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ACVD Exam > The Epidermis and Desmosomes > Flashcards

The Epidermis and Desmosomes Flashcards

1
Q

Describe the stratum basale/stratum germativum/basal layer.

A
  • Single row of columnar to cuboidal cells resting on the basement membrane zone
  • Most of the cells are mitotically active keratinocytes
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2
Q

Which are the primary keratins expressed in the stratum basale?

A

K5/K14 (but dogs also have K1/K6)

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3
Q

How thick is the stratum spinosum?

A
  • Typically 1-2 layers thick in haired skin
  • Thicker at foot pads, nasal planum, and mucocutaneous junctions (can be 20 cells thick)
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4
Q

What are the primary keratins in the stratum spinosum and how does this vary in hyperproliferative disorders?

A
  • Retain stable K5/K14 with new synthesis of K1/K10
  • Hyperproliferative disorders have down regulation of K1/K10 mRNA and protein while K6/K16 are favored
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5
Q

In what layer of the skin are lamellar granules (aka keratinosomes/membrane-coated granules/Odland bodies) formed?

A

Stratum spinosum

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6
Q

What are lamellar granules?

A
  • Secretory granules secreted into the intracellular space of the stratum granulosum
  • Contain precursors of stratum corneum lipids (glycoproteins, glycolipids, phospholipids, free sterols, glycosylceramides, acid hydrolases) and proteins that respond to signals that occur during the transition from the granular to cornified layer
  • Are secreted via exocytosis
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7
Q

When is profilaggrin produced?

A

Stratum granulosum (cleaved into filaggrin in the granular layer)

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8
Q

What is involucrin?

A
  • First major component to be activated that will be cross-linked in the emerging cornified envelope
  • Initiated in the spinous layer soon after K1/K10 expression
  • Glutamine-rich
  • Largest protein in the stratum corneum
  • Synthesized in the spinous layer
  • Cross-linked in the granular layer by transglutaminases
  • Is rigid and firm, forming an insoluble cell boundary and connecting corneocytes to the extracellular lipid layer
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9
Q

What are the two primary categories of things that occur in the stratum spinosum?

A

1) keratinocytes start differentiating
2) things that will be needed later start to be made

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10
Q

Describe the histopathologic appearance of the spinous layer.

A
  • Cells are lightly basophilic to eosinophilic, nucleated, and polyhedral to flattened cuboidal
  • Have a spine-like appearance of the cell margins which are abundant desmosomes
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11
Q

What is the final layer of the epidermis in which keratinocytes are alive?

A

Stratum granulosum

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12
Q

What is the primary roles of the stratum granulosum?

A
  • A final packaging stage which generates a number of structural components that will form the epidermal barrier
  • The final stage of granular cell differentiation into a corneocyte is the cell’s programed destruction, destroying almost all cellular contents with the exception of keratin filaments and filaggrin matrix
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13
Q

What are keratohyalin granules composed of?

A
  • Profilaggrin, keratin filaments, and loricrin
  • But not true granules as they lack a membrane
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14
Q

What are the two types of keratohyalin granules?

A
  • F granules
  • L granules
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15
Q

What are F granules?

A
  • Named for filaggrin
  • A type of keratohyalin granules
  • Irregularly shaped
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16
Q

What are L granules?

A
  • Contain loricrin
  • Are smaller and more rounded
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17
Q

Describe the fate of profilaggrin.

A
  • Profilaggrin becomes dephosphorylated and undergoes Ca2+- dependent proteolytic cleavage
  • Filaggrin is later degraded into the natural moisturizing factors, urocanic acid (UCA) and pyrrolidone carboxylic acid (PCA)
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18
Q

What is loricirin?

A
  • A cystine-rich, highly flexible protein with glycine loops
  • A major structural component of the cornified envelope, binding keratin filaments together in the corneocyte and anchoring them to the cross-linked envelope
  • Most prevalent structural protein in the stratum corneum (~80% of volume of cornified envelope)
  • Synthesized in the upper spinous layer and throughout the granular layers
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19
Q

How is keratin expression modified in the stratum granulosum?

A

Modified from K1/K10 to K2/K11

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20
Q

What is the stratum lucidum/stratum conjunctum?

A
  • A fully keratinized, compact, thin layer of dead cells which is anuclear, homogenous, and hyaline-like, containing refractile droplets and semifluid eleidin
  • Present in canine footpads (sometimes nasal planum) and coronary band of horses but absent elsewhere
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21
Q

What is the stratum corneum?

A

Outer layer of terminally differentiated keratinocytes that are constantly being shed (balanced by proliferation of basal layer)
- Multilayer zone of anucleate, flattened, lipid-depleted, protein-enriched corneocytes as the bricks and a continuous extracellular lipid matrix comprised of ceramides, FFAs, and cholesterol as the mortar

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22
Q

What does the lipid matrix of the stratum corneum do?

