bluuebunny/crossref_metadata_2025 huggingface dataset:
Preliminary investigation of skeletal muscle signal recognition particle receptor beta in response to aging in the rat
Authors: Receno Candace N , Doyle Robert P , DeRuisseau Lara R , DeRuisseau Keith C
Published: June 2021

The signal recognition particle receptor (SRPR) interacts with the signal recognition particle (SRP), which targets and transports nacent polypeptides destined for secretion or expression on the cell membrane. The SRP is likely important for normal muscle functioning since individuals with autoantibody production against the SRP can develop myopathy. The SRPR contains two subunits; one of which is the beta subunit that is integrated within the membrane of the endoplasmic reticulum (ER). We became interested in SRPR beta after an initial proteomic screening indicated altered expression of the protein in aged muscle. The objective of the current experiment was to further examine skeletal muscle SRPR beta protein expression in response to aging. We harvested extensor digitorum longus muscles from 8, 28, and 36‐ month old male Fisher 344xBrown Norway F1 hybrid rats (n = 4/group). Protein expression of SRPR beta was assessed using Western blot and was approximately 60% lower in the 36‐month old rats compared to younger animals (8‐month old group = 0.20 ± 0.04, 28‐month old group = 0.21 ± 0.05, 36‐month old group = 0.09 ± 0.03; values are mean ± SEM). This preliminary investigation is the first to examine SRPR protein expression in aging skeletal muscle and the findings suggest changes in SRPR beta may be associated with skeletal muscle alterations that occur in old age.

Supported by NIH 5R03AG032033 (KCD).
The Effects of IL‐6 Dosage and Duration on the Regulation of Protein Turnover in C2C12 Myotubes
Authors: GAO SONG , CARSON JAMES
Published: June 2021

One of hallmarks of cachexia is skeletal muscle wasting caused by an imbalance between the rates of protein synthesis and degradation. Circulating IL‐6 is chronically elevated in many types of cachexia, and has emerged as a key regulator of muscle mass. The purpose of this study was to investigate the influence of IL‐6 dosage and duration of exposure on signaling pathways regulating protein turnover in cultured C2C12 myotubes. Differentiated C2C12 myotubes were treated with two doses (20ng/ml and 100ng/ml) of IL‐6 for 4h, 24h and 48h. Protein samples were analyzed by Western blots. The low dose (20ng/ml) IL‐6 treatment transiently (4h) increased phosphorylation of ERK1/2 (T202/Y204), mTOR (S2448) and p70S6K (T389), through an Akt independent mechanism. Inhibition of Stat3 signaling by pyrrolidine dithioicarbamate (PDTC) abolished these anabolic effects of IL‐6. Chronic treatment (24h) of IL‐6 at this dosage caused reduced activation of p70S6K phosphorylation, and inhibition of mTOR phosphorylation. However, 100ng/ml IL‐6 showed an inhibitory effect on p70S6K phosphorylation at 4h, 24h and 48h, and 4EBP‐1 phosphorylation (T37/46) at 48h. Finally, Atrogin‐1 protein expression was elevated by 100ng/ml IL‐6 at all three time points. These results demonstrate IL‐6 dosage and duration of exposure can differentially effect the regulation of protein turnover in C2C12 muscle cells.
REDUCTION OF FATIGUE IN SKELETAL MUSCLE BY DIAZOXIDE: POSSIBLE PARTICIPATION OF MITOKATP.
Authors: Sánchez-Duarte Elizabeth , Montoya-Pérez Rocío , Trujillo-Trujillo Xóchitl , Vázquez-Rivera Dolores , Cortés-Rojo Christian , Meza-Carmen Victor , Saavedra-Molina Alfredo
Published: June 2021

The decrease in the ATP has an important role in the development of muscle fatigue and any event related to alteration of production of energy, this determine the tendency of muscle fatigue (Allen et al. 2008). KATP channels have been described in the inner mitochondrial membrane (mitoKATP) (Inoue et al. 1991). Garcia et al. (2009) showed that mitoKATP plays an important role in protecting the muscle during fatigue. The intention of this study was to determine the possible participation of mitoKATP channels during fatigue exploring the effect of Diazoxide (a selective activator) and selective inhibitor 5‐HD, in tension of slow skeletal muscle of chicken in a in vitro model of fatigue.

Anterior Latissimus Dorsi (ALD) muscle of Arbor acres variety chicken was used. The muscle was mounted on an experimental recording chamber by mecanoelectric transducer (Grass FT03), which through an amplifier and a analog‐digital interface (Digidata 1322A) allowed to acquire the muscle tension generated by a computer (Pentium 4) and a “software” of data acquisition (pCLAMP 9.2). The muscle was stimulated until the force decreased by 70‰ repetitive electrical stimulation, then applied Diazoxide for 6 min to observe its effect (10, 30 and 100 μM, and 500 μM of 5‐HD.

In a Diazoxide dose‐response curve, effect of 30 μM increased postfatige tension (40.67±8‰), combination 5‐HD with Diazoxide had no significant effect in fatigue. The results shows a protective effect of muscle by Diazoxide, however the lack of effect of 5‐HD may be due an unspecific interaction with channels of skeletal muscle.
Exercise Mitigates Beta‐2 Adrenergic Receptor Dysfunction By Decreasing Homocysteine In Diabetes
Authors: Mishra Paras Kumar , Joshua Irving G , Tyagi Suresh C
Published: June 2021

