Skeletal Muscle Lipid Metabolism Research Articles

Molecular Mechanisms Underpinning The Regulation Of Peak Fat Oxidation Rates During Exercise

PURPOSE: The molecular regulation of peak fat oxidation (PFO) during exercise remains poorly characterized. The aim of this study was to examine the relationship between the content of key proteins involved in adipose tissue and skeletal muscle fat metabolism with PFO. METHODS: Thirty-six healthy men and women adults [15 females; mean (SD) age 40 (11) years; V̇O2peak 42.5 (9.5) mL·kg BM-1·min-1; body fat %: 21.8 (8.2) %] completed two incremental exercise tests (separated by 7-28 days) to determine PFO via indirect calorimetry. A DEXA scan and adipose tissue and/or skeletal muscle biopsies were obtained 2-7 days after the second exercise test to determine the protein content of PLIN1, CGI-58, ATGL, HSL, ACSL1, and oestrogen receptor α (ERα) in adipose tissue, and FABPpm, ATGL, ACSL1, CTP1b and ERα in skeletal muscle. Sex comparisons were performed on sub-groups of males and females matched for aerobic capacity relative to fat free mass and classifications of the physical activity level index and fat mass index (n = 14 and 12 for adipose tissue and skeletal muscle comparison sub-groups, respectively). RESULTS: Moderate strength correlations were found between PFO (mg·kg FFM-1·min-1) and the protein content of ATGL [r = 0.41 (0.05 - 0.68), p < 0.05] and CPT1b [r = 0.41 (0.05 - 0.68), p < 0.05] in skeletal muscle. No other statistically significant bivariate correlations were found between PFO and the content of proteins in adipose tissue or skeletal muscle. Females had a greater PFO compared to males when expressed relative to fat-free mass [mean (SD): 7.1 (1.9) and 7.3 (1.7) vs 4.5 (1.3) and 4.8 (1.2) mg·kg FFM-1·min-1 in the adipose tissue and skeletal muscle-sub-groups, respectively, p < 0.05]. No statistically significant sex differences were found in the content of any of the measured proteins involved in lipid metabolism in adipose tissue or skeletal muscle. CONCLUSIONS: The molecular regulation of PFO may primarily lie within skeletal muscle rather than adipose tissue, involving processes relating to intramyocellular triglyceride hydrolysis (ATGL) and mitochondrial fatty acid transport (CPT1b). Future studies should explore alternative molecular mechanisms that may account for sexual dimorphism in exercise fuel metabolism.

High ammonia exposure regulates lipid metabolism in the pig skeletal muscle via mTOR pathway

Ambient ammonia exposure has been known to perturb lipid metabolism in farm animals, but the underlying mechanism is unclear. The current study was conducted to investigate how ambient ammonia exposure influences lipid metabolism in the pig model. Twelve pigs were randomly divided into two groups, either exposed to 0 or 35 mg/m3 atmospheric ammonia for 25 days. Serum ammonia remained unchanged (p > 0.05), but increased serum urea concentration was found (p < 0.05) after ammonia exposure. Ammonia exposure also caused an increased C18:0, C18:2n6c, C18:3n6, C18:3n3, C20:0, C20:2, C20:3n6, C20:3n3, C22:0 concentrations and fat content in the longissimus dorsi muscle (p < 0.05), and also serum total triglyceride (p = 0.0294) and ApoB (p = 0.0061) contents. Analysis of serum free amino acids profile revealed that concentrations of ornithine, tyrosine, asparagine, histidine, phenylalanine, leucine, isoleucine, glutamine and valine were significantly increased in the pigs exposed to 35 mg/m3 ammonia (p < 0.05). RNA-Seq analysis showed that genes encoding enzymes involved in lipid synthesis (FASN, SCD and FADS1) and uptake (LDLR) were up-regulated, whereas genes related to lipolysis (PNPLA4, ANGPTL4 and CEL), transport (CPT1A, CPT1B and CPT2) and β-oxidation (ACADL, ACADVL, UCP2 and UCP3) were down-regulated. Furthermore, exposure to 35 mg/m3 atmospheric ammonia increased expression of mTOR (p = 0.0377) and its downstream P70S6K (p = 0.0139) and p-P70S6K (p = 0.0431), but decreased AMPK (p < 0.0001) and p-AMPK (p = 0.0071) in the longissimus dorsi muscle. In conclusion, high concentration of atmospheric ammonia exposure greatly interferes with amino acid metabolism, resulting in increased BCAAs and aromatic amino acids. The increased BCAAs production can up-regulate lipid synthesis and down-regulate β-oxidation by activating mTOR signaling and inhibiting AMPK signaling.

