Enhancing Acsl4 in absence of mTORC2/Rictor drove β-cell dedifferentiation via inhibiting FoxO1 and promoting ROS production

Abstract

Rapamycin insensitive companion of mechanistic target of Rapamycin (Rictor), the key component of mTOR complex 2 (mTORC2), controls both β-cell proliferation and function. We sought to study whether long chain acyl-CoA synthetase 4 (Acsl4) worked downstream of Rictor/mTORC2 to maintain β-cell functional mass. We found Acsl4 was positively regulated by Rictor at transcriptional and posttranslational levels in mouse β-cell. Infecting adenovirus expressing Acsl4 in β-cell-specific-Rictor-knockout (βRicKO) islets and Min6 cells knocking down Rictor with lentivirus-expressing siRNA-oligos targeting Rictor(siRic), recovered the β-cell dysplasia but not dysfunction. Cell bioenergetic experiment performed with Seahorse XF showed that Acsl4 could not rescue the dampened glucose oxidation in Rictor-lacking β-cell, but further promoted lipid oxidation. Transposase-Accessible Chromatin (ATAC) and H3K27Ac chromatin immunoprecipitation (ChIP) sequencing studies reflected the epigenetic elevated molecular signature for β-cell dedifferentiation and mitigated oxidative defense/response. These results were confirmed by the observations of elevated acetylation and ubiquitination of FoxO1, increased protein levels of Gpx1 and Hif1an, excessive reactive oxygen species (ROS) production and diminished MafA in Acsl4 overexpressed Rictor-lacking β-cells. In these cells, antioxidant treatment significantly recovered MafA level and insulin content. Inducing lipid oxidation alone could not mimic the effect of Acsl4 in Rictor lacking β-cell. Our study suggested that Acsl4 function in β-cell was context dependent and might facilitate β-cell dedifferentiation with attenuated Rictor/mTORC2 activity or insulin signaling via posttranslational inhibiting FoxO1 and epigenetically enhancing ROS induced MafA degradation.