Skeletal Muscle Resistance Research Articles

Factors associated with poor long-term adherence after completing a pulmonary rehabilitation programme in patients with chronic obstructive pulmonary disease.

Although pulmonary rehabilitation programmes (PRPs) benefit patients with chronic obstructive pulmonary disease (COPD), poor adherence to these programmes is common. This study aimed to analyse the factors associated with poor long-term adherence after completing a PRP. We conducted a retrospective study of 70 patients with COPD who performed an 8-week outpatient PRP that included 24 sessions of aerobic training, skeletal muscle resistance exercises, physiotherapy and COPD education. The study classified the patients into 2 groups: (1) long-term adherence and (2) long-term non-adherence to the PRP. We considered long-term non-adherence when the patient did not attend the 32 weeks follow-up visit after beginning the PRP. We measured the degree of dyspnoea, quality of life, physical activity, anxiety-depression status, submaximal exercise capacity and COPD exacerbations in both groups. The patients' median age was 69.6 [63.8-75.0] years, and 71.4% were men. The median forced expiratory volume in 1 second was 60.0 [47.7-68.0] % of that predicted. We observed total COPD exacerbations and severe COPD exacerbations in the last year in 32 (45.7%) and 22 (31.4%) patients, respectively. Dyspnoea, physical activity and quality of life significantly improved after completing the PRP. Long-term non-adherence to the PRP was observed in 32 (45.7%) patients. In the single regression model, severe COPD exacerbations (p = 0.04) and dyspnoea (p = 0.03) were associated with long-term non-adherence to the PRP. In the multiple regression model, only severe COPD exacerbations remained as an associated factor (OR 2.7; 95% CI 1.1-8,1; p = 0.04). Approximately half of patients who complete PRPs present long-term non-adherence to the programme. Severe COPD exacerbations are associated with long-term non-adherence.

RF04 | PSUN334 Mineralocorticoid receptors mediate diet - induced lipid infiltration of skeletal muscle and insulin resistance

Abstract Excess blood lipids increase the total intramyocellular (IMC) lipid content and ectopic fat storage resulting in lipotoxicity and insulin resistance in skeletal muscle, which is one of the main targets of insulin whose action is central for the maintenance of glucose homeostasis. Consumption of a diet high in fat and refined sugars, a Western Diet (WD), has been shown to activate mineralocorticoid receptors (MRs) to promote insulin resistance. However, our understanding of the precise mechanisms by which enhanced MR activation promotes skeletal muscle insulin resistance remains unclear. In this study we investigated the roles and mechanisms by which enhanced MR signaling in soleus muscle promotes ectopic lipid accumulation and related insulin resistance in diet-induced obesity. Six week-old C57BL6J mice were fed either a mouse chow diet or WD with or without spironolactone (1 mg/kg/day) for 16 weeks. Spironolactone attenuated 16 weeks of WD - induced in vivo glucose intolerance and improved soleus insulin metabolic signaling (protein kinase B and AMP kinase α pathways). Improved insulin sensitivity was accompanied by increased Glut-4 expression in conjunction with decreased IMC lipid content and reduced free fatty acid (FFA) levels and CD36 expression in soleus skeletal muscle tissue. Related to this, miR-99a was identified to negatively target CD36(www.targetscan.org/vert_72/) and elevated CD36 induced excessive FFA uptake, ectopic lipid accumulation, as well as systemic and tissue insulin resistance. Furthermore, in skeletal muscle cells spironolactone prevented enhanced MR signaling mediated reduction of miR-99a and related increased CD36. These data indicate that inhibition of MR activation with spironolactone reversed diet - induced reduction of miR-99a, thereby reducing CD36 expression, leading to reduced IMC lipid content and improved soleus insulin sensitivity. Presentation: Saturday, June 11, 2022 1:48 p.m. - 1:53 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Control of blood pressure in the cold: differentiation of skin and skeletal muscle vascular resistance.

