Skeletal Muscle Gene Expression Research Articles

Exploring diet-induced promoter hypomethylation and PDK4 overexpression: implications for type 2 diabetes mellitus.

Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by limited metabolic flexibility in the body. Such limitation implicates the pyruvate dehydrogenase kinase 4 (PDK4) gene Poor nutrition, frequently observed among Southeast Asians usually involves excessive intakes of carbohydrates and monosodium glutamate (MSG), that have been frequently linked to an increased risk of T2DM. The 14-week study aimed to assess the effects of high-carbohydrate (HC), high-MSG (HMSG), and a combination of high-carbohydrate and high-MSG (HCHMSG) diets on the development of T2DM using male mice. To assess the effects, the male mice were divided into four groups: control (C), HC, HMSG, and HCHMSG for 14weeks. After 14weeks, both the HC and HCHMSG groups showed signs of T2DM (168.83 ± 32.33; 156.42 ± 32.46). The blood samples from the HMSG, HC, and HCHMSG groups (57.67 ± 2.882; 49.22 ± 7.36; 48.9 ± 6.43) as well as skeletal muscle samples from the HMSG, HC, and HCHMSG groups (57.78 ± 8.54; 42.13 ± 7.25; 37.57 ± 10.42) exhibited a gradual hypomethylation. The HC groups particularly displayed significant PDK4 gene expression in skeletal muscle. A progressive overexpression of the PDK4 gene was observed as well in the HMSG, HCHMSG, and HC groups (2.03 ± 3.097; 3.21 ± 2.94; 5.86 ± 2.54). These findings suggest that T2DM can be induced by high-carbohydrate and high-MSG diets. However, the sole consumption of high MSG did not lead to the development of T2DM. Further research should focus on conducting long-term studies to fully comprehend the impact of a high MSG diet on individuals with pre-existing T2DM.

The tissue-specific metabolic effects of the PPARα agonist ciprofibrate in insulin-resistant male individuals: a double-blind, randomized, placebo-controlled crossover study.

Insulin resistance is characterized by ectopic fat accumulation leading to cardiac diastolic dysfunction and nonalcoholic fatty liver disease. The objective of this study was to determine whether treatment with the peroxisome proliferator-activated receptor-α (PPARα) agonist ciprofibrate has direct effects on cardiac and hepatic metabolism and can improve insulin sensitivity and cardiac function in insulin-resistant volunteers. Ten insulin-resistant male volunteers received 100 mg/d of ciprofibrate and placebo for 5 weeks in a randomized double-blind crossover study. Insulin-stimulated metabolic rate of glucose (MRgluc) was measured using dynamic 18 F-fluorodeoxyglucose-positron emission tomography(18 F-FDG-PET). Additionally, cardiac function, whole-body insulin sensitivity, intrahepatic lipid content, skeletal muscle gene expression, 24-hour blood pressure, and substrate metabolism were measured. Whole-body insulin sensitivity, energy metabolism, and body composition were unchanged after ciprofibrate treatment. Ciprofibrate treatment decreased insulin-stimulated hepatic MRgluc and increased hepatic lipid content. Myocardial net MRgluc tended to decrease after ciprofibrate treatment, but ciprofibrate treatment had no effect on cardiac function and cardiac energy status. In addition, no changes in PPAR-related gene expression in muscle were found. Ciprofibrate treatment increased hepatic lipid accumulation and lowered MRgluc, without affecting whole-body insulin sensitivity. Furthermore, parameters of cardiac function or cardiac energy status were not altered upon ciprofibrate treatment.

Omics-driven investigation of the biology underlying intrinsic submaximal working capacity and its trainability.

