Ribosome-associated quality control (RQC) is a pivotal biological process that governs the fidelity of messenger RNA (mRNA) homeostasis and protein synthesis. Defects in RQC are implicated in cellular dysfunction and proteotoxicity, but their impact on aging remains elusive. Here, we show that Pelota, the ribosome rescue factor, promotes longevity and protects against age-related pathological phenotypes in multiple metazoan species. By performing a targeted genetic screen, we find that Pelota is indispensable for longevity in the nematode Caenorhabditis elegans. We show that Pelota mitigates premature senescence in cultured human cells, muscle aging in mice, and neuropathology in cellular and organoid models of Alzheimer's disease. Mechanistically, we demonstrate that Pelota maintains autophagy-mediated proteostasis, by preventing the hyperactivation of mechanistic target of rapamycin signaling. Overall, our work highlights the conserved functional significance of RQC, regulated by Pelota, in extending lifespan and protecting diverse species against age-associated disease phenotypes.

ABSTRACT Background Physical exercise has beneficial effects on various organs, including skeletal muscle. However, not all patients are capable of engaging in exercise to maintain muscle function, which underscores the importance of identifying molecular mechanisms of physical training that could lead to the discovery of exercise‐mimicking molecules. Methods This study sought to identify molecular mediators of exercise that could improve muscle function. We focused on the exercise‐induced microRNA (miR)‐129‐3p, investigating its role and effects on mitochondrial activity both in vivo and in vitro. The expression of miR‐129‐3p was analysed in skeletal muscle following exercise, and its downstream effects on the poly (ADP‐ribose) polymerase‐1 (Parp1)‐SIRT1‐PGC1α signalling pathway were elucidated. Functional studies were conducted using muscle‐specific overexpression of miR‐129‐3p in adult mice and intramuscular injection of AAV9‐miR‐129‐3p in obese mice to assess exercise capacity and muscle strength. Results Exercise was found to upregulate miR‐129‐3p in skeletal muscle (p < 0.05), which directly inhibits Parp1, a major NAD+‐consuming enzyme. This inhibition leads to increased NAD+ levels (p < 0.05), activating SIRT1 and subsequently reducing the acetylation of PGC1α, thereby enhancing mitochondrial function. Muscle‐specific overexpression of miR‐129‐3p in adult mice significantly enhanced exercise capacity (> 130%, p < 0.0001), while AAV9‐miR‐129‐3p injections ameliorated muscle weakness (twitch force, > 140%, p < 0.05; tetanic force, > 160%, p < 0.01) in obese mice. In human skeletal muscle myoblasts, miR‐129‐3p improved mitochondrial function via the PARP1‐SIRT1‐PGC1α signalling pathway. Conclusion Our findings suggest that miR‐129‐3p, induced by exercise, can mimic the beneficial effects of physical exercise. This highlights miR‐129‐3p as a potential therapeutic target for improving muscle health, especially in individuals unable to exercise.

BACKGROUND:Low back pain is a general phenomenon of aging, and surgery is an unavoidable choice to relieve severe back pain. The discarded surgical site during surgery is of high value for muscle and muscle-related research. This study investigated the age-dependent properties of patients' paraspinal muscles at the cellular level. METHODS:To define an association of paraspinal muscle degeneration with sarcopenia, we analyzed lumbar paraspinal muscle and myoblasts isolated from donors of various ages (25-77 years). Preoperative evaluations were performed by bioimpedance analysis using the InBody 720, magnetic resonance (MR) imaging of the lumbar spine, and lumbar extension strength using a lumbar extension dynamometer. In addition, the growth and differentiation capacity of myoblasts obtained from the donor was determined using proliferation assay and western blotting. RESULTS:The cross-sectional area of the lumbar paraspinal muscle decreased with age and was also correlated with the appendicular skeletal muscle index (ASM/height2). Human primary myoblasts isolated from paraspinal muscle preserved their proliferative capacity in vitro, which tended to decrease with donor age. The age-dependent decline in myoblast proliferation was correlated with levels of cell cycle inhibitory proteins (p16INK4a, p21CIP1, and p27KIP1) associated with cellular senescence. Primary myoblasts isolated from younger donors differentiated into multinucleate myotubes earlier and at a higher rate than those from older donors in vitro. Age-dependent decline in myogenic potential of the isolated primary myoblasts was likely correlated with the inactivation of myogenic transcription factors such as MyoD, myogenin, and MEF2c. CONCLUSIONS:Myoblasts isolated from human paraspinal muscle preserve myogenic potential that correlates with donor age, providing an in vitro model of sarcopenia.

