Project description:Disuse atrophy is a common clinical phenomenon which significantly impacts muscle function and activities of daily living. In this study, we did expression profiling to identify transcriptional pathways associated with muscle remodeling in a clinical model of disuse. Keywords: Differentiation design 28 Skeletal muscle biopsies from the medial gastrocnemius in patients with an ankle fracture (4 patients, 8 profiles) and from healthy volunteers (2 subjects, 4 profiles) subjected to 4-11 days of mobilization, as well as from the non-immobilized contralateral legs (16 profiles).
Project description:Short-term bed rest is used to simulate muscle disuse in humans. In our previous reports, we found that 5d of bed rest induced a ~4% loss of skeletal muscle mass in OLD (60-79 y) but not YOUNG (18-28 y) subjects. Identifying muscle transcriptional events in response to bed rest and age-related differences will help identify therapeutic targets to offset muscle loss in vulnerable older adult populations. Skeletal muscle dysregulation during bed rest in the old may be driven by alterations in molecules related to fibrosis, inflammation, and cell adhesion. This information may aide in the development of mechanistic-based therapies to combat muscle atrophy during short-term disuse. Short-term muscle disuse is also characterized by skeletal muscle insulin resistance, though this response is divergent across subjects. The mechanisms regulating inactivity-induced insulin resistance between populations that are more or less susceptible to disuse-induced insulin resistance are not known, and delineated by age. High Susceptibility participants were uniquely characterized with muscle gene responses described by a decrease in pathways responsible for lipid uptake and oxidation, decreased capacity for triglyceride export (APOB), increased lipogenesis (i.e., PFKFB3, FASN), and increased amino acid export (SLC43A1).
Project description:Disuse atrophy is a common clinical phenomenon which significantly impacts muscle function and activities of daily living. In this study, we did expression profiling to identify transcriptional pathways associated with muscle remodeling in a clinical model of disuse. Keywords: Differentiation design
Project description:To identify atrophy genes directly targeted by Bcl-3 transactivator at a genome wide level, we performed whole transcript expression array and ChIP-seq for muscles from weight bearing or 5-day hind limb unloaded mice. Genes that showed increased expression with unloading and a Bcl-3 peak in the promoter (from ChIP-seq data) were considered as Bcl-3 direct targets during disuse atrophy. Using ChIP array, we identified 241 direct targets for Bcl-3. Our data describe Bcl-3 as a global regulator both of the proteolysis and the change in energy metabolism that are essential components of muscle atrophy due to disuse. Disuse skeletal muscle atrophy was induced by hind limb unloading. Weight bearing (WB) or 5-day hind limb unloaded (HU) muscles were harvested for total RNA isolation and processed for whole transcript expression profiling. We chose to examine gene expression and Bcl-3 binding from 5-day unloaded muscles because our previous time course study of disuse atrophy suggested that most genes are differentially regulated at this time point, and thus, would best represent the time for Bcl-3 binding to the gene targets of the NF-kB transcriptional network.
Project description:A mechanistic understanding of the age-related impairment to skeletal muscle regrowth following disuse atrophy as well as therapies to augment recovery in the aged are currently lacking. Mechanotherapy in the form of cyclic compressive loading has been shown to benefit skeletal muscle under a variety of paradigms, but not during the recovery from disuse in aged muscle. To determine whether mechanotherapy promotes extracellular matrix (ECM) remodeling, a critical aspect of muscle recovery after atrophy, we performed single cell RNA sequencing (scRNA-seq) of gastrocnemius muscle cell populations, stable isotope tracing of intramuscular collagen, and histology of the ECM in adult and aged rats recovering from disuse, with and without mechanotherapy. ECM remodeling-related gene expression in fibro-adipose progenitor cells (FAPs) was absent in aged compared to adult muscle following 7 days of recovery, and instead were enriched in chemoattractant genes. There was a significantly lower expression of genes related to phagocytic activity in aged macrophages during recovery, despite enriched chemokine gene expression of numerous stromal cell populations, including FAPs and endothelial cells. Mechanotherapy reprogrammed the transcriptomes of both FAPs and macrophages in aged muscle recovering from disuse to restore ECM-and phagocytosis-related gene expression, respectively. Stable isotope labeling of intramuscular collagen and histological evaluation confirmed mechanotherapy-mediated remodeling of the ECM in aged muscle recovering from disuse. In summary, our results highlight mechanisms underlying age-related impairments during the recovery from disuse atrophy and promote mechanotherapy as an intervention that reprograms the muscle transcriptional environment more similar to that of adult skeletal muscle.
Project description:The primary goal of this study was to determine the role of AMPKalpha during disuse atrophy. Skeletal muscle-specific tamoxifen-inducible AMPKlpha1/alpha2 double knockout (KO) mice were generated and KO was induced for 4 weeks. After 2 weeks of KO, mice were hindlimb unloaded (HU) for 2 weeks to induce atrophy or maintained ambulatory (AMB). We observed that AMPKalpha double KO impaired skeletal muscle transcriptional profiles that may have carried over with HU.
