Skeletal Muscle Gene Expression Research Articles

Increase in cathepsin K gene expression in Duchenne muscular dystrophy skeletal muscle.

Dystrophinopathy is caused by alterations in the dystrophin gene. The severe phenotype, Duchenne muscular dystrophy (DMD), is caused by a lack of dystrophin in skeletal muscles, resulting in necrosis and regenerating fibers, inflammatory cells, and muscle fibrosis. Progressive muscle weakness is a characteristic finding of this condition. Here, we encountered a rare case of a 10-year-old patient with asymptomatic dystrophinopathy with no dystrophin expression and investigated the reason for the absence of muscle weakness to obtain therapeutic insights for DMD. Using RNA-seq analysis, gene expression in skeletal muscles was compared among patients with asymptomatic dystrophinopathy, three patients with typical DMD, and two patients without dystrophinopathy who were leading normal daily lives. Cathepsin K (CTSK), myosin heavy chain 3 (MYH3), and nodal modulator 3-like genes exhibited a >8-fold change, whereas crystallin mu gene (CRYM) showed a <1/8-fold change in patients with typical DMD compared with their expression in the patient with asymptomatic dystrophinopathy. Additionally, CTSK and MYH3 expression exhibited a >16-fold change (P < 0.01), whereas CRYM expression showed a <1/16-fold change (P < 0.01) in patients with typical DMD compared with their expression in those without dystrophinopathy. CTSK plays an essential role in skeletal muscle loss, fibrosis, and inflammation in response to muscles injected with cardiotoxin, one of the most common reagents that induce muscle injury. Increased CTSK expression is associated with muscle injury or necrosis in patients with DMD. The lack of muscle weakness in the patient with asymptomatic dystrophinopathy might be attributed to the low CTSK expression in the muscles. To the best of our knowledge, this is the first report to demonstrate that CTSK expression was significantly higher in the skeletal muscles of patients with DMD with a typical phenotype than in those without dystrophinopathy.

Knockout of Hsp70 genes significantly affects locomotion speed and gene expression in leg skeletal muscles of Drosophila melanogaster.

The functions of the Hsp70 genes were studied using a line of D. melanogaster with knockout of six these genes out of thirteen. Namely, effect of knockout of Hsp70 genes on negative geotaxis climbing (locomotor) speed and the ability to adapt to climbing training (0.5-1.5 h/day, 7 days/week, 19 days) were examined. Seven- and 23-day-old Hsp70- flies demonstrated a comparable reduction (2-fold) in locomotor speed and widespread changes in leg skeletal muscle transcriptome (RNA-seq), compared to w1118 flies. To identify the functions of genes related to decreased locomotor speed the overlapped differentially expressed genes at both time points were analyzed: the up-regulated genes encoded extracellular proteins, regulators of drug metabolism and antioxidant response, while down-regulated genes encoded regulators of carbohydrate metabolism and transmembrane proteins. Additionally, in Hsp70- flies, activation of transcription factors related to disruption of the fibril structure and heat shock response (Hsf) were predicted, using the position weight matrix approach. In the control flies, adaptation to chronic exercise training was associated mainly with gene response to a single exercise bout, while the predicted transcription factors were related to stress/immune (Hsf, NF-kB, etc.) and early gene response. In contrast, Hsp70- flies demonstrated no adaptation to training, as well as significantly impaired gene response to a single exercise bout. In conclusion, the knockout of Hsp70 genes not only reduced physical performance, but also disrupted adaptation to chronic physical training, which is associated with changes in leg skeletal muscle transcriptome and impaired gene response to a single exercise bout.

Expression of mitochondrial oxidative stress response genes in muscle is associated with mitochondrial respiration, physical performance, and muscle mass in the Study of Muscle, Mobility, and Aging.

Gene expression in skeletal muscle of older individuals may reflect compensatory adaptations in response to oxidative damage that preserve tissue integrity and maintain function. Identifying associations between oxidative stress response gene expression patterns and mitochondrial function, physical performance, and muscle mass in older individuals would further our knowledge of mechanisms related to managing molecular damage that may be targeted to preserve physical resilience. To characterize expression patterns of genes responsible for the oxidative stress response, RNA was extracted and sequenced from skeletal muscle biopsies collected from 575 participants (≥70 years old) from the Study of Muscle, Mobility, and Aging. Expression levels of 21 protein-coding RNAs related to the oxidative stress response were analyzed in relation to six phenotypic measures, including maximal mitochondrial respiration from muscle biopsies (Max OXPHOS), physical performance (VO2 peak, 400-m walking speed, and leg strength), and muscle size (thigh muscle volume and whole-body D3Cr muscle mass). The mRNA level of the oxidative stress response genes most consistently associated across outcomes are preferentially expressed within the mitochondria. Higher expression of mRNAs that encode generally mitochondria located proteins SOD2, TRX2, PRX3, PRX5, and GRX2 were associated with higher levels of mitochondrial respiration and VO2 peak. In addition, greater SOD2, PRX3, and GRX2 expression was associated with higher physical performance and muscle size. Identifying specific mechanisms associated with high functioning across multiple performance and physical domains may lead to targeted antioxidant interventions with greater impacts on mobility and independence.

