Skeletal muscle fibre type-dependent effects of atorvastatin on the PI3K/Akt/mTOR signalling pathway and atrophy-related genes in rats.

BACKGROUND: One of the probable causes of statin myotoxicity is an imbalance between protein synthesis and degradation. These processes are regulated by the PI3K/Akt/mTOR pathway and the ubiquitin‒proteasome system (UPS). The aim of this study was to assess whether the effects of atorvastatin on PI3K/Akt/mTOR pathway downstream proteins, the FoxO3a transcription factor and the UPS genes, i.e., MuRF-1 and MAFbx, depend on muscle fibre type. METHODS AND RESULTS: Atorvastatin (50 mg/kg) was administered to Wistar rats. The levels of selected PI3K/Akt/mTOR pathway proteins were assayed via Western blotting, whereas MuRF-1, MAFbx and FoxO3a mRNA levels were measured using reverse transcription quantitative polymerase chain reaction (RT‒qPCR). Gomöri trichrome staining was performed to assess skeletal muscle pathology. A decrease in the P-Akt/Akt ratio was observed in the gastrocnemius muscle (MG), whereas an increase in the P-Akt/Akt ratio was observed in the soleus muscle (SOL). FoxO3a gene expression increased in the SOL and extensor digitorum longus (EDL) muscles. MuRF-1 gene expression increased in the MG, and MAFbx expression increased in the EDL. No histopathological changes were observed in any of the tested muscles. CONCLUSIONS: In the absence of overt muscle damage, atorvastatin decreased the P-Akt/Akt ratio in the MG, indicating an increase in inactive Akt. Consistent with the decrease in Akt activation, rpS6 phosphorylation decreased. In SOL, atorvastatin increased the P-Akt/Akt ratio, indicating Akt activation. P-FoxO3a and the P-FoxO3a/FoxO3a ratio increased, suggesting that FoxO3a inactivation occurred. Moreover, in the SOL, atorvastatin did not affect the expression of atrophy-related genes. These findings indicate that atorvastatin has no adverse effect on the Akt pathway in the SOL. Our results showed that the effects of atorvastatin on the Akt signalling pathway and atrophy-related gene expression depend on muscle type.

The Role of Non-Coding RNAs in Regulating Cachexia Muscle Atrophy.

Cachexia is a late consequence of various diseases that is characterized by systemic muscle loss, with or without fat loss, leading to significant mortality. Multiple signaling pathways and molecules that increase catabolism, decrease anabolism, and interfere with muscle regeneration are activated. Non-coding RNAs (ncRNAs), such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), play vital roles in cachexia muscle atrophy. This review mainly provides the mechanisms of specific ncRNAs to regulate muscle loss during cachexia and discusses the role of ncRNAs in cachectic biomarkers and novel therapeutic strategies that could offer new insights for clinical practice.

(-)-Epicatechin treatment modify the expression of genes related to atrophy in gastrocnemius muscle of male rats obese by programing.

The aim of this study is to determine if the offspring of mothers with obesity, present disorders in the expression of genes related to atrophy or protein synthesis in the muscle and if these disorders are modified with the (-)-epicatechin (Epi) treatment. Six male offspring per group were randomly assigned to the control groups [C and offspring of maternal obesity (MO)] or the Epi intervention groups, Epi treatment for 13 weeks (C + Epi long or MO + Epi long), or Epi administration for two weeks (C + Epi short or MO + Epi short). The effect of Epi in the gastrocnemius tissue was evaluated, analyzing mRNA and protein levels of Murf1, MAFbx, Foxo1, NFkB, and p70S6K-alpha. After the analysis by two-way ANOVA, we found an influence of the Epi long treatment over the model, by decreasing the Murf1 gene expression in both groups treated with the flavonoid (C + Epi long and MO + Epi long) (p = 0.036). Besides, Epi long treatment over the NFκB expression, by decreasing the fold increase in both groups treated with the flavonoid (C + Epi long and MO + Epi long) (p = 0.038). We not find any interaction between the variables or changes in the MAFbx, Foxo1 mRNA, neither in the phosphorylated/total protein ratio of NFκB, Foxo1, or p70S6K-alpha. In conclusions, treatment with a long protocol of Epi, reduces the mRNA of the muscle atrophy genes Murf 1 and NFkB, in the gastrocnemius muscle; however, these changes are not maintained at protein level.