Submaximal exercise capacity is an indicator of cardiorespiratory fitness with clinical and public health implications. Submaximal exercise capacity and its response to exercise programs are characterized by heritability levels of about 40%. Using physical working capacity (power output) at a heart rate of 150 beats/min (PWC150) as an indicator of submaximal exercise capacity in subjects of the HERITAGE Family Study, we have undertaken multi-omics and in silico explorations of the underlying biology of PWC150 and its response to 20 wk of endurance training. Our goal was to illuminate the biological processes and identify panels of genes associated with human variability in intrinsic PWC150 (iPWC150) and its trainability (dPWC150). Our bioinformatics approach was based on a combination of genome-wide association, skeletal muscle gene expression, and plasma proteomics and metabolomics experiments. Genes, proteins, and metabolites showing significant associations with iPWC150 or dPWC150 were further queried for the enrichment of biological pathways. We compared genotype-phenotype associations of emerging candidate genes with reported functional consequences of gene knockouts in mouse models. We investigated the associations between DNA variants and multiple muscle and cardiovascular phenotypes measured in HERITAGE subjects. Two panels of prioritized genes of biological relevance to iPWC150 (13 genes) and dPWC150 (6 genes) were identified, supporting the hypothesis that genes and pathways associated with iPWC150 are different from those underlying dPWC150. Finally, the functions of these genes and pathways suggested that human variation in submaximal exercise capacity is mainly driven by skeletal muscle morphology and metabolism and red blood cell oxygen-carrying capacity.NEW & NOTEWORTHY Multi-omics and in silico explorations of the genes and underlying biology of submaximal exercise capacity and its response to 20 wk of endurance training were undertaken. Prioritized genes were identified: 13 genes for variation in submaximal exercise capacity in the sedentary state and 5 genes for the response level to endurance training, with no overlap between them. Genes and pathways associated with submaximal exercise capacity in the sedentary state are different from those underlying trainability.

Acute Effects of Single Versus Combined Inhaled β2-Agonists Salbutamol and Formoterol on Time Trial Performance, Lung Function, Metabolic and Endocrine Variables

BackgroundHigh prevalence rates of β2-agonist use among athletes in competitive sports makes it tempting to speculate that illegitimate use of β2-agonists boosts performance. However, data regarding the potential performance-enhancing effects of inhaled β2-agonists and its underlying molecular basis are scarce.MethodsIn total, 24 competitive endurance athletes (12f/12m) participated in a clinical double-blinded balanced four-way block cross-over trial to investigate single versus combined effects of β2-agonists salbutamol (SAL) and formoterol (FOR), to evaluate the potential performance enhancement of SAL (1200 µg, Cyclocaps, Pb Pharma GmbH), FOR (36 µg, Sandoz, HEXAL AG) and SAL + FOR (1200 µg + 36 µg) compared to placebo (PLA, Gelatine capsules containing lactose monohydrate, Pharmacy of the University Hospital Ulm). Measurements included skeletal muscle gene and protein expression, endocrine regulation, urinary/serum β2-agonist concentrations, cardiac markers, cardiopulmonary and lung function testing and the 10-min time trial (TT) performance on a bicycle ergometer as outcome variables. Blood and urine samples were collected pre-, post-, 3 h post- and 24 h post-TT.ResultsMean power output during TT was not different between study arms. Treatment effects regarding lung function (p < 0.001), echocardiographic (left ventricular end-systolic volume p = 0.037; endocardial global longitudinal strain p < 0.001) and metabolic variables (e.g. NR4A2 and ATF3 pathway) were observed without any influence on performance. In female athletes, total serum β2-agonist concentrations for SAL and FOR were higher. Microarray muscle gene analysis showed a treatment effect for target genes in energy metabolism with strongest effect by SAL + FOR (NR4A2; p = 0.001). Of endocrine variables, follicle-stimulating hormone (3 h Post–Post-TT), luteinizing hormone (3 h Post–Pre-TT) and insulin (Post–Pre-TT) concentrations showed a treatment effect (all p < 0.05).ConclusionsNo endurance performance-enhancing effect for SAL, FOR or SAL + FOR within the permitted dosages compared to PLA was found despite an acute effect on lung and cardiac function as well as endocrine and metabolic variables in healthy participants. The impact of combined β2-agonists on performance and sex-specific thresholds on the molecular and cardiac level and their potential long-term performance enhancing or health effects have still to be determined.Trial registration: Registered at Eudra CT with the number: 2015-005598-19 (09.12.2015) and DRKS with number DRKS00010574 (16.11.2021, retrospectively registered).

