Skeletal Muscle Resistance Research Articles

Effects of aerobic exercise on Nrf2-SOD pathway in the gastrocnemius of rats with high-glucose and high-fat diet

Objective: To investigate the changes of nuclear factor erythroid 2-related factor 2 (Nrf2) and superoxide dismutase (SOD) in the prevention of insulin resistance in skeletal muscle of rats by aerobic exercise. Methods: Twenty-four 12-month old Sprague-Dawley (SD) rats were randomly divided into control (C), insulin resistance model (IR) and insulin resistance model and exercise (IRE) groups. IR was induced by high- glucose and high-fat diet. Rats of IRE received the increasing load running on the treadmill for 6 W. The activity of total superoxide dismutase (T-SOD), catalase (CAT), Malonaldehyde (MDA) and glutathione / L-glutathione oxidized (GSH/GSSG) were measured by experiment kits. The content of 8-hydroxy-2 deoxyguanosine (8-OHdG) was measured by ELISA Kits. The expressions of Nrf2 and Glucose transporters 4 (GLUT4) in gastrocnemius were detected by Western Blot. Results: ①Compared with IR, the content of HOMA-IR was decreased in IRE (P＜0.05), while the content of muscle glycogen was increased in IRE (P＜0.01). ② The activities of T-SOD, CAT, and GSH/GSSG in IRE were significantly increased compared with those in IR (P＜0.01). Compared with IR, the contents of 8-OHdG and MDA in IRE were significantly decreased (P＜0.01). ③ The expressions of Nrf2 and GLUT4 in gastrocnemius of IRE rats were increased than those in IR (P＜0.01). Conclusion: The Nrf2 pathway was activated in gastrocnemius of rats after aerobic exercise, which promoted the activity of antioxidant enzymes, and prevented IR induced by high- glucose and high-fat diet.

The effects of amino acid/protein supplementation in hemodialysis patients: study protocol for a systematic review and meta-analysis

BackgroundMultiple factors including older age, comorbidities, inflammation, metabolic acidosis, dialysis-related hypercatabolism and anabolic resistance of skeletal muscle, extraction of circulating amino acids through hemodialysis and inadequate dietary protein intake due to anorexia, and strictly limited dietary phosphorus intake are likely to contribute to the high prevalence of malnutrition and metabolic abnormalities, more aptly called protein-energy wasting, in patients on hemodialysis. The consensus from the International Society of Renal Nutritional and Metabolism states that nutritional supplementation is effective for replenishing protein and energy stores. Although we hypothesize that amino acid/protein supplementation can overcome the anabolic resistance of skeletal muscle tissue and attenuate or even prevent the accelerated loss of skeletal muscle mass and strength through nutritional status improvement in patients on hemodialysis, whether amino acid and/or protein administration is associated with improvements in these outcomes is unknown. The main objective of this study is to systematically review the impact of amino acid/protein supplementation on skeletal muscle mass, muscle strength, physical function, and quality of life in end-stage renal disease patients requiring hemodialysis.MethodsPublished randomized controlled trials (RCTs) assessing the effectiveness of amino acid/protein supplementation in hemodialysis patients with respect to body composition, muscle mass, muscle strength, physical function, and quality of life will be included. The bibliographic databases include MEDLINE, the Web of Science, the Cochrane Central Register of Controlled Trials, and Embase. The risk of bias of the included RCTs will be assessed using the Cochrane Collaboration’s tool by two independent reviewers. The primary outcome will be skeletal muscle mass, muscle strength, and physical function, and the secondary outcome will be quality of life. This review protocol is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocol (PRISMA-P) 2015 checklist.Ethics and disseminationEthical approval is not required because this study does not include confidential personal data or involve patient interventions. This review is expected to inform readers on the effect of amino acid/protein supplementation in patients undergoing hemodialysis. The findings will be presented at conferences and submitted to a peer-reviewed journal for publication.Trial registrationThe trial registration number is (CRD42020181087), and the trial was registered on 5 July 2020.

Obesity-related hypoxia via miR-128 decreases insulin-receptor expression in human and mouse adipose tissue promoting systemic insulin resistance.