High expression of transcription factor EGR1 is associated with postoperative muscle atrophy in patients with knee osteoarthritis undergoing total knee arthroplasty.

BACKGROUND: Muscle atrophy is a typical affliction in patients affected by knee Osteoarthritis (KOA). This study aimed to examine the potential pathogenesis and biomarkers that coalesce to induce muscle atrophy, primarily through the utilization of bioinformatics analysis. METHODS: Two distinct public datasets of osteoarthritis and muscle atrophy (GSE82107 and GSE205431) were subjected to differential gene expression analysis and gene set enrichment analysis (GSEA) to probe for common differentially expressed genes (DEGs) and conduct transcription factor (TF) enrichment analysis from such genes. Venn diagrams were used to identify the target TF, followed by the construction of a protein-protein interaction (PPI) network of the common DEGs governed by the target TF. Hub genes were determined through the CytoHubba plug-in whilst their biological functions were assessed using GSEA analysis in the GTEx database. To validate the study, reverse transcriptase real-time quantitative polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA), and Flow Cytometry techniques were employed. RESULTS: A total of 138 common DEGs of osteoarthritis and muscle atrophy were identified, with 16 TFs exhibiting notable expression patterns in both datasets. Venn diagram analysis identified early growth response gene-1 (EGR1) as the target TF, enriched in critical pathways such as epithelial mesenchymal transition, tumor necrosis factor-alpha signaling NF-κB, and inflammatory response. PPI analysis revealed five hub genes, including EGR1, FOS, FOSB, KLF2, and JUNB. The reliability of EGR1 was confirmed by validation testing, corroborating bioinformatics analysis trends. CONCLUSIONS: EGR1, FOS, FOSB, KLF2, and JUNB are intricately involved in muscle atrophy development. High EGR1 expression directly regulated these hub genes, significantly influencing postoperative muscle atrophy progression in KOA patients.

Causal role of immune cells in muscle atrophy: mendelian randomization study.

Immune system and inflammation had a great influence on the progression of muscle atrophy. However, the causal relationship with specific immune cell traits remained uncertain. The aim of this study was to elucidate the genetic influences on these associations, providing insights into the underlying mechanisms of muscle atrophy. A bidirectional two-sample Mendelian randomization (MR) analysis was conducted to investigate the causal relationship between immune cell phenotypes and muscle atrophy. Data on immune cell phenotypes were obtained from a research cohort containing data on 731 immune cell phenotypes and data on muscle atrophy were sourced from a Finnish database. MR analysis was performed using the MR-Egger method, weighted median, inverse variance weighting, heterogeneity testing, sensitivity analysis, and multiplicity analysis, with results subjected to false discovery rate(FDR) correction. Additionally, the UK Biobank cohort was utilized as an external validation. A total of 31 immune phenotypes with causal relationships with muscle atrophy were identified, including various phenotypes of conventional dendritic cells, myeloid cells, T cells/B cells/natural killer cells, regulatory cells, and T cell maturation stages. Among them, 12 immune phenotypes were identified as exhibiting a positive causal relationship with muscle atrophy, while 19 immune phenotypes were demonstrated to have a negative causal association, highlighting the complex interactions between immune cells and muscle health. The results of the reverse MR analysis indicated that a negative correlation between muscle atrophy and CD28 on secreting Treg (OR = 0.9038, 95%CI:0.8308 ~ 0.9832, P = 0.0186). A significant positive correlation was revealed by external datasets between the CD25 on IgD + CD38- immune phenotype and the risk of muscle atrophy, which was consistent with the trend observed in the training group (OR = 1.1041, 95% CI: 1.1005-1.1076, P = 0.0263). No evidence of pleiotropy was observed, and the reliability of these findings was demonstrated by the leave-one-out analysis. The findings highlight significant correlations between certain immune cell features and muscle atrophy, providing potential targets for further investigation of immunological mechanisms and therapeutic interventions for this condition.