Targeting NAT10 protects against sepsis-induced skeletal muscle atrophy by inhibiting ROS/NLRP3

AimsTo identify N-acetyltransferase 10 (NAT10) and its downstream signaling pathways in myocytes and skeletal muscle, and to investigate its role in inflammation-induced muscle atrophy. Materials and methodsCecal ligation and puncture models were used to induce sepsis in C57BL/6 mice, which were treated with either a NAT10 inhibitor or a control agent. The therapeutic effect of NAT10 inhibitor was investigated by evaluating the mass, morphology, and molecular characteristics of mouse skeletal muscle. C2C12 cells were stimulated with LPS, and the expression of the NAT10 gene, downstream protein content, and atrophy phenotype were analyzed using a NAT10 inhibitor, to further explore the atrophic effect of NAT10 on C2C12 differentiated myotubes. ResultsGene set enrichment analysis revealed that NAT10 expression was elevated in the Lateral femoris muscle of patients with ICUAW. In vitro and in vivo experiments showed that sepsis or LPS induced the upregulation of NAT10 expression in skeletal muscles and C2C12 myotubes. Skeletal muscle mass, tissue morphology, gene expression, and protein content were associated with atrophic response in sepsis models. Remodelin ameliorated the LPS-induced skeletal muscle weight loss, as well as muscular atrophy, and improved survival. Remodelin reversed the atrophy program that was induced by inflammation through the downregulation of the ROS/NLRP3 pathway, along with the inhibition of the expression of MuRF1 and Atrogin-1. ConclusionNAT10 is closely related to skeletal muscle atrophy during sepsis. Remodelin improves the survival rate of mice by improving the systemic inflammatory response and skeletal muscle atrophy by downregulating the ROS/NLRP3 signaling pathway.

The isolated effects of local cold application on proteolytic and myogenic signaling

Post-exercise cooling studies reveal inhibitory effects on markers of skeletal muscle growth. However, the isolated effect of local cold application has not been adequately addressed. It is unclear if the local cold or the combination of local cold and exercise is driving negatively altered skeletal muscle gene expression. The purpose was to determine the effects of a 4 h local cold application to the vastus lateralis on the myogenic and proteolytic response. Participants (n = 12, 27 ± 6 years, 179 ± 9 cm, 82.8 ± 13.0 kg, 18.4 ± 7.1 %BF) rested with a thermal wrap placed on each leg with either circulating cold fluid (10 °C, COLD) or no fluid circulation (room temperature, RT). Muscle samples were collected to quantify mRNA (RT-qPCR) and proteins (Western Blot) associated with myogenesis and proteolysis. Temperatures in COLD were lower than RT at the skin (13.2 ± 1.0 °C vs. 34.8 ± 0.9 °C; p < 0.001) and intramuscularly (20.5 ± 1.3 °C vs. 35.6 ± 0.8 °C, p < 0.001). Myogenic-related mRNA, MYO-G and MYO-D1, were lower in COLD (p = 0.001, p < 0.001, respectively) whereas myogenic-mRNA, MYF6, was greater in COLD (p = 0.002). No other myogenic associated genes were different between COLD and RT (MSTN, p = 0.643; MEF2a, p = 0.424; MYF5, p = 0.523; RPS3, p = 0.589; RPL3-L, p = 0.688). Proteolytic-related mRNA was higher in COLD (FOXO3a, p < 0.001; Atrogin-1, p = 0.049; MURF-1, p < 0.001). The phosphorylation:total protein ratio for the translational repressor of muscle mass, 4E-BP1Thr37/46, was lower in COLD (p = 0.043), with no differences in mTORser2448 (p = 0.509) or p70S6K1Thr389 (p = 0.579). Isolated local cooling over 4 h exhibits inhibited myogenic and higher proteolytic skeletal muscle molecular response.

