Skeletal Muscle Resistance Research Articles

Endogenous Acetylcholine Limits α1‐Adrenergic Vasoconstriction During Exercise in Humans

Sympathetic vasoconstriction is markedly attenuated within the vasculature of contracting compared to quiescent skeletal muscle (“functional sympatholysis”), yet the mechanisms that modulate post‐junctional α‐adrenergic signaling in active muscle remain poorly understood. In rodents, application of the endothelium‐dependent agonist acetylcholine (ACh) blunts sympathetic vasoconstriction in skeletal muscle resistance vessels, and we have recently demonstrated that intra‐arterial administration of ACh enhances functional sympatholysis in humans. Thus, we sought to determine whether endogenous ACh is involved in this integrative control of vascular tone during exercise. In 16 healthy volunteers (8 F, 8 M; 26 ± 1 yrs), we assessed the vasoconstrictor response to intra‐arterial phenylephrine (PE; α1 agonist) at rest and during rhythmic handgrip exercise under control conditions and during local inhibition of muscarinic ACh receptors via intra‐arterial atropine. We measured forearm blood flow (FBF; Doppler ultrasound) and calculated vascular conductance (FVC) at rest and during 4 min of dynamic handgrip contractions at two exercise intensities (15 and 25% of maximal voluntary contraction, MVC). Adenosine was infused during the resting trials to elevate FBF to levels similar to those observed during exercise. After the vascular response to exercise or adenosine reached steady‐state, we assessed vasoconstriction during infusion of PE for 2 min. The magnitude of sympatholysis was calculated as the percent reduction in vasoconstriction during exercise compared to rest. As expected, the vasoconstrictor response (Δ FVC) to PE was attenuated during exercise at 15 (−20 ± 2%) and 25% MVC (−12 ± 2%) compared with rest (−40 ± 4%; P < 0.05), indicating functional sympatholysis. Atropine did not affect sensitivity to PE at rest (−38 ± 4%; P = 0.60). During 15% MVC exercise, atropine augmented vasoconstriction to PE in women (−25 ± 2 vs. −19 ± 2%, P < 0.05), whereas it did not affect the response in men (−22 ± 2 vs. −22 ± 3%, P = 0.88). During higher intensity exercise, atropine reduced the magnitude of functional sympatholysis by ~50% such that a greater degree of vasoconstriction occurred in response to PE in both women (−22 ± 4 vs. −11 ± 4%, P < 0.05) and men (−22 ± 2 vs. −12 ± 2%, P < 0.05) compared to control conditions. These findings demonstrate that inhibition of muscarinic receptors reduces the ability of contracting muscle to limit sympathetic vasoconstriction in an intensity‐ and sex‐dependent manner, supporting a novel, physiological role for ACh in functional sympatholysis in humans.Support or Funding InformationSupported by HL119337 & HL142240This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Actions of chronic physiological 3-hydroxyisobuterate treatment on mitochondrial metabolism and insulin signaling in myotubes

Branched-chain amino acids (BCAAs) are essential in the diet and may provide benefit for those who partake in regular physical activity and resistance training, yet circulating BCAAs have been repeatedly shown to correlate with severity of insulin resistance in obese/diseased populations. Recently, the valine catabolite 3-hydroxyisobuterate (3HIB) was shown to promote insulin resistance in skeletal muscle by increasing lipid content in vivo. The purpose of this study was to investigate the mechanistic effects of 3HIB on skeletal muscle insulin signaling, metabolism, and related gene expression in vitro. Given these previous observations, we hypothesized that 3HIB would depress skeletal muscle metabolism and insulin sensitivity. C2C12 myotubes were treated with 3HIB for up to 48 hours using both physiological (25-100 μmol/L) and supraphysiological (5 mmol/L) concentrations. Metabolic gene expression was measured via quantitative real-time polymerase chain reaction, mitochondrial metabolism was measured via O2 consumption, and glycolytic metabolism was quantified using extracellular acidification rate. Western blot was used to assess insulin sensitivity following insulin stimulation (indicated by phospho-AKT expression). 3HIB did not alter expressional indicators of mitochondrial biogenesis, glycolysis, BCAA catabolism, or lipogenesis. Chronic physiological 3HIB treatment significantly increased peak oxygen consumption, whereas supraphysiological 3HIB treatment suppressed basal and peak mitochondrial and glycolytic metabolism. Both physiological and supraphysiological 3HIB reduced pAkt expression during insulin stimulation. These findings suggest that 3HIB may reduce muscle insulin sensitivity in cultured myotubes, supporting a potentially causal role of 3HIB in the development of insulin resistance in highly metabolic cell types.

