[Microglial cell death induced by polyamines]

Abstract

Pathological activation of microglia, which quiescently reside in physiological CNS, causes various neurodegenerative diseases. Endogenous polyamines, spermidine (SPD) and spermine (SPM) are known to be activators of cell proliferation and differentiation. We examined the effect of polyamines on microglial activation in culture. Cultured microglia prepared from the whole brains of newborn rats produced nitric oxide (NO) by the stimulation with lipopolysaccharide (LPS). LPS-induced NO production was remarkably inhibited by SPD and SPM. Cell viability assessed by total mitochondrial activity decreased by the incubation with SPD and SPM for 24 h. In astrocyte culture, on the other hand, polyamines showed no significant effect on either LPS-induced NO production or cell viability. After the treatment with SPM for 24 h, the cells changed into small round shapes, and were markedly stained with propidium iodide. By the staining with Hoechst33342, condensation and fragmentation of the nucleus were often observed. Semiquantitative analysis of fragmented DNA with the ELISA technique revealed that a large amount of fragmented DNA appeared in cytosol prior to disruption of the cell membrane, suggesting that polyamines induced apoptosis. Fragmented DNA in cytosol increased dose dependently with SPM. These results suggest that particular polyamines induce cell death through apoptosis at low concentrations in cultured microglia