High-Intensity Interval Training’s Effect on Cognitive Functions

HIIT has been known to improve cognitive function. In addition to its effect on the hippocampal area. After HIIT training, BDNF levels also increase in the spinal cord, cerebellum and several cortical areas through increasing levels of Insulin-like Growth Factor-1 (IGF-1). In neurons, BDNF is present not only in the cytoplasm, but also near the dendritic spines, which influences their development. BDNF stimulates the process of neuroplasticity, which is manifested in neurogenesis, stimulation of the plasticity of serotoninergic, dopaminergic, cholinergic or noradrenergic neurons, dendritogenesis, and synaptogenesis. Moreover, BDNF facilitates the growth and survival of neurons and microglial cells. It also participates in cell differentiation, potentiation of signal transmission, induction, and maintenance of long-term potentiation of the synapse enhancement. Because of these properties, BDNF enhances cognition and takes part in emotional processes, spatial orientation and learning, as well as body coordination. Evidence suggests that IGF-1 is a major determinant of the effect of physical exercise on BDNF levels and thus on cognition more generally. There is an upregulation of Fndc5 gene expression in skeletal muscle and an increase in irisin after prolonged resistance training in rats and humans following HIIT training. When hippocampal Fndc5 was upregulated during exercise, BDNF and other neuroprotective genes were also activated in the rat hippocampus. Exercise-induced adult hippocampal neurogenesis is associated with increased Fndc5 and BDNF genes thus enhancing cognition. Then, stroke is associated with neuroinflammation that affects the processes of neuroplasticity in the lesion core, penumbra and small areas such as the spinal cord.

SPSB1-mediated inhibition of TGF-β receptor-II impairs myogenesis in inflammation.

Sepsis-induced intensive care unit-acquired weakness (ICUAW) features profound muscle atrophy and attenuated muscle regeneration related to malfunctioning satellite cells. Transforming growth factor beta (TGF-β) is involved in both processes. We uncovered an increased expression of the TGF-β receptor II (TβRII)-inhibitor SPRY domain-containing and SOCS-box protein 1 (SPSB1) in skeletal muscle of septic mice. We hypothesized that SPSB1-mediated inhibition of TβRII signalling impairs myogenic differentiation in response to inflammation. We performed gene expression analyses in skeletal muscle of cecal ligation and puncture- (CLP) and sham-operated mice, as well as vastus lateralis of critically ill and control patients. Pro-inflammatory cytokines and specific pathway inhibitors were used to quantitate Spsb1 expression in myocytes. Retroviral expression plasmids were used to investigate the effects of SPSB1 on TGF-β/TβRII signalling and myogenesis in primary and immortalized myoblasts and differentiated myotubes. For mechanistical analyses we used coimmunoprecipitation, ubiquitination, protein half-life, and protein synthesis assays. Differentiation and fusion indices were determined by immunocytochemistry, and differentiation factors were quantified by qRT-PCR and Western blot analyses. SPSB1 expression was increased in skeletal muscle of ICUAW patients and septic mice. Tumour necrosis factor (TNF), interleukin-1β (IL-1β), and IL-6 increased the Spsb1 expression in C2C12 myotubes. TNF- and IL-1β-induced Spsb1 expression was mediated by NF-κB, whereas IL-6 increased the Spsb1 expression via the glycoprotein 130/JAK2/STAT3 pathway. All cytokines reduced myogenic differentiation. SPSB1 avidly interacted with TβRII, resulting in TβRII ubiquitination and destabilization. SPSB1 impaired TβRII-Akt-Myogenin signalling and diminished protein synthesis in myocytes. Overexpression of SPSB1 decreased the expression of early (Myog, Mymk, Mymx) and late (Myh1, 3, 7) differentiation-markers. As a result, myoblast fusion and myogenic differentiation were impaired. These effects were mediated by the SPRY- and SOCS-box domains of SPSB1. Co-expression of SPSB1 with Akt or Myogenin reversed the inhibitory effects of SPSB1 on protein synthesis and myogenic differentiation. Downregulation of Spsb1 by AAV9-mediated shRNA attenuated muscle weight loss and atrophy gene expression in skeletal muscle of septic mice. Inflammatory cytokines via their respective signalling pathways cause an increase in SPSB1 expression in myocytes and attenuate myogenic differentiation. SPSB1-mediated inhibition of TβRII-Akt-Myogenin signalling and protein synthesis contributes to a disturbed myocyte homeostasis and myogenic differentiation that occurs during inflammation.

