Aging disrupts gene expression timing during muscle regeneration
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ABSTRACT: Skeletal muscle function and regenerative capacity decline during aging, yet factors driving these changes are incompletely understood. Muscle regeneration requires temporally coordinated transcriptional programs to drive myogenic stem cells to activate, proliferate, fuse to form myofibers, and to mature myonuclei, restoring muscle function after injury. We assessed global changes in myogenic transcription programs distinguishing muscle regeneration in aged mice from young mice by comparing pseudotime trajectories from single-nucleus RNA sequencing of myogenic nuclei. Aging-specific differences in coordinating myogenic transcription programs necessary for restoring muscle function occur following muscle injury, likely contributing to compromised regeneration in aged mice. Differences in pseudotime alignment of myogenic nuclei when comparing aged to young mice via Dynamic Time-Warping revealed pseudotemporal differences becoming progressively more severe as regeneration proceeds. Disruptions in timing of myogenic gene expression programs may contribute to incomplete skeletal muscle regeneration and declines in muscle function as organisms age.
Project description:Skeletal muscle regeneration is driven by the interaction of myogenic and non-myogenic cells. In aging, regeneration is impaired due to dysfunctions of myogenic and non-myogenic cells, but this is not understood comprehensively. We collected an integrated atlas of 273,923 single-cell transcriptomes from muscles of young, old, and geriatric mice (~5, 20, 26 months-old) at six time-points following myotoxin injury. We identified eight cell types, including T and NK cells and macrophage subtypes, that displayed accelerated or delayed response dynamics between ages. Through pseudotime analysis, we observed myogenic cell states and trajectories specific to old and geriatric ages. To explain these age differences, we assessed cellular senescence by scoring experimentally derived and curated gene-lists. This pointed to an elevation of senescent-like subsets specifically within muscle stem cells in aged muscles in both single-cell and spatial transcriptomics datasets. This resource provides a holistic portrait of the altered cellular states underlying skeletal muscle regenerative decline across mouse lifespan.
Project description:Healthy skeletal muscle can regenerate after ischaemic, mechanical, or toxin-induced injury, but ageing impairs that regeneration potential. This has been largely attributed to dysfunctional satellite cells and reduced myogenic capacity. Understanding which signalling pathways are associated with reduced myogenesis and impaired muscle regeneration can provide valuable information about the mechanisms driving muscle ageing and prompt the development of new therapies. To investigate this, we developed a high-throughput in vitro model to assess muscle regeneration in chemically injured C2C12 and human myotube-derived young and aged myoblast cultures. We observed a reduced regeneration capacity of aged cells, as indicated by an attenuated recovery towards preinjury myotube size and myogenic fusion index at the end of the regeneration period, in comparison with younger muscle cells that were fully recovered. RNA-sequencing data showed significant enrichment of KEGG signalling pathways, PI3K-Akt, and downregulation of GO processes associated with muscle development, differentiation, and contraction in aged but not in young muscle cells. Data presented here suggests that repair in response to in vitro injury is impaired in aged vs. young muscle cells. Our study establishes a framework that enables further understanding of the factors underlying impaired muscle regeneration in older age.
Project description:Skeletal muscle regeneration is driven by the interaction of myogenic and non-myogenic cells. In aging, regeneration is impaired due to various dysfunctions of myogenic and non-myogenic cells, but this is not understood comprehensively. We collected an integrated atlas of 273,923 single-cell transcriptomes from muscles of young, old, and geriatric mice (4, 20, 26 months-old) at six time-points following myotoxin injury. We identified eight cell types, including T and NK cells and multiple macrophage subtypes that displayed accelerated or delayed dynamics between ages. Through pseudotime analysis, we observed myogenic cell states and trajectories specific to old and geriatric ages. To explain these age differences, we assessed cellular senescence by scoring experimentally derived and curated gene-lists, which pinpointed stalled senescent-like subsets specifically within the self-renewing muscle stem cells as elevated in older muscles. This resource provides a holistic portrait of the altered cellular states underlying skeletal muscle regeneration decline across mouse lifespan.
