Skeletal muscle metabolic adaptations to endurance exercise training are attainable in mice with simvastatin treatment

Endurance training and hydroxyurea have synergistic effects on muscle function and energetics in sickle cell disease mice

Sickle cell disease (SCD) is an hemoglobinopathy resulting in the production of an abnormal Hb (HbS) which can polymerize in deoxygenated conditions, leading to the sickling of red blood cells (RBC). These alterations can decrease the oxygen-carrying capacity leading to impaired function and energetics of skeletal muscle. Any strategy which could reverse the corresponding defects could be of interest. In SCD, endurance training is known to improve multiples muscle properties which restores patient's exercise capacity but present reduced effects in anemic patients. Hydroxyurea (HU) can increase fetal hemoglobin production which can reduce anemia in patients. The present study was conducted to determine whether HU can improve the effects of endurance training to improve muscle function and energetics. Twenty SCD Townes mice have been trained for 8 weeks with (n = 11) or without (n = 9) HU. SCD mice muscle function and energetics were analyzed during a standardized rest-exercise-recovery protocol, using Phosphorus-31 Magnetic resonance spectroscopy (31P-MRS) and transcutaneous stimulation. The combination of training and HU specifically decreased fatigue index and PCr consumption while muscle oxidative capacity was improved. These results illustrate the potential synergistic effects of endurance training and HU on muscle function and energetics in sickle cell disease.

Relationships between endurance exercise training-induced muscle fiber-type shifting and autophagy in slow- and fast-twitch skeletal muscles of mice

PURPOSE

Endurance exercise induces muscle fiber-type shifting and autophagy; however, the potential role of autophagy in muscle fiber-type transformation remains unclear. This study examined the relationship between muscle fiber-type shifting and autophagy in the soleus (SOL) and extensor digitorum longus (EDL) muscles, which are metabolically discrete muscles.

METHODS

Male C57BL/6J mice were randomly assigned to sedentary control (CON) and exercise (EXE) groups. After 1 week of acclimation to treadmill running, the mice in the EXE group ran at 12-15 m/min, 60 min/day, 5 days/week for 6 weeks. All mice were sacrificed 90 min after the last exercise session, and the targeted tissues were rapidly dissected. The right side of the tissues was used for western blot analysis, whereas the left side was subjected to immunohistochemical analysis.

RESULTS

Endurance exercise resulted in muscle fiber-type shifting (from type IIa to type I) and autophagy (an increase in LC3-II) in the SOL muscle. However, muscle fiber-type transformation and autophagy were not correlated in the SOL and EDL muscles. Interestingly, in contrast to the canonical autophagy signaling pathways, our study showed that exercise-induced autophagy concurs with enhanced anabolic (increased p-AKTSer473/AKT and p-mTOR/mTORSer2448 ratios) and suppressed catabolic (reduced p-AMPKThr172/AMPK ratio) states.

CONCLUSION

Our findings demonstrate that chronic endurance exercise-induced muscle fiber-type transformation and autophagy occur in a muscle-specific manner (e.g., SOL). More importantly, our study suggests that endurance training-induced SOL muscle fiber-type transition may underlie metabolic modulations caused by the AMPK and AKT/mTOR signaling pathways rather than autophagy.

Migration increases mitochondrial oxidative capacity without increasing reactive oxygen species emission in a songbird

Birds remodel their flight muscle metabolism prior to migration to meet the physiological demands of migratory flight, including increases in both oxidative capacity and defence against reactive oxygen species. The degree of plasticity mediated by changes in these mitochondrial properties is poorly understood but may be explained by two non-mutually exclusive hypotheses: variation in mitochondrial quantity or in individual mitochondrial function. We tested these hypotheses using yellow-rumped warblers (Setophaga coronata), a Nearctic songbird which biannually migrates 2000-5000 km. We predicted higher flight muscle mitochondrial abundance and substrate oxidative capacity, and decreased reactive oxygen species emission in migratory warblers captured during autumn migration compared with a short-day photoperiod-induced non-migratory phenotype. We assessed mitochondrial abundance via citrate synthase activity and assessed isolated mitochondrial function using high-resolution fluororespirometry. We found 60% higher tissue citrate synthase activity in the migratory phenotype, indicating higher mitochondrial abundance. We also found 70% higher State 3 respiration (expressed per unit citrate synthase) in mitochondria from migratory warblers when oxidizing palmitoylcarnitine, but similar H2O2 emission rates between phenotypes. By contrast, non-phosphorylating respiration was higher and H2O2 emission rates were lower in the migratory phenotype. However, flux through electron transport system complexes I-IV, II-IV and IV was similar between phenotypes. In support of our hypotheses, these data suggest that flight muscle mitochondrial abundance and function are seasonally remodelled in migratory songbirds to increase tissue oxidative capacity without increasing reactive oxygen species formation.

