Nitrosative Stress in Astronaut Skeletal Muscle in Spaceflight

Long-duration mission (LDM) astronauts from the International Space Station (ISS) (>180 ISS days) revealed a close-to-normal sarcolemmal nitric oxide synthase type-1 (NOS1) immunoexpression in myofibers together with biochemical and quantitative qPCR changes in deep calf soleus muscle. Nitro-DIGE analyses identified functional proteins (structural, metabolic, mitochondrial) that were over-nitrosylated post- vs. preflight. In a short-duration mission (SDM) astronaut (9 ISS days), s-nitrosylation of a nodal protein of the glycolytic flux, specific proteins in tricarboxylic acid (TCA) cycle, respiratory chain, and over-nitrosylation of creatine kinase M-types as signs of impaired ATP production and muscle contraction proteins were seen. S-nitrosylation of serotransferrin (TF) or carbonic anhydrase 3 (CA3b and 3c) represented signs of acute response microgravity muscle maladaptation. LDM nitrosoprofiles reflected recovery of mitochondrial activity, contraction proteins, and iron transporter TF as signs of muscle adaptation to microgravity. Nitrosated antioxidant proteins, alcohol dehydrogenase 5/S-nitrosoglutathione reductase (ADH5/GSNOR), and selenoprotein thioredoxin reductase 1 (TXNRD1) levels indicated signs of altered redox homeostasis and reduced protection from nitrosative stress in spaceflight. This work presents a novel spaceflight-generated dataset on s-nitrosylated muscle protein signatures from astronauts that helps both to better understand the structural and molecular networks associated to muscular nitrosative stress and to design countermeasures to dysfunction and impaired performance control in human spaceflight missions.

Oxidative stress and metabolism meet epigenetic modulation in physical exercise

Physical exercise is established as an important factor of health and generally is recommended for its positive effects on several tissues, organs, and systems. These positive effects come from metabolic adaptations that also include oxidative eustress, in which physical activity increases ROS production and antioxidant mechanisms, although this depends on the intensity of the exercise. Muscle metabolism through mechanisms such as aerobic and anaerobic glycolysis, tricarboxylic acid cycle, and oxidative lipid metabolism can produce metabolites and co-factors which directly impact the epigenetic machinery. In this review, we clearly reinforce the evidence that exercise regulates several epigenetic mechanisms and explain how these mechanisms can be regulated by metabolic products and co-factors produced during exercise. In fact, recent evidence has demonstrated the importance of epigenetics in the gene expression changes implicated in metabolic adaptation after exercise. Importantly, intermediates of the metabolism generated by continuous, acute, moderate, or strenuous exercise control the activity of epigenetic enzymes, therefore turning on or turning off the gene expression of specific programs which can lead to physiological adaptations after exercise.

Determinants of the maximal functional reserve during repeated supramaximal exercise by humans: The roles of Nrf2/Keap1, antioxidant proteins, muscle phenotype and oxygenation

When high-intensity exercise is performed until exhaustion a "functional reserve" (FR) or capacity to produce power at the same level or higher than reached at exhaustion exists at task failure, which could be related to reactive oxygen and nitrogen species (RONS)-sensing and counteracting mechanisms. Nonetheless, the magnitude of this FR remains unknown. Repeated bouts of supramaximal exercise at 120% of VO2max interspaced with 20s recovery periods with full ischaemia were used to determine the maximal FR. Then, we determined which muscle phenotypic features could account for the variability in functional reserve in humans. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation (near-infrared spectroscopy) were measured, and resting muscle biopsies were obtained from 43 young healthy adults (30 males). Males and females had similar aerobic (VO2max per kg of lower extremities lean mass (LLM): 166.7 ± 17.1 and 166.1 ± 15.6 ml kg LLM-1.min-1, P = 0.84) and anaerobic fitness (similar performance in the Wingate test and maximal accumulated oxygen deficit when normalized to LLM). The maximal FR was similar in males and females when normalized to LLM (1.84 ± 0.50 and 2.05 ± 0.59 kJ kg LLM-1, in males and females, respectively, P = 0.218). This FR depends on an obligatory component relying on a reserve in glycolytic capacity and a putative component generated by oxidative phosphorylation. The aerobic component depends on brain oxygenation and phenotypic features of the skeletal muscles implicated in calcium handling (SERCA1 and 2 protein expression), oxygen transport and diffusion (myoglobin) and redox regulation (Keap1). The glycolytic component can be predicted by the protein expression levels of pSer40-Nrf2, the maximal accumulated oxygen deficit and the protein expression levels of SOD1. Thus, an increased capacity to modulate the expression of antioxidant proteins involved in RONS handling and calcium homeostasis may be critical for performance during high-intensity exercise in humans.

Regular Sport Activity Is Able to Reduce the Level of Genomic Damage

Regular physical activity is considered one of the most valid tools capable of reducing the risk of onset of many diseases in humans. However, it is known that intense physical activity can induce high levels of genomic damage, while moderate exercise can elicit a favorable adaptive response by the organism. We evaluated, by the buccal micronuclei assay, the frequencies of micronuclei, nuclear buds and binucleated cells in a sample of amateur athletes practicing different disciplines, comparing the obtained data with those of subjects who practiced sports just occasionally and subjects that did not practice sport at all. The aim was to evaluate whether physical activity affects background levels of genomic damage and whether the different sports disciplines, as well as some gene polymorphisms, differentially affect these levels. A total of 206 subjects, 125 athletes and 81 controls, were recruited. Athletes showed significantly lower values of micronuclei, nuclear buds and binucleated cells with respect to controls. Sprinters and Martial Artists displayed significantly higher frequencies of micronuclei than other categories of athletes. Finally, neither sex nor gene polymorphisms seemed to influence the levels of genomic damage, confirming that the observed genomic damage is probably due to the nature of the sport activity.

Intraoperative Hemi-Diaphragm Electrical Stimulation Demonstrates Attenuated Mitochondrial Function without Change in Oxidative Stress in Cardiothoracic Surgery Patients

Mechanical ventilation during cardiothoracic surgery is life-saving but can lead to ventilator-induced diaphragm dysfunction (VIDD) and prolong ventilator weaning and hospital length of stay. Intraoperative phrenic nerve stimulation may preserve diaphragm force production to offset VIDD; we also investigated changes in mitochondrial function after stimulation. During cardiothoracic surgeries (n = 21), supramaximal, unilateral phrenic nerve stimulation was performed every 30 min for 1 min. Diaphragm biopsies were collected after the last stimulation and analyzed for mitochondrial respiration in permeabilized fibers and protein expression and enzymatic activity of biomarkers of oxidative stress and mitophagy. Patients received, on average, 6.2 ± 1.9 stimulation bouts. Stimulated hemidiaphragms showed lower leak respiration, maximum electron transport system (ETS) capacities, oxidative phosphorylation (OXPHOS), and spare capacity compared with unstimulated sides. There were no significant differences between mitochondrial enzyme activities and oxidative stress and mitophagy protein expression levels. Intraoperative phrenic nerve electrical stimulation led to an acute decrease of mitochondrial respiration in the stimulated hemidiaphragm, without differences in biomarkers of mitophagy or oxidative stress. Future studies warrant investigating optimal stimulation doses and testing post-operative chronic stimulation effects on weaning from the ventilator and rehabilitation outcomes.

Two weeks of high-intensity interval training increases skeletal muscle mitochondrial respiration via complex-specific remodeling in sedentary humans

Aerobic training remodels the quantity and quality (function per unit) of skeletal muscle mitochondria to promote substrate oxidation, however, there remain key gaps in understanding the underlying mechanisms during initial training adaptations. We used short-term high-intensity interval training (HIIT) to determine changes to mitochondrial respiration and regulatory pathways that occur early in remodeling. Fifteen normal-weight sedentary adults started seven sessions of HIIT over 14 days and 14 participants completed the intervention. We collected vastus lateralis biopsies before and 48 h after HIIT to determine mitochondrial respiration, RNA sequencing, and Western blotting for proteins of mitochondrial respiration and degradation via autophagy. HIIT increased respiration per mitochondrial protein for lipid (+23% P = 0.020), complex I (+18%, P = 0.0015), complex I + II (+14%, P < 0.0001), and complex II (+24% P < 0.0001). Transcripts that increased with HIIT identified several gene sets of mitochondrial respiration, particularly for complex I, whereas transcripts that decreased identified pathways of DNA and chromatin remodeling. HIIT lowered protein abundance of autophagy markers for p62 (-19%, P = 0.012) and LC3 II/I (-20%, P = 0.004) in whole tissue lysates but not isolated mitochondria. Meal tolerance testing revealed HIIT increased the change in whole body respiratory exchange ratio and lowered cumulative plasma insulin concentrations. Gene transcripts and respiratory function indicate remodeling of mitochondria within 2 wk of HIIT. Overall changes are consistent with increased protein quality driving rapid improvements in substrate oxidation.NEW & NOTEWORTHY Aerobic training stimulates mitochondrial metabolism in skeletal muscle that is linked to improvements to whole body fuel metabolism. The mechanisms driving changes to the quantity and quality (function per unit) of mitochondria are less known. We used seven sessions of high-intensity interval training (HIIT) to determine functional changes and mechanisms of mitochondrial remodeling in skeletal muscle. HIIT increased mitochondrial respiration per mass for fatty acids, complex I, and complex II substrates. HIIT-induced remodeling pathways including gene transcripts for mitochondrial respiration (via RNA sequencing of muscle tissue) and proteins related to complex I respiration. We conclude that an early feature of aerobic training is increased mitochondrial protein quality via improved respiration and induction of mitochondrial transcriptional patterns.

