Skeletal Muscle Gene Expression Research Articles

Non-cell autonomous mechanisms control mitochondrial gene dysregulation in polycystic ovary syndrome.

Polycystic ovary syndrome (PCOS) is a common endocrine disorder associated with insulin resistance and impaired energy metabolism in skeletal muscle, the aetiology of which is currently unclear. Here, we mapped the gene expression profile of skeletal muscle from women with PCOS and determined if cultured primary myotubes retain the gene expression signature of PCOS in vivo. Transcriptomic analysis of vastus lateralis biopsies collected from PCOS women showed lower expression of genes associated with mitochondrial function, while the expression of genes associated with the extracellular matrix was higher compared to controls. Altered skeletal muscle mRNA expression of mitochondrial-associated genes in PCOS was associated with lower protein expression of mitochondrial complex II–V, but not complex I, with no difference in mitochondrial DNA content. Transcriptomic analysis of primary myotube cultures established from biopsies did not display any differentially expressed genes between controls and PCOS. Comparison of gene expression profiles in skeletal muscle biopsies and primary myotube cultures showed lower expression of mitochondrial and energy metabolism-related genes in vitro, irrespective of the group. Together, our results show that the altered mitochondrial-associated gene expression in skeletal muscle in PCOS is not preserved in cultured myotubes, indicating that the in vivo extracellular milieu, rather than genetic or epigenetic factors, may drive this alteration. Dysregulation of mitochondrial-associated genes in skeletal muscle by extracellular factors may contribute to the impaired energy metabolism associated with PCOS.

Impaired Muscle Mitochondrial Function in Familial Partial Lipodystrophy.

Familial partial lipodystrophy (FPL), Dunnigan variety is characterized by skeletal muscle hypertrophy and insulin resistance besides fat loss from the extremities. The cause for the muscle hypertrophy and its functional consequences is not known. To compare muscle strength and endurance, besides muscle protein synthesis rate between subjects with FPL and matched controls (n = 6 in each group). In addition, we studied skeletal muscle mitochondrial function and gene expression pattern to help understand the mechanisms for the observed differences. Body composition by dual-energy X-ray absorptiometry, insulin sensitivity by minimal modelling, assessment of peak muscle strength and fatigue, skeletal muscle biopsy and calculation of muscle protein synthesis rate, mitochondrial respirometry, skeletal muscle transcriptome, proteome, and gene set enrichment analysis. Despite increased muscularity, FPL subjects did not demonstrate increased muscle strength but had earlier fatigue on chest press exercise. Decreased mitochondrial state 3 respiration in the presence of fatty acid substrate was noted, concurrent to elevated muscle lactate and decreased long-chain acylcarnitine. Based on gene transcriptome, there was significant downregulation of many critical metabolic pathways involved in mitochondrial biogenesis and function. Moreover, the overall pattern of gene expression was indicative of accelerated aging in FPL subjects. A lower muscle protein synthesis and downregulation of gene transcripts involved in muscle protein catabolism was observed. Increased muscularity in FPL is not due to increased muscle protein synthesis and is likely due to reduced muscle protein degradation. Impaired mitochondrial function and altered gene expression likely explain the metabolic abnormalities and skeletal muscle dysfunction in FPL subjects.

Research Progress on the Effect of Exercise Rehabilitation on Functional Level and Physical Fitness

