Significance: DNA methylation and histone modifications are two key epigenetic mechanisms in regulating gene expression, heterochromatin assembly, and genome stability. In mammals, maintenance of DNA methylation is mainly mediated by DNA methyltransferase 1 (DNMT1) in a replication-dependent manner. The spatiotemporal regulation of DNMT1 is essential for faithful propagation of DNA methylation patterns between cell generations. Here, we report the direct readout of the heterochromatic mark H3K9me3 by the RFTS domain of DNMT1, which serves to enhance the enzymatic stimulation of DNMT1 by previously characterized H3 ubiquitylation and mediates the cellular colocalization of DNMT1 and H3K9me3. This study uncovers a direct link between the repressive histone modification and DNMT1-mediated DNA methylation.

Trimethylation of histone H3 lysine 9 (H3K9me3) is crucial for the regulation of gene repression and heterochromatin formation, cell-fate determination and organismal development¹. H3K9me3 also provides an essential mechanism for silencing transposable elements^1,2,3,4. However, previous studies have shown that canonical H3K9me3 readers (for example, HP1 (refs. ^5,6,7,8,9) and MPP8 (refs. ^10,11,12)) have limited roles in silencing endogenous retroviruses (ERVs), one of the main transposable element classes in the mammalian genome¹³. Here we report that trinucleotide-repeat-containing 18 (TNRC18), a poorly understood chromatin regulator, recognizes H3K9me3 to mediate the silencing of ERV class I (ERV1) elements such as LTR12 (ref. ¹⁴). Biochemical, biophysical and structural studies identified the carboxy-terminal bromo-adjacent homology (BAH) domain of TNRC18 (TNRC18(BAH)) as an H3K9me3-specific reader. Moreover, the amino-terminal segment of TNRC18 is a platform for the direct recruitment of co-repressors such as HDAC–Sin3–NCoR complexes, thus enforcing optimal repression of the H3K9me3-demarcated ERVs. Point mutagenesis that disrupts the TNRC18(BAH)-mediated H3K9me3 engagement caused neonatal death in mice and, in multiple mammalian cell models, led to derepressed expression of ERVs, which affected the landscape of cis-regulatory elements and, therefore, gene-expression programmes. Collectively, we describe a new H3K9me3-sensing and regulatory pathway that operates to epigenetically silence evolutionarily young ERVs and exert substantial effects on host genome integrity, transcriptomic regulation, immunity and development.

Diabetic cardiomyopathy (DCM), a severe complication of diabetes, is characterized by mitochondrial dysfunction, oxidative stress, and DNA damage. Despite its severity, the intrinsic factors governing cardiomyocyte damage in DCM remain unclear. It is hypothesized that impaired iron–sulfur (Fe–S) cluster synthesis plays a crucial role in the pathogenesis of DCM. Reduced S‐sulfhydration of cysteine desulfurase (NFS1) is a novel mechanism that contributes to mitochondrial dysfunction and PARthanatos in DCM. Mechanistically, hydrogen sulfide (H ₂ S) supplementation restores NFS1 S‐sulfhydration at cysteine 383 residue, thereby enhancing Fe–S cluster synthesis, improving mitochondrial function, increasing cardiomyocyte viability, and alleviating cardiac damage. This study provides novel insights into the interplay between Fe–S clusters, mitochondrial dysfunction, and PARthanatos, highlighting a promising therapeutic target for DCM and paving the way for potential clinical interventions to improve patient outcomes.