Project description:Traumatic injury often results in muscle loss and impairment, which is worsened under aged and diseased conditions. Activation of resident stem cells or transplantation of myogenic stem cells can promote muscle regeneration. However, major challenges remain in harvesting sufficient autologous myogenic stem cells and expanding such cells efficiently for muscle regeneration therapies. Here, we identified a chemical cocktail that selectively induced a robust expansion of myogenic stem cells from readily-obtainable dermal cells and from muscle stromal cells. By differential plating and lineage tracing, we showed that Pax7+ cells were the major source for chemical-induced myogenic stem cells (CiMCs). We further performed single-cell RNA sequencing (scRNA-seq) analysis to characterize the transcriptomic profile of CiMCs and demonstrate a specific expansion of myogenic cells from heterogeneous dermal cell population. Upon transplantation into the injured muscle, CiMCs were efficiently engrafted and improved functional muscle regeneration in both adult and aged mice. In addition, CiMC transplantation rescued muscle function in mice with Duchenne muscular dystrophy (DMD). Furthermore, an in situ therapeutic modality using this cocktail was developed by loading the chemical cocktail into injectable nanoparticles, which enabled a sustained release of the cocktail in injured muscle and a local expansion of resident satellite cells for muscle regeneration in adult and aged mice. These findings will lead to the development of novel in vitro and in situ stem cell therapies for effective skeletal muscle repair.
Project description:Traumatic injury often results in muscle loss and impairment, which is worsened under aged and diseased conditions. Activation of resident stem cells or transplantation of myogenic stem cells can promote muscle regeneration. However, major challenges remain in harvesting sufficient autologous myogenic stem cells and expanding such cells efficiently for muscle regeneration therapies. Here, we identified a chemical cocktail that selectively induced a robust expansion of myogenic stem cells from readily-obtainable dermal cells and from muscle stromal cells. By differential plating and lineage tracing, we showed that Pax7+ cells were the major source for chemical-induced myogenic stem cells (CiMCs). We further performed single-cell RNA sequencing (scRNA-seq) analysis to characterize the transcriptomic profile of CiMCs and demonstrate a specific expansion of myogenic cells from heterogeneous dermal cell population. Upon transplantation into the injured muscle, CiMCs were efficiently engrafted and improved functional muscle regeneration in both adult and aged mice. In addition, CiMC transplantation rescued muscle function in mice with Duchenne muscular dystrophy (DMD). Furthermore, an in situ therapeutic modality using this cocktail was developed by loading the chemical cocktail into injectable nanoparticles, which enabled a sustained release of the cocktail in injured muscle and a local expansion of resident satellite cells for muscle regeneration in adult and aged mice. These findings will lead to the development of novel in vitro and in situ stem cell therapies for effective skeletal muscle repair.
Project description:Skeletal muscle holds an intrinsic capability of growth and regeneration both in physiological conditions and in case of injury. Chronic muscle illnesses, generally caused by genetic and acquired factors, lead to deconditioning of the skeletal muscle structure and function, and are associated with a significant loss in muscle mass. At the same time, progressive muscle wasting is a hallmark of aging. Given the paracrine properties of myogenic stem cells, extracellular vesicle-derived signals have been studied for their potential implication in both the pathogenesis of degenerative neuromuscular diseases and as a possible therapeutic target. In this study, we screened the content of extracellular vesicles from animal models of muscle hypertrophy and muscle wasting associated with chronic disease and aging. Analysis of the transcriptome, protein cargo and microRNAs (miRNAs) allowed us to identify a hypertrophic miRNA signature amenable for targeting muscle wasting, consisting of miR-1 and miR-208a. We tested this signature among others in vitro on mesoangioblasts (MABs), vessel-associated adult stem cells, and we observed an increase in the efficiency of myogenic differentiation. Furthermore, injections of miRNA-treated MABs in aged mice resulted in an improvement in skeletal muscle features, such as muscle weight, strength and cross-sectional area compared to controls. Overall, we provide evidence that the extracellular vesicle-derived miRNA signature we identified enhances the myogenic potential of myogenic stem cells.
Project description:Muscle denervation due to injury, disease or aging results in impaired motor function. Restoring neuromuscular communication requires axonal regrowth and regeneration of neuromuscular synapses. Muscle activity inhibits neuromuscular synapse regeneration. The mechanism by which muscle activity regulates regeneration of synapses is poorly understood. Dach2 and Hdac9 are activity-regulated transcriptional co-repressors that are highly expressed in innervated muscle and suppressed following muscle denervation. Here, we report that Dach2 and Hdac9 inhibit regeneration of neuromuscular synapses. Importantly, we identified Myog and Gdf5 as muscle-specific Dach2/Hdac9-regulated genes that stimulate neuromuscular regeneration in denervated muscle. Interestingly, Gdf5 also stimulates presynaptic differentiation and inhibits branching of regenerating neurons. Finally, we found that Dach2 and Hdac9 suppress miR206 expression, a microRNA involved in enhancing neuromuscular regeneration. RNAseq on innervated and 3 day denervated adult soleus muscle from wildtype mice is compared with that from 3 day denervated soleus muscle from Dach2/Hdac9 deleted mice to identify Dach2/Hdac9-regulated genes.
