Activation and proliferation of the isolated microglia by colony stimulating factor-1 and possible involvement of protein kinase C.

Microglia were isolated from primary mixed brain cell culture of normal newborn mice and then cultivated. They were able to be maintained in vitro for 1-2 months, but incorporated little [3H]thymidine under normal culture conditions. When treated with the conditioned medium of L929 mouse fibroblast cells as a crude CSF-1 (mouse macrophage-colony stimulating factor) or purified CSF-1, microglia showed morphological changes and increased in both cell number and [3H]thymidine uptake. In addition, crude CSF-1 increased lysosomal enzyme activity and superoxide anion formation of microglia up to 2 and 3.8 fold as control value, respectively. These effects of CSF-1 were not observed in the purified astrocyte culture. Purified microglia had CSF-1 receptors which were recognized by the anti-CSF-1 receptor antibody that arose from a peptide of a product of proto-oncogene, c-fms. 12-O-Tetradecanoylphorbol-13-acetate (TPA) also increased microglia cell number and their biochemical activities, suggesting the possible involvement of protein kinase C activation. Protein kinase inhibitors, such as staurosporine or H-7, inhibited the effects of both CSF-1 and TPA. These results indicate that microglia may be regulated in its biochemical and proliferation activities by CSF-1 and that this may occur via activation of protein kinase C.