Project description:Hibernation is energy saving adaptation involving suppression of activity to survive in highly seasonal environments. Immobility and disuse generate muscle loss in most mammalian species. In contrast to other mammals, bears and ground squirrels demonstrate limited muscle atrophy over the physical inactivity of winter hibernation. This suggests that hibernating mammals have adaptive mechanisms to prevent disuse muscle atrophy. To identify common transcriptional program underlying molecular mechanisms preventing muscle loss, we conducted a large-scale gene expression screening in hind limb muscles comparing hibernating and summer active black bears and arctic ground squirrels by the use of custom 9,600 probe cDNA microarrays. The molecular pathway analysis showed an elevated proportion of overexpressed genes involved in all stages of protein biosynthesis and ribosome biogenesis in muscle of both species during hibernation that implies induction of translation at different hibernation states. The induction of protein biosynthesis likely contributes to attenuation of disuse muscle atrophy through prolonged periods of immobility and starvation. This adaptive mechanism allows hibernating mammals to maintain full musculoskeletal function and preserve mobility during and immediately after hibernation, thus promoting survival. The lack of directional changes in genes of protein catabolic pathways does not support the importance of metabolic suppression for preserving muscle mass during winter. Coordinated reduction of multiply genes involved in oxidation reduction and glucose metabolism detected in both species is consistent with metabolic suppression and lower energy demand in skeletal muscle during inactivity of hibernation. Black bears sampled during winter hibernation were compared with the animals sampled during summer. Muscle tissue were hybridized on a custom 12,800 cDNA probe nylon membrane microarray platform . Six hibernating and six summer active bears were studied in the experiment.
Project description:Muscle atrophy is a physiological response to disuse and malnutrition, but hibernating bears are largely resistant to this phenomenon. Unlike other mammals, they efficiently reabsorb amino acids from urine, periodically activate muscle contraction, and their adipocytes differentially responds to insulin. The contribution of myocytes to the reduced atrophy remains largely unknown. Here we show how metabolism and atrophy signaling are regulated in skeletal muscle of hibernating grizzly bear.
Project description:Disuse-induced muscle atrophy is a common clinical problem observed mainly in older adults, intensive care units patients, or astronauts. Previous studies presented biological sex divergence in progression of disuse-induced atrophy along with differential changes in molecular mechanisms possibly underlying muscle atrophy. The aim of this study was to perform transcriptomic profiling of male and female mice during the onset and progression of unloading disuse-induced atrophy. Male and female mice underwent hindlimb unloading (HU) for 24, 48, 72 and 168h (n=8/group). Muscles were weighed for each cohort and gastrocnemius was used for RNA-sequencing analysis. Females exhibited muscle loss as early as 24h of HU, while males after 168h of HU. In males, pathways related to proteasome degradation were upregulated throughout 168-h HU, while in females these pathways were upregulated up to 72-h HU. Lcn2, a gene contributing to regulation of myogenesis, was upregulated by 6.46–19.86-fold across all time points in females only. A reverse expression of Fosb, a gene related to muscle degeneration, was observed between males (4.27-fold up) and females (4.57-fold down) at 24-h HU. Mitochondrial pathways related to TCA cycle were highly downregulated at 168h of HU in males, while in females this downregulation was less pronounced. Collagen-related pathways were consistently downregulated throughout 168-h HU only in females, suggesting a potential biological sex-specific protective mechanism against disuse-induced fibrosis. In conclusion, females may have protection against HU-induced skeletal muscle mitochondrial degeneration and fibrosis through transcriptional mechanisms, although they may be more vulnerable to HU-induced muscle wasting compared to males.
Project description:Hibernation is energy saving adaptation involving suppression of activity to survive in highly seasonal environments. Immobility and disuse generate muscle loss in most mammalian species. In contrast to other mammals, bears and ground squirrels demonstrate limited muscle atrophy over the physical inactivity of winter hibernation. This suggests that hibernating mammals have adaptive mechanisms to prevent disuse muscle atrophy. To identify common transcriptional program underlying molecular mechanisms preventing muscle loss, we conducted a large-scale gene expression screening in hind limb muscles comparing hibernating and summer active black bears and arctic ground squirrels by the use of custom 9,600 probe cDNA microarrays. The molecular pathway analysis showed an elevated proportion of overexpressed genes involved in all stages of protein biosynthesis and ribosome biogenesis in muscle of both species during hibernation that implies induction of translation at different hibernation states. The induction of protein biosynthesis likely contributes to attenuation of disuse muscle atrophy through prolonged periods of immobility and starvation. This adaptive mechanism allows hibernating mammals to maintain full musculoskeletal function and preserve mobility during and immediately after hibernation, thus promoting survival. The lack of directional changes in genes of protein catabolic pathways does not support the importance of metabolic suppression for preserving muscle mass during winter. Coordinated reduction of multiply genes involved in oxidation reduction and glucose metabolism detected in both species is consistent with metabolic suppression and lower energy demand in skeletal muscle during inactivity of hibernation. Arctic ground squirrels sampled during winter hibernation were compared with the animals sampled during summer. Muscle was hybridized on a custom 9,600 probes nylon membrane microarray platform. Ten in late torpor, four in early arousal, then in late arousal were studied in experiments.