KERATINOCYTES AND KERATINIZATION

Transcription

1 KERATINOCYTES AND KERATINIZATION The human skin is a large organ comprising a sheetlike investment of the whole body that adapts admirably to its contours and neatly conforms to the movements of the organism within. George Odland Physio., Biochem., and Mol. Biol of the Skin EPIDERMIS OVERVIEW EPIDERMAL CHARACTERISTICS TISSUE RENEWAL CELLULAR PROLIFERATION CORNIFICATION STRUCTURE/FUNCTION CONSEQUENCES OF FAILURE

2 KERATINOCYTES AND KERATINIZATION EPIDERMIS: - the outermost layer of the skin - stratified squamous epithelia -avascular - interactions between all the cell types of the skin are critically important for maintenance of the skin - varies in thickness depending on the anatomic site µm thick - up to µm thick on palms and soles

3 CELLS TYPES IN THE EPIDERMIS At least five cell types are found in the epidermis: Melanocytes Langerhans cells Merkel cells Lymphocytes Keratinocytes

4 EPIDERMAL APPENDAGES -Hair - Sebaceous glands - Eccrine glands - The basement membrane that separates the epidermis from the dermis is continuous throughout the appendages

5 FUNCTIONS OF THE EPIDERMIS - Form a protective barrier from physical insults Chemical Biological Temperature Mechanical - Protect body homeostasis Temperature regulation Prevent fluid loss - Immune surveillance - Sensory organ

6 CHARACTERISTICS OF THE EPIDERMIS THAT ACCOUNT FOR FUNCTION TISSUE RENEWAL Continuous self-renewal of keratinocytes STRENGTH Both intracellular and intercellular strength CORNIFICATION Process that creates a water impermeable barrier

7 CONSEQUENCES OF EPIDERMAL FAILURE: DEATH Toxic Epidermal Necrolysis life-threatening consequences are dehydration and infection Mutations in genes that severely compromise epidermal function are embryonic/neonatal lethal

8 TISSUE RENEWAL Fine balance between new cell replication and cell death Characteristics of Self-renewing Epidermis: Keratinocyte Stem Cells Keratinocyte Proliferation Keratinocyte Terminal Differentiation Fuchs and Raghavan (2002), Nature Rev. 3: 199

9 KERATINOCYTE STEM CELLS - stem cells are slowly replicating cells - a stem cell divides into another stem cell or a cell committed to differentiation - stem cells are protected in a specific tissue niche, maintained by cell-ecm and cell-cell interactions - stem cells are located within the bulge region of the hair follicle and at the base of rete ridges of interfollicular epidermis Fuchs and Raghavan (2002), Nature Rev. 3: 199

10 KERATINOCYTE STEM CELLS - stem cells are slowly replicating cells - a stem cell divides into another stem cell or a cell committed to differentiation - stem cells are protected in a specific tissue niche, maintained by cell-ecm and cell-cell interactions - stem cells are located within the bulge region of the hair follicle and at the base of rete ridges of interfollicular epidermis Fuchs and Raghavan (2002), Nature Rev. 3: 199

11 KERATINOCYTE STEM CELLS - stem cells or the bulge region are multipotent, they can generate hair, sebaceous gland, or epidermal keratinocytes - stem cells allow for the maintenance of the cell population in the epidermis with little to no damage to the tissue genome - at times of tissue damage, stem cells increase their rate of proliferation to repopulate the wounded area Taylor et al., Cell 102: 451

12 KERATINOCYTE STEM CELLS Control of stem cell function by Wnt family and/or Delta/Notch pathways Fuchs and Raghavan (2002), Nature Rev. 3: 199

13 KERATINOCYTE STEM CELLS shh glycogen kinase 3b hdfz2 fizzled Dfz2 zw3arm β-catenin hh wg patched ptch smoothened Wnt1 smo sonic hedgehog fu Wnt1 TGFβ BMP CI Gli1 Activated cell Dean, Bioch. Biophy. Acta 1332: M43 Stem cell

14 STEM CELL CONSEQUENCES OF FAILURE Mutations in patched (ptch), Gli1 lead to basal cell carcinoma

15 STEM CELL CONSEQUENCES OF FAILURE Loss of stem cells may lead to phenotype of aged epidermis? -flattening of the epidermal/dermal junction -keratinocyte cell size becomes variable -nuclear atypia -loss of melanocytes -loss of Langerhans cells -slowed injury response -slowed chemical clearance -decreased immune response -decreased resistance to mechanical stress -increased incidence of cancer

