KERATINOCYTES AND KERATINOCYTES AND KERATINIZATIONKERATINIZATION

M.YOUSRY ABDEL-MAWLAM.YOUSRY ABDEL-MAWLA

SKIN STRUCTURESKIN STRUCTURE

SKIN or INTEGUMENT: Roles

chemical-mechanical PROTECTION water loss radiation

bugs immune

SENSORY

THERMOREGULATION

METABOLISM vitamin D fat storage

COMMUNICATION

MECHANICAL friction surface scratching

WABeresford

SKIN or INTEGUMENT: Structures

EPIDERMIS keratinized stratified squamous epithelium

DERMIS dense irregular, mostly collagenous CT

HYPODERMIS adipose connective tissue

ADNEXA (accessories) sweat & sebaceous glands, hair follicles & hairs, nails, mammary glands , nerves & nervous receptors, special blood vessels

EPIDERMIS: Cell types

Keratinocytes

Langerhans APC cell immunity

Melanocyte to make & transfer pigment

Merkel cell sensory

dead

alive

Nerve cell represented by its axon

EPIDERMIS: Layers & events

STRATUM CORNEUM of dead, but attached, ‘hardened & wrapped‘ cells , will slough offS. GRANULOSUM multiple syntheses

to make cornified cellsS. SPINOSUM upward migration of keratinocytes, while keratins IFs increase & change

S. BASALE mitosis of stem cells

Keratinocyte differentiation

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capillary loop

Meissner’s corpuscle

DERMIS Papillary layer}

}DERMIS Reticular layer

}HYPODERMISFat cells

Sweat gland

EPIDERMIS}duct

Pacinian corpuscle

THICK, HAIRLESS SKIN

capillary loop

EPIDERMIS}Pacinian corpuscle

THICK, HAIRLESS SKIN

no hair follicles no sebaceous glands

sweat gland opens at top of ridge

dermal papilla

dense thick collagen fibers + elastic fibers

secretory profiles of coiled tubule

coiled duct of sweat gland &

THIN HAIRY SKIN

Papilla of Hair follicle

Root sheath

Hair shaft Sebaceous gland

Arrector pili muscleSweat gland

D

E

R

M

I

S

Epidermis

HYPODERMIS

Matrix

SKIN or INTEGUMENT: Roles - Correlations

PROTECTION chemical- mechanical water loss, bugs

immune

SENSORY

THERMOREGULATION

METABOLISM vitamin D fat storage

COMMUNICATION

MECHANICAL

keratin, melanin, sebum thick epithelium , hair, dermal papillae

Langerhans cells dermal lymphocytes

sensory receptors & fibers

blood flow, sweat gands, hair, fat

keratinocytes adipocytes

blood flow, pigment, hair, facial skin

‘fingerprint’ ridges, sweat glands, nails

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MOLECULAR EPIDERMIS

CORNEUM CELLS

ANCHORING FIBRILS

LAMINA DENSA

LAMINA LUCIDA

HEMIDESMOSOMES

BASAL CELL

type VII collagen

laminin type IV collagen

epiligrin BM 600anchoring

filaments

glycolipid cadherin-P T-transglutaminase 1

keratins

hemidesmosomal proteins integrin a6b4

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HAIR FOLLICLE 4

There are two cuticles, so that the hair’s can separate from the follicle’s for the hair to move & be coated with greasy sebum

HAIR SHAFTMedulla

OUTER ROOT SHEATH

CT sheath

CortexCuticle

DERMAL PAPILLA

MATRIX

13

4

5

6

Medulla

Cortex

Cuticle

Cuticle

Huxley’s layerHenle’s layer

INNER ROOT SHEATH

HAIR SHAFT

OUTER ROOT SHEATH

is continuous with the epidermis

2

includes pigment cells for hair color

CYCLE OF HAIR GROWTH

Rate of growth

ANAGENCATAGEN

ANAGENTimeTELOGEN

TELOGEN (end) quiescence

shedding

ANAGEN regrowth of matrix & papilla, then hair

ANAGEN growth

CATAGEN breakdown

EPIDERMAL CHARACTERISTICS EPIDERMAL CHARACTERISTICS

TISSUE RENEWALTISSUE RENEWALTISSUE STRENGTHTISSUE STRENGTHCORNIFICATIONCORNIFICATIONSTRUCTURESTRUCTUREFUNCTIONFUNCTIONSEQUENCES OF FAILURESEQUENCES OF FAILURE

