All about biology of Keratinocytes & skin barrier function. This can help postgraduates to understand basics of dermatology.

2. Human keratinocytes

3. Cytoskeleton
DNA
Microtubules
Actin

4. Functions of the Cytoskeleton
1. Give shape to cell
2. Give support to cytoplasm
3. Organize organelles
4. Transport of vesicles between organelles
5. Interact mechanically with environment
6. Allow cell movement
7. Segregation of chromosomes during mitosis

5. 3 Major Types of Cytoskeletal Protein Filaments
• Each has distinct mechanical properties
• Each formed from a different protein subunit
Intermediate
filaments
(8-16nm)
Microtubules
(Tubulin)
(25 nm)
Microfilaments
(Actin filaments)
(6nm)

6. Intermediate filaments form a strong
network across sheets of cells
Distribute mechanical stress forces
Immunofluorescence micrograph of sheet
of epithelial cells in culture
IF’s shown in green
Cell boundaries in blue

7. IF’s are connected cell-to-cell via desmosomes

8. IF’s have a rope-like structure
Electron micrograph of intermediate filaments

9. Formation of intermediate filaments
• Two monomers form dimer
• Two dimers form tetramer with staggered anti-parallel ends

10. Formation of intermediate filaments
• Tetramers pack in helical array containing 8 tetramers
• 8 tetramers add to growing filament

11. 4 classes of intermediate filaments (IF)

12. Keratin filaments are most diverse class
 Keratins have a common domain
structure that they share with the
other intermediate filament
proteins
 Every epithelial cell type has
distinctive set of keratin proteins
 Specialized keratins in hair, nails

13. keratinization (Cornification)
• Production of keratin
• Terminal differentiation
• Loss of nuclei and organelles
• Metabolism ceases and the cells
are almost completely filled by
keratin

14. Keratin
 Multigene family of proteins that form the
largest component of the intermediate filament
cytoskeleton of epithelial cells (epidermis) and
related appendages

15. Keratin
 The epithelial keratins are co-expressed in
specific pairings obligatory heteropolymers
(heterodimers), each pair consists of one
acidic and one basic keratin that become the
basic building blocks of epithelial intermediate
filaments.

16. Keratin
Keratin
subfamily
pH Members Chromosome
Keratin Type I acidic (K9–K20) 17
Keratin Type II basic (K1–K8) 12

17. Keratin
 Keratin II express in the cells before Keratin I
and induce its synthesis
 There are more than 50 individual members.
Based upon their biochemical properties (e.g.
isoelectric point, molecular weight), keratins
are classified.

19. Keratin
Differential expression of keratin proteins depend
on:
1. Cell type
2. Tissue type
3. Stage of embryonic development
4. Degree of differentiation
5. Disease states
6. Drugs

20. Examples of keratin pairs
KERATIN TYPE SITE
K5/K14(less abundantly, K15) Basal cell layer (proliferation)
K1/K10 Suprabasal compartment (differentiation)
K6/K16(K17) Found normally in:
1. Palmoplantar epidermis
2. In keratinocytes of the nail bed
3. Hair follicle
4. Sebaceous glands
5. Sweat glands
Rapidly induced by:
a) Injury and wounding
b) UV radiation
c) Hyperproliferative conditions (psoriasis,
LP, DLE, warts)
K4/K13 Non-cornifying cells of the mucosa

21. Keratin
Functions of keratin in the epidermis:
1. Crucial role in keratinization
2. Integral part of the structural network that
make hemidesmosomes, desmosomes, BM
(Structural integrity)
3. Maintaining spatial relation between the
nucleus and cytoplasmic organelles
4. Transfer of information between the nucleus
and cell surface and vice versa i.e. cell
signaling.

22. A mutant form of keratin makes skin more
prone to blistering
• Disease with mutant keratin: epidermolysis bullosa simplex
Cross section of normal skin Cross section of skin with mutant
keratin protein disrupting keratin
filament network

23. Questions- intermediate filaments
T/F: IF’s form a network across sheets of cells to give them strength.
True
T/F: IF’s are directly connected to IF’s in other cells without intermediary
factors.
False- connect through desmosomes.
Hair and nails contain which IF?
Keratin
T/F: nuclear lamins are a type of IF?
True

25. PROLIFERATION&
DIFFERENTIATION
 Keratinocytes proliferate in the basal layer
(MITOSIS)
 As the cells move away from the BM they lose
their capacity for cell division and they become
committed to terminal differentiation
 Terminal differentiation (KERATINIZATION): is a
complex process that results in the production of
the impermeable stratum corneum

26. Granules of suprabasal layers
 Keratohyalin granules
1. Profilaggrin filaggrin [filament + aggregating]
2. Loricrin
 Lamellar granules (Odland bodies-lamellar
bodies) contain:
1. Lipids (e.g. ceramides, Phospholipids,),
2. Hydrolytic enzymes (e.g. proteases, acid
phosphatases, glucosidases, lipases)
3. Proteins (e.g. corneodesmosin).

