Skeletal Muscle Resistance Research Articles

Daily Remote Ischaemic Preconditioning for Intermittent Claudication: A Sham Controlled Randomised Trial

Remote ischaemic preconditioning (RIPC) is a promising non-invasive strategy in which brief episodes of ischaemia and reperfusion can increase skeletal muscle resistance to ischaemia and improve mobility. This study aimed to determine whether 28 consecutive days of RIPC improves intermittent claudication (IC) symptoms compared with sham intervention. This single centre, parallel, randomised, sham controlled, double blind trial was conducted from January 2022 to April 2023 in outpatient settings. Forty two patients with stable IC Fontaine stage IIa or IIb were randomised to RIPC or sham for 28 days. The prespecified primary outcome was a change in the maximal walking distance (MWD) after 28 days measured with a treadmill test. A > 10% change in MWD was considered clinically significant. Change in intermittent claudication distance (ICD), time to relief from claudication (TRC), and health related quality of life (HRQoL) measured with the VascuQoL-6 questionnaire were the secondary outcomes (ClinicalTrials.gov ID: NCT05084066). Forty one men (RIPC = 23, sham = 18) aged 64.9 ± 7.4 years were analysed. A change of > 10% in MWD occurred in 14 patients in the RIPC group vs. eight patients in the sham group (relative risk 1.37, 95% confidence interval 0.74 - 2.25; p = .35). Changes in ICD, TRC, and HRQoL between the groups were not statistically significant. In this trial, RIPC did not significantly improve MWD, ICD, or TRC compared with treatment with a sham device.

Skeletal muscle from TBC1D4 p.Arg684Ter variant carriers is severely insulin resistant but exhibits normal metabolic responses during exercise.

In the Greenlandic Inuit population, 4% are homozygous carriers of a genetic nonsense TBC1D4 p.Arg684Ter variant leading to loss of the muscle-specific isoform of TBC1D4 and an approximately tenfold increased risk of type 2 diabetes1. Here we show the metabolic consequences of this variant in four female and four male homozygous carriers and matched controls. An extended glucose tolerance test reveals prolonged hyperglycaemia followed by reactive hypoglycaemia in the carriers. Whole-body glucose disposal is impaired during euglycaemic-hyperinsulinaemic clamp conditions and associates with severe insulin resistance in skeletal muscle only. Notably, a marked reduction in muscle glucose transporter GLUT4 and associated proteins is observed. While metabolic regulation during exercise remains normal, the insulin-sensitizing effect of a single exercise bout is compromised. Thus, loss of the muscle-specific isoform of TBC1D4 causes severe skeletal muscle insulin resistance without baseline hyperinsulinaemia. However, physical activity can ameliorate this condition. These observations offer avenues for personalized interventions and targeted preventive strategies.

Skeletal myocyte-specific knockout of Ptpn1 and Ptpn2 enhances inflammatory response in muscle and increases mortality in polymicrobial sepsis

Abstract Background Critically ill patients often suffer from heart and skeletal muscle atrophy and failure (intensive care unit acquired weakness; ICUAW). Inflammation and sepsis are major risk factors for ICUAW. Critically ill patients with sepsis frequently develop insulin resistance that decreases protein synthesis and increases protein degradation in muscle eventually leading to ICUAW. The link between inflammation and insulin resistance is not well understood, but protein tyrosine phosphatases (PTP), that inhibit insulin signaling via insulin receptor (INSR) dephosphorylation as well as inflammation-associated pathways, are implicated. Hypothesis: We hypothesized that PTP1B and TC-PTP mediate inflammation-induced insulin resistance and muscle atrophy in heart and skeletal muscle. Methods and Results qRT-PCR analyses showed that the proinflammatory cytokines tumor necrosis factor (TNF), interleukin (IL)-1β, and IL-6 caused a ~2-fold increase in Ptpn1/PTP1B and Ptpn2/TC-PTP mRNA expression in C2C12 myocytes as well as in neonatal rat ventricular cardiomyocytes. Inhibition of the IL-6/GP130 pathway by siRNA and inhibitors in myocytes in vitro and skeletal muscle specific gp130 knockout mice in vivo attenuated IL-6-induced Ptpn1/PTP1B and Ptpn2/TC-PTP mRNA expression. CLP-induced polymicrobial sepsis was associated with a significant increase in gene expression and protein content of pro-inflammatory cytokines (Tnf, Il1b, Ifng) and leukocyte markers (CD68, CD11c, F4/80) in muscle of skeletal myocyte specific double knockout (Ptpn1+Ptpn2loxP/loxP, MCK cre, dKO) compared to wildtype (Ptpn1+Ptpn2loxP/loxP) mice in sepsis. This also resulted in a lower survival rate of dKO mice in sepsis (42% WT vs. 23% dKO). Immunohistological analyses revealed centralized nuclei, macrophage/monocyte infiltration and enhanced regeneration (Myh3, Pax7, Ki67) in tibialis anterior muscle of septic dKO mice. A strong activation of the NLRP3-inflammasome, as indicated by cleavage of caspase 1, GSDMD, GSDME and caspase 8, indicative for a pronounced inflammation and activated cell death pathways was observed in muscle of septic dKO mice. Conclusion The proinflammatory cytokine IL-6 increases the expression of Ptpn1 and Ptpn2 and enhances overall PTP activity. Selective inhibition of the IL-6R/GP130 signaling pathway by JAK2- and STAT3-inhibition as well as Gp130 deletion in myocytes in vivo attenuates those effects. Muscle-specific deletion of Ptpn1 and Ptpn2 in skeletal muscle leads to increased mortality, enhanced pro-inflammatory response and induced inflammatory, programmed cell death pathways in sepsis. Our data show that Ptpn1 and Ptpn2 play a key anti-inflammatory role in skeletal muscle.

