Regulatory role of osteogenic growth peptide in proliferation, osteogenesis, and hemopoiesis

Bone marrow regeneration after injury is preceded by local and systemic osteogenic reactions. Recently, an osteogenic growth peptide was characterized in the regenerating marrow. The osteogenic growth peptide also is abundant in normal serum where it is markedly and transiently increased after marrow injury. This increase and the osteogenic growth peptide-induced stimulation of bone formation in vivo suggest a role for this peptide in mediating the systemic osteogenic response. In vitro, the osteogenic growth peptide is an autocrine mitogen for osteoblastic and fibroblastic cells. It also stimulates alkaline phosphatase activity and matrix mineralization. The serum osteogenic growth peptide is downregulated in osteoporotic ovariectomized mice. The osteogenic growth peptide levels as well as the bone loss, tetracycline uptake, and serum osteocalcin are reversed by exogenously administered osteogenic growth peptide. In normal mice, the osteogenic growth peptide increases white blood cell counts and total femoral bone marrow cellularity. These increases include all the hemopoietic lineages. When given to mice for 1 week before ablative radiotherapy and bone marrow transplantation, synthetic osteogenic growth peptide stimulates the bone marrow transplant engraftment; optimal osteogenic growth peptide doses doubled the survival rate. These data indicate that osteogenic growth peptide has an important role in the pathogenesis and treatment of systemic bone loss and provide a basis for further development of an antiosteoporotic osteogenic growth peptide therapy. It is suggested also that the osteogenic growth peptide promotes hemopoiesis secondary to the stimulation of the stromal (particularly osseous) microenvironment.