27. Stratum Corneum
Continuous sheet of corneocytes (Cornified Cells)
Connected by corneodesmosomes
Embedded in an intercellular matrix enriched in
non-polar lipids and organized as lamellar lipid
layers
Corneocytes + Intercellular lipid

29. NORMAL THICKNESS OF THE
EPIDERMIS
DIFFERENTIATION PROLIFERATION
There is a balance between the processes of proliferation and desquamation that
results in a complete renewal approximately every 28 days

30. Disturbed
balance
Increased
thickness of the
epidermis

31. KERATINIZATION
EPIDERMAL DIFFERENTIATION

34. At the beginning of the granular layer
1. Keratohyalin granules Formation (KHG) (contains Profilaggrin)
2. Cell envelope proteins cross-linking (Involucrin and Loricrin)
3. Odland bodies get released into the ICS
In the spinous layer: Formation of
1. Lamellar bodies 2. KIF
As the cells enter the spinous layer
Switch of keratin synthesis
from K5/K14 to K1/K10
Initiation of
differentiation

37. As keratinocytes are transformed from mitotically active cells in the basal layer to fully
differentiated, enucleated squames in the cornified layer. Keratohyalin (profilaggrin- and
loricrin-containing) and lamellar (lipid-containing) granules extrude their contents in the
granular layer, leading to bundling of keratin filaments and replacement of the plasma
membrane with the highly cross-linked, lipid-covered cornified cell envelope

38. In the transitional zone
1. Filaggrin (keratin
bundling protein) acts as a
glue matrix that facilitates
dense packing of KIF into
k. macrofibrils
2. activity of
keratinocytes,
3. Loss of organelles
4. Dehydration
5. extracelluar Ca++,
6. activity of
transglutaminase,
deposition of loricrin, cross
linking of involucrin
On entering the transitional zone
between the granular cell layer and
the Cornified layer
Profilaggrin is transformed into filaggrin

39. In response to certain signals probably an increase in calcium concentration during the
transition from the granular layers to the SC the lamellar bodies move to the apex of the
upper-most granular cells, fuse with the plasma membrane, and secrete their content into the
intercellular spaces through exocytosis.
Components of the stratum corneum

40. Corneocytes are shed into the
environment
In upper stratum corneum
1. Formation of corneocyte bound lipid envelope
2. Plasma membrane and desmosomes become discontinuous,
corneodesmosomes are residual intercellular desmosomal
interconnections.
In lower stratum corneum
1. Dead keratinocytes packed with keratin macrofibrils
2. corneocyte bound protein envelope just beneath the plasma
membrane

42. Desquamation of surface keratinocytes from the
stratum corneum is regulated by proteolytic
degradation of the cells’ desmosomes.

43. Any defect along this pathway
leads to
DIORDERS OF KERATINIZATION

44. Genetic defects in the supra-
basal keratins results in:
I. Hyperkeratosis e.g.:
- In icthyosis- retension hyperkeratosis
II. Barrier function defect

45. DISORDERS OF
KERATINIZATION
1. Icthyosis
2. Palmoplantar keratodermas / Erythrokeratoderma
3. Porokeratosis
4. Peeling skin syndromes
5. Discrete keratotic disorders
6. Miscellaneous circumscribed keratotic disorders
7. Filiform keratoses
8. Confluent and reticulate papillomatosis

46. Ichthyosis vulgaris

47. Diffuse
palmoplantar
keratoderma

48. Focal
palmoplantar
keratoderma

49. Porokeratosis

50. Barrier functions
 The skin barrier prevents excessive water loss (TEWL) (inside-
outside barrier) and the entry of harmful substances from
environment (outside-inside barrier).
 The physical barrier is predominantly located in the stratum
corneum & also by tight junctions of viable keratinocytes.
 The 10-20μm thick stratum corneum forms a continuous sheet
of protein enriched cells embedded in an intercellular matrix,
enriched in non-polar lipids & organized as lamellar lipid
layers.
 S. corneum proteins, lipids and low-molecular-weight by-
products of keratohyalin breakdown, referred to as natural
moisturizing factors (NMF) , bind and retain water in the s
corneum, thus maintaining its elasticity

51. Natural moisturizing factor (NMF)
 Collection of water-soluble
compounds that are only
found in the stratum corneum.
 These compounds compose
approximately 20-30% of the
dry weight of the corneocyte.
 NMF components absorb
water from the atmosphere
and combine it with their own
water content allowing the
outermost layers of the
stratum corneum to stay
hydrated.
 The lipid layer surrounding
the corneocyte helps seal the
corneocyte to prevent loss of
NMF.
Because NMF components are water
soluble, they are easily leached from
the cells with water contact - which is
why repeated contact with water
actually makes the skin drier.