16 KERATINOCYTE PROLIFERATION - most of proliferation done by transient amplifying cells (TA cells) - in normal epidermis, all TA cells remain attached to basement membrane - transition from stem cell to TA cell is the first step in keratinocyte differentiation - TA cells migrate laterally along the basement membrane

17 KERATINOCYTE PROLIFERATION - TA cells only divide 2-3 times before they withdraw from the cell cycle - 2 mm punch biopsy contains a replication unit - TA cells carry-out cell proliferation for tissue without risk for long-term genetic damage to tissue - increased expression of c-myc associated with transition from stem cell to TA cell -NFκB, retinoids, vitamin D, AP1 regulate proliferation and differentiation

18 KERATINOCYTE PROLIFERATION CONSEQUENCES OF FAILURE Dysregulation of proliferation can lead to hypo- and hyperproliferative diseases PSORIASIS

19 KERATINOCYTE PROLIFERATION CONSEQUENCES OF FAILURE Dysregulation of proliferation can lead to hypo- and hyperproliferative diseases VENOUS STATIS ULCER

20 KERATINOCYTE TERMINAL DIFFERENTIATION - when a keratinocyte releases from the basement membrane, it undergoes changes in morphology and gene expression - gradual change in cell strength and water impermeability - terminally differentiated keratinocytes synthesize a cornified cell envelope and undergo programmed cell death Fuchs and Raghavan (2002), Nature Rev. 3: 199

21 KERATINOCYTE TERMINAL DIFFERENTIATION Keratinocyte morphology and function stratum corneum keratinocytes contain thickened cell envelopes, contain no nucleus, imbedded in lipid matrix stratum granulosum cells become elongated, usually 1-2 cell layers thick, accumulate amorphous keratohyaline granules Differentiation-specific proteins expressed no new proteins expressed keratins K1 and K10 loricrin, filaggrin transglutaminase 3 stratum spinosum cells increase in size, increased cytoplasm:nucleus ratio, cell layer 4-6 cells thick, no further cell division stratum basale cuboidal cells, cells within this layer proliferate, all cells attached to the basement membrane, one cell layer thick keratins K1 and K10 involucrin, envoplakin periplakin, σ keratins K5 and K14 integrins, p63

22 KERATINOCYTE TERMINAL DIFFERENTIATION Keratinocyte morphology and function stratum corneum keratinocytes contain thickened cell envelopes, contain no nucleus, imbedded in lipid matrix stratum granulosum cells become elongated, usually 1-2 cell layers thick, accumulate amorphous keratohyaline granules Differentiation-specific proteins expressed no new proteins expressed keratins K1 and K10 loricrin, filaggrin transglutaminase 3 stratum spinosum cells increase in size, increased cytoplasm:nucleus ratio, cell layer 4-6 cells thick, no further cell division stratum basale cuboidal cells, cells within this layer proliferate, all cells attached to the basement membrane, one cell layer thick keratins K1 and K10 involucrin, envoplakin periplakin, σ keratins K5 and K14 integrins, p63

23 KERATINOCYTE TERMINAL DIFFERENTIATION Keratinocyte morphology and function stratum corneum keratinocytes contain thickened cell envelopes, contain no nucleus, imbedded in lipid matrix stratum granulosum cells become elongated, usually 1-2 cell layers thick, accumulate amorphous keratohyaline granules Differentiation-specific proteins expressed no new proteins expressed keratins K1 and K10 loricrin, filaggrin transglutaminase 3 stratum spinosum cells increase in size, increased cytoplasm:nucleus ratio, cell layer 4-6 cells thick, no further cell division stratum basale cuboidal cells, cells within this layer proliferate, all cells attached to the basement membrane, one cell layer thick keratins K1 and K10 involucrin, envoplakin periplakin, σ keratins K5 and K14 integrins, p63