Regulation of Skeletal Muscle Resistance Arteriolar Tone: Temporal Variability in Vascular Responses

Introduction: A full understanding of the integration of the mechanisms of vascular tone regulation requires an interrogation of the temporal behavior of arterioles across vasoactive challenges. Building on previous work, the purpose of the present study was to start to interrogate the temporal nature of arteriolar tone regulation with physiological stimuli. Methods: We determined the response rate of ex vivo proximal and in situ distal resistance arterioles when challenged by one-, two-, and three-parameter combinations of five major physiological stimuli (norepinephrine, intravascular pressure, oxygen, adenosine [metabolism], and intralumenal flow). Predictive machine learning models determined which factors were most influential in controlling the rate of arteriolar responses. Results: Results indicate that vascular response rate is dependent on the intensity of the stimulus used and can be severely hindered by altered environments, caused by application of secondary or tertiary stimuli. Advanced analytics suggest that adrenergic influences were dominant in predicting proximal arteriolar response rate compared to metabolic influences in distal arterioles. Conclusion: These data suggest that the vascular response rate to physiologic stimuli can be strongly influenced by the local environment. Translating how these effects impact vascular networks is imperative for understanding how the microcirculation appropriately perfuses tissue across conditions.

Oxidised phosphatidylcholine induces sarcolemmal ceramide accumulation and insulin resistance in skeletal muscle.

Intracellular ceramide accumulation in specific cellular compartments is a potential mechanism explaining muscle insulin resistance in the pathogenesis of type 2 diabetes. Muscle sarcolemmal ceramide accumulation negatively impacts insulin sensitivity in humans, but the mechanism explaining this localised accumulation is unknown. Previous reports revealed that circulating oxidised LDL is elevated in serum of individuals with obesity and type 2 diabetes. Oxidised phosphatidylcholine, which is present in oxidised LDL, has previously been linked to ceramide pathway activation, and could contribute to localised ceramide accumulation in skeletal muscle. We hypothesised that oxidised phosphatidylcholine inversely correlates with insulin sensitivity in serum, and induces sarcolemmal ceramide accumulation and decreases insulin sensitivity in muscle. We used LC-MS/MS to quantify specific oxidised phosphatidylcholine species in serum from a cross-sectional study of 58 well-characterised individuals spanning the physiological range of insulin sensitivity. We also performed in vitro experiments in rat L6 myotubes interrogating the role of specific oxidised phosphatidylcholine species in promoting sarcolemmal ceramide accumulation, inflammation and insulin resistance in skeletal muscle cells. Human serum oxidised phosphatidylcholine levels are elevated in individuals with obesity and type 2 diabetes, inversely correlated with insulin sensitivity, and positively correlated with sarcolemmal C18:0 ceramide levels in skeletal muscle. Specific oxidised phosphatidylcholine species, particularly 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), increase total ceramide and dihydroceramide and decrease total sphingomyelin in the sarcolemma of L6 myotubes by de novo ceramide synthesis and sphingomyelinase activation. POVPC also increases inflammatory signalling and causes insulin resistance in L6 myotubes. These data suggest that circulating oxidised phosphatidylcholine species promote ceramide accumulation and decrease insulin sensitivity in muscle, help explain localised sphingolipid accumulation and muscle inflammatory response, and highlight oxidised phosphatidylcholine species as potential targets to combat insulin resistance.