Loss of SELENOW aggravates muscle loss with regulation of protein synthesis and the ubiquitin-proteasome system.

Sarcopenia is characterized by accelerated muscle mass and function loss, which burdens and challenges public health worldwide. Several studies indicated that selenium deficiency is associated with sarcopenia; however, the specific mechanism remains unclear. Here, we demonstrated that selenoprotein W (SELENOW) containing selenium in the form of selenocysteine functioned in sarcopenia. SELENOW expression is up-regulated in dexamethasone (DEX)-induced muscle atrophy and age-related sarcopenia mouse models. Knockout (KO) of SELENOW profoundly aggravated the process of muscle mass loss in the two mouse models. Mechanistically, SELENOW KO suppressed the RAC1-mTOR cascade by the interaction between SELENOW and RAC1 and induced the imbalance of protein synthesis and degradation. Consistently, overexpression of SELENOW in vivo and in vitro alleviated the muscle and myotube atrophy induced by DEX. SELENOW played a role in age-related sarcopenia and regulated the genes associated with aging. Together, our study uncovered the function of SELENOW in age-related sarcopenia and provides promising evidence for the prevention and treatment of sarcopenia.

Muscle-derived IL-1ß regulates EcSOD expression via the NBR1-p62-Nrf2 pathway in muscle during cancer cachexia.

Oxidative stress contributes to the loss of skeletal muscle mass and function in cancer cachexia. However, this outcome may be mitigated by an improved endogenous antioxidant defence system. Here, using the well-established oxidative stress-inducing muscle atrophy model of Lewis lung carcinoma (LLC) in 13-week-old male C57BL/6J mice, we demonstrate that extracellular superoxide dismutase (EcSOD) levels increase in the cachexia-prone extensor digitorum longus muscle. LLC transplantation significantly increased interleukin-1ß (IL-1ß) expression and release from extensor digitorum longus muscle fibres. Moreover, IL-1ß treatment of C2C12 myotubes increased NBR1, p62 phosphorylation at Ser351, Nrf2 nuclear translocation and EcSOD protein expression. Additional studies in vivo indicated that intramuscular IL-1ß injection is sufficient to stimulate EcSOD expression, which is prevented by muscle-specific knockout of p62 and Nrf2 (i.e. in p62 skmKO and Nrf2 skmKO mice, respectively). Finally, since an increase in circulating IL-1ß may lead to unwanted outcomes, we demonstrate that targeting this pathway at p62 is sufficient to drive muscle EcSOD expression in an Nrf2-dependent manner. In summary, cancer cachexia increases EcSOD expression in extensor digitorum longus muscle via muscle-derived IL-1ß-induced upregulation of p62 phosphorylation and Nrf2 activation. These findings provide further mechanistic evidence for the therapeutic potential of p62 and Nrf2 to mitigate cancer cachexia-induced muscle atrophy. KEY POINTS: Oxidative stress plays an important role in muscle atrophy during cancer cachexia. EcSOD, which mitigates muscle loss during oxidative stress, is upregulated in 13-week-old male C57BL/6J mice of extensor digitorum longus muscles during cancer cachexia. Using mouse and cellular models, we demonstrate that cancer cachexia promotes muscle EcSOD protein expression via muscle-derived IL-1ß-dependent stimulation of the NBR1-p62-Nrf2 signalling pathway. These results provide further evidence for the potential therapeutic targeting of the NBR1-p62-Nrf2 signalling pathway downstream of IL-1ß to mitigate cancer cachexia-induced muscle atrophy.

