Respiration In Skeletal Muscle Research Articles

Endurance training increases mitochondrial myoglobin and enhances its interaction with complex IV in rat plantaris muscle.

Endurance exercise training is known to increase mitochondrial respiration in skeletal muscle. However, the molecular mechanisms behind this are not fully understood. Myoglobin (Mb) is a member of the globin family, which is highly expressed in skeletal and cardiac muscles. We recently found that Mb localizes inside mitochondria in skeletal muscle and interacts with cytochrome c oxidase subunit IV (COXIV), a subunit of mitochondrial complex IV, which regulates respiration by augmenting complex IV activity. In the present study, we investigated the effect of endurance training on Mb-COXIV interaction within mitochondria in rat skeletal muscle. Eight-week-old male Wistar rats were subjected to 6-week treadmill running training. Forty-eight hours after the last training session, the plantaris muscle was removed under anesthesia and used for biochemical analysis. The endurance training increased mitochondrial content in the skeletal muscle. It also augmented complex IV-dependent oxygen consumption and complex IV activity in isolated mitochondria from skeletal muscle. Furthermore, endurance training increased Mb expression at the whole muscle level. Importantly, mitochondrial Mb content and Mb-COXIV binding were increased by endurance training. These findings suggest that an increase in mitochondrial Mb and the concomitant enhancement of Mb interaction with COXIV may contribute to the endurance training-induced upregulation of mitochondrial respiration by augmenting complex IV activity.

Decreased Pyruvate but Not Fatty Acid Driven Mitochondrial Respiration in Skeletal Muscle of Growth Restricted Fetal Sheep.

Fetuses with intrauterine growth restriction (FGR) have impaired oxidative and energy metabolism, with persistent consequences on their postnatal development. In this study, we test the hypothesis that FGR skeletal muscle has lower mitochondrial respiration rate and alters the transcriptomic profiles associated with energy metabolism in an ovine model. At late gestation, mitochondrial oxygen consumption rates (OCRs) and transcriptome profiles were evaluated in the skeletal muscle collected from FGR and control fetuses. The ex vivo mitochondrial OCRs were reduced (p < 0.01) in permeabilized FGR soleus muscle compared to the control muscle but only with pyruvate as the metabolic substrate. Mitochondrial OCRs were similar between the FGR and control groups for palmitoyl-carnitine (fatty acid-driven) or pyruvate plus palmitoyl-carnitine metabolic substrates. A total of 2284 genes were differentially expressed in the semitendinosus muscle from growth restricted fetuses (false discovery rate (FDR) ≤ 0.05). A pathway analysis showed that the upregulated genes (FGR compared to control) were overrepresented for autophagy, HIF-1, AMPK, and FOXO signaling pathways (all with an FDR < 0.05). In addition, the expression of genes modulating pyruvate's entry into the TCA cycle was downregulated, whereas the genes encoding key fatty acid oxidation enzymes were upregulated in the FGR muscle. These findings show that FGR skeletal muscle had attenuated mitochondrial pyruvate oxidation, possibly associated with the inability of pyruvate to enter into the TCA cycle, and that fatty acid oxidation might compensate for the attenuated energy metabolism. The current study provided phenotypic and molecular evidence for adaptive deficiencies in FGR skeletal muscle.

High-fat diet increases electron transfer flavoprotein synthesis and lipid respiration in skeletal muscle during exercise training in female mice.

