Acetylation has recently emerged as an important mechanism for controlling a broad array of proteins mediating cellular adaptation to metabolic fuels. Acetylation is governed, in part, by SIRTs (sirtuins), class III NAD+-dependent deacetylases that regulate lipid and glucose metabolism in liver during fasting and aging. However, the role of acetylation or SIRTs in pathogenic hepatic fuel metabolism under nutrient excess is unknown. In the present study, we isolated acetylated proteins from total liver proteome and observed 193 preferentially acetylated proteins in mice fed on an HFD (high-fat diet) compared with controls, including 11 proteins not previously identified in acetylation studies. Exposure to the HFD led to hyperacetylation of proteins involved in gluconeogenesis, mitochondrial oxidative metabolism, methionine metabolism, liver injury and the ER (endoplasmic reticulum) stress response. Livers of mice fed on the HFD had reduced SIRT3 activity, a 3-fold decrease in hepatic NAD+ levels and increased mitochondrial protein oxidation. In contrast, neither SIRT1 nor histone acetyltransferase activities were altered, implicating SIRT3 as a dominant factor contributing to the observed phenotype. In Sirt3−/− mice, exposure to the HFD further increased the acetylation status of liver proteins and reduced the activity of respiratory complexes III and IV. This is the first study to identify acetylation patterns in liver proteins of HFD-fed mice. Our results suggest that SIRT3 is an integral regulator of mitochondrial function and its depletion results in hyperacetylation of critical mitochondrial proteins that protect against hepatic lipotoxicity under conditions of nutrient excess.

Strategies to reduce obesity have become public health priorities as the prevalence of obesity has risen in the United States and around the world. While the anti-inflammatory and hypotriglyceridemic properties of long-chain omega-3 polyunsaturated fatty acids (n-3 PUFAs) are well known, their antiobesity effects and efficacy against metabolic syndrome, especially in humans, are still under debate. In animal models, evidence consistently suggests a role for n-3 PUFAs in reducing fat mass, particularly in the retroperitoneal and epididymal regions. In humans, however, published research suggests that though n-3 PUFAs may not aid weight loss, they may attenuate further weight gain and could be useful in the diet or as a supplement to help maintain weight loss. Proposed mechanisms by which n-3 PUFAs may work to improve body composition and counteract obesity-related metabolic changes include modulating lipid metabolism; regulating adipokines, such as adiponectin and leptin; alleviating adipose tissue inflammation; promoting adipogenesis and altering epigenetic mechanisms.

We have shown previously that mice with a targeted disruption in the stearoyl-CoA desaturase 1 gene (SCD1 ؊/؊ ) have increased insulin sensitivity compared with control mice. Here we show that the SCD1 ؊͞؊ mice have increased insulin signaling in muscle. The basal tyrosine phosphorylation of the insulin receptor and insulin receptor substrates 1 and 2 are elevated. The tyrosine phosphorylation of insulin-like growth factor-1 receptor was similar between SCD1 ؉͞؉ and SCD1 ؊͞؊ mice. The association of insulin receptor substrates 1 and 2 with ␣p85 subunit of phosphatidylinositol 3-kinase as well as the phosphorylation of Akt-Ser-473 and Akt-Thr-308 are also elevated in the SCD1 ؊͞؊ mice. Interestingly, the mRNA levels, protein mass, and activity of the protein-tyrosine phosphatase-1B implicated in the attenuation of the insulin signal are reduced in the SCD1 ؊͞؊ mice, whereas the levels of the leukocyte antigen-related protein phosphatase are similar between two groups of mice. The content of glucose transporter 4 in the plasma membrane and basal as well as insulin-mediated glucose uptake are increased in the SCD1 ؊͞؊ mice. In addition, the muscle glycogen content and the activities of glycogen synthase and phosphorylase are increased in the SCD1 ؊͞؊ mice. We hypothesize that loss of SCD1 function induces increased insulin signaling at least in part by a reduction in the expression of protein-tyrosine phosphatase 1B. SCD1 could be a therapeutic target in the treatment of diabetes.

