Aged Muscle Research Articles

Growth hormone/IGF-I-dependent signaling restores decreased expression of the myokine SPARC in aged skeletal muscle

Skeletal muscle exerts many beneficial effects on the human body including the contraction-dependent secretion of peptides termed myokines. We have recently connected the myokine secreted protein acidic and rich in cysteine (SPARC) to the formation of intramuscular adipose tissue (IMAT) in skeletal muscle from aged mice and humans. Here, we searched for inducers of SPARC in order to uncover novel treatment approaches for IMAT. Endurance exercise in mice as well as forskolin treatment in vitro only modestly activated SPARC levels. However, through pharmacological treatments in vitro, we identified IGF-I as a potent inducer of SPARC expression in muscle cells, likely through a direct activation of its promoter via phosphatidylinositol 4,5-bisphospate 3-kinase (PI3K)-dependent signaling. We employed two different mouse models of growth hormone (GH)/IGF-I deficiency to solidify our understanding of the relationship between IGF-I and SPARC in vivo. GH administration robustly increased intramuscular SPARC levels (3.5-fold) in GH releasing hormone receptor-deficient mice and restored low intramuscular SPARC expression in skeletal muscle from aged mice. Intramuscular glycerol injections induced higher levels of adipocyte markers (adiponectin, perilipin) in aged compared to young mice, which was not prevented by GH treatment. Our study provides a roadmap for the study of myokine regulation during aging and demonstrates that the GH/IGF-I axis is critical for SPARC expression in skeletal muscle. Although GH treatment did not prevent IMAT formation in the glycerol model, targeting SPARC by exercise or by activation of IGF-I signaling might offer a novel therapeutic strategy against IMAT formation during aging.Key messagesIGF-I regulates the myokine SPARC in muscle cells directly at the promoter level.GH/IGF-I is able to restore the decreased SPARC levels in aged skeletal muscle.The glycerol model induces higher adipocyte markers in aged compared to young muscle.GH treatment does not prevent IMAT formation in the glycerol model.

TurnoveR: A Skyline External Tool for Analysis of Protein Turnover in Metabolic Labeling Studies.

In spite of its central role in biology and disease, protein turnover is a largely understudied aspect of most proteomic studies due to the complexity of computational workflows that analyze in vivo turnover rates. To address this need, we developed a new computational tool, TurnoveR, to accurately calculate protein turnover rates from mass spectrometric analysis of metabolic labeling experiments in Skyline, a free and open-source proteomics software platform. TurnoveR is a straightforward graphical interface that enables seamless integration of protein turnover analysis into a traditional proteomics workflow in Skyline, allowing users to take advantage of the advanced and flexible data visualization and curation features built into the software. The computational pipeline of TurnoveR performs critical steps to determine protein turnover rates, including isotopologue demultiplexing, precursor-pool correction, statistical analysis, and generation of data reports and visualizations. This workflow is compatible with many mass spectrometric platforms and recapitulates turnover rates and differential changes in turnover rates between treatment groups calculated in previous studies. We expect that the addition of TurnoveR to the widely used Skyline proteomics software will facilitate wider utilization of protein turnover analysis in highly relevant biological models, including aging, neurodegeneration, and skeletal muscle atrophy.

Proteomic features of skeletal muscle adaptation to resistance exercise training as a function of age.

Resistance exercise training (RET) can counteract negative features of muscle ageing but older age associates with reduced adaptive capacity to RET. Altered muscle protein networks likely contribute to ageing RET adaptation; therefore, associated proteome-wide responses warrant exploration. We employed quantitative sarcoplasmic proteomics to compare age-related proteome and phosphoproteome responses to RET. Thigh muscle biopsies were collected from eight young (25 ± 1.1years) and eight older (67.5 ± 2.6years) adults before and after 20weeks supervised RET. Muscle sarcoplasmic fractions were pooled for each condition and analysed using Isobaric Tags for Relative and Absolute Quantification (iTRAQ) labelling, tandem mass spectrometry and network-based hub protein identification. Older adults displayed impaired RET-induced adaptations in whole-body lean mass, body fat percentage and thigh lean mass (P > 0.05). iTRAQ identified 73 differentially expressed proteins with age and/or RET. Despite possible proteomic stochasticity, RET improved ageing profiles for mitochondrial function and glucose metabolism (top hub; PYK (pyruvate kinase)) but failed to correct altered ageing expression of cytoskeletal proteins (top hub; YWHAZ (14-3-3 protein zeta/delta)). These ageing RET proteomic profiles were generally unchanged or oppositely regulated post-RET in younger muscle. Similarly, RET corrected expression of 10 phosphoproteins altered in ageing, but these responses were again different vs. younger adults. Older muscle is characterised by RET-induced metabolic protein profiles that, whilst not present in younger muscle, improve untrained age-related proteomic deficits. Combined with impaired cytoskeletal adhesion responses, these results provide a proteomic framework for understanding and optimising ageing muscle RET adaptation.