BackgroundInsulin resistance in visceral adipose tissue (VAT), skeletal muscle and liver is a prominent feature of most patients with obesity. How this association arises remains poorly understood. The objective of this study was to demonstrate that the decrease in insulin receptor (INSR) expression and insulin signaling in VAT from obese individuals is an early molecular manifestation that might play a crucial role in the cascade of events leading to systemic insulin resistance.MethodsTo clarify the role of INSR and insulin signaling in adipose tissue dysfunction in obesity, we first measured INSR expression in VAT samples from normal-weight subjects and patients with different degrees of obesity. We complemented these studies with experiments on high-fat diet (HFD)-induced obese mice, and in human and murine adipocyte cultures, in both normoxic and hypoxic conditions.FindingsAn inverse correlation was observed between increasing body mass index and decreasing INSR expression in VAT of obese humans. Our results indicate that VAT-specific downregulation of INSR is an early event in obesity-related adipose cell dysfunction, which increases systemic insulin resistance in both obese humans and mice. We also provide evidence that obesity-related hypoxia in VAT plays a determinant role in this scenario by decreasing INSR mRNA stability. This decreased stability is through the activation of a miRNA (miR-128) that downregulates INSR expression in adipocytes.InterpretationWe present a novel pathogenic mechanism of reduced INSR expression and insulin signaling in adipocytes. Our data provide a new explanation linking obesity with systemic insulin resistance.FundingThis work was partly supported by a grant from Nutramed (PON 03PE000_78_1) and by the European Commission (FESR FSE 2014-2020 and Regione Calabria).

Administration of kynurenic acid reduces hyperlipidemia-induced inflammation and insulin resistance in skeletal muscle and adipocytes

Kynurenic acid (KA), an endogenous product of L-tryptophan metabolism in the kynurenine pathway, regulates adipose tissue energy homeostasis and inflammation. However, its role in palmitate-induced insulin resistance and detailed underlying mechanisms in skeletal muscles and adipose tissues are unclear. Herein, we report that KA ameliorated palmitate-induced inflammation and insulin resistance in differentiated C2C12 and 3T3-L1 cell lines as well as soleus skeletal muscle and subcutaneous adipose tissues in mice. Palmitate-induced inflammatory markers, such as nuclear factor κB translocation, inhibitory κBα phosphorylation, pro-inflammatory cytokine expression, and impaired insulin signaling, were markedly attenuated by KA both in vitro and in vivo. KA significantly increased AMP-activated protein kinase (AMPK) phosphorylation and sirtuin 6 (SIRT6) expressions in C2C12 myocytes and 3T3-L1 adipocytes and skeletal muscle and adipose tissues of mice. siRNA-mediated AMPK or SIRT6 inhibition significantly mitigated the suppressive effects of KA on palmitate-induced inflammation and insulin resistance. KA significantly stimulated expression of genes involved in fatty acid oxidation in C2C12 myocytes and skeletal muscle of mice. Moreover, KA inhibits lipogenesis in 3T3-L1 adipocytes. AMPK or SIRT6 siRNA markedly reversed these changes. The siRNA targeting Gpr35 abrogated the effects of KA on AMPK phosphorylation in C2C12 myocytes and 3T3-L1 adipocytes, except SIRT6 expression. It has therefore been shown that KA could potentially alleviate inflammation and insulin resistance in skeletal muscle and adipose tissues through Gpr35/AMPK and SIRT6-mediated pathways.

PPARδ Attenuates Alcohol-Mediated Insulin Resistance by Enhancing Fatty Acid-Induced Mitochondrial Uncoupling and Antioxidant Defense in Skeletal Muscle.

Alcohol consumption leads to the dysfunction of multiple organs including liver, heart, and skeletal muscle. Alcohol effects on insulin resistance in liver are well evidenced, whereas its effects in skeletal muscle remain controversial. Emerging evidence indicates that alcohol promotes adipose tissue dysfunction, which may induce organ dysregulation. We show that consumption of ethanol (EtOH) reduces the activation of 5′AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) as well as the protein of carnitine palmitoyltransferase 1 (CPT1) and glucose transporter type 4 (GLUT4) in C2C12 myotube. We observed that chronic EtOH consumption increases free fatty acid levels in plasma and triglyceride (TG) accumulation in skeletal muscle and that these increases induce insulin resistance and decrease glucose uptake. Hence, ethanol dysregulates metabolic factors and induces TG accumulation. We found peroxisome proliferator-activated receptor β/δ (PPARδ) activation recovers AMPK activation and increases carnitine-acylcarnitine translocase (CACT) protein. These effects may contribute to enhance mitochondrial activation via uncoupling protein 3 (UCP3) when fatty acids are used as a substrate, thus reduces EtOH-induced increases in TG levels in skeletal muscle. In addition, PPARδ activation recovered EtOH-induced loss of protein kinase B (AKT) phosphorylation at serine 473 via rapamycin-insensitive companion of mammalian target of rapamycin (Rictor) activation. Importantly, PPARδ activation enhanced mitochondrial uncoupling via UCP3. Taken together, the study shows PPARδ enhances fatty acid utilization and uncoupled respiration via UCP3 and protects against EtOH-induced lipotoxicity and insulin resistance in skeletal muscle.

