Project description:Skeletal muscle myofibers, categorized into slow-twitch (type I) and fast-twitch (type II) fibers based on myosin heavy chain (MHC) isoforms, exhibit varying fatigue resistance and metabolic reliance. Type I myofibers are fatigue-resistant with high mitochondrial density and oxidative metabolism, while Type II myofibers fatigue quickly due to glycolytic metabolism and fewer mitochondria. Endurance training induces remodeling of myofiber and mitochondrial, increasing slow-twitch myofibers and enhancing mitochondrial oxidative capacity, improving muscle fitness. In our study, conducted using single-cell techniques, we delved deeply into the transcriptomic differences between type I and type IIb myofibers. In response to endurance training, type I myofibers exhibited heightened signals in essential adaptive responses, such as fatty acid oxidation, mitochondrial biogenesis, and protein synthesis, compared to type IIb myofibers. By analyzing untrained myofibers, we identified specific signaling pathways that explain the differences in their responses to endurance training. These findings provide nuanced insights into the molecular mechanisms governing endurance adaptations in fast and slow-twitch muscles, offering valuable guidance for tailored exercise routines and potential therapeutic interventions.
Project description:Loss of muscle mass and function—a hallmark of skeletal muscle aging—is known as sarcopenia. Moreover, mammalian aging is reportedly driven by loss of epigenetic information. However, the effect of epigenetic alterations on skeletal muscle homeostasis is unknown. In this study, we show that chronic elevation of global DNA methylation results in a myopathy-like phenotype and age-related changes in skeletal muscle. Overexpression of muscle de novo methyltransferase 3a (Dnmt3a) increased central nucleus-positive myofibers, predominantly in fast-twitch myofibers, and shifted muscle fiber type to stress-resistant slow-twitch myofibers, accompanied by increased inflammatory and senescent signatures, decreased mitochondrial OXPHOS complex I protein level, and reduced basal autophagy in skeletal muscle. Chronic Dnmt3a overexpression decreased muscle mass and strength, and impaired tolerance to endurance exercise with age. This age-related decline in endurance exercise capacity was accompanied by an augmented inflammatory signature in a manner that is enhanced with age and promoted muscle atrophy. Network analysis identified Akt1 as a potential hub gene. Dnmt3a expression not only reduced sensitivity to starvation-induced muscle atrophy by suppressing the FoxO-regulated autophagy and ubiquitin–proteasome systems, but also reduced the restorability from starvation-induced muscle atrophy. These data suggest that increased global DNA methylation disrupts skeletal muscle homeostasis, promotes age-related muscle atrophy, and reduces muscle metabolic elasticity.
Project description:Loss of muscle mass and function—a hallmark of skeletal muscle aging—is known as sarcopenia. Moreover, mammalian aging is reportedly driven by loss of epigenetic information. However, the effect of epigenetic alterations on skeletal muscle homeostasis is unknown. In this study, we show that chronic elevation of global DNA methylation results in a myopathy-like phenotype and age-related changes in skeletal muscle. Overexpression of muscle de novo methyltransferase 3a (Dnmt3a) increased central nucleus-positive myofibers, predominantly in fast-twitch myofibers, and shifted muscle fiber type to stress-resistant slow-twitch myofibers, accompanied by upregulation of chemokine and immune system-related genes and reduced basal autophagy in skeletal muscle. Dnmt3a overexpression reduced muscle androgen receptor signaling, decreased muscle mass and strength, and impaired tolerance to endurance exercise with age. Network analysis identified Akt1 as a potential hub gene. Dnmt3a expression reduced sensitivity to starvation-induced muscle atrophy by suppressing the FoxO-regulated autophagy and ubiquitin–proteasome systems. These data suggest that increased global DNA methylation disrupts skeletal muscle homeostasis, promotes age-related decline in muscle function, and reduces muscle plasticity.
