ABSTRACT: Skeletal muscle tissues are comprised of muscle fibers, muscle stem cells (MuSCs), immune cells, endothelial cells, motor/sensory nerves with Schwann cells, and interstitial mesenchymal cells. Each cell population plays a unique role in muscle physiology and homeostasis. The mesenchymal progenitors in the skeletal muscle have been identified as a subpopulation that reside between muscle fibers, whose role is to coordinate muscle regeneration in a finely tuned manner by supporting the expansion and differentiation of MuSCs. These cells have been referred to as fibro/adipogenic progenitor cells (FAPs), termed according to their differentiation potentials in specific in vitro culture conditions and known to cause fibrous tissue and fatty degeneration under pathological environments and result in compromised muscle function. To gain insight into how Bap1 plays a role in skeletal muscle homeostasis, we performed RNA sequencing analysis using freshly isolated Sca1 positive cells from 1.5-week-old WT or cKO hindlimb muscles
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.
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.
Project description:Purpose: To study the requirement of Osr1 expression for FAP function during skeletal muscle regeneration. Methods: We sequenced total mRNAs isolated from adult FAPs FACS sorted from 3 and 7 day post injured hindlimb skeletal muscle of Ctrl (Osr1flox/+ CAGG Cre+) and Osr1 cKO (Osr1flox/flox CAGG Cre+) mice. Results: Loss of Osr1 leads to pro-fibrotic orientation of FAPs and impairs both FAP-macrophage and FAP-MuSCs communication network resulting in impaired regenerative myogenesis and persistent fibrosis. Conclusions: Osr1 is a key transcriptional regulator of FAP regenerative function protecting FAPs from assuming a detrimental pro-fibrotic and anti-myogenic state.
Project description:Skeletal muscle experiences a decline in lean mass and regenerative potential with age, in part due to intrinsic changes in progenitor cells. However, it remains unclear if age-related changes in progenitors persist across a differentiation trajectory or if new age-related changes manifest in differentiated cells. To investigate this possibility, we performed single cell RNA-seq on muscle mononuclear cells from young and aged mice and profiled muscle stem cells (MuSCs) and fibro/adipose progenitors (FAPs) after differentiation. Differentiation increased the magnitude of age-related change in MuSCs and FAPs, but also masked a subset of age-related changes present in progenitors. Using a dynamical systems approach and RNA velocity, we found that aged MuSCs follow the same differentiation trajectory as young cells, but stall in differentiation near a commitment decision. Our results suggest that age-related changes are plastic across differentiation trajectories and that fate commitment decisions are delayed in aged myogenic cells.
Project description:The purpose of this study is to investigate how GDF10 regulates early myoblast differentiation and fusion. We found that melatonin can enhance fibro-adipogenic progenitors (FAPs) paracrine signaling to support muscle regeneration. Through combining transcriptome analysis and single-cell transcriptome analysis, we identified GDF10 as a type of myogenic factor specifically secreted by FAPs, which plays a beneficial role in promoting muscle fiber development and regeneration. To determine the underlying mechanism by which GDF10 regulates myogenesis, we performed RNA-seq on myoblasts treated with GDF10 or vehicle for 6 hours in vitro. We found that GDF10 promoted myoblast fusion by regulating LKB1-AMPK-MYOG-MYMK signaling during differentiation. In summary, our study revealed novel insights into the mechanism by which melatonin promotes muscle regeneration by mediating the interplay between FAPs and muscle stem cells (MuSCs).
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:The regenerative capacity of skeletal muscle relies on muscle stem cells (MuSCs, or satellite cells) and its niche interactions with different neighboring cells. To understand the cellular diversity within adult skeletal muscle tissue, we harvested mononuclear cells from hindlimb skeletal muscles, sorted into single cells and profiled them by single-cell RNA-seq. To further understand and compare the expression profile between MuSCs and a novel smooth-muscle/mesenchymal-like cells (SMMCs) population, we isolated the two cell types by FACS and profiled them respectively by bulk RNA-seq.
Project description:Skeletal muscle possesses the ability to adapt its size in response to milieus, which is called plasticity. Resistance training induces the increment of muscle mass called muscle hypertrophy. Muscle stem cells (MuSC; also known as muscle stem cells) function to supply new nuclei for myofiber during the overload in muscle. We hypothesize that mesenchymal progenitors (also called FAPs) -derived factor induces MuSC proliferation. In order to identify such factors, RNA-seq of overloaded FAPs were performed.
Project description:Skeletal muscle possesses the ability to adapt its size in response to milieus, which is called plasticity. Resistance training induces the increment of muscle mass called muscle hypertrophy. Muscle stem cells (MuSC; also known as muscle stem cells) function to supply new nuclei for myofiber during the overload in muscle. We found that Yap1 and Taz in mesenchymal progenitors (also called FAPs) are critical for MuSC proliferation in overloaded muscles. We hypothsize that Yap1/Taz-dependent mesenchymal progenitors derived factor induces MuSC proliferation. In order to identify such factors, RNA-seq of overloaded FAPs were performed.
Project description:The female sex hormone estrogens plays a critical role in maintaining muscle mass and muscle stem cell (MuSCs) functions. However, it is still unclear about downstream pathways of estrogens including its receptors that are expressed in both skeletal muscle tissue and MuSCs. To study the specific role of estrogen receptor β (ERβ), one of two main types of estrogen receptors, in skeletal muscle and MuSCs, we generated muscle-specific ERβ-knockout (mKO) mice and muscle stem cell-specific ERβ-knockout (scKO) mice. Here, we show that muscle-specific ERβ-deficient induced decreased muscle strength and fast-type muscle mass in young female mice. Furthermore, muscle stem cell-specific ERβ-deficient young female mice but not male exhibited impaired muscle regeneration ability after acute muscle injury, accompanied by a decreased proliferation rate of muscle stem cells. RNA sequencing analysis showed that the loss of ERβ in muscle stem cells changes the expression of cell cycle associated genes and niche component factors including laminin and collagen. Thus, our characterization of mKO and scKO mice indicate that the estrogen-ERβ pathway is a sex-specific regulatory mechanism that controls both skeletal muscle mass and the proliferation of muscle stem cell in females and could be of importance in a therapeutic context.