Isolation of cells from ovine fetal long bone and characterization of their osteoblastic activities during in vitro mineralization.

Studies about bone formation and regulation are complex due to a close relationship between bone cells. Primary cell cultures allow to understand osteoblastic function. We isolated cells from the cortical metacarpal bone of 85 or 120 day-old ovine fetuses by an enzymatic method. After first passage and cell amplification, the growth medium (DMEM, ascorbic acid and fetal calf serum 10%) was replaced at confluence by a mineralization medium (MM: DMEM, ascorbic acid, beta-glycerophosphate, insulin). Alkaline phosphatase (ALP) activity in cell-matrix layer increased after 4 days of cultures in MM and maximized at day 6. We also measured osteocalcin, ALP and IGF-I secretion simultaneously during mineralization. PTH, PTHrP and 1.25(OH)2D3 decreased ALP activity in cell-matrix layer after 4 days of treatment in MM without fetal calf serum (FCS). Cells from 120 day-old fetuses were cultivated in MM with 10% FCS during 32 days to induce mineralization. Inorganic phosphorus concentration increased in medium between days 5 and 12, Ca concentration decreased in medium after 12 days of culture. Mineralization started at day 12, in the same time ALP activity appeared in medium. Osteocalcin secretion increased between days 6 and 12, decreased at day 14 and increased from day 16 until day 32. Ovine fetal bone cells produced IGF-I until first days of culture in MM. Such ovine osteoblast phenotype cells having the capacity to differentiate and mineralize in vitro would be a model to study the endocrine regulation of osteoblastic function in large mammals.