Role of AMPK in regulation of LC3 lipidation as a marker of autophagy in skeletal muscle

Lipophagy: exploring its association with male reproductive system disorders and investigating potential mechanisms

BACKGROUND

Lipid metabolism, one of the three major metabolic processes, plays a crucial role in male fertility, particularly when lipid homeostasis is disrupted. Lipid droplets (LDs), cellular organelles that store lipids primarily in the form of triglycerides and cholesterol esters, serve as central hubs in lipid metabolism.The degradation of LDs is regulated by lipases and lipophagy.

OBJECTIVE: 

This review explores the various forms of lipophagy, its molecular mechanisms, and its critical role in male fertility. Specifically, it examines the association between lipophagy and male infertility, sexual dysfunction, and reproductive cancers.

METHODS: 

This review synthesizes current research on the molecular pathways regulating lipophagy, focusing on its impact on male reproductive health.

RESULTS: 

Lipophagy is essential for maintaining lipid homeostasis in male reproductive tissues. Dysfunction of lipophagy is associated with impaired sperm function, infertility, sexual dysfunction, and an increased risk of reproductive cancers in men.

CONCLUSION: 

Lipophagy plays a pivotal role in regulating lipid metabolism and maintaining male fertility. It may serve as a potential therapeutic target for treating male reproductive disorders.

Proteomic characterization of the medial prefrontal cortex in chronic restraint stress mice

Depression is a prominent contributor to global disability. A growing body of data suggests that depression is associated with the pathophysiology of the medial prefrontal cortex (mPFC), but the underlying mechanisms remain poorly understood. Mice were subjected to chronic restraint stress (CRS) for 3 weeks to create depression models during this investigation. Protein tandem mass tag (TMT) quantification and LC-MS/MS analysis were conducted to examine proteome patterns. Afterwards, to further explore the enrichment of differential proteins and the signaling pathways involved, we annotated these differentially expressed proteins. We confirmed that CRS mice developed depression-like and anxiety-like behaviors. Among the 8081 measured proteins, a total of 15 proteins were found to be differentially expressed. These proteins exhibited functional enrichment in a variety of biological functions, and among these pathways, alterations in synaptic function and autophagy are noteworthy. In addition, we identified a differentially expressed protein called Wnt2b and found that CRS may disrupt synaptic plasticity by affecting the activation of the Wnt2b/β-catenin pathway. Our findings showed depression-like behaviors in the CRS mouse model and molecular alterations in the mPFC, which may help explain the pathogenesis of depression and identify novel antidepressant medication targets. SIGNIFICANCE: Depression is a prevalent and frequent chronic mental illness and is now a significant contributor to global disability. In this study, we used chronic restraint stress to establish a mouse model of depression, and differentially expressed proteins in the medial prefrontal cortex of depressed model mice were detected by TMT proteomics. Our study verified the presence of altered synaptic function and excessive autophagy in the mPFC of CRS-induced mice from a proteomic perspective. Furthermore, we demonstrated that CRS may disrupt synaptic plasticity by affecting the activation of the Wnt2b/β-catenin pathway, which may be a key link in the pathogenesis of depression and may provide new insights for identifying new antidepressant drug targets.

The Autophagic and Apoptotic Death of Forebrain Neurons of Rats with Global Brain Ischemia Is Diminished by the Intranasal Administration of Insulin: Possible Mechanism of Its Action

Insulin is a promising neuroprotector. To better understand the mechanism of insulin action, it was important to show its ability to diminish autophagic neuronal death in animals with brain ischemic and reperfusion injury. In forebrain ischemia and reperfusion, the number of live neurons in the hippocampal CA1 region and frontal cortex of rats decreased to a large extent. Intracerebroventricular administration of the autophagy and apoptosis inhibitors to ischemic rats significantly increased the number of live neurons and showed that the main part of neurons died from autophagy and apoptosis. Intranasal administration of 0.5 IU of insulin per rat (before ischemia and daily during reperfusion) increased the number of live neurons in the hippocampal CA1 region and frontal brain cortex. In addition, insulin significantly diminished the level of autophagic marker LC3B-II in these forebrain regions, which markedly increased during ischemia and reperfusion. Our studies demonstrated for the first time the ability of insulin to decrease autophagic neuronal death, caused by brain ischemia and reperfusion. Insulin administered intranasally activated the Akt-kinase (activating the mTORC1 complex, which inhibits autophagy) and inhibited the AMP-activated protein kinase (which activates autophagy) in the hippocampus and frontal cortex of rats with brain ischemia and reperfusion.

Total paeony glycoside relieves neuroinflammation to exert antidepressant effect via the interplay between NLRP3 inflammasome, pyroptosis and autophagy

BACKGROUND

Depression is a common mental illness characterised by abnormal and depressed emotions. Total paeony glycoside (TPG) is a naturally active saponin extracted from the traditional Chinese medicine Radix Paeoniae rubra. However, the antidepressant and neuroinflammatory effects of TPG have not been thoroughly studied.

PURPOSE

To study the therapeutic potential of TGP in depression caused by neuronal injury and neuroinflammation and to explore the mechanism of TGP and the relationship between the NLRP3 inflammasome, pyroptosis, and autophagy.

STUDY DESIGN

A chronic unpredictable mild stress (CUMS)-induced depression model and a cell model of corticosterone (CORT)-induced hippocampal neuron injury were established to evaluate the therapeutic effects of TPG.

METHODS

The composition of TPG was analysed using high-performance liquid chromatography and mass spectrometry. The effects of TPG and fluoxetine on depression-like behaviour, neuronal injury, neuroinflammation, pyroptosis, and mitochondrial autophagy in the mice models were evaluated.

RESULTS

TGP alleviated depression-like behaviours in mice and inhibited hippocampal neuronal apoptosis. The secretion of inflammatory cytokines was significantly reduced in CORT-induced hippocampal neuron cells and in the serum of a mouse model of CUMS-induced depression. In addition, TGP treatment reduced the levels of NLRP3 family pyrin structural domains, including NLRP3, pro-caspase-1, caspase-1, and IL-1β, and the pyroptosis related proteins such as GSDMD-N. Importantly, TPG attenuated mitochondrial dysfunction, promoted the clearance of damaged mitochondria, and the activation of mitochondrial autophagy, which reduced ROS accumulation and NLRP3 inflammasome activation. An in-depth study observed that the regulatory effect of TPG on autophagy was attenuated by the autophagy inhibitor 3-methyladenine (3-MA) in vitro and in vivo. However, administration of the caspase-1 inhibitor Belnacasan (VX-765) successfully inhibited pyroptosis and showed a synergistic therapeutic effect with TPG.

CONCLUSION

These results indicate that TPG can repair neuronal damage by activating autophagy, restoring mitochondrial function, and reducing inflammation-mediated pyroptosis, thereby playing an important role in the alleviation of neuroinflammation and depression. This study suggests new potential drugs and treatment strategies for neuroinflammation-related diseases and depression.

The intensity-dependent effects of exercise and superimposing environmental heat stress on autophagy in peripheral blood mononuclear cells from older men

Autophagy is a vital cellular process, essential to maintaining cellular function during acute physiological stressors including exercise and heat stress. We previously showed that autophagy occurs during exercise in an intensity-dependent manner in peripheral blood mononuclear cells (PBMCs) from young men, with elevated responses in the heat. However, given autophagy declines with age, it is unclear whether a similar pattern of response occurs in older adults. Therefore, we evaluated autophagy and the cellular stress response [i.e., apoptosis, inflammation, and the heat shock response (HSR)] in PBMCs from 10 healthy older men [mean (SD): aged 70 yr (5)] in response to 30 min of semirecumbent cycling at low, moderate, and vigorous intensities [40, 55, and 70% maximal oxygen consumption (V̇o2max), respectively] in a temperate (25°C) environment, with an additional vigorous-intensity bout (70% of V̇o2max) performed in a hot environment (40°C). Responses were evaluated before and after exercise, as well as throughout a 6-h seated recovery period performed in the same environmental conditions as the respective exercise bout. Proteins were assessed via Western blot. Although we observed elevations in mean body temperature with each increase in exercise intensity, autophagy was only stimulated during vigorous-intensity exercise, where we observed elevations in LC3-II (P < 0.05). However, when the same exercise was performed in the heat, the LC3-II response was attenuated, which was accompanied by significant p62 accumulation (P < 0.05). Altogether, our findings demonstrate that older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot environments, potentially underlying heat-induced cellular vulnerability in older men.NEW & NOTEWORTHY We demonstrate that autophagic stimulation occurs in response to short-duration (30-min) vigorous-intensity exercise in peripheral blood mononuclear cells from older adults; however, no changes in autophagy occur during low- or moderate-intensity exercise. Moreover, older adults exhibit autophagic impairments when the same vigorous-intensity exercise is performed in hot ambient conditions. When paired with an attenuated heat shock response, as well as elevated apoptotic responses, older men may exhibit greater cellular vulnerability to exertional heat stress.