When bigger isn't better: understanding the anabolic resistance of obese skeletal muscle.

When bigger isn't better: understanding the anabolic resistance of obese skeletal muscle.

Rapid changes in the microvascular circulation of skeletal muscle impair insulin delivery during sepsis.

Sepsis costs the healthcare system $23 billion annually and has a mortality rate between 10 and 40%. An early indication of sepsis is the onset of hyperglycemia, which is the result of sepsis-induced insulin resistance in skeletal muscle. Previous investigations have focused on events in the myocyte (e.g., insulin signaling and glucose transport and subsequent metabolism) as the causes for this insulin-resistant state. However, the delivery of insulin to the skeletal muscle is also an important determinant of insulin action. Skeletal muscle microvascular blood flow, which delivers the insulin to the muscle, is known to be decreased during sepsis. Here we test whether the reduced capillary blood flow to skeletal muscle belies the sepsis-induced insulin resistance by reducing insulin delivery to the myocyte. We hypothesize that decreased capillary flow and consequent decrease in insulin delivery is an early event that precedes gross cardiovascular alterations seen with sepsis. This hypothesis was examined in mice treated with either lipopolysaccharide (LPS) or polymicrobial sepsis followed by intravital microscopy of the skeletal muscle microcirculation. We calculated insulin delivery to the myocyte using two independent methods and found that LPS and sepsis rapidly reduce insulin delivery to the skeletal muscle by ~50%; this was driven by decreases in capillary flow velocity and the number of perfused capillaries. Furthermore, the changes in skeletal muscle microcirculation occur before changes in both cardiac output and arterial blood pressure. These data suggest that a rapid reduction in skeletal muscle insulin delivery contributes to the induction of insulin resistance during sepsis.

Fu Brick Tea Alleviates Chronic Kidney Disease of Rats with High Fat Diet Consumption through Attenuating Insulin Resistance in Skeletal Muscle.

Fu brick tea is a unique post-fermented dark tea product which undergoes controlled fermentation by "golden flower" fungus Eurotium cristatum. This study examined the effects of Fu brick tea aqueous extract (FTE) to alleviate insulin resistance, chronic kidney disease (CKD), and its regulatory mechanism in high fat diet (HFD)-induced obese rats. Sixteen-week administration of FTE at 400 mg/kg bw in rats significantly antagonized HFD-induced insulin resistance and CKD with elevations in serum leptin, TC, TG, LDL-C, blood urea nitrogen, uric acid, and creatinine levels, respectively ( p < 0.05). FTE treatment decreased the glomerular area, the thickness of basement membrane of renal tubules, and kidney fibrosis in HFD-fed rats. FTE alleviated insulin resistance through down-regulation of SIRP-α expression and activation of the insulin signaling Akt/GLUT4, FoxO1, and mTOR/S6K1 pathways in skeletal muscle. Furthermore, FTE prevented the HFD-caused kidney dysfunction and lipid or collagen accumulation, which was accompanied by the inhibition of GSK-3β phosphorylation and the action of PI3K/Akt and nuclear accumulation of Nrf2 in kidney. These results indicated that FTE alleviated insulin resistance and CKD through modulating insulin signal transduction cascades in skeletal muscle and enhanced the Nrf2 expression in kidney.