Project description:Background: skeletal muscle is a complex, versatile tissue composed of a variety of functionally diverse fiber types. Although the biochemical, structural and functional properties of myofibers have been the subject of intense investigation for the last decades, understanding molecular processes regulating fiber type diversity is still complicated by the heterogeneity of cell types present in the whole muscle organ. Methodology/Principal Findings: we have produced a first catalogue of genes expressed in mouse slow-oxidative (type 1) and fast-glycolytic (type 2B) fibers through transcriptome analysis at the single fiber level (microgenomics). Individual fibers were obtained from murine soleus and EDL muscles and initially classified by myosin heavy chain isoform content. Gene expression profiling on high density DNA oligonucleotide microarrays showed that both qualitative and quantitative improvements were achieved, compared to results with standard muscle homogenate. First, myofiber profiles were virtually free from non-muscle transcriptional activity. Second, thousands of muscle-specific genes were identified, leading to a better definition of gene signatures in the two fiber types as well as the detection of metabolic and signaling pathways that are differentially activated in specific fiber types. Several regulatory proteins showed preferential expression in slow myofibers. Discriminant analysis revealed novel genes that could be useful for fiber type functional classification. Conclusions/Significance: as gene expression analyses at the single fiber level significantly increased the resolution power, this innovative approach would allow a better understanding of the adaptive transcriptomic transitions occurring in myofibers under physiological and pathological conditions.
Project description:Background: Skeletal muscle myocytes have evolved into slow and fast-twitch types. These types are functionally distinct as a result of differential gene and protein expression. However, an understanding of the complexity of gene and protein variation between myofibers is unknown. Methods: We performed deep, whole cell, single cell RNA-seq on intact and fragments of skeletal myocytes from the mouse flexor digitorum brevis muscle. We compared the genomic expression data of 171 of these cells with two human proteomic datasets. The first was a spatial proteomics survey of mosaic patterns of protein expression utilizing the Human Protein Atlas (HPA) and the HPASubC tool. The second was a mass-spectrometry (MS) derived proteomic dataset of single human muscle fibers. Immunohistochemistry and RNA-ISH were used to understand variable expression. Results: scRNA-seq identified three distinct clusters of myocytes (a slow/fast 2A cluster and two fast 2X clusters). Utilizing 1,605 mosaic patterned proteins from visual proteomics, and 596 differentially expressed proteins by MS methods, we explore this fast 2X division. Only 36 genes/proteins were mosaic across all three studies, of which nine are newly described as variable between fast/slow twitch myofibers. An additional 414 genes/proteins were identified by two methods. Immunohistochemistry and RNA-ISH generally validated variable expression across methods presumably due to species-related differences. Conclusions: In this first integrated proteogenomic analysis of mature skeletal muscle myocytes we validate the main fiber types and greatly expand the known repertoire of twitch-type specific genes/proteins. We also demonstrate the importance of integrating genomic and proteomic datasets.
Project description:SILAC based protein correlation profiling using size exclusion of protein complexes derived from Mus musculus tissues (Heart, Liver, Lung, Kidney, Skeletal Muscle, Thymus)
Project description:SILAC based protein correlation profiling using size exclusion of protein complexes derived from seven Mus musculus tissues (Heart, Brain, Liver, Lung, Kidney, Skeletal Muscle, Thymus)
Project description:Skeletal muscle is composed of both slow-twich oxidative myofibers and fast-twitch glycolytic myofibers that differentially impact muscle metabolism, function, and eventually whole-body physiology. In the present study, we find that the mesodermal transcription factor T-box 15 (Tbx15) is highly and specifically expressed in glycolytic myofibers. Ablation of Tbx15 in vivo leads to a decrease in muscle size due to a decrease in the number of glycolytic fibers, associated with a small increase in the number of oxidative fibers. This shift in fiber composition results in muscles with slower myofiber contraction and relaxation, and also results in decreased whole-body oxygen consumption, decreased spontaneous activity, increased adiposity, and glucose intolerance. In order to identify genes regulated by Tbx15, we utilized C2C12 myoblasts with either a stable retroviral over-expression or stable lentiviral knockdown of Tbx15. RNA was extracted and biotin labelled complementary RNA (cRNA) was prepared from three independent transfections of the four stable C2C12 myoblast cell lines: shTbx15, shGFP, pBABE-Empty-puro, pBABE-Tbx15-puro. Cells were collected at 90% confluency, and subjected to microarray analysis. Affymetrix M430 2.0 Chips were used.