1878-P: The Role and Potential Mechanism of LncRNA Gm15441 in Skeletal Muscle Glucose and Lipid Metabolism

It has been established that Long noncoding RNAs (lncRNAs) play a pivotal role in regulating systemic glucose and lipid homeostasis. Previously, we identified a insulin-resistance (IR) related lncRNA named Gm15441, which was upregualted in skeletal muscle from db/db mice by RNA-sequencing. Here, we explored the relationship between Gm15441 and skeletal muscle function in vitro and in vivo and the possible mechanism involved in that process. Real-time PCR analyses revealed Gm15441 was abundant in skeletal muscle compared to other metabolic tissues. Additionally, Gm15441 expression was observed upregualted in IR cells (pamitate-treated C2C12 myotubes) and mice (db/db, ob/ob and aged mice). Overexpression of Gm15441 by plasmid transfection in C2C12 myotubes decreased Glut4, p-Akt/Akt and p-Irs1/Irs1 protein levels and attenuated glucose uptake capacity by the 2-NBDG method. Gm15441 overexpression also impaired mitochondrial oxygen consumption and Pgc1α expression. Moreover, adeno-associated viral (AAV) vectors to induce Gm15441 expression in skeletal muscles. Six-week-old male mice were administered with AAV-GFP or AAV-Gm15441 vectors followed with or without high-fat diet (HFD) for 14 weeks. Body weight gain and food intake were not different among the groups, but AAV-Gm15441 mice under HFD showed decreased glucose tolerance and insulin sensitivity. These mice exhibited ectopic lipid accumulation in skeletal muscle by HE staining, although no difference was observed in skeletal muscle weights and serum TG. A global mRNA analysis further indicated a possible regulatory role of Pparα-Pgc1α pathway in Gm15441-mediated dysregulation of glucose-lipid metabolism. Collectively, these findings improve our understanding of lncRNAs involved in skeletal muscle glucose-lipid metabolism and represent potential therapeutic targets to IR and associated metabolic diseases. Key words: lncRNA, Gm15441, skeletal muscle, insulin resistance, Pgc1α. Disclosure L. You: None. Y. Zeng: None. N. Gu: None. C. Ji: None.

Nitrate and Nitrite Treatment Modulate Performance and Available Fuel Sources In Zebrafish Muscle and Liver

Abstract Objectives Treatment with nitrate, but not nitrite, improves exercise performance but the mechanisms responsible are not fully understood. Thus, we tested the hypothesis that nitrate and nitrite treatment alter exercise performance through regulation of genes related to glucose and lipid metabolism in skeletal muscle and liver. Furthermore, we tested the hypothesis that nitrate treatment caused increased abundance and utilization of metabolic fuels in muscle that require less oxygen for energy production. Methods Adult zebrafish fish were exposed to sodium nitrate (606.9 mg NaNO3/L water), sodium nitrite (19.5 mg NaNO2/L of water), or control water for 21 days (n = 9–12/treatment). Liver and muscle gene expression were analyzed by quantitative real-time PCR and liver and muscle metabolomes were assessed by 1H-NMR untargeted metabolomics. Results Nitrite treatment significantly increased carnitine palmitoyl transferase 1b (cpt1b) expression in the liver and significantly decreased acetyl-CoA carboxylase (acaca) expression in skeletal muscle. Nitrate treatment significantly increased expression of peroxisome proliferator activated receptor-γ (pparg) muscle while acaca significantly decreased in skeletal muscle. Nitrate treatment also induced significant increases in metabolic fuels, such as ATP and creatine phosphate, and fuel sources including β-hydroxybutyrate and glycolytic intermediates in rested skeletal muscle. After a graded exercise test, these metabolites decreased in skeletal muscle of nitrate-treated fish while they increased with exercise in the skeletal muscle of control-treated zebrafish. Conclusions Our data are consistent with the hypothesis that nitrate treatment altered lipid and carbohydrate metabolism of zebrafish, in part, through a pparg mediated mechanism in the liver, and may improve exercise performance through utilization of fuel sources that require less oxygen during exercise. In contrast, our data indicate that nitrite may attenuate exercise performance, in part, by promoting dependence on fatty acid oxidation in the liver of zebrafish. These mechanisms may mediate improved exercise tolerance in populations with cardiovascular disease. Funding Sources Celia Strickland and G. Kenneth Austin III Endowment and National Institutes of Health.

