Neutrophils are essential components of innate immunity, executing a range of effector functions including phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs). A key hallmark of NET formation is the presence of citrullinated histone H3 (CitH3), produced by peptidylarginine deiminases (PAD2 and PAD4) to facilitate chromatin decondensation. While NETs play critical antimicrobial roles, excessive or dysregulated NET formation, termed NETosis, can drive tissue injury, chronic inflammation, and organ dysfunction across a wide spectrum of diseases. Beyond its structural role within NETs, CitH3 acts as a damage-associated molecular pattern (DAMP), amplifying immune activation and pathological inflammation. Elevated CitH3 levels have been identified as biomarkers in sepsis, viral infections, ischemia–reperfusion injury, organ transplantation, diabetic wounds, autoimmune diseases, and cancer. Despite increasing recognition of CitH3’s pathogenic contributions, its therapeutic potential remains largely untapped. This review summarizes recent advances in understanding the role of CitH3 in NETosis and immune dysfunction, highlights emerging strategies targeting CitH3 therapeutically, and identifies critical knowledge gaps. Collectively, these insights position CitH3 as a promising druggable biomarker for the diagnosis, prognosis, and treatment of acute and chronic inflammatory diseases.

Sepsis-induced acute lung injury (ALI) is prevalent in patients with sepsis and has a high mortality rate. Peptidyl arginine deiminase 2 (PADI2) and PADI4 play crucial roles in mediating the host’s immune response in sepsis, but their specific functions remain unclear. Our study shows that Padi2 ^–/– Padi4 ^–/– double KO (DKO) improved survival, reduced lung injury, and decreased bacterial load in Pseudomonas aeruginosa (PA) pneumonia–induced sepsis mice. Using single-cell RNA-Seq (scRNA-Seq), we found that the deletion of Padi2 and Padi4 reduced the Nlrp3 ⁺ proinflammatory macrophages and fostered Chil3 ⁺ myeloid cell differentiation into antiinflammatory macrophages. Additionally, we observed the regulatory role of the NLRP3/Ym1 axis upon DKO, confirmed by Chil3 knockdown and Nlrp3 -KO experiments. Thus, eliminating Padi2 and Padi4 enhanced the polarization of Ym1 ⁺ M2 macrophages by suppressing NLRP3, aiding in inflammation resolution and lung tissue repair. This study unveils the PADIs/NLRP3/Ym1 pathway as a potential target in treatment of sepsis-induced ALI.

Mitsugumin 53 (MG53, also TRIM72) is a muscle-enriched tripartite motif protein with a well-established role in acute membrane repair and cytoprotection in striated muscle and other stressed tissues. MG53 is a core component of cellular repair machinery, rapidly sensing membrane disruption and coordinating membrane resealing, mitochondrial preservation, and anti-inflammatory modulation. In contrast to its high expression in skeletal muscle, endogenous MG53 expression in the adult human heart is minimal, raising the question of how MG53 exerts cardioprotective effects in the human heart. Recent studies help address this by identifying MG53 as a circulating regenerative myokine. MG53 is secreted from skeletal muscle into the bloodstream and can reach distal organs, including the heart. These findings support a muscle-to-heart endocrine model in which MG53 mediates tissue crosstalk and helps provide repair capacity to the myocardium when intrinsic cardiac MG53 is low. Here, we summarize recent advances in MG53 biology, emphasizing molecular mechanisms and inter-organ communication underlying cardioprotection. We further highlight translational strategies leveraging recombinant MG53- and MG53-based therapeutics and discuss challenges that must be addressed for future clinical applications. Collectively, these insights support MG53 as an endocrine repair factor linking skeletal muscle to cardiac repair and a potential regenerative cardiovascular target.