High-fat diet (HFD) and exercise remodel skeletal muscle mitochondria. The electron transfer flavoproteins (ETF) transfer reducing equivalents from β-oxidation into the electron transfer system. Exercise may stimulate the synthesis of ETF proteins to increase lipid respiration. We determined mitochondrial remodeling for lipid respiration through ETF in the context of higher mitochondrial abundance/capacity seen in female mice. We hypothesized HFD would be a greater stimulus than exercise to remodel ETF and lipid pathways through increased protein synthesis alongside increased lipid respiration. Female C57BL/6J mice (n = 15 per group) consumed HFD or low-fat diet (LFD) for 4 weeks then remained sedentary (SED) or completed 8 weeks of treadmill training (EX). We determined mitochondrial lipid respiration, RNA abundance, individual protein synthesis, and abundance for ETFα, ETFβ, and ETF dehydrogenase (ETFDH). HFD increased absolute and relative lipid respiration (p = 0.018 and p = 0.034) and RNA abundance for ETFα (p = 0.026), ETFβ (p = 0.003), and ETFDH (p = 0.0003). HFD increased synthesis for ETFα and ETFDH (p = 0.0007 and p = 0.002). EX increased synthesis of ETFβ and ETFDH (p = 0.008 and p = 0.006). Higher synthesis rates of ETF were not always reflected in greater protein abundance. Greater synthesis of ETF during HFD indicates mitochondrial remodeling which may contribute higher mitochondrial lipid respiration through enhanced ETF function.

A Maternal Western-Style Diet Impairs Skeletal Muscle Lipid Metabolism in Adolescent Japanese Macaques.

In lean, active adolescent offspring, a postweaning Western-style diet (pwWD) leads to shifts in body fat distribution that are associated with poorer insulin sensitivity. Fatty acid-linked oxidative metabolism was reduced in skeletal muscles from offspring exposed to maternal Western-style diet (mWD) even when weaned to a healthy control diet for years. Reduced oxidative phosphorylation complex I-V and VDAC1 abundance partially explain decreased skeletal muscle respiration in mWD offspring. Prior exposure to mWD results in greater fold increase with pwWD in saturated lipids and bioactive lipid molecules (i.e. ceramide and sphingomyelin) associated with insulin resistance.

Resistance Training Improves Hypertrophic and Mitochondrial Adaptation in Skeletal Muscle.

Resistance training is employed for pursuing muscle strength characterized by activation of mammalian target of rapamycin (mTOR)-mediated hypertrophic signaling for protein production. Endurance training elevates peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) signaling of mitochondrial adaptations for oxidative phosphorylation. Now, emerging evidence suggests that, like endurance training, resistance training also elicits profound effects on mitochondrial adaptations in skeletal muscle, which means that resistance training yields both strength and endurance phenotypes in myofibers, which has treatment value for the muscle loss and poor aerobic capacity in humans. Our review outlines a brief overview of muscle hypertrophic signals with resistance training, and focuses on the effects of resistance training on mitochondrial biogenesis and respiration in skeletal muscle. This study provides novel insights into the therapeutic strategy of resistance training for the metabolically dysfunctional individuals with declined mitochondrial function.

Relationship of Muscle Apolipoprotein E Expression with Markers of Cellular Stress, Metabolism, and Blood Biomarkers in Cognitively Healthy and Impaired Older Adults.

Individuals with mild cognitive impairment (MCI) have reduced lipid-stimulated mitochondrial respiration in skeletal muscle. A major risk factor for Alzheimer's disease (AD), the apolipoprotein E4 (APOE4) allele, is implicated in lipid metabolism and is associated with metabolic and oxidative stress that can result from dysfunctional mitochondria. Heat shock protein 72 (Hsp72) is protective against these stressors and is elevated in the AD brain. Our goal was to characterize skeletal muscle ApoE and Hsp72 protein expression in APOE4 carriers in relationship to cognitive status, muscle mitochondrial respiration and AD biomarkers. We analyzed previously collected skeletal muscle tissue from 24 APOE4 carriers (60y+) who were cognitively healthy (CH, n = 9) or MCI (n = 15). We measured ApoE and Hsp72 protein levels in muscle and phosphorylated tau181 (pTau181) levels in plasma, and leveraged previously collected data on APOE genotype, mitochondrial respiration during lipid oxidation, and VO2 max. Muscle ApoE (p = 0.013) and plasma pTau181 levels (p < 0.001) were higher in MCI APOE4 carriers. Muscle ApoE positively correlated with plasma pTau181 in all APOE4 carriers (R2 = 0.338, p = 0.003). Hsp72 expression negatively correlated with ADP (R2 = 0.775, p = <0.001) and succinate-stimulated respiration (R2 = 0.405, p = 0.003) in skeletal muscle of MCI APOE4 carriers. Plasma pTau181 negatively tracked with VO2 max in all APOE4 carriers (R2 = 0.389, p = 0.003). Analyses were controlled for age. This work supports a relationship between cellular stress in skeletal muscle and cognitive status in APOE4 carriers.