Impaired mitophagosome-lysosome fusion mediates olanzapine-induced aging

The lifespan of schizophrenia patients is significantly shorter than the general population. Olanzapine is one of the most commonly used antipsychotic drugs (APDs) for treating patients with psychosis, including schizophrenia and bipolar disorder. Despite their effectiveness in treating positive and negative symptoms, prolonged exposure to APDs may lead to accelerated aging and cognitive decline, among other side effects. Here we report that dysfunctional mitophagy is a fundamental mechanism underlying accelerated aging induced by olanzapine, using in vitro and in vivo (Caenorhabditis elegans) models. We showed that the aberrant mitophagy caused by olanzapine was via blocking mitophagosome-lysosome fusion. Furthermore, olanzapine can induce mitochondrial damage and hyperfragmentation of the mitochondrial network. The mitophagosome-lysosome fusion in olanzapine-induced aging models can be restored by a mitophagy inducer, urolithin A, which alleviates defective mitophagy, mitochondrial damage, and fragmentation of the mitochondrial network. Moreover, the mitophagy inducer ameliorated behavioral changes induced by olanzapine, including shortened lifespan, and impaired health span, learning, and memory. These data indicate that olanzapine impairs mitophagy, leading to the shortened lifespan, impaired health span, and cognitive deficits. Furthermore, this study suggests the potential application of mitophagy inducers as therapeutic strategies to reverse APD-induced adverse effects associated with accelerated aging.

Polyamines and Physical Activity in Musculoskeletal Diseases: A Potential Therapeutic Challenge

Autophagy dysregulation is commonplace in the pathogenesis of several invalidating diseases, such as musculoskeletal diseases. Polyamines, as spermidine and spermine, are small aliphatic cations essential for cell growth and differentiation, with multiple antioxidant, anti-inflammatory, and anti-apoptotic effects. Remarkably, they are emerging as natural autophagy regulators with strong anti-aging effects. Polyamine levels were significantly altered in the skeletal muscles of aged animals. Therefore, supplementation of spermine and spermidine may be important to prevent or treat muscle atrophy. Recent in vitro and in vivo experimental studies indicate that spermidine reverses dysfunctional autophagy and stimulates mitophagy in muscles and heart, preventing senescence. Physical exercise, as polyamines, regulates skeletal muscle mass inducing proper autophagy and mitophagy. This narrative review focuses on the latest evidence regarding the efficacy of polyamines and exercise as autophagy inducers, alone or coupled, in alleviating sarcopenia and aging-dependent musculoskeletal diseases. A comprehensive description of overall autophagic steps in muscle, polyamine metabolic pathways, and effects of the role of autophagy inducers played by both polyamines and exercise has been presented. Although literature shows few data in regard to this controversial topic, interesting effects on muscle atrophy in murine models have emerged when the two "autophagy-inducers" were combined. We hope these findings, with caution, can encourage researchers to continue investigating in this direction. In particular, if these novel insights could be confirmed in further in vivo and clinical studies, and the two synergic treatments could be optimized in terms of dose and duration, then polyamine supplementation and physical exercise might have a clinical potential in sarcopenia, and more importantly, implications for a healthy lifestyle in the elderly population.

Association of Subclinical Thyroid Dysfunction with Cognitive Impairment in Rats: The Role of Autophagy

BACKGROUND

We investigated the effect of subclinical hyperthyroidism and subclinical hypothyroidism on cognitive function in rats and the role of autophagy in this process.

METHODS

Forty Wistar rats were randomized into normal control (NC), hyperthyroidism (Hyper), hypothyroidism (Hypo), subclinical hyperthyroidism (sHyper), and subclinical hypothyroidism (sHypo) groups. Cognitive function (spatial learning and memory) was tested by the Morris water maze test. Hippocampal histopathology was analyzed by H&E staining, and expression levels of caspase-3 in hippocampal CA1 neurons were measured. In addition, immunoblot analysis was performed to detect hippocampal autophagy-related proteins.

RESULTS

Escape latency from day 1 to day 4 was significantly longer in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). In addition, the number of rats crossing the virtual platform was significantly lower in the Hypo, Hyper, and sHyper groups than in the NC group (P < 0.01). Compared with the NC group, all four groups had significantly lower residence time in the target quadrant (P < 0.05). Beclin-1 and LC3-II protein expression in hippocampal tissues was significantly higher in the Hyper and sHyper groups than in the NC group (P < 0.01). Beclin-1 and LC3-II protein expression in hippocampal tissues did not significantly differ between the sHypo group and NC group (P > 0.05).

CONCLUSIONS

Subclinical thyroid dysfunction in rats might lead to cognitive impairment. Subclinical hyperthyroidism might be associated with excessive activation of autophagy and hippocampal neuron damage and necrosis.

Role of AMPK in autophagy

Adenosine monophosphate-activated protein kinase (AMPK) is a significant energy sensor in the maintenance of cellular energy homeostasis. Autophagy is a highly conserved catabolic process that involves an intracellular degradation system in which cytoplasmic components, such as protein aggregates, organelles, and other macromolecules, are directed to the lysosome through the self-degradative process to maintain cellular homeostasis. Given the triggered autophagy process in various situations including the nutrient deficit, AMPK is potentially linked with different stages of autophagy. Above all, AMPK increases ULK1 activity by directly phosphorylating Ser467, Ser555, Thr574, and Ser637 at least four sites, which increases the recruitment of autophagy-relevant proteins (ATG proteins) to the membrane domains which affects autophagy at the initiation stage. Secondly, AMPK inhibits VPS34 complexes that do not contain pro-autophagic factors and are thus involved in isolation membrane forming processes, by direct phosphorylation of VPS34 on Thr163 and Ser165. After phosphorylation, AMPK can govern autophagosome formation through recruiting downstream autophagy-related proteins to the autophagosome formation site. Finally, the AMPK-SIRT1 signaling pathway can be activated by upregulating the transcription of autophagy-related genes, thereby enhancing autophagosome-lysosome fusion. This review provides an introduction to the role of AMPK in different stages of autophagy.

Protective Effects of the Chalcone-Based Derivative AN07 on Inflammation-Associated Myotube Atrophy Induced by Lipopolysaccharide

Inflammation is a major cause of skeletal muscle atrophy in various diseases. 2-Hydroxy-4′-methoxychalcone (AN07) is a chalcone-based peroxisome-proliferator-activated receptor gamma (PPARγ) agonist with various effects, such as antiatherosclerosis, anti-inflammation, antioxidative stress, and neuroprotection. In this study, we examined the effects of AN07 on protein homeostasis pathway and mitochondrial function in inflammation-associated myotube atrophy induced by lipopolysaccharides (LPS). We found that AN07 significantly attenuated NF-κB activation, inflammatory factors (TNF-α, IL-1β, COX-2, and PGE2), Nox4 expression, and reactive oxygen species levels in LPS-treated C2C12 myotubes. Moreover, AN07 increased SOD2 expression and improved mitochondrial function, including mitochondrial membrane potential and mitochondrial oxygen consumption rate. We also demonstrated that AN07 attenuated LPS-induced reduction of myotube diameter, MyHC expression, and IGF-1/IGF-1R/p-Akt-mediated protein synthesis signaling. Additionally, AN07 downregulated LPS-induced autophagy–lysosomal protein degradation molecules (LC3-II/LC3-I and degraded p62) and ubiquitin–proteasome protein degradation molecules (n-FoxO1a/MuRF1/atrogin-1). However, the regulatory effects of AN07 on protein synthesis and degradation signaling were inhibited by the IGF-1R inhibitor AG1024 and the PI3K inhibitor wortmannin. In addition, the PPARγ antagonist GW9662 attenuated the effects of AN07 against LPS-induced inflammation, oxidation, and protein catabolism. In conclusion, our findings suggest that AN07 possesses protective effects on inflammation-induced myotube atrophy and mitochondrial dysfunction.

The autophagic response to exercise in peripheral blood mononuclear cells from young men is intensity-dependent and is altered by exposure to environmental heat

Autophagy is essential to maintaining cellular homeostasis in all eukaryotic cells and to tolerance of acute stressors such as starvation, heat, and recovery following exercise. Limited information exists regarding the exercise intensity-dependent autophagic response in humans, and it is unknown how environmental heat stress may modulate this response. Therefore, we evaluated autophagy and accompanying pathways of cellular stress (the heat shock response [HSR], apoptosis, and acute inflammation) in peripheral blood mononuclear cells (PBMCs) from 10 young men (mean [SD]; 22 [2] years) before, immediately after and up to 6h post-exercise recovery from 30 minutes of low-, moderate-, and high-intensity semi-recumbent cycling (40, 55 and 70% of maximal oxygen consumption (VO_2max), respectively)in a temperate environment (25°C) and at 70% of VO_2max in a hot environment (40°C). Changes in protein content were analyzed via Western blot. Each increase in exercise intensity was associated with elevations in mean body temperature. LC3-II increased following moderate-intensity exercise, with further increases following high-intensity exercise (p < 0.05). However, an increase in beclin-2 and ULK1, with a decrease in p62 was only observed after high-intensity exercise, which was paralleled by elevated TNF-α and cleaved-caspase-3, with the HSR peaking at 6h after exercise (p < 0.05). When exercise was performed in the heat, greater LC3-II and cleaved-caspase-3 accumulation was observed, however beclin-2 declined in recovery (p < 0.05). Therefore, our findings indicate that autophagy in PBMCs during exercise may be associated with greater heat strain exhibited during increasing exercise intensities, which is modulated by exposure to heat.