24 KERATINOCYTE TERMINAL DIFFERENTIATION Keratinocyte morphology and function stratum corneum keratinocytes contain thickened cell envelopes, contain no nucleus, imbedded in lipid matrix stratum granulosum cells become elongated, usually 1-2 cell layers thick, accumulate amorphous keratohyaline granules Differentiation-specific proteins expressed no new proteins expressed keratins K1 and K10 loricrin, filaggrin transglutaminase 3 stratum spinosum cells increase in size, increased cytoplasm:nucleus ratio, cell layer 4-6 cells thick, no further cell division stratum basale cuboidal cells, cells within this layer proliferate, all cells attached to the basement membrane, one cell layer thick keratins K1 and K10 involucrin, envoplakin periplakin, σ keratins K5 and K14 integrins, p63

25 KERATINOCYTE TERMINAL DIFFERENTIATION CONSEQUENCES OF FAILURE NORMAL SKIN ICHTHYOSIS VULGARIS LAMELLAR ICHTHYOSIS Stained with an α-filaggrin antibody

26 KERATINOCYTE INTRACELLULAR STRENGTH - Keratins are members of the intermediate filament (IF) gene family - there are over 50 members of the IF gene family that are expressed in a tissue- and differentiation-specific manner - IF proteins have a conserved central rod domain of helical coiled-coil segments - the amino- and carboxy-terminal sequences of IF proteins are variable Coulombe and Omary, Curr Opin Cell Biol 14: 110

27 KERATINOCYTE INTRACELLULAR STRENGTH - keratins heterodimerize with specific pairing partners: one Type I family one Type II family - the heterodimers then oligomerize into longer fibrils Alberts et al., Molecular Biology of the Cell

28 KERATINOCYTE INTRACELLULAR STRENGTH - keratins heterodimerize with specific pairing partners: one Type I family one Type II family - the heterodimers then oligomerize into longer fibrils - fibrils continue to assemble until IF is nm in diameter Fuchs and Cleveland, Science 279: 514

29 KERATINOCYTE INTRACELLULAR STRENGTH Tissue Type I keratin expressed Type II keratin expressed Basal cells Suprabasal cells Hyperproliferative skin Simple epithelia (also Merkel cells) K14 (50 kd) K10 (56.5 kd) K11 (56 kd) K16 (48 kd) K18 (46 kd) K5 (58 kd) K1 (67 kd) K2 (65 kd) K6 (56 kd) K8 (52 kd) Fuchs and Cleveland, Science 279: 514

30 KERATINOCYTE INTRACELLULAR STRENGTH - keratin filaments extend from the nuclear membrane to desmosomal plaques at the cell membrane - keratins enable keratinocytes to sustain mechanical and non-mechanical stress Coulombe and Omary, Curr Opin Cell Biol 14: 110

31 KERATINOCYTE INTRACELLULAR STRENGTH CONSEQUENCES OF FAILURE -Major defects in keratin molecules are incompatible with life -Minor defects in keratin molecules lead to major debilitating skin disease Genodermatoses Epidermolysis Bullosa Simplex Epidermolytic hyperkeratosis Palmoplantar keratoderma, epidermolytic Palmoplantar keratoderma, diffuse non-epidermolytic Palmoplantar keratoderma, focal non-epidermolytic Ichthyosis hystrix type Curth-Macklin Keratin mutation identified K5, K14 K1, K10 K1, K9 K1 K16 K1

32 KERATINOCYTE INTRACELLULAR STRENGTH CONSEQUENCES OF FAILURE EPIDERMOLYSIS BULLOSUS SIMPLEX -mutation of K5 or K14 -fragility in basal layer keratinocytes Alberts et al., Molecular Biology of the Cell

33 KERATINOCYTE INTRACELLULAR STRENGTH CONSEQUENCES OF FAILURE EPIDERMOLYSIS BULLOSUS SIMPLEX Alberts et al., Molecular Biology of the Cell

34 KERATINOCYTE INTRACELLULAR STRENGTH CONSEQUENCES OF FAILURE EPIDERMOLYTIC HYPERKERATOSIS -mutation in either K1 or K10 -fragility in spinous layer keratinocytes

35 KERATINOCYTE INTERCELLULAR STRENGTH Three types of interactions hold keratinocytes together in epidermal sheets: Hemidesmosomes Desmosomes Adherens Junctions Green and Gaudry, Nature Rev Mol Cell Biol 1: 209

