Role of SIRT1 in C5b-9 mediated oligodendrocyte cell cycle activation

Abstract

Abstract SIRT1 is a NAD-dependent histone deacetylase involved in the regulation of transcription, apoptosis, metabolism and differentiation. We have previously demonstrated that sublytic levels of complement C5b-9 terminal complex increased the survival of oligodendrocytes (OLGs) and induced their dedifferentiation. In this study we investigated the role of SIRT1 in OLGs differentiation and the effect of sublytic levels of C5b-9 on SIRT1 expression. We also investigated the downstream effects of SIRT1 by measuring histone H3 Lysine 9 trimethylation (H3K9me3) and expression of cyclin D1. OLG progenitor cells purified from the brain of rat pups were differentiated in vitro and stimulated with sublytic C5b-9 or C5b6 for 3, 6 and 18 h. The level of SIRT1 mRNA was measured using real-time PCR and SIRT1, cyclin D1 and H3K9me3 protein expression were measured using western blotting. We found a decreased expression of SIRT1 mRNA and protein, a decreased level of H3K9me3 and an increased expression of cyclin D1 during OLG differentiation. Stimulation of OLGs with sublytic C5b-9 for 3h resulted in a significant decrease in SIRT1 mRNA and protein levels while stimulation with C5b6 had no effect. SIRT1 protein level in OLGs after 8h of exposure to C5b-9 were significantly lower than in C5b6 treated cells. H3K9me3 levels also decreased significantly after stimulation with C5b-9 as compared with unstimulated or C5b6-treated OLGs. Cyclin D1 expression increased after stimulation with C5b-9, indicating cell cycle activation. Our data show that C5b-9 stimulation of OLGs reduces SIRT1 expression, contributing to cell cycle activation by decreasing repressive trimethylation of histone H3 lysine 9.