A
  • Serves as the mortar
  • Mechanical protection
  • Barrier to water loss
  • Regulates permeation of soluble substances
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23
Q

What keratins are primarily expressed in the stratum corneum?

A

K1/K10/K2e

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24
Q

What are the major proteins of the stratum corneum?

A
  • Involucrin
  • Loricrin
  • Envoplankin
  • Periplankin
  • Small protein rich proteins (SPRPs)
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25
Q

What do envoplankin and periplankin do in stratum corneum?

A

Link the cornified envelope to desmosomes and keratin filaments

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26
Q

What do small protein rich proteins do in the stratum corneum?

A

Cross-link with loricrin in the cornified envelope

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27
Q

What is desquamation?

A
  • A process of enzymatic cleavage of corneodesmosomes
  • Balance between KLKs, LEKTI
  • Promoted by acidic pH, decreases in Ca, increased natural moisturizing factors, and decreased water
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28
Q

What is KLK7?

A
  • Stratum corneum chymotryptic enzyme aka kallikrein 7
  • One of the two serine proteases of the kallikrein family that are implicated in dequamation
  • Degrades corneodesmosin and desmocollin 1
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29
Q

What is KLK5?

A
  • Stratum corneum tryptic enzyme aka kallikrein 5
  • One of the two serine proteases of the kallikrein family that are implicated in dequamation
  • Degrades corneodesmosin, desmocollin 1, and desmoglein 1
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30
Q

What is corneodesmosin?

A
  • Synthesized as a glycine- and serine-rich glycoprotein in lamellar bodies then released from the lamellar bodies and associated with desmosomal desmogleins and desmocollines until activated by chemotryptic enzymes
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31
Q

What is LEKTI?

A
  • Lymphoepithelial Kazal-type inhibitor
  • Inhibits desquamation
  • A serine protease inhibitor secreted from lamellar bodies
  • Most effective at neutral pH
32
Q

Rank the layers of the epidermis based on Ca2+ concentration.

A

Granulosum>spinosum>basale>corneum

33
Q

What are the roles of Ca2+ on keratinocyte differentiation?

A
  • Depletion regulates lamellar body exocytosis
  • Regulator of protein synthesis (primarily transglutaminase 1 activity)
  • Important for cell-to-cell adhesion
34
Q

What is Darier disease (keratosis follicularis)?

A
  • A disease with an increase in transepidermal water loss, altered calcium regulation, loss of adhesion between suprabasalar epidermal cells, and abnormal keratinization
  • Caused by one gene involved in Ca transport, SERCA2
35
Q

What is Hailey-Hailey disease (benign chronic pemphigus)?

A
  • Loss of cell-cell adhesion
  • Caused by a calcium-regulating gene, ATP2C1
36
Q

What are desmosomes?

A
  • The major cell adhesion junction of the epidermis
  • Serve to anchor apposing keratinocyte cell surface membranes to the intracellular keratinocyte intermediate filament network
  • Create a 3 dimensional scaffolding that stabilizes epithelia in the face of stress and trauma
37
Q

What are the 3 major categories of desmosomal proteins?

A
  • Desmosomal cadherins
  • Armadillo family proteins
  • Plankins
38
Q

What are the desmosomal cadherins?

A
  • Desmogleins and desmocollins
  • Transmembrane glycoproteins whose extracellular domains interact to form the trans-adhesive interface between cells
  • Structure is 5 cadherin repeats plus an extracellular anchor domain separated by a Ca binding motif
39
Q

What are the desmosomal armadillo family proteins?

A
  • Plankoglobin and plankophilins
40
Q

What are the desmosomal plankins?

A
  • Desmoplankin
  • Envoplankin
  • Periplankin
41
Q

Which desmosomal cadherins are primary expressed in the superficial epidermis?

A
  • Dsg1
  • Dsg4
  • Dsc1
42
Q

Which protein is the target for pemphigus foliaceous in dogs?

A

Dsc1

43
Q

Which desmosomal cadherins are primary expressed in the deep epidermis near the basal layer?

A
  • Dsg2
  • Dsg3
  • Dsc2
  • Dsc3
44
Q

Which protein is the primary target for pemphigus vulgaris in dogs?

A

Dsg3

45
Q

What type of desmosomal cadherin combinations contribute the strongest adhesion?

A

Heterophilic (Dsg-Dsc) contribute to the strongest adhesion but homophilic interactions also occur

46
Q

What does plankoglobulin do?

A
  • Directly binds the cytoplasmic tails of cadherins (including E-cadherin)
  • Are also in the nucleus where they modulate gene transcription
  • Recruit desmosomal proteins to the plaque similar to α- catenin in adherins junctions
47
Q

What does plankophilin do?

