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BMS2.19 ECM (PINTAR) > ECM > Flashcards

ECM Flashcards

1
Q

Ground substance:

A
  • Water, ions, and macromolecules in the ECM
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2
Q

Ground substance + cells =

A

connective tissue

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3
Q

The basal surface of the epithelium of most tissues is underlain with:

A
  • basement membranes
    • sheets of ECM that separate cells.
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4
Q

The 3 layers of basement membrane that can defined at EM level and that are enriched in specific ECM components:

A
  • lamina rara/lucida/interna
  • lamina densa
  • lamina reticularis.
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5
Q

Schematic of basement membrane organization:

A
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6
Q

There is a continuum (no clear boundary) between the ECM and the cell due to:

A
  • integrins
  • syndecans
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7
Q

ECM components in lamina rara/lucida/interna:

A
  • laminin 5
  • type XVII collagen
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8
Q

ECM components in lamina densa:

A
  • laminin 1
  • type IV collagen
  • perlecan
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9
Q

ECM components in lamina reticularis:

A
  • made primarily by fibroblasts
  • type III collagen
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10
Q

Stroma:

A
  • Major component of adult ECM
  • located outside the lamina reticularis of basement membrane
  • secreted by fibroblasts and specialized mesenchymal cells
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11
Q

What ECM components are in the stroma?

A
  • fibronectin
  • collagen types I, III, VII
  • elastic fibers
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12
Q

Characteristics and function of collagen:

A
  • provides tensile strength
  • resistant to stretching
  • most abundant protein in body (25% of all)
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13
Q

Collagen structure:

A
  • Triple-stranded helical molecules containing three monomer α-chains wrapped around each other
  • imparts strength to the molecule
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14
Q

α-chain amino acid composition of collagen:

A

Repeating Gly-X-Y

  • Glycine present as every third amino acid
    • Gly-H side chain fits inside helix
    • if altered, helix unstable
  • X and Y are often proline and lysine
    • hydroxylated forms can H-bond
    • lysine can be de-aminated to cross-link
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15
Q

The four classes of collagen:

A
  1. fibril-forming (fibrillar) (types 1-3, 5, 11)
  2. fibril-associated (types 9, 12)
  3. network-forming (types 4, 7)
  4. transmembrane (type 17)
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16
Q

The three important fibril-forming collagens:

A
  • Type I
  • Type II
  • Type III
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17
Q

Type I collagen:

A
  • most abundant (>90% all collagen)
  • in tendons, bones, lungs, skin
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18
Q

Type II collagen:

A
  • cartilage (50% cartilage dry weight)
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19
Q

Type III collagen:

A
  • widely distributed
    • skin, aorta
  • stained with silver
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20
Q

Steps in the biosynthesis of fibril-forming collagens (9):

A
  1. synthesis of PRO-α-chain (RER)
  2. signal peptide removed (golgi)
  3. hydroxylation of select prolines and lysines (golgi)
  4. glycosylation of select hydroxylysines (golgi)
  5. self-assembly of 3 PRO-α-chains (golgi)
  6. procollagen triple helix formation (golgi)
  7. secretion from golgi to ECM (vesicle)
  8. cleavage of propeptides (ECM)
  9. self-assembly into fibril (ECM)
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21
Q

Vitamin C and collagen biosynthesis:

A
  • Vitamin C required as co-factor for hydroxylase.
    • Deficient = scurvy
  • hydroxylation does not occur and collagen α chains degraded.
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22
Q

Steps in formation of tropocollagen:

A
  • After secretion for Golgi, extension peptides (pro peptides) of fibril-forming collagen molecules (types I, II, III) are cleaved.
    • cleaved propeptides = tropocollagen
  • fibril assembly then occurs
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23
Q

Why do Type III collagen “reticular” stain with silver?

A
  • more carbohydrates
  • thinner fibrils
  • more branched
  • few bundles
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24
Q

What is this an image of?

A

Type III collagen “reticular” stained with silver

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25
Q

What is this an image of?

