Apoptosis of cultured microglia by the deprivation of macrophage colony-stimulating factor.

Promotion of microglial proliferation and differentiation by colony-stimulating factors (CSFs) and disappearances of microglia at the late neonatal stage by decreasing of CSFs have been reported. In this study, the effects of the deprivation of macrophage CSF (M-CSF) on enriched microglia in cultures were examined by cytochemical methods including in situ nick-end labeling for DNA fragmentation, and Carrazi's hematoxylin nuclear staining. When M-CSF was deprived from the culture medium: (1) at least 40% of the cells were weakly labeled by nick-end within 3 h and more than 70% of the cells were clearly labeled by 16 h; and (2) nuclear condensation or fragmentation, and formation of apoptotic bodies were observed within 48 h. LeY-positive immunoreactivity, identified as a characteristic of cells undergoing apoptosis, was observed on cells positively labeled by nick-end and condensed nucleus, and ones budding apoptotic bodies. From these results, it is conceivable that microglia undergo apoptosis when M-CSF is deprived from the culture medium and, therefore, require CSFs for their survival. This in vitro phenomenon suggests that one of the mechanisms of microglial disappearance in vivo after synaptogenesis may be due to apoptosis by decreasing level of CSFs.