 in P19 cellsrdquo Frontiers inBioscience-Elite vol 2 no 1 pp 127ndash132 2010

[185] X S Liu M Chopp R L Zhang et al ldquoMicroRNA profilingin subventricular zone after stroke MiR-124a regulates pro-liferation of neural progenitor cells through notch signalingpathwayrdquo PLoS ONE vol 6 no 8 Article ID e23461 2011

[186] M Patterson X Gaeta K Loo et al ldquoLet-7 miRNAs can actthrough NOTCH to regulate human gliogenesisrdquo Stem CellReports vol 3 no 5 pp 758ndash773 2014

[187] L Zhang X Wang and P Chen ldquoMiR-204 down regulatesSIRT1 and reverts SIRT1-induced epithelial-mesenchymal tran-sition anoikis resistance and invasion in gastric cancer cellsrdquoBMC Cancer vol 13 article 290 2013

[188] H K Lee S Finniss S Cazacu C Xiang and C BrodieldquoMesenchymal stem cells deliver exogenous miRNAs to neuralcells and induce their differentiation and glutamate transporterexpressionrdquo Stem Cells and Development vol 23 no 23 pp2851ndash2861 2014

[189] J Zhou S Ghoroghi A Benito-Martin et al ldquoCharacterizationof induced pluripotent stem cell microvesicle genesis morphol-ogy and pluripotent contentrdquo Scientific Reports vol 6 ArticleID 19743 2016

[190] S Tomasoni L Longaretti C Rota et al ldquoTransfer of growthfactor receptor mRNA via exosomes unravels the regenerativeeffect of mesenchymal stem cellsrdquo Stem Cells and Developmentvol 22 no 5 pp 772ndash780 2013

[191] H Xin Y Li Y Cui J J Yang Z G Zhang andM Chopp ldquoSys-temic administration of exosomes released from mesenchymalstromal cells promote functional recovery and neurovascularplasticity after stroke in ratsrdquo Journal of Cerebral Blood Flow andMetabolism vol 33 no 11 pp 1711ndash1715 2013

[192] C Villarroya-Beltri F Baixauli C Gutierrez-Vazquez FSanchez-Madrid and M Mittelbrunn ldquoSorting it out regula-tion of exosome loadingrdquo Seminars in Cancer Biology vol 28no 1 pp 3ndash13 2014

[193] D Frohlich W P Kuo C Fruhbeis et al ldquoMultifaceted effectsof oligodendroglial exosomes on neurons impact on neuronalfiring rate signal transduction and gene regulationrdquo Philosoph-ical Transactions of the Royal Society B Biological Sciences vol369 no 1652 Article ID 20130510 2014


[194] K M Kanninen N Bister J Koistinaho and T Malm ldquoExo-somes as new diagnostic tools in CNS diseasesrdquo Biochimica etBiophysica Acta (BBA)mdashMolecular Basis of Disease vol 1862no 3 pp 403ndash410 2016

[195] O G de Jong M C Verhaar Y Chen et al ldquoCellular stressconditions are reflected in the protein and RNA content ofendothelial cell-derived exosomesrdquo Journal of ExtracellularVesicles vol 1 pp 1ndash12 2012

[196] P Kucharzewska H C Christianson J E Welch et al ldquoExo-somes reflect the hypoxic status of glioma cells and mediatehypoxia-dependent activation of vascular cells during tumordevelopmentrdquo Proceedings of the National Academy of Sciencesof the United States of America vol 110 no 18 pp 7312ndash73172013

[197] J Skog T Wurdinger S van Rijn et al ldquoGlioblastomamicrovesicles transport RNAand proteins that promote tumourgrowth and provide diagnostic biomarkersrdquoNature Cell Biologyvol 10 no 12 pp 1470ndash1476 2008

[198] M W Graner O Alzate A M Dechkovskaia et al ldquoProteomicand immunologic analyses of brain tumor exosomesrdquo TheFASEB Journal vol 23 no 5 pp 1541ndash1557 2009