Impact of GLP-1 receptor agonist versus omega-3 fatty acids supplement on obesity-induced alterations of mitochondrial respiration.

To compare administration of the glucagon-like peptide-1 (GLP-1) analogue, exenatide, versus dietary supplementation with the omega-3 fatty acid-rich Calanus oil on obesity-induced alterations in mitochondrial respiration. Six-week-old female C57BL/6JOlaHSD mice were given high fat diet (HFD, 45% energy from fat) for 12 weeks to induce obesity. Thereafter, they were divided in three groups where one received exenatide (10 μg/kg/day) via subcutaneously implanted mini-osmotic pumps, a second group received 2% Calanus oil as dietary supplement, while the third group received HFD without any treatment. Animals were sacrificed after 8 weeks of treatment and tissues (skeletal muscle, liver, and white adipose tissue) were collected for measurement of mitochondrial respiratory activity by high-resolution respirometry, using an Oroboros Oxygraph-2k (Oroboros instruments, Innsbruck, Austria). It was found that high-fat feeding led to a marked reduction of mitochondrial respiration in adipose tissue during all three states investigated - LEAK, OXPHOS and ETS. This response was to some extent attenuated by exenatide treatment, but not with Calanus oil treatment. High-fat feeding had no major effect on hepatic mitochondrial respiration, but exenatide treatment resulted in a significant increase in the various respiratory states in liver. Mitochondrial respiration in skeletal muscle was not significantly influenced by high-fat diet or any of the treatments. The precise evaluation of mitochondrial respiration considering absolute oxygen flux and ratios to assess flux control efficiency avoided misinterpretation of the results. Exenatide increased hepatic mitochondrial respiration in high-fat fed mice, but no clear beneficial effect was observed in skeletal muscle or fat tissue. Calanus oil did not negatively affect respiratory activity in these tissues, which maintains its potential as a dietary supplement, due to its previously reported benefits on cardiac function.

Accuracy of handgrip and respiratory muscle strength in identifying sarcopenia in older, community-dwelling, Brazilian women

Certain cut-off points for sarcopenia screening and diagnosis are arbitrary and based on European populations, with normative references often obtained from healthy young adults. Although respiratory skeletal muscle strength tests represent low-cost clinical measures commonly performed in clinical practice by health professionals, a gap remains regarding whether respiratory skeletal muscle strength tests are adequate and sensitive measures for sarcopenia screening. This study aimed to verify the value of handgrip and respiratory muscle strength as possible discriminators to identify sarcopenia and to establish cut-off points for sarcopenia screening in community-dwelling, Brazilian women. In a cross-sectional study, 154 community-dwelling, Brazilian women (65–96 years) were assessed for appendicular skeletal muscle mass, handgrip (HGS), and respiratory muscular strength, including maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP). The data were analyzed using the ROC curve and the Youden Index determined cut-off points. Statistical significance was set at 5%. 88 participants (57%) were sarcopenic. MEP (OR 0.98 [95%CI 0.97, 1.00], p = 0.023) and HGS (OR 0.82 [95% CI 0.75, 0.90], p < 0.001) were independent factors for sarcopenia in older. The optimal cut-off points for identifying sarcopenia were ≤ 77 cmH2O for MEP (AUC = 0.72), and ≤ 20 kg for HGS (AUC = 0.80). Simple muscular strength tests, including HGS and MEP, may be considered in the identification of sarcopenia in older, community-dwelling, Brazilian women. Future work is still needed to assess external validation of the proposed cut-offs before the clinical application.

Impact of Coenzyme Q10 Supplementation on Skeletal Muscle Respiration, Antioxidants, and the Muscle Proteome in Thoroughbred Horses.

