Collagen

Question 1

What is ECM composed of?

Answer 1

50% water
proteins 
glycoproteins 
proteoglycans 
GAGs

Question 2

What is significant about size of collagen proteins?

Answer 2

Proteins are very large and difficult to work with- 6x as large as globular protein

Question 3

What is Glycoprotein and where is it formed?

Answer 3

Protein with carbohydrate attached to it (attachment occurs within the golgi)
Glycosyltransferase performs glycosylation which helps with folding and function of protein

Question 4

What is a Proteoglycan?

Answer 4

Protein is becoming smaller than the side chains, so modifications are large and majority is that side chain.
Side chains are negatively charged aiding in water attraction
i.e. Aggrecan, Perlecan, Decorin, Syndecan

Question 5

How does collagen placement differ in skin vs tendons vs cornea?

Answer 5

Skin- fibres are crosslinked
Tendons- parallel fibres
Cornea- transparent due to parallel lamellae placement of collagen

Question 6

What are some structural shapes formed by collagen?

Answer 6

Beaded string
Hexagon
Parallel
Fibril
Network forming (can act as sieve) 
Anchoring fibrils

Question 7

What amino acid repeat forms collagen?

Answer 7

Gly-X-Y repeat
X typically proline
Y typically hydroxyproline

Question 8

Why is glycine important in collagen?

Answer 8

It is small and neutral and is the only amino acid that can sit in the centre of the trimer alpha-chain of collagen

Question 9

Where does collagen synthesis occur?

Answer 9

Endoplasmic reticulum

Question 10

How does collagen production occur?

Answer 10

1. Synthesis of pro-alpha chain
2. Hydroxylation of selected proline and lysines
3. Glycosylation of selected hydroxy-lysines
4. Self-assembly of 3 pro-alpha chains
5. Procollagen triple-helix formation
6. Secretion
7. cleavage of propeptides
8. self-assembly of single triple helix collagen into fibril
9. Aggregation of collagen fibrils to form collagen fiber

Question 11

What proteins cleave propeptide collagens?

Answer 11

C and N proteinase

Question 12

How does lysyl oxidase aid in collagen formation?

Answer 12

Lysyl oxidase acts on lysine residues to help in formation of covalent link- helps form cross linking of collagen

Question 13

What is the turn-over half-life of collagen?

Answer 13

120 years
In adulthood there is no collagen turnover in healthy states.
There is no degradation of collagen in core of tissues. Periphery of tissues do have daily turnover of collagen

Question 14

Where do post-translational modifications of collagen occur?

Answer 14

Everything occurs in the endoplasmic reticulum, apart from the N and C proteinases cleaving the propeptide collagens

Question 15

What is the alpha chain of collagen, and does this chain differ in collagen types?

Answer 15

There are 3 alpha chains (aka polypeptide chains) that conjoin to form collagen.
You can have single alpha chain, dimers (homo or hetero), trimers- and they can vary depending on type of collagen being formed- I.e. collagen 4 is fibrous sheaths of tetramer collagen, whereas 1 is fibrous strands

Question 16

Where within collagen does most disease occur?

Answer 16

Within the glycine amino acid.

Can be dominant or recessive

Question 17

What is osteogenesis imperfecta?

Answer 17

Brittle bone disease
Autosomal recessive or dominant (severity is variable)
Collagen type 1 related disorder

Question 18

What structure is collagen type 1 and how does it relate to disease?

Answer 18

Heterotrimeric, fibrillar collagen- encoded by COL1A1 and COL1A2 genes
Accounts for 90% of brittle bone mutations

Question 19

What is the mechanism behind mild osteogenesis imperfecta?

Answer 19

Mild OI has reduced procollagen due to some null mutations (stop codon, promoter mutations, mRNA instability).
Only forming wild-type procollagen
Problems with enzymes that form collagen too

Question 20

How does HSP47 relate to collagen formation?

Answer 20

Lack of HSP47 results in aggregation of collagen within the endoplasmic reticulum

Question 21

What mutations are responsible for more sever forms of Osteogenisis imperfecta?

Answer 21

Glycine missense mutations
Dominant negative
Causes delay in folding, overly-modifying the collagen (protein becomes larger)

Question 22

What are the key issues resulting in mild vs severe osteogenesis imperfecta?

Answer 22

Lack of collagen = mild OI
Overly modified collagen= severe OI
Can also have a combined effect of both forms resulting in very severe OI

Question 23

How does location of mutation impact collagen and severity of osteogenesis imperfecta?

Answer 23

Mutation in C-end are more severe as the folding of collagen protein occurs here first thus a mutation will impact the rest of the protein
Folding occurs moving C -> N terminal

Question 24

What hydroxylation reactions occur within the ER when forming collagen, and what is the significance of them?

