Upregulation of fatty acyl-CoA thioesterases in the heart and skeletal muscle of rats fed a high-fat diet

TMT-labeled quantitative malonylome analysis on the longissimus dorsi muscle of Laiwu pigs reveals the role of ACOT7 in fat deposition

The Laiwu pig is an indigenous fatty pig breed distributed in North China, characterized by an extremely high level of intramuscular fat (IMF) content (9% ∼ 12%), but the regulatory mechanism underlying intramuscular fat deposition in skeletal muscle is still unknown. In this study, the TMT-labeled quantitative malonylome of the longissimus dorsi muscle in Laiwu pigs at the fastest IMF deposition stage (240 d vs 120 d) was compared to analyze the molecular mechanism of IMF variation in pigs. In Laiwu pigs aged 240 days/120 days, we identified 291 malonylated lysine sites across 188 proteins in the longissimus dorsi muscle. Among these, 38 sites across 31 proteins exhibited differential malonylation. Annotation analysis and enrichment analysis were performed for differentially malonylated proteins (DMPs). These DMPs were mainly clustered into 12 GO functional categories accounting for 5 biological processes, 4 cellular components and 3 molecular functions, and 2 signaling pathways by KEGG enrichment analysis. The function of differentially malonylated protein ACOT7 in the process of fat deposition was further investigated during the differentiation of 3 T3-L1 cells. The results showed that the protein level of ACOT7 in 3 T3-L1 cells decreased but the malonylated level of ACOT7 increased significantly. The malonyl-CoA that is synthesized by ACSF3 affected the malonylation level of ACOT7 in 3 T3-L1 cells. SIGNIFICANCE: The intramuscular fat (IMF) content, by affecting sensory quality traits of meat, such as tenderness, flavor and juiciness, plays an important role in meat quality. Using TMT-based quantitative malonylated proteome analysis, we identified malonylated proteins in LD muscle samples in two stages (120 d and 240 d) of development and further identified differentially malonylated proteins, such as SLC25A4, ANXA5, TPM3 and ACOT7, that are associated with intramuscular fat deposition and fat metabolism in pigs. These differentially malonylated proteins could serve as candidates for elucidating the molecular mechanism of IMF deposition in pigs. In addition, we found that the malonyl-CoA in 3 T3-L1 cells is mainly synthesized by ACSF3, affecting the malonylated level of ACOT7. The study provides some data concerning the role of protein malonylation in regulating the variation in porcine IMF content.

ACOT1 deficiency attenuates high-fat diet-induced fat mass gain by increasing energy expenditure

Acyl-CoA thioesterase 1 (ACOT1) catalyzes the hydrolysis of long-chain acyl-CoAs to free fatty acids and CoA and is typically upregulated in obesity. Whether targeting ACOT1 in the setting of high-fat diet-induced (HFD-induced) obesity would be metabolically beneficial is not known. Here we report that male and female ACOT1KO mice are partially protected from HFD-induced obesity, an effect associated with increased energy expenditure without alterations in physical activity or food intake. In males, ACOT1 deficiency increased mitochondrial uncoupling protein-2 (UCP2) protein abundance while reducing 4-hydroxynonenal, a marker of oxidative stress, in white adipose tissue and liver of HFD-fed mice. Moreover, concurrent knockdown (KD) of UCP2 with ACOT1 in hepatocytes prevented increases in oxygen consumption observed with ACOT1 KD during high lipid loading, suggesting that UCP2-induced uncoupling may increase energy expenditure to attenuate weight gain. Together, these data indicate that targeting ACOT1 may be effective for obesity prevention during caloric excess by increasing energy expenditure.

PFOA exposure causes variations of Acot1 among tissues in rats, and Acot1 in serum can be potentially used as a sensitive marker for health monitoring

Perfluorooctanoic acid (PFOA) is a type of 8-carbon perfluoroalkyl substances (PFASs) widely used in industrial and domestic products, which now is a persistent organic pollutant (POP) found in the environment. Its structure is similar to fatty acids, which enables it to induce the expression of ACOT genes. To investigate the expression levels of Acot1 in various tissues and organs after exposure to PFOA for 28 days in rats, and to compare the variations of Acot1 expression in different tissues, we sectioned samples and incubated with Acot1 antibody. The results show that the transcription and protein expression levels of Acot1 in the liver and kidney of rats increased significantly. Meanwhile, the transcription and protein expression of Acot1 gene were also detected in testis, muscle, and adipose. The results of immunohistochemistry were also verified by western blot detection, and we detected the transcription of Acot1 gene in these tissues and found that they all increased in varying degrees. In this study, the expression of Acot1 protein in rat serum was detected for the first time, and the expression of Acot1 in rat serum was found to be significantly increased after PFOA exposure. In addition, the expression level of Acot1 in rat organism was found to be higher than that in the control group after 4 days of depuration for 7 days of acute PFOA exposure, and Acot1 protein expression also showed an increase with increasing exposure time, indicating that Acot1 can be used as a sensitive biomarker for health monitoring of PFOA occupational workers or exposed persons.

A composite strategy of genome-wide association study and copy number variation analysis for carcass traits in a Duroc pig population

BACKGROUND

Carcass traits are important in pig breeding programs for improving pork production. Understanding the genetic variants underlies complex phenotypes can help explain trait variation in pigs. In this study, we integrated a weighted single-step genome-wide association study (wssGWAS) and copy number variation (CNV) analyses to map genetic variations and genes associated with loin muscle area (LMA), loin muscle depth (LMD) and lean meat percentage (LMP) in Duroc pigs.

RESULTS

Firstly, we performed a genome-wide analysis for CNV detection using GeneSeek Porcine SNP50 Bead chip data of 3770 pigs. A total of 11,100 CNVs were detected, which were aggregated by overlapping 695 CNV regions (CNVRs). Next, we investigated CNVs of pigs from the same population by whole-genome resequencing. A genome-wide analysis of 21 pigs revealed 23,856 CNVRs that were further divided into three categories (851 gain, 22,279 loss, and 726 mixed), which covered 190.8 Mb (~ 8.42%) of the pig autosomal genome. Further, the identified CNVRs were used to determine an overall validation rate of 68.5% for the CNV detection accuracy of chip data. CNVR association analyses identified one CNVR associated with LMA, one with LMD and eight with LMP after applying stringent Bonferroni correction. The wssGWAS identified eight, six and five regions explaining more than 1% of the additive genetic variance for LMA, LMD and LMP, respectively. The CNVR analyses and wssGWAS identified five common regions, of which three regions were associated with LMA and two with LMP. Four genes (DOK7, ARAP1, ELMO2 and SLC13A3) were highlighted as promising candidates according to their function.