55. Lipid Composition & Role of
Lipids in the Stratum Corneum
The major lipid classes in the SC are
I. Ceramides.
II. Cholesterol.
III. Free fatty acids

56. CERAMIDES
 Is an amide linked fatty acid containing a long-
chain amino alcohol called sphingoid base.
 Glucosyl-ceramide is enriched in the epidermis
and spleen.
 Ceramide is a major lipid component in the
SC, accounting for 30 to 50 % of lipids by
weight.
 Terminal differentiation is a key factor in
accumulating ceramides.

57. CHOLESTEROL
 In the epidermis is synthesized in situ from
acetate & also basal cells are capable of
reabsorbing cholesterol from circulation.

58. TEWL
 The normal movement of water from the SC
into the atmosphere is known as trans-
epidermal water loss (TEWL).
 TEWL used to assess the barrier function of
the st. corneum used to predict irritancy of
substances or to contribute to the assessment
of clinical methods.

59. Percutaneous Absorption
 Skin allows some permeation of almost every
substances and rates of penetration is different for
different materials
 Percutaneous absorption studied both in vitro and in vivo
In vitro – using sheets of epidermis or st. corneum
In vivo – corticosteroids – vasoconstriction
nicotine – vasodilation
histamine –wheal
pilocarpine –sweating
anesthesia – local anesthetics

60. Protection against – UV radiation
 The skin has 3 barrier to UV radiation
I. Melanin barrier
II. Protein barrier
III. Absorption of radiation by epidermal
lipids may contribute to protection from
UV radiation.

61. Skin failure
 A loss of normal temperature control with inability to
maintain the core temperature, failure to prevent
percutaneous loss of fluid, electrolytes and protein with
resulting imbalance and failure of the mechanical barrier
to penetration of foreign materials
 If generalized It is a dermatological emergency
 Causes are
1. Stevens Johnson syndrome (SJS)
2. Toxic epidermal necrolysis (TEN)
3. Pustular psoriasis
4. Erythroderma of various causes
5. Pemphigus vulgaris (PV)
6. Graft vs. host disease (GVHD)

62. Regional variation in barrier function
 Differences esp. in the composition and
organization of lipids in the epithelial barriers
result in regional variation in permeability
 The epidermis over scrotum and eyelids are
particularly thin
 Scrotum is particularly permeable to all
substances.
 Face, forehead & dorsa of hands are more
permeable to water than the trunk, arms & legs.
 The palms & soles particularly impermeable to
nearly all molecules except water.

63. AGE RELATED VARIATION IN
PERMEABILITY
 The aged skin is more permeable to chemical
substances.
 The aged skin is more dry.
 Although substances enter aged skin more
easily than young skin , they are removed
more slowly into the circulation because of
changes in the dermal matrix and reduction in
vasculature.
 The water binding capacity is and the
renewal time after damage is in old age.

64. Dermatoses with skin barrier
impairment
 Mild impairment in skin barrier in skin condition without
inflammation
1- Icthyosis vulgaris
2- Darier disease.
 Pronounced impairment in skin barrier is associated with
inflammatory disease
1. Irritant & allergic contact dermatitis
2. Atopic dermatitis
3. Seborrhoeic Dermatitis
4. Psoriasis
5. Cutaneous T-cell lymphoma .
 Most of the blistering diseases especially inflammatory
related shows an increase in TEWL especially after
loosening of the blister roof .

65. Therapeutic importance of barrier
 In inflammatory diseases treatment with corticosteroids,
cyclosporine, tacrolimus, pimecrolimus & UV light has
been shown to reduce cell inflammation as well as to
improve barrier function thus helping to normalize
proliferation & differentiation.
 Because of side effects their treatment should be used
for short time only.
 In contrast application of bland cream & ointments
containing lipids & lipid like substances, hydrocarbon,
fatty acid , cholesterol esters & triglycerides can be used
without side effects for long term treatment of mild to
moderate inflammatory disease.

66. Therapeutic importance of barrier
 Creams and ointments are partially correct or
stimulate barrier repair & St. corneum hydration,
thus influences epidermal proliferation &
differentiation.
 It has been proposed that lipid mixture containing
the three key lipid groups:
1. Ceramides.
2. Cholesterol.
3. Free fatty acids.
able to improve skin barrier function & st. corneum
hydration in atopic dermatitis.

67. References

68. THANK YOU