The essence of rehabilitation is the recovery and reconstruction of body function,and cardiopulmonary function is not only the core of body function, but also the core element of physical fitness. As one of the important interventions of modern rehabilitation treatment, exercise rehabilitation is the fundamental way to improve the level of body function, and plays a key role in the process of disease rehabilitation. The forms of exercise rehabilitation are widely used in clinic including aerobic exercise, high intensity interval training,muscle strength training, and traditional exercise and so on. Different forms of exercise rehabilitation can improve the level of body function and promote physical fitness in varying degrees. The main functions include regulating blood pressure, blood lipids and blood glucose, improving balance and muscle strength,increasing bone mineral density, enhancing cardiorespiratory fitness and walking ability, improving cognitive and memory functions,regulating emotions, promoting mental health, and improving the quality of life, etc., so as to achieve the goal of shortening the process of disease rehabilitation and improving its curative effect. However, there are differences in the dimensions and degrees of the influence of different forms of exercise rehabilitation on functional level and physical fitness. Among them, aerobic exercise mainly has a positive impact on cardiorespiratory fitness, glucose and lipid metabolism,emotional regulation, cognition and memory and other dimensions, and its mechanism involves the increase of endogenous cannabinoid in circulation and the integrity of white matter fibers and so on. Compared with moderate intensity aerobic exercise, high intensity interval training can improve cardiorespiratory fitness and cardiac metabolic health more timely and its mechanism involves the increase of muscle mitochondrial production capacity and the regulation of partial gene expression in skeletal muscle. Muscle strength training can improve blood glucose control and reduce the risk of chronic diseases and death by increasing muscle strength and endurance, especially for postmenopausal women and overweight/obese elderly. Traditional exercises, such as Taijiquan and Baduanjin, are important interventions of rehabilitation in traditional Chinese medicine, which have definite effect in improving balance, cognition and memory, and are worthy of clinical promotion and application. At present, how to choose the best form of exercise rehabilitation and the best course of treatment for people with different functional disorders and different disease status remains to be further clarified by follow-up clinical and basic research.

Systemic delivery of a DUX4-targeting antisense oligonucleotide to treat facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most prevalent skeletal muscle dystrophies. Skeletal muscle pathology in individuals with FSHD is caused by inappropriate expression of the transcription factor DUX4, which activates different myotoxic pathways. At the moment there is no molecular therapy that can delay or prevent skeletal muscle wasting in FSHD. In this study, a systemically delivered antisense oligonucleotide (ASO) targeting the DUX4 transcript was tested in vivo in ACTA1-MCM;FLExDUX4 mice that express DUX4 in skeletal muscles. We show that the DUX4 ASO was well tolerated and repressed the DUX4 transcript, DUX4 protein, and mouse DUX4 target gene expression in skeletal muscles. In addition, the DUX4 ASO alleviated the severity of skeletal muscle pathology and partially prevented the dysregulation of inflammatory and extracellular matrix genes. DUX4 ASO-treated ACTA1-MCM;FLExDUX4 mice performed better on a treadmill; however, the hanging grid and four-limb grip strength tests were not improved compared to control ASO-treated ACTA1-MCM;FLExDUX4 mice. This study shows that systemic delivery of ASOs targeting DUX4 is a promising therapeutic strategy for FSHD and strategies that further improve the ASO efficacy in skeletal muscle are warranted.

A Modular Mathematical Model of Exercise-Induced Changes in Metabolism, Signaling, and Gene Expression in Human Skeletal Muscle.

Skeletal muscle is the principal contributor to exercise-induced changes in human metabolism. Strikingly, although it has been demonstrated that a lot of metabolites accumulating in blood and human skeletal muscle during an exercise activate different signaling pathways and induce the expression of many genes in working muscle fibres, the systematic understanding of signaling–metabolic pathway interrelations with downstream genetic regulation in the skeletal muscle is still elusive. Herein, a physiologically based computational model of skeletal muscle comprising energy metabolism, Ca2+, and AMPK (AMP-dependent protein kinase) signaling pathways and the expression regulation of genes with early and delayed responses was developed based on a modular modeling approach and included 171 differential equations and more than 640 parameters. The integrated modular model validated on diverse including original experimental data and different exercise modes provides a comprehensive in silico platform in order to decipher and track cause–effect relationships between metabolic, signaling, and gene expression levels in skeletal muscle.

