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MFM > Extracellular Matrix > Flashcards

Extracellular Matrix Flashcards

1
Q

what role does the ECM play in connective tissue?

A

carries mechanical load

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2
Q

what role does the ECM play in epithelia?

A

holds epithelial tissues together, because the cells are directly jointed to each other via membrane junctions and carry mechanical loads themselves

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3
Q

in epithelial tissue, where are components of ECM produced and secreted?

A

fibroblasts

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4
Q

2 major types of ECM in the body?

A
  1. ECM associated with epithelial tissue (basal lamina)

2. ECM associated with connective tissue

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5
Q

what are the major components of the basal lamina?

A

glycoproteins and proteoglycan

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6
Q

major glycoproteins in the basal lamina?

A

laminin, type IV collagen, nidogen, fibronectin

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7
Q

major proteoglycans in basal lamina?

A

perlecan

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8
Q

unique fct of basal lamina in the kidney glomerulus?

A

lies between 2 cell sheets and functions as a selective filter

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9
Q

what is basal lamina?

A

thin, tough, flexible sheet of ECM, essential component of epithelial cells, surrounds muscle cells, fat cells and schwann cells

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10
Q

how is the basal lamina formed?

A

interactions between laminin, type IV collagen, nidogen and perlecan

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11
Q

what do nidogen and perlecan do?

A

link laminin and type IV collagen networks

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12
Q

where is laminin in the cell?

A

anchored at the cell surface through binding of their tail regions to receptors, but head regions are free to interact with other molecules, so it organizes the rest of the ECM sheet structure

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13
Q

what is laminin in the cell?

A

major glycoprotein that is a heterotrimeric complex of alpha, beta and gamma subunits, primary organizer of the sheet structure because its ends can bind to multiple components of the basal lamina for structural support

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14
Q

what does the long end of laminin bind to?

A

integrins, dystroglycans, perlecan

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15
Q

what does the short end of the laminin bind to?

A

integrins

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16
Q

what does the “armpit” of laminin bind to?

A

nidogen

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17
Q

what 2 tissues is collagen an important component of?

A

connective tissue and basal lamina (epithelium)

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18
Q

action of collagen

A

resists tensile forces

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19
Q

buildup of collagen?

A

3 polypeptides (each called alpha chain)wound around one another to form superhelix, which then assemble into polymers called collagen fibrils, which then pack together to form collagen fibers

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20
Q

which protein is the chief protein in bone, tendon and skin?

A

collagen

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21
Q

what cells produce collagen ?

A

fibroblasts in the skin and tendons, osteoblasts in bone

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22
Q

3 families of collagen?

A

fibrillar, sheet forming, anchoring/linking

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23
Q

where are fibrillar collagens found?

A

bone

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24
Q

where are sheet forming collagens found?

A

basal lamina

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25
Q

where are anchoring/linking collagens found?

A

skeletal muscle

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26
Q

what role does fibrillar collagen play in the eye?

A

provides optically clear path for light, because orthogonal collagen fiber layers make the transparent cornea, also forms the scaffolding for vitreous body

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27
Q

what role does fibrillar collagen play in bone?

A

type I collagen fibrils form layers reinforced by calcium phosphate crystals

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28
Q

what role does fibrillar collagen play in tendons, ligaments, bones, other dense connective tissue, and cartilage?

A

provides tensile strength, form scaffolding, resists compression, and attracts water via trapping glycosaminoglycans and proteoglycans

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29
Q

what post-translational modifications occur for collagen?

A
  1. hydroxylation on prolines and lysines in the ER/Golgi compartment
  2. glycosylation of hydroxylysines
  3. cleavage by proteases
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30
Q

types of sheet forming collagens

A

type IV, type VIII and type X(?)

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31
Q

what is Descemet’s membrane?

A

a special basement membrane under the endothelium of the cornea made of hexagonal nets of type VIII collagen

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32
Q

what sheet forming collagen is found in the basal lamina, around muscle cells and nerve cells?

A

type IV collagen, net like polymers

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33
Q

types of fibrillar collagen?

A

type I, II, III, V, XI

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34
Q

types of anchoring/linking collagens?

