THE PROTEOGLYCANS OF THE CARTILAGINOUS END-PLATE OF THE HUMAN INTERVERTEBRAL DISC CHANGE AFTER MATURITY

Lumbar spines collected postmortem were assigned to one of two groups: group 1-three spines with healthy discs, or group 2-three spines with severely degenerated discs. The proteoglycans (PGs) of the cartilaginous endplate (CEP) were extracted with 4 M guanidinium chloride containing protease inhibitors and were purified by caesium chloride density gradient ultracentrifugation. On Sepharose CL-2B chromatography, the most dense 20% of the gradient (the Al fraction) showed two subfractions, one eluting near the void volume and one partitioned by the gel. Both fractions resembled those of the nucleus pulposus and the anulus fibrosus in the number of components seen on agarose-polyacrylamide gel electrophoresis. Both fractions changed with ageing/degeneration; the ratio of keratan sulphate to chondroitin sulphate, which was about 1 in group 1, increased to about 3 in group 2; the hydrodynamic volumes fell; the electrophoretically distinguishable component of lowest mobility disappeared while new, highly mobile components appeared; and the water content decreased slightly. Clearly, the PGs of the CEP of degenerated intervertebral discs differed from those of healthy discs; this supports the view that the CEP participates in the process of ageing/degeneration in the disc.