Elevated levels of homocysteine (Hcy) known as hyperhomocysteinemia (HHcy) are associated with diabetes. Hcy decreases beta2‐AR response by (i) inhibiting Gs (stimulatory) adenylyl cyclase ‐dependent protein kinase signaling and (ii) directly competing with beta2‐AR for binding. Attenuation of beta2‐AR response causes down regulation of AKT (anti‐stress factor) and induction of matrix metalloproteinase‐9 (MMP‐9) that leads to contractile dysfunction. To test the hypothesis that during diabetes the intolerance to exercise is, in part, due to attenuation of beta2‐AR and Gs by HHcy that down regulates AKT and induces MMP‐9 leading to contractile dysfunction, C57BL/6J and beta‐ AR++/++ transgenic mice with and without high fat diet and db/db mice were put on swimming exercise. We demonstrated that beta2‐AR is down regulated, whereas MMP‐9 and Hcy are up regulated in the diabetic heart. Additionally, beta2‐AR antagonist impairs contractile function of cardiomyocytes, while the beta‐AR agonist improves it. Interestingly, exercise induces beta2‐AR response and improves contractile function of cardiomyocytes in db/db mice. The stimulation of beta2‐AR along with exercise has synergistic effect on improvement in contractile function in diabetes. These results suggest attenuation of sympathetic tone in diabetes and therapeutic potential of beta2‐AR agonist and exercise for diabetic cardiomyopathy.
Interleukin‐6/JAK/STAT3‐induced satellite cell proliferation is regulated through induction of Cyclin D1
Authors: Kurosaka Mitsutoshi , Machida Shuichi
Published: June 2021

OBJECTIVE

To determine the signaling mechanisms by which Interleukin‐6 (IL‐6) induces proliferative potential of satellite cells in culture.

METHODS

Satellite cells were isolated from 30 male F344 rats (average 11 weeks). Recombinant human IL‐6 at a concentration 1 or 10 ng/ml was added to the culture medium. Immunocytochemical analysis was performed to quantify phosphorylated STAT3 (pSTAT3)+/MyoD+cells and Cyclin D1+/MyoD+ cells. In addition, co‐localization of SOCS3and myogenin were detected by immunocytochemical staining. Cyclin D1 and SOCS3 mRNA was measured using RT‐PCR.

Results

We previously confirmed that 1 ng/ml rhIL‐6 at concentration induces satellite cell proliferation. In the present experiments, the numbers of pSTAT3+/MyoD+cells and Cyclin D1+/MyoD+ cells and Cyclin D1 mRNA were was significantly higher following treatment with 1 ng/ml rhIL‐6 compared with control media (p < 0.05). The number of Cyclin D1+/MyoD+ cells also increased following treatment with 10 ng/ml rhIL‐6, which contrasts with our previous findings that this dose of IL‐6 inhibited satellite cell proliferation. In the present study, 10 ng/ml rhIL‐6 induced greater SOCS3 mRNA expression compared with 1 ng/ml and control media, and also increased the number of cells that co‐express SOCS3and myogenin.

CONCLUSION

IL‐6 induces a dose‐dependent increase in proliferative potential of satellite cells through activation of JAK/STAT3/Cyclin D1 pathway.

This work was supported by KAKENHI (22700659).
Studies of mitochondrial and non‐mitochondrial sources implicate NADPH oxidase(s) in the increased skeletal muscle superoxide generation that occurs during contractile activity
Authors: Sakellariou Giorgos K , Vasilaki Aphrodite , Palomero Jesus , Kayani Anna , Zibrik Lea , McArdle Anne , Jackson Malcolm J
Published: June 2021

Superoxide generated by skeletal muscle acts to modulate force generation and contraction‐induced changes in gene expression. This study identified the sub‐cellular sites of muscle fibre superoxide generation. Single isolated mature fibres from mouse flexor digitorum brevis loaded with superoxide‐sensitive fluorescent probes, specific inhibitors of potential pathways and immunolocalisation techniques were used. Comparison of voltage dependent anion channel or Bax channel inhibitors following contractile activity or treatment with the mitochondrial compex III inhibitor, antimycin A, indicated that superoxide could exit mitochondria via these channels, but they did not contribute to contraction‐induced increases in cytosolic superoxide. NADPH oxidase inhibitors decreased superoxide at rest and following contractions compared with controls. Protein and mRNA expression of NADPH oxidase subunits were demonstrated in fibres. At rest, NOX2, NOX4 and p22phox subunits localized to the sarcolemma and transverse tubules and the regulatory subunits p40phox and p67phox localized to the cytoplasm. Following contractions, p40phox was observed to translocate from the fibre cytosol to the sarcolemma. NADPH oxidase is a major contributor to cytosolic superoxide in muscle and its activation by contractions involves translocation of p40phox from the cytosol to the sarcolemma.

Funded by NIA (AG‐20591)
Ataxia telangiectasia mutated (ATM) influences AICAR‐stimulated glucose transport
Authors: Spears Larry , McKuin Michael R. , Renth Allyson L. , Kennedy Anne R. , Fisher Jonathan S.
Published: June 2021

Literature reports suggest that ATM can activate the AMP‐activated protein kinase (AMPK), a protein that can stimulate glucose transport in skeletal muscle. We hypothesized that AICAR, an AMPK activator, would increase AMPK phosphorylation and glucose transport in an ATM‐dependent manner. Extensor digitorum longus (EDL) muscles from wild‐type mice were exposed to 2 mM AICAR for one hour in the absence or presence of KU55933, a specific inhibitor of ATM. In separate procedures, wild‐type and ATM‐deficient (ATM−/−) EDL were exposed to AICAR. AICAR‐stimulated glucose transport was prevented by the ATM inhibitor despite no effect on AICAR‐stimulated phosphorylation of AMPK. AICAR increased glucose transport in EDL from wild‐type but not ATM−/− mice despite normal AICAR‐stimulated phosphorylation of AMPK in ATM−/− mice. Preliminary work (n=2–3) suggests that AICAR‐stimulated phosphorylation of TBC1D1 at S237 is prevented by inhibition of ATM. Our results suggest that ATM plays a role in AICAR‐stimulated glucose transport. However, contrary to our original hypothesis, ATM's influence occurs independent of AMPK phosphorylation, perhaps at the level of TBC1D1. Supported by USPHS award R15DK080437.
mRNA Expression Signatures of Human Skeletal Muscle Atrophy Identify a Natural Compound that Increases Muscle Mass
Authors: Kunkel Steven D , Suneja Manish , Ebert Scott M , Bongers Kale S , Fox Daniel K , Dyle Miachael C , Alipour Fariborz , Shields Richard K , Adams Christopher M
Published: June 2021