Lifelong physical activity is associated with promoter hypomethylation of genes involved in metabolism, myogenesis, contractile properties and oxidative stress resistance in aged human skeletal muscle

Lifelong regular physical activity is associated with reduced risk of type 2 diabetes (T2D), maintenance of muscle mass and increased metabolic capacity. However, little is known about epigenetic mechanisms that might contribute to these beneficial effects in aged individuals. We investigated the effect of lifelong physical activity on global DNA methylation patterns in skeletal muscle of healthy aged men, who had either performed regular exercise or remained sedentary their entire lives (average age 62 years). DNA methylation was significantly lower in 714 promoters of the physically active than inactive men while methylation of introns, exons and CpG islands was similar in the two groups. Promoters for genes encoding critical insulin-responsive enzymes in glycogen metabolism, glycolysis and TCA cycle were hypomethylated in active relative to inactive men. Hypomethylation was also found in promoters of myosin light chain, dystrophin, actin polymerization, PAK regulatory genes and oxidative stress response genes. A cluster of genes regulated by GSK3β-TCF7L2 also displayed promoter hypomethylation. Together, our results suggest that lifelong physical activity is associated with DNA methylation patterns that potentially allow for increased insulin sensitivity and a higher expression of genes in energy metabolism, myogenesis, contractile properties and oxidative stress resistance in skeletal muscle of aged individuals.

Aspalathin-Enriched Green Rooibos Extract Reduces Hepatic Insulin Resistance by Modulating PI3K/AKT and AMPK Pathways.

We previously demonstrated that an aspalathin-enriched green rooibos extract (GRE) reversed palmitate-induced insulin resistance in C2C12 skeletal muscle and 3T3-L1 fat cells by modulating key effectors of insulin signalling such as phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/AKT) and AMP-activated protein kinase (AMPK). However, the effect of GRE on hepatic insulin resistance is unknown. The effects of GRE on lipid-induced hepatic insulin resistance using palmitate-exposed C3A liver cells and obese insulin resistant (OBIR) rats were explored. GRE attenuated the palmitate-induced impairment of glucose and lipid metabolism in treated C3A cells and improved insulin sensitivity in OBIR rats. Mechanistically, GRE treatment significantly increased PI3K/AKT and AMPK phosphorylation while concurrently enhancing glucose transporter 2 expression. These findings were further supported by marked stimulation of genes involved in glucose metabolism, such as insulin receptor (Insr) and insulin receptor substrate 1 and 2 (Irs1 and Irs2), as well as those involved in lipid metabolism, including Forkhead box protein O1 (FOXO1) and carnitine palmitoyl transferase 1 (CPT1) following GRE treatment. GRE showed a strong potential to ameliorate hepatic insulin resistance by improving insulin sensitivity through the regulation of PI3K/AKT, FOXO1 and AMPK-mediated pathways.

Fatty acid type-specific regulation of SIRT1 does not affect insulin sensitivity in human skeletal muscle.

The nicotinamide adenine dinucleotide-dependent deacetylase, sirtuin (SIRT)1, in skeletal muscle is reduced in insulin-resistant states. However, whether this is an initial mechanism responsible for mediating insulin resistance in human skeletal muscle remains to be investigated. Also, SIRT1 acts as a mitochondrial gene transcriptional regulator and is induced by a short-term, high-fat diet (HFD) in human skeletal muscle. Whether saturated or unsaturated fatty acids (FAs) in the diet are important for this is unknown. We subjected 17 healthy, young men to a eucaloric control (Con) diet and 1 of 2 hypercaloric [+75% energy (E%)] HFDs for 3 d enriched in either saturated (Sat) FA (79 E% fat; Sat) or unsaturated FA (78 E% fat; Unsat). After Sat, SIRT1 protein content and activity in skeletal muscle increased ( P < 0.05; ∼40%) while remaining unchanged after Unsat. Whole-body insulin sensitivity and insulin-stimulated leg glucose uptake were reduced ( P < 0.01; ∼20%) to a similar extent compared to Con after both HFDs. We demonstrate a novel FA type-dependent regulation of SIRT1 protein in human skeletal muscle. Moreover, regulation of SIRT1 does not seem to be an initiating factor responsible for mediating insulin resistance in human skeletal muscle.-Fritzen, A. M., Lundsgaard, A.-M., Jeppesen, J. F., Sjøberg, K. A., Høeg, L. D., Deleuran, H. H., Wojtaszewski, J. F. P., Richter, E. A., Kiens, B. Fatty acid type-specific regulation of SIRT1 does not affect insulin sensitivity in human skeletal muscle.