Rev-erbαheterozygosity produces a dose-dependent phenotypic advantage in mice.

Numerous mutational studies have demonstrated that circadian clock proteins regulate behavior and metabolism. Nr1d1(Rev-erbα) is a key regulator of circadian gene expression and a pleiotropic regulator of skeletal muscle homeostasis and lipid metabolism. Loss of Rev-erbα expression induces muscular atrophy, high adiposity, and metabolic syndrome in mice. Here we show that, unlike knockout mice, Nr1d1 heterozygous mice are not susceptible to muscular atrophy and in fact paradoxically possess larger myofiber diameters and improved neuromuscular function, compared to wildtype mice. Heterozygous mice lacked dyslipidemia, a characteristic of Nr1d1 knockout mice and displayed increased whole-body fatty-acid oxidation during periods of inactivity (light cycle). Heterozygous mice also exhibited higher rates of glucose uptake when fasted, and had elevated basal rates of gluconeogenesis compared to wildtype and knockout littermates. Rev-erbα ablation suppressed glycolysis and fatty acid-oxidation in white-adipose tissue (WAT), whereas partial Rev-erbα loss, curiously stimulated these processes. Our investigations revealed that Rev-erbα dose-dependently regulates glucose metabolism and fatty acid oxidation in WAT and muscle.

Involvement of ammonia metabolism in the improvement of endurance performance by tea catechins in mice

Blood ammonia increases during exercise, and it has been suggested that this increase is both a central and peripheral fatigue factor. Although green tea catechins (GTCs) are known to improve exercise endurance by enhancing lipid metabolism in skeletal muscle, little is known about the relationship between ammonia metabolism and the endurance-improving effect of GTCs. Here, we examined how ammonia affects endurance capacity and how GTCs affect ammonia metabolism in vivo in mice and how GTCs affect mouse skeletal muscle and liver in vitro. In mice, blood ammonia concentration was significantly negatively correlated with exercise endurance capacity, and hyperammonaemia was found to decrease whole-body fat expenditure and fatty acid oxidation–related gene expression in skeletal muscle. Repeated ingestion of GTCs combined with regular exercise training improved endurance capacity and the expression of urea cycle–related genes in liver. In C2C12 myotubes, hyperammonaemia suppressed mitochondrial respiration; however, pre-incubation with GTCs rescued this suppression. Together, our results demonstrate that hyperammonaemia decreases both mitochondrial respiration in myotubes and whole-body aerobic metabolism. Thus, GTC-mediated increases in ammonia metabolism in liver and resistance to ammonia-induced suppression of mitochondrial respiration in skeletal muscle may underlie the endurance-improving effect of GTCs.

Short-chain fatty acids as potential regulators of skeletal muscle metabolism and function.

A key metabolic activity of the gut microbiota is the fermentation of non-digestible carbohydrate, which generates short-chain fatty acids (SCFAs) as the principal end products. SCFAs are absorbed from the gut lumen and modulate host metabolic responses at different organ sites. Evidence suggests that these organ sites include skeletal muscle, the largest organ in humans, which plays a pivotal role in whole-body energy metabolism. In this Review, we evaluate the evidence indicating that SCFAs mediate metabolic cross-talk between the gut microbiota and skeletal muscle. We discuss the effects of three primary SCFAs (acetate, propionate and butyrate) on lipid, carbohydrate and protein metabolism in skeletal muscle, and we consider the potential mechanisms involved. Furthermore, we highlight the emerging roles of these gut-derived metabolites in skeletal muscle function and exercise capacity, present limitations in current knowledge and provide suggestions for future work.

Genome-Wide Association Study of Body Weight Traits in Chinese Fine-Wool Sheep.