What is the central question of this study? Why does blood pressure increases during cold air exposure? Specifically, what is the contribution of skin and skeletal muscle vascular resistance during whole body versus isolated face cooling? What is the main finding and its importance? Whole-body cooling caused an increase in blood pressure through an increase in skeletal muscle and cutaneous vascular resistance. However, isolated mild face cooling caused an increase in blood pressure predominately via an increase in cutaneous vasoconstriction. The primary aim of this investigation was to determine the individual contribution of the cutaneous and skeletal muscle circulations to the cold-induced pressor response. To address this, we examined local vascular resistances in the cutaneous and skeletal muscle of the arm and leg. Thirty-four healthy individuals underwent three different protocols, whereby cold air to clamp skin temperature (27°C) was passed over (1) the whole-body, (2) the whole-body, but with the forearm pre-cooled to clamp cutaneous vascular resistance, and (3) the face. Cold exposure applied to the whole body or isolated to the face increased mean arterial pressure (all, P<0.001) and total peripheral resistance (all, P<0.047) compared to thermal neutral baseline. Whole-body cooling increased femoral (P<0.005) and brachial artery resistance (P<0.003) compared to thermoneutral baseline. Moreover, when the forearm was pre-cooled to remove the contribution of cutaneous resistance (P=0.991), there was a further increase in lower arm vasoconstriction (P=0.036) when whole-body cooling was superimposed. Face cooling also caused a reflex increase in lower arm cutaneous (P=0.009) and brachial resistance (P=0.050), yet there was no change in femoral resistance (P=0.815) despite a reflex increase in leg cutaneous resistance (P=0.010). Cold stress causes an increase in blood pressure through a change in total peripheral resistance that is largely due to cutaneous vasoconstriction with face cooling, but there is additional vasoconstriction in the skeletal muscle vasculature with whole-body cooling.

Effect of Intermittent Fasting on Muscle Glycogen Stores in Rats with High-Calorie Diet

Insulin resistance in skeletal muscle is important since it is normally responsible for most of the insulin-mediated glucose disposal and contains the largest glycogen storage regulated by insulin sensitivity. A high-calorie diet is known to be a risk factor for insulin resistance. Lifestyle modification by regulating caloric intake through intermittent fasting (IF) is recommended to prevent insulin resistance. This study aims to analyze the effect of eight weeks of intermittent fasting on skeletal muscle glycogen stores in rats with a four-week high-calorie diet. A total 24 healthy male Wistar rats were divided into four groups, Ad-libitum with a standard diet (AL-SD) Ad-libitum with a high-calorie diet (AL-HCD) IF with a standard diet (IF-SD) IF with a high-calorie diet (IF-HCD). Muscles were obtained and stained with PAS stain to evaluate glycogen expression based on color intensity. The results of the glycogen expression score were obtained as follows, AL-SD=2.113±0.589 AL-HCD=1.827±0.375 IF-SD=2.109±0.499 IF-HCD=1.979±0.334. Although there was no significant difference between groups (p> 0.05), IF can prevent excessive reduction of glycogen stores in subjects with a HCD compared to the AL-HCD group. In conclusion, this study suggests that IF might improve the reduction of glycogen stores in muscles due to a high-calorie diet.

Kaempferol 3-O-rutinoside from Antidesma acidum Retz. Stimulates glucose uptake through SIRT1 induction followed by GLUT4 translocation in skeletal muscle L6 cells