A
  • collagen fibrils in EM
  • note striations
  • Types I, II, III, V, and XI can form fibrils
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26
Q

Function of fibril associated collagens:

A
  • decorate outside of fibrils
  • have some interruption of triple helix
    • less rigid; can bend and form “hinge”
  • functionally important for joint integrity
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27
Q

Fibril Associated Collagen Type IX:

A
  • Decorates outside of Type II collagen of chondrocytes (cartilage)
  • interruption in helix - less rigid - forms hinge
    • important for joint integrity
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28
Q

What are the two major types of network forming collagens?

A
  • type IV and type VII

EXTENSION PEPTIDES NEVER CLEAVED IN NETWORK FORMING COLLAGENS

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29
Q

Type IV Collagen:

A
  • network forming collagen
  • major component of basal lamina (lamina densa)
  • multiple regions where triple helix is interrupted
  • extension peptides not cleaved
    • C-TERMINUS FORMS CHICKEN-WIRE ARRAY.
    • N-TERMINUS ALLOWS MULTI-LAYER BINDING.
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30
Q

Type VII Collagen:

A
  • network forming collagen
  • connects lamina densa to ECM components
    • reticular fibers or stroma
31
Q

Type XVII Collagen:

A
  • attaches basement membrane to epithelial surface via anchoring filaments.
  • Mutation leads to blistering.
32
Q

Mutations in what two collagen types leads to a blistering disease?

A

type VII (7)

type XVII (17)

33
Q

Post-translational processing of collagen occurs where?

A

both intracellularly and in the ECM

  • propeptides (extension sequences) are cleaved in the ECM to form tropocollagen
34
Q

Collagen fiber is assembled where?

A
  • extracellularly with many collagen molecules cross-linked and aligned for maximal stability and strength
35
Q

What gives strength to collagen fibers?

A
  • triple-stranded helical molecules
  • hydroxylated proline and lysine in α-chains
    • hydrogen bonding
  • deamination of lysine in α-chains
    • cross-linking of fibrils occurs
36
Q

Characteristics and function of elastin:

A
  • allow stretching and recoil of connective tissues
  • highly cross-linked via unique amino acids
  • elastin monomers assembled extracellularly
  • interspersed with collagen
37
Q

The two major molecular components in elastic fibers:

A
  • cross-linked elastin monomers
  • microfibrils (composed of fibrillin)
38
Q

One tissue with high elastic fiber content is the:

A

aorta

  • other elastin-dense tissues are the skin and lung
39
Q

Marfan Syndrome:

A
  • due to missense mutations in fibrillin 1 gene
  • leads to elongated extremities and enhanced rupture of the aorta.
40
Q

Hyperextendable skin is due to:

A

excess type III collagen

41
Q

Elastoderma-reduced recoil is due to:

A

altered elastin

42
Q

Epidermolysis bullosa is due to:

A
  • Type VII anchoring fibrils disrupted
  • Epithelium and Basement Membrane peeled away
43
Q

Glycosaminoglycans (GAG) Structure:

A
  • Long, unbranched polysaccharide chains.
  • consist of repeating disaccharides that contain alternating amino sugar + uronic acid
44
Q

Three important GAGs:

A
  • hyaluronic acid
  • chondroitin sulfate
  • heparan sulfate
45
Q

All classes of GAG are sulfated on an amino sugar except:

A

hyaluronic acid

46
Q

GAG characteristics:

A
  • negatively charged
  • highly extended
  • bind water and osmotically active cations
  • resist compression (joints, vitreous)
  • occupy a huge space
47
Q

What two GAGs are sulfated and attach to protein?

A
  • chondroitin sulfate
  • heparan sulfate
48
Q

Proteoglycans are:

A
  • Glycosaminoglycans (GAGs) covalently coupled to a “core” protein.

hyaluronic acid is the exception;

it is a GAG that does not bind to protein

49
Q

Aggrecan description, location, and function:

A
  • proteoglycan found in cartilage
  • provides mechanical support
50
Q

Aggrecan structure:

A
  • hyaluronic acid backbone
  • link proteins non-covalently bind proteoglycans (chondroitin/keratan sulfate + core protein) to the hyaluronic acid backbone
51
Q

What two collagens and one proteoglycan co-exist in the chondrocyte matrix?

