bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of a Pharmacological Inhibitor on P‐38 MAPK in Drosophila melanogaster during Rapid Cold Hardening
Authors: Gardner Daniel Dennis , Kelty Jonathan
Published: June 2021

Recent data suggests that p‐38 MAPK signaling may be involved in rapid cold hardening (RCH) of the house fly Musca Domestica, the Antarctic midge Belgica Antarctica, and the flesh fly Sarcophaga crassipalpis. Accordingly, this study used pharmacological techniques to determine whether p‐38 MAPK signaling is required for RCH in Drosophila melanogaster. As in prior studies, RCH afforded protection against cold shock injury for flies reared on drug‐free medium (yeast paste) for 48 h beginning within 6 h following eclosion; whereas no flies transferred directly from 23° C to −6° C for 1 h survived, 74% of those exposed to 1° C for 2 h immediately prior to a 1 h exposure to −6°C survived. By contrast, rearing flies on yeast paste containing 1 μg/mL SB 239063 impaired the capacity to rapidly cold harden; all flies fed SB 239063 were killed by a 1 h exposure to −6°C, regardless of whether they were first subjected to a RCH treatment. Similarly, preliminary data suggests that pharmacological inhibition of p38‐MAPK interferes with the protection of clinging behavior by rapid cold hardening.
Adaptation of isolated spiny dogfish shark choroid plexus to manipulation of extracellular Zn and exposure to Cd
Authors: Villalobos A R , Meyers C.E. , Stuart S.D. Francis , Zarate S.M. , Ellis E.A. , Perry D. , Taylor R.J. , Young R.K.
Published: June 2021

The choroid plexus forms the blood‐cerebrospinal fluid (CSF) barrier, secretes CSF and transports solutes between blood and CSF. We reported for spiny dogfish shark (S. acanthias) that choroid plexus accumulated essential metals, e.g., zinc (Zn), and contaminant heavy metals to concentrations similar to those in kidney and liver. Using isolated dogfish choroid plexus, our objective is to characterize regulation of gene expression and modulation of epithelial ultrastructure by the essential mineral Zn and the contaminant metal, cadmium (Cd). To begin, effects of Zn supplementation or depletion and exposure to Cd on metallothionein (MT) gene expression were analyzed by qRT‐PCR; epithelial ultrastructure was viewed by transmission electron microscopy (TEM). Initial TEM images of Zn‐supplemented and Zn‐depleted choroid plexus show modest changes in apical microvilli and no remarkable variations in basolateral in‐foldings as compared to control tissues. Nevertheless, 10 μM Zn supplementation increased MT mRNA by 275‐fold at 24 h and by 620‐fold at 48h, whereas 24‐h chelation of extracellular Zn with 10 μM diethylentriamene pentaacetate reduced MT mRNA by 60%. 500 nM Cd increased MT mRNA by 65‐fold at 24 h. These initial data suggest that in dogfish choroid plexus although epithelial ultrastructure might remain unchanged, altered Zn availability and Cd exposure regulate MT gene expression. NSF‐IOS#1052654
DXA & MRI measures of tissue composition: implications for muscle quality in older women varying in physical activity
Authors: Larson Rebecca Danti , Johnson Curtis L , Guest Dolores D , Das Bhibha M , Ward Christie L , Chen Danchin D , Georgiadis John G , Evans Ellen M
Published: June 2021

Muscle quality (MQ), defined as strength per muscle quantity, impacts physical function in older women and is also influenced by physical activity. The aims of this pilot study were to investigate if: 1) physical activity impacts upper leg composition assessed in normal weight older women, and 2) muscle assessments, via DXA or MRI, would alter MQ estimates. Non‐obese (BMI < 25 kg/m2) older women (60–80 y) who were sedentary (SED; n = 8) or physically active (PA; n = 10) were assessed for thigh subcutaneous adipose tissue (SAT), intermuscular adipose tissue (IMAT) and muscle (MUSC) via MRI, and mineral free lean mass (MFLM) via DXA. Strength was assessed via maximal isometric (IM) and isokinetic (60 and 180 deg/sec; IK60, IK180) contractions using an isokinetic dynamometer. MQ‐IM, MQ‐IK60, and MQ‐IK180 were calculated as Nm/kg or Nm/m3. SED and PA groups did not differ in SAT, IMAT, MUSC, and MFLM (all p>0.05). MQ‐IM, MQ‐IK60. and MQ‐IK180 did not differ between groups, regardless of muscle assessment method (p>0.05). Combining groups, the % lean/muscle estimated by DXA was greater than MRI (51.4% vs. 38.3%; p<0.05). One source of error could be relative IMAT as it averaged 10.7% and the difference between % lean/muscle estimates was 13.1% and trended toward association (r = 0.25). The quantification of muscle in the context of MQ warrants further investigation in a larger sample varying in adiposity. Supported by NIH‐HL090455
Phosphatidic Acid and Mechanical Stimuli Activate mTOR Signaling via an ERK‐independent Mechanism
Authors: Hornberger Troy A. , You Jae-Sung
Published: June 2021

Signaling by mTOR is both necessary and sufficient for the induction of hypertrophy in response to increased mechanical loading. Recently it has been suggested that mechanical stimuli (MS) induce mTOR signaling via a mechanism that is dependent on phosphatidic acid (PA). The mechanism via which PA activates mTOR signaling is not clear, but at least two models have been proposed; 1) direct binding of PA to mTOR, or 2) PA‐induced activation of ERK which then stimulates mTOR. In order to more clearly define the role of ERK in the regulation of mTOR by PA and MS, we first performed experiments in which C2C12 myoblasts were stimulated with exogenous PA. The results indicated that exogenous PA was sufficient to induce signaling through both ERK and mTOR, however, inhibition of ERK with UO126 did not prevent the ability of PA to induce mTOR signaling. Next, we performed experiments in which mouse EDL muscles were subjected to intermittent stretch as a source of MS. The results indicated that MS was sufficient to induce an increase in PA, as well as, signaling through both ERK and mTOR. Similar to the results observed with exogenous PA, inhibiting ERK with UO126 did not prevent the ability of MS to induce mTOR signaling. Taken together, these results indicate that both exogenous PA and MS induce mTOR signaling through an ERK‐independent mechanism that potentially involves a direct interaction of PA with mTOR. Support: NIH grant AR057347 to TAH
Skeletal muscle force is preserved in NOX4 deficient mice
Authors: Frye Gregory , Ahn Bumsoo , Brandes Ralf P. , Schröder Katrin , Ferreira Leonardo F.
Published: June 2021