Social jet lag impairs exercise volume and attenuates physiological and metabolic adaptations to voluntary exercise training

Social jet lag (SJL) is a misalignment between sleep and wake times on workdays and free days. SJL leads to chronic circadian rhythm disruption and may affect nearly 70% of the general population, leading to increased risk for cardiometabolic diseases. This study investigated the effects of SJL on metabolic health, exercise performance, and exercise-induced skeletal muscle adaptations in mice. Ten-week-old C57BL/6J mice (n = 40) were allocated to four groups: control sedentary (CON-SED), control exercise (CON-EX), social jet lag sedentary (SJL-SED), and social jet lag exercise (SJL-EX). CON mice were housed under a 12:12-h light-dark cycle. SJL was simulated by implementing a 4-h phase delay for 3 days to simulate "weekends," followed by a 4-h phase advance back to "weekdays," for 6 wk. EX mice had free access to a running wheel. Graded exercise tests (GXTs) and glucose tolerance tests (GTTs) were performed at baseline and after intervention to monitor the effects of exercise and social jet lag on cardiorespiratory and metabolic health, respectively. SJL led to alterations in activity and running patterns and clock gene expression in skeletal muscle and decreased average running distance (P < 0.05). SJL-SED mice gained significantly more weight compared with CON-SED and SJL-EX mice (P < 0.01). SJL impaired fasting blood glucose and glucose tolerance compared with CON mice (P < 0.05), which was partially restored by exercise in SJL-EX mice. SJL also blunted improvements in exercise performance and mitochondrial content in the quadriceps. These data suggest that SJL blunted some cardiometabolic adaptations to exercise and that proper circadian hygiene is necessary for maintaining health and performance.NEW & NOTEWORTHY In mice, disrupting circadian rhythms with social jet lag for 6 wk caused significant weight gain, higher fasting blood glucose, and impaired glucose tolerance compared with control. Voluntary exercise in mice experiencing social jet lag prevented weight gain, though the mice still experienced increased fasting blood glucose and impaired exercise performance compared with trained mice not experiencing social jet lag. Social jet lag seems to be a potent circadian rhythm disruptor that impacts exercise-induced training adaptations.

Resistance wheel running improves contractile strength, but not metabolic capacity, in a murine model of volumetric muscle loss injury

The primary objective of this study was to determine if low- or high-resistance voluntary wheel running leads to functional improvements in muscle strength (i.e., isometric and isokinetic torque) and metabolic function (i.e., permeabilized fibre bundle mitochondrial respiration) after a volumetric muscle loss (VML) injury. C57BL/6J mice were randomized into one of four experimental groups at age 12 weeks: uninjured control, VML untreated (VML), low-resistance wheel running (VML-LR) and high-resistance wheel running (VML-HR). All mice, excluding the uninjured, were subject to a unilateral VML injury to the plantar flexor muscles and wheel running began 3 days post-VML. At 8 weeks post-VML, peak isometric torque was greater in uninjured compared to all VML-injured groups, but both VML-LR and VML-HR had greater (∼32%) peak isometric torque compared to VML. All VML-injured groups had less isokinetic torque compared to uninjured, and there was no statistical difference among VML, VML-LR and VML-HR. No differences in cumulative running distance were observed between VML-LR and VML-HR groups. Because adaptations in VML-HR peak isometric torque were attributed to greater gastrocnemius muscle mass, atrophy- and hypertrophy-related protein content and post-translational modifications were explored via immunoblot; however, results were inconclusive. Permeabilized fibre bundle mitochondrial oxygen consumption was 22% greater in uninjured compared to VML, but there was no statistical difference among VML, VML-LR and VML-HR. Furthermore, neither wheel running group demonstrated a change in the relative protein content of the mitochondrial biogenesis transcription factor, peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α). These results indicate that resistance wheel running alone only has modest benefits in the VML-injured muscle. NEW FINDINGS: What is the central question of the study? Does initiation of a resistance wheel running regimen following volumetric muscle loss (VML) improve the functional capacity of skeletal muscle? What is the main finding and its importance? Resistance wheel running led to greater muscle mass and strength in mice with a VML injury but did not result in a full recovery. Neither low- nor high-resistance wheel running was associated with a change in permeabilized muscle fibre respiration despite runners having greater whole-body treadmill endurance capacity, suggesting resilience to metabolic adaptations in VML-injured muscle. Resistance wheel running may be a suitable adjuvant rehabilitation strategy, but alone does not fully mitigate VML pathology.

Mitochondrial Fission as a Therapeutic Target for Metabolic Diseases: Insights into Antioxidant Strategies

Mitochondrial fission is a crucial process in maintaining metabolic homeostasis in normal physiology and under conditions of stress. Its dysregulation has been associated with several metabolic diseases, including, but not limited to, obesity, type 2 diabetes (T2DM), and cardiovascular diseases. Reactive oxygen species (ROS) serve a vital role in the genesis of these conditions, and mitochondria are both the main sites of ROS production and the primary targets of ROS. In this review, we explore the physiological and pathological roles of mitochondrial fission, its regulation by dynamin-related protein 1 (Drp1), and the interplay between ROS and mitochondria in health and metabolic diseases. We also discuss the potential therapeutic strategies of targeting mitochondrial fission through antioxidant treatments for ROS-induced conditions, including the effects of lifestyle interventions, dietary supplements, and chemicals, such as mitochondrial division inhibitor-1 (Mdivi-1) and other mitochondrial fission inhibitors, as well as certain commonly used drugs for metabolic diseases. This review highlights the importance of understanding the role of mitochondrial fission in health and metabolic diseases, and the potential of targeting mitochondrial fission as a therapeutic approach to protecting against these conditions.