Skeletal muscle atrophy is a common and debilitating condition that lacks a pharmacologic therapy. To develop a potential therapy, we identified 63 mRNAs that were regulated by fasting in both human and mouse muscle, and 29 mRNAs that were regulated by both fasting and spinal cord injury in human muscle. We used these two unbiased mRNA expression signatures of muscle atrophy to query the Connectivity Map, which singled out ursolic acid as a compound whose signature was opposite to those of atrophy‐inducing stresses. A natural compound enriched in apples, ursolic acid reduced muscle atrophy and stimulated muscle hypertrophy in mice. It did so by enhancing skeletal muscle insulin/IGF‐I signaling, and inhibiting atrophy‐associated skeletal muscle mRNA expression. Importantly, ursolic acid's effects on muscle were accompanied by reductions in adiposity, fasting blood glucose and plasma cholesterol and triglycerides. These findings identify a potential therapy for muscle atrophy and perhaps other metabolic diseases. This work was supported by the Doris Duke Charitable Foundation, NIH, Department of Veterans Affairs and University of Iowa Institute for Clinical and Translational Science and University of Iowa Research Foundation.
Heat acclimation mediated cytoprotective memory: Do epigenetic mechanisms play a role? A lesson from the heart
Authors: Horowitz Michal
Published: June 2021

Heat‐acclimation (AC) is a “within lifetime” phenotypicadaptation to long‐term elevations in ambient temperatures. Changes at all levels of body organization improve function in the heat. An inseparable benefit of AC is tolerance to novel stressors, via cross‐tolerance; the outcome of constitutive growth of cytoprotective molecule‐reserves, precluding the need for de novo synthesis upon subsequent stress. In the heart, AC is displayed by greater pressure generation and ischemic/reperfusion tolerance. The benefits of AC decay with time; its reacquisition, however, is much faster than the time required to initially achieve acclimatory homeostasis. Gene chip analyses, show constitutive alterations in gene expression, including maintaining elevated levels of cytoprotective molecules, during the decline of AC, despite losing the physiological AC phenotype, and suggest epigenetic‐based memory. The molecular memory of the AC cardiophenotype involves chromatin remodeling via P‐MSK1/2 binding to the promoters of hsp70 and hsp90, maintaining a constitutive euchromatin state in the promoter of the hsp70 and hsp90 genes during acclimation decline. Constitutive histone H4 acetylation, HSF‐1 binding to the hsp70 promoter, greater HSP‐70 reserves and hsp70 mRNA/HSP during loss and reacquisition of AC are among the predisposing factors to rapid cytoprotection and cytoprotective memory.
The impact of IL‐6 supplementation on murine intestinal permeability and systemic cytokine levels following heat stroke
Authors: Phillips Neil Andre , Clanton Thomas L
Published: June 2021

Acute heat illness is associated with elevated circulating IL‐6, but its role in this setting is not well understood. We tested the hypothesis that IL‐6 plays a protective role in heat by inhibiting pro‐inflammatory cytokines and protecting the intestine from increases in permeability. Mice were given 0.8 ng IL‐6 IP. Two hrs later they were anesthetized, then gavaged with 4 kDa FITC‐dextran (FD4). Core temperature was gradually raised to 42.4°C over 4 hrs. After a 2 hr recovery at 37°C arterial blood samples were collected to measure cytokines and plasma FD4 (a measure of intestine permeability). Heat treatment increased plasma FD4 (P< 0.05) and elevated IL‐6, IL‐10, IP‐10, CCL5, CXCL1 and G‐CSF (P< 0.05) without affecting TNF‐α, IL‐1β, or IFN‐γ. Pre‐treatment with IL‐6 lowered plasma FD4 (P< 0.005) but had only modest effects on circulating cytokines. The results show that IL‐6 supplementation had strong protective effects on GI barrier integrity but little influence on the cytokine profile following heat exposure. The data suggest that IL‐6 protects the intestine during heat exposure by a mechanism not involving the inhibition of circulating pro‐inflammatory cytokines. AHA 7990119
Prolactin's role during acute and chronic heat stress in growing pigs
Authors: Sanz-Fernandez Maria Victoria , Pearce S. C. , Upah N. C. , Long L. R. , Nayeri A. , Sucu E. , Gabler N. K. , Patience J. F. , Hsu W. H. , Rhoads R. P. , Baumgard L. H.
Published: June 2021

Heat stress (HS) increases circulating prolactin (PRL) in a variety of animal models (reasons remain unknown), but whether or not HS elevates PRL in growing pigs is ill‐defined. Crossbred gilts (77±2 kg) were housed in individual pens and allocated to treatments: 1) HS conditions (36°C; 50% humidity) and ad libitum feeding (n=13) or 2) thermo‐neutral (TN) conditions (19°C; 61% humidity) and pair‐feeding (n=16) to eliminate the confounding effects of dissimilar feed intake. Pigs were sacrificed at d1 or 7 of environmental exposure. Rectal temperatures (Tr) and respiratory rates (RR) were obtained 4X daily and blood and intestinal tissues harvested at death. HS pigs had increased Tr (P<0.01; 40.1 vs. 38.4°C), RR (P<0.01; 111 vs. 36 bpm) and reduced feed intake (P<0.05; 57%). By design, TN pigs’ intake mirrored the HS pattern. PRL was higher (P<0.05) in HS pigs (0.97 vs. 0.64 ng/ml). In acute HS (24 h), PRL was negatively correlated with feed intake (r = −0.71; P<0.05), ileal transepithelial resistance (TER; r = −0.85; P<0.01) and tended to be negatively correlated with colonic TER (r = −0.69; P=0.06). In chronic HS (d7), PRL tended to be only inversely correlated with glucose (r = −0.81; P<0.10). In TN pigs, PRL was not correlated with any of the measured variables. Together, PRL appears to participate in both the acute HS response and the acclimation to chronic environmental hyperthermia.