Effect of Photobiomodulation on Denervation-Induced Skeletal Muscle Atrophy and Autophagy: A Study in Mice

OBJECTIVE

The purpose of this study was to investigate whether photobiomodulation (PBM) can protect against and attenuate muscle atrophy owing to complete peripheral nerve lesion in mice by acting on autophagy.

METHODS

C57BL/10 mice underwent right sciatic nerve transection to induce tibialis anterior muscle atrophy. After 6 hours of denervation, the mice received PBM (wavelength, 830 nm) daily, transcutaneously over the tibialis anterior muscle region for 5 or 14 days. Some mice with sciatic nerve lesion did not receive PBM. Mice that did not have sciatic nerve lesion and PBM were used as controls. After 5 and 14 days, the right tibialis anterior muscle was examined using histomorphometric (cross-sectional area of muscle fibers), Western blot (levels of the autophagy marker LC3), and immunofluorescence analyses (number of LC3 puncta in the muscle fibers).

RESULTS

The cross-sectional area of the tibialis anterior muscle fibers decreased after 5 and 14 days of denervation. PBM protected against muscle fiber atrophy after 5 days of denervation and attenuated muscle fiber atrophy after 14 days of denervation. After 5 days of muscle denervation, autophagy did not change, as demonstrated by the comparable levels of LC3-I/II ratio and LC3 puncta between the controls and the mice with atrophic muscle; PBM did not change this profile. After 14 days of denervation, an increased LC3-I/II ratio suggested an ongoing autophagy, which was not affected by PBM.

CONCLUSION

PBM attenuated the tibialis anterior muscle atrophy induced by sciatic nerve transection in the mice after at least 5 and 14 days of muscle denervation, without affecting autophagy. The transient protective effect of PBM was observed as early as 5 days after the of complete nerve lesion.

Asiatic acid alleviates ischemic myocardial injury in mice by modulating mitophagy- and glycophagy-based energy metabolism

Myocardial infarction (MI) causes disturbances in myocardial energy metabolism, ultimately leading to a poor prognosis. Cytosolic glycogen autophagy (glycophagy) and mitochondrial autophagy (mitophagy) are upregulated in MI to optimize energy metabolism but to a limited extent. Asiatic acid (AA), a pentacyclic triterpene derived from the traditional Chinese herb Centella asiatica, displays anti-inflammatory, antioxidant, and antiapoptotic activities. AA has been found to alleviate focal cerebral and liver ischemic injury by reversing mitochondrial dysfunction. In this study, we investigated whether AA exerted cardioprotective effects against MI by activating glycophagy and mitophagy to improve the energy balance. In vitro cardioprotective effects were examined in neonatal mouse cardiomyocytes subjected to oxygen-glucose deprivation for 12 h. Treatment with AA (2-50 μM) significantly increased cell viability and improved the energy metabolism evidenced by increased ATP level and phosphocreatine/ATP ratio. In vivo cardioprotective effects were studied in a mouse model of MI. Administration of AA (5-125 mg·kg^-1·d^-1, ig) significantly reduced infarct size and ischemic myocardial injury, and improved cardiac function. AA treatment also promoted mitophagy and relieved mitochondrial edema evidenced by increased number of mitophagosomes in ischemic myocardium in vivo and increased mitochondria-light chain 3 (LC3)-II colocalization in ODG-treated cardiomyocytes in vitro. Mitophagy activation was accompanied by activation of the AMPK signaling pathway. Knockdown of AMPK abolished AA-activated mitophagy. Furthermore, we showed that glycophagy was upregulated in OGD cardiomyocytes evidenced by increased starch binding domain protein 1 (STBD1)-GABA type A receptor-associated protein-like 1(GABARAPL1) interaction and extracellular acidification rate, whereas AA treatment further promoted glycophagy accompanied by PI3K/Akt activation. PI3K inhibitor LY294002 or Akt inhibitor GSK690693 blocked the effects of AA on glycophagy and glycolysis. Finally, simultaneous inhibition of glycophagy and mitophagy abolished the cardioprotective effects and energy regulation of AA. These results demonstrate that AA protects ischemic cardiomyocytes by modulating glycophagy- and mitophagy-based energy metabolism through the PI3K/Akt and AMPK pathways.

Knockdown of miRNA-134-5p rescues dendritic deficits by promoting AMPK-mediated mitophagy in a mouse model of depression

Neuronal dendrites and dendritic spines are essential for normal synaptic transmission and may be critically involved in the pathophysiology of various neurological disorders, including depression. Emerging data supports the role of mitochondria in dendritic protrusions in modulating the development and morphological plasticity of spines. Mitophagy, a mitochondria-specific form of autophagy, is the fundamental process of clearing damaged mitochondria to maintain cellular homeostasis. As a brain-specific microRNA, miR-134 is localized to the synaptodendritic compartment of hippocampal neurons and negatively regulates the development of dendritic spines. However, the role of miR-134 in mitophagy related to dendritic deficits in the pathophysiology of depression remains unclear. In this study, we showed that miR-134-5p knockdown abrogated depressive-like behavioral symptoms and corrected aberrant spine morphology in hippocampal neurons of chronic unpredictable mild stress (CUMS) mice. Moreover, knockdown of miR-134-5p triggered autophagy in dendrites, improved mitochondrial impairment, and induced the generation of autophagosomes in the hippocampus of CUMS mice. We further found that AMP-activated protein kinase (AMPK), which mediates the impairment of defective mitochondria via mitophagy, can bind directly to miR-134-5p and is negatively regulated by this miRNA. This study demonstrates that miR-134-5p exerts an enormous effect on dendritic deficits by promoting AMPK-mediated mitophagy and provides a potential new target for antidepressant drug research and development.

Long-Chain Poly-d-Lysines Interact with the Plasma Membrane and Induce Protective Autophagy and Intense Cell Necrosis

Polylysines have been frequently used in drug delivery and antimicrobial and cell adhesion studies. Because of steric hindrance, chirality plays a major role in the functional difference between poly-l-lysine (PLL) and poly-d-lysine (PDL), especially when they interact with the plasma membranes of mammalian cells. Therefore, it is speculated that the interaction between chiral polylysines and the plasma membrane may cause different cellular behaviors. Here, we carefully investigated the interaction pattern of PLL and PDL with plasma membranes. We found that PDL could be anchored onto the plasma membrane and interact with the membrane lipids, leading to the rapid morphological change and death of A549 cells (a human lung cancer cell line) and HPAEpiCs (a human pulmonary alveolar epithelial cell line). In contrast, PLL exhibited good cytocompatibility and was not anchored onto the plasma membranes of these cells. Unlike PLL, PDL could trigger protective autophagy to prevent cells in a certain degree, and the PDL-caused cell death occurred via intense necrosis (featured by increased intracellular Ca²⁺ content and plasma membrane disruption). In addition, it was found that the short-chain PDL with a repeat unit number of 9 (termed DL9) could locate in lysosomes and induce autophagy at high concentrations, but it could not elicit drastic cell death, which proved that the repeat unit number of polylysine could affect its cellular action. This research confirms that the interaction between chiral polylysines and the plasma membrane can induce autophagy and intense necrosis, which provides guidance for the future studies of chiral molecules/drugs.

Apoptosis-Inducing Factor Deficiency Induces Tissue-Specific Alterations in Autophagy: Insights from a Preclinical Model of Mitochondrial Disease and Exercise Training Effects

We analyzed the effects of apoptosis-inducing factor (AIF) deficiency, as well as those of an exercise training intervention on autophagy across tissues (heart, skeletal muscle, cerebellum and brain), that are primarily affected by mitochondrial diseases, using a preclinical model of these conditions, the Harlequin (Hq) mouse. Autophagy markers were analyzed in: (i) 2, 3 and 6 month-old male wild-type (WT) and Hq mice, and (ii) WT and Hq male mice that were allocated to an exercise training or sedentary group. The exercise training started upon onset of the first symptoms of ataxia in Hq mice and lasted for 8 weeks. Higher content of autophagy markers and free amino acids, and lower levels of sarcomeric proteins were found in the skeletal muscle and heart of Hq mice, suggesting increased protein catabolism. Leupeptin-treatment demonstrated normal autophagic flux in the Hq heart and the absence of mitophagy. In the cerebellum and brain, a lower abundance of Beclin 1 and ATG16L was detected, whereas higher levels of the autophagy substrate p62 and LAMP1 levels were observed in the cerebellum. The exercise intervention did not counteract the autophagy alterations found in any of the analyzed tissues. In conclusion, AIF deficiency induces tissue-specific alteration of autophagy in the Hq mouse, with accumulation of autophagy markers and free amino acids in the heart and skeletal muscle, but lower levels of autophagy-related proteins in the cerebellum and brain. Exercise intervention, at least if starting when muscle atrophy and neurological symptoms are already present, is not sufficient to mitigate autophagy perturbations.

