Inhibition of ceramide synthesis prevents diabetes, steatosis, and cardiovascular disease in rodents. Six different ceramide synthases (CerS) that differ in tissue distribution and substrate specificity account for the diversity in acyl-chain composition of distinct ceramide species. Haploinsufficiency for ceramide synthase 2 (CerS2), the dominant isoform in the liver that preferentially makes very-long-chain (C22/C24/C24:1) ceramides, led to compensatory increases in long-chain C16-ceramides and conferred susceptibility to diet-induced steatohepatitis and insulin resistance. Mechanistic studies revealed that these metabolic effects were likely due to impaired β-oxidation resulting from inactivation of electron transport chain components. Inhibiting global ceramide synthesis negated the effects of CerS2 haploinsufficiency in vivo, and increasing C16-ceramides by overexpressing CerS6 recapitulated the phenotype in isolated, primary hepatocytes. Collectively, these studies reveal that altering sphingolipid acylation patterns impacts hepatic steatosis and insulin sensitivity and identify CerS6 as a possible therapeutic target for treating metabolic diseases associated with obesity.

Homozygous staggerer mice (sg/sg) display decreased and dysfunctional retinoic acid receptor-related orphan receptor ␣ (ROR␣) expression. We observed decreases in serum (and liver) triglycerides and total and high density lipoprotein serum cholesterol in sg/sg mice. Moreover, the sg/sg mice were characterized by reduced adiposity (associated with decreased fat pad mass and adipocyte size). Candidate-based expression profiling demonstrated that the dyslipidemia in sg/sg mice is associated with decreased hepatic expression of SREBP-1c, and the reverse cholesterol transporters, ABCA1 and ABCG1. This is consistent with the reduced serum lipids. The molecular mechanism did not involve aberrant expression of LXR and/or ChREBP. However, ChIP and transfection analyses revealed that ROR␣ is recruited to and regulates the activity of the SREBP-1c promoter. Furthermore, the lean phenotype in sg/sg mice is also characterized by significantly increased expression of PGC-1␣, PGC-1␤, and lipin1 mRNA in liver and white and brown adipose tissue from sg/sg mice. In addition, we observed a significant 4-fold increase in ␤ 2 -adrenergic receptor mRNA in brown adipose tissue. Finally, dysfunctional ROR␣ expression protects against diet-induced obesity. Following a 10-week high fat diet, wild-type but not sg/sg mice exhibited a ϳ20% weight gain, increased hepatic triglycerides, and notable white and brown adipose tissue accumulation. In summary, these changes in gene expression (that modulate lipid homeostasis) in metabolic tissues are involved in decreased adiposity and resistance to dietinduced obesity in the sg/sg mice, despite hyperphagia. In conclusion, we suggest this orphan nuclear receptor is a key modulator of fat accumulation and that selective ROR modulators may have utility in the treatment of obesity.The spontaneously arising mouse mutant, staggerer (sg), 4 was initially described and analyzed several decades ago (1).The homozygous mice display ataxia, cerebellar defects, tremor, and imbalance. Subsequently, the gene encoding retinoic acid receptor-related orphan receptor ␣ (ROR␣) (2, 3) was mapped to mouse chromosome 9 in the immediacy of the sg locus (4, 5). ROR␣ is an orphan member of the nuclear receptor superfamily (6). Several studies have identified cholesterol sulfate (and derivatives) as potential ligands for this nuclear receptor (7, 8), however, further studies are required to resolve this issue.The sg mutation has been shown to be an intragenic deletion in the coding region of ROR␣, removing an exon downstream of the DNA binding domain (4,5). This results in a frameshift mutation that affects the co-expressed isoforms ROR␣1 and -␣4 (5). ROR␣ transcript levels are significantly reduced in staggerer (sg/sg) mice, and it has been clearly demonstrated that the sg phenotype is associated with the expression of dysfunctional ROR␣ (9). Moreover, ROR␣-deficient mice display many aspects of the staggerer phenotype (9, 10). Mamontova et al. (11) demonstrated that male and female homozygous staggerer (sg/sg) are charac...