FUNCTIONS OF THE EPIDERMISFUNCTIONS OF THE EPIDERMIS

Form a protective barrier from physical insultsForm a protective barrier from physical insults ChemicalChemical BiologicalBiological TemperatureTemperature MechanicalMechanical -Protect body homeostasis-Protect body homeostasis Temperature regulationTemperature regulation Prevent fluid lossPrevent fluid loss -Immune surveillance-Immune surveillance -Sensory organ-Sensory organ

CONSEQUENCES OF EPIDERMAL CONSEQUENCES OF EPIDERMAL FAILURE:FAILURE:DEATHDEATH

Toxic Epidermal NecrolysisToxic Epidermal Necrolysis –life-threatening –life-threatening consequences are dehydration and infectionconsequences are dehydration and infection

Mutations in genes that severely compromise Mutations in genes that severely compromise epidermal function are embryonic/neonatal lethalepidermal function are embryonic/neonatal lethal

CHARACTERISTICS OF THE CHARACTERISTICS OF THE EPIDERMIS EPIDERMIS

TISSUE RENEWAL–Continuous self-TISSUE RENEWAL–Continuous self-renewal of keratinocytesrenewal of keratinocytes

STRENGTH–Both intracellular and STRENGTH–Both intracellular and intercellular strengthintercellular strength

CORNIFICATION–Process that creates a CORNIFICATION–Process that creates a water impermeable barrierwater impermeable barrier

Self-renewing tissue requiresSelf-renewing tissue requires

A highly regulated process A highly regulated process that balances cellular that balances cellular proliferation and cell deathproliferation and cell death

TISSUE RENEWALTISSUE RENEWAL

Stem cellsStem cells Proliferating cellsProliferating cells Terminal Terminal

differentiationdifferentiation

Two functions required of proliferating cells in a self-Two functions required of proliferating cells in a self-renewing tissue:renewing tissue:

Maintain the integrity of the Maintain the integrity of the genomegenome

Stem cellsStem cells - -located within located within the bulge region of the hair the bulge region of the hair follicle and at the base of follicle and at the base of rete ridgesof interfollicularrete ridgesof interfollicular

epidermisepidermis Maintain the correct cell Maintain the correct cell

number in epidermisnumber in epidermis

Transient amplifying cellsTransient amplifying cells - -located immediately located immediately adjacent to clusters of adjacent to clusters of stem cellsstem cells

KERATINOCYTE STEM CELLSKERATINOCYTE STEM CELLS pluripotent cellspluripotent cells slowly replicating cells slowly replicating cells

(label retaining cells)(label retaining cells) replicate replicate

symmetrically (a stem symmetrically (a stem cell can divide into cell can divide into two equal daughter two equal daughter stem cells)stem cells)

How does a stem cell remain a stem How does a stem cell remain a stem cell?cell?

Most agree the local microenvironment Most agree the local microenvironment (including both mesenchymal and (including both mesenchymal and keratinocyte cell-cell interactions. But right keratinocyte cell-cell interactions. But right now there are very few details on what now there are very few details on what keeps the cellskeeps the cells “stemness”“stemness”

Example of two proteins implicated in the Example of two proteins implicated in the maintenance ofmaintenance of stemnessstemness

β-cateninβ-catenin mycmyc

β-cateninβ-catenin - -Identified as part of the cytoplasmic Identified as part of the cytoplasmic plaque in adherens junctions “structural protein” plaque in adherens junctions “structural protein” link between cadherins and actin filamentslink between cadherins and actin filaments

Keratinocyte stem cells have a high level of free, Keratinocyte stem cells have a high level of free, non-cadherin -associatednon-cadherin -associated β-catenin β-catenin

KERATINOCYTE STEM CELLSKERATINOCYTE STEM CELLS

β-cateninβ-catenin Constitutively active β-Constitutively active β-

catenincatenin leads to highly enriched leads to highly enriched

stem cell populationβstem cell populationβ

Dominant-negative β-Dominant-negative β-catenincatenin

stimulates exit from stem stimulates exit from stem cellcell

compartment into transientcompartment into transient amplifying cellsβ-amplifying cellsβ-

KERATINOCYTE STEM CELL SKERATINOCYTE STEM CELL Smyc (c-myc)myc (c-myc)Proto-oncogene involved with induction of Proto-oncogene involved with induction of

cell proliferationIn the epidermis.cell proliferationIn the epidermis. mycmyc stimulates exit from the stem cell stimulates exit from the stem cell

compartment into transient amplifying cellscompartment into transient amplifying cells

