CHCHD4-TRIAP1 regulation of innate immune signaling mediates skeletal muscle adaptation to exercise
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ABSTRACT: Exercise training can stimulate the formation of fatty acid oxidizing slow-twitch skeletal muscle fibers which are inversely correlated with obesity, but the molecular mechanism underlying this transformation requires further elucidation. Here, we report that the downregulation of the mitochondrial disulfide relay carrier CHCHD4 in skeletal muscle by exercise training decreases the import of TP53-regulated inhibitor of apoptosis 1 (TRIAP1) into mitochondria, which reduces cardiolipin levels and promotes VDAC oligomerization. The subsequent release of mtDNA into the cytosol activates innate immune signaling through cGAS and NFKB, downregulating MyoD and promoting the formation of oxidative slow-twitch fibers. In mice, CHCHD4 haploinsufficiency was sufficient to activate this pathway, leading to increased oxidative muscle fibers and decreased fat accumulation with aging. The identification of a specific mediator regulating muscle fiber transformation provides an opportunity to understand further the molecular underpinnings of complex metabolic conditions such as obesity and could have therapeutic implications.
Project description:Global microarray (HG U133 Plus 2.0) was used for the first time to investigate the effects of resistance exercise on the transcriptome in slow-twitch myosin heavy chain (MHC) I and fast-twitch MHC IIa muscle fibers of young and old women. Vastus lateralis muscle biopsies were obtained pre and 4hrs post resistance exercise in the beginning (untrained state) and at the end (trained state) of a 12 wk progressive resistance training program.
Project description:Global microarray (HG U133 Plus 2.0) was used for the first time to investigate the effects of resistance exercise on the transcriptome in slow-twitch myosin heavy chain (MHC) I and fast-twitch MHC IIa muscle fibers of young and old women. Vastus lateralis muscle biopsies were obtained pre and 4hrs post resistance exercise in the beginning (untrained state) and at the end (trained state) of a 12 wk progressive resistance training program. A total of 14 females were included in this investigation. The participants included 8 young (23±2y) and 6 old (85±1y) females. All subjects participated in 12 wks of progressive resistance training consisting of bilateral knee extensions with 3x10 reps at 70% of 1-RM, and 3d/wk for a total of 36 training sessions. Vastus lateralis biopsies were obtained in conjunction with the 1st and 36th (last) training session and included a basal biopsy and another biopsy 4hrs post the resistance exercise session. From each biopsy sample, we isolated individual muscle fibers. After myosin isoform identification of isolated fibers (SDS-PAGE), RNA extraction of 20 MHC I and 20 MHC IIa muscle fibers per biopsy sample followed. Thus, each resulting sample contained total RNA from 20 muscle fibers of identical fiber type (MHC I or MHC IIa). A total of 70 samples were analyzed on separate microarray chips, and samples were not pooled between subjects. The study design allowed us to examine the acute effects of resistance exercise on the transcriptome in MHC I and MHC IIa muscle fibers in the untrained and trained state.
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:Skeletal muscle plays an important role in the health-promoting effects of exercise training, yet the underlying mechanisms are not fully elucidated. Proteomics of skeletal muscle is challenging due to presence of non-muscle tissues and existence of different fiber types confounding the results. This can be circumvented by analysis of pure fibers; however this requires isolation of fibers from fresh tissues. We developed a workflow enabling proteomics analysis of isolated muscle fibers from freeze-dried muscle biopsies and identified >4000 proteins. We investigated effects of exercise training on the pool of slow and fast muscle fibers. Exercise altered expression of >500 proteins irrespective of fiber type covering several metabolic processes, mainly related to mitochondria. Furthermore, exercise training altered proteins involved in regulation of post-translational modifications, transcription, Ca++ signaling, fat, and glucose metabolism in a fiber type-specific manner. Our data serves as a valuable resource for elucidating molecular mechanisms underlying muscle performance and health. Finally, our workflow offers methodological advancement allowing proteomic analyses of already stored freeze-dried human muscle biopsies.
Project description:Skeletal muscle is highly developed after birth, consisting of glycolytic fast- and oxidative slow-twitch fibers; however, the mechanisms of fiber type-specific differentiation are poorly understood. Here, we found an unexpected role for mitochondrial fission in the differentiation of fast-twitch oxidative fibers. Depletion of the mitochondrial fission factor dynamin-related protein 1 (Drp1) in mouse skeletal muscle and cultured myotubes resulted in the specific reduction of fast-twitch muscle fibers independently of respiratory function. Altered mitochondrial fission caused the activation of the Akt/mammalian target of rapamycin (mTOR) pathway via the mitochondrial accumulation of mTOR complex 2 (mTORC2), and rapamycin administration rescued the reduction of fast-twitch fibers in vivo and in vitro. Under Akt/mTOR activation, the mitochondria-related cytokine growth differentiation factor-15 was upregulated, which repressed fast-twitch fiber differentiation. Our findings reveal a novel role for mitochondrial dynamics in the activation of mTORC2 on mitochondria, resulting in the differentiation of muscle fibers.
