Contractile activity attenuates autophagy suppression and reverses mitochondrial defects in skeletal muscle cells

Trichinella spiralis inhibits myoblast differentiation by targeting SQSTM1/p62 with a secreted E3 ubiquitin ligase

Trichinella spiralis infection is associated with the formation of cysts within host skeletal muscle cells, thereby enabling immune evasion and subsequent growth and development; however, the pathogenic factors involved in this process and their mechanisms remain elusive. Here, we found that Ts-RNF secreted by T. spiralis is required for its growth and development in host cells. Further study revealed that Ts-RNF functions as an E3 ubiquitin ligase that targets the UBA domain of SQSTM1/p62 by forming K63-type ubiquitin chains. This modification interferes with autophagic flux, leading to impaired mitochondrial clearance and abnormal myotube differentiation and fusion. Our results established that T. spiralis increases its escape by interfering with host autophagy via the secretion of an E3 ubiquitin ligase.

Betaine attenuates age-related suppression in autophagy via Mettl21c/p97/VCP axis to delay muscle loss

Age-related impairment of autophagy accelerates muscle loss and lead to sarcopenia. Betaine can delay muscle loss as a dietary methyl donor via increasing S-adenosyl-L-methionine (SAM, a crucial metabolite for autophagy regulation) in methionion cycle. However, whether betaine can regulate autophagy level to attenuate degeneration in aging muscle remains unclear. Herein, male C57BL/6J young mice (YOU, 2-month-old), old mice (OLD, 15-month-old), and 2%-betaine-treated old mice (BET, 15-month-old) were employed and raised for 12 weeks. All mice underwent body composition examination and grip strength test before being sacrificed. Betaine alleviated age-related decline in muscle mass and strength. Meanwhile, betaine preserved the expression autophagy markers (Atg5, Atg7, LC3-II, and Beclin1) both at transcriptional and translational level during the aging process. RNA-sequencing results generated from mice gastrocnemius muscle found Mettl21c, a SAM-dependent autophagy-regulating methyltransferase, was significantly higher expressed in BET and YOU group. Results were further validated by qPCR and western bloting. In vitro, C2C12 cells with or without Mettl21c RNA interference were treated different concentration of betaine (0 mM, 10 mM) under methionine-starved condition. Compared with control group, betaine upregulated autophagy markers expression and autophagy flux. By increasing the SAM level, betaine facilitated trimethylation of p97 (Mettl21c downstream effector) into valosin-containing protein (VCP). Increased VCP promoted autophagic turnover of cellular components, ATP production, and cell differentiation. Knock-down of Metthl21c dismissed improvements mentioned above. Collectively, betaine could enhance aged skeletal muscle autophagy level via Mettl21c/p97/VCP axis to delay muscle loss.

Quadriceps muscle atrophy after non-invasive anterior cruciate ligament injury: evidence linking to autophagy and mitophagy

Introduction: Anterior cruciate ligament (ACL) injury is frequently accompanied by quadriceps muscle atrophy, a process closely linked to mitochondrial health and mitochondria-specific autophagy. However, the temporal progression of key quadricep atrophy-mediating events following ACL injury remains poorly understood. To advance our understanding, we conducted a longitudinal study to elucidate key parameters in quadriceps autophagy and mitophagy. Methods: Long-Evans rats were euthanized at 7, 14, 28, and 56 days after non-invasive ACL injury that was induced via tibial compression overload; controls were not injured. Vastus lateralis muscle was extracted, and subsequent immunoblotting analysis was conducted using primary antibodies targeting key proteins involved in autophagy and mitophagy cellular processes. Results: Our findings demonstrated dynamic changes in autophagy and mitophagy markers in the quadriceps muscle during the recovery period after ACL injury. The early response to the injury was characterized by the induction of autophagy at 14 days (Beclin1), indicating an initial cellular response to the injury. Subsequently, at 14 days we observed increase in the elongation of autophagosomes (Atg4B), suggesting a potential remodeling process. The autophagosome flux was also augmented between 14- and 28 days (LC3-II/LC3-I ratio and p62). Notably, at 56 days, markers associated with the elimination of damaged mitochondria were elevated (PINK1, Parkin, and VDAC1), indicating a possible ongoing cellular repair and restoration process. Conclusion: These data highlight the complexity of muscle recovery after ACL injury and underscore the overlooked but crucial role of autophagy and mitophagy in promoting the recovery process.