Passive Stretch Improves Insulin-stimulated Glucose Transport Together With Downregulation Of TXNIP In Rat Soleus Muscle

PURPOSE: Although passive stretch is known to stimulate muscle glucose transport independently of insulin action, it is unclear whether stretch increases susceptibility of glucose transport to insulin and improves insulin resistance in skeletal muscles. Therefore, we examined the effect of stretch on insulin-stimulated glucose transport in insulin resistant soleus muscles of immobilized rats. In addition, we examined the possibility that stretch decreases protein expression of TXNIP which is known to be a key negative regulator of insulin signaling. METHODS: Rats were divided into non-immobilized control and immobilized groups. Non-immobilized control rats were allowed to move freely in their cages. Immobilized rats were anesthetized and their both hindlimbs were immobilized for 6 h. Unilateral soleus muscles of immobilized rats were shortened by plantarflexing the ankle joint throughout 6 h immobilization. Contralateral muscles were stretched for 1 h by dorsiflexing the ankle joint following 5 h shortening by plantarflexing. We measured basal and insulin (50μU/ml) stimulated 2-deoxyglucose (2DG) uptake rate in isolated soleus muscles. Moreover, TXNIP protein expression was evaluated in these muscles. RESULTS: Although insulin (50μU/ml) increased glucose transport by 1.9-fold in soleus muscles of non-immobilized control rats (p<0.05), insulin did not significantly increase glucose transport in shortened muscles of immobilized rats. This result shows that insulin resistance is induced in these shortened muscles. On the other hand, 1 h passive stretch restored insulin resistance of glucose transport in muscles of immobilized rats (insulin-stimulated 2DG uptake in control, 3.12±0.29; shortened, 1.73±0.17; stretched, 3.04±0.31μmol/g muscle/20min). In addition, TXNIP protein was increased in shortened muscles of immobilized rats as compared with muscles of control rats (p<0.05). Moreover, elevated TXNIP expression in these muscles was returned to control level after 1 h passive stretch (TXNIP in control, 100±9; shortened, 166±8; stretched, 107±9 arbitrary units). CONCLUSIONS: Passive stretch improves insulin-stimulated glucose transport in insulin-resistant soleus muscles of immobilized rats. This may be due to stretch-induced downregulation in TXNIP protein expression.

1757-P: Tyrosine Phosphorylation of Phospholipase C in Human Skeletal Muscle Insulin Resistance

Insulin resistance in skeletal muscle is among the primary contributors to the development of type 2 diabetes (T2D), a leading cause of heart disease, stroke, etc. Over 26 million U.S. adults have T2D. Molecular mechanisms for skeletal muscle insulin resistance remain elusive, limiting strategies to prevent/treat T2D. Phospholipase C, gamma 1 (PLCG1, aka PLC-γ1) serves as a signal transducer of tyrosine kinases and regulates various downstream signaling pathways in vitro. PLCG1 has been shown to interact with insulin receptor (IR) via its pleckstrin homology domain and plays a significant role in insulin-stimulated glucose uptake in adipocytes. Moreover, phosphorylation of tyrosine residue 771 (pTyr771) of PLCG1 has been shown to regulate PLCG1 activity. However, no prior publication shows that PLCG1 pTyr771 is linked with insulin resistance and T2D. Previously, we observed that insulin-stimulated PLCG1 pTyr771 is impaired in skeletal muscle from subjects with T2D compared to lean controls. In the present work, we mutated Tyr771 of PLCG1 to phenylalanine, and observed reduced insulin-stimulated AKT and AS160 phosphorylation in primary human skeletal muscle cells derived from an insulin sensitive participant. To identify the upstream regulator of PLCG1, we carried out in vitro kinase assay by incubating PLCG1 with insulin receptor. PLCG1 was expressed and purified from E. coli. The insulin receptor (active cytoplasmic terminus) was expressed and purified from insect cells. After incubating PLCG1 with insulin receptor in vitro for 30 min in the presence of ATP, PLCG1 phosphorylation was determined by HPLC-ESI-MS/MS. The result demonstrated that insulin receptor phosphorylated Tyr771 of PLCG1. Western blotting using pTyr771 specific antibodies confirmed these findings. In summary, these results suggest that reduced insulin-stimulated pTyr771 may contribute to the development of insulin resistance and T2D, and the insulin receptor is an upstream regulator of PLCG1 pTyr771. Disclosure X. Zhang: None. A.H. Mestareehi: None. B. Seyoum: None. Z. Yi: None. Funding American Diabetes Association (1-13-TS-27 to Z.Y.); National Institutes of Health (R01DK107666, R01DK081750 to Z.Y.), (T32HL120822 to A.H.M.); DOTS Scholars (to A.H.M., Z.Y.)