A

type VI, VII, XII and XIV

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35
Q

general function of anchoring collagens?

A

link fibrillar and sheet forming collagens to other structures

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36
Q

example of anchoring collagen in the basal lamina?

A

dimers of type VII collagen polymerize to form anchoring fibrils that link type IV collagen to basal lamina of stratified epithelia to plaques in the underlying connective tissue

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37
Q

what does type IX collagen do?

A

links glycosaminoglycans to type II collagen fibrils

38
Q

action of fibroblasts?

A

main synthesizers of ECM components, synthesize collagen fibers as fibroblasts move through tissue, reorganize deposited collagen by crawling along them and pulling on them

39
Q

what cell determines arrangement of collagen fibers in the ECM?

A

fibroblasts, that synthesize collagen as they move through tissues

40
Q

pathology of osteogenesis imperfecta?

A

mutations in one or more collagen gene, resulting in poor quality of collagen or insufficient quantities of collagen, most prevalent = type I

41
Q

what is osteogenesis imperfecta?

A

genetic disorder characterized by brittle bones, short stature and spinal curvature

42
Q

pathology of type I-4 ehlers-danlos syndrome?

A

mutations in collagen genes, resulting in defective collagen synthesis

43
Q

pathology of type 6 ehlers-danlos syndrome?

A

mutation in gene encoding lysyl hydroxylase, so collagen molecules are not hydroxylated and cannot be processed properly

44
Q

function of lysyl hydroxylase?

A

adds hydroxyl groups to lysine

45
Q

characteristics of ehlers-danlos syndrome?

A

hyper flexible joints, fragile skin, blood vessels easily rupture

46
Q

what is fibronectin?

A

large glycoprotein composed of 2 subunits joined by disulfide bonds at one end in soluble form or insoluble

47
Q

function of fibronectin?

A

provides cells a linkage to the collagen fibrils in the ECM through its interactions with integrins

48
Q

2 forms of fibronectin?

A
  1. soluble form in blood or body fluids

2. insoluble fibronectin fibrils in ECM

49
Q

what are glycosaminoglycans?

A

highly negatively charged (hydrophilic) unbranched polysaccharide chains of repeating disaccharide units that are usually linked to core proteins (proteoglycans)

50
Q

4 main groups of GAGs

A
  1. hyaluronan
  2. chondroitin sulfate/dermatan sulfate
  3. heparan sulfate
  4. keratan sulfate
51
Q

GAGs in ECM

A

fill most of ECM due to their highly extended conformations that occupy a large volume relative to their mass, also because they are strongly hydrophilic they readily form gels at low concentrations

52
Q

unique characteristic of hyaluronan (hyaluronic acid)

A

the only GAG not linked to a core protein, and therefore is not synthesized in the ER. therefore, not released from the cell via exocytosis, but spun out directly via hyaluronan synthase in the plasma membrane

53
Q

complexity of hyaluronan?

A

simplest GAG of repeats of up to 25,000 disaccharide units

54
Q

types of proteoglycans

A

aggrecan, decorin

55
Q

what is aggrecan

A

a huge proteoglycan molecule that is a major component of cartilage

56
Q

what is decorin

A

small proteoglycan that binds to collagen fibrils and regulates fibril assembly

57
Q

how do aggrecans contribute to cell signaling?

A
  1. binds to fibroblast growth factor (FGF), allowing them to cross link and activate their cell surface receptor
  2. immobilizes chemokines at sites of inflammation
  3. inhibits transforming growth factor beta (TGF beta) by binding and sequestering
58
Q

what role do aggrecans play?

A

can combine with hyaluronan to produce very large aggrecan aggregates that are commonly found in the cartilage matrix to resist compressive forces

59
Q

where is aggrecan made, processed and modified?

A

rough ER, addition of polysaccharide chain occurs in lumen of ER, additional modifications in golgi and is released via exocytosis

60
Q

what molecules join together to make aggregates in the extracellular environment?

A

proteoglycan (aggrecan) and hyaluronan

61
Q

synthesis of hyaluronan

A

made by hyaluronan synthase at the plasma membrane and is spun out directly

62
Q

what is syndecan?