Answer 24

Hydroxylation is important for folding and stability of protein
Hydroxylation of lysine allows for it to act as substrate for the sugars to be added to

Question 25

How do chondrocytes differ throughout the zones of cartilage?

Answer 25

Superficial- elongated and thin, 1-3 cells thin middle- enlarged and hypertrophy Deep- stacked

Question 26

How does cartilage differ throughout the zones of cartilage?

Answer 26

Superficial- parallel to joint allowing for sheer force resistant Middle- Oblique Deep- vertical This transition helps with resisting compressive forces

Question 27

What is the calcified zone in articular cartilage?

Answer 27

Have hydroxyapatite crystals which anchor the articular cartilage onto bone

Question 28

What is the tide mark in articular cartilage?

Answer 28

Acellular line that marks border between non-calcified and calcified zone

Question 29

What are the important proteoglycans in articular cartilage?

Answer 29

Hyaluronan and aggrecan

Question 30

How can cartilage turnover be regulated?

Answer 30

Chondrocytes can regulate degradation and synthesis. Degradation: MMP degrades the collagen and proteoglycan- this can be inhibited by TIMPs (produced by chondrocytes) Synthesis: Synthesis of ECM- Collagen, proteoglycans, and proteins Increased growth factors (IGF-1, TGF-b) Reduced cytokines and NSAIDS

Question 31

What type of cell is found in fibrocartilage?

Answer 31

Fibrochondrocytes

Question 32

Why can inflammation be bad for cartilage?

Answer 32

Lysozymes may be released which can rapidly degrade cartilage.

Question 33

What are the 4 signs of osteoarthritis on x-ray?

Answer 33

Subchondral sclerosis Joint space narrowing Subchondral cysts Osteophyte formation

Question 34

What do oral glucosamines do?

Answer 34

Inhibit inflammatory breakdown of proteoglycans which will protect chondrocytes Help in anabolic formation of cartilage (they are a component) They have low risk profile, therefore may be advantageous to corticosteroids

Question 35

What are the zones of the meniscus?

Answer 35

White zone- inner 2/3rds of cartilage where blood does not reach Red zone- the outer 1/3rd where small amounts of blood can still reach

Question 36

What are surgical repairs of cartilage using arthroscopy?

Answer 36

Microfracture- induce bleeding and haematoma/inflammation and repair Meniscectomy- remove part of torn meniscus Meniscal Repair- may be able to stitch back torn meniscus if in red zone

Question 37

What are forms of cartilage transplant?

Answer 37

Osteo-Articular Transplant- Chondrocytes from Mesenchymal Stem Cells- grow chondrocytes Autologous Chondrocyte Implantation - take chondrocytes from non-weight bearing area, allow chondrocyte proliferation and build onto scaffold, and then implant into same patient Cadaver- as cartilage is avascular, you can use cadavers Osteotomy- modify bone elsewhere to change weight bearing portions

Question 38

What is the difference between mature and immature bone?

Answer 38

Mature -All cortical and cancellous -Osteoblasts lay bone matrix in sheets (lamellae) -Parallel, organized collagen fibers Immature -Randomly aligned (woven) collagen fibers -Only typically seen in adults in injured bone (in callus)

Question 39

What is indirect bone healing?

Answer 39

Forming bone via a process involving hematoma formation -> soft callus (days) -> bony callus -> bone remodelling Differential tissue formation and build up to bone

Question 40

What is direct fracture healing?

Answer 40

Direct formation of bone without the process of callus formation to restore skeletal continuity Need to align and compress the bone No callus formation is seen

Question 41

What are the steps of indirect bone healing?

Answer 41

1. Haematoma- secretion of growth factors, immune cells, fibroblast (forming granulation tissue) 2. Soft callus (1 week- 1 month)- forming soft woven bone. 10% strain at fracture (so cast will be left on) 3. Hard callus- mineralization happening, but disorganized. Strain is decreasing 4. Remodelling- Stable bridge with low strain environment is now present, so osteoclasts tunnel over this gap and break down woven bone, and osteoblasts follow laying down organized lamellar bone (will only happen with a reduced strain environment)

Question 42

What is the strain theory?

Answer 42

In bone, intermediate granulation tissue is formed first to allow for a reduction in strain. Reduction in strain will result in proper healing of injury.

Question 43

What are the blood supplies to the bone?

Answer 43

Nutrient artery Periosteal vessels Epiphyseal and metaphyseal vessels

Question 44

What are some fractures that are prone to problems with healing?

Answer 44

Proximal pole of scaphoid fractures (as blood supply is retrograde) Talar neck Intracapsular hip (vessels coming up neck that supply the head, distal supply, so damage impedes blood supply) Surgical neck of humerus (same set-up as hip)