Pharmaceutical Agents for Contractile-Metabolic Dysfunction After Volumetric Muscle Loss

Volumetric muscle loss (VML) injuries represent a majority of military service member casualties and are common in civilian populations following blunt and/or penetrating traumas. Characterized as a skeletal muscle injury with permanent functional impairments, there is currently no standard for rehabilitation, leading to lifelong disability. Toward developing rehabilitative strategies, previous research demonstrates that the remaining muscle after a VML injury lacks similar levels of plasticity or adaptability as healthy, uninjured skeletal muscle. This may be due, in part, to impaired innervation and vascularization of the remaining muscle, as well as disrupted molecular signaling cascades commonly associated with muscle adaptation. The primary objective of this study was to assess the ability of four pharmacological agents with a strong record of modulating muscle contractile and metabolic function to improve functional deficits in a murine model of VML injury. Male C57BL/6 mice underwent a 15% multimuscle VML injury of the posterior hindlimb and were randomized into drug treatment groups (formoterol [FOR], 5-aminoimidazole-4-carboxamide riboside [AICAR], pioglitazone [PIO], or sildenafil [SIL]) or untreated VML group. At the end of 60 days, the injury model was first validated by comparison to age-matched injury-naive mice. Untreated VML mice had 22% less gastrocnemius muscle mass, 36% less peak-isometric torque, and 27% less maximal mitochondrial oxygen consumption rate compared to uninjured mice (p < 0.01). Experimental drug groups were, then, compared to VML untreated, and there was minimal evidence of efficacy for AICAR, PIO, or SIL in improving contractile and metabolic functional outcomes. However, FOR-treated VML mice had 18% greater peak isometric torque (p < 0.01) and permeabilized muscle fibers had 36% greater State III mitochondrial oxygen consumption rate (p < 0.01) compared to VML untreated mice, suggesting an overall improvement in muscle condition. There was minimal evidence that these benefits came from greater mitochondrial biogenesis and/or mitochondrial complex protein content, but could be due to greater enzyme activity levels for complex I and complex II. These findings suggest that FOR treatment is candidate to pair with a rehabilitative approach to maximize functional improvements in VML-injured muscle. Impact statement Volumetric muscle loss (VML) injuries result in deficiencies in strength and mobility, which have a severe impact on patient quality of life. Despite breakthroughs in tissue engineering, there are currently no treatments available that can restore function to the affected limb. Our data show that treatment of VML injuries with clinically available and FDA-approved formoterol (FOR), a beta-agonist, significantly improves strength and metabolism of VML-injured muscle. FOR is therefore a promising candidate for combined therapeutic approaches (i.e., regenerative rehabilitation) such as pairing FOR with structured rehabilitation or cell-seeded biomaterials as it may provide greater functional improvements than either strategy alone.

Mitochondrial Dysfunctions and Potential Molecular Markers in Sport Horses

Mitochondria are an essential part of most eukaryotic cells. The crucial role of these organelles is the production of metabolic energy, which is converted into ATP in oxidative phosphorylation. They are also involved in and constitute apoptosis, the site of many metabolic processes. Some of the factors that negatively affect mitochondria are stress, excessive exercise, disease, and the aging process. Exercise can cause the release of large amounts of free radicals, inflammation, injury, and stress. All of these factors can contribute to mitochondrial dysfunction, which can consistently lead to inflammatory responses, tissue damage, organ dysfunction, and a host of diseases. The functions of the mitochondria and the consequences of their disturbance can be of great importance in the breeding and use of horses. The paper reviews mitochondrial disorders in horses and, based on the literature, indicates genetic markers strongly related to this issue.

Impact of Atorvastatin on Skeletal Muscle Mitochondrial Activity, Locomotion and Axonal Excitability-Evidence from ApoE-/- Mice

The cardiovascular benefit of statins is well established. However, only 20% of high-risk patients remain adequately adherent after 5 years of treatment. Among reasons for discontinuation, statin associated-muscle pain symptoms are the most prevalent. Aim of the present study was to evaluate the impact of high dose atorvastatin on skeletal muscle mitochondrial activity, aerobic and anaerobic exercise, and axonal excitability in a murine model of atherosclerosis. ApoE^-/- mice were fed 12 weeks a high-fat high-cholesterol diet alone or containing atorvastatin (40 mg/Kg/day). Outcomes were the evaluation of muscle mitochondrial functionality, locomotion, grip test, and axonal excitability (compound action potential recording analysis of Aα motor propioceptive, Aβ mechanoceptive and C nociceptive fibres). Atorvastatin led to a reduction in muscle mitochondrial biogenesis and mitochondrial ATP production. It did not affect muscular strength but led to a time-dependent motor impairment. Atorvastatin altered the responsiveness of mechanoceptive and nociceptive fibres, respectively, the Aβ and C fibres. These findings point out to a mild sensitization on mechanical, tactile and pain sensitivity. In conclusion, although the prevalence of muscular side effects from statins may be overestimated, understanding of the underlying mechanisms can help improve the therapeutic approach and reassure adherence in patients needing-to-be-treated.

The impact of statin therapy and aerobic exercise training on skeletal muscle and whole-body aerobic capacity

Background

Statin use is widely recognized for improving cardiovascular health, but questions remain on how statin use influences skeletal muscle, particularly mitochondrial function.

Study objective design and participants

The influence of statin therapy and exercise (EX) on aerobic capacity was determined. In Study1, skeletal muscle aerobic capacity was measured before and after 80 mg atorvastatin therapy. In Study2, aerobic capacity (skeletal muscle and whole body) was measured before and after a 12-week exercise randomized control trial in older adults (age = 67 ± 5 yrs.), a subset of which were on chronic low-moderate intensity statin therapy.