The effect of pre-exercise alkalosis on lactate/pH regulation and mitochondrial respiration following sprint-interval exercise in humans

Purpose: The purpose of this study was to evaluate the effect of pre-exercise alkalosis, induced via ingestion of sodium bicarbonate, on changes to lactate/pH regulatory proteins and mitochondrial function induced by a sprint-interval exercise session in humans. Methods: On two occasions separated by 1 week, eight active men performed a 3 × 30-s all-out cycling test, interspersed with 20 min of recovery, following either placebo (PLA) or sodium bicarbonate (BIC) ingestion. Results: Blood bicarbonate and pH were elevated at all time points after ingestion in BIC vs PLA (p < 0.05). The protein content of monocarboxylate transporter 1 (MCT1) and basigin (CD147), at 6 h and 24 h post-exercise, and sodium/hydrogen exchanger 1 (NHE1) 24 h post-exercise, were significantly greater in BIC compared to PLA (p < 0.05), whereas monocarboxylate transporter 4 (MCT4), sodium/bicarbonate cotransporter (NBC), and carbonic anhydrase isoform II (CAII) content was unchanged. These increases in protein content in BIC vs. PLA after acute sprint-interval exercise may be associated with altered physiological responses to exercise, such as the higher blood pH and bicarbonate concentration values, and lower exercise-induced oxidative stress observed during recovery (p < 0.05). Additionally, mitochondrial respiration decreased after 24 h of recovery in the BIC condition only, with no changes in oxidative protein content in either condition. Conclusion: These data demonstrate that metabolic alkalosis induces post-exercise increases in several lactate/pH regulatory proteins, and reveal an unexpected role for acidosis in mitigating the loss of mitochondrial respiration caused by exercise in the short term.

Polyphenol Supplementation and Antioxidant Status in Athletes: A Narrative Review

Antioxidants in sports exercise training remain a debated research topic. Plant-derived polyphenol supplements are frequently used by athletes to reduce the negative effects of exercise-induced oxidative stress, accelerate the recovery of muscular function, and enhance performance. These processes can be efficiently modulated by antioxidant supplementation. The existing literature has failed to provide unequivocal evidence that dietary polyphenols should be promoted specifically among athletes. This narrative review summarizes the current knowledge regarding polyphenols' bioavailability, their role in exercise-induced oxidative stress, antioxidant status, and supplementation strategies in athletes. Overall, we draw attention to the paucity of available evidence suggesting that most antioxidant substances are beneficial to athletes. Additional research is necessary to reveal more fully their impact on exercise-induced oxidative stress and athletes' antioxidant status, as well as optimal dosing methods.

Adding High-Intensity Interval Training to Classical Resistance Training Does Not Impede the Recovery from Inactivity-Induced Leg Muscle Weakness

Inactivity is known to induce muscle weakness, and chronically increased levels of reactive oxygen species (ROS) are proposed to have a central causative role in this process. Intriguingly, high-intensity interval training (HIIT), which involves bursts of high ROS production, can have positive effects in pathological conditions with chronically increased ROS. Here, young male volunteers were exposed to 3 weeks of unloading of the dominant leg followed by 3 weeks of resistance training without (Ctrl group) or with the addition of all-out cycling HIIT. Changes in muscle thickness were assessed by ultrasonography, and contractile function was studied by measuring the torque during maximal voluntary contractions (MVC). The results show an ~6% decrease in vastus lateralis thickness after the unloading period, which was fully restored after the subsequent training period in both the Ctrl and HIIT groups. MVC torque was decreased by ~11% after the unloading period and recovered fully during the subsequent training period in both groups. All-out cycling performance was improved by the 3 weeks of HIIT. In conclusion, the decline in muscle size and function after 3 weeks of unloading was restored by 3 weeks of resistance training regardless of whether it was combined with HIIT.

Cardiac-specific VEGFB overexpression reduces lipoprotein lipase activity and improves insulin action in rat heart

Cardiac muscle uses multiple sources of energy including glucose and fatty acid (FA). The heart cannot synthesize FA and relies on obtaining it from other sources, with lipoprotein lipase (LPL) breakdown of lipoproteins suggested to be a key source of FA for cardiac use. Recent work has indicated that cardiac vascular endothelial growth factor B (VEGFB) overexpression expands the coronary vasculature and facilitates metabolic reprogramming that favors glucose utilization. We wanted to explore whether this influence of VEGFB on cardiac metabolism involves regulation of LPL activity with consequent effects on lipotoxicity and insulin signaling. The transcriptomes of rats with and without cardiomyocyte-specific overexpression of human VEGFB were compared by using RNA sequencing. Isolated perfused hearts or cardiomyocytes incubated with heparin were used to enable measurement of LPL activity. Untargeted metabolomic analysis was performed for quantification of cardiac lipid metabolites. Cardiac insulin sensitivity was evaluated using fast-acting insulin. Isolated heart and cardiomyocytes were used to determine transgene-encoded VEGFB isoform secretion patterns and mitochondrial oxidative capacity using high-resolution respirometry and extracellular flux analysis. In vitro, transgenic cardiomyocytes incubated overnight and thus exposed to abundantly secreted VEGFB isoforms, in the absence of any in vivo confounding regulators of cardiac metabolism, demonstrated higher basal oxygen consumption. In the whole heart, VEGFB overexpression induced an angiogenic response that was accompanied by limited cardiac LPL activity through multiple mechanisms. This was associated with a lowered accumulation of lipid intermediates, diacylglycerols and lysophosphatidylcholine, that are known to influence insulin action. In response to exogenous insulin, transgenic hearts demonstrated increased insulin sensitivity. In conclusion, the interrogation of VEGFB function on cardiac metabolism uncovered an intriguing and previously unappreciated effect to lower LPL activity and prevent lipid metabolite accumulation to improve insulin action. VEGFB could be a potential cardioprotective therapy to treat metabolic disorders, for example, diabetes.NEW & NOTEWORTHY In hearts overexpressing vascular endothelial growth factor B (VEGFB), besides its known angiogenic response, multiple regulatory mechanisms lowered coronary LPL. This was accompanied by limited cardiac lipid metabolite accumulation with an augmentation of cardiac insulin action. Our data for the first time links VEGFB to coronary LPL in regulation of cardiac metabolism. VEGFB may be cardioprotective in metabolic disorders like diabetes.

Promoting a pro-oxidant state in skeletal muscle: Potential dietary, environmental, and exercise interventions for enhancing endurance-training adaptations

Accumulating evidence now shows that supplemental antioxidants including vitamin C, vitamin E and N-Acetylcysteine consumption can suppress adaptations to endurance-type exercise by attenuating reactive oxygen and nitrogen species (RONS) formation within skeletal muscle. This emerging evidence points to the importance of pro-oxidation as an important stimulus for endurance-training adaptations, including mitochondrial biogenesis, endogenous antioxidant production, insulin signalling, angiogenesis and growth factor signaling. Although sustained oxidative distress is associated with many chronic diseases, athletes have, on average, elevated levels of certain endogenous antioxidants to maintain redox homeostasis. As a result, trained athletes may have a better capacity to buffer oxidants during and after exercise, resulting in a reduced oxidative eustress stimulus for adaptations. Thus, higher levels of RONS input and exercise-induced oxidative stress may benefit athletes in the pursuit of continuous endurance training redox adaptations. This review addresses why athletes should be looking to enhance exercise-induced oxidative stress and how it can be accomplished. Methods covered include high-intensity interval training, hyperthermia and heat stress, dietary antioxidant restriction and modified antioxidant timing, dietary antioxidants and polyphenols as adjuncts to exercise, and vitamin C as a pro-oxidant.

