bluuebunny/crossref_metadata_2025_split huggingface dataset:
A within‐subject comparison of changes in core temperature with hypoxia‐induced manipulations of relative exercise intensity
Authors: Coombs Geoff , Ravanelli Nicholas , Cramer Matthew , Imbeault Pascal , Jay Ollie 
Published: November 2023

Traditionally, relative exercise intensity (i.e., %VO2max) has been thought to determine changes in core temperature during exercise in compensable environments; however, recent evidence from our laboratory has suggested otherwise. Using independent group designs, we have demonstrated that to make unbiased comparisons of changes in core temperature, exercise intensities should be set to elicit a fixed metabolic heat production (Hprod) per unit of total body mass (W/kg), irrespective of large differences in %VO2max (Jay et al. Am J Physiol. 2011) or absolute Hprod (Cramer & Jay, J Appl Physiol. 2014). Using a within‐subject design, the present study assessed whether changes in core temperature during exercise at a given Hprod in W/kg are altered by differences in %VO2max, secondary to acute hypoxia exposure (~13% O2) compared to normoxia (21% O2). It was also assessed whether the change in core temperature during exercise at a fixed %VO2max in hypoxic (HYP) conditions will be similar to normoxia (NORM) despite a 31±8% reduction in hypoxic VO2max and therefore a much lower Hprod. Four participants (1.78±0.04 m, 69.9±5.3 kg, 27±5 y) cycled for 45 min at 34°C, 45% RH in a climate‐controlled chamber. Measurements of esophageal temperature (Tes) and rectal temperature (Tre) were recorded every 5 s, and indirect calorimetry was recorded breath‐by‐breath. Preliminary data indicate that 45‐min ΔTes during exercise at a fixed Hprod (NORM: 6.3±0.4 W/kg; HYP: 6.9±0.4 W/kg; P=0.13) were similar between conditions (NORM: 0.52±0.22°C; HYP: 0.47±0.27°C; P=0.61), while ΔTre were also similar (NORM: 0.71±0.26°C; HYP: 0.74±0.27°C; P=0.41), despite large differences in relative exercise intensity (NORM: 40±8%VO2max; HYP: 62±8% VO2max; P=0.02). However, when a subsequent bout of hypoxic exercise was normalized for %VO2max (NORM: 40±8%VO2max; HYP: 46±4% VO2max; P=0.07), ΔTes in the hypoxic condition were lower compared to the normoxic condition (NORM: 0.52±0.22°C; HYP: 0.34±0.25°C; P<0.01) and ΔTre was lower as well (NORM: 0.71±0.26°C; HYP: 0.52±0.30°C; P=0.04) due to a lower Hprod (NORM: 6.3±0.4 W/kg; HYP: 5.3±0.6 W/kg; P=0.02). In conclusion, our within‐subject comparison provides further evidence that changes in core temperature are determined by exercise at a fixed Hprod in W/kg, despite large differences in relative exercise intensity, and that exercise at a fixed %VO2max, but different Hprod in W/kg, results in different changes in core temperature.Support or Funding InformationThis project was supported by a Discovery grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada, and also in part by a research grant from the Gatorade Sports Science Institute.