Muscle degeneration in aging Drosophila flies: the role of mechanical stress.

Muscle wasting is a universal hallmark of aging which is displayed by a wide range of organisms, although the causes and mechanisms of this phenomenon are not fully understood. We used Drosophila to characterize the phenomenon of spontaneous muscle fiber degeneration (SMFD) during aging. We found that SMFD occurs across diverse types of somatic muscles, progresses with chronological age, and positively correlates with functional muscle decline. Data from vital dyes and morphological markers imply that degenerative fibers most likely die by necrosis. Mechanistically, SMFD is driven by the damage resulting from muscle contractions, and the nervous system may play a significant role in this process. Our quantitative model of SMFD assessment can be useful in identifying and validating novel genetic factors that influence aging-related muscle wasting.

Apolipoprotein E knockout, but not cholesteryl ester transfer protein (CETP)-associated high-density lipoprotein cholesterol (HDL-C) lowering, exacerbates muscle wasting in dysferlin-null mice.

BACKGROUND: Dysferlin-deficient limb-girdle muscular dystrophy type 2B (Dysf) mice are notorious for their mild phenotype. Raising plasma total cholesterol (CHOL) via apolipoprotein E (ApoE) knockout (KO) drastically exacerbates muscle wasting in Dysf mice. However, dysferlinopathic patients have abnormally reduced plasma high-density lipoprotein cholesterol (HDL-C) levels. The current study aimed to determine whether HDL-C lowering can exacerbate the mild phenotype of dysferlin-null mice. METHODS: Human cholesteryl ester transfer protein (CETP), a plasma lipid transfer protein not found in mice that reduces HDL-C, and/or its optimal adapter protein human apolipoprotein B (ApoB), were overexpressed in Dysf mice. Mice received a 2% cholesterol diet from 2 months of age and characterized through ambulatory and hanging functional tests, plasma analyses, and muscle histology. RESULTS: CETP/ApoB expression in Dysf mice caused reduced HDL-C (54.5%) and elevated ratio of CHOL/HDL-C (181.3%) compared to control Dysf mice in plasma, but without raising CHOL. Compared to the severe muscle pathology found in high CHOL Dysf/ApoE double knockout mice, Dysf/CETP/ApoB mice did not show significant changes in ambulation, hanging capacity, increases in damaged area, collagen deposition, or decreases in cross-sectional area and healthy myofibre coverage. CONCLUSIONS: CETP/ApoB over-expression in Dysf mice decreases HDL-C without increasing CHOL or exacerbating muscle pathology. High CHOL or nonHDL-C caused by ApoE KO, rather than low HDL-C, likely lead to rodent muscular dystrophy phenotype humanization.

Zfp697 is an RNA-binding protein that regulates skeletal muscle inflammation and remodeling.

Skeletal muscle atrophy is a morbidity and mortality risk factor that happens with disuse, chronic disease, and aging. The tissue remodeling that happens during recovery from atrophy or injury involves changes in different cell types such as muscle fibers, and satellite and immune cells. Here, we show that the previously uncharacterized gene and protein Zfp697 is a damage-induced regulator of muscle remodeling. Zfp697/ZNF697 expression is transiently elevated during recovery from muscle atrophy or injury in mice and humans. Sustained Zfp697 expression in mouse muscle leads to a gene expression signature of chemokine secretion, immune cell recruitment, and extracellular matrix remodeling. Notably, although Zfp697 is expressed in several cell types in skeletal muscle, myofiber-specific Zfp697 genetic ablation in mice is sufficient to hinder the inflammatory and regenerative response to muscle injury, compromising functional recovery. We show that Zfp697 is an essential mediator of the interferon gamma response in muscle cells and that it functions primarily as an RNA-interacting protein, with a very high number of miRNA targets. This work identifies Zfp697 as an integrator of cell-cell communication necessary for tissue remodeling and regeneration.