Coenzyme Q10 protects against burn-induced mitochondrial dysfunction and impaired insulin signaling in mouse skeletal muscle.

Mitochondrial dysfunction is associated with metabolic alterations in various disease states, including major trauma (e.g., burn injury). Metabolic derangements, including muscle insulin resistance and hyperlactatemia, are a clinically significant complication of major trauma. Coenzyme Q10 (CoQ10) is an essential cofactor for mitochondrial electron transport, and its reduced form acts as a lipophilic antioxidant. Here, we report that burn injury induces impaired muscle insulin signaling, hyperlactatemia, mitochondrial dysfunction (as indicated by suppressed mitochondrial oxygen consumption rates), morphological alterations of the mitochondria (e. g., enlargement, and loss of cristae structure), mitochondrial oxidative stress, and disruption of mitochondrial integrity (as reflected by increased mitochondrial DNA levels in the cytosol and circulation). All of these alterations were significantly alleviated by CoQ10 treatment compared with vehicle alone. These findings indicate that CoQ10 treatment is efficacious in protecting against mitochondrial dysfunction and insulin resistance in skeletal muscle of burned mice. Our data highlight CoQ10 as a potential new strategy to prevent mitochondrial damage and metabolic dysfunction in burn patients.

Mechanisms Involved in Glycemic Control Promoted by Exercise in Diabetics.

Diabetes mellitus is a metabolic disease characterized by high glycemic levels for long periods. This disease has a high prevalence in the world population, being currently observed an increase in its incidence. This fact is mainly due to the sedentary lifestyle and hypercaloric diets. Non-pharmacological interventions for glycemic control include exercise, which promotes changes in skeletal muscle and adipocytes. Thus, increased glucose uptake by skeletal muscle and decreased insulin resistance through modulating adipocytes are the main factors that improve glycemic control against diabetes. It was sought to elucidate mechanisms involved in the improvement of glycemic control in diabetics in front of the exercise.

6-Gingerol Improves Ectopic Lipid Accumulation, Mitochondrial Dysfunction, and Insulin Resistance in Skeletal Muscle of Ageing Rats: Dual Stimulation of the AMPK/PGC-1α Signaling Pathway via Plasma Adiponectin and Muscular AdipoR1.

This study investigates the dual actions of 6-gingerol in stimulating both plasma adiponectin and muscular adiponectin receptor signaling in naturally ageing rats. Twenty-two-month-old male SD rats were treated with 6-gingerol (0.2 mgkg-1 , once daily) for 7 weeks. 6-Gingerol can attenuate age-associated high plasma triglyceride, glucose, and insulin concentrations under fasting conditions as well as suppress the increase in the HOMA-IR index and inhibit the decrease of muscular p-Akt/Akt protein in ageing rats, which indicates an improvement of systemic and muscular insulin sensitivity. Accompanying these changes, treatment with 6-gingerol attenuates excessive triglyceride accumulation, enhances mitochondrial function, and promotes a transition from a fast- to slow-fiber type and muscle oxidative metabolism in the red gastrocnemius of ageing rats. More importantly, 6-gingerol not only increases the plasma and adipose tissue adiponectin concentrations, but also elevates muscular AdipoR1 expression and activates downstream AMPK phosphorylation as well as upregulates PGC-1α in vivo and in vitro. 6-Gingerol may improve ectopic lipid accumulation, mitochondrial dysfunction, and insulin resistance in skeletal muscle of ageing rats. These effects rely, at least in part, on the elevated plasma adiponectin concentration and muscle AdipoR1 level to dually activate the AMPK/PGC-1α signaling pathway.