The regulatory network of potential transcription factors and MiRNAs of mitochondria-related genes for sarcopenia.

Background: Mitochondrial dysfunction is a significant contributor to sarcopenia, but the mechanism remains unclear. Methods: In the present study, we downloaded GSE117525 and GSE8479 datasets from Gene Expression Omnibus (GEO), then the weighted correlation network analysis (WGCNA) was used to construct scale-free co-expression networks respectively. The key genes of aging muscle were obtained by overlapping key modules of two networks. Receiver operating characteristic (ROC) curve was drawn to explore the diagnostic efficacy of key genes. Finally, a transcription factor-key gene network was constructed based on ChEA3 platform and hTFtarget database, and a miRNA-key gene network was constructed using starBase and the multimiR R package. Results: The most positively or negatively correlated modules of the two datasets were identified, and genes related to oxidative phosphorylation and mitochondrial ribosomal proteins were identified as key genes. The diagnostic values were confirmed with ROC curves by self-verification (GSE117525 and GSE8479) and external verification (GSE47881). Then, Yin Yang 1 (YY1) was identified as the most important transcription factor of the transcription factor-key gene network. In addition, miRNAs related to key genes were also predicted. Conclusion: The findings of the present study provide a novel insight into the pathological mechanism of sarcopenia.

Beneficial effects of whey protein peptides on muscle loss in aging mice models.

Aging-related muscle loss is a hallmark of aging and is the cause of some negative outcomes. An optimized diet and supplements have a positive effect in slowing down the process of muscle loss. D-galactose(d-gal) has been used widely to develop aging model. This study explored the beneficial effects of whey protein peptides (WPPs) on sarcopenia in d-gal-induced aging mice. A total of 72 SPF male C57BL/6N mice were used in this study. Sixty mice were modeled by injected intraperitoneally with d-gal (100 mg/kg body weight for 6 weeks), and the other 12 mice were used as control, and injected with the same amount of normal saline. After 6 weeks, the modeled mice were randomly divided into the model control group, whey protein group (1.5 g/kg*bw), and three WPPs intervention groups (0.3 g/kg*bw, 1.5 g/kg*bw, 3.0 g/kg*bw), according to serum malondialdehyde (MDA) level. The test samples were orally given to mice by daily garaged. During the 30 days intervention period, the model control group, whey protein group, and WPPs group continued receiving intraperitoneal injections of d-gal, whereas the control group continued receiving intraperitoneal injections of normal saline. The results showed that WPPs could significantly improve the grip strength of aged mice. WPPs could significantly increase lean mass of aged mice and increase muscle weight of gastrocnemius and extensor digitorum longus. WPPs could significantly increase the level of insulin-like growth factor-1 (IGF-1) and reduce level of interleukin (IL)-1, IL-6, tumor necrosis factor-alpha (TNF-α) in serum. WPPs could affect the muscle fiber size in d-gal-induced aging mice. Its specific mechanism may be related to the activation of IGF-1/Akt/mTOR protein synthesis signaling pathway and reduction of the level of inflammation. These results indicate that WPPs can improve aging-related sarcopenia. Compared with whey protein, WPPs supplement seems a better form for sarcopenia.

