NEFA-induced ROS impaired insulin signalling through the JNK and p38MAPK pathways in non-alcoholic steatohepatitis

The aim of this study was to investigate the changes in hepatic oxidative phosphorylation (OXPHOS) complexes (COs) in patients and cows with non-alcoholic steatohepatitis (NASH) and to investigate the mechanism that links mitochondrial dysfunction and hepatic insulin resistance induced by non-esterified fatty acids (NEFAs). Patients and cows with NASH displayed high blood NEFAs, TNF-alpha and IL-6 concentrations, mitochondrial dysfunction and insulin resistance. The protein levels of peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1), mitofusin-2 (Mfn-2) and OXPHOS complexes (human: COI and COIII; cow: COI-IV) were significantly decreased in patients and cows with NASH. NEFA treatment significantly impaired mitochondrial function and, increased reactive oxygen species (ROS) production, and excessive ROS overactivated the JNK and p38MAPK pathways and induced insulin resistance in cow hepatocytes. PGC-1 alpha and Mfn-2 overexpression significantly decreased the NEFA-induced ROS production and TNF-alpha and IL-6 mRNA expressions, reversed the inhibitory effect of NEFAs on mitochondrial function and attenuated the overactivation of the ROS-JNK/p38MAPK pathway, alleviated insulin resistance induced by NEFAs in cow hepatocytes and HepG2 cells. These findings indicate that NEFAs induce mitochondrial dysfunction and insulin resistance mediated by the ROS-JNK/p38MAPK pathway. PGC-1 alpha or Mfn-2 overexpression reversed the lipotoxicity of NEFAs on mitochondrial dysfunction and insulin resistance. Our study clarified the mechanism that links hepatic mitochondrial dysfunction and insulin resistance in NASH.