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Extracellular Maatrix Flashcards

1
Q

What is the Extracellular matrix

A
  • A complex network of proteins and carbohydrates deposited by and filling spaces between cells
  • ## Comprises both fibrillar and non-fibrillar components
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2
Q

Key functions of ECM

A

Provides physical support
Determines mechanical and physicochemical properties of tissue
Influences growth adhesion and differentiation status if cells
Essential for development tissue function and organogenesis

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3
Q

3 major components of connective tissue

A

Collagen: Type I,II,III (fibrillar) and type IV (non fibrillar component of basement)
Multi adhesive glycoproteins: fibronectin,fibrinogen,laminins
Proteoglycans: Basement membrane eg perlecan,aggregating proteoglycans eg aagregan,small leucine rich proteoglycans eg decorin

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4
Q

What different types of connective tissue are there

A

Tendon and skin-tough and flexible
Bone-hard and dense
Cartilage-resilient and shock absorbing

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5
Q

How do different properties of connective tissue come about

A

Due to difference in ECM components

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6
Q

What are the 2 things gene mutations can affect in ECM to cause human disorders

A

ECM proteins and ECM catabolism

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7
Q

ECM protein diseases and where mutation is

A

Osteogenesis imperfecta-type 1 collagen
Marfans syndrome-fibrillin1
Alports syndrome-type IV collagen (alpha5)
Epidermolysis bullosa-laminin 5(in all three chains)
Congenital muscular dystrophy-laminin 2 (alpha 2 chain)

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8
Q

ECM catabolism syndromes

A

Mucopolysaccharidoses (MPSs) which lead to inability to degrade glycosaminoglycans (GAGs)

e.g. Hurler’s syndrome, leads to build up of ECM molecules
Loss of L-alpha-iduronidase

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9
Q

What does excessive ECM deposition cause

A

Fibrotic disorders due to excessive production

  • Liver fibrosis- caused by cirrhosis
  • Kidney fibrosis- caused by diabetic nephropathy
  • Lung fibrosis- caused by idiopathic pulmonary fibrosis (IPF)
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10
Q

Disorder due to excessive loss of ECM

A

osteoarthritis

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11
Q

How is collagen arranged in skin, mature bone and cornea and how does this relate to its function?

A

Successive layers nearly at right angles to one another

This resists tensile force in all directions

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12
Q

Structure of collagens

A

3 alpha chains which may be different
Homotrimers are same collagen and heterotrimers are different collagens.
2 a1(1) and 1 a2(1)

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13
Q

Composition of type I and II and III collagens

A

I: chains from two different genes to [alpha2(I)]

Both only have 1 chain type so compositions are $[alpha1(II)]_3$ and $[alpha1(III)]_3$
They are homotrimers

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14
Q

What is the structure of the triple helix

A

Gly-X-y in each alpha chain
Gly is glycine
X is usually proline
Y is usually hydroxyproline

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15
Q

Why is glycine always third

A

The triple helices have to pack together tightly and glycine is smallest amino acid so is small enough to occupy the interior of the helices with it’s H side chain

This gives a stiff triple helix structure in collagen

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16
Q

What happens to the non-collagenous domains at N- and C- termini after secretion in the case of fibrillar collagens?

A

They are removed

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17
Q

Steps of collagen synthesis

A

1) synthesis of pro-alpha chains

2) hydroxylation of proline and lysine

3)glycolysatuon of hydroxylisines

4)self assembly of 3 pro alpha chains

5)pro collagen triple helix formation

6)secretion and cleavage

7)aggregation of collagen fibres
- Occurs in Fibroblasts

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18
Q

What two compounds are involved in the cross linking of collagen

A

Lysine
Hydroxylysine

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19
Q

How do cross links between collagen molecules help with function

A

Provide tensile strength and stability

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20
Q

How are hydrogen bonds formed between collagen

A

Prolyl and Lysyl Hydroxylases use Fe2+ and Vitamin C as co-factors to form hydroxylysine and hydroxyproline

Allowing them to form hydrogen bonds with one another

21
Q

What happens to collagen if there is a vitamin C deficiency

A

Underhydroxylated collagens, so there are dramatic consequences for tissue stability

Scurvy

22
Q

Ehlers danlos syndromes

A

Group of inherited connective tissue disorders whose symptoms include stretchy/elastic skin and loose joints (joint hypermobility)

Several disorders arise due to collagen mutations which negatively affect collagen production, structure and processing

23
Q

Non fibrillar collagens

A

Type I,IX- fibril associated collagens that associate with fibrillar collagens to regulate their organisation
Type IV- network forming collagen and is less T in all basement membranes . It has uncleared N and C termini allowing it to interact with ither collagen molecules to form a network of collagen