TISSUE‐SPECIFIC AND CONCURRENT CIRCADIAN RHYTHM OF SIRT3 AND NICOTINAMIDE PHOSPHORIBOSYL TRANSFERASE EXPRESSION IN LIVER AND SKELETAL MUSCLE
Authors: Loehr Amanda R. , Dyer Normonique A. , Brandauer Josef 
Published: November 2023

Nicotinamide phosphoribosyl transferase (Nampt) catalyzes the rate‐limiting reaction in nicotinamide dinucleotide (NAD) recycling. Nampt thus indirectly controls the activity of SIRT3, a mitochondrial NAD‐dependent protein deacetylase which regulates mitochondrial content and metabolism. Since Nampt is expressed in a circadian oscillation and many clock‐controlled acetylation modifications affect mitochondrial proteins, this suggests that SIRT3 is involved in circadian regulation of mitochondrial biology. We assessed the expression of Nampt and SIRT3 in various mouse tissues (liver, tibialis anterior, and diaphragm) at six time points of the 24‐hour cycle in an extended darkness (ED) period, i.e., in the absence of ambient light. 36 female ICR mice were maintained on a regular 12:12 hour light:dark cycle for 2 weeks. Following a 12‐hour dark period, mice were maintained in a dark environment for the remainder of the experimental period. Nampt and SIRT3 expression levels were positively correlated in all tissues (r, 0.526 to 0.797, all p < 0.05), but circadian variations were tissue‐specific. Liver Nampt and SIRT3 expression peaked 8‐hours into the ED period. Relative to peak expression, liver Nampt decreased by 24% at 12‐hours ED (p < 0.05) while SIRT3 expression decreased 26% at 16‐hours ED (p = 0.08). In tibialis anterior muscle, both Nampt and SIRT3 expression peaked at the beginning of the ED period. At 20‐hours ED, Nampt expression was 27% lower (p < 0.05) and and SIRT3 expression was decreased by 40% (p = 0.06). Conversely, both SIRT3 and Nampt expression in the diaphragm decreased over the first 8‐hours of the ED period but increased significantly by 20‐hours ED (Nampt, 50%, SIRT3, 72%, p < 0.01 for both). Our results suggest a tissue‐specific circadian regulation of mitochondrial proteins and energy metabolism that persists in the absence of regular light‐dark cycles.Support or Funding InformationThis work was supported by a grant to Gettysburg College from the Howard Hughes Medical Institute through the Precollege and Undergraduate Science Education Program (AL), an Integrative Organismal Systems Fellowship by the American Physiological Society and a Kolbe Research Fellowship (ND), and a Gettysburg College Professional Development Grant (JB).
PGC‐1α4 Expression is Down‐regulated by ERK1/2 MAPK Signaling Axis of IL‐6
Authors: Brown Jacob , Rosa Megan , Lee David , Brown Lemuel , Perry Richard , Carson James , Dridi Sami , Washington Tyrone , Greene Nicholas 
Published: November 2023

Loss of muscle mass and function are associated with reduced quality of life in many disease conditions. Recently, the peroxisome proliferator‐activated receptor γ coactivator‐1α4 (PGC‐1α4) isoform has been shown to promote gains in skeletal muscle mass; however the mechanism of regulation under normal and stress (inflammatory) conditions is still unknown.PURPOSETo elicit signaling mechanisms regulating the gene expression of Pgc‐1α4 during inflammation and particularly by IL‐6.METHODSAnimal Experiments: Female C57BL/6J (WT) and C57BL/6J × IL‐6−/− (IL‐6 KO) mice were euthanized 10 weeks of age and tibialis anterior muscles were excised and snap frozen in liquid nitrogen. Tissue Culture: C2C12 myotubes were treated with