Characteristics of skeletal muscle mitochondrial biogenesis induced by moderate-intensity exercise and weight loss in obesity

Physical performance during energy deficiency in humans: An evolutionary perspective

Energy deficiency profoundly disrupts normal endocrinology, metabolism, and physiology, resulting in an orchestrated response for energy preservation. As such, despite energy deficit is typically thought as positive for weight-loss and treatment of cardiometabolic diseases during the current obesity pandemic, in the context of contemporary sports and exercise nutrition, chronic energy deficiency is associated to negative health and athletic performance consequences. However, the evidence of energy deficit negatively affecting physical capacity and sports performance is unclear. While severe energy deficiency can negatively affect physical capacity, humans can also improve aerobic fitness and strength while facing significant energy deficit. Many athletes, also, compete at an elite and world-class level despite showing clear signs of energy deficiency. Maintenance of high physical capacity despite the suppression of energetically demanding physiological traits seems paradoxical when an evolutionary viewpoint is not considered. Humans have evolved facing intermittent periods of food scarcity in their natural habitat and are able to thrive in it. In the current perspective it is argued that when facing limited energy availability, maintenance of locomotion and physical capacity are of high priority given that they are essential for food procurement for survival in the habitat where humans evolved. When energetic resources are limited, energy may be allocated to tasks essential for survival (e.g. locomotion) while minimising energy allocation to traits that are not (e.g. growth and reproduction). The current perspective provides a model of energy allocation during energy scarcity supported by observation of physiological and metabolic responses that are congruent with this paradigm.

A Scoping Review Investigating the "Gene-Dosage Theory" of Mitochondrial DNA in the Healthy Skeletal Muscle

This review provides an overview of the evidence regarding mtDNA and valid biomarkers for assessing mitochondrial adaptions. Mitochondria are small organelles that exist in almost all cells throughout the human body. As the only organelle, mitochondria contain their own DNA, mitochondrial DNA (mtDNA). mtDNA-encoded polypeptides are subunits of the enzyme complexes in the electron transport chain (ETC) that are responsible for production of ATP to the cells. mtDNA is frequently used as a biomarker for mitochondrial content, since changes in mitochondrial volume are thought to induce similar changes in mtDNA. However, some exercise studies have challenged this "gene-dosage theory", and have indicated that changes in mitochondrial content can adapt without changes in mtDNA. Thus, the aim of this scoping review was to summarize the studies that used mtDNA as a biomarker for mitochondrial adaptions and address the question as to whether changes in mitochondrial content, induce changes in mtDNA in response to aerobic exercise in the healthy skeletal muscle. The literature was searched in PubMed and Embase. Eligibility criteria included: interventional study design, aerobic exercise, mtDNA measurements reported pre- and postintervention for the healthy skeletal muscle and English language. Overall, 1585 studies were identified. Nine studies were included for analysis. Eight out of the nine studies showed proof of increased oxidative capacity, six found improvements in mitochondrial volume, content and/or improved mitochondrial enzyme activity and seven studies did not find evidence of change in mtDNA copy number. In conclusion, the findings imply that mitochondrial adaptions, as a response to aerobic exercise, can occur without a change in mtDNA copy number.

Linoleic Acid-Rich Oil Alters Circulating Cardiolipin Species and Fatty Acid Composition in Adults: A Randomized Controlled Trial

SCOPE

Higher circulating linoleic acid (LA) and muscle-derived tetralinoleoyl-cardiolipin (LA4 CL) are each associated with decreased cardiometabolic disease risk. Mitochondrial dysfunction occurs with low LA4 CL. Whether LA-rich oil fortification can increase LA4 CL in humans is unknown. The aims of this study are to determine whether dietary fortification with LA-rich oil for 2 weeks increases: 1) LA in plasma, erythrocytes, and peripheral blood mononuclear cells (PBMC); and 2) LA4 CL in PBMC in adults.

METHODS AND RESULTS

In this randomized controlled trial, adults are instructed to consume one cookie per day delivering 10 g grapeseed (LA-cookie, N = 42) or high oleate (OA) safflower (OA-cookie, N = 42) oil. In the LA-cookie group, LA increases in plasma, erythrocyte, and PBMC by 6%, 7%, and 10% respectively. PBMC and erythrocyte OA increase by 7% and 4% in the OA-cookie group but is unchanged in the plasma. PBMC LA4 CL increases (5%) while LA3 OA1 CL decreases (7%) in the LA-cookie group but are unaltered in the OA-cookie group.

CONCLUSIONS

LA-rich oil fortification increases while OA-oil has no effect on LA4 CL in adults. Because LA-rich oil fortification reduces cardiometabolic disease risk and increases LA4 CL, determining whether mitochondrial dysfunction is repaired through dietary fortification is warranted.

Targeting skeletal muscle mitochondrial health in obesity

Metabolic demands of skeletal muscle are substantial and are characterized normally as highly flexible and with a large dynamic range. Skeletal muscle composition (e.g., fiber type and mitochondrial content) and metabolism (e.g., capacity to switch between fatty acid and glucose substrates) are altered in obesity, with some changes proceeding and some following the development of the disease. Nonetheless, there are marked interindividual differences in skeletal muscle composition and metabolism in obesity, some of which have been associated with obesity risk and weight loss capacity. In this review, we discuss related molecular mechanisms and how current and novel treatment strategies may enhance weight loss capacity, particularly in diet-resistant obesity.

In Search of the Holy Grail: Toward a Unified Hypothesis on Mitochondrial Dysfunction in Age-Related Diseases

Cardiolipin (CL) is a mitochondrial signature phospholipid that plays a pivotal role in mitochondrial dynamics, membrane structure, oxidative phosphorylation, mtDNA bioenergetics, and mitophagy. The depletion or abnormal acyl composition of CL causes mitochondrial dysfunction, which is implicated in the pathogenesis of aging and age-related disorders. However, the molecular mechanisms by which mitochondrial dysfunction causes age-related diseases remain poorly understood. Recent development in the field has identified acyl-CoA:lysocardiolipin acyltransferase 1 (ALCAT1), an acyltransferase upregulated by oxidative stress, as a key enzyme that promotes mitochondrial dysfunction in age-related diseases. ALCAT1 catalyzes CL remodeling with very-long-chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA). Enrichment of DHA renders CL highly sensitive to oxidative damage by reactive oxygen species (ROS). Oxidized CL becomes a new source of ROS in the form of lipid peroxides, leading to a vicious cycle of oxidative stress, CL depletion, and mitochondrial dysfunction. Consequently, ablation or the pharmacological inhibition of ALCAT1 have been shown to mitigate obesity, type 2 diabetes, heart failure, cardiomyopathy, fatty liver diseases, neurodegenerative diseases, and cancer. The findings suggest that age-related disorders are one disease (aging) manifested by different mitochondrion-sensitive tissues, and therefore should be treated as one disease. This review will discuss a unified hypothesis on CL remodeling by ALCAT1 as the common denominator of mitochondrial dysfunction, linking mitochondrial dysfunction to the development of age-related diseases.

Impact of obesity on the molecular response to a single bout of exercise in a preliminary human cohort

OBJECTIVE

The health benefits of exercise are well documented, but several exercise-response parameters are attenuated in individuals with obesity. The goal of this pilot study was to identify molecular mechanisms that may influence exercise response with obesity.

METHODS

A multi-omics comparison of the transcriptome, proteome, and phosphoproteome in muscle from a preliminary cohort of lean individuals (n = 4) and individuals with obesity (n = 4) was performed, before and after a single bout of 30 minutes of unilateral cycling at 70% maximal oxygen uptake (VO₂ peak). Mass spectrometry and RNA sequencing were used to interrogate the proteome, phosphoproteome, and transcriptome from muscle biopsy tissue.

RESULTS

The main findings are that individuals with obesity exhibited transcriptional and proteomic signatures consistent with reduced mitochondrial function, protein synthesis, and glycogen synthesis. Furthermore, individuals with obesity demonstrated markedly different transcriptional, proteomic, and phosphoproteomic responses to exercise, particularly biosynthetic pathways of glycogen synthesis and protein synthesis. Casein kinase II subunit alpha and glycogen synthase kinase-3β signaling was identified as exercise-response pathways that were notably altered by obesity.

CONCLUSIONS

Opportunities to enhance exercise responsiveness by targeting specific molecular pathways that are disrupted in skeletal muscle from individuals with obesity await a better understanding of the precise molecular mechanisms that may limit exercise-response pathways in obesity.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

Effects of Extreme Weight Loss on Cardiometabolic Health in Children With Metabolic Syndrome: A Metabolomic Study

Objectives: To evaluate the effect of extreme weight loss programs on circulating metabolites and their relationship with cardiometabolic health in children with metabolic syndrome.