Program with last minute abstracts of the Padua Days on Muscle and Mobility Medicine, 27 February - 2 March, 2024 (2024Pdm3)

During the 2023 Padua Days on Muscle and Mobility Medicine the 2024 meeting was scheduled from 28 February to 2 March 2024 (2024Pdm3). During autumn 2023 the program was expanded with Scientific Sessions which will take place over five days (in 2024 this includes February 29), starting from the afternoon of 27 February 2024 in the Conference Rooms of the Hotel Petrarca, Thermae of Euganean Hills (Padua), Italy. As per consolidated tradition, the second day will take place in Padua, for the occasion in the Sala San Luca of the Monastery of Santa Giustina in Prato della Valle, Padua, Italy. Confirming the attractiveness of the Padua Days on Muscle and Mobility Medicine, over 100 titles were accepted until 15 December 2023 (many more than expected), forcing the organization of parallel sessions on both 1 and 2 March 2024. The five days will include lectures and oral presentations of scientists and clinicians from Argentina, Austria, Belgium, Brazil, Bulgaria, Canada, Denmark, Egypt, France, Germany, Iceland, Ireland, Italy, Romania, Russia, Slovenia, Switzerland, UK and USA. Only Australia, China, India and Japan are missing from this edition. But we are confident that authors from those countries who publish articles in the PAGEpress: European Journal of Translational Myology (EJTM: 2022 ESCI Clarivate's Impact Factor: 2.2; SCOPUS Cite Score: 3.2) will decide to join us in the coming years. Together with the program established by 31 January 2024, the abstracts will circulate during the meeting only in the electronic version of the EJTM Issue 34 (1) 2024. See you soon in person at the Hotel Petrarca in Montegrotto Terme, Padua, for the inauguration scheduled the afternoon of 27 February 2024 or on-line for free via Zoom. Send us your email address if you are not traditional participants listed in Pdm3 and EJTM address books.

Mitochondria as a target for exercise-mitigated type 2 diabetes

Type 2 diabetes mellitus (T2DM) is one of most common metabolic diseases and continues to be a leading cause of death worldwide. Although great efforts have been made to elucidate the pathogenesis of diabetes, the underlying mechanism still remains unclear. Notably, overwhelming evidence has demonstrated that mitochondria are tightly correlated with the development of T2DM, and the defects of mitochondrial function in peripheral insulin-responsive tissues, such as skeletal muscle, liver and adipose tissue, are crucial drivers of T2DM. Furthermore, exercise training is considered as an effective stimulus for improving insulin sensitivity and hence is regarded as the best strategy to prevent and treat T2DM. Although the precise mechanisms by which exercise alleviates T2DM are not fully understood, mitochondria may be critical for the beneficial effects of exercise.

TFEB SUMOylation in macrophages accelerates atherosclerosis by promoting the formation of foam cells through inhibiting lysosomal activity

Atherosclerosis (AS) is a serious cardiovascular disease. One of its hallmarks is hyperlipidemia. Inhibiting the formation of macrophage foam cells is critical for alleviating AS. Transcription factor EB (TFEB) can limit the formation of macrophage foam cells by upregulating lysosomal activity. We examined whether TFEB SUMOylation is involved in this progress during AS. In this study, we investigated the role of TFEB SUMOylation in macrophages in AS using TFEB SUMOylation deficiency Ldlr-/- (TFEB-KR: Ldlr-/-) transgenic mice and TFEB-KR bone marrow-derived macrophages. We observed that TFEB-KR: Ldlr-/- atherosclerotic mice had thinner plaques and macrophages with higher lysosomal activity when compared to WT: Ldlr-/- mice. TFEB SUMOylation in macrophages decreased after oxidized low-density lipoprotein (OxLDL) treatment in vitro. Compared with wild type macrophages, TFEB-KR macrophages exhibited less lipid deposition after OxLDL treatment. Our study demonstrated that in AS, deSUMOylation of TFEB could inhibit the formation of macrophage foam cells through enhancing lysosomal biogenesis and autophagy, further reducing the accumulation of lipids in macrophages, and ultimately alleviating the development of AS. Thus, TFEB SUMOylation can be a switch to modulate macrophage foam cells formation and used as a potential target for AS therapy.

Combined effects of high fat diet and exercise on autophagy in white adipose tissue of mice

AIM

The effects of nutrition and exercise on autophagy are not well studied. This study aimed to investigate the combined effects of high-fat diets (HFD) and exercise training (ET) on autophagy in white adipose tissue of mice.

MATERIALS AND METHODS

Male C57BL/6 mice were assigned into four groups of 7 mice per group: (1) Control, (2) high-fat diet-induced obesity (HFD-Ob), (3) exercise training (ET), and (4) high-fat diet with exercise training (HFD-ET). The HFD-Ob group was fed a high-fat diet for 14 weeks, while the ET group continuously ran on a treadmill for five sessions per week for seven weeks, and the HFD-ET group had both HFD and exercise training. qReal-time-PCR and western blot were used to measure the mRNA and protein levels of autophagy markers in white adipose tissue.

RESULTS

Mice from the HFD group showed higher levels in autophagy-related gene5 (ATG5, p = 0.04), ATG7 (p = 0.002), cathepsin B (CTSB, p = 0.0004), LC3-II (p = 0.03) than control. Mice in the ET group displayed higher levels of genes for ATG7 (p = 0.0003), microtubule-associated protein1-light chain 3 (LC3, p = 0.05), lysosome-associated membrane protein 2 (LAMP2, p = 0.04) and cathepsin L (CTSL, p = 0.03) than control. Mice from the HFD-ET group had higher levels of genes for ATG7 (p = 0.05) and CTSL (p = 0.043) and lower levels of genes for CTSB (p = 0.045) compared to the HFD group and lower levels of LAMP2 (p = 0.02) compared to the ET group.

