Muscle-resident Cells Research Articles

Single-nucleus transcriptomics reveals subsets of degenerative myonuclei after rotator cuff tear-induced muscle atrophy.

Rotator cuff tear (RCT) is the primary cause of shoulder pain and disability and frequently trigger muscle degeneration characterised by muscle atrophy, fatty infiltration and fibrosis. Single-nucleus RNA sequencing (snRNA-seq) was used to reveal the transcriptional changes in the supraspinatus muscle after RCT. Supraspinatus muscles were obtained from patients with habitual shoulder dislocation (n = 3) and RCT (n = 3). In response to the RCT, trajectory analysis showed progression from normal myonuclei to ANKRD1+ myonuclei, which captured atrophy-and fatty infiltration-related regulons (KLF5, KLF10, FOSL1 and BHLHE40). Transcriptomic alterations in fibro/adipogenic progenitors (FAPs) and muscle satellite cells (MuSCs) have also been studied. By predicting cell-cell interactions, we observed communication alterations between myofibers and muscle-resident cells following RCT. Our findings reveal the plasticity of muscle cells in response to RCT and offer valuable insights into the molecular mechanisms and potential therapeutic targets of RCT.

Transcriptional evidence for transient regulation of muscle regeneration by brown adipose transplant in the rotator cuff.

Chronic rotator cuff(RC) injuries can lead to a degenerative microenvironment that favors chronic inflammation, fibrosis, and fatty infiltration. Recovery of muscle structure and function will ultimately require a complex network of muscle resident cells, including satellite cells, fibro-adipogenic progenitors (FAPs), and immune cells. Recent work suggests that signaling from adipose tissue and progenitors could modulate regeneration and recovery of function, particularly promyogenic signaling from brown or beige adipose (BAT). In this study, we sought to identify cellular targets of BAT signaling during muscle regeneration using a RCBAT transplantation mouse model. Cardiotoxin injured supraspinatus muscle had improved mass at 7 days postsurgery (dps) when transplanted with exogeneous BAT. Transcriptional analysis revealed transplanted BAT modulates FAP signaling early in regeneration likely via crosstalk with immune cells. However, this conferred no long-term benefit as muscle mass and function were not improved at 28 dps. To eliminate the confounding effects of endogenous BAT, we transplanted BAT in the "BAT-free" uncoupling protein-1diphtheria toxin fragment A (UCP1-DTA) mouse and here found improved muscle contractile function, but not mass at 28 dps. Interestingly, the transplanted BAT increased fatty infiltration in all experimental groups, implying modulation of FAP adipogenesis during regeneration. Thus, we conclude that transplanted BAT modulates FAP signaling early in regeneration,but does not grant long-term benefits.

Identifying Cell Population Heterogeneity in Cerebral Palsy Muscle

Cerebral Palsy (CP) is a neuromuscular condition that affects movement and muscle tone, and often leads to contractures. Muscle satellite cells (MuSCs) have been shown to decrease in CP, but the overall resident muscle cell populations have not been characterized. Our objective is to identify differences in the cell populations and transcriptomes of muscle biopsies taken from CP and typically developing patients (TD) using single cell RNA sequencing. We hypothesize that cells taken from CP patient muscle will have a different distribution amongst populations. Gene enrichment, psuedotime analysis, subclustering, and interactome analysis were conducted to investigate muscle resident cell populations. The results demonstrated that, while there was not a significant disparity between cell populations of CP and TD muscle, there were differences in the subpopulations of MuSCs and fibro-adipogenic progenitors (FAPs). These results indicate that FAPs from CP patients tend to be more pro-fibrotic and may signal to MuSCs to undergo apoptosis. This study may help to identify molecular and cellular targets for CP therapies. Funding provided by the Hartwell Foundation. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Muscle stem cells as immunomodulator during regeneration.

The skeletal muscle is well known for its remarkable ability to regenerate after injuries. The regeneration is a complex and dynamic process that involves muscle stem cells (also called muscle satellite cells, MuSCs), fibro-adipogenic progenitors (FAPs), immune cells, and other muscle-resident cell populations. The MuSCs are the myogenic cell populaiton that contribute nuclei directly to the regenerated myofibers, while the other cell types collaboratively establish a microenvironment that facilitates myogenesis of MuSCs. The myogenic process includes activation, proliferation and differentiationof MuSCs, and subsequent fusion their descendent mononuclear myocytes into multinuclear myotubes. While the contributions of FAPs and immune cells to this microenvironment have been wellstudied, the influence of MuSCs on other cell types remains poorly understood. This review explores recent evidence supporting the potential role of MuSCs as immunomodulators during muscle regeneration, either through cytokine production or ligand-receptor interactions.