1726-P: Male Mice Lacking Estrogen Receptor Beta Develop Obesity but Are Protected from Diet-Induced Insulin Resistance in Skeletal Muscle

Estrogen has an important role in regulating female metabolism. Whereas the role of estrogen receptor (ER) α on female reproductive system is well defined, the role of ERβ (encoded by Esr2) remains unclear. Here we examined the metabolic effects of high-fat diet (HFD) in male Esr2-/- mice on BALB/c background (n=8∼9). After 6 weeks of HFD, Esr2-/- mice became more obese than wild type (WT) mice (Figure 1; *P&amp;lt;0.05). Surprisingly, metabolic cage study showed significantly increased energy expenditure in Esr2-/- mice, likely resulting from skeletal muscle as lean mass tended to be higher in these mice (Figure 2). We performed a hyperinsulinemic-euglycemic clamp to measure insulin sensitivity in awake mice. Despite being more obese, HFD-fed Esr2-/- mice tended to show increased insulin sensitivity with 20% increases in whole body glucose turnover and glycolysis (Figure 3). This was mostly due to a significant increase (52%) in skeletal muscle glucose uptake in HFD-fed Esr2-/- mice (Figure 4). Interestingly, glucose uptake into brown fat tended to be reduced by 50% in HFD-fed Esr2-/- mice. In conclusion, these results indicate that deletion of Esr2 in male mice increases diet-induced obesity, but selectively prevents muscle insulin resistance. Our findings implicate a potential therapeutic role of estrogen signaling to treat insulin resistance. Disclosure R.H. Friedline: None. H. Noh: None. S. Suk: None. C. Goral: None. K.A. Dunphy: None. A.L. Roberts: None. D.A. Tran: None. L.A. Tauer: None. X. Hu: None. L.H. Kim: None. A.M. Kim: None. D. Jerry: None. J.K. Kim: None. Funding National Institutes of Health (5U2CDK093000)

Skeletal muscle enhancer interactions identify genes controlling whole-body metabolism

Obesity and type 2 diabetes (T2D) are metabolic disorders influenced by lifestyle and genetic factors that are characterized by insulin resistance in skeletal muscle, a prominent site of glucose disposal. Numerous genetic variants have been associated with obesity and T2D, of which the majority are located in non-coding DNA regions. This suggests that most variants mediate their effect by altering the activity of gene-regulatory elements, including enhancers. Here, we map skeletal muscle genomic enhancer elements that are dynamically regulated after exposure to the free fatty acid palmitate or the inflammatory cytokine TNFα. By overlapping enhancer positions with the location of disease-associated genetic variants, and resolving long-range chromatin interactions between enhancers and gene promoters, we identify target genes involved in metabolic dysfunction in skeletal muscle. The majority of these genes also associate with altered whole-body metabolic phenotypes in the murine BXD genetic reference population. Thus, our combined genomic investigations identified genes that are involved in skeletal muscle metabolism.

1883-P: Metformin Increases Protein Phosphatase 2A Activity in Primary Skeletal Muscle Cells Derived from Lean Healthy Insulin-Sensitive Human Participants

Skeletal muscle insulin resistance is one of the primary contributors of type 2 diabetes (T2D). Metformin is the first-line drug for the treatment of T2D. Main known effects of metformin include inhibition of glucose production in liver and attenuation of insulin resistance in skeletal muscle. However, molecular mechanism of metformin’s action in skeletal muscle is not well understood. Protein phosphatase 2A (PP2A), a major serine/threonine phosphatase, plays a pivotal role in cellular processes (e.g., signal transduction, apoptosis), and acts through dephosphorylating key signaling molecules such as AKT, AMPK, etc. However, whether or not PP2A plays a role in metformin-induced insulin sensitivity improvement in human skeletal muscle cells remains to be elucidated. In the present study, hyperinsulinemic-euglycemic clamp was performed to assess insulin sensitivity in human subjects and skeletal muscle biopsy samples were obtained. Primary human skeletal muscle cells (shown to retain metabolic characteristics of donors) were cultured from these muscle biopsies from 8 lean insulin sensitive participants (4 Female and 4 male; age: 21.4±0.8 yrs; BMI: 22.1±0.7 kg/m2; 2-hour OGTT: 96.5± 6.3 mg/dl; HbA1c: 5.3±0.1 %; fasting plasma glucose: 87.5±1.4 mg/dl; M-value; 10.9±0.8 mg/kgBW/min). The cells were expanded, differentiated into myotubes, and treated with 50µM metformin (the physiologic concentration) for 24 hours before harvesting. PP2A activity was measured by a phosphatase activity assay (Millipore). The results indicated that metformin increased the activity of PP2A in the myotubes derived from all 8 participants, and the average fold increase is 1.59±0.13 (p&amp;lt;0.05). These results provided the first evidence to suggest that metformin promotes activation of PP2A in human skeletal muscle cells derived from lean insulin sensitive participants, and may help to understand metformin’s action in skeletal muscle in humans. Disclosure A.H. Mestareehi: None. B. Seyoum: None. Z. Msallaty: None. A.P. Mallisho: None. X. Zhang: None. A. Kowluru: None. Z. Yi: None. Funding American Diabetes Association (1-13-TS-27 to Z.Y.); National Institutes of Health (R01DK107666, R01DK081750 to Z.Y.), (T32HL120822 to A.H.M.); DOTS Scholars (to A.H.M., Z.Y.)

