Hart, Corey R.

Abstract Obesity is associated with several skeletal muscle impairments which can be improved through an aerobic exercise prescription. The possibility that exercise responsiveness is diminished in people with obesity has been suggested but not well‐studied. The purpose of this study was to investigate how obesity influences acute exercise responsiveness in skeletal muscle and circulating amino metabolites. Non‐obese (NO; n = 19; 10F/9M; BMI = 25.1 ± 2.8 kg/m 2 ) and Obese (O; n = 21; 14F/7M; BMI = 37.3 ± 4.6 kg/m 2 ) adults performed 30 min of single‐leg cycling at 70% of VO 2 peak. 13 C 6 ‐Phenylalanine was administered intravenously for muscle protein synthesis measurements. Serial muscle biopsies (vastus lateralis) were collected before exercise and 3.5‐ and 6.5‐h post‐exercise to measure protein synthesis and gene expression. Targeted plasma metabolomics was used to quantitate amino metabolites before and 30 and 90 min after exercise. The exercise‐induced fold change in mixed muscle protein synthesis trended ( p = 0.058) higher in NO (1.28 ± 0.54‐fold) compared to O (0.95 ± 0.42‐fold) and was inversely related to BMI (R 2 = 0.140, p = 0.027). RNA sequencing revealed 331 and 280 genes that were differentially expressed after exercise in NO and O, respectively. Gene set enrichment analysis showed O had six blunted pathways related to metabolism, cell to cell communication, and protein turnover after exercise. The circulating amine response further highlighted dysregulations related to protein synthesis and metabolism in adults with obesity at the basal state and in response to the exercise bout. Collectively, these data highlight several unique pathways in individuals with obesity that resulted in a modestly blunted exercise response.

Obesity is associated with several skeletal muscle impairments which can be improved through an aerobic exercise prescription. The possibility that exercise responsiveness is diminished in people with obesity has been suggested but not well‐studied. PURPOSE The purpose of this study was to investigate how obesity influences acute exercise responsiveness within skeletal muscle. METHODS Non‐obese (NO; n=19; 10F/9M; BMI=25.1 ± 2.8 kg/m 2 ) and Obese (O; n=21; 14F/7M; BMI=37.3 ± 4.6 kg/m 2 ) adults performed 30 minutes of single‐leg cycling at 70% of VO 2 peak. Serial muscle biopsies (vastus lateralis) were collected before exercise and 3 and 6 hours post‐exercise to measure protein synthesis and gene expression. RESULTS The exercise‐induced fold change in mixed muscle protein synthesis trended (p=0.058) higher in NO (1.28 ± 0.54‐fold) compared to O (0.95 ± 0.42‐fold) and was inversely related to BMI (r=‐.374, p=0.027). RNA sequencing revealed 331 and 280 genes that were up or downregulated after exercise in NO and O, respectively. Gene set enrichment analysis showed O had blunted post‐exercise pathways related to MAPK signaling, chemokine‐mediated signaling, FC receptor mediated stimulation signaling, cell proliferation, apoptosis, and RNA polymerase II promotion. Quantitative polymerase chain reaction of select metabolic ( PGC1a, PGC1b, TFAM, PDK4, IRS, MAPK, and PRKAA1 ) and muscle growth ( SLC, TBC, MSTN, MyoD, TRIM32, FOX03, and FBXO3) genes were similar between groups 3 and 6 hours after exercise. Conclusion These data highlight several unique pathways in individuals with obesity that result in a blunted exercise response.

AbstractObjectiveThe health benefits of exercise are well documented, but several exercise‐response parameters are attenuated in individuals with obesity. The goal of this pilot study was to identify molecular mechanisms that may influence exercise response with obesity.MethodsA multi‐omics comparison of the transcriptome, proteome, and phosphoproteome in muscle from a preliminary cohort of lean individuals (n = 4) and individuals with obesity (n = 4) was performed, before and after a single bout of 30 minutes of unilateral cycling at 70% maximal oxygen uptake (VO2 peak). Mass spectrometry and RNA sequencing were used to interrogate the proteome, phosphoproteome, and transcriptome from muscle biopsy tissue.ResultsThe main findings are that individuals with obesity exhibited transcriptional and proteomic signatures consistent with reduced mitochondrial function, protein synthesis, and glycogen synthesis. Furthermore, individuals with obesity demonstrated markedly different transcriptional, proteomic, and phosphoproteomic responses to exercise, particularly biosynthetic pathways of glycogen synthesis and protein synthesis. Casein kinase II subunit alpha and glycogen synthase kinase‐3β signaling was identified as exercise‐response pathways that were notably altered by obesity.ConclusionsOpportunities to enhance exercise responsiveness by targeting specific molecular pathways that are disrupted in skeletal muscle from individuals with obesity await a better understanding of the precise molecular mechanisms that may limit exercise‐response pathways in obesity.