Methods: This study was a quasi-experimental design with a pretest and post-test. Thirty children with metabolic syndrome and aged 10–17years were recruited to an extreme weight loss program (i.e., exercise combined with diet control). The primary outcomes included plasma metabolites, body composition, and cardiometabolic risk factors. A total of 324 metabolites were quantitatively detected by an ultra-performance liquid chromatography coupled to tandem mass spectrometry system, and the variable importance in the projection (VIP) value of each metabolite was calculated by the orthogonal projection to latent structures discriminant analysis. The fold change (FC) and p value of each metabolite were used to screen differential metabolites with the following values: VIP>1, p value<0.05, and |log2FC|>0.25. Pathway enrichment and correlation analyses between metabolites and cardiometabolic risk factors were also performed.

Result: A large effect size was observed, presenting a weight loss of −8.9kg (Cohen’s d=1.00, p<0.001), body mass index reduction of −3.3kg/m² (Cohen’s d=1.47, p<0.001), and body fat percent reduction of −4.1 (%) (Cohen’s d=1.22, p<0.001) after the intervention. Similar improvements were found in total cholesterol (Cohen’s d=2.65, p<0.001), triglycerides (Cohen’s d=2.59, p<0.001), low-density lipoprotein cholesterol (Cohen’s d=2.81, p<0.001), glucose metabolism, and blood pressure. A total of 59 metabolites were changed after the intervention (e.g., aminoacyl-tRNA biosynthesis, glycine, serine, and threonine metabolism; nitrogen metabolism, tricarboxylic acid cycle, and phenylalanine, tyrosine, and tryptophan biosynthesis). The changes in metabolites (e.g., amino acids, fatty acids, organic acids, and carnitine) were related to lipid metabolism improvement (p<0.05). Organic acids and carnitines were associated with changes in the body composition (p<0.05).

Conclusion: Exercise combined with dietary control improved the body composition and cardiometabolic health in children with metabolic syndrome, and these changes may be related to plasma metabolites.

Effect of Aerobic Exercise-induced Weight Loss on the Components of Daily Energy Expenditure

INTRODUCTION

Exercise usually results in less weight loss than expected. This suggests increased energy intake and/or deceased expenditure counteract the energy deficit induced by exercise. The aim of this study was to evaluate changes in components of daily energy expenditure (doubly labeled water and room calorimetry) after 24 wk of exercise training with two doses of aerobic exercise.

METHODS

This was an ancillary study in 42 (29 women, 13 men) sedentary, middle-age (47.8 ± 12.5 yr) individuals with obesity (35 ± 3.7 kg·m-2) enrolled in the Examination of Mechanisms of Exercise-induced Weight Compensation study. Subjects were randomized to three groups: healthy living control group (n = 13), aerobic exercise that expended 8 kcal·kg-1 of body weight per week (8 KKW, n = 14), or aerobic exercise that expended 20 kcal per kilogram of weight per week (20 KKW, n = 15). Total daily energy expenditure (TDEE) was measured in free-living condition by doubly labeled water and in sedentary conditions in a metabolic chamber over 24 h (24EE). Energy intake was calculated over 14 d from TDEE before and after the intervention using the intake-balance method.

RESULTS

Significant weight loss occurred with 20 KKW (-2.1 ± 0.7 kg, P = 0.04) but was only half of expected. In the 20 KKW group free-living TDEE increased by ~4% (P = 0.03), which is attributed to the increased exercise energy expenditure (P = 0.001), while 24EE in the chamber decreased by ~4% (P = 0.04). Aerobic exercise at 8 KKW did not induce weight change, and there was no significant change in any component of EE. There was no significant change in energy intake for any group (P = 0.53).

CONCLUSIONS

Structured aerobic exercise at a dose of 20 KKW produced less weight loss than expected possibly due to behavioral adaptations leading to reduced 24EE in a metabolic chamber without any change in energy intake.

The lifecycle of skeletal muscle mitochondria in obesity

Skeletal muscle possesses dramatic metabolic plasticity that allows for the rapid adaptation in cellular energy transduction to meet the demands of the organism. Obesity elicits changes in skeletal muscle structure and function, resulting in the accumulation of intramuscular lipids. The accumulation of intramuscular lipids in obesity is associated with impaired skeletal muscle mitochondrial content and function. Mitochondria exist as a dynamic network that is regulated by the processes of biogenesis, fusion, fission, and mitophagy. In this review, we outline adaptations in molecular pathways that regulate mitochondrial structure and function in obesity. We highlight the emerging role of dysregulated skeletal muscle macroautophagy and mitochondrial turnover in obesity. Future research should further elucidate the role of mitophagy in observed reductions in mitochondrial content and function during obesity.

Maternal Inactivity Programs Skeletal Muscle Dysfunction in Offspring Mice by Attenuating Apelin Signaling and Mitochondrial Biogenesis

Although maternal exercise (ME) becomes increasingly uncommon, the effects of ME on offspring muscle metabolic health remain largely undefined. Maternal mice are subject to daily exercise during pregnancy, which enhances mitochondrial biogenesis during fetal muscle development; this is correlated with higher mitochondrial content and oxidative muscle fibers in offspring muscle and improved endurance capacity. Apelin, an exerkine, is elevated due to ME, and maternal apelin administration mirrors the effect of ME on mitochondrial biogenesis in fetal muscle. Importantly, both ME and apelin induce DNA demethylation of the peroxisome proliferator-activated receptor γ coactivator-1α (Ppargc1a) promoter and enhance its expression and mitochondrial biogenesis in fetal muscle. Such changes in DNA methylation were maintained in offspring, with ME offspring muscle expressing higher levels of PGC-1α1/4 isoforms, explaining improved muscle function. In summary, ME enhances DNA demethylation of the Ppargc1a promoter in fetal muscle, which has positive programming effects on the exercise endurance capacity and protects offspring muscle against metabolic dysfunction.

Son et al. demonstrate that maternal exercise facilitates fetal muscle development, which improves muscle function and exercise endurance in offspring. Maternal administration of apelin, an exerkine, mirrors the beneficial effects of maternal exercise on mitochondrial biogenesis and fetal muscle development. These findings suggest apelin and its receptor as potential drug targets for improving fetal muscle development of sedentary mothers.

Effects of 3-month high-intensity interval training vs. moderate endurance training and 4-month follow-up on fat metabolism, cardiorespiratory function and mitochondrial respiration in obese adults

PURPOSE

The purpose of this study was to investigate, in obese adults, changes in body composition, physical capacities, fat oxidation and ex vivo mitochondrial respiration induced by a 3-month either moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT); afterwards, the patients were followed for four months.

METHODS

Thirty-two patients (mean age 39 years; mean body mass index [BMI] 36 kg∙m^-2) participated in this study attending ~ 34 sessions of training. At baseline (PRE), at the end of the program (POST) and after follow-up, body composition, peak O₂ uptake (V'O₂peak) and fat oxidation rate were measured. Vastus lateralis biopsies for the evaluation of mitochondrial respiration were performed only at PRE and POST.

RESULTS

At POST, body mass (BM) and fat mass (FM) decreased (- 6 and - 14%, respectively, P < 0.05) in MICT and HIIT; V'O₂peak increased in both groups (+ 6 and + 16%, respectively, P < 0.05). Maximal fat oxidation rate increased only after HIIT (P < 0.001). Maximal ADP-stimulated mitochondrial respiration normalized by citrate synthase increased (P < 0.05) by 67% and 36% in MICT and HIIT, respectively, without significant difference. After follow-up, BM and FM were still lower (- 4 and - 20%, respectively, P < 0.050) compared with baseline in both groups. Only after HIIT, V'O₂peak (+ 8%) and maximal fat oxidation rate were still higher (P < 0.05).

CONCLUSIONS

HIIT was more effective in improving and maintaining V'O₂peak and fat oxidation. These results may be relevant for an appropriate prescription of training programs designed to optimize aerobic fitness in obese subjects.