Combination of transcriptomics and proteomics for analyzing potential biomarker and molecular mechanism underlying skeletal muscle atrophy.

BACKGROUND: The skeletal muscle atrophy is prevalently occurred in numerous chronic disease complications. Despite its important clinical significance, there are currently no therapeutic drugs, so new biomarkers and molecular mechanisms need to be discovered urgently. METHODS: Transcriptome and proteome sequencing data were collected from normal and skeletal muscle atrophic mice. The differentially expressed genes (DEGs) and proteins (DEPs) were analyzed. Applying PPI analysis to obtain overlapping genes and proteins, which were next subjected to GO and KEGG enrichment analysis. Combined analysis of transcriptomics and proteomics was performed to get key genes that were simultaneously found in GO and KEGG enrichment results. Subsequently, RT-qPCR and immunofluorescence were constructed to verify the expression of screened key genes. RESULTS: By combination of transcriptomics, proteomics and RT-qPCR results, we identified 14 key genes (Cav1, Col3a1, Dnaja1, Postn, Ptges3, Cd44, Clec3b, Igfbp6, Lamc1, Alb, Itga6, Mmp2, Timp2 and Cd9) that were markedly different in atrophic mice. Single-gene GSEA and immunofluorescence suggested Cd9 was probably the biomarker for skeletal muscle atrophy. CONCLUSIONS: Our study hinted that Cd9 was potential biomarker and may interfere with skeletal muscle atrophy through process of aerobic respiration, oxidative phosphorylation, and metabolism of amino acids and fatty acids. SIGNIFICANCE: The present study holds the subsequent significance: Frist, we investigated biomarkers for skeletal muscle atrophy using multi-omics approach. A total of 14 genes were markedly different in skeletal muscle atrophic mice. We finally found Cd9 is a potential biomarker for skeletal muscle atrophy. Our work presents novel biomarkers and potential regulatory mechanisms for the early detection and intervention of muscle atrophy.

Epigenetics of Skeletal Muscle Atrophy.

Skeletal muscle atrophy, characterized by diminished muscle strength and mass, arises from various causes, including malnutrition, aging, nerve damage, and disease-related secondary atrophy. Aging markedly escalates the prevalence of sarcopenia. Concurrently, the incidence of muscle atrophy significantly rises among patients with chronic ailments such as heart failure, diabetes, and chronic obstructive pulmonary disease (COPD). Epigenetics plays a pivotal role in skeletal muscle atrophy. Aging elevates methylation levels in the promoter regions of specific genes within muscle tissues. This aberrant methylation is similarly observed in conditions like diabetes, neurological disorders, and cardiovascular diseases. This study aims to explore the relationship between epigenetics and skeletal muscle atrophy, thereby enhancing the understanding of its pathogenesis and uncovering novel therapeutic strategies.

Gene expression differences associated with intrinsic hindfoot muscle loss in the jerboa, Jaculus jaculus.

Vertebrate animals that run or jump across sparsely vegetated habitats, such as horses and jerboas, have reduced the number of distal limb bones, and many have lost most or all distal limb muscle. We previously showed that nascent muscles are present in the jerboa hindfoot at birth and that these myofibers are rapidly and completely lost soon after by a process that shares features with pathological skeletal muscle atrophy. Here, we apply an intra- and interspecies differential RNA-Seq approach, comparing jerboa and mouse muscles, to identify gene expression differences associated with the initiation and progression of jerboa hindfoot muscle loss. We show evidence for reduced hepatocyte growth factor and fibroblast growth factor signaling and an imbalance in nitric oxide signaling; all are pathways that are necessary for skeletal muscle development and regeneration. We also find evidence for phagosome formation, which hints at how myofibers may be removed by autophagy or by nonprofessional phagocytes without evidence for cell death or immune cell activation. Last, we show significant overlap between genes associated with jerboa hindfoot muscle loss and genes that are differentially expressed in a variety of human muscle pathologies and rodent models of muscle loss disorders. All together, these data provide molecular insight into the process of evolutionary and developmental muscle loss in jerboa hindfeet.