Glutathione redox status regulates regenerative myogenic gene expression and functional recovery of human skeletal muscle in response to exercise-induced injury

Glutathione redox status regulates regenerative myogenic gene expression and functional recovery of human skeletal muscle in response to exercise-induced injury

Diacylglycerol kinase delta overexpression improves glucose clearance and protects against the development of obesity

Background and aimDiacylglycerol kinase (DGK) isoforms catalyze an enzymatic reaction that removes diacylglycerol (DAG) and thereby terminates protein kinase C signaling by converting DAG to phosphatidic acid. DGKδ (type II isozyme) downregulation causes insulin resistance, metabolic inflexibility, and obesity. Here we determined whether DGKδ overexpression prevents these metabolic impairments. MethodsWe generated a transgenic mouse model overexpressing human DGKδ2 under the myosin light chain promoter (DGKδ TG). We performed deep metabolic phenotyping of DGKδ TG mice and wild-type littermates fed chow or high-fat diet (HFD). Mice were also provided free access to running wheels to examine the effects of DGKδ overexpression on exercise-induced metabolic outcomes. ResultsDGKδ TG mice were leaner than wild-type littermates, with improved glucose tolerance and increased skeletal muscle glycogen content. DGKδ TG mice were protected against HFD-induced glucose intolerance and obesity. DGKδ TG mice had reduced epididymal fat and enhanced lipolysis. Strikingly, DGKδ overexpression recapitulated the beneficial effects of exercise on metabolic outcomes. DGKδ overexpression and exercise had a synergistic effect on body weight reduction. Microarray analysis of skeletal muscle revealed common gene ontology signatures of exercise and DGKδ overexpression that were related to lipid storage, extracellular matrix, and glycerophospholipids biosynthesis pathways. ConclusionOverexpression of DGKδ induces adaptive changes in both skeletal muscle and adipose tissue, resulting in protection against high fat diet-induced obesity. DGKδ overexpression recapitulates exercise-induced adaptations on energy homeostasis and skeletal muscle gene expression profiles.

Characterising 24-h skeletal muscle gene expression alongside metabolic & endocrine responses under diurnal conditions.

Skeletal muscle plays a central role in the storage, synthesis, and breakdown of nutrients, yet little research has explored temporal responses of this human tissue, especially with concurrent measures of systemic biomarkers of metabolism. To characterise temporal profiles in skeletal muscle expression of genes involved in carbohydrate metabolism, lipid metabolism, circadian clocks, and autophagy and descriptively relate them to systemic metabolites and hormones during a controlled laboratory protocol. Ten healthy adults (9M/1F, mean ± SD: age: 30 ± 10 y; BMI: 24.1 ± 2.7 kg·m-2) rested in the laboratory for 37 hours with all data collected during the final 24 hours of this period (i.e., 0800-0800 h). Participants ingested hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 2200-0700 h. Blood samples were collected hourly for endocrine and metabolite analyses, with muscle biopsies occurring every 4 h from 1200 h to 0800 h the following day to quantify gene expression. Plasma insulin displayed diurnal rhythmicity peaking at 1804 h. Expression of skeletal muscle genes involved in carbohydrate metabolism (Name - Acrophase; GLUT4 - 1440 h; PPARGC1A -1613 h; HK2 - 1824 h) and lipid metabolism (FABP3 - 1237 h; PDK4 - 0530 h; CPT1B - 1258 h) displayed 24 h rhythmicity that reflected the temporal rhythm of insulin. Equally, circulating glucose (0019 h), NEFA (0456 h), glycerol (0432 h), triglyceride (2314 h), urea (0046 h), CTX (0507 h) and cortisol concentrations (2250 h) also all displayed diurnal rhythmicity. Diurnal rhythms were present in human skeletal muscle gene expression as well systemic metabolites and hormones under controlled diurnal conditions. The temporal patterns of genes relating to carbohydrate and lipid metabolism alongside circulating insulin are consistent with diurnal rhythms being driven in part by the diurnal influence of cyclic feeding and fasting.