Metabolic perturbations associated with hIAPP-induced insulin resistance in skeletal muscles: Implications to the development of type 2 diabetes

The human islet amyloid polypeptide (hIAPP) tends to misfold and self-assemble to form amyloid fibrils, which has been associated with the loss of function and viability of pancreatic β-cells in type 2 diabetes mellitus (T2DM). The role of hIAPP in the development of insulin resistance (a hallmark of T2DM) in skeletal muscles – the major sites for glucose utilization – needs further investigation. Even though, insulin-resistant conditions have been known to stimulate hIAPP aggregation, the events that lead to the development of insulin resistance due to hIAPP aggregation in skeletal muscles remain unidentified. Here, we have attempted to identify metabolic perturbations in L6 myotubes that were exposed to increasing concentrations of recombinant hIAPP for different time durations. It was observed that hIAPP exposure was associated with increased mitochondrial and cellular ROS levels, loss in mitochondrial membrane potential and viability of the myotubes. Metabolomic investigations of hIAPP-treated myotubes revealed significant perturbations in o-phosphocholine, sn-glycero-3-phosphocholine and dimethylamine levels (p < 0.05). Therefore, we anticipate that defects in glycerophospholipid metabolism and the associated oxidative stress and membrane damage may play key roles in the development of insulin resistance due to protein misfolding in skeletal muscles. In summary, the perturbed metabolites and their pathways have not only the potential to be used as early biomarkers to predict the onset of insulin resistance and T2DM but also as therapeutic targets for the effective management of the same.

Glucosamine inhibits myoblast proliferation and differentiation, and stimulates myotube atrophy through distinct signal pathways

Glucosamine (GlcN) is one of the dietary supplements used in the treatment of osteoarthritis. Endogenously, GlcN is synthesized from glucose through the hexosamine pathway. In addition to ameliorating arthritis, several biological functions of GlcN have been reported, including insulin resistance in skeletal muscle. However, the regulatory role of GlcN in skeletal muscle development is not clear. We therefore investigated the effect of GlcN on myoblast proliferation, differentiation, and myotube development and their underlying mechanisms in C2C12 cells. Myoblast proliferation was measured by MTT assay. The expressions of MyoD, myogenin (MyoG), and myosin heavy chain (MyHC) were identified as determinants of myoblast differentiation. Expressions of atrogin-1 and muscle RING-finger protein-1 (MuRF-1) were identified as markers of myotube atrophy. The results show that treatment with GlcN significantly reduced myoblast proliferation and phosphorylation of Stat3 and S6K. These findings suggest that GlcN can inhibit growth of myoblasts through inhibiting phosphorylation of Stat3 and S6K. In addition, GlcN significantly suppressed the expression of MyoD, MyoG, and MyHC, as well as myotube formation. Pretreatment of C2C12 myoblast cells with ER stress inhibitors significantly blocked GlcN-inhibited MyHC expression and myotube formation. It can be concluded that GlcN suppressed myogenic differentiation via a pathway that involved ER stress. Moreover, GlcN decreased myotube diameter and expression of MyHC, as well as increased MuRF-1 in C2C12 myotubes. Meanwhile, GlcN also reduced the expressions of phosphorylated Akt and mTOR were stimulated after GlcN treatment in C2C12 myotubes. Thus, GlcN induced skeletal muscle atrophy by inhibiting the protein synthesis pathway. Chronic GlcN infusion also caused skeletal muscle atrophy in mice. In conclusion, GlcN regulated important stages of skeletal muscle development through different signaling pathways.

Enhanced ECCD36 signaling promotes skeletal muscle insulin resistance in female mice.

