stem cells in the vascular system kristina boström may 2005
TRANSCRIPT
Cells that undergo asymmetric division resulting in self-renewal of the parent stem cell as well as a daughter cell capable of differentiating down specific lineages.
The tissue specific, committed stem cells provide a supply of terminally differentiated cells for physiologic tissue turnover for the life of the individual.
Stem Cell - Definition
A stem cell, which is committed to give rise to the expected tissues, may differentiate into cells other than these expected tissues, the so-called unexpected tissues. Termed TRANSDIFFERENTIATION.
However, it is equally plausible that uncommitted stem cells exist within the tissue and have the potential of differentiating into many or all tissues. It is hard to generate convincing data (Wagers & Weissman, Cell 2004).
Stem Cell Plasticity
Horwitz. Arch Med Res, 2004
Committed stem cell Uncommitted stem cell
EndotheliumInternal elastic lamina
MediaExternal elastic lamina
Adventitia
Differentiation between the arterial and venous
side of the vasculature.
Layers of the Vascular Wall
ANGIOGENESIS
Goumans et al. Trends Cardiovasc Med 2003
Formation of Endothelial Tubes
VASCULOGENESIS
Drake. Birth Defects Res 2003
Areas of Potential Adult Vasculogenesis
Atherosclerotic plaquesTumor formationBone disordersInflammatory diseases
Drake. Birth Defects Res 2003
ARTERIOGENESISRecruitment of SMC precursors and SMC differentiation
Stenmark & Abman. Annu Rev Physiol 2005
The tenet of stem cell biology is that the cells only differentiate into cell types associated with the tissue from which they were isolated. Called into question! - more plastic than thought.
Hemangioblasts - Cells with hematopoietic and endothelial potential Were believed to exists only in embryos
Endothelial progenitor cells (EPC) can be isolated from peripheral blood mononuclear cells (PBMNC) by flow cytometry by e.g. CD34 which previously was associated with hematopoietic stem cells.
Overturned Dogma!!
ENDOTHELIAL PROGENITOR CELLS (EPC)
- 0.0001 - 0.02% of peripheral blood cells
- CD34+ AC133+ VEGFR2+ lin- cells
- Study vasculogenesis- Determine progenitor state in patients- Clinical trials of expanded cell populations
Asahara et al. Science 1997
1. Isolated putative ECP from human peripheral blood.2. Two antigens shared by angioblasts and HSC: CD34 and Flk-1 (=
VEGFR-2 and KDR).
Tested for incorporation of EPC in three animal models
A. Human MBC34+ cells into athymic mice with hindlimb ischemia- (heterologous transplantation).
B. ß-Gal overexpressing mice MB, MBFlk1+ or MBFlk1- injected into mice on same background but without ß-Gal. Incorporation in hind limb ischemia. - (homologous transplantation).
C. Injected DiI-labeled rabbit CD34+ or CD34- MB into rabbits with hindlimb ischemia. Found DiI labeling 1-6 weeks afterwards in ischemic limb. - (autologous transplantation).
Asahara et al. Science 1997;275:964
Incorportion on EPC from Peripheral Blood into Ischemic HindlimbAutologous Rabbit Model
Evidence of a CD34+ cells from BM and circulation differentiate into EPC
Grown in presence of bFGF, IGF-1 and VEGFStained positive for CD34 and VEGFR2.Stained for vWF and took up Ac-LDL.
Tested in 1. Canine BM transplant model with genetically distinct donor and
recipient. 2. 6-8 months after BM transplant, Dacron graft impervious to in-growth
of vessels was implanted in the descending aorta.3. 12 weeks later, only donor cells covered the Dacron graft.
Shi et al. Blood 1998;92:362
Multipotent adults progenitor cells (MAPC) from human BM
Murine Lewis lung carcinoma spheroids in NOD-SCID mice
Studied tumor angiogenesis
J. Clin. Invest. 2002;109:337
1. None of the >4,000 ECs examined had more than two sex chromosomes, consistent with an absence of cell fusion.
2. Y chromosome signals were not detected in sex-matched female recipients, excluding the vertical transmission of male cells.
3. None of the recipients evaluated before hematopoietic engraftment demonstrated donor-derived ECs, indicating a close linkage between the recovery of hematopoiesis and EC outcomes.
(Jiang et al. PNAS 2004)
To determine the EC potential of human BM and PBC, blood vessels in sex-matched transplant recipients were evaluated
Iwami et al. J Cell Mol Med 2004
Putative Cascade and Expressional Profiles of Human BM-derived EPC Differentiation
Endothelial Progenitor Cells
Positive for CD34 and VEGFR2 expression.Sometimes CD133 (AC133, prominin) - more likely to
reflect immature progenitor cells.
CD34+/VEGFR2+ cells may also represent shedded EC of the vessel wall.
Proof of EC characteristics after outgrowth and differentiation in vitro.
May also be isolated from fetal liver or umbilical cord blood.
No data on lifetime in vivo of EPC under physiological or pathological conditions.
PhysiologicalAge Gender (estrogen)Embryonal developmentExercise
PathologicSmokingStable coronary artery diseaseMyocardial infarction (tissue ischemia)Vascular trauma
DrugsStatins
Growth factorsVEGFG-CSF/GM-CSFSDF-1ErythropoietinPPARgamma
Important factors for mobilization and proliferation of EPC:
EPC dependent on what environment it enters into.