recombinant IL‐6 (50 ng/ml), recombinant TNF‐α (20 ng/ml), Pyrrolidine dithiocarbamate (PDTC inhibitor of STAT 3 and NFκB, 50 μM), PD98059 (20 μM; MEK1/2 inhibitor preventing ERK1/2 activity), U0126 (10 μM; MEK1/2 inhibitor preventing ERK1/2 activity), and SB202190 (10 μM; inhibitor of p38 MAP kinase). RNA was isolated from WT and IL‐6 KO mice as well as C2C12 myotubes. RNA was analyzed by real time RT‐PCR for mRNA content analysis of 18S and Pgc‐1α4. Protein analysis was performed by immunoblot for P‐STAT3, STAT3, P‐ERK 1/2 and ERK 1/2 to confirm function of pharmacological inhibitors and normalized to Ponceau S. A student t‐test or one‐way ANOVA was employed as appropriate with α set at 0.05.RESULTSPgc‐1α4 mRNA content was 10‐fold greater in IL‐6 KO mice compared to WT. In C2C12 myotubes, recombinant IL‐6 significantly repressed Pgc‐1α4 mRNA content by ~70% while Pgc‐1α4 content in TNF‐α and PDTC treated cells were not different from control. In the following experiments, 70% repression of Pgc‐1α4 mRNA by IL‐6 was reversed when IL‐6 was combined with ERK1/2 inhibition via MEK (PD098059 + IL6 and U0126 + IL‐6). To determine if MEK1/2 – ERK MAPK repression of Pgc‐1α4 mRNA is a specific function of ERK‐MAPK or a general function of MAPKs, the experiment was repeated with a p38 MAPK inhibitor (SB202190). As in the previous experiments, IL‐6 suppressed Pgc‐1α4 mRNA by ~70%; moreover, p38 MAPK inhibition by SB202190 did not affect the IL‐6 repression of Pgc‐1α4 mRNA. Confirming the pharmacologic function, a significant 40% increase in the P‐STAT3/STAT3 ratio and the P‐ERK/ ERK ratio with IL‐6 treatment was observed, while inhibitors of STAT3 (PDTC) and ERK 1/2 (PD098059) significantly decreased these ratios by 30% and 50 % when compared to vehicle, respectively.CONCLUSIONPGC‐1α4 expression is repressed by IL‐6 through the ERK1/2 signaling axis. These findings may have significant impact in treatment to prevent and ameliorate muscle wasting conditions.Support or Funding InformationFunded by the University of Arkansas
Changes in Titin Isoform Composition Following Knockout of Bmal1, a Core Molecular Clock Factor, in Skeletal Muscle
Authors: Riley Lance A , Zhang Xiping , Esser Karyn A 
Published: November 2023

Recent work from our lab has shown that disruption of the endogenous molecular clock mechanism in skeletal muscle is sufficient to induce muscle weakness with changes in fiber type and fibrosis. To begin to discern the molecular mechanisms that link the changes in the molecular clock with changes in muscle function, we tested whether the muscle of inducible, skeletal muscle specific Bmal1 knockout (iMSBmal1−/−) mice would also exhibit changes in sarcomeric protein expression. One of the proteins we focused on was titin, the giant filamentous protein that maintains sarcomeric structure, underlies passive tension, and serves as a scaffold for many proteins and signaling molecules. In our studies, we determined that the tibialis anterior muscle of the iMSBmal1−/− mice exhibits a significant increase in the longer, more compliant isoform of titin (38% long isoform/total titin in iMSBmal1−/− mice vs. 19% in iMSBmal1+/+ mice). While there is no change in the total amount of titin expressed, comparisons of results from a microarray data set between the two treatment groups indicate that probe sets covering the PEVK region were significantly up‐regulated in the gastrocnemius muscle of these mice. This region of titin pre‐mRNA is known to be