The PKA-SREBP1c Pathway Plays a Key Role in the Protective Effects of Lactobacillus johnsonii JNU3402 Against Diet-Induced Fatty Liver in Mice

Abstract

Scope: The present study aims to assess the protective effect of Lactobacillus johnsonii JNU3402 (LJ3402) against diet-induced non-alcoholic fatty liver disease (NAFLD) and determine the mechanism underlying its beneficial effect on the liver in mice. Methods and results: Seven-week-old male mice are fed a high-fat diet (HFD) with or without oral supplementation of LJ3402 for 14 weeks. In mice fed an HFD, LJ3402 administration alleviates liver steatosis, diet-induced obesity, and insulin resistance with a decreased hepatic expression of sterol-regulatory element-binding protein-1c (SREBP-1c), fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), and an increased phosphorylation of SREBP-1c. The mechanistic study shows that LJ3402 inhibits SREBP-1c transcriptional activity by enhancing protein kinase A (PKA)-mediated phosphorylation and reduces the expression of its lipogenic target genes in AML12 and HepG2 cells, thereby attenuating hepatic lipid accumulation. Moreover, silencing the PKA α catalytic subunit or the inhibition of PKA activity by H89 abolishes LJ3402 suppression of free fatty acid (FFA)-induced SREBP-1c activity in hepatocytes. In addition, LJ3402 administration elevates the plasma lactate levels in mice fed an HFD; this lactate increases PKA-mediated SREBP-1c phosphorylation in AML12 cells with a decreased expression of its target genes, reducing hepatic lipid accumulation. Conclusion: LJ3402 attenuates HFD-induced fatty liver in mice through the lactate-PKA-SREBP-1c pathway.