CONCLUSION

There were increases in autophagosome formation in the white adipose tissue from mice in the HFD and ET groups. A combination of HFD and ET enhances autophagosome formation and modulates lysosomal degradation in white adipose tissue.

p53 regulates skeletal muscle mitophagy and mitochondrial quality control following denervation-induced muscle disuse

Persistent inactivity promotes skeletal muscle atrophy, marked by mitochondrial aberrations that affect strength, mobility, and metabolic health leading to the advancement of disease. Mitochondrial quality control (MQC) pathways include biogenesis (synthesis), mitophagy/lysosomal turnover, and the mitochondrial unfolded protein response, which serve to maintain an optimal organelle network. Tumor suppressor p53 has been implicated in regulating muscle mitochondria in response to cellular stress; however, its role in the context of muscle disuse has yet to be explored, and whether p53 is necessary for MQC remains unclear. To address this, we subjected p53 muscle-specific KO (mKO) and WT mice to unilateral denervation. Transcriptomic and pathway analyses revealed dysregulation of pathways pertaining to mitochondrial function, and especially turnover, in mKO muscle following denervation. Protein and mRNA data of the MQC pathways indicated activation of the mitochondrial unfolded protein response and mitophagy-lysosome systems along with reductions in mitochondrial biogenesis and content in WT and mKO tissue following chronic denervation. However, p53 ablation also attenuated the expression of autophagy-mitophagy machinery, reduced autophagic flux, and enhanced lysosomal dysfunction. While similar reductions in mitochondrial biogenesis and content were observed between genotypes, MQC dysregulation exacerbated mitochondrial dysfunction in mKO fibers, evidenced by elevated reactive oxygen species. Moreover, acute experiments indicate that p53 mediates the expression of transcriptional regulators of MQC pathways as early as 1 day following denervation. Together, our data illustrate exacerbated mitochondrial dysregulation with denervation stress in p53 mKO tissue, thus indicating that p53 contributes to organellar maintenance via regulation of MQC pathways during muscle atrophy.

Nrf2 contributes to the benefits of exercise interventions on age-related skeletal muscle disorder via regulating Drp1 stability and mitochondrial fission

The progressive and generalized loss of skeletal muscle mass and function, also known as sarcopenia, underlies disability, increasing adverse outcomes and poor quality of life in older people. Exercise interventions are commonly recommended as the primary treatment for sarcopenia. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a vital role in regulating metabolism, mitochondrial function, and the ROS-dependent adaptations of skeletal muscle, as the response to exercise. To investigate the contribution of Nrf2 to the benefits of exercise interventions in older age, aged (∼22 month old) Nrf2 knockout (Nrf2-KO) mice and age-matched wild-type (WT) C57BL6/J mice were randomly divided into 2 groups (sedentary or exercise group). We found that exercise interventions improved skeletal muscle function and restored the sarcopenia-like phenotype in WT mice, accompanied with the increasing mRNA level of Nrf2. While these alternations were minimal in Nrf2-KO mice after exercise. Further studies indicated that Nrf2 could increase the stability of Drp1 through deubiquitinating and promote Drp1-dependent mitochondrial fission to attenuate mitochondrial disorder. We also observed the effects of sulforaphane (SFN), a Nrf2 activator, in restoring mitochondrial function in senescent C2C12 cells and improving sarcopenia in older WT mice, which were abolished by Nrf2 deficiency. These results indicated that some benefits of exercise intervention to skeletal muscle were Nrf2 mediated, and a future work should focus on Nrf2 signaling to identify a pharmacological treatment for sarcopenia.

Human cardiac ischemia-reperfusion injury: Blunted stress response with age

BACKGROUND AND AIM

Autophagy is a cytoprotective recycling mechanism, capable of digesting dysfunctional cellular components, and this process is associated with pro-survival outcomes. Autophagy may decline in the aging myocardium, thereby contributing to cardiac dysfunction. However, it remains to be established how autophagy responds to ischemia-reperfusion stress with age.

METHODS

Samples from the right atrium were collected from young (≤50 years; n = 5) and aged (≥70 years; n = 11) patients before and immediately following cardioplegic arrest during coronary artery bypass grafting surgery, a model of human ischemia-reperfusion injury.

RESULTS

Mitochondrial content, as assessed by a cohort of mitochondrial markers, exhibited an overall decrease in the aging myocardium (p = 0.01). In response to IR, COX-I (0.63 vs. 0.91, p = 0.01) increased in young, but not in aged patients (interaction effect p = 0.08). Reductions in LC3-I (0.48 vs. 0.28, p = 0.02) along with declines in TFEB and TFE3 (0.63 vs. 0.20, p = 0.05; 0.71 vs. 0.20, p = 0.01) were observed with age suggesting an impairment in the aged myocardium. Aged patients also displayed an inability to mount an appropriate response to IR compared to their young counterparts, specifically, increases in v-ATPase and NIX (1.06 vs 0.69, p = .01; 1.15 vs 0.69, p = .001) were not seen in the aged.

