Keratin 5 (basic, type 2)

Keratin 14 (acidic, type 1)

Keratin 1 (basic, type 2)

Keratin 10 (acidic, type 1)

assemble into web like bundles to form intermediate filaments

Functions in the degradation of filaggrin monomers to natural moisturizing factors (NMF)

A cysteine-dependent aspartate directed protease

Keratin 2 (basic, type 2)

This keratin is considered a marker of keratinocyte differentiation

Periplakin

Envoplakin

Involucrin

Loricrin

Small proline-rich proteins

Synthesized in the epidermis as an inactive precursor protein which is later processed by cathespin D for activation

Cross-links proteins in the cornified cell envelope

The major constituent of keratohyalin granules in the stratum granulosum

A large insoluble highly phosphorylated histadine-rich protein

Contains tandemly arranged FLG repeats that are flanked on either side by two partial FLG repeats N- and C-terminal domains (these domains are important in processing)

Break down products of filaggrin monomers

Pyrrolidone carboxylic acid and urocanic acid

Cytoplasmic - plaque proteins are incorporated into the cornified cell envelope and separated from tonofilaments attacted to the intermediate filament cytoskeleton

Extracellular - comprised of desmosomal cadherins (desmoglein-1, desmocollin-1 and corneodesmosin)

A chymotrypsin-like serine protease that degrades the extracellular components of corneodesmosomes. Corneodesmosin is cleaned first followed by desmoglein1 and desmocollin 1.

Cathespin is also involved

KLK5 and KLK7 and KL14

Inhibits the enzymatoc activities of KLK5 and KLK7

Synthesized in the SG and released by lamellar granules into the extracellular space

Encoded by SPINK5

Phospholipids

Glycosylceramides

Sphingomyelin

Cholesterol

Lipoooxygenase 3

12R-lipooxygenase

Ceramides

Cholesterol

Long-chain FFAs

A class of lipid molecules consisting of sphingoid bases that are amide linked to fatty acids

Converted to glycosylceramides and sphingomyelins for incorporation into lamellar granules and then converted back to ceramides by β-glucocerebrosidase and amid sphingomyelinase

A major lipid class in the SC

Synthesized in keratinocytes and metabolized into cholesterol sulfate with is degraded back to cholesterol in the intracellular space by steroid sulphatase

Expressed in the upper epidermis

Synthesizes or remodels glycerophospholipids that play an important role in epidermal lipid barrier function

required for acylceramide synthesis

Epidermal differentiation complex (includes s100 fused-type proteins, filaggrin-2, hornerin and others)

Chromosome 17

PNPLA1

PNPLA1 acts as an ω-O-acyltransferase required for acylcetamide (EFA).

NIPAL1 (ichthyin)

Hey magnesium transporter for fatty acid transport protein (FATP4)

Cholesterol sulfate is processed to free cholesterol by steroid sulfatase.

phospholipids are broken down to three fatty acids by phospholipases.

Ceramides are broken down by Ceramidase, sphingosine kinase, S1P Lysase and other enzymes

Pro flag rim is processed to flag rim and then to free amino acids (NMF) by cascade-14, matripase, mesotrypsin, peptidylimidase, breonycin hydrolases and others.

End consequence = The pH, calcium ion concentration and moisture drop, free amino acids increase and conditions progressively favor activation of proteases well causing inactivation of their inhibitors.

Keratin 71

Keratin 25 has been associated with curly hair coats in horses.

Keratin 27 has been associated w we with curly hair coats in cattle.