Heat stress, prolactin

USDA/AFRI
Improved temperature regulation following heat acclimation in well‐healed skin graft subjects exercising in the heat
Authors: Pearson James , Ganio Matt S , AI Lucas Rebekah , Crandall Craig G
Published: June 2021

Burn victims with grafted skin have impaired heat dissipation. The effect of heat acclimation on temperature regulation in these individuals is unclear. This study tested the hypothesis that burn victims with significant amounts of grafted skin can heat acclimate. Two groups of burn survivors were evaluated: 20–40% body surface area (BSA) grafted (N=13) and 45–75% BSA grafted (N=7). Six non‐injured subjects served as controls. Subjects exercised for 45 min at 1 l/min O2 uptake in an environmental chamber (40°C, 30% RH) on days 1 and 7 of a heat acclimation regimen (45% VO2 max, 90 min per day; 40°C, 30% RH). Core body temperature (Tcore) was measured using an ingestible pill. On day 1 Tcore increased to a greater extent during exercise in the 45–75% BSA group (1.14 ± 0.34°C; P < 0.05) relative to 20–40% BSA (0.81 ± 0.23°C) and control groups (0.62 ± 0.32°C). On day 7, while the increase in Tcore during exercise for the 45–75% BSA group (0.78 ± 0.32°C) remained greater relative to controls (0.41 ± 0.24°C; P = 0.05), the increase in this grafted group was less than on day 1 (P = 0.03). However, the increase in Tcore in the 20–40% BSA group after heat acclimation on day 7 (0.68 ± 0.28) was not different to day 1 (P = 0.26). Temperature regulation is impaired in individuals with skin grafts covering 45–75%, but not 20–40% BSA. Importantly, temperature regulation can improve after heat acclimation in individuals with ≥45% BSA grafted.

NIH GM068865
Variability in Orthostatic Tolerance during Heat Stress: Role of Reductions in Cerebral Perfusion
Authors: Lee Joshua F. , Harrison Michelle L. , Brown Skyler , Brothers R. Matthew
Published: June 2021

The mechanism(s) responsible for heat stress induced reductions in orthostatic tolerance are unclear. Although a high degree of variability exists in the level of reduction in tolerance amongst individuals, syncope will always occur when cerebral perfusion is inadequate. Thus, heat stress mediated reductions in cerebral perfusion may explain the variation in tolerance in this thermal condition. This study tested the hypothesis that individuals with the greatest heat‐stress induced reduction in orthostatic tolerance would have the largest reduction in cerebral perfusion in this thermal condition. On different days, lower body negative pressure (LBNP) was imposed on 15 individuals during normothermia, and after a 1.5 °C rise in core temperatures (Tc). Tolerance was quantified as cumulative stress index (CSI) and the difference in CSI (CSIdiff) between thermal conditions was used to categorize individuals most (HighDif) and least (LowDif) affected. Heat stress reduced cerebral vascular conductance (CVC) relative to normothermia in both groups (P<0.05 for each); however, the magnitude of reduction in CVC was similar between groups (HighDif: 31.3±24.9 cm·s−1·mmHg−1; LowDif: 11.4±19.2 cm·s−1·mmHg−1, P=0.18). Our data indicate that variability in heat stress induced reductions in orthostatic tolerance is not related to reductions in cerebral perfusion in this thermal condition.
Scheduled exercise modulates daily rhythms of behavior, physiology, and gene expression in mice
Authors: Schroeder Analyne Manzano , Loh Dawn H , Jordan Maria C , Roos Kenneth P , Colwell Christopher S
Published: June 2021

Light is the primary environmental signal that synchronizes the circadian system coordinating the temporal patterning of behavior and underlying biological processes. Other cues such as activity may be able to influence the output of this system. In our studies, we used scheduled wheel access to manipulate magnitude and phasing of locomotor activity and explored subsequent effects on daily rhythms of heart rate (HR) and body temperature in WT mice. Mice were subject to 5 wheel access conditions: no access, free access, Zeitgeber (ZT) 12–18, ZT 18–24 and ZT 0–6 access. We found that giving the mice the opportunity to run on a wheel can significantly increase activity levels and therefore considered as exercise. Furthermore, shifting the phase of exercise with wheel access altered the temporal patterning of rhythms in HR and body temperature. We also examined the effects of wheel access induced exercise on the molecular clock underlying the generation of circadian rhythms. Using the Per2:LUC knockin mouse, we found that exercise at ZT 0–6 shifted the phase of PER2:LUC expression in the SCN and peripheral tissues. We conclude that wheel access induced exercise can be used to shape daily rhythms of activity in mice and influence the rhythms of other biological outputs such as HR and body temperature. Activity can also influence the phasing of PER2:LUC expression in the SCN and peripheral tissues.
Cardiac vagal modulation during static and dynamic breathhold dives in elite divers
Authors: Kiviniemi Antti , Breskovic Toni , Uglesic Lovro , Kuch Benjamin , Zubin Petra , Sieber Arne , Tulppo Mikko P , Dujic Zeljko
Published: June 2021

Marked bradycardia occurs at the end of breath‐hold dives. However, vagal modulation of heart rate (HR) during maximal static (SA) and dynamic (DA) underwater apneas is not well‐known. HR, HR variability (SD1) and arterial oxygen saturation (SpO2) were analyzed at the immersed baseline and at initial‐, mid‐ and end‐apnea (each 30 s) of maximal underwater SA and DA in nine breath‐hold divers. DA lasted 78±8 s and SA 225±20 s (mean±SEM) and resulted in similar decreases in SpO2 (78±3 and 75±3 %, p=0.352, respectively). Initially, DA increased HR from 80±5 to 122±5 bpm (p<0.001), followed by decrease in HR at mid‐apnea and end‐apnea (101±6 and 80±8 bpm). During SA, HR decreased at mid‐apnea (from 78±4 to 66±3 bpm, p=0.004) but did not decrease further at end‐apnea phase. SD1 decreased at the initial phase of DA (from 28±5 to 10±4 ms, p=0.005) being lower compared with SA (24±4 ms, p=0.005). At the end of DA and SA, SD1 tended to increase above the baseline (67±16 and 66±10 ms, p=0.088 and p=0.093, respectively) and did not differ from each other (p=0.804). We concluded that apnea blunts the effects of exercise on HR variability at the end of DA when despite the higher HR. This indicates complex interplay between vagal and sympathetic responses to apnea and exercise. Supported by TEKES, Finland, Paavo Nurmi Foundation, Finland and Croatian Ministry of Science.
Activity of preoptic area neurons supports thermal effector activation during fever
Authors: Morrison Shaun F , Tupone Domenico
Published: June 2021

