Glucose Metabolism In Skeletal Muscle Research Articles

ATP-binding cassette family C member 1 constrains metabolic responses to high-fat diet.

Glucocorticoids modulate glucose homeostasis, acting on metabolically active tissues such as liver, skeletal muscle, and adipose tissue. Intracellular regulation of glucocorticoid action in adipose tissue impacts metabolic responses to obesity. ATP-binding cassette family C member 1 (ABCC1) is a transmembrane glucocorticoid transporter known to limit the accumulation of exogenously administered corticosterone in adipose tissue. However, the role of ABCC1 in the regulation of endogenous glucocorticoid action and its impact on fuel metabolism has not been studied. Here, we investigate the impact of Abcc1 deficiency on glucocorticoid action and high fat-diet (HFD)-induced obesity. In lean mice, deficiency of Abcc1 increased endogenous corticosterone levels in skeletal muscle and adipose tissue but did not impact insulin sensitivity. In contrast, Abcc1-deficient mice on HFD displayed impaired glucose and insulin tolerance, and fasting hyperinsulinemia, without alterations in tissue corticosterone levels. Proteomics and bulk RNA sequencing revealed that Abcc1 deficiency amplified the transcriptional response to an obesogenic diet in adipose tissue but not in skeletal muscle. Moreover, Abcc1 deficiency impairs key signalling pathways related to glucose metabolism in both skeletal muscle and adipose tissue, in particular those related to OXPHOS machinery and Glut4. Together, our results highlight a role for ABCC1 in regulating glucose homeostasis, demonstrating diet-dependent effects that are not associated with altered tissue glucocorticoid concentrations.

Preventive and Therapeutic Efficacy of Roselle Beverage Residue in Late-Stage Type 2 Diabetic Rats

The residue from roselle beverage production is rich in polyphenols and dietary fiber. We investigated its potential as a preventive and therapeutic agent for type 2 diabetes mellitus (T2DM). Male Wistar rats were fed a high-fat high-fructose diet (HFFD) for 17 weeks, reaching insulin resistance by week 9, and induced to T2DM with streptozotocin (STZ) at week 13. Roselle beverage residue (RBR) was administered ad libitum mixed at 6% with the HFFD. Rats received HFFD+RBR as a preventive strategy starting at week 1 (healthy) and week 9 (insulin resistant), whereas the treatment strategy in T2DM rats started at week 14 alone or in combination with metformin (200 mg/kg/day), with a control metformin-treated group. All RBR-supplemented groups showed reduced serum glucose levels (1.4-fold to 1.8-fold) compared with the HFFD+STZ control group. Preventive RBR administration enhanced pancreatic function, leading to improved insulin sensitivity (6.5-fold to 7.9-fold). Gene expression analysis identified slight alterations in hepatic and skeletal muscle glucose metabolism. Additionally, RBR supplementation demonstrated a preventive role in mitigating hyperuricemia (2.1-fold to 2.2-fold), with no effect on glomerular hyperfiltration. While the exact mechanisms underlying RBR effects remain to be fully elucidated, our findings highlight its promising potential as a dietary supplement for preventing and treating T2DM.

Lactobacillus-derived protoporphyrin IX and SCFAs regulate the fiber size via glucose metabolism in the skeletal muscle of chickens.

The gut microbiota contributes to skeletal muscle energy metabolism and is an indirect factor affecting meat quality. However, the role of specific gut microbes in energy metabolism and fiber size of skeletal muscle in chickens remains largely unknown. In this study, we first performed cecal microbiota transplantation from Chinese indigenous Jingyuan chickens (JY) to Arbor Acres chickens (AA), to determine the effects of microbiota on skeletal muscle fiber and energy metabolism. Then, we used metagenomics, gas chromatography, and metabolomics analysis to identify functional microbes. Finally, we validated the role of these functional microbes in regulating the fiber size via glucose metabolism in the skeletal muscle of chickens through feeding experiments. The results showed that the skeletal muscle characteristics of AA after microbiota transplantation tended to be consistent with that of JY, as the fiber diameter was significantly increased, and glucose metabolism level was significantly enhanced in the pectoralis muscle. L. plantarum, L. ingluviei, L. salivarius, and their mixture could increase the production of the microbial metabolites protoporphyrin IX and short-chain fatty acids, therefore increasing the expression levels of genes related to the oxidative fiber type (MyHC SM and MyHC FRM), mitochondrial function (Tfam and CoxVa), and glucose metabolism (PFK, PK, PDH, IDH, and SDH), thereby increasing the fiber diameter and density. These three Lactobacillus species could be promising probiotics to improve the meat quality of chicken.IMPORTANCEThis study revealed that the L. plantarum, L. ingluviei, and L. salivarius could enhance the production of protoporphyrin IX and short-chain fatty acids in the cecum of chickens, improving glucose metabolism, and finally cause the increase in fiber diameter and density of skeletal muscle. These three microbes could be potential probiotic candidates to regulate glucose metabolism in skeletal muscle to improve the meat quality of chicken in broiler production.