CONCLUSION

Our data demonstrate a reduced cardiac mitochondrial content and a blunted mitochondrial response to ischemia with age, accompanied by a possible impairment in mitophagy. These findings support an age-associated inability of the atrial myocardium to mount appropriate adaptive responses to stress.

Transcriptomic meta-analysis of disuse muscle atrophy vs. resistance exercise-induced hypertrophy in young and older humans

BACKGROUND

Skeletal muscle atrophy manifests across numerous diseases; however, the extent of similarities/differences in causal mechanisms between atrophying conditions in unclear. Ageing and disuse represent two of the most prevalent and costly atrophic conditions, with resistance exercise training (RET) being the most effective lifestyle countermeasure. We employed gene-level and network-level meta-analyses to contrast transcriptomic signatures of disuse and RET, plus young and older RET to establish a consensus on the molecular features of, and therapeutic targets against, muscle atrophy in conditions of high socio-economic relevance.

METHODS

Integrated gene-level and network-level meta-analysis was performed on publicly available microarray data sets generated from young (18-35 years) m. vastus lateralis muscle subjected to disuse (unilateral limb immobilization or bed rest) lasting ≥7 days or RET lasting ≥3 weeks, and resistance-trained older (≥60 years) muscle.

RESULTS

Disuse and RET displayed predominantly separate transcriptional responses, and transcripts altered across conditions were mostly unidirectional. However, disuse and RET induced directly inverted expression profiles for mitochondrial function and translation regulation genes, with COX4I1, ENDOG, GOT2, MRPL12, and NDUFV2, the central hub components of altered mitochondrial networks, and ZMYND11, a hub gene of altered translation regulation. A substantial number of genes (n = 140) up-regulated post-RET in younger muscle were not similarly up-regulated in older muscle, with young muscle displaying a more pronounced extracellular matrix (ECM) and immune/inflammatory gene expression response. Both young and older muscle exhibited similar RET-induced ubiquitination/RNA processing gene signatures with associated PWP1, PSMB1, and RAF1 hub genes.

CONCLUSIONS

Despite limited opposing gene profiles, transcriptional signatures of disuse are not simply the converse of RET. Thus, the mechanisms of unloading cannot be derived from studying muscle loading alone and provides a molecular basis for understanding why RET fails to target all transcriptional features of disuse. Loss of RET-induced ECM mechanotransduction and inflammatory profiles might also contribute to suboptimal ageing muscle adaptations to RET. Disuse and age-dependent molecular candidates further establish a framework for understanding and treating disuse/ageing atrophy.

Role of Mitochondrial Dysfunction in the Pathology of Amyloid-β

Mitochondrial dysfunction has been widely reported in several neurodegenerative disorders, including in the brains of patients with Alzheimer's disease (AD), Parkinson's disease, and Huntington disease. An increasing number of studies have implicated altered glucose and energy metabolism in patients with AD. There is compelling evidence of abnormalities in some of the key mitochondrial enzymes involved in glucose metabolism, including the pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes, which play a great significance role in the pathogenesis of AD. Changes in some of the enzyme activities of the mitochondria found in AD have been linked with the pathology of amyloid-β (Aβ). This review highlights the role of mitochondrial function in the production and clearance of Aβ and how the pathology of Aβ leads to a decrease in energy metabolism by affecting mitochondrial function.

Substrate stiffness differentially impacts autophagy of endothelial cells and smooth muscle cells

Stiffening of blood vessels is one of the most important characteristics in the process of many cardiovascular pathologies such as atherosclerosis, angiosteosis, and vascular aging. Increased stiffness of the vascular extracellular matrix drives artery pathology and alters phenotypes of vascular cell. Understanding how substrate stiffness impacts vascular cell behaviors is of great importance to the biomaterial design in tissue engineering, regenerative medicine, and medical devices. Here we report that changing substrate stiffness has a significant impact on the autophagy of vascular endothelial cells (VECs) and smooth muscle cells (VSMCs). Interestingly, our findings demonstrate that, with the increase of substrate stiffness, the autophagy level of VECs and VSMCs showed differential changes: endothelial autophagy levels reduced, leading to the reductions in a range of gene expression associated with endothelial function; while, autophagy levels of VSMCs increased, showing a transition from contractile to the synthetic phenotype. We further demonstrate that, by inhibiting cell autophagy, the expressions of endothelial functional gene were further reduced and the expression of VSMC calponin increased, suggesting an important role of autophagy in response of the cells to the challenge of microenvironment stiffness changing. Although the underlying mechanism requires further study, this work highlights the relationship of substrate stiffness, autophagy, and vascular cell behaviors, and enlightening the design principles of surface stiffness of biomaterials in cardiovascular practical applications.

Exercise Is Muscle Mitochondrial Medicine

Exercise stimulates the biogenesis of mitochondria in muscle. Some literature supports the use of pharmaceuticals to enhance mitochondria as a substitute for exercise. We provide evidence that exercise rejuvenates mitochondrial function, thereby augmenting muscle health with age, in disease, and in the absence of cellular regulators. This illustrates the power of exercise to act as mitochondrial medicine in muscle.