24
Q

Basement membranes

A

Flexible, thin mats of ECM underlying epithelial sheets and tubes containing collagens, glycoproteins and proteoglycans
Found in muscle,peripheral nerve and fat cells
Important in kidney as form part of filtration u it as glomerular basement membrane

25
What happens in diabetic nephropathy
Accumulation of ECM leading to highly thickened basement membrane which results in less renal filtration and can lead to renal failure
26
Alpert syndrome
- What happens in Alport syndrome? Mutations in **collagen IV** result in **abnormally split and laminated GBM** which is associated with a progressive loss of kidney function and hearing loss
27
Elastic fibres
Made of core elastin protein and microfibrils rich in fibrillin
28
Why are collagen and elastic fibres interwoven
To limit extent if stretching
29
What is fibrillin important for
The integrity if elastic fibres
30
What condition are mutations in fibrillin1 associated with
Marfans syndrome Causing long spider like fingers long slender limbs and predisposition to aortic ruptures Altered fibrillin 1 affects strength of connective tissue
31
What is elastins structure
Has 2 types of segments that alternate along the polypeptide chain- **hydrophobic** regions and **alpha-helical** regions rich in alanine and lysine Many lysine side chains are covalently cross-linked
32
Architecture of ECM proteins
Modular- they are composed of characteristic protein domains of 50-200 amino acids- this structure allows for the multifunctionality of ECM proteins Many large modular proteins are multi-adhesive, binding various matrix components and cell-surface receptors -
33
Laminins structure
They are heterotrimeric proteins made up of an alpha-chain, beta chain and a gamma-chain Forming cross chained molecules Are v large proteins
34
What makes laminins multi adhesive properties
They can interact with a variety of cell surface receptors including integrins and dystroglycan Can self-associate as part of the basement membrane matrix but also interact with other matrix components like type IV collagen, nidogen and proteoglycan
35
What two diseases arise from mutation in one of the chains
- Epidermolysis ****bullosa - **Congenital muscular dystrophy**, (which mutation causes this and what are 3 major symptoms?) Alpha-2 chain in Laminin-2 **Hypotonia** (abnormally decreased muscle tension), **generalised weakness** and **deformities of the joints**
36
What two forms of fibronectins exist as
Insoluble fibrillar matrix Soluble plasma matrix
37
Fibronectin function
Regulate cell adhesion Migration Tissue repair Has disukphide bonds
38
How is fibronectin involved in the binding of collagen fiber to actin filament?
Fibronectin binds to collagen fiber and the integrin receptor on the other side which provides linkage between matrix and cytoskeleton Adaptor protein binds to other end of integrin Actin filament binds to adaptor protein
39
Proteoglycans
Core proteins to which 1 or more glycosamjnoglycan is covalently attached GAG chains made of disaccharide elevating units
40
Proteoglycan families
- basement membrane proteoglycans e.g. perlecan - aggregating proteoglycans (interact with hyaluronan) e.g. aggrecan - small leucine-rich proteoglycans e.g. decorin - cell surface proteoglycans e.g. syndecans 1-4
41
Cartilage
A matrix rich in collagen with large GAG quantities trapped in mesh The balance of swelling pressure is negated by tension in the collagen fibres which generates great tensile strength Cartilage lines the knee joint (synovial cartilage) and can support pressures in hundreds of kg/cm^2 -
42
4 main groups GAG chains are grouped in
Hyaluronjc acid(in core protein) Heparan sulfate Keratan sulfate chondroitin sulfate and dermatan sulfate
43
Where are GAGs synthesised and attached, and how is hyaluronan distinct?
All are synthesised and attached to their core proteins in ER and Golgi apparatus in cells Except hyaluronan which is spun out directly from an enzyme embedded in the plasma membrane
44
How does Aggrecan's presence lead to large quantities of water being retained by the environment it is in?
GAGs are highly sulfated, increasing negative charge Also present are large numbers of negatively charged carboxyl groups Multiple negative charges **attract osmotically active Na+ ions**, which leads to **large quantities of water retained in highly -ve environment**
45
How is aggrecan perfectly suited to resist compressive forces in cartilage matrix?
**Aggrecan** is a major constituent of the cartilage extracellular matrix. Under compressive load, water is given up but is regained once the load is reduced Suited to resist compressive forces High negative charges allow this to occur as it attracts Na+ leading water to be retained
46
Osteoarthritis
Erosive disease resulting in excessive ECM degradation The cushioning properties of cartilage over bone ends is lost aggrecan is cleaved by aggrecanases and metalloproteinases which results in a loss of aggrecan fragments to synovial fluid
47
Congenital muscular dystrophy
Cause by laminins a2 deficiency Fails to interact with integrity and dystroglycan which is needed for adhesion and basement membrane assembly thus causes muscle weakness
48
Hylaronan
Glycoaminoglycan Has no core protein Found in highly viscous tissue eg vitreous humor of eye Protects cartilaginous surface from damage

Pom (44 decks)

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