Reply to: "NNMT aggravates hepatic steatosis but alleviates liver injury in alcoholic liver disease" and "Two sides of NNMT in alcoholic and non-alcoholic fatty liver development"

NNMT is involved in deoxynivalenol-induced hepatocyte toxicity via promoting ferroptosis

Deoxynivalenol (DON) is a common contamination mycotoxin that which exerts significant hepatotoxicity, posing a serious threat to human and animal health. Ferroptosis has been linked to the development of hepatotoxicity induced by DON. However, the mechanism by which DON promotes ferroptosis in hepatocytes is not well understood. Although studies have shown that DON upregulates the expression of nicotinamide N-Methyltransferase (NNMT), its role in DON hepatotoxicity has not been elucidated. In this study, we found that DON inhibited SLC7A11/GPX4 and increased cytosolic free Fe2 + and lipid ROS, thereby inducing ferroptosis of HepG2 cells. Overexpression of NNMT markedly downregulated the expression of SLC7A11, GPX4, GCLC, and NQO1, exacerbated the DON-induced increase in free Fe2+ and lipid ROS, thus promoting ferroptosis. Silencing or inhibition of NNMT produced opposite effects and abolished the DON-induced ferroptosis. Further application of SLC7A11 and GPX4 inhibitor treatments confirmed that following DON exposure, NNMT triggered ferroptosis by inhibiting SLC7A11 and GPX4, to reduce cell viability and inhibit cell growth. Taken together, this study found that DON-induced NNMT may enhance ferroptosis by inhibiting the SLC7A11/GPX4 proteins in HepG2 cells. These findings provide valuable insights for controlling DON hepatotoxicity and hepatocellular carcinoma.

Exploring NNMT: from metabolic pathways to therapeutic targets

Cellular metabolism-related epigenetic modulation plays a pivotal role in the maintenance of cellular homeostasis. Nicotinamide N-methyltransferase (NNMT) serves as a crucial link between cellular metabolism and epigenetics by catalyzing nicotinamide methylation using the universal methyl donor S-adenosyl-L-methionine. This direct connection bridges the methylation-mediated one-carbon metabolism with nicotinamide adenine dinucleotide levels. Numerous studies have revealed tissue-specific differences in NNMT expression and activity, indicating that its varied physiological and pathological roles depend on its distribution. In this review, we provide an overview of the NNMT involvement in various pathological conditions, including cancer, liver disease, obesity, diabetes, brain disease, pulmonary disease, cardiovascular disease, and kidney disease. By synthesizing this information, our article aims to enhance our understanding of the cellular mechanisms underlying NNMT biology related to diverse diseases and lay the molecular groundwork for developing therapeutic strategies for pharmacological interventions.