Tumour-induced alterations in single-nucleus transcriptome of atrophying muscles indicate enhanced protein degradation and reduced oxidative metabolism.

BACKGROUND: Tumour-induced skeletal muscle wasting in the context of cancer cachexia is a condition with profound implications for patient survival. The loss of muscle mass is a significant clinical obstacle and is linked to reduced tolerance to chemotherapy and increased frailty. Understanding the molecular mechanisms driving muscle atrophy is crucial for the design of new therapeutics. METHODS: Lewis lung carcinoma tumours were utilized to induce cachexia and muscle atrophy in mice. Single-nucleus libraries of the tibialis anterior (TA) muscle from tumour-bearing mice and their non-tumour-bearing controls were constructed using 10X Genomics applications following the manufacturer's guidelines. RNA sequencing results were analysed with Cell Ranger software and the Seurat R package. Oxygen consumption of mitochondria isolated from TA muscle was measured using an Oroboros O2k-FluoRespirometer. Mouse primary myotubes were treated with a recombinant ectodysplasin A2 (EDA-A2) protein to activate EDA-A2 receptor (EDA2R) signalling and study changes in gene expression and oxygen consumption. RESULTS: Tumour-bearing mice were sacrificed while exhibiting moderate cachexia. Average TA muscle weight was reduced by 11% (P = 0.0207) in these mice. A total of 12 335 nuclei, comprising 6422 nuclei from the control group and 5892 nuclei from atrophying muscles, were studied. The analysis of single-nucleus transcriptomes identified distinct myonuclear gene signatures and a shift towards type IIb myonuclei. Muscle atrophy-related genes, including Atrogin1, MuRF1 and Eda2r, were upregulated in these myonuclei, emphasizing their crucial roles in muscle wasting. Gene set enrichment analysis demonstrated that EDA2R activation and tumour inoculation led to similar expression patterns in muscle cells, including the stimulation of nuclear factor-kappa B, Janus kinase-signal transducer and activator of transcription and transforming growth factor-beta pathways and the suppression of myogenesis and oxidative phosphorylation. Muscle oxidative metabolism was suppressed by both tumours and EDA2R activation. CONCLUSIONS: This study identified tumour-induced transcriptional changes in muscle tissue at single-nucleus resolution and highlighted the negative impact of tumours on oxidative metabolism. These findings contribute to a deeper understanding of the molecular mechanisms underlying muscle wasting.

Identification of a novel nonsense SLC16A2 gene mutation in an infant with severe neurologic phenotype: A case report.

RATIONALE: Allan-Herndon-Dudley syndrome (AHDS) results from a pathogenic variant in the hemizygous subunit of the SLC16A2 gene, which encodes monocarboxylate transporter 8 and follows an X-linked recessive pattern. AHDS manifests as neuropsychomotor developmental delay, intellectual disability, movement disorders, and thyroid hormone abnormalities. It is frequently misdiagnosed as cerebral palsy or hypothyroidism. PATIENT CONCERNS: A 9-month-old male infant exhibited poor head control, hypodynamia, motor retardation, hypertonic limbs, and thyroid abnormalities. Despite levothyroxine supplementation and rehabilitation therapy, no improvements were observed. Whole-exome sequencing identified a novel nonsense mutation in SLC16A2 (c.124G > T, p.E42X), which unequivocally established the diagnosis. DIAGNOSES: AHDS was confirmed. INTERVENTIONS: Levothyroxine treatment commenced early in infancy, followed by 3 months of rehabilitation therapy, starting at 5 months of age. The combined administration of levothyroxine and methimazole was initiated at 1 year and 10 months of age, respectively. OUTCOMES: While improvements were noted in thyroid hormone levels, neurological developmental delays persisted. LESSONS: AHDS should be considered in patients presenting with atypical neurological features and thyroid hormone abnormalities such as elevated triiodothyronine and decreased thyroxine levels. The early utilization of exome sequencing aids in prompt diagnosis. The identified SLC16A2 nonsense mutation correlates with severe neurological phenotypes and adds to the spectrum of genetic variations associated with AHDS.

