Autophagy is essential to support skeletal muscle plasticity in response to endurance exercise

Autophagy and aging: Maintaining the proteome through exercise and caloric restriction

Accumulation of dysfunctional and damaged cellular proteins and organelles occurs during aging, resulting in a disruption of cellular homeostasis and progressive degeneration and increases the risk of cell death. Moderating the accrual of these defunct components is likely a key in the promotion of longevity. While exercise is known to promote healthy aging and mitigate age‐related pathologies, the molecular underpinnings of this phenomenon remain largely unclear. However, recent evidences suggest that exercise modulates the proteome. Similarly, caloric restriction (CR), a known promoter of lifespan, is understood to augment intracellular protein quality. Autophagy is an evolutionary conserved recycling pathway responsible for the degradation, then turnover of cellular proteins and organelles. This housekeeping system has been reliably linked to the aging process. Moreover, autophagic activity declines during aging. The target of rapamycin complex 1 (TORC1), a central kinase involved in protein translation, is a negative regulator of autophagy, and inhibition of TORC1 enhances lifespan. Inhibition of TORC1 may reduce the production of cellular proteins which may otherwise contribute to the deleterious accumulation observed in aging. TORC1 may also exert its effects in an autophagy‐dependent manner. Exercise and CR result in a concomitant downregulation of TORC1 activity and upregulation of autophagy in a number of tissues. Moreover, exercise‐induced TORC1 and autophagy signaling share common pathways with that of CR. Therefore, the longevity effects of exercise and CR may stem from the maintenance of the proteome by balancing the synthesis and recycling of intracellular proteins and thus may represent practical means to promote longevity.

Voluntary running protects against neuromuscular dysfunction following hindlimb ischemia-reperfusion in mice

Ischemia-reperfusion (IR) due to temporary restriction of blood flow causes tissue/organ damages under various disease conditions, including stroke, myocardial infarction, trauma, and orthopedic surgery. In the limbs, IR injury to motor nerves and muscle fibers causes reduced mobility and quality of life. Endurance exercise training has been shown to increase tissue resistance to numerous pathological insults. To elucidate the impact of endurance exercise training on IR injury in skeletal muscle, sedentary and exercise-trained mice (5 wk of voluntary running) were subjected to ischemia by unilateral application of a rubber band tourniquet above the femur for 1 h, followed by reperfusion. IR caused significant muscle injury and denervation at neuromuscular junction (NMJ) as early as 3 h after tourniquet release as well as depressed muscle strength and neuromuscular transmission in sedentary mice. Despite similar degrees of muscle atrophy and oxidative stress, exercise-trained mice had significantly reduced muscle injury and denervation at NMJ with improved regeneration and functional recovery following IR. Together, these data suggest that endurance exercise training preserves motor nerve and myofiber structure and function from IR injury and promote functional regeneration. NEW & NOTEWORTHY This work provides the first evidence that preemptive voluntary wheel running reduces neuromuscular dysfunction following ischemia-reperfusion injury in skeletal muscle. These findings may alter clinical practices in which a tourniquet is used to modulate blood flow.

Targeting mitochondrial quality control for treating sarcopenia: lessons from physical exercise

INTRODUCTION

Mitochondrial dysfunction is a hallmark of aging and hence is a candidate target for intervention. Sarcopenia of aging is a prevalent condition and is associated with numerous negative health outcomes. Alterations in mitochondrial homeostasis have been reported in sarcopenic muscle. Area covered: We discuss the evidence that points to mitochondrial dysfunction having a causative role in sarcopenia and the mechanisms involved in the accumulation of damaged mitochondria in the aged muscle. We also discuss the effects of physical exercise on mitochondrial quality control and muscle health in advanced age. Expert opinion: In the aged muscle, the mitochondrial quality control axis is altered at several levels, including proteostasis, biogenesis, dynamics, and autophagy. Mitochondrial dysfunction arising from impaired quality control is thought to play a major role in the pathogenesis of sarcopenia. Physical exercise is the most effective strategy for the management of sarcopenia. Improvements in mitochondrial health and plasticity may mediate several beneficial effects of exercise in muscle. A greater understanding of the molecular changes that occur in the aged muscle following exercise and how they impact mitochondrial homeostasis is necessary for the exploration of potential targets that are amenable for interventions.

Methods in renal research: Measurement of autophagic flux in the renal cortex ex vivo

The role of autophagy in the kidney and many nephrological diseases has gained prominence in recent years. Much of this research has been focused on markers of autophagy that are static and reveal little about the state of this dynamic pathway. Other mechanistic investigations are limited to in vitro studies, that often provide circumstantial evidence of autophagic flux. Here we describe a method for measuring autophagic flux ex vivo that allows more direct observations to be made in situ regarding the state of autophagic flux within the renal cortex of a single animal.

Alterations of autophagy in knee cartilage by treatment with treadmill exercise in a rat osteoarthritis model

The aim of the present study was to investigate potential alterations in the articular cartilage in a rat model of monosodium iodoacetate (MIA)-induced osteoarthritis (OA) with or without treatment with moderate treadmill exercise. A total of 30 male Sprague-Dawley rats were randomly divided into three groups (n=10), including the control, OA and OA with treadmill exercise (OAE) groups. Rats were evaluated upon completing the treadmill exercise program (speed, 18 m/min; 30 min/day; 5 days/week for 4 weeks). Interleukin (IL)-1β and IL-4 levels in the serum and intra-articular lavage fluid (IALF) were measured by ELISA. Alterations in articular cartilage and synovium were also evaluated by histology, immunohistochemistry, western blotting and reverse transcription-quantitative polymerase chain reaction. The results revealed that IL-1β in the serum and IALF decreased in the OAE group, whereas IL-4 increased, and histological evaluation indicated that the OAE group had a clear treatment response. However, the expression of type II collagen in the articular cartilage increased in the OAE group as compared with the OA group, whereas ADAMTS5 expression decreased. In contrast to light chain 3B (LC3B), the protein expression levels of BECLIN1 and sequestosome 1 (SQSTM1) were increased in the OA group. In addition, a significant increase was observed between OA and OAE groups in LC3B and SQSTM1 protein levels, whereas no change was observed in BECLIN1 levels between the OA and OAE groups in the superficial and deep zones. The results of western blotting demonstrated that LC3II was notably decreased in the OA group and partially increased in the OAE group. The mRNA expression levels of LC3B and SQSTM1 increased in the OA and OAE groups, with a significant difference observed between the two groups, while a concomitant decrease was detected in BECLIN1 levels. In conclusion, 30 min of treadmill exercise had an evident protective effect in the articular cartilage of rats with MIA-induced OA and may promote autophagy in the articular cartilage.