The Effect of Acute and Chronic Thermotherapy on Type 2 Diabetic Skeletal Muscle Gene Expression and Inflammatory Markers

Background: Type 2 diabetes (T2D) is a chronic illness associated with resistance to or defective insulin secretion. This study investigates the effects of thermotherapy on cell viability, gene expression and inflammation in skeletal muscle cell lines. Methods: Healthy and T2D human skeletal muscle cell lines (HSMM and D-HSMM, respectively) were subjected to acute or chronic thermo-therapy (AT or CT, respectively). CT consisted of a 30 min exposure to 40 °C, three times a week for three weeks; AT was a one-time exposure. Results: A significant decrease in D-HSMM cell viability percentage followed AT; however, no significant change occurred in CT. HSMM yielded the highest elevations of genes following CT. In D-HSMM, both treatments yielded gene upregulation. Both treatments significantly down-regulated IL-1β, IL-6, IL-10 and TNF-α in HSMM. AT significantly decreased IL-1β, IL-6 and upregulated IL-10 and TNF-α levels in D-HSMM, while CT yielded a reduction in IL-4, TNF-α and an upregulation of IL-6 and IL-10. Conclusions: An increase in gene expression indicates actin activity and cellular responses, suggesting an increase in transcriptional regulation. The upregulation of IL-6 and IL-10 in D-HSMM negatively correlated with a decrease in TNF-α and IL-1β, indicating improved adverse inflammatory effects associated with the disease.

AMP-Activated Protein Kinase Abundance and Activation is increased with the β-Adrenergic agonist Zilpaterol Hydrochloride in Muscle from Feedlot Cattle

The objective of this research was to evaluate the effect of Zilpaterol Hydrochloride (ZH) on myogenic or adipogenic gene and protein expression in skeletal muscle. Two feeding trials and one cell culture experiments were conducted. Semimembranosus muscle tissue was collected from steers that had been fed a diet containing 8.3 mg of ZH/kg DM for the last 0 or 20 d of the finishing period with a 3 d withdrawal period. To test the mode of action an in vitromodel was used with, isolated bovine satellite cells isolated from muscle tissue. Real Time-QPCR (RTQPCR) was used to measure the relative mRNA abundance of Adenosine Monophosphate Protein Kinase α (AMPK), Myosin Heavy Chain (MHC) I, MHCIIA, MHCIIX, Insulin-like Growth Factor I (IGF-I), β-adrenergic receptor (βAR) 1 and 2, peroxisome proliferator-activated receptor gamma (PPARγ), and Stearoyl-CoA Desaturase (SCD). Western blotting was used to measure the relative protein abundance of AMPK and Phosphorylated-AMPK (pAMPK). No differences were detected in relative mRNA abundance of AMPK, MHCIIA, IGF-I, βAR1 and βAR2. However, MHCI, SCD, and PPARγ mRNA expression was decreased and MHCIIX mRNA increased from ZH fed cattle compared to non-ZH. For one experiment, AMPK protein expression increased, while in another experiment, AMPK phosphorylation increased with ZH fed animals. The increase in MHCIIX mRNA with ZH fed cattle indicated the start of a fiber type shift towards larger diameter fibers. This shift may have been due to increased expression and phosphorylation of AMPK. These data suggest that the shift increase in MHCIIX was likely due to the ZH administration.

Effect of repeated bouts of fasting and refeeding on body composition and proteolysis gene expression in skeletal muscles and liver of C57BL/6J mice

Effect of repeated bouts of fasting and refeeding on body composition and proteolysis gene expression in skeletal muscles and liver of C57BL/6J mice

Retinoic acid exerts sexually dimorphic effects on muscle energy metabolism and function

The retinol dehydrogenase Rdh10 catalyzes the rate-limiting reaction that converts retinol into retinoic acid (RA), an autacoid that regulates energy balance and reduces adiposity. Skeletal muscle contributes to preventing adiposity, by consuming nearly half the energy of a typical human. We report sexually dimorphic differences in energy metabolism and muscle function in Rdh10+/− mice. Relative to wild-type (WT) controls, Rdh10+/− males fed a high-fat diet decrease reliance on fatty-acid oxidation and experience glucose intolerance and insulin resistance. Running endurance decreases 40%. Rdh10+/− females fed this diet increase fatty acid oxidation and experience neither glucose intolerance nor insulin resistance. Running endurance increases 220%. We therefore assessed RA function in the mixed-fiber type gastrocnemius muscles (GM), which contribute to running, rather than standing, and are similar to human GM. RA levels in Rdh10+/− male GM decrease 38% relative to WT. Rdh10+/− male GM increase expression of Myog and reduce Eif6 mRNAs, which reduce and enhance running endurance, respectively. Cox5A, complex IV activity, and ATP decrease. Increased centralized nuclei reveal existence of muscle malady and/or repair in GM fibers. Comparatively, RA in Rdh10+/− female GM decreases by less than half the male decrease, from a more modest decrease in Rdh10 and an increase in the estrogen-induced retinol dehydrogenase Dhrs9. Myog mRNA decreases. Cox5A, complex IV activity, and ATP increase. Centralized GM nuclei do not increase. We conclude that Rdh10/RA affects whole body energy use and insulin resistance partially through sexual dimorphic effects on skeletal muscle gene expression, structure, and mitochondria activity.