Stem cell failure in epidermisStem cell failure in epidermis Loss of stem cells may lead to phenotype of aged Loss of stem cells may lead to phenotype of aged

epidermis?epidermis? -flattening of the epidermal/dermal junction-flattening of the epidermal/dermal junction -keratinocyte cell size becomes variable-keratinocyte cell size becomes variable -nuclear atypia-nuclear atypia -loss of melanocytes-loss of melanocytes -loss of Langerhanscells-loss of Langerhanscells -slowed injury response-slowed injury response -slowed chemical clearance-slowed chemical clearance -decreased immune response-decreased immune response -decreased resistance to mechanical stress-decreased resistance to mechanical stress -increased incidence of cancer-increased incidence of cancer

KERATINOCYTE ProliferationKERATINOCYTE Proliferation

most of proliferation most of proliferation done by transient done by transient amplifyingcells (amplifyingcells (TA TA cellscells))

-in normal epidermis, -in normal epidermis, all TA cells remain all TA cells remain attached to basement attached to basement membranemembrane

-transition from stem -transition from stem cell to TA cell is the cell to TA cell is the first step in first step in keratinocytes keratinocytes differentiationdifferentiation

Epidermal proliferationEpidermal proliferation

in normal epidermis, all in normal epidermis, all TATA cells remain cells remain attached to basement attached to basement membranemembrane

-transition from stem -transition from stem cell to cell to TATA cell is the first cell is the first step in keratinocyte step in keratinocyte differentiationdifferentiation

-TA-TA cells migrate cells migrate laterally along the laterally along the basement membranebasement membrane

Epidermal proliferationEpidermal proliferation

--TATA cells migrate cells migrate laterally along the laterally along the basement basement membranemembrane

--TATA cells have a cells have a restricted ability to restricted ability to proliferate -usually proliferate -usually divide only 3-5 timesdivide only 3-5 times

Epidermal proliferationEpidermal proliferation

Once Once TA TA cells stop cells stop proliferating, they proliferating, they lose their lose their attachment to the attachment to the basement basement membrane membrane

Proceed towards Proceed towards terminal terminal differentiationdifferentiation

Vitamin DVitamin D in epidermis proliferation in epidermis proliferation

Vitamin DVitamin D and the and the Vitamin D receptorVitamin D receptor

––active molecule is active molecule is 1α,25(OH)2D31α,25(OH)2D3

-binds to VDR inside of -binds to VDR inside of cellcell

-functions as a -functions as a homodimer, or homodimer, or heterodimer with RXR, heterodimer with RXR, RAR, THRRAR, THR

-Dimers are -Dimers are transcriptional factorstranscriptional factors

Vitamin DVitamin D in the epidermis in the epidermis::

Activation of the VDR inActivation of the VDR in quiescent quiescent or or slowly cycling cells stimulates a slowly cycling cells stimulates a proliferativeproliferative response response

-activation of the VDR in -activation of the VDR in prfolieratingprfolierating cells cells stimulates a stimulates a differentiationdifferentiation response response

Epidermal proliferationEpidermal proliferation

NF-κBNF-κB

transcription factor associated with response to cell stresstranscription factor associated with response to cell stress -maintained inactive in cytoplasm through association -maintained inactive in cytoplasm through association

with IκBwith IκB

cell stress activates IKK complex of IKKα, IKKβ, and IKKγleads cell stress activates IKK complex of IKKα, IKKβ, and IKKγleads to phosphorylation of IκBto phosphorylation of IκB

-phosphorylation of IκB leads to degradation and release of -phosphorylation of IκB leads to degradation and release of NF-κBNF-κB

-NF-κBis now free to enter nucleus and activate transcription-NF-κBis now free to enter nucleus and activate transcription

Epidermis proliferation sequences Epidermis proliferation sequences of failureof failure

Dysregulation of proliferation can lead to Dysregulation of proliferation can lead to hypo-proliferativehypo-proliferative

&& hyperproliferative diseaseshyperproliferative diseases

KERATINOCYTE TERMINAL KERATINOCYTE TERMINAL DIFFERENTIATIONDIFFERENTIATION

--when awhen a keratinocyte releases from the keratinocyte releases from the basement membrane, it undergoes changes basement membrane, it undergoes changes in morphology and gene expressionin morphology and gene expression