Prostaglandin E2 (PGE2) in the preoptic area (POA) mimics fever by stimulating thermogenesis in brown adipose tissue (BAT), skeletal muscle via shivering and the heart via tachycardia, as well as by reducing heat loss via skin vasoconstriction. PGE2‐evoked stimulations of BAT, shivering EMGs and heart rate (HR) are postulated to arise from disinhibition of thermogenesis‐promoting neurons in the dorsomedial hypothalamus (DMH), and possibly in the rostral raphe pallidus (rRPa), due to the EP3 receptor (EP3‐R)‐mediated inhibition of GABAergic, warm‐sensitive neurons in the POA that project to inhibit DMH (and possibly rRPa) neurons. We tested the hypothesis that neurons in the medial preoptic (MPO) provide the necessary excitatory drive to downstream, thermogenesis‐promoting neurons for febrile heat production. Bilateral muscimol injection in the MPO completely inhibited the shivering EMGs and reversed the increases in BAT temperature and HR following injection of PGE2 into the POA. We conclude that the MPO contains neurons whose activity is necessary to support thermogenesis during fever. The data are consistent with a model in which a population of MPO neurons provides a tonically‐active, excitatory (glutamatergic) input to DMH (and rRPa?) neurons that drives thermogenesis upon disinhibition of DMH neurons during EP3‐R activation in the POA and potentially during cold exposure. Support NIH grant NS40987.
Estimating Core Temperature during Exercise in Heat Using Non‐Invasive Measurements
Authors: Xu Xiaojiang , Karis Anthony J , Mullen Stephen P , Patel Tejash , Buller Mark J , Santee William R
Published: June 2021

The goal was to develop a non‐invasive method to estimate core temperature (Tc) from a combination of skin temperature (Ts) and heat flux (HF) during exercise in the heat. Nine test volunteers participated in three sessions at 25°C/50% RH; 35°C/75% RH; and 42°C/20%RH. Each session consisted of two 1 hour treadmill walks at ~300 W and ~550 W intensity separated by a 30 min break. Tc, heart rate and Ts/HF from 6 sites on the head, thigh, and torso were measured. Correlation analysis was used to select individual sites that showed a close association between Tc and Ts/HF. Multiple regression analysis was then used to derive equations (EQ) to estimate Tc from Ts/HF using 3 sites on the torso: the sternum (ST), the pectoralis muscle (PE) and the scapula (SC). For EQ developed using Ts/HF at each individual site, the coefficients of determination (R2) were 0.82, 0.86 and 0.86 for PE, ST and SC respectively. For EQ developed using Ts/HF from both ST and SC (EQ‐SS), R2 was 0.92. EQ‐SS was evaluated for accuracy using the validation data (n=4). The root mean square error (RMSE) for each individual ranged from 0.20°C to 0.26°C and R2 from 0.8 to 0.9. For Tc <38°C, a less critical zone, differences between predicted and measured Tc were higher. For Tc >38°C, a more critical zone, the differences were smaller; most were within 0.4°C. Thus this method appears to be viable for Tc monitoring for the prevention of heat illness and injury.
Skin sympathetic nerve activity component synchronized with cardiac cycle is involved in hyperosmotic suppression of cutaneous vasodilation in hyperthermia
Authors: Kamijo Yoshi-ichiro , Okada Yoshiyuki , Ikegawa Shigeki , Okazaki Kazunobu , Goto Masaki , Nose Hiroshi
Published: June 2021

Recently, we have reported that a component of the SSNA spike synchronized with the cardiac cycle increased with an increase in esophageal temperature (Tes) and the increase was suppressed by hypovolemia with suppressed cutaneous vasodilation, suggesting that the component was an active vasodilator signal for skin vessels. Since cutaneous vasodilation in hyperthermia is also suppressed by hyperosmolality, in the present study, we hypothesized that this component was suppressed by hyperosmolality. Accordingly, skin sympathetic nerve activity (SSNA; microneurography) from the peroneal nerve, laser‐Doppler blood flow (LDF) on the ipsilateral dorsal foot, mean arterial pressure (MAP; sonometry), and Tes were measured before and during 45‐min of passive warming in 17 healthy males in isosmolality (IG, n=10) and hyperosmolality (HG, n=7) groups. In HG, hyperosmolality by ~7mOsm·kgH2O−1 was attained by hypertonic saline infusion after an administration of diuretic to adjust blood volume similar to that in IG. Although the SSNA component increased with an increase in Tes by ~0.5°C by the end of warming in both groups, the increase was significantly lower in HG than IG (P<0.0001), accompanied by a less increase in cutaneous vascular conductance (CVC=LDF/MAP) in HG than IG (P<0.0001). These results support our idea that the component might be an active cutaneous vasodilator signal.
Induction of a radio‐adaptive response by low‐dose gamma irradiation in mouse cardiac myocytes
Authors: Seawright John , Westby Christian M. , Wu Honglu
Published: June 2021