Altered skeletal muscle metabolic pathways, age, systemic inflammation, and low cardiorespiratory fitness associate with improvements in disease activity following high-intensity interval training in persons with rheumatoid arthritis

BackgroundExercise training, including high-intensity interval training (HIIT), improves rheumatoid arthritis (RA) inflammatory disease activity via unclear mechanisms. Because exercise requires skeletal muscle, skeletal muscle molecular pathways may contribute. The purpose of this study was to identify connections between skeletal muscle molecular pathways, RA disease activity, and RA disease activity improvements following HIIT.MethodsRA disease activity assessments and vastus lateralis skeletal muscle biopsies were performed in two separate cohorts of persons with established, seropositive, and/or erosive RA. Body composition and objective physical activity assessments were also performed in both the cross-sectional cohort and the longitudinal group before and after 10 weeks of HIIT. Baseline clinical assessments and muscle RNA gene expression were correlated with RA disease activity score in 28 joints (DAS-28) and DAS-28 improvements following HIIT. Skeletal muscle gene expression changes with HIIT were evaluated using analysis of covariance and biological pathway analysis.ResultsRA inflammatory disease activity was associated with greater amounts of intramuscular adiposity and less vigorous aerobic exercise (both p < 0.05). HIIT-induced disease activity improvements were greatest in those with an older age, elevated erythrocyte sedimentation rate, low cardiorespiratory fitness, and a skeletal muscle molecular profile indicative of altered metabolic pathways (p < 0.05 for all). Specifically, disease activity improvements were linked to baseline expression of RA skeletal muscle genes with cellular functions to (1) increase amino acid catabolism and interconversion (GLDC, BCKDHB, AASS, PYCR, RPL15), (2) increase glycolytic lactate production (AGL, PDK2, LDHB, HIF1A), and (3) reduce oxidative metabolism via altered beta-oxidation (PXMP2, ACSS2), TCA cycle flux (OGDH, SUCLA2, MDH1B), and electron transport chain complex I function (NDUFV3). The muscle mitochondrial glycine cleavage system (GCS) was identified as critically involved in RA disease activity improvements given upregulation of multiple GCS genes at baseline, while GLDC was significantly downregulated following HIIT.ConclusionIn the absence of physical activity, RA inflammatory disease activity is associated with transcriptional remodeling of skeletal muscle metabolism. Following exercise training, the greatest improvements in disease activity occur in older, more inflamed, and less fit persons with RA. These exercise training-induced immunomodulatory changes may occur via reprogramming muscle bioenergetic and amino acid/protein homeostatic pathways.Trial registrationClinicalTrials.gov, NCT02528344. Registered on 19 August 2015.

Abstract 133: Skeletal muscle transcriptome profiling of human pancreatic cancer cachexia: single largest study in cachexia