Nutritional status affects Igf1 regulation of skeletal muscle myogenesis, myostatin, and myofibrillar protein degradation pathways in gopher rockfish (Sebastes carnatus)

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) affects Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

Platinum-based anticancer drugs-induced downregulation of myosin heavy chain isoforms in skeletal muscle of mouse

Cisplatin, a platinum-based anticancer drug used frequently in cancer treatment, causes skeletal muscle atrophy. It was predicted that the proteolytic pathway is enhanced as the mechanism of this atrophy. Therefore, we investigated whether a platinum-based anticancer drug affects the expression of the major proteins of skeletal muscle, myosin heavy chain (MyHC). Mice were injected with cisplatin or oxaliplatin for four consecutive days. C2C12 myotubes were treated using cisplatin and oxaliplatin. Administration of platinum-based anticancer drug reduced quadriceps mass and muscle strength compared to the control group. Protein levels of all MyHC isoforms were reduced in the platinum-based anticancer drug groups. However, only Myh2 (MyHC-IIa) gene expression in skeletal muscle of mice treated with platinum-based anticancer drugs was found to be reduced. Treatment of C2C12 myotubes with platinum-based anticancer drugs reduced the protein levels of all MyHCs, and treatment with the proteasome inhibitor MG-132 restored this reduction. The expression of Mef2c, which was predicted to act upstream of Myh2, was reduced in the skeletal muscle of mice treated systemically with platinum-based anticancer drug. Degradation of skeletal muscle MyHCs by proteasomes may be a factor that plays an important role in muscle mass loss in platinum-based anticancer drug-induced muscle atrophy.

Physical Performance and Skeletal Muscle Transcriptional Adaptations Are Not Impacted by Exercise Training Frequency in Mice with Lower Extremity Peripheral Artery Disease.

Exercise training is an important therapeutic strategy for lower extremity peripheral artery disease (PAD). However, the effects of different exercise frequency on physiological adaptations remain unknown. Thus, this study compared the effects of a 7-week moderate-intensity aerobic training performed either three or five times/week on skeletal muscle gene expression and physical performance in mice with PAD. Hypercholesterolemic male ApoE-deficient mice were subjected to unilateral iliac artery ligation and randomly assigned to sedentary or exercise training regimens either three or five times/week. Physical performance was assessed using a treadmill test to exhaustion. Expression of genes related to glucose and lipid metabolism, mitochondrial biogenesis, muscle fiber-type, angiogenesis, and inflammation was analyzed in non-ischemic and ischemic gastrocnemius muscles by real-time polymerase chain reaction. Physical performance was improved to the same extent in both exercise groups. For gene expression patterns, no statistical differences were observed between three or five times/week exercised mice, both in the non-ischemic and ischemic muscles. Our data show that exercising three to five times a week induces similar beneficial effects on performance. Those results are associated with muscular adaptations that remain identical between the two frequencies.

Skeletal muscle gene expression dysregulation in long-term spaceflights and aging is clock-dependent

The circadian clock regulates cellular and molecular processes in mammals across all tissues including skeletal muscle, one of the largest organs in the human body. Dysregulated circadian rhythms are characteristic of aging and crewed spaceflight, associated with, for example, musculoskeletal atrophy. Molecular insights into spaceflight-related alterations of circadian regulation in skeletal muscle are still missing. Here, we investigated potential functional consequences of clock disruptions on skeletal muscle using published omics datasets obtained from spaceflights and other clock-altering, external (fasting and exercise), or internal (aging) conditions on Earth. Our analysis identified alterations of the clock network and skeletal muscle-associated pathways, as a result of spaceflight duration in mice, which resembles aging-related gene expression changes observed in humans on Earth (e.g., ATF4 downregulation, associated with muscle atrophy). Furthermore, according to our results, external factors such as exercise or fasting lead to molecular changes in the core-clock network, which may compensate for the circadian disruption observed during spaceflights. Thus, maintaining circadian functioning is crucial to ameliorate unphysiological alterations and musculoskeletal atrophy reported among astronauts.