Changes in expression of the autophagy-related genes microtubule-associated protein 1 light chain 3β and autophagy related 7 in skeletal muscle of fattening Japanese Black cattle: a pilot study

Objective

Autophagy is a bulk degradation system for intracellular proteins which contributes to skeletal muscle homeostasis, according to previous studies in humans and rodents. However, there is a lack of information on the physiological role of autophagy in the skeletal muscle of meat animals. This study was planned as a pilot study to investigate changes in expression of two major autophagy-related genes, microtubule-associated protein 1 light chain 3β (MAP1LC3B) and autophagy related 7 (ATG7) in fattening beef cattle, and to compare them with skeletal muscle growth.

Methods

Six castrated Japanese Black cattle (initial body weight: 503±20 kg) were enrolled in this study and fattened for 7 months. Three skeletal muscles, M. longissimus, M. gluteus medius, and M. semimembranosus, were collected by needle biopsy three times during the observation period, and mRNA levels of MAP1LC3B and ATG7 were determined by quantitative reverse-transcription polymerase chain reaction. The expression levels of genes associated with the ubiquitin-proteasome system, another proteolytic mechanism, were also analyzed for comparison with autophagy-related genes. In addition, ultrasonic scanning was repeatedly performed to measure M. longissimus area as an index of muscle growth.

Results

Our results showed that both MAP1LC3B and ATG7 expression increased over the observation period in all three skeletal muscles. Interestingly, the increase in expression of these two genes in M. longissimus was highly correlated with ultrasonic M. longissimus area and body weight. On the other hand, the expression of genes associated with the ubiquitin-proteasome system was unchanged during the same period.

Conclusion

These findings suggest that autophagy plays an important role in the growth of skeletal muscle of fattening beef cattle and imply that autophagic activity affects meat productivity.

Increased autophagy signaling but not proteasome activity in human skeletal muscle after prolonged low-intensity exercise with negative energy balance

Little is known about the molecular regulation of skeletal muscle protein turnover during exercise in field conditions where energy is intake inadequate. Here, 17 male and 7 female soldiers performed an 8 days long field-based military operation. Vastus lateralis muscle biopsies, in which autophagy, the ubiquitin-proteasome system, and the mTORC1 signaling pathway were studied, were collected before and after the operation. The 187 h long operation resulted in a 15% and 29% negative energy balance as well as a 4.1% and 4.6% loss of body mass in women and men, respectively. After the operation protein levels of ULK1 as well as the phosphorylation of ULK1^Ser317 and ULK1^Ser555 had increased by 11%, 39%, and 13%, respectively, and this was supported by a 17% increased phosphorylation of AMPK^Thr172 (P < 0.05). The LC3b-I/II ratio was threefold higher after compared to before the operation (P < 0.05), whereas protein levels of p62/SQSTM1 were unchanged. The β1, β2, and β5 activity of the proteasome and protein levels of MAFbx did not change, whereas levels of MuRF-1 were slightly reduced (6%, P < 0.05). Protein levels and phosphorylation status of key components in the mTORC1 signaling pathway remained at basal levels after the operation. Muscle levels of glycogen decreased from 269 ± 12 to 181 ± 9 mmol·kg dry·muscle^-1 after the exercise period (P < 0.05). In conclusion, the 8 days of field-based exercise resulted in induction of autophagy without any increase in proteasome activity or protein ubiquitination. Simultaneously, the regulation of protein synthesis through the mTORC1 signaling pathway was maintained.

Modelling performance and skeletal muscle adaptations with exponential growth functions during resistance training

System theory is classically applied to describe and to predict the effects of training load on performance. The classic models are structured by impulse-type transfer functions, nevertheless, most biological adaptations display exponential growth kinetics. The aim of this study was to propose an extension of the model structure taking into account the exponential nature of skeletal muscle adaptations by using a genetic algorithm. Thus, the conventional impulse-type model was applied in 15 resistance trained rodents and compared with exponential growth-type models. Even if we obtained a significant correlation between actual and modelled performances for all the models, our data indicated that an exponential model is associated with more suitable parameters values, especially the time constants that correspond to the positive response to training. Moreover, positive adaptations predicted with an exponential component showed a strong correlation with the main structural adaptations examined in skeletal muscles, i.e. hypertrophy (R² = 0.87, 0.96 and 0.99, for type 1, 2A and 2X cross-sectional area fibers, respectively) and changes in fiber-type composition (R² = 0.81 and 0.79, for type 1 and 2A fibers, respectively). Thus, an exponential model succeeds to describe both performance variations with relevant time constants and physiological adaptations that take place during resistance training.

Combined Aerobic and Resistance Training Effects on Glucose Homeostasis, Fitness, and Other Major Health Indices: A Review of Current Guidelines

The combination of aerobic and resistance training (AER + RES) is recommended by almost every major organization to improve health-related risk factors associated with sedentary behavior. Since the release of the Physical Activity Guidelines for Americans in 2008, several large well-controlled trials and ancillary reports have been published that provide further insight into the effects of AER + RES on health-related outcomes. The current manuscript examines the literature on the effects of AER + RES on major clinical outcomes, including glucose homeostasis, cardiorespiratory fitness (CRF), and muscular strength, as well as other important clinical outcomes, including metabolic syndrome, hypertension, dyslipidemia, and quality of life. Collectively, research suggests that AER + RES and AER or RES alone improves glycemic control and insulin sensitivity compared with continued sedentary behavior. Significant changes in CRF are also observed, suggesting a reduction in cardiovascular disease-related mortality risk. Reduced adiposity, especially abdominal adiposity, and increased strength may also interact with CRF to promote additional health benefits associated with AER + RES. While findings from our review support current physical activity guidelines, a paucity of research limits the generalizability of the results.