NADPH oxidase levels are elevated in various cardiovascular diseases. The NOX4 isoform of NADPH oxidase generates reactive oxygen species that promotes calcium release in skeletal muscle. NOX4 knockdown depresses maximal tetanic force in mouse EDL muscle. We tested the hypotheses that NOX4 deficient mice would have decreased muscle force, rightward shift in the force‐frequency relationship, and accelerated fatigue in vitro. We studied intact soleus muscle from genetic control (C57BL/6J) and NOX 4 knockout mice (n = 7/group; 2 males/group) at 95%O2 and 37°C. Our initial experiments suggest no difference in maximal soleus tetanic force (Po) between groups (in N/cm2; Control 32 ± 6, NOX 4−/− 36 ± 4). Neither the stimulus frequency that elicited 50% Po (Control 53 ± 3 Hz; NOX4−/− 53 ± 8 Hz) nor muscle fatigue (not shown) was affected by NOX4 deficiency. Our study suggests that skeletal muscle force is preserved in mice lacking NOX4 isoform of NADPH oxidase.
Heart failure increases neutral sphingomyelinase activity and ceramide content in rat diaphragm
Authors: Ferreira Leonardo , Deevska Gergana M. , Nikolova-Karakashian Mariana , Yoo Jeung-ki , Christou Demetra D.
Published: June 2021

Patients with chronic heart failure (CHF) have skeletal muscle weakness and elevated secretory sphingomyelinase activity. Sphingomyelinase (SMase) acts through ceramide to depress skeletal muscle force in vitro. We hypothesized that diaphragm weakness in CHF is accompanied by increases in SMase activity and tissue ceramide content. We studied rats 14–16 weeks after myocardial infarction (n = 5–10) and sham surgery (n = 10–13). CHF was confirmed by a decrease in left‐ventricular fractional shortening measured by echocardiography (Sham 38 ± 2%, CHF 28 ± 1%; P < 0.05). Skeletal muscle dysfunction in CHF was confirmed by decreased maximal tetanic force of diaphragm strips (in N/cm2: Sham 30 ± 0.6, CHF 26 ± 0.5; P < 0.05). CHF elicited a 27% increase (P < 0.05) in neutral SMase (N‐SMase) activity. Consistent with this finding, total ceramide content was elevated in CHF diaphragm (in pmol/mg protein: Sham, 280 ± 5 and CHF, 343 ± 16; P < 0.05)—subspecies heightened (P < 0.05) in CHF were C18, C18:1, C20, C20:1, C20:4, C22:1. Acid SMase activity was unchanged in CHF. Similarly, there were no changes in the content of either sphingosine or sphingosine‐1‐phosphate (P > 0.05). Our data suggests that increased diaphragm ceramide content is a consequence of N‐SMase activation in CHF. Activation of N‐SMase and heightening of ceramide content may contribute to skeletal muscle weakness.

Funding support: NIH 1K99HL098453‐01, 4R00HL098453‐02
Both Reactive Oxygen Species and Nitric Oxide Mediate TNF‐induced Diaphragm Dysfunction
Authors: Stasko Shawn , Hardin Brian , Smith Jeff , Arbogast Sandrine , Moylan Jennifer , Reid Michael B
Published: June 2021

Serum tumor necrosis factor–alpha (TNF) is elevated in chronic inflammatory diseases that cause muscle weakness including chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), and cancer. Beyond stimulating atrophy, TNF can act directly on muscle fibers to increase cytosolic oxidant activity which depresses specific force, evidence of contractile dysfunction. Our current study evaluated the roles of specific oxidant cascades ‐‐ reactive oxygen species (ROS) and nitric oxide (NO) derivatives ‐‐ as mediators of TNF‐induced dysfunction. We tested the hypothesis that muscle‐derived ROS and NO both contribute to TNF‐induced dysfunction. Mouse diaphragm fiber bundles were studied in vitro. We found that TNF exposure stimulated a 25% increase in overall oxidant activity (P<0.05; DCF oxidation assay) and depressed specific force at stimulus frequencies of 1–300 Hz (P<0.05). Both effects were diminished by pretreatment with either superoxide dismutase (SOD; degrades superoxide anion) or catalase (degrades H202), confirming ROS involvement. TNF exposure also stimulated a 39% increase in NO activity (P<0.05; DAF assay) that was abolished by pretreatment with N (omega)‐nitro‐l‐arginine methyl ester (L‐NAME; inhibits NO synthase). L‐NAME pretreatment or genetic deficiency of neuronal NO synthase (nNOS) preserved specific force of TNF‐treated muscle (P<0.05). We conclude that muscle‐derived ROS and NO are both required for TNF‐induced dysfunction and speculate that peroxynitrite may be a common downstream mediator of TNF action. Supported by NIH grants HL08341 (fellowship to SAS) and AR055974 (MBR).
Effects of estradiol on avian myogenic satellite cell proliferation and expression of heparan sulfate proteoglycans, MyoD and myogenin
Authors: McFarland Douglas C. , Velleman Sandra G. , Pesall Jane E. , Coy Cynthia S.
Published: June 2021