Neither myonuclear accretion nor a myonuclear domain size ceiling is a feature of the attenuated hypertrophic potential of aged human skeletal muscle

Ageing limits growth capacity of skeletal muscle (e.g. in response to resistance exercise), but the role of satellite cell (SC) function in driving this phenomenon is poorly defined. Younger (Y) (~ 23 years) and older (O) men (~ 69 years) (normal-weight BMI) underwent 6 weeks of unilateral resistance exercise training (RET). Muscle biopsies were taken at baseline and after 3-/6-week training. We determined muscle size by fibre CSA (and type), SC number, myonuclei counts and DNA synthesis (via D2O ingestion). At baseline, there were no significant differences in fibre areas between Y and O. RET increased type I fibre area in Y from baseline at both 3 weeks and 6 weeks (baseline: 4509 ± 534 µm2, 3 weeks; 5497 ± 510 µm2P < 0.05, 6 weeks; 5402 ± 352 µm2P < 0.05), whilst O increased from baseline at 6 weeks only (baseline 5120 ± 403 µm2, 3 weeks; 5606 ± 620 µm2, 6 weeks; 6017 ± 482 µm2P < 0.05). However, type II fibre area increased from baseline in Y at both 3 weeks and 6 weeks (baseline: 4949 ± 459 µm2, 3 weeks; 6145 ± 484 µm2 (P < 0.01), 6 weeks; 5992 ± 491 µm2 (P < 0.01), whilst O showed no change (baseline 5210 ± 410 µm2, 3 weeks; 5356 ± 535 µm2 (P = 0.9), 6 weeks; 5857 ± 478 µm2 (P = 0.1). At baseline, there were no differences in fibre myonuclei number between Y and O. RET increased type I fibre myonuclei number from baseline in both Y and O at 3 weeks and 6 weeks with RET (younger: baseline 2.47 ± 0.16, 3 weeks; 3.19 ± 0.16 (P < 0.001), 6 weeks; 3.70 ± 0.29 (P < 0.0001); older: baseline 2.29 ± 0.09, 3 weeks; 3.01 ± 0.09 (P < 0.001), 6 weeks; 3.65 ± 0.18 (P < 0.0001)). Similarly, type II fibre myonuclei number increased from baseline in both Y and O at 3 weeks and 6 weeks (younger: baseline 2.49 ± 0.14, 3 weeks; 3.31 ± 0.21 (P < 0.001), 6 weeks; 3.86 ± 0.29 (P < 0.0001); older: baseline 2.43 ± 0.12, 3 weeks; 3.37 ± 0.12 (P < 0.001), 6 weeks; 3.81 ± 0.15 (P < 0.0001)). DNA synthesis rates %.d−1 exhibited a main effect of training but no age discrimination. Declines in myonuclei addition do not underlie impaired muscle growth capacity in older humans, supporting ribosomal and proteostasis impairments as we have previously reported.

Aberrant mitochondrial homeostasis at the crossroad of musculoskeletal ageing and non-small cell lung cancer.

Cancer cachexia is accompanied by muscle atrophy, sharing multiple common catabolic pathways with sarcopenia, including mitochondrial dysfunction. This study investigated gene expression from skeletal muscle tissues of older healthy adults, who are at risk of age-related sarcopenia, to identify potential gene biomarkers whose dysregulated expression and protein interference were involved in non-small cell lung cancer (NSCLC). Screening of the literature resulted in 14 microarray datasets (GSE25941, GSE28392, GSE28422, GSE47881, GSE47969, GSE59880 in musculoskeletal ageing; GSE118370, GSE33532, GSE19804, GSE18842, GSE27262, GSE19188, GSE31210, GSE40791 in NSCLC). Differentially expressed genes (DEGs) were used to construct protein-protein interaction networks and retrieve clustering gene modules. Overlapping module DEGs were ranked based on 11 topological algorithms and were correlated with prognosis, tissue expression, and tumour purity in NSCLC. The analysis revealed that the dysregulated expression of the mammalian mitochondrial ribosomal proteins, Mitochondrial Ribosomal Protein S26 (MRPS26), Mitochondrial Ribosomal Protein S17 (MRPS17), Mitochondrial Ribosomal Protein L18 (MRPL18) and Mitochondrial Ribosomal Protein L51 (MRPL51) were linked to reduced survival and tumour purity in NSCLC while tissue expression of the same genes followed an opposite direction in healthy older adults. These results support a potential link between the mitochondrial ribosomal microenvironment in ageing muscle and NSCLC. Further studies comparing changes in sarcopenia and NSCLC associated cachexia are warranted.

