Diet-induced obesity alters signalling pathways and induces atrophy and apoptosis in skeletal muscle in a prediabetic rat model

Impaired skeletal muscle regeneration in diabetes: From cellular and molecular mechanisms to novel treatments

Diabetes represents a major public health concern with a considerable impact on human life and healthcare expenditures. It is now well established that diabetes is characterized by a severe skeletal muscle pathology that limits functional capacity and quality of life. Increasing evidence indicates that diabetes is also one of the most prevalent disorders characterized by impaired skeletal muscle regeneration, yet underlying mechanisms and therapeutic treatments remain poorly established. In this review, we describe the cellular and molecular alterations currently known to occur during skeletal muscle regeneration in people with diabetes and animal models of diabetes, including its associated comorbidities, e.g., obesity, hyperinsulinemia, and insulin resistance. We describe the role of myogenic and non-myogenic cell types on muscle regeneration in conditions with or without diabetes. Therapies for skeletal muscle regeneration and gaps in our knowledge are also discussed, while proposing future directions for the field.

Oleanolic acid alleviates obesity-induced skeletal muscle atrophy via the PI3K/Akt signaling pathway

Oleanolic acid (OA) is a pentacyclic triterpene with reported protective effects against various diseases, including diabetes, hepatitis, and different cancers. However, the effects of OA on obesity-induced muscle atrophy remain largely unknown. This study investigated the effects of OA on skeletal muscle production and proliferation of C2C12 cells. We report that OA significantly increased skeletal muscle mass and improved glucose intolerance and insulin resistance. OA inhibited dexamethasone (Dex)-induced muscle atrophy in C2C12 myoblasts by regulating the PI3K/Akt signaling pathway. In addition, it also inhibited expression of MuRF1 and Atrogin1 genes in skeletal muscle of obese mice suffering from muscle atrophy, and increased the activation of PI3K and Akt, thereby promoting protein synthesis, and eventually alleviating muscle atrophy. Taken together, these findings suggest OA may have potential for the prevention and treatment of muscle atrophy.

Time-restricted feeding combined with resistance exercise prevents obesity and improves lipid metabolism in the liver of mice fed a high-fat diet

Nonalcoholic fatty liver disease (NAFLD), a condition characterized by the accumulation of fat in the liver, is estimated to be the most common liver disease worldwide. Obesity is a major risk factor and contributor, and, accordingly, weight loss can improve NAFLD. Previous studies in preclinical models of diet-induced obesity and fatty liver disease have shown the independent benefits of resistance exercise training (RT) and time-restricted feeding (TRF) in preventing weight gain and hepatic build-up of fat. Here, we tested the combined effect of TRF and RT on obesity and NAFLD in mice fed a high-fat diet. Our results showed that both TRF-8-h food access in the active phase-and RT-consisting of three weekly sessions of ladder climbing-attenuated body weight gain, improved glycemic homeostasis, and decreased the accumulation of lipids in the liver. TRF combined with RT improved the respiratory exchange rate, energy expenditure, and mitochondrial respiration in the liver. Furthermore, gene expression analysis in the liver revealed lower mRNA expression of lipogenesis and inflammation genes along with increased mRNA of fatty acid oxidation genes in the TRF + RT group. Importantly, combined TRF + RT was shown to be more efficient in preventing obesity and metabolic disorders. In conclusion, TRF and RT exert complementary actions compared with isolated interventions, with significant effects on metabolic disorders and NAFLD in mice.NEW & NOTEWORTHY Whether time-restricted feeding (TRF) combined with resistance exercise training (RT) may be more efficient compared with these interventions alone is still unclear. We show that when combined with RT, TRF provided additional benefits, being more effective in increasing energy expenditure, preventing weight gain, and regulating glycemic homeostasis than each intervention alone. Thus, our results demonstrate that TRF and RT have complementary actions on some synergistic pathways that prevented obesity and hepatic liver accumulation.

GLP-1RA Liraglutide and Semaglutide Improves Obesity-Induced Muscle Atrophy via SIRT1 Pathway

Background

Obesity is related to the loss of skeletal muscle mass and function (sarcopenia). The co-existence of obesity and sarcopenia is called sarcopenic obesity (SO). Glucagon like peptide-1 receptor agonists (GLP-1RA) are widely used in the treatment of diabetes and obesity. However, the protective effects of GLP-1RA on skeletal muscle in obesity and SO are not clear. This study investigated the effects of GLP-1RA liraglutide and semaglutide on obesity-induced muscle atrophy and explored the underlying mechanisms.

Methods

Thirty-six male C57BL/6J mice were randomly divided into two groups and fed a regular diet and a high-fat diet for 18 weeks, respectively. After establishing an obesity model, mice were further divided into six groups: control group, liraglutide (LIRA) group, semaglutide (SEMA) group, high-fat diet (HFD) group, HFD + LIRA group, HFD + SEMA group, and subcutaneous injection for 4 weeks. The body weight, muscle mass, muscle strength, glycolipid metabolism, muscle atrophy markers, myogenic differentiation markers, GLUT4 and SIRT1 were analyzed. C2C12 myotube cells treated with palmitic acid (PA) were divided into four groups: control group, PA group, PA + LIRA group, PA + SEMA group. The changes in glucose uptake, myotube diameter, lipid droplet infiltration, markers of muscle atrophy, myogenic differentiation markers, GLUT4 and SIRT1 were analyzed, and the changes in related indicators were observed after the addition of SIRT1 inhibitor EX527.

Results

Liraglutide and semaglutide reduced HFD-induced body weight gain, excessive lipid accumulation and improved muscle atrophy. Liraglutide and semaglutide eliminated the increase of muscle atrophy markers in skeletal muscle and C2C12 myotubes. Liraglutide and semaglutide restored impaired glucose tolerance and insulin resistance. However, these beneficial effects were attenuated by inhibiting SIRT1 expression.

Conclusion

Liraglutide and semaglutide protects skeletal muscle against obesity-induced muscle atrophy via the SIRT1 pathway.

A chronic high-fat diet does not exacerbate muscle atrophy in fast-twitch skeletal muscle of aged mice

NEW FINDINGS

What is the central question of this study? Ageing leads to a loss of mass in skeletal muscle, but the effect of obesity on ageing-related muscle wasting is unclear. In this study, we aimed to demonstrate the specific effect of obesity on fast-twitch skeletal muscle in ageing. What is the main finding and its importance? Our findings show that the obesity induced by long-term ingestion of a high-fat diet does not aggravate muscle wasting in fast-twitch skeletal muscle of aged mice, indicating that the present study provides morphological characteristics for skeletal muscle of sarcopenic obesity.

ABSTRACT

Obesity and ageing reduce muscle mass and lead to deficits in muscle maintenance, but it is not known whether obesity accelerates muscle wasting additively in the setting of ageing. We investigated morphological characteristics in fast-twitch extensor digitorum longus (EDL) muscle of mice fed a low-fat diet (LFD) or a high-fat diet (HFD) for 4 or 20 months. The fast-twitch EDL muscle was harvested, and the muscle fibre-type composition, individual muscle cross-sectional area and myotube diameter were measured. We found an increase in the percentage of type IIa and IIx myosin heavy chain fibres in the whole EDL muscle, but a decrease in type IIB myosin heavy chain in both HFD protocols. The cross-sectional area and myofibre diameter were lower in both groups of aged mice (after 20 months of LFD or HFD) compared with young mice (after 4 months of the diets), but there were no differences between mice fed LFD or HFD for 20 months. These data suggest that long-term feeding of HFD does not aggravate muscle wasting in fast-twitch EDL muscle of male mice.

Rice Germ Attenuates Chronic Unpredictable Mild Stress-Induced Muscle Atrophy

Chronic stress leads to hypothalamic-pituitary-adrenal axis dysfunction, increasing cortisol levels. Glucocorticoids (GCs) promote muscle degradation and inhibit muscle synthesis, eventually causing muscle atrophy. In this study, we aimed to evaluate whether rice germ supplemented with 30% γ-aminobutyric acid (RG) attenuates muscle atrophy in an animal model of chronic unpredictable mild stress (CUMS). We observed that CUMS raised the adrenal gland weight and serum adrenocorticotropic hormone (ACTH) and cortisol levels, and these effects were reversed by RG. CUMS also enhanced the expression of the GC receptor (GR) and GC-GR binding in the gastrocnemius muscle, which were attenuated by RG. The expression levels of muscle degradation-related signaling pathways, such as the Klf15, Redd-1, FoxO3a, Atrogin-1, and MuRF1 pathways, were enhanced by CUMS and attenuated by RG. Muscle synthesis-related signaling pathways, such as the IGF-1/AKT/mTOR/s6k/4E-BP1 pathway, were reduced by CUMS and enhanced by RG. Moreover, CUMS raised oxidative stress by enhancing the levels of iNOS and acetylated p53, which are involved in cell cycle arrest, whereas RG attenuated both iNOS and acetylated p53 levels. Cell proliferation in the gastrocnemius muscle was reduced by CUMS and enhanced by RG. The muscle weight, muscle fiber cross-sectional area, and grip strength were reduced by CUMS and enhanced by RG. Therefore, RG attenuated ACTH levels and cortisol-related muscle atrophy in CUMS animals.