The objective of this study was to determine the effects of estradiol on avian myogenic satellite cell proliferation and the gene expression of proteins recognized as important in regulating skeletal muscle growth and development. Estradiol (0 M 10−5M, 10−6M, 10−9M, or 10−12M) was administered in basal medium containing additional nutrients. Female‐derived pectoralis major (PM) satellite cell proliferation was stimulated at a level of 10−9 M following 4 days of treatment. Male PM satellite cell proliferation was increased beginning at 10−12M estradiol. Likewise, male biceps femoris satellite cells demonstrated increased proliferation in the presence of 10−12M estradiol. Turkey embryonic myoblast proliferation, however, was not responsive to estradiol following 3 days administration under these conditions. Syndecan‐4 and glypican‐1 expression in male PM cells was not effected by physiological levels of estradiol (10−9M). However, MyoD and myogenin expression decreased in these cells when exposed to 10−12M and 10−9M estradiol, respectively. Expression of syndecan‐4, glypican‐1 and MyoD in embryonic myoblasts was not effected by estradiol. However, myogenin expression was decreased when administered 10−12M estradiol. The results demonstrate a direct effect of estradiol on avian satellite cell proliferation independent of syndecan‐4 and glypican‐1, and decreased expression of MyoD and myogenin coinciding with increased cellular proliferation.
Administration of recombinant adeno‐associated virus vector to the diaphragm through direct intramuscular injection
Authors: Smuder Ashley J , Falk Darin J , Nelson W Bradley , Powers Scott K
Published: June 2021

Ventilatory insufficiency due to impaired diaphragm function is the leading cause of morbidity and mortality in many conditions (e.g. muscular dystrophy). Currently, pharmacological inhibitors and genetically modified animals are used to study many diseases affecting the diaphragm. However, these methodologies are problematic due to the occurrence of off‐target effects and possible consequences of life‐long genetic alterations. Further, conventional approaches to gene transfection (i.e., plasmid injection and electroporation) are not possible due to the size and location of the diaphragm and thus alternative methods are needed to alter gene expression. Therefore, we have developed a method for the delivery of recombinant adeno‐associated virus vectors (rAAV) to the rat diaphragm via direct intramuscular injection. We hypothesized that by directly injecting rAAV we could selectively target diaphragm muscle fibers and establish a novel animal model for studying signaling pathways and also provide a strategy for effectively using gene therapy to rescue the diaphragm in disease states. Our results demonstrate that the morphology of the rat diaphragm is sufficient to allow direct injection and provide support for the use of rAAV as an intervention to study the diaphragm during conditions that promote diaphragm dysfunction.

Supported by NIH RO1 HL087839 to SKP, T32 HD043730 to AJS and F32 HL095282 to DJF
Characterization of Gz‐Coupled Dopamine D3 Receptors in Gastric Smooth Muscle
Authors: Rajagopal Senthilkumar , Kumar Divya P , Bhattacharya Sayak , Grider John R , Murthy Karnam S
Published: June 2021

Five dopamine receptors comprising Gs‐coupled D1‐like receptors (D1 and D5) and Gi/z‐coupled D2‐like receptors (D2, D3 and D4) have been cloned. Previous studies demonstrated the expression of all five receptors in the gut with selective localization of D2 receptors in the enteric neurons and D4 receptors in mucosal layer.

AIM

To determine the expression of dopamine receptors in gastric smooth muscle cells and identify their signaling pathways.

METHODS

Expression of dopamine receptors was determined by RT‐PCR and Western blot in rabbit gastric muscle cells. G protein activity was measured by dopamine‐induced increase in Gα binding to [35S]GTPγS. Adenylyl cyclase (AC) activity was measured as increase in cAMP by RIA and muscle relaxation by scanning micrometry.

RESULTS

Muscle cells predominantly expressed D3, and low levels of D1, D2 and D5 receptors. Dopamine activated preferentially Gαz (and to a smaller extent Gαi3), but not Gαs, Gαi1, Gαi2, or Gαq. Consistent with activation of Gz, dopamine inhibited isoproterenol‐ or forskolin‐induced AC activity and muscle relaxation. The effect of dopamine on Gαz and AC activity, and muscle relaxation was blocked by the selective antagonist of D3, but not D2, D4, D1/D5 receptors or pertussis toxin.

CONCLUSION

Dopamine D3 receptors on gastric muscle cells mediate inhibition of adenylyl cyclase activity and muscle relaxation via pertussis toxin insensitive G protein Gz.
Rapamycin administration does not impair basal protein metabolism in human skeletal muscle
Authors: Dickinson Jared M , Drummond Micah J , Fry Christopher S , Gundermann David M , Walker Dillon K , Volpi Elena , Rasmussen Blake B
Published: June 2021

We have previously shown that administration of the mTORC1 inhibitor, rapamycin, to humans blocks the increase in skeletal muscle protein synthesis (MPS) in response to resistance exercise and amino acid ingestion. Whether rapamycin administration impairs basal MPS in human skeletal muscle is unknown. Six young (26±2y) subjects were studied during two separate 4h trials, in which each trial was divided into two, 2h basal periods. The trials were identical except during one trial a single oral dose (16mg) of rapamycin was administered immediately prior to the second basal period. Muscle biopsies (vastus lateralis) were obtained at 0, 2 and 4h, marking the beginning and end of each basal period, to examine MPS, mTORC1 signaling, and markers of autophagy (LC3BI and LC3BII protein). During the control trial, MPS, whole body protein breakdown (phenylalanine Ra), mTORC1 signaling and markers of autophagy were similar between both basal periods (p>0.05). During the rapamycin trial, these variables were similar to the control trial (p>0.05) and were unaltered by rapamycin administration (p>0.05). Thus, basal protein metabolism and mTORC1 signaling were not affected by rapamycin administration. We conclude that rapamycin administration only impairs mTORC1 signaling and MPS in human skeletal muscle when combined with a stimulus such as resistance exercise or increased amino acid availability.