Time-of-day does not impact skeletal muscle contractile function, fatigability, or contraction-stimulated glucose uptake

Time-of-day impacts different aspects of mammalian physiology, such as the sleep/wake cycle, blood pressure, and body temperature. These time-of-day changes, or “circadian cycles”, are regulated by a central clock in the central suprachiasmatic nucleus of the hypothalamus and peripheral clocks located in other tissues, such as the liver, heart, and skeletal muscle. Interestingly, a growing body of data suggests that exercise performance and capacity also vary by time-of-day, with chronobiological effects on skeletal muscle metabolism and contractile function (i.e., force production) being proposed as important mediators. However, to date, no studies have specifically investigated the effect of time-of-day on skeletal muscle contractile function or glucose metabolism. The objective of this work was to assess ex vivo skeletal muscle contractile function, fatigability, and contraction-stimulated glucose uptake in the extensor digitorum longus (EDL) and soleus from 13-week-old female C57BL/6NJ mice at four different times-of-day (Light cycle time-points: Zeitgeber Time [ZT] ZT1 and ZT7; Dark cycle time-points: ZT13 and ZT19). We used an ex vivo approach as it allowed us to study skeletal muscle in isolation, and thus, independent of other factors that might influence contractile function or glucose metabolism (e.g., nerve function, humoral factors, etc.). We hypothesized that skeletal muscle contractile function, fatigability and contraction-stimulated glucose uptake would not be different by time-of-day. To control for meal-timing, mice were orally gavaged with dextrose (2 g/kg) and then fasted (3 hours) before contractile testing, which consisted of a force-frequency test (1-120 Hz, 0.3 ms pulse, 35 volts; 300 ms and 400 ms train for EDL and soleus, respectively) followed by a 15 minute fatigue test in which the muscles were repeatedly stimulated (EDL: 100 Hz stimulation every 15 seconds; Soleus: 30 Hz stimulation every 2 seconds). Glucose uptake was measured during the fatigue test using the [3H]-2-deoxyglucose (2DOG) uptake approach, with the contralateral muscle being the rested control. Significantly, contractile function, including peak twitch tension and maximal tetanic tension (EDL — ZT1: 281±13; ZT7: 300±21; ZT13: 261±28; ZT19: 280±40 kPa, P = 0.7661, one-way ANOVA; Soleus — ZT1: 117±16; ZT7: 115±18; ZT13: 117±11; ZT19: 111±10 kPa, P = 0.9923, one-way ANOVA) were not different by time-of-day. Similarly, fatigability, as measured as the tension·time integral during the 15 min fatigue test was not different by time-of-day (EDL — ZT1: 640±89; ZT7: 686±92; ZT13: 708±110; ZT19: 683±142 kPa·min, P = 0.9803, one-way ANOVA; Soleus — ZT1: 245±42; ZT7: 261±35; ZT13: 200±41; ZT19: 244±34 kPa·min, P = 0.7019, one-way ANOVA). Finally, while contraction significantly increased 2DOG uptake above basal by ~1.6-fold and ~1.8-fold in the soleus and EDL, respectively, this increase was not different by time-of-day. Taken together, these results demonstrate that time-of-day does not impact skeletal muscle contractile function, fatigability, or contraction-stimulated glucose uptake, regardless of muscle type. By extension, skeletal muscle, per se, is unlikely to be a contributing factor to the documented effects of time-of-day on whole-body exercise performance. This was funded by the UC San Diego Medical Scientist Training Program and NIH R21 AG067495. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Impaired exercise-induced increase in serum IGF-1 in humans with obesity