Mesenchymal stromal cells ameliorate diabetes-induced muscle atrophy through exosomes by enhancing AMPK/ULK1-mediated autophagy

BACKGROUND

Diabetes and obesity are associated with muscle atrophy that reduces life quality and lacks effective treatment. Mesenchymal stromal cell (MSC)-based therapy can ameliorate high fat-diet (HFD) and immobilization (IM)-induced muscle atrophy in mice. However, the effect of MSCs on muscle atrophy in type 2 diabetes mellitus (T2DM) and the potential mechanism is unclear. Here, we evaluated the efficacy and explored molecular mechanisms of human umbilical cord MSCs (hucMSCs) and hucMSC-derived exosomes (MSC-EXO) on diabetes- and obesity-induced muscle atrophy.

METHODS

Diabetic db/db mice, mice fed with high-fat diet (HFD), mice with hindlimb immobilization (IM), and C2C12 myotubes were used to explore the effect of hucMSCs or MSC-EXO in alleviating muscle atrophy. Grip strength test and treadmill running were used to measure skeletal muscle strength and performance. Body composition, muscle weight, and muscle fibre cross-sectional area (CSA) was used to evaluate muscle mass. RNA-seq analysis of tibialis anterior (TA) muscle and Western blot analysis of muscle atrophy signalling, including MuRF1 and Atrogin 1, were performed to investigate the underlying mechanisms.

RESULTS

hucMSCs increased grip strength (P = 0.0256 in db/db mice, P = 0.012 in HFD mice, P = 0.0097 in IM mice), running endurance (P = 0.0154 in HFD mice, P = 0.0006 in IM mice), and muscle mass (P = 0.0004 in db/db mice, P = 0.0076 in HFD mice, P = 0.0144 in IM mice) in all models tested, with elevated CSA of muscle fibres (P < 0.0001 in db/db mice and HFD mice, P = 0.0088 in IM mice) and reduced Atrogin1 (P = 0.0459 in db/db mice, P = 0.0088 in HFD mice, P = 0.0016 in IM mice) and MuRF1 expression (P = 0.0004 in db/db mice, P = 0.0077 in HFD mice, P = 0.0451 in IM mice). MSC-EXO replicated all these hucMSC-mediated changes (P = 0.0103 for grip strength, P = 0.013 for muscle mass, P < 0.0001 for CSA of muscle fibres, P = 0.0171 for Atrogin1 expression, and P = 0.006 for MuRF1 expression). RNA-seq revealed that hucMSCs activated the AMPK/ULK1 signalling and enhanced autophagy. Knockdown of AMPK or inhibition of autophagy with 3-methyladenine (3-MA) diminished the beneficial anti-atrophy effects of hucMSCs or MSC-EXO.

CONCLUSIONS

Our results suggest that human umbilical cord mesenchymal stromal cells mitigate diabetes- and obesity-induced muscle atrophy via enhancing AMPK/ULK1-mediated autophagy through exosomes, with implications of applying hucMSCs or hucMSC-derived exosomes to treat muscle atrophy.

Energy metabolism in skeletal muscle cells from donors with different body mass index

Obesity and physical inactivity have a profound impact on skeletal muscle metabolism. In the present work, we have investigated differences in protein expression and energy metabolism in primary human skeletal muscle cells established from lean donors (BMI&lt;25 kg/m2) and individuals with obesity (BMI&gt;30 kg/m2). Furthermore, we have studied the effect of fatty acid pretreatment on energy metabolism in myotubes from these donor groups. Alterations in protein expression were investigated using proteomic analysis, and energy metabolism was studied using radiolabeled substrates. Gene Ontology enrichment analysis showed that glycolytic, apoptotic, and hypoxia pathways were upregulated, whereas the pentose phosphate pathway was downregulated in myotubes from donors with obesity compared to myotubes from lean donors. Moreover, fatty acid, glucose, and amino acid uptake were increased in myotubes from individuals with obesity. However, fatty acid oxidation was reduced, glucose oxidation was increased in myotubes from subjects with obesity compared to cells from lean. Pretreatment of myotubes with palmitic acid (PA) or eicosapentaenoic acid (EPA) for 24 h increased glucose oxidation and oleic acid uptake. EPA pretreatment increased the glucose and fatty acid uptake and reduced leucine fractional oxidation in myotubes from donors with obesity. In conclusion, these results suggest that myotubes from individuals with obesity showed increased fatty acid, glucose, and amino acid uptake compared to cells from lean donors. Furthermore, myotubes from individuals with obesity had reduced fatty acid oxidative capacity, increased glucose oxidation, and a higher glycolytic reserve capacity compared to cells from lean donors. Fatty acid pretreatment enhances glucose metabolism, and EPA reduces oleic acid and leucine fractional oxidation in myotubes from donor with obesity, suggesting increased metabolic flexibility after EPA treatment.

Mulberry (Morus alba L.) Leaf Extract and 1-Deoxynojirimycin Improve Skeletal Muscle Insulin Resistance via the Activation of IRS-1/PI3K/Akt Pathway in db/db Mice

Mulberry (Morus alba L.) leaves have been used to lower blood glucose in patients with diabetes. We evaluated the effects of mulberry leaves extract (MLE) and 1-deoxynojirimycin (1-DNJ) in improving insulin resistance through the activation of the IRS-1/PI3K/Akt pathway in the skeletal muscle of db/db mice. Histological analysis revealed an amelioration of muscle deformation and increased muscle fiber size. MLE and 1-DNJ positively raised the protein expression of related glucose uptake and increased the translocation of glucose transporter type 4 (GLUT4) to the membrane. Furthermore, MLE and 1-DNJ activated the IRS-1/PI3K/Akt pathway in the skeletal muscle and, subsequently, modulated the protein levels of glycogen synthase kinase-3beta (GSK-3β) and glycogen synthase (GS), leading to elevated muscle glycogen content. These findings suggest that MLE and 1-DNJ supplementation improves insulin resistance by modulating the insulin signaling pathway in the skeletal muscle of db/db mice.

Role of mitochondria-associated endoplasmic reticulum membranes in insulin sensitivity, energy metabolism, and contraction of skeletal muscle

Skeletal muscle has a critical role in the regulation of the energy balance of the organism, particularly as the principal tissue responsible for insulin-stimulated glucose disposal and as the major site of peripheral insulin resistance (IR), which has been related to accumulation of lipid intermediates, reduced oxidative capacity of mitochondria and endoplasmic reticulum (ER) stress. These organelles form contact sites, known as mitochondria-associated ER membranes (MAMs). This interconnection seems to be involved in various cellular processes, including Ca²⁺ transport and energy metabolism; therefore, MAMs could play an important role in maintaining cellular homeostasis. Evidence suggests that alterations in MAMs may contribute to IR. However, the evidence does not refer to a specific subcellular location, which is of interest due to the fact that skeletal muscle is constituted by oxidative and glycolytic fibers as well as different mitochondrial populations that appear to respond differently to stimuli and pathological conditions. In this review, we show the available evidence of possible differential responses in the formation of MAMs in skeletal muscle as well as its role in insulin signaling and the beneficial effect it could have in the regulation of energetic metabolism and muscular contraction.

Slc2a6 regulates myoblast differentiation by targeting LDHB

Background

Type 2 diabetes mellitus is a global health problem. It often leads to a decline in the differentiation capacity of myoblasts and progressive loss of muscle mass, which in turn results in deterioration of skeletal muscle function. However, effective therapies against skeletal muscle diseases are unavailable.

Methods

Skeletal muscle mass and differentiation ability were determined in db/+ and db/db mice. Transcriptomics and metabolomics approaches were used to explore the genetic mechanism regulating myoblast differentiation in C2C12 myoblasts.

Results

In this study, the relatively uncharacterized solute carrier family gene Slc2a6 was found significantly up-regulated during myogenic differentiation and down-regulated during diabetes-induced muscle atrophy. Moreover, RNAi of Slc2a6 impaired the differentiation and myotube formation of C2C12 myoblasts. Both metabolomics and RNA-seq analyses showed that the significantly differentially expressed genes (e.g., LDHB) and metabolites (e.g., Lactate) during the myogenic differentiation of C2C12 myoblasts post-Slc2a6-RNAi were enriched in the glycolysis pathway. Furthermore, we show that Slc2a6 regulates the myogenic differentiation of C2C12 myoblasts partly through the glycolysis pathway by targeting LDHB, which affects lactic acid accumulation.

Conclusion

Our study broadens the understanding of myogenic differentiation and offers the Slc2a6-LDHB axis as a potential therapeutic target for the treatment of diabetes-associated muscle atrophy.