Exercise and Training Regulation of Autophagy Markers in Human and Rat Skeletal Muscle

Autophagy is a key intracellular mechanism by which cells degrade old or dysfunctional proteins and organelles. In skeletal muscle, evidence suggests that exercise increases autophagosome content and autophagy flux. However, the exercise-induced response seems to differ between rodents and humans, and little is known about how different exercise prescription parameters may affect these results. The present study utilised skeletal muscle samples obtained from four different experimental studies using rats and humans. Here, we show that, following exercise, in the soleus muscle of Wistar rats, there is an increase in LC3B-I protein levels immediately after exercise (+109%), and a subsequent increase in LC3B-II protein levels 3 h into the recovery (+97%), despite no change in Map1lc3b mRNA levels. Conversely, in human skeletal muscle, there is an immediate exercise-induced decrease in LC3B-II protein levels (−24%), independent of whether exercise is performed below or above the maximal lactate steady state, which returns to baseline 3.5 h following recovery, while no change in LC3B-I protein levels or MAP1LC3B mRNA levels is observed. SQSTM1/p62 protein and mRNA levels did not change in either rats or humans following exercise. By employing an ex vivo autophagy flux assay previously used in rodents we demonstrate that the exercise-induced decrease in LC3B-II protein levels in humans does not reflect a decreased autophagy flux. Instead, effect size analyses suggest a modest-to-large increase in autophagy flux following exercise that lasts up to 24 h. Our findings suggest that exercise-induced changes in autophagosome content markers differ between rodents and humans, and that exercise-induced decreases in LC3B-II protein levels do not reflect autophagy flux level.

Morroniside ameliorates inflammatory skeletal muscle atrophy via inhibiting canonical and non-canonical NF-κB and regulating protein synthesis/degradation

No drug options exist for skeletal muscle atrophy in clinical, which poses a huge socio-economic burden, making development on drug interventions a general wellbeing need. Patients with a variety of pathologic conditions associated with skeletal muscle atrophy have systemically elevated inflammatory factors. Morroniside, derived from medicinal herb Cornus officinalis, possesses anti-inflammatory effect. However, whether and how morroniside combat muscle atrophy remain unknown. Here, we identified crucial genetic associations between TNFα/NF-κB pathway and grip strength based on population using 377,807 European participants from the United Kingdom Biobank dataset. Denervation increased TNFα in atrophying skeletal muscles, which inhibited myotube formation in vitro. Notably, morroniside treatment rescued TNFα-induced myotube atrophy in vitro and impeded skeletal muscle atrophy in vivo, resulting in increased body/muscles weights, No. of satellite cells, size of type IIA, IIX and IIB myofibers, and percentage of type IIA myofibers in denervated mice. Mechanistically, in vitro and/or in vivo studies demonstrated that morroniside could not only inhibit canonical and non-canonical NF-κB, inflammatory mediators (IL6, IL-1b, CRP, NIRP3, PTGS2, TNFα), but also down-regulate protein degradation signals (Follistatin, Myostatin, ALK4/5/7, Smad7/3), ubiquitin-proteasome molecules (FoxO3, Atrogin-1, MuRF1), autophagy-lysosomal molecules (Bnip3, LC3A, and LC3B), while promoting protein synthesis signals (IGF-1/IGF-1R/IRS-1/PI3K/Akt, and BMP14/BMPR2/ALK2/3/Smad5/9). Moreover, morroniside had no obvious liver and kidney toxicity. This human genetic, cells and mice pathological evidence indicates that morroniside is an efficacious and safe inflammatory muscle atrophy treatment and suggests its translational potential on muscle wasting.

New Insights into the Roles and Mechanisms of Spermidine in Aging and Age-Related Diseases

High incidences of morbidity and mortality associated with age-related diseases among the elderly population are a socio-economic challenge. Aging is an irreversible and inevitable process that is a risk factor for pathological progression of diverse age-related diseases. Spermidine, a natural polyamine, plays a critical role in molecular and cellular interactions involved in various physiological and functional processes. Spermidine has been shown to modulate aging, suppress the occurrence and severity of age-related diseases, and prolong lifespan. However, the precise mechanisms through which spermidine exerts its anti-aging effects have not been established. In this review, we elucidate on the mechanisms and roles underlying the beneficial effects of spermidine in aging from a molecular and cellular perspective. Moreover, we provide new insights into the promising potential diagnostic and therapeutic applications of spermidine in aging and age-related diseases.

Sorafenib prevents the proliferation and induces the apoptosis of liver cancer cells by regulating autophagy and hypoxia-inducible factor-1

Sorafenib has been approved as a systemic drug for advanced liver cancer; however, the underlying mechanisms remain unclear. The present study aimed to investigate the effects of sorafenib on the proliferation, autophagy and apoptosis of HepG2 cells under hypoxia. Briefly, reverse transcription-quantitative PCR and western blotting was performed to quantify HIF-1, LC3II/I, mTOR and p70s6K expression levels. Cell proliferation was determined using the Cell Counting Kit-8 assay and the cell apoptosis rate was evaluated using flow cytometry. The results demonstrated that autophagy and apoptosis were induced by hypoxia, and that sorafenib further enhanced hypoxia-induced autophagy and apoptosis in HepG2 cells in a dose-dependent manner. Furthermore, the mechanism of sorafenib-mediated autophagy in liver cancer cell were investigated by using chloroquine (CQ). The results showed that CQ significantly inhibited autophagy by decreasing LC3II/LC3I ratio in HepG2 cells treated with sorafenib and/or hypoxia. By contrast, sorafenib could increase the expression of hypoxia-inducible factor-1 (HIF-1) and of the autophagy marker (LC3II/I) and decrease the expression of mammalian target of rapamycin and p70 ribosomal S6 kinase in HepG2 cells under normoxia and hypoxia conditions, suggesting that sorafenib could induce hypoxia and autophagy in liver cancer cells. In addition, sorafenib was demonstrated to prevent proliferation and induce apoptosis of HepG2 cells under normoxia and hypoxia. Sorafenib could also prevent the malignant behavior of HepG2 by inducing hypoxia and autophagy. In summary, the findings from the present study suggested that sorafenib may inhibit liver cancer progression by activating autophagy and HIF-1 signaling pathway.

High intensity interval training induces dysregulation of mitochondrial respiratory complex and mitophagy in the hippocampus of middle-aged mice

Autophagy is involved in aging-related cognitive impairment. Aerobic exercise training can improve cognitive function in the elderly and this effect may be associated with autophagic mechanisms and mitochondrial respiratory function. High intensity interval training (HIIT) has beneficial effects on heart and skeletal muscles by activating autophagy and/or mitophagy, but the effects of HIIT on autophagy/mitophagy in the aging brain are unknown. This study investigated the effects of HIIT on the mitochondrial respiratory complex and autophagy/mitophagy, and its relation to brain function. Thirteen middle-aged male ICR mice underwent HIIT for 7 weeks. The exercise program reduced the spontaneous behavior and exploration activities of the mice. The phosphorylation level of cAMP response element binding protein (CREB) and the protein expression of brain-derived neurotrophic factor (BDNF) decreased after the 7-week HIIT. Exercise downregulated the protein expression of Complex Ⅰ and upregulated the protein expression of Complex Ⅲ, Complex Ⅳ and Complex Ⅴ. HIIT also decreased the expression of mitophagy-related proteins in the mitochondrial fractions of the hippocampus. However, HIIT did not change the expression of autophagy-related proteins LC3, P62, Atg5, Atg7, Beclin-1 and Lamp2 in the total lysate of the hippocampus. These data indicated that HIIT might have negative effects on the plasticity of the hippocampus in middle-aged mice. The effects may be related to the dysregulation of CREB-BDNF signaling, mitochondrial respiratory complex and mitophagy induced by HIIT.

Post-Effort Changes in Autophagy- and Inflammation-Related Gene Expression in White Blood Cells of Healthy Young Men

Acute, strenuous physical exertion requiring high levels of energy production induces the production of reactive oxygen species and metabolic disturbances that can damage the mitochondria. Thus, selective autophagic elimination of defective mitochondria may improve resistance to oxidative stress and potentially to inflammation. The main goal of this study was to evaluate the impacts of intense effort on changes in the expression of select genes related to post-effort inflammation and autophagy. Thirty-five men aged 16–21 years were recruited to the study. The impacts of both aerobic (endurance) and anaerobic (speed) efforts on selected genes encoding chemokines (CXCL5, 8–12) were analyzed. Significant increases in the expression of all studied genes excluding CXCL12 were observed. Moreover, both types of effort induced an increase in the expression of genes encoding IL-2, -4, -6, -10, IFN-γ and TNF-α, excluding IL-17A. Generally, these efforts caused a significant increase in the relative expression of apoptosis- (BCL2 and BAX) and autophagy- (BNIP3, BECN1, MAP1LC3B, ATG5, ATG7, ATG12, ATG16L1 and SQSTM1) related genes. It seems that the duration of physical activity and its bioenergetic cost has an important impact on the degree of increase in expression of this panel of autophagy-related genes. Anaerobic effort is more strenuous than aerobic effort and requires a higher bioenergetic investment. This may explain the stronger impact of anaerobic effort on the expression of the studied genes. This observation seems to support the protective role of autophagy proposed in prior studies.

Triptolide prevents LPS-induced skeletal muscle atrophy via inhibiting NF-κB/TNF-α and regulating protein synthesis/degradation pathway

BACKGROUND AND PURPOSE

Increasing evidence suggests systemic inflammation-caused skeletal muscle atrophy as a major clinical feature of cachexia. Triptolide obtained from Tripterygium wilfordii Hook F possesses potent anti-inflammatory and immunosuppressive effects. The present study aims to evaluate the protective effects and molecular mechanisms of triptolide on inflammation-induced skeletal muscle atrophy.