Changes in circulating insulin-like growth factor 1 (IGF-1) implicate regulation of skeletal muscle metabolism, including protein and glucose metabolism. Previous studies have shown that an acute bout of exercise increases serum IGF-1 concentrations in healthy, lean humans. However, exercise-induced changes in serum IGF-1 concentrations in humans with obesity remain unknown. We compared changes in plasma IGF-1 during and after an acute bout of endurance exercise between humans with and without obesity. Eight subjects with obesity (i.e., OB: BMI = 34.48 ± 2.96) and eight subjects without obesity (i.e., LN: BMI = 24.45 ± 2.43 kg/m2) exercised for 45 min in a cycle ergometer at 65% of their maximum oxygen uptake, after an overnight 10-h fast. Blood draws were taken immediately before exercise, at 15 and 30 minutes (i.e., during exercise), and at 55, 75, 95, and 115 minutes after the start of the exercise. Serum concentrations of total IGF-1 and insulin were determined using commercially available ELISA assays (Alpco 22-IGFHU-E01 and 80-INSHU-E10.1, respectively). Plasma glucose concentrations were determined using an automatic analyzer (YSI glucose analyzer). One-way repeated measures analyses of variance were carried out to detect significant changes over time within each group. Independent t tests were used to determine group differences at each time point. Alpha level was set at p ≤ 0.05 and data are reported as mean ± SD. There were no significant ( p > 0.05) differences between groups for IGF-1 serum concentrations at baseline (LN = 205.61 ± 40.07 ng/mL, OB = 200.89 ± 80.40 ng/mL) nor during or after exercise. Significant increases from baseline in serum IGF-1 concentrations were detected in the LN group at 15 min (231.30 ± 50.47 ng/mL, p = 0.007) and 30 min (227.94 ± 49.02 ng/mL, p = 0.04) during exercise, followed by significant decreases from baseline at 95 min (189.99 ± 34.73 ng/mL, p = 0.052) and 115 min (196.42 ± 40.39 ng/mL, p = 0.023). No significant ( p > 0.05) differences from baseline were observed in the obese group neither during nor after exercise. Higher serum insulin concentrations were observed in the OB group at baseline (LN = 5.55 ± 2.62 μIU/mL, OB = 11.07 ± 5.76 μIU/mL, p = 0.027) but significant group differences no longer existed ( p > 0.05) during exercise and up to 55 min after exercise; however, insulin concentrations for the OB group were significantly greater than those measured in the LN group at 75 min ( p = 0.028), 95 min ( p = 0.008), and 115 min ( p = 0.007) after exercise. Moreover, a significant increase from baseline was measured 55 min after exercise in the lean group (8.22 ± 3.13 μIU/mL, p = 0.005), whereas no significant changes were observed in the OB groups at any time point ( p > 0.05). No significant ( p > 0.05) group differences were detected for plasma glucose concentrations at any time point, and despite a significant decrease from baseline observed in the LN group at 115 min after exercise (baseline = 83.32 ± 7.66 mg/dL, 115 min = 81.02 ± 7.00 mg/dL, p = 0.044). In conclusion, endurance exercise increases serum IGF-1 concentrations in humans without obesity, but this response is impaired in humans with obesity. National Institute of Health (NIH)\National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Grant/Award Number: R01DK123441. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cold exposure affects glucose metabolism, lipid droplet deposition and mitophagy in skeletal muscle of newborn goats

Cold exposure is a common stressor for newborn goats. Skeletal muscle plays an important role in maintaining whole-body homeostasis of glucose and lipid metabolism. However, the molecular mechanisms underlying regulation of skeletal muscle of newborn goats by cold exposure remains unclear. In this study, we found a significant increase (P < 0.01) in serum glucagon levels after 24 h of cold exposure (COLD, 6°C), while glucose and insulin concentrations were significantly decreased (P < 0.01) compared to room temperature (RT, 25°C). Additionally, we found that cold exposure reduced glycogen content (P < 0.01) in skeletal muscle. Pathway enrichment analysis revealed that cold exposure activated skeletal muscle glucose metabolism pathways (including insulin resistance and the insulin signaling pathway) and mitophagy-related pathways. Cold exposure up-regulated the expression of genes involved in fatty acid and triglyceride synthesis, promoting skeletal muscle lipid deposition. Notably, cold exposure induced mitophagy in skeletal muscle.

Evaluation of skeletal muscle function in male rats with doxorubicin-induced myopathy following various exercise techniques: the significant role of glucose transporter 4

A common anthracycline antibiotic used to treat cancer patients is doxorubicin (DOX). One of the effects of DOX therapy is skeletal muscle fatigue. Our goal in this research was to study the beneficial effect of exercise on DOX-induced damaged muscle fibers and compare the effect of different exercise strategies (prophylactic, post- toxicity and combined) on DOX toxicity. Five groups were created from 40 male rats: group I, control group; group II, DOX was administered intraperitoneally for 2 weeks over 6 equal injections (each 2.5 mg/kg); group III, rats trained for 3 weeks before DOX; group IV, rats trained for 8 weeks after DOX; and group V, rats were trained for 3 weeks before DOX followed by 8 weeks after. Measures of oxidative damage (H2O2, catalase), inflammation (TNF-α), and glucose transporter 4 (GLUT4) expression on skeletal muscle were assessed. Also, Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) was estimated. Skeletal performance was evaluated by contraction time (CT), half relaxation time (1/2 RT), and force-frequency relationship by the end of this research. The current study demonstrated a detrimental effect of DOX on skeletal performance as evidenced by a significant increase in CT and 1/2 RT compared to control; in addition, H2O2, TNF-α, and HOMA-IR were significantly increased with a significant decrease in GLUT4 expression and catalase activity. Combined exercise therapy showed a remarkable improvement in skeletal muscle performance, compared to DOX, CT, and 1/2 RT which were significantly decreased; H2O2 and TNF-α were significantly decreased unlike catalase antioxidant activity that significantly increased; in addition, skeletal muscle glucose metabolism was significantly improved as GLUT4 expression significantly increased and HOMA-IR was significantly decreased. Exercise therapy showed significant improvement in all measured parameters relative to DOX. However, combined exercise therapy showed the best improvement relative to both pre-exercise and post-exercise groups.

