Polycomb Ezh1 maintains murine muscle stem cell quiescence through non-canonical regulation of Notch signaling

Zn‐DHM Nanozymes Enhance Muscle Regeneration Through ROS Scavenging and Macrophage Polarization in Volumetric Muscle Loss Revealed by Single‐Cell Profiling

Volumetric muscle loss (VML) is a severe condition in which the loss of skeletal muscle surpasses the body's intrinsic repair capabilities, leading to irreversible functional deficits and potential disability, with persistent inflammation and impaired myogenic differentiation. To address these challenges, a novel zinc‐dihydromyricetin (Zn‐DHM) nanozyme with superoxide dismutase (SOD)‐like activity is developed, designed to neutralize excessive reactive oxygen species (ROS) and restore oxidative balance. Zn‐DHM mitigates oxidative stress and promotes polarization of macrophages from the proinflammatory M1 phenotype to the anti‐inflammatory M2 phenotype, thereby reducing chronic inflammation and creating a conducive environment for muscle repair. Further, Zn‐DHM significantly enhances the myogenic differentiation of C2C12 cells, accelerating wound healing processes. These studies confirm the biosafety and low toxicity of Zn‐DHM. As per a murine tibialis anterior VML model, Zn‐DHM effectively suppresses inflammation and markedly improves skeletal muscle repair outcomes. Single‐cell RNA sequencing reveals that Zn‐DHM treatment increases the expression of M2 macrophage markers and enhances the proliferation and differentiation capacity of muscle stem cells (MuSCs). In addition, intercellular communication analysis reveals interactions between MuSCs and macrophages in the Zn‐DHM treatment group, suggesting that these interactions may drive tissue regeneration through the activation of the GAS and Notch signaling pathways.

Metabolic regulation in adult and aging skeletal muscle stem cells

Adult stem cells maintain homeostasis and enable regeneration of most tissues. Quiescence, proliferation, and differentiation of stem cells and their progenitors are tightly regulated processes governed by dynamic transcriptional, epigenetic, and metabolic programs. Previously thought to merely reflect a cell's energy state, metabolism is now recognized for its critical regulatory functions, controlling not only energy and biomass production but also the cell's transcriptome and epigenome. In this review, we explore how metabolic pathways, metabolites, and transcriptional and epigenetic regulators are functionally interlinked in adult and aging skeletal muscle stem cells.

A conserved switch to less catalytically active Polycomb repressive complexes in non-dividing cells

Polycomb repressive complex 2 (PRC2), composed of the core subunits EED, SUZ12, and either EZH1 or EZH2, is critical for maintaining cellular identity in multicellular organisms. PRC2 deposits H3K27me3, which is thought to recruit the canonical form of PRC1 (cPRC1) to promote gene repression. Here, we show that EZH1-PRC2 and cPRC1 are the primary Polycomb complexes on target genes in non-dividing, quiescent cells. Furthermore, these cells are resistant to PRC2 inhibitors. While PROTAC-mediated degradation of EZH1-PRC2 in quiescent cells does not reduce H3K27me3, it partially displaces cPRC1. Our results reveal an evolutionarily conserved switch to less catalytically active Polycomb complexes in non-dividing cells and raise concerns about using PRC2 inhibitors in cancers with significant populations of non-dividing cells.

PRC2-EZH1 contributes to circadian gene expression by orchestrating chromatin states and RNA polymerase II complex stability

Circadian rhythmicity of gene expression is a conserved feature of cell physiology. This involves fine-tuning between transcriptional and post-transcriptional mechanisms and strongly depends on the metabolic state of the cell. Together these processes guarantee an adaptive plasticity of tissue-specific genetic programs. However, it is unclear how the epigenome and RNA Pol II rhythmicity are integrated. Here we show that the PcG protein EZH1 has a gateway bridging function in postmitotic skeletal muscle cells. On the one hand, the circadian clock master regulator BMAL1 directly controls oscillatory behavior and periodic assembly of core components of the PRC2-EZH1 complex. On the other hand, EZH1 is essential for circadian gene expression at alternate Zeitgeber times, through stabilization of RNA Polymerase II preinitiation complexes, thereby controlling nascent transcription. Collectively, our data show that PRC2-EZH1 regulates circadian transcription both negatively and positively by modulating chromatin states and basal transcription complex stability.