Ethnopharmacological relevanceAntidesma acidum Retz, a perennial herb is known for its anti-diabetic potential among the traditional health care providers of the tribal communities of Manipur, India. Scientific validation of the ancient knowledge on traditional use of this plant with the help of modern tools and techniques can promote further research and its use in health care. Aim of the studyType 2 Diabetes (T2D) is a complex metabolic disorder and linked with hyperglycemia occurring from insufficiency in insulin secretion, action, or both. The aim of this study was to scientifically validate the traditional myth behind the uses of this plant material against diabetes. More specifically, it was aimed to determine the effect of methanolic extract of A. acidum leaves and/or any of its bioactive phytochemical(s), in enhancing insulin sensitization and subsequently stimulating the insulin signaling cascade of glucose metabolism. Materials and methodsMethanol was used for extraction from the leaf powder of A. acidum followed by bioactivity guided fractionation and isolation of most active component. Biological evaluation was performed to determine the glucose uptake ability against insulin resistance in skeletal muscle (L6) cells. To understand the detailed mechanism of actions of the purified compound, several molecular biology and structural biology experiments such as Western blot, siRNA transfection assay and molecular docking study were performed. Results and discussionBioactivity guided isolation of pure compound and spectral data analysis led us to identify the active component as Kaempferol 3-O-rutinoside (KOR) for the first time from the leaf of A. acidum. Over expression of NAD-dependent histone deacetylase, Sirtuin 1 (SIRT1) was observed following KOR treatment. SIRT1 plays an important role in the metabolic pathway and over expression of SIRT implies that it involves in insulin signaling directly or indirectly. Molecular docking and simulation study showed the strong involvement between KOR and SIRT1.Treatment with KOR resulted in significant over expression of SIRT1followed by upregulation of insulin-dependent p-IRS, AKT and AMPK signaling molecules, and stimulation of the GLUT4 translocation, which ultimately enhanced the glucose uptake in sodium palmitate-treated insulin resistant L6 myotubes. Further, the effect of KOR on IRS1, AKT and AMPK phosphorylation, GLUT4 translocation, and glucose uptake was attenuated in SIRT1-knockdown myotubes. ConclusionOverall, the results of this study suggest that Kaempferol 3-O-rutinoside is the active component presents in the leaf of A. acidum which increases glucose consumption by inducing SIRT1 activation and consequently improves insulin sensitization. These results may find future applications in drug discovery research against T2DM.

Effect of Carica papaya on IRS-1/Akt Signaling Mechanisms in High-Fat-Diet-Streptozotocin-Induced Type 2 Diabetic Experimental Rats: A Mechanistic Approach.

Despite rigorous endeavors, existing attempts to handle type 2 diabetes (T2DM) are still a long way off, as a substantial number of patients do not meet therapeutic targets. Insulin resistance in skeletal muscle is discerned as a forerunner in the pathogenesis of T2DM and can be detected years before its progress. Studies have revealed the antidiabetic properties of Carica papaya (C. papaya), but its molecular mechanism on insulin receptor substrate-1 (IRS-1)/Akt signaling mechanisms is not yet known. The present study aimed to evaluate the role of C. papaya on IRS1 and Akt in high-fat-diet–streptozotocin-induced type 2 diabetic rats and also to analyze the bioactive compounds of C. papaya against IRS-1 and Akt via in silico analysis. Ethanolic extract of the leaves of C. papaya (600 mg/kg of body weight) was given daily for 45 days postinduction of T2DM up to the end of the study. Gluconeogenic enzymes, glycolytic enzymes, gene expression, and immunohistochemical analysis of IRS-1 and Akt in skeletal muscle were evaluated. C. papaya treatment regulated the levels of gluconeogenic and glycolytic enzymes and the levels of IRS-1 and Akt in skeletal muscle of type 2 diabetic animals. In silico studies showed that trans-ferulic acid had the greatest hit rate against the protein targets IRS-1 and Akt. C. papaya restored the normoglycemic effect in diabetic skeletal muscle by accelerating the expression of IRS-1 and Akt.

Naringin Ameliorates Skeletal Muscle Atrophy and Improves Insulin Resistance in High-Fat-Diet-Induced Insulin Resistance in Obese Rats.

Obesity causes progressive lipid accumulation and insulin resistance within muscle cells and affects skeletal muscle fibres and muscle mass that demonstrates atrophy and dysfunction. This study investigated the effects of naringin on the metabolic processes of skeletal muscle in obese rats. Male Sprague Dawley rats were divided into five groups: the control group with normal diet and the obese groups, which were induced with a high-fat diet (HFD) for the first 4 weeks and then treated with 40 mg/kg of simvastatin and 50 and 100 mg/kg of naringin from week 4 to 8. The naringin-treated group showed reduced body weight, biochemical parameters, and the mRNA expressions of protein degradation. Moreover, increased levels of antioxidant enzymes, glycogen, glucose uptake, the expression of the insulin receptor substrate 1 (IRS-1), the glucose transporter type 4 (GLUT4), and the mRNA expressions of protein synthesis led to improved muscle mass in the naringin-treated groups. The in vitro part showed the inhibitory effects of naringin on digestive enzymes related to lipid and glucose homeostasis. This study demonstrates the potential benefits of naringin as a supplement for treating muscle abnormalities in obese rats by modulating the antioxidative status, regulating protein metabolism, and improved insulin resistance in skeletal muscle of HFD-induced insulin resistance in obese rats.