Contextualizing the biological relevance of standardized high-resolution respirometry to assess mitochondrial function in permeabilized human skeletal muscle

Aim

This study sought to provide a statistically robust reference for measures of mitochondrial function from standardized high‐resolution respirometry with permeabilized human skeletal muscle (ex vivo), compare analogous values obtained via indirect calorimetry, arterial‐venous O₂ differences and ³¹P magnetic resonance spectroscopy (in vivo) and attempt to resolve differences across complementary methodologies as necessary.

Methods

Data derived from 831 study participants across research published throughout March 2009 to November 2019 were amassed to examine the biological relevance of ex vivo assessments under standard conditions, ie physiological temperatures of 37°C and respiratory chamber oxygen concentrations of ~250 to 500 μmol/L.

Results

Standard ex vivo‐derived measures are lower (Z ≥ 3.01, P ≤ .0258) en masse than corresponding in vivo‐derived values. Correcting respiratory values to account for mitochondrial temperatures 10°C higher than skeletal muscle temperatures at maximal exercise (~50°C): (i) transforms data to resemble (Z ≤ 0.8, P > .9999) analogous yet context‐specific in vivo measures, eg data collected during maximal 1‐leg knee extension exercise; and (ii) supports the position that maximal skeletal muscle respiratory rates exceed (Z ≥ 13.2, P < .0001) those achieved during maximal whole‐body exercise, e.g. maximal cycling efforts.

Conclusion

This study outlines and demonstrates necessary considerations when actualizing the biological relevance of human skeletal muscle respiratory control, metabolic flexibility and bioenergetics from standard ex vivo‐derived assessments using permeabilized human muscle. These findings detail how cross‐procedural comparisons of human skeletal muscle mitochondrial function may be collectively scrutinized in their relationship to human health and lifespan.

PGC-1α protects from myocardial ischaemia-reperfusion injury by regulating mitonuclear communication

The recovery of blood supply after a period of myocardial ischaemia does not restore the heart function and instead results in a serious dysfunction called myocardial ischaemia‐reperfusion injury (IRI), which involves several complex pathophysiological processes. Mitochondria have a wide range of functions in maintaining the cellular energy supply, cell signalling and programmed cell death. When mitochondrial function is insufficient or disordered, it may have adverse effects on myocardial ischaemia‐reperfusion and therefore mitochondrial dysfunction caused by oxidative stress a core molecular mechanism of IRI. Peroxisome proliferator‐activated receptor gamma co‐activator 1α (PGC‐1α) is an important antioxidant molecule found in mitochondria. However, its role in IRI has not yet been systematically summarized. In this review, we speculate the role of PGC‐1α as a key regulator of mitonuclear communication, which may interacts with nuclear factor, erythroid 2 like ‐1 and ‐2 (NRF‐1/2) to inhibit mitochondrial oxidative stress, promote the clearance of damaged mitochondria, enhance mitochondrial biogenesis, and reduce the burden of IRI.

Electrically stimulated contractile activity-induced transcriptomic responses and metabolic remodeling in C2C12 myotubes: twitch vs. tetanic contractions

The contraction of myotubes using electrical pulse stimulation is a research tool used to mimic muscle contractile activity and exercise in rodents and humans. Most protocols employed in previous work used low-frequency twitch contractions. However, high-frequency tetanus contractions that are more physiologically relevant to muscle contractions in vivo are poorly characterized. In this report, the similarities and differences in acute responses and chronic adaptations with different contractile modes using twitches (2 Hz, continuous, 3 h) and tetanus (66 Hz, on: 5 s/off: 5 s, 3 h) were investigated. RNA sequencing-based transcriptome analysis and subsequent bioinformatics analysis suggest that tetanus may promote bioenergetic remodeling rather than twitch. Based on in silico analyses, metabolic remodeling after three contractile sessions of twitch and tetanus were investigated. Although twitch and tetanus had no significant effect on glycolysis, both types of contraction upregulated glucose oxidation capacity. Both twitch and tetanus qualitatively caused mitochondrial adaptations (increased content, respiratory chain enzyme activity, and respiratory function). The magnitude of adaptation was much greater under tetanus conditions. Our findings indicate that the contraction of myotubes by tetanus may be a useful experimental model, especially in the study of metabolic adaptations in C₂C₁₂ myotubes.

The mechanism of m6A methyltransferase METTL3-mediated autophagy in reversing gefitinib resistance in NSCLC cells by β-elemene