Young bone marrow transplantation prevents aging-related muscle atrophy in a senescence-accelerated mouse prone 10 model.

Young bone marrow transplantation (YBMT) has been shown to stimulate vascular regeneration in pathological conditions, including ageing. Here, we investigated the benefits and mechanisms of the preventive effects of YBMT on loss of muscle mass and function in a senescence-associated mouse prone 10 (SAMP10) model, with a special focus on the role of growth differentiation factor 11 (GDF-11). Nine-week-old male SAMP10 mice were randomly assigned to a non-YBMT group (n=6) and a YBMT group (n=7) that received the bone marrow of 8-week-old C57BL/6 mice. Compared to the non-YBMT mice, the YBMT mice showed the following significant increases (all P < 0.05 in 6-7 mice): endurance capacity (>61.3%); grip strength (>37.9%), percentage of slow myosin heavy chain fibres (>14.9-15.9%). The YBMT also increased the amounts of proteins or mRNAs for insulin receptor substrate 1, p-Akt, p-extracellular signal-regulated protein kinase1/2, p-mammalian target of rapamycin, Bcl-2, peroxisom proliferator-activated receptor-γ coactivator (PGC-1α), plus cytochrome c oxidase IV and the numbers of proliferating cells (n = 5-7, P < 0.05) and CD34+/integrin-α7+ muscle stem cells (n = 5-6, P < 0.05). The YMBT significantly decreased the levels of gp91phox, caspase-9 proteins and apoptotic cells (n = 5-7, P < 0.05) in both muscles; these beneficial changes were diminished by the blocking of GDF-11 (n = 5-6, P < 0.05). An administration of mouse recombinant GDF-11 improved the YBMT-mediated muscle benefits (n = 5-6, P < 0.05). Cell therapy with young bone marrow from green fluorescent protein (GFP) transgenic mice exhibited GFP+ myofibres in aged muscle tissues. These findings suggest that YBMT can prevent muscle wasting and dysfunction by mitigating apoptosis and proliferation via a modulation of GDF-11 signalling and mitochondrial dysfunction in SAMP10 mice.

Metabolomic profiling of postmortem aged muscle in Japanese Brown beef cattle revealed an interbreed difference from Japanese Black beef.

Japanese Brown (JBR) cattle, especially the Kochi (Tosa) pedigree (JBRT), is a local breed of moderately marbled beef. Despite the increasing demand, the interbreed differences in muscle metabolites from the highly marbled Japanese Black (JBL) beef remain poorly understood. We aimed to determine flavor-related metabolites and postmortem metabolisms characteristic to JBRT beef in comparison with JBL beef. Lean portions of the longissimus thoracis (loin) muscle from four JBRT cattle were collected at 0, 1, and 14 d postmortem. The muscle metabolomic profiles were analyzed using capillary electrophoresis time-of-flight mass spectrometry. The difference in postmortem metabolisms and aged muscle metabolites were analyzed by statistical and bioinformatic analyses between JBRT (n = 12) and JBL cattle (n = 6). A total of 240 metabolite annotations were obtained from the detected signals of the JBRT muscle samples. Principal component analysis separated the beef samples into three different aging point groups. According to metabolite set enrichment analysis, postmortem metabolic changes were associated with the metabolism of pyrimidine, nicotinate and nicotinamide, purine, pyruvate, thiamine, amino sugar, and fatty acid; citric acid cycle; and pentose phosphate pathway as well as various amino acids and mitochondrial fatty acid metabolism. The aged JBRT beef showed higher ultimate pH and lower lactate content than aged JBL beef, suggesting the lower glycolytic activity in postmortem JBRT muscle. JBRT beef was distinguished from JBL beef by significantly different compounds, including choline, amino acids, uridine monophosphate, inosine 5'-monophosphate, fructose 1,6-diphosphate, and betaine, suggesting interbreed differences in the accumulation of nucleotide monophosphate, glutathione metabolism, and phospholipid metabolism. Glycolysis, purine metabolism, fatty acid catabolism, and protein degradation were the most common pathways in beef during postmortem aging. The differentially expressed metabolites and the relevant metabolisms in JBRT beef may contribute to the development of a characteristic flavor.