Main outcome measures

Muscle oxidative capacity was determined from the phosphocreatine recovery rate constant (kPCr) using ³¹P Magnetic Resonance Spectroscopy. Whole body peak oxygen uptake (VO₂ peak) was measured during a graded exercise test with indirect calorimetry.

Results

High dose statin therapy resulted in a 12% reduction in muscle oxidative capacity (pre = 1.34 ± 0.34 min^-1, post = 1.17 ± 0.25 min^-1, p = 0.004). Similarly, chronic low-moderate dose statin therapy was associated with lower muscle oxidative capacity at baseline (1.50 ± 0.35 min^-1) compared to non-statin users (1.88 ± 0.047 min^-1, p = 0.019). Following EX, muscle oxidative capacity increased by 35-40% (statin: Pre: 1.39 ± 0.44 vs. Post: 1.88 ± 0.47 min^-1, no statin Pre: 1.86 ± 0.58 vs. Post: 2.58 ± 0.85 min^-1) compared to control groups (Pre: 1.74 ± 0.27 vs Post: 1.75 ± 0.49 min^-1, p = 0.001). VO₂ peak increased by 11% for EX groups (Pre: 18.8 ± 2.8 vs. Post: 20.8 ± 3.0 ml·kg^-1·min^-1) following training compared to a small decline in controls (Pre: 21.8 ± 3.7 vs. Post: 20.8 ± 3.04 ml·kg^-1·min^-1, p = 0.001).

Conclusions

Statin therapy resulted in reduced muscle oxidative capacity. Aerobic exercise improved skeletal muscle oxidative capacity and whole-body aerobic capacity during statin therapy.

Effect of statin treatment in obese selenium-supplemented mice lacking selenocysteine lyase

People with obesity are often dyslipidemic and prescribed statins to prevent cardiovascular events. A common side effect of statin use is myopathy. This could potentially be caused by the reduction of selenoproteins that curb oxidative stress, in turn, affecting creatine metabolism. We determined if statins regulate hepatic and muscular selenoprotein expression, oxidative stress and creatine metabolism. Mice lacking selenocysteine lyase (Scly KO), a selenium-provider enzyme for selenoprotein synthesis, were fed a high-fat, Se-supplemented diet and treated with simvastatin. Statin improved creatine metabolism in females and oxidative responses in both sexes. Male Scly KO mice were heavier than females after statin treatment. Hepatic selenoproteins were unaffected by statin and genotype in females. Statin upregulated muscular Gpx1 in females but not males, while Scly loss downregulated muscular Gpx1 in males and Selenon in females. Osgin1 was reduced in statin-treated Scly KO males after AmpliSeq analysis. These results refine our understanding of the sex-dependent role of selenium in statin responses.

Adrenal stress hormone action in skeletal muscle during exercise training: An old dog with new tricks?

Exercise is a key component of a healthy lifestyle as it helps maintain a healthy body weight and reduces the risk of various morbidities and co-morbidities. Exercise is an acute physiological stress that initiates a multitude of processes that attempt to restore physiological homeostasis and promote adaptation. A component of the stress response to exercise is the rapid release of hormones from the adrenal gland including glucocorticoids, the catecholamines and aldosterone. While each hormone targets several tissues throughout the body, skeletal muscle is of interest as it is central to physical function and various metabolic processes. Indeed, adrenal stress hormones have been shown to elicit specific performance benefits on the muscle. However, how the acute, short-lived release of these stress hormones during exercise influences adaptations of skeletal muscle to long-term training remains largely unknown. Thus, the objective of this review was to briefly highlight the known impact of adrenal stress hormones on skeletal muscle metabolism and function (Old Dog), and critically examine the current evidence supporting a role for these endogenous hormones in mediating long-term training adaptations in skeletal muscle (New Tricks).

Optogenetic activation of muscle contraction in vivo

Purpose: Optogenetics is an emerging alternative to traditional electrical stimulation to initiate action potentials in activatable cells both ex vivo and in vivo. Optogenetics has been commonly used in mammalian neurons and more recently, it has been adapted for activation of cardiomyocytes and skeletal muscle. Therefore, the aim of this study was to evaluate the stimulation feasibility and sustain isometric muscle contraction and limit decay for an extended period of time (1s), using non-invasive transdermal light activation of skeletal muscle (triceps surae) in vivo.

MATERIALS AND METHODS

We used inducible Cre recombination to target expression of Channelrhodopsin-2 (ChR2(H134R)-EYFP) in skeletal muscle (Acta1-Cre) in mice. Fluorescent imaging confirmed that ChR2 expression is localized in skeletal muscle and does not have specific expression in sciatic nerve branch, therefore, allowing for non-nerve mediated optical stimulation of skeletal muscle. We induced muscle contraction using transdermal exposure to blue light and selected 10 Hz stimulation after controlled optimization experiments to sustain prolonged muscle contraction.

RESULTS

Increasing the stimulation frequency from 10 Hz to 40 Hz increased the muscle contraction decay during prolonged 1s stimulation, highlighting frequency dependency and importance of membrane repolarization for effective light activation. Finally, we showed that optimized pulsed optogenetic stimulation of 10 Hz resulted in comparable ankle torque and contractile functionality to that of electrical stimulation.

CONCLUSIONS

Our results demonstrate the feasibility and repeatability of non-invasive optogenetic stimulation of muscle in vivo and highlight optogenetic stimulation as a powerful tool for non-invasive in vivo direct activation of skeletal muscle.