Experimental Subarachnoid Hemorrhage Drives Catecholamine-Dependent Cardiac and Peripheral Microvascular Dysfunction.

Subarachnoid hemorrhage (SAH) is a devastating cerebral event caused by an aneurysmal rupture. In addition to neurological injury, SAH has significant effects on cardiac function and the peripheral microcirculation. Since these peripheral complications may exacerbate brain injury, the prevention and management of these peripheral effects are important for improving the overall clinical outcome after SAH. In this investigation, we examined the effects of SAH on cardiac function and vascular reactivity in a well-characterized blood injection model of SAH. Standard echocardiographic and blood pressure measurement procedures were utilized to assess cardiac function and hemodynamic parameters in vivo; we utilized a pressure myography approach to assess vascular reactivity in cremaster skeletal muscle resistance arteries ex vivo. We observed that elevated catecholamine levels in SAH stun the myocardium, reduce cardiac output and augment myogenic vasoconstriction in isolated cremaster arteries. These cardiac and vascular effects are driven by beta- and alpha-adrenergic receptor signaling, respectively. Clinically utilized adrenergic receptor antagonists can prevent cardiac injury and normalize vascular function. We found that tumor necrosis factor (TNF) gene deletion prevents the augmentation of myogenic reactivity in SAH: since membrane-bound TNF serves as a mechanosensor in the arteries assessed, alpha-adrenergic signaling putatively augments myogenic vasoconstriction by enhancing mechanosensor activity.

MON-647 Mechanisms of Insulin Resistance in Skeletal Muscle in Women with PCOS

Polycystic ovary syndrome (PCOS) is the most common female endocrine disorder affecting metabolic, reproductive and mental health of 8-13% of reproductive-age women. Insulin resistance (IR) appears to underpin the pathophysiology of PCOS and is present in approximately 85% of women with PCOS. This underlying IR has been identified as unique from, but synergistic with, obesity-induced IR (1). Skeletal muscle accounts for up to 85% of whole body insulin-stimulated glucose uptake, however, in PCOS this is reduced about 27% when assessed by hyperinsulinemic euglycemic clamp (2). Interestingly, this reduced insulin-stimulated glucose uptake observed in skeletal muscle tissue is not retained in cultured myotubes (3), suggesting that environmental factors may play a role in this PCOS-specific IR. Yet, the molecular mechanisms regulating IR remain unclear (4). Previous work suggested that Transforming Growth Factor Beta (TGFβ) superfamily ligands may be involved in the metabolic morbidity associated with PCOS (5). In this study, we investigated the effects of TGFβ1 (1, 5ng/ml), and the Anti-Müllerian hormone (AMH; 5, 10, 30ng/ml), a novel TGFβ superfamily ligand elevated in women with PCOS, as causal factors of IR in cultured myotubes from women with PCOS (n=10) and healthy controls (n=10). AMH negatively affected glucose uptake and insulin signalling increasing p-IRS1 (ser312) in a dose-dependent manner in myotubes from both women with and without PCOS. AMH did not appear to activate the canonical TGFβ/BMP signalling pathway. Conversely, TGFβ1 had an opposite effect in both PCOS and control myotubes cultures, decreasing phosphorylation of IRS1 (ser312) and enhancing glucose uptake via Smad2/3 signalling. In conclusion, these results suggest that AMH may play a role in skeletal muscle IR observed in PCOS, however, further research is required to elucidate its mechanisms of action and broader impact in this syndrome.

Exercise Training Attenuates Sarcopenic Obesity‐Induced Insulin Resistance and Mitochondrial Dysfunction in the Rat Skeletal Muscle

