Basic fibroblast growth factor mediates its effects on committed myeloid progenitors by direct action and has no effect on hematopoietic stem cells

Basic fibroblast growth factor or fibroblast growth factor-2 (FGF) has been shown to affect myeloid cell proliferation and hypothesized to stimulate primitive hematopoietic cells. We sought to evaluate the effect of FGF on hematopoietic stem cells and to determine if FGF mediated its effects on progenitor cells directly or through the induction of other cytokines. To address the direct effects of FGF, we investigated whether FGF induced production of interleukin-1 beta (IL-1 beta), tumor necrosis factor alpha, IL-6, granulocyte colony- stimulating factor, or granulocyte-macrophage colony-stimulating factor by two types of accessory cells, bone marrow (BM) fibroblasts and macrophages. We further evaluated whether antibodies to FGF-induced cytokines affected colony formation. To determine if FGF was capable of stimulating multipotent progenitors, we assessed the output of different colony types after stimulation of BM mononuclear cells (BMMC) or CD34+ BMMC and compared the effects of FGF with the stem cell active cytokine, kit ligand (KL). In addition, a subset of CD34+ BMMC with characteristics of hematopoietic stem cells was isolated by functional selection and their response to FGF was evaluated using proliferation, colony-forming, and single-cell polymerase chain reaction (PCR) assays. We determined that FGF had a stimulatory effect on the production of a single cytokine, IL-6, but that the effects of FGF on colony formation were not attributable to that induction. FGF was more restricted in its in vitro effects on BM progenitors than KL was, having no effect on erythroid colony formation. FGF did not stimulate stem cells and FGF receptors were not detected on stem cells as evaluated by single-cell reverse transcription PCR. In contrast, FGF receptor gene expression was detected in myeloid progenitor populations. These data support a directly mediated effect for FGF that appears to be restricted to lineage-committed myeloid progenitor cells. FGF does not appear to modulate the human hematopoietic stem cell.