Skeletal muscle effects of two different 10-week exercise regimens, voluntary wheel running, and forced treadmill running, in mice: A pilot study

Physical activity and exercise induce a complex pattern of adaptation reactions in a broad variety of tissues and organs, particularly the cardiovascular and the musculoskeletal systems. The underlying mechanisms, however, specifically the molecular changes that occur in response to training, are still incompletely understood. Animal models help to systematically elucidate the mechanisms of exercise adaptation. With regard to endurance-based running exercise in mice, two basic regimens have been established: forced treadmill running (FTR), usually consisting of several sessions per week, and voluntary wheel running (VWR). However, the effects of these two programs on skeletal muscle molecular adaptation patterns have never been directly compared. To address this issue, in a pilot study, we analyzed the effects of two ten-week training regimens in juvenile, male, C57BL/6 mice: moderate-intensity forced treadmill running three-times-a-week, employing a protocol that has been widely used in similar studies before, and voluntary wheel running. Our data suggest that there are similarities, but also characteristic differences in the molecular responses of different skeletal muscle species to the two training regimens. In particular, we found that VWR induces a significant fiber type shift toward more type IIX fibers in the slow, oxidative soleus muscle (p = .0053), but not in the other three muscles analyzed. In addition, while training-induced expression patterns of the two metabolic markers Ppargc1a, encoding Pgc-1α (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) and Nr4a3 (nuclear receptor subfamily 4 group A member 3) were roughly similar, downregulation of the Mstn (myostatin) gene and the "atrogene" Fbox32 could only be observed in response to VWR in specific muscles, such as in the gastrocnemius (p = .0015 for Mstn) and in the tibialis anterior (p = .0053 for Fbox32) muscles, suggesting that molecular adaptation reactions to the two training regimens show distinct characteristics.

Mitochondrial dysfunction in skeletal muscle of fukutin-deficient mice is resistant to exercise- and 5-aminoimidazole-4-carboxamide ribonucleotide-induced rescue

NEW FINDINGS

What is the central question of this study? Does fukutin deficiency in skeletal muscle cause mitochondrial dysfunction, and if so, can AMP-activated protein kinase (AMPK) stimulation via 5-aminoimidazole-4-carboxamide ribonucleotide attenuate this through regulation of mitochondrial biogenesis and autophagy? What is the main finding and its importance? Mitochondrial dysfunction is associated with fukutin deficiency and AMPK stimulation may benefit muscle contractility to a greater extent than mitochondrial function.

ABSTRACT

Disruptions in the dystrophin-glycoprotein complex (DGC) are clearly the primary basis underlying various forms of muscular dystrophies and dystroglycanopathies, but the cellular consequences of DGC disruption are still being investigated. Mitochondrial abnormalities are becoming an apparent consequence and contributor to dystrophy disease pathology. Herein, we demonstrate that muscle-specific deletion of the fukutin gene (Myf5/fktn-KO mice (Fktn KO)), a model of secondary dystroglycanopathy, results in ∼30% lower muscle strength (P < 0.001) and 16% lower mitochondrial respiratory function (P = 0.002) compared to healthy littermate controls (LM). We also observed ∼80% lower expression of the gene for peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α) (P = 0.004), a primary transcription factor for mitochondrial biogenesis, in Fktn KO mice that likely contributes to the mitochondrial defects. PGC-1α is post-translationally regulated via phosphorylation by AMP-activated protein kinase (AMPK). Treatment with the AMPK agonist 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) failed to rescue mitochondrial deficits in Fktn KO mice (P = 0.458) but did have beneficial (∼30% greater) effects on recovery of muscle contractility following injury in both LM and Fktn KO mice compared to saline treatment (P = 0.006). The beneficial effects of AMPK stimulation via AICAR on muscle contractile function may be partially explained by AMPK's other role of regulating skeletal muscle autophagy, a cellular process critical for clearance of damaged and/or dysfunctional organelles. Two primary conclusions can be drawn from this data: (1) fukutin deletion produces intrinsic muscular metabolic defects that likely contribute to dystroglycanopathy disease pathology, and (2) AICAR treatment accelerates recovery of muscle contractile function following injury suggesting AMPK signalling as a possible target for therapeutic strategies.

Impact of aerobic exercise type on blood flow, muscle energy metabolism, and mitochondrial biogenesis in experimental lower extremity artery disease

Exercise training (ET) is recommended for lower extremity artery disease (LEAD) management. However, there is still little information on the hemodynamic and metabolic adaptations by skeletal muscle with ET. We examined whether hindlimb perfusion/vascularization and muscle energy metabolism are altered differently by three types of aerobic ET. ApoE^−/− mice with LEAD were assigned to one of four groups for 4 weeks: sedentary (SED), forced treadmill running (FTR), voluntary wheel running (VWR), or forced swimming (FS). Voluntary exercise capacity was improved and equally as efficient with FTR and VWR, but remained unchanged with FS. Neither ischemic hindlimb perfusion and oxygenation, nor arteriolar density and mRNA expression of arteriogenic-related genes differed between groups. ¹⁸FDG PET imaging revealed no difference in the steady-state levels of phosphorylated ¹⁸FDG in ischemic and non-ischemic hindlimb muscle between groups, nor was glycogen content or mRNA and protein expression of glucose metabolism-related genes in ischemic muscle modified. mRNA (but not protein) expression of lipid metabolism-related genes was upregulated across all exercise groups, particularly by non-ischemic muscle. Markers of mitochondrial content (mitochondrial DNA content and citrate synthase activity) as well as mRNA expression of mitochondrial biogenesis-related genes in muscle were not increased with ET. Contrary to FTR and VWR, swimming was ineffective in improving voluntary exercise capacity. The underlying hindlimb hemodynamics or muscle energy metabolism are unable to explain the benefits of running exercise.