In addition to cancer, astronauts may be at risk for radiation‐induced cardiovascular diseases. While it is believed that these radiation‐induced disorders are a result of abnormal tissue remodeling, the mechanisms remain unclear. We assessed the expression and radio‐adaptive response of genes associated with fibrosis, apoptosis, and oxidative and inflammatory stress in cardiac myocytes. Seven week old, male, C57Bl/6 mice were exposed to 6Gy (H) or 5cGy followed 24hr later with 6Gy (LH) 137Cs γ radiation and sacrificed 4, 24, or 72hr after final irradiation. Using RT‐PCR, the expression of pro‐apoptotic Bad and Bax, procell survival Bcl2 and Bcl2l2, fibrosis Vegfa, and oxidative stress genes Sod2 and GPx4 showed a reduced fold regulation change (Bad,‐6; Bax,‐7; Bcl2,‐5; Bcl2l2,‐4; Vegfa, −12; Sod2,‐6; GPx4,‐ 29) 4h after H compared to control. Regulation of Casp3, Casp9, Trp53, and Myc also trended downward but did not achieve statistical significance. 24hr after H, genetic down‐regulation was no longer present. The genetic expression in the 4h LH group was similar to control. These data suggest that the effect of a single high dose of radiation on cardiac myocytes is short lived but can be prevented by pre‐exposure to a much lower dose. This knowledge may serve to guide the development of countermeasures to preserve the cardiovascular health of astronauts. Support: NASA, Johnson Space Center Human Research Project
Regulation of rDNA transcription and ribosome biogenesis at the onset of skeletal muscle hypertrophy
Authors: von Walden Ferdinand , Farrants Ann-Kristin Östlund , Nader Gustavo A.
Published: June 2021

We investigated the regulation of ribosomal (r)DNA gene transcription and ribosome production at the onset of skeletal muscle hypertrophy. Mice were subjected to functional overload of the plantaris muscle by bilateral removal of the synergist muscles. Mechanical loading resulted in muscle hypertrophy with an increase in rRNA content. rDNA transcription as determined by 45S pre‐RNA abundance paralleled the increase in rRNA content. Increased transcription and protein expression of c‐Myc and its downstream POL I regulon (POL1RB, TIF‐1A, PAF53, TTF1 & TAF1C) was consistent with the increase in rRNA. Other factors involved in rDNA transcription (UBF) and chromatin remodeling (WSTF) were induced by mechanical loading in a similar fashion. Chromatin‐IP revealed that these factors, together with histone H3 lysine 9 acetylation abundance relative to H3 were also enriched at the rDNA promoter. Our results demonstrate that mechanical loading induces ribosome production via epigenetic and transcriptional mechanisms at the rDNA promoter.

Supported by the Swedish Research Council (VR) and the Swedish Nat Ctr for Sports Res (CIF)
Effect of Photo‐Irradiation on Mitochondrially‐Associated Signaling in C2C12 Muscle Cells
Authors: Nguyen Linda M-D , Larkin Kelly A , Borsa Paul A , Adhihetty Peter J
Published: June 2021

Laser therapy (phototherapy) is a clinical treatment used to promote tissue healing and improve muscle function in patients with musculoskeletal injury. However, the underlying cellular and molecular mechanisms responsible for the positive clinical outcomes are poorly understood. One proposed mechanism suggests specific wavelengths (710–1100‐nm) of light are preferentially absorbed by, and activate mitochondria in skeletal muscle to alter mitochondrial bioenergetics/biogenesis and potentially improve muscle regeneration post‐injury. To elucidate the underlying mechanisms, we applied varying treatment doses of phototherapy (0.42, 2.57, 8.14, 14.85, 22.80 and 29.60 J/cm2; 810–935nm; LiteCure LCT‐1000) to cultured muscle cells (C2C12 myotubes) and examined the activation of key mitochondrial biogenesis signalling proteins (AMPK, p38). Laser treatment caused phosphorylated‐AMPK (P‐AMPK) to increase in a traditional dose‐dependent manner, while phosphorylated‐p38 (P‐p38) exhibited a biphasic dose‐response. Thus, our preliminary findings indicate laser therapy evokes differential alterations in mitochondrial‐associated signaling molecules in C2C12 cells. Whether these acute phototherapy‐induced signaling changes will lead to an increase in functional mitochondria with longer‐term phototherapy in C2C12 cells has yet to be determined and is a focus of our future work.
Rapamycin prevents muscle growth and the increase in MHCIIa induced by voluntary wheel running
Authors: Patchen Bonnie , Swoap Steven J
Published: June 2021

Mammalian target of rapamycin (mTOR) and its downstream signaling proteins are known to be involved in skeletal muscle adaptation in response to resistance training. As both muscle hypertrophy and endurance running induce a transition to a slower muscle fiber phenotype, we tested the hypothesis that inhibition of the mTOR pathway with oral rapamycin would prevent the fast‐to‐slow transition in response to voluntary wheel running. C57Bl/6J mice were randomly assigned to a control diet or a diet containing rapamycin and fed for 5 weeks. Mice were then given access to a running wheel or a locked wheel for 7 additional weeks. Rapamycin had no effect on body mass or daily running distance, suggesting that rapamycin treatment did not adversely affect running performance. Western blot analysis of mTOR targets demonstrated that rapamycin inhibited mTOR signaling. Wheel running elevated soleus to body mass ratios only in control fed mice. Wheel running increased the expression of the MHCIIa isoform in the triceps, which was prevented by rapamycin. These data support the hypothesis that the mTOR signaling pathway plays a role in the phenotypic changes that occur in muscle with wheel running.
The effects of exercise on skeletal muscle GSK3β in a spinal cord injury pain model
Authors: Jones Terry E. , Wood Melissa K. , Brewer Kori L. , Bareiss Sonja K.
Published: June 2021

Spinal cord injury (SCI) causes central and peripheral nervous system changes in glycogen synthase kinase 3β (GSK3β) activity. This protein is expressed in skeletal muscle and is reported to decrease in activity with aerobic training. The objective was to determine the content of total and phosphorylated GSK3β (pGSK3β) in muscle from spinal cord injured (SCI) rats and if exercise altered their content. Rats were randomly assigned to control (CON), sedentary (SCI), or exercise groups (SCI/Ex). The SCI and SCI/Ex group underwent excitotoxic SCI injury (a chronic pain model) while CON underwent a saline injection. Animals were treadmill exercised for 12 days. Soleus muscles were excised. Muscle homogenates were used for Western blot analysis probing for total GSK3β and pGSK3β. The protein content of total GSK3β was significantly decreased 30% in SCI/Ex compared to control and SCI. pGSK3β was not significantly different between groups but was reduced 13% and 29% between control and SCI or SCI/Ex, respectively, suggesting a potential increase in activity. These results suggest that GSK3β may be regulated in an alternative fashion in a chronic pain model. The Wooten Laboratory for Neurodegenerative Disease Research supports this work.
Thin‐beam ultrasound overestimation of blood flow: How wide is your beam?
Authors: Buck Tahisha M , Sieck Dylan C , Halliwill John R
Published: June 2021