Consumption of a Western diet (WD) increases CD36 expression in vascular, hepatic, and skeletal muscle tissues promoting lipid metabolic disorders and insulin resistance. We further examined the role of endothelial cell-specific CD36 (ECCD36) signaling in contributing to skeletal muscle lipid metabolic disorders, insulin resistance, and their underlying molecular mechanisms. Female ECCD36 wild-type (ECCD36+/+) and knock-out (ECCD36-/-) mice, aged 6 wk, were provided with either a WD or a standard chow diet for a duration of 16 wk. ECCD36+/+ WD mice were characterized by elevated fasting plasma glucose and insulin levels, increased homeostatic model assessment for insulin resistance, and glucose intolerance that was blunted in ECCD36-/- mice. Improved insulin sensitivity in ECCD36-/- mice was characterized by increased phosphoinositide 3-kinases/protein kinase B signaling that further augmented glucose transporter type 4 expression and glucose uptake. Meanwhile, 16 wk of WD feeding also increased skeletal muscle free fatty acid (FFA) and lipid accumulation, without any observed changes in plasma FFA levels. These lipid metabolic disorders were blunted in ECCD36-/- mice. Moreover, ECCD36 also mediated in vitro palmitic acid-induced lipid accumulation in cultured ECs, subsequently leading to the release of FFAs into the culture media. Furthermore, consumption of a WD increased FFA oxidation, mitochondrial dysfunction, impaired mitochondrial respiratory, skeletal muscle fiber type transition, and fibrosis. These WD-induced abnormalities were blunted in ECCD36-/- mice. These findings demonstrate that endothelial-specific ECCD36 signaling participates in skeletal muscle FFA uptake, ectopic lipid accumulation, mitochondrial dysfunction, insulin resistance, and associated skeletal muscle dysfunction in diet-induced obesity.NEW & NOTEWORTHY ECCD36 exerts "extra endothelial cell" actions in skeletal muscle insulin resistance. ECCD36 is a major mediator of Western diet-induced lipid metabolic disorders and insulin resistance in skeletal muscle. Mitochondrial dysfunction is associated with diet-induced CD36 activation and related skeletal muscle insulin resistance.

Extract of Phyllanthus emblica L. fruit stimulates basal glucose uptake and ameliorates palmitate-induced insulin resistance through AMPK activation in C2C12 myotubes

BackgroundThe fruit of Phyllanthus emblica L., a traditional medicine in China and India, is used to treat diabetes mellitus. Its water extract (WEPE) has demonstrated hypoglycemic effects in diabetic rats, but its mechanisms on glucose utilization and insulin resistance in skeletal muscle remain unclear. Therefore, this study aims to investigate the effects and underlying mechanisms of WEPE on glucose utilization and insulin resistance using C2C12 myotubes.MethodsEffects of WEPE on glucose uptake, GLUT4 translocation, and AMPK and AKT phosphorylation were investigated in C2C12 myotubes and palmitate-treated myotubes. An AMPK inhibitor and siRNA were used to explore the mechanisms of WEPE. Glucose uptake was determined using a 2-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) amino)-2-deoxyglucose (2-NBDG) uptake assay, and protein expression and GLUT4 translocation were assessed via western blotting.ResultsIn normal myotubes, WEPE significantly stimulated glucose uptake and GLUT4 translocation to the plasma membrane at concentrations of 125 and 250 µg/mL. This was accompanied by an increase in the phosphorylation of AMPK and its downstream targets. However, both compound C and AMPK siRNA blocked the WEPE-induced GLUT4 translocation and glucose uptake. Moreover, pretreatment with STO-609, a calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) inhibitor, inhibited WEPE-induced AMPK phosphorylation and attenuated the WEPE-stimulated glucose uptake and GLUT4 translocation. In myotubes treated with palmitate, WEPE prevented palmitate-induced insulin resistance by enhancing insulin-mediated glucose uptake and AKT phosphorylation. It also restored the insulin-mediated translocation of GLUT4 from cytoplasm to membrane. However, these effects of WEPE on glucose uptake and GLUT4 translocation were blocked by pretreatment with compound C.ConclusionsWEPE significantly stimulated basal glucose uptake though CaMKKβ/AMPK pathway and markedly ameliorated palmitate-induced insulin resistance by activating the AMPK pathway in C2C12 myotubes.

Fucoxanthin Mitigates High-Fat-Induced Lipid Deposition and Insulin Resistance in Skeletal Muscle through Inhibiting PKM1 Activity.