Exercise Training Protects against Atorvastatin-Induced Skeletal Muscle Dysfunction and Mitochondrial Dysfunction in the Skeletal Muscle of Rats

Statins are used to prevent and treat atherosclerotic cardiovascular disease, but they also induce myopathy and mitochondrial dysfunction. Here, we investigated whether exercise training prevents glucose intolerance, muscle impairment, and mitochondrial dysfunction in the skeletal muscles of Wistar rats treated with atorvastatin (5 mg kg-1 day-1) for 12 weeks. The rats were assigned to the following three groups: the control (CON), atorvastatin-treated (ATO), and ATO plus aerobic exercise training groups (ATO+EXE). The ATO+EXE group exhibited higher glucose tolerance and forelimb strength and lower creatine kinase levels than the other groups. Mitochondrial respiratory and Ca2+ retention capacity was significantly lower in the ATO group than in the other groups, but exercise training protected against atorvastatin-induced impairment in both the soleus and white gastrocnemius muscles. The mitochondrial H2O2 emission rate was relatively higher in the ATO group and lower in the ATO+EXE group, in both the soleus and white gastrocnemius muscles, than in the CON group. In the soleus muscle, the Bcl-2, SOD1, SOD2, Akt, and AMPK phosphorylation levels were significantly higher in the ATO+EXE group than in the ATO group. In the white gastrocnemius muscle, the SOD2, Akt, and AMPK phosphorylation levels were significantly higher in the ATO+EXE group than in the ATO group. Therefore, exercise training might regulate atorvastatin-induced muscle damage, muscle fatigue, and mitochondrial dysfunction in the skeletal muscles.

What and How Can Physical Activity Prevention Function on Parkinson's Disease?

Aim

This study was aimed at investigating the effects and molecular mechanisms of physical activity intervention on Parkinson's disease (PD) and providing theoretical guidance for the prevention and treatment of PD.

Methods

Four electronic databases up to December 2019 were searched (PubMed, Springer, Elsevier, and Wiley database), 176 articles were selected. Literature data were analyzed by the logic analysis method.

Results

(1) Risk factors of PD include dairy products, pesticides, traumatic brain injury, and obesity. Protective factors include alcohol, tobacco, coffee, black tea, and physical activity. (2) Physical activity can reduce the risk and improve symptoms of PD and the beneficial forms of physical activity, including running, dancing, traditional Chinese martial arts, yoga, and weight training. (3) Different forms of physical activity alleviate the symptoms of PD through different mechanisms, including reducing the accumulation of α-syn protein, inflammation, and oxidative stress, while enhancing BDNF activity, nerve regeneration, and mitochondrial function.

Conclusion

Physical activity has a positive impact on the prevention and treatment of PD. Illustrating the molecular mechanism of physical activity-induced protective effect on PD is an urgent need for improving the efficacy of PD therapy regimens in the future.

Mitochondrial-specific autophagy linked to mitochondrial dysfunction following traumatic freeze injury in mice

The objective of this study was to interrogate the link between mitochondrial dysfunction and mitochondrial-specific autophagy in skeletal muscle. C57BL/6J mice were used to establish a time course of mitochondrial function and autophagy induction after fatigue (n = 12), eccentric contraction-induced injury (n = 20), or traumatic freeze injury (FI, n = 28); only FI resulted in a combination of mitochondrial dysfunction, i.e., decreased mitochondrial respiration, and autophagy induction. Moving forward, we tested the hypothesis that mitochondrial-specific autophagy is important for the timely recovery of mitochondrial function after FI. Following FI, there is a significant increase in several mitochondrial-specific autophagy-related protein contents including dynamin-related protein 1 (Drp1), BCL1 interacting protein (BNIP3), Pink1, and Parkin (~2-fold, P < 0.02). Also, mitochondrial-enriched fractions from FI muscles showed microtubule-associated protein light chain B1 (LC3)II colocalization suggesting autophagosome assembly around the damaged mitochondrial. Unc-51 like autophagy activating kinase (Ulk1) is considered necessary for mitochondrial-specific autophagy and herein we utilized a mouse model with Ulk1 deficiency in adult skeletal muscle (myogenin-Cre). While Ulk1 knockouts had contractile weakness compared with littermate controls (-27%, P < 0.02), the recovery of mitochondrial function was not different, and this may be due in part to a partial rescue of Ulk1 protein content within the regenerating muscle tissue of knockouts from differentiated satellite cells in which Ulk1 was not genetically altered via myogenin-Cre. Lastly, autophagy flux was significantly less in injured versus uninjured muscles (-26%, P < 0.02) despite the increase in autophagy-related protein content. This suggests autophagy flux is not upregulated to match increases in autophagy machinery after injury and represents a potential bottleneck in the clearance of damaged mitochondria by autophagy.