Skeletal Muscle Pathophysiology: The Emerging Role of Spermine Oxidase and Spermidine

Skeletal muscle comprises approximately 40% of the total body mass. Preserving muscle health and function is essential for the entire body in order to counteract chronic diseases such as type II diabetes, cardiovascular diseases, and cancer. Prolonged physical inactivity, particularly among the elderly, causes muscle atrophy, a pathological state with adverse outcomes such as poor quality of life, physical disability, and high mortality. In murine skeletal muscle C2C12 cells, increased expression of the spermine oxidase (SMOX) enzyme has been found during cell differentiation. Notably, SMOX overexpression increases muscle fiber size, while SMOX reduction was enough to induce muscle atrophy in multiple murine models. Of note, the SMOX reaction product spermidine appears to be involved in skeletal muscle atrophy/hypertrophy. It is effective in reactivating autophagy, ameliorating the myopathic defects of collagen VI-null mice. Moreover, spermidine treatment, if combined with exercise, can affect D-gal-induced aging-related skeletal muscle atrophy. This review hypothesizes a role for SMOX during skeletal muscle differentiation and outlines its role and that of spermidine in muscle atrophy. The identification of new molecular pathways involved in the maintenance of skeletal muscle health could be beneficial in developing novel therapeutic lead compounds to treat muscle atrophy.

Effect of Resistance Exercise on Muscle Metabolism and Autophagy in sIBM

PURPOSE

Sporadic inclusion body myositis (sIBM), a muscular degenerative disease in the elderly, is an inflammatory myopathy characterized by muscle weakness in the wrist flexor, quadriceps, and tibialis anterior muscles. We aimed to identify the therapeutic effect of resistance exercise (RE) in improving sIBM symptoms in an sIBM animal model.

METHODS

Six-week-old male Wistar rats were divided into a sham group (sham, n = 12), chloroquine-control group (CQ-con, n = 12), and chloroquine-RE group (CQ-RE, n = 12). The rats were subjected to 1 wk of exercise adaptation and 8 wk of exercise (three sessions per week). Protein expression was measured by Western blotting. Rimmed vacuoles (RV) were identified by hematoxylin and eosin staining and modified Gömöri trichrome staining, and amyloid deposition was examined by Congo red staining.

RESULTS

The effects of CQ and RE differed depending on myofiber characteristics. Soleus muscles showed abnormal autophagy in response to CQ, which increased RV generation and amyloid-β accumulation, resulting in atrophy. RE generated RV and decreased amyloid deposition in soleus muscles and also improved autophagy without generating hypertrophy. This reduced the atrophy signal transduction, resulting in decreased atrophy compared with the CQ-con group. Despite no direct effect of CQ, flexor hallucis longus muscles showed loss of mass because of reduced activity or increased inflammatory response; however, RE increased the hypertrophy signal, resulting in reduced autophagy and atrophy.

CONCLUSIONS

These results demonstrate that RE had a preventive effect on sIBM induced by CQ treatment in an animal model. However, because the results were from an animal experiment, a more detailed study should be conducted over a longer period, and the effectiveness of different RE programs should also be investigated.

Effects of intermittent hypoxic training performed at high hypoxia level on exercise performance in highly trained runners

This study exanimated the effects of intermittent hypoxic training (IHT) conducted at a high level of hypoxia with recovery at ambient air on aerobic/anaerobic capacities at sea level and hematological variations. According to a double-blind randomized design, fifteen highly endurance-trained runners completed a 6-weeks regimented training with 3 sessions per week consisting of intermittent runs (6x work-rest ratio of 5':5') on a treadmill at 80-85% of maximal aerobic speed ([Formula: see text]). Nine athletes (hypoxic group, HG) performed the exercise bouts at FI0₂ = 10.6-11.4% while six athletes (normoxic group, NG) exercised at ambient air. Running time to exhaustion at a velocity corresponding to 95% [Formula: see text] significantly increased for HG while no effect was found for NG. Regarding [Formula: see text], no significant effects were found in either training group. In addition, the decline of jumping performances over a 45s-continuous maximal vertical jump test (i.e. anaerobic capacity index) tended to be lower in HG compared to NG. The levels of the studied hematological variables, including erythropoietin and hematocrit, did not significantly change for either HG or NG. These results highlight that our IHT protocol may induce additional effects on aerobic performance without compromising the anaerobic capacity index in highly-trained athletes.

mTOR Signaling Pathway and Protein Synthesis: From Training to Aging and Muscle Autophagy

In muscle tissue there is a balance between the processes muscle synthesis and degradation. The mammalian target of rapamycin (mTOR) signaling pathway plays a critical role in regulating protein synthesis in order to maintain muscular protein turnover and trophism. Studies have shown that both down- and upregulation mechanisms are involved in this process in a manner dependent on stimulus and cellular conditions. Additionally, mTOR signaling has recently been implicated in several physiological conditions related to cell survival, such as self-digestion (autophagy), energy production, and the preservation of cellular metabolic balance over the lifespan. Here we briefly describe the mTOR structure and its regulatory protein synthesis pathway. Furthermore, the role of mTOR protein in autophagy, aging, and mitochondrial function in muscle tissue is presented.

Impact of resistance training on the autophagy-inflammation-apoptosis crosstalk in elderly subjects

Aging is associated with a decline in autophagy and a state of low-grade inflammation which further affects apoptosis and autophagy. Importantly, these alterations could reverse with regular physical activity. This study assessed the effects of a resistance exercise training program on autophagy, NLRP3 inflammasome, and apoptosis in peripheral blood mononuclear cells (PBMCs) from old subjects. Twenty-six healthy women and men (age, 69.6±1.5 yr) were randomized to a training (TG) or a control (CG) group. TG performed an 8-week resistance training program, while CG followed their daily routines. Protein expression of beclin-1, Atg12, Atg16 and LAMP-2 increased following the training program, while expression of p62/SQSTM1 and phosphorylation of ULK-1 at Ser757 were significantly lower. Resistance exercise also induced a decrease in NLRP3 expression and in the caspase-1/procaspase-1 ratio. Expression of Bcl-2 and Bcl-xL, as well as the Bad/BcL-2 ratio were reduced, and there was a significant decrease in the protein content of caspase-3. The results obtained seem to indicate that 8-week resistance training stimulates autophagy, prevents NLRP3 inflammasome activation, and reduces apoptosis in PBMCs from elderly subjects. These data could have a significant impact in prevention and rehabilitation programs currently employed in elderly population.