Role of Exosomes Derived from Adipose Tissue under Obese Conditions in Skeletal Muscle and Liver Cells: Commonalities and Differences.

To determine the correlation between obesity and insulin resistance in skeletal muscle and liver tissues, this study isolates exosomes from adipose tissue under obese conditions and investigates the effect of adipose tissue-derived exosomes (Ad-exosomes) in mouse muscle (C2C12 cells) and liver cell lines (AML12 cells). The study isolates exosomes from the adipose tissue of normal diet-fed mice or high-fat diet (HFD)-fed obese mice and confirms the uptake into differentiated C2C12 and AML12 cells. Ad-exosomes from HFD-fed mice induce insulin resistance, triglyceride (TG) accumulation, endoplasmic reticulum stress, and inflammation in both C2C12 and AML12 cells. Interestingly, the study finds that the TG accumulation induces by Ad-exosomes from HFD-fed obese mice is dramatically increased in AML12 cells compared with that in the differentiated C2C12 cells, and glucose uptake following the same treatment is decreased in C2C12 cells and increased in AML12 cells. In addition, Ad-exosomes from HFD-fed obese mice cause not only TG accumulation but also lipogenesis in AML12 cells. The results suggest that Ad-exosomes from HFD-fed obese mice cause insulin resistance in both the muscles and liver, but their effects on metabolism during the development of insulin resistance vary between tissues.

Aerobic Exercise Prevents Chronic Inflammation and Insulin Resistance in Skeletal Muscle of High-Fat Diet Mice.

Obesity is commonly accompanied by chronic tissue inflammation and leads to insulin resistance. Aerobic exercise is an essential treatment for insulin resistance and has anti-inflammatory effects. However, the molecular mechanisms of exercise on obesity-associated inflammation and insulin resistance remain largely unknown. Here, we evaluated the effects of aerobic exercise on inflammation and insulin resistance in skeletal muscles of high-fat diet (HFD) mice. Male C57BL/6J mice were fed a high-fat diet or a normal diet for 12 weeks, and then aerobic training was performed on a treadmill for 8 weeks. Body weight, fasting blood glucose, food intake levels, and glucose and insulin tolerance were evaluated. The levels of cytokines, skeletal muscle insulin resistance, and inflammation were also analyzed. Eight weeks of aerobic exercise attenuated HFD-induced weight gain and glucose intolerance, and improved insulin sensitivity. This was accompanied by enhanced insulin signaling. Exercise directly resulted in a significant reduction of lipid content, inflammation, and macrophage infiltration in skeletal muscles. Moreover, exercise alleviated HFD-mediated inflammation by suppressing the activation of the NF-κB pathway within skeletal muscles. These results revealed that aerobic exercise could lead to an anti-inflammatory phenotype with protection from skeletal muscle insulin resistance in HFD-induced mice.

Sclerostin aggravates insulin signaling in skeletal muscle and hepatic steatosis via upregulation of ER stress by mTOR-mediated inhibition of autophagy under hyperlipidemic conditions.

Recently, sclerostin (SCL), a circulating glycoprotein, was proposed to be a novel myokine involved in developing metabolic disorders. The association between SCL levels and insulin resistance in skeletal muscle, liver, and adipose tissue was studied in individuals with aggravated glucose tolerance. Thus, we hypothesized that elevated circulating SCL might affect skeletal muscle insulin signaling and hepatic lipid metabolism, and aimed to investigate the effects of SCL on skeletal muscle insulin resistance and hepatic steatosis in obesity using in vitro and in vivo experimental models under hyperlipidemic conditions. In the current study, we found elevated SCL messenger RNA expression levels in myocytes in obese patients. In addition to a higher blood level, SCL was expressed at an elevated level in the skeletal muscle of mice fed a high-fat diet (HFD). Higher SCL release levels and expression were also noticed in palmitate-treated C2C12 myocytes. SCL suppression by in vivo transfection improves skeletal muscle insulin resistance and hepatic steatosis in HFD-fed mice. The treatment of C2C12 myocytes with recombinant SCL aggravated insulin signaling. Furthermore, treatment with SCL augmented lipogenic lipid deposition in human primary hepatocytes. Treatment with SCL upregulated mammalian target of rapamycin (mTOR) phosphorylation and suppressed autophagy markers, thereby causing endoplasmic reticulum (ER) stress. 4-Phenylbutyric acid, a pharmacological ER stress inhibitor, abolished the effects of SCL on insulin signaling in C2C12 myocytes and lipid accumulation in primary hepatocytes. In conclusion, SCL promotes skeletal muscle insulin resistance and hepatic steatosis by upregulating ER stress via the mTOR/autophagy-mediated pathway. The present study suggests that antagonizing SCL might be a novel therapeutic strategy for simultaneously managing insulin resistance and hepatic steatosis in obesity.

