Interconversion potential of cloned human marrow adipocytes in vitro

Information on the interconversion potential of adipocytes and other end ce lls characteristic of the stromal fibroblastic cell lineages, key in the un derstanding of bone turnover in metabolic diseases such as osteoporosis, is limited. The object of the present study was: i) to isolate relatively pur e populations of adipocytes from human bone marrow; ii) to clone single adi pocytes from these populations; and iii) to examine in vitro the interconve rsion potential of the progeny of these single-cloned adipocytes between th e osteogenic and adipogenic phenotypes. Adipogenic colonies were isolated f rom the low-density floating fraction of normal bone marrow cells cultured in adipogenic media for 4 days. Single adipocytes were isolated and cloned by limiting dilution, Cloned adipocytes were found to dedifferentiate into fibroblast-like cells, and subsequently to differentiate into two morpholog ically distinct cell types: osteoblasts and adipocytes in appropriate cultu re systems. The adipocytic phenotype was confirmed by morphology, oil red O staining, and immunocytochemistry using antiserum to aP2, The osteogenic p henotype was confirmed by alkaline phosphatase, osteocalcin immunostaining using specific osteocalcin antiserum, and formation of mineralized cell agg regates. These findings demonstrate the extent of plasticity between the di fferentiation of adipocytic and osteogenic cells in human bone marrow strom al cell cultures, We have shown the ability of isolated clonal adipogenic c ells to redifferentiate into cells of the osteogenic and adipogenic lineage and the interconversion potential of human marrow stromal cells in vitro. These results provide further evidence that the osteogenic and adipogenic c ells share a common multipotential precursor. (Bone 24:549-554; 1999) (C) 1 999 by Elsevier Science Inc. All rights reserved.