N⁶-methyladenosine (m⁶A) modification can alter gene expression by regulating RNA splicing, stability, translocation, and translation. Emerging evidence shows that m⁶A modification plays an important role in cancer development and progression, including cell proliferation, migration and invasion, cell apoptosis, autophagy, and drug resistance. Until now, the role of m⁶A modification mediated autophagy in cancer drug resistance is still unclear. In this study, we found that m⁶A methyltransferase METTL3-mediated autophagy played an important role in reversing gefitinib resistance by β-elemene in non-small cell lung cancer (NSCLC) cells. Mechanistically, in vitro and in vivo studies indicated that β-elemene could reverse gefitinib resistance in NSCLC cells by inhibiting cell autophagy process in a manner of chloroquine. β-elemene inhibited the autophagy flux by preventing autophagic lysosome acidification, resulting in increasing expression of SQSTM1 and LC3B-II. Moreover, both β-elemene and gefitinib decreased the level of m⁶A methylation of gefitinib resistance cells. METTL3 was higher expressed in lung adenocarcinoma tissues than that of paired normal tissues, and was involved in the gefitinib resistance of NSCLC cells. Furthermore, METTL3 positively regulated autophagy by increasing the critical genes of autophagy pathway such as ATG5 and ATG7. In conclusion, our study unveiled the mechanism of METTL3-mediated autophagy in reversing gefitinib resistance of NSCLC cells by β-elemene, which shed light on providing potential molecular-therapy target and clinical-treatment method in NSCLC patients with gefitinib resistance.

Exercise and metabolic health: beyond skeletal muscle

Regular exercise is a formidable regulator of insulin sensitivity and overall systemic metabolism through both acute events driven by each exercise bout and through chronic adaptations. As a result, regular exercise significantly reduces the risks for chronic metabolic disease states, including type 2 diabetes and non-alcoholic fatty liver disease. Many of the metabolic health benefits of exercise depend on skeletal muscle adaptations; however, there is plenty of evidence that exercise exerts many of its metabolic benefit through the liver, adipose tissue, vasculature and pancreas. This review will highlight how exercise reduces metabolic disease risk by activating metabolic changes in non-skeletal-muscle tissues. We provide an overview of exercise-induced adaptations within each tissue and discuss emerging work on the exercise-induced integration of inter-tissue communication by a variety of signalling molecules, hormones and cytokines collectively named 'exerkines'. Overall, the evidence clearly indicates that exercise is a robust modulator of metabolism and a powerful protective agent against metabolic disease, and this is likely to be because it robustly improves metabolic function in multiple organs. Graphical abstract.

Physical activity and exercise: Strategies to manage frailty

Frailty, a consequence of the interaction of the aging process and certain chronic diseases, compromises functional outcomes in the elderly and substantially increases their risk for developing disabilities and other adverse outcomes. Frailty follows from the combination of several impaired physiological mechanisms affecting multiple organs and systems. And, though frailty and sarcopenia are related, they are two different conditions. Thus, strategies to preserve or improve functional status should consider systemic function in addition to muscle conditioning. Physical activity/exercise is considered one of the main strategies to counteract frailty-related physical impairment in the elderly. Exercise reduces age-related oxidative damage and chronic inflammation, increases autophagy, and improves mitochondrial function, myokine profile, insulin-like growth factor-1 (IGF-1) signaling pathway, and insulin sensitivity. Exercise interventions target resistance (strength and power), aerobic, balance, and flexibility work. Each type improves different aspects of physical functioning, though they could be combined according to need and prescribed as a multicomponent intervention. Therefore, exercise intervention programs should be prescribed based on an individual's physical functioning and adapted to the ensuing response.

Acute Heat Exposure Alters Autophagy Signaling in C2C12 Myotubes

Autophagy is a major intracellular degradation process that is essential for the clearance of unnecessary proteins/organelles and the maintenance of cellular homeostasis. The inhibition of autophagy results in cellular consequences associated with many skeletal muscle pathologies, and therapies designed to elevate autophagic activity may provide protection from such pathologies. Acute exposure to low levels of heat has therapeutic effects; however, the impact of heat on skeletal muscle autophagy remains unclear. In the present study, C2C12 myotubes were maintained at 37°C thermoneutral (TN) or heated at 40°C heat treatment (HT) for 1 h. Myotubes were harvested immediately after heating, or returned to 37°C for recovery of 2 or 24 h. HT resulted in an elevation in pAMPK (T172), Beclin-1, and LC3 II, a marker for autophagosome formation, but no change in p62. In the context of autophagy inhibition with Bafilomycin A1, HT resulted in lower LC3 II compared to TN. The applied heat load induced the heat shock response, as evidenced by immediate upregulation of HSF1 and Hsp70. Hsp70 continued to increase during recovery, whereas pHsp27 was downregulated acutely in response to HT, but retuned to TN levels by 2 h of recovery. HT also reduced the phosphorylation of the MAP-kinases p38 and JNK. These findings suggest that an acute, short bout of mild heat may be beneficial to skeletal muscle by increasing AMPK activity, markers of autophagasome formation, and the heat shock response.

Effects of the tetrahedral framework nucleic acids on the skeletal muscle regeneration in vitro and in vivo

The challenges associated with muscle degenerative diseases and volumetric muscle loss (VML) emphasizes the prospects of muscle tissue regeneration.