36 KERATINOCYTE INTERCELLULAR STRENGTH HEMIDESMOSOMES - adhesion site that links the keratin cytoskeletal components of a cell to extracellular matrix (basement membrane) - Transmembrane components: integrins α6β4 BPAG2 (BP180) -Plaque components: BPAG1 (BP230) plectin -Cytoskeletal component: keratin Fuchs and Raghavan (2002), Nature Rev. 3: 199

37 KERATINOCYTE INTERCELLULAR STRENGTH DESMOSOMES - adhesion site that links the keratin cytoskeletal components of two cells - Transmembrane components: desmogleins desmocollins -Plaque components: desmoplakins plakoglobin plakophilin keratoclamin -Cytoskeletal component: keratin Fuchs and Raghavan (2002), Nature Rev. 3: 199

38 KERATINOCYTE INTERCELLULAR STRENGTH ADHERENS JUNCTIONS - adhesion site that links the actin cytoskeletal components of two cells - Transmembrane components: E-cadherin -Plaque components: β-catenin α-catenin vinculin VASP p120ctn -Cytoskeletal component: actin Fuchs and Raghavan (2002), Nature Rev. 3: 199

39 KERATINOCYTE INTERCELLULAR STRENGTH CONSEQUENCES OF FAILURE Autoimmune Bullous Diseases Genodermatoses Bullous Diseases Pemphigus foliaceus (α-desmoglein 1) Pemphigus vulgaris (α-desmoglein 3) Bullous pemphigoid (α-bpag2) Generalized atrophic benign EB (BPAG2) EB simplex-md (plectin) Bullous pemphigoid (α-bpag1) Junctional EB-pyloric atresia (α6-integrin or β4-integrin)

40 KERATINOCYTE INTERCELLULAR STRENGTH CONSEQUENCES OF FAILURE BULLOUS PEMPHIGOID

41 KERATINOCYTE INTERCELLULAR STRENGTH CONSEQUENCES OF FAILURE PEMPHIGUS FOLIACEUS PEMPHIGUS VULGARIS

42 KERATINOCYTE CORNIFICATION -process that begins in cells of the upper spinous layers -the induction of proteins that comprise the cornified cell envelope (CCE) are expressed as intracellular [Ca2+] rise in differentiating keratinocytes -chromosome 1q21 contains cluster of genes called the Epidermal Differentiation Complex

43 KERATINOCYTE CORNIFICATION - newly synthesized envoplakin, periplakin, and involucrin form heterotrimers that associate with the cell membrane - transglutaminase 1 crosslinks these proteins via ε-(γ-lysine) isopeptide linkages - this scaffold forms along the entire inner surface of the cell membrane ENVOPLAKIN PERIPLAKIN INVOLUCRIN TG 1 TG 3 K5/K14 K1/K10 Kalinin et al., J Cell Sci 114: 3069

44 KERATINOCYTE CORNIFICATION - lamellar bodies (containing free-fatty acids, cholesterols, and ceramides) bud off from the Golgi complex - at the transition from the granular layer to the cornified layer, the lamellar bodies fuse with the cell membrane and extrude their contents into extracellular space - also at transition, filaggrin becomes post-translationally modified and directs the aggregation of keratin proteins ENVOPLAKIN PERIPLAKIN INVOLUCRIN TG 1 TG 3 K5/K14 K1/K10 PHOSPHOLIPID ω-oh-ceramide FATTY ACIDS CHOLESTEROL Kalinin et al., J Cell Sci 114: 3069

45 ENVOPLAKIN KERATINOCYTE CORNIFICATION - loricrin that was produced in the granular cell is crosslinked to SPR proteins via transglutaminase 3 - the loricrin-spr complexes become fixed to the previously assembled scaffold via transglutaminase 1 - organelles, microtubules, microfilaments, and the nucleus are degraded via programmed cell death - the mature corneocyte contains bundled keratins contained within CCE imbedded in lipid lamellae PERIPLAKIN INVOLUCRIN TG 1 TG 3 K5/K14 K1/K10 PHOSPHOLIPID ω-oh-ceramide FATTY ACIDS CHOLESTEROL LORICRIN SMALL PROLINE- RICH PROTEIN OTHER PROTEINS Kalinin et al., J Cell Sci 114: 3069

46 KERATINOCYTE CORNIFICATION CONSEQUENCES OF FAILURE VOHWINKEL S SYNDROME loricrin mutation X-LINKED ICHTHYOSIS Steroid sulfatase deficiency