Poor endothelialization usually leads to enhanced vascular disease.
Diabetes mellitus: decreased proliferation capacity, reduced adhesiveness and ability to form capillary tubes in vitro. Diabetics shed more EC into circulation.
Hypercholesterolemia - dysfunction in mature EC.
SDF-1 attracts progenitors to ischemic tissuesCXCR4VEGF
2-integrins and 41-integrins are capable of mediating cell-cell interactions important for adhesion.
Chemotaxis, Adhesion, Migration
Neovascularization
- Circulating mature EC do not improve neovascularization.- Tissue injury stimulate EPC incorporation.- Incorporation varies in the literature, between 0>50%.- The >50% predominantly detected in models of tumor angiogenesis.- Even if low incorporation, EPC may have other characteristics that promote neovascularization such as release of proangiogenic factors.
Endothelial Regeneration
- Dacron vascular grafts and ventricular assist devices covered by endothelial progenitors.- Denudation of artery after balloon injury re-endothelialized.- Rapid re-endothelialization may improve atherosclerosis and prevent restenosis.
Werner et al. Circ. Res. 2003
Carotid Injury Model
EPC Contribute to Re-Endothelialization after Vascular Injury
EC visualized using FITC-labeled lection
Potential for therapy of EPC
Critical limb ischemiaMyocardial infarctionVascular graftsStrokePulmonary hypertensionDiabetic retinopathyNeoplasm
Necessity to develop standardized methods to isolates, phenotype, and evaluate quality of cells.
The number in the circulation may limit therapeutic use.
EndotheliumInternal elastic lamina
MediaExternal elastic lamina
Adventitia
Differentiation between the arterial and venous
side of the vasculature.
Layers of the Vascular Wall
The bone marrow contains two apparently discrete populations of stem cells. In addition to the HSC/EPC, there are also bone marrow stromal cells or mesenchymal stem cells (MSC).
Less characterized than the HSC/EPC and its exact location within the bone marrow is less clear.
Low density in bone marrow aspirate.
Markers for MSC
Adherent cells
WGA binding and Sca-1 (null mice, late osteoporosis)
Enriched population: Sca-1+Lin-CD31-CD45-30% plating efficiency
STRO-1+ : Includes all CFU-F
CD105 (endoglin)
Negative for CD34, CD45, CD11b
Location of MSC in bone marrow
Most likely in the vessel wall in the bone marrow.
Would be similar to vascular smooth muscle cells and pericytes, or endosteal cells.
Cultured MSCExpress alpha-SMC (70%)H-caldesmonMetavinculinCalponinSM-MHCProteins constituting basal laminaSimilar response to PDGF as pericytesSTRO-1+
Potential for differentiation into a variety of cell types
The MSC may be guided into specific, single-lineage differentiation by culture in serum-free “induction media” containing growth factors and specific treatments.
MSC in the Artery Wall
SMC precursors in adults: concept of a continuous replacement of connective tissue with e.g. marrow cells, analogously to continuous replacement of blood cells.
However, they may also be the source of ectopic tissue formation commonly seen in diseased vascular wall.
(Liu et al. Trends Cardiovasc Med 2004)
Chimeric male -SM-actin and calponin positive cell in neointima in female after sex-mismatched BM transplantation
MSC in Circulation and Artery Wall
Artery wall may function as a recipient and a donor of MSC.May enter circulation and engraft elsewhere
Cells in circulation may be derived from marrow or other places
Vasculature and microvasculature present in all organs and tissuesAll adult stem cells may be vascular stem cells
Calcifying Vascular Cells (CVC) - A Cloned Subpopulation of SMC
Form condensations and nodules.
Osteoblastic differentiation and calcification occur in the nodules.
CVC express MGP and BMP-2.
Regulation of Vascular Stem Cell Lineage
TGF-ß superfamily of growth factorsBMPsTGF-ßs
Microenvironment, matrix
Hemodynamic factorsGraftsPulmonary hypertension
Hu et al. J Clin Invest 2004
Adventitial Cells Contribute to Neointima Formation in Irradiated Vein Graft
Type and Extent of Injury May Determine from Where SMC Progenitors Come
INJURY ORIGIN OF SMCLimited medial-VSMC damage Medial/intimal VSCMSevere medial-VSMC damageIngrowth from adjoining vesselsFull medial-VSMC disrupture Recruitment from non-BM sources
Recruitment from BM
5-100% of SMC cells in arterial injury from bone marrow in transplant models
Factors Affecting Engraftment of MSC
AGAINSTHealed vascular injuryExternal vs internal vascular injuryHyperlipidemiaLow estrogenLow erythropoietinDiabetes
FORInflammationInjury Ischemic injuryAtherosclerosis, neointimaVascular graftCancerExercise
Potential for Therapy of MSC
ParalysisStrokeHeart attackNeurodegenerative diseasesOsteogenesis imperfecta
Acute Myocardial Infarction and Heart Failure
In AMI, homing factors appears to be up-regulated in the injury areaThus, EPC and MSC will enter that area
SDF-1 is a homing factor for EPC; MSC do not react
Once the injury area has healed - no homing of cells
G-CSF may be used to increase EPC pool
Improvement from vascularization, increased ejection fractionImprovement from actual cardiac muscle regeneration