Fuzhu jiangtang granules combined with metformin reduces insulin resistance in skeletal muscle of diabetic rats via PI3K/Akt signaling

Context: Fuzhu Jiangtang Granules (FJG) are a traditional Chinese used in the treatment of diabetes mellitus. However, the antidiabetic mechanism of FJG is not clear.Objective: This study evaluates and determines the antidiabetic mechanism of FJG using a Zucker diabetic fatty (ZDF) rat model.Materials and methods: ZDF (fa/fa) rats were divided into four groups (n = 6): diabetes mellitus (DM), metformin (Met, 0.134 g/kg b.w./day), FJG (0.64 g/kg b.w./day), and combination (Com, 0.134 g/kg b.w./day of Met and 0.64 g/kg b.w./day of FJG). Six ZDF (fa/+) rats served as a normal control. After 6 weeks, biochemical parameters gene and protein expression were detected.Results: The FBG, bodyweight, triglyceride (TG), total cholesterol (TC), free fatty acid (FFA), insulin levels, and HOMA-IR were lower in the FJG than in the DM group (p < 0.05, p < 0.01). In an oral glucose tolerance test, the AUC in the FJG group was significantly lower (p < 0.01). The levels of superoxide dismutase and catalase were higher in the FJG than in the DM group (p < 0.01); the malondialdehyde content and TNF-α were significantly decreased in the FJG group (p < 0.01). FJG increased the mRNA expression of IR and GLUT4 significantly (p < 0.05, p < 0.01). The protein levels of IR, p-IRS1 tyr989, m-PI3Kp85, p-Akt and GLUT4 were increased in the FJG (p < 0.05, p < 0.01), but the protein levels of p-IRS1 ser1101/612/307 were significantly decreased in the JG group (p < 0.01).Discussion and conclusions: The antidiabetic mechanism of FJG may be related to regulation of the insulin-signaling pathway in skeletal muscle. These aspects require further research.

Reduced physical activity in young and older adults: metabolic and musculoskeletal implications.

Background:Although the health benefits of regular physical activity and exercise are well established and have been incorporated into national public health recommendations, there is a relative lack of understanding pertaining to the harmful effects of physical inactivity. Experimental paradigms including complete immobilization and bed rest are not physiologically representative of sedentary living. A useful ‘real-world’ approach to contextualize the physiology of societal downward shifts in physical activity patterns is that of short-term daily step reduction.Results:Step-reduction studies have largely focused on musculoskeletal and metabolic health parameters, providing relevant disease models for metabolic syndrome, type 2 diabetes (T2D), nonalcoholic fatty liver disease (NAFLD), sarcopenia and osteopenia/osteoporosis. In untrained individuals, even a short-term reduction in physical activity has a significant impact on skeletal muscle protein and carbohydrate metabolism, causing anabolic resistance and peripheral insulin resistance, respectively. From a metabolic perspective, short-term inactivity-induced peripheral insulin resistance in skeletal muscle and adipose tissue, with consequent liver triglyceride accumulation, leads to hepatic insulin resistance and a characteristic dyslipidaemia. Concomitantly, various inactivity-related factors contribute to a decline in function; a reduction in cardiorespiratory fitness, muscle mass and muscle strength.Conclusions:Physical inactivity maybe particularly deleterious in certain patient populations, such as those at high risk of T2D or in the elderly, considering concomitant sarcopenia or osteoporosis. The effects of short-term physical inactivity (with step reduction) are reversible on resumption of habitual physical activity in younger people, but less so in older adults. Nutritional interventions and resistance training offer potential strategies to prevent these deleterious metabolic and musculoskeletal effects.Impact:Individuals at high risk of/with cardiometabolic disease and older adults may be more prone to these acute periods of inactivity due to acute illness or hospitalization. Understanding the risks is paramount to implementing countermeasures.

