bluuebunny/crossref_metadata_2025_split huggingface dataset:
The α7β1 Integrin Directly Regulates SLC7A5 (LAT1) Amino Acid Transporter Transcription in Skeletal Muscle
Authors: Mahmassani Ziad , Son Kook , Chen Jie , Boppart Marni 
Published: November 2023

INTRODUCTIONThe α7β1 integrin is a focal adhesion protein found at the costameres of skeletal muscle and it provides a critical link between the actin cytoskeleton and laminin in the basement membrane. We have demonstrated that overexpression of the α7BX2 integrin subunit in muscle (MCK:α7BX2) enhances myofiber growth in the gastrocnemius following multiple bouts of eccentric exercise. Results from a recent microarray analysis suggest that the α7β1 integrin alone, in the absence of mechanical strain, initiates transcription of genes that allow for protection from stress, modulation of protein synthesis and regulation of substrate utilization.PURPOSEThe purpose of this study was to determine the extent to which the α7 integrin can directly regulate transcription of targeted genes using in vitro analysis.METHODSTwo separate small hairpin RNAs (shRNAs) in the pLKO.1‐puro vector for mouse ITGA7 were virally transduced into C2C12 myoblasts, with a scramble vector as a control. Myoblasts were differentiated and targeted gene expression (RPL13a, NOSIP, ANG, SLC7A5, GYS1, NDRG2, HSP40, HSPa5, and ATF6) was assessed using qPCR.RESULTSshRNA knockdown of the α7 integrin using either shRNA construct in C2C12 myotubes suppressed gene expression of the amino acid transporter SLC7A5 (LAT1), yet one increased and the other suppressed NDRG2, a stress‐responsive regulator of protein synthesis in striated muscle (P < 0.05).CONCLUSIONThe results from these studies suggest that the α7β1 integrin can directly regulate transcription of both SLC7A5 and NDRG2 in skeletal muscle under baseline (non‐exercised or loaded) conditions. The majority of alterations in gene transcription observed with array analysis, however, likely occur in cells outside the myofiber. Future studies are necessary to determine if integrin expression provides the basis for altered proteostasis in the context of disuse and disease.Support or Funding InformationNIH NIAMS 1 R21 AR065578A, NIH NIAMS R01AR048914.
Ribosome biogenesis is activated during the early period of resistance training in rat skeletal muscle
Authors: Kotani Takaya , Takegaki Junya , Nakada Satoshi , Takagi Ryo , Tomiya Shigeto , Tsutaki Arata , Nakazato Koichi , Ishii Naokata 
Published: November 2023

Resistance training (RT) induces skeletal muscle hypertrophy. Recently, it has been suggested that ribosome biogenesis plays an important part in RT‐induced skeletal muscle hypertrophy. However, influence of number of RT bouts is unclear.PurposeThe present study aimed to investigate the change of ribosomal RNA (rRNA) and ribosome protein content with changing the number of RT bouts.MethodMale Sprague‐Dawley rats were randomly assigned into six groups: Control (Cont), resistance‐trained with 1bout (1B), 2bouts (2B), 3bouts (3B), 6bouts (6B) and 18bouts(18B). RT protocol consisted of 50 repetitions of maximal isometric contraction of the gastrocnemius muscle by direct electric stimulation. Groups other than 1B performed 3 bouts of training per week. Muscle samples were collected 3h, 6h and 48h after the final exercise session in 1B to 3B, and 48h after the final exercise session in 6B and 18B.ResultsThe content of 18S+28S rRNA and rpS6 increased in 1B to 3B, but no significant difference was seen between 3B, 6B and 18B.ConclusionThe present showed that ribosome biogenesis is activated during the early period of RT. These results suggested that activation of ribosome biogenesis may contribute to increase protein synthesis during the later period, thereby leading to muscle hypertrophy.
Two Weeks of Reduced Steps Disrupts Integrated Rates of Muscle Protein Synthesis and Glycemic Control in Healthy Older Adults
Authors: McGlory Chris , Stokes Tanner , von Allmen Mark , Morton Robert , Smith Brennan , Steinberg Gregory , Phillips Stuart 
Published: November 2023

