L06 - Biochemistry of cartilage and bone Flashcards
What types of macromolecules compose the ECM around a cell?
Insoluble fibers
Soluble polymers
Adhesive glycoproteins
Describe the structure of collagen?
Gly-X-Y repeats
3 α chains: 2 α1, 1 α2 forms triple helix
Typically staggered ends
Describe the assembly of collagen.
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
How does extra-cellular matrix components dictate tissue function?
Function depends on component:
- Type
- Organization
- Relative amount
What is the partition of organic and inorganic molecules in Bone matrix?
Dense matrix:
70% inorganic
30% organic (90% collagen)
List the inorganic and organic component of Bone matrix?
Inorganic: Calcium phosphate as hydroxyapatite crystals
Organic: Mainly type I collagen in layers, with Proteoglycans, GAGs, Glycoproteins
What type of collagen is Heterotypic?
Type V that fits inside layers of Type !
Which collagen types coat the surface of fibrillar collagen ?
Type IX, XII, XIV (FACIT)
What is the role of collagen type IV?
Abundant in basement membrane
What is the role of collagen type VI?
Beaded filament found in desmosomes in muscles
What pathology arises from malfunction of collagen type VII?
Anchoring fibril in connecting epidermis and dermis
Malfunction = epidermolysis bullosa
What is the structure of soluble polymers in the ECM?
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
What are the 2 types of Glycosaminoglycans (GAG) in the ECM?
- Unsulphated: Hyaluronic acid
- Sulphated: chondroitin sulphate, heparan sulphate, keratan sulphate, dermatan sulphate
How can hyaluronic acid act as a lubricant in joints?
Large and highly negatively charged due to carboxyl group»_space; attracts lots of water »_space; acts as lubricant
List 3 functions of Hyaluronic acid in the MSS?
- Lubricant in synovial joints
- Resist compressive force in cartilage
- Fills joint space and maintain structure
Difference between Hyaluronic acid and proteoglycan?
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
What is the structure of proteoglycans?
One or more GAG side chains attached to a core protein
List some extracellular Lecticans?
aggrecan, brevican, neurocan, versican
List some SLRPs?
Short leucine repeat proteoglycans (SLRPs): decorin, biglycan, lumican
What is the structure of Perlecan?
heparan sulphate proteoglycan, up to ~10 GAG side chains
What are some membrane- bound proteoglycans?
Syndecan, Glypican
List 4 functions of proteoglycans?
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
What is the KEY function of adhesive glycoproteins?
interact with cells and other macromolecules in ECM
How does adhesive glycoproteins interact with ECM?
Via Functional peptide domains
> > prescribe interactions with surface receptors, other matrix molecules
Apart from interacting with cells and macromolecules in the ECM, give other functions of adhesive glycoprotein?
regulate fibril formation
interaction with inorganic phase (e.g. mineralized connective tissues: bone, dentine)
There is only one type of Fibronectin. True or False?
False
- Functional form = disulphide-bonded dimer
- Different isoforms by alternative splicing (increases diversity in function)
Function of Fibronectin?
Forms fibrillar matrix (further stabilized by extensive disulphide bonding):
1) Promotes cell adhesion
2) Affects cell morphology, migration, differentiation
How does Fibronectin interact with cells? Mechanism?
Binds to Cell surfaces via integrin receptors, Arg-Gly-Asp (RGD) motif
Also binds to Collagen, heparin/heparan sulphate proteglycans, fibrin
What mediates interactions between cell and matrix?
Matrix receptors:
Integrins and Discoidin domain receptors (DDRs)
(+Syndecan, Fibronectin receptors…etc)
What is the structure of Integrins?
Heterodimers (22 known types)
α chain / subunit (17 types): divalent cation, disulphide bond
β chain / subunit (8 types): cysteine-rich domain
What gives diversity to integrin molecules?
Many types of α and β chain
A single β chain can interact with multiple α chains = diversity to bind different ligands
How does integrin (matrix receptor) cause intracellular changes? Mechanism?
Mediate weak cell-matrix and cell-cell interactions
Bind / interact with ECM (sequence-specific: RGD) and cytoskeleton to signal nucleus to regulate gene expression
Explain how cell-matrix interactions can be fine tuned and specific?
Multiple interactions through different matrix receptors
What is the sequence of ECM homeostasis?
Gene expression > matrix assembly > matrix turnover > gene expression
What are some enzymes involved in matrix turnover?
mostly Matrix metalloproteinases (MMPs)
others: Hyaluronidase, chondroitinase, Serine proteinases, elastase, cathepsins
List some subtypes of MMPs?
Matrix metalloproteinases
collagenases, gelatinases, stromlysin
What acts against the action of MMPs?
Activity regulated by tissue inhibitors of matrix metalloproteinases (TIMPs)
What are the 2 mechanisms in place to regulate MMP activity?
inhibitors of matrix metalloproteinases (TIMPs)
synthesized as inactive proenzymes that only work at specific sites of ECM proteins
What are some diseases caused by imbalance of matrix degradation and remodeling?
Osteoarthritis
Intervertebral disc degeneration
Rheumatoid arthritis
Osteoporosis
What part of the ECM degenerates in Intervertebral disc degeneration?
Aggrecan degradation: proteolytic fragmentation of aggrecan structure increases with age
Aggrecan is a proteoglycan that resists compression and acts as a space filler
How does the ECM change in RA?
Trigger + abnormal immunity»_space; trigger inflammation»_space; abnormally activates MMPs»_space; accelerated breakdown of ECM
How is the ECM affected in Osteogenesis imperfecta?
mutant type I collagen = Low bone density
How is the ECM affected in Marfan syndrome?
mutant fibrillin-1 (FBN1) = ECM protein which regulates TGF-β signaling
