Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy.

Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5' AMP-activated protein kinase (AMPKα1/α2/ß2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment.

[Research progress on the role of TANK-binding kinase 1 in PINK1/Parkin-dependent and -independent mitophagy].

Mitophagy is a process that selectively removes excess or damaged mitochondria and plays an important role in regulating intracellular mitochondrial mass and maintaining mitochondrial energy metabolism. TANK-binding kinase 1 (TBK1) is a multifunctional serine/threonine protein kinase, which is involved in the regulation of PTEN-induced putative kinase 1 (PINK1)/Parkin-dependent and -independent mitophagy. Recent studies have shown that TBK1 phosphorylates the autophagy related proteins, such as optineurin (OPTN), p62/sequestosome-1, Ras-related GTP binding protein 7 (Rab7), and mediates the binding of nuclear dot protein 52 (NDP52) to UNC-51 like autophagy activating kinase 1 (ULK1) complex, as well as the binding of TAX1-binding protein 1 (TAX1BP1) to microtubule-associated protein 1 light chain 3 (LC3), thereby enhancing PINK1/Parkin-dependent mitophagy. In addition, TBK1 is a direct substrate of AMP-activated protein kinase (AMPK)/ULK1 pathway, and its activation phosphorylates dynamin-related protein 1 (Drp1) and Rab7 to promote PINK1/Parkin-independent mitophagy. This article reviews the role and mechanism of TBK1 in regulating PINK1/Parkin-dependent and -independent mitophagy.

[Advances in the study of mitophagy-related receptor proteins].

Cells selectively scavenge redundant or damaged mitochondria by mitophagy, which is an important mechanism of mitochondrial quality control. Recent studies have shown that mitophagy is mainly regulated by autophagy-related genes (Atgs) in yeast cells, while mitochondrial membrane associated proteins such as PTEN-induced putative kinase 1 (PINK1), NIX/BNIP3L, BNIP3, FUN14 domain containing 1 (FUNDC1), FKBP8/FKBP38, Bcl-2-like protein 13 (Bcl2L13), nucleotide binding domain and leucine-rich-repeat-containing proteins X1 (NLRX1), prohibitin 2 (PHB2) and lipids such as cardiolipin (CL) are the key mitophagic receptors in mammalian cells, which can selectively recognize damaged mitochondria, recruit them into isolation membranes by binding to microtubule-associated protein 1 light chain 3 (LC3) or γ-aminobutyric acid receptor-associated protein (GABARAP), and then fuse with lysosomes to eliminate the trapped mitochondria. This article reviews recent research progress of mitophagy-related receptor proteins.

[The role and mechanism of leucyl-tRNA synthetase in the regulation of protein synthesis in aging skeletal muscle].

The imbalance of protein metabolism is the major cause of skeletal muscle atrophy, and the decrease of protein synthesis directly leads to the occurrence and development of age-related sarcopenia. The canonical role of leucyl-tRNA synthetase (LeuRS) is ligating leucine to the cognate tRNA, and thus it plays a central role in genetic coding. With the further studies of LeuRS in recent years, LeuRS has been found to control protein homeostasis in aging skeletal muscle via its non-canonical role. In this paper, we reviewed the structure and biological features of aminoacyl-tRNA synthetase and LeuRS, and summarized the recent advances in studies on the effects of LeuRS in regulating aging skeletal muscle protein synthesis as an intracellular leucine sensor. Moreover, we also analyzed the potential role of LeuRS in activation of mammalian target of rapamycin complex 1 (mTORC1) signaling transduction pathway in response to anabolic stimuli such as exercise and amino acids ingestion. This paper may provide some new ideas for the prevention, diagnosis and treatment of age-related sarcopenia.

Effects of concurrent aerobic and resistance training on vascular health in type 2 diabetes: a systematic review and meta-analysis.