CONCLUSIONS

We determined an overall validation rate for the CNV detection accuracy of low-density chip data and constructed a genomic CNV map for Duroc pigs using resequencing, thereby proving a value genetic variation resource for pig genome research. Furthermore, our study utilized a composite genetic strategy for complex traits in pigs, which will contribute to the study for elucidating the genetic architecture that may be influenced and regulated by multiple forms of variations.

Myocardial Injury Caused by Chronic Alcohol Exposure—A Pilot Study Based on Proteomics

Chronic alcohol exposure can cause myocardial degenerative diseases, manifested as cardiac insufficiency, arrhythmia, etc. These are defined as alcoholic cardiomyopathy (ACM). Alcohol-mediated myocardial injury has previously been studied through metabolomics, and it has been proved to be involved in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway concerning unsaturated fatty acids biosynthesis and oxidative phosphorylation, which tentatively explored the mechanism of ACM induced by chronic drinking. To further study alcohol-induced myocardial injury, myocardial specimens from a previously successfully established mouse model of ACM were subjected to histological, echocardiographic, and proteomic analyses, and validated by real-time quantitative polymerase chain reaction (qPCR). Results of histopathology and echocardiography showed the hypertrophy of cardiomyocytes, the dilation of ventricles, and decreased cardiac function. Proteomic results, available via ProteomeXchange with identifier PXD032949, revealed 56 differentially expressed proteins (DEPs) were identified, which have the potential to be involved in the KEGG pathway related to fatty acid biosynthesis disorders, lipid metabolism disorders, oxidative stress, and, ultimately, in the development of dilated cardiomyopathy (DCM). The present study further elucidates the underlying effects of myocardial injury due to chronic alcohol intake, laying a foundation for further studies to clarify the potential mechanisms of ACM.

Messages from the Small Intestine Carried by Extracellular Vesicles in Prediabetes: A Proteomic Portrait

Extracellular vesicles (EVs) mediate communication in physiological and pathological conditions. In the pathogenesis of type 2 diabetes, inter-organ communication plays an important role in its progress and metabolic surgery leads to its remission. Moreover, gut dysbiosis is emerging as a diabetogenic factor. However, it remains unclear how the gut senses metabolic alterations and whether this is transmitted to other tissues via EVs. Using a diet-induced prediabetic mouse model, we observed that protein packaging in gut-derived EVs (GDE), specifically the small intestine, is altered in prediabetes. Proteins related to lipid metabolism and to oxidative stress management were more abundant in prediabetic GDE compared to healthy controls. On the other hand, proteins related to glycolytic activity, as well as those responsible for the degradation of polyubiquitinated composites, were depleted in prediabetic GDE. Together, our findings show that protein packaging in GDE is markedly modified during prediabetes pathogenesis, thus suggesting that prediabetic alterations in the small intestine are translated into modified GDE proteomes, which are dispersed into the circulation where they can interact with and influence the metabolic status of other tissues. This study highlights the importance of the small intestine as a tissue that propagates prediabetic metabolic dysfunction throughout the body and the importance of GDE as the messengers. Data are available via ProteomeXchange with identifier PXD028338.

Acyl-Coa Thioesterases: A Rheostat That Controls Activated Fatty Acids Modulates Dengue Virus Serotype 2 Replication

During infection with dengue viruses (DENVs), the lipid landscape within host cells is significantly altered to assemble membrane platforms that support viral replication and particle assembly. Fatty acyl-CoAs are key intermediates in the biosynthesis of complex lipids that form these membranes. They also function as key signaling lipids in the cell. Here, we carried out loss of function studies on acyl-CoA thioesterases (ACOTs), a family of enzymes that hydrolyze fatty acyl-CoAs to free fatty acids and coenzyme A, to understand their influence on the lifecycle of DENVs. The loss of function of the type I ACOTs 1 (cytoplasmic) and 2 (mitochondrial) together significantly increased DENV serotype 2 (DENV2) viral replication and infectious particle release. However, isolated knockdown of mitochondrial ACOT2 significantly decreased DENV2 protein translation, genome replication, and infectious virus release. Furthermore, loss of ACOT7 function, a mitochondrial type II ACOT, similarly suppressed DENV2. As ACOT1 and ACOT2 are splice variants, these data suggest that functional differences and substrate specificities due to the location (cytosol and mitochondria, respectively) of these proteins may account for the differences in DENV2 infection phenotype. Additionally, loss of mitochondrial ACOT2 and ACOT7 expression also altered the expression of several ACOTs located in multiple organelle compartments within the cell, highlighting a complex relationship between ACOTs in the DENV2 virus lifecycle.

Early fish domestication affects methylation of key genes involved in the rapid onset of the farmed phenotype

Animal domestication is a process of environmental modulation and artificial selection leading to permanent phenotypic modifications. Recent studies showed that phenotypic changes occur very early in domestication, i.e., within the first generation in captivity, which raises the hypothesis that epigenetic mechanisms may play a critical role on the early onset of the domestic phenotype. In this context, we applied reduced representation bisulphite sequencing to compare methylation profiles between wild Nile tilapia females and their offspring reared under farmed conditions. Approximately 700 differentially methylated CpG sites were found, many of them associated not only with genes involved in muscle growth, immunity, autophagy and diet response but also related to epigenetic mechanisms, such as RNA methylation and histone modifications. This bottom-up approach showed that the phenotypic traits often related to domestic animals (e.g., higher growth rate and different immune status) may be regulated epigenetically and prior to artificial selection on gene sequences. Moreover, it revealed the importance of diet in this process, as reflected by differential methylation patterns in genes critical to fat metabolism. Finally, our study highlighted that the TGF-β1 signalling pathway may regulate and be regulated by several differentially methylated CpG-associated genes. This could be an important and multifunctional component in promoting adaptation of fish to a domestic environment while modulating growth and immunity-related traits.

Differential protein expression during growth on model and commercial mixtures of naphthenic acids in Pseudomonas fluorescens Pf-5

Naphthenic acids (NAs) are carboxylic acids with the formula (Cn H2n+Z O2 ) and are among the most toxic, persistent constituents of oil sands process-affected waters (OSPW), produced during oil sands extraction. Currently, the proteins and mechanisms involved in NA biodegradation are unknown. Using LC-MS/MS shotgun proteomics, we identified proteins overexpressed during the growth of Pseudomonas fluorescens Pf-5 on a model NA (4'-n-butylphenyl)-4-butanoic acid (n-BPBA) and commercial NA mixture (Acros). By day 11, >95% of n-BPBA was degraded. With Acros, a 17% reduction in intensity occurred with 10-18 carbon compounds of the Z family -2 to -14 (major NA species in this mixture). A total of 554 proteins (n-BPBA) and 631 proteins (Acros) were overexpressed during growth on NAs, including several transporters (e.g., ABC transporters), suggesting a cellular protective response from NA toxicity. Several proteins associated with fatty acid, lipid, and amino acid metabolism were also overexpressed, including acyl-CoA dehydrogenase and acyl-CoA thioesterase II, which catalyze part of the fatty acid beta-oxidation pathway. Indeed, multiple enzymes involved in the fatty acid oxidation pathway were upregulated. Given the presumed structural similarity between alkyl-carboxylic acid side chains and fatty acids, we postulate that P. fluorescens Pf-5 was using existing fatty acid catabolic pathways (among others) during NA degradation.