To our knowledge, this is the first study to suggest that skeletal muscle mitochondrial deficits are associated with cancer-associated weight loss in humans. Mitochondrial deficits and alterations in the phospholipid metabolome were concurrent with reductions in whole body and skeletal muscle functional capacity. Whether mitochondrial deficits are causal or secondary to cancer-associated weight loss and functional deficits remains to be determined, but this study supports further exploration of mitochondria as a driver of cancer-associated losses in muscle mass and function.

INTRODUCTION Heart failure (HF) is characterized by reduced exercise capacity resulting from central and peripheral mechanisms. A primary peripheral mechanism is augmented neural feedback (via group III/IV afferents) arising from the locomotor muscles. This enhanced locomotor neural feedback may result from a variety of mechanisms including increased 1) metabo and/or mechanoreceptor expression, 2) metabolite production, and/or 3) mechano/metaboreceptor sensitivity. Previous studies have shown elevated expression of purinergic 2X3 (P2X3) and cyclooxygenase (COX‐2) in HF compared to sham animal models. However, it is unknown if metabo and/or mechanoreceptor (e.g., Piezo 1 and 2) expression are elevated in human HF. Further, it is unclear if altered receptor expression is related to the cardiovascular and ventilatory responses during exercise attributed to locomotor neural afferent feedback. The purpose of this study was to 1) determine if differences exist in the expression of skeletal muscle proteins associated with metabo/mechanoreflex activity between healthy individuals (CTL) and HF patients and 2) determine relationships between protein expression and the change in ventilatory and cardiovascular responses with locomotor muscle afferent inhibition during exercise. We hypothesized that 1) HF patients will demonstrate greater skeletal muscle protein expression associated with mechano/metaboreflex activity and 2) the increased protein expression will be associated with changes in ventilation, mean arterial pressure (MAP), and catecholamines during locomotor muscle afferent feedback inhibition in HF patients. METHODS In a randomized, placebo controlled cross‐over design, 10 CTL and 6 systolic HF (Age: 60±12 vs. 60±4 yrs, p=0.96; BMI: 26±3 vs. 31±5 kg/m 2 , p=0.01, respectively) patients completed cycling exercise at 60%VO 2 peak with lumbar intrathecal fentanyl or sham. Arterial blood pressure and catecholamines were measured via radial artery catheter during exercise. On a follow up visit, a muscle biopsy from the vastus lateralis was performed to isolate and measure COX‐2, P2X3, transient receptor potential vanilloid type 1 (TRPV1), Piezo 1, and Piezo 2 protein expression. RESULTS Protein expression of P2X3, COX‐2, and TRPV1 were greater in HF compared to CTL (all, p<0.05), with no difference between groups in Piezo 1 and 2 protein expression (p>0.05). HF compared to CTL had a greater decrease in ventilation with fentanyl compared to sham (−11±8 vs. −3±9%, p=0.04, respectively), with no difference between groups in MAP or norepinephrine (p>0.05). In HF, COX expression was negatively related to the change in ventilation (r= −0.87, p=0.02), MAP (r= −0.93, p<0.01), and norepinephrine (r= −0.85, p=0.03) with fentanyl. CONCLUSIONS These data demonstrate that metaborecptors (i.e. P2X3, COX‐2, and TRPV1) are elevated in HF compared to CTL. Furthermore, protein expression of COX‐2 was related to the cardiovascular and ventilatory changes observed with fentanyl in HF patients. These findings suggest that elevated expression of metaboreflex associated proteins contribute to the augmented locomotor muscle afferent feedback during exercise in HF. Support or Funding Information NHLBI RO1 HL126638 AHA 18POST3990251 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Aging is associated with altered mitochondrial physiology and exercise responsiveness in skeletal muscle. Activation of the unfolded protein response in the endoplasmic reticulum (UPR