Single-Cell RNA-Sequencing Provides Insight into Skeletal Muscle Evolution during the Selection of Muscle Characteristics.

Skeletal muscle comprises a large, heterogeneous assortment of cell populations that interact to maintain muscle homeostasis, but little is known about the mechanism that controls myogenic development in response to artificial selection. Different pig (Sus scrofa) breeds exhibit distinct muscle phenotypes resulting from domestication and selective breeding. Using unbiased single-cell transcriptomic sequencing analysis (scRNA-seq), the impact of artificial selection on cell profiles is investigated in neonatal skeletal muscle of pigs. This work provides panoramic muscle-resident cell profiles and identifies novel and breed-specific cells, mapping them on pseudotime trajectories. Artificial selection has elicited significant changes in muscle-resident cell profiles, while conserving signs of generational environmental challenges. These results suggest that fibro-adipogenic progenitors serve as a cellular interaction hub and that specific transcription factors identified here may serve as candidate target regulons for the pursuit of a specific muscle phenotype. Furthermore, a cross-species comparison of humans, mice, and pigs illustrates the conservation and divergence of mammalian muscle ontology. The findings of this study reveal shifts in cellular heterogeneity, novel cell subpopulations, and their interactions that may greatly facilitate the understanding of the mechanism underlying divergent muscle phenotypes arising from artificial selection.

Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis

Inclusion body myositis (IBM) is unique across the spectrum of idiopathic inflammatory myopathies (IIM) due to its distinct clinical presentation and refractoriness to current treatment approaches. One explanation for this resistance may be the engagement of cell-autonomous mechanisms that sustain or promote disease progression of IBM independent of inflammatory activity. In this study, we focused on senescence of tissue-resident cells as potential driver of disease. For this purpose, we compared IBM patients to non-diseased controls and immune-mediated necrotizing myopathy patients. Histopathological analysis suggested that cellular senescence is a prominent feature of IBM, primarily affecting non-myogenic cells. In-depth analysis by single nuclei RNA sequencing allowed for the deconvolution and study of muscle-resident cell populations. Among these, we identified a specific cluster of fibro-adipogenic progenitors (FAPs) that demonstrated key hallmarks of senescence, including a pro-inflammatory secretome, expression of p21, increased β-galactosidase activity, and engagement of senescence pathways. FAP function is required for muscle cell health with changes to their phenotype potentially proving detrimental. In this respect, the transcriptomic landscape of IBM was also characterized by changes to the myogenic compartment demonstrating a pronounced loss of type 2A myofibers and a rarefication of acetylcholine receptor expressing myofibers. IBM muscle cells also engaged a specific pro-inflammatory phenotype defined by intracellular complement activity and the expression of immunogenic surface molecules. Skeletal muscle cell dysfunction may be linked to FAP senescence by a change in the collagen composition of the latter. Senescent FAPs lose collagen type XV expression, which is required to support myofibers’ structural integrity and neuromuscular junction formation in vitro. Taken together, this study demonstrates an altered phenotypical landscape of muscle-resident cells and that FAPs, and not myofibers, are the primary senescent cell type in IBM.

The Contribution of Muscle Innate Immunity to Uremic Cachexia.

Protein energy wasting (PEW) is a common complication both in chronic kidney disease (CKD) and end-stage kidney disease (ESKD). Of note, PEW is one of the stronger predictors of morbidity and mortality in this patient population. The pathogenesis of PEW involves several mechanisms, including anorexia, insulin resistance, acidosis and low-grade inflammation. In addition, "sterile" muscle inflammation contributes to PEW at an advanced CKD stage. Both immune and resident muscle cells can activate innate immunity; thus, they have critical roles in triggering "sterile" tissue inflammation. Toll-like receptor 4 (TLR4) can detect endogenous danger-associated molecular patterns generated or retained in blood in uremia and induce a sterile muscle inflammatory response via NF-κB in myocytes. In addition, TLR4, though the activation of the NLRP3 inflammasome, links the sensing of metabolic uremic stress in muscle to the activation of pro-inflammatory cascades, which lead to the production of IL-1β and IL-18. Finally, uremia-induced accelerated cell senescence is associated with a secretory phenotype that favors fibrosis in muscle. Targeting these innate immune pathways could lead to novel therapies for CKD-related PEW.