Adaptations in Mitochondrial Enzymatic Activity Occurs Independent of Genomic Dosage in Response to Aerobic Exercise Training and Deconditioning in Human Skeletal Muscle

Mitochondrial DNA (mtDNA) replication is thought to be an integral part of exercise-training-induced mitochondrial adaptations. Thus, mtDNA level is often used as an index of mitochondrial adaptations in training studies. We investigated the hypothesis that endurance exercise training-induced mitochondrial enzymatic changes are independent of genomic dosage by studying mtDNA content in skeletal muscle in response to six weeks of knee-extensor exercise training followed by four weeks of deconditioning in one leg, comparing results to the contralateral untrained leg, in 10 healthy, untrained male volunteers. Findings were compared to citrate synthase activity, mitochondrial complex activities, and content of mitochondrial membrane markers (porin and cardiolipin). One-legged knee-extensor exercise increased endurance performance by 120%, which was accompanied by increases in power output and peak oxygen uptake of 49% and 33%, respectively (p < 0.01). Citrate synthase and mitochondrial respiratory chain complex I–IV activities were increased by 51% and 46–61%, respectively, in the trained leg (p < 0.001). Despite a substantial training-induced increase in mitochondrial activity of TCA and ETC enzymes, there was no change in mtDNA and mitochondrial inner and outer membrane markers (i.e., cardiolipin and porin). Conversely, deconditioning reduced endurance capacity by 41%, muscle citrate synthase activity by 32%, and mitochondrial complex I–IV activities by 29–36% (p < 0.05), without any change in mtDNA and porin and cardiolipin content in the previously trained leg. The findings demonstrate that the adaptations in mitochondrial enzymatic activity after aerobic endurance exercise training and the opposite effects of deconditioning are independent of changes in the number of mitochondrial genomes, and likely relate to changes in the rate of transcription of mtDNA.

Mitochondrial ultrastructural adaptations in fast muscles of mice lacking IL15RA

The pro-inflammatory cytokine interleukin-15 (IL15) and its receptor α (IL15RA) participate in the regulation of musculoskeletal function and metabolism. Deletion of the Il15ra gene in mice increases spontaneous activity, improves fatigue resistance in the glycolytic extensor digitorum longus (EDL) and protects from diet-induced obesity. In humans, IL15RA single-nucleotide polymorphisms (SNPs) have been linked to muscle strength, metabolism and performance in elite endurance athletes. Taken together, these features suggest a possible role for IL15RA in muscle mitochondrial structure and function. Here, we have investigated the consequences of loss of IL15RA on skeletal muscle fiber-type properties and mitochondrial ultrastructure. Immunostaining of the EDL for myosin heavy chain (MyHC) isoforms revealed no significant changes in fiber type. Electron microscopy (EM) analysis of the EDL indicated an overall higher mitochondria content, and increased cristae density in subsarcolemmal and A-band mitochondrial subpopulations. The higher cristae density in Il15ra ^-/- mitochondria was associated with higher OPA1 and cardiolipin levels. Overall, these data extend our understanding of the role of IL15RA signaling in muscle oxidative metabolism and adaptation to exercise.

Calorie Restriction-induced Weight Loss and Exercise Have Differential Effects on Skeletal Muscle Mitochondria Despite Similar Effects on Insulin Sensitivity

Background

Skeletal muscle insulin resistance and reduced mitochondrial capacity have both been reported to be affected by aging. The purpose of this study was to compare the effects of calorie restriction-induced weight loss and exercise on insulin resistance, skeletal muscle mitochondrial content, and mitochondrial enzyme activities in older overweight to obese individuals.

Methods

Insulin-stimulated rates of glucose disposal (Rd) were determined using the hyperinsulinemic euglycemic clamp before and after completing 16 weeks of either calorie restriction to induce weight loss (N = 7) or moderate exercise (N = 10). Mitochondrial volume density, mitochondria membrane content (cardiolipin), and activities of electron transport chain (rotenone-sensitive NADH-oxidase), tricarboxylic acid (TCA) cycle (citrate synthase) and β-oxidation pathway (β-hydroxyacyl CoA dehydrogenase; β-HAD) were measured in percutaneous biopsies of the vastus lateralis before and after the interventions.

Results

Rd improved similarly (18.2% ± 9.0%, p < .04) with both weight loss and exercise. Moderate exercise significantly increased mitochondrial volume density (14.5% ± 2.0%, p < .05), cardiolipin content (22.5% ± 13.4%, p < .05), rotenone-sensitive NADH-oxidase (65.7% ± 13.2%, p = .02) and β-HAD (30.7% ± 6.8%, p ≤ .03) activity, but not citrate synthase activity (10.1% ± 4.0%). In contrast, calorie restriction-induced weight loss did not affect mitochondrial content, NADH-oxidase or β-HAD, yet increased citrate synthase activity (44.1% ± 21.1%, p ≤ .04). Exercise (increase) or weight loss (decrease) induced a remodeling of cardiolipin with a small (2%-3%), but significant change in the relative content of tetralinoleoyl cardiolipin.

Conclusion

Exercise increases both mitochondria content and mitochondrial electron transport chain and fatty acid oxidation enzyme activities within skeletal muscle, while calorie restriction-induced weight loss did not, despite similar improvements in insulin sensitivity in overweight older adults.

Local muscle cooling does not impact expression of mitochondrial-related genes

Recovery that takes place in a cold environment after endurance exercise elevates PGC-1α mRNA whereas ERRα and NRF2 mRNA expression are inhibited. However, the effect of local skeletal muscle cooling on mitochondrial-related gene expression is unknown.

PURPOSE

To determine the impact of local skeletal muscle cooling during recovery from an acute bout of exercise on mitochondrial-related gene expression.

METHODS

Recreationally-trained male cyclists (n=8, age 25±3 y, height 181±6cm, weight 79±8kg, 12.8±3.6% body fat, VO_2peak 4.52±0.88L·min^-1 protocol) completed a 90-min variable intensity cycling protocol followed by 4h of recovery. During recovery, ice was applied intermittently to one leg (ICE) while the other leg served as a control (CON). Intramuscular temperature was recorded continuously. Muscle biopsies were taken from each vastus lateralis at 4h post-exercise for the analysis of mitochondrial-related gene expression.

RESULTS

Intramuscular temperature was colder in ICE (26.7±1.1°C) than CON (35.5±0.1°C) throughout the 4h recovery period (p<0.001). There were no differences in expression of PGC-1α, TFAM, NRF1, NRF2, or ERRα mRNA between ICE and CON after the 4h recovery period.

CONCLUSION

Local muscle cooling after exercise does not impact the expression of mitochondrial biogenesis-related genes compared to recovery from exercise in control conditions. When these data are considered with previous research, the stimuli for cold-induced gene expression alterations may be related to factors other than local muscle temperature. Additionally, different intramuscular temperatures should be examined to determine dose-response of mitochondrial-related gene expression.

Acylcarnitines as markers of exercise-associated fuel partitioning, xenometabolism, and potential signals to muscle afferent neurons

NEW FINDINGS

What is the central question of this study? Does improved metabolic health and insulin sensitivity following a weight-loss and fitness intervention in sedentary, obese women alter exercise-associated fuel metabolism and incomplete mitochondrial fatty acid oxidation (FAO), as tracked by blood acylcarnitine patterns? What is the main finding and its importance? Despite improved fitness and blood sugar control, indices of incomplete mitochondrial FAO increased in a similar manner in response to a fixed load acute exercise bout; this indicates that intramitochondrial muscle FAO is inherently inefficient and is tethered directly to ATP turnover. With insulin resistance or type 2 diabetes mellitus, mismatches between mitochondrial fatty acid fuel delivery and oxidative phosphorylation/tricarboxylic acid cycle activity may contribute to inordinate accumulation of short- or medium-chain acylcarnitine fatty acid derivatives [markers of incomplete long-chain fatty acid oxidation (FAO)]. We reasoned that incomplete FAO in muscle would be ameliorated concurrent with improved insulin sensitivity and fitness following a ∼14 week training and weight-loss intervention in obese, sedentary, insulin-resistant women. Contrary to this hypothesis, overnight-fasted and exercise-induced plasma C4-C14 acylcarnitines did not differ between pre- and postintervention phases. These metabolites all increased robustly with exercise (∼45% of pre-intervention peak oxygen consumption) and decreased during a 20 min cool-down. This supports the idea that, regardless of insulin sensitivity and fitness, intramitochondrial muscle β-oxidation and attendant incomplete FAO are closely tethered to absolute ATP turnover rate. Acute exercise also led to branched-chain amino acid acylcarnitine derivative patterns suggestive of rapid and transient diminution of branched-chain amino acid flux through the mitochondrial branched-chain ketoacid dehydrogenase complex. We confirmed our prior novel observation that a weight-loss/fitness intervention alters plasma xenometabolites [i.e. cis-3,4-methylene-heptanoylcarnitine and γ-butyrobetaine (a co-metabolite possibly derived in part from gut bacteria)], suggesting that host metabolic health regulated gut microbe metabolism. Finally, we considered whether acylcarnitine metabolites signal to muscle-innervating afferents; palmitoylcarnitine at concentrations as low as 1-10 μm activated a subset (∼2.5-5%) of these neurons ex vivo. This supports the hypothesis that in addition to tracking exercise-associated shifts in fuel metabolism, muscle acylcarnitines act as signals of exertion to short-loop somatosensory-motor circuits or to the brain.