EXPERIMENTAL APPROACH

The effects of triptolide on skeletal muscle atrophy were investigated in LPS-treated C2C12 myotubes and C57BL/6 mice. Protein expressions and mRNA levels were analysed by western blot and qPCR, respectively. Skeletal muscle mass, volume and strength were measured by histological analysis, micro-CT and grip strength, respectively. Locomotor activity was measured using the open field test.

KEY RESULTS

Triptolide (10-100 fM) up-regulated protein synthesis signals (IGF-1/p-IGF-1R/IRS-1/p-Akt/p-mTOR) and down-regulated protein degradation signal atrogin-1 in C2C12 myotubes. In LPS (100 ng·ml^-1 )-treated C2C12 myotubes, triptolide up-regulated MyHC, IGF-1, p-IGF-1R, IRS-1 and p-Akt. Triptolide also down-regulated ubiquitin-proteasome molecules (n-FoxO3a/atrogin-1/MuRF1), proteasome activity, autophagy-lysosomal molecules (LC3-II/LC3-I and Bnip3) and inflammatory mediators (NF-κB, Cox-2, NLRP3, IL-1β and TNF-α). However, AG1024, an IGF-1R inhibitor, suppressed triptolide-mediated effects on MyHC, myotube diameter, MuRF1 and p62 in LPS-treated C2C12 myotubes. In LPS (1 mg·kg^-1 , i.p.)-challenged mice, triptolide (5 and 20 μg·kg^-1 ·day^-1 , i.p.) decreased plasma TNF-α levels and it increased skeletal muscle volume, cross-sectional area of myofibers, weights of the gastrocnemius and tibialis anterior muscles, forelimb grip strength and locomotion.

CONCLUSIONS AND IMPLICATIONS

These findings reveal that triptolide prevented LPS-induced inflammation and skeletal muscle atrophy and have implications for the discovery of novel agents for preventing muscle wasting.

Potential cytotoxicity of silver nanoparticles: Stimulation of autophagy and mitochondrial dysfunction in cardiac cells

In the present study, we elucidated the potential cytotoxicity of AgNPs in H9c2 rat cardiomyoblasts and assessed the underlying toxicological manifestations responsible for their toxicity thereof. The results indicated that the exposure of AgNPs to H9c2 cardiac cells decreased cell viability in a dose-dependent manner and caused cell cycle arrest followed by induction of apoptosis. The AgNPs treated cardiac cells showed a generation of reactive oxygen species (ROS) and mitochondrial dysfunction where mitochondrial ATP was reduced and the expression of AMPK1α increased. AgNPs also induced ROS-mediated autophagy in H9c2 cells. There was a significant time-dependent increase in intracellular levels of Atg5, Beclin1, and LC3BII after exposure to AgNPs, signifying the autophagic response in H9c2 cells. More importantly, the addition of N-acetyl-L-cysteine (NAC) inhibited autophagy and significantly reduced the cytotoxicity of AgNPs in H9c2 cells. The study highlights the prospective toxicity of AgNPs on cardiac cells, collectively signifying a potential health risk.

Manifestations of Age on Autophagy, Mitophagy and Lysosomes in Skeletal Muscle

Sarcopenia is the loss of both muscle mass and function with age. Although the molecular underpinnings of sarcopenia are not fully understood, numerous pathways are implicated, including autophagy, in which defective cargo is selectively identified and degraded at the lysosome. The specific tagging and degradation of mitochondria is termed mitophagy, a process important for the maintenance of an organelle pool that functions efficiently in energy production and with relatively low reactive oxygen species production. Emerging data, yet insufficient, have implicated various steps in this pathway as potential contributors to the aging muscle atrophy phenotype. Included in this is the lysosome, the end-stage organelle possessing a host of proteolytic and degradative enzymes, and a function devoted to the hydrolysis and breakdown of defective molecular complexes and organelles. This review provides a summary of our current understanding of how the autophagy-lysosome system is regulated in aging muscle, highlighting specific areas where knowledge gaps exist. Characterization of the autophagy pathway with a particular focus on the lysosome will undoubtedly pave the way for the development of novel therapeutic strategies to combat age-related muscle loss.

Long noncoding RNA GAS8-AS1: A novel biomarker in human diseases

Long non-coding RNAs (lncRNAs) represent a group of ncRNAs with more than 200 nucleotides. These RNAs can specifically regulate gene expression at both the transcriptional and the post-transcriptional levels, and increasing evidence indicates that they play vital roles in a variety of disease-related cellular processes. The lncRNA GAS8 antisense RNA 1 (GAS8-AS1, also known as C16orf3) is located in the second intron of GAS8 and has been reported to be both abnormally expressed in several diseases and closely correlated with many clinical characteristics. GAS8-AS1 has been shown to affect many biological functions, including cell proliferation, migration, invasiveness, and autophagy using several signaling pathways. In this review, we have summarized current studies on GAS8-AS1 roles in disease and discuss its potential clinical utility. GAS8-AS1 may be a promising biomarker for both diagnoses and prognoses, and a novel target for many disease therapies.

Effects of osteoblast autophagy on glucocorticoid-induced femoral head necrosis

Objectives

This study aims to explore the mechanism by which osteoblast autophagy participated in glucocorticoid-induced femoral head necrosis (FHN).

Materials and methods

Thirty male specific-pathogen-free C57 mice (age, one month; weighing 20-25 g) were randomly divided into blank control, dexamethasone and rapamycin-dexamethasone groups (n=10). After six weeks of intervention, right femoral head was obtained to observe morphology and to calculate percentage of empty lacunae. MC3T3-E1 cells were randomly divided into normal, dexamethasone, rapamycin and dexamethasone-rapamycin groups, and cultured for 24 h. Microtubule-associated protein 1 light chain 3 (LC3)-I, LC3-II, mammalian target of rapamycin (mTOR) and Beclin-1 protein expressions were detected by Western blot.

Results

In rapamycin-dexamethasone group, some bone trabeculae in medullary cavity ruptured and atrophied, and subchondral bone underwent local necrosis. The total apoptosis rates of dexamethasone and rapamycin-dexamethasone groups surpassed that of blank control group, and the former two groups had significantly different rates (p<0.001). LC3-II/LC3-I of dexamethasone group was lower than those of rapamycin and dexamethasone-rapamycin groups (p<0.001), and the ratio of rapamycin group surpassed that of dexamethasone-rapamycin group (p<0.001). Dexamethasone group had higher mTOR protein expression than those of rapamycin and dexamethasone- rapamycin groups (p<0.001), and the expression of rapamycin group was lower than that of dexamethasone-rapamycin group (p<0.001). The Beclin-1 protein expression of dexamethasone group was lower than those of rapamycin and dexamethasone- rapamycin groups (p<0.001), and the expression of rapamycin group exceeded that of dexamethasone-rapamycin group (p<0.05).

Conclusion

Osteoblast autophagy may play a crucial protective role in dexamethasone-induced FHN. The attenuation of autophagy may be related to the affected expressions of key autophagy regulators mTOR and Beclin-1.

circPGAM1 enhances autophagy signaling during laryngocarcinoma drug resistance by regulating miR-376a

circRNAs have been shown to be involved in cancer progression. It is unclear whether circPGAM1 exerts its effect on laryngocarcinoma drug resistance. In this study, we employed colony formation and MTT assay to determine colony number and cell viability under cisplatin treatment. TUNEL experiment was used to evaluate apoptosis of laryngocarcinoma cells in the presence of cisplatin. Xenograft tumor experiment was performed to assess in vivo tumor growth of SNU46 cells. We found that circPGAM1 enhanced colony formation and viability of SNU46 and M4E cells. In contrast, circPGAM1 caused attenuated cell apoptosis. Furthermore, we also confirmed that circPGAM1 played a key role in tumor growth in animal model and clinical patients. miR-376a was identified and proved to act as key effector for circPGAM1-mediated drug resistance. Finally, autophagy-related gene ATG2A was shown to rescue miR-376a-modulated drug resistance of laryngocarcinoma cells. Herein, we illuminate the role of circPGAM1 in laryngocarcinoma drug resistance, thereby facilitating development of targeted therapy for treating laryngocarcinoma.

Semaglutide-mediated protection against Aβ correlated with enhancement of autophagy and inhibition of apotosis

BACKGROUND

Semaglutide, a glucagon-like peptide-1 (GLP-1) analogue with an extended half-life of approximately 1 week has being come into clinic trial to treat parkingson's disease but little is known about its effect to prevent against Alzheimer's disease (AD). The goal of the present study was to explore the potential mechanisms of semaglutide to protect against AD.

METHODS

We treated SH-SY5Y cell line with Aβ_25-35 as an AD model. Further, SH-SY5Y cells damaged by Aβ_25-35 were treated by semaglutide. Autophagy-related proteins and apoptosis-related proteins were measured to explore molecular mechanisms for semaglutide to protect against Aβ_25-35.

RESULTS

Semaglutide enhanced autophagy by increasing the expression of LC3II, Atg7, Beclin-1 and P62 which were inhibited by Aβ_25-35. Further we showed that semaglutide inhibited apoptosis by inhibiting the expression of Bax induced by Aβ_25-35 and increasing the expression of Bcl2 inhibited by Aβ_25-35.

CONCLUSION

Our results provide a clue for the hypothesis that autophagy enhancement and apoptosis inhibition may be involved in the effect of semaglutide to protect against Aβ _25-35.