Transient periods of physical inactivity can result in losses of skeletal muscle mass and reductions in insulin sensitivity. These metabolic impairments may not be fully recovered, particularly in older individuals.1 We aimed to examine the impact of two weeks of reduced steps followed by two weeks of recovery, on lean body mass (LBM), integrated rates of myofibrillar protein synthesis (MPS), single fiber cross‐sectional area (fCSA), and indices of glycemic control (HOMA‐IR and MATSUDA) in response to an oral glucose tolerance test. We also examined changes in oxidative phosphorylation protein complex content, phosphorylation of other related signaling molecules, and concentration of circulating inflammatory markers. Twenty‐two healthy older adults (12 men, 10 women, 69±4yr [all data mean±SD]) underwent 7d of monitored normal activity at baseline (BL) before reducing their daily step‐count from 7362±3294 to 990±97 steps.d−1 for 14d (SR). Habitual step count was then recovered for a period of 14d (RC). Integrated rates of muscle protein synthesis (MPS) were reduced from BL at SR (BL 1.51±0.07 to SR 1.33±0.05 %.d−1, p<0.05) and were not restored at RC (1.34±0.14 %.d−1). Women displayed significantly greater rates of integrated MPS at BL compared to men (1.56±0.06 vs. 1.47±0.04 %.d−1, p<0.05). HOMA‐IR increased from BL to SR (2.6±0.4 to 3.8±0.9, p<0.05) and MATSUDA decreased (3.9±0.7 to 2.9±0.4, p<0.05), neither recovered at RC. Glucose AUC was significantly elevated from BL at SR (368±137 to 442±142, p<0.05) and was not fully recovered from SR at RC (393±15). Insulin AUC increased from BL to SR (3372±889 to 3972±1008, p<0.05) and was still elevated at RC (3865±716). Circulating plasma TNF‐a was significantly increased from BL at SR (11.78±2.84 to 15.41±4.64 pg.mL−1, p<0.05) and was still elevated above BL at RC (14.28±3.76 pg.mL−1). Plasma IL‐6 concentration was also significantly increased from BL at SR (8.33±3.06 to 10.84± 4.35 pg.mL−1, p<0.05) and remained elevated at RC (9.99±4.37 pg.mL−1). There was no detectable impact of step reduction on LBM, fCSA, fiber type distribution, or the content of oxidative phosphorylation protein complexes at any time point. Additionally, step reduction failed to impact the phosphorylation status of ACCSer212, AktSer473, mTORSer2448, Ulk1Ser757, and Ulk1Ser55 at BL, SR, and RC. These data demonstrate that two weeks of step reduction leads to lowered rates of MPS that are accompanied by appearance of a diabetic phenotype, and markers of an inflammatory state, which are not recovered on return to a normal daily step count in healthy older adults. Ultimately, proactive interventions such as exercise or pharmaceuticals may be required to reverse decrements in metabolic health with transient periods of physical inactivity in this population.Support or Funding InformationSupported by the Canadian Diabetes Association
Post‐ or Pre‐Injury Concentric Contractions Do Not Reduce Eccentric‐Contraction‐Induced Myofiber Damage in a Murine Model of Dysferlin‐linked Muscular Dystrophy
Authors: Begam Morium , Collier Alyssa F , Basel Chantel A , Blackmer Jacob M , Hass Joshua J , Konja Jasmine T , Samojedny Amber L , Roche Joseph A 
Published: November 2023

BackgroundConcentric contractions have been shown to reduce delayed onset muscle soreness following eccentric contractions in healthy human subjects. Dysferlin‐deficient muscle undergoes severe delayed onset myofiber damage over several days after eccentric contractions. The goal of our study was to test the hypothesis that concentric contractions reduce eccentric‐contraction‐induced myofiber damage in dysferlin‐deficient muscle.MethodsWe studied the tibialis anterior (TA) muscle in 3–4 month old, male, dysferlin‐null BLAJ mice. We elicited TA muscle contractions by depolarizing the fibular nerve with an electrical stimulator; and used a custom‐built dynamometer to measure contractile torque and expose the TA muscle to eccentric contractions (one bout; 40 repetitions; 90–160 □ plantarflexion superimposed on maximal tetany of ankle dorsiflexors). We exposed one group of mice to a single bout of 20, maximal, unloaded concentric contractions soon after eccentric contractions (ConEx after EccEx; N = 4 mice); exposed a second group to 6 sessions of maximal, unloaded concentric contractions (40 repetitions/session) over 2 weeks (ConEx before EccEx; N = 4); and designated a third group as controls (Untreated; N =4). We studied contractile torque before, immediately after, and 3 days after eccentric contractions. We collected TA muscles 3 days after eccentric contractions to histologically assess myofiber damage through hematoxylin and eosin staining, and through immunoglobulin‐G (IgG) and desmin immunofluorescent labeling.ResultsSummarized in Table 1.ConclusionNeither post‐ nor pre‐injury concentric contractions reduce eccentric‐contraction‐induced myofiber damage in dysferlin‐deficient skeletal muscle.Support or Funding InformationFunded by a Faculty Startup Package to JAR. Dysferlin‐null BLAJ mice were a kind gift from the Jain Foundation Inc.
Physiological and Histological Data