ER ) and mitochondria (UPR MT ) is linked with exercise‐induced adaptations in skeletal muscle, but the possibility that these processes impact exercise responsiveness and mitochondrial function in older humans has not been fully elucidated. The purpose of this study was to evaluate age‐related changes in UPR ER and UPR MT gene transcripts and protein abundance in response to a single bout of exercise. Muscle biopsies were obtained from 12 young (27±5 yr) and 12 older (75±5 yr) well‐matched, healthy men and women before exercise and 18h following a single bout of unilateral leg extension. Before exercise, a gene set enrichment analysis (GSEA) revealed that 27 genes associated with the UPR ER were upregulated in the older subjects compared to the young (enrichment false discovery rate [FDR] = 0.0842). After exercise, GSEA indicated upregulated UPR ER genes in both the young (FDR = 0.0405) and older subjects (FDR = 0.0619), however, pathway activation analysis revealed significantly greater activation of UPR ER and UPR MT gene transcripts post‐exercise in the younger subjects ( P < 0.05). In contrast, age did not affect key UPR‐regulatory protein abundance 18h post‐exercise. Interestingly, statistically significant correlations were observed in the young subjects between the mitochondrial transcriptional coactivator, peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) and key regulatory genes associated with the UPR ER (GRP78, R = 0.67; ATF6, R = 0.70) and the UPR MT (HSPE1, R = 0.61; HSPD1, R = 0.55; and HSPA9, R = 0.79), which were not evident in the older subjects. In conclusion, transcriptomic analysis revealed an age‐related decline in the adaptive UPR ER and UPR MT transcriptional response following a single bout of exercise that could potentially explain, in part, impaired exercise responsiveness and mitochondrial dysfunction with age. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Skeletal muscle is vital to metabolic health and physical function. Skeletal muscle mitochondria have been extensively interrogated as organelles whose function and dysfunction are closely tied with chronic diseases such as diabetes and sarcopenia. There is accumulating evidence suggesting that chronic inflammation that is prevalent with aging and obesity is associated with skeletal muscle abnormalities such as functional impairments in mitochondria. Despite compelling links between inflammation, oxidative stress, and skeletal muscle dysfunction, the local effects of inflammatory cytokines on skeletal muscle mitochondrial physiology are currently not well‐understood. The purpose of this study was to determine how the inflammatory cytokine interleukin‐6 (IL‐6) influences skeletal muscle mitochondrial function. To determine the acute effects of IL‐6, mitochondria were isolated from skeletal muscle of healthy male mice (C57BL6) and were exposed to IL‐6 (IL6 + ,50 ng/ml) or vehicle (CTRL) for one hour. Multiplexed measurements of mitochondrial respiration (high‐resolution respirometry) and reactive oxygen species production (ROS, fluorometry) revealed that IL‐6 significantly increased ROS production as a percent of oxygen (4.14%±0.40) compared to CTRL (2.74%±0.34). Similarly, IL‐6 increased ROS production in differentiated C2C12 myotubes that were incubated for 18 hrs with 50 ng/mL IL‐6 (4.71%±.57) compared to CTRL (2.21%±.34). To evaluate the possibility that IL‐6 triggers ROS production by stimulating the mitochondrial transition pore (mPTP), isolated mitochondria were ale treated with cyclosporin A (CsA), a mPTP inhibitor in the presence or absence of IL‐6. Inhibition of mPTP attenuated IL‐6 induced ROS production (IL6+ (4.14%±0.40) vs. IL6+/CsA (2.78%±0.58). These results suggest that IL‐6 triggers an increase in mitochondrial ROS production that appears to be mediated by opening of the mPTP. Prolonged opening of the mPTP caused by chronically elevated IL‐6 may contribute to increased oxidative stress that is evident in skeletal muscle with aging and obesity. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .

Key points Healthy older adults exhibit lower cardiorespiratory fitness () than young in the absence of any age‐related difference in skeletal muscle mitochondrial capacity, suggesting central haemodynamics plays a larger role in age‐related declines in . Total physical activity did not differ by age, but moderate‐to‐vigorous physical activity was lower in older compared to young adults. Moderate‐to‐vigorous physical activity is associated with and muscle oxidative capacity, but physical inactivity cannot entirely explain the age‐related reduction in . AbstractDeclining fitness () is a hallmark of ageing and believed to arise from decreased oxygen delivery and reduced muscle oxidative capacity. Physical activity is a modifiable lifestyle factor that is critical when evaluating the effects of age on parameters of fitness and energy metabolism. The objective was to evaluate the effects of age and sex on , muscle mitochondrial physiology, and physical activity in young and older adults. An additional objective was to assess the contribution of skeletal muscle oxidative capacity to age‐related reductions in and determine if age‐related variation in and muscle oxidative capacity could be explained on the basis of physical activity levels. In 23 young and 52 older men and women measurements were made of , mitochondrial physiology in permeabilized muscle fibres, and free‐living physical activity by accelerometry. Regression analyses were used to evaluate associations between age and , mitochondrial function, and physical activity. Significant age‐related reductions were observed for (P < 0.001), but not muscle mitochondrial capacity. Total daily step counts did not decrease with age, but older adults showed lower moderate‐to‐vigorous physical activity, which was associated with (R2 = 0.323, P < 0.001) and muscle oxidative capacity (R2 = 0.086, P = 0.011). After adjusting for sex and physical activity, age was negatively associated with but not muscle oxidative capacity. Healthy older adults exhibit lower but preserved mitochondrial capacity compared to young. Physical activity, particularly moderate‐to‐vigorous, is a key factor in observed age‐related changes in fitness and muscle oxidative capacity, but cannot entirely explain the age‐related reduction in .

Adipose inflammation is proposed to be at the nexus of the systemic inflammation and metabolic derangements associated with obesity. The present study provides evidence to support adipose inflammation as a central feature of the pathophysiology of obesity. Adipose inflammation is associated with systemic and peripheral metabolic derangements, including increased systemic inflammation, reduced insulin sensitivity and reduced skeletal muscle mitochondrial respiration.

New Findings What is the central question of this study? How do locomotor muscle metabo‐ and mechanoreceptor expression compare in heart failure patients and controls? Do relationships exist between the protein expression and cardiopulmonary responses during exercise with locomotor muscle neural afferent feedback inhibition? What is the main finding and its importance? Heart failure patients exhibited greater protein expression of transient receptor potential vanilloid type 1 and cyclooxygenase‐2 than controls. These findings are important as they identify receptors that may underlie the augmented locomotor muscle neural afferent feedback in heart failure. AbstractHeart failure patients with reduced ejection fraction (HFrEF) exhibit abnormal locomotor group III/IV afferent feedback during exercise; however, the underlying mechanisms are unclear. Therefore, the purpose of this study was to determine (1) metabo‐ and mechanoreceptor expression in HFrEF and controls and (2) relationships between receptor expression and changes in cardiopulmonary responses with afferent inhibition. Ten controls and six HFrEF performed 5 min of cycling exercise at 65% peak workload with lumbar intrathecal fentanyl (FENT) or placebo (PLA). Arterial blood pressure and catecholamines were measured via radial artery catheter. A vastus lateralis muscle biopsy was performed to quantify cyclooxygenase‐2 (COX‐2), purinergic 2X3 (P2X3), transient receptor potential vanilloid type 1 (TRPV1), acid‐sensing ion channel 3 (ASIC3), Piezo 1 and Piezo 2 protein expression. TRPV1 and COX‐2 protein expression was greater in HFrEF than controls (both P < 0.04), while P2X3, ASIC3, and Piezo 1 and 2 were not different between groups (all P > 0.16). In all participants, COX‐2 protein expression was related to the percentage change in ventilation (r = −0.66) and mean arterial pressure (MAP) (r = −0.82) (both P < 0.01) with FENT (relative to PLA) during exercise. In controls, TRPV1 protein expression was related to the percentage change in systolic blood pressure (r = −0.77, P = 0.02) and MAP (r = −0.72, P = 0.03) with FENT (relative to PLA) during exercise. TRPV1 and COX‐2 protein levels are elevated in HFrEF compared to controls. These findings suggest that the elevated TRPV1 and COX‐2 expression may contribute to the exaggerated locomotor muscle afferent feedback during cycling exercise in HFrEF.