Single cell sequencing maps skeletal muscle cellular diversity as disease severity increases in dystrophic mouse models

Duchenne muscular dystrophy (DMD) is caused by out-of-frame mutations in the DMD gene resulting in the absence of a functional dystrophin protein, leading to a devastating and progressive lethal muscle-wasting disease. Little is known about cellular heterogeneity as disease severity increases. Advances in single-cell RNA sequencing (scRNA-seq) enabled us to explore skeletal muscle-resident cell populations in healthy, dystrophic, and severely dystrophic mouse models. We found increased frequencies of activated fibroblasts, fibro-adipogenic progenitor cells, and pro-inflammatory macrophages in dystrophic gastrocnemius muscles and an upregulation of extracellular matrix genes on endothelial cells in dystrophic and severely dystrophic muscles. We observed a pronounced risk of clotting, especially in the severely dystrophic mice with increased expression of plasminogen activator inhibitor-1 in endothelial cells, indicating endothelial cell impairment as disease severity increases. This work extends our understanding of the severe nature of DMD which should be considered when developing single or combinatorial approaches for DMD.

A glitch in the matrix: the pivotal role for extracellular matrix remodeling during muscle hypertrophy.

Multinuclear muscle fibers are the most voluminous cells in skeletal muscle and the primary drivers of growth in response to loading. Outside the muscle fiber, however, is a diversity of mononuclear cell types that reside in the extracellular matrix (ECM). These muscle-resident cells are exercise-responsive and produce the scaffolding for successful myofibrillar growth. Without proper remodeling and maintenance of this ECM scaffolding, the ability to mount an appropriate response to resistance training in adult muscles is severely hindered. Complex cellular choreography takes place in muscles following a loading stimulus. These interactions have been recently revealed by single-cell explorations into muscle adaptation with loading. The intricate ballet of ECM remodeling involves collagen production from fibrogenic cells and ECM modifying signals initiated by satellite cells, immune cells, and the muscle fibers themselves. The acellular collagen-rich ECM is also a mechanical signal-transducer and rich repository of growth factors that may directly influence muscle fiber hypertrophy once liberated. Collectively, high levels of collagen expression, deposition, and turnover characterize a well-trained muscle phenotype. The purpose of this review is to highlight the most recent evidence for how the ECM and its cellular components affect loading-induced muscle hypertrophy. We also address how the muscle fiber may directly take part in ECM remodeling, and whether ECM dynamics are rate limiting for muscle fiber growth.

Decoding the transcriptome of denervated muscle at single-nucleus resolution.

BackgroundSkeletal muscle exhibits remarkable plasticity under both physiological and pathological conditions. One major manifestation of this plasticity is muscle atrophy that is an adaptive response to catabolic stimuli. Because the heterogeneous transcriptome responses to catabolism in different types of muscle cells are not fully characterized, we applied single‐nucleus RNA sequencing (snRNA‐seq) to unveil muscle atrophy related transcriptional changes at single nucleus resolution.MethodsUsing a sciatic denervation mouse model of muscle atrophy, snRNA‐seq was performed to generate single‐nucleus transcriptional profiles of the gastrocnemius muscle from normal and denervated mice. Various bioinformatics analyses, including unsupervised clustering, functional enrichment analysis, trajectory analysis, regulon inference, metabolic signature characterization and cell–cell communication prediction, were applied to illustrate the transcriptome changes of the individual cell types.ResultsA total of 29 539 muscle nuclei (normal vs. denervation: 15 739 vs. 13 800) were classified into 13 nuclear types according to the known cell markers. Among these, the type IIb myonuclei were further divided into two subgroups, which we designated as type IIb1 and type IIb2 myonuclei. In response to denervation, the proportion of type IIb2 myonuclei increased sharply (78.12% vs. 38.45%, P < 0.05). Concomitantly, trajectory analysis revealed that denervated type IIb2 myonuclei clearly deviated away from the normal type IIb2 myonuclei, indicating that this subgroup underwent robust transcriptional reprogramming upon denervation. Signature genes in denervated type IIb2 myonuclei included Runx1, Gadd45a, Igfn1, Robo2, Dlg2, and Sh3d19 (P < 0.001). The gene regulatory network analysis captured a group of atrophy‐related regulons (Foxo3, Runx1, Elk4, and Bhlhe40) whose activities were enhanced (P < 0.01), especially in the type IIb2 myonuclei. The metabolic landscape in the myonuclei showed that most of the metabolic pathways were down‐regulated by denervation (P < 0.001), while some of the metabolic signalling, such as glutathione metabolism, was specifically activated in the denervated type IIb2 myonulei. We also investigated the transcriptomic alterations in the type I myofibres, muscle stem cells, fibro‐adipogenic progenitors, macrophages, endothelial cells and pericytes and characterized their signature responses to denervation. By predicting the cell–cell interactions, we observed that the communications between myofibres and muscle resident cells were diminished by denervation.ConclusionsOur results define the myonuclear transition, metabolic remodelling, and gene regulation networks reprogramming associated with denervation‐induced muscle atrophy and illustrate the molecular basis of the heterogeneity and plasticity of muscle cells in response to catabolism. These results provide a useful resource for exploring the molecular mechanism of muscle atrophy.