Dietary l-carnitine supplementation recovers the increased pH and hardness in fillets caused by high-fat diet in Nile tilapia (Oreochromis niloticus)

The wide use of high-fat diet (HFD) causes negative effects on flesh quality in farmed fish. l-carnitine, a lipid-lowering additive, enhances mitochondrial fatty acid β-oxidation. However its roles in alleviating the effects of HFD on flesh quality in fish are unknown. We fed Nile tilapia with medium-fat diet (MFD, 6% dietary lipid), high-fat diet (HFD, 12% dietary lipid) and HFCD supplemented with l-carnitine (HFCD + 400 mg/kg l-carnitine) for 10 weeks. The HFD-fed fish had higher fat deposition, pH value, myofiber density and flesh hardness than those fed on MFD. However, feeding the fish with the HFCD improved lipid catabolism, which increased significantly lactic acid content and myofiber diameter in muscle, thus reduced pH and hardness values. HFCD also reduced endoplasmic reticulum stress and myofiber apoptosis caused by HFD in the fish. Our study suggests that dietary l-carnitine supplementation alleviates the negative effects of HFD on flesh quality of farmed fish.

Fruit of Schisandra chinensis and its bioactive component schizandrin B ameliorate obesity-induced skeletal muscle atrophy

Schisandra chinensis fruit (Omiza in Korean), used for the production tea or liquor, and is known to enhance skeletal muscle function. However, the effect of Omiza extract (OM) on obesity-induced skeletal muscle atrophy remains unclear. This study investigated the effect of OM on skeletal muscle mass and performance in obese mice. OM increased skeletal muscle weight, size and improved skeletal muscle performance. Further, it also suppressed obesity-induced increases in proinflammatory cytokines, MuRF1, and Atrogin1 in mouse skeletal muscle and enhanced the expression of MHC and the phosphorylation of AKT/mTOR signaling molecules, thereby suppressing myostatin expression and regulating Smad-FOXO signaling. Schizandrin B, a major component of OM inhibited palmitic acid induced atrophy in C2C12 cells via Smad-FOXO regulation, suggesting that it partially contributed to the effects of OM against obesity-induced muscle atrophy. Taken together, OM may have the potential to prevent and treat obesity-induced muscle atrophy.

Aerobic exercise prevents apoptosis in skeletal muscles of high-fat-fed ovariectomized rats

[Purpose]

Aging and obesity are associated with skeletal muscle atrophy-related signaling pathways, including apoptosis. Many studies have shown that menopause is associated with an increased risk of skeletal muscle atrophy. There is an increasing need to develop strategies that will improve the risk of skeletal muscle atrophy through exercise interventions. However, the effect of exercise on estrogen deficiency-induced apoptosis in skeletal muscles is poorly understood. Therefore, we examined the effects of low-intensity exercise on ovariectomy (OVX)-induced apoptosis of the soleus and plantaris muscles.

[Methods]

The ovaries of all female Sprague-Dawley rats aged 8 weeks, were surgically removed to induce postmenopausal status. The rats were randomly divided into three treatment groups: (1) NSV (normal-diet-sedentary-OVX); (2) HSV (high-fat-diet-sedentary-OVX); and (3) HEV (high-fat-diet-exercise-OVX). The exercise groups were regularly running for 30-40 min/day at 15-18 m/minute, five times/week, for eight weeks.

[Results]

The mRNA levels of Bax significantly decreased in the exercised soleus muscle, and caspase-3 decreased in the plantaris. The skeletal muscle TUNEL-positive apoptotic cells in the high-fat-diet-sedentary OVX rats improved in the treadmill exercise group. Additionally, nuclear caspase-3 levels decreased in the treadmill exercise group compared to those in both sedentary groups. These results suggest that low-intensity treadmill exercise prevents skeletal muscle apoptosis in HFD-fed OVX rats.

[Conclusion]

Induction of HFD in estrogen-deficient mice increased apoptosis in skeletal muscle, which could also be alleviated by low-intensity aerobic exercise. These results may indicate a crucial therapeutic effect of treadmill exercise in preventing skeletal muscle apoptosis in menopausal or post-menopausal women.

Silymarin Prevents High-Fat Diet-Induced Muscle Atrophy by Regulating Protein Degradation and Synthesis in Mice

Silymarin is found in Silybum marianum. We investigated the effect of silymarin on muscle atrophy in obese mice. The experimental mice were divided into three groups: CON, normal diet; HFD, 60% high-fat diet (HF); and SILY: 50 mg silymarin +60% HF. It was confirmed that increases in body weight and fat mass in the SILY group were significantly inhibited. Moreover, the muscle mass in SILY mice was significantly higher than that in the HFD group. The grip strength in HFD group was significantly reduced, whereas in the SILY group it was higher than that in HFD group. In HFD mice, the mRNA levels of protein degradation factors (muscle ring-finger protein 1 [MuRF-1] and Atrogin-1) were increased and protein synthesis factors (phosphoinositide 3-kinase [PI3K] and Akt) were decreased. However, silymarin was found to elevate the degradation factors as compared with HFD group, whereas it reduced the synthesis factors. The results suggest that silymarin could prevent not only obesity but also muscle atrophy.

Impaired proteostasis in obese skeletal muscle relates to altered immunoproteasome activity

Obesity-associated inflammation and/or oxidative stress can damage intramuscular proteins and jeopardize muscle integrity. The immunoproteasome (iProt) is vital to remove oxidatively modified proteins, but this function may be compromised with obesity. We sought to elucidate whether diet-induced obesity alters intramuscular iProt content and activity in mice to identify a possible mechanism for impaired muscle proteostasis in the obese state. Total proteasome content and activity and estimates of muscle oxidative damage, inflammation, muscle mass and strength were also assessed. Twenty-three male, 5-week-old C57BL/6J mice were fed a high-fat, high-sucrose (HFS; 45% kcal fat, 17% sucrose, n = 12) or low-fat, low-sucrose (LFS; 10% kcal fat, 0% sucrose, n = 11) diet for 12 weeks. Strength was assessed via a weightlifting test. Despite no change in pro-inflammatory cytokines (P > 0.05), oxidative protein damage was elevated within the gastrocnemius (P = 0.036) and tibialis anterior (P = 0.033) muscles of HFS-fed mice. Intramuscular protein damage coincided with reduced iProt and total proteasome activity (P < 0.05), and reductions in relative muscle mass (P < 0.001). Therefore, proteasome dysregulation occurs in obese muscle and may be a critical link in muscle oxidative stress. Novelty: Our results show for the first time that immunoproteasome and total proteasome function is significantly reduced within obese muscle. Visceral fat mass is a significant predictor of diminished proteasome activity in skeletal muscle. Proteasome function is inversely correlated with an intramuscular accumulation of oxidatively damaged proteins.

Effect of nebivolol on altered skeletal and cardiac muscles induced by dyslipidemia in rats: impact on oxidative and inflammatory machineries

AIM

High cholesterol diet is greatly linked to deleterious health consequences. In this work we tried to explore direct effects of high cholesterol diet on striated (skeletal and cardiac) muscle tissues and the mechanisms by which nebivolol could improve such harmful effects.

METHODS

The study included 24 healthy adult male albino rats weighing 200-220 grams that were assigned into four groups: control group, control drug group, high cholesterol diet fed groups; one untreated the other was treated with nebivolol.

RESULTS

In the cholesterol fed group, we found decreased blood HDL and NO with elevated total cholesterol, triglycerides, myoglobin, CK, LDH, ALP, in addition to elevated muscle tissue levels of HIF-1, NF-kB, MDA, and decreased expression of both eNOS, reduced GSH. Wire hanging test time was shorter in the high cholesterol group than control group rats, which was confirmed histologically by increased striated muscle fibre thickness and cytochrome area %. Nebivolol treatment ameliorated the effects of high cholesterol diet.

CONCLUSION

High cholesterol diet caused myopathic changes in rat striated muscle tissues mostly due to oxidative stress associated with enhanced NF-kB and HIF-1 expression. Nebivolol appears beneficial in the management of hypercholesterolaemia-induced striated muscle injury.

Effects of Root Extract of Morinda officinalis in Mice with High-Fat-Diet/Streptozotocin-Induced Diabetes and C2C12 Myoblast Differentiation

Type 2 diabetes is the most common type of diabetes and causes a decline in muscle quality. In this study, we investigated the effects of the root extract of Morinda officinalis (MORE) on skeletal muscle damage in mice with high-fat-diet (HFD)/streptozotocin (STZ)-induced diabetes and the expression of myogenic and biogenesis regulatory proteins in C2C12 myoblast differentiation. An in vivo model comprised C57BL/6N mice fed HFD for 8 weeks, followed by a single injection of STZ at 120 mg/kg. MORE was administered at 100 and 200 mg/kg once daily (p.o.) for 4 weeks. The changes in body weight, calorie intake, and serum levels of glucose, insulin, total cholesterol (TCHO), HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), aspartate transaminase (AST), and alanine aminotransferase (ALT) were investigated in diabetic mice. The histological changes in the gastrocnemius muscle were observed by H&E staining, and then the myofiber size was measured. The expression of the myogenic (MHC, myogenin, and MyoD) and biogenesis (PGC-1α, SIRT1, NRF1, and TFAM) regulatory proteins was examined in the muscle tissues and differentiated C2C12 myoblasts by Western blot, respectively. The administration of MORE at 200 mg/kg in mice with HFD/STZ-induced diabetes significantly reduced weight gains, calorie intake, insulin resistance, and serum levels of glucose, TCHO, LDL-C, AST, and ALT. MORE administration at 100 and 200 mg/kg significantly increased serum insulin and HDL-C levels in diabetic mice. In addition, MORE significantly increased the expression of MHC, myogenin, MyoD, PGC-1α, SIRT1, NRF1, and TFAM in muscle tissues as well as increased the myofiber size in diabetic mice. In C2C12 myoblast differentiation, MORE treatment at 0.5, 1, and 2 mg/mL significantly increased the expression of myogenic and biogenesis regulatory proteins in a dose-dependent manner. MORE improves diabetes symptoms in mice with HFD/STZ-induced diabetes by improving muscle function. This suggests that MORE could be used to prevent or treat diabetes along with muscle disorders.