Project description:Skeletal muscle tissue plays a key metabolic role in the organism, partly via signaling to other tissues. Intercellular signaling via small extracellular vesicles (sEV) is emerging as an important mechanism in homeostasis, regeneration and disease, but the roles of sEV derived from muscle cells are poorly defined. In a culture model of physiologically relevant muscle cell states, we observed quantitative differences in secretion of sEV with size ~150 nm and marker profile (Alix, TSG101, flotillin-1, CD9) consistent with exosomes. Unexpectedly, rates of sEV secretion were reversibly increased as myoblasts entered and exited G0, correlating with expression of Kibra, a regulator of EV biogenesis. Perturbation of Kibra led to corresponding alterations of sEV secretion, supporting a role in enhanced sEV biogenesis in G0. Proteomic profiling of sEV revealed a set of proteins common to all muscle cell states, as well as state-specific proteins. Functionally, donor sEV purified from all muscle cell states were able to activate a Wnt reporter in target cells, suggesting preservation of signaling capability. However, only G0-derived sEV were able to induce endogenous myogenic markers and phenotypic differentiation to myotubes. Taken together, we provide evidence that quiescence in myogenic cells is associated with quantitative and qualitative alterations in sEV secretion and signaling function. Given the enhanced secretion and unique signaling properties of sEV from G0 muscle cells in culture, we propose that sEV produced by quiescent muscle stem cells may play an important role in vivo, during muscle homeostasis and regeneration.
Project description:Abstract: Transcription factors (TFs) play key roles in regulating differentiation and function of stem cells, including muscle satellite cells (MuSCs), a resident stem cell population responsible for postnatal regeneration of the skeletal muscle. Sox11 belongs to the Sry-related HMG-box (SOX) family of TFs that play diverse roles in stem cell behavior and tissue specification. Analysis of single-cell RNA-sequencing (scRNA-seq) datasets identify a specific enrichment of Sox11 mRNA in differentiating but not quiescent MuSCs. Consistent with the scRNA-seq data, Sox11 levels increase during differentiation of murine primary myoblasts in vitro. scRNA-seq data comparing muscle regeneration in young and old mice further demonstrate that Sox11 expression is reduced in aged MuSCs. Age-related decline of Sox11 expression is associated with reduced chromatin contacts within the topologically associated domains. Unexpectedly, Myod1Cre-driven deletion of Sox11 in embryonic myoblasts has no effects on muscle development and growth, resulting in apparently healthy muscles that regenerate normally. Pax7CreER or Rosa26CreER driven (MuSC-specific or global) deletion of Sox11 in adult mice similarly has no effects on MuSC differentiation or muscle regeneration. These results identify Sox11 as a novel myogenic differentiation marker with reduced expression in quiescent and aged MuSCs, but the specific function of Sox11 in myogenesis remain to be elucidated.
Project description:During aging, the number and functionality of muscle stem cells (MuSCs) decreases leading to impaired regeneration of aged skeletal muscle. In addition to intrinsic changes in aged MuSCs, extracellular matrix (ECM) proteins deriving from other cell types, e.g., fibrogenic-adipogenic progenitor cells (FAPs), contribute to the aging phenotype of MuSCs and impaired regeneration in the elderly. So far, no comprehensive analysis on how age-dependent changes in the whole skeletal muscle proteome affect MuSC function have been conducted. Here, we investigated age-dependent changes in the proteome of different skeletal muscle types by applying deep quantitative mass spectrometry. We identified 183 extracellular matrix proteins that show different abundances in skeletal muscles of old mice. By integrating single cell sequencing data, we reveal that transcripts of those ECM proteins are mainly expressed in FAPs, suggesting that FAPs are the main contributors to ECM remodelling during aging. We functionally investigated one of those ECM molecules, namely Smoc2, which is aberrantly expressed during aging. We show that Smoc2 levels are elevated during regeneration and that its accumulation in the aged MuSC niche causes impairment of MuSCs function through constant activation of integrin/MAPK signaling. In vivo, supplementation of exogenous Smoc2 hampers the regeneration of young muscles following serial injuries, leading to a phenotype reminiscent of regenerating aged skeletal muscle. Taken together, we provide a comprehensive resource of changes in the composition of the ECM of aged skeletal muscles, we pinpoint the cell types driving these changes, and we identify a new niche protein causing functional impairment of MuSCs thereby hampering the regeneration capacity of skeletal muscles.