Project description:A single bout of exercise induces changes in gene expression in skeletal muscle. Regular exercise results in an adaptive response involving changes in muscle architecture and biochemistry, and is an effective way to manage and prevent common human diseases such as obesity, cardiovascular disorders and type II diabetes. Our study is a transcriptome-wide analysis of skeletal muscle tissue in a large cohort of untrained Thoroughbred horses before and after a bout of high-intensity exercise and again after an extended period of training. We hypothesized that regular high-intensity exercise training primes the transcriptome for the demands of high-intensity exercise.
Project description:Regular physical activity is a key concept associated with a variety of health-related outcomes and successful ageing. While many of the beneficial effects of physical activity are undisputed, much of the adaptive mechanisms that lead to these benefits are not yet known. The skeletal muscle is a key contributor to physical performance and is also the target organ for many of the adaptive processes associated with exercise. Skeletal muscle is highly plastic, and changes in physical activity lead to a plethora of adaptive processes that, when repeated over time, result in structural and functional adaptations. Here we use single cell sequencing in humans to outline the effects of physical activity on cellular composition and cell type-specific processes in skeletal muscle. We show that myogenic cells in human skeletal muscle can be divided into three groups characterized by different degrees of cell maturation, and that exercise stimulates subpopulation of undifferentiated stem/progenitor myogenic cells to mature toward slow- or fast-twitch fibers. The cell type-specific adaptive mechanisms induced by exercise presented here contribute to the understanding of the skeletal muscle adaptations triggered by physical activity and may ultimately have implications for physiological and pathological processes affecting skeletal muscle, such as sarcopenia, cachexia, and glucose homeostasis.
Project description:We sequenced mRNA from embryonic heart of zebrafish larvae 4 days post fertilization, adult heart of 6-month-old WIK fish, and adult muscle of adult fish consisting of both fast-twitch and slow-twitch fibers.
Project description:This experiment was conducted to identify target microRNAs of the peroxisome proliferator-activated receptor (PPAR) in skeletal muscle of transgenic mice that overexpressed PPARalpha or PPARbeta. We have recently demonstrated that skeletal muscle-specific PPARb transgenic (MCK-PPARb) mice exhibit increased exercise endurance, whereas MCK-PPARa mice have reduced exercise performance. Accordingly, we sought to determine whether PPARb and PPARa drive distinct programs involved in muscle fiber type determination. Myosin heavy chain (MHC) immunohistochemical staining of soleus muscle revealed a marked increase in type 1 fibers in the MCK-PPARb muscle compared to non-transgenic (NTG) littermates but a profound reduction in MCK-PPARa muscle. miRNA profiling revealed that levels of miR-208b and miR-499 were increased in MCK-PPARb muscle but reduced in MCK-PPARa muscle. miR-208b and miR-499, which are embedded in the Myh7 and Myh7b genes, respectively, have been shown previously to regulate slow-twitch muscle genes. Lastly, combined inhibition of miR-208b and miR-499 abolished the enhancing effects of PPARb on MHC1 expression in skeletal myotubes, while forced expression of miR-499 in MCK-PPARa muscle completely reversed the type 1 fiber program and exercise capacity. Taken together, these findings demonstrate that miR-208b and miR-499 are necessary to mediate the effects of PPARb and PPARa on muscle fiber type determination. Comparison of microRNA expression from soleus muscles isolated from wild-type (non-transgenic (NTG)) and PPARalpha-overexpressing (MCK-PPARa) mice, and comparison of microRNA expression from soleus muscles isolated from wild-type (NTG) and PPARbeta-overexpressing (MCK-PPARb) mice. Three replicates of each are analyzed.
Project description:Amyotrophic lateral sclerosis (ALS) is a lethal motor neuron disease that progressively debilitates neuronal cells that control voluntary muscle activity. In a mouse model of ALS that expresses mutated human superoxide dismutase 1 (SOD1-G93A) skeletal muscle is one of the tissues affected early by mutant SOD1 toxicity. Fast-twitch and slow-twitch muscles are differentially affected in ALS patients and in the SOD1-G93A model, fast-twitch muscles being more vulnerable. We used miRNA microarrays to investigate miRNA alterations in fast-twitch (EDL) and slow-twitch (soleus) skeletal muscles of symptomatic SOD1-G93A animals and their age-matched wild type littermates.