Skeletal muscle energy metabolism in obesity

Comparing energy metabolism in human skeletal muscle and primary skeletal muscle cells in obesity, while focusing on glucose and fatty acid metabolism, shows many common changes. Insulin-mediated glucose uptake in skeletal muscle and primary myotubes is decreased by obesity, whereas differences in basal glucose metabolism are inconsistent among studies. With respect to fatty acid metabolism, there is an increased uptake and storage of fatty acids and a reduced complete lipolysis, suggesting alterations in lipid turnover. In addition, fatty acid oxidation is decreased, probably at the level of complete oxidation, as β -oxidation may be enhanced in obesity, which indicates mitochondrial dysfunction. Metabolic changes in skeletal muscle with obesity promote metabolic inflexibility, ectopic lipid accumulation, and formation of toxic lipid intermediates. Skeletal muscle also acts as an endocrine organ, secreting myokines that participate in interorgan cross talk. This review highlights interventions and some possible targets for treatment through action on skeletal muscle energy metabolism. Effects of exercise in vivo on obesity have been compared with simulation of endurance exercise in vitro on myotubes (electrical pulse stimulation). Possible pharmaceutical targets, including signaling pathways and drug candidates that could modify lipid storage and turnover or increase mitochondrial function or cellular energy expenditure through adaptive thermogenic mechanisms, are discussed.

Treatment potential of LPCN 1144 on liver health and metabolic regulation in a non-genomic, high fat diet induced NASH rabbit model

PURPOSE

Low free testosterone (T) level in men is independently associated with presence and severity of Non-Alcoholic Steatohepatitis (NASH). The histological and molecular effects of oral testosterone prodrug LPCN 1144 treatment on hepatic fibrosis and NASH features are unknown. A metabolic syndrome-induced NASH model in rabbits consuming high fat diet (HFD) has been previously used to assess treatment effects of injectable T on hepatic fibrosis and NASH features. Here we present results on LPCN 1144 in this HFD-induced, NASH preclinical model.

METHODS

Male rabbits were randomly assigned to five groups: regular diet (RD), HFD, HFD + 1144 vehicle (HFD + Veh), HFD + 1144 (1144), and HFD + 1144 + α-tocopherol (1144 + ALPHA). Rabbits were sacrificed after 12 weeks for liver histological, biochemical and genetic analyses. Histological scores were obtained through Giemsa (inflammation), Masson's trichrome (steatosis and ballooning), and Picrosirius Red (fibrosis) staining.

RESULTS

Compared to RD, HFD and HFD + Veh significantly worsened NASH features and hepatic fibrosis. Considering HFD and HFD + Veh arms, histological and biomarker features were not significantly different. Both 1144 and 1144 + ALPHA arms improved mean histological scores of NASH as compared to HFD arm. Importantly, percentage of fibrosis was improved in both 1144 (p < 0.05) and 1144 + ALPHA (p = 0.05) treatment arms vs. HFD. Both treatment arms also reduced HFD-induced inflammation and fibrosis mRNA markers. Furthermore, 1144 treatments significantly improved HFD-induced metabolic dysfunctions.

CONCLUSIONS

Histological and biomarker analyses demonstrate that LPCN 1144 improved HFD-induced hepatic fibrosis and NASH biochemical, biomolecular and histochemical features. These preclinical findings support a therapeutic potential of LPCN 1144 in the treatment of NASH and of hepatic fibrosis.

CXCL2 Impairs Functions of Bone Marrow Mesenchymal Stem Cells and Can Serve as a Serum Marker in High-Fat Diet-Fed Rats

In modern society excessive consumption of a high-fat diet (HFD) is a significant risk factor for many diseases such as diabetes, osteoarthritis and certain cancers. Resolving cellular and molecular mechanisms underlying HFD-associated disorders is of great importance to human health. Mesenchymal stem cells (MSCs) are key players in tissue homeostasis and adversely affected by prolonged HFD feeding. Low-grade systemic inflammation induced by HFD is characterized by increased levels of pro-inflammatory cytokines and alters homeostasis in many organs. However, whether, which and how HFD associated inflammatory cytokines impair MSCs remain unclear. Here we demonstrated that HFD induced serum cytokines disturbances, especially a continuous elevation of serum CXCL2 level in rats. Coincidentally, the differentially expressed genes (DEGs) of bone marrow MSCs (BMSCs) which functions were impaired in HFD rats were enriched in cytokine signaling. Further mechanism analysis revealed that CXCL2 treatment in vitro suppresses the adipogenic potential of BMSCs via Rac1 activation, and promoted BMSC migration and senescence by inducing over-production of ELMO1 and reactive oxygen species (ROS) respectively. Moreover, we found that although glycolipid metabolism indicators can be corrected, the CXCL2 elevation and BMSC dysfunctions cannot be fully rescued by diet correction and anti-inflammatory aspirin treatment, indicating the long-lasting deleterious effects of HFD on serum CXCL2 levels and BMSC functions. Altogether, our findings identify CXCL2 as an important regulator in BMSCs functions and may serve as a serum marker to indicate the BMSC dysfunctions induced by HFD. In addition, our findings underscore the intricate link among high-fat intake, chronic inflammation and BMSC dysfunction which may facilitate development of protective strategies for HFD associated diseases.

Metabolomic and transcriptomic profiling of adult mice and larval zebrafish leptin mutants reveal a common pattern of changes in metabolites and signaling pathways

BACKGROUND

Leptin plays a critical role in the regulation of metabolic homeostasis. However, the molecular mechanism and cross talks between leptin and metabolic pathways leading to metabolic homeostasis across different species are not clear. This study aims to explore the effects of leptin in mice and zebrafish larvae by integration of metabolomics and transcriptomics. Different metabolomic approaches including mass spectrometry, nuclear magnetic resonance (NMR) and high-resolution magic-angle-spinning NMR spectrometry were used to investigate the metabolic changes caused by leptin deficiency in mutant ob/ob adult mice and lepb^-/- zebrafish larvae. For transcriptome studies, deep RNA sequencing was used.

RESULTS

Thirteen metabolites were identified as common biomarkers discriminating ob/ob mice and lepb^-/- zebrafish larvae from their respective wild type controls: alanine, citrulline, ethanolamine, glutamine, glycine, histidine, isoleucine, leucine, methionine, phenylalanine, putrescine, serine and threonine. Moreover, we also observed that glucose and lipid levels were increased in lepb^-/- zebrafish larvae compared to the lepb^+/+ group. Deep sequencing showed that many genes involved in proteolysis and arachidonic acid metabolism were dysregulated in ob/ob mice heads and lepb mutant zebrafish larvae compared to their wild type controls, respectively.

CONCLUSIONS

Leptin deficiency leads to highly similar metabolic alterations in metabolites in both mice and zebrafish larvae. These metabolic changes show similar features as observed during progression of tuberculosis in human patients, mice and zebrafish larvae. In addition, by studying the transcriptome, we found similar changes in gene regulation related to proteolysis and arachidonic acid metabolism in these two different in vivo models.

The lifecycle of skeletal muscle mitochondria in obesity

Skeletal muscle possesses dramatic metabolic plasticity that allows for the rapid adaptation in cellular energy transduction to meet the demands of the organism. Obesity elicits changes in skeletal muscle structure and function, resulting in the accumulation of intramuscular lipids. The accumulation of intramuscular lipids in obesity is associated with impaired skeletal muscle mitochondrial content and function. Mitochondria exist as a dynamic network that is regulated by the processes of biogenesis, fusion, fission, and mitophagy. In this review, we outline adaptations in molecular pathways that regulate mitochondrial structure and function in obesity. We highlight the emerging role of dysregulated skeletal muscle macroautophagy and mitochondrial turnover in obesity. Future research should further elucidate the role of mitophagy in observed reductions in mitochondrial content and function during obesity.