The effect of Acot2 overexpression or downregulation on the preadipocyte differentiation in Chinese Red Steppe cattle

The quality and nutritional value of beef is closely linked to its content of intramuscular fat (IMF). The differentiation of preadipocytes and the deposition of lipid droplets in the adipocytes are the key to regulate the IMF content. The differentiation of adipocytes is regulated by a series of transcription factors and genes. Acyl-CoA thioesterase 2 (Acot2) hydrolyzes the acyl-coenzyme A (CoA) into free fatty acids and CoA and has the potential to maintain the free fatty acids and acyl CoA at the cellular level. In this work, we detected the expression of the Acot2 gene during the adipocyte differentiation in Chinese Red Steppe cattle, and then interfered and overexpressed the Acot2 gene in the preadipocytes to explore its regulatory role in the adipocyte differentiation. The results showed that the expression and regulation of Acot2 mainly occurred at the later stage of the adipocyte differentiation. The interference with the Acot2 gene significantly inhibited the lipid droplets accumulation and triglyceride content, while its overexpression significantly promoted both of them. The results of this study show that the Acot2 gene is a positive regulator of the adipocyte differentiation and may become a new target to improve the beef quality.

The Role of Brown Adipose Tissue in the Development and Treatment of Nonalcoholic Steatohepatitis: An Exploratory Gene Expression Study in Mice

Brown adipose tissue (BAT) might be a beneficial mediator in the development and treatment of nonalcoholic steatohepatitis (NASH). We aim to evaluate the gene expression of BAT activity-related genes during the development and the dietary and surgical treatment of NASH. BAT was collected from male C57BL/6J mice that received a high fat-high sucrose diet (HF-HSD) or a normal chow diet (NCD) for 4 and 20 weeks (n=8-9 per dietary group and timepoint) and from mice that underwent dietary intervention (return to NCD) (n=8), roux-en-y gastric bypass (RYGB) (n=6), or sham procedure (n=6) after 12 weeks HF-HSD. Expression of BAT genes involved in lipid metabolism (Cd36 and Cpt1b; p<0.05) and energy expenditure (Ucp1 and Ucp3; p<0.05) were significantly increased after 4 weeks HF-HSD compared with NCD, whereas in the occurrence of NASH after 20 weeks HF-HSD no difference was observed. We observed no differences in gene expression regarding lipid metabolism or energy expenditure at 8 weeks after dietary intervention (no NASH) compared with HF-HSD mice (NASH), nor in mice that underwent RYGB compared with SHAM. However, dietary intervention and RYGB both decreased the BAT gene expression of inflammatory cytokines (Il1b, Tnf-α and MCP-1; p<0.05). Gene expression of the batokine neuregulin 4 was significantly decreased after 20 weeks HF-HSD (p<0.05) compared with NCD, but was restored by dietary intervention and RYGB (p<0.05). In conclusion, BAT is hallmarked by dynamic alterations in the gene expression profile during the development of NASH and can be modulated by dietary intervention and bariatric surgery.

Metabolomic-proteomic combination analysis reveals the targets and molecular pathways associated with hydrogen sulfide alleviating NAFLD

AIMS

Nonalcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease worldwide. Exogenous H₂S has been shown to effectively mitigate NAFLD, although little is known about the underlying targets and molecular mechanisms.

METHODS

C57BL/6 mice were fed with normal fat diet (NFD) or high fat diet (HFD) for a total 16 weeks, and HFD-fed mice were treated with saline or NaHS beginning in 12th week. The combination analysis of metabolomics and proteomics of liver tissues was firstly performed to discover the candidate targets and potential molecular pathways involved in H₂S mitigating the NAFLD.

KEY FINDINGS

Compared with NaCl, H₂S relieved NAFLD by reducing liver weight, body weight and lipid accumulation in liver, and improving liver pathology and serum biochemical parameters. There were 40 overlapping metabolites in the intersection analysis between comparative analysis of HFD + NaCl vs NFD and HFD + NaHS vs HFD + NaCl based on liver metabolomics. Moreover, a total of 58 proteins were obtained whose changes were reversed after treatment with H₂S. A combined analysis of liver metabolomics and proteomics was then conducted, revealing 8 shared molecular pathways, as well as the enrichment of unsaturated fatty acids. In addition, Plin2 may also be a potential target of H₂S via the regulation of lipid droplet degradation in alleviating NAFLD.

SIGNIFICANCE

We performed the first study combining metabolomics and proteomics to explore the mechanisms behind the alleviation of NAFLD by H₂S. Our results not only provide evidence that H₂S alleviates NAFLD but also reveals its possible molecular mechanisms and targets.

Short high-fat diet interferes with the physiological maturation of the late adolescent mouse heart

Dietary fats are essential for cardiac function. The metabolites of fats known as fatty acids provide most of the energy for cardiac tissue, serve as building blocks for membranes and regulate important signaling cascades. Despite their importance, excess fat intake can cause cardiac dysfunction. The detrimental effects of high-fat diet (HFD) on cardiac health are widely investigated in long-term studies but the short-term effects of fats have not been thoroughly studied. To elucidate the near-term effects of a HFD on the growth and maturation of late adolescent heart we subjected 11-week-old mice to an 8-week long HFD (42% of calories from fat, 42% from carbohydrate, n = 8) or chow diet (12% of calories from fat, 66% from carbohydrate, n = 7) and assessed their effects on the heart in vivo and in vitro. Our results showed that excessive fat feeding interferes with normal maturation of the heart indicated by the lack of increase in dimensions, volume, and stroke volume of the left ventricles of mice on high fat diet that were evident in mice on chow diet. In addition, differences in regional strain during the contraction cycle between mice on HFD and chow diet were seen. These changes were associated with reduced activity of the growth promoting PI3K-Akt1 signaling cascade and moderate changes in glucose metabolism without changes in calcium signaling. This study suggests that even a short period of HFD during late adolescence hinders cardiac maturation and causes physiological changes that may have an impact on the cardiac health in adulthood.