Glucose and lipid metabolism dysregulation in skeletal muscle contributes to the development of metabolic disorders. The efficacy of fucoxanthin in alleviating lipid metabolic disorders in skeletal muscle remains poorly understood. In this study, we systematically investigated the impact of fucoxanthin on mitigating lipid deposition and insulin resistance in skeletal muscle employing palmitic acid-induced lipid deposition in C2C12 cells and ob/ob mice. Fucoxanthin significantly alleviated PA-induced skeletal muscle lipid deposition and insulin resistance. In addition, fucoxanthin prominently upregulated the expression of lipid metabolism-related genes (Pparα and Cpt-1), promoting fatty acid β-oxidation metabolism. Additionally, fucoxanthin significantly increased the expression of Pgc-1α and Tfam, elevated the mtDNA/nDNA ratio, and reduced ROS levels. Further, we identified pyruvate kinase muscle isozyme 1 (PKM1) as a high-affinity protein for fucoxanthin by drug affinity-responsive target stability and LC-MS and confirmed their robust interaction by CETSA, microscale thermophoresis, and circular dichroism. Supplementation with pyruvate, the product of PKM1, significantly attenuated the beneficial effects of fucoxanthin on lipid deposition and insulin resistance. Mechanistically, fucoxanthin reduced glucose glycolysis rate and enhanced mitochondrial biosynthesis and fatty acid β-oxidation through inhibiting PKM1 activity, thereby alleviating lipid metabolic stress. These findings present a novel clinical strategy for treating metabolic diseases using fucoxanthin.

Activation of the ROS/TXNIP/NLRP3 pathway disrupts insulin-dependent glucose uptake in skeletal muscle of insulin-resistant obese mice

Oxidative stress and the activation of the nucleotide-binding domain, leucine-rich-containing family, pyrin domain containing 3 (NLRP3) inflammasome have been linked to insulin resistance in skeletal muscle. In immune cells, the exacerbated generation of reactive oxygen species (ROS) activates the NLRP3 inflammasome, by facilitating the interaction between thioredoxin interacting protein (TXNIP) and NLRP3. However, the precise role of ROS/TXNIP-dependent NLRP3 inflammasome activation in skeletal muscle during obesity-induced insulin resistance remains undefined. Here, we induced insulin resistance in C57BL/6J mice by feeding them for 8 weeks with a high-fat diet (HFD) and explored whether the ROS/TXNIP/NLRP3 pathway was involved in the induction of insulin resistance in skeletal muscle. Skeletal muscle fibers from insulin-resistant mice exhibited increased oxidative stress, as evidenced by elevated malondialdehyde levels, and altered peroxiredoxin 2 dimerization. Additionally, these fibers displayed augmented activation of the NLRP3 inflammasome, accompanied by heightened ROS-dependent proximity between TXNIP and NLRP3, which was abolished by the antioxidant N-acetylcysteine (NAC). Inhibition of the NLRP3 inflammasome with MCC950 or suppressing the ROS/TXNIP/NLRP3 pathway with NAC restored insulin-dependent glucose uptake in muscle fibers from insulin-resistant mice. These findings provide insights into the mechanistic link between oxidative stress, NLRP3 inflammasome activation, and obesity-induced insulin resistance in skeletal muscle.

Adipocyte-specific inactivation of NAMPT, a key NAD+ biosynthetic enzyme, causes a metabolically unhealthy lean phenotype in female mice during aging.

Nicotinamide adenine dinucleotide (NAD+) is a universal coenzyme regulating cellular energy metabolism in many cell types. Recent studies have demonstrated the close relationships between defective NAD+ metabolism and aging and age-associated metabolic diseases. The major purpose of the present study was to test the hypothesis that NAD+ biosynthesis, mediated by a rate-limiting NAD+ biosynthetic enzyme, nicotinamide phosphoribosyltransferase (NAMPT), is essential for maintaining normal adipose tissue function and whole body metabolic health during the aging process. To this end, we provided in-depth and comprehensive metabolic assessments for female adipocyte-specific Nampt knockout (ANKO) mice during aging. We first evaluated body fat mass in young (≤4-mo-old), middle aged (10-14-mo-old), and old (≥18-mo-old) mice. Intriguingly, adipocyte-specific Nampt deletion protected against age-induced obesity without changing energy balance. However, data obtained from the hyperinsulinemic-euglycemic clamp procedure (HECP) demonstrated that, despite the lean phenotype, old ANKO mice had severe insulin resistance in skeletal muscle, heart, and white adipose tissue (WAT). Old ANKO mice also exhibited hyperinsulinemia and hypoadiponectinemia. Mechanistically, loss of Nampt caused marked decreases in WAT gene expression of lipogenic targets of peroxisome proliferator-activated receptor gamma (PPAR-γ) in an age-dependent manner. In addition, administration of a PPAR-γ agonist rosiglitazone restored fat mass and improved metabolic abnormalities in old ANKO mice. In conclusion, these findings highlight the importance of the NAMPT-NAD+-PPAR-γ axis in maintaining functional integrity and quantity of adipose tissue, and whole body metabolic function in female mice during aging.NEW & NOTEWORTHY Defective NAD+ metabolism is associated with aging and age-associated metabolic diseases. In the present study, we provided in-depth metabolic assessments in female mice with adipocyte-specific inactivation of a key NAD+ biosynthetic enzyme NAMPT and revealed an unexpected role of adipose tissue NAMPT-NAD+-PPAR-γ axis in maintaining functional integrity and quantity of adipose tissue and whole body metabolic health during the aging process.