Sucrose-Enriched and Carbohydrate-Free High-Fat Diets Distinctly Affect Substrate Metabolism in Oxidative and Glycolytic Muscles of Rats.

Skeletal muscle substrate preference for fuel is largely influenced by dietary macronutrient availability. The abundance of dietary carbohydrates promotes the utilization of glucose as a substrate for energy production, whereas an abundant dietary fat supply elevates rates of fatty acid (FA) oxidation. The objective of this study was to determine whether an obesogenic, high-fat, sucrose-enriched (HFS) diet or a carbohydrate-free ketogenic diet (KD) exert distinct effects on fat, glucose, and ketone metabolism in oxidative and glycolytic skeletal muscles. Male Wistar rats were fed either a HFS diet or a KD for 16 weeks. Subsequently, the soleus (Sol), extensor digitorum longus (EDL), and epitrochlearis (Epit) muscles were extracted to measure palmitate oxidation, insulin-stimulated glucose metabolism, and markers of mitochondrial biogenesis, ketolytic capacity, and cataplerotic and anaplerotic machinery. Sol, EDL, and Epit muscles from KD-fed rats preserved their ability to elevate glycogen synthesis and lactate production in response to insulin, whereas all muscles from rats fed with the HFS diet displayed blunted responses to insulin. The maintenance of metabolic flexibility with the KD was accompanied by muscle-fiber-type-specific adaptive responses. This was characterized by the Sol muscle in KD-fed rats enhancing mitochondrial biogenesis and ketolytic capacity without elevating its rates of FA oxidation in comparison with that in HFS feeding. Conversely, in the Epit muscle, rates of FA oxidation were increased, whereas the ketolytic capacity was markedly reduced by the KD in comparison with that by HFS feeding. In the EDL muscle, the KD also increased rates of FA oxidation, although it did so without altering its ketolytic capacity when compared to HFS feeding. In conclusion, even though obesogenic and ketogenic diets have elevated contents of fat and alter whole-body substrate partitioning, these two dietary interventions are associated with opposite outcomes with respect to skeletal muscle metabolic flexibility.

Saengmaeksan, a traditional polyherbal formulation containing Panax ginseng, improves energy metabolism during exercise.

Saengmaeksan (SMS), a representative oriental medicine that contains Panax ginseng Meyer, Liriope muscari, and Schisandra chinensis (1:2:1), is used to improve body vitality and enhance physical activity. However, there is limited scientific evidence to validate the benefits of SMS. Here, we investigated the in vitro and in vivo regulatory effects of SMS and its constituents on energy metabolism and the underlying molecular mechanisms. For this, quantitative real-time polymerase chain reaction, 3D holotomographic microscopy, western blotting, and glucose uptake experiments using 18F-fluoro-2-deoxy-D-glucose (18F-FDG) were performed using L6 cells to investigate in vitro energy metabolism changes. In addition, 18F-fluorocholine (18F-FCH) and 18F-FDG positron emission tomography/computed tomography (PET/CT) analyses, immunohistochemistry, and respiratory gas analysis were performed in mice post-endurance exercise on a treadmill. In the energy metabolism of L6 cells, a significant reversal in glucose uptake was observed in the SMS-treated group, as opposed to an increase in uptake over time compared to the untreated control group. Furthermore, P. ginseng alone and SMS significantly decreased the volume of lipid droplets. SMS also regulated the phosphorylation of extracellular signal-regulated kinase (ERK), phosphorylation of p38, mitochondrial morphology, and the expression of apurinic/apyrimidinic endonuclease 1/redox factor-1 (APE/Ref-1) in H2O2-stimulated L6 cells. In addition, SMS treatment was found to regulate whole body and muscle energy metabolism in rats subjected to high-intensity exercise, as well as glucose and lipid metabolism in skeletal muscle. Therefore, SMS containing P. ginseng ameliorated imbalanced energy metabolism through oxidative stress-induced APE/Ref-1 expression. SMS may be a promising supplemental option for metabolic performance.