Myo-inositol and d-chiro-inositol oral supplementation ameliorate cardiac dysfunction and remodeling in a mouse model of diet-induced obesity

Obesity is an independent risk factor to develop cardiac functional and structural impairments. Here, we investigated the effects of supplementation of inositols on the electrical, structural, and functional cardiac alterations in the mouse model of high fat diet (HFD) induced obesity. Three groups of C57BL6 mice (n = 16 each) were studied: j) HFD feeding; jj) HFD feeding + inositols from week 9 to 13; jjj) standard diet feeding. Study observation period was 13 weeks. Inositols were administered as mixture of myo-inositol and d-chiro-inositol in the drinking water. Effects of inositols were evaluated based on electrical, structural, and functional cardiac features, autonomic sympatho-vagal balance and arrhythmogenic susceptibility to adrenergic challenge. Heart samples were collected for histological evaluations and transcriptional analyses of genes involved in defining the shape and propagation of the action potential, fatty acid metabolism and oxidative stress. Inositol supplementation significantly restored control values of heart rate and QTc interval on ECG and of sympatho-vagal balance. Moreover, it blunted the increase in left ventricular mass and cardiomyocyte hypertrophy, reversed diastolic dysfunction, reduced the susceptibility to arrhythmic events and restored the expression level of cardiac genes altered by HFD. The present study shows, for the first time, how a short period of supplementation with inositols is able to ameliorate the HFD-induced electrical, structural and functional heart alterations including ventricular remodeling. Results provide a new insight into the cardioprotective effect of inositols, which could pave the way for a novel therapeutic approach to the treatment of HFD obesity-induced heart dysfunction.

Structure, function, and regulation of thioesterases

Thioesterases are present in all living cells and perform a wide range of important biological functions by catalysing the cleavage of thioester bonds present in a diverse array of cellular substrates. Thioesterases are organised into 25 families based on their sequence conservation, tertiary and quaternary structure, active site configuration, and substrate specificity. Recent structural and functional characterisation of thioesterases has led to significant changes in our understanding of the regulatory mechanisms that govern enzyme activity and their respective cellular roles. The resulting dogma changes in thioesterase regulation include mechanistic insights into ATP and GDP-mediated regulation by oligomerisation, the role of new key regulatory regions, and new insights into a conserved quaternary structure within TE4 family members. Here we provide a current and comparative snapshot of our understanding of thioesterase structure, function, and regulation across the different thioesterase families.

Multiple mitochondrial thioesterases have distinct tissue and substrate specificity and CoA regulation, suggesting unique functional roles

Acyl-CoA thioesterases (Acots) hydrolyze fatty acyl-CoA esters. Acots in the mitochondrial matrix are poised to mitigate β-oxidation overload and maintain CoA availability. Several Acots associate with mitochondria, but whether they all localize to the matrix, are redundant, or have different roles is unresolved. Here, we compared the suborganellar localization, activity, expression, and regulation among mitochondrial Acots (Acot2, -7, -9, and -13) in mitochondria from multiple mouse tissues and from a model of Acot2 depletion. Acot7, -9, and -13 localized to the matrix, joining Acot2 that was previously shown to localize there. Mitochondria from heart, skeletal muscle, brown adipose tissue, and kidney robustly expressed Acot2, -9, and -13; Acot9 levels were substantially higher in brown adipose tissue and kidney mitochondria, as was activity for C4:0-CoA, a unique Acot9 substrate. In all tissues, Acot2 accounted for about half of the thioesterase activity for C14:0-CoA and C16:0-CoA. In contrast, liver mitochondria from fed and fasted mice expressed little Acot activity, which was confined to long-chain CoAs and due mainly to Acot7 and Acot13 activities. Matrix Acots occupied different functional niches, based on substrate specificity (Acot9 versus Acot2 and -13) and strong CoA inhibition (Acot7, -9, and -13, but not Acot2). Interpreted in the context of β-oxidation, CoA inhibition would prevent Acot-mediated suppression of β-oxidation, while providing a release valve when CoA is limiting. In contrast, CoA-insensitive Acot2 could provide a constitutive siphon for long-chain fatty acyl-CoAs. These results reveal how the family of matrix Acots can mitigate β-oxidation overload and prevent CoA limitation.

Alterations in the Transcriptional Profile of the Liver Tissue and the Therapeutic Effects of Propolis Extracts in Alcohol-induced Steatosis in Rats

The hepatoprotective effects of the ethanolic extracts of propolis (EEP) on alcohol-induced liver steatosis were investigated in Wistar rats. Chronic alcoholic fatty liver was induced by administration of 52% alcohol to male Wistar rats at the dose of 1% body weight for 7 weeks. Then animals were simultaneously treated with 50% ethanol solutions of EEP or normal saline at the dose of 0.1% body weight for 4 further weeks. Serological analyses and liver histopathology studies were performed to investigate the development of steatosis. Microarray analysis was conducted to investigate the alterations of hepatic gene expression profiling. Our results showed that 4-week treatment of EEP helped to restore the levels of various blood indices, liver function enzymes and the histopathology of liver tissue to normal levels. Results from the microarray analysis revealed that the hepatic expressions of genes involved in lipogenesis were significantly down-regulated by EEP treatment, while the transcriptional expressions of functional genes participating in fatty acids oxidation were markedly increased. The ability of EEP to reduce the negative effects of alcohol on liver makes propolis a potential natural product for the alternative treatment of alcoholic fatty liver.

Increasing Acyl CoA thioesterase activity alters phospholipid profile without effect on insulin action in skeletal muscle of rats

Increased lipid metabolism in muscle is associated with insulin resistance and therefore, many strategies have been employed to alter fatty acid metabolism and study the impact on insulin action. Metabolism of fatty acid requires activation to fatty acyl CoA by Acyl CoA synthases (ACSL) and fatty acyl CoA can be hydrolysed by Acyl CoA thioesterases (Acot). Thioesterase activity is low in muscle, so we overexpressed Acot7 in muscle of chow and high-fat diet (HFD) rats and investigated effects on insulin action. Acot7 overexpression modified specific phosphatidylcholine and phosphatidylethanolamine species in tibialis muscle of chow rats to levels similar to those observed in control HFD muscle. The changes in phospholipid species did not alter glucose uptake in tibialis muscle under hyperinsulinaemic/euglycaemic clamped conditions. Acot7 overexpression in white extensor digitorum longus (EDL) muscle increased complete fatty acid oxidation ex-vivo but was not associated with any changes in glucose uptake in-vivo, however overexpression of Acot7 in red EDL reduced insulin-stimulated glucose uptake in-vivo which correlated with increased incomplete fatty acid oxidation ex-vivo. In summary, although overexpression of Acot7 in muscle altered some aspects of lipid profile and metabolism in muscle, this had no major effect on insulin-stimulated glucose uptake.