spliced out in the presence of the RNA binding protein RBM20. Using this logic, we noted that expression of Rbm20 mRNA is decreased approximately 24% in iMSBmal1−/− gastrocnemius muscle compared to iMSBmal1+/+ controls suggesting that the molecular clock could be acting through this protein to modify titin alternative splicing. Ongoing studies are focusing on the connection between the molecular clock and RBM20 and if the change in RBM20 expression is responsible for the difference in titin spliceform expression.Support or Funding InformationNIH AR066082
Combined Oxandrolone and Propranolol Therapy Attenuate Protein Breakdown in Severely Burned Pediatric Patients
Authors: Chao Tony , Herndon David N , Porter Craig , Malagaris Ioannis , Abdelrahman Doaa Reda , Suman Oscar E , Sidossis Labros S 
Published: November 2023

IntroductionSevere burn result in prolonged hypermetabolism and increased skeletal muscle catabolism. Propranolol has been shown to blunt the hypermetabolic stress response to burns while oxandrolone was shown to improve muscle protein synthesis efficiency. However, the effect of combined oxandrolone and propranolol therapy on skeletal muscle fractional synthesis (FSR) and breakdown (FBR) rates are not known. The objective of this study is to determine the effects of oxandrolone and propranolol (oxprop) treatment on skeletal muscle protein turnover in severely burned pediatric patients. In this placebo controlled clinical trial, we hypothesize that oxprop will improve skeletal muscle protein turnover in pediatric burn patients.MethodWe studied 24 pediatric patients with severe burns (≥ 30% total body surface area; TBSA) during their inpatient hospitalization. Patients were randomized to placebo (14 control) or oxprop (10). Protein kinetics were determined with bolus injections of 13C6 and 15N phenylalanine at 2 and 4 weeks post‐injury. Skeletal muscle biopsies were obtained from the m. vastus lateralis. Plasma and muscle intracellular and bound protein pool enrichments were determined by gas chromatography‐mass spectrometry (GCMS). A Mann‐Whitney test was performed between groups. Significance was determined at p<0.05.ResultsPatients were similar in age (8 ± 6yr) and TBSA (53 ± 17% vs 48 ± 8%) between the control and oxprop groups. Muscle FSR was not different between control and oxprop at 2 weeks (0.13 ± 0.04%/h vs 0.08 ± 0.01%/h, p=0.73) or 4 weeks (0.16 ± 0.03%/h vs 0.13 ± 0.02%/h, p=0.92). FBR was not different between control and oxprop at 2 weeks (0.27 ± 0.05%/h vs 0.20 ± 0.02%/h, p=0.27). At 4 weeks, FBR in the oxprop group was significantly less than control (0.14 ± 0.02%/h vs 0.28 ± 0.04%/h, p<0.05). Protein net balance was not different between control and oxprop at 2 weeks (−0.14 ± 0.03%/h vs −0.12 ± 0.03%/h, p=0.33). At 4 weeks, net balance was improved in oxprop versus control (−0.01 ± 0.02%/h vs −0.12 ± 0.04%/h, p<0.05).ConclusionCombined oxandrolone and propranolol therapy significantly improves skeletal muscle protein turnover in pediatric burn patients after 4 weeks of treatment. The improvement in skeletal muscle protein net balance with oxprop treatment is achieved by blunting protein breakdown. Treatment with oxandrolone and propranolol for 4 weeks can blunt the catabolic effect seen in severe burn injury.Support or Funding InformationNIH (P50 GM060338, R01 GM056687, R01 HD049471 and T32 GM008256), NIDILRR (90DP00430100) and Shriners Hospitals for Children (84080, 84090, 71006, 71008 and 71009) grants.
