Project description:This project aimed to assess the role of pharmacological inhibition of the aryl hydrocarbon receptor (AhR) on skeletal muscle and cortical bone health in aged mice. As part of a broader systems biology approach, proteomic profiling was employed to investigate molecular mediators of neuromuscular junction (NMJ) function in skeletal muscle tissue. The study compared vehicle-treated versus BAY2416964-treated aged mice, revealing key differentially expressed proteins involved in axonal development and NMJ stability.
Project description:Embryonic mouse diaphragm is a primary model for studying myogenesis and neuro-muscular synaptogenesis, both of which represent processes regulated by spatially organized genetic programs of myonuclei located in distinct myodomains. However, a spatial gene expression pattern of embryonic mouse diaphragm has not been reported. Here we provide spatially resolved gene expression data for horizontally sectioned embryonic mouse diaphragms at E14.5 and E18.5. These data reveal gene signatures for specific muscle regions with distinct maturity and fiber type composition, as well as for a central neuromuscular junction and a peripheral myotendinous junction compartments. Comparing spatial expression patterns of wild type mice with those of mouse mutants lacking either the skeletal muscle calcium channel CaV1.1 or b-catenin, reveals curtailed muscle development and dysregulated expression of genes potentially involved in NMJ formation. Altogether, these datasets provide a powerful recourse for further studies of muscle development and NMJ formation in the mouse embryo.
Project description:During aging and neuromuscular diseases, there is a progressive loss of skeletal muscle volume and function, which is often associated with denervation and a loss of muscle stem cells (MuSCs). A relationship between MuSCs and innervation has not been established however. Herein, we administered neuromuscular trauma to a MuSC lineage tracing model and observed a subset of MuSCs specifically engraft in a position proximal to the neuromuscular junction (NMJ). In aging and in a model of neuromuscular degeneration (Sod1-/-), this localized engraftment behavior was reduced. Genetic rescue of motor neurons in Sod1-/- mice reestablished integrity of the NMJ and partially restored MuSC ability to engraft into NMJ proximal positions. Using single cell RNA-sequencing of MuSCs, we demonstrate that a subset of MuSCs are molecularly distinguishable from MuSCs responding to myofiber injury. These data reveal unique features of MuSCs that respond to synaptic perturbations caused by aging and other stressors.
Project description:X-linked Spinal and Bulbar Muscular Atrophy (SBMA) is a rare, late-onset neuromuscular disease caused by a CAG repeat expansion mutation in the androgen receptor (AR) gene. SBMA is characterized by progressive muscle atrophy of both neurogenic and myopathic etiologies. Previous work has established that mutant AR expression in skeletal muscle could be a significant contributor to neuromuscular decline, yet the mechanisms involved remain ill-defined. As AR is a nuclear hormone receptor transcription factor, we sought to define early changes in gene expression in skeletal muscle of pre-symptomatic SBMA mice, with a focus on transcriptional changes at the neuromuscular junction (NMJ). We describe loss of key NMJ-specific genes in synaptic muscle regions of pre-symptomatic SBMA mice, while extrasynaptic muscle features a coordinated loss of sarcomere genes that coincides with ectopic re-expression of certain NMJ genes. Furthermore, SBMA muscle prominently features dysregulated calcium flux, likely stemming from a compensatory response to early atrophy that greatly exacerbates over time. The SERCA activator CDN1163 conferred a mild rescue in function and muscle size in SBMA mice, while genetic deletion of the gene encoding Myf6/MRF4, a negative regulator of sarcomere gene expression and predicted AR interactor, did not ameliorate muscle atrophy. These studies suggest that modulation of calcium flux could be a promising pharmacological target in SBMA.
Project description:The neuromuscular junction (NMJ) is the synapse formed between motor neurons and skeletal muscle fibers. Its stability relies on the continued expression of genes in a subset of myonuclei, called NMJ myonuclei. Here, we use single-nuclei RNA-sequencing (snRNA-seq) to identify numerous undescribed NMJ-specific transcripts. To elucidate how the NMJ transcriptome is regulated, we also performed snRNA-seq on sciatic nerve transected, botulinum toxin injected and Musk knockout muscles. These data show that NMJ gene expression is not only driven by agrin-Lrp4/MuSK signaling, but is also affected by electrical activity and trophic factors other than agrin. By selecting three previously undescribed NMJ genes Etv4, Lrtm1 and Pdzrn4, we further characterize novel contributors to NMJ stability and function. AAV-mediated overexpression and AAV-CRISPR/Cas9-mediated knockout show that Etv4 is sufficient to upregulate expression of ~50% of the NMJ genes in non-synaptic myonuclei, while muscle-specific knockout of Pdzrn4 induces NMJ fragmentation. Further investigation of Pdzrn4 revealed that it localizes to the Golgi apparatus and interacts with MuSK protein. Collectively, our data provide a rich resource of NMJ transcripts, highlight the importance of ETS transcription factors at the NMJ and suggest a novel pathway for NMJ post-translational modifications.
