Leucyl tRNA synthetase ameliorates cholestatic liver injury by inhibiting integrated stress response in mice

Aminoacyl-tRNA synthetases, as pivotal enzymes in protein biosynthesis, have been linked to the development of certain diseases when specific isoforms are dysregulated. However, the involvement of leucyl-tRNA synthetase (LARS) in hepatic pathologies remains unexplored. In this study, a marked upregulation of LARS was observed in cholestatic liver tissues. Mice with liver-specific LARS knockdown manifested substantially attenuated hepatic injury, evidenced by reductions in serum alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase levels, as well as dysregulated bile acid homoeostasis, diminished hepatic necrosis, fibrosis, and hepatocyte apoptosis. Conversely, hepatic overexpression of LARS resulted in exacerbated liver injury. To mimic cholestatic injury in vitro, AML-12 cells were exposed to taurocholic acid (TCA), where it was found that LARS deficiency alleviated TCA-induced cellular damage and apoptosis. Mechanistically, bile acids were found to induce an integrated stress response (ISR) via up-regulating the phosphorylation of general control nonderepressible (GCN) 2 levels. Notably, LARS deficiency was shown to attenuate the TCA-induced GCN2 phosphorylation upregulation, while no modulatory effect was detected on GCN2 expression in the absence of TCA. Furthermore, BDL decreased the hepatic leucine contents and tRNA cahrging ratio, which was reversed by LARS knockdown. GCN2 knockdown reversed the effect of LARS overexpression on AML-12 cell viability. Collectively, these findings delineate a regulatory role for LARS in modulating cholestatic liver injury, likely through the suppression of leucine-tRNA-GCN2 activation and ISR signaling pathway.