KLF10: a point of convergence in cancer cachexia.

PURPOSE OF THE REVIEW: Cancer-associated cachexia is a wasting syndrome entailing loss in body mass and a shortened life expectancy. There is currently no effective treatment to abrogate this syndrome, which leads to 20-30% of deaths in patients with cancer. While there have been advancements in defining signaling factors/pathways in cancer-induced muscle wasting, targeting the same in the clinic has not been as successful. Krüppel-like factor 10 (KLF10), a transcription factor implicated in muscle regulation, is regulated by the transforming growth factor-beta signaling pathway. This review proposes KLF10 as a potential convergence point of diverse signaling pathways involved in muscle wasting. RECENT FINDINGS: KLF10 was discovered as a target of transforming growth factor-beta decades ago but more recently it has been shown that deletion of KLF10 rescues cancer-induced muscle wasting. Moreover, KLF10 has also been shown to bind key atrophy genes associated with muscle atrophy in vitro . SUMMARY: There is an elevated need to explore targets in cachexia, which will successfully translate into the clinic. Investigating a convergence point downstream of multiple signaling pathways might hold promise in developing effective therapies for cachexia.

AAV-NRIP gene therapy ameliorates motor neuron degeneration and muscle atrophy in ALS model mice.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is characterized by progressive motor neuron (MN) degeneration, leading to neuromuscular junction (NMJ) dismantling and severe muscle atrophy. The nuclear receptor interaction protein (NRIP) functions as a multifunctional protein. It directly interacts with calmodulin or α-actinin 2, serving as a calcium sensor for muscle contraction and maintaining sarcomere integrity. Additionally, NRIP binds with the acetylcholine receptor (AChR) for NMJ stabilization. Loss of NRIP in muscles results in progressive motor neuron degeneration with abnormal NMJ architecture, resembling ALS phenotypes. Therefore, we hypothesize that NRIP could be a therapeutic factor for ALS. METHODS: We used SOD1 G93A mice, expressing human SOD1 with the ALS-linked G93A mutation, as an ALS model. An adeno-associated virus vector encoding the human NRIP gene (AAV-NRIP) was generated and injected into the muscles of SOD1 G93A mice at 60 days of age, before disease onset. Pathological and behavioral changes were measured to evaluate the therapeutic effects of AAV-NRIP on the disease progression of SOD1 G93A mice. RESULTS: SOD1 G93A mice exhibited lower NRIP expression than wild-type mice in both the spinal cord and skeletal muscle tissues. Forced NRIP expression through AAV-NRIP intramuscular injection was observed in skeletal muscles and retrogradely transduced into the spinal cord. AAV-NRIP gene therapy enhanced movement distance and rearing frequencies in SOD1 G93A mice. Moreover, AAV-NRIP increased myofiber size and slow myosin expression, ameliorated NMJ degeneration and axon terminal denervation at NMJ, and increased the number of α-motor neurons (α-MNs) and compound muscle action potential (CMAP) in SOD1 G93A mice. CONCLUSIONS: AAV-NRIP gene therapy ameliorates muscle atrophy, motor neuron degeneration, and axon terminal denervation at NMJ, leading to increased NMJ transmission and improved motor functions in SOD1 G93A mice. Collectively, AAV-NRIP could be a potential therapeutic drug for ALS.

Dystrophin S3059 phosphorylation partially attenuates denervation atrophy in mouse tibialis anterior muscles.