Mitochondrial Metabolism in Cancer Cachexia: Novel Drug Target

BACKGROUND

Cancer cachexia is a metabolic syndrome prevalent in the majority of the advanced cancers and is associated with complications such as anorexia, early satiety, weakness, anaemia, and edema, thereby reducing performance and impairing quality of life. Skeletal muscle wasting is a characteristic feature of cancer-cachexia and mitochondria is responsible for regulating total protein turnover in skeletal muscle tissue.

METHODS

We carried out exhaustive search for cancer cachexia and role of mitochondria in the same in various databases. All the relevant articles were gathered and the pertinent information was extracted out and compiled which was further structured into different sub-sections.

RESULTS

Various findings on the mitochondrial alterations in connection to its disturbed normal physiology in various models of cancer-cachexia have been recently reported, suggesting a significant role of the organelle in the pathogenesis of the complications involved in the disorder. It has also been reported that reduced mitochondrial oxidative capacity is due to reduced mitochondrial biogenesis as well as altered balance between fusion and fission protein activities. Moreover, autophagy in mitochondria (termed as mitophagy) is reported to play an important role in cancer cachexia.

CONCLUSION

The present review aims to put forth the changes occurring in mitochondria and hence explore possible targets which can be exploited in cancer-induced cachexia for treatment of such a debilitating condition.

circPAN3 exerts a profibrotic role via sponging miR-221 through FoxO3/ATG7-activated autophagy in a rat model of myocardial infarction

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Cardiac fibrosis is the scarring process occurs commonly with CVDs impairing the function and structure of heart. Herein, we investigated the role of circPAN3 in the pathogenesis of cardiac fibrosis.

METHODS

A rat myocardial infarction (MI) model was constructed to evaluate the role of circPAN3. Expression of circPAN3 in MI was determined, and si-circPAN3 was applied to verify its profibrotic effects. With an in vitro model, cardiac fibroblasts were stimulated by transforming growth factor beta 1 (TGFβ1). Immunofluorescent staining was employed to assess the fibrosis-related markers, as well as autophagy activity. CCK-8 and transwell assays were performed to determine cell proliferation and migration. Luciferase reporter assay and RNA pull-down were subjected to verify the interaction of circPAN3/miR-221. The enrichment of FoxO3 on the promoter region of ATG7 was detected using CHIP assay.

RESULTS

Elevated circPAN3 was found in rat MI heart tissue, of which knockdown attenuated cardiac fibrosis after MI. In an in vitro model exposing with TGFβ1, increasing cell proliferation and migration were observed, whereas these effects were abolished by circPAN3 knockdown, as well as autophagy activity. miR-221 was identified as a target to be involved in circPAN3-mediated cardiac fibrosis after MI. miR-221 negatively regulated FoxO3, thus causing the inhibition of ATG7 transcription. The regulatory network of circPAN3/miR-221/FoxO3/ATG7 in cardiac fibrosis was further determined in vivo.

CONCLUSION

circPAN3 exhibited profibrotic effects during autophagy-mediated cardiac fibrosis via miR-221/FoxO3/ATG7 axis, which may serve as potential biomarkers for cardiac fibrosis therapeutics.

Overexpression of NDRG2 in skeletal muscle does not ameliorate the effects of stress in vivo

NEW FINDINGS

What is the central question of this study? Do elevated levels of the stress-response protein NDRG2 protect against fasting and chronic disease in mouse skeletal muscle? What is the main finding and its importance? NDRG2 levels increased in the tibialis anterior muscle in response to fasting and the effects of motor neurone disease. No alleviation of the stress-related and proteasomal pathways, mitochondrial dysfunction or muscle mass loss was observed even with the addition of exogenous NDRG2 indicating that the increase in NDRG2 is a normal adaptive response.

ABSTRACT

Skeletal muscle mass loss and dysfunction can arise from stress, which leads to enhanced protein degradation and metabolic impairment. The expression of N-myc downstream-regulated gene 2 (NDRG2) is induced in response to different stressors and is protective against the effects of stress in some tissues and cell types. Here, we investigated the endogenous NDRG2 response to the stress of fasting and chronic disease in mice and whether exogenous NDRG2 overexpression through adeno-associated viral (AAV) treatment ameliorated the response of skeletal muscle to these conditions. Endogenous levels of NDRG2 increased in the tibialis anterior muscle in response to 24 h fasting and with the development of the motor neurone disease, amyotrophic lateral sclerosis, in SOD1^G93A transgenic mice. Despite AAV-induced overexpression and increased expression with fasting, NDRG2 was unable to protect against the activation of proteasomal and stress pathways in response to fasting. Furthermore, NDRG2 was unable to reduce muscle mass loss, mitochondrial dysfunction and elevated oxidative and endoplasmic reticulum stress levels in SOD1^G93A mice. Conversely, elevated NDRG2 levels did not exacerbate these stress responses. Overall, increasing NDRG2 levels might not be a useful therapeutic strategy to alleviate stress-related disease pathologies in skeletal muscle.

Long-lived post-mitotic cell aging: is a telomere clock at play?

Senescence is a cellular response to stress for both dividing and post-mitotic cells. Noteworthy, long-lived post-mitotic cells (collectively named LLPMCs), which can live for decades in the organism, can exhibit a distinct type of cellular aging characterized by a progressive functional decline not associated to an overt senescence phenotype. The age-related drivers of senescence and aging in LLPMCs remain largely unknown. There is evidence that an increased production of reactive oxygen species (ROS) due to dysfunctional mitochondria, coupled with an inherent inability of cellular-degradation mechanisms to remove damaged molecules, is responsible for senescence and aging in LLPMC. Although telomeric DNA shortening, by nature linked to cell division, is generally not considered as a driver of LLPMC aging and senescence, we discuss recent reports revealing the existence of age-related telomere changes in LLPMC. These findings reveal unexpected roles for telomeres in LLPMC function and invite us to consider the hypothesis of a complex telomere clock involved in both dividing and non-dividing cell aging.

ApoA-1 improves glucose tolerance by increasing glucose uptake into heart and skeletal muscle independently of AMPKα2

OBJECTIVE

Acute administration of the main protein component of high-density lipoprotein, apolipoprotein A-I (ApoA-1), improves glucose uptake in skeletal muscle. The molecular mechanisms mediating this are not known, but in muscle cell cultures, ApoA-1 failed to increase glucose uptake when infected with a dominant-negative AMP-activated protein kinase (AMPK) virus. We therefore investigated whether AMPK is necessary for ApoA-1-stimulated glucose uptake in intact heart and skeletal muscle in vivo.

METHODS

The effect of injection with recombinant human ApoA-1 (rApoA-1) on glucose tolerance, glucose-stimulated insulin secretion, and glucose uptake into skeletal and heart muscle with and without block of insulin secretion by injection of epinephrine (0.1 mg/kg) and propranolol (5 mg/kg), were investigated in 8 weeks high-fat diet-fed (60E%) wild-type and AMPKα2 kinase-dead mice in the overnight-fasted state. In addition, the effect of rApoA-1 on glucose uptake in isolated skeletal muscle ex vivo was studied.

RESULTS

rApoA-1 lowered plasma glucose concentration by 1.7 mmol/l within 3 h (6.1 vs 4.4 mmol/l; p < 0.001). Three hours after rApoA-1 injection, glucose tolerance during a 40-min glucose tolerance test (GTT) was improved compared to control (area under the curve (AUC) reduced by 45%, p < 0.001). This was accompanied by an increased glucose clearance into skeletal (+110%; p < 0.001) and heart muscle (+100%; p < 0.001) and an increase in glucose-stimulated insulin secretion 20 min after glucose injection (+180%; p < 0.001). When insulin secretion was blocked during a GTT, rApoA-1 still enhanced glucose tolerance (AUC lowered by 20% compared to control; p < 0.001) and increased glucose clearance into skeletal (+50%; p < 0.05) and heart muscle (+270%; p < 0.001). These improvements occurred to a similar extent in both wild-type and AMPKα2 kinase-dead mice and thus independently of AMPKα2 activity in skeletal- and heart muscle. Interestingly, rApoA-1 failed to increase glucose uptake in isolated skeletal muscles ex vivo.

CONCLUSIONS

In conclusion, ApoA-1 stimulates in vivo glucose disposal into skeletal and heart muscle independently of AMPKα2. The observation that ApoA-1 fails to increase glucose uptake in isolated muscle ex vivo suggests that additional systemic effects are required.

Autophagy in aging and longevity

Our understanding of the process of autophagy and its role in health and diseases has grown remarkably in the last two decades. Early work established autophagy as a general bulk recycling process which involves the sequestration and transport of intracellular material to the lysosome for degradation. Currently, autophagy is viewed as a nexus of metabolic and proteostatic signalling that can determine key physiological decisions from cell fate to organismal lifespan. Here, we review the latest literature on the role of autophagy and lysosomes in stress response and longevity. We highlight the connections between autophagy and metabolic processes, the network associated with its regulation, and the links between autophagic dysfunction, neurodegenerative diseases, and aging.