Spermidine coupled with exercise rescues skeletal muscle atrophy from D-gal-induced aging rats through enhanced autophagy and reduced apoptosis via AMPK-FOXO3a signal pathway

The quality control of skeletal muscle is a continuous requirement throughout the lifetime, although its functions and quality present as a declining trend during aging process. Dysfunctional or deficient autophagy and excessive apoptosis may contribute to the atrophy of senescent skeletal muscle. Spermidine, as a natural polyamine, can be involved in important cellular functions for lifespan extension and stress resistance in several model organisms through activating autophagy. Similarly, cellular autophagic responses to exercise have also been extensively investigated. In the present study, in order to confirm the mitigation or amelioration of skeletal muscle atrophy in aging rats through spermidine coupled with exercise intervention and explore corresponding mechanisms, the rat model with aging-related atrophy of skeletal muscle was established by intraperitoneal injection of D-galactose (D-gal) (200 mg/kgd), and model rats were subjected to the intervention with spermidine (5 mg/kgd) or swimming (60 min/d, 5 d/wk) or combination for 42 days. Spermidine coupled with exercise could attenuate D-gal-induced aging-related atrophy of skeletal muscle through induced autophagy and reduced apoptosis with characteristics of more autophagosomes, activated mitophagy, enhanced mitochondrial quality, alleviated cell shrinkage, and less swollen mitochondria under transmission scanning microscopic observation. Meanwhile, spermidine coupled with exercise could induce autophagy through activating AMPK-FOXO3a signal pathway with characterization of increased Beclin1 and LC3-II/LC3-I ratio, up-regulated anti-apoptotic Bcl-2, down-regulated pro-apoptotic Bax and caspase-3, as well as activated AMPK and FOXO3a. Therefore, spermidine combined with exercise can execute the prevention or treatment of D-gal-induced aging-related skeletal muscle atrophy through enhanced autophagy and reduced apoptosis mediated by AMPK-FOXO3a signal pathway.

Ampk phosphorylation of Ulk1 is required for targeting of mitochondria to lysosomes in exercise-induced mitophagy

Mitochondrial health is critical for skeletal muscle function and is improved by exercise training through both mitochondrial biogenesis and removal of damaged/dysfunctional mitochondria via mitophagy. The mechanisms underlying exercise-induced mitophagy have not been fully elucidated. Here, we show that acute treadmill running in mice causes mitochondrial oxidative stress at 3-12 h and mitophagy at 6 h post-exercise in skeletal muscle. These changes were monitored using a novel fluorescent reporter gene, pMitoTimer, that allows assessment of mitochondrial oxidative stress and mitophagy in vivo, and were preceded by increased phosphorylation of AMP activated protein kinase (Ampk) at tyrosine 172 and of unc-51 like autophagy activating kinase 1 (Ulk1) at serine 555. Using mice expressing dominant negative and constitutively active Ampk in skeletal muscle, we demonstrate that Ulk1 activation is dependent on Ampk. Furthermore, exercise-induced metabolic adaptation requires Ulk1. These findings provide direct evidence of exercise-induced mitophagy and demonstrate the importance of Ampk-Ulk1 signaling in skeletal muscle.Exercise is associated with biogenesis and removal of dysfunctional mitochondria. Here the authors use a mitochondrial reporter gene to demonstrate the occurrence of mitophagy following exercise in mice, and show this is dependent on AMPK and ULK1 signaling.

Monitoring and Measuring Autophagy

Autophagy is a cytoplasmic degradation system, which is important for starvation adaptation and cellular quality control. Recent advances in understanding autophagy highlight its importance under physiological and pathological conditions. However, methods for monitoring autophagic activity are complicated and the results are sometimes misinterpreted. Here, we review the methods used to identify autophagic structures, and to measure autophagic flux in cultured cells and animals. We will also describe the existing autophagy reporter mice that are useful for autophagy studies and drug testing. Lastly, we will consider the attempts to monitor autophagy in samples derived from humans.

Disrupted Skeletal Muscle Mitochondrial Dynamics, Mitophagy, and Biogenesis during Cancer Cachexia: A Role for Inflammation

Chronic inflammation is a hallmark of cancer cachexia in both patients and preclinical models. Cachexia is prevalent in roughly 80% of cancer patients and accounts for up to 20% of all cancer-related deaths. Proinflammatory cytokines IL-6, TNF-α, and TGF-β have been widely examined for their regulation of cancer cachexia. An established characteristic of cachectic skeletal muscle is a disrupted capacity for oxidative metabolism, which is thought to contribute to cancer patient fatigue, diminished metabolic function, and muscle mass loss. This review's primary objective is to highlight emerging evidence linking cancer-induced inflammation to the dysfunctional regulation of mitochondrial dynamics, mitophagy, and biogenesis in cachectic muscle. The potential for either muscle inactivity or exercise to alter mitochondrial dysfunction during cancer cachexia will also be discussed.

Transcriptome profiling of Arabian horse blood during training regimens

BACKGROUND

Arabian horses are believed to be one of the oldest and most influential horse breeds in the world. Blood is the main tissue involved in maintaining body homeostasis, and it is considered a marker of the processes taking place in the other tissues. Thus, the aim of our study was to identify the genetic basis of changes occurring in the blood of Arabian horses subjected to a training regimen and to compare the global gene expression profiles between different training periods (T₁: after a slow canter phase that is considered a conditioning phase, T₂: after an intense gallop phase, and T₃: at the end of the racing season) and between trained and untrained horses (T₀). RNA sequencing was performed on 37 samples with a 75-bp single-end run on a HiScanSQ platform (Illumina), and differentially expressed genes (DEGs) were identified based on DESeq2 (v1.11.25) software.

RESULTS

An increase in the number of DEGs between subsequent training periods was observed, and the highest amount of DEGs (440) was detected between untrained horses (T₀) and horses at the end of the racing season (T₃). The comparisons of the T₂ vs. T₃ transcriptomes and the T₀ vs. T₃ transcriptomes showed a significant gain of up-regulated genes during long-term exercise (up-regulation of 266 and 389 DEGs in the T₃ period compared to T₂ and T₀, respectively). Forty differentially expressed genes were detected between the T₁ and T₂ periods, and 296 between T₂ and T₃. Functional annotation showed that the most abundant genes up-regulated in exercise were involved in pathways regulating cell cycle (PI3K-Akt signalling pathway), cell communication (cAMP-dependent pathway), proliferation, differentiation and apoptosis, as well as immunity processes (Jak-STAT signalling pathway).

CONCLUSIONS

We investigated whether training causes permanent transcriptome changes in horse blood as a reflection of adaptation to conditioning and the maintenance of fitness to compete in flat races. The present study identified the overrepresented molecular pathways and genes that are essential for maintaining body homeostasis during long-term exercise in Arabian horses. Selected DEGs should be further investigated as markers that are potentially associated with racing performance in Arabian horses.