A Review of free fatty acid-induced cell signaling, angiopoietin-like protein 4, and skeletal muscle differentiation

Postnatal skeletal muscle differentiation from quiescent satellite cells is a highly regulated process, although our understanding of the contribution of nutritional factors in myogenesis is limited. Free fatty acids (FFAs) are known to cause detrimental effects to differentiated skeletal muscle cells by increasing oxidative stress which leads to muscle wasting and insulin resistance in skeletal muscle. In addition, FFAs are thought to act as inhibitors of skeletal muscle differentiation. However, the precise molecular mechanisms underlying the effects of FFAs on skeletal muscle differentiation remains to be elucidated. There is a clear relationship between dietary FFAs and their ability to suppress myogenesis and we propose the hypothesis that the FFA-mediated increase in angiopoietin-like protein 4 (ANGPTL4) may play a role in the inhibition of differentiation. This review discusses the role of FFAs in skeletal muscle differentiation to-date and proposes potential mechanisms of FFA-induced ANGPTL4 mediated inhibition of skeletal muscle differentiation.

Mineralocorticoid Receptors Mediate Diet-Induced Lipid Infiltration of Skeletal Muscle and Insulin Resistance.

Excess circulating lipids increase total intramyocellular (IMC) lipid content and ectopic fat storage, resulting in lipotoxicity and insulin resistance in skeletal muscle. Consumption of a diet high in fat and refined sugars-a Western diet (WD)-has been shown to activate mineralocorticoid receptors (MRs) and promote insulin resistance. However, our understanding of the precise mechanisms by which enhanced MR activation promotes skeletal muscle insulin resistance remains unclear. In this study, we investigated the mechanisms by which enhanced MR signaling in soleus muscle promotes ectopic skeletal muscle lipid accumulation and related insulin resistance. Six-week-old C57BL/6J mice were fed either a mouse chow diet or a WD with or without spironolactone (1 mg/kg/day) for 16 weeks. Spironolactone attenuated 16 weeks of WD-induced in vivo glucose intolerance and insulin resistance, and improved soleus insulin metabolic signaling. Improved insulin sensitivity was accompanied by increased glucose transporter 4 (Glut4) expression in conjunction with decreased soleus free fatty acid and IMC lipid content, as well as CD36 expression. Additionally, spironolactone prevented WD-induced soleus mitochondria dysfunction. Furthermore, MR signaling also mediated WD/aldosterone-induced reductions in soleus microRNA (miR)-99a, which was identified to negatively target CD36 and prevented palmitic acid-induced increases in CD36 expression, lipid droplet formation, mitochondria dysfunction, and insulin resistance in C2C12 cells. These data indicate that inhibition of MR activation with spironolactone prevented diet-induced abnormal expression of miR-99a, which had the capacity to reduce CD36, leading to reduced IMC lipid content and improved soleus mitochondria function and insulin sensitivity.

Overexpression of TRIM32 promotes pancreatic β-cell autophagic cell death through Akt/mTOR pathway under high glucose conditions.

