Mammalian Sir2-related protein (SIRT) 2–mediated modulation of resistance to axonal degeneration in slow Wallerian degeneration mice: A crucial role of tubulin deacetylation

Abstract

It has been shown that Wallerian degeneration, an anterograde degeneration of transected axons, is markedly delayed in a mutant mouse called slow Wallerian degeneration ( Wld S ). These mice also show resistance to axonal degeneration caused by microtubule depolymerizing drugs, suggesting that axonal microtubules are stabilized. Here, we have focused on tubulin acetylation, a post-translational modification associated with microtubule stability. We found that the basal level of microtubule acetylation was increased in cultured cerebellar granule cells from Wld S mice. Nicotinamide but not 3-aminobenzamide, an inhibitor for poly(ADP)ribose polymerase, enhanced tubulin acetylation and resistance to axonal degeneration in cultured cerebellar granule cells from wild-type (WT) mice, suggesting that mammalian Sir2-related protein (SIRT) 2, a nicotinamide adenine dinucleotide (NAD)–dependent tubulin deacetylase, could modulate resistance to axonal degeneration. Indeed, the levels of NAD and SIRT2 were decreased in the cytoplasm from Wld S granule cells. Moreover, SIRT2 overexpression abrogated microtubule hyperacetylation and resistance to axonal degeneration in these cells. Conversely, SIRT2 knockdown by using a lentiviral vector expressing small interfering RNA, enhanced microtubule acetylation and resistance to axonal degeneration in WT granule cells. Taken together, these results suggest that SIRT2-mediated tubulin deacetylation is involved in both microtubule hyperacetylation and resistance to axonal degeneration in Wld S granule cells.