EXPRESSION OF BASIC FIBROBLAST GROWTH-FACTOR AND ITS RECEPTORS IN HUMAN FETAL MICROGLIA CELLS

The presence of basic fibroblast growth factor (bFGF) and FGF receptor s was investigated in microglia cells derived from human fetal brain l ong-term cultures. Production of bFGF was suggested through the capabi lity of microglial extracts to stimulate plasminogen activator (PA) sy nthesis in endothelial cells. The identity of PA-stimulating activity with bFGF was confirmed by its high affinity for heparin and its cross -reactivity with polyclonal antibodies to human recombinant bFGF. Thes e antibodies recognized a cell-associated M(r) 18,000 protein as well as trace amounts of the M(r) 24,000 bFGF isoform in Western blot. All microglial cells showed bFGF immunoreactivity in the cytoplasm and, so metimes, in the nucleus. Scatchard plot analysis of I-125-bFGF binding data revealed the presence of low affinity heparan-sulphate proteogly cans (380,000 +/- 60,000 sites/cell; K-d = 730 +/- 200 nM) and of high affinity tyrosine-kinase receptors (10,300 + 2500 sites/cell; K-d = 3 0 +/- 9 pM). Immunocytochemistry confirmed the presence of FGF recepto r (1/flg) on the cell surface of some, but not all microglial cells, w ith prevalent association to ameboid microglia. Transcripts for FGF re ceptors 1, 2, 3 and 4 were found in microglia by Northern blot analysi s. Co-expression of bFGF and its receptors in human fetal microglia su ggests an autocrine role of bFGF in these cells.