Sarcopenia is characterized by progressive loss of skeletal muscle mass and function and is a major contributor to frailty, disability, and mortality in older adults. Store-operated calcium entry (SOCE) is a crucial regulator of skeletal muscle calcium homeostasis, and impaired SOCE has been linked to age-related muscle weakness. Here, we identify the synaptophysin family member synaptophysin-like protein 2, also known as mitsugumin 29 (MG29; encoded by the human gene SYPL2 and the mouse ortholog Mg29), as a key organizer of triad membrane cholesterol and lipid signaling required for normal SOCE during aging. Using Mg29^−/− mice as a model of accelerated sarcopenia, together with RNA interference against Mg29 in adult muscle and primary myotubes, we quantified changes in muscle morphology, contractile function, SOCE activity, and targeted lipidomic profiles. Reduced MG29 expression led to decreased muscle fiber cross-sectional area, reduced specific force, blunted SOCE, and marked alterations in membrane cholesterol content and fatty acid-derived lipid mediators. Cholesterol depletion by methyl-β-cyclodextrin in wild-type myotubes produced SOCE defects similar to those observed in aged wild-type and young Mg29^−/− muscles, indicating that MG29-dependent maintenance of membrane cholesterol is required for normal SOCE. Acute Mg29 knockdown also altered myogenic differentiation, the expression of calcium-handling and stress-response genes, and the release and consumption of specific polyunsaturated fatty acid-derived lipid mediators. Together, these findings identify MG29 as a critical regulator of SOCE and lipid signaling in skeletal muscle and suggest that its age-related decline contributes to sarcopenia by disrupting triad membrane organization and excitation–contraction coupling.

Sarcopenia is characterized by progressive loss of skeletal muscle mass and function and is a major contributor to frailty, disability, and mortality in older adults. Store-operated calcium entry (SOCE) is a crucial regulator of skeletal muscle calcium homeostasis, and impaired SOCE has been linked to age-related muscle weakness. Here, we investigated the role of the synaptophysin family member synaptophysin-like protein 2, also known as mitsugumin 29 (MG29/SYPL2) in regulating SOCE, muscle structure, and lipid signaling during aging. Using knockout mice (mg29−/−) as a model of accelerated sarcopenia, in combination with RNA interference against MG29/SYPL2 in adult muscle and primary myotubes, we quantified changes in muscle morphology, contractile function, SOCE activity, and targeted lipidomic profiles. We found that reduced MG29/SYPL2 expression leads to decreased muscle fiber cross-sectional area, reduced specific force, blunted SOCE, and marked alterations to membrane cholesterol content as well as fatty acid–derived lipid mediators. Cholesterol depletion by methyl-β-cyclodextrin in wild-type myotubes produced similar SOCE defects as those observed in aged wild-type and young mg29−/− muscles, indicating that MG29/SYPL2-dependent maintenance of membrane cholesterol is required for normal SOCE. Acute MG29/SYPL2 knockdown also modified myogenic differentiation, expression of calcium-handling and stress-response genes, and the release and consumption of specific polyunsaturated fatty acid–derived lipid mediators. Together, these findings identify MG29/SYPL2 as a critical regulator of SOCE and lipid signaling in skeletal muscle and suggest that its age-related decline contributes to sarcopenia by disrupting triad membrane organization and excitation-contraction coupling.

Peptidylarginine deiminase 2 (PAD2) catalyzes protein citrullination and is implicated in inflammatory bowel disease and colorectal cancer. However, its role in regulating the intestinal epithelium and the influence of biological sex and the microbiome remain poorly defined. This study investigated the relationships among PAD2 deficiency, sex-divergent epithelial states, β-catenin regulation, and the intestinal microbiome. Global PAD2 knockout and wild-type littermate mice of both sexes were characterized under basal conditions and following dextran sodium sulfate-induced colitis. Intestinal epithelial phenotypes were assessed by histology, immunofluorescence, immunoblotting, quantitative RT-PCR, and immunoprecipitation. Gut microbial communities were evaluated by shotgun metagenomics, while broad-spectrum antibiotic treatment, fecal protein immunoblotting, and recombinant human PAD2 exposure in vitro were used to examine relationships among antibiotic-sensitive factors, β-catenin regulation, and epithelial phenotypes. PAD2 deficiency was associated with distinct epithelial states in male and female colons before injury. Male KO mice displayed increased β-catenin phosphorylation and increased susceptibility to DSS colitis, whereas female KO mice demonstrated increased total β-catenin abundance and preservation of structural epithelial features following injury. Female KO microbiota exhibited genotype-associated differences in microbial community composition by exploratory Bray-Curtis PERMANOVA. Broad-spectrum antibiotic treatment altered the female epithelial phenotype, reduced active β-catenin, and progressively depleted luminal PAD2-immunoreactive proteins. Exogenous recombinant human PAD2 increased epithelial protein citrullination and altered active β-catenin abundance in HT29 cells. Collectively, these findings demonstrate both sex-specific and sex-divergent colonic phenotypes while supporting a framework connecting PAD2 biology, epithelial architecture, and the microbial environment during intestinal maintenance and injury.