The purpose of this study was to determine the effects of sarcopenic obesity (aging‐induced sarcopenia plus high fat diet‐induced obesity) and exercise training on insulin resistance, mitochondrial function (hydrogen peroxide (H2O2) emission and calcium(Ca2+) retention capacity) and mitochondrial dynamics (fusion; Opa1, Mfn1, Mfn2 and fission; Drp1, Fis1) in the rat skeletal muscle.Sprague‐Dawley rats were randomly divided into four groups: 4‐month young control (YC), 20‐month old control (OC; sarcopenia), old high fat diet group (OH; sarcopenic obesity), and old high fat diet and exercise group (OH+EX). After obesity was induced by 7 weeks of 60% high fat feeding in old groups, treadmill exercise was performed 6 times a week for 7 weeks. Oral glucose tolerance test was performed to determine insulin resistance. Mitochondrial function (H2O2 emission, Ca2+ retention capacity) was measured in permeabilized skeletal muscle (soleus and white gastrocnemius). Also, mitochondrial dynamics (fusion and fission) were analyzed using Western immunoblot in skeletal muscle.Insulin resistance was induced in OC and OH compared with YC. Conversely, insulin resistance was mitigated in OH+EX compared with OC and OH. Excessive mitochondrial H2O2 emission was found in white gastrocnemius of OC and OH compared with YC. However, exercise training attenuated aging and obesity‐induced mitochondrial H2O2 emission in OH+EX compared with OC and OH. Although mitochondrial Ca2+ retention capacity was not significant between groups in type I muscle (soleus), it was dramatically downregulated by aging and obesity and conversely upregulated by exercise training in type IIb muscle (white gastrocnemius) in OH+EX compared with OC and OH. In addition, exercise training protected against the imbalance between mitochondrial fusion and fission, showing that aerobic exercise training improved aging and obesity (sarcopenic obesity)‐induced decrease in Opa1 and Mfn2 protein levels and, conversely, reduced the increase in Drp1 and Fis1 protein levels in type IIb muscle in OH+EX compared with OC and OH.Our data demonstrated that sarcopenic obesity induced more insulin resistance, mitochondrial dysfunction, and mitochondrial remodeling than sarcopenia in skeletal muscle. However, exercise training mitigated sarcopenic obesity‐induced impairment in insulin resistance and mitochondrial function in skeletal muscle, suggesting that aerobic exercise training plays an essential role in attenuating sarcopenic obesity‐induced insulin resistance through the regulation of mitochondrial function in the skeletal muscle.Support or Funding InformationThis work was supported by the Ministry of Education of the Republic of Korea and the National Research Foundation (2018R1A2A3074577, 2019S1A5C2A03082727).

MOTS‐c inhibits high‐fat diet‐induced muscle wasting by suppressing myostatin expression via the PTEN/AKT/FOXO1 signaling pathway

Insulin resistance is thought to contribute to the development of muscle wasting. MOTS‐c, a novel mitochondrial‐derived peptide, improves insulin resistance in skeletal muscle, but its effects on muscle wasting have yet to be explored. Here, we used a diet‐induced obese mouse model to examine the effect of MOTS‐c administration on high fat diet‐induced muscle wasting. Three weeks of MOTS‐c administration by intraperitoneal (IP) injection in high‐fat diet fed mice resulted in higher total skeletal muscle mass of soleus, gastrocnemius, and plantaris compared to its high‐fat diet fed control group. Myostatin mRNA expression levels were significantly decreased in the MOTS‐c treated group compared to the high‐fat diet fed controls in the gastrocnemius muscle. Furthermore, myostatin mRNA expression negatively correlated with the total skeletal muscle mass of soleus, gastrocnemius, and plantaris. To examine the detailed mechanism of MOTS‐c action, we injected high‐fat diet fed mice with MOTS‐c for eight weeks and detected significantly lower plasma myostatin levels than high‐fat diet fed controls, as well as mRNA expression of myostatin and atrogin‐1 in the skeletal muscle. We further examined the upstream signaling pathways of myostatin regulation in the skeletal muscle and showed that MOTS‐c treatment inhibited PTEN activity, leading to elevated AKT phosphorylation and inhibition of FOXO1 transcription activity, resulting in myostatin and atrogin‐1 suppression. These results suggest that potent MOTS‐c analogues could potentially treat conditions such as high‐fat diet‐induced skeletal muscle wasting, as well as other muscle wasting phenotypes including sarcopenia, and that circulating levels of myostatin may serve as a pharmacodynamic biomarker of MOTS‐c activity.

Effects of Astaxanthin on Inflammation and Insulin Resistance in a Mouse Model of Gestational Diabetes Mellitus.

Gestational diabetes mellitus (GDM) is a condition in which a hormone made by the placenta prevents the body from using insulin effectively. It is important to find an effective treatment. A mouse model of GDM was used to testify the effects of astaxanthin on glucose tolerance and insulin sensitivity. Production of inflammatory cytokines, reactive oxygen species (ROS), and glucose transporter type 4 (GLUT4) translocation and insulin-related signaling were measured in the presence of astaxanthin both in vivo and in vitro. It was found that astaxanthin improved insulin sensitivity, glucose tolerance, and litter size of offspring and reduced birth weight of offspring and inflammation in GDM mouse. Moreover, astaxanthin increased GLUT4 translocating to membrane without altering its secretion/expression and glucose uptake and consumption in C2C12 skeletal muscle cells. Furthermore, ROS generation and insulin-related signaling inhibited by tumor necrosis factor α was restored by astaxanthin. It is concluded that astaxanthin has the potential to attenuate GDM symptoms by regulating inflammation and insulin resistance in skeletal muscle of pregnant mice. Our findings suggest that astaxanthin could be a promising and effective molecule to treat GDM.

