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Extracellular matrix Flashcards

1
Q

What is an extracellular matrix?

A

A complex network of proteins and carbohydrates filling spaces between cells

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2
Q

What is the extracellular matrix made up of?

A

both fibrillar and non-fibrillar components

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3
Q

What are the 4 key functions of the extracellular matrix?

A
  • Provides physical support
  • Determines the mechanical and physicochemical properties of the tissue
  • Influences the growth,
    adhesion and differentiation status of the cells and tissues with which it interacts
  • Essential for development, tissue function and organogenesis
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4
Q

What is connective tissue made up of?

A

Extracellular matrix and component materials

components: versican and laminin

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5
Q

What are connective tissues made up of?

A

Collagens
Type I, II, III (fibrillar)
Type IV (basement membrane)

Multi-adhesive glycoproteins
Fibronectin, Fibrinogen
Laminins (basement membrane)

Proteoglycans
Aggrecan, Versican, Decorin
Perlecan (basement membrane)

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6
Q

What are the human disorders resulting from ECM abnormalities?

A
  1. Gene mutations affecting matrix proteins
  2. . Gene mutations affecting ECM catabolism
  3. . Fibrotic disorders due to excessive ECM deposition
  4. Disorders due to excessive loss of ECM
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7
Q

What are collagens?

A
  • Family of fibrous proteins
  • Major proteins in bone, tendon and skin
    ( most abundant proteins)
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8
Q

How are collagen fibrils aligned in the skin as well as mature bone and cornea?

A

successive layers nearly at right angles to each other

These tissues resist tensile force in all directions

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9
Q

molecular arrangements of collagen fibres?

A

Each collagen molecule comprises three α chains, forming a triple helix.

Can be composed of one or more different α chains

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10
Q

What is the composition of collagen I ?

A

has chains from two different genes - its composition is [α1(I)]2 [α2(I)]

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11
Q

What is the composition of collagen II and III ?

A

have only one chain type – their compositions are, therefore, [α1(II)]3 and [α1(III)]3

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12
Q

What is the arrangement of an α chain?

A

characteristic gly-x-y repeat

x- often proline) (y- often hydroxyproline

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13
Q

How are collagen fibres assembled?

A

one α chain –>
3 α chains –>
collagen fibril –>
collagen fibre

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14
Q

What do all newly synthesised collagen chains have?

A

non-collagenous domains at N- and C-termini.

but after secretion they are usually removed

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15
Q

Collagen biosynthesis pathway?

A

Procollagen –>
Collagen –>
Fibril formation –>
Cross-linking

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16
Q

Fibrillar collagen biosynthesis

A

synthesis of pro-a chain –>
hydroxylation of selected prolines and lysines –>
glycosylation of selected hydroxylysines –>
self-assembly of the pro-a chains –>
procollagen triple-helix formation –>
secretion (through secretory vesicles or into the ER/ Golgi compartment) –> (procollagen molecule)
cleavage of propeptides –>
(collagen molecule) self-assembly into fibril –>
(collagen fibril) aggregation of collagen fibrils to form a collagen fibre

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17
Q

What does crosslinking provide?

A

tensile strength and stability

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18
Q

What is involved in cross-linking?

A

Both lysine and hydroxy-lysine residues are involved

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19
Q

What is the extent of cross-links?

A

the type and extent is tissue specific and changes with age

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20
Q

What do prolyl and lysyl hydroxylases require?

A

Fe2+
vitamin C

contribute to interchain hydrogen bond formation

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21
Q

What does Vitamin C deficiency result in?

A

underhydroxylated collagens, with dramatic consequences for tissue stability (scurvy)

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22
Q

What is ehlers-danlos syndromes (EDS)?

A

a group of inherited connective tissue disorders whose symptoms include stretchy skin and loose joints

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23
Q

What do mutations in collagen affect?

A
  • collagen production
  • collagen structure
  • collagen processing
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24
Q

Not all collagen form fibrils

A

Fibril-associated collagens associate with fibrillar collagens and regulate the organisation of collagen fibrils