Type 2 diabetes mellitus (T2DM) is a growing worldwide epidemic and is characterized by progressive pancreatic β-cell dysfunction and insulin resistance. Tripartite motif protein 32 (TRIM32) belongs to the TRIM family protein and has been shown to be involve in insulin resistance in skeletal muscle and the liver. However, the effect of TRIM32 on pancreatic β-cell dysfunction and its mechanism remains unknown. In the current study, we found that serum TRIM32 concentrations of T2DM in patients were significantly elevated compared to those in healthy controls, which indicated that TRIM32 might be used as a diagnostic biomarker in T2DM patients. In INS-1 cells, exposure to high glucose (HG) conditions caused a significant elevation in TRIM32 expression and TRIM32 was located in the nucleus. Overexpression of TRIM32 in INS-1 cells exacerbated the effects of HG-induced autophagy and impaired insulin secretion. In contrast, the silencing of TRIM32 produced the opposite effect. Furthermore, TRIM32 overexpression decreased the phosphorylation levels of Akt and mTOR under HG conditions. However, the activation of Akt/mTOR by MHY1485 reversed the effects of TRIM32 on HG-treated INS-1 cells. Collectively, the present results suggested that TRIM32 participates in the development of T2DM by modulating autophagic cell death and insulin secretion, which might occur through the Akt/mTOR pathway. Thus, TRIM32 might be a promising target in T2DM therapy.

Globular adiponectin ameliorates insulin resistance in skeletal muscle by enhancing the LKB1-mediated AMPK activation via SESN2

Adiponectin has been demonstrated to be a mediator of insulin sensitivity; however, the underlined mechanisms remain unclear. SESN2 is a stress-inducible protein that phosphorylates AMPK in different tissues. In this study, we aimed to validate the amelioration of insulin resistance by globular adiponectin (gAd) and to reveal the role of SESN2 in the improvement of glucose metabolism by gAd. We used a high-fat diet-induced wild-type and SESN2−/− C57BL/6J insulin resistance mice model to study the effects of six-week aerobic exercise or gAd administration on insulin resistance. In vitro study, C2C12 myotubes were used to determine the potential mechanism by overexpressing or inhibiting SESN2. Similar to exercise, six-week gAd administration decreased fasting glucose, triglyceride and insulin levels, reduced lipid deposition in skeletal muscle and reversed whole-body insulin resistance in mice fed on a high-fat diet. Moreover, gAd enhanced skeletal muscle glucose uptake by activating insulin signaling. However, these effects were diminished in SESN2−/− mice. We found that gAd administration increased the expression of SESN2 and Liver kinase B1 (LKB1) and increased AMPK-T172 phosphorylation in skeletal muscle of wild-type mice, while in SESN2−/− mice, LKB1 expression was also increased but the pAMPK-T172 was unchanged. At the cellular level, gAd increased cellular SESN2 and pAMPK-T172 expression. Immunoprecipitation experiment suggested that SESN2 promoted the formation of complexes of AMPK and LKB1 and hence phosphorylated AMPK. In conclusion, our results revealed that SESN2 played a critical role in gAd-induced AMPK phosphorylation, activation of insulin signaling and skeletal muscle insulin sensitization in mice with insulin resistance.

In vivo transomic analyses of glucose-responsive metabolism in skeletal muscle reveal core differences between the healthy and obese states

Metabolic regulation in skeletal muscle is essential for blood glucose homeostasis. Obesity causes insulin resistance in skeletal muscle, leading to hyperglycemia and type 2 diabetes. In this study, we performed multiomic analysis of the skeletal muscle of wild-type (WT) and leptin-deficient obese (ob/ob) mice, and constructed regulatory transomic networks for metabolism after oral glucose administration. Our network revealed that metabolic regulation by glucose-responsive metabolites had a major effect on WT mice, especially carbohydrate metabolic pathways. By contrast, in ob/ob mice, much of the metabolic regulation by glucose-responsive metabolites was lost and metabolic regulation by glucose-responsive genes was largely increased, especially in carbohydrate and lipid metabolic pathways. We present some characteristic metabolic regulatory pathways found in central carbon, branched amino acids, and ketone body metabolism. Our transomic analysis will provide insights into how skeletal muscle responds to changes in blood glucose and how it fails to respond in obesity.

