A NOVEL ANGIOGENIC MOLECULE PRODUCED AT THE TIME OF CHONDROCYTE HYPERTROPHY DURING ENDOCHONDRAL BONE-FORMATION

Angiogenesis is a pivotal event in endochondral ossification. Vessels grow into the hypertrophic cartilage and erode it to produce a scaffol d on which osteoblasts settle to produce woven bone. A new culture sys tem was used to determine whether growth-plate chondrocytes produce an angiogenic molecule. Chondrocytes from primary growth plates of bovin e fetuses were separated into maturationally distinct subpopulations. When cultured these cells produce an extensive extracellular matrix an d the prehypertrophic cells mature to express the hypertrophic phenoty pe defined by the synthesis of type X collagen and matrix calcificatio n. The culture medium collected from the hypertrophic cells contains a chemoattractant, nonmitogenic molecule for bovine endothelial cells w hich can induce angiogenesis in vivo in the rabbit cornea model. This molecule has a M(r) of approximately 120 x 10(3). The production of th is molecule by hypertrophic cells is enhanced by both 1,25-(OH)(2) vit amin D-3 and 24,25-(OH)(2) vitamin D-3 at 10(-8)-10(-12) M, but only i n pre- and early hypertrophic cells. In contrast, these metabolites ha ve either no effect or an inhibitory effect on the more mature hypertr ophic cells. These results describe for the first time the production of an angiogenic molecule by hypertrophic chondrocytes. They demonstra te an important role for vitamin-D-3 metabolites in regulating hypertr ophy and angiogenesis during normal skeletal growth and differentiatio n. Thus, a defective regulation of these processes, due to the lack of vitamin-D metabolites, may explain the observed enlargement of the hy pertrophic zone and impairment of skeletal growth in rickets which is induced clinically and experimentally by a deficiency of vitamin D. (C ) 1996 Academic Press, Inc.