Macrophage immunomodulation accelerates skeletal muscle functional recovery in aged mice following disuse atrophy.

Poor recovery of muscle size and strength with aging coincides with a dysregulated macrophage response during the early stages of regrowth. Immunomodulation in the form of ex vivo cytokine (macrophage-colony stimulating factor) or polarized macrophage delivery has been demonstrated to improve skeletal muscle regeneration. However, it is unclear if these macrophage-promoting approaches would be effective to improve skeletal muscle recovery following disuse in aged animals. Here, we isolated bone marrow-derived macrophages from donor mice of different ages under various experimental conditions and polarized them into proinflammatory macrophages. Macrophages were delivered intramuscularly into young adult or aged recipient mice during the early recovery period following a period of hindlimb unloading (HU). Delivery of proinflammatory macrophages from donor young adults or aged mice was sufficient to increase muscle function of aged mice during the recovery period. Moreover, proinflammatory macrophages derived from aged donor mice collected during recovery were similarly able to increase muscle function of aged mice following disuse. In addition to the delivery of macrophages, we showed that the intramuscular injection of the cytokine, macrophage-colony stimulating factor, to the muscle of aged mice following HU was able to increase muscle macrophage content and muscle force production during recovery. Together, these results suggest that macrophage immunomodulation approaches in the form of ex vivo proinflammatory macrophage or macrophage-colony stimulating factor delivery during the early recovery phase following disuse atrophy were sufficient to restore the loss of aged skeletal muscle function.NEW & NOTEWORTHY A single intramuscular administration of polarized macrophages into muscles of aged mice following a bout of disuse atrophy was sufficient to improve functional recover similarly to young adults after disuse atrophy regardless of the age or experimental condition of the donor mice. Additionally, intramuscular delivery of macrophage-colony stimulating factor into aged mice was similarly effective. Targeting macrophage function early during the regrowth phase may be a novel tool to bolster muscle recovery in aging.

In Vitro Regeneration Capacity In Response To Chemical Injury Is Compromised In Aged Vs Young Muscle Cells

Healthy skeletal muscle can regenerate after ischemic, mechanical or toxin-induced injury. However, age-related changes in skeletal muscle cells and their niche may impair the regeneration potential. While strategies to regenerate muscle are being developed, in vitro models to investigate the regenerative potential after injury in aged versus young muscle cells are lacking. PURPOSE: This study aims to develop in vitro muscle models of injury and regeneration using cells from older and young donors. METHODS: Differentiated C2C12 murine and human myoblasts from old and young donors were injured after exposure to 12% barium chloride for 6 h. Regeneration was assessed by morphological analysis including myotube width, number of nuclei and fusion index. For that cells were stained with phalloidin and DAPI to label the cytoskeleton and nuclei of muscle cells, respectively. Images were acquired with the Leica fluorescence microscope and analysed using ImageJ. Timepoints were pre-injury (control), post-injury, end of proliferation and end of differentiation. RESULTS: The number of myonuclei post-injury remained unaltered compared to pre-injury among all cell lines (p > 0.05). Three days post-injury, nuclei number reached significance only in murine (p = 0.0006) and young (p = 0.03) muscle cells, whereas aged myotubes showed a significant increase in the total number of myonuclei at the end of the regeneration period (p = 0.01). Myotube diameter at the end of the regeneration recovered to pre-injury state in C2C12 and young but was significantly smaller in aged cells (p = 0.04). CONCLUSION: Delayed peak in proliferation and significantly smaller myotubes in aged compared to young and murine muscle cells at the end of the experiment could be attributed to declined proliferation rate of resident satellite cells that causes suspended myogenesis and regenerative response in older muscle cells. Barium chloride injury model is an easily reproducible in vitro approach that could be applied to study age and/or disease-related regenerative changes in different cell lines. KEYWORDS: regeneration, injury, skeletal muscle, ageing

Creatine supplementation for older adults: Focus on sarcopenia, osteoporosis, frailty and Cachexia.