In theory, mean blood velocity is overestimated by current ultrasound systems using thin‐beam ultrasound. However, if beam and vessel width are known, this overestimation may be correctable. To test this, we developed a string‐phantom based method to measure the effective beam width on a standard vascular ultrasound system (GE Vingmed System 5, Horton, Norway) and used a flow phantom to compare beam‐width estimates of mean velocity to half the peak velocity. We assumed that during steady‐state flow in the flow phantom, mean velocity should equal half the peak velocity. When insonating at a depth of 2 cm, effective beam width was 2.449±0.005 mm (mean±SE). From this, the calculated error correction factor was 0.786 (to correct for a predicted overestimation of 27.2%) for a flow phantom diameter of 6.5 mm based on a parabolic velocity model. We found that, across a range of velocities (8 to 60 cm/s), uncorrected mean velocity overestimated half the peak velocity by 31.7±0.7%, whereas corrected mean velocity overestimated by 3.5±0.6% (P<0.05 vs uncorrected). These findings suggest that while overestimation of mean velocity by thin‐beam ultrasound is a practical concern, it can be minimized if beam and vessel width are known.
Cumulative effects of successive bouts of maximal exercise on heart rate fluctuations
Authors: da Silva Soares Pedro Paulo , Calvão Angelo Mondaini , Sá Fernanda Lopes , Penna Thadeu Josino Pereira , de Menezes Márcio Argollo
Published: June 2021

The aim of the present study was to investigate the cumulative effects of two bouts of maximal exercise on heart rate (HR) by spectral and detrended fluctuation analysis (DFA). Rowers (n=14, 11 males, 24±6 years old) performed two maximal (2k1 and 2k2) tests. HRV and DFA were calculated before (PRE1) and after 2k1 (POS1), four hours after POS1 (PRE2) and after 2k2 (POS2). The HF power was reduced from PRE1 (1527±1349 ms2) to POS1 (224±339 ms2) and from PRE2 (908±861 ms2) to POS2 (214±234 ms2, respectively, p<0.05) and in PRE2 was lower than PRE1 (p<0.05), with similar reductions in POS1 and POS2 (p>0.05). DFA in the time domain was used as a non‐linear method to quantify HR fluctuations detrended from its nonstationary background, giving a more precise measure of the fractality and long‐range correlations in the time series. DFA analysis is able to assess that HR fluctuations in POS2 were lower that POS1, moreover, the exponent α related to the fractal measure departs from a purely random one (α=0.5), evidencing long‐range correlations in HR variability, with slightly different exponents in PRE and POS groups. DFA showed that after 2k2 there was an additional reduction on HR fluctuations. These data suggest cumulative effects of exercise on HR dynamics and both methods give complementary information.

Support: CNPq 481434/2008‐9 and FAPERJ E‐26/111.345/2011
Sequential Effects of Training (T) on GABAergic Neurons in Central Autonomic Areas
Authors: Michelini Lisete C. , Zampieri Thais T , Silva Sebastiao D , Ceroni Alexandre , Ruggeri Adriana
Published: June 2021

We showed previously the efficacy of T to alter neuronal plasticity of OTergic preautonomic circuitry. Here we identify the sequential effects of T on GABAergic neurons in central autonomic areas of normotensive and hypertensive rats. WKY and SHR were trained (55% VO2 max, 5 days/week, 1h/day) or kept sedentary (S) for 12 weeks. At weeks 0, 1, 2, 4, 8 and 12, after pressure (BP) and heart rate (HR) recordings, rats were anesthetized and perfused (PBS or PFA 4%) for brain removal. Punches of fresh PVN, NTS and RVLM were used for GAD mRNA expression (RT‐PCR, HPRT as reporter gene); fixed brains were processed for GAD immunofluorescence (ir). Compared to PVN, GAD expression was lower in the VBS (−37%) and higher in the NTS (+20%), mainly in SHR (+94%). T‐induced resting bradycardia (−10%) appeared earlier in SHR (T2 vs T8 in WKY); BP fall in SHR (−7%) was evident at T8–T12. T was accompanied by increased GAD expression in the PVN (+1.6‐fold in both groups, T1–T8); changes in RVLM and NTS appeared later (T8–T12). GADir confirmed both the presence of GABAergic neurons in autonomic areas and the effects of training. PVN GAD expression was positively correlated with resting bradycardia (YWKY=−0.005x+2.9, r=−0.45; YSHR=− 0.010x+5.1, r=−0.73, P<0.05). T‐induced improvement of PVN GABAergic signaling contributes to the appearance of resting bradycardia, a characteristic marker of training.
Characterize ASIC3 in Muscle Sensory Neurons with Femoral Artery Occlusion
Authors: Xing Jihong , Lu Jian , Li Jianhua
Published: June 2021