Six weeks of high intensity cycle training reduces H2O2 emission and increases antioxidant protein levels in obese adults with risk factors for type 2 diabetes

Obesity has been associated with increased production of reactive oxygen species (ROS), which may be involved in the development of cardiovascular disease and type 2 diabetes (T2D). Endurance exercise lowers ROS production and increases antioxidant capacity in muscle cells, but it is currently unknown whether high intensity interval training (HIT) elicits the same effects. Twelve sedentary obese subjects at risk of developing T2D took part in a six-week intervention, performing three HIT sessions per week (five 1-min sets of high-intensity cycling (125% of VO₂peak), with 90 s recovery in between sets). Muscle biopsies were obtained for assessment of ROS production (H₂O₂ emission), mitochondrial respiratory capacity, and antioxidant protein levels before and after the intervention. H₂O₂ emission decreased 60.4% after the intervention (Succinate 3 mmol･l^-1), concurrent with a 35.1% increase in protein levels of the antioxidant manganese superoxide dismutase (MnSOD) and a trend towards increased levels of the antioxidant catalase (p = 0.06, 72.9%). These findings were accompanied by a 19% increased mitochondrial respiratory capacity (CI + II), a 6.9% increased VO₂peak and a 1.7% lower body fat percentage. These effects were achieved after just 15 min of high-intensity work and 40 min of total time spent per week. Overall, this suggests that a relatively small amount of HIT is sufficient to induce beneficial effects on ROS production and antioxidant status in muscle cells, which may lower oxidative stress and potentially protect against the development of cardiovascular disease.

Ketogenesis controls mitochondrial gene expression and rescues mitochondrial bioenergetics after cervical spinal cord injury in rats

A better understanding of the secondary injury mechanisms that occur after traumatic spinal cord injury (SCI) is essential for the development of novel neuroprotective strategies linked to the restoration of metabolic deficits. We and others have shown that Ketogenic diet (KD), a high fat, moderate in proteins and low in carbohydrates is neuroprotective and improves behavioural outcomes in rats with acute SCI. Ketones are alternative fuels for mitochondrial ATP generation, and can modulate signaling pathways via targeting specific receptors. Here, we demonstrate that ad libitum administration of KD for 7 days after SCI rescued mitochondrial respiratory capacity, increased parameters of mitochondrial biogenesis, affected the regulation of mitochondrial-related genes, and activated the NRF2-dependent antioxidant pathway. This study demonstrates that KD improves post-SCI metabolism by rescuing mitochondrial function and supports the potential of KD for treatment of acute SCI in humans.

Regular, Intense Exercise Training as a Healthy Aging Lifestyle Strategy: Preventing DNA Damage, Telomere Shortening and Adverse DNA Methylation Changes Over a Lifetime

Exercise training is one of the few therapeutic interventions that improves health span by delaying the onset of age-related diseases and preventing early death. The length of telomeres, the 5'-TTAGGG n -3' tandem repeats at the ends of mammalian chromosomes, is one of the main indicators of biological age. Telomeres undergo shortening with each cellular division. This subsequently leads to alterations in the expression of several genes that encode vital proteins with critical functions in many tissues throughout the body, and ultimately impacts cardiovascular, immune and muscle physiology. The sub-telomeric DNA is comprised of heavily methylated, heterochromatin. Methylation and histone acetylation are two of the most well-studied examples of the epigenetic modifications that occur on histone proteins. DNA methylation is the type of epigenetic modification that alters gene expression without modifying gene sequence. Although diet, genetic predisposition and a healthy lifestyle seem to alter DNA methylation and telomere length (TL), recent evidence suggests that training status or physical fitness are some of the major factors that control DNA structural modifications. In fact, TL is positively associated with cardiorespiratory fitness, physical activity level (sedentary, active, moderately trained, or elite) and training intensity, but is shorter in over-trained athletes. Similarly, somatic cells are vulnerable to exercise-induced epigenetic modification, including DNA methylation. Exercise-training load, however, depends on intensity and volume (duration and frequency). Training load-dependent responses in genomic profiles could underpin the discordant physiological and physical responses to exercise. In the current review, we will discuss the role of various forms of exercise training in the regulation of DNA damage, TL and DNA methylation status in humans, to provide an update on the influence exercise training has on biological aging.

Functional reserve and sex differences during exercise to exhaustion revealed by post-exercise ischaemia and repeated supramaximal exercise

KEY POINTS

Females have lower fatigability than males during single limb isometric and dynamic contractions, but whether sex-differences exist during high-intensity whole-body exercise remains unknown. This study shows that males and females respond similarly to repeated supramaximal whole-body exercise, and that at task failure a large functional reserve remains in both sexes. Using post-exercise ischaemia with repeated exercise, we have shown that this functional reserve depends on the glycolytic component of substrate-level phosphorylation and is almost identical in both sexes. Metaboreflex activation during post-exercise ischaemia and the O₂ debt per kg of active lean mass are also similar in males and females after supramaximal exercise. Females have a greater capacity to extract oxygen during repeated supramaximal exercise and reach lower P ETC O 2 , experiencing a larger drop in brain oxygenation than males, without apparent negative repercussion on performance. Females had no faster recovery of performance after accounting for sex differences in lean mass.

ABSTRACT

The purpose of this study was to ascertain what mechanisms explain sex differences at task failure and to determine whether males and females have a functional reserve at exhaustion. Exercise performance, cardiorespiratory variables, oxygen deficit, and brain and muscle oxygenation were determined in 18 males and 18 females (21-36 years old) in two sessions consisting of three bouts of constant-power exercise at 120% of V ̇ O 2 max until exhaustion interspaced by 20 s recovery periods. In one of the two sessions, the circulation of both legs was occluded instantaneously (300 mmHg) during the recovery periods. Females had a higher muscle O₂ extraction during fatiguing supramaximal exercise than males. Metaboreflex activation, and lean mass-adjusted O₂ deficit and debt were similar in males and females. Compared to males, females reached lower P ETC O 2 and brain oxygenation during supramaximal exercise, without apparent negative consequences on performance. After the occlusions, males and females were able to restart exercising at 120% of V ̇ O 2 max , revealing a similar functional reserve, which depends on glycolytic component of substrate-level phosphorylation and its rate of utilization. After ischaemia, muscle O₂ extraction was increased, and muscle V ̇ O 2 was similarly reduced in males and females. The physiological response to repeated supramaximal exercise to exhaustion is remarkably similar in males and females when differences in lean mass are considered. Both sexes fatigue with a large functional reserve, which depends on the glycolytic energy supply, yet females have higher oxygen extraction capacity, but reduced P ETC O 2 and brain oxygenation.

Mitoquinone mesylate (MitoQ) prevents sepsis-induced diaphragm dysfunction

Sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. There are no pharmacological treatments for this syndrome, but studies suggest that diaphragm weakness is linked to mitochondrial free radical generation. We hypothesized that administration of mitoquinone mesylate (MitoQ), a mitochondrially targeted free radical scavenger, would prevent sepsis-induced diaphragm dysfunction. We compared diaphragm function in 4 groups of male mice: 1) sham-operated controls treated with saline (0.3 mL ip), 2) sham-operated treated with MitoQ (3.5 mg/kg/day given intraperitoneally in saline), 3) cecal ligation puncture (CLP) mice treated with saline, and 4) CLP mice treated with MitoQ. Forty-eight hours after surgery, we assessed diaphragm force generation, myosin heavy chain content, state 3 mitochondrial oxygen consumption (OCR), and aconitase activity. We also determined effects of MitoQ in female mice with CLP sepsis and in mice with endotoxin-induced sepsis. CLP decreased diaphragm specific force generation and MitoQ prevented these decrements (e.g. maximal force averaged 30.2 ± 1.3, 28.0 ± 1.3, 12.8 ± 1.9, and 30.0 ± 1.0 N/cm² for sham, sham + MitoQ, CLP, and CLP + MitoQ groups, respectively, P < 0.001). CLP also reduced diaphragm mitochondrial OCR and aconitase activity; MitoQ blocked both effects. Similar responses were observed in female mice and in endotoxin-induced sepsis. Moreover, delayed MitoQ treatment (by 6 h) was as effective as immediate treatment. These data indicate that MitoQ prevents sepsis-induced diaphragm dysfunction, preserving force generation. MitoQ may be a useful therapeutic agent to preserve diaphragm function in critically ill patients with sepsis.NEW & NOTEWORTHY This is the first study to show that mitoquinone mesylate (MitoQ), a mitochondrially targeted antioxidant, treats sepsis-induced skeletal muscle dysfunction. This biopharmaceutical agent is without known side effects and is currently being used by healthy individuals and in clinical trials in patients with various diseases. When taken together, our results suggest that MitoQ has the potential to be immediately translated into treatment for sepsis-induced skeletal muscle dysfunction.

Short-term intensified training temporarily impairs mitochondrial respiratory capacity in elite endurance athletes

The maintenance of healthy and functional mitochondria is the result of a complex mitochondrial turnover and herein quality-control program that includes both mitochondrial biogenesis and autophagy of mitochondria. The aim of this study was to examine the effect of an intensified training load on skeletal muscle mitochondrial quality control in relation to changes in mitochondrial oxidative capacity, maximal oxygen consumption, and performance in highly trained endurance athletes. Elite endurance athletes (n = 27) performed high-intensity interval exercise followed by moderate-intensity continuous exercise 3 days per week for 4 wk in addition to their usual volume of training. Mitochondrial oxidative capacity, abundance of mitochondrial proteins, markers of autophagy, and antioxidant capacity of skeletal muscle were assessed in skeletal muscle biopsies before and after the intensified training period. The intensified training period increased several autophagy markers suggesting an increased turnover of mitochondrial and cytosolic proteins. In permeabilized muscle fibers, mitochondrial respiration was ∼20% lower after training although some markers of mitochondrial density increased by 5%-50%, indicative of a reduced mitochondrial quality by the intensified training intervention. The antioxidative proteins UCP3, ANT1, and SOD2 were increased after training, whereas we found an inactivation of aconitase. In agreement with the lower aconitase activity, the amount of mitochondrial LON protease that selectively degrades oxidized aconitase was doubled. Together, this suggests that mitochondrial respiratory function is impaired during the initial recovery from a period of intensified endurance training whereas mitochondrial quality control is slightly activated in highly trained skeletal muscle.NEW & NOTEWORTHY We show that mitochondrial respiration is temporarily impaired after a period of intensified exercise training in elite athletes. In parallel, proteins involved in the antioxidative response including SOD2, UCP3, and ANT2 were upregulated, whereas mitochondrial biogenesis was slightly activated. Despite the mitochondrial respiratory impairments, physical performance was improved a few days after the intense training period.