Coenzyme Q10 (CoQ10) is an essential component of the mitochondrial electron transfer system and a potent antioxidant. The impact of CoQ10 supplementation on mitochondrial capacities and the muscle proteome is largely unknown. This study determined the effect of CoQ10 supplementation on muscle CoQ10 concentrations, antioxidant balance, the proteome, and mitochondrial respiratory capacities. In a randomized cross-over design, six Thoroughbred horses received 1600 mg/d CoQ10 or no supplement (control) for 30-d periods separated by a 60-d washout. Muscle samples were taken at the end of each period. Muscle CoQ10 and glutathione (GSH) concentrations were determined using mass spectrometry, antioxidant activities by fluorometry, mitochondrial enzyme activities and oxidative stress by colorimetry, and mitochondrial respiratory capacities by high-resolution respirometry. Data were analyzed using mixed linear models with period, supplementation, and period × supplementation as fixed effects and horse as a repeated effect. Proteomics was performed by tandem mass tag 11-plex analysis and permutation testing with FDR < 0.05. Concentrations of muscle CoQ10 (p = 0.07), GSH (p = 0.75), and malondialdehyde (p = 0.47), as well as activities of superoxide dismutase (p = 0.16) and catalase (p = 0.66), did not differ, whereas glutathione peroxidase activity (p = 0.003) was lower when horses received CoQ10 compared to no supplement. Intrinsic (relative to citrate synthase activity) electron transfer capacity with complex II (ECII) was greater, and the contribution of complex I to maximal electron transfer capacity (FCRPCI and FCRPCIG) was lower when horses received CoQ10 with no impact of CoQ10 on mitochondrial volume density. Decreased expression of subunits in complexes I, III, and IV, as well as tricarboxylic acid cycle (TCA) enzymes, was noted in proteomics when horses received CoQ10. We conclude that with CoQ10 supplementation, decreased expression of TCA cycle enzymes that produce NADH and complex I subunits, which utilize NADH together with enhanced electron transfer capacity via complex II, supports an enhanced reliance on substrates supplying complex II during mitochondrial respiration.

Relationship between stress response and mitochondrial respiration in skeletal muscle of apolipoprotein E4 (APOE4) carriers

AbstractBackgroundExpression of the stress‐inducible chaperone protein, heat shock protein 70 (HSP70/72), is elevated in the Alzheimer’s disease (AD) brain. This may result from mitochondrial stress, as AD mitochondria are characterized by reduced complex IV activity and ATP levels. Further, patients with mild cognitive impairment (MCI) have reduced lipid‐stimulated mitochondrial respiration in skeletal muscle, providing evidence that mitochondrial dysfunction occurs peripherally, manifests early in the disease, and is related to lipid metabolism. Interestingly, the primary genetic risk factor for sporadic AD, the apolipoprotein E4 (APOE4) allele, plays an important role in lipid metabolism. The goal of this study was to characterize the skeletal muscle stress response in APOE4 carriers and the relationship with muscle mitochondrial function.MethodWe analyzed skeletal muscle tissue from previously collected biopsies (vastus lateralis) from 23 older adults (65+) who were cognitively healthy (CH, n=8) or MCI (n=15) and at genetic risk for AD (APOE4 carriers). We measured HSP72 protein levels via Western blot and leveraged previously collected data on APOE4 genotype, mitochondrial respiration (basal, state 3, state 3S, uncoupled), plasma cholesterol and platelet citrate synthase activity, the latter of which is a marker of mitochondrial content. Analyses were controlled for age and sex.ResultHSP72 expression negatively correlated with basal respiration (R2 = 0.518, p = 0.002), ADP‐stimulated respiration (R2 = 0.775, p = &lt;0.001) and succinate‐stimulated respiration (R2 = 0.405, p = 0.011) in the presence of the lipid, palmitoyl‐carnitine, in skeletal muscle of APOE4 carriers with MCI, but not in CH APOE4 carriers. HSP72 expression negatively correlated with platelet citrate synthase activity (R2 = 0.518, p = 0.002) in APOE4 carriers with MCI, but not in CH APOE4 carriers. HSP72 expression positively correlated with plasma cholesterol in all participants (R2 = 0.182, p = 0.042).ConclusionThis work supports a potential role for the heat shock response in responding to peripheral mitochondrial dysfunction and elevated cholesterol levels during cognitive decline in APOE4 carriers. Further work is needed to determine if this stress response serves a protective role.