Skeletal muscle cystathionine γ-lyase deficiency promotes obesity and insulin resistance and results in hyperglycemia and skeletal muscle injury upon HFD in mice

ABSTRACT Objectives The objective of this study was to investigate whether skeletal muscle cystathionine γ-lyase (CTH) contributes to high-fat diet (HFD)-induced metabolic disorders using skeletal muscle Cth knockout (CthΔskm ) mice. Methods The Cth Δskm mice and littermate Cth-floxed (Cthf/f ) mice were fed with either HFD or chow diet for 13 weeks. Metabolomics and transcriptome analysis were used to assess the impact of CTH deficiency in skeletal muscle. Results Metabolomics coupled with transcriptome showed that CthΔskm mice displayed impaired energy metabolism and some signaling pathways linked to insulin resistance (IR) in skeletal muscle although the mice had normal insulin sensitivity. HFD led to reduced CTH expression and impaired energy metabolism in skeletal muscle in Cthf/f mice. CTH deficiency and HFD had some common pathways enriched in the aspects of amino acid metabolism, carbon metabolism, and fatty acid metabolism. CthΔskm +HFD mice exhibited increased body weight gain, fasting blood glucose, plasma insulin, and IR, and reduced glucose transporter 4 and CD36 expression in skeletal muscle compared to Cthf/f +HFD mice. Impaired mitochondria and irregular arrangement in myofilament occurred in CthΔskm +HFD mice. Omics analysis showed differential pathways enriched between CthΔskm mice and Cthf/f mice upon HFD. More severity in impaired energy metabolism, reduced AMPK signaling, and increased oxidative stress and ferroptosis occurred in CthΔskm +HFD mice compared to Cthf/f +HFD mice. Discussion Our results indicate that skeletal muscle CTH expression dysregulation contributes to metabolism disorders upon HFD.

Inhibitory Regulation of FOXO1 in PPARδ Expression Drives Mitochondrial Dysfunction and Insulin Resistance.

Forkhead box protein O1 (FoxO1) regulates muscle growth, but the metabolic role of FoxO1 in skeletal muscle and its mechanisms remain unclear. To explore the metabolic role of FoxO1 in skeletal muscle, we generated skeletal muscle-specific FoxO1 inducible knockout (mFoxO1 iKO) mice and fed them a high-fat diet to induce obesity. We measured insulin sensitivity, fatty acid oxidation, mitochondrial function, and exercise capacity in obese mFoxO1 iKO mice, and assessed the correlation between FoxO1 and mitochondrial-related protein in the skeletal muscle of diabetic patients. Obese mFoxO1 iKO mice exhibited improved mitochondrial respiratory capacity, which was followed by attenuated insulin resistance, enhanced fatty acid oxidation, and improved skeletal muscle exercise capacity. Transcriptional inhibition of FoxO1 in peroxisome proliferator-activated receptor δ (PPARδ) expression was confirmed in skeletal muscle and deletion of PPARδ abolished the beneficial effects of FoxO1 deficiency. FoxO1 protein levels were higher in the skeletal muscle of diabetic patients and negatively correlated with PPARδ and electron transport chain protein levels. These findings highlight FoxO1 as a new repressor in PPARδ gene expression in skeletal muscle and suggest that FoxO1 links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ.