240 Prolonged Maternofetal Inflammation in the Pregnant Ewe at Mid-Gestation Increases Subsequent Fetal Inflammatory Tone and Disrupts Skeletal Muscle Growth and Glucose Metabolism Near Term

Abstract Chronic maternofetal inflammation in late gestation (i.e., peak fetal growth) causes fetal intrauterine growth restriction (IUGR) in sheep, which was associated with deficits in growth, body composition, and metabolic function before and after birth. However, the impact of sustained maternofetal inflammation during mid-gestation (i.e., peak placental growth and development) has not been explored. Therefore, our objective was to determine the effects of sustained maternofetal inflammation during this critical window on subsequent fetal inflammatory tone, metabolism, and myoblast (i.e., muscle stem cell) function. Pregnant ewes were injected every 3rd day from the 50th to 65th d of gestational age (dGA; term = 150 dGA) with saline (control; n = 12) or bacterial lipopolysaccharide endotoxin to induce maternofetal inflammation and IUGR (MI-IUGR; n = 12). Fetuses were surgically catheterized on dGA 118 to collect blood samples, and a hyperinsulinemic-euglycemic clamp (HEC) was performed on dGA 123. Fetuses were necropsied on dGA 125 to collect semitendinosus muscle samples. Fetal plasma TNFα concentrations tended to be greater (P = 0.07) for MI-IUGR fetuses (440 ± 45 pg/m l) than for controls (348 ± 24 pg/mL). Fetal blood O2 partial pressures were 12% less (P &amp;lt; 0.05) and maternofetal O2 gradients tended to be 11% greater (P = 0.08) for MI-IUGR fetuses than for controls. Hindlimb-specific glucose uptake rates did not differ between fetal groups, but hindlimb-specific glucose oxidation rates were reduced (P &amp;lt; 0.05) by 15% under basal conditions and by 27% under hyperinsulinemic conditions for MI-IUGR fetuses compared with controls. Semitendinosus glycogen content and β2 adrenoceptor content did not differ between fetal groups, but semitendinosus content of the TNFα receptor, TNFR1, was 41% greater (P &amp;lt; 0.05) for MI-IUGR fetuses than for controls. Immunohistochemistry revealed 18% fewer (P &amp;lt; 0.05) proliferating myoblasts (pax7+/Ki67+) and 38% fewer (P &amp;lt; 0.05) differentiated myoblasts (myogenin+) in semitendinosus from MI-IUGR fetuses compared with controls, which coincided with 13% smaller (P &amp;lt; 0.05) muscle fibers. From these findings, we conclude that sustained maternofetal inflammation during peak placental development at mid-gestation resulted in enhanced fetal inflammatory tone near term, which in turn impaired myoblast function, muscle fiber hypertrophy, and muscle glucose metabolism.

DOCK3 regulates normal skeletal muscle regeneration and glucose metabolism.

DOCK (dedicator of cytokinesis) is an 11-member family of typical guanine nucleotide exchange factors (GEFs) expressed in the brain, spinal cord, and skeletal muscle. Several DOCK proteins have been implicated in maintaining several myogenic processes such as fusion. We previously identified DOCK3 as being strongly upregulated in Duchenne muscular dystrophy (DMD), specifically in the skeletal muscles of DMD patients and dystrophic mice. Dock3 ubiquitous KO mice on the dystrophin-deficient background exacerbated skeletal muscle and cardiac phenotypes. We generated Dock3 conditional skeletal muscle knockout mice (Dock3 mKO) to characterize the role of DOCK3 protein exclusively in the adult muscle lineage. Dock3 mKO mice presented with significant hyperglycemia and increased fat mass, indicating a metabolic role in the maintenance of skeletal muscle health. Dock3 mKO mice had impaired muscle architecture, reduced locomotor activity, impaired myofiber regeneration, and metabolic dysfunction. We identified a novel DOCK3 interaction with SORBS1 through the C-terminal domain of DOCK3 that may account for its metabolic dysregulation. Together, these findings demonstrate an essential role for DOCK3 in skeletal muscle independent of DOCK3 function in neuronal lineages.

Myopathies of endocrine origin: A review for physicians

Myopathies are a common manifestation of endocrine disorders. Endocrine myopathies are often overlooked while considering differential diagnoses in patients with musculoskeletal symptoms. The hindrance to mobility and the musculoskeletal discomfort owing to these myopathies are important causes of disability and depreciated quality of life in these patients. Endocrine myopathies occur due to the effects of endogenous or iatrogenic hormonal imbalance on skeletal muscle protein and glucose metabolism, disrupting the excitation-contraction coupling. Abnormalities of the pituitary, thyroid, parathyroid, adrenal, and gonadal hormones have all been associated with myopathies and musculoskeletal symptoms. Endocrine myopathies can either be the complication of a secondary endocrine disorder or a presenting symptom of a missed underlying disorder. Therefore, an underlying endocrine abnormality must always be excluded in all patients with musculoskeletal symptoms. This review presents a compilation of various endocrine myopathies, their etiopathogenesis, clinical presentation, diagnostic modalities, and treatment protocols.