Proteomics of the Rat Myocardium during Development of Type 2 Diabetes Mellitus Reveals Progressive Alterations in Major Metabolic Pathways

Congestive heart failure and poor clinical outcome after myocardial infarction are known complications in patients with type-2 diabetes mellitus (T2DM). Protein alterations may be involved in the mechanisms underlying these disarrays in the diabetic heart. Here we map proteins involved in intracellular metabolic pathways in the Zucker diabetic fatty rat heart as T2DM develops using MS based proteomics. The prediabetic state only induced minor pathway changes, whereas onset and late T2DM caused pronounced perturbations. Two actin-associated proteins, ARPC2 and TPM3, were up-regulated at the prediabetic state indicating increased actin dynamics. All differentially regulated proteins involved in fatty acid metabolism, both peroxisomal and mitochondrial, were up-regulated at late T2DM, whereas enzymes of branched chain amino acid degradation were all down-regulated. At both onset and late T2DM, two members of the serine protease inhibitor superfamily, SERPINA3K and SERPINA3L, were down-regulated. Furthermore, we found alterations in proteins involved in clearance of advanced glycation end-products and lipotoxicity, DCXR and CBR1, at both onset and late T2DM. These proteins deserve elucidation with regard to their role in T2DM pathogenesis and their respective role in the deterioration of the diabetic heart. Data are available via ProteomeXchange with identifiers PXD009538, PXD009554, and PXD009555.

Fenofibrate reverses changes induced by high-fat diet on metabolism in mice muscle and visceral adipocytes

The effect of fenofibrate on the metabolism of skeletal muscle and visceral white adipose tissue of diet-induced obese (DIO) mice was investigated. C57BL/6J male mice were fed either a control or high-fat diet for 8 weeks. Fenofibrate (50 mg/Kg BW, daily) was administered by oral gavage during the last two weeks of the experimental period. Insulin-stimulated glucose metabolism in soleus muscles, glucose tolerance test, insulin tolerance test, indirect calorimetry, lipolysis of visceral white adipose tissue, expression of miR-103-3p in adipose tissue, and miR-1a, miR-133a/b, miR-206, let7b-5p, miR-23b-3p, miR-29-3p, miR-143-3p in soleus muscle, genes related to glucose and fatty acid metabolism in adipose tissue and soleus muscle, and proteins (phospho-AMPKα2, Pgc1α, Cpt1b), intramuscular lipid staining, and activities of fatty acid oxidation enzymes in skeletal muscle were investigated. In DIO mice, fenofibrate prevented weight gain induced by HFD feeding by increasing energy expenditure; improved whole body glucose homeostasis, and in skeletal muscle, increased insulin dependent glucose uptake, miR-1a levels, reduced intramuscular lipid accumulation, and phospho-AMPKα2 levels. In visceral adipose tissue of obese mice, fenofibrate decreased basal lipolysis rate and visceral adipocytes hypertrophy, and induced the expression of Glut-4, Irs1, and Cav-1 mRNA and miR-103-3p suggesting a higher insulin sensitivity of the adipocytes. The evidence is presented herein that beneficial effects of fenofibrate on body weight, glucose homeostasis, and muscle metabolism might be related to its action in adipose tissue. Moreover, fenofibrate regulates miR-1a-3p in soleus and miR-103-3p in adipose tissue, suggesting these microRNAs might contribute to fenofibrate beneficial effects on metabolism.

Acyl-CoA thioesterase 7 is involved in cell cycle progression via regulation of PKCζ-p53-p21 signaling pathway

Acyl-CoA thioesterase 7 (ACOT7) is a major isoform of the ACOT family that catalyzes hydrolysis of fatty acyl-CoAs to free fatty acids and CoA-SH. However, canonical and non-canonical functions of ACOT7 remain to be discovered. In this study, for the first time, ACOT7 was shown to be responsive to genotoxic stresses such as ionizing radiation (IR) and the anti-cancer drug doxorubicin in time- and dose-dependent manners. ACOT7 knockdown induced cytostasis via activation of the p53-p21 signaling pathway without a DNA damage response. PKCζ was specifically involved in ACOT7 depletion-mediated cell cycle arrest as an upstream molecule of the p53-p21 signaling pathway in MCF7 human breast carcinoma and A549 human lung carcinoma cells. Of the other members of the ACOT family, including ACOT1, 4, 8, 9, 11, 12, and 13 that were expressed in human, ACOT4, 8, and 12 were responsive to genotoxic stresses. However, none of those had a role in cytostasis via activation of the PKCζ-p53-p21 signaling pathway. Analysis of the ACOT7 prognostic value revealed that low ACOT7 levels prolonged overall survival periods in breast and lung cancer patients. Furthermore, ACOT7 mRNA levels were higher in lung cancer patient tissues compared to normal tissues. We also observed a synergistic effect of ACOT7 depletion in combination with either IR or doxorubicin on cell proliferation in breast and lung cancer cells. Together, our data suggest that a low level of ACOT7 may be involved, at least in part, in the prevention of human breast and lung cancer development via regulation of cell cycle progression.

Chronic high-fat feeding impairs adaptive induction of mitochondrial fatty acid combustion-associated proteins in brown adipose tissue of mice

Since brown adipose tissue (BAT) is involved in thermogenesis using fatty acids as a fuel, BAT activation is a potential strategy for treating obesity and diabetes. However, whether BAT fatty acid combusting capacity is preserved in these conditions has remained unclear. We therefore evaluated expression levels of fatty acid oxidation-associated enzymes and uncoupling protein 1 (Ucp1) in BAT by western blot using a diet-induced obesity C57BL/6J mouse model. In C57BL/6J mice fed a high-fat diet (HFD) over 2–4 weeks, carnitine palmitoyltransferase 2 (Cpt2), acyl-CoA thioesterase (Acot) 2, Acot11 and Ucp1 levels were significantly increased compared with baseline and control low-fat diet (LFD)-fed mice. Similar results were obtained in other mouse strains, including ddY, ICR and KK-Ay, but the magnitudes of the increase in Ucp1 level were much smaller than in C57BL/6J mice, with decreased Acot11 levels after HFD-feeding. In C57BL/6J mice, increased levels of these mitochondrial proteins declined to near baseline levels after a longer-term HFD-feeding (20 weeks), concurrent with the accumulation of unilocular, large lipid droplets in brown adipocytes. Extramitochondrial Acot11 and acyl-CoA oxidase remained elevated. Treatment of mice with Wy-14,643 also increased these proteins, but was less effective than 4 week-HFD, suggesting that mechanisms other than peroxisome proliferator-activated receptor α were also involved in the upregulation. These results suggest that BAT enhances its fatty acid combusting capacity in response to fat overload, however profound obesity deprives BAT of the responsiveness to fat, possibly via mitochondrial alteration.