The interactive effect of sustained sleep restriction and resistance exercise on skeletal muscle transcriptomics in young females.

Both sleep loss and exercise regulate gene expression in skeletal muscle, yet little is known about how the interaction of these stressors affects the muscle transcriptome. The aim of this study was to investigate the effect of nine nights of sleep restriction, with repeated resistance exercise (REx) sessions, on the skeletal muscle transcriptome of young, trained females. Ten healthy females aged 18-35 years undertook a randomised cross-over study of nine nights' sleep restriction (SR; 5-h time in bed) and normal sleep (NS; ≥7 h time in bed) with a minimum 6-week washout. Participants completed four REx sessions per condition (day 3, 5, 7 and 9). Muscle biopsies were collected both pre- and post-REx on days 3 and 9. Gene and protein expression were assessed by RNA sequencing and Western Blot, respectively. Three or nine nights of sleep restriction had no effect on the muscle transcriptome independently of exercise. However, close to 3000 transcripts were differentially regulated (FDR < 0.05) 48 h post the completion of three resistance exercise sessions in both NS and SR conditions. Only 39% of downregulated and 18% of upregulated genes were common between both conditions, indicating a moderating effect of sleep restriction on the response to exercise. Sleep restriction and resistance exercise interacted to alter the enrichment of skeletal muscle transcriptomic pathways in young, resistance-trained females. Performing exercise when sleep restricted may not provide the same adaptive response for individuals as if they were fully rested.

The effects of exposure to and timing of a choline-deficient diet during pregnancy and early postnatal life on the skeletal muscle transcriptome of the offspring

Nonalcoholic fatty liver disease (NAFLD) is related to muscle loss, but the precise mechanism underlying this association remains unclear. The aim of the present study was thus to determine the influence of maternal fatty liver and dietary choline deficiency during pregnancy and/or lactation periods on the skeletal muscle gene expression profile among 24-day-old male rat offspring. Histological examination of skeletal muscle tissue specimens obtained from offspring of dams suffering from fatty liver, provided with proper choline intake during pregnancy and lactation (NN), fed a choline-deficient diet during both periods (DD), deprived of choline only during pregnancy (DN), or only during lactation (ND), was performed. The global transcriptome pattern was assessed using a microarray approach (Affymetrix® Rat Gene 2.1 ST Array Strip). The relative expression of selected genes was validated by real-time PCR (qPCR). Morphological differences in fat accumulation in skeletal muscle related to choline supply were observed. The global gene expression profile was consistent with abnormal morphological changes. Mettl21c gene was overexpressed in all choline-deficient groups compared to the NN group, while two genes, Cdkn1a and S100a4, were downregulated. Processes of protein biosynthesis were upregulated, and processes related to cell proliferation and lipid metabolism were inhibited in DD, DN, and ND groups compared to the NN group. Prenatal and early postnatal exposure to fatty liver and dietary choline deficiency leads to changes in the transcriptome profile in skeletal muscle of 24-day old male rat offspring and is associated with muscle damage, but the mechanism of it seems to be different at different developmental stages of life. Adequate choline intake during pregnancy and lactation can prevent severe muscle disturbance in the progeny of females suffering from fatty liver.

The Natural Flavanoid Senolytic Fisetin Mitigates Age-Related Changes in Frailty, Grip Strength, and the Skeletal Muscle Transcriptome in Old Mice