Increase in the constrictor effects of Rho-kinase in skeletal muscle and coronary arteries of rats with chronic hypothyroidism

Aim. The deficit of thyroid function is known to be accompanied by an increase in the overall peripheral vascular resistance. This work tested the hypothesis that long-term hypothyroidism leads to an increase in the vasoconstrictor effect of Rho-kinase in skeletal muscle and heart resistance arteries of adult rats.Materials and methods.Male Wistar rats consumed the antithyroid drug propylthiouracil (PTU) in drinking water (0.025%), starting at 10 weeks of age. The rats of the control group received PTU-free water. After 14 weeks, the contractile responses of the gastrocnemius muscle arteries (to the α1-adrenoceptor agonist methoxamine) and the septal coronary artery (to the thromboxane A2 receptor agonist U46619) were isometrically recorded. The contribution of the Rho-kinase to the arterial contractile responses was assessed using inhibitor Y27632 (3 μM).Results.The consumption of propylthiouracil was accompanied by a marked decrease of thyroid hormone concentrations and an increase in total cholesterol serum level as well as a decrease in body weight. Maximal contractile responses of studied arteries were also reduced in hypothyroid rats. However, basal tone and reactivity to the moderate concentrations of agonists in arteries of hypothyroid rats were increased compared to control animals. Y27632 significantly weakened the contractile responses of the arteries and negated the differences between the two groups of rats.Conclusion.Chronic hypothyroidism leads to an increase in the activity of the Rho-kinase signaling pathway in the arteries of the gastrocnemius muscle and heart, which results in the increase of the spontaneous tone of the arteries and their reactivity to agonists.

The diabetic phenotype is preserved in myotubes established from type 2 diabetic subjects: a critical appraisal.

Cultured human myotubes offer a unique model to distinguish between primary and environmental factors in the aetiology of insulin resistance in human skeletal muscle. The objective of this review was to summarize our and other group studies on insulin resistance in human myotubes established from lean, obese and type 2 diabetes (T2D) subjects. Overall, studies of human myotubes established from lean, obese and T2D subjects clearly show that part of the diabetic phenotype observed invivo is preserved in diabetic myotubes. Diabetic myotubes express a primary coordinated impairment of lipid oxidation, oxidative phosphorylation (OXPHOS) and insulin-stimulated glucose metabolism. Currently, both the responsible molecular mechanisms as well as the extent to which these alterations depend on genetic and/or epigenetic alterations have yet to be identified. Based on the data, it is hypothesized that the impaired insulin-mediated glucose metabolism, impaired OXPHOS and reduced lipid oxidation observed in diabetic myotubes are caused by the reduced peroxisome proliferator-activated receptor gamma coactivator-1α (PGC1α) expression.

Cytosolic lipid excess-induced mitochondrial dysfunction is the cause or effect of high fat diet-induced skeletal muscle insulin resistance: a molecular insight.

Mitochondria play a central role in the energy homeostasis in eukaryotic cells by generating ATP via oxidative metabolism of nutrients. Excess lipid accumulation and impairments in mitochondrial function have been considered as putative mechanisms for the pathogenesis of skeletal muscle insulin resistance. Accumulation of lipids in tissues occurs due to either excessive fatty acid uptake, decreased fatty acid utilization or both. Consequently, elevated levels cytosolic lipid metabolites, triglycerides, diacylglycerol and ceramides have been demonstrated to adversely affect glucose homeostasis. Several recent studies indicate that reduced insulin-stimulated ATP synthesis and reduced expression of mitochondrial enzymes and PPAR-γ coactivator, in high fat feeding (lipid overload) are associated with insulin resistance. Despite the fact, few notable studies suggest mitochondrial dysfunction is prevalent in type 2 diabetes mellitus; it is still not clear whether the defects in mitochondrial function are the cause of insulin resistance or the consequential effects of insulin resistance itself. Thus, there is a growing interest in understanding the intricacies of mitochondrial function and its association with cytosolic lipid excess. This review therefore critically examines the molecular cascades linking cytosolic lipid excess and mitochondrial dysfunction in the pathogenesis of high fat diet-induced insulin resistance in skeletal muscle. The sequential processes following the excess intake of high fat diet in skeletal muscle includes, accumulation of cytosolic fatty acids, increased production of reactive oxygen species, mutations and ageing, and decreased mitochondrial biogenesis. The consequent mitochondrial dysfunction is then leading to decreased β-oxidation, respiratory functions and glycolysis and increased glucolipotoxicity. These events collectively induce the insulin resistance in skeletal muscle.