Objective: To determine the impacts of concurrent aerobic and resistance training on vascular structure (IMT) and function (PWV, FMD, NMD) in type 2 diabetes (T2D). Methods: The electronic databases PubMed, Web of Science Core Collection, Cochrane Library, Embase, Scopus, CINAHL, and SPORTDiscus were systematically searched for articles on "type 2 diabetes" and "concurrent training" published from inception to August 2, 2022. We included randomized controlled trials that examined the effects of concurrent training versus passive controls on IMT, PWV, FMD and NMD in T2D. Results: Ten studies were eligible, including a total of 361 participants. For IMT, concurrent training showed a slight decrease by 0.05 mm (95% CI -0.11 to 0.01, p > 0.05). concurrent training induced an overall significant improvement in FMD by 1.47% (95% CI 0.15 to 2.79, p < 0.05) and PWV by 0.66 m/s (95% CI -0.89 to -0.43, p < 0.01) in type 2 diabetics. However, concurrent training seemed to exaggerate the impaired NMD (WMD = -2.30%, 95% CI -4.02 to -0.58, p < 0.05). Conclusions: Concurrent training is an effective method to improve endothelial function and artery stiffness in T2D. However, within 24 weeks concurrent training exacerbates vascular smooth muscle dysfunction. More research is needed to explore whether longer and/or higher-intensity concurrent training interventions could enhance the vascular structure and smooth muscle function in this population. Systematic review registration: www.crd.york.ac.uk/PROSPERO/, identifier CRD42022350604.

Role of MST1 in the regulation of autophagy and mitophagy: implications for aging-related diseases.

As a key mechanism to maintain cellular homeostasis under stress conditions, autophagy/mitophagy is related to the occurrence of metabolic disorders, neurodegenerative diseases, cancer, and other aging-related diseases, but the relevant signal pathways regulating autophagy have not been clarified. Mammalian sterile 20-like kinase 1 (MST1) is a central regulatory protein of many metabolic pathways involved in the pathophysiological processes of aging and aging-related diseases and has become a critical integrator affecting autophagic signaling. Recent studies show that MST1 not only suppresses autophagy through directly phosphorylating Beclin-1 and/or inhibiting the protein expression of silent information regulator 1 (SIRT1) in the cytoplasm, but also inhibits BCL2/adenovirus E1B protein-interacting protein 3 (BNIP3)-, FUN14 domain containing 1 (FUNDC1)-, and Parkin (Parkinson protein 2)-mediated mitophagy by interacting with factors such as Ras association domain family 1A (RASSF1A). Indeed, a common pharmacological strategy for anti-aging is to induce autophagy/mitophagy through MST1 inhibition. This article reviews the role and mechanism of MST1 in regulating autophagy during aging, to provide evidence for the development of drugs targeting MST1.

Advances in the Role of Leucine-Sensing in the Regulation of Protein Synthesis in Aging Skeletal Muscle.

Skeletal muscle anabolic resistance (i.e., the decrease in muscle protein synthesis (MPS) in response to anabolic stimuli such as amino acids and exercise) has been identified as a major cause of age-related sarcopenia, to which blunted nutrition-sensing contributes. In recent years, it has been suggested that a leucine sensor may function as a rate-limiting factor in skeletal MPS via small-molecule GTPase. Leucine-sensing and response may therefore have important therapeutic potential in the steady regulation of protein metabolism in aging skeletal muscle. This paper systematically summarizes the three critical processes involved in the leucine-sensing and response process: (1) How the coincidence detector mammalian target of rapamycin complex 1 localizes on the surface of lysosome and how its crucial upstream regulators Rheb and RagB/RagD interact to modulate the leucine response; (2) how complexes such as Ragulator, GATOR, FLCN, and TSC control the nucleotide loading state of Rheb and RagB/RagD to modulate their functional activity; and (3) how the identified leucine sensor leucyl-tRNA synthetase (LARS) and stress response protein 2 (Sestrin2) participate in the leucine-sensing process and the activation of RagB/RagD. Finally, we discuss the potential mechanistic role of exercise and its interactions with leucine-sensing and anabolic responses.

Exercise May Promote Skeletal Muscle Hypertrophy via Enhancing Leucine-Sensing: Preliminary Evidence.