Multi-frequency bioimpedance: a non-invasive tool for muscle-health assessment of adults with cerebral palsy.

Muscle contracture development is a major complication for individuals with cerebral palsy (CP) and has lifelong implications. In order to recognize contracture development early and to follow up on preventive interventions aimed at muscle health development, non-invasive, and easy to use methods are needed. The aim of the present study was to assess whether multi-frequency Bioimpedance (mfBIA) can be used to detect differences between skeletal muscle of individuals with CP and healthy controls. The mfBIA technique was applied to the medial gastrocnemius muscle of n = 24 adults with CP and n = 20 healthy controls of both genders. The phase angle (PA) and the centre frequency (fc) were significantly lower in individuals with CP when compared to controls; PA: - 25% for women and - 31.8% for men (P < 0.0001); fc: - 5.6% for women and - 5.2% for men (P < 0.009). The reactance (Xc) and the extracellular resistance (Re) of skeletal muscle from individuals with CP were significantly higher when compared to controls; Xc: + 9.9% for women and + 28.9% for men (P < 0.0001); Re: + 39.7% for women and + 91.2% for men (P < 0.0001). The present study shows that several mfBIA parameters differ significantly between individuals with CP and healthy controls. Furthermore, these changes correlated significantly with the severity of CP, as assessed using the GMFCS scale. The present data indicate that mfBIA shows promise in terms of being a useful diagnostic tool, capable of characterizing muscle health and its development in individuals with cerebral palsy.

Avaliação do limiar anaeróbio pela variabilidade da frequência cardíaca em diabéticos tipo 2

INTRODUÇÃO: A diabetes é um problema de saúde pública devido a sua alta prevalência, morbidade e mortalidade. O tipo 2 é mais prevalente e representa de 90 a 95% dos casos, sendo as complicações mais comuns o acúmulo de gordura no músculo esquelético e a resistência à insulina. O exercício físico regular contribui para regulação da glicemia, destacando-se o limiar anaeróbio como importante marcador para prescrição de exercícios físicos. OBJETIVO: Avaliar o limiar anaeróbio de indivíduos com diabetes tipo 2 através da variabilidade da frequência cardíaca. MATERIAIS E MÉTODOS: Estudo de caráter transversal, recrutou 18 participantes de ambos os sexos em uma unidade básica de saúde do município de Lagarto-SE, esse foram divididos em 2 grupos de 9 indivíduos. Na análise estatística utilizou-se o teste de Shapiro-Wilk para avaliação da normalidade e posteriormente Anova com pós teste de Tukey para comparação dos grupos. O grupo 1 composto de indivíduos diabéticos tipo 2 e o grupo 2 de indivíduos saudáveis. Também foi avaliada a média da frequência cardíaca em repouso e após o teste de esforço progressivo. RESULTADOS: As características de idade foram homogêneas sendo o grupo 1 com média de 62,1 (±13,9) anos e grupo 2 de 62,0 (±7,0) anos. A média da frequência de repouso foi de 79,8 bpm do grupo diabéticos e 78 bpm do grupo comparação, no limiar anaeróbio foi de 111,5 no grupo 1 e 119 no grupo 2. O tempo para atingir o L.A foi similar entre os grupos, 9,5 min no grupo experimental e 8 min no grupo comparação. CONCLUSÃO: Os valores do limiar anaeróbio de ambos os grupos foram considerados de baixo condicionamento físico, estes não apresentaram diferença estatística.

Pharmacological inhibition of TLR4 ameliorates muscle and liver ceramide content after disuse in previously physically active mice.

Toll-like receptor 4 (TLR4) is a proposed mediator of ceramide accumulation, muscle atrophy, and insulin resistance in skeletal muscle. It is currently unknown whether pharmacological inhibition of TLR4, using the TLR4-specific inhibitor TAK-242 during muscle disuse, is able to prevent changes in intracellular ceramide species and consequently preserve muscle size and insulin sensitivity in physically active mice. To address this question, we subjected running wheel-conditioned C57BL/6 male mice (13 wk old; ∼10/group) to 7 days of hindlimb suspension (HS), 7 days of continued wheel running (WR), or daily injections of TAK-242 during HS (HS + TAK242) for 7 days. We measured hindlimb muscle morphology, intramuscular and liver ceramide content, HOMA-IR, mRNA proxies of ceramide turnover and lipid trafficking, and muscle fatty acid and glycerolipid content. As a result, soleus and liver ceramide abundance was greater (P < 0.05) in HS vs. WR but was reduced with TLR4 inhibition (HS + TAK-242 vs. HS). Muscle mass declined (P < 0.01) with HS (vs. WR), but TLR4 inhibition did not prevent this loss (soleus: P = 0.08; HS vs. HS + TAK-242). HOMA-IR was impaired (P < 0.01) in HS versus WR mice, but only fasting blood glucose was reduced with TLR4 inhibition (HS + TAK-242 vs HS, P < 0.05). Robust decreases in muscle Spt2 and Cd36 mRNA and muscle lipidomic trafficking may partially explain reductions in ceramides with TLR4 inhibition. In conclusion, pharmacological TLR4 inhibition in wheel-conditioned mice prevented ceramide accumulation during the early phase of hindlimb suspension (7 days) but had little effect on muscle size and insulin sensitivity.