NIAMS R01AR049877, NIA P30AG024832, NIH T32HD07539, NCRR 1UL1RR029876
Chronic rapamycin administration maintains mitochondrial protein synthesis in heart and skeletal muscle
Authors: Drake Joshua , Peelor Frederick F. , Biela Laurie M. , Miller Richard A. , Hamilton Karyn L. , Miller Benjamin F.
Published: June 2021

Suppression of mammalian target of rapamycin (mTOR) signaling with rapamycin increases lifespan. Rapamycin could increase longevity by decreasing global protein synthesis (PS) but this remains to be demonstrated in vivo. A reduction of PS results in energy savings that could be diverted towards somatic maintenance of proteins (e.g. mitochondrial proteins) that promote longevity. Mice fed rapamycin (14 ppm; Rap) for 13.5 weeks were compared to controls (Con). During the last 4 weeks drinking water was supplemented with 8% deuterium oxide (D2O). The fraction of new protein was determined by the increase in D2O labeled alanine bound to proteins during the labeling period. Skeletal muscle from Rap mice had lower protein synthesis over 4 weeks in mixed (Rap=0.48±0.05, Con=0.55±0.05) and cytoplasmic (cyto) (Rap=0.57±0.03, Con=0.62±0.02) fractions, but not in the mitochondrial (mito) fraction (Rap=0.38±0.04, Con=0.41±0.05). Conversely, no change in synthesis was seen in any fraction of heart muscle (Mixed: Rap=0.65±0.08, Con=0.66±0.05; Cyto: Rap=0.74±0.04, Con=0.76±0.04; Mito: Rap=0.59±0.04, Con=0.63±0.03). The results suggest that Rap diminishes synthesis of cytoplasmic and mixed fraction proteins and maintains mitochondrial proteins in skeletal muscle, but not in heart muscle. Further analysis of tissue specific protein dynamics is likely to give new insights into how rapamycin extends lifespan.
Proteins controlling catabolic and stress pathways are upregulated during total knee arthroplasty
Authors: Bailey Ashley N , Hocker Austin D , Senesac Hilary A , Ratchford Stephen M , Shah Steven N , Jewett Brian A , Dreyer Hans C
Published: June 2021

BACKGROUND

Skeletal muscle atrophy is common following total knee arthroscopy (TKA). A tourniquet is routinely used during TKA to create a bloodless field. Subsequent ischemia‐reperfusion (I/R) within muscle cells and tissue beds may activate cellular catabolic and stress pathways. We hypothesized that I/R increases gene expression and signaling proteins involved in muscle protein catabolism.

PURPOSE

To measure changes in transcripts and proteins involved in catabolic and stress pathways in older subjects undergoing TKA.

METHODS

Subjects between the ages 60–80 were studied in the operating room during surgery. Muscle biopsies were obtained at baseline (after anesthesia, immediately prior to tourniquet inflation), during maximal ischemia (just prior to tourniquet deflation), and during reperfusion.

RESULTS

Total protein for FOXO3a, MAFbx, MuRF1, p‐38 MAPKs, and JNK were elevated relative to baseline during ischemia and reperfusion (p≤0.05). MAFbx, MuRF1, p‐38alpha, and JNK mRNA expression were increased during ischemia and reperfusion relative to baseline (p≤0.05).

CONCLUSION

These preliminary results suggest that I/R injury in muscle cells activates catabolic and stress pathways at the transcriptional and translational level during TKA in older adults.

Support: NIH/NICHD K01HD057332.
The Effects of Calorie Restriction on Skeletal Muscle Glucose Uptake and Insulin Signaling in 24 Month‐old Rats
Authors: Sequea Donel Angelo , Sharma Naveen , Arias Edward , Cartee Gregory
Published: June 2021

Calorie restriction (CR; eating ~60% of ad libitum, AL, intake) enhances insulin‐mediated glucose uptake (GU) and phosphorylation of Akt (an essential signaling protein for GU) in isolated rat skeletal muscle (predominantly fast twitch epitrochlearis and predominantly slow twitch soleus) in 9 month‐old rats. The primary aim of this study was to determine if CR also improves glucose uptake in both epitrochlearis and soleus of male, Fischer 344 Brown Norway rats at 24 months of age. A secondary aim was to determine if CR enhances Akt and/or Akt's substrate AS160 (also important for GU) phosphorylation in 24 mo‐old rats. We hypothesized that CR improves insulin stimulated GU in both muscles through enhancement of Akt phosphorylation with enhanced AS160 phosphorylation. In vitro muscle incubation experiments were performed on rats at 24 months of age with or without 1.2nM insulin. CR increased insulin mediated GU in both muscles. Concomitantly, pAkt(T308 and S473) was increased with CR in both muscles. There was no diet effect observed in pAS160(T642) or in total GLUT4 in either muscle. Calorie restriction in old 24 month rats enhanced insulin stimulated GU; likely dependent on enhanced Akt phosphorylation but independent of enhanced AS160 phosphorylation on T642 in epitrochlearis and soleus muscle.
Resveratrol Attenuates Age‐associated Functional Deterioration and Augmentation of Cardiac Fibrosis
Authors: YU Angus , Sin Thomas , Siu Parco
Published: June 2021

Resveratrol is a potential anti‐aging compound that may preserve cardiac function with aging. This study aimed to examine the protective effects of resveratrol on age‐associated physiological deterioration and cardiac fibrosis.

Adult male senescence accelerated mice were assigned to young, aged and aged with resveratrol treatment groups (n=10 per group). Mice in the resveratrol treatment group were fed with 5mg/kg/day resveratrol for 8 months. Echocardiography, endurance capacity test and basal activity test were used to assess cardiac function, resistance against fatigue and basal activity level, respectively. Masson trichrome stain was performed in ventricular muscle to determine cardiac fibrosis.

Fractional shortening of aged mice was reduced by 9.4% compared to young mice (P<0.05) whereas cardiac function of resveratrol‐fed mice was similar to that of young mice. Endurance capacity and basal activity of aged mice were decreased by 94% and 44% respectively (P<0.05) but the decreases were significantly attenuated by resveratrol. The increase in percentage of fibrotic area with aging (P<0.05) was reduced by resveratrol (P<0.05).