[199] A Kalani A Tyagi andN Tyagi ldquoExosomes mediators of neu-rodegeneration neuroprotection and therapeuticsrdquo MolecularNeurobiology vol 49 no 1 pp 590ndash600 2014

[200] J Lin J Li B Huang et al ldquoExosomes novel biomarkers forclinical diagnosisrdquoTheScientificWorld Journal vol 2015 ArticleID 657086 8 pages 2015

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Anatomy Research International

PeptidesInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom

International Journal of

Volume 2014

Zoology


Molecular Biology International

GenomicsInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


BioinformaticsAdvances in

Marine BiologyJournal of



Signal TransductionJournal of


BioMed Research International

Evolutionary BiologyInternational Journal of



Biochemistry Research International

ArchaeaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Genetics Research International


Advances in

Virolog y

Hindawi Publishing Corporationhttpwwwhindawicom

Nucleic AcidsJournal of

Volume 2014

Stem CellsInternational



Enzyme Research



Microbiology


that stem cell-derived exosomes might be a new treatmentfor several CNS disorders considering a new interplay withneurogenic niches Thus we propose that engineered stemcell-derived exosomes targeted to the neurogenic niche areagents with therapeutic potential

2 Management of CNS DisordersCurrent State

Even when animal models are indispensable and have pro-vided researchers with important and detailed informationon the development and impact of neurological disordersmostmodels are still incapable of faithfully reproducing thesedisorders [4 5] thus providing an incomplete tool to fully testthe advantages of new drugs or treatments Further compli-cations arise when considering that many disorders progressslowly and as mentioned before that seemingly differentdisorders may be happening simultaneously Furthermorea disorder may express an important number of apparentlydisparate debilitating problems (Huntington Disease egis characterized not only by movement disorders but bya wide array of cognitive and behavioral disabilities [6])Considering these adversities a considerable amount of efforthas been placed not only on treating a specific disorder butalso on discovering biomarkers that may facilitate predictingor recognizing neurodegenerative pathologies during theearly stages of its development where treatments are usuallymost effective

The currently used methods to diagnose neurodegener-ative disorders ante-mortem may range from neuropsycho-logical assessments (eg cognitive tests to evaluate memoryloss in patients suffering from Alzheimer disease (AD) [7])to neuroimaging These methods are not always reliable duein part to the difficulty imposed when trying to differentiatethem from other disorders that share common featuresFor instance diagnosis of Parkinsonrsquos Disease (PD) can beconfounded by other diseases that present clinical syndromesof parkinsonism and a study applying recent criteria [8]to diagnose patients with AD was highly successful (95)when considering nondemented patients but this successrate decreased almost by half when considering a populationof patients with other types of dementia [9]These difficultiesare being tackled and they can be divided for organizationalpurposes in attempts to discover reliable biomarkers on theone hand and endeavors to find appropriate therapies on theother hand

21 Common Biomarkers for CNS Diseases Currently usedbiomarkers rely heavily on imaging technologies which canbe used to study from whole brain structures to proteinaggregates Magnetic resonance imaging (MRI) has beenused for example to associate changes in ventricular volumewith cortical senile plaques (SP) and neurofibrillary tangles(NFT) common features of AD thus being proposed asa diagnostic strategy [10] Nevertheless it may be difficultto separate the changes observed in AD patients from thechanges observed in those suffering other types of dementiaor even the elderly people [11 12] Diffusion MRI has proven

successful in identifying PD patients from those sufferingfrom parkinsonism [13] and diffusion-weighed MRI andcomputer tomography (CT) are the most common ways ofdetecting early cases of acute stroke [14 15] Despite thesometimes prohibitive costs positron emission tomography(PET) is a promising option for early diagnostic of a disorderas well as a powerful tool to determine the success of atreatment over time although the injection of radioactivetracers in the blood makes PET a slightly more invasivetechnique Newly developed tracers for PET have expandedthe possibilities of this technique allowing it to detect notonly the activity of the brain through blood flow and glucoseconsumption but also parameters that may signal the devel-opment of a neurological disorder [16] Examples of thesetracers include 18F-DOPA which has been used to diagnosePD and compounds that bind to amyloid plaques such as18F-florbetapir which presents a higher uptake inADpatientsthan controls [17] and has been recently approved by the FDA[18] Magnetic resonance spectroscopy has also been used todiagnose early stages of PD showing an interesting potentialwhen considering the noninvasiveness of this technology andthe lower associated costs [19]