-Basal- relatively low

-Spinous- very low

-Granular- highest

-Cornified- very low

-Autoantibodies in humans:

-Desmoglein-3: PV

-Desmoglein-1: PF

-Major autoantigens in dogs:

-Desmoglein-3: PV

-Desmocollin-1: PF

-Areas of intercellular contact

-Closely connected to actin microfilament cytoskeleton

-Cadherin-catenin complex binds actin:

-E-cadherin- transmembrane molecule

-Cytoplasmic catenins (B-catenin, p120 catenin, a-catenin)

-Channels in the plasma membrane

-Link cytoplasm of neighboring cells

-Allow selective exchange of ions, second messengers, and small metabolites

-Connexins are basic components

-6 connexins---> connexon

-Connexons in plasma membranes of adjoining cells associate to form gap junctions

-Enzymatic cleavage of corneodesmosomes

-Serine proteases

-SCCE (stratum corneum chymotryptic enzyme)...aka kallikrein 7 (KLK7)---> degrades corneodesmosin, desmocollin-1

-SCTE (stratum corneum tryptic enzyme)... aka kallikrein 5 (KLK5)--->degrades corneodesmosin, desmocollin-1 and desmoglein-1

-LEKTI (lympho-epithelial Kazal type inhibitor)---> composed of serine protease inhibitor, secreted from lamellar bodies, effective inhibition at neutral pH

-Balance between KLKs and LEKTI regulates normal desquamation

-Serine and glycine rich protein---> forms "glycine loops" that act like velcro and mediate reversible intermolecular adhesion and glycine loops also in keratins and loricrin

-Secreted from lamellar bodies

-Incorporated into desmoglea

-Plays a key role in stratum corneum cohesion

1) Desmosomes and Corneodesmosomes

2) Tight Junctions

3) Adherens junctions

4) Gap junctions

-Very close intercellular contacts (seal intercellular space)

-Control paracellular movement of molecules (semipermeable size and ion-specific barrier)

-Perform "fence function"

-restrict molecule diffusion within cell membrane

-demarcate apical and basolateral regions

-Transmembrane molecules include the following:

-Claudins-critical component

-Occludin

-Junctional adhesion molecules (JAMs)-IgG-like

-Intracellular proteins

-Zonula occludens (ZO) proteins

-interact with claudins, occludin and actin

-Sites of intercellular adhesion

-Link neighboring keratinocytes and their KIFs

-Provide structural strength for epidermis

-Constantly rearranging as keratinocytes migrate suprabasally

-Desmoglea- extracellular portion between adhered keratinocytes

-Within keratinocyte cell membrane

(Outer dense plaque and Inner dense plaque-connects to keratin intermediate filaments)

Name each of the proteins and their purpose involved in the following:

Desmosomal cadherins, Armadillo proteins, and Plakin gene family proteins

-Desmosomal cadherins (Transmembrane calcium-dependent)---> desmogleins, desmocollins

-Armadillo proteins (bind to cadherins)--->Plakoglobin, Plakophilins

-Plakin gene family proteins---> Desmoplakin, Envoplakin, periplakin

-Lipid precursors (Glucosylceramides, Sphingomyelin, Phospholipids)

-Desquamation proteases (SCCE/KLK7 and SCTE/KLK5)

-Lipid hydrolases (B-glucocerebrosidase, Acid sphingomyelinase, Phospholipase A2)

-Cholesterol

-Corneodesmosin

-Steroid sulfatase

-Antimicrobial peptides

-From precursors: Glucosylceramides, Sphingomyelin

-Major Lipid component of stratum corneum: minor in other tissues

-Ceramide are lipids (fats) that are found naturally in high concentrations in the uppermost layers of the skin

-They make up over 50% of skin's composition and play a vital role in skin appearance

-Fatty acids and sphingosine base come together to form ceramides

-Amide- linked fatty acid attached to sphingoid base

-Type of sphingolipid

(sphingolipids ubiquitous in mammalian tissues with tissue-specific distribution)

-Unique to stratum corneum (149)

-very long chain fatty acids

-EOS/Cer 1, EOH/Cer 4, EOP/Cer 9

-Linoleic acid (omega-6 EFA) is component

-Bonded to involucrin in CE and interdigitate with other lipids

-Key to stratum corneum barrier function

-synthesized in the lower epidermis

-Some incorporated into lamellar bodies and secreted unchanged

-Some converted to cholesterol sulfate and metabolized to cholesterol by steroid sulfatase

-Cholesterol sulfate impairs desquamation

-Intracellular transport

-Microfilaments- actin (7nm diameter)

-Microtubules- alpha and beta-tubulin (20nm diameter)