Excessive exercise training causes mitochondrial functional impairment and decreases glucose tolerance in healthy volunteers

Exercise training positively affects metabolic health through increased mitochondrial oxidative capacity and improved glucose regulation and is the first line of treatment in several metabolic diseases. However, the upper limit of the amount of exercise associated with beneficial therapeutic effects has not been clearly identified. Here, we used a training model with a progressively increasing exercise load during an intervention over 4 weeks. We closely followed changes in glucose tolerance, mitochondrial function and dynamics, physical exercise capacity, and whole-body metabolism. Following the week with the highest exercise load, we found a striking reduction in intrinsic mitochondrial function that coincided with a disturbance in glucose tolerance and insulin secretion. We also assessed continuous blood glucose profiles in world-class endurance athletes and found that they had impaired glucose control compared with a matched control group.

Enhanced Skeletal Muscle Oxidative Capacity and Capillary-to-Fiber Ratio Following Moderately Increased Testosterone Exposure in Young Healthy Women

Background: Recently, it was shown that exogenously administered testosterone enhances endurance capacity in women. In this study, our understanding on the effects of exogenous testosterone on key determinants of oxygen transport and utilization in skeletal muscle is expanded.

Methods: In a double-blinded, randomized, placebo-controlled trial, 48 healthy active women were randomized to 10 weeks of daily application of 10 mg of testosterone cream or placebo. Before and after the intervention, VO₂ max, body composition, total hemoglobin (Hb) mass and blood volumes were assessed. Biopsies from the vastus lateralis muscle were obtained before and after the intervention to assess mitochondrial protein abundance, capillary density, capillary-to-fiber (C/F) ratio, and skeletal muscle oxidative capacity.

Results: Maximal oxygen consumption per muscle mass, Hb mass, blood, plasma and red blood cell volumes, capillary density, and the abundance of mitochondrial protein levels (i.e., citrate synthase, complexes I, II, III, IV-subunit 2, IV-subunit 4, and V) were unchanged by the intervention. However, the C/F ratio, specific mitochondrial respiratory flux activating complex I and linked complex I and II, uncoupled respiration and electron transport system capacity, but not leak respiration or fat respiration, were significantly increased following testosterone administration compared to placebo.

Conclusion: This study provides novel insights into physiological actions of increased testosterone exposure on key determinants of oxygen diffusion and utilization in skeletal muscle of women. Our findings show that higher skeletal muscle oxidative capacity coupled to higher C/F ratio could be major contributing factors that improve endurance performance following moderately increased testosterone exposure.

Effects of including sprints during prolonged cycling on hormonal and muscular responses and recovery in elite cyclists

This study investigated the acute effects of including 30‐second sprints during prolonged low‐intensity cycling on muscular and hormonal responses and recovery in elite cyclists. Twelve male cyclists (VO_2max, 73.4 ± 4.0 mL/kg/min) completed a randomized crossover protocol, wherein 4 hours of cycling at 50% of VO_2max were performed with and without inclusion of three sets of 3 × 30 seconds maximal sprints (E&S vs E, work‐matched). Muscle biopsies (m. vastus lateralis) and blood were sampled at Pre, immediately after (Post) and 3 hours after (3 h) finalizing sessions. E&S led to greater increases in mRNA levels compared with E for markers of fat metabolism (PDK4, Δ‐Log2 fold change between E&S and E ± 95%CI Post; 2.1 ± 0.9, Δ3h; 1.3 ± 0.7) and angiogenesis (VEGFA, Δ3h; 0.3 ± 0.3), and greater changes in markers of muscle protein turnover (myostatin, ΔPost; −1.4 ± 1.2, Δ3h; −1.3 ± 1.3; MuRF1, ΔPost; 1.5 ± 1.2, all P < .05). E&S showed decreased mRNA levels for markers of ion transport at 3h (Na⁺‐K⁺ α1; −0.6 ± 0.6, CLC1; −1.0 ± 0.8 and NHE1; −0.3 ± 0.2, all P < .05) and blunted responses for a marker of mitochondrial biogenesis (PGC‐1α, Post; −0.3 ± 0.3, 3h; −0.4 ± 0.3, P < .05) compared with EE&S and E showed similar endocrine responses, with exceptions of GH and SHBG, where E&S displayed lower responses at Post (GH; −4.1 ± 3.2 μg/L, SHBG; −2.2 ± 1.9 nmol/L, P < .05). Both E&S and E demonstrated complete recovery in isokinetic knee extension torque 24 hours after exercise. In conclusion, we demonstrate E&S to be an effective exercise protocol for elite cyclists, which potentially leads to beneficial adaptations in skeletal muscle without impairing muscle recovery 24 hours after exercise.

Contribution of oxygen extraction fraction to maximal oxygen uptake in healthy young men

We analysed the importance of systemic and peripheral arteriovenous O₂ difference ( a-v¯O2 difference and a‐v_fO₂ difference, respectively) and O₂ extraction fraction for maximal oxygen uptake ( V˙O2max). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V˙O2max. Articles (n = 17) publishing individual data (n = 154) on V˙O2max, maximal cardiac output ( Q˙max; indicator‐dilution or the Fick method), a-v¯O2 difference (catheters or the Fick equation) and systemic O₂ extraction fraction were identified. For the peripheral responses, group‐mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a‐v_fO₂ difference and O₂ extraction fraction (arterial and femoral venous catheters) were obtained. Q˙max and two‐LBF increased linearly by 4.9‐6.0 L · min^–1 per 1 L · min^–1 increase in V˙O2max (R² = .73 and R² = .67, respectively; both P < .001). The a-v¯O2 difference increased from 118‐168 mL · L^–1 from a V˙O2max of 2‐4.5 L · min^–1 followed by a reduction (second‐order polynomial: R² = .27). After accounting for a hypoxemia‐induced decrease in arterial O₂ content with increasing V˙O2max (R² = .17; P < .001), systemic O₂ extraction fraction increased up to ~90% ( V˙O2max: 4.5 L · min^–1) with no further change (exponential decay model: R² = .42). Likewise, leg O₂ extraction fraction increased with V˙O2max to approach a maximal value of ~90‐95% (R² = .83). Muscle O₂ diffusing capacity and the equilibration index Y increased linearly with V˙O2max (R² = .77 and R² = .31, respectively; both P < .01), reflecting decreasing O₂ diffusional limitations and accentuating O₂ delivery limitations. In conclusion, although O₂ delivery is the main limiting factor to V˙O2max, enhanced O₂ extraction fraction (≥90%) contributes to the remarkably high V˙O2max in endurance‐trained individuals.

Convergent changes in muscle metabolism depend on duration of high-altitude ancestry across Andean waterfowl

High-altitude environments require that animals meet the metabolic O2 demands for locomotion and thermogenesis in O2-thin air, but the degree to which convergent metabolic changes have arisen across independent high-altitude lineages or the speed at which such changes arise is unclear. We examined seven high-altitude waterfowl that have inhabited the Andes (3812-4806 m elevation) over varying evolutionary time scales, to elucidate changes in biochemical pathways of energy metabolism in flight muscle relative to low-altitude sister taxa. Convergent changes across high-altitude taxa included increased hydroxyacyl-coA dehydrogenase and succinate dehydrogenase activities, decreased lactate dehydrogenase, pyruvate kinase, creatine kinase, and cytochrome c oxidase activities, and increased myoglobin content. ATP synthase activity increased in only the longest established high-altitude taxa, whereas hexokinase activity increased in only newly established taxa. Therefore, changes in pathways of lipid oxidation, glycolysis, and mitochondrial oxidative phosphorylation are common strategies to cope with high-altitude hypoxia, but some changes require longer evolutionary time to arise.

Mitochondrial oxygen affinity increases after sprint interval training and is related to the improvement in peak oxygen uptake

AIMS

The body responds to exercise training by profound adaptations throughout the cardiorespiratory and muscular systems, which may result in improvements in maximal oxygen consumption (VO₂ peak) and mitochondrial capacity. By convenience, mitochondrial respiration is often measured at supra-physiological oxygen levels, an approach that ignores any potential regulatory role of mitochondrial affinity for oxygen (p50_mito ) at physiological oxygen levels.