Exercise and Weight Loss Improve Muscle Mitochondrial Respiration, Lipid Partitioning, and Insulin Sensitivity After Gastric Bypass Surgery

Both Roux-en-Y gastric bypass (RYGB) surgery and exercise can improve insulin sensitivity in individuals with severe obesity. However, the impact of RYGB with or without exercise on skeletal muscle mitochondria, intramyocellular lipids, and insulin sensitivity index (SI) is unknown. We conducted a randomized exercise trial in patients (n = 101) who underwent RYGB surgery and completed either a 6-month moderate exercise (EX) or a health education control (CON) intervention. SI was determined by intravenous glucose tolerance test. Mitochondrial respiration and intramyocellular triglyceride, sphingolipid, and diacylglycerol content were measured in vastus lateralis biopsy specimens. We found that EX provided additional improvements in SI and that only EX improved cardiorespiratory fitness, mitochondrial respiration and enzyme activities, and cardiolipin profile with no change in mitochondrial content. Muscle triglycerides were reduced in type I fibers in CON, and sphingolipids decreased in both groups, with EX showing a further reduction in a number of ceramide species. In conclusion, exercise superimposed on bariatric surgery-induced weight loss enhances mitochondrial respiration, induces cardiolipin remodeling, reduces specific sphingolipids, and provides additional improvements in insulin sensitivity.

Defects in mitochondrial efficiency and H2O2 emissions in obese women are restored to a lean phenotype with aerobic exercise training

The notion that mitochondria contribute to obesity-induced insulin resistance is highly debated. Therefore, we determined whether obese (BMI 33 kg/m(2)), insulin-resistant women with polycystic ovary syndrome had aberrant skeletal muscle mitochondrial physiology compared with lean, insulin-sensitive women (BMI 23 kg/m(2)). Maximal whole-body and mitochondrial oxygen consumption were not different between obese and lean women. However, obese women exhibited lower mitochondrial coupling and phosphorylation efficiency and elevated mitochondrial H2O2 (mtH2O2) emissions compared with lean women. We further evaluated the impact of 12 weeks of aerobic exercise on obesity-related impairments in insulin sensitivity and mitochondrial energetics in the fasted state and after a high-fat mixed meal. Exercise training reversed obesity-related mitochondrial derangements as evidenced by enhanced mitochondrial bioenergetics efficiency and decreased mtH2O2 production. A concomitant increase in catalase antioxidant activity and decreased DNA oxidative damage indicate improved cellular redox status and a potential mechanism contributing to improved insulin sensitivity. mtH2O2 emissions were refractory to a high-fat meal at baseline, but after exercise, mtH2O2 emissions increased after the meal, which resembles previous findings in lean individuals. We demonstrate that obese women exhibit impaired mitochondrial bioenergetics in the form of decreased efficiency and impaired mtH2O2 emissions, while exercise effectively restores mitochondrial physiology toward that of lean, insulin-sensitive individuals.

Cardiac effects of echinocandins after central venous administration in adult rats

Echinocandins have become the agents of choice for early and specific antifungal treatment in critically ill patients. In vitro studies and clinical case reports revealed a possible impact of echinocandin treatment on cardiac function. The aim of our study was to evaluate echinocandin-induced cardiac failure. Using an in vivo rat model, we assessed hemodynamic parameters and time to hemodynamic failure after central venous application (vena jugularis interna) of anidulafungin (low-dose group, 2.5 mg/kg body weight [BW]; high-dose group, 25 mg/kg BW), caspofungin (low-dose group, 0.875 mg/kg BW; high-dose group, 8.75 mg/kg BW), micafungin (low-dose group, 3 mg/kg BW; high-dose group, 30 mg/kg BW), and placebo (0.9% sodium chloride). Left ventricular heart tissue was collected to determine mitochondrial enzyme activity via spectrophotometric measurements. mRNA expression of transcriptional regulators and primary mitochondrial transcripts, mitochondrial DNA (mtDNA) content, and citrate synthase activity were also explored. Animals receiving high-dose anidulafungin or caspofungin showed an immediate decrease in hemodynamic function. All of the subjects in these groups died during the observation period. Every animal in the untreated control group survived (P < 0.001). Hemodynamic failure was not noticed in the anidulafungin and caspofungin low-dose groups. Micafungin had no impact on cardiac function. In analyzing mitochondrial enzyme activity and mitochondrial transcripts, we found no association between echinocandin administration and the risk for hemodynamic failure. Further experimental studies are needed to elucidate the underlying mechanisms involved in cardiotoxic echinocandin effects. In addition, randomized controlled clinical trials are needed to explore the clinical impact of echinocandin treatment in critically ill patients.

An active lifestyle induces positive antioxidant enzyme modulation in peripheral blood mononuclear cells of overweight/obese postmenopausal women

AIMS

The aim of this study was to investigate the effects of an active lifestyle on mitochondrial functioning, viability, bioenergetics, and redox status markers in peripheral blood mononuclear cells (PBMC) of overweight/ obese postmenopausal women.

MATERIALS AND METHODS

We performed a cross-sectional study with postmenopausal women aged 45–64 years and body mass index N 25 kg/m2, divided into physically active (n = 23) and sedentary (n = 12) groups. Mitochondria functioning and viability, bioenergetics and redox status parameters were assessed in PBMC with spectrophotometric and fluorometric assays.

KEY FINDINGS

No differences were found in the enzyme activity of complexes I and II of the electron transport chain (ETC), mitochondrial superoxide dismutase (MnSOD) activity, methyl-tetrazolium reduction levels and reduced glutathione and oxidized glutathione levels between the groups. However, the physically active group presented higher levels of reactive oxygen species (ROS) (P= 0.04) and increased catalase (CAT) (P= 0.029), total (P= 0.011) and cytosolic SOD (CuZnSOD) (P= 0.009) activities.

SIGNIFICANCE

An active lifestyle that includes aerobic exercise for at least 30 min, three times per week may improve antioxidant enzyme activities in PBMC in overweight/obese postmenopausal women, without changes in the activity of the ETC enzymes. However, this low intensity physical activity is not able to induce relevant mitochondrial adaptations.

Vitamin E and vitamin C do not reduce insulin sensitivity but inhibit mitochondrial protein expression in exercising obese rats

Controversy exists as to whether supplementation with the antioxidants vitamin E and vitamin C blocks adaptation to exercise. Exercise is a first-line means to treat obesity and its complications. While diet-induced obesity alters mitochondrial function and induces insulin resistance (IR), no data exist as to whether supplementation with vitamin E and vitamin C modify responses to exercise in pre-existing obesity. We tested the hypothesis that dietary supplementation with vitamin E (0.4 g α-tocopherol acetate/kg) and vitamin C (0.5 g/kg) blocks exercise-induced improvements on IR and mitochondrial content in obese rats maintained on a high-fat (45% fat energy (en)) diet. Diet-induced obese, sedentary rats had a 2-fold higher homeostasis model assessment of insulin resistance and larger insulin area under the curve following glucose tolerances test than rats fed a low-fat (10% fat en) diet. Exercising (12 weeks at 5 times per week in a motorized wheel) of obese rats normalized IR indices, an effect not modified by vitamin E and vitamin C. Vitamin E and vitamin C supplementation with exercise elevated mtDNA content in adipose and skeletal muscle to a greater extent (20%) than exercise alone in a depot-specific manner. On the other hand, vitamin C and vitamin E decreased exercise-induced increases in mitochondrial protein content for complex I (40%) and nicotinamide nucleotide transhydrogenase (35%) in a muscle-dependent manner. These data indicate that vitamin E and vitamin C supplementation in obese rodents does not modify exercise-induced improvements in insulin sensitivity but that changes in mitochondrial biogenesis and mitochondrial protein expression may be modified by antioxidant supplementation.