Sarcopenia refers to the age-related reduction in strength, muscle mass and functionality which increases the risk for falls, injuries and fractures. Sarcopenia is associated with other age-related conditions such as osteoporosis, frailty and cachexia. Identifying treatments to overcome sarcopenia and associated conditions is important from a global health perspective. There is evidence that creatine monohydrate supplementation, primarily when combined with resistance training, has favorable effects on indices of aging muscle and bone. These musculoskeletal benefits provide some rationale for creatine being a potential intervention for treating frailty and cachexia. The purposes of this narrative review are to update the collective body of research pertaining to the effects of creatine supplementation on indices of aging muscle and bone (including bone turnover markers) and present possible justification and rationale for its utilization in the treatment of frailty and cachexia in older adults.

Contribution of stroke-related changes in neuromuscular factors to gear ratio during isometric contraction of medial gastrocnemius muscle: A simulation study

BackgroundIt is not clear which neuromuscular factors are most closely associated with the loss of variable fascicle gearing after chronic stroke. The purpose of this simulation study is to determine the effects of stroke-related changes in key neuromuscular factors on the gear ratio. MethodsA modified Hill-type model of the medial gastrocnemius was developed to determine the gear ratio for a given muscle activation level and musculotendon length. Model parameters were then systematically adjusted to simulate known stroke-related changes in neuromuscular factors, and the gear ratio was computed for each change in the parameters. A Monte Carlo simulation was performed to understand which neuromuscular factors and fiber behavior-related parameters are most relevant to the loss of variable gearing. Dominance analyses were also conducted to quantify the relative importance of fiber behavior-related parameters on the gear ratio. FindingsThe gear ratio decreases significantly with smaller pennation angle and with shorter optimal fiber length. In addition, muscle thickness and pennation angle at optimal fiber length appear to be the most important muscle architectural parameters. Dominance analyses further suggest that primary determinants of gear ratio include initial pennation angle, fiber rotation-shortening ratio, initial muscle thickness, and fiber rotation. InterpretationOur findings provide insight that the pennation angle may play an important role for efficient muscular contraction, implying that maintaining muscle architecture and/or improving fiber/fascicle rotation could a key goal in rehabilitation interventions. Our findings will help us to better interpret altered gearing behavior in aging and pathological muscles.

Potential Satellite Cell-Linked Biomarkers in Aging Skeletal Muscle Tissue: Proteomics and Proteogenomics to Monitor Sarcopenia.

Sarcopenia (Sp) is the loss of skeletal muscle mass associated with aging which causes an involution of muscle function and strength. Satellite cells (Sc) are myogenic stem cells, which are activated by injury or stress, and repair muscle tissue. With advancing age, there is a decrease in the efficiency of the regenerative response of Sc. Diagnosis occurs with the Sp established by direct assessments of muscle. However, the detection of biomarkers in real-time biofluids by liquid biopsy could represent a step-change in the understanding of the molecular biology and heterogeneity of Sp. A total of 13 potential proteogenomic biomarkers of Sp by their physiological and biological interaction with Sc have been previously described in the literature. Increases in the expression of GDF11, PGC-1α, Sirt1, Pax7, Pax3, Myf5, MyoD, CD34, MyoG, and activation of Notch signaling stimulate Sc activity and proliferation, which could modulate and delay Sp progression. On the contrary, intensified expression of GDF8, p16INK4a, Mrf4, and activation of the Wnt pathway would contribute to early Sp development by directly inducing reduced and/or altered Sc function, which would attenuate the restorative capacity of skeletal muscle. Additionally, tissue biopsy remains an important diagnostic tool. Proteomic profiling of aged muscle tissues has shown shifts toward protein isoforms characteristic of a fast-to-slow transition process and an elevated number of oxidized proteins. In addition, a strong association between age and plasma values of growth differentiation factor 15 (GDF-15) has been described and serpin family A member 3 (serpin A3n) was more secreted by atrophied muscle cells. The identification of these new biomarkers holds the potential to change personalized medicine because it could predict in real time the course of Sp by monitoring its evolution and assessing responses to potential therapeutic strategies.

