K E R A T I N I Z A T I O N

1. KERATINOCYTES AND KERATINOCYTES AND
KERATINIZATIONKERATINIZATION
M.YOUSRY ABDEL-MAWLAM.YOUSRY ABDEL-MAWLA

2. SKIN STRUCTURESKIN STRUCTURE

3. 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

4. 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

5. EPIDERMIS: Cell types
Keratinocytes
Langerhans
APC cell
immunity
Melanocyte to
make & transfer
pigment
Merkel cell
sensory
dead
alive
Nerve cell
represented by its
axon

6. EPIDERMIS: Layers & events
STRATUM CORNEUM of dead, but
attached, ‘hardened & wrapped‘ cells , will
slough off
S. GRANULOSUM multiple syntheses
to make cornified cells
S. SPINOSUM upward
migration of keratinocytes,
while keratins IFs increase &
change
S. BASALE mitosis of stem cells
Keratinocyte
differentiation
}
}

7. capillary
loop
Meissner’s
corpuscle
DERMIS
Papillary layer}
}
DERMIS
Reticular layer
}
HYPODERMIS
Fat cells
Sweat gland
EPIDERMIS
}
duct
Pacinian
corpuscle
THICK, HAIRLESS SKIN

8. 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 &

9. THIN HAIRY SKIN
Papilla of Hair follicle
Root
sheath
Hair shaft Sebaceous gland
Arrector pili muscle
Sweat gland
D
E
R
M
I
S
Epidermis
H
Y
P
O
D
E
R
M
I
S
Matrix

10. Autonomic motor
Sweat gland
D
E
R
M
I
S
Epidermis
Vessel
vasomotor
THIN HAIRY SKIN: Innervation
Arrector pili muscle
pilomotor
sudomotorSensory

11. 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

12. {
MOLECULAR EPIDERMIS
CORNEUM
CELLS
ANCHORING FIBRILS
LAMINA DENSA
LAMINA LUCIDA
HEMIDESMOSOMES
BASAL CELL
type VII collagen
laminin
type IV collagen
epiligrin
BM 600
anchoring
filaments
glycolipid
cadherin-P
T-transglutaminase 1
keratins
hemidesmosomal proteins
integrin a6b4
{

13. 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
{
{

14. HAIR FOLLICLE: LAYERS at one cross-section
Medulla
Cortex
Cuticle
Cuticle
Huxley’s layer
Henle’s layer
OUTER ROOT
SHEATH
CT sheath
INNER ROOT SHEATH
HAIR SHAFT
4
3
2
1
Before getting lost in the layering, note the 4 main
parts. For the matrix & dermal papilla, see next
Hair
bulb

15. HAIR FOLLICLE: LAYERS longitudinal
HAIR SHAFT
Medulla
OUTER ROOT
SHEATH
CT sheath
Cortex
Cuticle
DERMAL PAPILLA nourishes & controls the matrix
MATRIX
Cuticle
Huxley’s layer
Henle’s layer
INNER ROOT SHEATH
1
2
3
4
5
6
OUTER ROOT
SHEATH
Medulla
Cortex
Cuticle
CT sheath
Cuticle
Huxley’s layer
Henle’s layer
INNER ROOT SHEATH
HAIR SHAFT
grows
&
1
2

16. 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 SHAFT
Medulla
OUTER ROOT
SHEATH
CT sheath
Cortex
Cuticle
DERMAL PAPILLA
MATRIX
13
4
5
6
Medulla
Cortex
Cuticle
Cuticle
Huxley’s layer
Henle’s layer
INNER ROOT SHEATH
HAIR SHAFT
OUTER ROOT
SHEATH
is continuous with
the epidermis
2
includes
pigment cells
for hair color

17. CYCLE OF HAIR GROWTH
Rate
of
growth
ANAGEN
CATAGEN
ANAGEN
Time
TELOGEN
TELOGEN (end)
quiescence
shedding
ANAGEN
regrowth of matrix
& papilla, then hair
ANAGEN
growth
CATAGEN
breakdown

18. EPIDERMAL CHARACTERISTICS EPIDERMAL CHARACTERISTICS
TISSUE RENEWALTISSUE RENEWAL
TISSUE STRENGTHTISSUE STRENGTH
CORNIFICATIONCORNIFICATION
STRUCTURESTRUCTURE
FUNCTIONFUNCTION
SEQUENCES OF FAILURESEQUENCES OF FAILURE

20. 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

21. 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

22. 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 CORNIFICATION–Process that creates
a water impermeable barriera water impermeable barrier

23. 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

24. TISSUE RENEWALTISSUE RENEWAL
Stem cellsStem cells
Proliferating cellsProliferating cells
Terminal Terminal
differentiationdifferentiation

25. 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

26. 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)

27. 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

28. 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

30. 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-

31. KERATINOCYTE STEM CELL SKERATINOCYTE STEM CELL S
myc (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

32. 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

34. 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

35. Epidermal proliferationEpidermal proliferation
in normal epidermis, in normal epidermis,
all 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 cell is the
first step in first step in
keratinocyte keratinocyte
differentiationdifferentiation
-TA-TA cells migrate cells migrate
laterally along the laterally along the
basement membranebasement membrane

36. 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

37. 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

38. 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

39. 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

40. Epidermal proliferationEpidermal proliferation
NF-κBNF-κB
transcription factor associated with response to cell transcription factor associated with response to cell
stressstress
-maintained inactive in cytoplasm through association -maintained inactive in cytoplasm through association
with IκBwith IκB
cell stress activates IKK complex of IKKα, IKKβ, and cell stress activates IKK complex of IKKα, IKKβ, and
IKKγleads to phosphorylation of IκBIKKγleads to 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

41. 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

42.  KERATINOCYTE TERMINAL KERATINOCYTE TERMINAL
DIFFERENTIATIONDIFFERENTIATION

43. --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

46. 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 size,increased cytoplasm:nucleus ratio, cell
layer4-6 cells thick, no further cell divisionlayer4-6 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.

47. Differentiation-specificDifferentiation-specific
proteins 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

49. 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))

50. Epidermal Differentiation ComplexEpidermal Differentiation Complex
Chromosome 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

51. Epidermis Tissue StrengthEpidermis Tissue Strength
1- 1- Intracellular –Intermediate FilamentsIntracellular –Intermediate Filaments
2-Intracellular -Adhesion Molecules2-Intracellular -Adhesion Molecules

52. 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

53. 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

55. --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

56. 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

58. 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

60. DesmosomesDesmosomes
adhesion site that links the adhesion site that links the
keratincyto keratincyto
skeletalcomponents of two skeletalcomponents of two
cellscells
-Transmembrane -Transmembrane
components:components:
desmogleinsdesmogleins
desmocollinsdesmocollins
-Plaque components:-Plaque components:
DesmoplakinDesmoplakin
splakoglobin splakoglobin
plakophilin plakophilin
keratoclamin-keratoclamin-
Cytoskeletal component:Cytoskeletal component:
keratinkeratin

61. Adherens JunctionsAdherens Junctions::
-adhesion site that -adhesion site that
links the actin links the actin
cytoskeletal cytoskeletal
components of two components of two
cells-cells-
Transmembrane Transmembrane
components:E-components:E-
cadherincadherin
Plaque Plaque
components:catenincomponents:catenin
-Cytoskeletal -Cytoskeletal
component: actinscomponent: actins

62. 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

63. 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

65. 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
ComplexComplex

75. THANK THANK
YOUYOU