Not Only Protein: Dietary Supplements to Optimize the Skeletal Muscle Growth Response to Resistance Training: The Current State of Knowledge

Regarding skeletal muscle hypertrophy, resistance training and nutrition, the most often discussed and proposed supplements include proteins. Although, the correct amount, quality, and daily distribution of proteins is of paramount importance for skeletal muscle hypertrophy, there are many other nutritional supplements that can help and support the physiological response of skeletal muscle to resistance training in terms of muscle hypertrophy. A healthy muscle environment and a correct whole muscle metabolism response to the stress of training is a prerequisite for the increase in muscle protein synthesis and, therefore, muscle hypertrophy. In this review, we discuss the role of different nutritional supplements such as carbohydrates, vitamins, minerals, creatine, omega-3, polyphenols, and probiotics as a support and complementary factors to the main supplement i.e., protein. The different mechanisms are discussed in the light of recent evidence.

Not Only Protein: Dietary Supplements to Optimize the Skeletal Muscle Growth Response to Resistance Training: The Current State of Knowledge.

Regarding skeletal muscle hypertrophy, resistance training and nutrition, the most often discussed and proposed supplements include proteins. Although, the correct amount, quality, and daily distribution of proteins is of paramount importance for skeletal muscle hypertrophy, there are many other nutritional supplements that can help and support the physiological response of skeletal muscle to resistance training in terms of muscle hypertrophy. A healthy muscle environment and a correct whole muscle metabolism response to the stress of training is a prerequisite for the increase in muscle protein synthesis and, therefore, muscle hypertrophy. In this review, we discuss the role of different nutritional supplements such as carbohydrates, vitamins, minerals, creatine, omega-3, polyphenols, and probiotics as a support and complementary factors to the main supplement i.e., protein. The different mechanisms are discussed in the light of recent evidence.

Effect of Supplementation with Omega-3 Polyunsaturated Fatty Acids on Metabolic Modulators in Skeletal Muscle of Rats with an Obesogenic High-Fat Diet.

Previous studies provided evidence of the benefits of omega-3 polyunsaturated fatty acids (ω-3 PUFA) on the cardiovascular system and inflammation. However, its possible effect on skeletal muscle is unknown. This study aimed to evaluate whether ω-3 PUFA reverses the dysregulation of metabolic modulators in the skeletal muscle of rats on a high-fat obesogenic diet. For this purpose, an animal model was developed using male Wistar rats with a high-fat diet (HFD) and subsequently supplemented with ω-3 PUFA. Insulin resistance was assessed, and gene and protein expression of metabolism modulators in skeletal muscle was also calculated using PCR-RT and Western blot. Our results confirmed that in HFD rats, zoometric parameters and insulin resistance were increased compared to SD rats. Furthermore, we demonstrate reduced gene and protein expression of peroxisome proliferator-activated receptors (PPARs) and insulin signaling molecules. After ω-3 PUFA supplementation, we observed that glucose (24.34%), triglycerides (35.78%), and HOMA-IR (40.10%) were reduced, and QUICKI (12.16%) increased compared to HFD rats. Furthermore, in skeletal muscle, we detected increased gene and protein expression of PPAR-α, PPAR-γ, insulin receptor (INSR), insulin receptor substrate 1 (ISR-1), phosphatidylinositol-3-kinase (PI3K), and glucose transporter 4 (GLUT-4). These findings suggest that ω-3 PUFAs decrease insulin resistance of obese skeletal muscle.

Ketogenic diet ameliorates high-fat diet-induced insulin resistance in mouse skeletal muscle by alleviating endoplasmic reticulum stress

ObjectiveKetogenic diets (KD) have been shown to alleviate insulin resistance (IR) by exerting anti-lipogenic and insulin sensitizing effects in the liver through a variety of pathways. The present study sought to investigate whether a ketogenic diet also improves insulin sensitization in skeletal muscle cells through alleviating endoplasmic reticulum stress. MethodsHigh-fat diet-induced IR mice were allowed to a 2-week ketogenic diet. Insulin resistance and glucose tolerance were evaluated through GTT, ITT, and HOMA-IR. The C2C12 myoblasts exposed to palmitic acid were used to evaluate the insulin sensitization effects of β-hydroxybutyric acid (β-OHB). Molecular mechanisms concerning ER stress signaling activation and glucose uptake were assessed. ResultsThe AKT/GSK3β pathway was inhibited, ER stress signaling associated with IRE1, PERK, and BIP was activated, and the number of Glut4 proteins translocated to membrane decreased in the muscle of HFD mice. However, all these changes were reversed after 2 weeks of feeding on a ketogenic diet. Consistently in C2C12 myoblasts, the AKT/GSK3β pathway was inhibited by palmitic acid (PA) treatment. The endoplasmic reticulum stress-related proteins, IRE1, and BIP were increased, and the number of Glut4 proteins on the cell membrane decreased. However, β-OHB treatment alleviated ER stress and improved the glucose uptake of C2C12 cells. ConclusionOur data reveal that KD ameliorated HFD-induced insulin resistance in skeletal muscle, which was partially mediated by inhibiting endoplasmic reticulum stress. The insulin sensitization effect of β-OHB is associated with up regulation of AKT/GSK3β pathway and the increase in the number of Glut4 proteins on the cell membrane.