beta 1-3-Adrenoreceptor (AR)-deficient mice are unable to regulate energy expenditure and develop diet-induced obesity on a high-fat diet. We determined previously that beta2-AR agonist treatment activated expression of the mRNA encoding the orphan nuclear receptor, NOR-1, in muscle cells and plantaris muscle. Here we show that beta2-AR agonist treatment significantly and transiently activated the expression of NOR-1 (and the other members of the NR4A subgroup) in slow-twitch oxidative soleus muscle and fast-twitch glycolytic tibialis anterior muscle. The activation induced by beta-adrenergic signaling is consistent with the involvement of protein kinase A, MAPK, and phosphorylation of cAMP response element-binding protein. Stable cell lines transfected with a silent interfering RNA targeting NOR-1 displayed decreased palmitate oxidation and lactate accumulation. In concordance with these observations, ATP production in the NOR-1 silent interfering RNA (but not control)-transfected cells was resistant to (azide-mediated) inhibition of oxidative metabolism and expressed significantly higher levels of hypoxia inducible factor-1alpha. In addition, we observed the repression of genes that promote fatty acid oxidation (peroxisomal proliferator-activated receptor-gamma coactivator-1alpha/beta and lipin-1alpha) and trichloroacetic acid cycle-mediated carbohydrate (pyruvate) oxidation [pyruvate dehydrogenase phosphatase 1 regulatory and catalytic subunits (pyruvate dehydrogenase phosphatases-1r and -c)]. Furthermore, we observed that beta2-AR agonist administration in mouse skeletal muscle induced the expression of genes that activate fatty acid oxidation and modulate pyruvate use, including PGC-1alpha, lipin-1alpha, FOXO1, and PDK4. Finally, we demonstrate that NOR-1 is recruited to the lipin-1alpha and PDK-4 promoters, and this is consistent with NOR-1-mediated regulation of these genes. In conclusion, NOR-1 is necessary for oxidative metabolism in skeletal muscle.

In the original publication of this article, the name of an author was inadvertently misspelled. The corrected author name is Bhagirath Chaurasia. The spelling is now correct in the online version of the article. The authors apologize for the inconvenience.

Objective Ectopic fat deposition is associated with increased tissue production of ceramides. Recent genetic mouse studies suggest that specific sphingolipid C16:0 ceramide produced by ceramide synthase 6 (CerS6) plays an important role in the development of insulin resistance. However, the therapeutic potential of CerS6 inhibition not been demonstrated. Therefore, we pharmacologically investigated the selective ablation of CerS6 using antisense oligonucleotides (ASO) in obese insulin resistance animal models. Methods We utilized ASO as therapeutic modality, CerS6 ASO molecules designed and synthesized were initially screened for in-vitro knock-down (KD) potency and cytotoxicity. ASOs with >85% inhibition of CerS6 mRNA were selected for further investigations. Most promising ASOs verified for in-vivo KD efficacy in healthy mice. CerS6 ASO (AAGATGAGCCGCACC) was found most active with hepatic reduction of CerS6 mRNA expression. Prior to longitudinal metabolic studies, we performed a dose titration target engagement analysis with CerS6 ASO in healthy mice to select the optimal dose. Next, we utilized leptin deficiency ob/ob and high fat diet (HFD) induced obese mouse models for pharmacological efficacy study. Results CerS6 expression were significantly elevated in the liver and brown adipose, this was correlated with significantly elevated C16:0 ceramide concentrations in plasma and liver. Treatment with CerS6 ASO selectively reduced CerS6 expression by ∼90% predominantly in the liver and this CerS6 KD resulted in a significant reduction of C16:0 ceramide by about 50% in both liver and plasma. CerS6 KD resulted in lower body weight gain and accompanied by a significant reduction in whole body fat and fed/fasted blood glucose levels (1% reduction in HbA1c). Moreover, ASO-mediated CerS6 KD significantly improved oral glucose tolerance (during oGTT) and mice displayed improved insulin sensitivity. Thus, CerS6 appear to play an important role in the development of obesity and insulin resistance. Conclusions Our investigations identified specific and selective therapeutic valid ASO for CerS6 ablation in in-vivo. CerS6 should specifically be targeted for the reduction of C16:0 ceramides, that results in amelioration of insulin resistance, hyperglycemia and obesity. CerS6 mediated C16:0 ceramide reduction could be a potentially attractive target for the treatment of insulin resistance, obesity and type 2 diabetes.