MiR-33a targets FOSL1 and EN2 as a clinical prognostic marker for sarcopenia by glioma.

To determine the relationship between glioma and muscle aging and to predict prognosis by screening for co-expressed genes, this study examined the relationship between glioma and sarcopenia. The study identified eight co-downregulated miRNAs, three co-upregulated miRNAs, and seven genes associated with overall glioma survival, namely, KRAS, IFNB1, ALCAM, ERBB2, STAT3, FOSL1, and EN2. With a multi-factor Cox regression model incorporating FOSL1 and EN2, we obtained ROC curves of 0.702 and 0.709, respectively, suggesting that glioma prognosis can be predicted by FOSL1 and EN2, which are differentially expressed in both cancer and aged muscle. FOSL1 and EN2 were analyzed using Gene Set Enrichment Analysis to identify possible functional pathways. RT-qPCR and a dual-luciferase reporter gene system verified that hsa-miR-33a targets FOSL1 and EN2. We found that hsa-mir-33a co-targeting FOSL1 and EN2 has a good predictive value for glioblastoma and skeletal muscle reduction.

Global chromatin accessibility profiling analysis reveals a chronic activation state in aged muscle stem cells

SummaryRegulation of chromatin accessibility is critical for cell fate decisions. Chromatin structure responds to extrinsic environments rapidly. The traditional adult stem cell isolation approach requires tissue dissociation, which triggers stem cell activation and leads to alterations in chromatin structure. To preserve the in vivo chromatin states, we utilized the PFA-perfusion-based isolation approach and characterized the DNA regulatory landscapes during muscle stem cell quiescence exit and aging. We showed that aged SCs display a chronically activated chromatin signature. Detailed analysis of the chromatin accessibility profiles identified key enhancer elements for SC quiescence. Constant activation of the enhancer elements promotes stemness and prevents SCs from differentiation, whereas genetic deletion causes cell-cycle arrest and leads to defects in activation. Our comprehensive characterization of the chromatin accessibility and transcriptomic landscapes in SC quiescence and aging broadens our understanding of these processes and identifies key distal regulatory elements for SC function.

The CRTC-CREB axis functions as a transcriptional sensor to protect against proteotoxic stress in Drosophila

cAMP Responsible Element Binding Protein (CREB) is an evolutionarily conserved transcriptional factor that regulates cell growth, synaptic plasticity and so on. In this study, we unexpectedly found proteasome inhibitors, such as MLN2238, robustly increase CREB activity in adult flies through a large-scale compound screening. Mechanistically, reactive oxidative species (ROS) generated by proteasome inhibition are required and sufficient to promote CREB activity through c-Jun N-terminal kinase (JNK). In 293 T cells, JNK activation by MLN2238 is also required for increase of CREB phosphorylation at Ser133. Meanwhile, transcriptome analysis in fly intestine identified a group of genes involved in redox and proteostatic regulation are augmented by overexpressing CRTC (CREB-regulated transcriptional coactivator). Intriguingly, CRTC overexpression in muscles robustly restores protein folding and proteasomal activity in a fly Huntington’s disease (HD) model, and ameliorates HD related pathogenesis, such as protein aggregates, motility, and lifespan. Moreover, CREB activity increases during aging, and further enhances its activity can suppress protein aggregates in aged muscles. Together, our results identified CRTC/CREB downstream ROS/JNK signaling as a conserved sensor to tackle oxidative and proteotoxic stresses. Boosting CRTC/CREB activity is a potential therapeutic strategy to treat aging related protein aggregation diseases.

The role of the aging microenvironment on the fate of PDGFRβ lineage cells in skeletal muscle repair