The dystrophin protein has well-characterized roles in force transmission and maintaining membrane integrity during muscle contraction. Studies have reported decreased expression of dystrophin in atrophying muscles during wasting conditions, and that restoration of dystrophin can attenuate atrophy, suggesting a role in maintaining muscle mass. Phosphorylation of S3059 within the cysteine-rich region of dystrophin enhances binding between dystrophin and ß-dystroglycan, and mimicking phosphorylation at this site by site-directed mutagenesis attenuates myotube atrophy in vitro. To determine whether dystrophin phosphorylation can attenuate muscle wasting in vivo, CRISPR-Cas9 was used to generate mice with whole body mutations of S3059 to either alanine (DmdS3059A) or glutamate (DmdS3059E), to mimic a loss of, or constitutive phosphorylation of S3059, on all endogenous dystrophin isoforms, respectively. Sciatic nerve transection was performed on these mice to determine whether phosphorylation of dystrophin S3059 could attenuate denervation atrophy. At 14 days post denervation, atrophy of tibialis anterior (TA) but not gastrocnemius or soleus muscles, was partially attenuated in DmdS3059E mice relative to WT mice. Attenuation of atrophy was associated with increased expression of ß-dystroglycan in TA muscles of DmdS3059E mice. Dystrophin S3059 phosphorylation can partially attenuate denervation-induced atrophy, but may have more significant impact in less severe modes of muscle wasting.

Epigenetic control of skeletal muscle atrophy.

Skeletal muscular atrophy is a complex disease involving a large number of gene expression regulatory networks and various biological processes. Despite extensive research on this topic, its underlying mechanisms remain elusive, and effective therapeutic approaches are yet to be established. Recent studies have shown that epigenetics play an important role in regulating skeletal muscle atrophy, influencing the expression of numerous genes associated with this condition through the addition or removal of certain chemical modifications at the molecular level. This review article comprehensively summarizes the different types of modifications to DNA, histones, RNA, and their known regulators. We also discuss how epigenetic modifications change during the process of skeletal muscle atrophy, the molecular mechanisms by which epigenetic regulatory proteins control skeletal muscle atrophy, and assess their translational potential. The role of epigenetics on muscle stem cells is also highlighted. In addition, we propose that alternative splicing interacts with epigenetic mechanisms to regulate skeletal muscle mass, offering a novel perspective that enhances our understanding of epigenetic inheritance's role and the regulatory network governing skeletal muscle atrophy. Collectively, advancements in the understanding of epigenetic mechanisms provide invaluable insights into the study of skeletal muscle atrophy. Moreover, this knowledge paves the way for identifying new avenues for the development of more effective therapeutic strategies and pharmaceutical interventions.

Myogenic microRNAs as Therapeutic Targets for Skeletal Muscle Mass Wasting in Breast Cancer Models.

Breast cancer is the type of cancer with the highest prevalence in women worldwide. Skeletal muscle atrophy is an important prognostic factor in women diagnosed with breast cancer. This atrophy stems from disrupted skeletal muscle homeostasis, triggered by diminished anabolic signalling and heightened inflammatory conditions, culminating in an upregulation of skeletal muscle proteolysis gene expression. The importance of delving into research on modulators of skeletal muscle atrophy, such as microRNAs (miRNAs), which play a crucial role in regulating cellular signalling pathways involved in skeletal muscle protein synthesis and degradation, has been recognised. This holds true for conditions of homeostasis as well as pathologies like cancer. However, the determination of specific miRNAs that modulate skeletal muscle atrophy in breast cancer conditions has not yet been explored. In this narrative review, we aim to identify miRNAs that could directly or indirectly influence skeletal muscle atrophy in breast cancer models to gain an updated perspective on potential therapeutic targets that could be modulated through resistance exercise training, aiming to mitigate the loss of skeletal muscle mass in breast cancer patients.