Modulation of Insulin Resistance and the Adipocyte-Skeletal Muscle Cell Cross-Talk by LCn-3PUFA.

The cross-talk between skeletal muscle and adipose tissue is involved in the development of insulin resistance (IR) in skeletal muscle, leading to the decrease in the anabolic effect of insulin. We investigated if the long chain polyunsaturated n-3 fatty acids (LCn-3PUFA), eicosapentaenoic and docosapentaenoic acids (EPA and DPA, respectively) could (1) regulate the development of IR in 3T3-L1 adipocytes and C2C12 muscle cells and (2) inhibit IR in muscle cells exposed to conditioned media (CM) from insulin-resistant adipocytes. Chronic insulin (CI) treatment of adipocytes and palmitic acid (PAL) exposure of myotubes were used to induce IR in the presence, or not, of LCn-3PUFA. EPA (50 µM) and DPA (10 µM) improved PAL-induced IR in myotubes, but had only a partial effect in adipocytes. CM from adipocytes exposed to CI induced IR in C2C12 myotubes. Although DPA increased the mRNA levels of genes involved in fatty acid (FA) beta-oxidation and insulin signaling in adipocytes, it was not sufficient to reduce the secretion of inflammatory cytokines and prevent the induction of IR in myotubes exposed to adipocyte’s CM. Treatment with DPA was able to increase the release of adiponectin by adipocytes into CM. In conclusion, DPA is able to protect myotubes from PAL-induced IR, but not from IR induced by CM from adipocytes.

Effects of Vaspin on Insulin Resistance in Rats and Underlying Mechanisms

Insulin resistance (IR) is the main pathogenesis of metabolic syndrome and a shared pathophysiological change in conditions such as diabetes mellitus, adiposity, hypertension, and atherosclerosis. Visceral adipose tissue-derived serpin (Vaspin) is a newly discovered adipocytokine with insulin-sensitizing and anti-inflammatory effects. To examine if vaspin can improve insulin resistance in rats fed a high-fat diet via the insulin receptor substrate/phosphatidylinositol 3 kinase/protein kinase B/glucose transport (IRS/PI3K/Akt/Glut) and inhibitory κB alpha/nuclear factor-kappa B (IκBα/NF-κB) signalling pathways, thirty male Sprague-Dawley (SD) rats were randomly divided into three groups: the normal control group (NC group, n = 10), high-fat diet group (HFD group, n = 10) and vaspin intervention group (HFD + vaspin group, n = 10). Results showed that intervention with vaspin significantly decreased fasting blood glucose (FBG) and fasting insulin (FINS) concentrations in HFD − fed rats without significantly affecting body weight or triglyceride (TG) or total cholesterol (TC) levels. The areas under the intraperitoneal glucose tolerance test (IPGTT) and the insulin tolerance test (ITT) curves were significantly decreased in HFD + vaspin group compared with the HFD group, and the glucose infusion rate (GIR) showed the same trends. Western blot, real-time polymerase chain reaction (RT-PCR) and immunofluorescence staining showed that vaspin could improve insulin resistance in liver, skeletal muscle and adipose tissue by activating the IRS/PI3K/Akt/Glut signalling pathway and inhibiting the IκBα/NF-κB signalling pathway.