METHODS

In this study, we examined the p50_mito of mitochondria isolated from the Vastus lateralis and Triceps brachii in 12 healthy volunteers before and after a training intervention with seven sessions of sprint interval training using both leg cycling and arm cranking. The changes in p50_mito were compared to changes in whole-body VO₂ peak.

RESULTS

We here show that p50_mito is similar in isolated mitochondria from the Vastus (40 ± 3.8 Pa) compared to Triceps (39 ± 3.3) but decreases (mitochondrial oxygen affinity increases) after seven sessions of sprint interval training (to 26 ± 2.2 Pa in Vastus and 22 ± 2.7 Pa in Triceps, both P < .01). The change in VO₂ peak modelled from changes in p50_mito was correlated to actual measured changes in VO₂ peak (R²  = .41, P = .002).

CONCLUSION

Together with mitochondrial respiratory capacity, p50_mito is a critical factor when measuring mitochondrial function, it can decrease with sprint interval training and should be considered in the integrative analysis of the oxygen cascade from lung to mitochondria.

Nitric oxide regulates ganoderic acid biosynthesis by the S-nitrosylation of aconitase under heat stress in Ganoderma lucidum

Nitric oxide (NO) is an important signalling molecule in stress response of organisms. We previously reported that NO decreases heat stress (HS)-induced ganoderic acid (GA) accumulation in Ganoderma lucidum. To explore the mechanisms by which NO modulates GA biosynthesis under HS, the effect of NO on the reactive oxygen species (ROS) content was examined. The results showed that NO decreased the production of mitochondrial ROS (mitROS) by 60% under HS. Further research revealed that NO reduced the mitROS content by inhibiting aconitase (Acon) activity. The GA content in Acon-silenced (Aconi) strains treated with NO donor did not differ significantly from that in untreated Aconi strains. To study the mechanism by which Acon activity is inhibited, the S-nitrosylation level of Acon was determined. Biotin-switch technology and mass spectrometry analysis were used to show that Acon is S-nitrosylated at the Cys-594 amino acid residue. Substitution of Cys-594 with a Ser, which cannot be S-nitrosylated, abolished the responsiveness of Acon to the NO-induced reduction in its enzymatic activity. These findings demonstrate that NO inhibits Acon activity through S-nitrosylation at Cys-594. In summary, these findings describe mechanism by which NO regulates GA biosynthesis via S-nitrosylation of Acon under HS condition in G. lucidum.

MitoTEMPOL, a mitochondrial targeted antioxidant, prevents sepsis-induced diaphragm dysfunction

Clinical studies indicate that sepsis-induced diaphragm dysfunction is a major contributor to respiratory failure in mechanically ventilated patients. Currently there is no drug to treat this form of diaphragm weakness. Sepsis-induced muscle dysfunction is thought to be triggered by excessive mitochondrial free radical generation; we therefore hypothesized that therapies that target mitochondrial free radical production may prevent sepsis-induced diaphragm weakness. The present study determined whether MitoTEMPOL, a mitochondrially targeted free radical scavenger, could reduce sepsis-induced diaphragm dysfunction. Using an animal model of sepsis, we compared four groups of mice: 1) sham-operated controls, 2) animals with sepsis induced by cecal ligation puncture (CLP), 3) sham controls given MitoTEMPOL (10 mg·kg^-1·day^-1 ip), and 4) CLP animals given MitoTEMPOL. At 48 h after surgery, we measured diaphragm force generation, mitochondrial function, proteolytic enzyme activities, and myosin heavy chain (MHC) content. We also examined the effects of delayed administration of MitoTEMPOL (by 6 h) on CLP-induced diaphragm weakness. The effects of MitoTEMPOL on cytokine-mediated alterations on muscle cell superoxide generation and cell size in vitro were also assessed. Sepsis markedly reduced diaphragm force generation. Both immediate and delayed MitoTEMPOL administration prevented sepsis-induced diaphragm weakness. MitoTEMPOL reversed sepsis-mediated reductions in mitochondrial function, activation of proteolytic pathways, and decreases in MHC content. Cytokines increased muscle cell superoxide generation and decreased cell size, effects that were ablated by MitoTEMPOL. MitoTEMPOL and other compounds that target mitochondrial free radical generation may be useful therapies for sepsis-induced diaphragm weakness.

SS31, a mitochondrially targeted antioxidant, prevents sepsis-induced reductions in diaphragm strength and endurance

Sepsis-induced diaphragm dysfunction contributes to respiratory failure and mortality in critical illness. There are no treatments for this form of diaphragm weakness. Studies show that sepsis-induced muscle dysfunction is triggered by enhanced mitochondrial free radical generation. We tested the hypothesis that SS31, a mitochondrially targeted antioxidant, would attenuate sepsis-induced diaphragm dysfunction. Four groups of mice were studied: 1) sham-operated controls, 2) sham-operated+SS31 (10 mg·kg-1·day-1), 3) cecal ligation puncture (CLP), and 4) CLP+SS31. Forty-eight hours postoperatively, diaphragm strips with attached phrenic nerves were isolated, and the following were assessed: muscle-field-stimulated force-frequency curves, nerve-stimulated force-frequency curves, and muscle fatigue. We also measured calpain activity, 20S proteasomal activity, myosin heavy chain (MHC) levels, mitochondrial function, and aconitase activity, an index of mitochondrial superoxide generation. Sepsis markedly reduced diaphragm force generation; SS31 prevented these decrements. Diaphragm-specific force generation averaged 30.2 ± 1.4, 9.4 ± 1.8, 25.5 ± 2.3, and 27.9 ± 0.6 N/cm2 for sham, CLP, sham+SS31, and CLP+SS31 groups (P < 0.001). Similarly, with phrenic nerve stimulation, CLP depressed diaphragm force generation, effects prevented by SS31. During endurance trials, force was significantly reduced with CLP, and SS31 prevented these reductions (P < 0.001). Sepsis also increased diaphragm calpain activity, increased 20S proteasomal activity, decreased MHC levels, reduced mitochondrial function (state 3 rates and ATP generation), and reduced aconitase activity; SS31 prevented each of these sepsis-induced alterations (P ≤ 0.017 for all indices). SS31 prevents sepsis-induced diaphragm dysfunction, preserving force generation, endurance, and mitochondrial function. Compounds with similar mechanisms of action may be useful therapeutically to preserve diaphragm function in patients who are septic and critically ill.NEW & NOTEWORTHY Sepsis-induced diaphragm dysfunction is a major contributor to mortality and morbidity in patients with critical illness in intensive care units. Currently, there is no proven pharmacological treatment for this problem. This study provides the novel finding that administration of SS31, a mitochondrially targeted antioxidant, preserves diaphragm myosin heavy chain content and mitochondrial function, thereby preventing diaphragm weakness and fatigue in sepsis.

An integrative approach to the regulation of mitochondrial respiration during exercise: Focus on high-intensity exercise

During exercise, muscle ATP demand increases with intensity, and at the highest power output, ATP consumption may increase more than 100-fold above the resting level. The rate of mitochondrial ATP production during exercise depends on the availability of O₂, carbon substrates, reducing equivalents, ADP, P_i, free creatine, and Ca²⁺. It may also be modulated by acidosis, nitric oxide and reactive oxygen and nitrogen species (RONS). During fatiguing and repeated sprint exercise, RONS production may cause oxidative stress and damage to cellular structures and may reduce mitochondrial efficiency. Human studies indicate that the relatively low mitochondrial respiratory rates observed during sprint exercise are not due to lack of O₂, or insufficient provision of Ca²⁺, reduced equivalents or carbon substrates, being a suboptimal stimulation by ADP the most plausible explanation. Recent in vitro studies with isolated skeletal muscle mitochondria, studied in conditions mimicking different exercise intensities, indicate that ROS production during aerobic exercise amounts to 1-2 orders of magnitude lower than previously thought. In this review, we will focus on the mechanisms regulating mitochondrial respiration, particularly during high-intensity exercise. We will analyze the factors that limit mitochondrial respiration and those that determine mitochondrial efficiency during exercise. Lastly, the differences in mitochondrial respiration between men and women will be addressed.

Mitochondrial respiration variability and simulations in human skeletal muscle: The Gene SMART study

Mitochondrial respiration using the oxygraph‐2k respirometer (Oroboros) is widely used to estimate mitochondrial capacity in human skeletal muscle. Here, we measured mitochondrial respiration variability, in a relatively large sample, and for the first time, using statistical simulations, we provide the sample size required to detect meaningful respiration changes following lifestyle intervention. Muscle biopsies were taken from healthy, young men from the Gene SMART cohort, at multiple time points. We utilized samples for each measurement with two technical repeats using two respirometer chambers (n = 160 pairs of same muscle after removal of low‐quality samples). We measured the Technical Error of measurement (TE_M) and the coefficient of variation (CV) for each mitochondrial complex. There was a high correlation between measurements from the two chambers (R > 0.7 P < .001) for all complexes, but the TE_M was large (7.9‐27 pmol s⁻¹ mg⁻¹; complex dependent), and the CV was >15% for all complexes. We performed statistical simulations of a range of effect sizes at 80% power and found that 75 participants (with duplicate measurements) are required to detect a 6% change in mitochondrial respiration after an intervention, while for interventions with 11% effect size, ~24 participants are sufficient. The high variability in respiration suggests that the typical sample sizes in exercise studies may not be sufficient to capture exercise‐induced changes.