Abstract 3810: Muscle invasion produced drug-resistant and bone metastatic prostate cancer

Abstract Overtreatment of prostate cancer is a significant source of patient morbidity and cost. The human prostate is bounded by a smooth muscle capsule, and aggressive tumors invade through the muscle layer, called extracapsular extension (ECE), to escape organ confinement. The presence of ECE defines pT3a pathologic stage and is associated with increased risk of biochemical recurrence, metastases, and cancer-specific mortality. Although muscle invasion is required for ECE and metastatic spread, both the invasive tumor network phenotypes and muscle responses are understudied. The goal was to probe the molecular events of ECE to understand this critical step in metastasis. Muscle invasion of prostate cancer cell lines was tested in vivo by injecting cells into the peritoneal cavity of male NSG mice. The cells colonize the inferior surface of the muscular respiratory diaphragm and invade through to the superior surface. To explore transcriptional regulators, we performed whole genome RNAseq on cells from three compartments: (1) “Inferior” non-invading cells on the underside of the diaphragm; (2) “Muscle-resident” cells that have invaded and now reside within the diaphragm muscle; and (3) “Superior” cells that have completely traversed the diaphragm. Tumors cells reaching the superior side of the diaphragm were established ex vivo as polyclonal cell lines termed the “KM” series. RNAseq reveals 1,482 differentially expressed sequences (DES) between Inferior and Muscle-resident cells, 253 DES between Muscle-resident and Superior cells, and 896 DES between Inferior and Superior cells (padj &amp;lt;0.05, |fold change| ≥ 1.3). Further, we identified 84 DES that overlap between the Superior vs. Muscle-resident and Inferior vs. Muscle-resident groups, highlighting candidate gene changes unique to cancer cells in a muscle microenvironment. Importantly, 4,076 differentially expressed, mouse-specific RNA sequences (padj &amp;lt; 0.05, |fold change| ≥ 2.0) highlight pathways within muscle that respond to the presence of invasive tumors. Strikingly, the KM series have aggressive features including newly acquired bone metastasis and resistance to a taxane. The gene expression patterns imply a dominant effect of the muscle microenvironment in evoking a new and transient tumor transcriptional response as revealed by the DESs. Independent of this response, the KM sub-populations successfully navigating the muscle were more aggressive in laboratory assays, including bone metastatic potential and chemotherapeutic resistance. These studies support the hypothesis that successful invasion into and through a contractile muscle layer results in aggressive cancer cells. Using the in vivo assay provides the unique ability to parse out unexplored patterns of changes that occur in early, muscle-invasive disease to improve prostate cancer patient selection for definitive treatment versus active surveillance. Citation Format: Kendra D. Marr, Beatrice S. Knudsen, Jaime M. Gard, Malia Bird, Raymond B. Nagle, Anne E. Cress. Muscle invasion produced drug-resistant and bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3810.

