Transcriptional Landscape Established by the Euchromatic Histone-lysine N-methyltransferase Pathway During Pancreas Ontogenesis and Pancreatitis.

The Euchromatic Histone-lysine N-Methyltransferase 1/2 (EHMT1/2) complex, responsible for catalyzing mono- and di-methylation of histone H3K9, has emerged as key regulator of embryogenesis and carcinogenesis. We have recently shown that EHMT2 inactivation antagonizes oncogenic KRAS-mediated pancreatic cancer initiation and promotion by altering growth and immune gene expression networks. The current study unravels the transcriptional landscape regulated by EHMT2 during pancreatic development and acute pancreatitis. We performed conditional knockout of EHMT2 in the pancreas using the Pdx1-Cre model, comparing perinatal (10-day-old) vs. young adult mice (4-week-old). Notably, despite carrying EHMT2 inactivation, both the whole animal and pancreas develop normally through adulthood. The transcriptional landscape resulting from EHMT2 inactivation, however, is different in perinatal mice from young adults, suggesting that this epigenomic regulator plays a role in modulating distinct gene networks during the development of this organ. Congruent with a role for EHMT2 in gene silencing, we show that its inactivation in both life stages primarily resulted in gene expression signatures dominated by upregulated transcripts. Notably, among these genes, we find pancreas-specific clusters, including those encoding zymogen granules, during the transition to young adult, suggesting that EHMT2 facilitates acinar cell-fate decisions. DEGs from young adults with EHMT2 loss displayed prominent activation of TP53 signaling-related and DNA damage response gene networks that were not present in the perinatal cohort, demonstrating that cell cycle arrest accompanies this differentiation event. We also find de-repression of genes that participate in early endodermal development, metabolism, and inflammation. Studies on acute pancreatitis, induced by repeated injections of the CCK-agonist peptide, caerulein, show that EHMT2 inactivation results in more severe disease compared to that in controls, as measured by histological scoring of edema, inflammatory cell infiltrate, and necrosis. More importantly, and congruent with our histological assessment, EHMT2 inactivation in acinar epithelial cells regulates the expression of key inflammation-associated genes that reprograms the non-epithelial responses to pancreatitis. Digital cytology analysis demonstrated that the transcriptional landscape resulting from EHMT2 inactivation triggers a more aggressive inflammatory response for the pancreas. This data demonstrates that, although not critical to development of the organ, EHMT2 is involved in pancreas-specific gene expression. Lastly, during pancreatitis, EHMT2 behaves as an important regulator of inflammation, extending our knowledge of epigenomic mechanisms underlying development, homeostasis, and diseases of the pancreas.