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Lamin A is a component of the inner nuclear membrane that, together with epigenetic factors, organizes the genome in higher order structures required for transcriptional control. Mutations in the lamin A/C gene cause several diseases belonging to the class of laminopathies, including muscular dystrophies. Nevertheless, molecular mechanisms involved in the pathogenesis of lamin A-dependent dystrophies are still largely unknown. The polycomb group (PcG) of proteins are epigenetic repressors and lamin A interactors, primarily involved in the maintenance of cell identity. Using a murine model of Emery-Dreifuss muscular dystrophy (EDMD), we show here that lamin A loss deregulated PcG positioning in muscle satellite stem cells, leading to derepression of non-muscle-specific genes and [p16.sup.INK4a], a senescence driver encoded in the Cdkn2a locus. This aberrant transcriptional program caused impairment in self-renewal, loss of cell identity, and premature exhaustion of the quiescent satellite cell pool. Genetic ablation of the Cdkn2a locus restored muscle stem cell properties in lamin A/C-null dystrophic mice. Our findings establish a direct link between lamin A and PcG epigenetic silencing and indicate that lamin A-dependent muscular dystrophy can be ascribed to intrinsic epigenetic dysfunctions of muscle stem cells., Introduction The nuclear lamina (NL) is located in the inner part of the nuclear membrane and is composed of a complex network of type V filament proteins, the lamins (1, [...]

Background: Chemotherapy is the first line of treatment for cancer patients. However, the side effects cause severe muscle atrophy or chemotherapy‐induced cachexia. Previously, the NF‐κB/MuRF1‐dependent pathway was shown to induce chemotherapy‐induced cachexia. We hypothesized that acute collateral toxic effects of chemotherapy on muscles might involve other unknown pathways promoting chemotherapy‐induced muscle atrophy. In this study, we investigated differential effects of chemotherapeutic drugs and probed whether alternative molecular mechanisms lead to cachexia. Methods: We employed mouse satellite stem cell‐derived primary muscle cells and mouse C2C12 progenitor cell‐derived differentiated myotubes as model systems to test the effect of drugs. The widely used chemotherapeutic drugs, such as daunorubicin (Daun), etoposide (Etop), and cytarabine (Ara‐C), were tested. Molecular mechanisms by which drug affects the muscle cell organization at epigenetic, transcriptional, and protein levels were measured by employing chromatin immunoprecipitations, endogenous gene expression profiling, co‐immunoprecipitation, complementation assays, and confocal microscopy. Myotube function was examined using the electrical stimulation of myotubes to monitor contractile ability (excitation–contraction coupling) post drug treatment. Results: Here, we demonstrate that chemotherapeutic drugs disrupt sarcomere organization and thereby the contractile ability of skeletal muscle cells. The sarcomere disorganization results from severe loss of molecular motor protein MyHC‐II upon drug treatment. We identified that drugs impede chromatin targeting of SETD7 histone methyltransferase and disrupt association and synergetic function of SETD7 with p300 histone acetyltransferase. The compromised transcriptional activity of histone methyltransferase and acetyltransferase causes reduced histone acetylation and low occupancy of active RNA polymerase II on MyHC‐II, promoting drastic down‐regulation of MyHC‐II expression (~3.6‐fold and ~4.5‐fold reduction of MyHC‐IId mRNA levels in Daun and Etop treatment, respectively. P < 0.0001). For MyHC‐IIa, gene expression was down‐regulated by ~2.6‐fold and ~4.5‐fold in Daun and Etop treatment, respectively (P < 0.0001). Very interestingly, the drugs destabilize SUMO deconjugase SENP3. Reduction in SENP3 protein level leads to deregulation of SETD7–p300 function. Importantly, we identified that SUMO deconjugation independent role of SENP3 regulates SETD7–p300 functional axis. Conclusions: The results show that the drugs critically alter SENP3‐dependent synergistic action of histone‐modifying enzymes in muscle cells. Collectively, we defined a unique epigenetic mechanism targeted by distinct chemotherapeutic drugs, triggering chemotherapy‐induced cachexia. [ABSTRACT FROM AUTHOR]

