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:Loss of muscle mass and strength following disuse followed by impaired muscle recovery likely contribute to sarcopenia in older adults. Metformin and leucine individually have shown positive effects in skeletal muscle during atrophy conditions but have not been evaluated in combination nor under the conditions of disuse atrophy and recovery in aging. The purpose of this study was to determine if a dual treatment of metformin and leucine (MET+LEU) would prevent disuse-induced atrophy and/or promote muscle recovery in aged mice (22-24 mo). We were also interested if these muscle responses correspond to changes in satellite cells and ECM abundance. Aged mice were subjected to 14 days of hindlimb unloading (HU) followed by 7 or 14 days of reloading (7 or 14d RL). Metformin (MET), leucine (LEU), or MET+LEU was administered via drinking water and were compared to Vehicle-treated mice. We observed that MET+LEU increased whole body grip strength, muscle specific force and satellite cell abundance during HU but did not alter muscle size during HU or RL. Moreover, MET+LEU treatment increased ECM turnover driven by a decrease in collagen IV content during 7 and 14d RL. Transcriptome analysis revealed that MET+LEU altered Gene Set Enrichment Analysis hallmark pathways related to inflammation and myogenesis during HU. Together , MET+LEU was able to improve muscle quality during disuse and recovery in aging possibly by increasing muscle satellite cell content and reducing excessive ECM accumulation.
Project description:Aged skeletal muscle is characterized by impaired muscle recovery following disuse and coincides with an impaired muscle pro-inflammatory macrophage response. Macrophage inflammatory status (polarization) is regulated by its metabolic state, but to date, little is understood of macrophage metabolism and its relation to macrophage polarization in the context of muscle recovery and aging. Therefore, the purpose of this study was to thoroughly characterize macrophage metabolism and polarization in aged muscle during early recovery from disuse atrophy using single cell RNA sequencing and functional assays. Young (4-5 mo) and old (20-22 mo) male C57BL/6 mice underwent 14 days of hindlimb unloading followed by 4 days of ambulatory recovery. CD45+ cells were isolated from solei muscles and analyzed using 10x Genomics single cell RNA sequencing. We found that aged M1 macrophage clusters were characterized with an impaired inflammatory and glycolytic transcriptome and this impairment was accompanied by a suppression of HIF-1α and its immediate downstream target GLUT1.
Project description:Microgravity exposure as well as chronic muscle disuse are two of the main causes of physiological adaptive skeletal muscle atrophy in humans and murine animals in physiological condition. The aim of this study was to investigate, at both morphological and global gene expression level, skeletal muscle adaptation to microgravity in mouse soleus and extensor digitorum longus (EDL). Adult male mice C57BL/N6 were flown aboard the BION-M1 biosatellite for 30 days on orbit (BF) or housed in a replicate flight habitat on Earth (BG) as reference flight control. In this study, we investigated for the first time gene expression adaptation to 30 days of microgravity exposure in mouse soleus and EDL, highlighting potential new targets for improvement of countermeasures able to ameliorate or even prevent microgravity-induced atrophy in future spaceflights.
Project description:Rodent hind limb unloading was used as a model for reduced muscle activity and eventual atrophy. After a 10 day period of unloading, mice in this study were “reloaded” for 3 days and regained use of their hind limbs. We report the application of Next-generation sequencing (NGS) technology for high-throughput profiling of mRNA in soleus muscle of adult (6 mo) and aged (22-24 mo) mice. Our goal was to determine the effects of hind limb unloading and reloading on mRNA profiles in soleus muscle and compare between adult and aged mice. We find that there are distinct response in the profile of fatty acid oxidation, TCA cycle, ETC oxidative phosphorylation gene expression patterns in response to unloading and reloading. The repsonses are generally simialr between young and old mice.