Simple SummaryBody weight traits are economically important in the sheep industry, and it is critical to explore their underlying genetic architecture. Hence, four body weight traits, including birth, weaning, yearling, and adult weights were examined. Through a genome-wide association study on Chinese fine-wool sheep, several candidate single-nucleotide polymorphisms (SNPs) and genes were found potentially associated with the traits of interest. The results of this study may facilitate the potential use of the genes involved in growth and production traits for the genetic improvement of productivity in sheep.Body weight is an important economic trait for sheep and it is vital for their successful production and breeding. Therefore, identifying the genomic regions and biological pathways that contribute to understanding variability in body weight traits is significant for selection purposes. In this study, the genome-wide associations of birth, weaning, yearling, and adult weights of 460 fine-wool sheep were determined using resequencing technology. The results showed that 113 single nucleotide polymorphisms (SNPs) reached the genome-wide significance levels for the four body weight traits and 30 genes were annotated effectively, including AADACL3, VGF, NPC1, and SERPINA12. The genes annotated by these SNPs significantly enriched 78 gene ontology terms and 25 signaling pathways, and were found to mainly participate in skeletal muscle development and lipid metabolism. These genes can be used as candidate genes for body weight in sheep, and provide useful information for the production and genomic selection of Chinese fine-wool sheep.

Exchange protein directly activated by cAMP (Epac) 1 plays an essential role in stress-induced exercise capacity by regulating PGC-1α and fatty acid metabolism in skeletal muscle.

Exchange protein directly activated by cAMP (Epac) mediates cAMP-mediated cell signal independent of protein kinase A (PKA). Mice lacking Epac1 displayed metabolic defect suggesting possible functional involvement of skeletal muscle and exercise capacity. Epac1 was highly expressed, but not Epac 2, in the extensor digitorum longus (EDL) and soleus muscles. The exercise significantly increased protein expression of Epac 1 in EDL and soleus muscle of wild-type (WT) mice. A global proteomics and pathway analyses revealed that Epac 1 deficiency mainly affected "the energy production and utilization" process in the skeletal muscle. We have tested their forced treadmill exercise tolerance. Epac1-/- mice exhibited significantly reduced exercise capacity in the forced treadmill exercise and lower number of type 1 fibers than WT mice. The basal protein level of proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) was reduced in the Epac1-/- mice. Furthermore, increasing expression of PGC-1α by exercise was also significantly attenuated in the skeletal muscle of Epac1-/- mice. The expressions of downstream target genes of PGC-1α, which involved in uptake and oxidation of fatty acids, ERRα and PPARδ, and fatty acid content were lower in muscles of Epac1-/-, suggesting a role of Epac1 in forced treadmill exercise capacity by regulating PGC-1α pathway and lipid metabolism in skeletal muscle. Taken together, Epac1 plays an important role in exercise capacity by regulating PGC-1α and fatty acid metabolism in the skeletal muscle.

Regulation mechanisms of positive cold tolerance in Mongolian sheep

Abstract Mongolian sheep survive well on the Mongolian plateau during tremendously cold winters, but their cold response mechanisms are not well understood. By comparing with Dorper sheep originating from South Africa, we expected to reveal the cold tolerance mechanisms of Mongolian sheep on the basis of transcriptome data, further providing molecular evidence for the targeted breeding of sheep. Based on the mRNA data of RNA-seq, we selected candidate genes among the differentially expressed genes; 7 from adipose tissue, 33 from skeletal muscle, and 10 from the liver. According to enriched KEGG pathways and previous research results, the effects of the above candidate genes mainly involved weakening the synthesis of long-chain fatty acids, raising the adaptive thermogenesis and browning adipogenesis in fat, reducing glucose 6-phosphate, stimulating citrulline generation and enhancing lipid metabolism in skeletal muscle, and postponing cell senescence in the liver. The findings also demonstrate the regulation mechanisms of cold tolerance in different tissues of Mongolian sheep.

Angiotensin-converting enzyme 2 regulates endoplasmic reticulum stress and mitochondrial function to preserve skeletal muscle lipid metabolism

