IMMORTALIZATION OF HUMAN MARROW STROMAL CELLS BY RETROVIRAL TRANSDUCTION WITH A TEMPERATURE-SENSITIVE ONCOGENE - IDENTIFICATION OF BIPOTENTIAL PRECURSOR CELLS CAPABLE OF DIRECTED DIFFERENTIATION TO EITHER AN OSTEOBLAST OR ADIPOCYTE PHENOTYPE

The etiology of osteoporosis is multifactorial, but there is evidence from both animal and human studies that the volume of marrow adipose t issue increases when bone volume is reduced in osteoporosis, The cell- related mechanism that may account for this inverse relationship betwe en the volume of marrow adipose tissue and bone remains to be clarifie d, although it is known that both adipocytes and osteoblasts are deriv ed from stromal cell precursors in bone marrow, We report that retrovi ral transduction with a temperature-sensitive oncogene (SV40 large T a ntigen) can generate bipotential cell lines from human marrow stroma t hat are capable of directed differentiation, in vitro, down either an osteogenic or adipocytic lineage pathway, One such clone, designated h OP 7, expresses type alpha 1(I) procollagen and has low alkaline phosp hatase (AP) activity under basal culture conditions that is reminiscen t of an osteoprogenitor cell, Exposure of hOP 7 cells to dexamethasone upregulates AP activity and enables the cells to mineralize their ext racellular matrix, Also, treatment with calcitriol induces osteocalcin expression and both PTH and PGE(2) induce/augment cAMP formation, Inc ubation with normal rabbit serum, however, causes the cells to become adipogenic as demonstrated by histological staining with Oil-red-O, ex pression of mRNA for the early and late adipocyte markers lipoprotein lipase and glycerol 3-phosphate dehydrogenase, respectively, and loss of type alpha 1(I) procollagen mRNA, The generation of homogeneous pop ulations of these cells, as confirmed by Southern blot analysis, demon strates the capacity of a human clonal cell line to differentiate in e ither an osteogenic or adipogenic direction. (C) 1998 by Elsevier Scie nce Inc. All rights reserved.