Aconitases: Non-redox Iron-Sulfur Proteins Sensitive to Reactive Species

Mammalian aconitases (mitochondrial and cytosolic isoenzymes) are unique iron-sulfur cluster-containing proteins in which the metallic center participates in the catalysis of a non-redox reaction. Within the cubane iron-sulfur cluster of aconitases only three of the four iron ions have cysteine thiolate ligands; the fourth iron ion (Fe_α) is solvent exposed within the active-site pocket and bound to oxygen atoms from either water or substrates to be dehydrated. The catalyzed reaction is the reversible isomerization of citrate to isocitrate with an intermediate metabolite, cis-aconitate. The cytosolic isoform of aconitase is a moonlighting enzyme; when intracellular iron is scarce, the complete disassembly of the iron-sulfur cluster occurs and apo-aconitase acquires the function of an iron responsive protein and regulates the translation of proteins involved in iron metabolism. In the late 1980s and during the 1990s, cumulative experimental evidence pointed out that aconitases are main targets of reactive oxygen and nitrogen species such as superoxide radical (O₂^•-), hydrogen peroxide (H₂O₂), nitric oxide (^•NO), and peroxynitrite (ONOO^-). These intermediates are capable of oxidizing the cluster, which leads to iron release and consequent loss of the catalytic activity of aconitase. As the reaction of the Fe-S cluster with O₂^•- is fast (∼10⁷ M^-1 s^-1), quite specific, and reversible in vivo, quantification of active aconitase has been used to evaluate O₂^•- formation in cells. While ^•NO is modestly reactive with aconitase, its reaction with O₂^•- yields ONOO^-, a strong oxidant that readily leads to the disruption of the Fe-S cluster. In the case of cytosolic aconitase, it has been seen that H₂O₂ and ^•NO promote activation of iron responsive protein activity in cells. Proteomic advances in the 2000s confirmed that aconitases are main targets of reactive species in cellular models and in vivo, and other post-translational oxidative modifications such as protein nitration and carbonylation have been detected. Herein, we (1) outline the particular structural features of aconitase that make these proteins specific targets of reactive species, (2) characterize the reactions of O₂^•-, H₂O₂, ^•NO, and ONOO^- and related species with aconitases, (3) discuss how different oxidative post-translational modifications of aconitase impact the different functions of aconitases, and (4) argue how these proteins might function as redox sensors within different cellular compartments, regulating citrate concentration and efflux from mitochondria, iron availability in the cytosol, and cellular oxidant production.

Human muscular mitochondrial fusion in athletes during exercise

The main objective of this work was to investigate whether mitochondrial fusion occurs in the skeletal muscle of well-trained athletes in response to high-intensity exercise. Well-trained swimmers (n = 9) performed a duration-matched sprint interval training (SIT) and high-intensity high-volume training (HIHVT) session on separate days. Muscle samples from triceps brachii were taken before, immediately after, and 3 h after the training sessions. Transmission electron microscopy (TEM) was applied to assess mitochondrial morphology. Moreover, expression of genes coding for regulators of mitochondrial fusion and fission were assessed by real-time quantitative PCR. In addition, mitofusin (MFN)2 and optic atrophy 1 (OPA1) were quantified by Western blot analysis. TEM analyses showed that mitochondrial morphology remained altered for 3 h after HIHVT, whereas SIT-induced changes were only evident immediately after exercise. Only SIT increased MFN1 and MFN2 mRNA expression, whereas SIT and HIHVT both increased MFN2 protein content 3 h after exercise. Notably, only HIHVT increased OPA1 protein content. Mitochondrial morphologic changes that suggest fusion occurs in well-adapted athletes during exercise. However, HIHVT appears as a more robust inducer of mitochondrial fusion events than SIT. Indeed, SIT induces a rapid and transient change in mitochondrial morphology.-Huertas, J. R., Ruiz-Ojeda, F. J., Plaza-Díaz, J., Nordsborg, N. B., Martín-Albo, J., Rueda-Robles, A., Casuso, R. A. Human muscular mitochondrial fusion in athletes during exercise.

Acute High-Intensity Exercise Impairs Skeletal Muscle Respiratory Capacity

PURPOSE

The effect of an acute bout of exercise, especially high-intensity exercise, on the function of mitochondrial respiratory complexes is not well understood, with potential implications for both the healthy population and patients undergoing exercise-based rehabilitation. Therefore, this study sought to comprehensively examine respiratory flux through the different complexes of the electron transport chain in skeletal muscle mitochondria before and immediately after high-intensity aerobic exercise.

METHODS

Muscle biopsies of the vastus lateralis were obtained at baseline and immediately after a 5-km time trial performed on a cycle ergometer. Mitochondrial respiratory flux through the complexes of the electron transport chain was measured in permeabilized skeletal muscle fibers by high-resolution respirometry.

RESULTS

Complex I + II state 3 (state 3CI + CII) respiration, a measure of oxidative phosphorylation capacity, was diminished immediately after the exercise (pre, 27 ± 3 ρm·mg·s; post, 17 ± 2 ρm·mg·s; P < 0.05). This decreased oxidative phosphorylation capacity was predominantly the consequence of attenuated complex II-driven state 3 (state 3CII) respiration (pre, 17 ± 1 ρm·mg·s; post, 9 ± 2 ρm·mg·s; P < 0.05). Although complex I-driven state 3 (3CI) respiration was also lower (pre, 20 ± 2 ρm·mg·s; post, 14 ± 4 ρm·mg·s), this did not reach statistical significance (P = 0.27). In contrast, citrate synthase activity, proton leak (state 2 respiration), and complex IV capacity were not significantly altered immediately after the exercise.

CONCLUSIONS

These findings reveal that acute high-intensity aerobic exercise significantly inhibits skeletal muscle state 3CII and oxidative phosphorylation capacity. This, likely transient, mitochondrial defect might amplify the exercise-induced development of fatigue and play an important role in initiating exercise-induced mitochondrial adaptations.

Stay Fit, Stay Young: Mitochondria in Movement: The Role of Exercise in the New Mitochondrial Paradigm

Skeletal muscles require the proper production and distribution of energy to sustain their work. To ensure this requirement is met, mitochondria form large networks within skeletal muscle cells, and during exercise, they can enhance their functions. In the present review, we discuss recent findings on exercise-induced mitochondrial adaptations. We emphasize the importance of mitochondrial biogenesis, morphological changes, and increases in respiratory supercomplex formation as mechanisms triggered by exercise that may increase the function of skeletal muscles. Finally, we highlight the possible effects of nutraceutical compounds on mitochondrial performance during exercise and outline the use of exercise as a therapeutic tool in noncommunicable disease prevention. The resulting picture shows that the modulation of mitochondrial activity by exercise is not only fundamental for physical performance but also a key point for whole-organism well-being.

High-intensity exercise training enhances mitochondrial oxidative phosphorylation efficiency in a temperature-dependent manner in human skeletal muscle: implications for exercise performance

The purpose of the present study was to investigate whether exercise training-induced adaptations in human skeletal muscle mitochondrial bioenergetics are magnified under thermal conditions resembling sustained intense contractile activity and whether training-induced changes in mitochondrial oxidative phosphorylation (OXPHOS) efficiency influence exercise efficiency. Twenty healthy men performed 6 wk of high-intensity exercise training [i.e., speed endurance training (SET; n = 10)], or maintained their usual lifestyle (n = 10). Before and after the intervention, mitochondrial respiratory function was determined ex vivo in permeabilized muscle fibers under experimentally-induced normothermia (35°C) and hyperthermia (40°C) mimicking in vivo muscle temperature at rest and during intense exercise, respectively. In addition, activity and content of muscle mitochondrial enzymes and proteins were quantified. Exercising muscle efficiency was determined in vivo by measurements of leg hemodynamics and blood parameters during one-legged knee-extensor exercise. SET enhanced maximal OXPHOS capacity and OXPHOS efficiency at 40°C, but not at 35°C, and attenuated hyperthermia-induced decline in OXPHOS efficiency. Furthermore, SET increased expression of markers of mitochondrial content and up-regulated content of MFN2, DRP1, and ANT1. Also, SET improved exercise efficiency and capacity. These findings indicate that muscle mitochondrial bioenergetics adapts to high-intensity exercise training in a temperature-dependent manner and that enhancements in mitochondrial OXPHOS efficiency may contribute to improving exercise performance.-Fiorenza, M., Lemminger, A. K., Marker, M., Eibye, K., Iaia, F. M., Bangsbo, J., Hostrup, M. High-intensity exercise training enhances mitochondrial oxidative phosphorylation efficiency in a temperature-dependent manner in human skeletal muscle: implications for exercise performance.