Mitochondrial adaptations to exercise do not require Bcl2-mediated autophagy but occur with BNIP3/Parkin activation

Understanding the mechanisms regulating mitochondrial respiratory function and adaptations to metabolic challenges, such as exercise and high dietary fat, is necessary to promote skeletal muscle health and attenuate metabolic disease. Autophagy is a constitutively active degradation pathway that promotes mitochondrial turnover and transiently increases postexercise. Recent evidence indicates Bcl2 mediates exercise-induced autophagy and skeletal muscle adaptions to training during high-fat diet. We determined if improvements in mitochondrial respiration due to exercise training required Bcl2-mediated autophagy using a transgenic mouse model of impaired inducible autophagy (Bcl2^AAA ). Mitochondrial adaptations to a treadmill exercise training protocol, in either low-fat or high-fat diet fed mice, did not require Bcl2-mediated autophagy activation. Instead, training increased protein synthesis rates and basal autophagy in the Bcl2^AAA mice, while acute exercise activated BNIP3 and Parkin autophagy. High-fat diet stimulated lipid-specific mitochondrial adaptations. These data demonstrate increases in basal mitochondrial turnover, not transient activation with exercise, mediate adaptations to exercise and high-fat diet.

Exercise Mitigates the Loss of Muscle Mass by Attenuating the Activation of Autophagy during Severe Energy Deficit

The loss of skeletal muscle mass with energy deficit is thought to be due to protein breakdown by the autophagy-lysosome and the ubiquitin-proteasome systems. We studied the main signaling pathways through which exercise can attenuate the loss of muscle mass during severe energy deficit (5500 kcal/day). Overweight men followed four days of caloric restriction (3.2 kcal/kg body weight day) and prolonged exercise (45 min of one-arm cranking and 8 h walking/day), and three days of control diet and restricted exercise, with an intra-subject design including biopsies from muscles submitted to distinct exercise volumes. Gene expression and signaling data indicate that the main catabolic pathway activated during severe energy deficit in skeletal muscle is the autophagy-lysosome pathway, without apparent activation of the ubiquitin-proteasome pathway. Markers of autophagy induction and flux were reduced by exercise primarily in the muscle submitted to an exceptional exercise volume. Changes in signaling are associated with those in circulating cortisol, testosterone, cortisol/testosterone ratio, insulin, BCAA, and leucine. We conclude that exercise mitigates the loss of muscle mass by attenuating autophagy activation, blunting the phosphorylation of AMPK/ULK1/Beclin1, and leading to p62/SQSTM1 accumulation. This includes the possibility of inhibiting autophagy as a mechanism to counteract muscle loss in humans under severe energy deficit.

Rosuvastatin Attenuates Myocardial Ischemia-Reperfusion Injury via Upregulating miR-17-3p-Mediated Autophagy

Myocardial diseases usually appear ischemic. Reperfusion therapy is one of the effective methods that can improve clinical therapeutic efficacy. However, reperfusion results in myocardial injury named I/R injury. Rosuvastatin (RS) is HMG-CoA reductase inhibitor. We investigated the role of RS in the myocardial I/R injury in vitro and its active mechanism. Oxygen-glucose deprivation/reoxygenation (OGD/R) model was applied to investigate I/R in vitro. OGD/R decreased cell viability and increased levels of miR-17-3p and lactate dehydrogenase (LDH) leakage. Besides, RS decreased cleaved caspase-3 level and LDH leakage, promoted the levels of miR-17-3p and LC3II/LC3I, and increased cell viability when H9C2 cell was treated by OGD/R. miR-17-3p inhibitor reduced the H9C2 cell viability and LC3II/LC3I level, whereas miR-17-3p mimics increased H9C2 cell viability and LC3II/LC3I level. RS promoted cell viability and increased LC3II/LC3I level while it lowered LDH leakage, apoptosis rate, and the levels of cleaved caspase-3 and Cyto c. Our study suggested that RS reduced I/R injury in cardiocyte via cleaved caspase-3/Cyto c apoptosis signaling pathway and autophagy. Moreover, the autophagy happens to cardiocyte by upregulating the expression of miR-17-3p.

Low-dose Dexamethasone Increases Autophagy in Cerebral Cortical Neurons of Juvenile Rats with Sepsis Associated Encephalopathy

Studies have shown that a certain dose of dexamethasone can improve the survival rate of patients with sepsis, and in sepsis associated encephalopathy (SAE), autophagy plays a regulatory role in brain function. Here, we proved for the first time that small-dose dexamethasone (SdDex) can regulate the autophagy of cerebral cortex neurons in SAE rats and plays a protective role. Cortical neurons were cultured in vitro in a septic microenvironment and a sepsis rat model was established. The small-dose dexamethasone (SdDex) or high-dose dexamethasone (HdDex) was used to intervene in neurons or SAE rats. Through fluorescence microscopy and western blot analysis, the expressions of microtubule-associated protein 1 light chain 3 (LC3), p62/sequestosome1 (p62/SQSTM1), mammalian target of rapamycin (mTOR) signaling pathway related proteins, and apoptosis-related proteins were detected. Theresultsshowthat compared with those in SAE rats, the cortical pathological changes in SAE rats treated with SdDex were improved, and damaged substances were encapsulated and degraded by autophagosomes in neurons. Additionally, similar to neurons in vitro, cortical autophagy was further activated and the mTOR signaling pathway was inhibited. After HdDex treatment, the mTOR signaling pathway in cortex is inhibited, but further activation of autophagy is not obvious, the cortical pathological changes were further worsened and the ultrastructure of neurons was disturbed. Furthermore, the HdDex group exhibited the most obvious apoptosis. SdDex can regulate autophagy of cortical neurons by inhibiting the mTOR signaling pathway and plays a protective role. Brain damage induced by HdDex may be related to the activation of apoptosis.

Iron dysregulation in vascular dementia: Focused on the AMPK/autophagy pathway

Recent researches suggested that iron dysregulation play an important role in the pathogenesis of vascular dementia (VD). Iron deposition had been found in hippocampus in vascular dementia model in recent research. Nevertheless, the underlying mechanisms of iron deposition and its neurotoxicity in vascular dementia was still unclear. Thus, our research was aimed at whether the neurotoxicity of iron was associated with autophagy regulation. We established a chronic cerebral hypoperfusion model in the rat brain in order to mimic the vascular dementia using permanent bilateral common carotid artery occlusion (2VO). The preparation of iron overloaded rats model by intraperitoneal injection of iron dextran. Following, we tested the learning and memory function of each group using Morris Water Maze. Consequently, we analyzed the iron content and iron transport related molecules (TFR1, DMT1) in hippocampus. Furthermore, we examined the effect of iron deposition on autophagy-related molecules including AMPK, Beclin1 and LC3 and the number of autophagosomes in hippocampus. Last, we tested the apoptosis of neurons in hippocampus. We found that iron deposition in hippocampus in model groups which accompanied the decline of learning and memory function. And the expression of TFR1 and DMT1 were up-regulated in model groups. Moreover, iron deposition up-regulated the expression of AMPK, Beclin1 and LC3 and increase the number of autophagosomes in hippocampus. And the expression of Bax was up-regulated and Bcl-2 was down-regulated in iron deposition groups. To sum up, our data suggested that iron deposition increased AMPK/autophagy pathway associated molecules in the hippocampus and promoted neuronal apoptosis, which might be a new pathogenesis in vascular dementia.

Exercise and exercise training-induced increase in autophagy markers in human skeletal muscle

Moderately trained male subjects (mean age 25 years; range 19–33 years) completed an 8‐week exercise training intervention consisting of continuous moderate cycling at 157 ± 20 W for 60 min (MOD; n = 6) or continuous moderate cycling (157 ± 20 W) interspersed by 30‐sec sprints (473 ± 79 W) every 10 min (SPRINT; n = 6) 3 days per week. Sprints were followed by 3:24 min at 102 ± 17 W to match the total work between protocols. A muscle biopsy was obtained before, immediately and 2 h after the first training session as well as at rest after the training session. In both MOD and SPRINT, skeletal muscle AMPK^Thr172 and ULK^Ser317 phosphorylation was elevated immediately after exercise, whereas mTOR^Ser2448 and ULK^Ser757 phosphorylation was unchanged. Two hours after exercise LC3I, LC3II and BNIP3 protein content was overall higher than before exercise with no change in p62 protein. In MOD, Beclin1 protein content was higher immediately and 2 h after exercise than before exercise, while there were no differences within SPRINT. Oxphos complex I, LC3I, BNIP3 and Parkin protein content was higher after the training intervention than before in both groups, while there was no difference in LC3II and p62 protein. Beclin1 protein content was higher after the exercise training intervention only in MOD. Together this suggests that exercise increases markers of autophagy in human skeletal muscle within the first 2 h of recovery and 8 weeks of exercise training increases the capacity for autophagy and mitophagy regulation. Hence, the present findings provide evidence that exercise and exercise training regulate autophagy in human skeletal muscle and that this in general was unaffected by interspersed sprint bouts.