Peripheral and respiratory muscle impairment during murine acute lung injury

Acute respiratory distress syndrome is associated with skeletal muscle compromise, which decreases survival and impairs functional capacity. A comparative analysis of peripheral and respiratory muscles' atrophy and dysfunction in acute lung injury (ALI) has not been performed. We aimed to evaluate diaphragmatic and peripheral muscle mass and contractility in an ALI animal model. ALI was induced in C57BL/6 mice by intratracheal lipopolysaccharides instillation. Muscle mass and in vitro contractility were evaluated at different time points in hindlimb soleus (slow‐twitch) and extensor digitorum longus (EDL, fast‐twitch), as well as in the main respiratory muscle diaphragm. Myogenic precursor satellite cell‐specific transcription factor Pax7 expression was determined by Western blot. Lung injury was associated with atrophy of the three studied muscles, although it was more pronounced and persistent in the diaphragm. Specific contractility was reduced during lung injury in EDL muscle but restored by the time lung injury has resolved. Specific force was not affected in soleus and diaphragm. A persistent increase in Pax7 expression was detected in diaphragm and EDL muscles after induction of ALI, but not in soleus muscle. Different peripheral and respiratory skeletal muscles are distinctly affected during the course of ALI. Each of the studied muscles presented a unique pattern in terms of atrophy development, contractile dysfunction and Pax7 expression.

Natural History of Histopathologic Changes in Cardiomyopathy of Golden Retriever Muscular Dystrophy.

BackgroundDuchenne muscular dystrophy (DMD) is an X-linked inherited myopathy that causes progressive skeletal and cardiac muscle disease. Heart lesions were described in the earliest DMD reports, and cardiomyopathy is now the leading cause of death. However, diagnostics and treatment for cardiomyopathy have lagged behind those for appendicular and respiratory skeletal muscle disease. Most animal model studies have been done in the mdx mouse, which has a relatively mild form of cardiomyopathy. Dogs with the genetically homologous condition, Golden Retriever muscular dystrophy (GRMD), develop progressive cardiomyopathy analogous to that seen in DMD. Previous descriptive studies of GRMD cardiomyopathy have mostly been limited to selective sampling of the hearts from young dogs.Methods and ResultsWe systematically assessed cardiac lesions in 31 GRMD and carrier dogs aged 3 to 76 months and a separate cohort of 2–10-year-old normal hounds. Both semi-quantitative lesion scoring and quantitation of the cross-sectional area of fibrosis distinguished dogs with GRMD disease from normal dogs. The carriers generally had intermediate involvement but had even greater fibrosis than GRMD dogs. Fatty infiltration was the most prominent feature in some older GRMD dogs. Vascular hypertrophy was increased in GRMD dogs and correlated positively with lesion severity. Purkinje fiber vacuolation was also increased but did not correlate with lesion severity. Histopathologic changes correlated with late gadolinium enhancement on cardiac MRI.ConclusionThese features are generally compatible with those of DMD and further validate GRMD as a useful model to study cardiomyopathy pathogenesis and treatment. Additionally, the nature of some degenerative lesions suggests that functional hypoxia or non-thrombotic ischemia may contribute to disease progression.

Metformin Treatment in Old Rats and Effects on Mitochondrial Integrity.