Targeting Muscle-Resident Single Cells Through in vivo Electro-Enhanced Plasmid Transfer in Healthy and Compromised Skeletal Muscle

Skeletal muscle is composed of syncytial muscle fibers, and by various mononucleated cellular types, such as muscle stem cells, immune cells, interstitial and stromal progenitors. These cell populations play a crucial role during muscle regeneration, and alterations of their phenotypic properties have been associated with defective repair and fibrosis in aging and dystrophic muscle. Studies involving in vivo gene modulation are valuable to investigate the mechanisms underlining cell function and dysfunction in complex pathophysiological settings. Electro-enhanced transfer of plasmids using square-wave generating devices represents a cost-effective approach that is widely used to transport DNA to muscle fibers efficiently. Still, it is not clear if this method can also be applied to mononuclear cells present in muscle. We demonstrate here that it is possible to efficiently deliver DNA into different muscle–resident cell populations in vivo. We evaluated the efficiency of this approach not only in healthy muscle but also in muscles of aging and dystrophic animal models. As an exemplificative application of this method, we used a strategy relying on a reporter gene-based plasmid containing regulatory sequences from the collagen 1 locus, and we determined collagen expression in various cell types reportedly involved in the production of fibrotic tissue in the dystrophic settings. The results enclosed in this manuscript reveal the suitability in applying electro-enhanced transfer of plasmid DNA to mononucleated muscle-resident cells to get insights into the molecular events governing diseased muscle physiology.

Cellular and molecular modulation of rotator cuff muscle pathophysiology.

Rotator cuff (RC) tendon tears are common shoulder injuries that result in irreversible and persistent degeneration of the associated muscles, which is characterized by severe inflammation, atrophy, fibrosis, and fatty infiltration. Although RC muscle degeneration strongly dictates the overall clinical outcomes, strategies to stimulate RC muscle regeneration have largely been overlooked to date. In this review, we highlight the current understanding of the cellular processes that coordinate muscle regeneration, and the roles of muscle resident cells, including immune cells, fibroadipogenic progenitors, and muscle satellite cells in the pathophysiologic regulation of RC muscles following injury. This review also provides perspectives for potential therapies to alleviate the hallmarks of RC muscle degeneration to address current limitations in postsurgical recovery.

Exercise/Resistance Training and Muscle Stem Cells.

Skeletal muscle has attracted attention as endocrine organ, because exercise-dependent cytokines called myokines/exerkines are released from skeletal muscle and are involved in systemic functions. While, local mechanical loading to skeletal muscle by exercise or resistance training alters myofiber type and size and myonuclear number. Skeletal muscle-resident stem cells, known as muscle satellite cells (MuSCs), are responsible for the increased number of myonuclei. Under steady conditions, MuSCs are maintained in a mitotically quiescent state but exit from that state and start to proliferate in response to high physical activity. Alterations in MuSC behavior occur when myofibers are damaged, but the lethal damage to myofibers does not seem to evoke mechanical loading-dependent MuSC activation and proliferation. Given that MuSCs proliferate without damage, it is unclear how the different behaviors of MuSCs are controlled by different physical activities. Recent studies demonstrated that myonuclear number reflects the size of myofibers; hence, it is crucial to know the properties of MuSCs and the mechanism of myonuclear accretion by MuSCs. In addition, the elucidation of mechanical load-dependent changes in muscle resident cells, including MuSCs, will be necessary for the discovery of new myokines/exerkines and understating skeletal muscle diseases.

Agent-based model provides insight into the mechanisms behind failed regeneration following volumetric muscle loss injury.

Skeletal muscle possesses a remarkable capacity for repair and regeneration following a variety of injuries. When successful, this highly orchestrated regenerative process requires the contribution of several muscle resident cell populations including satellite stem cells (SSCs), fibroblasts, macrophages and vascular cells. However, volumetric muscle loss injuries (VML) involve simultaneous destruction of multiple tissue components (e.g., as a result of battlefield injuries or vehicular accidents) and are so extensive that they exceed the intrinsic capability for scarless wound healing and result in permanent cosmetic and functional deficits. In this scenario, the regenerative process fails and is dominated by an unproductive inflammatory response and accompanying fibrosis. The failure of current regenerative therapeutics to completely restore functional muscle tissue is not surprising considering the incomplete understanding of the cellular mechanisms that drive the regeneration response in the setting of VML injury. To begin to address this profound knowledge gap, we developed an agent-based model to predict the tissue remodeling response following surgical creation of a VML injury. Once the model was able to recapitulate key aspects of the tissue remodeling response in the absence of repair, we validated the model by simulating the tissue remodeling response to VML injury following implantation of either a decellularized extracellular matrix scaffold or a minced muscle graft. The model suggested that the SSC microenvironment and absence of pro-differentiation SSC signals were the most important aspects of failed muscle regeneration in VML injuries. The major implication of this work is that agent-based models may provide a much-needed predictive tool to optimize the design of new therapies, and thereby, accelerate the clinical translation of regenerative therapeutics for VML injuries.