Background: Changes in skeletal muscle (SKM) with aging are characterized, in part, by reduced SKM strength and altered gene expression, both of which contribute to increased frailty. The age-related accumulation of excess senescent cells promotes the sequela of SKM aging and contributes to increased frailty. Thus, reducing senescent cell burden represents a promising therapeutic approach to improve SKM function and reduce frailty with aging. Senolytics are compounds that clear excess senescent cells. Currently available synthetic pharmacological senolytic agents harbor poor safety profiles and have low translational application; thus, new approaches are required. Fisetin (FIS) is a natural flavonoid senolytic compound that may fit this need. However, whether FIS supplementation lowers frailty and mitigates the sequela of SKM aging remains unknown. Hypothesis: FIS supplementation in old mice will ameliorate age-related changes in frailty, SKM strength, and senescence-related gene expression in SKM. Methods: We assessed frailty (via a validated frailty index) and SKM strength (via forelimb grip strength) in old (27 mo) male and female C57BL6/N mice following intermittent oral supplementation of either FIS (OFIS, N=39/19 female; 100 mg/kg/day in vehicle [10% EtOH; 30% PEG400; 60% Phosal 50 PG]; 1 week on — 2 weeks off — 1 week on) or vehicle (OC, N=31/13 female). mRNA expression was assessed in isolated quadriceps SKM via bulk RNA sequencing (N=10/group; 5 female). Results were also compared to a young (6 mo) control reference group (YC, N=10; 5 female). Sex differences were not observed, therefore, data were combined for male and female mice. Data are mean ± SEM. Results: Frailty was higher (OC: 0.27 ± 0.01 vs. YC: 0.01 ± 0.004; p&lt;0.05) and grip strength was lower (OC: 2.9g ± 0.01 vs. YC: 4.4g ± 0.02; p&lt;0.05) in old relative to young mice. Pathways associated with cellular senescence were enriched in SKM of OC compared to YC. Some of the most overly expressed genes with aging were related to cellular senescence (e.g., Ankrd1, Gadd45a, Cdkn1a). FIS supplementation reduced the age-related increase in frailty by ~15% (OFIS, 0.23 ± 0.01; p&lt;0.05 vs. OC) and diminished the age-related decline in grip strength by ~30% (OFIS, 3.3g ± 0.1; p&lt;0.05 vs. OC). FIS altered the overall SKM transcriptome in old mice characterized by (1) a less distinct aging phenotype vs. YC analyzed via principal component analysis; and (2) less or no longer enriched cellular senescence-related pathways. A total of six genes were different in OFIS vs. OC (p&lt;0.05; Log 2-fold change ± 0.5). Notably, Adh1 (alcohol dehydrogenase 1; positively associated with longevity) was higher and Ddit4 (DNA damage inducible transcript 4; positively related to DNA damage-induced senescence) was lower. Conclusions: Intermittent oral supplementation with FIS may be an effective therapeutic strategy to treat the sequela of SKM aging and frailty. However, to elicit greater changes in frailty and SKM strength with aging, a stronger or longer FIS dosing paradigm may be required. F32 HL167552; K01 DK115524; AHA 23CDA1056582; F31 HL165885; F31 HL164004; R01 AG055822-S1; K99 HL159241. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

In vivo dynamics of hydrogen peroxide and regulation of antioxidant gene expression in mouse skeletal muscle under cooling stimulus

Introduction: The dynamics of reactive oxygen species (ROS) in the cytosol and mitochondria function as signaling factors that regulates diverse cellular adaptations. Hydrogen peroxide (H2O2) is considered one of the most influential ROS in regulating physiological function; being a ubiquitous molecule with a long half-life and high diffusing capacity compared to other ROS (e.g., superoxide and hydroxyl radicals). Temperature changes within skeletal muscle myocytes constitute an environmental factor that modulates the expression of antioxidant-related genes. Although muscle temperature reduction by icing is a typical physical therapy modality, the relationship between cooling stimuli and in vivo H2O2 dynamics remains unclear. The purpose of this investigation was to elucidate the H2O2 dynamics in the cytosol and mitochondria induced by cooling stimuli and to determine the relationship between these dynamics and the expression of antioxidant-related genes. Specifically, we tested the hypothesis that cooling would reduce [H2O2] in intracellular compartments (cytosol and mitochondria) and suppress antioxidant-related gene expression levels. Methods: Experiment 1. in vivo H2O2 dynamics observation: Cytosolic and mitochondrial H2O2-sensitive fluorescent proteins (HyPer7, n = 6 and MLS-HyPer7, n = 9) were expressed by electroporation in the anterior tibialis muscle (TA) of male C57/BL6 mice (9-14 week of age). The TA was exposed under anesthesia, and cytosolic and mitochondrial [H2O2] were measured when the muscle temperature was reduced from 35 °C to 0 °C using in vivo bioimaging techniques. Experiment 2. Mice (9-12 week of age) were divided into an icing (ICE) group that received cooling stimulation (muscle temperature reduced from 35 °C to 13 °C and back to 35°C, total 6 sets for 60 min, n = 6) and a control (CONT) group (muscle temperature 35 °C for 60 min, n = 6). At 3 hours after temperature intervention, the TA was removed and mRNA levels were measured by Real-time PCR. Results: Experiment 1. In vivo [H2O2] in each compartment were significantly lower in the cytosol (over the range 28-6°C) and mitochondria (over the range 29-1°C) compared to 35 °C conditions. A decreasing phase of [H2O2] in both compartments was observed from 35 °C to around 13 °C, but, subsequently increasing [H2O2] were observed in the lower temperature range (i.e., 12 to 0 °C). Experiment 2: The ICE group significantly increased mRNA levels of antioxidant enzyme-related genes Nfe2l2 and HSF1 compared to CONT (1.2 ± 0.1-fold and 1.1 ± 0.1-fold, respectively, P &lt; 0.01). On the other hand, mRNA levels of mitochondria-related genes such as PGC1α and COX4 were unchanged. Conclusions: This investigation is the first to reveal the H2O2 and related gene expression impact of cooling stimuli in an in vivo model. Cooling mouse skeletal muscle produced temperature-dependent decreases in [H2O2] that reversed with more severe cooling. In both cytosolic and mitochondrial compartments, the lowest point for [H2O2] was found to be 13°C. Repeated cooling cycles (between 35 and 13 °C) with their attendant decreasing [H2O2] elevated antioxidant-related mRNA levels. These results support that icing therapy may improve the antioxidant capacity of muscle despite decreasing muscle ROS levels. This study was supported in part by a Grant-in-Aid for Japan Society for the Promotion of Science (JSPS) for Grant-in-Aid for JSPS Fellows (no. JP23KJ0967) and JSPS KAKENHI Grant (No. JP20H04074). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Cell-type specific effects of mineralocorticoid receptor gene expression suggest intercellular communication regulating fibrosis in skeletal muscle disease.

