The Journal of Bone and Joint Surgery, Vol 69, Issue 1 76-82, Copyright © 1987 by Journal of Bone and Joint Surgery, Inc
Elaboration of neutral proteoglycanase by growth-plate tissue cultures
P Mercier, MG Ehrlich, A Armstrong and HJ Mankin
This report describes the properties of a neutral protease that was
synthesized and secreted into medium by intact cartilaginous growth plate
in tissue culture. Bovine cartilaginous growth plate was grown for seven
days in tissue culture, during which time the chondrocytes remained viable
and metabolically active as determined by quantitation of trypan-blue
exclusion and incorporation of 3H-cytidine. Protease activity, assayed by
viscometry using proteoglycan monomer from cartilage as a substrate, was
absent on day 1 but was present at high levels on days 2 through 5. The
protease activity did not require activation and was highest at neutral and
alkaline pH. Protease activity was abolished by twenty-millimolar EDTA but
was unaffected by pepstatin, iodoacetate, and soybean trypsin inhibitor. In
contrast to the high levels of activity of neutral protease that were
present in tissue cultures of the intact growth plate, no protease activity
could be detected when chondrocytes from the cartilaginous growth plate
were grown in cell culture, even after sonication of the cells or
activation with aminophenyl mercuric acetate or trypsin. Since hypertrophic
chondrocytes probably do not survive the disruption of tissue that is
involved in establishing cell cultures, these observations suggest that
neutral protease is probably released into the medium by the hypertrophic
chondrocytes that are present in the cultures of cartilaginous growth-plate
tissue. It appears that the organization of the growth plate in tissue
culture, as well as the maturation of proliferating chondrocytes into
hypertrophic chondrocytes in tissue culture, may be required for synthesis
of the neutral protease and its extracellular secretion by hypertrophic
chondrocytes.