Enhancement of Exercise Performance by 48 Hours, and 15-Day Supplementation with Mangiferin and Luteolin in Men

The natural polyphenols mangiferin and luteolin have free radical-scavenging properties, induce the antioxidant gene program and down-regulate the expression of superoxide-producing enzymes. However, the effects of these two polyphenols on exercise capacity remains mostly unknown. To determine whether a combination of luteolin (peanut husk extract containing 95% luteolin, PHE) and mangiferin (mango leave extract (MLE), Zynamite^®) at low (PHE: 50 mg/day; and 140 mg/day of MLE containing 100 mg of mangiferin; L) and high doses (PHE: 100 mg/day; MLE: 420 mg/day; H) may enhance exercise performance, twelve physically active men performed incremental exercise to exhaustion, followed by sprint and endurance exercise after 48 h (acute effects) and 15 days of supplementation (prolonged effects) with polyphenols or placebo, following a double-blind crossover design. During sprint exercise, mangiferin + luteolin supplementation enhanced exercise performance, facilitated muscle oxygen extraction, and improved brain oxygenation, without increasing the VO₂. Compared to placebo, mangiferin + luteolin increased muscle O₂ extraction during post-exercise ischemia, and improved sprint performance after ischemia-reperfusion likely by increasing glycolytic energy production, as reflected by higher blood lactate concentrations after the sprints. Similar responses were elicited by the two doses tested. In conclusion, acute and prolonged supplementation with mangiferin combined with luteolin enhances performance, muscle O₂ extraction, and brain oxygenation during sprint exercise, at high and low doses.

Principles of Exercise Prescription, and How They Influence Exercise-Induced Changes of Transcription Factors and Other Regulators of Mitochondrial Biogenesis

Physical inactivity represents the fourth leading risk factor for mortality, and it has been linked with a series of chronic disorders, the treatment of which absorbs ~ 85% of healthcare costs in developed countries. Conversely, physical activity promotes many health benefits; endurance exercise in particular represents a powerful stimulus to induce mitochondrial biogenesis, and it is routinely used to prevent and treat chronic metabolic disorders linked with sub-optimal mitochondrial characteristics. Given the importance of maintaining a healthy mitochondrial pool, it is vital to better characterize how manipulating the endurance exercise dose affects cellular mechanisms of exercise-induced mitochondrial biogenesis. Herein, we propose a definition of mitochondrial biogenesis and the techniques available to assess it, and we emphasize the importance of standardizing biopsy timing and the determination of relative exercise intensity when comparing different studies. We report an intensity-dependent regulation of exercise-induced increases in nuclear peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, nuclear phosphorylation of p53 (serine 15), and PGC-1α messenger RNA (mRNA), as well as training-induced increases in PGC-1α and p53 protein content. Despite evidence that PGC-1α protein content plateaus within a few exercise sessions, we demonstrate that greater training volumes induce further increases in PGC-1α (and p53) protein content, and that short-term reductions in training volume decrease the content of both proteins, suggesting training volume is still a factor affecting training-induced mitochondrial biogenesis. Finally, training-induced changes in mitochondrial transcription factor A (TFAM) protein content are regulated in a training volume-dependent manner and have been linked with training-induced changes in mitochondrial content.

Training-Induced Changes in Mitochondrial Content and Respiratory Function in Human Skeletal Muscle

A sedentary lifestyle has been linked to a number of metabolic disorders that have been associated with sub-optimal mitochondrial characteristics and an increased risk of premature death. Endurance training can induce an increase in mitochondrial content and/or mitochondrial functional qualities, which are associated with improved health and well-being and longer life expectancy. It is therefore important to better define how manipulating key parameters of an endurance training intervention can influence the content and functionality of the mitochondrial pool. This review focuses on mitochondrial changes taking place following a series of exercise sessions (training-induced mitochondrial adaptations), providing an in-depth analysis of the effects of exercise intensity and training volume on changes in mitochondrial protein synthesis, mitochondrial content and mitochondrial respiratory function. We provide evidence that manipulation of different exercise training variables promotes specific and diverse mitochondrial adaptations. Specifically, we report that training volume may be a critical factor affecting changes in mitochondrial content, whereas relative exercise intensity is an important determinant of changes in mitochondrial respiratory function. As a consequence, a dissociation between training-induced changes in mitochondrial content and mitochondrial respiratory function is often observed. We also provide evidence that exercise-induced changes are not necessarily predictive of training-induced adaptations, we propose possible explanations for the above discrepancies and suggestions for future research.

A novel mutation in nuclear prelamin a recognition factor-like causes diffuse pulmonary arteriovenous malformations

Two daughters in a Chinese consanguineous family were diagnosed as diffuse pulmonary arteriovenous malformations (PAVMs) and screened using whole exome sequencing (WES) and copy number variations (CNVs) chips. Though no mutation was found in the established causative genes of capillary malformation-AVMs (CM-AVMs) or PAVMs, Ser161Ile (hg19 NM_022493 c.482G>T) mutation in nuclear prelamin A recognition factor-like (NARFL) was identified. Ser161Ile mutation in NARFL conservation region was predicted to be deleterious and absent in 500 population controls and Exome Aggregation Consortium (ExAC) Database. And there was a dosage effect of the mutation on mRNA levels among family members and population controls, consistent with the instability of mutant mRNA in vitro. Accordingly, in lung tissue of the proband, NARFL protein expression was reduced but Fe3+ was overloaded with vascular endothelial growth factor (VEGF) overexpression. Furthermore, NARFL-knockdown cell lines demonstrated decreased activity of cytosolic aconitase, while NARFL-knockout zebrafish presented ectopic subintestinal vessels sprouts and upregulated VEGF. So we concluded that the Ser161Ile mutant induced NARFL deficiency and eventually diffuse PAVMs probably through VEGF pathway. In a word, we detected a functional mutation in NARFL, which might be the pathogenic gene in this pedigree.

Exercise and Mitochondrial Dynamics: Keeping in Shape with ROS and AMPK

Exercise is a robust stimulus for mitochondrial adaptations in skeletal muscle which consequently plays a central role in enhancing metabolic health. Despite this, the precise molecular events that underpin these beneficial effects remain elusive. In this review, we discuss molecular signals generated during exercise leading to altered mitochondrial morphology and dynamics. In particular, we focus on the interdependence between reactive oxygen species (ROS) and redox homeostasis, the sensing of cellular bioenergetic status via 5’ adenosine monophosphate (AMP)-activated protein kinase (AMPK), and the regulation of mitochondrial fission and fusion. Precisely how exercise regulates the network of these responses and their effects on mitochondrial dynamics is not fully understood at present. We highlight the limitations that exist with the techniques currently available, and discuss novel molecular tools to potentially advance the fields of redox biology and mitochondrial bioenergetics. Ultimately, a greater understanding of these processes may lead to novel mitochondria-targeted therapeutic strategies to augment or mimic exercise in order to attenuate or reverse pathophysiology.

Exercise training increases skeletal muscle mitochondrial volume density by enlargement of existing mitochondria and not de novo biogenesis

AIMS

(i) To determine whether exercise-induced increases in muscle mitochondrial volume density (Mito_VD ) are related to enlargement of existing mitochondria or de novo biogenesis and (ii) to establish whether measures of mitochondrial-specific enzymatic activities are valid biomarkers for exercise-induced increases in Mito_VD .

METHOD

Skeletal muscle samples were collected from 21 healthy males prior to and following 6 weeks of endurance training. Transmission electron microscopy was used for the estimation of mitochondrial densities and profiles. Biochemical assays, western blotting and high-resolution respirometry were applied to detect changes in specific mitochondrial functions.

RESULT

Mito_VD increased with 55 ± 9% (P < 0.001), whereas the number of mitochondrial profiles per area of skeletal muscle remained unchanged following training. Citrate synthase activity (CS) increased (44 ± 12%, P < 0.001); however, there were no functional changes in oxidative phosphorylation capacity (OXPHOS, CI+II_P ) or cytochrome c oxidase (COX) activity. Correlations were found between Mito_VD and CS (P = 0.01; r = 0.58), OXPHOS, CI+CIIP (P = 0.01; R = 0.58) and COX (P = 0.02; R = 0.52) before training; after training, a correlation was found between Mito_VD and CS activity only (P = 0.04; R = 0.49). Intrinsic respiratory capacities decreased (P < 0.05) with training when respiration was normalized to Mito_VD. This was not the case when normalized to CS activity although the percentage change was comparable_. CONCLUSIONS: Mito_VD was increased by inducing mitochondrial enlargement rather than de novo biogenesis. CS activity may be appropriate to track training-induced changes in Mito_VD.