Different Resistance Exercise Loading Paradigms Similarly Affect Skeletal Muscle Gene Expression Patterns of Myostatin-Related Targets and mTORC1 Signaling Markers.

Although transcriptome profiling has been used in several resistance training studies, the associated analytical approaches seldom provide in-depth information on individual genes linked to skeletal muscle hypertrophy. Therefore, a secondary analysis was performed herein on a muscle transcriptomic dataset we previously published involving trained college-aged men (n = 11) performing two resistance exercise bouts in a randomized and crossover fashion. The lower-load bout (30 Fail) consisted of 8 sets of lower body exercises to volitional fatigue using 30% one-repetition maximum (1 RM) loads, whereas the higher-load bout (80 Fail) consisted of the same exercises using 80% 1 RM loads. Vastus lateralis muscle biopsies were collected prior to (PRE), 3 h, and 6 h after each exercise bout, and 58 genes associated with skeletal muscle hypertrophy were manually interrogated from our prior microarray data. Select targets were further interrogated for associated protein expression and phosphorylation induced-signaling events. Although none of the 58 gene targets demonstrated significant bout x time interactions, ~57% (32 genes) showed a significant main effect of time from PRE to 3 h (15↑ and 17↓, p < 0.01), and ~26% (17 genes) showed a significant main effect of time from PRE to 6 h (8↑ and 9↓, p < 0.01). Notably, genes associated with the myostatin (9 genes) and mammalian target of rapamycin complex 1 (mTORC1) (9 genes) signaling pathways were most represented. Compared to mTORC1 signaling mRNAs, more MSTN signaling-related mRNAs (7 of 9) were altered post-exercise, regardless of the bout, and RHEB was the only mTORC1-associated mRNA that was upregulated following exercise. Phosphorylated (phospho-) p70S6K (Thr389) (p = 0.001; PRE to 3 h) and follistatin protein levels (p = 0.021; PRE to 6 h) increased post-exercise, regardless of the bout, whereas phospho-AKT (Thr389), phospho-mTOR (Ser2448), and myostatin protein levels remained unaltered. These data continue to suggest that performing resistance exercise to volitional fatigue, regardless of load selection, elicits similar transient mRNA and signaling responses in skeletal muscle. Moreover, these data provide further evidence that the transcriptional regulation of myostatin signaling is an involved mechanism in response to resistance exercise.

Estrogen receptor alpha deficiency in cardiomyocytes reprograms the heart-derived extracellular vesicle proteome and induces obesity in female mice.

Dysregulation of estrogen receptor alpha (ERα) has been linked with increased metabolic and cardiovascular disease risk. Here, we generate and characterize cardiomyocyte-specific ERα knockout (ERαHKO) mice to assess the role of ERα in the heart. The most striking phenotype was obesity in female ERαHKO but not male ERαHKO mice. Female ERαHKO mice showed cardiac dysfunction, mild glucose and insulin intolerance and reduced ERα gene expression in skeletal muscle and white adipose tissue. Transcriptomic, proteomic, lipidomic and metabolomic analyses revealed evidence of contractile and/or metabolic dysregulation in heart, skeletal muscle and white adipose tissue. We show that heart-derived extracellular vesicles from female ERαHKO mice contain a distinct proteome associated with lipid and metabolic regulation, and have the capacity to metabolically reprogram the target skeletal myocyte proteome with functional impacts on glycolytic capacity and reserve. This multi-omics study uncovers a cardiac-initiated and sex-specific cardiometabolic phenotype regulated by ERα and provides insights into extracellular vesicle-mediated interorgan communication.