Project description:Our laboratory previously demonstrated that perivascular stem/stromal cells (CD146+ pericytes) can effectively recover muscle mass after a period of immobilization in young adult mice. However, cell-based therapies are problematic in aged mouse models due to lack of viability upon transplantation. Therefore, the purpose of this study was to develop a pericyte-based, cell-free strategy to recover muscle mass after disuse in aged mice. Single-cell RNA sequencing (scRNA-Seq) was performed on adult mouse skeletal muscle after two weeks of unilateral hindlimb immobilization, which revealed that muscle-resident pericytes uniquely upregulate the long noncoding RNA Malat1, a negative regulator of Nrf2, and fail to induce antioxidant gene expression in response to reactive oxygen species (ROS; H2O2). This information was used to guide the design of a strategy in which healthy donor pericytes were stimulated with ROS to produce small extracellular vesicles (EVs) that were subsequently transplanted into 4- and 24-26-month-old C57BL/6 mice after two weeks of unilateral hindlimb immobilization. H2O2-primed healthy muscle-derived pericytes produced EVs in culture that effectively reduced restored myofiber CSA in both adult (p=0.009) and aged (p=0.006) muscle after disuse. In contrast, unprimed pericyte-derived EVs did not influence myofiber size. Neither primed, nor unprimed EVs recovered capillary density, yet both stimulated collagen turnover. Healthy ROS-primed pericyte-derived small EVs effectively improve skeletal muscle recovery after immobilization, representing a novel cell-free approach to rebuild muscle mass in older adults after a period of disuse.
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:Arrestin Domain Containing 2 and 3 (Arrdc2/3) are genes whose mRNA contents are decreased in young skeletal muscle following mechanical overload. Arrdc3 is linked to the regulation of signaling pathways in non-muscle cells that could influence skeletal muscle size. Despite a similar amino acid sequence, Arrdc2 function remains undefined. The purpose of this study was to further explore the relationship of Arrdc2/Arrdc3 expression with changes in mechanical load in young and aged muscle and define the effect of Arrdc2/3 expression on myotube diameter. In young and aged mice, mechanical load was decreased using hindlimb suspension while mechanical load was increased by reloading previously unloaded muscle or inducing high force contractions. Arrdc2 and Arrdc3 mRNAs were overexpressed in C2C12 myotubes using adenoviruses. Myotube diameter was determined 48 h post-transfection and RNA sequencing was performed on those samples. Arrdc2 and Arrdc3 mRNA content was higher in the unloaded muscle within 1 day of disuse and remained higher up through 10 days. The induction of Arrdc2 mRNA was more pronounced in aged muscle than young muscle in response to unloading. Reloading previously unloaded muscle of young and aged mice restored Arrdc2 and Arrdc3 levels to ambulatory levels. Increasing mechanical load beyond normal ambulatory levels lowered Arrdc2 but not Arrdc3 mRNA in young and aged muscle. Arrdc2, not Arrdc3, overexpression was sufficient to lower myotube diameter in C2C12 cells in part by altering the transcriptome favoring muscle atrophy. These data are consistent with Arrdc2 contributing to disuse atrophy, particularly in aged muscle.
Project description:Skeletal muscle atrophy is one of the critical issues which elderly people face. The precise mechanism underlying muscle atrophy during aging is not fully understood. In order to identify miRNA whose expression is changed in age-associated muscle atrophy, we performed miRNA expression profiling of skeletal muscles in young and aged rats. Microarray analysis revealed differential miRNA expression in EDL and soleus muscles of aged rats compared with those of young rats. We next investigated whether the age-associated changes of miRNA expression observed in rats were recapitulated in mice and found that the expression level of miR-206 in EDL muscle and that of miR-196a in EDL and soleus muscles were respectively higher and lower in aged rodents than in young rodents. In mouse C2C12 myoblasts and myotubes, introduction of miR-196a decreased the protein level of Forkhead-box transcription factor Foxo1, a known target of miR-196a, indicating that miR-196a may regulate Foxo1 expression also in skeletal muscles. Furthermore, miR-196a overexpression exacerbated cell death caused by an exposure to hydrogen peroxide. Lastly, we demonstrated that expression of Foxo1 was elevated in EDL and soleus muscles of aged mice compared with those of young mice. These results suggest that miRNAs are involved in skeletal muscle atrophy during aging and that decreased miR-196a expression may protect skeletal muscle cells from oxidative stress in part through induction of Foxo1.