Deficient endoplasmic reticulum-mitochondrial phosphatidylserine transfer causes liver disease

Abstract

Non-alcoholic fatty liver is the most common liver disease worldwide. Here, we show that the mitochondrial protein mitofusin 2 (Mfn2) protects against liver disease. Reduced Mfn2 expression was detected in liver biopsies from patients with non-alcoholic steatohepatitis (NASH). Moreover, reduced Mfn2 levels were detected in mouse models of steatosis or NASH, and its re-expression in a NASH mouse model ameliorated the disease. Liver-specific ablation of Mfn2 in mice provoked inflammation, triglyceride accumulation, fibrosis, and liver cancer. We demonstrate that Mfn2 binds phosphatidylserine (PS) and can specifically extract PS into membrane domains, favoring PS transfer to mitochondria and mitochondrial phosphatidylethanolamine (PE) synthesis. Consequently, hepatic Mfn2 deficiency reduces PS transfer and phospholipid synthesis, leading to endoplasmic reticulum (ER) stress and the development of a NASH-like phenotype and liver cancer. Ablation of Mfn2 in liver reveals that disruption of ER-mitochondrial PS transfer is a new mechanism involved in the development of liver disease.

This study was supported by the MINECO (SAF2016-75246R), the Generalitat de Catalunya (2014SGR48, 2017SGR696, ICREA Acadèmia), INFLAMES (PIE-14/00045, ISCIII), CIBERDEM, ISCIII, INTERREG IV-B-SUDOE-FEDER (DIOMED, SOE1/P1/E178), and “la Caixa” Foundation. S.F.-V. acknowledges support from the Miguel Servet tenure-track program (CP10/00438 and CPII16/00008) from the Fondo de Investigación Sanitaria, co-financed by the ERD. We gratefully acknowledge institutional funding from the MINECO through the Centres of Excellence Severo Ochoa Award and from the CERCA Programme of the Generalitat de Catalunya.