Our data demonstrate that resveratrol can ameliorate the age‐associated decline in physiological parameters and augmentation of cardiac fibrosis. Further investigation is needed to understand the precise protective mechanisms of resveratrol in the aged heart.
Effect of resveratrol and caloric restriction on mitochondrial regulation and apoptotic susceptibility in aged rat skeletal muscle
Authors: Malamo Angelina G , Silvestre Jason , Adams Mark E , Nguyen Linda M-D , Joseph Anna M , Dutta Debapriya , Xu Jinze , Dirain Marvin L , Tuckerman Danny M , Leeuwenburgh Christiaan , Adhihetty Peter J
Published: June 2021

Sarcopenia is an age‐related loss in muscle mass partially attributable to mitochondrial‐mediated apoptosis. Caloric restriction (CR) and resveratrol (RSV) treatment in rodents induces beneficial mitochondrial alterations which may serve to suppress sarcopenia. Doxorubicin (DOX) is a chemotherapeutic agent that induces cell death via mitochondria. We investigated whether RSV (50 mg/kg/day; 6 weeks) and/or CR (20% reduced AL; 6 weeks) could 1) induce mitochondrial biogenesis, 2) attenuate apoptotic susceptibility and, 3) reduce DOX‐induced toxicity, in aged rodent muscle. Aged F344xBN rats (26 mo) were split into 8 groups (n=4): ad libitum (AL), CR, RSV, RSV+CR and injected with DOX (20 mg/kg; IP) or saline prior (24h) to sacrifice. Mitochondrial content/regulation (cyto c, COX activity, PGC‐1á, SIRT3) and apoptotic susceptibility (Bax:Bcl‐2) were assessed in hindlimb muscle. Surprisingly, mitochondrial indices were unaffected by CR, RSV or CR+RSV, and DOX did not affect any group. CR+RSV reduced (50%) the Bax:Bcl2 ratio compared to AL while RSV and CR independently showed trends for reductions. DOX treatment enhanced the Bax:Bcl‐2 in AL while CR, RSV and CR+RSV tended to suppress this DOX‐induction. Our data indicates aged muscle, and DOX‐treatment, increases apoptotic susceptibility and CR+RSV treatment provides modest protection without altering mitochondrial content/regulation.
Association between uric acid, lean mass, and muscle strength gains in the elderly
Authors: Johannsen Neil Michael , Welsch Michael A. , Credeur Daniel , Hollis Brandon , Church Timothy S. , Allen Jason D.
Published: June 2021

Purpose

To examine associations between UA, lean mass, and muscle strength and determine the relationship between UA and strength gains with exercise training.

Methods

Fifty‐two older (70+y) men and women (n=33) completed 4 wk of aerobic endurance training (AET) or regional specific exercise (RSTS). Body composition was assessed by DXA and UA was measured enzymatically. Total strength was the sum of maximal isotonic (leg and chest press, seated row) and isometric handgrip strength. AET consisted of walking and biking, 3 d/wk (45 min/session; 50–85% of HRR) and RSTS of 8 exercises (15 contractions/min for 5 min starting at 40% MVC) including all major muscle groups.

Results

Mean±SD baseline age, weight, and UA levels were 74.9±4.4 y, 81.5±16.0 kg, and 5.8±1.2 mg/dl, resp. UA was associated with baseline body weight (r=0.48, P<0.001), lean mass (r=0.47, P<0.001), and strength (r=0.31, P=0.02). RSTS and men had greater strength gains (P=0.02 and P=0.001). Baseline and sex adjusted change in strength was greater in RSTS participants in the highest tertile of baseline UA (43.4±17.7 kg; mean±95%CI) compared to the low (16.0±16.2 kg) and middle (16.3±15.5 kg) tertiles within RSTS and to AET participants in the high UA tertile (19.5±16.6 kg).

Conclusion

UA is associated with lean mass and muscle strength and, in individuals over 70y, high UA is associated with larger strength gains after RSTS independent of sex. Research support from NIH grant 1RC1AG035822‐01 (PI‐ Jason D. Allen, PhD).
Alzheimer's disease is associated with muscle weakness
Authors: Bush Bernard , Lloyd Jesse , DeRuisseau Keith , Keslacy Stefan
Published: June 2021

Decreased physical capacity observed in people suffering from Alzheimer's disease (AD) is associated with morbidity and mortality. The underlying mechanisms are not known.

Purpose

To determine if muscle weakness occurs in an animal model of AD.

Methods

18 month‐old AD (APP/PS1) (n=8) were compared to WT mice (n=10). Soleus muscles were extracted under anesthesia and processed for ex‐vivo muscle function. Data were collected using a force transducer and analyzed using dynamic mechanical analysis (DMA) software. Muscle slides were assessed for Abeta accumulation using thioflavin‐S histochemical staining.

Results

We did not observe a difference in normalized peak force for the soleus between APP/PS1 and WT animals (2.08 vs. 2.99 N/cm2 respectively, p=0.12). However, normalized specific tension was lower for APP/PS1 compared to age‐matched WT mice (13.09 vs. 18.12 N/cm2, p=0.023). Our preliminary data suggested that accumulation of Abeta occurred in the muscle of APP/PS1 animals.

Conclusion

APP/PS1 mice demonstrated muscle function weakness and could represent a good model to better understand the diminished physical capacity observed in AD patients.
Activin IIB receptor blockade improves muscular function in a mouse model of spinal muscular atrophy
Authors: Liu Min , Barton Elisabeth R , Sweeney H. Lee
Published: June 2021