A

membrane spanning proteoglycan whose intracellular domain interacts with the actin cytoskeleton and signaling molecules within the cell

63
Q

where is syndecan found?

A

on the surface of fibroblasts, they modulate integrin function by interacting with fibronectin on the cell surface (and via cytoskeletal and signal molecules inside the cell)

64
Q

what is betaglycan?

A

proteoglycan found on cell surface that binds to TGFbeta and presents it to the TGFbeta receptors

65
Q

action of aggrecans with TFGbeta?

A

inhibits it by binding and sequestering

66
Q

what are elastic fibers?

A

loose and unstructured polypeptide chains that are covalently cross linked into a rubber like elastic meshwork

67
Q

where are elastic fibers found?

A

ECM of connective tissue of smooth muscle, blood vessels, skin and lungs

68
Q

action of elastic fibers?

A

allows tissues to stretch and then relax to their original form, usually collagen fibers are interwoven to limit extent of stretching and prevent tearing

69
Q

2 components of elastic fibers?

A

elastin and microfibrils

70
Q

what is microfibrils

A

polymers composed of glycoprotein fibrillin

71
Q

function of neutrophil elastase

A

an enzyme that cleaves elastin that is produced by neutrophils in response to inflammation

72
Q

result of alpha-1-antitrypsin deficiency

A

no alpha-1-antitrypsin to inhibit elastase, so elastin is destroyed, limiting elasticity of the tissue and giving rise to COPD or emphysema

73
Q

what is alpha-1-antitrypsin

A

protease made in liver that inhibits neutrophil elastase

74
Q

what is marfan syndrome?

A

disorder of connective tissue due to mutation in fibrillin-1 gene

75
Q

pathology of marfan syndrome?

A

mutation in fibrillin-1 gene, leading to defects in elastin fibers. deficit in elastin fibers reduces sequestering of TGF-beta, so increased TGF-beta contributes to symptoms

76
Q

characteristics of marfan syndrome

A

above average height, long, slender limbs, at high risk for aortal aneurysm and aortal dissection

77
Q

how much of the aortal tissue is elastin fibers?

A

50%

78
Q

function of elastin fibers with TGF-beta?

A

elastin fibers bind to TGF-beta and sequester it in the ECM, preventing it from binding to its receptor on target cells

79
Q

what are matrix metalloproteinases (MMPs)

A

major class of tightly controlled enzymes that degrade ECM components, there are several members in the class that each have a specific target in the ECM

80
Q

what do MMPs require to work

A

binding of Ca or Zinc

81
Q

2 reasons why ECM degradation is important?

A
  1. cell migration/room to divide
  2. some growth factors are deposited in the ECM and must be freed by degradation of the ECM components to have access to their receptors on the surfaces of target cells
82
Q

what are serine proteases on the MMP

A

have a highly reactive serine in the active site

83
Q

how are MMPs regulated? (3)

A
  1. local activation
  2. confinement by cell surface receptors
  3. secretion of protease inhibitors
84
Q

example of a local activation degradation

A

plasminogen, an abundant inactive protease precursor in the blood, is cleaved by plasminogen activators near sites of blood clots to yield plasmin (to help break up blood clots)

85
Q

what is plasmin

A

enzyme that helps break up blood clots, degrades fibrin

86
Q

what is fibrin

A

ECM molecule that is a component of blood clots

87
Q

example of confinement by cell surface receptor degradation

A

urokinase-type plasminogen activator (uPA), binds to receptors on growing tips of axons and the leading edge of migrating cells, degrades the ECM in front of them to clear a path for their migration

88
Q

MOA of confinement by cell surface receptor?

A

cells have receptors on their surface that bind proteases, confining the enzyme to the sites where it is needed

89
Q

which method do some cancer cells utilize for metastasizing?

A

confinement by cell surface receptors

90
Q

example of secretion of inhibitors

A

tissue inhibitors of metalloproteinases (TIMPs), bind tightly to activated MMPs and block their activity. protect cell adhesion and migration proteins from being targeted by active MMPs

91
Q

what may cancer cells express to help metastasize?

A

membrane type 1 matrix metalloproteinase (MT1-MMP), that activates other MMP-2 to further degrade ECM and break through the basal lamina

MFM (39 decks)

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