MOTS-c reduces myostatin and muscle atrophy signaling

Obesity and type 2 diabetes are metabolic diseases, often associated with sarcopenia and muscle dysfunction. MOTS-c, a mitochondrial-derived peptide, acts as a systemic hormone and has been implicated in metabolic homeostasis. Although MOTS-c improves insulin sensitivity in skeletal muscle, whether MOTS-c impacts muscle atrophy is not known. Myostatin is a negative regulator of skeletal muscle mass and also one of the possible mediators of insulin resistance-induced skeletal muscle wasting. Interestingly, we found that plasma MOTS-c levels are inversely correlated with myostatin levels in human subjects. We further demonstrated that MOTS-c prevents palmitic acid-induced atrophy in differentiated C2C12 myotubes, whereas MOTS-c administration decreased myostatin levels in plasma in diet-induced obese mice. By elevating AKT phosphorylation, MOTS-c inhibits the activity of an upstream transcription factor for myostatin and other muscle wasting genes, FOXO1. MOTS-c increases mTORC2 and inhibits PTEN activity, which modulates AKT phosphorylation. Further upstream, MOTS-c increases CK2 activity, which leads to PTEN inhibition. These results suggest that through inhibition of myostatin, MOTS-c could be a potential therapy for insulin resistance-induced skeletal muscle atrophy as well as other muscle wasting phenotypes including sarcopenia.NEW & NOTEWORTHY MOTS-c, a mitochondrial-derived peptide reduces high-fat-diet-induced muscle atrophy signaling by reducing myostatin expression. The CK2-PTEN-mTORC2-AKT-FOXO1 pathways play key roles in MOTS-c action on myostatin expression.

FGF19 protects skeletal muscle against obesity-induced muscle atrophy, metabolic derangement and abnormal irisin levels via the AMPK/SIRT-1/PGC-α pathway

Obesity is associated with biological dysfunction in skeletal muscle. As a condition of obesity accompanied by muscle mass loss and physical dysfunction, sarcopenic obesity (SO) has become a novel public health problem. Human fibroblast growth factor 19 (FGF19) plays a therapeutic role in metabolic diseases. However, the protective effects of FGF19 on skeletal muscle in obesity and SO are still not completely understood. Our results showed that FGF19 administration improved muscle loss and grip strength in young and aged mice fed a high‐fat diet (HFD). Increases in muscle atrophy markers (FOXO‐3, Atrogin‐1, MuRF‐1) were abrogated by FGF19 in palmitic acid (PA)‐treated C2C12 myotubes and in the skeletal muscle of HFD‐fed mice. FGF19 not only reduced HFD‐induced body weight gain, excessive lipid accumulation and hyperlipidaemia but also promoted energy expenditure (PGC‐1α, UCP‐1, PPAR‐γ) in brown adipose tissue (BAT). FGF19 treatment restored PA‐ and HFD‐induced hyperglycaemia, impaired glucose tolerance and insulin resistance (IRS‐1, GLUT‐4) and mitigated the PA‐ and HFD‐induced decrease in FNDC‐5/irisin expression. However, these beneficial effects of FGF19 on skeletal muscle were abolished by inhibiting AMPK, SIRT‐1 and PGC‐1α expression. Taken together, this study suggests that FGF19 protects skeletal muscle against obesity‐induced muscle atrophy, metabolic derangement and abnormal irisin secretion partially through the AMPK/SIRT‐1/PGC‐α signalling pathway, which might be a potential therapeutic target for obesity and SO.

Differential Protein Metabolism and Regeneration in Gastrocnemius Muscles in High-fat Diet Fed Mice and Pre-hibernation Daurian Ground Squirrels: A Comparison between Pathological and Healthy Obesity

We focused on pathological obesity induced by excessive fat intake (nutritional obesity) in non-hibernator and healthy obesity due to pre-hibernation (PRE) fat storage in hibernator to study the effects of different types of obesity on skeletal muscle protein metabolism and cell regeneration. Kunming mice were fed with high-fat diet for 3 months to construct a pathological obesity model. Daurian ground squirrels fattened naturally before hibernation were used as a healthy obesity model. Body weight, adipose tissue wet weight, gastrocnemius muscle wet weight, muscle fiber cross-sectional area (CSA) and fiber type distribution were measured. The protein expression levels related to protein degradation (MuRF-1, atrogin-1, calpain1, calpain2, calpastatin, desmin, troponin T, Beclin-1, LC3-II), protein synthesis (P-Akt, P-mTORC1, P-S6K1, P-4E-BP1) and cell regeneration (MyoD, myogenin, myostatin) were detected by Western blot. As a result, the body weight and adipose tissue wet weight were both significantly increased in high fat obese (OB) mice and pre-hibernation fat (PRE) ground squirrels. The muscle wet weight, ratio of muscle wet weight to body weight, and muscle fiber CSA were significantly decreased, while the percentage of MHC I fiber isoform was significantly increased in gastrocnemius muscle of OB mice compared with the control (CON) group. The protein expression levels of P-Akt, P-mTORC1, P-4E-BP1 and myogenin were significantly decreased, while those of calpain1, calpain2, MuRF-1 and myostatin were significantly increased in the OB mice. In the ground squirrels, the muscle wet weight, muscle fiber CSA and percentage of MHC I fiber isoform all showed no change in the gastrocnemius muscle in the PRE group compared with the summer active (SA) group. The protein expression levels of P-Akt, P-mTORC1, P-S6K1 and MyoD were significantly increased, while those of Beclin-1 and LC3-II were significantly decreased in the PRE ground squirrels. This study demonstrated that the decrease in protein expression levels in the Akt/mTOR pathway (P-Akt, P-mTORC1 and P-4E-BP1) and cell regeneration (myogenin) and the increase in protein expression levels of the calpain pathway (calpain1 and calpain2) and ubiquitin-proteasome pathway (MuRF-1) were involved in the mechanism of muscle atrophy in gastrocnemius muscle of the pathologically obese Kunming mice induced by high-fat diet. In contrast, the increased protein expression levels of the Akt/mTOR pathway (P-Akt, P-mTORC1 and P-S6K1) and cell regeneration (MyoD), and the decreased protein expression levels of the autophagy lysosomal pathway (Beclin-1 and LC3-II) were involved in the mechanism of anti-atrophy in gastrocnemius muscle of the healthy obese ground squirrels fattened before hibernation.

Association of Monocyte Chemotactic Protein-1 and Dickkopf-1 with Body Composition and Physical Performance in Community-Dwelling Older Adults in Singapore

Objective

We aim to determine the association of monocyte chemotactic protein-1 (MCP-1) and dickkopft-1 (DKK-1) as potential biomarkers that may predict changes in body composition and physical performance in healthy older adults from Singapore.

Methods

Two-hundred community-dwelling older adults (mean age: 67.9 years; 68.5% females) were classified into elevated versus non-elevated groups based on quintile cut-offs of MCP-1 and DKK-1 levels (156.02 pg/mL and 606.31 pg/mL, respectively). Multiple linear regression was performed to examine the relationship between MCP-1 and DKK-1 with body composition and physical performance, adjusted for age, gender and ethnicity.

Results

MCP-1 was significantly associated with higher fat mass, fat mass index, percentage body fat, waist circumference and trunk-limb ratio for fat mass (all p<0.01), and repeated chair stand (p=0.004). DKK-1 was not associated with body composition and physical performance measures. Utilising the Asian Working Group for Sarcopenia (AWGS) 2019 criteria, there were 39 (19.5%) sarcopenia and 161 (80.5%) non-sarcopenia participants respectively, with MCP-1 levels significantly higher in sarcopenia compared with non-sarcopenia (p=0.046), but not for DKK-1 (p=0.525).

Conclusions

Elevated MCP-1 are associated with changes in fat composition, physical performance and sarcopenia, suggesting its usefulness in identifying at-risk group with sarcopenic obesity.

The Influence of Obesity and Associated Fatty Acids on Placental Inflammation

PURPOSE

Maternal obesity, affecting nearly 1 in 4 pregnancies, is associated with increased circulating saturated fatty acids, such as palmitate. These fatty acids are implicated in placental inflammation, which may in turn exacerbate both maternal-fetal tolerance and responses to pathogens, such as group B Streptococcus. In this review, we address the question, "How do obesity and associated fatty acids influence placental inflammation?"

METHODS

In this narrative review, we searched PubMed and Google Scholar using combinations of the key words placental inflammation or pregnancy and lipids, fatty acids, obesity, palmitate, or other closely related search terms. We also used references found within these articles that may have been absent from our original search queries. We analyzed methods and key results of these articles to compare and contrast their findings, which were occasionally at odds with each other.

FINDINGS

Although obesity can be studied as a whole, complex phenomena with in vivo mouse models and human samples from patients with obesity, in vitro modeling often relies on the treatment of cells or tissues with ≥1 fatty acids and occasionally other compounds (eg, glucose and insulin). We found that palmitate, most commonly used in vitro to recreate hallmarks of obesity, induces apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation in many placental cell types. We compare this to in vivo models of obesity wherever possible. We found that obesity as a whole may have more complex regulation of these phenomena (apoptosis, oxidative stress, mitochondrial dysfunction, autophagy defects, and inflammasome activation) compared with in vitro models of fatty acid treatment (primarily palmitate) because of the presence of unsaturated fatty acids (ie, oleate), which may have anti-inflammatory effects.

