Aggregate degradation by growth plate proteases.

For long bone growth to occur, calcification of the matrix must begin in the lower hypertrophic zone of the growth plate. It generally is accepted that physeal proteoglycans help regulate mineralization, and that, at least in vitro, smaller proteoglycan fragments are less inhibitory of mineral formation. It also has been shown that proteoglycan degrading enzymes are concentrated in the hypertrophic zone, where calcification occurs. Thus, one can hypothesize that these enzymes are involved in the calcification process. Proteoglycans appear mainly as the aggregate form in the physis, and this study demonstrates the ability of the naturally occurring physeal enzymes to degrade proteoglycan aggregate, without first disaggregating it. Because the matrix constituents probably limit hypertrophic cell size and shape, this degradation may have some relationship to the rate of growth of the physis.