Introduction: Duchenne muscular dystrophy (DMD) is a fatal striated muscle degenerative disease. DMD is caused by loss of dystrophin protein, which results in sarcolemmal instability and cycles of myofiber degeneration and regeneration. Pathology is exacerbated by overactivation of infiltrating immune cells and fibroblasts, which leads to chronic inflammation and fibrosis. Mineralocorticoid receptors (MR), a type of nuclear steroid hormone receptors, are potential therapeutic targets for DMD. MR antagonists show clinical efficacy on DMD cardiomyopathy and preclinical efficacy on skeletal muscle in DMD models. Methods: We have previously generated myofiber and myeloid MR knockout mouse models to dissect cell-specific functions of MR within dystrophic muscles. Here, we compared skeletal muscle gene expression from both knockouts to further define cell-type specific signaling downstream from MR. Results: Myeloid MR knockout increased proinflammatory and profibrotic signaling, including numerous myofibroblast signature genes. Tenascin C was the most highly upregulated fibrotic gene in myeloid MR-knockout skeletal muscle and is a component of fibrosis in dystrophic skeletal muscle. Surprisingly, lysyl oxidase (Lox), canonically a collagen crosslinker, was increased in both MR knockouts, but did not localize to fibrotic regions of skeletal muscle. Lox localized within myofibers, including only a region of quadriceps muscles. Lysyl oxidase like 1 (Loxl1), another Lox family member, was increased only in myeloid MR knockout muscle and localized specifically to fibrotic regions. Discussion: This study suggests that MR signaling in the dystrophic muscle microenvironment involves communication between contributing cell types and modulates inflammatory and fibrotic pathways in muscle disease.

Inhibitory Regulation of FOXO1 in PPARδ Expression Drives Mitochondrial Dysfunction and Insulin Resistance.

Forkhead box protein O1 (FoxO1) regulates muscle growth, but the metabolic role of FoxO1 in skeletal muscle and its mechanisms remain unclear. To explore the metabolic role of FoxO1 in skeletal muscle, we generated skeletal muscle-specific FoxO1 inducible knockout (mFoxO1 iKO) mice and fed them a high-fat diet to induce obesity. We measured insulin sensitivity, fatty acid oxidation, mitochondrial function, and exercise capacity in obese mFoxO1 iKO mice, and assessed the correlation between FoxO1 and mitochondrial-related protein in the skeletal muscle of diabetic patients. Obese mFoxO1 iKO mice exhibited improved mitochondrial respiratory capacity, which was followed by attenuated insulin resistance, enhanced fatty acid oxidation, and improved skeletal muscle exercise capacity. Transcriptional inhibition of FoxO1 in peroxisome proliferator-activated receptor δ (PPARδ) expression was confirmed in skeletal muscle and deletion of PPARδ abolished the beneficial effects of FoxO1 deficiency. FoxO1 protein levels were higher in the skeletal muscle of diabetic patients and negatively correlated with PPARδ and electron transport chain protein levels. These findings highlight FoxO1 as a new repressor in PPARδ gene expression in skeletal muscle and suggest that FoxO1 links insulin resistance and mitochondrial dysfunction in skeletal muscle via PPARδ.

Autophagy gene expression in skeletal muscle of older individuals is associated with physical performance, muscle volume and mitochondrial function in the study of muscle, mobility and aging (SOMMA).