Free radical scavenging polyphenols isolated from Phyllanthus niruri L. ameliorates hyperglycemia via SIRT1 induction and GLUT4 translocation in in vitro and in vivo models

Type 2 diabetes milletus (T2DM) is a complex multifaceted disorder characterized by insulin resistance in skeletal muscle. Phyllanthus niruri L. is well reported sub-tropical therapeutically beneficial ayurvedic medicinal plant from Euphorbiaceae family used in various body ailments such as metabolic disorder including diabetes. The present study emphasizes on the therapeutic potential of Phyllanthus niruri L. and its phytochemical(s) against insulin resistance conditions and impaired antioxidant activity thereby aiding as an anti-hyperglycemic agent in targeting T2DM. Three compounds were isolated from the most active ethyl acetate fraction namely compound 1 as 1-O-galloyl-6-O-luteoyl-β-D-glucoside, compound 2 as brevifolincarboxylic acid and compound 3 as ricinoleic acid. Compounds 1 and 2, the two polyphenols enhanced the uptake of glucose and inhibited ROS levels in palmitate induced C2C12 myotubes. PNEAF showed the potent enhancement of glucose uptake in palmitate-induced insulin resistance condition in C2C12 myotubes and significant ROS inhibition was observed in skeletal muscle cell line. PNEAF treated IR C2C12 myotubes and STZ induced Wistar rats elevated SIRT1, PGC1-α signaling cascade through phosphorylation of AMPK and GLUT4 translocation resulting in insulin sensitization. Our study revealed an insight into the efficacy of marker compounds isolated from P. niruri and its enriched ethyl acetate fraction as ROS scavenging agent and helps in attenuating insulin resistance condition in C2C12 myotubes as well as in STZ induced Wistar rat by restoring glucose metabolism. Overall, this study can provide prospects for the marker-assisted development of P. niruri as a phytopharmaceutical drug for the insulin resistance related diabetic complications.

Genistein in combination with Chlorogenic acid ameliorates insulin resistance and oxidative stress in skeletal muscle of high-fat diet fed mice

Objectives: Increasing evidence has demonstrated that oxidative stress plays a significant role in the pathogenesis of muscle insulin resistance. The beneficial impacts of genistein (GEN) and chlorogenic acid (CGA) on insulin resistance have already been revealed. However, their combined effects on skeletal muscle oxidative stress and insulin resistance have not been completely understood. The aim of the present study was to determine the effect of GEN in combination with CGA on skeletal muscle insulin resistance in high-fat diet (HFD) fed C57BL/6 mice.&#x0D; Methods: C57BL/6 male mice were fed an HFD for 15 weeks. The mice were then divided into five groups: standard chow diet (SCD), HFD, HFD + GEN, HFD + CGA, and HFD + GEN + CGA for 10 weeks.&#x0D; Results: The findings indicated that single treatment with GEN or CGA, and with a stronger effect of GEN+CGA combined treatment, decreased body weight gain and improved glucose intolerance. Moreover, following treatment with GEN and CGA alone or in combination with further effect, the level of plasma and muscle triglyceride (TG) were reduced. Furthermore, the combination therapy of GEN and CGA with greater efficacy than the single treatments, could decrease several oxidative stress markers in the skeletal muscle. Treatment with GEN and CGA alone or in combination could increase the expression of NF-E2–related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P): Quinone Oxidoreductase 1 (NQO1).&#x0D; Conclusion: The data of this study suggest that the combination of GEN and CGA might ameliorate insulin resistance and reduce oxidative stress in the skeletal muscle of mice fed HFD.