A
  • Bind directly to desmoplankin
  • May also directly bind keratins and desmosomal cadherins which are thought to aid in the clustering and lateral stability of the desmosomal plaque
48
Q

What does desmoplankin do?

A
  • Binds directly to keratin, providing a link between KIFs and the desmosomal plaque
  • Plays a critical role in development
49
Q

What does the outer dense plaque contain?

A
  • Desmosomal cadherin cytoplasmic tails
  • Plankiglobin
  • Desmoplankin N-terminal domain
  • Plankophilin
50
Q

What disease process happens when something goes wrong with the outer dense plaque?

A

Bullous pemphigoid

51
Q

What congenital diseases occur when something goes wrong with plankoglobins and desmoplankins?

A
  • Ectodermal dysplasias
  • Skin fragility
52
Q

What is the primary target(s) of paraneoplasic pemphigus?

A

Plankoglobins and desmoplankins

53
Q

What congenital diseases occur when something goes wrong with α6β4?

A

Junctional epidermolysis bullosa

54
Q

What is the primary target of bullous pemphigoid?

A

α6β4

55
Q

What is the primary target of mucous membrane pemphigoid?

A

α6β4

56
Q

What does the inner dense plaque contain?

A

Desmoplankin interacting with KIFs

57
Q

What do adherens junctions do?

A
  • Link epithelia cells
  • Attach to actin cytoskeleton
  • Involve transmembrane E-cadherin proteins
  • Bind in a Ca-dependent manner
58
Q

What are gap junctions and where are they primarily found?

A
  • Aggregates of intracelluar channels (connexons) that permit transfer of ions and small molecules
  • More present in basal layers
59
Q

What are tight junctions and where are they primarily found?

A
  • Join cells to form an impermeable barrier
  • Most present in SG2 (middle of the granular layer)
60
Q

Describe holoclones?

A
  • Epidermal stem cells
  • Slow dividing cells
  • Proposed to maintain an “immortal strand” of DNA at each division
  • May divide symmetrically (useful when skin needs to be stabilized) or asymmetrically
61
Q

What are meroclones?

A
  • Transit amplifying cells
  • Rapidly dividing
  • Typically divides symmetrically
62
Q

What are paraclones?

A

Terminally differentiated/daughter cells

63
Q

How does calcium regulate stem cell fate and maintenance?

A
  • Low calcium environment promotes maintenance and prevents differentiation, thereby stimulating proliferation
  • High calcium environment inhibits it
64
Q

What are the categories of regulatory mediators which play a role in keratinocyte stem cell differentiation?

A
  • Stimuli that direct progenitor cells toward a particular type of terminal differentiation
  • Molecules and pathways characteristic of the microenvironment and stem cell homeostasis
  • Molecules that differently alter stem cells and transit amplifying cell proliferation
  • Positive and negative regulators involved in commitment and terminal differentiation
65
Q

What stimuli are involved in directing progenitor epithelial cells into hair follicle cells?

A
  • Positively by Wnt/β-catenin
  • Negatively by DiKK1 and Lef1/Tcf
66
Q

What stimuli are involved in directing hair follicle stem cells into sebaceous cells?

A

BLIMP1

67
Q

What molecules are involved in maintenance of stem cell quiescence in the hair follicle?

A
  • NFATc1
  • Bmp6
68
Q

What molecules are involved in maintenance of stem cell quiescence in the epidermis?

A

Lrig1

69
Q

What molecules are involved in modifying the differentiation of stem cells into transit amplifying cells and stem cell renewal?

A
  • Myc
  • p63
  • miR203 microRNA
  • Histone
70
Q

What are negative regulators of terminal differentiation?

A
  • Extracellular matrix
  • pcG repression
71
Q

What are markers for stem cells in the epidermis?

A
  • β-integrin
  • CD71 (transferrin receptor)
  • LRIG1
72
Q

What markers of proliferation are upregulated in psoriasis?

A
  • Ki67
  • C-myc
73
Q

What is the [interfollicular] epidermal proliferative unit?

A
  • A proliferative unit arranged in a hexagon consisting of approximately 10 basal cells with a clonogenic cell in the center overlaid by the suprabasal and corneocyte progeny
  • Functionally independent and self-renewing
74
Q

What is the epidermal differentiation complex in humans?

A
  • Genes present in a 2mb region of the human chromosome 1q21
  • Epigenetic mechanisms play an important role in growth and differentiation of keratinocytes by regulating expression of the cassette of genes in this region
  • Encode structural proteins involucrin, loricrin, and SPRPs as well as a number of Ca-binding proteins including profilaggrin, trichohyalin and several S100A proteins
75
Q
A

A= intermediate filaments
B= desmoplankin
C= desmoglein
D= desmocollin
E= plakophilin
F= plakoglobin

ACVD Exam (21 decks)

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