-Scaffold composed of intermediate filaments (7-12 nm diameter and made of keratin)

-nucleus and organelles are degraded

-KIF and filaggrin tightly bundled

-CE replaced plasma membrane

-Desmosomes modified into corneodesmosomes

-Involucrin

-Loricrin

-Envoplakin, periplakin

-Small proline-rich peptides (SPRs)

-Multiple other proteins

-Bundles KIFs into a tight arrangement

-Degraded in stratum corneum and release:

-Pyrrolidone carboxylic acid and amino acids maintain epidermal hydration and pH

-Urocanic acid--->photoprotection

-Caspase-14 involved in the degradation

-Key to epidermal barrier funciton

-Histadine-rich, cationic protein

-Precursor: profilaggrin

-Synthesis starts after K1 and K10

-Consists of multiple filaggrin units between N- and C- terminal domains

-Calcium may be involved in profilaggrin processing

-May have a role in calcium-dependent events of cornification

-component of keratohyalin granules

-Type 1: Acidic, smaller than type 2, K9-19 in the epidermis

-Type 2: Basic to neutral, larger than type 1, K1-8 in the epidermis

***Acidic and basic proteins form pairs

-Central alpha-helical rod domain

-Amino (N)-terminal head and carboxy (C)-terminal tail that exhibit "glycine loops"

1) Specialized control of apoptosis

2) Bundling of keratin filaments to contract and flatten cells (filaggrin)

3) Replacement of cells membrane with cornified envelope (TG1)

4) Formation of lipid bilayers and CLE

5) Desquamation (pH dependent)

1) Transglutaminases (TGM1)

2) Cross-link structural proteins (loricrin, involucrin, small proline-rich peptides, filaggrin

3) Cornified envelope replaces the plasma membrane[image]

-Norwich Terrier

-Mutation in keratin 10 (splice mutation in the gene encoding keratin 10 (KRT10)[image]

-Autosomal recessive congenital ichthyosis 

-The term "Lamellar Ichthyosis" was once synonymous with TGM1 deficiency

-Many other mutations can cause the phenotype

-Lamellar ichthyosis is often still used for TGM1 (but not specific)

-Transglutaminase 1

-Birth

-Thick parchment paper-like scale

-Malassezia ++++

-Scale versus crust? changes your differential diagnosis

-Scale= stratum corneum (Keratin squames)

-Crust= debris, bacteria, serum, necrotic granulocytes, keratin, etc

1) Type 1: Acidic, smaller than type II, K9-19 in the epidermis

2) Type 2: Basic to neutral, larger than type 1, K1-8 in epidermis

*Acidic and basic proteins form pairs

-Component of keratohyalin granules

-Precursor: profilaggrin

-Histidine-rich, cationic protein

-Synthesis starts after K1 and K10

-Consists of multiple filaggrin units between N- and C- terminal domains (N-terminal has a calcium binding domain and calcium is likely involved in profilaggrin processing)

1) Involucrin

2) Loricrin

3) Envoplakin, periplakin

4) Small proline-rich peptides (SPRs)

5) Multiple other proteins[image]

1) Involucrin: Glutamine-rich protein, connects corneocytes to the extracellular lipid layer

2) Loricrin: Cysteine-rich highly flexible protein with glycine loops, major structural component (>70%)

1) Nucleus and organelles degraded

2) KIF and filaggrin tightly bundled

3) CE replaced plasma membrane

4) Desmosomes modified into corneodesmosomes

1) Ceramides

2) Free fatty acids

3) Cholesterol

• Hydrolytic enzymes
• phospholipids
• ceramides
• glycoyl ceramides
• sterols

[image]

1) Phospholipids---> free fatty acids and glycerol

2) Free fatty acids (acidify stratum corneum and assists enzymes; B-glucocerebrosidase, Acid sphingomyelinase)