Skeletal muscle communicates with other organs via myokines, which are secreted by muscle during exercise and exert various effects. Despite much investigation of the exercise, the underlying molecular mechanisms are still not fully understood. Here, we applied an in vitro exercise model in which cultured C2C12 myotubes were subjected to electrical pulse stimulation (EPS), which mimics contracting muscle. Based on the significantly up- and down-regulated genes in EPS, we constructed an in silico model to predict exercise responses at the transcriptional level. The in silico model revealed similarities in the transcriptomes of the EPS and exercised animals. Comparative analysis of the EPS data and exercised mouse muscle identified putative biomarkers in exercise signaling pathways and enabled to discover novel exercise-induced myokines. Biochemical analysis of selected exercise signature genes in muscle from exercised mice showed that EPS mimics in vivo exercise, at least in part, at the transcriptional level. Consequently, we provide a novel myokine, Amphiregulin (AREG), up-regulated both in vitro and in vivo, that would be a potential target for exercise mimetics.

Muscle fibers are generally formed as multinucleated fibers that are differentiated from myoblasts. Several reports have identified transcription factors and proteins involved in the process of muscle differentiation to date, but the role of microRNAs (miRNAs) in myogenesis is still unclear. Here, comparative analysis of the miRNA expression profiles in mouse myoblasts and gastrocnemius (GA) muscle uncovered miR‐3074‐3p as a novel miRNA showing markedly reduced expression in fully differentiated adult skeletal muscle. Interestingly, elevating miR‐3074‐3p promoted myogenesis in C2C12 cells, primary myoblasts, and HSMMs, resulting in increased mRNA expression of myogenic makers such as Myog and MyHC. Using a target prediction program, we identified Caveolin‐1 (Cav1) as a target mRNA of miR‐3074‐3p and verified that miR‐3074‐3p directly interacted with the 3′ untranslated region (UTR) of Cav1 mRNA. Consistent with the findings in miR‐3074‐3p‐overexpressing myoblasts, knockdown of Cav1 promoted myogenesis in C2C12 cells and HSMMs. Taken together, our study suggests that miR‐3074‐3p is a positive regulator of myogenic differentiation by targeting Cav1.Support or Funding InformationWe thank S.‐Y. Kim (Genome Editing Research Center in KRIBB) for the advice and discussion in the miRNA analysis. This study was supported by grants from the Bio & Medical Technology Development Program (2017M3A9D8048708) of the National Research Foundation (NRF) funded by the Korean government (Ministry of Science and ICT), the UST Young Scientist Research Program through University of Science and Technology (2019YS07) and the KRIBB Research Initiative Program.

