MBOAT7 Down-Regulation by Hyperinsulinemia Induces Fat Accumulation in Hepatocytes

Abstract

Background & Aims: Naturally occurring variation in Membrane-bound O-acyltransferase domain-containing 7 (MBOAT7), an enzyme involved in phospholipid acyl-chain remodeling, has been associated with steatosis and hepatic disorders. We examined the relationship between hepatic MBOAT7 down-regulation and fat accumulation. Methods: Hepatic MBOAT7 expression was surveyed in 119 obese individuals and in experimental models. MBOAT7 was acutely silenced by antisense oligonucleotides in C57Bl/6 mice, and by CRISPR/Cas9 in HepG2. Results: In obese individuals, hepatic MBOAT7 mRNA decreased from normal liver to steatohepatitis, independently of diabetes, inflammation and MBOAT7 genotype. Mboat7 levels were reduced in murine models of fatty liver, and by hyperinsulinemia. In wild-type mice, Mboat7 was down-regulated by refeeding and insulin, concomitantly with insulin signaling activation. Acute hepatic Mboat7 silencing promoted hepatic steatosis in vivo and enhanced expression of fatty acid transporter Fatp1. MBOAT7-/- HepG2 showed altered phospholipids remodeling consistent with decreased enzymatic activity, increased triglyceride accumulation, enhanced lipogenesis and FATP1 expression, while FATP1 deletion rescued the phenotype. Conclusions: These results suggest that MBOAT7 down-regulation by hyperinsulinemia contributes to hepatic fat accumulation, impairing phospholipids remodeling and up-regulating FATP1. Funding Statement: LV was supported by MyFirst Grant AIRC n.16888, Ricerca Finalizzata Ministero della Salute RF-2016-02364358, Ricerca corrente Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, LV and AG. received funding from the European Union (EU) Programme Horizon 2020 (under grant agreement No. 777377) for the project LITMUS-“ Liver Investigation: Testing Marker Utility in Steatohepatitis”. MM was supported by Fondazione Italiana per lo Studio del Fegato (AISF) ‘Prof. Mario Coppo’ fellowship. AG received funding from the European Union (EU) Programme Horizon 2020 under grant agreement no. 634413 for the project EPoS-“Elucidating Pathways of Steatohepatitis”. Declaration of Interests: The authors declare no conflict of interest relevant to the present manuscript. Ethics Approval Statement: Informed written consent was obtained from each patient and the study protocol was approved by the Ethical Committee of the Fondazione IRCCS Ca’ Granda of Milan and conforms to the ethical guidelines of the 1975 Declaration of Helsinki. We received an approval from an Animal Use Committee for the animal work from the University of Milan and the Italian Ministry of Health Review Boards, in the context of the protocol 8/14, as indicated in the material and methods section in the manuscript. The authorization number of this protocol is 295/2012–A, received on 12/20/2012.