Single cell RNA-seq comparing regeneration of young and aged skeletal muscles
Ontology highlight
ABSTRACT: 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:Muscle stem cells (MuSCs) are required for muscle regeneration. In resting muscles, MuSCs are kept in quiescence. After injury, MuSCs undergo rapid activation, proliferation and differentiation to repair damaged muscles. Age-associated impairments in stem cell functions correlate with a decline in somatic tissue regeneration capacity during aging. However, the mechanisms underlying the molecular regulation of adult stem cell aging remain elusive. Here, we obtained quisecent MuSCs from young, old, geriatric mice for high resolution mass spectrometry Bruker timsTOF Pro. By comparison of young proteome to old MuSCs proteome or geriatric MuSC proteome, we identified the pathways that are differentially during aging.
Project description:Skeletal muscle possesses remarkable regenerative ability owing to the resident muscle stem cells (MuSCs). A prominent feature of quiescent MuSCs is a high content of heterochromatin. However, little is known about the mechanisms by which heterochromatin is maintained in MuSCs. We found that the mammalian Hairless (Hr) gene is expressed in quiescent MuSCs. Using a mouse model in which Hr can be specifically ablated in MuSCs, we demonstrate that Hr expression is critical for MuSC function and muscle regeneration. We show that Hr is a histone demethylase antagonist that preserves Histone 3 Lysine 9 trimethylation (H3K9me3) and maintains heterochromatin structure. Loss of Hr results in reduced H3K9me3 levels, reduced heterochromatin, increased susceptibility of MuSCs to genotoxic stress, and the accumulation of DNA damage. Our study not only elucidates the molecular mechanism by which Hr regulates histone demethylases, but also demonstrates the importance of heterochromatin maintenance in stem cell function.
Project description:Skeletal muscle possesses remarkable regenerative ability owing to the resident muscle stem cells (MuSCs). A prominent feature of quiescent MuSCs is a high content of heterochromatin. However, little is known about the mechanisms by which heterochromatin is maintained in MuSCs. We found that the mammalian Hairless (Hr) gene is expressed in quiescent MuSCs. Using a mouse model in which Hr can be specifically ablated in MuSCs, we demonstrate that Hr expression is critical for MuSC function and muscle regeneration. We show that Hr is a histone demethylase antagonist that preserves Histone 3 Lysine 9 trimethylation (H3K9me3) and maintains heterochromatin structure. Loss of Hr results in reduced H3K9me3 levels, reduced heterochromatin, increased susceptibility of MuSCs to genotoxic stress, and the accumulation of DNA damage. Our study not only elucidates the molecular mechanism by which Hr regulates histone demethylases, but also demonstrates the importance of heterochromatin maintenance in stem cell function.
Project description:Adult skeletal muscle regeneration is mainly driven by muscle stem cells (MuSCs), which are highly heterogeneous. Although recent studies have started to characterize the heterogeneity of MuSCs, whether a subset of cells with distinct exists within MuSCs remains unanswered. Here, we found that a population of MuSCs, marked by Gli1 expression, is required for muscle regeneration. The Gli1+ MuSC population displayed advantages in proliferation and differentiation both in vitro and in vivo. Depletion of this population led to delayed muscle regeneration, while transplanted Gli1+ MuSCs supported muscle regeneration more effectively than Gli1- MuSCs. Further analysis revealed that even in the uninjured muscle, Gli1+ MuSCs had elevated mTOR signaling activity, increased cell size and mitochondrial numbers compared to Gli1- MuSCs, indicating Gli1+ MuSCs are displaying the features of primed MuSCs. Moreover, Gli1+ MuSCs greatly contributed to the formation of GAlert cells after muscle injury. Collectively, our findings demonstrate that Gli1+ MuSCs represent a distinct MuSC population which is more active in the homeostatic muscle and enters the cell cycle shortly after injury. This cell population functions as the tissue-resident sentinel that rapidly responds to injury and initiates muscle regeneration.
Project description:Quiescent adult muscle stem cells (MuSCs) regenerate skeletal muscle upon injury throughout life. However, aged skeletal muscles fail to maintain stem cell quiescence, leading to declines in MuSC number and functionality. Although autophagy plays an important role in the maintenance of MuSC quiescence, how quiescent MuSCs and their autophagy levels are maintained throughout life is largely unknown. The current study reveals how GnRH, a hypothalamic hormone, maintains the quiescence of adult MuSCs by preventing the onset of senescence and how the decline of sex steroids in organismal ageing is implicated in MuSC ageing.
