PROTEOGLYCAN HETEROGENEITY IN THE NORMAL ADULT OVINE INTERVERTEBRAL DISC

Proteoglycans (PGs) were isolated from 4 M GuHCl extracts of young adu lt ovine Intervertebral disc (IVD) tissues using sequential CsCl densi ty gradient centrifugation, and a combination of gel-permeation and hy drophobic chromatography. A total of six PG sub-populations were ident ified in both the Annulus fibrosus (AF) and Nucleus pulposus (NP), i.e . two high buoyant density aggregatable PGs, two high buoyant density non-aggregatable PGs and two small, low-intermediate buoyant density, non-aggregatable, DS-rich PG species. These latter PGs were identified as biglycan and decorin on the basis of analyses of their core protei n native size, and glycosaminoglycan composition. Additional low-inter mediate buoyant density PG species were also evident in the non-aggreg atable PG pool, particularly in extracts of NP tissues. These PGs did not bind to the octyl affinity matrix under the experimental condition s employed and thus were readily separated from the DS-PGs by hydropho bic chromatography, their constituent glycosaminoglycans (CS and KS) a lso differed and were of a smaller size to the CS and KS chains isolat ed from the large high buoyant density PGs, the small PGs which did no t bind to octylsepharose may therefore represent distinct PG species i n their own right. Differences were evident in the absolute size, and in the distribution of individual PG species in the respective IVD tis sues but the NP always contained a larger proportion of high buoyant d ensity non-aggregatable PGs of somewhat smaller size than those isolat ed from the AF. Decorin and biglycan, however, were generally more abu ndant in AF tissues.