Abstract Cancer cachexia is a devastating syndrome characterized by severe depletion of muscle and fat loss. More than 80% of patients with pancreatic ductal adenocarcinoma (PDAC) cancer suffer from cachexia. Virtually all of the mechanistic understanding of cachexia comes from preclinical models; it remains to be seen how much of these molecular findings reflect in human cachexia. To translate the findings, it is important to have a better understanding of the human biology of cachexia. To address this knowledge gap, we performed a single large transcriptome profiling of skeletal muscle biopsies from 18 controls and 55 patients with resectable PDAC. RNA was isolated from rectus abdominus muscle and subjected to total RNA sequencing. Each sample was sequenced to 100 million reads. Differentially expressed (DE) genes were identified using Deseq2 and were subjected to pathway analysis. Further, we performed a sex-stratified analysis to understand if a sex-specific gene pattern exists. To better understand the relationship between clinical variables of cachexia such as 1- and 6-month weight loss, BMI, and skeletal muscle index versus gene expression, we built a sex-specific correlation network using weighted gene co-expression network analysis (WGCNA). As age was significantly different between controls and PDAC, we also performed age-adjusted gene expression analysis. In the overall analysis, 598 genes were DE between controls and PDAC groups. Novel upstream transcription factors including EGR1, EGR2 and EGR3 were identified. Many inflammatory pathways such as IL-6, IL-8, JAK/STAT, and p53 signaling were identified. In sex-specific analyses, 802 genes were DE in males, and 511 in females. Only 86 genes overlapped between males and females, suggesting that gene expression is modulated in a sex-specific fashion. WGCNA identified many significant modules at 1-month weight loss indicating that the gene changes could be dynamic in early stages of weight loss. The key correlated modules in males were enriched for pathways such as Wnt signaling, IL-6 signaling, lipid metabolism and hypoxia signaling. In females, the correlated modules were predominantly associated with DNA repair pathways and epigenetic pathways such as chromatin organization and apoptosis. Overall, this is the single largest cachexia-specific transcriptome profiling performed to date to comprehensively document RNA changes in PDAC cachexia. Our results suggest a strong sex influence at the gene, pathway, and WGCNA analysis levels. The catalog of genes identified from the study can be used be a rich resource for validation of pre-clinical observations and hypothesis generation. Efforts are underway to build an interactive database for public access. Citation Format: Ashok Narasimhan, Xiaoling Zhong, Jun Wan, Sheng Liu, Leonidas G. Koniaris, Teresa A. Zimmers. Skeletal muscle transcriptome profiling of human pancreatic cancer cachexia: single largest study in cachexia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 133.

Impact of Hypoxic Exercise Recovery on Skeletal Muscle Glycogen and Gene Expression.

Slivka, Dustin, Charles Dumke, Walter Hailes, and Brent Ruby. Impact of hypoxic exercise recovery on skeletal muscle glycogen and gene expression. High Alt Med Biol. 22:300-307, 2021. Background: The impact of altitude during recovery from exercise is largely unknown. The purpose of this study was to determine the acute gene response and muscle glycogen re-synthesis after exercise when exposed to simulated high altitude during recovery. Materials and Methods: Twelve male participants (age, 25 ± 2 years; height, 178 ± 7 cm; weight, 78.8 ± 7.8 kg; VO2peak, 4.25 ± 0.59 l/min; Wpeak 307 ± 44 W; and body fat, 13.1% ± 1.2%) completed two trials (random order), which consisted of cycling for 90 minutes in laboratory conditions and then recovering for 6 hours in laboratory conditions (975 m; normoxia) or at a high simulated altitude (5,000 m; hypoxia). Results: Skeletal muscle biopsies from the vastus lateralis were obtained before exercise, after exercise, and 6 hours after exercise for the measurement of metabolic gene expression and muscle glycogen. Muscle glycogen decreased with exercise (61% ± 13%, p < 0.05) and increased with recovery (78% ± 35%, p < 0.05) with no difference between trials (p > 0.05). Hypoxia-inducible factor (HIF)-1α, HIF-2α, optic atrophy gene 1 (OPA-1), mitofusin 2 (MFN-2), and peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) gene expression were suppressed after altitude exposure (p < 0.05), while mitochondrial fission 1 protein (FIS-1), phosphofructokinase (PFK), Cytochrome c oxidase (COX), and hexokinase (HK) were unaffected by altitude exposure (p > 0.05). Conclusions: High-altitude exposure during recovery from exercise inhibits gene expression associated with mitochondrial development without affecting muscle glycogen re-synthesis.