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BAT activation is a potential strategy for treating obesity and diabetes.

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BAT enhances its fatty acid combusting capacity in response to high-fat feeding.

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Profound obesity deprives BAT of the responsiveness to fat overload.

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Susceptibility to BAT activation could depend on the degree of obesity.

Interindividual variation in gene expression responses and metabolite formation in acetaminophen-exposed primary human hepatocytes

Acetaminophen (APAP) is a readily available over-the-counter drug and is one of the most commonly used analgesics/antipyretics worldwide. Large interindividual variation in susceptibility toward APAP-induced liver failure has been reported. However, the exact underlying factors causing this variability in susceptibility are still largely unknown. The aim of this study was to better understand this variability in response to APAP by evaluating interindividual differences in gene expression changes and APAP metabolite formation in primary human hepatocytes (PHH) from several donors (n = 5) exposed in vitro to a non-toxic to toxic APAP dose range. To evaluate interindividual variation, gene expression data/levels of metabolites were plotted against APAP dose/donor. The correlation in APAP dose response between donors was calculated by comparing data points from one donor to the data points of all other donors using a Pearson-based correlation analysis. From that, a correlation score/donor for each gene/metabolite was defined, representing the similarity of the omics response to APAP in PHH of a particular donor to all other donors. The top 1 % highest variable genes were selected for further evaluation using gene set overrepresentation analysis. The biological processes in which the genes with high interindividual variation in expression were involved include liver regeneration, inflammatory responses, mitochondrial stress responses, hepatocarcinogenesis, cell cycle, and drug efficacy. Additionally, the interindividual variation in the expression of these genes could be associated with the variability in expression levels of hydroxyl/methoxy-APAP and C8H13O5N-APAP-glucuronide. The before-mentioned metabolites or their derivatives have also been reported in blood of humans exposed to therapeutic APAP doses. Possibly these findings can contribute to elucidating the causative factors of interindividual susceptibility toward APAP.

Metabolic and tissue-specific regulation of acyl-CoA metabolism

Acyl-CoA formation initiates cellular fatty acid metabolism. Acyl-CoAs are generated by the ligation of a fatty acid to Coenzyme A mediated by a large family of acyl-CoA synthetases (ACS). Conversely, acyl-CoAs can be hydrolyzed by a family of acyl-CoA thioesterases (ACOT). Here, we have determined the transcriptional regulation of all ACS and ACOT enzymes across tissues and in response to metabolic perturbations. We find patterns of coordinated regulation within and between these gene families as well as distinct regulation occurring in a tissue- and physiologically-dependent manner. Due to observed changes in long-chain ACOT mRNA and protein abundance in liver and adipose tissue, we determined the consequence of increasing cytosolic long-chain thioesterase activity on fatty acid metabolism in these tissues by generating transgenic mice overexpressing a hyperactive mutant of Acot7 in the liver or adipose tissue. Doubling cytosolic acyl-CoA thioesterase activity failed to protect mice from diet-induced obesity, fatty liver or insulin resistance, however, overexpression of Acot7 in adipocytes rendered mice cold intolerant. Together, these data suggest distinct modes of regulation of the ACS and ACOT enzymes and that these enzymes act in a coordinated fashion to control fatty acid metabolism in a tissue-dependent manner.

Gut microbiota as an epigenetic regulator: pilot study based on whole-genome methylation analysis

The core human gut microbiota contributes to the developmental origin of diseases by modifying metabolic pathways. To evaluate the predominant microbiota as an epigenetic modifier, we classified 8 pregnant women into two groups based on their dominant microbiota, i.e., Bacteroidetes, Firmicutes, and Proteobacteria. Deep sequencing of DNA methylomes revealed a clear association between bacterial predominance and epigenetic profiles. The genes with differentially methylated promoters in the group in which Firmicutes was dominant were linked to risk of disease, predominantly to cardiovascular disease and specifically to lipid metabolism, obesity, and the inflammatory response. This is one of the first studies that highlights the association of the predominant bacterial phyla in the gut with methylation patterns. Further longitudinal and in-depth studies targeting individual microbial species or metabolites are recommended to give us a deeper insight into the molecular mechanism of such epigenetic modifications.

IMPORTANCE

Epigenetics encompasses genomic modifications that are due to environmental factors and do not affect the nucleotide sequence. The gut microbiota has an important role in human metabolism and could be a significant environmental factor affecting our epigenome. To investigate the association of gut microbiota with epigenetic changes, we assessed pregnant women and selected the participants based on their predominant gut microbiota for a study on their postpartum methylation profile. Intriguingly, we found that blood DNA methylation patterns were associated with gut microbiota profiles. The gut microbiota profiles, with either Firmicutes or Bacteroidetes as a dominant group, correlated with differential methylation status of gene promoters functionally associated with cardiovascular diseases. Furthermore, differential methylation of gene promoters linked to lipid metabolism and obesity was observed. For the first time, we report here a position of the predominant gut microbiota in epigenetic profiling, suggesting one potential mechanism in obesity with comorbidities, if proven in further in-depth studies.

Transcriptomic profiling suggests a role for IGFBP5 in premature senescence of endothelial cells after chronic low dose rate irradiation

PURPOSE

Ionizing radiation has been recognized to increase the risk of cardiovascular diseases (CVD). However, there is no consensus concerning the dose-risk relationship for low radiation doses and a mechanistic understanding of low dose effects is needed.

MATERIAL AND METHODS

Previously, human umbilical vein endothelial cells (HUVEC) were exposed to chronic low dose rate radiation (1.4 and 4.1 mGy/h) during one, three and six weeks which resulted in premature senescence in cells exposed to 4.1 mGy/h. To gain more insight into the underlying signaling pathways, we analyzed gene expression changes in these cells using microarray technology. The obtained data were analyzed in a dual approach, combining single gene expression analysis and Gene Set Enrichment Analysis.

RESULTS

An early stress response was observed after one week of exposure to 4.1 mGy/h which was replaced by a more inflammation-related expression profile after three weeks and onwards. This early stress response may trigger the radiation-induced premature senescence previously observed in HUVEC irradiated with 4.1 mGy/h. A dedicated analysis pointed to the involvement of insulin-like growth factor binding protein 5 (IGFBP5) signaling in radiation-induced premature senescence.