Cardiolipin profiles as a potential biomarker of mitochondrial health in diet-induced obese mice subjected to exercise, diet-restriction and ephedrine treatment

Cardiolipin (CL) is crucial for mitochondrial energy metabolism and structural integrity. Alterations in CL quantity or CL species have been associated with mitochondrial dysfunction in several pathological conditions and diseases, including mitochondrial dysfunction-related compound attrition and post-market withdrawal of promising drugs. Here we report alterations in the CL profiles in conjunction with morphology of soleus muscle (SM) and brown adipose tissue (BAT) in diet-induced obese (DIO) mice, subjected to ephedrine treatment (EPH: 200 mg kg(-1)  day(-1) orally), treadmill exercise (EX: 10 meters per min, 1 h per day), or dietary restriction (DR: 25% less of mean food consumed by the EX group) for 7 days. Mice from the DR and EPH groups had a significant decrease in percent body weight and reduced fat mass compared with DIO controls. Morphologic alterations in the BAT included brown adipocytes with reduced cytoplasmic lipid droplets and increased cytoplasmic eosinophilia in the EX, DR and EPH groups. Increased cytoplasmic eosinophilia in the BAT was ultrastructurally manifested by increased mitochondrial cristae, fenestration of mitochondrial cristae, increased electron density of mitochondrial matrix, and increased complexity of shape and elongation of mitochondria. Mitochondrial ultrastructural alterations in the SM of the EX and DR groups included increased mitochondrial cristae, cup-shaped mitochondria and mitochondrial degeneration. All four CL species (tri-linoleoyl-mono-docosahexaenoyl, tetralinoleoyl, tri-linoleoyl-mono-oleoyl, and di-linoleoyl-di-oleoyl) were increased in the BAT of the DR and EPH groups and in the SM of the EPH and EX groups. In conclusion, cardiolipin profiling supported standard methods for assessing mitochondrial biogenesis and health, and may serve as a potential marker of mitochondrial dysfunction in preclinical toxicity studies.

Adiposity and insulin resistance in humans: the role of the different tissue and cellular lipid depots

Human adiposity has long been associated with insulin resistance and increased cardiovascular risk, and abdominal adiposity is considered particularly adverse. Intra-abdominal fat is associated with insulin resistance, possibly mediated by greater lipolytic activity, lower adiponectin levels, resistance to leptin, and increased inflammatory cytokines, although the latter contribution is less clear. Liver lipid is also closely associated with, and likely to be an important contributor to, insulin resistance, but it may also be in part the consequence of the lipogenic pathway of insulin action being up-regulated by hyperinsulinemia and unimpaired signaling. Again, intramyocellular triglyceride is associated with muscle insulin resistance, but anomalies include higher intramyocellular triglyceride in insulin-sensitive athletes and women (vs men). Such issues could be explained if the "culprits" were active lipid moieties such as diacylglycerol and ceramide species, dependent more on lipid metabolism and partitioning than triglyceride amount. Subcutaneous fat, especially gluteofemoral, appears metabolically protective, illustrated by insulin resistance and dyslipidemia in patients with lipodystrophy. However, some studies suggest that deep sc abdominal fat may have adverse properties. Pericardial and perivascular fat relate to atheromatous disease, but not clearly to insulin resistance. There has been recent interest in recognizable brown adipose tissue in adult humans and its possible augmentation by a hormone, irisin, from exercising muscle. Brown adipose tissue is metabolically active, oxidizes fatty acids, and generates heat but, because of its small and variable quantities, its metabolic importance in humans under usual living conditions is still unclear. Further understanding of specific roles of different lipid depots may help new approaches to control obesity and its metabolic sequelae.

Short term exercise induces PGC-1α, ameliorates inflammation and increases mitochondrial membrane proteins but fails to increase respiratory enzymes in aging diabetic hearts

PGC-1α, a transcriptional coactivator, controls inflammation and mitochondrial gene expression in insulin-sensitive tissues following exercise intervention. However, attributing such effects to PGC-1α is counfounded by exercise-induced fluctuations in blood glucose, insulin or bodyweight in diabetic patients. The goal of this study was to investigate the role of PGC-1α on inflammation and mitochondrial protein expressions in aging db/db mice hearts, independent of changes in glycemic parameters. In 8-month-old db/db mice hearts with diabetes lasting over 22 weeks, short-term, moderate-intensity exercise upregulated PGC-1α without altering body weight or glycemic parameters. Nonetheless, such a regimen lowered both cardiac (macrophage infiltration, iNOS and TNFα) and systemic (circulating chemokines and cytokines) inflammation. Curiously, such an anti-inflammatory effect was also linked to attenuated expression of downstream transcription factors of PGC-1α such as NRF-1 and several respiratory genes. Such mismatch between PGC-1α and its downstream targets was associated with elevated mitochondrial membrane proteins like Tom70 but a concurrent reduction in oxidative phosphorylation protein expressions in exercised db/db hearts. As mitochondrial oxidative stress was predominant in these hearts, in support of our in vivo data, increasing concentrations of H₂O₂ dose-dependently increased PGC-1α expression while inhibiting expression of inflammatory genes and downstream transcription factors in H9c2 cardiomyocytes in vitro. We conclude that short-term exercise-induced oxidative stress may be key in attenuating cardiac inflammatory genes and impairing PGC-1α mediated gene transcription of downstream transcription factors in type 2 diabetic hearts at an advanced age.

Proteomic analysis of the inhibitory effect of epigallocatechin gallate on lipid accumulation in human HepG2 cells

Background

(−)-Epigallocatechin-3-gallate (EGCG), the most abundant catechin found in green tea, effectively reduces body weight and tissue and blood lipid accumulation. To explore the mechanism by which EGCG inhibits cellular lipid accumulation in free fatty acid (FFA) induced HepG2 cell culture, we investigated the proteome change of FFA-induced HepG2 cells exposed to EGCG using two-dimensional gel electrophoresis and mass spectrometry.

Results

In this study, 36 protein spots showed a significant change in intensity by more than 1.5-fold from the control group to the FFA group and from the FFA group to the FFA + EGCG group. Among them, 24 spots were excised from gels and identified by LC-MS/MS. In total, 18 proteins were successfully identified. All identified proteins were involved in lipid metabolism, glycometabolism, antioxidant defense, respiration, cytoskeleton organization, signal transduction, DNA repair, mRNA processing, iron storage, or were chaperone proteins. This indicated that these physiological processes may play roles in the mechanism of inhibition of lipid accumulation by EGCG in FFA-induced HepG2 cells. Western blotting analysis was used to verify the expression levels of differentially expressed proteins, which agree with the proteomic results.

Conclusions

From the proteomic analysis, we hypothesized that EGCG reduced cellular lipid accumulation in FFA-induced HepG2 cells through the activation of AMP-activated protein kinase (AMPK) resulting from the generation of reactive oxygen species (ROS). The induction of ROS may be a result of EGCG regulation of the antioxidant defense system. Activation of AMPK shifted some FFA toward oxidation, away from lipid and triglyceride storage, and suppressed hepatic gluconeogenesis. The findings of this study improve our understanding of the molecular mechanisms of inhibition of lipid accumulation by EGCG in HepG2 cells.

Emerging roles of cardiolipin remodeling in mitochondrial dysfunction associated with diabetes, obesity, and cardiovascular diseases

Cardiolipin (CL) is a phospholipid exclusively localized in inner mitochondrial membrane where it is required for oxidative phosphorylation, ATP synthesis, and mitochondrial bioenergetics. The biological functions of CL are thought to depend on its acyl chain composition which is dominated by linoleic acids in metabolically active tissues. This unique feature is not derived from the de novo biosynthesis of CL, rather from a remodeling process that involves in phospholipases and transacylase/acyltransferase. The remodeling process is also believed to be responsible for generation of CL species that causes oxidative stress and mitochondrial dysfunction. CL is highly sensitive to oxidative damages by reactive oxygen species (ROS) due to its high content in polyunsaturated fatty acids and location near the site of ROS production. Consequently, pathological remodeling of CL has been implicated in the etiology of mitochondrial dysfunction commonly associated with diabetes, obesity, heart failure, neurodegeneration, and aging that are characterized by oxidative stress, CL deficiency, and abnormal CL species. This review summarizes recent progresses in molecular, enzymatic, lipidomic, and metabolic studies that support a critical regulatory role of pathological CL remodeling as a missing link between oxidative stress and mitochondrial dysfunction in metabolic diseases and aging.

Role of lipotoxicity in endothelial dysfunction

Vascular endothelial dysfunction is determined by both genetic and environmental factors that cause decreased bioavailability of the vasodilator nitric oxide. This is a hallmark of atherosclerosis, hypertension, and coronary heart disease, which are major complications of metabolic disorders, including diabetes and obesity. Several therapeutic interventions, including changes in lifestyle as well as pharmacologic treatments, are useful for improving endothelial dysfunction in the face of lipotoxicity. This review discusses the current understanding of molecular and physiologic mechanisms underlying lipotoxicity-mediated endothelial dysfunction as well as relevant therapeutic approaches to ameliorate dyslipidemia and consequent endothelial dysfunction that have the potential to improve cardiovascular and metabolic outcomes.

