A role for the NAD-dependent deacetylase Sirt1 in the regulation of autophagy

Abstract

We demonstrate a role for the NAD-dependent deacetylase Sirt1 in the regulation of autophagy. In particular, transient increased expression of Sirt1 is sufficient to stimulate basal rates of autophagy. In addition, we show that Sirt1 ؊/؊ mouse embryonic fibroblasts do not fully activate autophagy under starved conditions. Reconstitution with wild-type but not a deacetylase-inactive mutant of Sirt1 restores autophagy in these cells. We further demonstrate that Sirt1 can form a molecular complex with several essential components of the autophagy machinery, including autophagy genes (Atg)5, Atg7, and Atg8. In vitro, Sirt1 can, in an NAD-dependent fashion, directly deacetylate these components. The absence of Sirt1 leads to markedly elevated acetylation of proteins known to be required for autophagy in both cultured cells and in embryonic and neonatal tissues. Finally, we show that Sirt1 ؊/؊ mice partially resemble Atg5 ؊/؊ mice, including the accumulation of damaged organelles, disruption of energy homeostasis, and early perinatal mortality. Furthermore, the in utero delivery of the metabolic substrate pyruvate extends the survival of Sirt1 ؊/؊ pups. These results suggest that the Sirt1 deacetylase is an important in vivo regulator of autophagy and provide a link between sirtuin function and the overall cellular response to limited nutrients. mitochondria ͉ starvation ͉ acetylation ͉ aging M acroautophagy, referred to hereafter as autophagy, is an intracellular process that allows for the degradation of proteins and organelles (1-3). Morphologically, autophagy is characterized by the formation of a double-membrane structure termed the autophagosome. In yeast, the process of autophagy can be stimulated by the withdrawal of various nutrients, and evidence suggests that at least 16 separate autophagy genes (Atg) are ultimately required for the formation of the autophagosome and the subsequent induction of autophagy (1-3). Mammalian cells can also respond to nutrient withdrawal by inducing autophagy. Genetic studies have suggested that autophagy is required to maintain the animal's energetic needs during the small window of time immediately after birth but before neonates can get milk nutrients from their mothers (4). In addition, two recent studies have demonstrated that brain conditional knockouts of either Atg7 or Atg5 significantly accelerated the development of neuropathologies usually restricted to older animals (5, 6).The sirtuins are a family of NAD-dependent deacetylases that have been linked to the regulation of life span. Increased expression of Sir2 can extend the life span of model organisms, and under certain experimental conditions, it appears that the activity of Sir2 is required for the life-extending benefits of caloric restriction in organisms such as yeast and flies (7). As opposed to these relatively simple organisms, mammalian species have seven different sirtuin family members (8, 9). The closest relative of yeast Sir2 is termed Sirt1 in mammalian cells. We have demonstrated that mice subjected t...

AMPK activation protects cells from oxidative stress‐induced senescence via autophagic flux restoration and intracellular NAD + elevation

“…Given that NAD + is a coenzyme of Sirt family deacetylases that positively regulates autophagy (Lee et al ., 2008), and restrain aging (Gomes et al ., 2013), the activity of Sirt1 was monitored. As the findings, the activity of Sirt1 was increased by AMPK activation in senescent cells (Fig.…”

“…According to the results we obtained and those published by others (Fig. S10D) (Lee et al ., 2008; Ou et al ., 2014), we think that a conceivable molecular link between NAD + synthesis and autophagic activation is the Sirt family proteins because NAD + works as a critical coenzyme of Sirt deacetylases, and Sirt has been confirmed to have a role in activating autophagy. Although it is currently unclear why adding NMN cannot restore the autophagic flux in H 2 O 2 ‐treated cells (Fig.…”

Resveratrol Improves Motoneuron Function and Extends Survival in SOD1G93A ALS Mice

“…Increasing evidence suggests that autophagic abnormalities may contribute to ALS physiopathology [44] and resveratrol has been reported as a modulator of autophagia through Sirt1 activation [45]. Thus, we examined the autophagic state of the animals after resveratrol treatment.…”

Loss of sirtuin 1 and mitofusin 2 contributes to enhanced ischemia/reperfusion injury in aged livers

“…SIRT1 can activate autophagy through various pathways, including modulation of forkhead box transcription factors (FOX), ATG5, ATG7, LC3, and BECN1 (Huang et al., 2015; Lee et al., 2008; Sun et al., 2015). We recently reported that a gradual depletion of this deacetylase with extended ischemia is a causal to mitochondrial dysfunction and cell death (Biel et al., 2016).…”