Resistance Training with Co-ingestion of Anti-inflammatory Drugs Attenuates Mitochondrial Function

Aim: The current study aimed to examine the effects of resistance exercise with concomitant consumption of high vs. low daily doses of non-steroidal anti-inflammatory drugs (NSAIDs) on mitochondrial oxidative phosphorylation in skeletal muscle. As a secondary aim, we compared the effects of eccentric overload with conventional training. Methods: Twenty participants were randomized to either a group taking high doses (3 × 400 mg/day) of ibuprofen (IBU; 27 ± 5 year; n = 11) or a group ingesting a low dose (1 × 75 mg/day) of acetylsalicylic acid (ASA; 26 ± 4 year; n = 9) during 8 weeks of supervised knee extensor resistance training. Each of the subject's legs were randomized to complete the training program using either a flywheel (FW) device emphasizing eccentric overload, or a traditional weight stack machine (WS). Maximal mitochondrial oxidative phosphorylation (CI+II_P) from permeabilized skeletal muscle bundles was assessed using high-resolution respirometry. Citrate synthase (CS) activity was assessed using spectrophotometric techniques and mitochondrial protein content using western blotting. Results: After training, CI+II_P decreased (P < 0.05) in both IBU (23%) and ASA (29%) with no difference across medical treatments. Although CI+II_P decreased in both legs, the decrease was greater (interaction p = 0.015) in WS (33%, p = 0.001) compared with FW (19%, p = 0.078). CS activity increased (p = 0.027) with resistance training, with no interactions with medical treatment or training modality. Protein expression of ULK1 increased with training in both groups (p < 0.001). The increase in quadriceps muscle volume was not correlated with changes in CI+II_P (R = 0.16). Conclusion: These results suggest that 8 weeks of resistance training with co-ingestion of anti-inflammatory drugs reduces mitochondrial function but increases mitochondrial content. The observed changes were not affected by higher doses of NSAIDs consumption, suggesting that the resistance training intervention was the prime mediator of the decreased mitochondrial phosphorylation. Finally, we noted that flywheel resistance training, emphasizing eccentric overload, rescued some of the reduction in mitochondrial function seen with conventional resistance training.

Aerobic efficiency is associated with the improvement in maximal power output during acute hyperoxia

This study investigated the relationship between aerobic efficiency during cycling exercise and the increase in physical performance with acute hyperoxic exposure (FiO2 ~31%) (HOX) and also tested the hypothesis that fat oxidation could be increased by acute hyperoxia. Fourteen males and four females were recruited for two sessions, where they exercised for 2 × 10 min at 100 W to determine efficiency. HOX and normoxia (NOX) were administered randomly on both occasions to account for differences in nitrogen exchange. Thereafter, a progressive ramp test was performed to determine VO_2max and maximal power output (W_max). After 30 min rest, workload was set to 80% of maximal power output (W_max) for a time to exhaustion test (TTE). At 100W gross efficiency was reduced from 19.4% during NOX to 18.9% during HOX (P ≤ 0.0001). HOX increased fat oxidation at 100 W by 52% from 3.41 kcal min^-1 to 5.17 kcal min^-1 (P ≤ 0.0001) with a corresponding reduction in carbohydrate oxidation. W_max increased by 2.4% from 388.8 (±82.1) during NOX to 397.8 (±83.5) during HOX (P ≤ 0.0001). SaO₂ was higher in HOX both at the end of the maximal exercise test and TTE. Subjects with a high level of efficiency in NOX had a larger improvement in Wmax with HOX, in agreement with the hypothesis that an optimum level of efficiency exists that maximizes power production. No association between mitochondrial excess capacity and endurance performance was found; increases in oxygen supply seemed to increase maximal aerobic power production and maintain/increase endurance capacity at the same relative workload.

High-intensity high-volume swimming induces more robust signaling through PGC-1α and AMPK activation than sprint interval swimming in m. triceps brachii

We aimed to test whether high-intensity high-volume training (HIHVT) swimming would induce more robust signaling than sprint interval training (SIT) swimming within the m. triceps brachii due to lower metabolic and oxidation. Nine well-trained swimmers performed the two training procedures on separate randomized days. Muscle biopsies from m. triceps brachii and blood samples were collected at three different time points: a) before the intervention (pre), b) immediately after the swimming procedures (post) and c) after 3 h of rest (3 h). Hydroperoxides, creatine kinase (CK), and lactate dehydrogenase (LDH) were quantified from blood samples, and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) and the AMPK^pTHR172/AMPK ratio were quantified by Western blot analysis. PGC-1α, sirtuin 3 (SIRT3), superoxide-dismutase 2 (SOD2), and vascular endothelial growth factor (VEGF) mRNA levels were also quantified. SIT induced a higher release of LDH (p < 0.01 at all time points) and CK (p < 0.01 at post) than HIHVT, but neither SIT nor HIHVT altered systemic hydroperoxides. Additionally, neither SIRT3 nor SOD2 mRNA levels increased, while PGC-1α transcription increased at 3 h after SIT (p < 0.01) and after HIHVT (p < 0.001). However, PGC-1α protein was higher after HIHVT than after SIT (p < 0.05). Moreover, the AMPK^pTHR172/AMPK ratio increased at post after SIT (p < 0.05), whereas this effect was delayed after HIHVT as it increased after 3 h (p < 0.05). In addition, VEGF transcription was higher in response to HIHVT (p < 0.05). In conclusion, SIT induces higher muscular stress than HIHVT without increasing systemic oxidation. In addition, HIHVT may induce more robust oxidative adaptations through PGC-1α and AMPK.

Exercise-induced mitochondrial dysfunction: a myth or reality?

Beneficial effects of physical activity on mitochondrial health are well substantiated in the scientific literature, with regular exercise improving mitochondrial quality and quantity in normal healthy population, and in cardiometabolic and neurodegenerative disorders and aging. However, several recent studies questioned this paradigm, suggesting that extremely heavy or exhaustive exercise fosters mitochondrial disturbances that could permanently damage its function in health and disease. Exercise-induced mitochondrial dysfunction (EIMD) might be a key proxy for negative outcomes of exhaustive exercise, being a pathophysiological substrate of heart abnormalities, chronic fatigue syndrome (CFS) or muscle degeneration. Here, we overview possible factors that mediate negative effects of exhaustive exercise on mitochondrial function and structure, and put forward alternative solutions for the management of EIMD.

Physiological adaptations to interval training and the role of exercise intensity

Interval exercise typically involves repeated bouts of relatively intense exercise interspersed by short periods of recovery. A common classification scheme subdivides this method into high-intensity interval training (HIIT; 'near maximal' efforts) and sprint interval training (SIT; 'supramaximal' efforts). Both forms of interval training induce the classic physiological adaptations characteristic of moderate-intensity continuous training (MICT) such as increased aerobic capacity (V̇O2 max ) and mitochondrial content. This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism. With respect to skeletal muscle adaptations, cellular stress and the resultant metabolic signals for mitochondrial biogenesis depend largely on exercise intensity, with limited work suggesting that increases in mitochondrial content are superior after HIIT compared to MICT, at least when matched-work comparisons are made within the same individual. It is well established that SIT increases mitochondrial content to a similar extent to MICT despite a reduced exercise volume. At the whole-body level, V̇O2 max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve V̇O2 max despite differences in training volume. There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume. Furthermore, the interactions between intensity and duration and frequency have not been thoroughly explored. While interval training is clearly a potent stimulus for physiological remodelling in humans, the integrative response to this type of exercise warrants further attention, especially in comparison to traditional endurance training.

Does Swimming at a Moderate Altitude Favor a Lower Oxidative Stress in an Intensity-Dependent Manner? Role of Nonenzymatic Antioxidants

Casuso, Rafael A., Jerónimo Aragón-Vela, Gracia López-Contreras, Silvana N. Gomes, Cristina Casals, Yaira Barranco-Ruiz, Jordi J. Mercadé, and Jesus R. Huertas. Does swimming at a moderate altitude favor a lower oxidative stress in an intensity-dependent manner? Role of nonenzymatic antioxidants. High-Alt Med Biol. 18:46-55, 2017.-we aimed to describe oxidative damage and enzymatic and nonenzymatic antioxidant responses to swimming at different intensities in hypoxia. We recruited 12 highly experienced swimmers who have been involved in competitive swimming for at least 9 years. They performed a total of six swimming sessions carried out at low (LOW), moderate (MOD), or high (HIGH) intensity at low altitude (630 m) and at 2320 m above sea level. Blood samples were collected before the session (Pre), after the cool down (Post), and after 15 minutes of recovery (Rec). Blood lactate (BL) and heart rate were recorded throughout the main part of the session. Average velocities did not change between hypoxia and normoxia. We found a higher BL in response to MOD intensity in hypoxia. Plasmatic hydroperoxide level decreased at all intensities when swimming in hypoxia. This effect coincided with a lower glutation peroxidase activity and a marked mobilization of the circulating levels of α-tocopherol and coenzyme Q10 in an intensity-dependent manner. Our results suggest that, regardless of the intensity, no oxidative damage is found in response to hypoxic swimming in well-trained swimmers. Indeed, swimmers show a highly efficient antioxidant system by stimulating the mobilization of nonenzymatic antioxidants.