The role of FoxO1 in interleukin-1β-induced autostimulation in retina endothelial cells and retinas of diabetic rats

Diabetic retinopathy is a chronic, low-grade inflammatory disease. The present study aimed to investigate the effect of forkhead transcription factor O1 (FoxO1) expression on interleukin-1β (IL-1β)-induced autostimulation, both in vitro in human retina microvascular endothelial cells (HRMECs), and in vivo in retinas isolated from streptozotocin-induced diabetic rats. High-glucose (HG) and recombinant IL-1β treatment were both shown to increase the expression of FoxO1 and IL-1β in HRMECs in a dose-dependent manner. IL-1 receptor antagonist (IL-1RA) and mitogen-activated protein kinase (MAPK) inhibitors reduced IL-1β-induced expression of FoxO1 in HRMECs. Moreover, the increased expressions of FoxO1 and IL-1β in the retinas of diabetic rats were significantly decreased by intravitreal injection of lentiviral vector-mediated FoxO1 small-interfering RNA. Together, these results suggest that HG triggers IL-1β synthesis in HRMECs. The produced IL-1β induces increased FoxO1 expression, as well as interacts with the IL-1 receptor to activate MAPK signaling and thereby induces IL-1β autostimulation. The IL-1β-induced autostimulation can be inhibited by downregulation of FoxO1, accompanied by a reduction of inflammation. Together, these findings identify novel functions for FoxO1 and IL-1β in diabetic retinopathy.

Intact initiation of autophagy and mitochondrial fission by acute exercise in skeletal muscle of patients with Type 2 diabetes

The present study finds important steps in the initiation of autophagy and mitochondrial fission are intact in skeletal muscle of patients with Type 2 diabetes (T2D) compared with non-diabetic, weight-matched controls.

Selection-, age-, and exercise-dependence of skeletal muscle gene expression patterns in a rat model of metabolic fitness

Intrinsic aerobic exercise capacity can influence many complex traits including obesity and aging. To study this connection we established two rat lines by divergent selection of untrained aerobic capacity. After 32 generations the high capacity runners (HCR) and low capacity runners (LCR) differed in endurance running distance and body fat, blood glucose, other health indicators, and natural life span. To understand the interplay among genetic differences, chronological age, and acute exercise we performed microarray-based gene expression analyses in skeletal muscle with a 2×2×2 design to simultaneously compare HCR and LCR, old and young animals, and rest and exhaustion. Transcripts for mitochondrial function are expressed higher in HCRs than LCRs at both rest and exhaustion and for both age groups. Expression of cell adhesion and extracellular matrix genes tend to decrease with age. This and other age effects are more prominent in LCRs than HCRs, suggesting that HCRs have a slower aging process and this may be partly due to their better metabolic health. Strenuous exercise mainly affects transcription regulation and cellular response. The effects of any one factor often depend on the other two. For example, there are ∼140 and ∼110 line-exercise "interacting" genes for old and young animals, respectively. Many genes highlighted in our study are consistent with prior reports, but many others are novel. The gene- and pathway-level statistics for the main effects, either overall or stratified, and for all possible interactions, represent a rich reference dataset for understanding the interdependence among lines, aging, and exercise.

Exercise-induced skeletal muscle signaling pathways and human athletic performance

Skeletal muscle is a highly malleable tissue capable of altering its phenotype in response to external stimuli including exercise. This response is determined by the mode, (endurance- versus resistance-based), volume, intensity and frequency of exercise performed with the magnitude of this response-adaptation the basis for enhanced physical work capacity. However, training-induced adaptations in skeletal muscle are variable and unpredictable between individuals. With the recent application of molecular techniques to exercise biology, there has been a greater understanding of the multiplicity and complexity of cellular networks involved in exercise responses. This review summarizes the molecular and cellular events mediating adaptation processes in skeletal muscle in response to exercise. We discuss established and novel cell signaling proteins mediating key physiological responses associated with enhanced exercise performance and the capacity for reactive oxygen and nitrogen species to modulate training adaptation responses. We also examine the molecular bases underpinning heterogeneous responses to resistance and endurance exercise and the dissociation between molecular 'markers' of training adaptation and subsequent exercise performance.

Autophagy plays a role in skeletal muscle mitochondrial biogenesis in an endurance exercise-trained condition

Mitochondrial homeostasis is tightly regulated by two major processes: mitochondrial biogenesis and mitochondrial degradation by autophagy (mitophagy). Research in mitochondrial biogenesis in skeletal muscle in response to endurance exercise training has been well established, while the mechanisms regulating mitophagy and the interplay between mitochondrial biogenesis and degradation following endurance exercise training are not yet well defined. The purpose of this study was to examine the effects of a short-term inhibition of autophagy in response to acute endurance exercise on skeletal muscle mitochondrial biogenesis and dynamics in an exercise-trained condition. Male wild-type C57BL/6 mice performed five daily bouts of 1-h swimming per week for 8 weeks. In order to measure autophagy flux in mouse skeletal muscle, mice were treated with or without 2 days of 0.4 mg/kg/day intraperitoneal colchicine (blocking the degradation of autophagosomes) following swimming exercise training. The autophagic flux assay demonstrated that swimming training resulted in an increase in the autophagic flux (~100 % increase in LC3-II) in mouse skeletal muscle. Mitochondrial fusion proteins, Opa1 and MFN2, were significantly elevated, and mitochondrial fission protein, Drp1, was also increased in trained mouse skeletal muscle, suggesting that endurance exercise training promotes both mitochondrial fusion and fission processes. A mitochondrial receptor, Bnip3, was further increased in exercised muscle when treated with colchicine while Pink/Parkin protein levels were unchanged. The endurance exercise training induced increases in mitochondrial biogenesis marker proteins, SDH, COX IV, and a mitochondrial biogenesis promoting factor, PGC-1α but this effect was abolished in colchicine-treated mouse skeletal muscle. This suggests that autophagy plays an important role in mitochondrial biogenesis and this coordination between these opposing processes is involved in the cellular adaptation to endurance exercise training.

Mechanisms of protein balance in skeletal muscle

Increased global demand for adequate protein nutrition against a backdrop of climate change and concern for animal agriculture sustainability necessitates new and more efficient approaches to livestock growth and production. Anabolic growth is achieved when rates of new synthesis exceed turnover, producing a positive net protein balance. Conversely, deterioration or atrophy of lean mass is a consequence of a net negative protein balance. During early life and periods of growth, muscle mass is driven by increases in protein synthesis at the level of mRNA translation. Throughout life, muscle mass is further influenced by degradative processes such as autophagy and the ubiquitin proteasome pathway. Multiple signal transduction networks guide and coordinate these processes alongside quality control mechanisms to maintain protein homeostasis (proteostasis). Genetics, hormones, and environmental stimuli each influence proteostasis control, altering capacity and/or efficiency of muscle growth. An overview of recent findings and current methods to assess muscle protein balance and proteostasis is presented. Current efforts to identify novel control points have the potential through selective breeding design or development of hormetic strategies to better promote growth and health span during environmental stress.