Spinal Muscular Atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons, resulting in progressive muscular atrophy and weakness. To determine the effects of activin Type IIB receptor (ActRIIB) blockade on muscle function in SMA, a systemic inhibition of ActRIIB signaling was performed via AAV‐mediated gene transfer of a soluble form of the extracellular domain of the ActRIIB (sActRIIB). Four‐week old male SMA mice (C/C mice: a new model for milder, possibly Type III SMA) were injected with 1E12 genome copies of AAV 2/8 LSP.sActRIIB via i.p. injection. In situ functional assessment of TA and EDL were performed at 8 weeks post injection. Synaptic efficacy of neuromuscular junction (NMJ) was assessed by comparing muscle tetanic tension between nerve and direct muscle stimulation. Treatment with ActRIIB blockade led to an increased skeletal muscle mass in all hindlimb muscles studied, with concomitant increases in peak tetanic force in both TA and EDL. However, the treated muscles showed a significant reduction in muscle specific force and the ratio of nerve/direct stimulation. This study indicates that ActRIIB blockade represents an effective therapeutic strategy to prevent muscle atrophy and enhance the muscle function in SMA, but the elevation of muscle mass may increase the loading of the motor units and/or NMJ. The long‐term consequences of this are now under investigation.
Growth‐related signaling increases with duty cycle following high force contractions in mouse tibialis anterior
Authors: Rahnert Jill , Burkholder Thomas J
Published: June 2021

High force contractions (HFC) activate multiple cascades related to protein synthesis. Although some studies have suggested force‐dependent activation of various growth‐related kinases, we found no correlation between force magnitude and several members of these signaling cascades when metabolic stress was minimized. HFC impose both mechanical and metabolic stresses, and we hypothesized that MAPK phosphorylation during high force isometric activation would be increased when the work‐to‐rest ratio (duty cycle, DC) and metabolic cost are increased. Mouse tibialis anterior muscles were subjected to high (H, 15%) or low (L, 1.5%) DC stimulation protocols, using long or short duration activations to further manipulate ATP depletion. Force‐time integrals were ~4X greater in HDC than LDC and fatigue was evident in all groups except LDC, short activations. ACC phosphorylation, indicative of AMPK activity, was greater in HDC protocols indicating greater energetic stress. FAK and p38 phosphorylation were also greater in HDC than LDC, which could reflect either force or energy‐depletion dependent signaling. Akt phosphorylation decreased most in LDC with long activations, but ERK was similarly phosphorylated by stimulation in all groups. Combined with our previous observation of force‐independent signaling, we conclude that metabolic stress is a major contributor to high force‐related signaling. DC05017
The effect of N‐acetylcysteine on contractile function and protein‐thiol oxidation in skeletal muscles of mdx mice
Authors: Pinniger Gavin Jon , Assan Evanna Binti , Terrill Jessica , Arthur Peter
Published: June 2021

Duchenne Muscular Dystrophy (DMD) is a fatal X‐linked recessive disease characterized by severe muscle weakness. We hypothesized that oxidation of skeletal muscle proteins such as myosin contributes to dystrophic muscle weakness seen in DMD boys and dystrophic mdx mice and that this muscle weakness will be attenuated by treatment with the antioxidant N‐acetylcysteine (NAC).

Six week old mdx mice and non‐dystrophic, C57 mice were treated with 2% NAC in drinking water for six weeks and compared to untreated mdx and C57 mice. Grip strength and body weight were measured weekly during the treatment period. After six weeks of treatment, the 12 week old mice were anaesthetized (sodium pentobarbitone; 40 mg/kg; IP) and the extensor digitorum longus (EDL) muscles were excised for analysis of contractile function and protein thiol‐oxidation.

In mdx mice, NAC treatment significantly increased normalized grip strength and maximum specific force in isolated EDL muscles (NAC = 13.1 ± 1.2 N/cm2; Untreated = 9.8 ± 0.8 N/cm2, p<0.05), and significantly reduced myosin protein‐thiol oxidation (NAC = 10.6 ± 0.8 %; Untreated = 13.7 ± 0.8 %, p<0.05). In non‐dystrophic C57 mice, NAC treatment significantly increased normalized grip strength by 36%, but had no significant effect on maximum specific force or myosin protein‐thiol oxidation in EDL muscles.

These data suggest that oxidative stress contributes to contractile dysfunction in dystrophic muscle via modification of thiol groups on the contractile protein myosin. Furthermore, this muscle weakness may be ameliorated with the anti‐oxidant, NAC.
Glibenclamide prevents the attenuation of the exercise pressor reflex by tempol in the ligated rats
Authors: Yamauchi Katsuya , Leal Anna K. , Stone Audrey J. , Kaufman Marc P.
Published: June 2021

In decerebrated rats, ligation of a femoral artery has been shown to exaggerate the exercise pressor reflex, an effect which is attenuated by tempol. The action of tempol has been attributed to its ability to scavenge superoxide radicals. Tempol, in addition, opens ATP sensitive potassium channels, an effect which could also explain its ability to attenuate the exercise pressor reflex in rats with ligated femoral arteries. To test this alternative explanation, we measured the effect of femoral arterial injection of glibenclamide (0.1 mg/kg), which blocks ATP sensitive potassium channels, on the tempol‐induced attenuation of the exercise pressor reflex in decerebrated rats whose femoral arteries had been occluded 72 hours before the start of the experiment. In the first group of rats (n=6), which were not given glibenclamide, tempol attenuated the exercise pressor reflex from 36 ± 5 to 15 ± 2 mmHg (P< 0.05). In the second group of rats (n=8), which were given glibenclamide just before tempol, the superoxide scavenger had no effect on the exercise pressor reflex, which averaged 28 ± 2 mmHg before tempol and 26 ± 2 mmHg afterwards (P> 0.05). We conclude that tempol attenuated the exercise pressor reflex by opening ATP sensitive potassium channels on the endings of group III and IV muscle afferents. Tempol does not appear to attenuate the exaggerated exercise pressor reflex by scavenging superoxide radicals.
KCa channels and EETs: major contributors to cutaneous thermal hyperemia
Authors: Brunt Vienna E , Minson Christopher T
Published: June 2021