Random errors in protein synthesis activate an age-dependent program of muscle atrophy in mice

Random errors in protein synthesis are prevalent and ubiquitous, yet their effect on organismal health has remained enigmatic for over five decades. Here, we studied whether mice carrying the ribosomal ambiguity (ram) mutation Rps2-A226Y, recently shown to increase the inborn error rate of mammalian translation, if at all viable, present any specific, possibly aging-related, phenotype. We introduced Rps2-A226Y using a Cre/loxP strategy. Resulting transgenic mice were mosaic and showed a muscle-related phenotype with reduced grip strength. Analysis of gene expression in skeletal muscle using RNA-Seq revealed transcriptomic changes occurring in an age-dependent manner, involving an interplay of PGC1α, FOXO3, mTOR, and glucocorticoids as key signaling pathways, and finally resulting in activation of a muscle atrophy program. Our results highlight the relevance of translation accuracy, and show how disturbances thereof may contribute to age-related pathologies.

EFFECTS OF PUERARIA LOBATA COMBINED WITH HIGH-INTENSITY INTERMITTENT TRAINING ON SKELETAL MUSCLE QUALITY AND GENE EXPRESSION

ABSTRACT Extraction of effective components from Pueraria lobata has important value for skeletal muscle quality and gene expression. The improvement effect of traditional high-intensity intermittent training on skeletal muscle has not been obvious, and it is difficult to guarantee the properties of some volatiles. Based on this, this paper analyzes the effect of high-intensity intermittent training on skeletal muscle quality and gene expression in Pueraria lobata. Based on a brief summary of extraction of Pueraria lobata, status of research on the pharmaceutical components of Pueraria lobata was summarized. Different specimens of Pueraria lobata were selected as research objects, and the process of high-intensity intermittent training was designed. High-intensity intermittent training, solvent extraction and water solvent extraction were combined together to design the fixed-bed continuous extraction scheme. According to the influence of Pueraria lobata on skeletal muscle quality, the influence of intermittent training on skeletal muscle quality was analyzed. The extraction results showed that Pueraria lobata combined with high-intensity intermittent training can effectively improve the content of skeletal muscle and ensure the effective expression of skeletal muscle gene.

242-OR: Single Nuclei Skeletal Muscle Chromatin and Gene Expression Profiling across 287 Individuals Reveals Cell Type-Specific Genetic Regulatory Architectures at T2D GWAS Loci

Skeletal muscle is the largest organ, by weight (&amp;gt;40%), in the human body; insulin resistance in this and other peripheral tissues is a hallmark of type 2 diabetes (T2D). Recent genome wide association study (GWAS) results show enrichment for T2D and fasting insulin SNPs in skeletal muscle regulatory regions. Identifying gene regulatory mechanisms underlying these associations requires pinpointing the set of causal variants, the target genes these variants regulate, and the specific skeletal muscle cell populations in which they function. Here, we generated single nuclei chromatin (snATAC) and transcription (snRNA) profiles across 287 frozen human skeletal muscle biopsies. We integrated 414,982 nuclei across the modalities with LIGER and identified 13 cell types, ranging in abundance from 38.1% (type 1 fiber) to &amp;lt;1% (adipocyte) of all nuclei. We further integrated genotypes and performed expression and chromatin accessibility quantitative trait loci (e/caQTL) scans in the five most abundant cell types (type 1, type 2a, type 2x, mesenchymal stem cell, endothelial). We identified &amp;gt;70k associations (5% FDR) ranging from shared to cell type-specific and performed colocalization with T2D GWAS signals. Of 73 T2D GWAS signals that colocalize with caQTL, 39 (53.4%) are cell type-specific, highlighting the importance of sn-caQTL maps for GWAS functional studies. For example, in mesenchymal stem cells, we identified a cell type-specific caQTL for an ARL15 intronic peak (rs702634, p=6.6x10-10), which colocalizes with the T2D GWAS signal (coloc H4 posterior probability = 0.95). To nominate target genes for this caQTL peak, we scanned peaks in promoters of genes in the 1 Mb neighborhood and computed co-accessibility scores using Cicero in an allele-specific manner, which identified the gene FST, ~493 kb away. FST encodes for follistatin which increases muscle growth and reduces fat mass and insulin resistance. Disclosure S. Parker: None. A. Varshney: None. Fusion tissue study: n/a. Amp-t2d skeletal muscle working group: n/a. Funding American Diabetes Association/Pathway to Stop Diabetes (1-14-INI-07 to S.P.); National Institutes of Health (R01DK117960, U01DK06237017, UM1DK126185)

Insulin Infusion Is Linked to Increased NPPC Expression in Muscle and Plasma C-type Natriuretic Peptide in Male Dogs.