The sympathetic nerve activity and arterial blood pressure responses to static muscle contraction are greater in rats with femoral artery ligation, likely due to enhanced ASIC3 expression in thin muscle afferent nerves. The current study was to characterize acid‐induced current with activation of ASIC3 in DRG neurons of control rats and rats with 24 hrs of femoral occlusion using whole‐cell patch clamp methods. Also, existence of ASIC3 in DRG neurons of thin fiber afferents was examined. The DRG neurons were labeled by injecting the fluorescence tracer DiI into the hindlimb muscles. The data showed that ~90% of current responses evoked by pH 6.7 in DRG neurons are ASIC3‐like. The peak current amplitude to pH 6.7 is significantly attenuated with rAPETx2, a specific ASIC3 antagonist. In addition, ASIC3‐like current responses to pH 6.7 are seen in small, medium and large size of DRG neurons and the distribution of the size of DRG neurons is similar in both groups. However, the peak current amplitude of DRG neuron response induced by stimulation of ASIC3 is larger in occluded rats than that in control rats. Moreover, the percentage of DRG neurons with ASIC3‐like currents is greater after arterial occlusion compared with control. Furthermore, the data showed that femoral occlusion mainly augments expression of ASIC3 within DRG neurons projecting C‐fiber afferents. Overall, these data suggest that (1) the majority of current responses to pH 6.7 are ASIC3‐like in DRG neurons with nerve endings in the hindlimb muscles; (2) a greater acid‐induced current responding to pH 6.7 is developed as the blood supply to the hindlimb is deficient, and (3) increased ASIC3 is largely seen in C‐fiber of DRG neurons after the hindlimb ischemia.
Neutralization of NGF Attenuates Augmented Sympathetic Nerve Responses to Activation of Chemically Sensitive Muscle Afferents in Rats with Femoral Artery Occlusion
Authors: Lu Jian , Xing Jihong , Li Jianhua
Published: June 2021

Arterial blood pressure and heart rate responses to static contraction of the hindlimb muscles are greater in rats whose femoral artery is previously ligated than in control rats. Also, the prior findings demonstrate that nerve growth factor (NGF) is amplified in dorsal root ganglion (DRG) neurons of occluded rats. NGF has been reported to sensitize responsiveness to mechanical and chemical stimuli via thin fiber afferent nerves. Thus, the present study was first to examine the role for NGF in engagement of the augmented sympathetic and pressor responses to muscle contraction and passive tendon stretch after 24 hrs of femoral artery ligation. The data showed that femoral occlusion‐augmented blood pressure response to contraction was significantly attenuated by the prior administration of NGF antibody into the hindlimb muscles. The effects of NGF neutralization were not seen as the sympathetic and pressor responses were evoked by stimulation of muscle mechanically sensitive afferent nerves with muscle stretch in occluded rats. In addition, chemically sensitive afferent nerves were stimulated by lactic acid injected into the arterial blood supply of the hindlimb muscles after the prior injection of NGF antibody, demonstrating that the reflex responses to lactic acid were significantly attenuated. Moreover, immunohistochemistry was employed to examine the number of DRG neurons that project C‐fiber and A‐fiber. The data showed that distribution of DRG neurons with thin fiber phenotypes was not notably altered as NGF was infused into the hindlimb muscles. However, NGF increased expression of acid sensing ion channel subtype 3 in DRG neurons with thin C‐fiber, but not A‐fiber. Overall, these data suggest that NGF increased in sensory nerves of occluded rats is likely engaged in augmented reflex sympathetic and blood pressure responses evoked by stimulation of chemically, but not mechanically sensitive muscle afferent nerves.
Baroreflex responsiveness is attenuated in African Americans during steady‐state leg exercise
Authors: Holwerda Seth William , Samels Mitchel R , Keller David M
Published: June 2021

Carotid baroreflex (CBR) responsiveness is impaired in African Americans (AA) compared to Caucasian Americans (CA) at rest. In addition, AA exhibit greater blood pressure responses to exercise compared to CA. We tested the hypothesis that CBR control of heart rate (HR) and mean arterial pressure (MAP) is reduced in AA compared to CA during steady‐state leg exercise. CBR control of HR and MAP was assessed in 11 AA and 11 CA subjects using 5s trials of neck pressure (NP, simulated hypotension: +45, +30, +15 Torr) and neck suction (NS, simulated hypertension: −20, −40, −60, −80 Torr). At rest, no racial differences were found in either the mean HR or the mean MAP responses to NP. While MAP responses to NS were similar between races at rest, the mean HR response to NS was attenuated in the AA group (−8.6±2.0bpm) compared to the CA group (−14.4±2.3bpm, p<0.05). During exercise (50% VO2peak), again no racial differences were found in either the mean HR or mean MAP responses to NP. However, the mean HR response to NS tended to be reduced in the AA group (−7.9±1.7bpm) compared to the CA group (− 11.0±3.1bpm, p=0.069) during exercise. Interestingly, the mean MAP response to NS was impaired in the AA group (− 6.5±0.8mmHg) compared to the CA group (−8.0±1.2mmHg, p<0.05) during exercise. These findings support inherent differences in CBR responsiveness in AA compared to CA during both rest and exercise.

Support by NIH Grant R15HL096103
Effect of Carotid Body Denervation (CBD) on Breathing and Central Neuromodulation
Authors: Miller Justin R , Muere C , Mouradian G , Neumueller S , Hodges M R , Pan L G , Forster H V
Published: June 2021

After CBD, goats hypoventilate and exhibit reduced CO2 sensitivity followed by a partial recovery in the weeks following (Pan et al, 1998). Currently, the contribution of central mechanisms in these changes is unknown; however, perturbations involving the carotid bodies have been show to affect central neuromodulator/neurotransmitter (NM/NT) levels within the respiratory network (Goiny et al, 1991; Hoop at al, 1999). Here, we tested the hypothesis that the time‐dependent changes in breathing following CBD are associated with altered central NM/NT levels within the pre‐Bötzinger Complex (pre‐BötC). In 6 awake adult goats, on several days pre‐ and post‐CBD we assessed resting PaCO2, CO2 sensitivity, and the NM/NT content of mock cerebrospinal fluid (mCSF) dialyzed into the pre‐BötC. From days 0–15 post‐CBD, we observed hypoventilation and reduced CO2 sensitivity, with a concomitant increase in GABA and Glycine and a decrease in serotonin and Substance‐P in the dialyzed mCSF. From days 16–30 post‐CBD, we observed a partial recovery of resting PaCO2, but little recovery of CO2 sensitivity or NMs/NTs. In conclusion, a shift in the balance of NMs/NTs toward net inhibition at the pre‐BötC may contribute to the hypoventilation and reduced CO2 sensitivity following CBD. Supported by NIH 25739 and Veterans Association