Chronology of UPR activation in skeletal muscle adaptations to chronic contractile activity

The mitochondrial and endoplasmic reticulum unfolded protein responses (UPR(mt) and UPR(ER)) are important for cellular homeostasis during stimulus-induced increases in protein synthesis. Exercise triggers the synthesis of mitochondrial proteins, regulated in part by peroxisome proliferator activator receptor-γ coactivator 1α (PGC-1α). To investigate the role of the UPR in exercise-induced adaptations, we subjected rats to 3 h of chronic contractile activity (CCA) for 1, 2, 3, 5, or 7 days followed by 3 h of recovery. Mitochondrial biogenesis signaling, through PGC-1α mRNA, increased 14-fold after 1 day of CCA. This resulted in 10-32% increases in cytochrome c oxidase activity, indicative of mitochondrial content, between days 3 and 7, as well as increases in the autophagic degradation of p62 and microtubule-associated proteins 1A/1B light chain 3A (LC3)-II protein. Before these adaptations, the UPR(ER) transcripts activating transcription factor-4, spliced X-box-binding protein 1, and binding immunoglobulin protein were elevated (1.3- to 3.8-fold) at days 1-3, while CCAAT/enhancer-binding protein homologous protein (CHOP) and chaperones binding immunoglobulin protein and heat shock protein (HSP) 70 were elevated at mRNA and protein levels (1.5- to 3.9-fold) at days 1-7 of CCA. The mitochondrial chaperones 10-kDa chaperonin, HSP60, and 75-kDa mitochondrial HSP, the protease ATP-dependent Clp protease proteolytic subunit, and the regulatory protein sirtuin-3 of the UPR(mt) were concurrently induced 10-80% between days 1 and 7 To test the role of the UPR in CCA-induced remodeling, we treated animals with the endoplasmic reticulum stress suppressor tauroursodeoxycholic acid and subjected them to 2 or 7 days of CCA. Tauroursodeoxycholic acid attenuated CHOP and HSP70 protein induction; however, this failed to impact mitochondrial remodeling. Our data indicate that signaling to the UPR is rapidly activated following acute contractile activity, that this is attenuated with repeated bouts, and that the UPR is involved in chronic adaptations to CCA; however, this appears to be independent of CHOP signaling.

Effects of aerobic training on markers of autophagy in the elderly

Autophagy is a molecular process essential for the maintenance of cellular homeostasis, which appears to (i) decline with age and (ii) respond to physical exercise. In addition, recent evidence suggests a crosstalk between autophagy and toll-like receptor (TLR)-associated inflammatory responses. This study assessed the effects of aerobic exercise training on autophagy and TLR signaling in older subjects. Twenty-nine healthy women and men (age, 69.7 ± 1.0 year) were randomized to a training (TG) or a control (CG) group. TG performed an 8-week aerobic training program, while CG followed their daily routines. Peripheral blood mononuclear cells were isolated from blood samples obtained before and after the intervention, and protein levels of protein 1 light chain 3 (LC3), sequestosome 1 (p62/SQSTM1), beclin-1, phosphorylated unc-51-like kinase (ULK-1), ubiquitin-like autophagy-related (Atg)12, Atg16, and lysosome-associated membrane protein (LAMP)-2 were measured. TLR2 and TLR4 signaling pathways were also analyzed. Peak oxygen uptake increased in TG after the intervention. Protein expression of beclin-1, Atg12, Atg16, and the LC3II/I ratio increased following the training program (p < 0.05), while expression of p62/SQSTM1 and phosphorylation of ULK-1 at Ser(757) were lower (p < 0.05). Protein content of TLR2, TLR4, myeloid differentiation primary response gen 88 (MyD88), and TIR domain-containing adaptor-inducing interferon (TRIF) were not significantly modified by exercise. The current data indicate that aerobic exercise training induces alterations in multiple markers of autophagy, which seem to be unrelated to changes in TLR2 and TLR4 signaling pathways. These results expand knowledge on exercise-induced autophagy adaptations in humans and suggest that the exercise type employed may be a key factor explaining the potential relationship between autophagy and TLR pathways.

AMPKγ3 is dispensable for skeletal muscle hypertrophy induced by functional overload

Mechanisms regulating skeletal muscle growth involve a balance between the activity of serine/threonine protein kinases, including the mammalian target of rapamycin (mTOR) and 5'-AMP-activated protein kinase (AMPK). The contribution of different AMPK subunits to the regulation of cell growth size remains inadequately characterized. Using AMPKγ3 mutant-overexpressing transgenic Tg-Prkag3(225Q) and AMPKγ3-knockout (Prkag3(-/-)) mice, we investigated the requirement for the AMPKγ3 isoform in functional overload-induced muscle hypertrophy. Although the genetic disruption of the γ3 isoform did not impair muscle growth, control sham-operated AMPKγ3-transgenic mice displayed heavier plantaris muscles in response to overload hypertrophy and underwent smaller mass gain and lower Igf1 expression compared with wild-type littermates. The mTOR signaling pathway was upregulated with functional overload but unchanged between genetically modified animals and wild-type littermates. Differences in AMPK-related signaling pathways between transgenic, knockout, and wild-type mice did not impact muscle hypertrophy. Glycogen content was increased following overload in wild-type mice. In conclusion, our functional, transcriptional, and signaling data provide evidence against the involvement of the AMPKγ3 isoform in the regulation of skeletal muscle hypertrophy. Thus, the AMPKγ3 isoform is dispensable for functional overload-induced muscle growth. Mechanical loading can override signaling pathways that act as negative effectors of mTOR signaling and consequently promote skeletal muscle hypertrophy.

Cachexia in chronic obstructive pulmonary disease: new insights and therapeutic perspective

Cachexia and muscle wasting are well recognized as common and partly reversible features of chronic obstructive pulmonary disease (COPD), adversely affecting disease progression and prognosis. This argues for integration of weight and muscle maintenance in patient care. In this review, recent insights are presented in the diagnosis of muscle wasting in COPD, the pathophysiology of muscle wasting, and putative mechanisms involved in a disturbed energy balance as cachexia driver. We discuss the therapeutic implications of these new insights for optimizing and personalizing management of COPD-induced cachexia.