The purpose of this study was to assess insulin-stimulated gene expression in canine skeletal muscle with a particular focus on NPPC, the gene that encodes C-type natriuretic peptide, a key hormonal regulator of cardiometabolic function. Four conscious canines underwent hyperinsulinemic, euglycemic clamp studies. Skeletal muscle biopsy and arterial plasma samples were collected under basal and insulin-stimulated conditions. Bulk RNA sequencing of muscle tissue was performed to identify differentially expressed genes between these 2 steady-state conditions. Our results showed that NPPC was the most highly expressed gene in skeletal muscle in response to insulin infusion, rising 4-fold between basal and insulin-stimulated conditions. In support of our RNA sequencing data, we found that raising the plasma insulin concentration 15-fold above basal elicited a 2-fold (P = 0.0001) increase in arterial plasma concentrations of N-terminal prohormone C-type natriuretic peptide. Our data suggest that insulin may play a role in stimulating secretion of C-type natriuretic peptide by skeletal muscle. In this context, C-type natriuretic peptide may act in a paracrine manner to facilitate muscle–vascular bed crosstalk and potentiate insulin-mediated vasodilation. This could serve to enhance insulin and glucose delivery, particularly in the postprandial absorptive state.

Skeletal Muscle Gene Expression Profile in Response to Caloric Restriction and Aging: A Role for SirT1.

SirT1 plays a crucial role in the regulation of some of the caloric restriction (CR) responsive biological pathways. Aging suppresses SirT1 gene expression in skeletal muscle, suggesting that aging may affect the role of CR in muscle. To determine the role of SirT1 in the regulation of CR regulated pathways in skeletal muscle, we performed high-throughput RNA sequencing using total RNA isolated from the skeletal muscles of young and aged wild-type (WT), SirT1 knockout (SirT1-KO), and SirT1 overexpression (SirT1-OE) mice fed to 20 wk ad libitum (AL) or 40% CR diet. Our data show that aging repressed the global gene expression profile, which was restored by CR via upregulating transcriptional and translational process-related pathways. CR inhibits pathways linked to the extracellular matrix and cytoskeletal proteins regardless of aging. Mitochondrial function and muscle contraction-related pathways are upregulated in aged SirT1 KO mice following CR. SirT1 OE did not affect whole-body energy expenditure or augment skeletal muscle insulin sensitivity associated pathways, regardless of aging or diet. Overall, our RNA-seq data showed that SirT1 and CR have different functions and activation of SirT1 by its activator or exercise may enhance SirT1 activity that, along with CR, likely have a better functional role in aging muscle.

Skeletal muscle transcriptome in healthy aging

Age-associated changes in gene expression in skeletal muscle of healthy individuals reflect accumulation of damage and compensatory adaptations to preserve tissue integrity. To characterize these changes, RNA was extracted and sequenced from muscle biopsies collected from 53 healthy individuals (22–83 years old) of the GESTALT study of the National Institute on Aging–NIH. Expression levels of 57,205 protein-coding and non-coding RNAs were studied as a function of aging by linear and negative binomial regression models. From both models, 1134 RNAs changed significantly with age. The most differentially abundant mRNAs encoded proteins implicated in several age-related processes, including cellular senescence, insulin signaling, and myogenesis. Specific mRNA isoforms that changed significantly with age in skeletal muscle were enriched for proteins involved in oxidative phosphorylation and adipogenesis. Our study establishes a detailed framework of the global transcriptome and mRNA isoforms that govern muscle damage and homeostasis with age.