METRNL attenuates lipid-induced inflammation and insulin resistance via AMPK or PPAR\u03b4-dependent pathways in skeletal muscle of mice

Physical activity has many beneficial effects on metabolic disorders, such as obesity, insulin resistance, and diabetes. Meteorin-like protein (METRNL), a novel secreted protein homologous to the neurotrophin Metrn, is induced after exercise in the skeletal muscle. Herein, we investigated the effects of METRNL on lipid-mediated inflammation and insulin resistance in skeletal muscle via AMP-activated protein kinase (AMPK) or peroxisome proliferator-activated receptor δ (PPARδ). Treatment with METRNL suppressed inflammatory markers, such as nuclear factor κB (NFκB) nuclear translocation, inhibitory κBα (IκBα) phosphorylation, interleukin-6 (IL-6) expression, and pro-inflammatory cytokines (such as TNFα and MCP-1). METRNL treatment also attenuated the impaired insulin response both in palmitate-treated differentiated C2C12 cells and the skeletal muscle of high-fat diet (HFD)-fed mice. Furthermore, METRNL administration rescued glucose intolerance and reduced HFD-induced body weight gain in mice; however, METRNL did not affect calorie intake. METRNL treatment increased AMPK phosphorylation and PPARδ expression both in differentiated C2C12 cells and mouse skeletal muscle. siRNA-mediated suppression of AMPK and PPARδ abrogated the suppressive effects of METRNL on palmitate-induced inflammation and insulin resistance. Moreover, METRNL augmented the mRNA expression of fatty acid oxidation-associated genes, such as carnitine palmitoyltransferase 1 (CPT1), acyl-CoA oxidase (ACO), and fatty acid binding protein 3 (FABP3). siRNAs for AMPK and PPARδ reversed these changes. In the current study, we report for the first time that METRNL alleviates inflammation and insulin resistance and induces fatty acid oxidation through AMPK or PPARδ-dependent signaling in skeletal muscle.

Abstract 418: Perm1 is a Novel Regulator of Mitochondrial Energetics in Cardiomyocytes

Mitochondrial oxidative metabolism and energy transduction pathways are critical for cardiac function. The expression of genes important for mitochondrial energetics is under the control of members of the peroxisome proliferator-activated receptor coactivator 1 (PGC-1) family and the estrogen-related receptor (ERR) subfamily. Perturbations in PGC-1 and/or ERR activities have been associated with impaired mitochondrial function and the development of heart failure. The mechanisms by which PGC-1 and ERR proteins regulate muscle specific transcriptional programs is not fully understood. P GC-1 and E RR-induced r egulator in m uscle 1 (Perm1) was recently identified in skeletal muscle as a muscle-specific key regulator of mitochondrial energetics. Although overexpression of Perm1 enhances oxidative capacity and fatigue resistance in mouse skeletal muscle, the underlying mechanisms remain to be elucidated. Perm1 is highly expressed in mouse and human hearts, and its expression level was reduced in pressure overload-induced heart failure in mice (49.9 ± 12.1% of sham, n=4, p&lt;0.05) and in patients with heart failure (45.5 ± 12.1% of donors, n=5, p&lt;0.05). Moreover, Perm1 is expressed in both the nucleus and the cytoplasm in primary cultured neonatal rat ventricular myocytes (NRVMs) and phenylephrine-induced cellular hypertrophy led to downregulation of Perm1 in both fractions (56.7 ± 1.7% of control). RNAseq followed by bioinformatic analysis revealed that siRNA-mediated Perm1 knockdown (KD) in NRVMs led to global downregulation of ERRα/PGC1α-target genes involved in oxidative phosphorylation, including the electron transport chain and TCA cycle ( Ndufs8; Ndufb8; Cox5a; Cox6a1; Coq2; Cox5a; Cox8a; Coq10b; Sdhb; Sdhd) . Basal respiration and ATP production rates were significantly reduced in Perm1-KD H9c2 rat ventricular myocyte-derived cells (60.4 ± 4.2% and 35.2 ± 8.8% of control cells that were transfected with scrambled-siRNA, both p&lt;0.05). This study demonstrates a novel role of Perm1 in cardiomyocytes that provides an additional layer of mitochondrial energetics regulation, presumably in an ERRα- and PGC1α-mediated manner, and suggests that downregulation of Perm1 may contribute to mitochondrial impairment during heart failure.