The pericyte as a possible osteoblast progenitor cell.

Bovine capillary and microvessel pericytes were grown in monolayer in standard tissue culture medium supplemented with 10% newborn calf serum at various oxygen tensions for up to ten weeks. The pericytes synthesized alkaline phosphatase and formed colonies that mineralized. Energy dispersive X-ray spectrometry revealed the presence of calcium and phosphate, showed positive staining for collagen and glycosaminoglycan, and, most importantly, demonstrated the synthesis of osteocalcin. Cell proliferation, hydroxyproline production, and alkaline phosphatase synthesis were greatest in 3% oxygen, whereas osteocalcin production was least in 3% oxygen. These findings demonstrate that the capillary or microvessel pericyte exhibits phenotypic expressions in vitro that are similar to that of in vitro bone cells, and these expressions may be somewhat oxygen dependent. It is suggested from these findings that the capillary or microvessel pericyte may be an osteoblast precursor cell.