L06 - Biochemistry of cartilage and bone

Question 1

What types of macromolecules compose the ECM around a cell?

Answer 1

Insoluble fibers
Soluble polymers
Adhesive glycoproteins

Question 2

Describe the structure of collagen?

Answer 2

Gly-X-Y repeats

3 α chains: 2 α1, 1 α2 forms triple helix

Typically staggered ends

Question 3

Describe the assembly of collagen.

Answer 3

1) C-terminal propeptide initiates triple helix formation in rough ER
2) Procollagen is secreted into extracellular space
3) Procollagen peptidase cleaves procollagen to form collagen

Question 4

How does extra-cellular matrix components dictate tissue function?

Answer 4

Function depends on component:

• Type
• Organization
• Relative amount

Question 5

What is the partition of organic and inorganic molecules in Bone matrix?

Answer 5

Dense matrix:
70% inorganic
30% organic (90% collagen)

Question 6

List the inorganic and organic component of Bone matrix?

Answer 6

Inorganic: Calcium phosphate as hydroxyapatite crystals

Organic: Mainly type I collagen in layers, with Proteoglycans, GAGs, Glycoproteins

Question 7

What type of collagen is Heterotypic?

Answer 7

Type V that fits inside layers of Type !

Question 8

Which collagen types coat the surface of fibrillar collagen ?

Answer 8

Type IX, XII, XIV (FACIT)

Question 9

What is the role of collagen type IV?

Answer 9

Abundant in basement membrane

Question 10

What is the role of collagen type VI?

Answer 10

Beaded filament found in desmosomes in muscles

Question 11

What pathology arises from malfunction of collagen type VII?

Answer 11

Anchoring fibril in connecting epidermis and dermis

Malfunction = epidermolysis bullosa

Question 12

What is the structure of soluble polymers in the ECM?

Answer 12

Linear polymers of repeating dissacharide units

1) Amine sugar (N-acetylglucosamine or N-acetlygalactasamine with one or more hydroxyl groups esterified with sulphate)
+
2) Uronic acid

Question 13

What are the 2 types of Glycosaminoglycans (GAG) in the ECM?

Answer 13

• Unsulphated: Hyaluronic acid

- Sulphated: chondroitin sulphate, heparan sulphate, keratan sulphate, dermatan sulphate

Question 14

How can hyaluronic acid act as a lubricant in joints?

Answer 14

Large and highly negatively charged due to carboxyl group&raquo_space; attracts lots of water &raquo_space; acts as lubricant

Question 15

List 3 functions of Hyaluronic acid in the MSS?

Answer 15

• Lubricant in synovial joints
• Resist compressive force in cartilage
• Fills joint space and maintain structure

Question 16

Difference between Hyaluronic acid and proteoglycan?

Answer 16

Both are GAGs

Hyaluronic acid is unsulphated, much longer, has NO core protein

Proteoglycans are sulphated, much shorter, have core proteins + GAG side chains has site for biological function

Question 17

What is the structure of proteoglycans?

Answer 17

One or more GAG side chains attached to a core protein

Question 18

List some extracellular Lecticans?

Answer 18

aggrecan, brevican, neurocan, versican

Question 19

List some SLRPs?

Answer 19

Short leucine repeat proteoglycans (SLRPs): decorin, biglycan, lumican

Question 20

What is the structure of Perlecan?

Answer 20

heparan sulphate proteoglycan, up to ~10 GAG side chains

Question 21

What are some membrane- bound proteoglycans?

Answer 21

Syndecan, Glypican

Question 22

List 4 functions of proteoglycans?

Answer 22

1) Provide hydrated space around cells (e.g. in ‘empty spaces’ of cartilage)
2) Act as selective sieves: regulate traffic of molecules, cells (size, charge)
3) Bind secreted signaling molecules (e.g. growth factors in ECM)
4) Bind and regulate proteases (degrade ECM), protease inhibitors

Question 23

What is the KEY function of adhesive glycoproteins?