Resolvin D3 improves the impairment of insulin signaling in skeletal muscle and nonalcoholic fatty liver disease through AMPK/autophagy-associated attenuation of ER stress

Resolvin D3 (RD3), an endogenous lipid mediator derived from omega-3 fatty acids, has been documented to attenuate inflammation in various disease models. Although it has been reported that omega-3 fatty acids attenuate metabolic disorders, the roles of RD3 in insulin signaling in skeletal muscle and hepatic lipid metabolism remain unclear. In the current study, we examined the role of RD3 in skeletal muscle insulin resistance and hepatic steatosis using in vitro and in vivo obesity models. In mouse primary hepatocytes, RD3 treatment reduced lipid accumulation and the production of lipogenic proteins (processed SREBP1 and SCD1) while improving insulin signaling in C2C12 myocytes. Furthermore, RD3 treatment ameliorated palmitate-induced ER stress markers (phospho-eIF2α and CHOP) in mouse primary hepatocytes and C2C12 myocytes. Treatment with RD3 increased phospho-AMPK expression and autophagy markers (LC3 conversion, p62 degradation, and autophagosome formation). AMPK siRNA or 3-MA reduced the effects of RD3 on C2C12 myocytes and mouse primary hepatocytes treated with palmitate. Finally, we confirmed the therapeutic effects of RD3 on skeletal muscle insulin resistance and hepatic lipid metabolism in high-fat diet (HFD)-fed mice. In vivo transfection-mediated suppression of AMPK restored all these changes in animal models. The results of the present study suggest that RD3 alleviates insulin resistance in skeletal muscle and hepatic steatosis via AMPK/autophagy signaling and provides an effective and safe therapeutic approach for treating metabolic disorders, including insulin resistance, type 2 diabetes, and NAFLD.

Metabolic Remodeling with Hepatosteatosis Induced Vascular Oxidative Stress in Hepatic ERK2 Deficiency Mice with High Fat Diets.

We previously demonstrated the marked hepatosteatosis and endothelial dysfunction in hepatocyte-specific ERK2 knockout mice (LE2KO) with a high-fat/high-sucrose diet (HFHSD), but detailed metabolic changes and the characteristics in insulin-sensitive organs were not tested. This study aimed to characterize metabolic remodeling with changes in insulin-sensitive organs, which could induce endothelial dysfunction in HFHSD-LE2KO. The serum glucose and fatty acid (FA) were modestly higher in HFHSD-LE2KO than HFHSD-Control. FA synthesis genes were up-regulated, which was associated with the decreased phosphorylation of AMPK and ACC, and with the up-regulation of SREBP-1 in the liver from HFHSD-LE2KO. In FA and amino acids fraction analysis, arachidonic acid/eicosapentaenoic acid ratio, L-ornithine/arginine ratio, asymmetric dimethylarginine and homocysteine levels were elevated in HFHSD-LE2KO. Insulin-induced phosphorylation of AKT was blunted in skeletal muscle. Serum leptin and IL-1β were elevated, and serum adiponectin was decreased with the enlargement of epididymal adipocytes. Finally, the enhanced superoxide levels in the aorta, which were blunted with CCCP, apocynin, and tempol, were observed in HFHSD-LE2KO. A pre-incubation of aortic rings with tempol improved endothelial dysfunction in HFHSD-LE2KO. HFHSD-LE2KO revealed an acceleration of FA synthesis in the liver leading to insulin resistance in skeletal muscle and the enlargement of visceral adipocytes. Global metabolic remodeling such as changes in arginine metabolism, ω3/ω6 ratio, and adipocytokines, could affect the vascular oxidative stress and endothelial dysfunction in HFHSD-LE2KO.

Saturated Fatty Acid-Induced Endoplasmic Reticulum Stress and Insulin Resistance Are Prevented by Imoxin in C2C12 Myotubes.

In obesity, plasma free fatty acids (FFAs) levels are elevated due to enlarged adipose tissue mass. Saturated fatty acids can induce prolonged ER stress and insulin resistance. Double-stranded RNA-dependent Protein Kinase (PKR) is activated under stress conditions in skeletal muscle. The current study aimed to investigate the effect of imoxin (IMX), a selective PKR inhibitor, on palmitate-induced ER stress and insulin resistance in C2C12 myotubes. Cells were treated with 5 μM imoxin and exposed to 0.5 mM bovine serum albumin (BSA)-conjugated PA for 24 h. A subset of cells was stimulated with 50 nM insulin for the last 15 min. Glucose uptake was monitored and protein levels involved in ER stress and insulin signaling were measured by Western blotting. Palmitate stimulated PKR phosphorylation, which was prevented by imoxin. Moreover, imoxin reduced protein levels of ER stress-related markers including glucose-regulating protein 78 (GRP78), CCAAT-enhancer-binding protein homologous protein (CHOP), activating transcription factor 6 (ATF6) and spliced X-box binding protein 1 (XBP-1s) which were induced by palmitate. Furthermore, imoxin ameliorated palmitate-induced suppression of phospho-insulin receptor beta (p-IRβ) and Akt phosphorylation in myotubes. In addition, imoxin promoted glucose uptake in response to insulin under palmitate exposure. Furthermore, imoxin reduced phospho-c-Jun N-terminal kinase (p-JNK) induced by palmitate treatment. These findings suggest that imoxin may protect against saturated fatty acid-induced ER stress and insulin resistance in skeletal muscle, which are potentially mediated by PKR.

