Abstract
Bone marrow stromal cells influence hematopoiesis through cell-cell interaction and release of hematopoietic growth factors. Macrophage colony-stimulating factor (M-CSF) is constitutively produced by several murine and human stromal cell lines and is induced by inflammatory mediators such as interleukin-1 alpha or tumor necrosis factor-alpha (TNF-alpha) in a variety of mesenchymal cells. Other potentially important regulatory molecules such as platelet-derived growth factor (PDGF) and basic fibroblast growth factor (bFGF), released by activated monocytes in response to inflammation, stimulate the growth of human stromal cells. However, the effect of these peptide mitogens on M-CSF expression in stromal cells has not been explored. In this study, we used TC-1 murine bone marrow-derived stromal cells that constitutively secrete M-CSF to determine the effect of PDGF and bFGF on cell proliferation and M-CSF gene expression. PDGF and bFGF, but not TNF- alpha, were potent mitogens for the TC-1 cells. Similar to mouse L cells, TC-1 murine stromal cells constitutively expressed two major mRNA transcripts of 4.4 and 2.2 kb that hybridized to a murine M-CSF cDNA. PDGF, bFGF, and TNF-alpha markedly stimulated the steady-state expression of M-CSF mRNA with different time-course kinetics. The increased expression of M-CSF mRNA was associated with enhanced secretion of M-CSF as determined by radioimmunoassay. These findings suggest that PDGF, bFGF, and TNF-alpha may regulate hematopoiesis indirectly through release of M-CSF by stromal cells and may modulate, at least in part, the hematopoietic response to inflammation.