Nonalcoholic steatohepatitis (NASH) is characterized by steatosis, inflammation, and oxidative stress. To investigate whether the transcription factor CCAAT/Enhancer binding protein (C/ EBP␤) is involved in the development of NASH, C57BL/6J wild-type (WT) or C/EBP␤ knockout (C/EBP␤؊/؊) mice were fed either a methionine and choline deficient (MCD) diet or standard chow. These WT mice fed a MCD diet for 4 weeks showed a 2-to 3-fold increase in liver C/EBP␤ messenger RNA and protein, along with increased expression of lipogenic genes peroxisome proliferators-activated receptor ␥ and Fas. WT mice also showed increased levels of the endoplasmic reticulum stress pathway proteins phosphorylated eukaryotic translation initiation factor ␣, phosphorylated pancreatic endoplasmic reticulum kinase, and C/EBP homologous protein, along with inflammatory markers phosphorylated nuclear factor B and phosphorylated C-jun N-terminal kinase compared to chow-fed controls. Cytochrome P450 2E1 protein and acetyl coA oxidase messenger RNA involved in hepatic lipid peroxidation were also markedly increased in WT MCD diet-fed group. In contrast, C/EBP␤؊/؊ mice fed a MCD diet showed a 60% reduction in hepatic triglyceride accumulation and decreased liver injury as evidenced by reduced serum alanine aminotransferase and aspartate aminotransferase levels, and by H&E staining. Immunoblots and real-time qPCR data revealed a significant reduction in expression of stress related proteins and lipogenic genes in MCD diet-fed C/EBP␤؊/؊ mice. Furthermore, circulating TNF␣ and expression of acute phase response proteins CRP and SAP were significantly lower in C/EBP␤؊/؊ mice compared to WT mice. Conversely, C/EBP␤ over-expression in livers of WT mice increased steatosis, nuclear factor-B, and endoplasmic reticulum stress, similar to MCD dietfed mice. Conclusion: Taken together, these data suggest a previously unappreciated molecular link between C/EBP␤, hepatic steatosis and inflammation and suggest that increased C/EBP␤ expression may be an important factor underlying events leading to NASH. (HEPATOLOGY 2007;45:1108-1117

Stearoyl-CoA desaturase (SCD) is a microsomal enzyme involved in the biosynthesis of oleate and palmitoleate. Mice with a targeted disruption of the SCD1 isoform (SCD1 ؊ / ؊ ) exhibit reduced adiposity and increased energy expenditure. To address whether the energy expenditure is attributable to increased thermogenesis, we investigated the effect of SCD1 deficiency on basal and coldinduced thermogenesis. SCD1 ؊ / ؊ mice have increased expression of uncoupling proteins in brown adipose tissue (BAT) relative to controls. The ␤ 3-adrenergic receptor ( ␤ 3-AR) expression was increased and the phosphorylation of cAMP response element binding protein and the protein level of peroxisome proliferator-activated receptor-␥ coactivator-1 ␣ were increased in the SCD1 ؊ / ؊ mice. Both lipolysis and fatty acid oxidation were increased in the SCD1 ؊ / ؊ mice. When exposed to 4 Њ C, SCD1 ؊ / ؊ mice showed hypothermia, hypoglycemia, and depleted liver glycogen. High levels of dietary oleate partially compensated for the hypothermia and rescued plasma glucose and liver glycogen. These results suggest that SCD1 deficiency stimulates basal thermogenesis through the upregulation of the ␤ 3-ARmediated pathway and a subsequent increase in lipolysis and fatty acid oxidation in BAT. The hypothermia and hypoglycemia in cold-exposed SCD1 ؊ / ؊ mice and the compensatory recovery by oleate indicate an important role of SCD1 gene expression in thermoregulation. -Lee, S-H., A. Dobrzyn, P. Dobrzyn, S. M. Rahman, M. Miyazaki, and J. M. Ntambi. Lack of stearoyl-CoA desaturase 1 upregulates basal thermogenesis but causes hypothermia in a cold environment.