Outcome Measure
Untreated (Mean ± S.E.M.)
ConEx after EccEx (Mean ± S.E.M.)
ConEx before EccEx (Mean ± S.E.M.)
Statistically Significant Difference

Torque ‐ Immediately After Eccentric Contractions (% Pre)
52 ± 8
46 ± 1
49 ± 2
No

Torque ‐ 3 Days After Eccentric Contractions (% Pre)
37 ± 9
34 ± 1
38 ± 2
No

% Damaged Fibers ‐ 3 Days After Eccentric Contractions (H&E Staining)
42 ± 3
44 ± 2
41 ± 2
No

% IgG+ and Desmin‐Fibers ‐ 3 Days After Eccentric Contractions
40 ± 3
43 ± 3
38 ± 3
No
Chronic Heat Shock Stress Impairs Myoblast Proliferation and Differentiation
Authors: Bolus Daniel , Shanmugam Gobinath , Narasimhan Madhusudhanan , Soorapppan Rajasekaran Namakkal 
Published: November 2023

Heat‐related illness and injury are becoming a growing safety concern for the agricultural, construction workers, miners, firefighters, manufacturing workers and other outdoor workforces who are exposed to heat stress (HS) in their routine lives. A primary response by a cell to an acute HS exposure is the induction of heat‐shock proteins (HSPs) that chaperones and facilitates cellular protein folding and remodeling processes.. Nonetheless, the effect of repeated bouts of hyperthermia and the sustained production of HSPs in the myoblast‐myotube model system of C2C12 cells have yet to be elucidated fully. In C2C12 myoblasts, we found that robust HS (43°C, dose/time) significantly decreased the proliferation by 25% on day 1 and day 2 of HS that was further decreased to 35% on day 3 of HS. This was accompanied by an accumulation of cells at S and G2 phase with reduced cell number in G1 phase indicating cell cycle arrest. In addition, the repeated HS induced no apparent changes in apoptosis (markers) and cell death as determined by FACS analysis. Immunoblot analysis and qPCR demonstrated a significant increase in the baseline expression of HSP25, 70, and 90 (among others) in cells after a single HS (43°C) for 60 min as a typical HS response. Importantly, the repeated HS for 60 min each on day 2 and 3 maintained the elevated levels of HSPs than the control cells. Further, the continuous HS exposure resulted in significant inhibition of the differentiation of C2C12 myocytes to myotubes and only 1/10th of the cells underwent differentiation in HS compared to control cells. This was associated with significantly higher levels of HSPs and reduced expression of myogenin, Myh2, and MyoD, the genes involved in the differentiation process. Finally, the scratch assay indicated that the wound closure was significantly delayed in HS cells relative to the control cells. Overall, these results suggest that a repeated exposure of HS may perturb the active process of proliferation, motility and differentiation and affect the repair mechanisms in an in vitro murine myoblasts‐myotube model.Support or Funding InformationThese studies were supported by awards/research funds from the U.S. National Institutes of Health (NIH) National Heart, Lung, and Blood Institute (R01HL118067), NIH National Institute on Aging (1R03AG042860‐01), the University of Utah, and the University of Alabama at Birmingham startup funds (to N.S.R.).
Morphological regeneration and functional recovery of neuromuscular junction after ischemic/reperfusion injury induced by tourniquet in mouse hind limb
Authors: Tu Huiyin , Zhang Dongze , Muelleman Robert L , Wadman Michael C , Li Yu‐Long 
Published: November 2023