ObjectiveEndoplasmic reticulum (ER) stress and mitochondrial function affected intramuscular fat accumulation. However, there is no clear evident on the effect of the regulation of ER stress and mitochondrial function by Angiotensin-converting enzyme 2 (ACE2) on the prevention of intramuscular fat metabolism. We investigated the effects of ACE2 on ER stress and mitochondrial function in skeletal muscle lipid metabolism.MethodsThe triglyceride (TG) content in skeletal muscle of ACE2 knockout mice and Ad-ACE2-treated db/db mice were detected by assay kits. Meanwhile, the expression of lipogenic genes (ACCα, SREBP-1c, LXRα, CPT-1α, PGC-1α and PPARα), ER stress and mitochondrial function related genes (GRP78, eIF2α, ATF4, BCL-2, and SDH6) were analyzed by RT-PCR. Lipid metabolism, ER stress and mitochondrial function related genes were analyzed by RT-PCR in ACE2-overexpression C2C12 cell. Moreover, the IKKβ/NFκB/IRS-1 pathway was determined using lysate sample from skeletal muscle of ACE2 knockout mice.ResultsACE2 deficiency in vivo is associated with increased lipid accumulation in skeletal muscle. The ACE2 knockout mice displayed an elevated level of ER stress and mitochondrial dysfunctions in skeletal muscle. In contrast, activation of ACE2 can ameliorate ER stress and mitochondrial function, which slightly accompanied by reduced TG content and down-regulated the expression of skeletal muscle lipogenic proteins in the db/db mice. Additionally, ACE2 improved skeletal muscle lipid metabolism and ER stress genes in the C2C12 cells. Mechanistically, endogenous ACE2 improved lipid metabolism through the IKKβ/NFκB/IRS-1 pathway in skeletal muscle.ConclusionsACE2 was first reported to play a notable role on intramuscular fat regulation by improving endoplasmic reticulum and mitochondrial function. This study may provide a strategy for treating insulin resistance in skeletal muscle.

Irradiation impairs mitochondrial function and skeletal muscle oxidative capacity: significance for metabolic complications in cancer survivors

BackgroundMetabolic complications are highly prevalent in cancer survivors treated with irradiation but the underlying mechanisms remain unknown. MethodsChow or high fat-fed C57Bl/6J mice were irradiated (6Gy) before investigating the impact on whole-body or skeletal muscle metabolism and profiling their lipidomic signature. Using a transgenic mouse model (Tg:Pax7-nGFP), we isolated muscle progenitor cells (satellite cells) and characterised their metabolic functions. We recruited childhood cancer survivors, grouped them based on the use of total body irradiation during their treatment and established their lipidomic profile. ResultsIn mice, irradiation delayed body weight gain and impaired fat pads and muscle weights. These changes were associated with impaired whole-body fat oxidation in chow-fed mice and altered ex vivo skeletal muscle fatty acid oxidation, potentially due to a reduction in oxidative fibres and reduced mitochondrial enzyme activity. Irradiation led to fasting hyperglycaemia and impaired glucose uptake in isolated skeletal muscles. Cultured satellite cells from irradiated mice showed decreased fatty acid oxidation and reduced glucose uptake, recapitulating the host metabolic phenotype. Irradiation resulted in a remodelling of lipid species in skeletal muscles, with the extensor digitorum longus muscle being particularly affected. A large number of lipid species were reduced, with several of these species showing a positive correlation with mitochondrial enzymes activity. In cancer survivors exposed to irradiation, we found a similar decrease in systemic levels of most lipid species, and lipid species that increased were positively correlated with insulin resistance (HOMA-IR). ConclusionIrradiation leads to long-term alterations in body composition, and lipid and carbohydrate metabolism in skeletal muscle, and affects muscle progenitor cells. Such changes result in persistent impairment of metabolic functions, providing a new mechanism for the increased prevalence of metabolic diseases reported in irradiated individuals. In this context, changes in the lipidomic signature in response to irradiation could be of diagnostic value.

Unraveling genomic associations with feed efficiency and body weight traits in chickens through an integrative approach