Answer 23

interact with cells and other macromolecules in ECM

Question 24

How does adhesive glycoproteins interact with ECM?

Answer 24

Via Functional peptide domains

> > prescribe interactions with surface receptors, other matrix molecules

Question 25

Apart from interacting with cells and macromolecules in the ECM, give other functions of adhesive glycoprotein?

Answer 25

regulate fibril formation interaction with inorganic phase (e.g. mineralized connective tissues: bone, dentine)

Question 26

There is only one type of Fibronectin. True or False?

Answer 26

False - Functional form = disulphide-bonded dimer - Different isoforms by alternative splicing (increases diversity in function)

Question 27

Function of Fibronectin?

Answer 27

Forms fibrillar matrix (further stabilized by extensive disulphide bonding): 1) Promotes cell adhesion 2) Affects cell morphology, migration, differentiation

Question 28

How does Fibronectin interact with cells? Mechanism?

Answer 28

Binds to Cell surfaces via integrin receptors, Arg-Gly-Asp (RGD) motif Also binds to Collagen, heparin/heparan sulphate proteglycans, fibrin

Question 29

What mediates interactions between cell and matrix?

Answer 29

Matrix receptors: Integrins and Discoidin domain receptors (DDRs) (+Syndecan, Fibronectin receptors...etc)

Question 30

What is the structure of Integrins?

Answer 30

Heterodimers (22 known types)  α chain / subunit (17 types): divalent cation, disulphide bond  β chain / subunit (8 types): cysteine-rich domain

Question 31

What gives diversity to integrin molecules?

Answer 31

Many types of α and β chain A single β chain can interact with multiple α chains = diversity to bind different ligands

Question 32

How does integrin (matrix receptor) cause intracellular changes? Mechanism?

Answer 32

Mediate weak cell-matrix and cell-cell interactions Bind / interact with ECM (sequence-specific: RGD) and cytoskeleton to signal nucleus to regulate gene expression

Question 33

Explain how cell-matrix interactions can be fine tuned and specific?

Answer 33

Multiple interactions through different matrix receptors

Question 34

What is the sequence of ECM homeostasis?

Answer 34

Gene expression > matrix assembly > matrix turnover > gene expression

Question 35

What are some enzymes involved in matrix turnover?

Answer 35

mostly Matrix metalloproteinases (MMPs) others: Hyaluronidase, chondroitinase, Serine proteinases, elastase, cathepsins

Question 36

List some subtypes of MMPs?

Answer 36

Matrix metalloproteinases collagenases, gelatinases, stromlysin

Question 37

What acts against the action of MMPs?

Answer 37

Activity regulated by tissue inhibitors of matrix metalloproteinases (TIMPs)

Question 38

What are the 2 mechanisms in place to regulate MMP activity?

Answer 38

inhibitors of matrix metalloproteinases (TIMPs) synthesized as inactive proenzymes that only work at specific sites of ECM proteins

Question 39

What are some diseases caused by imbalance of matrix degradation and remodeling?

Answer 39

Osteoarthritis Intervertebral disc degeneration Rheumatoid arthritis Osteoporosis

Question 40

What part of the ECM degenerates in Intervertebral disc degeneration?

Answer 40

Aggrecan degradation: proteolytic fragmentation of aggrecan structure increases with age Aggrecan is a proteoglycan that resists compression and acts as a space filler

Question 41

How does the ECM change in RA?

Answer 41

Trigger + abnormal immunity >> trigger inflammation >> abnormally activates MMPs >> accelerated breakdown of ECM

Question 42

How is the ECM affected in Osteogenesis imperfecta?

Answer 42

mutant type I collagen = Low bone density

Question 43

How is the ECM affected in Marfan syndrome?

Answer 43

mutant fibrillin-1 (FBN1) = ECM protein which regulates TGF-β signaling