The dual roles of autophagy in gliomagenesis and clinical therapy strategies based on autophagic regulation mechanisms

Autophagy, a self-digestion intracellular catabolic process, plays a crucial role in cellular homeostasis under conditions of starvation, oxidative stress and genotoxic stress. The capability of maintaining homeostasis contributes to preventing malignant behavior in normal cells. Many studies have provided compelling evidence that autophagy is involved in brain tumor recurrence and chemotherapy and radiotherapy resistance. Gliomas, as the primary central nervous system (CNS) tumors, are characterized by rapid, aggressive growth and recurrence and have a poor prognosis and bleak outlook even with modern multimodality strategies involving maximal surgical resection, radiotherapy and alkylating agent-based chemotherapy. Autophagy-associated signaling pathways, such as the extracellular signal-regulated kinase1/2 (ERK1/2) pathway, class I phosphatidylinositol 3-phosphate kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway and nuclear factor kappa-B (NF-κB) pathway, act as tumor suppressors or protect tumor cells against chemotherapy/radiotherapy-induced cytotoxicity in gliomagenesis. Through these pathways, both lethal autophagy and protective autophagy play crucial roles in tumor initiation, chemoresistance and glioma stem cell differentiation. Moreover, lethal autophagy and protective autophagy have been identified as novel therapeutic targets in glioma according to the mechanisms described above. Here, we discuss the multiple impacts of the autophagic response on distinct phases of gliomagenesis and the advanced progress of therapies based on this concept.

Assessing autophagy in murine skeletal muscle: current findings to modulate and quantify the autophagic flux

PURPOSE OF REVIEW

In addition to the currently available lysosomotropic drugs and autophagy whole-body knockout mouse models, we provide alternative methods that enable the modulation and detection of autophagic flux in vivo, discussing advantages and disadvantages of each method.

RECENT FINDINGS

With the autophagosome-lysosome fusion inhibitor colchicine in skeletal muscle and temporal downregulation of autophagy using a novel Autophagy related 5-short hairpin RNA (Atg5-shRNA) mouse model we mention two models that directly modulate autophagy flux in vivo. Furthermore, methods to quantify autophagy flux, such as mitophagy transgenic reporters, in situ immunofluorescent staining and multispectral imaging flow cytometry, in mature skeletal muscle and cells are addressed.

SUMMARY

To achieve clinical benefit, less toxic, temporary and cell-type-specific modulation of autophagy should be pursued further. A temporary knockdown as described for the Atg5-shRNA mice could provide a first insight into possible implications of autophagy inhibition. However, it is also important to take a closer look into the methods to evaluate autophagy after harvesting the tissue. In particular caution is required when experimental conditions can influence the final measurement and this should be pretested carefully.

Recent Data on Cellular Component Turnover: Focus on Adaptations to Physical Exercise

Significant progress has expanded our knowledge of the signaling pathways coordinating muscle protein turnover during various conditions including exercise. In this manuscript, the multiple mechanisms that govern the turnover of cellular components are reviewed, and their overall roles in adaptations to exercise training are discussed. Recent studies have highlighted the central role of the energy sensor (AMP)-activated protein kinase (AMPK), forkhead box class O subfamily protein (FOXO) transcription factors and the kinase mechanistic (or mammalian) target of rapamycin complex (MTOR) in the regulation of autophagy for organelle maintenance during exercise. A new cellular trafficking involving the lysosome was also revealed for full activation of MTOR and protein synthesis during recovery. Other emerging candidates have been found to be relevant in organelle turnover, especially Parkin and the mitochondrial E3 ubiquitin protein ligase (Mul1) pathways for mitochondrial turnover, and the glycerolipids diacylglycerol (DAG) for protein translation and FOXO regulation. Recent experiments with autophagy and mitophagy flux assessment have also provided important insights concerning mitochondrial turnover during ageing and chronic exercise. However, data in humans are often controversial and further investigations are needed to clarify the involvement of autophagy in exercise performed with additional stresses, such as hypoxia, and to understand the influence of exercise modality. Improving our knowledge of these pathways should help develop therapeutic ways to counteract muscle disorders in pathological conditions.

Parthenolide regulates oxidative stress-induced mitophagy and suppresses apoptosis through p53 signaling pathway in C2C12 myoblasts

Muscle redox disturbances and oxidative stress have emerged as a common pathogenetic mechanism and potential therapeutic intervention in some muscle diseases. Parthenolide (PTL), a sesquiterpene lactone found in large amounts in the leaves of feverfew, possesses anti-inflammatory, anti-migraine, and anticancer properties. Although PTL was reported to alleviate cancer cachexia and improve skeletal muscle characteristics in a cancer cachexia model, its actions on oxidative stress-induced damage in C2C12 myoblasts have not been reported and the regulatory mechanisms have not yet been defined. In our study, PTL attenuated H₂ O₂ -induced growth inhibition and morphological changes. Furthermore, PTL exhibited scavenging activity against reactive oxygen species and protected C2C12 cells from apoptosis in response to H₂ O₂ . Meanwhile, PTL suppressed collapse of the mitochondrial membrane potential, thereby contributing to normalizing H₂ O₂ -induced autophagy flux and mitophagy, correlating with inhibiting degradation of mitochondrial marker protein TIM23, the increase in LC3-II expression and the reduction of mitochondria DNA. Besides its protective effect on mitochondria, PTL also prevented H₂ O₂ -induced lysosomes damage in C2C12 cells. In addition, the phosphorylation of p53, cathepsin B, and Bax/Bcl-2 protein levels, and the translocation of Bax from the cytosol to mitochondria induced by H₂ O₂ in C2C12 cells was significantly reduced by PTL. In conclusion, PTL modulates oxidative stress-induced mitophagy and protects C2C12 myoblasts against apoptosis, suggesting a potential protective effect against oxidative stress-associated skeletal muscle diseases.