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25
What is the basement membrane formed from?
flexible-sheet like multilayered network | type IV collagen
26
What is the role of basement membranes?
regulators of tissue function
27
What are basement membranes?
are flexible, thin mats of extracellular matrix underlying epithelial sheets and tubes - contain a distinct repertoire of collagens, glycoproteins and proteoglycans
28
What do basement membranes surround?
muscle, peripheral nerve and fat cells and underlie most epithelia
29
What do they form an important part of in the kidney?
filtration unit as the Glomerular basement membrane (GBM)
30
What is the disorder diabetic nephropathy?
there is an accumulation of extracellular matrix leading to a highly thickened basement membrane. This restricts renal filtration and can lead to renal failure
31
What is Alport syndrome?
mutations in collagen IV result in an abnormally split and laminated GBM which is associated with a progressive loss of kidney function and also hearing loss
32
Are elastic fibres usually found by themselves?
no, collagen and elastic fibres are interwoven to limit the extent of stretching
33
What do elastic fibres consist of?
a core made up of the protein elastin, and microfibrils, which are rich in the protein fibrillin
34
What is Marfan's syndrome?
Mutations in the protein fibrillin-1 | skeletal, ocular, and cardiovascular systems are affected
35
What is elastin?
unusual protein consisting of two types of segments that alternate along the polypeptide chain: hydrophobic regions, and α-helical regions rich in alanine and lysine -Many lysine side chains are covalently cross-linked
36
What are some examples of multi-adhesive glycoproteins?
Laminins (associated with basement membranes) | fibronectin
37
How are extracellular matrix proteins organised?
- Most ECM proteins are very large - composed of characteristic protein domains of 50-200 amino acids - multifunctional: modular structure - - multi-adhesive, binding various matrix components and cell-surface receptors
38
What are lamins?
heterortrimeric proteins made up of an α chain, a β chain and a γ chain, which form a cross shaped molecules - very large proteins
39
What is the role of lamilins?
- multi-adhesive proteins which can interact with a variety of cell surface receptors including integrins and dystroglycan - self-associate as part of the basement membrane matrix - interact with other matrix components
40
What are the diseases from typical mutations in lamilin?
muscular dystrophy and epidermolysis bullosa
41
What are fibronectins?
a family of closely related glycoproteins of the extracellular matrix which are also found in body fluids - multi-adhesive proteins
42
How can fibronectins exist?
insoluble fibrillar matrix or as a soluble plasma protein
43
From how many genes are fibronectins derived?
from a single gene, with alternate splicing of mRNAs giving rise to the different types
44
What are the bonds in laminin?
large multidomain molecule linked together by disulphide bonds
45
What are the roles of laminins?
regulating cell adhesion and migration in a variety of processes, notably embryogenesis and tissue repair - promote blood clotting
46
What does laminin link to?
between the matrix and cytoskeleton
47
What are proteoglycans?
core proteins to which are covalently attached one or more glycosaminoglycan (GAG) chains
48
What are GAG chains made up of?
repeating disaccharide units with one of the two sugars being an amino sugar - many are sulfated or carboxylated, and as a result carry a high negative charge
49
What does the negative charge on GAG chains attract?
a cloud of cations including Na+, resulting in large amounts of water being sucked into the extracellular matrix
50
What are the different proteoglycan families? (4)
1. Basement membrane proteoglycans 2. Aggregating proteoglycans 3. Small leucine-rich proteoglycans 4. Cell surface proteoglycans
51
What is cartilage made up of?
matrix rich in collagen with large quantities of GAGs trapped within the meshwork
52
What are the 4 groups of GAG chains?
1. Hyaluronan 2. Chondroitin sulfate and dermatan sulfate 3. Heparan sulfate 4. Keratan sulfate
53
What is hyaluronan? (hyaluronic acid)
a carbohydrate chain without a core protein (is distinct form the other GAGs) It is unsulfated and made up of repeating disaccharides which can number up to 25,000 sugars
54
Where is hyaluronan found?
in the extracellular matrix of soft connective tissues | -- vitreous humour of the eye and in synovial fluid of joints
55
What is aggrecan?
major constituent of the cartilage extracellular matrix
56
What is the structure of aggrecan?
the GAGs are highly sulfated, increasing their negative charge - also contain large numbers of negatively carboxyl groups
57
What do the multiple negative charges on aggrecan attract?
cations such as Na+ that are osmotically active -->large quantities of water retained by the highly negatively charged environment
58
Why is aggrecan perfectly suited to resist compressive forces?
Under compressive load, water is given up, but regained once the load is reduced
59
What are the disorders resulting from ECM abnormalities?
osteoarthritis | fibrotic disease
60
What is osteoarthritis?
an erosive disease resulting in excessive extracellular matrix degradation (loss of cartilage)
61
What happens with aggrecan with age?
it is cleaved by aggrecanases and metalloproteinases | --> loss of aggrecan fragments to the synovial fluid
62
What is fibrotic disease?
a result of an excessive production of fibrous connective tissue

POM (Principles of Medicine) (17 decks)

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