CONCLUSION

Our findings motivate further research on the shape of the dose-response and the dose rate effect for radiation-induced vascular senescence.

Dietary fatty acids alter left ventricular myocardial gene expression in Wistar rats

Obesity increases the risk for cardiomyopathy in the absence of comorbidities. Myocardial structure is modified by dietary fatty acids. Left ventricular hypertrophy is associated with Western (WES) diet consumption, whereas intake of n-3 polyunsaturated fatty acids is associated with antihypertrophic effects. We previously observed no attenuation of left ventricular thickening after 3 months of docosahexaenoic acid (DHA) supplementation of a WES diet, compared with WES diet intake alone, in rats that had similar weight, adiposity, and insulin sensitivity to control animals. The objective of this study was to define left ventricular gene expression in these animals to determine whether diet alone was associated with a physiologic or pathologic hypertrophic response. We hypothesized that WES diet consumption would favor a pathologic or maladaptive myocardial gene expression pattern and that DHA supplementation would favor a physiologic or adaptive response. Microarray analysis identified 64 transcripts that were differentially expressed (P ≤ .001) within one or more treatment comparisons. Using quantitative real-time polymerase chain reaction, 29 genes with fold change at least 1.74 were successfully validated; all but 3 had similar directionality to that observed using microarray, and 2 genes, connective tissue growth factor and cathepsin M, were differentially expressed according to diet. WES blot analysis was performed on 4 proteins relevant to myocardial hypertrophy and metabolism. Acyl-CoA thioesterase 1, B-cell translocation gene 2, and carbonic anhydrase III showed directional change consistent with gene expression. Retinol saturase (all-trans-retinol 13,14-reductase), although not consistent with gene expression, was different according to diet, with increased concentrations in WES-fed rats compared with control and DHA-supplemented animals. Diet did not distinguish a transcriptome reflecting physiologic or pathologic myocardial hypertrophy; furthermore, the modest changes observed suggest that obesity and associated comorbidities may play a larger role than mere dietary fatty acid composition in development of cardiomyopathy.

Impaired transcriptional response of the murine heart to cigarette smoke in the setting of high fat diet and obesity

Smoking and obesity are each well-established risk factors for cardiovascular heart disease, which together impose earlier onset and greater severity of disease. To identify early signaling events in the response of the heart to cigarette smoke exposure within the setting of obesity, we exposed normal weight and high fat diet-induced obese (DIO) C57BL/6 mice to repeated inhaled doses of mainstream (MS) or sidestream (SS) cigarette smoke administered over a two week period, monitoring effects on both cardiac and pulmonary transcriptomes. MS smoke (250 μg wet total particulate matter (WTPM)/L, 5 h/day) exposures elicited robust cellular and molecular inflammatory responses in the lung with 1466 differentially expressed pulmonary genes (p < 0.01) in normal weight animals and a much-attenuated response (463 genes) in the hearts of the same animals. In contrast, exposures to SS smoke (85 μg WTPM/L) with a CO concentration equivalent to that of MS smoke (~250 CO ppm) induced a weak pulmonary response (328 genes) but an extensive cardiac response (1590 genes). SS smoke and to a lesser extent MS smoke preferentially elicited hypoxia- and stress-responsive genes as well as genes predicting early changes of vascular smooth muscle and endothelium, precursors of cardiovascular disease. The most sensitive smoke-induced cardiac transcriptional changes of normal weight mice were largely absent in DIO mice after smoke exposure, while genes involved in fatty acid utilization were unaffected. At the same time, smoke exposure suppressed multiple proteome maintenance genes induced in the hearts of DIO mice. Together, these results underscore the sensitivity of the heart to SS smoke and reveal adaptive responses in healthy individuals that are absent in the setting of high fat diet and obesity.

Expression and distribution of acyl-CoA thioesterases in the white adipose tissue of rats

Acyl-CoA thioesterases (Acots) are enzymes that catalyze the hydrolysis of fatty acyl-CoAs to free fatty acids and coenzyme A, and have the potential to regulate the intracellular levels of these molecules. In this study, we show that a cytosolic isoform, Acot1, is expressed and distributed in immature adipocytes located in the perivascular region of the white adipose tissue (WAT) of rats. Immunoblot analyses detected Acot1 in all of the WATs examined, while immunohistochemistry revealed positively stained layered structures surrounding the adventitia of blood vessels in the subcutaneous WAT. When the subcutaneous WAT was digested with collagenase and centrifuged, Acot1 was recovered in the stromal vascular fraction (SVF), and not in the large mature adipocytes. In the SVF, undigested cells attached to short tubular fragments of blood vessels showed positive immunostaining, as well as a proportion of the dispersed cells. These fibroblast-like cells contained fine particulate lipid droplets, stained by oil-red O dye, in their cytoplasm, or expressed fatty acid-binding protein 4, an adipocyte marker. After induction of adipocyte differentiation following a 15-day preculture without insulin, the dedifferentiated cells showed increased Acot1 expression with a diffuse distribution throughout the cytosol. These findings suggest that Acot1 expression is transiently upregulated at an early stage of adipocyte maturation, possibly to maintain cytosolic acyl-CoAs below a certain level until the cells acquire their full capability for fat storage.

Docosahexaenoic acid supplementation does not improve Western diet-induced cardiomyopathy in rats

Obesity increases risk for cardiomyopathy in the absence of hypertension, diabetes or ischemia. The fatty acid milieu, modulated by diet, may modify myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy. We sought to identify gross, cellular and ultrastructural myocardial changes associated with Western diet intake, and subsequent modification with docosahexaenoic acid (DHA) supplementation. Wistar and Sprague-Dawley (SD) rats received 1 of 3 diets: control (CON); Western (WES); Western + DHA (WES+DHA). After 12 weeks of treatment, echocardiography was performed and myocardial adiponectin, fatty acids, collagen, area occupied by lipid and myocytes, and ultrastructure were determined. Strain effects included higher serum adiponectin in Wistar rats, and differences in myocardial fatty acid composition. Diet effects were evident in that both WES and WES+DHA feeding were associated with similarly increased left ventricular (LV) diastolic cranial wall thickness (LVW(cr/d)) and decreased diastolic internal diameter (LVID(d)), compared to CON. Unexpectedly, WES+DHA feeding was associated additionally with increased thickness of the LV cranial wall during systole (LVW(cr/s)) and the caudal wall during diastole (LVW(ca/d)) compared to CON; this was observed concomitantly with increased serum and myocardial adiponectin. Diastolic dysfunction was present in WES+DHA rats compared to both WES and CON. Myocyte cross sectional area (CSA) was greater in WES compared to CON rats. In both fat-fed groups, transmission electron microscopy (TEM) revealed myofibril degeneration, disorganized mitochondrial cristae, lipid inclusions and vacuolation. In the absence of hypertension and whole body insulin resistance, WES+DHA intake was associated with more global LV thickening and with diastolic dysfunction, compared to WES feeding alone. Myocyte hypertrophy, possibly related to subcellular injury, is an early change that may contribute to gross hypertrophy. Strain differences in adipokines and myocardial fatty acid accretion may underlie heterogeneous data from rodent studies.

