No abstract

Diminished mitochondrial oxidative phosphorylation and aerobic capacity are associated with reduced longevity. We tested whether resveratrol (RSV), which is known to extend lifespan, impacts mitochondrial function and metabolic homeostasis. Treatment of mice with RSV significantly increased their aerobic capacity, as evidenced by their increased running time and consumption of oxygen in muscle fibers. RSV's effects were associated with an induction of genes for oxidative phosphorylation and mitochondrial biogenesis and were largely explained by an RSV-mediated decrease in PGC-1alpha acetylation and an increase in PGC-1alpha activity. This mechanism is consistent with RSV being a known activator of the protein deacetylase, SIRT1, and by the lack of effect of RSV in SIRT1(-/-) MEFs. Importantly, RSV treatment protected mice against diet-induced-obesity and insulin resistance. These pharmacological effects of RSV combined with the association of three Sirt1 SNPs and energy homeostasis in Finnish subjects implicates SIRT1 as a key regulator of energy and metabolic homeostasis.

Homeostatic mechanisms in mammals respond to hormones and nutrients to maintain blood glucose levels within a narrow range. Caloric restriction causes many changes in glucose metabolism and extends lifespan; however, how this metabolism is connected to the ageing process is largely unknown. We show here that the Sir2 homologue, SIRT1--which modulates ageing in several species--controls the gluconeogenic/glycolytic pathways in liver in response to fasting signals through the transcriptional coactivator PGC-1alpha. A nutrient signalling response that is mediated by pyruvate induces SIRT1 protein in liver during fasting. We find that once SIRT1 is induced, it interacts with and deacetylates PGC-1alpha at specific lysine residues in an NAD(+)-dependent manner. SIRT1 induces gluconeogenic genes and hepatic glucose output through PGC-1alpha, but does not regulate the effects of PGC-1alpha on mitochondrial genes. In addition, SIRT1 modulates the effects of PGC-1alpha repression of glycolytic genes in response to fasting and pyruvate. Thus, we have identified a molecular mechanism whereby SIRT1 functions in glucose homeostasis as a modulator of PGC-1alpha. These findings have strong implications for the basic pathways of energy homeostasis, diabetes and lifespan.

In mammals, maintenance of energy and nutrient homeostasis during food deprivation is accomplished through an increase in mitochondrial fatty acid oxidation in peripheral tissues. An important component that drives this cellular oxidative process is the transcriptional coactivator PGC-1alpha. Here, we show that fasting induced PGC-1alpha deacetylation in skeletal muscle and that SIRT1 deacetylation of PGC-1alpha is required for activation of mitochondrial fatty acid oxidation genes. Moreover, expression of the acetyltransferase, GCN5, or the SIRT1 inhibitor, nicotinamide, induces PGC-1alpha acetylation and decreases expression of PGC-1alpha target genes in myotubes. Consistent with a switch from glucose to fatty acid oxidation that occurs in nutrient deprivation states, SIRT1 is required for induction and maintenance of fatty acid oxidation in response to low glucose concentrations. Thus, we have identified SIRT1 as a functional regulator of PGC-1alpha that induces a metabolic gene transcription program of mitochondrial fatty acid oxidation. These results have implications for understanding selective nutrient adaptation and how it might impact lifespan or metabolic diseases such as obesity and diabetes.

Energy homeostasis in mammals is achieved through tight regulation of tissue-specific metabolic pathways that become dysregulated in metabolic diseases including diabetes and obesity. At the molecular level, main nutrient and hormonal signaling pathways impinge on expression of genes encoding for metabolic enzymes. Among the major components of this transcriptional circuitry are the PGC-1a transcriptional complexes. An important regulatory mechanism of this complex is through acetylation and SIRT1-mediated lysine de-acetylation under low nutrient conditions. Activation of SIRT1 can mimic several metabolic aspects of calorie restriction that target selective nutrient utilization and mitochondrial oxidative function to regulate energy balance. Thus, understanding the PGC-1a and SIRT1 pathways might have important implications for comprehending metabolic and age-associated diseases.

Hormonal and nutrient regulation of hepatic gluconeogenesis mainly occurs through modulation of the transcriptional coactivator PGC-1alpha. The identity of endogenous proteins and their enzymatic activities that regulate the functions and form part of PGC-1alpha complex are unknown. Here, we show that PGC-1alpha is in a multiprotein complex containing the acetyltransferase GCN5. PGC-1alpha is directly acetylated by GCN5 resulting in a transcriptionally inactive protein that relocalizes from promoter regions to nuclear foci. Adenoviral-mediated expression of GCN5 in cultured hepatocytes and in mouse liver largely represses activation of gluconeogenic enzymes and decreases hepatic glucose production. Thus, we have identified the endogenous PGC-1alpha protein complex and provided the molecular mechanism by which PGC-1alpha acetylation by GCN5 turns off the transcriptional and biological function of this metabolic coactivator. GCN5 might be a pharmacological target to regulate the activity of PGC-1alpha, providing a potential treatment for metabolic disorders in which hepatic glucose output is dysregulated.

Transcriptional control of metabolic circuits requires coordination between specific transcription factors and coregulators and is often deregulated in metabolic diseases. We characterized here the mechanisms through which the coactivator SRC-3 controls energy homeostasis. SRC-3 knock-out mice present a more favorable metabolic profile relative to their wild-type littermates. This metabolic improvement in SRC-3 ؊/؊ mice is caused by an increase in mitochondrial function and in energy expenditure as a consequence of activation of PGC-1␣. By controlling the expression of the only characterized PGC-1␣ acetyltransferase GCN5, SRC-3 induces PGC-1␣ acetylation and consequently inhibits its activity. Interestingly, SRC-3 expression is induced by caloric excess, resulting in the inhibition of PGC-1␣ activity and energy expenditure, whereas caloric restriction reduces SRC-3 levels leading to enhanced PGC-1␣ activity and energy expenditure. Collectively, these data suggest that SRC-3 is a critical link in a cofactor network that uses PGC-1␣ as an effector to control mitochondrial function and energy homeostasis.acetyltransferase ͉ caloric restriction ͉ cofactors ͉ deacetylase ͉ SIRT1

SUMMARY Alternative mRNA splicing provides transcript diversity and may contribute to human disease. We demonstrate that expression of several genes regulating RNA processing is decreased in both liver and skeletal muscle of obese humans. We evaluated a representative splicing factor, SFRS10, down-regulated in both obese human liver and muscle and in high fat-fed mice, and determined metabolic impact of reduced expression. SFRS10-specific siRNA induces lipogenesis and lipid accumulation in hepatocytes. Moreover, Sfrs10 heterozygous mice have increased hepatic lipogenic gene expression, VLDL secretion, and plasma triglycerides. We demonstrate that LPIN1, a key regulator of lipid metabolism, is a splicing target of SFRS10; reduced SFRS10 favors the lipogenic β isoform of LPIN1. Importantly, LPIN1β-specific siRNA abolished lipogenic effects of decreased SFRS10 expression. Together, our results indicate that reduced expression of SFRS10, as observed in tissues from obese humans, alters LPIN1 splicing, induces lipogenesis, and therefore contributes to metabolic phenotypes associated with obesity.