SiBaoChongCao exhibited anti-fatigue activities and ameliorated cancer cachexia in mice

SiBaoChongCao (SBCC) is a functional food product containing fermentation of Acremonium terricola belonging to the Cordyceps genus. SBCC at 1 and 2 g kg⁻¹ for 20 days exhibited anti-fatigue activities such as increasing exhaustive swimming and running time of mice and increasing the strength of muscle. The increased muscle endurance in SBCC-treated mice might be related to enhancement of muscle cell growth and differentiation and improvement of muscle response to exercise training, as shown by an increase in muscle cross-sectional area and elevation of MHC, MyoD, MyoG and PGC-1α levels. And, SBCC at 1.5 g kg⁻¹ could ameliorate cancer-related cachexia such as ameliorating decrease in body temperature and inhibiting fat tissue atrophy. The anti-cachexia effects of SBCC might be related to inhibition of inflammatory cytokine IL-6 secretion and suppression of over-lipolysis and lipid over-utilization through inhibiting the activation of AMPK and p38 MAPK and down-regulating the level of UCP1.

SBCC exhibits anti-fatigue activity by improving muscle endurance and ameliorates cancer cachexia by alleviating loss of fat and body temperature.

Endurance exercise increases the protein levels of PGC-1α and respiratory chain complexes in mouse skeletal muscle during atorvastatin administration

Statins and exercise reduce cardiovascular disease incidence. We investigated whether endurance exercise in mice induces mitochondrial adaptation in skeletal muscle and muscle injury during administration of atorvastatin, a member of the statin medication class. Male C57BL mice were assigned to one of three groups: control (Con), statin (Statin), or statin and exercise (Statin + Ex). Atorvastatin was administered, and exercise performed on a treadmill for 8 weeks. The levels of mitochondria-associated proteins, PGC-1α, and respiratory chain complex, (COX) I-V, in the quadriceps femoris, and serum creatine kinase, a muscle injury marker, were measured. PGC-1α and COX I-V were upregulated in the Statin + Ex group compared to those in the Statin and Con groups; serum creatine kinase levels were similar. Endurance training in mice induced mitochondrial adaptation in skeletal muscle without causing muscle injury, during atorvastatin administration.

Effect of heat load and dietary protein on oxygen pulse and energy cost for locomotion in heifers

The objectives of the present study were to evaluate the effect of heat load, bodyweight and dietary protein on oxygen pulse of heifers, to obtain the energy cost of walking on flat and sloping terrain, and to compare the energy cost of heifers during continuous walking and intermittent walking. In Experiment 1, the correlations of oxygen consumption, heart rate and oxygen pulse (O2P) with bodyweight, black globe temperature and temperature and humidity index were examined. Moreover, the effect of dietary protein on O2P was evaluated. The temperature and humidity index and black globe temperature had a low positive correlation with O2P and oxygen consumption, and a low negative correlation with heart rate. However, weight had no correlation with O2P. There was a linear increase in O2P with a very low adjustment with an increasing dietary crude protein concentration. In Experiment 2, the energy cost of heifers walking continuously at a constant speed in a terrain with 0%, 6% and 12% gradient was measured. The energy expenditure was similar among the terrain gradients. The heifers walking had a 16.6% higher energy expenditure than when they were standing. In Experiment 3, a comparison of the energy cost was made among heifers standing, continuously walking and intermittently walking at a constant speed on flat ground. The energy cost for walking was similar between continuous and intermittent walking. The heat load, bodyweight and dietary protein concentration had a low effect on O2P in dairy heifers. Therefore, measurements over a short time (5–15 min) are a reliable estimator of O2P through the day. Both intermittent and continuous walking can be used to evaluate energy expenditure.

The Effect of Diet on Improved Endurance in Male C57BL/6 Mice

The consumption of fruits and vegetables appears to help with maintaining an adequate level of exercise and improves endurance. However, the mechanisms that are involved in this process are not well understood. In the current study, the impact of diets enriched in fruits and vegetables (GrandFusion^®) on exercise endurance was examined in a mouse model. GrandFusion (GF) diets increased mitochondrial DNA and enzyme activity, while they also stimulated mitochondrial mRNA synthesis in vivo. GF diets increased both the mRNA expression of factors involved in mitochondrial biogenesis, peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α), mitochondrial transcription factor A (Tfam), estrogen-related receptor alpha (ERRα), nuclear respiratory factor 1 (NRF-1), cytochrome c oxidase IV (COXIV) and ATP synthase (ATPsyn). Mice treated with GF diets showed an increase in running endurance, rotarod perseverance and grip strength when compared to controls who were on a regular diet. In addition, GF diets increased the protein expression of phosphorylated AMP-activated protein kinase (AMPK), sirtuin 1 (SIRT1), PGC-1α and peroxisome proliferator-activated receptor delta (PPAR-δ), which was greater than exercise-related changes. Finally, GF reduced the expression of phosphorylated ribosomal protein S6 kinase 1 (p-S6K1) and decreased autophagy. These results demonstrate that GF diets enhance exercise endurance, which is mediated via mitochondrial biogenesis and function.

