AGE-DEPENDENT CHANGES IN PROTEOGLYCAN BIOSYNTHESIS IN HUMAN INTERVERTEBRAL DISKS

Proteoglycans from annulus fibrosus and nucleus pulposus of human inte rvertebral disc were investigated by electrophoresis in a composite ag arose-polyacrylamide gel and immunohistochemically using various monoc lonal antibodies against components of extracellular matrix. There wer e at least five different populations of proteoglycans in both annulus fibrosus and nucleus pulposus. Proteoglycans represented by individua l electrophoretic bands differed from each other in hydrodynamic size but all of them contained epitopes present in keratan sulphate. Chondr oitin sulphate could be detected inn populations with molecular weight above 200,000 daltons. We could postulate that the cleavage of proteo glycan chains starts at title C-terminal end. This is supported by the finding that the globular region G2 on tile protein core was detected in the same populations as keratan sulphate. We could confirm these r esults using tissue cultures of nucleus pulposus, inner and external p art of annulus fibrosus. Of interest is the finding that there is de n ovo synthesis of globular domain G1 only in structures of intervertebr al 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 aggregatio n of proteoglycans during the aging process.