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Changes in the proteoglycans of the intervertebral disc cartilaginous end-plate with ageing and degeneration Bishop, Paul Burton


This research examined the role of the cartilaginous end-plate (CEP) in ageing and degeneration of the human intervertebral disc (IVD). The matrix component affected primarily during degeneration of the IVD is proteoglycan (PG) (Pearce et al., 1987). The CEP, a hyaline cartilage found between the nucleus pulposus (NP) and the anulus fibrosus (AF) and the vertebral body, has been proposed as the source of the PG of the AF and NP. This study was undertaken to: 1) assess the similarity of CEP PG to PG from articular cartilage and IVD, (2) compare the CEP PG from healthy young discs with those from older degenerate discs (3) distinguish the changes in CEP PG due to ageing from those due to degeneration. The combined effects of ageing and degeneration were studied using end-plates from three healthy young spines and three post-mature spines; those to degeneration alone by comparison of two healthy with one degenerate disc in each of three spines. Altogether 86 CEP from 10 lumbar spines were examined. The CEP PG were prepared from 4M guanidinium chloride tissue extracts by density gradient ultracentrifugation under associative conditions. PG were separated into high and low molecular weight (M) components by Sepharose CL-2B chromatography. The PG and the high M and low M fractions were analysed for hexose (hex) and hexuronate (hexA) as measures of keratan sulphate and chondroitin sulphate, respectively. Also, the two fractions were analysed by composite agarose-polyacrylamide gel electrophoresis. The CEP PG resembled the IVD PG more closely than those of articular cartilage PG: the fraction excluded from Sepharose CL-2B was low, the hex/hexA ratio was high, and five electrophoretically distinct subspecies were seen. With degeneration, several properties of the CEP PG altered irrespective of age: the extractable .total proteoglycan fell, the ratio hex/hexA rose and number of electrophoretically distinct PG subspecies declined. With age, the sizes of the high M and low M fractions fell and the electrophoretic mobilities of the subspecies changed. These results suggested that degeneration involves both a conversion of aggregating to non-aggregating PG and the preferential biosynthesis of a keratan sulphate-rich over a chondroitin sulphate-rich PG.

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