Autophagy is essential for proteostasis, energetic balance, and cell defense and is a key pathway in aging. Identifying associations between autophagy gene expression patterns in skeletal muscle and physical performance outcomes would further our knowledge of mechanisms related with proteostasis and healthy aging. Muscle biopsies were obtained from participants in the Study of Muscle, Mobility, and Aging (SOMMA). For 575 participants, RNA was sequenced and expression of 281 genes related to autophagy regulation, mitophagy, and mTOR/upstream pathways was determined. Associations between gene expression and outcomes including mitochondrial respiration in muscle fiber bundles (MAX OXPHOS), physical performance (VO2 peak, 400 m walking speed, and leg power), and thigh muscle volume, were determined using negative binomial regression models. For autophagy, key transcriptional regulators including TFE3 and NFKB-related genes (RELA, RELB, and NFKB1) were negatively associated with outcomes. On the contrary, regulators of oxidative metabolism that also promote overall autophagy, mitophagy, and pexophagy (PPARGC1A, PPARA, and EPAS1) were positively associated with multiple outcomes. In line with this, several mitophagy, fusion, and fission-related genes (NIPSNAP2, DNM1L, and OPA1) were also positively associated with outcomes. For mTOR pathway and related genes, expression of WDR59 and WDR24, both subunits of GATOR2 complex (an indirect inhibitor of mTORC1), and PRKAG3, which is a regulatory subunit of AMPK, were negatively correlated with multiple outcomes. Our study identifies autophagy and selective autophagy such as mitophagy gene expression patterns in human skeletal muscle related to physical performance, muscle volume, and mitochondrial function in older persons which may lead to target identification to preserve mobility and independence.

Genome-Wide Genetic Analysis of Dropout in a Controlled Exercise Intervention in Sedentary Adults With Overweight or Obesity and Cardiometabolic Disease.

Despite the benefits of exercise, many individuals are unable or unwilling to adopt an exercise intervention. The purpose of this analysis was to identify putative genetic variants associated with dropout from exercise training interventions among individuals in the STRRIDE trials. We used a genome-wide association study approach to identify genetic variants in 603 participants initiating a supervised exercise intervention. Exercise intervention dropout occurred when a subject withdrew from further participation in the study or was otherwise lost to follow-up. Exercise intervention dropout was associated with a cluster of single-nucleotide polymorphisms with the top candidate being rs722069 (T/C, risk allele = C) (unadjusted p = 2.2 × 10-7, odds ratio = 2.23) contained within a linkage disequilibrium block on chromosome 16. In Genotype-Tissue Expression, rs722069 is an expression quantitative trait locus of the EARS2, COG7, and DCTN5 genes in skeletal muscle tissue. In subsets of the STRRIDE genetic cohort with available muscle gene expression (n = 37) and metabolic data (n = 82), at baseline the C allele was associated with lesser muscle expression of EARS2 (p < .002) and COG7 (p = .074) as well as lesser muscle concentrations of C2- and C3-acylcarnitines (p = .026). Our observations imply that exercise intervention dropout is genetically moderated through alterations in gene expression and metabolic pathways in skeletal muscle. Individual genetic traits may allow the development of a biomarker-based approach for identifying individuals who may benefit from more intensive counseling and other interventions to optimize exercise intervention adoption. STRRIDE I = NCT00200993; STRRIDE AT/RT = NCT00275145; STRRIDE-PD = NCT00962962.

Social jet lag impairs exercise volume and attenuates physiological and metabolic adaptations to voluntary exercise training.

Social jet lag (SJL) is a misalignment between sleep and wake times on workdays and free days. SJL leads to chronic circadian rhythm disruption and may affect nearly 70% of the general population, leading to increased risk for cardiometabolic diseases. This study investigated the effects of SJL on metabolic health, exercise performance, and exercise-induced skeletal muscle adaptations in mice. Ten-week-old C57BL/6J mice (n = 40) were allocated to four groups: control sedentary (CON-SED), control exercise (CON-EX), social jet lag sedentary (SJL-SED), and social jet lag exercise (SJL-EX). CON mice were housed under a 12:12-h light-dark cycle. SJL was simulated by implementing a 4-h phase delay for 3 days to simulate "weekends," followed by a 4-h phase advance back to "weekdays," for 6 wk. EX mice had free access to a running wheel. Graded exercise tests (GXTs) and glucose tolerance tests (GTTs) were performed at baseline and after intervention to monitor the effects of exercise and social jet lag on cardiorespiratory and metabolic health, respectively. SJL led to alterations in activity and running patterns and clock gene expression in skeletal muscle and decreased average running distance (P < 0.05). SJL-SED mice gained significantly more weight compared with CON-SED and SJL-EX mice (P < 0.01). SJL impaired fasting blood glucose and glucose tolerance compared with CON mice (P < 0.05), which was partially restored by exercise in SJL-EX mice. SJL also blunted improvements in exercise performance and mitochondrial content in the quadriceps. These data suggest that SJL blunted some cardiometabolic adaptations to exercise and that proper circadian hygiene is necessary for maintaining health and performance.NEW & NOTEWORTHY In mice, disrupting circadian rhythms with social jet lag for 6 wk caused significant weight gain, higher fasting blood glucose, and impaired glucose tolerance compared with control. Voluntary exercise in mice experiencing social jet lag prevented weight gain, though the mice still experienced increased fasting blood glucose and impaired exercise performance compared with trained mice not experiencing social jet lag. Social jet lag seems to be a potent circadian rhythm disruptor that impacts exercise-induced training adaptations.