Strong fluid movement near mammalian skeletal muscle improves their stability for force and metabolic studies at 37°C
Authors: Renaud Jean‐Marc , Paquette Mathieu 
Published: November 2023

Studying mammalian skeletal muscles at 37°C is challenging because of a high metabolic rate requiring rapid O2 diffusion and more importantly a high production rate of reactive oxygen species (ROS) requiring fast removal. Both problems can be circumvented when small muscles up to 10 mg wet weight are immersed in physiological solutions and superfused near the surface with rapid solution flow (10–15 ml/min). However, rapid superfusion is not feasible when using expensive drugs and radioactive markers representing conditions that require muscle incubation in small volume. The objective of this study was therefore to optimize the experimental conditions that will give rise to stable muscle preparations at 37°C when a rapid flow of physiological saline solution is not an option. We tested the hypothesis that in the absence of superfusion, one must create fluid movement in order to replace the convection effect of superfusion. Tetanic force can be maintained constant for hours when mouse FDB bundles (1–2 mg wet weight) were superfused whereas a continuous loss of force reaching 10% force by 25 min was observed when superfusion was interrupted. The decrease in tetanic force during fatigue, elicited with one contraction every sec for 3 min, was significantly faster and the final extent of the decrease greater in the absence than in the presence of superfusion. There was, on the other hand, no difference in the decrease in tetanic force between superfusion and gas bubbling both prior to fatigue and during fatigue. A lack of superfusion was also important for the glycogen content. Glycogen levels prior to fatigue were 119 μmoles glucose equivalent/g dry weight when superfusion was maintained while interrupting superfusion for 10 min reduced glycogen levels to 82 μmoles/g dry weight; representing a decrease of 37 μmoles/g dry weight. Following fatigue, glycogen levels were 77 μmoles/g dry muscle with superfusion and 43 μmoles/g dry weight in the absence of superfusion. Notably, the amount of glycogen depletion during fatigue was not different with and without superfusion, the values being 42 and 39 μmoles/g dry weight, respectively. The effect of interrupting superfusion on tetanic force was much greater following a first fatigue bout and 50 min recovery. That is, interrupting superfusion resulted in 35% decrease in tetanic force within 10 min, which was again prevented by gas bubbling or the addition of NAC or tiron, two known ROS scavengers. So, a lack of fluid movement near mammalian skeletal muscle muscles at 37°C results in large loss of tetanic force and glycogen. The loss of tetanic force can be prevented by applying gas bubbling near the muscle or by scavenging ROS.Support or Funding InformationStudy was supported by the National Science and Engineering Research Council of Canada (NRC)
Inhibition of Satellite Cells Proliferation with AraC Prolonged Survival of Adult Skeletal Muscle Fiber in Culture
Authors: Albadrani Hind Muteb , Renaud Jean Marc 
Published: November 2023

The skeletal muscle is a dynamic tissue that has the ability to change and modify itself to fit the level of required activity; a phenomenon called muscle plasticity. Most studies of muscle plasticity are carried out in situ, a condition for which it is difficult to study and discern between the intrinsic properties of skeletal muscle, the myokines released by muscle fibers and the neurotrophic factors released by neurons innervating skeletal muscles that play various roles in the mechanisms of muscle plasticity. Another approach is to study the morphological and behavior of single adult muscle fibers under culture conditions for which one can fully control the level of activity and exogenous factors affecting muscle plasticity. However, single muscle fiber survival has been shown to be limited to a few days. The objective of this study was to optimize fiber survival in culture. Mouse FDB fibers were separated by trituration following a 3 hrs collagenase treatment at 37°C. When tested the day of the preparation, FDB fibers have normal morphology, normal resting membrane potential and calcium release during contraction. However, when maintained in culture at 37°C, they either degenerated or supercontracted and intact fibers are basically depleted within 5–7 days. Satellite cells are known to proliferate when fibers are maintained in culture and we tested whether an inhibition of their proliferation improves fiber survival. Exposing fibers under resting conditions to 50 μM AraC, a mitotic inhibitor, significantly improved fiber survival by significantly reducing the number of degenerating fibers. We also determined that i) MEM is a better medium than DMEM; ii) changing 50% of the culture medium every two days improved fiber survival compared to changing the medium every day; and