Skeletal muscle SIRT1 and the genetics of metabolic health: therapeutic activation by pharmaceuticals and exercise

Silent mating type information regulation 2 homolog 1 (SIRT1) is implicated in the control of skeletal muscle mitochondrial content and function through deacetylation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and participation in the SIRT1/PGC-1α axis. The SIRT1/PGC-1α axis control of skeletal muscle mitochondrial biogenesis is an important therapeutic target for obesity and obesity-related metabolic dysfunction, as skeletal muscle mitochondrial dysfunction is implicated in the pathogenesis of multiple metabolic diseases. This review will establish the importance of the SIRT1/PGC-1α axis in the control of skeletal muscle mitochondrial biogenesis, and explore possible pharmacological and physiological interventions designed to activate SIRT1 and the SIRT1/PGC-1α axis in order to prevent and/or treat obesity and obesity-related metabolic disease. The current evidence supports a role for therapeutic activation of SIRT1 and the SIRT1/PGC-1α axis by both pharmaceuticals and exercise in the treatment and prevention of metabolic disease. Future research should be directed toward the feasibility of pharmaceutical activation of SIRT1 in humans and refining exercise prescriptions for optimal SIRT1 activation.

Effects of training at mild exercise intensities on quadriceps muscle energy metabolism in patients with chronic obstructive pulmonary disease

AIM

To study the effects of physical training at mild intensities on skeletal muscle energy metabolism in eight patients with chronic obstructive pulmonary disease (COPD) and eight paired healthy sedentary subjects.

METHODS

Energy metabolism of patients and controls vastus lateralis muscle was studied before and after 3 months of cycling training at mild exercises intensities.

RESULTS

The total amount of work accomplished was about 4059 ± 336 kJ in patients with COPD and 7531 ± 1693 kJ in control subjects. This work corresponds to a mechanical power set at 65.2 ± 7.5% of the maximum power for patients with COPD and 52 ± 3.3% of the maximum power in control group. Despite this low level of exercise intensities, we observed an improvement in mitochondrial oxidative phosphorylation through the creatine kinase system revealed by the increased apparent K(m) for ADP (from 105.5 ± 16.1 to 176.9 ± 26.5 μm, P < 0.05 in the COPD group and from 126.9 ± 16.8 to 177.7 ± 17.0, P > 0.05 in the control group). Meanwhile, maximal mechanical and metabolic power increased significantly from 83.1 ± 7.1 to 91.3 ± 7.4 Watts (P < 0.05) and from 16 ± 0.8 to 18.7 ± 0.98 mL O(2) kg(-1) min(-1) (P < 0.05) only in the COPD group.

CONCLUSION

This study shows that physical training at mild intensity is able to induce comparable changes in skeletal muscles oxidative energy metabolism in patients with COPD and sedentary healthy subjects, but different changes of maximal mechanical and metabolic power.

Biomarkers of mitochondrial content in skeletal muscle of healthy young human subjects

Skeletal muscle mitochondrial content varies extensively between human subjects. Biochemical measures of mitochondrial proteins, enzyme activities and lipids are often used as markers of mitochondrial content and muscle oxidative capacity (OXPHOS). The purpose of this study was to determine how closely associated these commonly used biochemical measures are to muscle mitochondrial content and OXPHOS. Sixteen young healthy male subjects were recruited for this study. Subjects completed a graded exercise test to determine maximal oxygen uptake (VO2peak) and muscle biopsies were obtained from the vastus lateralis. Mitochondrial content was determined using transmission electron microscopy imaging and OXPHOS was determined as the maximal coupled respiration in permeabilized fibres. Biomarkers of interest were citrate synthase (CS) activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I–V protein content, and complex I–IV activity. Spearman correlation coefficient tests and Lin's concordance tests were applied to assess the absolute and relative association between the markers and mitochondrial content or OXPHOS. Subjects had a large range of VO2peak (range 29.9–71.6ml min−1 kg−1) and mitochondrial content (4–15% of cell volume).Cardiolipin content showed the strongest association with mitochondrial content followed by CS and complex I activities. mtDNA was not related to mitochondrial content. Complex IV activity showed the strongest association with muscle oxidative capacity followed by complex II activity.We conclude that cardiolipin content, and CS and complex I activities are the biomarkers that exhibit the strongest association with mitochondrial content, while complex IV activity is strongly associated with OXPHOS capacity in human skeletal muscle.

Mitochondrial dysregulation in the pathogenesis of diabetes: potential for mitochondrial biogenesis-mediated interventions

Muscle mitochondrial metabolism is a tightly controlled process that involves the coordination of signaling pathways and factors from both the nuclear and mitochondrial genomes. Perhaps the most important pathway regulating metabolism in muscle is mitochondrial biogenesis. In response to physiological stimuli such as exercise, retrograde signaling pathways are activated that allow crosstalk between the nucleus and mitochondria, upregulating hundreds of genes and leading to higher mitochondrial content and increased oxidation of substrates. With type 2 diabetes, these processes can become dysregulated and the ability of the cell to respond to nutrient and energy fluctuations is diminished. This, coupled with reduced mitochondrial content and altered mitochondrial morphology, has been directly linked to the pathogenesis of this disease. In this paper, we will discuss our current understanding of mitochondrial dysregulation in skeletal muscle as it relates to type 2 diabetes, placing particular emphasis on the pathways of mitochondrial biogenesis and mitochondrial dynamics, and the therapeutic value of exercise and other interventions.

Exercise and the treatment of diabetes and obesity

An active lifestyle increases general health and is protects from a number of different conditions, including exercise and obesity. There is emerging evidence that exercise by itself exerts clinically beneficial effects in both lean and obese subjects, even in the absence of effects on weight.1 Recent results have brought an increasing understanding of the molecular mechanisms underlying the beneficial effects of exercise at the level of metabolism and changes in gene expression. There is a significant dose-response to the effect of exercise, and the current guidelines regarding exercise amount may need to be revised upwards. Furthermore, this treatment option should not be overlooked.

Substrate use and biochemical response to a 3,211-km bicycle tour in trained cyclists

The purpose of this study was to assess the physiological adaptations in physically fit individuals to a period of intensified training. Ten trained males cycled outdoors ~170 km day(-1) on 19 out of 21 days. Expired gas was collected on days 1 and 21 during maximal graded exercise and used for the determination of gross efficiency and whole body substrate use. Muscle biopsies were obtained before and after exercise on days 2 and 22 for the determination of mtDNA/gDNA ratio, gene expression, metabolic enzyme activity and glycogen use. Muscle glycogen before and after exercise, fat oxidation, and gross efficiency increased, carbohydrate oxidation decreased (p < 0.05), and VO(2max) did not change over the 21 days of training. Citrate synthase (CS), β-hydroxyacyl CoA dehydrogenase (β-HAD) and cytochrome c oxidase (COX) enzyme activity did not change with training. CS and β-HAD mRNA did not change with acute exercise or training. COX (subunit IV) mRNA increased with acute exercise (p < 0.05) but did not change over the 21 days. PGC-1α mRNA increased with acute exercise, but did not increase to the same degree on day 22 as it did on day 2 (p < 0.05). UCP3 mRNA decreased with training (p < 0.05). Acute exercise caused an increase in mitofusin2 (MFN2) mRNA (p < 0.05) and a trend for an increase in mtDNA/gDNA ratio (p = 0.057). However, training did not affect MFN2 mRNA or mtDNA/gDNA ratio. In response to 3,211 km of cycling, changes in substrate use and gross efficiency appear to be more profound than mitochondrial adaptations in trained individuals.

Exercise guidelines in pregnancy: new perspectives

In 2002, the American College of Obstetricians and Gynecologists published exercise guidelines for pregnancy, which suggested that in the absence of medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women. However, these guidelines did not define 'moderate intensity' or the specific amount of weekly caloric expenditure from physical activity required. Recent research has determined that increasing physical activity energy expenditure to a minimum of 16 metabolic equivalent task (MET) hours per week, or preferably 28 MET hours per week, and increasing exercise intensity to ≥60% of heart rate reserve during pregnancy, reduces the risk of gestational diabetes mellitus and perhaps hypertensive disorders of pregnancy (i.e. gestational hypertension and pre-eclampsia) compared with less vigorous exercise. To achieve the target expenditure of 28 MET hours per week, one could walk at 3.2 km per hour for 11.2 hours per week (2.5 METs, light intensity), or preferably exercise on a stationary bicycle for 4.7 hours per week (∼6-7 METs, vigorous intensity). The more vigorous the exercise, the less total time of exercise is required per week, resulting in ≥60% reduction in total exercise time compared with light intensity exercise. Light muscle strengthening performed over the second and third trimester of pregnancy has minimal effects on a newborn infant's body size and overall health. On the basis of this and other information, updated recommendations for exercise in pregnancy are suggested.