Protective effects of Acyl-coA thioesterase 1 on diabetic heart via PPARα/PGC1α signaling

Background

Using fatty acids (FAs) exclusively for ATP generation was reported to contribute to the development of diabetic cardiomyopathy. We studied the role of substrate metabolism related genes in the heart of the diabetes to find out a novel therapeutic target for diabetic cardiomyopathy.

Methods and Results

By microarray analysis of metabolic gene expression, acyl-CoA thioesterase 1 (acot1) was clearly upregulated in the myocardia of db/db mice, compared with normal control C57BL/Ks. Therefore, gain-of-function and loss-of-function approaches were employed in db/db mice to investigate the functions of ACOT1 in oxidative stress, mitochondrial dysfunction and heart function. We found that in the hearts of db/db mice which overexpressed ACOT1, H₂O₂ and malondialdehyde (MDA) were reduced, the activities of ATPases in mitochondria associated with mitochondrial function were promoted, the expression of uncoupling protein 3 (UCP3) contributing to oxygen wastage for noncontractile purposes was decreased, and cardiac dysfunction was attenuated, as determined by both hemodynamic and echocardiographic detections. Consistently, ACOT1 deficiency had opposite effects, which accelerated the cardiac damage induced by diabetes. Notably, by real-time PCR, we found that overexpression of ACOT1 in diabetic heart repressed the peroxisome proliferator-activated receptor alpha/PPARγ coactivator 1α (PPARα/PGC1α) signaling, as shown by decreased expression of PGC1α and the downstream genes involved in FAs use.

Conclusion

Our results demonstrated that ACOT1 played a crucial protective role in diabetic heart via PPARα/PGC1α signaling.

Long-term treatment with the pan-PPAR agonist tetradecylthioacetic acid or fish oil is associated with increased cardiac content of n-3 fatty acids in rat

BACKGROUND

Excess peroxisome proliferator-activated receptor (PPAR) stimulation has been associated with detrimental health effects including impaired myocardial function. Recently, supplementation with n-3 polyunsaturated fatty acids (PUFA) has been associated with improved left ventricular function and functional capacity in patients with dilated cardiomyopathy. We investigated the long-term effects of the pan-PPAR agonist tetradecylthioacetic acid (TTA) and/or high-dose fish oil (FO) on cardiac fatty acid (FA) composition and lipid metabolism. Male Wistar rats were given one out of four different 25% (w/v) fat diets: control diet; TTA diet; FO diet; or diet containing both TTA and FO.

RESULTS

After 50 weeks n-3 PUFA levels were increased by TTA and FO in the heart, whereas liver levels were reduced following TTA administration. TTA was associated with a decrease in arachidonic acid, increased activities of carnitine palmitoyltransferase II, fatty acyl-CoA oxidase, glycerol-3-phosphate acyltransferase, and fatty acid synthase in the heart. Furthermore, cardiac Ucp3 and Cact mRNA was upregulated.

CONCLUSIONS

Long-term treatment with the pan-PPAR agonist TTA or high-dose FO induced marked changes in PUFA composition and enzymatic activity involved in FA metabolism in the heart, different from liver. Changes included increased FA oxidation and a selective increase in cardiac n-3 PUFA.

Targeted deletion of thioesterase superfamily member 1 promotes energy expenditure and protects against obesity and insulin resistance

Mammalian acyl-CoA thioesterases (Acots) catalyze the hydrolysis of fatty acyl-CoAs to form free fatty acids plus CoA, but their metabolic functions remain undefined. Thioesterase superfamily member 1 (Them1; synonyms Acot11, StarD14, and brown fat inducible thioesterase) is a long-chain fatty acyl-CoA thioesterase that is highly expressed in brown adipose tissue and is regulated by both ambient temperature and food consumption. Here we show that Them1(-/-) mice were resistant to diet-induced obesity despite greater food consumption. Them1(-/-) mice exhibited increased O(2) consumption and heat production, which were accompanied by increased rates of fatty acid oxidation in brown adipose tissue and up-regulation of genes that promote energy expenditure. Them1(-/-) mice were also protected against diet-induced inflammation in white adipose tissue, as well as hepatic steatosis, and demonstrated improved glucose homeostasis. The absence of Them1 expression in vivo and in cell culture led to markedly attenuated diet- or chemically induced endoplasmic reticulum stress responses, providing a mechanism by which Them1 deficiency protects against insulin resistance and lipid deposition. Taken together, these data suggest that Them1 functions to decrease energy consumption and conserve calories. In the setting of nutritional excess, the overproduction of free fatty acids by Them1 provokes insulin resistance that is associated with inflammation and endoplasmic reticulum stress.

Lipotoxicity and cardiac dysfunction in mammals and Drosophila

The lipotoxic effects of obesity are important contributing factors in cancer, diabetes, and cardiovascular disease (CVD), but the genetic mechanisms, by which lipotoxicity influences the initiation and progression of CVD are poorly understood. Hearts, of obese and diabetic individuals, exhibit several phenotypes in common, including ventricular remodeling, prolonged QT intervals, enhanced frequency of diastolic and/or systolic dysfunction, and decreased fractional shortening. High systemic lipid concentrations are thought to be the leading cause of lipid-related CVD in obese or diabetic individuals. However, an alternative possibility is that obesity leads to cardiac-specific steatosis, in which lipids and their metabolites accumulate within the myocardial cells themselves and thereby disrupt normal cardiovascular function. Drosophila has recently emerged as an excellent model to study the fundamental genetic mechanisms of metabolic control, as well as their relationship to heart function. Two recent studies of genetic and diet-induced cardiac lipotoxicity illustrate this. One study found that alterations in genes associated with membrane phospholipid metabolism may play a role in the abnormal lipid accumulation associated with cardiomyopathies. The second study showed that Drosophila fed a diet high in saturated fats, developed obesity, dysregulated insulin and glucose homeostasis, and severe cardiac dysfunction. Here, we review the current understanding of the mechanisms that contribute to the detrimental effects of dysregulated lipid metabolism on cardiovascular function. We also discuss how the Drosophila model could help elucidate the basic genetic mechanisms of lipotoxicity- and metabolic syndrome-related cardiomyopathies in mammals.