Metformin, a commonly used well-tolerated treatment for type 2 diabetes, is being deployed in clinical trials to ameliorate aging in older nondiabetic humans. Concerningly, some experiments in model organisms have suggested that metformin use at old ages shortens life span and is toxic to mitochondria. The demonstrated safety of metformin therapy in humans and the conflicting data from model organisms compelled us to test the hypothesis that metformin treatment would be toxic to older rats. To define an effective dose in 30-month-old hybrid rats, we evaluated two doses of metformin (0.1%, 0.75% of the diet) and treated the rats for 4 months. Body mass decreased at the 0.75% dose. Neither dose affected mortality between 30 and 34 months of age. We assessed mitochondrial integrity by measuring mitochondrial DNA (mtDNA) copy number and deletion mutation frequency, and mitochondrial respiration in skeletal muscle and the heart. In skeletal muscle, we observed no effect of metformin on quadriceps mass, mtDNA copy number, or deletion frequency. In the heart, metformin-treated rats had higher mtDNA copy number, lower cardiac mass, with no change in mtDNA deletion frequency. Metformin treatment resulted in lower mitochondrial complex I-dependent respiration in the heart. We found that, in old rats, metformin did not compromise mtDNA integrity, did not affect mortality, and may have cardiac benefits. These data provide some reassurance that a metformin intervention in aged mammals is not toxic at appropriate doses.

Normal to Enhanced Intrinsic Mitochondrial Respiration in Skeletal Muscle of Middle- to Older-Aged Women and Men With Uncomplicated Type 1 Diabetes

We interrogated mitochondrial respiratory function and content in skeletal muscle biopsies of healthy adults 30-72 years old with and without uncomplicated type 1 diabetes (T1D). Participants (12/9 women/men) with type 1 diabetes (48±11 years old), without overt complications, were matched to participants without diabetes (control) (49±12 years old). Participants underwent a vastus lateralis biopsy to assess mitochondrial respiratory function, mitochondrial content and cristae density. Mitochondria area density was 27% lower in those with T1D versus controls.

500 Late-Breaking: Heart Rate During Exercise Is Positively Correlated with State IV Mitochondrial Respiration in the Equine Skeletal Muscle

Abstract Mitochondria are critical for oxidative phosphorylation in skeletal muscle, especially in athletic species such as the horse. Mitochondrial respiration increases with physical exercise, but the relationship between mitochondrial respiration and cardiovascular functions are not well described in the horse. The objective of this study was to determine if there is a relationship between heart rate (HR) during and after submaximal exercise tests (SETs) and skeletal muscle mitochondrial respiration in polo ponies. We hypothesized that horses with greater maximum HR and average HR during the exercise tests would have greater mitochondrial respiration in skeletal muscle. Twelve fit polo ponies (14.8 ± 1.7 years old, 10 mares and 2 geldings) were equipped with Polar equine heart rate monitors (Polar Electro Inc., Lake Success, NY) and underwent 26-minute SETs designed to mimic a polo chukker followed by a 30-minute recovery period. Muscle biopsy samples from the semitendinosus muscle were taken 2 weeks prior to the SET to determine mitochondrial oxygen consumption using the Oroboros O2k high-resolution respirometer (Oroboros Instruments, Innsbruck, Austria). Data were analyzed using the PROC CORR procedure (SAS Inst. Inc., Cary, NC). Correlations were considered strong at r &amp;gt; 0.6 and significant at P &amp;lt; 0.05. Maximum HR during SET and state IV respiration were positively correlated (P = 0.02, r = 0.68). Average HR during SET and state IV respiration were also positively correlated (P = 0.01, r = 0.72). However, correlations between maximum and average HR and state III respiration were not as strong (P ≥ 0.05, r &amp;lt; 0.6). These data suggest that state IV mitochondrial respiration (proton leak) in equine skeletal muscle may impact cardiac responses to high-intensity exercise. Horses with higher HR during exercise may have less efficient oxidative phosphorylation, resulting in earlier fatigue and/or greater formation of reactive oxygen species resulting from proton leak.

Intramuscular Injection of miR-1 Reduces Insulin Resistance in Obese Mice.

