Epitranscriptomic regulation of lipid oxidation and liver fibrosis via ENPP1 mRNA m6A modification

Background: Dysregulated lipid oxidation occurs in several pathological processes characterized by cell proliferation and migration. Nonetheless, the molecular mechanism of lipid oxidation is not well appreciated in liver fibrosis, which is accompanied by enhanced fibroblast proliferation and migration. Methods: We investigated the causes and consequences of lipid oxidation in liver fibrosis using cultured cells, animal models, and clinical samples. Results: Increased ecto-nucleotide pyrophosphatase/phosphodiesterase (ENPP1) expression caused increased lipid oxidation, resulting in the proliferation and migration of hepatic stellate cells (HSCs) that lead to liver fibrosis, whereas fibroblast-specific ENPP1 knockout reversing these results. Elevated ENPP1 and N-6-methyladenosine (m(6)A) levels were associated with high expression of Wilms tumor 1 associated protein (WTAP). Mechanistically, WTAP-mediated m(6)A methylation of the 3'UTR of ENPP1 mRNA and induces its translation dependent of YTH domain family proteins 1 (YTHDF1). Additionally, ENPP1 could interact with hypoxia inducible lipid droplet associated (HILPDA) directly; overexpression of ENPP1 further recruits HILPDA-mediated lipid oxidation, thereby promotes HSCs proliferation and migration, while inhibition of ENPP1 expression produced the opposite effect. Clinically, increased expression of WTAP, YTHDF1, ENPP1, and HILPDA, and increased m(6)A mRNA content, enhanced lipid oxidation, and increased collagen deposition in human liver fibrosis tissues. Conclusions: We describe a novel mechanism in which WTAP catalyzes m(6)A methylation of ENPP1 in a YTHDF1-dependent manner to enhance lipid oxidation, promoting HSCs proliferation and migration and liver fibrosis.