Hematopoietic colony stimulatory factor formation by murine mesangial cells: gene expression and biological activity

This study examined the ability of mesangial cells to synthesize colony-stimulating factors (CSF), cytoregulatory peptides associated with the differentiation and proliferation of hematopoietic cells. Conditioned media obtained from SV-40 transformed murine mesangial cells stimulated the growth of murine bone marrow progenitor cells of the myeloid series. Differential analysis of these cells showed the presence of both macrophages and granulocytes. Cellular identification of bone marrow colonies stimulated in response to mesangial cell conditioned media was examined by flow cytometric analysis and revealed the presence of F4/80 antigen positive macrophages (67%) and Gran-1 antigen positive granulocytes (21%). Neutralizing antibodies to macrophage colony-stimulating factor (M-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) but not antibody to interleukin-3 (IL-3), or stem cell factor (SCF) significantly inhibited the growth of the progenitor cells induced by mesangial cell conditioned media. Utilizing Northern blot analysis, murine mesangial cells expressed mRNA transcripts for M-CSF, GM-CSF, and granulocyte colony-stimulating factor (G-CSF). Further studies were performed to determine optimal incubation conditions for mesangial cell CSF gene expression. These studies revealed that both GM-CSF and G-CSF mRNA were maximally expressed at early time points (4 and 8 h of incubation), while M-CSF mRNA expression remained unchanged during the incubation of mesangial cells from 4-48 h. Incubation of mesangial cells with various concentrations of fetal bovine serum (FBS, 0.5-15%) markedly increased the mRNA expression of M-CSF, GM-CSF and G-CSF in a dose-dependent manner. These studies indicated that transformed murine mesangial cells are able to synthesize and secrete biologically active CSF that are associated with the migration and proliferation of circulating mononuclear cells in the glomerulus. Furthermore, observations regarding the role of duration of incubation and the media concentration of FBS on mesangial cell CSF mRNA expression may provide useful data to understand the optimal conditions for studies that examine the gene expression of basal or inducible CSF in mesangial cells.