G9a-mediated H3K9me2 orchestrates intestinal epithelial regeneration through epigenetic silencing of cell cycle-related genes.

Histone modifications play an important role in intestinal homeostasis and regeneration. Here, we identify histone H3 lysine 9 di-methylation (H3K9me2) as an epigenetic regulator of intestinal epithelial repair through mass spectrometry-based screening of histone modifications. We then find that H3K9me2 and its methyltransferase G9a levels are reduced during acute injury and progressively increase during regeneration in both mouse models and human clinical samples. Genetic ablation of G9a in intestinal epithelial cells or pharmacological inhibition of its enzymatic activity substantially impairs intestinal regeneration and reduces survival following irradiation. Mechanistically, integrative genomic analyses reveal that G9a-mediated H3K9me2 suppresses chromatin accessibility and transcriptional activity of cell cycle arrest genes, including Rb1cc1, Rb1, Cdkn1a, and Pten, thereby promoting intestinal stem cell proliferation. Furthermore, we elucidate that IL-4-STAT6 signaling controls G9a expression during regeneration, i.e., IL-4 upregulation leads to STAT6 phosphorylation and subsequent transcriptional activation of G9a. These findings establish the IL-4-STAT6-G9a-H3K9me2 regulatory axis as a critical epigenetic mechanism controlling intestinal regeneration with therapeutic potential for gastrointestinal disorders.