Pathobiology of the small leucine rich repeat proteoglycans in cartilage, intervertebral disc and tendon degeneration

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Back problems (M$700), OA (M$600), muscle and tendon disorders (M$500) accounted for 60% of musculoskeletal (MSK) health care expenditure in Australia in 1993-1994, were the second most common cause of presentations to a general practitioner, the third leading contributor to health system expenditure (>$3 billion) and accounted for ~300,000 hospital admissions, ~15 million medical services and over 13 million prescriptions. Significant disability due to MSK disease were noted in ~50% of people aged 65 years. Australian census data indicates that ageing trends will result in an increased incidence of MSK conditions as the longevity of the Australian population rises, exerting an ever increasing burden on the healthcare budget. Extreme levels of sporting or physical activity from traumatic loading of joints can lead to excessive loading of collagen fibres in MSK tissues leading to their failure and loss of tissue function. Common end stages of collagen fibre breakdown are preceded by matrix changes which may predispose MSK tissues to enzymatic and mechanical damage. One such change is an increased degradation of a family of small leucine-rich proteoglycans (SLRPs) which modulate the diameter, strength and assembly of collagen fibrils and bind and modify the effects of reparative growth factors and degradative cytokines within connective tissues. Altered synthesis of SLRPs and SLRP fragments have been identified in abnormal intervertebral disc, cartilage and tendon. Very little is known however about how these fragments are generated within these tissues and how they affect growth factor binding or collagen fibril formation. This deficiency will be addressed in our proposed study which will provide novel information on mechanisms of cartilage, intervertebral disc and tendon degeneration and potential therapeutic and diagnostic targets which may be exploited in future studies on the treatment of these musculoskeletal conditions.