-gradual change in cell strength and water -gradual change in cell strength and water impermeabilityimpermeability

-terminally differentiated keratinocytes -terminally differentiated keratinocytes synthesize asynthesize a cornifiedcornified cell envelope and cell envelope and undergoundergo programmed cell deathprogrammed cell death

Keratinocyte morphology and functionKeratinocyte morphology and function

Stratum corneum–keratinocytesStratum corneum–keratinocytes contain contain thickened cell envelopes, contain no nucleus, thickened cell envelopes, contain no nucleus, imbedded in lipid matriximbedded in lipid matrix

Stratum granulosumStratum granulosum–cells–cells become elongated, become elongated, usually 1-2 cell layers thick,accumulate amorphous usually 1-2 cell layers thick,accumulate amorphous keratohyaline granuleskeratohyaline granules

Stratum spinosumStratum spinosum–cells–cells increase in increase in size,increased cytoplasm:nucleus ratio, cell layer4-size,increased cytoplasm:nucleus ratio, cell layer4-6 cells thick, no further cell division6 cells thick, no further cell division

Stratum basaleStratum basale–cuboidal cells–cuboidal cells, cells within this , cells within this layer proliferate, all cells attached to thebasement layer proliferate, all cells attached to thebasement membrane, one cell layer thick.membrane, one cell layer thick.

Differentiation-specificDifferentiation-specificproteins expressed proteins expressed

Stratum corneumStratum corneum: : no new protein expressionno new protein expression ....

StratumStratum granulosumgranulosum : :keratins K1 and K10keratins K1 and K10, , loricrin, filaggrin, transglutaminase3loricrin, filaggrin, transglutaminase3

Stratum spinosumStratum spinosum: : keratins K1 and keratins K1 and K10,involucrin,envoplakin,periplakin, 14-3-3σK10,involucrin,envoplakin,periplakin, 14-3-3σ

Stratum basalStratum basal: : keratins K5 and K14integrins, keratins K5 and K14integrins, p63p63

Regulation of keratinocyte cell Regulation of keratinocyte cell transitionstransitions

Stem cells intoStem cells into TATA: : upregulation of upregulation of catenin,integrins andcatenin,integrins and vitamin Dvitamin D

TATA cells into squamous cellscells into squamous cells: : lossloss ofof integrins integrins and and vitamin Dvitamin D

Squamous cell into Granular cellSquamous cell into Granular cell: Epidermal : Epidermal differentiation complexdifferentiation complex((EDCEDC))

Epidermal Differentiation ComplexEpidermal Differentiation ComplexChromosome 1q21Chromosome 1q21

InvolucrinInvolucrin : :scaffolding protein, lipid scaffolding protein, lipid attachmentattachment

FilaggrinFilaggrin : :bundles keratin filamentsbundles keratin filaments LEP/XP-5SPR familyLEP/XP-5SPR family: : cross-bridging proteinscross-bridging proteins LoricrinLoricrin major reinforcement protein of CERmajor reinforcement protein of CER RepetinsRepetins : :cross-bridging proteincross-bridging protein S100 A1-A13S100 A1-A13 : :create membrane environment create membrane environment

of CE initiationof CE initiation SmallSmall proline rich SPRproline rich SPR : :cross-bridging cross-bridging

proteinsproteins TrichohyalinTrichohyalin : :flexible cross-bridging proteinflexible cross-bridging protein

Epidermis Tissue StrengthEpidermis Tissue Strength

1- 1- Intracellular –Intermediate FilamentsIntracellular –Intermediate Filaments2-Intracellular -Adhesion Molecules2-Intracellular -Adhesion Molecules

KERATINOCYTE KERATINOCYTE INTRACELLULAR STRENGTHINTRACELLULAR STRENGTH

Keratins are members of the intermediate Keratins are members of the intermediate filament (IF) gene familyfilament (IF) gene family

there are over 50 members of the IF gene there are over 50 members of the IF gene family that are expressed in a tissue-and family that are expressed in a tissue-and differentiation-specific mannerdifferentiation-specific manner

KERATINOCYTE KERATINOCYTE INTRACELLULAR STRENGTHINTRACELLULAR STRENGTH

--IF proteins have a conserved central rod domain of IF proteins have a conserved central rod domain of helical coiled-coil segmentshelical coiled-coil segments