The transcription factor SREBP1c (sterol-regulatory-element-binding protein 1c) is highly expressed in adipose tissue and plays a central role in several aspects of adipocyte development including the induction of PPARγ (peroxisome-proliferator-activated receptor γ), the generation of an endogenous PPARγ ligand and the expression of several genes critical for lipid biosynthesis. Despite its significance, the regulation of SREBP1c expression during adipogenesis is not well characterized. We have noted that in several models of adipogenesis, SREBP1c expression closely mimics that of known C/EBPβ (CCAAT/enhancer-binding protein β) targets. Inhibition of C/EBP activity during adipogenesis by expressing either the dominant-negative C/EBPβ LIP (liver-enriched inhibitory protein) isoform, the co-repressor ETO (eight-twenty one/MTG8) or using siRNAs (small interfering RNAs) targeting either C/EBPβ or C/EBPδ significantly impaired early SREBP1c induction. Furthermore, ChIP (chromatin immunoprecipitation) assays identified specific sequences in the SREBP1c promoter to which C/EBPβ and C/EBPδ bind in intact cells, demonstrating that these factors may directly regulate SREBP1c expression. Using cells in which C/EBPα expression is inhibited using shRNA (short hairpin RNA) and ChIP assays we show that C/EBPα replaces C/EBPβ and C/EBPδ as a regulator of SREBP1c expression in maturing adipocytes. These results provide novel insight into the induction of SREBP1c expression during adipogenesis. Moreover, the findings of the present study identify an important additional mechanism via which the C/EBP transcription factors may control a network of gene expression regulating adipogenesis, lipogenesis and insulin sensitivity.

CCAAT/enhancer-binding protein ␤ (C/EBP␤) plays a key role in initiation of adipogenesis in adipose tissue and gluconeogenesis in liver; however, the role of C/EBP␤ in hepatic lipogenesis remains undefined. Here we show that C/EBP␤ inactivation in Lepr db/db mice attenuates obesity, fatty liver, and diabetes. In addition to impaired adipogenesis, livers from C/EBP␤ ؊/؊ x Lepr db/db mice had dramatically decreased triglyceride content and reduced lipogenic enzyme activity. C/EBP␤ deletion in Lepr db/db mice down-regulated peroxisome proliferator-activated receptor ␥2 (PPAR␥2) and stearoyl-CoA desaturase-1 and up-regulated PPAR␣ independent of SREBP1c. Conversely, C/EBP␤ overexpression in wild-type mice increased PPAR␥2 and stearoyl-CoA desaturase-1 mRNA and hepatic triglyceride content. In FAO cells, overexpression of the liver inhibiting form of C/EBP␤ or C/EBP␤ RNA interference attenuated palmitate-induced triglyceride accumulation and reduced PPAR␥2 and triglyceride levels in the liver in vivo. Leptin and the anti-diabetic drug metformin acutely down-regulated C/EBP␤ expression in hepatocytes, whereas fatty acids up-regulate C/EBP␤ expression. These data provide novel evidence linking C/EBP␤ expression to lipogenesis and energy balance with important implications for the treatment of obesity and fatty liver disease.Obesity is the most common nutritional disorder in Western societies. Today in the United States, more than 60% of people are either overweight (body mass index (BMI) Ͼ 25) or obese (BMI Ͼ 30) (1). Obesity is frequently associated with type II diabetes, hypertension, and hyperlipidemia, all known risk factors for cardiovascular disease (2). Obesity is also a major risk factor for non-alcoholic fatty liver disease, one of the most common emerging liver diseases in Western countries coinciding with the worldwide obesity epidemic (3, 4). The underlying transcriptional events that contribute to obesity and its associated disorders are not well understood. Some of the genes that regulate body weight have been identified as well as additional neuropeptides, hormones, and nutritional factors that play a role in body weight regulation, particularly through the ␤-adrenergic system (5, 6). Discovery of the hormone leptin and its receptors, which suppress appetite and reduce fat mass, has dramatically increased our understanding of the regulation of energy balance (7,8). More recently, the study of specific transcription factor genes and their metabolism has provided powerful new tools for understanding the integrated mechanisms underlying obesity and diabetes (9 -11). This is most elegantly illustrated using tissue-specific gene knockouts and overexpression models to elucidate the mechanism of action of the PPAR 5 family of nuclear hormone receptors (12). The CCAAT/enhancer-binding protein (C/EBP) family includes five nuclear transcription factors, C/EBP ␣, ␤, ␥, ␦, and ⑀, encoded by separate genes located on different chromosomes (13,14). Collectively, C/EBPs are expressed across a variety of cell types, and...

Background: Role of CCAAT/enhancer-binding protein ␤ in obesity-induced inflammation remains unexplored. Results: Bone marrow-chimeric mice studies show that C/EBP␤ deletion regulates dietary-induced systemic inflammation and insulin resistance. Conclusion: C/EBP␤ expression in response to palmitate or high-fat diet controls transcriptional regulatory networks in macrophages and adipocytes critical for inflammation, lipid metabolism, and insulin resistance. Significance: Attenuating C/EBP␤ is an attractive target for ameliorating nutrition-induced inflammation.