Microbiota influences host exercise capacity via modulation of skeletal muscle glucose metabolism in mice

The microbiota enhances exercise performance and regulates host physiology and energy metabolism by producing beneficial metabolites via bacterial fermentation. In this study, we discovered that germ-free (GF) mice had a reduced capacity for aerobic exercise as well as low oxygen consumption rates and glucose availability. Surprisingly, GF mice showed lower body weight gain and lower fat mass than specific pathogen-free (SPF) mice. Therefore, we hypothesized that these paradoxical phenotypes could be mediated by a compensatory increase in lipolysis in adipose tissues owing to impaired glucose utilization in skeletal muscle. Our data revealed that gut microbiota depletion impairs host aerobic exercise capacity via the deterioration of glucose storage and utilization. The improved browning ability of GF mice may have contributed to the lean phenotype and negatively affected energy generation. These adaptations limit obesity in GF mice but impede their immediate fuel supply during exercise, resulting in decreased exercise performance.

Chronic UCN2 treatment desensitizes CRHR2 and improves insulin sensitivity

Urocortin 2 (UCN2) acts as a ligand for the G protein-coupled receptor corticotropin-releasing hormone receptor 2 (CRHR2). UCN2 has been reported to improve or worsen insulin sensitivity and glucose tolerance in vivo. Here we show that acute dosing of UCN2 induces systemic insulin resistance in male mice and skeletal muscle. Inversely, chronic elevation of UCN2 by injection with adenovirus encoding UCN2 resolves metabolic complications, improving glucose tolerance. CRHR2 recruits Gs in response to low concentrations of UCN2, as well as Gi and β-Arrestin at high concentrations of UCN2. Pre-treating cells and skeletal muscle ex vivo with UCN2 leads to internalization of CRHR2, dampened ligand-dependent increases in cAMP, and blunted reductions in insulin signaling. These results provide mechanistic insights into how UCN2 regulates insulin sensitivity and glucose metabolism in skeletal muscle and in vivo. Importantly, a working model was derived from these results that unifies the contradictory metabolic effects of UCN2.

581-P: The Effects of Resistance Training on Insulin Resistance Development in Female Rodents with Type 1 Diabetes

The etiology of insulin resistance (IR) development in type 1 diabetes (T1D) remains unclear; however, impaired glucose metabolism in skeletal muscle may play a role. While IR development has been established in male rodents with T1D, female rodents have yet to be examined in this context. Resistance exercise training (RT) has been shown to improve IR and is associated with a lower risk of hypoglycemia onset in T1D compared to aerobic exercise. The purpose of this study was to investigate the effects of RT on IR development in female rodents with T1D. Forty Sprague-Dawley 8-week-old female rats were divided into four groups: control sedentary (CS; n=10), control trained (CT; n=10), T1D sedentary (DS; n=10), T1D trained (DT; n=10). Multiple low-dose Streptozotocin injections (20 mg/kg each day for 7 consecutive days) were used to induce T1D. Blood glucose levels were maintained in normal range (4-9mmol/L) with one implanted insulin pellet (2IU/day). CT and DT underwent weighted ladder climbing 5 days/week for 6 weeks. Intravenous glucose tolerance tests (IVGTT) were conducted on all animals during weeks 4 and 7. Results demonstrate that DS animals exhibited significantly increased weekly blood glucose measures compared to all groups including DT (p&amp;lt;0.05), despite similar insulin dosage levels. This was concomitant with a significant increase in area under the curve following IVGTT from week 4 to week 7 in DS (p&amp;lt;0.05), indicative of a reduction in insulin sensitivity. DS animals also exhibited significantly greater glycogen content in white gastrocnemius muscle compared to all groups (p&amp;lt;0.05). These results indicate that female rodents with T1D develop poor glycemic control and IR which can be attenuated with RT, possibly related to differences in glycogen content within muscle. This data supports the negative role of elevated muscle glycogen on insulin sensitivity in T1D and the potential role of RT in ameliorating these metabolic changes. Disclosure M.Sammut: None. D.Mcbey: None. C.Melling: None.