TISSUE NA+ EXCESS UPON EXPERIMENTAL SALT-LOADING IS SYSTEMIC AND REFLECTS ISOTONIC OEDEMA

Objective: Skin was identified as a large depot for Na+ accumulation. Its proposed water-independent (hypertonic) nature has the potential to induce local pathogenic changes, including activation of the osmotic stress sensor TonEBP-mediated lymphangiogenic signalling. Blockade of this response led to salt-sensitive hypertension. Our study tested the hypertonic nature and organ-specific distribution of tissue Na+ accumulation upon salt-loading. Design and method: Twelve weeks-old male and female stroke-prone spontaneously hypertensive (SHRSP) and control Wistar-Kyoto (WKY) rats were treated with 1% NaCl in drinking water (high salt, HS) or normal water (NS) for 3 weeks (n = 8–10/sex/group). Tissue water and Na+/K+ content, as well as TonEBP gene expression in abdominal skin, liver, lung, myocardium and skeletal muscle were measured by gravimetric approach (wet–dry weight), flame photometry and qRT-PCR, respectively. The functional effects of in-vivo and ex-vivo exposure of resistance arteries to salt excess (HS treatment and incubation in +15 mM NaCl, respectively) were assessed and compared by wire myography. Results: Tissue Na+ increased in skin (+20.7%), but also liver (+10.3%), lungs (+14.8%) and skeletal muscle (+23.6%) in HS-SHRSP compared to NS; apart from skeletal muscle, it was consistently paralleled by water (skin: +14.1%; liver: +4.8%; lungs: +9.0%; p &lt; 0.05 for all). Patterns were similar between males and females and absent in WKY. In both strains and all organs, K+ + Na+ concentration was not affected by HS and sat within physiological limits, thus pointing against hypertonicity. Nevertheless, TonEBP gene expression changes matched Na+ and water isotonic accumulation in SHRSP-HS skin, liver and lungs. Hypertonic incubation did not induce hypercontractile responses but exacerbated the sensitivity to NO-mediated relaxation in arteries from both strains (δIC50, p &lt; 0.001). The effect of in-vivo HS, in keeping with classic hypertensive vascular changes, was opposite (p &lt; 0.001, in SHRSP only). Conclusions: If water independent, interstitial Na accumulation is unlikely to underpin the development of experimental hypertension via a direct impact on vascular function. Tissue Na+ excess upon HS rather reflects isotonic oedema accumulation and systemic changes in tissue architecture, not solely confined to skin, and sensed by TonEBP.

Interleukin-6 ablation does not alter morphofunctional heart characteristics but modulates physiological and inflammatory markers after strenuous exercise

Interleukin-6 (IL-6) is associated with pathological cardiac hypertrophy and can be dramatically increased in serum after an acute strenuous exercise session. However, IL-6 is also associated with the increased production and release of anti-inflammatory cytokines and the inhibition of tumor necrosis factor-alpha (TNF-α) after chronic moderate exercise. To elucidate the relevance of IL-6 in inflammatory and hypertrophic signaling in the heart in response to an acute strenuous exercise session, we combined transcriptome analysis using the BXD mice database and exercised IL-6 knockout mice (IL-6KO). Bioinformatic analysis demonstrated that low or high-levels of Il6 mRNA in the heart did not change the inflammation- and hypertrophy-related genes in BXD mice strains. On the other hand, bioinformatic analysis revealed a strong positive correlation between Il6 gene expression in skeletal muscle with inflammation-related genes in cardiac tissue in several BXD mouse strains, suggesting that skeletal muscle-derived IL-6 could alter the heart's intracellular signals, particularly the inflammatory signaling. As expected, an acute strenuous exercise session increased IL-6 levels in wild-type, but not in IL-6KO mice. Despite not showing morphofunctional differences in the heart at rest, the IL-6KO group presented a reduction in physical performance and attenuated IL-6, TNF-α, and IL-1beta kinetics in serum, as well as lower p38MAPK phosphorylation, Ampkalpha expression, and higher Acta1 and Tnf gene expressions in the left ventricle in the basal condition. In response to strenuous exercise, IL-6 ablation was linked to a reduction in the pro-inflammatory response and higher activation of classical physiological cardiac hypertrophy proteins.