The role of microRNAs in metabolic diseases has been recognized and modulation of them could be a promising strategy to treat obesity and obesity-related diseases. The major purpose of this study was to test the hypothesis that intramuscular miR-1 precursor replacement therapy could improve metabolic parameters of mice fed a high-fat diet. To this end, we first injected miR-1 precursor intramuscularly in high-fat diet-fed mice and evaluated glucose tolerance, insulin sensitivity, and adiposity. miR-1-treated mice did not lose weight but had improved insulin sensitivity measured by insulin tolerance test. Next, using an in vitro model of insulin resistance by treating C2C12 cells with palmitic acid (PA), we overexpressed miR-1 and measured p-Akt content and the transcription levels of a protein related to fatty acid oxidation. We found that miR-1 could not restore insulin sensitivity in C2C12 cells, as indicated by p-Akt levels and that miR-1 increased expression of Pgc1a and Cpt1b in PA-treated cells, suggesting a possible role of miR-1 in mitochondrial respiration. Finally, we analyzed mitochondrial oxygen consumption in primary skeletal muscle cells treated with PA and transfected with or without miR-1 mimic. PA-treated cells showed reduced basal respiration, oxygen consumption rate-linked ATP production, maximal and spare capacity, and miR-1 overexpression could prevent impairments in mitochondrial respiration. Our data suggest a role of miR-1 in systemic insulin sensitivity and a new function of miR-1 in regulating mitochondrial respiration in skeletal muscle.

Skeletal Muscle Function Is Dependent Upon BRCA1 to Maintain Genomic Stability.

Breast Cancer gene 1 (BRCA1) is a large, multifunctional protein that regulates a variety of mechanisms in multiple different tissues. Our work established that Brca1 is expressed in skeletal muscle and localizes to the mitochondria and nucleus. Here, we propose BRCA1 expression is critical for the maintenance of force production and mitochondrial respiration in skeletal muscle.

The Influence of High‐Fat Feeding and Exercise Training on Substrate‐Specific Mitochondrial Respiration in Skeletal Muscle of Female Mice

Objective High-fat diet (HFD) induced obesity is associated with excessive lipid supply which drives remodeling of skeletal muscle mitochondria. Exercise stimulates mitochondrial respiration but it is not clear if such adaptations are specific to lipids. Our objective was to determine if HFD-induced obesity would change the sensitivity and capacity for lipid oxidation, and if exercise modifies mitochondrial-specific respiration during HFD. Hypothesis We hypothesized that HFD-induced obesity would increase the sensitivity (intrinsic function) and capacity for lipid respiration while exercise would further augment overall capacity for skeletal muscle mitochondrial substrate oxidation in female mice. Methods We used a 2x2 designof diet and exercise in 10-week old female C57BL/6J mice (n=13-15 per group). Mice consumed diet (either 10% fat or 60% HFD) for 4 weeks then performed 8 weeks of treadmill training for 1 hour per day, 5 days per week or remained sedentary while continuing diet. HFD increased body-weight (P<0.01) by 4 weeks and fat mass measured by dual-energy x-ray absorptiometry at week 12 (P<0.01). We confirmed glucose and insulin intolerance at week 4 of HFD with no change after 8 weeks of treadmill training (P=0.435). Mice rested 24 hours prior to tissue collection. We isolated mitochondria from fresh quadriceps then performed high-resolution respirometry. We measured lipid sensitivity (Km) and capacity (Vmax) using titrations of octanoyl-carnitine (F-linked). Glutamate-succinate were used to determine non-lipid substrate oxidative phosphorylation capacity (N- and S-linked). Primary outcomes were analyzed using 2-way ANOVA (diet x exercise) with Tukey's multiple comparisons (α=0.05). Results The Km for lipid substrates was not different between diet (-7.7%, P=0.66) or exercise (+20.3%, P=0.26) groups. Absolute Vmax was 38% higher in HFD (P=0.018 versus low fat). There was a tendency for 27% higher Vmax after exercise (P=0.074 versus sedentary). For non-lipid substrates, HFD had 23% greater absolute N-linked respiration (P=0.04) and 19% greater S-linked respiration (P=0.02); however, no effects of exercise were detected. Normalizing respiration to mitochondrial protein content eliminated the HFD effects in all substrates. Conclusion We provide evidence that mitochondrial adaptations to HFD, in female mice, are driven primarily by increases in protein abundance rather than intrinsic factors as the normalization of respiration to mitochondrial protein content eliminated HFD effects for increased substrate respiration and there were no differences to lipid sensitivity between diet or exercise. Exercise did not appear to alter the mitochondrial respiratory response to HFD.