BackgroundTourniquet‐induced ischemia and subsequent reperfusion cause serious acute ischemia‐reperfusion (IR) injury in the neuromuscular junction (NMJ) and skeletal muscle. These injuries are associated with permanent neurological deficiency, and long‐term skeletal muscle contractile dysfunction, even complete limb paralysis. Monitoring structural and functional repair of the NMJ and skeletal muscle after tourniquet‐induced IR is beneficial to exploring the mechanisms responsible for tourniquet‐induced IR injury and finding effective therapeutic interventions. Here, we observed long‐term morphological and functional alterations of the NMJ in tourniquet‐induced hindlimb IR.MethodUnilateral hindlimb of C57/BL6 mice was subjected to 3 hours of ischemia by placing an orthodontic rubber band and followed different periods of reperfusion (1 day, 3 days, 1 weeks, 2 wekks, 4 weeks, and 6 weeks). At each time point of reperfusion, the gastrocnemius muscle was isolated for measurement of the NMJ morphology and function. Motor nerve terminals and nicotinic acetylcholine receptors (nAChRs) in the NMJ were measured by immunofluorescence staining. The end plate potential (EPP) was recorded by the intracellular recording technique.ResultsIn the NMJ of sham mice, the structure of the nAChR clusters remained intact pretzel‐like shape and motor nerve terminals innervated the nAChR clusters to form synapses for signal transmission. The number of fragments in one nAChR cluster was 1.83 ± 0.07 and all nAChR clusters were innervated by motor nerve terminals (100%). The amplitude of EPPs was 29.84 ± 1.02 mV. At 1 day and 3 days of reperfusion, the motor nerve terminals disappeared, the AChR clusters kept normal shape, and no EPPs were recorded. From 1 week to 6 weeks of reperfusion, the motor nerve terminals gradually reinnervated (46.88%, 88.05%, 99.2%, and 100% for 1, 2, 4, and 6 weeks of reperfusion, respectively). However, the AChR clusters were gradually fragmented and the number of fragments in one nAChR cluster increased with longer period of reperfusion (2.92 ± 0.14, 5.50 ± 0.30, 8.94 ± 0.67, and 6.88 ± 0.50 for for 1, 2, 4, and 6 weeks of reperfusion, respectively; p<0.05 vs. sham). The amplitude of EPPs also increased gradually with longer period of reperfusion, but the amplitude of EPPs at 6 weeks of reperfusion didn't restore towards the level seen in sham mice (13.92 ± 1.11 mV, p<0.05 vs. sham).ConclusionTourniquet‐induced ischemia and subsequent reperfusion impaired the NMJ. The morphological change of motor nerve terminals was faster than that of the nAChR clusters. The slow recovery of fragmented nAChR clusters could attenuate neuromuscular transmission.
A single bout of heat stress treatment increases Nrf2 and its target genes in mouse skeletal muscle
Authors: Tamura Yuki , Kitaoka Yu , Nakazato Koichi , Hatta Hideo 
Published: November 2023

In recent years, we have reported that heat stress induces various skeletal muscle adaptations (e.g. mitochondria, autophagy, unfolded protein response). In this study, we explored further possibilities of muscle adaptations by heat stress treatment using transcriptome approach and subsequent bioinformatics analysis. Immediately after treatment and three hours after a single bout of heat stress treatment (exposing mouse into a hot environment chamber; 40°C, 30 min), gastrocnemius muscles were collected and then examined changes in over 39,000 genes expression using Affimetrix microarray GeneChip. Consequently, we analyzed with bioinformatics algorithms TFactS and BioCarta to predict activated transcriptional factors and activated pathways, respectively. These computational analyses based on transcriptome data indicated that heat stress activates Nrf2 (Nfe2l2), a master transcriptional factor of antioxidant response, in skeletal muscle (TFactS: P<0.05; BioCarta: Fold Enrichment=7.2, P<0.05). We further confirmed by qPCR that heat stress increased Nrf2 (+39.4%, P<0.05) and its target genes such as Cat (+30.9%, P<0.05), Hmox1 (+182.6%, P<0.05), Gclc (+53.8%, P<0.05), Gclm (+32.1%, P<0.05), Gpx1 (+23.7%, P=0.07), Mt1a (+251.6%, P<0.05) and Sod1 (+27.8%, P<0.05) at 3h after treatment. Notably, there were non‐detectable changes in oxidative stress marker (4HNE‐conjugated protein) and gene expression of Nrf2‐independently inducible antioxidant enzyme (Sod2) at both immediately post‐treatment and 3h after treatment. Our observations suggest that the physiological significance of Nrf2 activation by heat stress may be other than defending oxidative stress.Support or Funding InformationThis study was supported by Grant‐in‐Aid for JSPS Research Fellow.
Hyperthermia and extracellular hyperosmolality affect sarcolemmal damage and protein oxidation in mammalian skeletal muscle in vitro
Authors: Laitano Orlando , Mattingly Alex J. , Robinson Gerard P. , Garcia Christian K. , Clanton Thomas L. 
Published: November 2023