An exploratory analysis of the effects of a weight loss plus exercise program on cellular quality control mechanisms in older overweight women

Obese older adults are particularly susceptible to sarcopenia and have a higher prevalence of disability than their peers of normal weight. Interventions to improve body composition in late life are crucial to maintaining independence. The main mechanisms underlying sarcopenia have not been determined conclusively, but chronic inflammation, apoptosis, and impaired mitochondrial function are believed to play important roles. It has yet to be determined whether impaired cellular quality control mechanisms contribute to this process. The objective of this study was to assess the effects of a 6-month weight loss program combined with moderate-intensity exercise on the cellular quality control mechanisms autophagy and ubiquitin-proteasome, as well as on inflammation, apoptosis, and mitochondrial function, in the skeletal muscle of older obese women. The intervention resulted in significant weight loss (8.0 ± 3.9 % vs. 0.4 ± 3.1% of baseline weight, p = 0.002) and improvements in walking speed (reduced time to walk 400 meters, - 20.4 ± 16% vs. - 2.5 ± 12%, p = 0.03). In the intervention group, we observed a three-fold increase in messenger RNA (mRNA) levels of the autophagy regulators LC3B, Atg7, and lysosome-associated membrane protein-2 (LAMP-2) compared to controls. Changes in mRNA levels of FoxO3A and its targets MuRF1, MAFBx, and BNIP3 were on average seven-fold higher in the intervention group compared to controls, but these differences were not statistically significant. Tumor necrosis factor-α (TNF-α) mRNA levels were elevated after the intervention, but we did not detect significant changes in the downstream apoptosis markers caspase 8 and 3. Mitochondrial biogenesis markers (PGC1α and TFAm) were increased by the intervention, but this was not accompanied by significant changes in mitochondrial complex content and activity. In conclusion, although exploratory in nature, this study is among the first to report the stimulation of cellular quality control mechanisms elicited by a weight loss and exercise program in older obese women.

Long-term synthesis rates of skeletal muscle DNA and protein are higher during aerobic training in older humans than in sedentary young subjects but are not altered by protein supplementation

Consuming protein following exercise has been shown to stimulate protein synthesis acutely in skeletal muscle and has been recommended to prevent sarcopenia. It is not known, however, whether acute stimulation persists long term or includes muscle cell division. We asked here whether consuming protein following exercise during aerobic training increases long-term protein and DNA synthesis rates in skeletal muscle of adult humans. Sixteen previously untrained participants (50 ± 8 yr) consumed either a carbohydrate or carbohydrate and protein drink following each session during 6 wk of treadmill training. A younger untrained group provided a nonexercising comparison. Participants were administered heavy water (²H₂O; deuterium oxide) continuously for 6 wk to isotopically label newly synthesized skeletal muscle proteins and DNA. Muscle biopsies were performed after 6 wk of training. Contrary to acute studies, consuming protein after exercise did not increase skeletal muscle protein synthesis rates. In contrast, muscle protein synthesis, DNA, and phospholipid synthesis were significantly higher in the older exercise groups than the younger sedentary group. The higher DNA replication rate could not be attributed to mitochondrial DNA and may be due to satellite cell activation. We conclude that postexercise protein supplementation does not increase rates of mixed protein synthesis over 6 wk and that aerobic exercise may stimulate long-term cell division (DNA synthesis) in skeletal muscle of humans. Measurements of long-term synthesis rates provide important insights into aging and exercise adaptations.

Alterations in muscular oxidative metabolism parameters in incremental treadmill exercise test in untrained rats

The present study investigates the effects of incremental exercise test on muscular oxidative metabolism. Thirty-six 2-month-old male Wistar rats were distributed in seven groups that performed exercise at different levels: first level (control), second level (0.6 km/h), third level (0.6 and 0.8 km/h), fourth level (0.6, 0.8 and 1.0 km/h), fifth level (0.6, 0.8, 1.0 and 1.2 km/h), sixth level (0.6, 0.8, 1.0, 1.2 and 1.4 km/h), and seventh level (0.6, 0.8, 1.0, 1.2, 1.4 and 1.6 km/h). At the end of the exercise challenge, level of blood lactate (BL), glycogen content (MG), creatine kinase (CK), complexes (CI, CII, CIII, CIV), oxidative damage, succinate dehydrogenase (SDH), cytochrome c oxidase as well as antioxidant enzymes (SOD and CAT) expression were measured. The speed of 1.0 km/h increased BL level, while 1.2 km/h decreased MG and increased serum CK. Increased SDH expression was observed after intensity levels 6 and 7, and cytochrome c oxidase expression increased after levels 5, 6 and 7, in comparison with lower intensity levels, ETC enzyme activities increased when exercise was applied at intensities of 0.8 km/h (CI), 1.0 km/h (CII and CIII), and 1.2 km/h (CIV). The increase in SOD expression did not occur as observed for superoxide production, except for rats that underwent exercise at level 7, but CAT expression increased significantly in all levels, starting from level 3. Our results show interesting alterations in the muscular metabolism parameters, and suggest a differential response of muscle oxidative metabolism when intense exercise is applied at different speeds.

Morphofunctional and Biochemical Approaches for Studying Mitochondrial Changes during Myoblasts Differentiation

This study describes mitochondrial behaviour during the C2C12 myoblast differentiation program and proposes a proteomic approach to mitochondria integrated with classical morphofunctional and biochemical analyses. Mitochondrial ultrastructure variations were determined by transmission electron microscopy; mitochondrial mass and membrane potential were analysed by Mitotracker Green and JC-1 stains and by epifluorescence microscope. Expression of PGC1α, NRF1α, and Tfam genes controlling mitochondrial biogenesis was studied by real-time PCR. The mitochondrial functionality was tested by cytochrome c oxidase activity and COXII expression. Mitochondrial proteomic profile was also performed. These assays showed that mitochondrial biogenesis and activity significantly increase in differentiating myotubes. The proteomic profile identifies 32 differentially expressed proteins, mostly involved in oxidative metabolism, typical of myotubes formation. Other notable proteins, such as superoxide dismutase (MnSOD), a cell protection molecule, and voltage-dependent anion-selective channel protein (VDAC1) involved in the mitochondria-mediated apoptosis, were found to be regulated by the myogenic process. The integration of these approaches represents a helpful tool for studying mitochondrial dynamics, biogenesis, and functionality in comparative surveys on mitochondrial pathogenic or senescent satellite cells.

Current understanding of the genetic basis for physical activity

Although it is well known that physical activity prevents and ameliorates a large number of conditions and chronic diseases, it is also incontrovertible that physical inactivity is becoming more prevalent. This paradox has led some to suggest that genetic/biological factors influence activity levels as opposed to the classical notion that voluntary activity is solely regulated by environmental factors. There is a plethora of recent data showing that there is considerable genetic influence on activity levels in both humans and animals and emerging evidence suggesting potential genomic locations for those genetic factors. Several independent lines of evidence suggest that dopamine receptor 1 (Drd1) and nescient helix loop helix (Nhlh2) are excellent candidate genes for the regulation of physical activity, with several other potential candidate genes only partially supported. This foundation provides the basis for continuing work to identify additional candidate genes, to identify other genetic factors that are involved in the regulation of physical activity, and to investigate the mechanisms by which these genes and genetic factors regulate activity.

Mitochondrial biogenesis and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) deacetylation by physical activity: intact adipocytokine signaling is required

OBJECTIVE Transcriptional peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) plays a key role in mitochondrial biogenesis and energy metabolism and is suggested to be involved in the exercise-induced increase in mitochondrial content. PGC-1α activity is regulated by posttranslational modifications, among them acetylation or phosphorylation. Accordingly, the deacetylase SIRT1 and the kinase AMPK increase PGC-1α activity. RESEARCH DESIGN AND METHODS We tested whether chronic treadmill exercise or a single exercise session modifies PGC-1α activation and mitochondrial biogenesis differentially in obese ob/ob mice with dysregulated adiponectin/leptin-mediated AMPK activation compared with C57BL/6J wild-type mice. RESULTS Exercise training (12 weeks) induced adiponectin and lowered plasma insulin and glucose, suggesting improved insulin sensitivity in wild-type mice. It enhanced mitochondrial biogenesis in red gastrocnemius muscle, as indicated by increased mRNA expression of transcriptional regulators and primary mitochondrial transcripts, increased mtDNA content, and citrate synthase activity. Parallel to this, we observed AMPK activation, PGC-1α deacetylation, and SIRT1 induction in trained wild-type mice. Although none of these exercise-induced changes were detected in ob/ob mice, comparable effects on mitochondrial respiration were observed. A single exercise session resulted in comparable changes in wild-type mice. These changes remained detectable 6 h after the exercise session but had disappeared after 24 h. Treatment of C2C12 myoblasts with leptin or adiponectin resulted in increased AMPK phosphorylation and PGC-1α deacetylation. CONCLUSIONS Chronic exercise induces mitochondrial biogenesis in wild-type mice, which may require intact AMPK activation by adipocytokines and involve SIRT1-dependent PGC-1α deacetylation. Trained ob/ob mice appear to have partially adapted to reduced mitochondrial biogenesis by AMPK/SIRT1/PGC-1α-independent mechanisms without mtDNA replication.