Diabetic angiopathy, a major complication of type 2 diabetes mellitus (T2DM), is driven by vascular dysfunction, metabolic reprogramming, and oxidative stress. NAD⁺-dependent deacetylase SIRT6, located in the nucleus, is recognized for its role in modulating cardiovascular and metabolic homeostasis through histone deacetylation. However, the functions and mechanisms of accumulation of cytoplasmic SIRT6 in T2DM remain to be elucidated. Herein, a previously unrecognized cytoplasmic role for SIRT6 is identified in promoting pathological glycolysis during diabetic vascular remodeling. Vascular smooth muscle cell (VSMC) proliferation is observed, which is correlated with protein deacetylation, especially SIRT6, which translocated to the cytoplasm mediated by Importin 13 (IPO13). Furthermore, the accumulation of cytoplasmic SIRT6 facilitates its interaction with enolase 3 (ENO3), a newly discovered downstream target. This interaction promotes ENO3 deacetylation, enhances downstream phosphoenolpyruvic acid (PEP) levels, and thereby drives glycolysis reprogramming, ultimately leading to the pathological changes associated with diabetic angiopathy. Notably, exogenous hydrogen sulfide (H₂S) restores S-sulfhydration of SIRT6 at cysteine 141, counteracting the SIRT6-ENO3 interaction, suppressing glycolysis, and mitigating VSMC hyperproliferation. This study provides novel insights into the SIRT6-ENO3 pathway through regulating vascular glycolysis reprogramming, highlighting the therapeutic potential of targeting SIRT6 in the management of diabetic angiopathy.

BACKGROUND: Diabetic cardiomyopathy, a severe complication of diabetes, is marked by mitochondrial dysfunction, metabolic inflammation, and progressive cardiac impairment. Although STING (stimulator of interferon genes) is well recognized as a central mediator of innate immunity, its noncanonical role in metabolic regulation and mitochondrial dynamics in the diabetic heart remains largely unexplored. METHODS: To elucidate the role of STING in diabetic cardiac remodeling, we used single-cell RNA sequencing, echocardiography, and transmission electron microscopy in both genetic (db/db) and chemically induced (high-fat diet [HFD] plus streptozotocin, HFD/streptozotocin) diabetic mouse models. STING knockout mice and primary neonatal mouse cardiomyocytes were used for mechanistic investigations and functional validation. Mitochondrial respiration and glycolytic flux were assessed using Seahorse extracellular flux analysis. Posttranslational modifications of STING, including S -palmitoylation and S -sulfhydration, were evaluated via acyl-biotin exchange and biotin-switch assays, respectively. ENO1 (enolase 1) enzymatic activity was measured in vitro to assess glycolytic reprogramming. Furthermore, ¹³ C-glucose tracing–based targeted metabolomics was performed to quantify cardiac metabolic flux in db/db mice. Glycolytic metabolites, including lactate and pyruvate, were quantified in cardiac tissues and cultured cardiomyocytes to assess glycolytic activity. RESULTS: Exposure to high-palmitate conditions induced mitochondrial DNA leakage, thereby activating the cGAS-STING signaling pathway in cardiomyocytes. Mechanistically, STING underwent aberrant translocation to mitochondria, where it interacted with the outer membrane protein TOM (translocase of outer mitochondrial membrane) 40 to impair mitochondrial protein import and disrupt mitochondrial homeostasis. In addition, mitochondrial STING functioned as a scaffold to recruit and activate the glycolytic enzyme ENO1, thereby enhancing its enzymatic activity, accelerating glycolytic flux, and promoting lactate accumulation in diabetic cardiac tissues. Notably, diabetes-associated depletion of endogenous hydrogen sulfide reduced S -sulfhydration of STING at Cys88/91, facilitating its S -palmitoylation and mitochondrial localization. Genetic ablation of STING or pharmacological restoration of hydrogen sulfide levels with GYY4137 effectively rescued mitochondrial dysfunction, decreased lactate overproduction, and preserved cardiac contractile performance in diabetic mice. CONCLUSIONS: These findings identify STING as a spatial immunometabolic modulator that bridges mitochondrial dysfunction with metabolic imbalance in diabetic cardiomyopathy. Enhancing STING S -sulfhydration or targeting its palmitoylation through hydrogen sulfide–based interventions represents a promising therapeutic strategy for the treatment of diabetic cardiomyopathy.