Locomotor muscle fibre heterogeneity and metabolism in the fastest large-bodied rorqual: the fin whale (Balaenoptera physalus)

From a terrestrial ancestry, the fin whale (Balaenoptera physalus) is one of the largest animals on Earth with a sprinter anti-predator strategy, and a characteristic feeding mode, lunge feeding, which involves bouts of high-intensity muscle activity demanding high metabolic output. We investigated the locomotor muscle morphology and metabolism of this cetacean to determine whether its muscle profile (1) explains this unique swimming performance and feeding behaviour, (2) is or is not homogeneous within the muscle, and (3) predicts allometric variations inherent to an extreme body size. A predominantly fast-glycolytic phenotype characterized the fin whale locomotor muscle, composed of abundant fast-twitch (type IIA) fibres with high glycolytic potential, low oxidative capacity, relatively small size, and reduced number of capillaries. Compared with superficial areas, deep regions of this muscle exhibited a slower and more oxidative profile, suggesting a division of labour between muscle strata. As expected, the fin whale locomotor muscle only expressed the two slowest myosin heavy chain isoforms (I and IIA). However, it displayed anaerobic (glycolytic) and aerobic (lipid-based metabolism) capabilities higher than would be predicted from the allometric perspective of its extreme body size. Relationships between muscle metabolism and body mass were fibre-type specific. The 'sprinter' profile of the fin whale swimming muscle, particularly of its superficial compartment, supports physiological demands during both high-speed swimming and the lunge, when energy expenditure reaches maximal or supramaximal levels. Comparatively, the slower and more oxidative profile of the deep compartment of this muscle seems to be well designed for sustained, low-intensity muscle activity during routine swimming.

Early rehabilitation for volumetric muscle loss injury augments endogenous regenerative aspects of muscle strength and oxidative capacity

Background

Volumetric muscle loss (VML) injuries occur due to orthopaedic trauma or the surgical removal of skeletal muscle and result in debilitating long-term functional deficits. Current treatment strategies do not promote significant restoration of function; additionally appropriate evidenced-based practice physical therapy paradigms have yet to be established. The objective of this study was to develop and evaluate early rehabilitation paradigms of passive range of motion and electrical stimulation in isolation or combination to understand the genetic and functional response in the tissue remaining after a multi-muscle VML injury.

Methods

Adult male mice underwent an ~ 20% multi-muscle VML injury to the posterior compartment (gastrocnemius, soleus, and plantaris muscle) unilaterally and were randomized to rehabilitation paradigm twice per week beginning 2 days post-injury or no treatment.

Results

The most salient findings of this work are: 1) that the remaining muscle tissue after VML injury was adaptable in terms of improved muscle strength and mitigation of stiffness; but 2) not adaptable to improvements in metabolic capacity. Furthermore, biochemical (i.e., collagen content) and gene (i.e., gene arrays) assays suggest that functional adaptations may reflect changes in the biomechanical properties of the remaining tissue due to the cellular deposition of non-contractile tissue in the void left by the VML injury and/or differentiation of gene expression with early rehabilitation.

Conclusions

Collectively this work provides evidence of genetic and functional plasticity in the remaining skeletal muscle with early rehabilitation approaches, which may facilitate future evidenced-based practice of early rehabilitation at the clinical level.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2095-6) contains supplementary material, which is available to authorized users.

Endurance training reduces exercise-induced acidosis and improves muscle function in a mouse model of sickle cell disease

Sickle cell disease (SCD) mice (Townes model of SCD) presented exacerbated exercise-induced acidosis and fatigability as compared to control animals. We hypothesize that endurance training could represent a valuable approach to reverse these muscle defects. Endurance-trained HbAA (HbAA-END, n=10), HbAS (HbAS-END, n=11) and HbSS (HbSS-END, n=8) mice were compared to their sedentary counterparts (10 HbAA-SED, 10 HbAS-SED and 9 HbSS-SED mice) during two rest - exercise - recovery protocols during which muscle energetics and function were measured. In vitro analyses of some proteins involved in muscle energetics, pH regulation and oxidative stress were also performed. Exercise-induced acidosis was lower in HbSS-END mice as compared to their sedentary counterparts during both moderate (p<0.001) and intense (p<0.1) protocols. The total force production measured during both protocols was higher in trained mice compared to sedentary animals. In vitro analyses revealed that enolase/citrate synthase ratio was reduced in HbSS-END (p<0.001) and HbAS-END (p<0.01) mice compared to their sedentary counterparts. In addition, malondialdehyde concentration was reduced in trained mice (p<0.05). In conclusion, endurance training would reverse the more pronounced exercise-induced acidosis, reduce oxidative stress and ameliorate some of the muscle function parameters in SCD mice.

Ulk1-mediated autophagy plays an essential role in mitochondrial remodeling and functional regeneration of skeletal muscle

Autophagy is a conserved cellular process for degrading aggregate proteins and dysfunctional organelle. It is still debatable if autophagy and mitophagy (a specific process of autophagy of mitochondria) play important roles in myogenic differentiation and functional regeneration of skeletal muscle. We tested the hypothesis that autophagy is critical for functional regeneration of skeletal muscle. We first observed time-dependent increases (3- to 6-fold) of autophagy-related proteins (Atgs), including Ulk1, Beclin1, and LC3, along with reduced p62 expression during C2C12 differentiation, suggesting increased autophagy capacity and flux during myogenic differentiation. We then used cardiotoxin (Ctx) or ischemia-reperfusion (I/R) to induce muscle injury and regeneration and observed increases in Atgs between days 2 and 7 in adult skeletal muscle followed by increased autophagy flux after day 7 Since Ulk1 has been shown to be essential for mitophagy, we asked if Ulk1 is critical for functional regeneration in skeletal muscle. We subjected skeletal muscle-specific Ulk1 knockout mice (MKO) to Ctx or I/R. MKO mice had significantly impaired recovery of muscle strength and mitochondrial protein content post-Ctx or I/R. Imaging analysis showed that MKO mice have significantly attenuated recovery of mitochondrial network at 7 and 14 days post-Ctx. These findings suggest that increased autophagy protein and flux occur during muscle regeneration and Ulk1-mediated mitophagy is critical for recovery for the mitochondrial network and hence functional regeneration.