Histone methylation modification and diabetic kidney disease: Potential molecular mechanisms and therapeutic approaches (Review)

Diabetic kidney disease (DKD) is the leading cause of chronic kidney disease and end‑stage renal disease, and is characterized by persistent proteinuria and decreased glomerular filtration rate. Despite extensive efforts, the increasing incidence highlights the urgent need for more effective treatments. Histone methylation is a crucial epigenetic modification, and its alteration can destabilize chromatin structure, thereby regulating the transcriptional activity of specific genes. Histone methylation serves a substantial role in the onset and progression of various diseases. In patients with DKD, changes in histone methylation are pivotal in mediating the interactions between genetic and environmental factors. Targeting these modifications shows promise in ameliorating renal histological manifestations, tissue fibrosis and proteinuria, and represents a novel therapeutic frontier with the potential to halt DKD progression. The present review focuses on the alterations in histone methylation during the development of DKD, systematically summarizes its impact on various renal parenchymal cells and underscores the potential of targeted histone methylation modifications in improving DKD outcomes.

Beyond the bulk: overview and novel insights into the dynamics of muscle satellite cells during muscle regeneration

Skeletal muscle possesses remarkable regenerative capabilities, fully recovering within a month following severe acute damage. Central to this process are muscle satellite cells (MuSCs), a resident population of somatic stem cells capable of self-renewal and differentiation. Despite the highly predictable course of muscle regeneration, evaluating this process has been challenging due to the heterogeneous nature of myogenic precursors and the limited insight provided by traditional markers with overlapping expression patterns. Notably, recent advancements in single-cell technologies, such as single-cell (scRNA-seq) and single-nucleus RNA sequencing (snRNA-seq), have revolutionized muscle research. These approaches allow for comprehensive profiling of individual cells, unveiling dynamic heterogeneity among myogenic precursors and their contributions to regeneration. Through single-cell transcriptome analyses, researchers gain valuable insights into cellular diversity and functional dynamics of MuSCs post-injury. This review aims to consolidate classical and new insights into the heterogeneity of myogenic precursors, including the latest discoveries from novel single-cell technologies.

Epigenetic control of skeletal muscle atrophy

Skeletal muscular atrophy is a complex disease involving a large number of gene expression regulatory networks and various biological processes. Despite extensive research on this topic, its underlying mechanisms remain elusive, and effective therapeutic approaches are yet to be established. Recent studies have shown that epigenetics play an important role in regulating skeletal muscle atrophy, influencing the expression of numerous genes associated with this condition through the addition or removal of certain chemical modifications at the molecular level. This review article comprehensively summarizes the different types of modifications to DNA, histones, RNA, and their known regulators. We also discuss how epigenetic modifications change during the process of skeletal muscle atrophy, the molecular mechanisms by which epigenetic regulatory proteins control skeletal muscle atrophy, and assess their translational potential. The role of epigenetics on muscle stem cells is also highlighted. In addition, we propose that alternative splicing interacts with epigenetic mechanisms to regulate skeletal muscle mass, offering a novel perspective that enhances our understanding of epigenetic inheritance's role and the regulatory network governing skeletal muscle atrophy. Collectively, advancements in the understanding of epigenetic mechanisms provide invaluable insights into the study of skeletal muscle atrophy. Moreover, this knowledge paves the way for identifying new avenues for the development of more effective therapeutic strategies and pharmaceutical interventions.

Epigenetic integration of signaling from the regenerative environment

Skeletal muscle has an extraordinary capacity to regenerate itself after injury due to the presence of tissue-resident muscle stem cells. While these muscle stem cells are the primary contributor to the regenerated myofibers, the process occurs in a regenerative microenvironment where multiple different cell types act in a coordinated manner to clear the damaged myofibers and restore tissue homeostasis. In this regenerative environment, immune cells play a well-characterized role in initiating repair by establishing an inflammatory state that permits the removal of dead cells and necrotic muscle tissue at the injury site. More recently, it has come to be appreciated that the immune cells also play a crucial role in communicating with the stem cells within the regenerative environment to help coordinate the timing of repair events through the secretion of cytokines, chemokines, and growth factors. Evidence also suggests that stem cells can help modulate the extent of the inflammatory response by signaling to the immune cells, demonstrating a cross-talk between the different cells in the regenerative environment. Here, we review the current knowledge on the innate immune response to sterile muscle injury and provide insight into the epigenetic mechanisms used by the cells in the regenerative niche to integrate the cellular cross-talk required for efficient muscle repair.