In the US Armed Services, the incidence of rhabdomyolysis is 5–7 fold higher in peak summer months, suggesting that muscle membrane injury could be amplified by heat or to secondary dehydration. In this study we tested the extent each of these variables influences damage by evaluating sarcolemmal integrity and ROS‐induced protein oxidation. Extensor digitorum longus (EDL) and soleus (SOL) muscles were dissected from 24 adult male C57BL6J mice and placed at optimal length in tissue baths containing 4 ml of Krebs (95%O2/5%CO2). Muscles were intermittently stimulated to perform non‐fatiguing twitches for 30 min. Buffer temperature and osmolality were manipulated to provide four experimental conditions: normothermia/isotonic (35°C and 285 mOsm/kg), normothermia/hypertonic (35°C and 300 mOsm/kg), hyperthermia/isotonic (41°C and 285 mOsm/kg), and hyperthermia/hypertonic (41°C and 300 mOsm/kg). We quantified the integrity of the sarcolemma using both procion orange leakage into the fibers and a fluorometric assay to detect leakage out of double‐stranded cell‐free DNA (cfDNA). To assess protein oxidation, we performed immunoblot assays for protein carbonyl derivatives. For SOL we did not observe a significant effect of hyperthermia and/or hyperosmolality on procion orange leakage, but we observed an increase in cfDNA (p = 0.03) and protein carbonyls with hyperthermia (p = 0.02). Interestingly, these effects were absent when hyperosmolality was superimposed on hyperthermia. For EDL, an increase in procion orange leakage was observed with hyperthermia alone (p = 0.04) and when hyperthermia and hyperosmolality were combined (p = 0.03), but the combination did not elicit changes in cfDNA in the buffer. EDL protein carbonyls were independently augmented with hyperthermia (p = 0.01) and hyperosmolality (p = 0.02), but also did not increase when hyperthermia was combined with hyperosmolality. In conclusion, hyperthermia caused sarcolemma damage in EDL muscle, both alone and when combined with hyperosmolality. SOL was more resistant to hyperthermia‐induced procion orange leakage, despite an increase release of extracellular cfDNA. Furthermore, physiological increases in extracellular osmolality prevented protein oxidation in hyperthermia in both muscle types. These observations suggest that different muscle types may respond differently to hyperthermic and osmotic challenges. The compensatory effect of hyperosmolality on hyperthermia‐induced oxidative stress is consistent with a role for ROS production in compensatory responses to cell swelling in the heat.Support or Funding InformationSupported by the BK and Betty Stevens Endowment and the Brazilian Council for the Development of Science and Technology (CNPq no. 249094/2013‐4).
H2S MEDIATES SENSORY LONG‐TERM FACILITATION OF THE CAROTID BODY
Authors: Peng Ying‐Jie , Yuan Guoxiang , Khan Shakil , Nanduri Jayasri , Kumar Ganesh , Snyder Solomon , Prabhakar Nanduri 
Published: November 2023

Chronic intermittent hypoxia (CIH) is a hallmark manifestation of sleep apnea. Rodents treated with CIH exhibit hypertension and increased sympathetic nerve activity, and these effects were attributed to carotid body (CB) chemoreflex. CIH leads to CB activation manifested by augmented sensory response to hypoxia, and sensory long‐term facilitation (LTF). The purpose of the present study is to determine the mechanisms underlying CB activation by CIH. Recent studies suggest that the gasotransmitter H2S mediates CB activation during acute hypoxia. Since CIH increases H2S production from the cystathionine‐ϒ‐lyase (CSE) in the CB through ROS signaling, we hypothesized that H2S mediates the CB activation by CIH. Experiments were performed on adult rats, CSE‐null and wild‐type mice treated with 10 days of CIH. CIH treated CBs displayed augmented sensory response to hypoxia, and sensory LTF in rats and wild‐type mice. CB activation by CIH was completely absent in rats treated with L‐Propargylglycine (L‐PAG) an inhibitor of CSE and in mice deficient in CSE. CIH treated rats and wild‐type mice showed hypertension, increased sympathetic nerve activity, and elevated plasma catecholamine levels ‐ all these effects were remarkably absent in L‐PAG treated rats and CSE null mice. These findings suggest that ROS‐dependent activation of CSE‐derived H2S synthesis mediates CB response to CIH and the ensuing hyperactive CB chemoreflex contributes to CIH‐induced sympathetic activation and hypertension.Support or Funding InformationSupported by NIH‐PO1‐HL90554