While it is accepted NO is responsible for ~60% of the plateau in cutaneous thermal hyperemia, a large portion of the response remains unknown. We sought to determine whether the remaining ~40% could be attributed to EDHFs via KCa channels, and whether the epoxyeicosatrienoic acids (EETs), derived via cytochrome P450, were the predominant EDHF active in the response. Four microdialysis fibers were placed in the forearm skin of 20 subjects. In Protocol 1 (n=10): (1) Control, (2) L‐NAME, (3) KCa channel inhibitor, tetraethylammonium (TEA), and (4) L‐NAME + TEA; in Protocol 2 (n=10): (1) Control, (2) L‐NAME, (3) cytochrome P450 inhibitor, sulfaphenazole, and (4) L‐NAME + Sulfaphenazole. Local heating to 42°C was performed and skin blood flow was measured with Laser Doppler flowmetry. All data are presented as % maximal cutaneous vascular conductance (CVC). All drug sites attenuated plateau CVC from the control site (85±2%) to 79±3% with sulfaphenazole, 71±3% with TEA, 39±3% with L‐NAME, 23±2% with L‐NAME + sulfaphenazole, and 13±2% with L‐NAME + TEA (not different from baseline). Furthermore, the initial peak was just 17±2% with L‐NAME + TEA. These data suggest EDHFs are responsible for the remaining 40% of the plateau phase, as administration of TEA in combination with L‐NAME abolished the majority of hyperemia. These data also suggest that EETs contribute to about half of the EDHF response.

Supported by NIH Grant HL081671
The effect of voluntary hypocapnic hyperventilation on thermoregulatory responses in exercising humans
Authors: Fujii Naoto , Honda Yasushi , Komura Ken , Tsuji Bun , Sugihara Akira , Watanabe Kazuhito , Kondo Narihiko , Nishiyasu Takeshi
Published: June 2021

We tested the hypothesis that voluntary hypocapnic hyperventilation (VHH) attenuates thermoregulatory responses in exercising humans. 10 healthy active males performed cycling exercise at 120W (30°C, 50%RH) during 1) spontaneous breathing, 2) eucapnic voluntary hyperventilation, and 3) VHH. Cutaneous vascular conductance was evaluated as cutaneous red blood cell flux measured by laser‐Doppler flowmeter/mean arterial blood pressure at forearm (CVCforearm) and forehead (CVCforehead). Forearm sweat rate was measured by ventilated capsule method. Our results indicated that esophageal temperature (Tes) threshold for increases in CVCforearm and CVCforehead was significantly or tended to be higher, while slope relating Tes with CVCforearm was significantly or tended to be lower in VHH than in the other two conditions. Neither Tes threshold nor slope for sweat rate was different among conditions. These results suggest that in exercising humans, although VHH does not affect sweat response, it attenuates cutaneous vasodilation response, and this attenuation is greater for forearm than forehead skin.

This study was supported by grants from the Ministry of Education, Science, and Culture of Japan. N. Fujii is the recipient of a research fellowship for young scientists from Japan Society of the Promotion of Science.
Effect of training modality on inter‐individual differences in shivering pattern in humans
Authors: Imbeault Marie-Andree , Oneid Paul , Jay Ollie , Worthylake Darcy , Haman François
Published: June 2021

Shivering electromyography in humans is characterized by two distinct types of myoelectric activity: continuous (4–8 Hz) and burst‐like (6–12 times/min), the latter displaying large inter‐individual differences (bursts/min) in men. The physiological reasons for this variation remain unclear. This study investigated the impact of two training modalities on shivering pattern. Two groups, endurance (E) and resistance (R) trained, were exposed to cold for 90 min using a liquid‐conditioned suit. The E trained group showed higher VO2 peak and lower anaerobic capacity compared to the R trained group (E: 72.1 ± 2.9 mlO2/kg/min vs. R: 60.8 ± 1.4 mlO2/kg/min, P=0.007; Peak power R: 1277 ± 67 W vs. E: 949 ± 62 W, P=0.004). Core temperature was maintained throughout cold exposure in both groups. Skin temperature significantly decreased in both groups during cold exposure compared to baseline with no difference observed between groups (P < 0.0001). No difference was found between groups for heat production and shivering pattern during cold exposure. The variance of burst frequency was similar within each group, i.e. a similar inter‐individual variation was observed in both groups despite their respective training modality. In conclusion, training modality does not alter shivering pattern in men. This study was funded by NSERC.
Skin temperature modulation of shivering response in humans
Authors: Imbeault Marie-Andree , Mantha Olivier Landry , Haman François
Published: June 2021

During cold exposure, increase in heat production is produced via the activation of shivering thermogenesis and nonshivering thermogenesis, the former being the main contributor to compensatory heat production in non‐acclimatized humans. In rats, it has been shown that shivering thermogenesis is modulated solely by skin thermoreceptors. The aim of this study was to determine if cold‐induced shivering is also principally modulated by cutaneous thermoreceptors in humans. Using a liquid‐conditioned suit, six non‐acclimatized men were exposed to cold (4ºC) for four 30‐min periods, each of them separated by 15 min of heat exposure (35ºC). Core temperature remained stable throughout exposures. Skin temperatures significantly decreased by 12% in average during the sequential cold/heat exposures compared to baseline (p<0.001). Shivering intensity increased significantly during cold exposures (3.3 ± 0.7 % MVC) and was significantly reduced during the heat exposures (0.5 ± 0.1 %MVC) (p=0.004). Accordingly, metabolic rate was significantly higher during cold exposures (0.40 ±0.0 LO2/min) compared to heat exposures (0.25 ± 0.0 LO2/min) (p=0.0003). In conclusion, cutaneous thermoreceptors are a major modulator of shivering in humans. This study was funded by NSERC.
Cold air breathing during isometric handgrip: effect of healthy aging on coronary blood flow
Authors: Muller Matthew David , Gao Zhaohui , Mast Jessica , Blaha Cheryl , Drew Rachel C , Leuenberger Urs A. , Sinoway Lawrence I.
Published: June 2021

Cold air inhalation and isometric exertion both trigger symptoms of angina, but the underlying causes are unknown. The current echocardiography‐based study sought to determine the effect of healthy aging on coronary blood flow velocity during a combined handgrip and cold air inhalation protocol (COLD+GRIP). Fifteen young (25±1 years) and eleven older (63±1 years) healthy subjects underwent a 2‐minute bout of isometric handgrip (30% MVC) while inspiring cold air (−15°C) through a custom system. Transthoracic echocardiography was used to measure coronary blood flow velocity in the LAD artery. Finometer‐derived mean arterial pressure (MAP), heart rate (HR), air temperature, and grip workload were monitored continuously. Unpaired t‐tests were used to assess group differences. Height, weight, BMI, grip workload, and resting HR were not different between groups. The change in HR during COLD+GRIP was significantly blunted in the older subjects (Δ=7±2 bpm) compared to younger subjects (Δ=20±3 bpm) while the change in MAP was not different between groups (OLD Δ=23±3 vs. YOUNG Δ=24±2 mmHg). The change in coronary blood flow velocity was also not different between groups (OLD Δ=5.3±1.1 vs. YOUNG Δ=6.8±2.1 cm/sec). In conclusion, healthy aging blunts the HR response to COLD+GRIP, which may act to prevent ischemia.