BackgroundFeed efficiency and growth rate have been targets for selection to improve chicken production. The incorporation of genomic tools may help to accelerate selection. We genotyped 529 individuals using a high-density SNP chip (600 K, Affymetrix®) to estimate genomic heritability of performance traits and to identify genomic regions and their positional candidate genes associated with performance traits in a Brazilian F2 Chicken Resource population. Regions exhibiting selection signatures and a SNP dataset from resequencing were integrated with the genomic regions identified using the chip to refine the list of positional candidate genes and identify potential causative mutations.ResultsFeed intake (FI), feed conversion ratio (FC), feed efficiency (FE) and weight gain (WG) exhibited low genomic heritability values (i.e. from 0.0002 to 0.13), while body weight at hatch (BW1), 35 days-of-age (BW35), and 41 days-of-age (BW41) exhibited high genomic heritability values (i.e. from 0.60 to 0.73) in this F2 population. Twenty unique 1-Mb genomic windows were associated with BW1, BW35 or BW41, located on GGA1–4, 6–7, 10, 14, 24, 27 and 28. Thirty-eight positional candidate genes were identified within these windows, and three of them overlapped with selection signature regions. Thirteen predicted deleterious and three high impact sequence SNPs in these QTL regions were annotated in 11 positional candidate genes related to osteogenesis, skeletal muscle development, growth, energy metabolism and lipid metabolism, which may be associated with body weight in chickens.ConclusionsThe use of a high-density SNP array to identify QTL which were integrated with whole genome sequence signatures of selection allowed the identification of candidate genes and candidate causal variants. One novel QTL was detected providing additional information to understand the genetic architecture of body weight traits. We identified QTL for body weight traits, which were also associated with fatness in the same population. Our findings form a basis for further functional studies to elucidate the role of specific genes in regulating body weight and fat deposition in chickens, generating useful information for poultry breeding programs.

Transcript profile of skeletal muscle lipid metabolism genes affected by diet in a piglet model of low birth weight.

Dysregulated skeletal muscle metabolism (DSMM) is associated with increased inter- and intramuscular fat deposition in low birth weight (L) individuals. The mechanisms behind DSMM in L individuals are not completely understood but decreased muscle mass and shifts in lipid and carbohydrate utilisation may contribute. Previously, we observed lower fat oxidation in a porcine model of low birth weight. To elucidate the biological activities underpinning this difference microfluidic arrays were used to assess mRNA associated with lipid metabolism in longissimus dorsi (LD) and semitendinosus (ST) skeletal muscle samples from thirty-six female L and normal birth weight (N) pigs. Plasma samples were collected from a sub-population to measure metabolite concentrations. Following overnight fasting, skeletal muscle and plasma samples were collected and the association with birth weight, diet and age was assessed. Reduced dietary fat was associated with decreased LD intermuscular fat deposition and beta-oxidation associated mRNA, in both birth weight groups. Lipid uptake and intramuscular fat deposition associated mRNA was reduced in only L pigs. Abundance of ST mRNA associated with lipolysis, lipid synthesis and transport increased in both birth weight groups. Lipid uptake associated mRNA reduced in only L pigs. These changes were associated with decreased plasma L glucose and N triacylglycerol. Post-dietary fat reduction, LD mRNA associated with lipid synthesis and inter- and intramuscular fat deposition increased in L, whilst beta-oxidation associated mRNA remains elevated for longer in N. In the ST, mRNA associated with lipolysis and intramuscular fat deposition increased in both birth weight groups, however this increase was more significant in L pigs and associated with reduced beta-oxidation. Analysis of muscle lipid metabolism associated mRNA revealed that profile shifts are a consequence of birth weight. Whilst, many of the adaptions to diet and age appear to be similar in birth weight groups, the magnitude of response and individual changes underpin the previously observed lower fat oxidation in L pigs.

Acetate Affects the Process of Lipid Metabolism in Rabbit Liver, Skeletal Muscle and Adipose Tissue.

Simple SummaryLots of short-chain fatty acids (SCFAs) are produced in the rabbit cecum after dietary fiber fermentation. In addition to supplying energy, SCFAs could regulate lipid metabolism, but the related mechanism is still unknown. In our experiment, we study the effect of acetate (major SCFAs, 70–80%) on rabbit lipid metabolism. The present study found that acetate alters the process of lipid metabolism in rabbit liver, skeletal muscle and adipose tissue, and inferred some signaling pathways related to the process. A mechanism of acetate-regulating lipid metabolism is useful to identify the function in fat metabolism of microbiological products from rabbit and rabbit processes for nutrition metabolism.Short-chain fatty acids (SCFAs) (a microbial fermentation production in the rabbit gut) have an important role in many physiological processes, which may be related to the reduced body fat of rabbits. In the present experiment, we study the function of acetate (a major SCFA in the rabbit gut) on fat metabolism. Ninety rabbits (40 days of age) were randomly divided into three groups: a sham control group (injection of saline for four days); a group experiencing subcutaneous injection of acetate for four days (2 g/kg BM per day, one injection each day, acetate); and a pair-fed sham treatment group. The results show that acetate-inhibited lipid accumulation by promoting lipolysis and fatty acid oxidation and inhibiting fatty acid synthesis. Activated G protein-coupled receptor 41/43, adenosine monophosphate activated protein kinase (AMPK) and extracellular-signal-regulated kinase (ERK) 1/2 signal pathways were likely to participate in the regulation in lipid accumulation of acetate. Acetate reduced hepatic triglyceride content by inhibiting fatty acid synthesis, enhancing fatty acid oxidation and lipid output. Inhibited peroxisome proliferator-activated receptor α (PPARα) and activated AMPK and ERK1/2 signal pathways were related to the process in liver. Acetate reduced intramuscular triglyceride level via increasing fatty acid uptake and fatty acid oxidation. PPARα was associated with the acetate-reduced intracellular fat content.

