Articular cartilage metabolism in degenerative joint disease Flashcards
Describe the cartilage in the young
Hypercellular
Little matrix
No zones
No tidemark
- Nutrient access from subchondral bone vasculature
Describe cartilage in adults
Hypocellular
Increased matrix
Zonal morphology
Tidemark
- Nutrient access from synovial membrane via fluid
Describe cartilage in elderly
Even fewer cells
- remaining cells have less metabolism since produce less cartilage proteins
Microstructural changes
Describe the microstructural changes in elderly cartilage
Collagen cross-linking: fibrils become cross-linked
Aggrecan changes: shorter chondroloitin sulphate chains
- therefore less H2O absorption
Matrix degradation products build up
Describe cartilage turnover in a healthy state
Equilibrium between degradation and replacement exists
What substance is responsible for degradation of cartilage as part of normal cell turnover?
Metalloproteinase
What is required for metalloproteinase activity?
Zinc and calcium
What are the different types of Metalloproteinases and what are their functions?
MMPs (matrix metalloproteinases)
- degrade collagen and other matrix proteins
Aggrecanases
- degrade aggrecan (main proteoglycan)
How do aggrecanases degrade aggrecan?
Detach aggrecan from hyaluronic acid and chop up protein chain into small parts
Describe cartilage turnover in a disease state
Unbalanced equilibrium => including degradation and decreased production
loss of aggrecan =>
loss of water =>
loss of ability to absorb compression
What is rheumatoid arthritis?
An inflammatory disease characterised by:
- inflamamtory cell influx
- increased secretion of cytokines
=> cartilage degradation
What is osteoarthritis?
A mechanical disease often occurs after injury/trauma
Genetic and environmental factors play a role
Stages:
- normal
- early stage
- intermediate stage
- late stage = chondrocyte clusters form
