Age-dependent changes in proteoglycan biosynthesis in human intervertebral discs

Proteoglycans from annulus fibrosus and nucleus pulposus of human intervertebral disc were investigated by electrophoresis in a composite agarose-polyacrylamide gel and immunohistochemically using various monoclonal antibodies against components of extracellular matrix. There were at least five different populations of proteoglycans in both annulus fibrosus and nucleus pulposus. Proteoglycans represented by individual electrophoretic bands differed from each other in hydrodynamic size but all of them contained epitopes present in keratan sulphate. Chondroitin sulphate could be detected in populations with molecular weight above 200,000 daltons. We could postulate that the cleavage of proteoglycan chains starts at the C-terminal end. This is supported by the finding that the globular region G2 on the protein core was detected in the same populations as keratan sulphate. We could confirm these results using tissue cultures of nucleus pulposus, inner and external part of annulus fibrosus. Of interest is the finding that there is de novo synthesis of globular domain G1 only in structures of intervertebral disc from a 16-year-old male and not in the tissue of a 69-year-old male. This might contribute to an explanation of decreased aggregation of proteoglycans during the aging process.