Intensified mitophagy in skeletal muscle with aging is downregulated by PGC-1alpha overexpression in vivo

Mitochondrial dysfunction plays an important role in the etiology of age-related muscle atrophy known as sarcopenia. PGC-1α is positioned at the center of crosstalk in regulating mitochondrial quality control, but its role in mitophagy in aged skeletal muscle is currently unclear. The present study investigated the effects of aging and PGC-1α overexpression via in vivo DNA transfection on key mitophagy protein markers, as well as mitochondrial dynamics related proteins, metabolic function and antioxidant capacity in mouse muscle. C57BL/6J mice at the age of 2 mo (young, Y; N = 14) and 24 mo (old, O; N = 14) were transfected in vivo with either PGC-1α DNA (OE, N = 7) or GFP (N = 7) into the tibialis anterior (TA) muscle followed by electroporation. PINK1 and Parkin protein contents were 3.6 and 1.4-fold higher (P < 0.01), whereas mitochondrial ubiquitination (Ub) increased 1.5-fold (P < 0.05), in O vs. Y mice. PGC-1 OE suppressed PINK and Parkin protein levels by 50-60% (P < 0.01), and decreased Ub by 20% (P < 0.05) in old mice. Aging significantly increased the protein content of LC3II (30%, P < 0.05), p62 (42%, P < 0.05), RheB (5.5-fold, P < 0.01), Beclin-1 (3-fold, P < 0.01) and Mfn2 (~4-fold, P < 0.01) in the TA muscle. However, these age-related increases in mitophagy markers were attenuated by PGC-1α OE. Furthermore, aging dramatically increased Fis-1 protein content by 14-fold (P < 0.01), along with a severe reduction of citrate synthase activity (64%, P < 0.01) and cytochrome c oxidase subunit IV (COXIV) protein content (85%, P < 0.01). PGC-1α OE mitigated the age effects on Fis-1 and Drp-1 (P < 0.05). Moreover, PGC-1α OE enhanced mitochondrial oxidative function and antioxidant enzyme activities, and decreased lipid peroxidation and inner membrane damage found in old mice (P < 0.01). In summary, our data demonstrate that mitophagy protein expression in skeletal muscle was enhanced at old age driven possibly by increased mitochondrial dysfunction, damage, and fission. PGC-1α OE was effective in ameliorating mitochondrial deficits but did not restore muscle fiber atrophy.

Training state and skeletal muscle autophagy in response to 36 h of fasting

The present study aimed at investigating fasting-induced responses in regulators and markers of autophagy in vastus lateralis muscle from untrained and trained human subjects. Untrained and trained subjects (based on maximum oxygen uptake, muscle citrate synthase activity, and oxidative phosphorylation protein level) fasted for 36 h with vastus lateralis muscle biopsies obtained at 2, 12, 24, and 36 h after a standardized meal. Fasting reduced ( P < 0.05) skeletal muscle microtubule-associated protein-1A/1B light chain 3 (LC3)I, LC3II, and adaptor protein sequestosome 1/p62 protein content in untrained subjects only. Moreover, skeletal muscle RAC-alpha serine/threonine-protein kinase (AKT)Thr308, AMP-activated protein kinase (AMPK)Thr172, and Unc-51-like autophagy-activating kinase-1 (ULK1)Ser555 phosphorylation state, as well as Bcl-2-interacting coiled-coil protein-1 (Beclin1) and ULK1Ser757 phosphorylation, was lower ( P < 0.05) in trained than untrained subjects during fasting. In addition, the plasma concentrations of several amino acids were higher ( P < 0.05) in trained than untrained subjects, and the plasma concentration profile of several amino acids was different in untrained and trained subjects during fasting. Taken together, these findings suggest that 36-h fasting has effects on some mediators of autophagy in untrained human skeletal muscle and that training state influences the effect of fasting on autophagy signaling and on mediators of autophagy in skeletal muscle.

NEW & NOTEWORTHY This study showed that skeletal muscle autophagy was only modestly affected in humans by 36 h of fasting. Hence, 36-h fasting has effects on some mediators of autophagy in untrained human skeletal muscle, and training state influences the effect of fasting on autophagy signaling and on mediators of autophagy in skeletal muscle.

Inhibition of autophagy enhances the antitumour activity of tigecycline in multiple myeloma

Accumulating evidence shows that tigecycline, a first‐in‐class glycylcycline, has potential antitumour properties. Here, we found that tigecycline dramatically inhibited the proliferation of multiple myeloma (MM) cell lines RPMI‐8226, NCI‐H929 and U266 in a dose and time‐dependent manner. Meanwhile, tigecycline also potently impaired the colony formation of these three cell lines. Mechanism analysis found that tigecycline led to cell cycle arrest at G0/G1 with down‐regulation of p21, CDK2 and cyclin D1, rather than induced apoptosis, in MM cells. Importantly, we found that tigecycline induced autophagy and an autophagy inhibitor bafilomycin A1 further amplified the tigecycline‐induced cytotoxicity, suggesting that autophagy plays a cytoprotective role in tigecycline‐treated MM cells. Mechanisms modulating autophagy found that tigecycline enhanced the phosphorylation of AMPK, but did not decrease the phosphorylation of Akt, to inhibit the phosphorylation of mTOR and its two downstream effectors p70S6K1 and 4E‐BP1. Tigecycline effectively inhibited tumour growth in the xenograft tumour model of RPMI‐8226 cells. Autophagy also occurred in tigecycline‐treated tumour xenograft, and autophagy inhibitor chloroquine and tigecycline had a synergistic effect against MM cells in vivo. Thus, our results suggest that tigecycline may be a promising candidate in the treatment of MM.

PKCα replaces AMPK to regulate mitophagy: Another PEDF role on ischaemic cardioprotection

Both decreased autophagy positive regulator AMP activated protein kinase (AMPK) level and promoted mitophagy are observed in oxygen‐glucose deprivation (OGD) cardiomyocytes treated with pigment epithelium‐derived factor (PEDF). This contradictory phenomenon and its underlying mechanisms have not been thoroughly elucidated. Our previous study reveals that PEDF increases the protein kinase Cα (PKCα) and phospho‐PKCα (p‐PKCα) contents to promote mitophagy. Thus, we investigated the association between PKCα and mitophagy. Here we identify an interaction between PKCα and Unc‐51‐like kinase 1 (ULK1), essential component of mitophagy. Further analyses show this is a direct interaction within a domain of ULK1 that termed the serine/threonine‐rich domain (S/T domain). Notably, a deletion mutant ULK1 that lacks the binding domain is defective in mediating PEDF‐induced mitophagy. Furthermore, we demonstrate that ULK1 is phosphorylated at Ser317/555/777 and Raptor is also phosphorylated by phospho‐PKCα. Phospho‐ULK1 (p‐ULK1) at these sites are all essential for PEDF‐induced mitophagy and reduce the release of mitochondrial ROS and DNA. This study therefore identifies a previously uncharacterized interaction between the ULK1 and PKCα that can replace the AMPK‐dependent mitophagy processes.

Regulation of apoptosis and autophagy in mouse and human skeletal muscle with aging and lifelong exercise training

Exercise training has been reported to prevent the age-induced decline in muscle mass and fragmentation of mitochondria, as well as to affect autophagy and mitophagy. The interaction between these pathways during aging as well as the similarity between such changes in human and mouse skeletal muscle is however not fully understood. Therefore the aim of the present study was to test the hypothesis that cellular degradation pathways, including apoptosis, autophagy and mitophagy are coordinately regulated in mouse and human skeletal muscle during aging and lifelong exercise training through a PGC-1α-p53 axis. Muscle samples were obtained from young untrained, aged untrained and aged lifelong exercise trained men, and from whole-body PGC-1α knockout mice and their littermate controls that were either lifelong exercise trained or sedentary young and aged. Lifelong exercise training prevented the aging-induced reduction in PGC-1α, p53 and p21 mRNA as well as the increase in LC3II and BNIP3 protein in mouse skeletal muscle, while aging decreased the BAX/Bcl-2 ratio, LC3I and BAX protein in mouse skeletal muscle without effects of lifelong exercise training. In humans, aging was associated with reduced PGC-1α mRNA as well as decreased p62 and p21 protein in skeletal muscle, while lifelong exercise training increased BNIP3 protein and decreased p53 mRNA. In conclusion, there was a divergent regulation of autophagy and apoptosis in mouse muscle with aging and lifelong exercise training, whereas healthy aged human skeletal muscle seemed rather robust to changes in apoptosis, autophagy and mitophagy markers compared with mouse muscle at the investigated age.

Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting

OBJECTIVE

Intermittent fasting (IF) is a term used to describe a variety of eating patterns in which no or few calories are consumed for time periods that can range from 12 hours to several days, on a recurring basis. This review is focused on the physiological responses of major organ systems, including the musculoskeletal system, to the onset of the metabolic switch: the point of negative energy balance at which liver glycogen stores are depleted and fatty acids are mobilized (typically beyond 12 hours after cessation of food intake).

RESULTS AND CONCLUSIONS

Emerging findings suggest that the metabolic switch from glucose to fatty acid-derived ketones represents an evolutionarily conserved trigger point that shifts metabolism from lipid/cholesterol synthesis and fat storage to mobilization of fat through fatty acid oxidation and fatty acid-derived ketones, which serve to preserve muscle mass and function. Thus, IF regimens that induce the metabolic switch have the potential to improve body composition in overweight individuals. Moreover, IF regimens also induce the coordinated activation of signaling pathways that optimize physiological function, enhance performance, and slow aging and disease processes. Future randomized controlled IF trials should use biomarkers of the metabolic switch (e.g., plasma ketone levels) as a measure of compliance and of the magnitude of negative energy balance during the fasting period.

AMPK in skeletal muscle function and metabolism

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK’s role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism (e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.—Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.