Thermogenesis and related metabolic targets in anti-diabetic therapy

Exercise, together with a low-energy diet, is the first-line treatment for type 2 diabetes type 2 diabetes . Exercise improves insulin sensitivity insulin sensitivity by increasing the number or function of muscle mitochondria mitochondria and the capacity for aerobic metabolism, all of which are low in many insulin-resistant subjects. Cannabinoid 1-receptor antagonists and β-adrenoceptor agonists improve insulin sensitivity in humans and promote fat oxidation in rodents independently of reduced food intake. Current drugs for the treatment of diabetes are not, however, noted for their ability to increase fat oxidation, although the thiazolidinediones increase the capacity for fat oxidation in skeletal muscle, whilst paradoxically increasing weight gain.There are a number of targets for anti-diabetic drugs that may improve insulin sensitivity insulin sensitivity by increasing the capacity for fat oxidation. Their mechanisms of action are linked, notably through AMP-activated protein kinase, adiponectin, and the sympathetic nervous system. If ligands for these targets have obvious acute thermogenic activity, it is often because they increase sympathetic activity. This promotes fuel mobilisation, as well as fuel oxidation. When thermogenesis thermogenesis is not obvious, researchers often argue that it has occurred by using the inappropriate device of treating animals for days or weeks until there is weight (mainly fat) loss and then expressing energy expenditure energy expenditure relative to body weight. In reality, thermogenesis may have occurred, but it is too small to detect, and this device distracts us from really appreciating why insulin sensitivity has improved. This is that by increasing fatty acid oxidation fatty acid oxidation more than fatty acid supply, drugs lower the concentrations of fatty acid metabolites that cause insulin resistance. Insulin sensitivity improves long before any anti-obesity effect can be detected.

Insulin resistance syndrome blunts the mitochondrial anabolic response following resistance exercise

Metabolic risk factors associated with insulin resistance syndrome may attenuate augmentations in skeletal muscle protein anabolism following contractile activity. The purpose of this study was to investigate whether or not the anabolic response, as defined by an increase in cumulative fractional protein synthesis rates (24-h FSR) following resistance exercise (RE), is blunted in skeletal muscle of a well-established rodent model of insulin resistance syndrome. Four-month-old lean (Fa/?) and obese (fa/fa) Zucker rats engaged in four lower body RE sessions over 8 days, with the last bout occurring 16 h prior to muscle harvest. A priming dose of deuterium oxide ((2)H(2)O) and (2)H(2)O-enriched drinking water were administered 24 h prior to euthanization for assessment of cumulative FSR. Fractional synthesis rates of mixed (-5%), mitochondrial (-1%), and cytosolic (+15%), but not myofibrillar, proteins (-16%, P = 0.012) were normal or elevated in gastrocnemius muscle of unexercised obese rats. No statistical differences were found in the anabolic response of cytosolic and myofibrillar subfractions between phenotypes, but obese rats were not able to augment 24-h FSR of mitochondria to the same extent as lean rats following RE (+14% vs. +28%, respectively). We conclude that the mature obese Zucker rat exhibits a mild, myofibrillar-specific suppression in basal FSR and a blunted mitochondrial response to contractile activity in mixed gastrocnemius muscle. These findings underscore the importance of assessing synthesis rates of specific myocellular subfractions to fully elucidate perturbations in basal protein turnover rates and differential adaptations to exercise stimuli in metabolic disease.

Subjects with early-onset type 2 diabetes show defective activation of the skeletal muscle PGC-1{alpha}/Mitofusin-2 regulatory pathway in response to physical activity

OBJECTIVE Type 2 diabetes is associated with insulin resistance and skeletal muscle mitochondrial dysfunction. We have found that subjects with early-onset type 2 diabetes show incapacity to increase Vo(2max) in response to chronic exercise. This suggests a defect in muscle mitochondrial response to exercise. Here, we have explored the nature of the mechanisms involved. RESEARCH DESIGN AND METHODS Muscle biopsies were collected from young type 2 diabetic subjects and obese control subjects before and after acute or chronic exercise protocols, and the expression of genes and/or proteins relevant to mitochondrial function was measured. In particular, the regulatory pathway peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha/mitofusin-2 (Mfn2) was analyzed. RESULTS At baseline, subjects with diabetes showed reduced expression (by 26%) of the mitochondrial fusion protein Mfn2 and a 39% reduction of the alpha-subunit of ATP synthase. Porin expression was unchanged, consistent with normal mitochondrial mass. Chronic exercise led to a 2.8-fold increase in Mfn2, as well as increases in porin, and the alpha-subunit of ATP synthase in muscle from control subjects. However, Mfn2 was unchanged after chronic exercise in individuals with diabetes, whereas porin and alpha-subunit of ATP synthase were increased. Acute exercise caused a fourfold increase in PGC-1alpha expression in muscle from control subjects but not in subjects with diabetes. CONCLUSIONS Our results demonstrate alterations in the regulatory pathway that controls PGC-1alpha expression and induction of Mfn2 in muscle from patients with early-onset type 2 diabetes. Patients with early-onset type 2 diabetes display abnormalities in the exercise-dependent pathway that regulates the expression of PGC-1alpha and Mfn2.

Alterations in the mitochondrial regulatory pathways constituted by the nuclear co-factors PGC-1alpha or PGC-1beta and mitofusin 2 in skeletal muscle in type 2 diabetes

Muscle mitochondrial metabolism is regulated by a number of factors, many of which are responsible for the transcription of nuclear genes encoding mitochondrial proteins such as PPARdelta, PGC-1alpha or PGC-1beta. Recent evidence indicates that proteins participating in mitochondrial dynamics also regulate mitochondrial metabolism. Thus, in cultured cells the mitochondrial fusion protein mitofusin 2 (Mfn2) stimulates respiration, substrate oxidation and the expression of subunits involved in respiratory complexes. Mitochondrial dysfunction has been reported in skeletal muscle of type 2 diabetic patients. Reduced mitochondrial mass and defective activity has been proposed to explain this dysfunction. Alterations in mitochondrial metabolism may be crucial to account for some of the pathophysiological traits that characterize type 2 diabetes. Skeletal muscle of type 2 diabetic patients shows reduced expression of PGC-1alpha, PGC-1beta, and Mfn2. In addition, a differential response to bilio-pancreatic diversion-induced weight loss in non-diabetic and type 2 diabetic patients has been reported. While non-diabetic morbidly obese subjects showed an increased expression of genes encoding Mfn2, PGC-1alpha, PGC-1beta, PPARdelta or SIRT1 in response to bariatric surgery-induced weight loss, no effect was detected in type 2 diabetic patients. These observations suggest the existence of a heritable component responsible for the abnormal control of the expression of genes encoding for modulators of mitochondrial biogenesis/metabolism, and which may participate in the development of the disease.

Deficiency of electron transport chain in human skeletal muscle mitochondria in type 2 diabetes mellitus and obesity

Insulin resistance in skeletal muscle in obesity and T2DM is associated with reduced muscle oxidative capacity, reduced expression in nuclear genes responsible for oxidative metabolism, and reduced activity of mitochondrial electron transport chain. The presented study was undertaken to analyze mitochondrial content and mitochondrial enzyme profile in skeletal muscle of sedentary lean individuals and to compare that with our previous data on obese or obese T2DM group. Frozen skeletal muscle biopsies obtained from lean volunteers were used to estimate cardiolipin content, mtDNA (markers of mitochondrial mass), NADH oxidase activity of mitochondrial electron transport chain (ETC), and activity of citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD), key enzymes of TCA cycle and beta-oxidation pathway, respectively. Frozen biopsies collected from obese or T2DM individuals in our previous studies were used to estimate activity of beta-HAD. The obtained data were complemented by data from our previous studies and statistically analyzed to compare mitochondrial content and mitochondrial enzyme profile in lean, obese, or T2DM cohort. The total activity of NADH oxidase was reduced significantly in obese or T2DM subjects. The cardiolipin content for lean or obese group was similar, and although for T2DM group cardiolipin showed a tendency to decline, it was statistically insignificant. The total activity of citrate synthase for lean and T2DM group was similar; however, it was increased significantly in the obese group. Activity of beta-HAD and mtDNA content was similar for all three groups. We conclude that the total activity of NADH oxidase in biopsy for lean group is significantly higher than corresponding activity for obese or T2DM cohort. The specific activity of NADH oxidase (per mg cardiolipin) and NADH oxidase/citrate synthase and NADH oxidase/beta-HAD ratios are reduced two- to threefold in both T2DM and obesity.