Genome-wide meta-analysis associates GPSM1 with type 2 diabetes, a plausible gene involved in skeletal muscle function.

Genome-wide association studies (GWASs) have identified many genetic variations associated with type 2 diabetes mellitus (T2DM) in Asians, but understanding the functional genetic variants that influence traits is often a complex process. In this study, fine mapping and other analytical strategies were performed to investigate the effects of G protein signaling modulator 1 (GPSM1) on insulin resistance in skeletal muscle. A total of 128 single-nucleotide polymorphisms (SNPs) within GPSM1 were analysed in 21,897 T2DM cases and 32,710 healthy controls from seven GWASs. The SNP rs28539249 in intron 9 of GPSM1 showed a nominally significant association with T2DM in Asians (OR = 1.07, 95% CI = 1.04-1.10, P < 10-4). The GPSM1 mRNA was increased in skeletal muscle and correlated with T2DM traits across obese mice model. An eQTL for the cis-acting regulation of GPSM1 expression in human skeletal muscle was identified for rs28539249, and the increased GPSM1 expression related with T2DM traits within GEO datasets. Another independent Asian cohort showed that rs28539249 is associated with the skeletal muscle expression of CACFD1, GTF3C5, SARDH, and FAM163B genes, which are functionally enriched for endoplasmic reticulum stress (ERS) and unfolded protein response (UPR) pathways. Moreover, rs28539249 locus was predicted to disrupt regulatory regions in human skeletal muscle with enriched epigenetic marks and binding affinity for CTCF. Supershift EMSA assays followed luciferase assays demonstrated the CTCF specifically binding to rs28539249-C allele leading to decreased transcriptional activity. Thus, the post-GWAS annotation confirmed the Asian-specific association of genetic variant in GPSM1 with T2DM, suggesting a role for the variant in the regulation in skeletal muscle.

Early weaning induces short- and long-term effects on pancreatic islets in Wistar rats of both sexes.

The World Health Organization recommends exclusive breastfeeding until 6months of age as an important strategy to reduce child morbidity and mortality. Studies have associated early weaning with the development of obesity and type 2 diabetes in adulthood. In our model, we demonstrated that early weaning leads to increased insulin secretion in adolescent males and reduced insulin secretion in adult offspring. Early weaned males exhibit insulin resistance in skeletal muscle. Early weaning did not change insulin signalling in the muscle of female offspring. Taking into account that insulin resistance is one of the primary factors for the development of type 2 diabetes mellitus, this work demonstrates the importance of breastfeeding in the fight against this disease. Early weaning (EW) leads to short- and long-term obesity and diabetes. This phenotype is also observed in experimental models, in which early-weaned males exhibit abnormal insulinaemia in adulthood. However, studies regarding the effect of EW on pancreatic islets are rare. We investigated the mechanisms by which glycaemic homeostasis is altered in EW models through evaluations of insulin secretion and its signalling pathway in offspring. Lactating Wistar rats and their pups were divided into the following groups: non-pharmacological EW (NPEW): mothers were wrapped with an adhesive bandage on the last 3days of lactation; pharmacological EW (PEW): mothers received bromocriptine to inhibit prolactin (1mg/kg body mass/day) on the last 3days of lactation; and control (C): pups underwent standard weaning at PN21. Offspring of both sexes were euthanized at PN45 and PN180. At PN45, EW males showed higher insulin secretion (vs. C). At PN170, PEW males exhibited hyperglycaemia in an oral glucose tolerance test (vs. C and NPEW). At PN180, EW male offspring were heavier; however, both sexes showed higher visceral fat. Insulin secretion was lower in EW offspring of both sexes. Males from both EW groups had lower glucokinase in islets, but unexpectedly, PEW males showed higher GLUT2, than did C. EW males exhibited lower insulin signalling in muscle. EW females exhibited no changes in these parameters compared with C. We demonstrated distinct alterations in the insulin secretion of EW rats at different ages. Despite the sex dimorphism in insulin secretion in adolescence, both sexes showed impaired insulin secretion in adulthood due to EW.