AbstractBackgroundThe microRNAs (miRNAs) down‐regulated in aged mouse skeletal muscle were mainly clustered within the delta‐like homologue 1 and the type III iodothyronine deiodinase (Dlk1‐Dio3) genomic region. Although clustered miRNAs are coexpressed and regulate multiple targets in a specific signalling pathway, the function of miRNAs in the Dlk1‐Dio3 cluster in muscle aging is largely unknown. We aimed to ascertain whether these miRNAs play a common role to regulate age‐related muscle atrophy.MethodsTo examine anti‐atrophic effect of miRNAs, we individually transfected 42 miRNA mimics in fully differentiated myotubes and analysed their diameters. The luciferase reporter assay using target 3′ untranslated region (UTR) and RNA pull‐down assay were employed to ascertain the target predicted by the TargetScan algorithm. To investigate the therapeutic potential of the miRNAs in vivo, we generated adeno‐associated virus (AAV) serotype 9 expressing green fluorescent protein (GFP) (AAV9‐GFP) bearing miR‐376c‐3p and infected it into the tibialis anterior muscle of old mice. We performed morphometric analysis and measured ex vivo isometric force using a force transducer. Human gluteus maximus muscle tissues (ages ranging from 25 to 80 years) were used to investigate expression levels of the conserved miRNAs in the Dlk1‐Dio3 cluster.ResultsWe found that the majority of miRNAs (33 out of 42 tested) in the cluster induced anti‐atrophic phenotypes in fully differentiated myotubes with increasing their diameters. Eighteen of these miRNAs, eight of which are conserved in humans, harboured predicted binding sites in the 3′ UTR of muscle atrophy gene‐1 (Atrogin‐1) encoding a muscle‐specific E3 ligase. Direct interactions were identified between these miRNAs and the 3′ UTR of Atrogin‐1, leading to repression of Atrogin‐1 and thereby induction of eIF3f protein content, in both human and mouse skeletal muscle cells. Intramuscular delivery of AAV9 expressing miR‐376c‐3p, one of the most effective miRNAs in myotube thickening, dramatically ameliorated skeletal muscle atrophy and improved muscle function, including isometric force, twitch force, and fatigue resistance in old mice. Consistent with our findings in mice, the expression of miRNAs in the cluster was significantly down‐regulated in human muscle from individuals > 50 years old.ConclusionsOur study suggests that genetic intervention using a muscle‐directed miRNA delivery system has therapeutic efficacy in preventing Atrogin‐1‐mediated muscle atrophy in sarcopenia.

Significance The molecular mechanisms by which gut microbes modulate host longevity remain elusive. Using genome-wide lifespan screens and extensive interspecies genetic analysis, we identified that the gut microbe-derived metabolite methylglyoxal (MG) modulated host longevity. MG is a reactive carbonyl species involved in the formation of advanced glycation end products, which are implicated in various human pathologies. We identified that Escherichia coli producing reduced levels of MG increased the lifespan of Caenorhabditis elegans due to inhibition of TORC2/SGK-1 and activation of DAF-16. These findings challenge the current paradigm that MG is toxic due to the formation of glycation adducts on biomolecules. Instead, our results highlight the importance of gut microbe-derived MG in regulating the host TORC2/SGK-1/DAF-16 signaling pathway in the interspecies context.

Skeletal muscle mass and power decrease with age, leading to impairment of mobility and metabolism in the elderly. Ca2+ signaling is crucial for myoblast differentiation as well as muscle contraction through activation of transcription factors and Ca2+-dependent kinases and phosphatases. Ca2+ channels, such as dihydropyridine receptor (DHPR), two-pore channel (TPC) and inositol 1,4,5-triphosphate receptor (ITPR), function to maintain Ca2+ homeostasis in myoblasts. Here, we observed a significant decrease in expression of type 1 IP3 receptor (ITPR1), but not types 2 and 3, in aged mice skeletal muscle and isolated myoblasts, compared with those of young mice. ITPR1 knockdown using shRNA-expressing viruses in C2C12 myoblasts and tibialis anterior muscle of mice inhibited myotube formation and muscle regeneration after injury, respectively, a typical phenotype of aged muscle. This aging phenotype was associated with repression of muscle-specific genes and activation of the epidermal growth factor receptor (EGFR)-Ras-extracellular signal-regulated kinase (ERK) pathway. ERK inhibition by U0126 not only induced recovery of myotube formation in old myoblasts but also facilitated muscle regeneration after injury in aged muscle. The conserved decline in ITPR1 expression in aged human skeletal muscle suggests utility as a potential therapeutic target for sarcopenia, which can be treated using ERK inhibition strategies.