Resveratrol ameliorates high-fat diet-induced insulin resistance and fatty acid oxidation via ATM-AMPK axis in skeletal muscle.

Resveratrol (RSV) is a polyphenolic phytoalexin that exhibits diverse pharmacological actions, including its effect on the insulin resistance. However, the mechanism through which RSV improves insulin resistance is not fully understood yet. The aim of this study was to determine the mechanism through which RSV ameliorates insulin resistance in skeletal muscle of high-fat diet (HFD)-induced mouse model, as well as palmitic acid (PA) treated L6 cells, with a specific focus on the response of RSV on fatty acid oxidation. Male C57BL6/J mice were randomly divided into three groups: normal diet-fed mice (ND), the high-fat diet-fed mice (HFD), HFD supplemented with RSV (100 mg/kg body weight [BW]/day orally; n = 10). Fasting plasma glucose, insulin, total cholesterol, triglyceride (TG), and free fatty acid levels were determined. The intraperitoneal glucose tolerance test was used to measure blood glucose and area under the curve. The quantitative insulin sensitivity index was calculated to assess insulin resistance. Skeletal muscles were collected for histology study and protein expression measurement. L6 cells were cultured with PA and the glucose concentration in the culture medium, and the intracellular TG levels were tested. RSV, chloroquine, palmitoyltransferase and Ku-55933 were administered to differentiate L6 cells. The HFD fed mice showed increased BW, hyperglycemia, and hyperlipidemia. The expressions of ataxia telangiectasia mutated (ATM), 5' adenosine monophosphate-activated protein kinase (AMPK), carnitine palmitoyltransferase 1, cytochrome oxidase subunit IV protein were significantly decreased in the skeletal muscles of HFD fed mice and PA-treated L6 cells. All these effects induced by HFD and PA were reversed by RSV treatment. ATM is a key factor to improve HFD-induced lipid metabolism and insulin resistance in skeletal muscles. The effects of RSV on ameliorating HFD-induced abnormal lipid metabolism and insulin resistance mediated through ATM-AMPK pathway may due to its improvement in fatty acid oxidation efficiency and sequential reduction in ROS production in skeletal muscle. These results provide important theoretical evidence for the application of RSV in the prevention and treatment of diabetes mellitus and related metabolic diseases.

Dysferlin deficiency alters lipid metabolism and remodels the skeletal muscle lipidome in mice

Defects in the gene coding for dysferlin, a membrane-associated protein, affect many tissues, including skeletal muscles, with a resultant myopathy called dysferlinopathy. Dysferlinopathy manifests postgrowth with a progressive loss of skeletal muscle function, early intramyocellular lipid accumulation, and a striking later replacement of selective muscles by adipocytes. To better understand the changes underpinning this disease, we assessed whole-body energy homeostasis, skeletal muscle fatty acid metabolism, lipolysis in adipose tissue, and the skeletal muscle lipidome using young adult dysferlin-deficient male BLAJ mice and age-matched C57Bl/6J WT mice. BLAJ mice had increased lean mass and reduced fat mass associated with increased physical activity and increased adipose tissue lipolysis. Skeletal muscle fatty acid metabolism was remodeled in BLAJ mice, characterized by a partitioning of fatty acids toward storage rather than oxidation. Lipidomic analysis identified marked changes in almost all lipid classes examined in the skeletal muscle of BLAJ mice, including sphingolipids, phospholipids, cholesterol, and most glycerolipids but, surprisingly, not triacylglycerol. These observations indicate that an early manifestation of dysferlin deficiency is the reprogramming of skeletal muscle and adipose tissue lipid metabolism, which is likely to contribute to the progressive adverse histopathology in dysferlinopathies.

