Collagen Flashcards
What is ECM composed of?
50% water proteins glycoproteins proteoglycans GAGs
What is significant about size of collagen proteins?
Proteins are very large and difficult to work with- 6x as large as globular protein
What is Glycoprotein and where is it formed?
Protein with carbohydrate attached to it (attachment occurs within the golgi)
Glycosyltransferase performs glycosylation which helps with folding and function of protein
What is a Proteoglycan?
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
How does collagen placement differ in skin vs tendons vs cornea?
Skin- fibres are crosslinked
Tendons- parallel fibres
Cornea- transparent due to parallel lamellae placement of collagen
What are some structural shapes formed by collagen?
Beaded string Hexagon Parallel Fibril Network forming (can act as sieve) Anchoring fibrils
What amino acid repeat forms collagen?
Gly-X-Y repeat
X typically proline
Y typically hydroxyproline
Why is glycine important in collagen?
It is small and neutral and is the only amino acid that can sit in the centre of the trimer alpha-chain of collagen
Where does collagen synthesis occur?
Endoplasmic reticulum
How does collagen production occur?
- Synthesis of pro-alpha chain
- Hydroxylation of selected proline and lysines
- Glycosylation of selected hydroxy-lysines
- Self-assembly of 3 pro-alpha chains
- Procollagen triple-helix formation
- Secretion
- cleavage of propeptides
- self-assembly of single triple helix collagen into fibril
- Aggregation of collagen fibrils to form collagen fiber
What proteins cleave propeptide collagens?
C and N proteinase
How does lysyl oxidase aid in collagen formation?
Lysyl oxidase acts on lysine residues to help in formation of covalent link- helps form cross linking of collagen
What is the turn-over half-life of collagen?
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
Where do post-translational modifications of collagen occur?
Everything occurs in the endoplasmic reticulum, apart from the N and C proteinases cleaving the propeptide collagens
What is the alpha chain of collagen, and does this chain differ in collagen types?
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
Where within collagen does most disease occur?
Within the glycine amino acid.
Can be dominant or recessive
What is osteogenesis imperfecta?
Brittle bone disease
Autosomal recessive or dominant (severity is variable)
Collagen type 1 related disorder
What structure is collagen type 1 and how does it relate to disease?
Heterotrimeric, fibrillar collagen- encoded by COL1A1 and COL1A2 genes
Accounts for 90% of brittle bone mutations
What is the mechanism behind mild osteogenesis imperfecta?
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
How does HSP47 relate to collagen formation?
Lack of HSP47 results in aggregation of collagen within the endoplasmic reticulum
What mutations are responsible for more sever forms of Osteogenisis imperfecta?
Glycine missense mutations
Dominant negative
Causes delay in folding, overly-modifying the collagen (protein becomes larger)
What are the key issues resulting in mild vs severe osteogenesis imperfecta?
Lack of collagen = mild OI
Overly modified collagen= severe OI
Can also have a combined effect of both forms resulting in very severe OI
How does location of mutation impact collagen and severity of osteogenesis imperfecta?
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
What hydroxylation reactions occur within the ER when forming collagen, and what is the significance of them?
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
How do chondrocytes differ throughout the zones of cartilage?
Superficial- elongated and thin, 1-3 cells thin
middle- enlarged and hypertrophy
Deep- stacked
How does cartilage differ throughout the zones of cartilage?
Superficial- parallel to joint allowing for sheer force resistant
Middle- Oblique
Deep- vertical
This transition helps with resisting compressive forces
What is the calcified zone in articular cartilage?
Have hydroxyapatite crystals which anchor the articular cartilage onto bone
What is the tide mark in articular cartilage?
Acellular line that marks border between non-calcified and calcified zone
What are the important proteoglycans in articular cartilage?
Hyaluronan and aggrecan
How can cartilage turnover be regulated?
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
What type of cell is found in fibrocartilage?
Fibrochondrocytes
Why can inflammation be bad for cartilage?
Lysozymes may be released which can rapidly degrade cartilage.
What are the 4 signs of osteoarthritis on x-ray?
Subchondral sclerosis
Joint space narrowing
Subchondral cysts
Osteophyte formation
What do oral glucosamines do?
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
What are the zones of the meniscus?
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
What are surgical repairs of cartilage using arthroscopy?
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
What are forms of cartilage transplant?
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
What is the difference between mature and immature bone?
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)
What is indirect bone healing?
Forming bone via a process involving hematoma formation -> soft callus (days) -> bony callus -> bone remodelling
Differential tissue formation and build up to bone
What is direct fracture healing?
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
What are the steps of indirect bone healing?
- Haematoma- secretion of growth factors, immune cells, fibroblast (forming granulation tissue)
- Soft callus (1 week- 1 month)- forming soft woven bone. 10% strain at fracture (so cast will be left on)
- Hard callus- mineralization happening, but disorganized. Strain is decreasing
- 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)
What is the strain theory?
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.
What are the blood supplies to the bone?
Nutrient artery
Periosteal vessels
Epiphyseal and metaphyseal vessels
What are some fractures that are prone to problems with healing?
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)