BackgroundDuring aging, perturbation of muscle progenitor cell (MPC) constituents leads to progressive loss of muscle mass and accumulation of adipose and fibrotic tissue. Mesenchymal stem cells (MSCs) give rise to adipocytes and fibroblasts that accumulate in injured and pathological skeletal muscle through constitutive activation of platelet-derived growth factor receptors (PDGFRs). Although the role of the PDGFRα has been widely explored, there is a paucity of evidence demonstrating the role of PDGFRβ in aged skeletal muscle.MethodsIn this study, we investigated the role of PDGFRβ lineage cells in skeletal muscle during aging by using Cre/loxP lineage tracing technology. The PDGFR-Cre mice were crossed with global double-fluorescent Cre reporter mice (mTmG) that indelibly marks PDGFRβ lineage cells. Those cells were analyzed and compared at different ages in the skeletal muscle of the mice.ResultsOur results demonstrated that PDGFRβ lineage cells isolated from the muscles of young mice are MPC-like cells that exhibited satellite cell morphology, expressed Pax7, and undergo myogenic differentiation producing myosin heavy chain expressing myotubes. Conversely, the PDGFRβ lineage cells isolated from muscles of old mice displayed MSC morphology with a reduced myogenic differentiation potential while expressing adipogenic and fibrotic differentiation markers. PDGFRβ lineage cells also gave rise to newly regenerated muscle fibers in young mice after muscle injury, but their muscle regenerative process is reduced in old mice.ConclusionsOur data suggest that PDGFRβ lineage cells function as MPCs in young mice, while the same PDGFRβ lineage cells from old mice undergo a fate switch participating in adipose and fibrotic tissue infiltration in aged muscle. The inhibition of fate-switching in PDGFRβ lineage cells may represent a potential approach to prevent fibrosis and fatty infiltration in skeletal muscle during the aging process.

Ablation of Ghrelin Receptor Mitigates the Metabolic Decline of Aging Skeletal Muscle.

The orexigenic hormone ghrelin has multifaceted roles in health and disease. We have reported that ablation of the ghrelin receptor, growth hormone secretagogue receptor (GHS-R), protects against metabolic dysfunction of adipose tissues in aging. Our further observation interestingly revealed that GHS-R deficiency phenocopies the effects of myokine irisin. In this study, we aim to determine whether GHS-R affects the metabolic functions of aging skeletal muscle and whether GHS-R regulates the muscular functions via irisin. We first studied the expression of metabolic signature genes in gastrocnemius muscle of young, middle-aged and old mice. Then, old GHS-R knockout (Ghsr−/−) mice and their wild type counterparts were used to assess the impact of GHS-R ablation on the metabolic characteristics of gastrocnemius and soleus muscle. There was an increase of GHS-R expression in skeletal muscle during aging, inversely correlated with the decline of metabolic functions. Remarkedly the muscle of old GHS-R knockout (Ghsr−/−) mice exhibited a youthful metabolic profile and better maintenance of oxidative type 2 muscle fibers. Furthermore, old Ghsr−/− mice showed improved treadmill performance, supporting better functionality. Also intriguing to note was the fact that old GHS-R-ablated mice showed increased expression of the irisin precursor FNDC5 in the muscle and elevated plasma irisin levels in circulation, which supports a potential interrelationship between GHS-R and irisin. Overall, our work suggests that GHS-R has deleterious effects on the metabolism of aging muscle, which may be at least partially mediated by myokine irisin.

Aging and skeletal muscle force control: Current perspectives and future directions.

During voluntary muscle contractions, force output is characterized by constant inherent fluctuations, which can be quantified either according to their magnitude or temporal structure, that is, complexity. The presence of such fluctuations when targeting a set force indicates that control of force is not perfectly accurate, which can have significant implications for task performance. Compared to young adults, older adults demonstrate a greater magnitude and lower complexity in force fluctuations, indicative of decreased steadiness, and adaptability of force output, respectively. The nature of this loss‐of‐force control depends not only on the age of the individual but also on the muscle group performing the task, the intensity and type of contraction and whether the task is performed with additional cognitive load. Importantly, this age‐associated loss‐of‐force control is correlated with decreased performance in a range of activities of daily living and is speculated to be of greater importance for functional capacity than age‐associated decreases in maximal strength. Fortunately, there is evidence that acute physical activity interventions can reverse the loss‐of‐force control in older individuals, though whether this translates to improved functional performance and whether lifelong physical activity can protect against the changes have yet to be established. A number of mechanisms, related to both motor unit properties and the behavior of motor unit populations, have been proposed for the age‐associated changes in force fluctuations. It is likely, though, that age‐associated changes in force control are related to increased common fluctuations in the discharge times of motor units.