Notochordal cells interact with nucleus pulposus cells: Regulation of proteoglycan synthesis

The disappearance of notochordal cells is correlated with early degenerativ e changes in the intervertebral disc, With increased disc degeneration ther e is a marked decrease in proteoglycan synthesis, resulting in loss of mech anical function. One possible mechanism for the decrease in proteoglycan sy nthesis is the loss of notochordal cells from the tissue. In this study, nu cleus pulposus cells cocultured with notochordal cells exhibit an increase in proteoglycan synthesis. Interestingly, purified notochordal cells synthe size little proteoglycan as observed by [S-35]sulfate incorporation into pr oteoglycans. The observed increase in proteoglycan synthesis does not appea r to be dependent on cell-cell contact; rather it is the result of soluble factor(s) produced by notochordal cells. Finally, no difference in chondroi tin sulfate chain size in notochordal-stimulated nucleus pulposus cells was observed which is consistent with an up-regulation in aggrecan core protei n synthesis. These results are consistent with canine breeds where notochor dal cells persist into adult age and disc degeneration is not observed. Thi s suggests notochordal cells play a vital role in maintaining disc integrit y. (C) 1999 Academic Press.