Aerobic training induces differential expression of genes involved in lipid metabolism in skeletal muscle and white adipose tissues

Aerobic training induces adaptive responses in skeletal muscles and white adipose tissues, thus facilitating lipid utilization as energy substrates during a physical exercise session. However, the effects of training on cytokines levels and on transcription factors involved in lipid metabolism in muscle and different white adipose depots are still unclear; therefore, these were the aims of the present study. Nineteen adult male Wistar rats were randomly assigned to a trained group or a control, non-trained group. The 10-week training protocol consisted of running on a treadmill, during 1 hour per day, 5 days per week, at 75% of maximum aerobic speed. As expected, trained rats improved their aerobic performance and had augmented citrate synthase activity in the soleus, while the control rats did not. Although body weight was not different between groups, the adiposity index and white adipose depots (ie, epididymal and retroperitoneal) were reduced in trained rats. Training reduced serum concentration of insulin, but failed to change serum concentrations of glucose, triacylglycerol, total cholesterol, and nonesterified fatty acids. Training increased sterol regulatory element-binding protein-1c expression in the gastrocnemius and epididymal adipose tissue, and reduced peroxisome proliferator-activated receptor γ (PPARγ) expression in most of the tissues analyzed. The expression of PPARα and carnitine palmitoyltransferase 1 increased in the gastrocnemius and mesenteric adipose tissue but reduced in epididymal adipose tissue. Triacylglycerol content and tribbles 3 expression reduced in the gastrocnemius of trained rats. Tumor necrosis factor-α and interleukin-6 were increased in all adipose depots evaluated. Collectively, our data indicate that the 10-week aerobic training changed gene expression to improve muscle oxidative metabolism and facilitate lipid degradation in adipose tissues. Our data also highlight the existence of adaptive responses that are distinct between the skeletal muscle and white adipose tissue and between different adipose depots.

Regulation of lipid metabolism in skeletal muscle by IDOL

Regulation of lipid metabolism in skeletal muscle by IDOL

SUN-LB006 Skeletal Muscle Krüppel-Like Factor 15 and PPARd Cooperate to Regulate Skeletal Muscle Lipid Metabolism

Skeletal muscle lipid metabolism significantly modulates systemic metabolic status; unsurprisingly, aberrant skeletal muscle nutrient handling is closely associated with metabolic diseases. The mechanisms underlying skeletal muscle regulation of lipid metabolism remain to be fully elucidated. Previous studies have shown that mice deficient in nuclear receptor PPARδ suffer from deranged skeletal muscle lipid handling; a similar phenotype is observed in mice deficient in the transcription factor Krüppel-like factor 15 (KLF15). Preliminary data support the existence of KLF15-PPARδ cooperativity in regulating skeletal muscle lipid metabolism, and thus we sought to 1) define the metabolic role of skeletal muscle specific KLF15; and 2) elucidate the molecular basis of KLF15-PPARδ interaction and impact on skeletal muscle lipid metabolism. We generated a skeletal muscle specific KLF15 knockout (K15-SKO) mouse and characterized the metabolic phenotype of this animal. K15-SKO mice have increased body weight and fat mass, elevated circulating free-fatty acids and triglyceride, insulin insensitivity, and glucose intolerance compared to controls. Importantly, K15-SKO mice demonstrated decreased skeletal muscle expression of a number of lipid flux genes, many of which are targets of PPARδ. To determine the necessity of KLF15 for PPARδ-mediated gene expression, we depleted KLF15 in C2C12 cells and looked at a number of PPARδ targets. The expression levels of Fatp1, Cpt1b, and Scl25a20 were attenuated - this response was unchanged in the presence or absence of GW501516 (GW), a PPARδ agonist. We used Seahorse cell metabolism analyzer to assess fatty acid oxidation and observed that knockdown of KLF15 reduces GW induction of palmitate oxygen consumption rates. We conducted co-transfection studies and determined that KLF15 and PPARδ act synergistically on the Fatp1 promoter. Co-immunoprecipitation studies confirmed physical interaction between KLF15 and PPARδ. Finally, control and K15-SKO mice were gavaged with GW for 10 days, and K15-SKO animals demonstrated attenuated induction of a number of PPARδ targets in skeletal muscle. Taken together, these data suggest that skeletal muscle specific KLF15 is critical in the regulation of lipid handling and necessary for optimal PPARδ-mediated regulation of skeletal muscle lipid metabolism.