Project description:Adult muscle stem cell (MuSC) behavior has been predominantly studied in the context of regeneration, a condition under which MuSCs exit quiescence and replicate upon activation before differentiating and fusing into myocytes. We use single-cell RNA-seq (scRNA-seq) to identify transcriptionally diverse subpopulations of MuSCs after 5 days of a growth stimulus.
Project description:Short-term fasting is beneficial for the regeneration of multiple tissue types. However, the effects of fasting on muscle regeneration are largely unknown. Here we report that fasting slows muscle repair both immediately after the conclusion of fasting as well as after multiple days of refeeding. We show that ketosis, either endogenously produced during fasting or a ketogenic diet, or exogenously administered, promotes a deep quiescent state in MuSCs. Although deep quiescent MuSCs are less poised to activate, slowing muscle regeneration, they have markedly improved survival when facing sources of cellular stress. Further, we show that ketone bodies, specifically b- hydroxybutyrate, directly promote MuSC deep quiescence via a non‐metabolic mechanism. We show that b-hydroxybutyrate functions as an HDAC inhibitor within MuSCs leading to acetylation and activation of an HDAC1 target protein p53. Finally, we demonstrate that p53 activation contributes to the deep quiescence and enhanced resilience observed during fasting.
Project description:In aging, skeletal muscle strength and regenerative capacity declines due, in part, to functional impairment of muscle stem cells MuSCs, yet the underlying mechanisms remain elusive. Here we capitalize on mass-cytometry to identify high CD47 expression as a hallmark of dysfunctional MuSCs CD47hi with impaired regenerative capacity that predominate with aging. The prevalent CD47 hi MuSC subset suppresses the residual functional CD47 lo MuSC subset through a paracrine signaling loop, leading to impaired proliferation. We uncover that elevated CD47 levels on aged MuSCs result from increased U1 snRNA expression, which disrupts alternative polyadenylation. The deficit in aged MuSC function in regeneration can be overcome either by morpholino-mediated blocking of CD47 alternative polyadenylation or antibody blockade of CD47 signaling, leading to improved regeneration in aged mice, with therapeutic implications. Our findings highlight a previously unrecognized age-dependent alteration in CD47 levels and function in MuSCs, which underlies reduced muscle repair in aging.
Project description:During aging, the regenerative capacity of skeletal muscle decreases due to intrinsic changes in muscle stem cells (MuSCs) and alterations in their niche. Here, we used quantitative mass spectrometry to characterize intrinsic changes in the MuSC proteome and remodeling of the MuSC niche during aging. We generated a network connecting age-affected ligands located in the niche and cell surface receptors on MuSCs. Thereby, we revealed signaling via Integrins, Lrp1, Egfr and Cd44 as the major cell communication axes perturbed through aging. We investigated the effect of Smoc2, a secreted protein that accumulates with aging, originating from fibro-adipogenic progenitors. Increased levels of Smoc2 contribute to the aberrant Itgb1/MAPK signaling observed during aging, thereby causing impaired MuSC functionality and muscle regeneration. By connecting changes in the proteome of MuSCs to alterations of their niche, our work will enable a better understanding of how MuSCs are affected during aging.
Project description:During aging, the regenerative capacity of skeletal muscle decreases due to intrinsic changes in muscle stem cells (MuSCs) and alterations in their niche. Here, we used quantitative mass spectrometry to characterize intrinsic changes in the MuSC proteome and remodeling of the MuSC niche during aging. We generated a network connecting age-affected ligands located in the niche and cell surface receptors on MuSCs. Thereby, we revealed signaling via Integrins, Lrp1, Egfr and Cd44 as the major cell communication axes perturbed through aging. We investigated the effect of Smoc2, a secreted protein that accumulates with aging, originating from fibro-adipogenic progenitors. Increased levels of Smoc2 contribute to the aberrant Itgb1/MAPK signaling observed during aging, thereby causing impaired MuSC functionality and muscle regeneration. By connecting changes in the proteome of MuSCs to alterations of their niche, our work will enable a better understanding of how MuSCs are affected during aging.