3) Glycerol- helps with hydration

-EOS/Cer1, EOH/Cer4, EOP/Cer9

-Unique to Stratum corneum

-Very long chain fatty acids

-Linoleic acid (ω-6 EFA) is component

-Bonded to involucrin in CE and interdigitate with other lipids

-Key to stratum corneum barrier function

-Amide-linked fatty acid attached to sphingoid base

-Type of sphingolipid (Sphingolipids ubiquitous in mammalian tissues with tissue-specific distribution) [image] 

1) Sphingomyelin

2) Phospholipids

3) Glucosylceramides

[image]

1) CE replaces cell membrane

2) KIFs linked to CE at type 2 head domains

3) Loricrin inside, involucrin outside

1) Lipid precursors (Glucosylceramides, Sphingomyelin, Phospholipids)

2) Desquamation proteases (SSCE/KLK7, SCTE/KLK5)

3) Lipid hydrolases (B-glucocerebrosidase, Acid sphingomyelinase, Phospholipase A2)

4) Cholesterol

5) Corneodesmosin

6) Steroid sulfatase

7) Antimicrobial peptides

-Basal- relatively low

-Spinous- very low

-Granular- highest

-Cornified- very low

-Enzymatic cleavage of corneodesmosomes

-Serine proteases (SCCE- stratum corneum chymotryptic enzyme- aka kallikrein 7 degrades corneodesmosin, desmocollin-1)

-SCTE- stratum corneum tryptic enzyme- aka kallikrein 6 degrades corneodesmosin, desmocollin-1 and desmoglein-1

-High calcium in the granular layer regulates transglutaminase activity, lamellar body exocytosis, cleavage of profilaggrin to filaggrin

-Extracellular calcium ions required for desmosomal adhesion

-LEKTI (lympho-epithelial Kazal type inhibitor)

-Serine protease inhibitor

-Secreated from lamellar bodies

-Effective inhibition at neutral pH

-Balance between KLKs and LEKTI regulates normal desquamation

-Connexons in plasma membranes of adjoining cells associate to form gap junctions

-6 connexins---> connexon

-Gap junctions are channels in plasma membrane

-Link cytoplasm of neighboring cells

-Allow selective exchange of ions, second messengers and small metabolites

-Synthesized in the lower epidermis

-Some incorporated into lamellar bodies and secreted unchanged

-Some converted to cholesterol sulfate

-Metabolized to cholesterol by steroid sulfatase

-Cholesterol sulfate impairs desquamation

-Familial Pawpad hyperkeratosis/hereditary footpad hyperkeratosis

-In mice, results in wooly haircoat

-Is also mutated in CKCS with CKCSID (dry eye curly coat syndrome)

-Mutated in humans with palmoplantar keratoderma

-Delay in terminal differentiation of footpad keratinocytes

-Daily soaks in 50% propylene glycol may help decrease cracked footpads

• The cornified envelope replaces the plasma membrane of differentiating keratinocytes and consists of keratins enclosed within insoluble proteins which as crosslinked by transglutaminases and surrounded by a lipid envelope.

• Proliferation activation: Keratin 6, 16, 17
• Pawpad: Keratin 6, 9 and 16

• Spinous cells retain the stable K5/K14 keratins that are produced in the basal layer and only synthesize new messenger RNA (mRNA) for these proteins in hyperproliferative disorders
• Instead, the new synthesis of the K1/K10 keratin pair occurs in this epidermal layer
• In psoriasis, actinic keratosis and wound healing, synthesis of K1 and K10 mRNA and protein is downregulated, and the synthesis and translation of messages for K6 and K16 are favored

• Cornification defects
  • Autosomal recessive congenital ichthyosis
    • Epidermolytic- rare Norfolk terrier- Protein core
    • Nonepidermolytic- Golden retriever- PNPLA-1-Lipid envelope and ECM
      • • American bulldog- NIPAL4 (Ichthyn)-Lipid envelope and ECM
        • Jack Russel Terrier- TGM 1- Cornified envelope
  • Malassezia overgrowth is common
  • Generalized
• • [image]

• LEKTI (lympho-epithelial Kazal type inhibitor)
  • Serine protease inhibitor
  • Secreted from lamellar bodies
  • effective inhibition at neutral pH
• Balance between KLKs and LEKTI
  • regulates normal desquamation