Mustn1 is a smooth muscle cell-secreted microprotein that modulates skeletal muscle extracellular matrix composition

ObjectiveSkeletal muscle plasticity and remodeling are critical for adapting tissue function to use, disuse, and regeneration. The aim of this study was to identify genes and molecular pathways that regulate the transition from atrophy to compensatory hypertrophy or recovery from injury. Here, we have used a mouse model of hindlimb unloading and reloading, which causes skeletal muscle atrophy, and compensatory regeneration and hypertrophy, respectively. MethodsWe analyzed mouse skeletal muscle at the transition from hindlimb unloading to reloading for changes in transcriptome and extracellular fluid proteome. We then used qRT-PCR, immunohistochemistry, and bulk and single-cell RNA sequencing data to determine Mustn1 gene and protein expression, including changes in gene expression in mouse and human skeletal muscle with different challenges such as exercise and muscle injury. We generated Mustn1-deficient genetic mouse models and characterized them in vivo and ex vivo with regard to muscle function and whole-body metabolism. We isolated smooth muscle cells and functionally characterized them, and performed transcriptomics and proteomics analysis of skeletal muscle and aorta of Mustn1-deficient mice. ResultsWe show that Mustn1 (Musculoskeletal embryonic nuclear protein 1, also known as Mustang) is highly expressed in skeletal muscle during the early stages of hindlimb reloading. Mustn1 expression is transiently elevated in mouse and human skeletal muscle in response to intense exercise, resistance exercise, or injury. We find that Mustn1 expression is highest in smooth muscle-rich tissues, followed by skeletal muscle fibers. Muscle from heterozygous Mustn1-deficient mice exhibit differences in gene expression related to extracellular matrix and cell adhesion, compared to wild-type littermates. Mustn1-deficient mice have normal muscle and aorta function and whole-body glucose metabolism. We show that Mustn1 is secreted from smooth muscle cells, and that it is present in arterioles of the muscle microvasculature and in muscle extracellular fluid, particularly during the hindlimb reloading phase. Proteomics analysis of muscle from Mustn1-deficient mice confirms differences in extracellular matrix composition, and female mice display higher collagen content after chemically induced muscle injury compared to wild-type littermates. ConclusionsWe show that, in addition to its previously reported intracellular localization, Mustn1 is a microprotein secreted from smooth muscle cells into the muscle extracellular space. We explore its role in muscle ECM deposition and remodeling in homeostasis and upon muscle injury. The role of Mustn1 in fibrosis and immune infiltration upon muscle injury and dystrophies remains to be investigated, as does its potential for therapeutic interventions.

Serum myostatin as a candidate disease severity and progression biomarker of spinal muscular atrophy.

The identification of biomarkers for spinal muscular atrophy is crucial for predicting disease progression, severity, and response to new disease-modifying therapies. This study aimed to investigate the role of serum levels of myostatin and follistatin as biomarkers for spinal muscular atrophy, considering muscle atrophy secondary to denervation as the main clinical manifestation of the disease. The study evaluated the differential gene expression of myostatin and follistatin in a lesional model of gastrocnemius denervation in mice, as well as in a meta-analysis of three datasets in transgenic mice models of spinal muscular atrophy, and in two studies involving humans with spinal muscular atrophy. Subsequently, a case-control study involving 27 spinal muscular atrophy patients and 27 controls was conducted, followed by a 12-month cohort study with 25 spinal muscular atrophy cases. Serum levels of myostatin and follistatin were analysed using enzyme-linked immunosorbent assay at a single centre in southern Brazil. Skeletal muscle gene expression of myostatin decreased and of follistatin increased following lesional muscle denervation in mice, consistent with findings in the spinal muscular atrophy transgenic mice meta-analysis and in the iliopsoas muscle of five patients with spinal muscular atrophy type 1. Median serum myostatin levels were significantly lower in spinal muscular atrophy patients (98 pg/mL; 5-157) compared to controls (412 pg/mL; 299-730) (P < 0.001). Lower myostatin levels were associated with greater disease severity based on clinician-rated outcomes (Rho = 0.493-0.812; P < 0.05). After 12 months, there was a further reduction in myostatin levels among spinal muscular atrophy cases (P = 0.021). Follistatin levels did not differ between cases and controls, and no significant changes were observed over time. The follistatin:myostatin ratio was significantly increased in spinal muscular atrophy subjects and inversely correlated with motor severity. Serum myostatin levels show promise as a novel biomarker for evaluating the severity and progression of spinal muscular atrophy. The decrease in myostatin levels and the subsequent favourable environment for muscle growth may be attributed to denervation caused by motor neuron dysfunction.