22 Searching for New Noninvasive Biomarkers for CNSDiseases Relevance of Exosomes andMicroRNAs Body fluidsare also promising sources of molecular biomarkers whichcan be divided into three categories molecules (eg 8-hydroxydeoxyguanosine a byproduct of DNA oxidation thatis found at higher levels in the urine of PD patients)proteins (eg protein aggregates) andRNAs (eg noncodingmicroRNAs see below) [20] The advantage of biomarkersobtained from body fluids (ie cerebrospinal fluid CSFblood plasma serum saliva and urine) is the possibilityof searching for a large number of molecules at once forexample by the use of proteomics or genomics at earlierstages than those exposed by imaging Efforts are being madeto measure the higher levels of glial fibrillary acidic protein(GFAP) in blood for example as an earlymarker of traumaticbrain injuries and stroke as well as a way to follow up on aspecific treatment for these patients [21] Having a biomarkerthat can be accessed from a body fluid has the addedadvantage of not relying onmore expensive technology (suchas imaging equipment) and in some instances (eg salivaandurine) of avoiding invasivemethods altogetherThemaindisadvantage of obtaining biomarkers from body fluids is thelow levels of molecules and the heterogeneity of these assuch samples arise from a wide number of tissues Thus tocircumvent this difficulty and to improve the specificity ofthe biomarker small circulating extracellular vesicles termedexosomes have gathered the interest of biomedical researchesThese extracellular nanovesicles can be isolated from allbodily fluids and they carry a complex cargo consisting ofvarious types of RNA (eg ribosomal RNAs long noncodingRNAs and microRNAs) proteins lipids and DNA that inpart depends on the tissue of origin and its ldquohealth or diseaserdquostate [22ndash24] Catalytically active enzymes like PTEN as wellas bioactive lipids such as prostaglandins can be transferedby exosomes to target cells [25 26]


























MS [78] ALS [79]








































Exosomesources

Targetengineering

Cargoengineering

Exosomeisolation

Delivery

miR-9 [183]miR-124 [185]

let-7 [186]miR-204-5p [187]


Immunoaffinity [27]


Systemic [130 155 191]

MSCs [190]

iPSCs [189]

Notch [181]Cx26 [159]







10 Conclusion





Competing Interests


Acknowledgments


References
























































































































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


























MS [78] ALS [79]








































Exosomesources

Targetengineering

Cargoengineering

Exosomeisolation

Delivery

miR-9 [183]miR-124 [185]

let-7 [186]miR-204-5p [187]


Immunoaffinity [27]


Systemic [130 155 191]

MSCs [190]

iPSCs [189]

Notch [181]Cx26 [159]







10 Conclusion





Competing Interests


Acknowledgments


References
























































































































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology


































Exosomesources

Targetengineering

Cargoengineering

Exosomeisolation

Delivery

miR-9 [183]miR-124 [185]

let-7 [186]miR-204-5p [187]


Immunoaffinity [27]


Systemic [130 155 191]

MSCs [190]

iPSCs [189]

Notch [181]Cx26 [159]







10 Conclusion





Competing Interests


Acknowledgments


References
























































































































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




Competing Interests


Acknowledgments


References
























































































































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology




























































































































































































Volume 2014

Zoology






















Advances in

Virolog y



Volume 2014




Enzyme Research



Microbiology

review article potential therapies by stem cell-derived...

Documents