Similarities in the phenotypic expression of pericytes and bone cells

Bovine brain microvessel pericytes, bone cells, and fibroblasts were grown in tissue culture in 3%, 21%, or 60% oxygen for 7 weeks. Alkaline phosphatase activity was highest in bone cells and pericytes grown in 3% oxygen, with the activity higher in the former than the latter. Alkaline phosphatase activity was very low in fibroblasts at every oxygen concentration. Osteocalcin concentration was higher in bone cells than in pericytes, was not detected in fibroblasts, and in bone cells and pericytes the concentration was highest in 21% oxygen. Other bovine brain microvessel pericytes were grown in 3% or 21% oxygen for 3 to 24 days in the presence or absence of bone morphogenetic protein 2 and in the presence or absence of parathyroid hormone. At Day 3 of culture, alkaline phosphatase activity was highest in 21% oxygen in the presence of bone morphogenetic protein 2. By Day 17 of culture, alkaline phosphatase activity was highest in 3% oxygen whether bone morphogenetic protein was present or not. Cyclic adenosine monophosphate production in pericytes in response to parathyroid hormone stimulation was very modest when compared with that of bone cells, and this response was not found to be significantly altered by bone morphogenetic protein 2, duration of culture, or the oxygen concentration during incubation. These findings show that the microvessel pericyte is capable of exhibiting several oxygen dependent, phenotypic characteristics ascribed to osteoblasts.