AMPK, a metabolic sensor, is involved in isoeugenol-induced glucose uptake in muscle cells

Isoeugenol exerts various beneficial effects on human health. However, the mechanisms underlying these effects are poorly understood. In this study, we observed that isoeugenol activated AMP-activated protein kinase (AMPK) and increased glucose uptake in rat L6 myotubes. Isoeugenol-induced increase in intracellular calcium concentration and glucose uptake was inhibited by STO-609, an inhibitor of calcium/calmodulin-dependent protein kinase kinase (CaMKK). Isoeugenol also increased the phosphorylation of protein kinase C-α (PKCα). Chelation of calcium with BAPTA-AM blocked isoeugenol-induced AMPK phosphorylation and glucose uptake. Isoeugenol stimulated p38MAPK phosphorylation that was inhibited after pretreatment with compound C, an AMPK inhibitor. Isoeugenol also increased glucose transporter type 4 (GLUT4) expression and its translocation to the plasma membrane. GLUT4 translocation was not observed after the inhibition of AMPK and CaMKK. In addition, isoeugenol activated the Akt substrate 160 (AS160) pathway, which is downstream of the p38MAPK pathway. Knockdown of the gene encoding AS160 inhibited isoeugenol-induced glucose uptake. Together, these results indicate that isoeugenol exerts beneficial health effects by activating the AMPK/p38MAPK/AS160 pathways in skeletal muscle.

Thyroid Hormone Stimulation of Autophagy Is Essential for Mitochondrial Biogenesis and Activity in Skeletal Muscle

Thyroid hormone (TH) and autophagy share similar functions in regulating skeletal muscle growth, regeneration, and differentiation. Although TH recently has been shown to increase autophagy in liver, the regulation and role of autophagy by this hormone in skeletal muscle is not known. Here, using both in vitro and in vivo models, we demonstrated that TH induces autophagy in a dose- and time-dependent manner in skeletal muscle. TH induction of autophagy involved reactive oxygen species (ROS) stimulation of 5'adenosine monophosphate-activated protein kinase (AMPK)-Mammalian target of rapamycin (mTOR)-Unc-51-like kinase 1 (Ulk1) signaling. TH also increased mRNA and protein expression of key autophagy genes, microtubule-associated protein light chain 3 (LC3), Sequestosome 1 (p62), and Ulk1, as well as genes that modulated autophagy and Forkhead box O (FOXO) 1/3a. TH increased mitochondrial protein synthesis and number as well as basal mitochondrial O2 consumption, ATP turnover, and maximal respiratory capacity. Surprisingly, mitochondrial activity and biogenesis were blunted when autophagy was blocked in muscle cells by Autophagy-related gene (Atg)5 short hairpin RNA (shRNA). Induction of ROS and 5'adenosine monophosphate-activated protein kinase (AMPK) by TH played a significant role in the up-regulation of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A), the key regulator of mitochondrial synthesis. In summary, our findings showed that TH-mediated autophagy was essential for stimulation of mitochondrial biogenesis and activity in skeletal muscle. Moreover, autophagy and mitochondrial biogenesis were coupled in skeletal muscle via TH induction of mitochondrial activity and ROS generation.

Beneficial effects of exercise on age-related mitochondrial dysfunction and oxidative stress in skeletal muscle

Mitochondria are negatively affected by ageing leading to their inability to adapt to higher levels of oxidative stress and this ultimately contributes to the systemic loss of muscle mass and function termed sarcopenia. Since mitochondria are central mediators of muscle health, they have become highly sought-after targets of physiological and pharmacological interventions. Exercise is the only known strategy to combat sarcopenia and this is largely mediated through improvements in mitochondrial plasticity. More recently a critical role for mitochondrial turnover in preserving muscle has been postulated. Specifically, cellular pathways responsible for the regulation of mitochondrial turnover including biogenesis, dynamics and autophagy may become dysregulated during ageing resulting in the reduced clearance and accumulation of damaged organelles within the cell. When mitochondrial quality is compromised and homeostasis is not re-established, myonuclear cell death is activated and muscle atrophy ensues. In contrast, acute and chronic exercise attenuates these deficits, restoring mitochondrial turnover and promoting a healthier mitochondrial pool that leads to the preservation of muscle. Additionally, the magnitude of these exercise-induced mitochondrial adaptations is currently debated with several studies reporting a lower adaptability of old muscle relative to young, but the processes responsible for this diminished training response are unclear. Based on these observations, understanding the molecular details of how advancing age and exercise influence mitochondria in older muscle will provide invaluable insight into the development of exercise protocols that will maximize beneficial adaptations in the elderly. This information will also be imperative for future research exploring pharmacological targets of mitochondrial plasticity.

The benefits of coffee on skeletal muscle

Coffee is consumed worldwide with greater than a billion cups of coffee ingested every day. Epidemiological studies have revealed an association of coffee consumption with reduced incidence of a variety of chronic diseases as well as all-cause mortality. Current research has primarily focused on the effects of coffee or its components on various organ systems such as the cardiovascular system, with relatively little attention on skeletal muscle. Summary of current literature suggests that coffee has beneficial effects on skeletal muscle. Coffee has been shown to induce autophagy, improve insulin sensitivity, stimulate glucose uptake, slow the progression of sarcopenia, and promote the regeneration of injured muscle. Much more research is needed to reveal the full scope of benefits that coffee consumption may exert on skeletal muscle structure and function.

Muscle LIM protein/CSRP3: a mechanosensor with a role in autophagy

Muscle LIM protein (MLP) is a microtubule-associated protein expressed in cardiac and muscle tissues that belongs to the cysteine-rich protein (CSRP/CRP) family. MLP has a central role during muscle development and for architectural maintenance of muscle cells. However, muscle cells rely on autophagy during differentiation and for structural maintenance. To study the role of MLP in autophagy, we have used C2C12 mouse myoblasts silenced or overexpressing MLP. Our results show that MLP contributes to the correct autophagosome formation and flux by interacting with LC3 as demonstrated by co-immunoprecipitation and PLA assay. In fact, MLP silencing results in decreased LC3-II staining and absent degradation of long-lived proteins. Moreover, MLP silencing impaired myoblasts differentiation as measured by decreased expression of MyoD1, MyoG1 and myosin heavy chain. Ultrastructural analysis revealed the presence of large empty autophagosomes in myoblasts and multimembranous structures in myotubes from MLP-silenced clones. Impaired autophagy in MLP-silenced cells resulted in increased susceptibility to apoptotic cell death. In fact, treatment of MLP-silenced C2C12 myoblasts and myotubes with staurosporine resulted in increased caspase-3 and PARP cleavage as well as increased percentage of cell death. In conclusion, we propose that MLP regulates autophagy during muscle cell differentiation or maintenance through a mechanism involving MLP/LC3-II interaction and correct autophagosome formation.