Divergent trajectories of cellular bioenergetics, intermediary metabolism and systemic redox status in survivors and non-survivors of critical illness

BackgroundNumerous pathologies result in multiple-organ failure, which is thought to be a direct consequence of compromised cellular bioenergetic status. Neither the nature of this phenotype nor its relevance to survival are well understood, limiting the efficacy of modern life-support. MethodsTo explore the hypothesis that survival from critical illness relates to changes in cellular bioenergetics, we combined assessment of mitochondrial respiration with metabolomic, lipidomic and redox profiling in skeletal muscle and blood, at multiple timepoints, in 21 critically ill patients and 12 reference patients. ResultsWe demonstrate an end-organ cellular phenotype in critical illness, characterized by preserved total energetic capacity, greater coupling efficiency and selectively lower capacity for complex I and fatty acid oxidation (FAO)-supported respiration in skeletal muscle, compared to health. In survivors, complex I capacity at 48 h was 27% lower than in non-survivors (p = 0.01), but tended to increase by day 7, with no such recovery observed in non-survivors. By day 7, survivors’ FAO enzyme activity was double that of non-survivors (p = 0.048), in whom plasma triacylglycerol accumulated. Increases in both cellular oxidative stress and reductive drive were evident in early critical illness compared to health. Initially, non-survivors demonstrated greater plasma total antioxidant capacity but ultimately higher lipid peroxidation compared to survivors. These alterations were mirrored by greater levels of circulating total free thiol and nitrosated species, consistent with greater reductive stress and vascular inflammation, in non-survivors compared to survivors. In contrast, no clear differences in systemic inflammatory markers were observed between the two groups. ConclusionCritical illness is associated with rapid, specific and coordinated alterations in the cellular respiratory machinery, intermediary metabolism and redox response, with different trajectories in survivors and non-survivors. Unravelling the cellular and molecular foundation of human resilience may enable the development of more effective life-support strategies.

Fatigability and Cardiorespiratory Impairments in Parkinson's Disease: Potential Non-Motor Barriers to Activity Performance.

Parkinson’s disease (PD) is the second most common neurodegenerative condition after Alzheimer’s disease, affecting an estimated 160 per 100,000 people 65 years of age or older. Fatigue is a debilitating non-motor symptom frequently reported in PD, often manifesting prior to disease diagnosis, persisting over time, and negatively affecting quality of life. Fatigability, on the other hand, is distinct from fatigue and describes the magnitude or rate of change over time in the performance of activity (i.e., performance fatigability) and sensations regulating the integrity of the performer (i.e., perceived fatigability). While fatigability has been relatively understudied in PD as compared to fatigue, it has been hypothesized that the presence of elevated levels of fatigability in PD results from the interactions of homeostatic, psychological, and central factors. Evidence from exercise studies supports the premise that greater disturbances in metabolic homeostasis may underly elevated levels of fatigability in people with PD when engaging in physical activity. Cardiorespiratory impairments constraining oxygen delivery and utilization may contribute to the metabolic alterations and excessive fatigability experienced in individuals with PD. Cardiorespiratory fitness is often reduced in people with PD, likely due to the combined effects of biological aging and impairments specific to the disease. Decreases in oxygen delivery (e.g., reduced cardiac output and impaired blood pressure responses) and oxygen utilization (e.g., reduced skeletal muscle oxidative capacity) compromise skeletal muscle respiration, forcing increased reliance on anaerobic metabolism. Thus, the assessment of fatigability in people with PD may provide valuable information regarding the functional status of people with PD not obtained with measures of fatigue. Moreover, interventions that target cardiorespiratory fitness may improve fatigability, movement performance, and health outcomes in this patient population.