The interaction between SARS-CoV-2 and ACE2 may have consequences for skeletal muscle viral susceptibility and myopathies.

The interaction between SARS-CoV-2 and ACE2 may have consequences for skeletal muscle viral susceptibility and myopathies.

A reference single-cell transcriptomic atlas of human skeletal muscle tissue reveals bifurcated muscle stem cell populations

Single-cell RNA-sequencing (scRNA-seq) facilitates the unbiased reconstruction of multicellular tissue systems in health and disease. Here, we present a curated scRNA-seq dataset of human muscle samples from 10 adult donors with diverse anatomical locations. We integrated ~ 22,000 single-cell transcriptomes using Scanorama to account for technical and biological variation and resolved 16 distinct populations of muscle-resident cells using unsupervised clustering of the data compendium. These cell populations included muscle stem/progenitor cells (MuSCs), which bifurcated into discrete “quiescent” and “early-activated” MuSC subpopulations. Differential expression analysis identified transcriptional profiles altered in the activated MuSCs including genes associated with aging, obesity, diabetes, and impaired muscle regeneration, as well as long non-coding RNAs previously undescribed in human myogenic cells. Further, we modeled ligand-receptor cell-communication interactions and observed enrichment of the TWEAK-FN14 pathway in activated MuSCs, a characteristic signature of muscle wasting diseases. In contrast, the quiescent MuSCs have enhanced expression of the EGFR receptor, a recognized human MuSC marker. This work provides a new benchmark reference resource to examine human muscle tissue heterogeneity and identify potential targets in MuSC diversity and dysregulation in disease contexts.

Single-cell analyses uncover granularity of muscle stem cells.

Satellite cells are the main muscle-resident cells responsible for muscle regeneration. Much research has described this population as being heterogeneous, but little is known about the different roles each subpopulation plays. Recent advances in the field have utilized the power of single-cell analysis to better describe and functionally characterize subpopulations of satellite cells as well as other cell groups comprising the muscle tissue. Furthermore, emerging technologies are opening the door to answering as-yet-unresolved questions pertaining to satellite cell heterogeneity and cell fate decisions.

Potential Therapies Using Myogenic Stem Cells Combined with Bio-Engineering Approaches for Treatment of Muscular Dystrophies.

Muscular dystrophies (MDs) are a group of heterogeneous genetic disorders caused by mutations in the genes encoding the structural components of myofibres. The current state-of-the-art treatment is oligonucleotide-based gene therapy that restores disease-related protein. However, this therapeutic approach has limited efficacy and is unlikely to be curative. While the number of studies focused on cell transplantation therapy has increased in the recent years, this approach remains challenging due to multiple issues related to the efficacy of engrafted cells, source of myogenic cells, and systemic injections. Technical innovation has contributed to overcoming cell source challenges, and in recent studies, a combination of muscle resident stem cells and gene editing has shown promise as a novel approach. Furthermore, improvement of the muscular environment both in cultured donor cells and in recipient MD muscles may potentially facilitate cell engraftment. Artificial skeletal muscle generated by myogenic cells and muscle resident cells is an alternate approach that may enable the replacement of damaged tissues. Here, we review the current status of myogenic stem cell transplantation therapy, describe recent advances, and discuss the remaining obstacles that exist in the search for a cure for MD patients.

High-Dimensional Single-Cell Cartography Reveals Novel Skeletal Muscle-Resident Cell Populations.

Adult tissue repair and regeneration require stem-progenitor cells that can self-renew and generate differentiated progeny. Skeletal muscle regenerative capacity relies on muscle satellite cells (MuSCs) and their interplay with different cell types within the niche. However, our understanding of skeletal muscle tissue cellular composition is limited. Here, using a combined approach of single-cell RNA sequencing and mass cytometry, we precisely mapped 10 different mononuclear cell types in adult mouse muscle. We also characterized gene signatures and determined key discriminating markers of each cell type. We identified two previously understudied cell populations in the interstitial compartment. One expresses the transcription factor scleraxis and generated tenocytes invitro. The second expresses markers of smooth muscle and mesenchymal cells (SMMCs) and, while distinct from MuSCs, exhibited myogenic potential and promoted MuSC engraftment following transplantation. The blueprint presented here yields crucial insights into muscle-resident cell-type identities and can be exploited to study muscle diseases.