iii) a collagen/laminin mixture as adhering substrate to improve fiber adhesion to glass coverslip gave rise to a better fiber survival than Matrigel. Together, the use of AraC, MEM, collagen/laminin and changing medium every two days resulted in having more than 60% of the fibers maintaining normal morphology up to 18 days. A large loss of fibers was then observed over the next 3 days primarily because of supercontraction. The results suggest i) that when satellite cells are allowed to proliferate they may contribute to the degeneration of fibers under resting conditions and ii) that the release of myokines by skeletal muscle fibers likely play a role in fiber survival (as removing 50% of medium every day lowered fiber survival).Support or Funding InformationThe study was supported by the National Science and Engineering Research Council of Canada (NSERC)
Perfluorooctanoic Acid Reduces Viability and Decreases Expression of Peroxisome Proliferator‐Activated Receptor Alpha (PPARα) and Estrogen Receptor Alpha (ERα) mRNA in MCF‐7 Human Breast Cancer Cells
Authors: Smith April N , Cannon Jennifer D 
Published: November 2023

Perfluorooctanoic acid (PFOA) is a synthetic fluoropolymer introduced into the environment post‐World War II as a component of a variety of industrial and consumer products. Human exposure occurs through these products, as well as through contaminated food, water, and air, or through occupational exposure. It is a very stable molecule with a half‐life of almost 4 years in humans. PFOA is a documented endocrine disruptor. It has been shown to decrease hormone production in some steroidogenic cells, however the effects of PFOA and its mechanism of action on hormone‐responsive cells remain unclear. The aims of this study were to determine the effects of PFOA on viability of MCF‐7 breast cancer cells as well as its effects on the expression of peroxisome proliferator‐activated receptors (PPARs) and estrogen receptors (ERs), both of which have defined roles in cell proliferation. Cells were treated with PFOA (100nm ‐ 100μM) for 24h to 48h before measuring cell viability using the CellTiter‐Blue Cell Viability Assay. The expression of PPARα, PPARβ, and PPARγ, as well as ERα and ERβ were determined by real‐time PCR. Cells treated with 100μM PFOA for 48h showed a significant, 25% decrease in cell viability (p<0.05) compared to untreated cells. This reduction in viability was preceded by a significant decline in both PPARα and ERα gene expression. This was observed in MCF‐7 cells treated with both 50μM and 100μM PFOA for 24h. There was no significant difference in the levels of PPARβ or PPARγ mRNA between PFOA treated and untreated cells, and the levels of ERβ mRNA were too low to be quantitated. These data suggest the PFOA‐induced decrease in cell viability in MCF‐7 cells is associated with a decrease in the expression of both PPARα and ERα mRNA.Support or Funding InformationAugusta University's Center for Undergraduate Research and Department of Biological Sciences
Maternal Chronic Intermittent Hypoxia During Gestation Programs Hypercholesterolemia in the Offspring
Authors: Ciriello John , Iqbal Waseem , Hardy Daniel 
Published: November 2023

Chronic intermittent hypoxia (CIH) is the underlying pathophysiological condition seen in individuals with obstructive sleep apnea. We have recently demonstrated that offspring exposed to maternal CIH during pregnancy exhibit reduced Liver X Receptor (LXR) protein leading to augmented expression of hepatic enzymes promoting gluconeogenesis. As LXR also plays an important role in cholesterol homeostasis, this study was done to determine the impact of diminished LXR expression on cholesterol handling by the liver in the offspring of CIH exposed pregnant mothers. Pregnant female Sprague‐Dawley rats were exposed daily to CIH (6.5% nadir; 18 cycles/h; 8h/day) from gestational day‐1 to day‐20. Control mothers were exposed to room air during pregnancy. Offspring were sacrificed at postnatal 6 and 12 weeks of age to assess early life and long‐term alterations in liver function. At both ages, male CIH offspring had significantly (p<0.05) higher total circulating cholesterol levels concomitant with significantly (p<0.05) greater body fat deposition compared to offspring exposed to gestational normoxia. Western blot analysis revealed that adult male CIH offspring at both ages had significantly (p<0.05) lower protein expression of the cholesterol catabolizing enzyme cholesterol 7α‐hydroxylase (CYP7A1), the cholesterol efflux transporter ATP‐binding cassette transporter G8 (ABCG8), and the low density lipoprotein receptor (LDLR) compared to the offspring exposed to gestational normoxia. Taken together, these data indicate that gestational CIH‐induced hypercholesterolemia in the offspring results from diminished expression of LXR target genes associated with cholesterol breakdown, excretion, and removal from the circulation.Support or Funding InformationSupported in part by HSFO and CIHR