Protein composition of the muscle mitochondrial reticulum during postnatal development

KEY POINTS

Muscle mitochondrial networks changed from a longitudinal, fibre parallel orientation to a perpendicular configuration during postnatal development. Mitochondrial dynamics, mitophagy and calcium uptake proteins were abundant during early postnatal development. Mitochondrial biogenesis and oxidative phosphorylation proteins were upregulated throughout muscle development. Postnatal muscle mitochondrial network formation is accompanied by a change in protein expression profile from mitochondria designed for co-ordinated cellular assembly to mitochondria highly specialized for cellular energy metabolism.

ABSTRACT

Striated muscle mitochondria form connected networks capable of rapid cellular energy distribution. However, the mitochondrial reticulum is not formed at birth and the mechanisms driving network development remain unclear. In the present study, we aimed to establish the network formation timecourse and protein expression profile during postnatal development of the murine muscle mitochondrial reticulum. Two-photon microscopy was used to observe mitochondrial network orientation in tibialis anterior (TA) muscles of live mice at postnatal days (P) 1, 7, 14, 21 and 42, respectively. All muscle fibres maintained a longitudinal, fibre parallel mitochondrial network orientation early in development (P1-7). Mixed networks were most common at P14 but, by P21, almost all fibres had developed the perpendicular mitochondrial orientation observed in mature, glycolytic fibres. Tandem mass tag proteomics were then applied to examine changes in 6869 protein abundances in developing TA muscles. Mitochondrial proteins increased by 32% from P1 to P42. In addition, both nuclear- and mitochondrial-DNA encoded oxidative phosphorylation (OxPhos) components were increased during development, whereas OxPhos assembly factors decreased. Although mitochondrial dynamics and mitophagy were induced at P1-7, mitochondrial biogenesis was enhanced after P14. Moreover, calcium signalling proteins and the mitochondrial calcium uniporter had the highest expression early in postnatal development. In conclusion, mitochondrial networks transform from a fibre parallel to perpendicular orientation during the second and third weeks after birth in murine glycolytic skeletal muscle. This structural transition is accompanied by a change in protein expression profile from mitochondria designed for co-ordinated cellular assembly to mitochondria highly specialized for cellular energy metabolism.

Regulation of autophagic and mitophagic flux during chronic contractile activity-induced muscle adaptations

Autophagy and mitophagy are important for training-inducible muscle adaptations, yet it remains unclear how these systems are regulated throughout the adaptation process. Here, we studied autophagic and mitophagic flux in the skeletal muscles of Sprague-Dawley rats (300-500 g) exposed to chronic contractile activity (CCA; 3 h/day, 9 V, 10 Hz continuous, 0.1 ms pulse duration) for 1, 2, 5, and 7 days (N = 6-8/group). In order to determine the flux rates, colchicine (COL; 0.4 mg/ml/kg) was injected 48 h before tissue collection, and we evaluated differences of autophagosomal protein abundances (LC3-II and p62) between colchicine- and saline-injected animals. We confirmed that CCA resulted in mitochondrial adaptations, including improved state 3 respiration as early as day 1 in permeabilized muscle fibers, as well significant increases in mitochondrial respiratory capacity and marker proteins in IMF mitochondria by day 7. Mitophagic and autophagic flux (LC3-II and p62) were significantly decreased in skeletal muscle following 7 days of CCA. Notably, the mitophagic system seemed to be downregulated prior (day 3-5) to changes in autophagic flux (day 7), suggesting enhanced sensitivity of mitophagy compared to autophagy with chronic muscle contraction. Although we detected no significant change in the nuclear translocation of TFEB, a regulator of lysosomal biogenesis, CCA increased total TFEB protein, as well as LAMP1, in skeletal muscle. Thus, chronic muscle activity reduces mitophagy in parallel with improved mitochondrial function, and this is supported by enhanced lysosomal degradation capacity.

Maintenance of Skeletal Muscle Mitochondria in Health, Exercise, and Aging

Mitochondria are critical organelles responsible for regulating the metabolic status of skeletal muscle. These organelles exhibit remarkable plasticity by adapting their volume, structure, and function in response to chronic exercise, disuse, aging, and disease. A single bout of exercise initiates signaling to provoke increases in mitochondrial biogenesis, balanced by the onset of organelle turnover carried out by the mitophagy pathway. This accelerated turnover ensures the presence of a high functioning network of mitochondria designed for optimal ATP supply, with the consequence of favoring lipid metabolism, maintaining muscle mass, and reducing apoptotic susceptibility over the longer term. Conversely, aging and disuse are associated with reductions in muscle mass that are in part attributable to dysregulation of the mitochondrial network and impaired mitochondrial function. Therefore, exercise represents a viable, nonpharmaceutical therapy with the potential to reverse and enhance the impaired mitochondrial function observed with aging and chronic muscle disuse.