Nicotinamide N-Methyltransferase Inhibition Mitigates Cerulein-Induced Pancreatic Fibrosis via Galectin-3-Mediated Regulation of Stellate Cell Activation and Macrophage M2 Polarization in Mice

Chronic pancreatitis (CP) is a chronic disease characterized by pancreatic fibrosis driven by pancreatic stellate cell activation and M2 polarization of macrophages. Nicotinamide n-methyltransferase (NNMT) is a methylase critically involved in fibrosis. Galectin-3 (LGALS3), a member of the galectin family, drives M2 macrophage polarization. This study explores the roles of NNMT and LGALS3 in CP. CP was induced in C57BL/6 mice via repeated intraperitoneal injections of 50 µg/kg cerulein. NNMT was upregulated in pancreatic tissues of CP mice, especially in mouse pancreatic stellate cells (mPSCs). Functional inhibition of NNMT in mPSCs, via lentiviral short-hairpin RNA-mediated knockdown or treatment with NNMT inhibitor, suppressed mPSC activation, proliferation, and migration. Moreover, conditioned medium from mPSCs with NNMT inhibition reduced M2 polarization of bone marrow-derived macrophages (BMDMs). In vivo, intraperitoneal administration of 20 mg/kg NNMT inhibitor for 28 days alleviated pancreatic collagen deposition and macrophage M2 polarization, resulting in reduced pancreatic fibrosis. RNA sequencing and bioinformatics analysis identified LGALS3 as a potential downstream target of NNMT. NNMT inhibition downregulated LGALS3 expression in mPSCs, and chromatin immunoprecipitation - quantitative polymerase chain reaction (ChIP-qPCR) confirmed that this suppression was associated with increased trimethylation of lysine 27 on histone H3 (H3K27me3) enrichment at the LGALS3 promoter. Lentivirus-mediated LGALS3 overexpression reversed the inhibitory effect of NNMT knockdown on BMDM M2 polarization. In conclusion, inhibition of NNMT alleviates mPSC activation and suppresses mPSC-induced macrophage M2 polarization via H3K27me3-mediated repression of LGALS3 transcription, with the ultimate effect of mitigating cerulein-induced pancreatic fibrosis.