A Signature of Exaggerated Adipose Tissue Dysfunction in Type 2 Diabetes Is Linked to Low Plasma Adiponectin and Increased Transcriptional Activation of Proteasomal Degradation in Muscle.

Insulin resistance in skeletal muscle in type 2 diabetes (T2D) is characterized by more pronounced metabolic and molecular defects than in obesity per se. There is increasing evidence that adipose tissue dysfunction contributes to obesity-induced insulin resistance in skeletal muscle. Here, we used an unbiased approach to examine if adipose tissue dysfunction is exaggerated in T2D and linked to diabetes-related mechanisms of insulin resistance in skeletal muscle. Transcriptional profiling and biological pathways analysis were performed in subcutaneous adipose tissue (SAT) and skeletal muscle biopsies from 17 patients with T2D and 19 glucose-tolerant, age and weight-matched obese controls. Findings were validated by qRT-PCR and western blotting of selected genes and proteins. Patients with T2D were more insulin resistant and had lower plasma adiponectin than obese controls. Transcriptional profiling showed downregulation of genes involved in mitochondrial oxidative phosphorylation and the tricarboxylic-acid cycle and increased expression of extracellular matrix (ECM) genes in SAT in T2D, whereas genes involved in proteasomal degradation were upregulated in the skeletal muscle in T2D. qRT-PCR confirmed most of these findings and showed lower expression of adiponectin in SAT and higher expression of myostatin in muscle in T2D. Interestingly, muscle expression of proteasomal genes correlated positively with SAT expression of ECM genes but inversely with the expression of ADIPOQ in SAT and plasma adiponectin. Protein content of proteasomal subunits and major ubiquitin ligases were unaltered in the skeletal muscle of patients with T2D. A transcriptional signature of exaggerated adipose tissue dysfunction in T2D, compared with obesity alone, is linked to low plasma adiponectin and increased transcriptional activation of proteasomal degradation in skeletal muscle.

The road not taken: Evolution of tetrodotoxin resistance in the Sierra garter snake (Thamnophis couchii) by a path less travelled.

The repeated evolution of tetrodotoxin (TTX) resistance provides a model for testing hypotheses about the mechanisms of convergent evolution. This poison is broadly employed as a potent antipredator defence, blocking voltage-gated sodium channels (Nav ) in muscles and nerves, paralysing and sometimes killing predators. Resistance in taxa bearing this neurotoxin and a few predators appears to come from convergent replacements in specific Nav residues that interact with TTX. This stereotyped genetic response suggests molecular and phenotypic evolution may be constrained and predictable. Here, we investigate the extent of mechanistic convergence in garter snakes (Thamnophis) that prey on TTX-bearing newts (Taricha) by examining the physiological and genetic basis of TTX resistance in the Sierra garter snake (Th.couchii). We characterize variation in this predatory adaptation across populations at several biological scales: whole-animal TTX resistance; skeletal muscle resistance; functional genetic variation in three Nav encoding loci; and levels of gene expression for one of these loci. We found Th.couchii possess extensive geographical variation in resistance at the whole-animal and skeletal muscle levels. As in other Thamnophis, resistance at both levels is highly correlated, suggesting convergence across the biological levels linking organism to organ. However, Th.couchii shows no functional variation in Nav loci among populations or difference in candidate gene expression. Local variation in TTX resistance in Th.couchii cannot be explained by the same relationship between genotype and phenotype seen in other taxa. Thus, historical contingencies may lead different species of Thamnophis down alternative routes to local adaptation.