ECM

Question 1

• What is the ECM?

Answer 1

Complex network of proteins and carbohydrates

Comprises of fibrillar and non-fibrillar components

Question 2

• What does fibrillar mean?

Answer 2

Fibre-making

Question 3

• What are the key functions of the ECM?

Answer 3

Provides physical support

Determines mechanical and physiochemical properties of tissue

Influences growth, adhesion and differentiation status of cells and tissues with which it interacts

Essential for development, organogenesis and tissue function

Question 4

• Where is the ECM?

- What is the ECM made of?

Answer 4

Spaces between cells

Collagens - e.g Type I, II, III (fibrillar) and Type IV (basement membrane)

Multi-adhesive glycoproteins

Proteoglycans

Question 5

• What properties do connective tissues in the tendon and skin have?
• What properties do connective tissues in the bone have?
• What properties do connective tissues in the cartilage have?

Answer 5

Tough and Flexible

Hard and Dense

Resilient and Shock-absorbing

Question 6

• Give an example of a fibrotic disorder due to excessive ECM deposition
• Give an example of a disorder due to excessive loss of ECM

Answer 6

Liver Fibrosis - cirrhosis
Kidney fibrosis - diabetic nephropathy
Lung fibrosis - idiopathic pulmonary fibrosis (IPF)

Osteoarthritis
cushioning properties of cartilage over the ends of bones are lost
aggrecan is cleaved by metalloproteinases and aggrecanases
loss of aggrecan fragments to synovial fluid

Question 7

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

Answer 7

Successive layers nearly at right angles to one another

This resists tensile force in all directions

Question 8

• Describe the structure of collagen

- What is the difference between a heterotrimer and a homotrimer?

Answer 8

3 alpha chains
Forming a triple helix

Heterotrimer is collagen with more than one type of alpha chain
Homotrimer is collagen with 3 of the same alpha chains

Question 9

• Describe the structure of an alpha chain

Answer 9

gly-x-y repeat

Glycine

X is often Proline

Y is often hydroxyproline

Each alpha chain is around 1000 amino acids long forming a left-handed helix

Question 10

• Explain the biosynthesis of fibrillar collagen

Answer 10

1. Occurs in Fibroblast
   
   2. Synthesis of pro-alpha chain
   3. Post-translational modifications - Hydroxylation of prolines and lysines and glycosylation of hydroxylysines
   4. Self-assembly of 3 pro-alpha chains
   5. Procollagen triple helix formation
   6. Secretion
   7. Cleavage of propeptides
   8. Self assembly into fibrils
   9. Aggregations of collagen fibrils to form a collagen fiber

Question 11

• Which compounds are involved in the cross-linking of collagen?
• How are hydrogen bonds formed between collagen molecules?

Answer 11

Lysine
Hydroxy-lysine

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

Question 12

• What happens therefore, if there is a Vitamin C deficiency And what is this condition called?

Answer 12

Underhydroxylated collagens, so there are dramatic consequences for tissue stability

Scurvy

Question 13

• What is Ehlers-Danlos Syndrome (EDS)

Answer 13

Group of inherited connective tissue disorders whose symptoms include fragile (stretchy) skin, blood vessels and loose joints

Negatively affecting collagen production, structure and processing

Question 14

• What property does Collagen type IV have that promotes its function?

Answer 14

Uncleaved N and C termini allow it to interact with other Collagen molecules to form a network of collagen

Allows it to act as a basement membrane

Question 15

• What is basement membrane (BM)?
• Where is BM found?
• what mutation is Alports syndrome associated with

Answer 15

Flexible, thin mats of extracellular matrix underlying epithelial sheets and tubes
Highly specialised ECM containing a distinct combination of collagen, glycoproteins and proteoglycans

Surround muscle, peripheral nerve and fat cells
Underlie most epithelia

mutation in type 4 collagen (alpha 5 chain)

Question 16

• What are Diabetic Nephropathy?

- What is Alport Syndrome?

Answer 16

Highly thickened BM which restricts renal filtration leading to renal failure

Mutations in Collagen IV result in abnormally split and laminated GBM, associated with progressive kidney function loss and hearing loss

Question 17

• What are elastic fibres made of?

- What condition are mutations in the protein fibrillin-1 associated with?

Answer 17

Core of protein elastin
Microfibrils - rich in the protein fibrillin

Marfan's syndrome - Spider-like fingers, tall and thin, long legs, arms, fingers, toes. overly flexible joints and scoliosis

Question 18

• What is elastin composed of?

Answer 18

2 types of segment that alternate along polypeptide chain:

Hydrophobic region

Alpha-helical regions rich in alanine and lysine (lysine chains are covalently cross linked)

Question 19

• Describe the structure of Laminins?

- What makes Laminins multi-adhesive properties?

Answer 19

They are heterotrimeric proteins made up of an alpha-chain, beta chain and a gamma-chain
Forming cross chained molecules

They are multi adhesive proteins that can interact with a variety of cell surface receptors including integrins and dystroglycan

Question 20

• What group of tissues tend to be affected by mutations of genes coding for Laminins?
• What causes congenital muscular dystrophy and what are the symptoms?
• what causes epidermolysis bullosa

Answer 20

Muscular

Alpha-2 chain in Laminin2
Hypotonia (abnormally decreased muscle tension), generalised weakness and deformities of the joints

mutation in all three chains of laminin 5

Question 21

• What 2 forms can fibronectins exist as?

- Explain the multi-domain structure of fibronectin

Answer 21

Insoluble fibrillar matrix
Soluble plasma matrix

Several domains are linked by disulphide bonds
Fibronectin then has several collagen binding sites and cell binding sites

Question 22

• How is fibronectin involved in the binding of collagen fiber to actin filament?

Answer 22

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

Question 23

• What are proteoglycans?

Answer 23

Core proteins covalently attached to one or more glycosaminoglycan (GAG) chains

Question 24

• What are the 4 proteoglycan families grouped upon their structural and functional characteristics

Answer 24

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

Question 25

- What are the functions of fibronectin?

Answer 25

Regulating cell adhesion and Migration in a variety of processes e.g. - embryogenesis and Tissue repair Important in wound healing to promote blood clotting

Question 26

- What are GAGs made of and what charge are they usually?

Answer 26

Repeating disaccharide units with one or two of these sugars being an amino sugar Negative as they are sulfated or carboxylated

Question 27

- What are the 4 main groups of GAGs according to the disaccharide repeating unit?

Answer 27

Hyaluronan Chondroitin sulfate and dermatan sulfate Heparan Sulfate Keratan Sulfate

Question 28

- What makes hyaluronan distinct from other GAGs? | - Where is hyaluronan found in high viscousity?

Answer 28

Simply a carbohydrate chain without a core protein Vitreous humour of the eye In synovial fluids of joints

Question 29

- Why do hyaluronan chains tend to occupy a relatively large volume?

Answer 29

Hyaluronan can undergo a very high degree of polymerisation

Question 30

- How does Aggrecan's presence lead to large quantities of water being retained by the environment it is in?

Answer 30

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

Question 31

- How is aggrecan perfectly suited to resist compressive forces in cartilage matrix?

Answer 31

Under compressive load, water is given up but is regained once the load is reduced Suited to resist compressive forces

Question 32

what are the functions of elastin and collagen and how do they work together

Answer 32

elastin- important for elasticity of tissues eg skin, blood vessels and lungs collagen is important for tensile strength of tissues they are woven together to limit the extent of stretching

Question 33

what do fibril associated collagens do and give examples

Answer 33

associate with fibrillar components regulate organisation of collagen fibrils types 9 and 12