This study supported by Wilderness Medical Society Grant (MDM), P01 HL096570 (LIS) and UL1 RR033184 (LIS)
Mitochondria function and structure in brown adipose tissue is influenced by maternal low salt intake during the perinatal period
Authors: Lopes Karen Lucasechi , Dos Santos Elisabete Alcantara , Furukawa Luzia Naoko Shinohara , Heimann Joel Claudio
Published: June 2021

Objective

To evaluate brown adipose tissue (BAT) structure and function in female offspring of dams fed low salt diet during the perinatal period.

Methods

Female Wistar rats were fed low (LS: 0.15%) or normal (NS: 1.3% NaCl) salt diet since 8 weeks of age. At 12 weeks of age they were mated. After weaning, all offspring, were fed standard chow. Body temperature (T) was measured during 24 hours in adult female offspring (oLS or oNS) exposed to a cold (C) or room temperature (RT) environment. Gene expression (GE) of uncoupling protein‐1 (UCP1). PPARγ (PP), PGC1α (PG) and FOX C2 (FO) and mitochondria surface area (MIT) by electron microscopy were analyzed in BAT. Serum coenzyme Q10 was measured by HPLC.

Results

(p<0.05, n=5/group): Compared to RT, during day time, T was lower in both offspring groups exposed to C. During night time, T was lower only in oNS exposed to C. Compared to oNS, GE of UCP1, PP and FO were lower (20%, 19%, and 57%, respectively) in oLS exposed to RT but not to C. GE of UCP1 and PG were higher (24% and 43%, respectively) in oLS exposed to C than in oLS exposed to RT. MIT was higher (76%) in oNS exposed to C than oNS exposed to RT. Compared to RT, Q10 was higher (110%) in oNS and lower (53%) in oLS exposed to C.

Conclusions

Low salt intake during the perinatal period is associated with alterations in the response to cold exposure and of gene expression of factors related to energy metabolism in the offspring.

Supported by FAPESP.
Gestational thermal environment alters postnatal response to heat stress
Authors: Johnson Jay S , Boddicker Rebecca , Pearce Sarah , Sanz-Fernandez M Victoria , Lucy Matthew , Safranski Tim , Gabler Nick , Rhoads Robert , Ross Jason , Patience John , Lonergan Steven , Baumgard Lance , Selsby Josh
Published: June 2021

Heat stress in production agriculture can result in losses due to reduced growth or death. Currently, available climate models predict that duration and regional expansion of heat stress is likely to increase. The purpose of the present study was to determine the extent to which prenatal hyperthermia alters the response to subsequent heat stress. Pregnant sows were exposed to thermoneutral (TN; n = 9; stable 25°C) or heat stress (HS; n = 7; 24 hr cyclic 25–35°C) conditions for the duration of gestation. After weaning, resultant offspring were allowed to mature to three months before exposure to a constant temperature of 35°C for a period of 24‐hrs. Rectal temperatures (Tr) increased similarly between groups; however, skin temperature (Ts) was significantly higher following 16 and 20 hrs of heating in HS compared to TN and the cumulative effect of heating on Ts tended to be 1% higher in HS compared to TN (P = 0.06). The difference between Tr and Ts was 1.3°C and 2.2°C greater (P < 0.05) following 16 and 20 hrs of heating, respectively, and the cumulative difference was approximately 50% greater in HS compared to TN. These data indicate heat stress applied during prenatal development could modify fetal programming such that the response to heat stress encountered later in life is altered. Supported by USDA/NIFA.
Reduced Vascular Smooth Muscle (VSM) Sensitivity to Contraction in ex vivo Hemorrhaged Rabbit Epigastric Artery (EA)
Authors: Ratz Paul H. , Barbee Robert Wayne , Miner Amy S. , Reynolds Penny S. , Contaifer Daniel
Published: June 2021

Compensation to hemorrhage includes vasoconstrictor‐induced VSM contraction. Severe hemorrhage can lead to reduced VSM reactivity to vasoconstrictors and decompensation. Vasoconstrictors not only cause VSM contraction, but also can activate a cellular negative feedback mechanism that causes prolonged VSM desensitization, termed VSM memory. To explore the hypothesis that VSM memory plays a role in decompensation, we studied EA reactivity ex vivo 45 min after severe hemorrhage. Compared to control rabbit EA removed before hemorrhage, EA after hemorrhage displayed depressed contractions to phenylephrine (PE) and histamine (HA). These data suggest that VSM memory participates in vascular decompensation during hemorrhagic shock. We more fully characterized VSM memory in rabbit and mouse arteries in vitro. Strong receptor stimulation (10–30 μM PE) for 30 min followed by PE washout to cause complete relaxation reduced the ability of G protein‐coupled receptor (GPCR) agonists (PE, HA, U‐46619 and vasopressin) and a non‐GPCR agonist (KCl) to subsequently contract renal, femoral, epigastric and mesenteric arteries for at least 1 hr after PE washout. These data indicate that high catecholamine concentrations can induce a generalized VSM desensitization in rabbit and mouse arteries (VSM memory) that may be responsible, in part, for vascular decompensation during hemorrhage. Funding: R01HL061320