The retinoic acid receptor-related orphan receptor (ROR) alpha has been demonstrated to regulate lipid metabolism. We were interested in the RORα1 dependent physiological functions in skeletal muscle. This major mass organ accounts for ∼40% of the total body mass and significant levels of lipid catabolism, glucose disposal and energy expenditure. We utilized the strategy of targeted muscle-specific expression of a truncated (dominant negative) RORα1ΔDE in transgenic mice to investigate RORα1 signaling in this tissue. Expression profiling and pathway analysis indicated that RORα influenced genes involved in: (i) lipid and carbohydrate metabolism, cardiovascular and metabolic disease; (ii) LXR nuclear receptor signaling and (iii) Akt and AMPK signaling. This analysis was validated by quantitative PCR analysis using TaqMan low-density arrays, coupled to statistical analysis (with Empirical Bayes and Benjamini–Hochberg). Moreover, westerns and metabolic profiling were utilized to validate the genes, proteins and pathways (lipogenic, Akt, AMPK and fatty acid oxidation) involved in the regulation of metabolism by RORα1. The identified genes and pathways were in concordance with the demonstration of hyperglycemia, glucose intolerance, attenuated insulin-stimulated phosphorylation of Akt and impaired glucose uptake in the transgenic heterozygous Tg-RORα1ΔDE animals. In conclusion, we propose that RORα1 is involved in regulating the Akt2-AMPK signaling pathways in the context of lipid homeostasis in skeletal muscle.

1 Ragaglitazar [(À) DRF 2725; NNC 61-0029] is a coligand of PPARa and PPARg. 2 In ob/ob mice, ragaglitazar showed significant reduction in plasma glucose, triglyceride and insulin (ED 50 values o0.03, 6.1 and o0.1 mg kg À1 ). These effects are three-fold better than rosiglitazone and KRP-297. 3 In Zucker fa/fa rats, ragaglitazar showed dose-dependent reduction in triglyceride and insulin, hepatic triglyceride secretion and triglyceride clearance kinetics (maximum of 74, 53, 32 and 50% at 3 mg kg À1 ), which are better than rosiglitazone and KRP-297. 4 In a high-fat-fed hyperlipidaemic rat model, the compound showed an ED 50 of 3.95, 3.78 mg kg À1 for triglyceride and cholesterol lowering, and 0.29 mg kg À1 for HDL-C increase. It also showed improvement in clearance of plasma triglyceride and hepatic triglyceride secretion rate. All these effects are 3 -10-fold better than fenofibrate and KRP-297. 5 Ragaglitazar treatment showed significant reduction in plasma Apo B and Apo CIII levels, and increase in liver CPT1 and CAT activity and ACO mRNA. Significant increase of both liver and fat LPL activity and fat aP2 mRNA was also observed. 6 In a high-fat-fed hamster model, ragaglitazar at 1 mg kg À1 showed 83 and 61% reduction in triglyceride and total cholesterol, and also 17% reduction in fat feed-induced body weight increase. In these hyperlipidaemic animal models, PPARg ligands failed to show any significant efficacy. Taken together, ragaglitazar shows better insulin-sensitizing and lipid-lowering potential, as compared to the standard compounds.

The class IIa histone deacetylases (HDACs) act as transcriptional repressors by altering chromatin structure through histone deacetylation. This family of enzymes regulates muscle development and phenotype, through regulation of muscle-specific genes including myogenin and MyoD (MYOD1). More recently, class IIa HDACs have been implicated in regulation of genes involved in glucose metabolism. However, the effects of HDAC5 on glucose metabolism and insulin action have not been directly assessed. Knockdown of HDAC5 in human primary muscle cells increased glucose uptake and was associated with increased GLUT4 (SLC2A4) expression and promoter activity but was associated with reduced GLUT1 (SLC2A1) expression. There was no change in PGC-1a (PPARGC1A) expression. The effects of HDAC5 knockdown on glucose metabolism were not due to alterations in the initiation of differentiation, as knockdown of HDAC5 after the onset of differentiation also resulted in increased glucose uptake and insulin-stimulated glycogen synthesis. These data show that inhibition of HDAC5 enhances metabolism and insulin action in muscle cells. As these processes in muscle are dysregulated in metabolic disease, HDAC inhibition could be an effective therapeutic strategy to improve muscle metabolism in these diseases. Therefore, we also examined the effects of the pan HDAC inhibitor, Scriptaid, on muscle cell metabolism. In myotubes, Scriptaid increased histone 3 acetylation, GLUT4 expression, glucose uptake and both oxidative and non-oxidative metabolic flux. Together, these data suggest that HDAC5 regulates muscle glucose metabolism and insulin action and that HDAC inhibitors can be used to modulate these parameters in muscle cells.