INTRODUCTION: The small leucine‐rich proteoglycans (SLRPs) are molecules which have many functions including tissue organisation and repair, protection of collagens from proteolysis, cellular proliferation and matrix adhesion. They are present in the intervertebral disc but their role in disc pathology is unclear. In degradative diseases such as osteoarthritis the SLRPS become fragmented in the cartilage, possibly altering their homeostatic functions resulting in loss of matrix integrity.
METHODS: Human samples of disc were obtained from patients with scoliosis (n=7, 19‐53y), degenerative disc disease (DDD) (n=6, 35‐51y) and herniated discs (n=5, 33‐68y). Proteoglycans were extracted in 4M GuHCl and characterised via enzymatic digestion and caesium chloride gradient centrifugation followed by Western blotting to identify the SLRPs (keratocan, decorin, biglycan, lumican and fibromodulin), as well as their degree of fragmentation.
RESULTS: All samples of disc demonstrated the presence of the SLRPs investigated. In addition to intact proteoglycans there was evidence of fragmentation of all the SLRPs assessed. In the scoliosis samples fragmentation of decorin, keratocan, biglycan and fibromodulin was observed in the males (all 19y) and older females (42 & 53y) but the two younger females (27 & 34y) showed little fragmentation. In herniated discs, biglycan showed much fragmentation whereas keratocan was less so. In DDD discs, fragmentation of the SLRPS was variable.
DISCUSSION: Although the numbers of samples investigated so far are low, there may be subtle differences in the fragmentation of SLRPs during different disease processes of the intervertebral disc, for example scoliosis. There is a suggestion that in the scoliosis samples, sex or age may influence the degree of fragmentation. If changes within the extracellular matrix prior to collagen destruction can be identified then these changes may prove useful as biomarkers of different pathologies.