Stromal-derived factor-1 promotes the growth, survival, and development of human bone marrow stromal stem cells.

The maintenance of bone marrow stromal stem cells (BMSSCs) is tightly controlled by the local microenvironment and by autocrine regulatory factors secreted by BMSSCs. To identify such factors, a cDNA subtraction library was generated from purified BMSSCs, based on their high expression of the STRO-1 antigen. Stromal-derived factor-1 (SDF-1) was one differentially expressed gene highly expressed by purified BMSSCs prior to culture. In vitro, immature preosteogenic cells expressed greater levels of SDF-1 when compared with mature cell types representative of osteoblasts and osteocytes/bone lining cells. Furthermore, SDF-1 expression was rapidly down-regulated when BMSSCs were cultured under osteoinductive conditions. BMSSCs were also shown to express functional cell surface SDF-1 receptors (CXCR4). Transduced BMSSC lines, secreting high SDF-1 levels, displayed an enhanced ability to form ectopic bone in vivo, in comparison with control BMSSC lines. Moreover, high SDF-1-expressing BMSSCs displayed an increased capacity for cellular growth and protection against interleukin-4-induced apoptosis. Similarly, fibroblast colony-forming units (CFU-Fs) also displayed increased growth and resistance to alpha-interferon-2a-induced apoptosis, in synergy with platelet-derived growth factor BB (PDGF-BB) and SDF-1 in vitro. These studies indicate that the chemokine, SDF-1, may play a role in the maintenance, survival, and osteogenic capacity of immature BMSSC populations.