Muscle weakness plays an important role in neuromuscular disorders comprising amyotrophic lateral sclerosis (ALS). However, it is not established whether muscle denervation originates from the motor neurons, the muscles or more likely both. Previous studies have shown that the expression of the SOD1G93A mutation in skeletal muscles causes denervation of the neuromuscular junctions, inability to regenerate and consequent atrophy, all clear symptoms of ALS. In this work, we used SOD1G93A mice, a model that best mimics some pathological features of both familial and sporadic ALS, and we investigated some biological effects induced by the activation of the P2X7 receptor in the skeletal muscles. The P2X7, belonging to the ionotropic family of purinergic receptors for extracellular ATP, is abundantly expressed in the healthy skeletal muscles, where it controls cell duplication, differentiation, regeneration or death. In particular, we evaluated whether an in vivo treatment in SOD1G93A mice with the P2X7 specific agonist 2′(3′)‐O‐(4‐Benzoylbenzoyl) adenosine5′‐triphosphate (BzATP) just before the onset of a pathological neuromuscular phenotype could exert beneficial effects in the skeletal muscles. Our findings indicate that stimulation of P2X7 improves the innervation and metabolism of myofibers, moreover elicits the proliferation/differentiation of satellite cells, thus preventing the denervation atrophy of skeletal muscles in SOD1G93A mice. Overall, this study suggests that a P2X7‐targeted and site‐specific modulation might be a strategy to interfere with the complex multifactorial and multisystem nature of ALS. [ABSTRACT FROM AUTHOR]

The correct 3D organization of the genome is known to influence the spatiotemporal expression of lineagespecific genes during stem cell differentiation and aging processes. We introduce a novel evolution of the SAMMY-seq technique to precisely map genomic regions separated by their biochemical properties. This single-handedly technique enables the identification of heterochromatic and euchromatic domains and their compartmentalization in the nuclear space. Crucial practical advantages of this method include: its applicability on as little as 10K cells; reduced costs; few manipulation steps and short execution time. In postnatal Muscle Stem Cells (MuSCs) we observed a reproducible distribution of euchromatic and heterochromatic genomic domains, in line with known epigenetic signatures. Our findings highlight how MuSCs over life exhibit a global steady chromatin organization, accompanied by solubility changes that favour processes such as MuSCs activation but may become obstacles during aging for proper pool maintenance. Still, we describe environmental alterations of the muscle niche, emphasizing a supportive population of MuSCs, namely FAPs, which exhibit dramatic transcriptional alterations during aging. Our extensive characterization of the environment and chromatin organization in MuSCs expands our understanding of quiescence, activation and aging processes, laying the groundwork for the study of the role of the epigenome in pathological conditions. [ABSTRACT FROM AUTHOR]

The alteration of the several roles that Lamin A/C plays in the mammalian cell leads to a broad spectrum of pathologies that - all together - are named laminopathies. Among those, the Emery Dreifuss Muscular Dystrophy (EDMD) is of particular interest as, despite the several known mutations of Lamin A/C, the genotype-phenotype correlation still remains poorly understood; this suggests that the epigenetic background of patients might play an important role during the time course of the disease. Historically, both a mechanical role of Lamin A/C and a regulative one have been suggested as the driving force of laminopathies; however, those two hypotheses are not mutually exclusive. Recent scientific evidence shows that Lamin A/C sustains the correct gene expression at the epigenetic level thanks to the Lamina Associated Domains (LADs) reorganization and the crosstalk with the Polycomb Group of Proteins (PcG). Furthermore, the PcG-dependent histone mark H3K27me3 increases under mechanical stress, finally pointing out the link between the mechano-properties of the nuclear lamina and epigenetics. Here, we summarize the emerging mechanisms that could explain the high variability seen in Emery Dreifuss muscular dystrophy. [ABSTRACT FROM AUTHOR]

Background: Beyond their role in post-transcriptional gene silencing, Dicer and Argonaute, two components of the RNA interference (RNAi) machinery, were shown to be involved in epigenetic regulation of centromeric heterochromatin and transcriptional gene silencing. In particular, RNAi mechanisms appear to play a role in repeat induced silencing and some aspects of Polycomb-mediated gene silencing. However, the functional interplay of RNAi mechanisms and Polycomb group (PcG) pathways at endogenous loci remains to be elucidated. Principal Findings: Here we show that the endogenous Dicer-2/Argonaute-2 RNAi pathway is dispensable for the PcG mediated silencing of the homeotic Bithorax Complex (BX-C). Although Dicer-2 depletion triggers mild transcriptional activation at Polycomb Response Elements (PREs), this does not induce transcriptional changes at PcG-repressed genes. Moreover, Dicer-2 is not needed to maintain global levels of methylation of lysine 27 of histone H3 and does not affect PRE-mediated higher order chromatin structures within the BX-C. Finally bioinformatic analysis, comparing published data sets of PcG targets with Argonaute-2-bound small RNAs reveals no enrichment of these small RNAs at promoter regions associated with PcG proteins. Conclusions: We conclude that the Dicer-2/Argonaute-2 RNAi pathway, despite its role in pairing sensitive gene silencing of transgenes, does not have a role in PcG dependent silencing of major homeotic gene cluster loci in Drosophila. [ABSTRACT FROM AUTHOR]