A Complex Pattern of Gene Expression in Tissue Affected by Viperid Snake Envenoming: The Emerging Role of Autophagy-Related Genes.

Viperid snake venoms induce severe tissue damage, characterized by the direct toxic action of venom components, i.e., phospholipases A2 (PLA2s) and metalloproteinases (SVMPs), concomitantly with the onset of endogenous inflammatory processes, in an intricate scenario of tissue alterations. Understanding the expression of relevant genes in muscle tissue will provide valuable insights into the undergoing pathological and inflammatory processes. In this study, we have used the Nanostring technology to evaluate the patterns of gene expression in mouse skeletal muscle 1 h, 6 h, and 24 h after injection of the venoms of Bothrops asper and Daboia russelii, two medically relevant species in Latin America and Asia, respectively, with somewhat different clinical manifestations. The dose of venoms injected (30 µg) induced local pathological effects and inflammation in muscle tissue. We focused our analysis on genes related to extracellular matrix (ECM) metabolism, immune system, programmed cell death, and autophagy. The results revealed a complex pattern of expression of genes. Regarding ECM metabolism and regulation, up-regulated genes included proteinase inhibitor Serpine 1, thrombospondin 1, collagens 1A1 and 4A1 (at 1 h in the case of B. asper), TIMP1, MMP-3 (at 24 h), and lysil oxidase (LOX). In contrast, collagen chains 5A3 and 5A1 were down-regulated, especially at 6 h. Transforming growth factor β (TGF-β) and several genes related to myofibroblast regulation were also up-regulated, which might be related to the development of fibrosis. Several genes related to cytokine and chemokine synthesis and regulation and NFκB signaling were also up-regulated. Our observations show a variable expression of genes associated with programmed cell death and autophagy, thus revealing a hitherto unknown role of autophagy in tissue affected by snake venoms. These results provide clues to understanding the complex pattern of gene expression in tissue affected by viperid snake venoms, which likely impacts the final pathophysiology of damaged tissue in envenomings.

Amphibian host-defense peptides with potential for Type 2 diabetes therapy – an updated review

Investigations conducted since 2018 have identified several host-defense peptides present in frog skin secretions whose properties suggest the possibility of their development into a new class of agent for Type 2 diabetes (T2D) therapy. Studies in vitro have described peptides that (a) stimulate insulin release from BRIN-BD11 clonal β-cells and isolated mouse islets, (b) display β-cell proliferative activity and protect against cytokine-mediated apoptosis and (c) stimulate production of the anti-inflammatory cytokine IL-10 and inhibit production of the pro-inflammatory cytokines TNF-α and IL-1β. Rhinophrynin-27, phylloseptin-3.2TR and temporin F are peptides with therapeutic potential. Studies in vivo carried out in db/db and high fat-fed mice have shown that twice-daily administration of [S4K]CPF-AM1 and [A14K]PGLa-AM1, analogs of peptides first isolated from the octoploid frog Xenopus amieti, over 28 days lowers circulating glucose and HbA1c concentrations, increases insulin sensitivity and improves glucose tolerance and lipid profile. Peptide treatment produced potentially beneficial changes in the expression of skeletal muscle genes involved in insulin signaling and islet genes involved in insulin secretion in these murine models of T2D. Lead compounds uncovered by the study of frog HDPs may provide a basis for the design of new types of agents that can be used, alone or in combination with existing therapies, for the treatment of T2D.

Celebrating a decade of exercise physiology and metabolism research in physiological reports.

During its first decade of life, Physiological Reports has become a home for well-conceived and rigorously performed exercise physiology and metabolism studies. The breadth of research within this area is impressive, covering exercise-induced increases in skeletal muscle gene expression to the effects of exercise on the gut microbiome. The purpose of the current review is to highlight some of the impactful exercise physiology and metabolism papers published in the journal and to look ahead to what areas exercise physiology publications might address in the next 10 years.