IMPLICATIONS

The interaction of unsaturated fatty acids with saturated fatty acids may ameliorate many inflammatory effects of saturated fatty acids alone, which complicates interpretation of in vitro studies that focus on a particular fatty acid in isolation. This complication may explain why certain studies of obesity in vivo have differing outcomes from studies of specific fatty acids in vitro.

The effects of diet composition and chronic obesity on muscle growth and function

Diet-induced obesity (DIO) is associated with glucose intolerance, insulin resistance (IR), and an increase in intramyocellular lipids (IMCL), which may lead to disturbances in glucose and protein metabolism. To this matter, it has been speculated that chronic obesity and elevated IMCL may contribute to skeletal muscle loss and deficits in muscle function and growth capacity. Thus, we hypothesized that diets with elevated fat content would induce obesity and insulin resistance, leading to a decrease in muscle mass and an attenuated growth response to increased external loading in adult male mice. Male C57BL/6 mice (8 wk of age) were subjected to five different diets, namely, chow, low-dat-diet (LFD), high-fat-diet (HFD), sucrose, or Western diet, for 28 wk. At 25 wk, HFD and Western diets induced a 60.4% and 35.9% increase in body weight, respectively. Interestingly, HFD, but not Western or sucrose, induced glucose intolerance and insulin resistance. Measurement of isometric torque (ankle plantar flexor and ankle dorsiflexor muscles) revealed no effect of DIO on muscle function. At 28 wk of intervention, muscle area and protein synthesis were similar across all diet groups, despite insulin resistance and increased IMCL being observed in HFD and Western diet groups. In response to 30 days of functional overload, an attenuated growth response was observed in only the HFD group. Nevertheless, our results show that DIO alone is not sufficient to induce muscle atrophy and contractile dysfunction in adult male C57BL/6 mice. However, diet composition does have an impact on muscle growth in response to increased external loading.NEW & NOTEWORTHY The effects of diet-induced obesity on skeletal muscle mass are complex and dependent on diet composition and diet duration. The present study results show that chronic exposure to high levels of fatty acids does not affect muscle mass, contractile function, or protein synthesis in obese C57BL/6 mice compared with the consumption of chow. Obesity did result in a delay in load-induced growth; however, only a 45% HFD resulted in attenuated growth following 30 days of functional overload.

The Impact of Dysmetabolic Sarcopenia Among Insulin Sensitive Tissues: A Narrative Review

Sarcopenia is a common muscular affection among elderly individuals. More recently, it has been recognized as the skeletal muscle (SM) expression of the metabolic syndrome. The prevalence of sarcopenia is increasing along with visceral obesity, to which it is tightly associated. Nonetheless, it is a still underreported entity by clinicians, despite the worsening in disease burden and reduced patient quality of life. Recognition of sarcopenia is clinically challenging, and variability in study populations and diagnostic methods across the clinical studies makes it hard to reach a strong evidence. Impaired insulin activity in SM is responsible for the altered molecular pathways and clinical manifestations of sarcopenia, which is morphologically expressed by myosteatosis. Lipotoxicity, oxidative stress and adipose tissue-derived inflammation lead to both alterations in glucose disposal and protein synthesis in SM, with raising insulin resistance (IR) and SM atrophy. In particular, hyperleptinemia and leptin resistance interfere directly with SM activity, but also with the release of Growth Hormone from the hypohysis, leading to a lack in its anabolic effect on SM. Moreover, sarcopenia is independently associated to liver fibrosis in Non-Alcoholic Fatty Liver Disease (NAFLD), which in turn worsens SM functionality through the secretion of proinflammatory heptokines. The cross-talk between the liver and SM in the IR setting is of crucial relevance, given the high prevalence of NAFLD and the reciprocal impact of insulin-sensitive tissues on the overall disease burden. Along with the efforts of non-invasive diagnostic approaches, irisin and myostatin are two myokines currently evaluated as potential biomarkers for diagnosis and prognostication. Decreased irisin levels seem to be potentially associated to sarcopenia, whereas increased myostatin has shown to negatively impact on sarcopenia in pre-clinical studies. Gene variants in irisin have been explored with regard to the impact on the liver disease phenotype, with conflicting results. The gut-muscle axis has gain relevance with the evidence that insulin resistance-derived gut dysbiosis is responsible for increased endotoxemia and reduction in short-chain free fatty acids, directly affecting and predisposing to sarcopenia. Based on the current evidence, more efforts are needed to increase awareness and improve the management of sarcopenic patients.

Biochemical and nutritional overview of diet-induced metabolic syndrome models in rats: what is the best choice?

Metabolic syndrome (MS) is a condition that includes obesity, insulin resistance, dyslipidemias among other, abnormalities that favors type 2 Diabetes Mellitus (T2DM) and cardiovascular diseases development. Three main diet-induced metabolic syndrome models in rats exist: High carbohydrate diet (HCHD), high fat diet (HFD), and high carbohydrate-high fat diet (HCHHFD). We analyzed data from at least 35 articles per diet, from different research groups, to determine their effect on the development of the MS, aimed to aid researchers in choosing the model that better suits their research question; and also the best parameter that defines obesity, as there is no consensus to determine this condition in rats. For the HCHD we found a mild effect on body weight gain and fasting blood glucose levels (FBG), but significant increases in triglycerides, fasting insulin, insulin resistance and visceral fat accumulation. HFD had the greater increase in the parameters previously mentioned, followed by HCHHFD, which had a modest effect on FBG levels. Therefore, to study early stages of MS a HCHD is recommended, while HFD and HCHHFD better reproduce more severe stages of MS. We recommend the assessment of visceral fat accumulation as a good estimate for obesity in the rat.

Skeletal Muscle Composition and Glucose Levels in Children Who Are Overweight and Obese

BACKGROUND

Skeletal muscle is overlooked in the realm of insulin resistance in children who are overweight and obese despite the fact that it accounts for the most glucose disposal.

OBJECTIVES

Therefore, this study examined fasted glucose levels and muscle cross-sectional area and echo intensity (EI) via ultrasound images of the first dorsal interosseous, vastus lateralis, and rectus femoris in children who are normal weight and overweight and obese aged 8-10 years.

METHODS

In total, 13 males (age = 9.0 [0.7] y) and 7 females (age = 9.0 [0.8] y) volunteered for this study. Independent samples t tests and effect sizes (ESs) were used to examine potential differences in skeletal muscle composition and glucose concentrations.

RESULTS

There were no significant differences between groups for glucose concentration (P = .07, ES = 0.86); however, the children who were overweight and obese had significantly greater EI (P < .01, ES = 0.98-1.63) for the first dorsal interosseous, vastus lateralis, and rectus femoris and lower cross-sectional area when normalized to EI when collapsed across muscles (P < .04, ES = 0.92). Glucose concentrations correlated with EI and cross-sectional area/EI for the vastus lateralis (r = .514 to -.593) and rectus femoris (r = .551 to -.513), but not the first dorsal interosseous.

DISCUSSION

There is evidence that adiposity-related pathways leading to insulin resistance and skeletal muscle degradation are active in young children who are overweight and obese.

Effect of Body Fat Percentage on Muscle Damage Induced by High-Intensity Eccentric Exercise

This study aimed to investigate the impact of percent body fat (%BF) on muscle damage after high-intensity eccentric exercise. Thirty healthy male undergraduates (mean age: 22.0 ± 2 years, height: 176.9 ± 5 cm, weight: 75.8 ± 11.6 kg) participated in this study, and they were classified according to their %BF into a high %fat group (HFG, ≥20%, n = 15) and a low %fat group (LFG, ≤15%, n = 15). For eccentric exercise, two sets of 25 reps were performed on a modified preacher curl machine using the elbow flexor muscle. Maximal isometric strength, muscle soreness (passive and active), creatine kinase (CK), and myoglobin (Mb) were measured as indices of muscle damage. The data were analyzed with repeated measures ANOVA. The results show that there is a significant group–time interaction for both CK and Mb after eccentric exercise (p = 0.007, p = 0.015, respectively), with a greater increase in the HFG than in the LFG. However, there was no significant group–time interaction for maximal isometric strength and muscle soreness (passive and active) (p > 0.05). These results suggest that %BF is a factor that alters the muscle damage indices CK and Mb, which indicate membrane disruption, after eccentric exercise.

