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Expression of basic fibroblast growth factor and its receptors in human fetal microglia cells
M Presta1, C Urbinati, P Dell'era
1Department of Biomedical Sciences and Biotechnology, School of Medicine, Brescia, Italy.
Abstract:
The presence of basic fibroblast growth factor (bFGF) and FGF receptors was investigated in microglia cells derived from human fetal brain long-term cultures. Production of bFGF was suggested through the capability of microglial extracts to stimulate plasminogen activator (PA) synthesis 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. These 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, sometimes, in the nucleus. Scatchard plot analysis of 125I-bFGF binding data revealed the presence of low affinity heparansulphate proteoglycans (380,000 +/- 60,000 sites/cell; Kd = 730 +/- 200 nM) and of high affinity tyrosine-kinase receptors (10,300 + 2500 sites/cell; Kd = 30 +/- 9 pM). Immunocytochemistry confirmed the presence of FGF receptor (1/flg) on the cell surface of some, but not all microglial cells, with prevalent association to ameboid microglia. Transcripts for FGF receptors 1, 2, 3 and 4 were found in microglia by Northern blot analysis. Co-expression of bFGF and its receptors in human fetal microglia suggests an autocrine role of bFGF in these cells.
Insights
Human fetal microglia produce basic fibroblast growth factor (bFGF) and express FGF receptors, suggesting bFGF plays an autocrine role in these cells. This research explores bFGF signaling in microglia.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- Microglia are key immune cells in the central nervous system.
- Basic fibroblast growth factor (bFGF) is involved in cell growth and repair.
- The role of bFGF in microglia has not been fully elucidated.
Purpose of the Study:
- To investigate the presence and function of basic fibroblast growth factor (bFGF) and its receptors in human fetal microglia.
- To determine if bFGF plays an autocrine role in microglial cells.
Main Methods:
- Primary human fetal brain-derived microglia cultures were used.
- Basic fibroblast growth factor (bFGF) production was assessed by stimulating plasminogen activator (PA) synthesis in endothelial cells.
- Western blot and immunocytochemistry were employed to identify bFGF and FGF receptors.
- Scatchard plot analysis was used to quantify receptor binding.
- Northern blot analysis detected FGF receptor transcripts.
Main Results:
- Microglial extracts stimulated PA synthesis, indicating bFGF production.
- Antibodies confirmed the presence of bFGF isoforms (18,000 and 24,000 M(r)) in microglia.
- bFGF immunoreactivity was observed in microglial cytoplasm and nuclei.
- Microglia expressed low-affinity heparan sulfate proteoglycans and high-affinity tyrosine-kinase FGF receptors.
- FGF receptor 1 (1/flg) was detected on the cell surface, particularly on ameboid microglia.
- Transcripts for FGF receptors 1, 2, 3, and 4 were found in microglia.
Conclusions:
- Human fetal microglia co-express basic fibroblast growth factor (bFGF) and its receptors.
- These findings suggest an autocrine role for bFGF in human fetal microglia.
- bFGF signaling may be important for microglial function during development.