Several studies have indicated a positive effect of exercise (especially resistance exercise) on the mTOR signaling that control muscle protein synthesis and muscle remodeling. However, the relationship between exercise, mTOR activation and leucine-sensing requires further clarification. Two month old Sprague-Dawley rats were subjected to aerobic exercise (treadmill running at 20 m/min, 6° incline for 60 min) and resistance exercise (incremental ladder climbing) for 4 weeks. The gastrocnemius muscles were removed for determination of muscle fibers diameter, cross-sectional area (CSA), protein concentration and proteins involved in muscle leucine-sensing and protein synthesis. The results show that 4 weeks of resistance exercise increased the diameter and CSA of gastrocnemius muscle fibers, protein concentration, the phosphorylation of mTOR (Ser2448), 4E-BP1(Thr37/46), p70S6K (Thr389), and the expression of LeuRS, while aerobic exercise just led to a significant increase in protein concentration and the phosphorylation of 4E-BP1(Thr37/46). Moreover, no difference was found for Sestrin2 expression between groups. The current study shows resistance exercise, but not aerobic exercise, may increase muscle protein synthesis and protein deposition, and induces muscle hypertrophy through LeuRS/mTOR signaling pathway. However, further studies are still warranted to clarify the exact effects of vary intensities and durations of aerobic exercise training.

Exercise modulates heat shock protein 27 activity in diabetic cardiomyopathy.

AIMS: Heat shock protein 27 regulates homeostasis of skeletal and cardiac muscle proteins in various stressful states including diabetes and exercise. Aerobic exercise can inhibit or ameliorate cardiac structural abnormality and dysfunction in diabetic cardiomyopathy. The aim of this study was to evaluate the role of HSP27 in aerobic exercise improving cardiac diastolic dysfunction in type 2 diabetic rats. METHODS: Forty male Sprague-Dawley rats were randomly divided into the following groups: control, control + aerobic exercise, diabetic, and diabetic + aerobic exercise. Diabetes was induced by feeding with a high-fat high-sugar diet for 7-weeks followed by a single intraperitoneal injection of streptozotocin (30 mg/kg) in male rats. Moderate aerobic exercise training was performed on a treadmill for 8 weeks after induction of diabetes. KEY FINDINGS: Aerobic exercise increased left ventricular end-diastolic internal diameter, left ventricular end-diastolic volume, myocardial HSP27 protein expression, HSP27-S82 phosphorylation levels, pHSP27-titin binding and improved cardiac muscle fibre alignment in diabetic rats. SIGNIFICANCE: Our study indicates that moderate aerobic exercise increases HSP27 activation, improves cardiomyocyte fibre alignment and restores cardiac diastolic function.

The Effect of Exercise on Gene Expression and Signaling in Mouse Melanoma Tumors.

PURPOSE: To screen for candidate hub genes associated with the effects of exercise on melanoma tumor tissues and to review the potential signaling pathways involved in this process using bioinformatics analysis. METHODS: The GSE62628 expression profile was downloaded from Gene Expression Omnibus database. This data set contains 10 melanoma tumor tissues from two groups of exercise and nonexercise mice. The R software was utilized to identify differentially expressed genes between samples, and functional annotation and pathway analysis were performed. Results were visualized using Cytoscape software. RESULTS: In total, 315 differentially expressed genes were obtained, including 294 upregulated and 21 downregulated genes. The functional analysis showed that these genes were mainly enriched in immune response, inflammatory response, and positive regulation of the ERK1/2 cascade in biological process functional groups. The top 10 candidate hub genes were C3, Kng1, C3ar1, Ptafr, Fgg, Alb, Pf4, Orm1, Aldh3b1, and Apob. The pathway analysis of the most significant module identified from the protein-protein interaction network revealed that the complement and coagulation cascades, Staphylococcus aureus infection, cytokine-cytokine receptor interaction, chemokine signaling pathway and phagosome were mainly involved. C3, C3ar1, Kng1, Ptafr, and Fgg may be the critical genes in the complement and coagulation cascades pathway, and S. aureus in the infection pathway. CONCLUSIONS: Exercise may ameliorate the immune response and inflammatory response in melanoma tissue, and further studies exploring their relationships are warranted.

Downhill Running Acutely Elicits Mitophagy in Rat Soleus Muscle.