Is inflammatory signaling involved in disease-related muscle wasting? Evidence from osteoarthritis, chronic obstructive pulmonary disease and type II diabetes

Muscle loss is an important feature that occurs in multiple pathologies including osteoarthritis (OA), chronic obstructive pulmonary disease (COPD) and type II diabetes (T2D). Despite differences in pathogenesis and disease-related complications, there are reasons to believe that some fundamental underlying mechanisms are inherent to the muscle wasting process, irrespective of the pathology. Recent evidence shows that inflammation, either local or systemic, contributes to the modulation of muscle mass and/or muscle strength, via an altered molecular profile in muscle tissue. However, it remains ambiguous to which extent and via which mechanisms inflammatory signaling affects muscle mass in disease. Therefore, the objective of the present review is to discuss the role of inflammation on skeletal muscle anabolism, catabolism and functionality in three pathologies that are characterized by an eventual loss in muscle mass (and muscle strength), i.e. OA, COPD and T2D. In OA and COPD, most rodent models confirmed that systemic (COPD) or muscle (OA) inflammation directly induces muscle loss or muscle dysfunctionality. However, in a patient population, the association between inflammation and muscular maladaptations are more ambiguous. For example, in T2D patients, systemic inflammation is associated with muscle loss whereas in OA patients this link has not consistently been established. T2D rodent models revealed that increased levels of advanced glycation end-products (AGEs) and a decreased mTORC1 activation play a key role in muscle atrophy, but it remains to be elucidated whether AGEs and mTORC1 are interconnected and contribute to muscle loss in T2D patients. Generally, if any, associations between inflammation and muscle are mainly based on observational and cross-sectional data. There is definitely a need for longitudinal evidence through well-powered randomized control trials that take into account confounders such as age, disease-phenotypes, comorbidities, physical (in) activity etc. This will allow to improve our understanding of the complex interaction between inflammatory signaling and muscle mass loss and hence contribute to the development of therapeutic strategies to combat muscle wasting in these diseases.

Obesity and ageing: Two sides of the same coin

Conditions and comorbidities of obesity mirror those of ageing and age-related diseases. Obesity and ageing share a similar spectrum of phenotypes such as compromised genomic integrity, impaired mitochondrial function, accumulation of intracellular macromolecules, weakened immunity, shifts in tissue and body composition, and enhanced systemic inflammation. Moreover, it has been shown that obesity reduces life expectancy by 5.8 years in men and 7.1 years in women after the age of 40. Shorter life expectancy could be because obesity holistically accelerates ageing at multiple levels. Besides jeopardizing nuclear DNA and mitochondrial DNA integrity, obesity modifies the DNA methylation pattern, which is associated with epigenetic ageing in different tissues. Additionally, other signs of ageing are seen in individuals with obesity including telomere shortening, systemic inflammation, and functional declines. This review aims to show how obesity and ageing are "two sides of the same coin" through discussing how obesity predisposes an individual to age-related conditions, illness, and disease. We will further demonstrate how the mechanisms that perpetuate the early-onset of chronic diseases in obesity parallel those of ageing.

Effect of intranasal instillation of Escherichia coli on apoptosis of spleen cells in diet-induced-obese mice

Splenic immune function was enhanced in diet-induced-obese (DIO) mice caused by Escherichia coli. The changes in spleen function on apoptosis were still unknown. Two hundred mice in groups Lean-E. coli and DIO-E. coli were intranasal instillation of E. coli. And another two hundred mice in groups Lean-PBS and DIO-PBS were given phosphate-buffered saline (PBS). Subsequently, spleen histology was analyzed. Then the rates of spleen cell (SC) apoptosis, and expression of the genes and proteins of Bcl-2, Bax, caspase-3 and caspase-9 were quantified in each group at 0 h (uninfected), 12 h, 24 h, and 72 h postinfection. The SC apoptosis rates of the DIO-E. coli groups were lower than those of the DIO-PBS groups at 12, 24 and 72 h (p < 0.05). Anti-apoptotic Bcl-2 expression gene and protein of the DIO-E. coli groups were higher than those of the DIO-PBS groups (p < 0.05). Gene expressions of pro-apoptotic Bax, caspase-3 and caspase-9 of the DIO-E. coli groups were lower than those of DIO-PBS groups at 12, 24 and 72 h (p < 0.05). The SC apoptosis rates of the Lean-E. coli groups were higher than those of the Lean- PBS groups at 12 h and 24 h (p < 0.05). Interestingly, the SC apoptosis rates in the DIO-E. coli groups were lower than those of the Lean-E. coli groups at 12 h (p < 0.05). In conclusion, our results suggested that the DIO mice presented stronger anti-apoptotic abilities than Lean mice in non-fatal acute pneumonia induced by E. coli infection, which is more conducive to protecting the spleen and improving the immune defense ability of the body.

Corticotropin releasing factor-overexpressing mouse is a model of chronic stress-induced muscle atrophy

Chronic stress and continually high glucocorticoid levels can induce muscle atrophy. Unfortunately, there is a lack of appropriate animal models for stress-induced muscle atrophy research. Corticotropin releasing factor-overexpressing (CRF-OE) mice are a transgenic model of chronic stress that exhibit increased plasma corticosterone levels and Cushing’s syndrome; however, the skeletal muscle pathology of the CRF-OE mouse has not been well studied. We observed that male, 19-week-old CRF-OE mice had significantly lower skeletal muscle mass, average cross-sectional myofiber area, and total muscle protein content than their wild type (WT) littermates. Muscle function determined by grip strength, wire-hang, and open field tests showed that 19-week-old male CRF-OE mice had impaired physical ability. Additionally, the skeletal muscles of CRF-mice exhibited decreased expression of factors involved in the IGF-1/AKT/mTOR protein synthesis pathway and increased ubiquitin proteasome pathway activity compared to the WT control mice. In conclusion, 19-week-old CRF-OE mice display numerous features of muscle atrophy and thus serve as a model for investigating stress-induced muscle atrophy and interventions to target the deleterious effects of stress on skeletal muscle.

Marjoram and sage oils protect against testicular apoptosis, suppressed Ki-67 expression and cell cycle arrest as a therapy for male infertility in the obese rats

Alterations in testicular apoptosis, cell cycle progression and proliferation rate in dietary-induced obese male rats and role of oral administration of marjoram (0.16 ml/kg BW) and sage (0.05 ml/kg BW) oils were evaluated. Results showed increased body weight, serum leptin, testicular lipid peroxidation, protein oxidation and nitric oxide, with reduction in serum testosterone, sperm count and endogenous enzymatic and non-enzymatic antioxidants in testis of the obese rats. Flow cytometry results revealed increased number of annexin-V (+ve) cells with activation of apoptotic proteins (Bax, caspase-3) and reduction of anti-apoptotic Bcl-2. Cell cycle arrest at phases S and G2/M with decline in expression of Bcl-2 and germ cell proliferation marker ki-67 was also validated, indicating lowered spermatogenesis in the obese rats. Supplementation of marjoram or sage oils displayed normalized body weight, sperm count, germ cells apoptosis and proliferation, suggesting the two oils as a new therapeutic approach against obesity promoted male infertility. PRACTICAL APPLICATIONS: Obese men have a greater chance of fertility problems compared to those with normal weight. Obesity-associated oxidative stress and free radicals production have shown to adversely affect sperm quality with activation of pro-apoptotic pathways, allowing germ cell death. Marjoram and sage essential oils are now being widely studied due to their antioxidant and radical scavenging properties. Our findings indicated effectiveness of the two oils for combating body weight gain, testicular oxidative stress, and apoptosis, which seemed to aid in increasing sperm count. The outcomes of this study may help scientists to formulate novel medications for improving fertility problems in men.

Natural constituents from food sources: potential therapeutic agents against muscle wasting

Skeletal muscle wasting is highly correlated with not only reduced quality of life but also higher morbidity and mortality. Although an increasing number of patients are suffering from various kinds of muscle atrophy and weakness, there is still no effective therapy available, and skeletal muscle is considered as an under-medicated organ. Food provided not only essential macronutrients but also functional substances involved in the modulation of the physiological systems of our body. Natural constituents from commonly consumed dietary plants, either extracts or compounds, have attracted more and more attention to be developed as agents for preventing and treating muscle wasting due to their safety and effectiveness, as well as structural diversity. This review provides an overview of the mechanistic aspects of muscle wasting, and summarizes the extracts and compounds from food sources as potential therapeutic agents against muscle wasting.

Mitochondrial Dysfunction in Skeletal Muscle Pathologies

Several molecular mechanisms are involved in the regulation of skeletal muscle function. Among them, mitochondrial activity can be identified. The mitochondria is an important and essential organelle in the skeletal muscle that is involved in metabolic regulation and ATP production, which are two key elements of muscle contractibility and plasticity. Thus, in this review, we present the critical and recent antecedents regarding the mechanisms through which mitochondrial dysfunction can be involved in the generation and development of skeletal muscle pathologies, its contribution to detrimental functioning in skeletal muscle and its crosstalk with other typical signaling pathways related to muscle diseases. In addition, an update on the development of new strategies with therapeutic potential to inhibit the deleterious impact of mitochondrial dysfunction in skeletal muscle is discussed.