Project description:The neuromuscular junction (NMJ) is the synapse formed between motor neurons and skeletal muscle fibers. Its stability relies on the continued expression of genes in a subset of myonuclei, called NMJ myonuclei. Here, we use single-nuclei RNA-sequencing (snRNA-seq) to identify numerous undescribed NMJ-specific transcripts. To elucidate how the NMJ transcriptome is regulated, we also performed snRNA-seq on sciatic nerve transected, botulinum toxin injected and Musk knockout muscles. These data show that NMJ gene expression is not only driven by agrin-Lrp4/MuSK signaling, but is also affected by electrical activity and trophic factors other than agrin. By selecting three previously undescribed NMJ genes Etv4, Lrtm1 and Pdzrn4, we further characterize novel contributors to NMJ stability and function. AAV-mediated overexpression and AAV-CRISPR/Cas9-mediated knockout show that Etv4 is sufficient to upregulate expression of ~50% of the NMJ genes in non-synaptic myonuclei, while muscle-specific knockout of Pdzrn4 induces NMJ fragmentation. Further investigation of Pdzrn4 revealed that it localizes to the Golgi apparatus and interacts with MuSK protein. Collectively, our data provide a rich resource of NMJ transcripts, highlight the importance of ETS transcription factors at the NMJ and suggest a novel pathway for NMJ post-translational modifications.
Project description:The neuromuscular junction (NMJ) is a specialized tripartite synapse composed of the motor axon terminal, covered by perisynaptic Schwann cells (PSCs), and the muscle fibre, separated by a basal lamina. It is exposed to different kind of injures such as mechanical traumas, pathogens including neurotoxins, and neuromuscular diseases such as amyotrophic lateral sclerosis and immune-mediated disorders, and has retained throughout vertebrate evolution an intrinsic ability for repair and regeneration, at variance from central synapses1. Following peripheral nerve injury, an intense but poorly defined crosstalk takes place at the NMJ among its components, functional to nerve terminal regeneration. To identify crucial factors released by PSCs and the muscle to induce nerve regrowth, we performed a transcriptome analysis of the NMJ at different time points after injection of -latrotoxin, a presynaptic neurotoxin isolated from the venom of the black widow spider. This toxin is a simple and controlled method to induce an acute, localized and reversible nerve terminal degeneration not blurred by inflammation, and can help to identify molecules involved in the intra- and inter-cellular signalling governing NMJ regeneration.
Project description:Understanding neuromuscular junction (NMJ) repair mechanisms is essential for addressing degenerative neuromuscular conditions. Here, we focus on the role of muscle-resident Schwann cells in NMJ reinnervation. Using an accepted model of progressive NMJ degeneration, Sod1-/- mice, we identified a clear NMJ ‘regenerative window’ that allowed us to define cellular and molecular regulators of synapse remodeling and muscle fiber reinnervation. High-resolution imaging and single-cell RNA sequencing provide a detailed analysis of Schwann cell number, morphology, and transcriptome revealing multiple subtypes, including a previously unrecognized terminal Schwann cell (tSC) population expressing a synapse promoting signature. We also discovered a novel SPP1-driven cellular interaction between myelin Schwann cells and tSCs and show that it promotes tSC proliferation and reinnervation following nerve injury in wild type mice. Our findings offer important insights into molecular regulators critical in NMJ reinnervation that are mediated through tSCs to maintain NMJ function.
Project description:Muscle fibroadipogenic progenitor (FAP) cells, which are muscular mesenchymal cells that originate from lateral plate mesoderm have been proposed to act as a critical regulator for adult muscle homeostasis1–7, including the maturation and proper functioning of the neuromuscular junction (NMJ)3, Prx-Bap1 paper. However, the mechanism and intercellular crosstalk by which FAPs regulate the stability and functionality of neuromuscular system remains unknown. Here we show that FAPs not only locally but also systemically regulate the neuromuscular system through the secretion of a serine-type endopeptidase Granzyme E which may imply the previously unidentified endocrine function of FAPs. Local transplantation of wild-type FAPs into the neuromuscular disease model (Prrx1Cre;Bap1f/f, hereafter, cKO) can readily prevent neuromuscular defects, including degeneration of the neuromuscular junction and loss of motor neurons. These effects are found not only in transplanted hindlimb muscles but also in the contralateral hindlimb and even forelimb muscles. Notably, subcutaneous administration of microparticles encapsulating FAP-conditioned media into cKO mice was sufficient to restore normal neuromuscular functions. By analyzing the transcriptomic and secretomic profiles of FAPs, we identified a novel protein, Granzyme E, which is specifically expressed in and secreted by FAPs, and which indispensably regulates the structure and function of NMJ and motor neuron survival. Our study has defined a unique mechanism of Granzyme E-dependent, systemic control of the neuromuscular system by FAPs, which would provide a comprehensive understanding on the neuromuscular systems and their crosstalk with non-neuronal cells. These findings may provide a therapeutic benefit to treat NMJ-related diseases.