DEPENDENCE OF MESENCHYMAL CELL RESPONSES ON DURATION OF EXPOSURE TO BONE MORPHOGENETIC PROTEIN-2 IN-VITRO

Bone morphogenetic proteins (BMPs) induce osteoblastic responses in cu ltures of pluripotent mesenchymal cells. The effects of chronic treatm ent of these cells with BMPs and of withdrawal following exposure, how ever, have not been fully elucidated. Thus, the aim of this study was to obtain information about the duration of exposure to recombinant hu man BMP-2 (rhBMP-2) required for expression and retention of osteoblas tic characteristics with subsequent formation of a mineralized extrace llular matrix in mesenchymal cell cultures. C3H10T1/2 cells and bone m arrow stromal cells were cultured with 1 ug/ml rhBMP-2 for either 0, 7 , 14, 21, or 28 days, with the remainder of the 4 week total culture p eriod in the absence of rhBMP-2. Growth and expression of osteoblastic characteristics were examined at the end of each week. C3H10T1/2 cell s responded to increasing duration of exposure to rhBMP-2 with increas ed cell growth. Additionally, the longer the cells were exposed to rhB MP-2, the more fully they expressed and sustained osteoblastic traits, i.e., they exhibited duration of exposure-dependent higher levels of alkaline phosphatase and osteocalcin and larger total amounts of miner al in the matrix. In comparison, exposure of bone marrow stromal cells to rh BMP-2 for at least 1 4 days restrained cell growth and prevente d detachment. With respect to osteoblastic traits, stromal cells expos ed to rhBMP-2 also exhibited a dependence on the duration of exposure, however, cultures treated for 14, 21, or 28 days exhibited similar le vels of alkaline phosphatase activity and comparable amounts of calciu m in the mineralizing matrix. (C) 1997 Wiley-Liss, Inc.