Autophagic adaptation is associated with exercise-induced fibre-type shifting in skeletal muscle

AIM

Acute exercise is known to activate autophagy in skeletal muscle. However, little is known about how basal autophagy in skeletal muscle adapts to chronic exercise. In the current study we aim to, firstly, examine whether long-term habitual exercise alters the basal autophagic signalling in plantaris muscle and, secondly, examine the association between autophagy and fibre-type shifting.

METHODS

Adult female Sprague-Dawley rats aged 2 months were randomly assigned to control and exercise groups. Animals in exercise group were kept in cages equipped with free access running wheels to perform habitual exercise for 5 months. Animals in the control group were caged in the absence of running wheels. Animals were sacrificed after the 5-month experimental period. Plantaris muscle tissues were harvested for analysis.

RESULTS

We showed that long-term habitual exercise enhanced basal autophagy, but without altering expressions of autophagy proteins in plantaris muscle. Interestingly, sirtuin protein, a possible regulator of autophagy, was upregulated in plantaris muscle. Furthermore, we suspected that different types of muscle fibre adapted to chronic exercise in different ways. Long-term habitual exercise resulted in fibre-type shifting from type IIX to IIA in both gastrocnemius muscle and plantaris muscle. Intriguingly, our analysis demonstrated that LC3-II protein abundance is positively correlated with the proportion of type IIA fibre whereas it was negatively correlated with the proportion of type IIX fibre in plantaris muscle. PGC-1α protein abundance was positively associated with the proportion of type IIA fibre and LC3-II in plantaris muscle.

CONCLUSION

These results suggest that basal autophagy is enhanced in plantaris muscle after long-term habitual exercise and associated with fibre-type shifting.

Grape polyphenols supplementation reduces muscle atrophy in a mouse model of chronic inflammation

OBJECTIVES

Polyphenols (PP) have demonstrated beneficial effects on low-grade inflammation and oxidative stress; however, little is known about their effect on highly inflamed muscle. The purposes of this study were (i) to evaluate muscle alteration induced by high-grade inflammation, and (ii) to test the effects of red grape PP supplementation on these alterations.

METHODS

We used a transgenic mice model (transforming growth factor [TGF] mice) to develop a high T cell-dependent inflammation and C57 BL/6 control (CTL) mice model. Skeletal muscles of TGF and CTL mice were investigated for inflammation, atrophy and oxidative stress markers. Isolated mitochondria from hindlimb muscles were used for respiration with pyruvate as substrate and oxidative damages were measured by Western blot. TGF mice were supplemented with a mixture of red grape polyphenols (50 mg/kg/d) for 4 wk. Data were analyzed by one-way analysis of variance (ANOVA) and post hoc Bonferroni's multiple comparison tests.

RESULTS

TGF mice presented skeletal muscle inflammation, oxidative stress, mitochondrial alteration and muscle atrophy. Atrophy was associated with two distinct pathways: (i) one linked to inflammation, NF-κB activation and increased ubiquitin ligase expression, and (ii) one dependent on reactive oxygen species (ROS) production leading to damaged mitochondria accumulation and activation of caspase-9 and 3. Supplementation of TGF mice with a mixture of red grape polyphenols (50 mg/kg/d) for 4 wk improved mitochondrial function and highly decreased caspases activation, which allowed muscle atrophy mitigation.

CONCLUSIONS

These observations suggest that nutritional dosages of red grape polyphenols might be beneficial for reducing skeletal muscle atrophy, even in a high-grade inflammation environment.

Phenotypic flexibility of skeletal muscle and heart masses and expression of myostatin and tolloid-like proteinases in migrating passerine birds

Migrant birds require large flight muscles and hearts to enhance aerobic capacity and support sustained flight. A potential mechanism for increasing muscle and heart masses during migration in birds is the muscle growth inhibitor myostatin and its metalloproteinase activators, tolloid-like proteinases (TLL-1 and TLL-2). We hypothesized that myostatin, TLL-1 and TLL-2 are downregulated during migration in pectoralis and hearts of migratory passerines to promote hypertrophy. We measured seasonal variation of tissue masses, mRNA expression of myostatin, TLL-1, and TLL-2, and myostatin protein levels in pectoralis muscle and heart for yellow warblers (Setophaga petechia), warbling vireos (Vireo gilvus), and yellow-rumped warblers (Setophaga coronata). Pectoralis mass was greatest in spring for warbling vireos and yellow warblers, but was stable between spring and fall for yellow-rumped warblers. Heart mass was higher in spring than in fall for yellow-rumped warblers, lowest in fall for warbling vireos, and seasonally stable for yellow warblers. Pectoralis and heart mRNA expression of myostatin and the TLLs did not differ significantly for any of the three species, offering little support for our hypothesis for a prominent role for myostatin in regulating migration-induced variation in pectoralis and heart masses. In contrast, pectoralis myostatin protein levels were lowest in spring for all three species, consistent with our hypothesis. Myostatin protein levels in heart, however, were seasonally stable for warbling vireos and yellow warblers, and increased in spring relative to fall for yellow-rumped warblers. These data offer mixed support for our hypothesis for the pectoralis, but suggest that myostatin is not a prominent regulator of migration-induced heart hypertrophy. Moreover, the different seasonal patterns for pectoralis mRNA and protein expression suggest that post-transcriptional modification of myostatin may contribute to pectoralis mass regulation during migration.

A time to reap, a time to sow: mitophagy and biogenesis in cardiac pathophysiology

Balancing mitophagy and mitochondrial biogenesis is essential for maintaining a healthy population of mitochondria and cellular homeostasis. Coordinated interplay between these two forces that govern mitochondrial turnover plays an important role as an adaptive response against various cellular stresses that can compromise cell survival. Failure to maintain the critical balance between mitophagy and mitochondrial biogenesis or homeostatic turnover of mitochondria results in a population of dysfunctional mitochondria that contribute to various disease processes. In this review we outline the mechanics and relationships between mitophagy and mitochondrial biogenesis, and discuss the implications of a disrupted balance between these two forces, with an emphasis on cardiac physiology. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".