Aerobic exercise reduced the amount of CHRONO bound to BMAL1 and ameliorated glucose metabolic dysfunction in skeletal muscle of high-fat diet-fed mice

AimsThe purpose of this study was to investigate the effects of aerobic exercise on the CHRONO-BMAL1 pathway and glucose metabolism in skeletal muscle of high-fat diet (HFD)-fed mice. Main methodsMale C57BL/6J mice were randomly allocated into four groups: normal chow diet with control (NCD + CON), NCD with exercise (NCD + EXE), HFD with control (HFD + CON) and HFD with exercise (HFD + EXE). The NCD and HFD groups were respectively fed a diet of 10 % and 60 % kilocalories from fat for 12 weeks. During the dietary intervention, EXE groups were subjected to 70 % VO2max intensity of treadmill exercise six times per week for 12 weeks. Body weight, energy intake, fat weight, serum lipid profiles, systemic glucose homeostasis, the amount of CHRONO bound to BMAL1, the enzymatic activity, mRNA and protein expression involved in glucose metabolism of skeletal muscle were measured. Key findingsThe results showed that the 12-week HFD feeding without exercise induced weight gain, serum dyslipidemia and insulin resistance. Furthermore, HFD increased the amount of CHRONO bound to BMAL1 and repressed the glucose metabolism in skeletal muscle. However, aerobic exercise prevented weight gain, serum dyslipidemia and systemic insulin resistance in the HFD-fed mice. Meanwhile, aerobic exercise also decreased the amount of CHRONO bound to BMAL1 and increased the glucose uptake, glucose oxidation and glycogenesis in skeletal muscle of the HFD-fed mice. SignificanceThese data suggested that aerobic exercise could counterbalance CHRONO interacted with BMAL1 and prevent glucose metabolism dysfunction of skeletal muscle, and finally maintain whole-body insulin sensitivity in the HFD-fed mice.

Effects of short-term endurance and strength exercise in the molecular regulation of skeletal muscle in hyperinsulinemic and hyperglycemic Slc2a4+/- mice.

Intriguingly, hyperinsulinemia, and hyperglycemia can predispose insulin resistance, obesity, and type 2 diabetes, leading to metabolic disturbances. Conversely, physical exercise stimulates skeletal muscle glucose uptake, improving whole-body glucose homeostasis. Therefore, we investigated the impact of short-term physical activity in a mouse model (Slc2a4+/-) that spontaneously develops hyperinsulinemia and hyperglycemia even when fed on a chow diet. Slc2a4+/- mice were used, that performed 5days of endurance or strength exercise training. Further analysis included physiological tests (GTT and ITT), skeletal muscle glucose uptake, skeletal muscle RNA-sequencing, mitochondrial function, and experiments with C2C12 cell line. When Slc2a4+/- mice were submitted to the endurance or strength training protocol, improvements were observed in the skeletal muscle glucose uptake and glucose metabolism, associated with broad transcriptomic modulation, that was, in part, related to mitochondrial adaptations. The endurance training, but not the strength protocol, was effective in improving skeletal muscle mitochondrial activity and unfolded protein response markers (UPRmt). Moreover, experiments with C2C12 cells indicated that insulin or glucose levels could contribute to these mitochondrial adaptations in skeletal muscle. Both short-term exercise protocols were efficient in whole-body glucose homeostasis and insulin resistance. While endurance exercise plays an important role in transcriptome and mitochondrial activity, strength exercise mostly affects post-translational mechanisms and protein synthesis in skeletal muscle. Thus, the performance of both types of physical exercise proved to be a very effective way to mitigate the impacts of hyperglycemia and hyperinsulinemia in the Slc2a4+/- mouse model.

Dietary Methionine Restriction Improves Gastrocnemius Muscle Glucose Metabolism through Improved Insulin Secretion and H19/IRS-1/Akt Pathway in Middle-Aged Mice

Methionine restriction (MR) improves glucose metabolism. In skeletal muscle, H19 is a key regulator of insulin sensitivity and glucose metabolism. Therefore, this study aims to reveal the underlying mechanism of H19 upon MR on glucose metabolism in skeletal muscle. Middle-aged mice were fed MR diet for 25 weeks. Mouse islets β cell line β-TC6 cells and mouse myoblast cell line C2C12 cells were used to establish the apoptosis or insulin resistance model. Our findings showed that MR increased B-cell lymphoma-2 (Bcl-2) expression, deceased Bcl-2 associated X protein (Bax), cleaved cysteinyl aspartate-specific proteinase-3 (Caspase-3) expression in pancreas, and promoted insulin secretion of β-TC6 cells. Meanwhile, MR increased H19 expression, insulin Receptor Substrate-1/insulin Receptor Substrate-2 (IRS-1/IRS-2) value, protein Kinase B (Akt) phosphorylation, glycogen synthase kinase-3β (GSK3β) phosphorylation, and hexokinase 2 (HK2) expression in gastrocnemius muscle and promoted glucose uptake in C2C12 cells. But these results were reversed after H19 knockdown in C2C12 cells. In conclusion, MR alleviates pancreatic apoptosis and promotes insulin secretion. And MR enhances gastrocnemius muscle insulin-dependent glucose uptake and utilization via the H19/IRS-1/Akt pathway, thereby ameliorating blood glucose disorders and insulin resistance in high-fat-diet (HFD) middle-aged mice.