Eight-Week Aerobic Training Activates Extracellular Matrix Biogenesis in Human Skeletal Muscle

We aimed to investigate the effect of 8 weeks of moderate endurance training without considerable mechanical stress on the activation of extracellular matrix (ECM) gene expression in human skeletal muscle. Mechanical stress activates ECM biogenesis in the skeletal muscles, therefore only aerobic exercise on a cycling ergometer with concentric muscle contractions was used in the study. Skeletal muscle samples from m. vastus lateralis were taken from seven young untrained males before and after 8 weeks of aerobic training. Changes in the transcriptome (RNA sequencing) and proteome (shotgun quantitative proteomics analysis) were assessed in the samples; ECM-associated proteins (or matrisome) were determined using the Matrisome DB database. After training period, a change (mainly an increase) in the content of 14 ECM proteins and 134 mRNAs of ECM proteins was found. The largest increase in protein content was found for collagens 1 and 3 (1.7 and 2.2 times, respectively) – the main proteins of the human skeletal muscle’s ECM, which was consistent with an increase in the corresponding mRNA by 10–20 times. In addition, an increase in the expression of more than a hundred mRNAs of collagens, glycoproteins, proteoglycans, and enzymatic regulators of ECM was found, which occurs simultaneously with of an increase in the expression of genes of growth factors (IGF1, PDGFs, TGFB1, MDK, etc.) playing an important role in ECM biogenesis regulation. In conclusion, 8-week aerobic exercise training without considerable mechanical stress is a powerful stimulus for the activation of ECM biogenesis in skeletal muscle.

Skeletal muscle and intermuscular adipose tissue gene expression profiling identifies new biomarkers with prognostic significance for insulin resistance progression and intervention response

Aims/hypothesisAlthough insulin resistance often leads to type 2 diabetes mellitus, its early stages are often unrecognised, thus reducing the probability of successful prevention and intervention. Moreover, treatment efficacy is affected by the genetics of the individual. We used gene expression profiles from a cross-sectional study to identify potential candidate genes for the prediction of diabetes risk and intervention response.MethodsUsing a multivariate regression model, we linked gene expression profiles of human skeletal muscle and intermuscular adipose tissue (IMAT) to fasting glucose levels and glucose infusion rate. Based on the expression patterns of the top predictive genes, we characterised and compared individual gene expression with clinical classifications using k-nearest neighbour clustering. The predictive potential of the candidate genes identified was validated using muscle gene expression data from a longitudinal intervention study.ResultsWe found that genes with a strong association with clinical measures clustered into three distinct expression patterns. Their predictive values for insulin resistance varied substantially between skeletal muscle and IMAT. Moreover, we discovered that individual gene expression-based classifications may differ from classifications based predominantly on clinical variables, indicating that participant stratification may be imprecise if only clinical variables are used for classification. Of the 15 top candidate genes, ST3GAL2, AASS, ARF1 and the transcription factor SIN3A are novel candidates for predicting a refined diabetes risk and intervention response.Conclusion/interpretationOur results confirm that disease progression and successful intervention depend on individual gene expression states. We anticipate that our findings may lead to a better understanding and prediction of individual diabetes risk and may help to develop individualised intervention strategies.Graphical abstract

Eutherian-Specific Functions of BetaM Acquired through Atp1b4 Gene Co-Option in the Regulation of MyoD Expression.

Vertebrate ATP1B4 genes represent a rare instance of orthologous gene co-option, resulting in radically different functions of the encoded BetaM proteins. In lower vertebrates, BetaM is a Na, K-ATPase β-subunit that is a component of ion pumps in the plasma membrane. In placental mammals, BetaM lost its ancestral role and, through structural alterations of the N-terminal domain, became a skeletal and cardiac muscle-specific protein of the inner nuclear membrane, highly expressed during late fetal and early postnatal development. We previously determined that BetaM directly interacts with the transcriptional co-regulator SKI-interacting protein (SKIP) and is implicated in the regulation of gene expression. This prompted us to investigate a potential role for BetaM in the regulation of muscle-specific gene expression in neonatal skeletal muscle and cultured C2C12 myoblasts. We found that BetaM can stimulate expression of the muscle regulatory factor (MRF), MyoD, independently of SKIP. BetaM binds to the distal regulatory region (DRR) of MyoD, promotes epigenetic changes associated with activation of transcription, and recruits the SWI/SNF chromatin remodeling subunit, BRG1. These results indicate that eutherian BetaM regulates muscle gene expression by promoting changes in chromatin structure. These evolutionarily acquired new functions of BetaM might be very essential and provide evolutionary advantages to placental mammals.