-the amino-and carboxy-terminal sequences of IF -the amino-and carboxy-terminal sequences of IF proteins are variableproteins are variable

keratins heterodimerize with specific pairing keratins heterodimerize with specific pairing partners:partners:

one Type I familyone Type I family one Type II familyone Type II family -the heterodimers then oligomerize into longer fibrils-the heterodimers then oligomerize into longer fibrils

fibrils continue to assemble until IF is 10-12 nm in fibrils continue to assemble until IF is 10-12 nm in diameterdiameter

--keratin filaments extend from the keratin filaments extend from the nuclear membrane to desmosomal nuclear membrane to desmosomal plaques at the cell membraneplaques at the cell membrane

-keratins enable keratinocytes to -keratins enable keratinocytes to sustain mechanical and non-sustain mechanical and non-mechanical stressmechanical stress

Genodermatoses Keratin Genodermatoses Keratin (mutation identified)(mutation identified)

Epidermolysis Bullosa SimplexEpidermolysis Bullosa Simplex : :K5, K14K5, K14 Epidermolytic hyperkeratosis:K1Epidermolytic hyperkeratosis:K1, K10, K10 Palmoplantar keratodermaPalmoplantar keratoderma, , epidermolytic:K1, epidermolytic:K1,

K9K9 Palmoplantar keratoderma, diffuse non-Palmoplantar keratoderma, diffuse non-

epidermolyticepidermolytic: K1: K1 Palmoplantar keratoderma, focal non-Palmoplantar keratoderma, focal non-

epidermolyticepidermolytic: : K16K16 Ichthyosis hystrix type Curth-MacklinIchthyosis hystrix type Curth-Macklin : : K1K1

KERATINOCYTEKERATINOCYTE INTERCELLULAR INTERCELLULAR STRENGTHSTRENGTH

Five types of interactions hold keratinocytes Five types of interactions hold keratinocytes together in epidermal sheets:together in epidermal sheets:

HemidesmosomesHemidesmosomes DesmosomesDesmosomes AdherensJunctionsAdherensJunctions Tight JunctionsTight Junctions Gap JunctionsGap Junctions

DesmosomesDesmosomes adhesion site that links the adhesion site that links the

keratincyto keratincyto skeletalcomponents of two skeletalcomponents of two cellscells

-Transmembrane components:-Transmembrane components: desmogleinsdesmogleins desmocollinsdesmocollins -Plaque components:-Plaque components: DesmoplakinDesmoplakin splakoglobin splakoglobin plakophilin plakophilin keratoclamin-keratoclamin- Cytoskeletal component:Cytoskeletal component: keratinkeratin

Adherens JunctionsAdherens Junctions::

1.1. -adhesion site that -adhesion site that links the actin links the actin cytoskeletal cytoskeletal components of two components of two cells-cells-

2.2. Transmembrane Transmembrane components:E-components:E-cadherincadherin

3.3. Plaque Plaque components:catenincomponents:catenin

4.4. -Cytoskeletal -Cytoskeletal component: actinscomponent: actins

Tight JunctionsTight Junctions --form at the apical form at the apical

end of lateral end of lateral membranes forming membranes forming paracellular paracellular diffusion barriersdiffusion barriers

-transmembrane -transmembrane components: components: junctional adhesion junctional adhesion molecules (JAM), molecules (JAM), claudins, occludinsclaudins, occludins

Tight JunctionsTight Junctions

intercellular channels intercellular channels between adjacent cells that between adjacent cells that allow the direct passage of allow the direct passage of low molecular weight low molecular weight metabolites between cells-metabolites between cells-

major protein -connexins, 15 major protein -connexins, 15 different human genes, different human genes, hexameric hemichannels hexameric hemichannels dock with similar proteins dock with similar proteins on adjacent cell-on adjacent cell-

three major classes of three major classes of connexin proteins: Gjα, connexin proteins: Gjα, GJβ, and GJγGJβ, and GJγ

CORNIFICATIONCORNIFICATION

--process that begins in cells of the upper process that begins in cells of the upper spinouslayersspinouslayers

-the induction of proteins that comprise the -the induction of proteins that comprise the cornifiedcell envelope (CCE) are expressed cornifiedcell envelope (CCE) are expressed as intracellular [Ca2+] rise in differentiating as intracellular [Ca2+] rise in differentiating keratinocyteskeratinocytes

-chromosome 1q21 contains cluster of genes -chromosome 1q21 contains cluster of genes called the Epidermal Differentiationcalled the Epidermal Differentiation Complex Complex

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