A
  • aggrecan
  • Type II collagen
  • Type IX collagen
52
Q

Perlecan description, location, and function:

A
  • proteoglycan found in basal lamina
  • provides structural and filtering function
53
Q

Perlecan structure:

A
  • core protein + heparan sulfate
  • completely extracellular
54
Q

Syndecan-1 description, location, and function:

A
  • integral transmembrane proteoglycan
    • found in fibroblasts and epithelial cell surfaces.
  • provides cell adhesion function and binds fibroblast growth factor (FGF)
55
Q

Syndecan-1 structure:

A
  • transmembrane core protein
  • heparan sulfate GAG
    • FGF co-receptor
    • signaling pathways
56
Q

Fibronectin and laminin are both:

A
  • adhesive glycoproteins that can interact with many other ECM molecules
57
Q

Fibronectin description and function:

A
  • adhesive glycoprotein
  • Specific domains mediate binding to:
    • cell surface (RGD sequence/integrins)
    • wound healing
    • matrix formation
58
Q

Fibronectin structure:

A
  • adhesive glycoprotein
  • two identical chains joined by disulfide linkages near the C-terminus
59
Q

Laminin description and function:

A
  • adhesive glycoprotein
  • mediates interactions between cell surface and basement membrane via integrins
    • RGD sequence
60
Q

Laminin structure:

A
  • Three major subunits arranged in pattern containing one long arm and three short arms.
61
Q

What collagens and proteoglycans make up the ECM of the basal lamina?

A
  • perlecan
  • fibronectin
  • laminin
  • type IV collagen
  • nidogen

INTEGRINS ALSO PRESENT

62
Q

Integrins can bind to:

A

collagen, laminin, and fibronectin

63
Q

Integrin structure and binding properties:

A
  • dimers composed of α and β subunits
    • both subunits can bind collagen, laminin, and fibronectin
      • RGD amino acid sequences of matrix components important for this
64
Q

What integrin subunit binds cytoskeleton (often actin) that can initiate formation of signaling complexes?

A

β subunit

65
Q

Steps in focal adhesion kinase (FAK) activation:

A
  1. fibronectin/laminin bind to extracellular component of integrin.
  2. integrin recruits cytoskeleton actin-binding proteins and binds actin.
  3. focal adhesion forms at site of bound integrin via Rho GTPase.
  4. focal adhesion kinase (FAK) recruited and activated.
66
Q

β1 integrins bind to:

A

extracellular molecules

(fibronectin; laminin)

67
Q

β2 integrins bind to:

A

Ig of endothelial cells (i.e. selectin)

found in white blood cells

68
Q

β3 integrins bind to:

A

fibrinogen

found in platelets

69
Q

β4 integrins bind to:

A

laminin 5 (part of anchoring filaments)

found in hemidesmosomes

70
Q

Leukocyte adhesion deficiency (inability of WBC to bind endothelium) is due to a mutation in what subunit of integrin?

A

β2

71
Q

Glanzmannʼs disease (inability to bind fibrinogen during clotting) is due to a mutation in what subunit?

A

β3

72
Q

How are specific integrins regulated, and what causes them to become active and available to bind with their substrates?

A
  1. independent extracellular signal binds to cell membrane surface receptor.
  2. intracellular signaling pathway initiated, conformational change of integrins occurs (integrin opens).
  • inactive = closed conformation
  • active = open conformation
73
Q

What is the signal that activates β2 integrins on leukocyte cells?

A
  • selectin on endothelial surface causes rolling of leukocyte down endothelial surface
    • causes activation of an intracellular signaling pathway in the leukocytes that activates/causes a conformational change in the β2 integrin of the leukocyte.
    • β2 integrin causes leukocyte arrest on the endothelial surface

BMS2.19 ECM (PINTAR) (1 decks)

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