3D reconstruction shows mouse skeletal muscle may decline in function across aging due to the MICOS complex

Mitochondria are active organelles, undergoing harmonized cycles of fission and fusion, driven by ‘mitochondrial dynamics,’ to retain their morphology, distribution, and size. Mitochondrial dynamics has emerged as a critical process in maintaining cellular homeostasis. Interestingly, it has been long respected that a decrease in mitochondrial function escorts aging in specific tissues. For example, skeletal muscle gradually loses mass, strength, endurance, and oxidative capacity during aging. This decrease might, in turn, contribute to the observed age-dependent decline in organ function by mutations or alterations in mitochondrial fusion and fission proteins associated with several diseases. However, new players in regulating mitochondrial shape and cristae shape have been recently studied, such as the mitochondrial contact site and cristae organizing system (MICOS) complex. The MICOS complex is a multi-protein interaction hub that helps define cristate and mitochondria architecture. However, the MICOS complex has not been implicated in regulating organelle structure changes during aging. Thus, we hypothesized that loss of the MICOS complex during aging may increase mitochondrial fragmentation, decrease nanotunnels, and alter cristae morphology. To do this, we examined the three-dimensional morphology of mitochondria networks in young (3-month) and aged (2-year) murine gastrocnemius muscle via serial block face-scanning electron microscopy and the Amira program for segmentation, analysis, and quantification. We found differences in mitochondrial network configuration, nanotunneling, size, shape, number, contact sites, MICOS dynamics, and gene expression in skeletal muscle during aging. We also found an association between OPA-1 and the MICOS complex in the gastrocnemius with mitochondrial aging. Furthermore, the loss of the MICOS complex was linked with decreased oxidative capacity and altered mitochondrial metabolism. Potentially, this suggests a novel relationship between the MICOS complex and aging in skeletal muscle.

Loss of skeletal muscle estrogen-related receptors leads to severe exercise intolerance

ObjectiveSkeletal muscle oxidative capacity is central to physical activity, exercise capacity and whole-body metabolism. The three estrogen-related receptors (ERRs) are regulators of oxidative metabolism in many cell types, yet their roles in skeletal muscle remain unclear. The main aim of this study was to compare the relative contributions of ERRs to oxidative capacity in glycolytic and oxidative muscle, and to determine defects associated with loss of skeletal muscle ERR function. MethodsWe assessed ERR expression, generated mice lacking one or two ERRs specifically in skeletal muscle and compared the effects of ERR loss on the transcriptomes of EDL (predominantly glycolytic) and soleus (oxidative) muscles. We also determined the consequences of the loss of ERRs for exercise capacity and energy metabolism in mice with the most severe loss of ERR activity. ResultsERRs were induced in human skeletal muscle in response to an exercise bout. Mice lacking both ERRα and ERRγ (ERRα/γ dmKO) had the broadest and most dramatic disruption in skeletal muscle gene expression. The most affected pathway was “mitochondrial function”, in particular Oxphos and TCA cycle genes, and transcriptional defects were more pronounced in the glycolytic EDL than the oxidative soleus. Mice lacking ERRβ and ERRγ, the two isoforms expressed highly in oxidative muscles, also exhibited defects in lipid and branch chain amino acid metabolism genes, specifically in the soleus. The pronounced disruption of oxidative metabolism in ERRα/γ dmKO mice led to pale muscles, decreased oxidative capacity, histochemical patterns reminiscent of minicore myopathies, and severe exercise intolerance, with the dmKO mice unable to switch to lipid utilization upon running. ERRα/γ dmKO mice showed no defects in whole-body glucose and energy homeostasis. ConclusionsOur findings define gene expression programs in skeletal muscle that depend on different combinations of ERRs, and establish a central role for ERRs in skeletal muscle oxidative metabolism and exercise capacity. Our data reveal a high degree of functional redundancy among muscle ERR isoforms for the protection of oxidative capacity, and show that ERR isoform-specific phenotypes are driven in part, but not exclusively, by their relative levels in different muscles.

The Effects of Anabolic-Androgenic Steroids on Gene Expression in Skeletal Muscle: A Systematic Review

The Effects of Anabolic-Androgenic Steroids on Gene Expression in Skeletal Muscle: A Systematic Review