Identification of Five Key Genes Involved in Intrinsic Apoptotic Pathway From Yellow Catfish Pelteobagrus fulvidraco and Their Transcriptional Responses to High Fat Diet (HFD)

The hypothesis of the present study is that apoptosis through an intrinsic mitochondrial pathway may mediate high fat diet (HFD)-induced changes in the metabolism of Pelteobagrus fulvidraco. To this end, we cloned the full-length cDNA sequences of Cycs, Apaf1, Casp9, Casp3a, and Casp3b involved in the mitochondria apoptotic pathway, and explored their mRNA tissue expressions and transcriptional responses to HFD. All of these members shared similar domains to their orthologous vertebrate genes. They were constitutively expressed in all analyzed tissues but varied from tissue to tissue. Compared to the control, HFD up-regulated the mRNA expression of partial genes among these five key genes (Cycs, Apaf1, Casp9, Casp3a, and Casp3b) in mesenteric fat, intestine, ovary and the kidney, indicating the induction of apoptosis in these tissues; in contrast, HFD down-regulated mRNA levels of partial genes among the five key genes (Cycs, Apaf1, Casp9, Casp3a, and Casp3b) in the heart, spleen and gill tissues, indicating the inhibition of apoptosis in these tissues. The present study will facilitate further exploration into the functions of these genes at the molecular level and disclose the critical involvement of these genes against nutrient changes, indicating that processes of apoptosis in various tissues may differentially be modified by HFD.

Omega-3 Fatty Acids-Enriched Fish Oil Activates AMPK/PGC-1α Signaling and Prevents Obesity-Related Skeletal Muscle Wasting

Obesity is known to cause skeletal muscle wasting. This study investigated the effect and the possible mechanism of fish oil on skeletal muscle wasting in an obese rat model. High-fat (HF) diets were applied to induce the defects of lipid metabolism in male Sprague-Dawley rats with or without substitution of omega-3 fatty acids-enriched fish oil (FO, 5%) for eight weeks. Diets supplemented with 5% FO showed a significant decrease in the final body weight compared to HF diet-fed rats. The decreased soleus muscle weights in HF diet-fed rats could be improved by FO substitution. The decreased myosin heavy chain (a muscle thick filament protein) and increased FOXO3A and Atrogin-1 (muscle atrophy-related proteins) protein expressions in soleus muscles of HF diet-fed rats could also be reversed by FO substitution. FO substitution could also significantly activate adenosine monophosphate (AMP)-activated protein kinase (AMPK) phosphorylation, peroxisome-proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC-1α), and PPARγ protein expression and lipoprotein lipase (LPL) mRNA expression in soleus muscles of HF diet-fed rats. These results suggest that substitution of FO exerts a beneficial improvement in the imbalance of lipid and muscle metabolisms in obesity. AMPK/PGC-1α signaling may play an important role in FO-prevented obesity-induced muscle wasting.

α-Ionone attenuates high-fat diet-induced skeletal muscle wasting in mice via activation of cAMP signaling

Skeletal muscle atrophy is a common and debilitating condition that lacks a pharmacological therapy. Our aim was to investigate the potential of α-ionone, a naturally occurring flavoring agent, in preventing muscle atrophy and to delineate the mechanisms involved. We found that α-ionone not only stimulated myogenesis but also attenuated palmitic-acid-induced atrophy of cultured skeletal myotubes, as evidenced by an increased myotube diameter and length, fusion index, and cellular protein content. These beneficial actions of α-ionone were abrogated by cAMP inhibitor. The antiatrophic effects of α-ionone on cultured myotubes were confirmed in a corresponding mouse model. The skeletal muscle mass, muscle protein content, myofiber diameter, and muscle strength were greater in α-ionone-treated mice than in untreated animals fed high-fat diet. Furthermore, α-ionone increased cAMP concentration and enhanced its downstream PKA-CREB signaling in skeletal muscle of mice fed high-fat diet. Thus, α-ionone is a promising agent that may enhance skeletal muscle mass and strength.

Atlas of Circadian Metabolism Reveals System-wide Coordination and Communication between Clocks

Metabolic diseases are often characterized by circadian misalignment in different tissues, yet how altered coordination and communication among tissue clocks relate to specific pathogenic mechanisms remains largely unknown. Applying an integrated systems biology approach, we performed 24-hr metabolomics profiling of eight mouse tissues simultaneously. We present a temporal and spatial atlas of circadian metabolism in the context of systemic energy balance and under chronic nutrient stress (high-fat diet [HFD]). Comparative analysis reveals how the repertoires of tissue metabolism are linked and gated to specific temporal windows and how this highly specialized communication and coherence among tissue clocks is rewired by nutrient challenge. Overall, we illustrate how dynamic metabolic relationships can be reconstructed across time and space and how integration of circadian metabolomics data from multiple tissues can improve our understanding of health and disease.

Panax notoginseng saponins alleviate skeletal muscle insulin resistance by regulating the IRS1-PI3K-AKT signaling pathway and GLUT4 expression

Panax notoginseng saponins (PNS) are a commonly used traditional medicine to treat diabetes in China. Recent studies have confirmed their anti-diabetic effects, but the underlying mechanisms have remained unclear. The present study was designed to explore whether PNS decrease hyperglycemia by improving insulin sensitivity in skeletal muscle and to elucidate the molecular mechanisms. The anti-diabetic effects of PNS were analyzed in a skeletal myoblast cell line, C2C12, and in high fat diet-induced diabetic KKAy mice. C2C12 cells were treated with PNS (50, 100, and 200 μg·L^-1 ) and examined for glucose uptake, cell viability and expression of components of the phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT) signaling pathway. KKAy mice were intraperitoneally injected with PNS (200 mg·kg^-1 ) for 6 weeks. Body weight, blood glucose, serum insulin, serum lipid, glucose and insulin tolerance were measured to evaluate the anti-diabetic effects of PNS. Pathological changes, apoptosis and the PI3K-AKT signaling pathway were analyzed in KKAy skeletal muscle. PNS significantly increased insulin-induced glucose uptake, but did not affect the cell viability of C2C12 cells. In addition, PNS reduced blood glucose and serum insulin levels and improved glucose tolerance and insulin tolerance of KKAy mice. Pathological changes and apoptosis of skeletal muscle were relieved by PNS treatment. Moreover, PNS treatment enhanced expression of mRNA encoding IRS1 and GLUT4, as well as the protein expression of phosphorylated (p) -insulin receptor substrate 1 (IRS1), p-PI3K, p-AKT and glucose transporter type 4 (GLUT4) in C2C12 and KKAy mouse muscle. Collectively, these data indicate that PNS reduces hyperglycemia and insulin resistance through up-regulating GLUT4 expression and the IRS1-PI3K-AKT signaling pathway. Furthermore, PNS alleviated diabetes skeletal muscle pathological damage. Thus, our data suggest that PNS may be promising anti-diabetic compounds.

A Short-Term High-Fat Diet Alters Glutathione Levels and IL-6 Gene Expression in Oxidative Skeletal Muscles of Young Rats

Obesity and ensuing disorders are increasingly prevalent worldwide. High-fat diets (HFD) and diet-induced obesity have been shown to induce oxidative stress and inflammation while altering metabolic homeostasis in many organs, including the skeletal muscle. We previously observed that 14 days of HFD impairs contractile functions of the soleus (SOL) oxidative skeletal muscle. However, the mechanisms underlying these effects are not clarified. In order to determine the effects of a short-term HFD on skeletal muscle glutathione metabolism, young male Wistar rats (100–125 g) were fed HFD or a regular chow diet (RCD) for 14 days. Reduced (GSH) and disulfide (GSSG) glutathione levels were measured in the SOL. The expression of genes involved in the regulation of glutathione metabolism, oxidative stress, antioxidant defense and inflammation were measured by RNA-Seq. We observed a significant 25% decrease of GSH levels in the SOL muscle. Levels of GSSG and the GSH:GSSG ratio were similar in both groups. Further, we observed a 4.5 fold increase in the expression of pro-inflammatory cytokine interleukin 6 (IL-6) but not of other cytokines or markers of inflammation and oxidative stress. We hereby demonstrate that a short-term HFD significantly lowers SOL muscle GSH levels. This effect could be mediated through the increased expression of IL-6. Further, the skeletal muscle antioxidant defense could be impaired under cellular stress. We surmise that these early alterations could contribute to HFD-induced insulin resistance observed in longer protocols.

The effect of type 2 diabetes mellitus and obesity on muscle progenitor cell function

In addition to its primary function to provide movement and maintain posture, the skeletal muscle plays important roles in energy and glucose metabolism. In healthy humans, skeletal muscle is the major site for postprandial glucose uptake and impairment of this process contributes to the pathogenesis of type 2 diabetes mellitus (T2DM). A key component to the maintenance of skeletal muscle integrity and plasticity is the presence of muscle progenitor cells, including satellite cells, fibroadipogenic progenitors, and some interstitial progenitor cells associated with vessels (myo-endothelial cells, pericytes, and mesoangioblasts). In this review, we aim to discuss the emerging concepts related to these progenitor cells, focusing on the identification and characterization of distinct progenitor cell populations, and the impact of obesity and T2DM on these cells. The recent advances in stem cell therapies by targeting diabetic and obese muscle are also discussed.