Low-Carbohydrate Diet Modulates Glucose–Lipid Utilization in Skeletal Muscle of Diabetic Mice

Type 2 diabetes is associated with many complications, including skeletal muscle atrophy. Ketogenic diets and low-carbohydrate diets (LCD) have recently been introduced as dietary interventions in patients with diabetes, but their effects on glucose and lipid metabolism in skeletal muscle have not been studied. In the current study, we compared the effects of LCD and ketogenic diet on glucose and lipid metabolism in skeletal muscle of diabetic mice. C57BL/6J mice with type 2 diabetes, constructed by a high-fat diet combined with streptozotocin, were fed a standard diet, a high-fat diet, an LCD, or a ketogenic diet for 14 weeks, respectively. Here, we found that the LCD, rather than the ketogenic diet, retained skeletal muscle weight and suppressed the expression of atrophy-related genes in diabetic mice. In addition, the LCD had more glycolytic/type IIb myofiber content and inhibited forkhead box O1 and pyruvate dehydrogenase kinase 4 expression, leading to improved glucose utilization. However, the ketogenic diet maintained more oxidative/type I myofibers. Moreover, compared with the ketogenic diet, the LCD decreased intramuscular triglycerides content and muscle lipolysis, suggesting improvement in lipid metabolism. Taken together, these data suggested that the LCD improved glucose utilization, and inhibited lipolysis and atrophy in skeletal muscle of diabetic mice, while the ketogenic diet showed metabolic disorders in skeletal muscle.

Associations of myosteatosis with disc degeneration: A 3T magnetic resonance imaging study in individuals with impaired glycaemia.

Intervertebral disc degeneration (IVDD) may be linked to dysregulations of skeletal muscle glucose metabolism and fatty alterations of muscle composition (Myosteatosis). Our aim was to evaluate the different associations of magnetic resonance imaging (MRI)-based paravertebral myosteatosis with lumbar disc degeneration in individuals with impaired glucose metabolism and normoglycaemic controls. In total, 304 individuals (mean age: 56.3±9.1years, 53.6% male sex, mean body mass index [BMI]: 27.6±4.7kg/m2 ) from a population-based cohort study who underwent 3-Tesla whole-body chemical-shift-encoded (six echo times) and T2-weighted single-shot-fast-spin-echo MRI were included. Lumbar disc degeneration was assessed at motion segments L1 to L5, categorized according to the Pfirrmann score and defined as Pfirrmann grade>2 and/or disc bulging/herniation on at least one segment. Fat content of the autochthonous back muscles and the quadratus lumborum muscle was quantified as proton density fat fraction (PDFFmuscle ). Logistic regression models adjusted for age, sex, BMI and regular physical activity were calculated to evaluate the association between PDFFmuscle and outcome IVDD. The overall prevalence of IVDD was 79.6%. There was no significant difference in the prevalence or severity distribution of IVDD between participants with or without impaired glucose metabolism (77.7% vs. 80.7%, P=0.63 and P=0.71, respectively). PDFFmuscle was significantly and positively associated with an increased risk for the presence of IVDD in participants with impaired glycaemia when adjusted for age, sex and BMI (PDFFautochthonous back muscles : odds ratio [OR] 2.16, 95% confidence interval [CI] [1.09, 4.3], P=0.03; PDFFquadratus lumborum : OR 2.01, 95% CI [1.04, 3.85], P=0.04). After further adjustment for regular physical activity, the results attenuated, albeit approaching statistical significance (PDFFautochthonous back muscles : OR 1.97, 95% CI [0.97, 3.99], P=0.06; PDFFquadratus lumborum : OR 1.86, 95% CI [0.92, 3.76], P=0.09). No significant associations were shown in healthy controls (PDFFautochthonous back muscles : OR 0.62, 95% CI [0.34, 1.14], P=0.13; PDFFquadratus lumborum : OR 1.06, 95% CI [0.6, 1.89], P=0.83). Paravertebral myosteatosis is positively associated with intervertebral disc disease in individuals with impaired glucose metabolism, independent of age, sex and BMI. Regular physical activity may confound these associations. Longitudinal studies will help to better understand the pathophysiological role of skeletal muscle in those with concomitant disturbed glucose haemostasis and intervertebral disc disease, as well as possible underlying causal relationships.