PURPOSE: This study aimed to investigate the effects of downhill treadmill running on mitochondrial structure/function and expression levels of mitophagy-related proteins in rat skeletal muscle. METHODS: A total of 48 male adult Sprague-Dawley rats were randomly divided into a control group (C, n = 8) and an exercise group (E, n = 40). Rats in the E group were exercised on a treadmill down a 16° decline at 16 m·min for 90 min and were further divided into 0 h (E0), 12 h (E12), 24 h (E24), 48 h (E48), and 72 h (E72) postexercise subgroups (n = 8 each). At each time point, the soleus muscle was collected under full anesthesia. Mitochondrial ultrastructural changes in skeletal muscle were observed by a transmission electron microscope. The content of quantitative enzyme citrate synthase and the activities of mitochondrial respiratory chain complex II and complex IV were measured by enzyme-linked immunosorbent assay. Protein expressions of skeletal muscle cytochrome c oxidase subunit 1 (COX1), PTEN-induced putative kinase 1 (PINK1), and mitochondrial Parkin microtubule-associated protein 1 light chain 3 (LC3) were determined by Western blot. Mitochondrial colocalizations with Parkin, ubiquitin (Ub), p62/sequestosome 1 (p62), and LC3 were measured by the immunofluorescence double labeling technique. RESULTS: After downhill treadmill running, the skeletal muscle mitochondrial structure changed dramatically, and a large amount of mitophagosomes were observed; the citrate synthase content and complex II activity were significantly lower (P < 0.05), whereas complex IV activity and COX1 protein level remained unchanged; the expression levels of PINK1, Parkin, Ub, p62, and LC3 were significantly higher than those in the C group (P < 0.05 or P < 0.01). CONCLUSION: A session of downhill treadmill running activated the PINK1/Parkin pathway and facilitated mitochondrial colocalizations with Ub, p62, and LC3, causing mitophagy and mitochondrial damage within the skeletal muscle.

Targeting Inflammation and Downstream Protein Metabolism in Sarcopenia: A Brief Up-Dated Description of Concurrent Exercise and Leucine-Based Multimodal Intervention.

Sarcopenia is defined as the progressive loss of muscle mass with age, and poses a serious threat to the physiological and psychological health of the elderly population with consequential economic and social burdens. Chronic low-grade inflammation plays a central role in the development of sarcopenia such that it alters cellular protein metabolism to favor proteolysis over synthesis, and thereby accelerates muscular atrophy. The purpose of this review is to highlight how exercise and nutrition intervention strategies can attenuate or treat sarcopenia. Resistance exercise increases not only muscle mass but also muscle strength, while aerobic exercise is able to ameliorate the age-related metabolic disorders. Concurrent exercise training integrates the advantages of both aerobic and resistance exercise, and may exert a significant synergistic effect in the aging organism. Higher protein intakes rich in the amino acid leucine appear to restore skeletal muscle protein metabolism balance by rescuing protein synthesis in older adults. There is good reason to believe that a multimodal treatment, a combination of exercise and increased leucine consumption in the diet, can combat some of the muscle loss associated with aging. Future research is needed to consolidate these findings to humans, and to further clarify to what extent and by which mechanisms protein metabolism might be directly involved in sarcopenia pathogenesis and the multimodal treatment responses.

Hypertrophy-Promoting Effects of Leucine Supplementation and Moderate Intensity Aerobic Exercise in Pre-Senescent Mice.

Several studies have indicated a positive influence of leucine supplementation and aerobic training on the aging skeletal muscle signaling pathways that control muscle protein balance and muscle remodeling. However, the effect of a combined intervention requires further clarification. Thirteen month old CD-1(®) mice were subjected to moderate aerobic exercise (45 min swimming per day with 3% body weight workload) and fed a chow diet with 5% leucine or 3.4% alanine for 8 weeks. Serum and plasma were prepared for glucose, urea nitrogen, insulin and amino acid profile analysis. The white gastrocnemius muscles were used for determination of muscle size and signaling proteins involved in protein synthesis and degradation. The results show that both 8 weeks of leucine supplementation and aerobic training elevated the activity of mTOR (mammalian target of rapamycin) and its downstream target p70S6K and 4E-BP1, inhibited the ubiquitin-proteasome system, and increased fiber cross-sectional area (CSA) in white gastrocnemius muscle. Moreover, leucine supplementation in combination with exercise demonstrated more significant effects, such as greater CSA, protein content and altered phosphorylation (suggestive of increased activity) of protein synthesis signaling proteins, in addition to lower expression of proteins involved in protein degradation compared to leucine or exercise alone. The current study shows moderate aerobic training combined with 5% leucine supplementation has the potential to increase muscle size in fast-twitch skeletal muscle during aging, potentially through increased protein synthesis and decreased protein breakdown.