Grape Seed Proanthocyanidin Extracts Antagonizes Glucolipotoxicity-induced Autophagy And Ferroptosis In MIN6 Cells Through Nrf2 Pathway

Objective:Autophagy and ferroptosis are involved in the regulation of pancreaticβcell dysfunction.Nuclear factor erythroid 2-related factor 2（Nrf2）is involved in regulating autophagy and antagonizing ferroptosis.Our previous study found that grape seed proanthocyanidin extracts（GSPE）antagonized glucolipotoxicity-induced pancreaticβcell injury by activating Nrf2 pathway,but the specific mechanism was not fully elucidated.Therefore,this study was to investigate the relationship between autophagy and ferroptosis inβ-cell injury induced by glucolipotoxicity and the possible protective mechanism of GSPE,so as to provide a basis for the prevention and treatment of T2DM.Methods:The pancreaticβ-cell injury model was established by treating high glucose（25mmol/L）and sodium palmitate（200μmol/L）（GP）in MIN6 cell.CCK8 method was used to detect the cell viability at 0h,6h,12h,24h and 48h.Western blot was used to detect the expression of ferroptosis key proteins glutathione peroxidase 4（GPX4）and acyl-Co A synthetase long-chain family member 4（ACSL4）and autophagy-related protein microtubule-associated protein 1 light chain 3（LC3Ⅱ）and P62 at different time（0h,12h,24h,48h）after GP intervention.MIN6 cells were treated with ferroptosis inducer erastin,ferroptosis inhibitor ferrostatin-1（Fer-1）,autophagy inducer rapamycin（RAPA）and autophagy inhibitor chloroquine（CQ）.CCK8 was used to detect cell viability;the fluorescence intensity of reactive oxygen species（ROS）was observed by fluorescence microscope.The contents of superoxide dismutase（SOD）,glutathione（GSH）and malondialdehyde（MDA）were measured by corresponding kits,and intracellular Fe²⁺was detected by Lillie staining.The changes of mitochondrial membrane potential were detected by JC-1 kit.Western Blot was used to detect the expression of GPX4,ACSL4,ferritin（FE）,nuclear receptor coactivator 4（NCOA4）,autophagy-related proteins LC3Ⅱand P62.Different doses of GSPE and si-Nrf2were intervened with GSPE,and the cell survival rate was detected by CCK8.The fluorescence intensity of ROS was observed by fluorescence microscope.The contents of SOD,GSH and MDA were measured by corresponding kits,and intracellular Fe²⁺was detected by Lillie staining.The changes of mitochondrial membrane potential were detected by JC-1 kit.Western Blot was used to detect the expression of GPX4,ACSL4,FE,NCOA4,LC3Ⅱand P62,as well as Nrf2 and its downstream protein heme oxygenase-1（HO-1）.Results:1.High glucose and sodium palmitate induced ferroptosis in MIN6 cells:GP and ferroptosis activator erastin significantly decreased cell viability,decreased SOD and GSH contents and mitochondrial membrane potential,increased MDA content,ROS fluorescence intensity and Fe²⁺content（P<0.05）,down-regulated GPX4 and NCOA4 proteins,and up-regulated ACSL4 and FE proteins（P<0.05）.Compared with GP group,Fer-1 significantly increased cell viability,SOD and GSH contents and mitochondrial membrane potential,decreased MDA content,ROS fluorescence intensity and Fe²⁺content（P<0.05）,up-regulated GPX4 and NCOA4 proteins,and down-regulated ACSL4 and FE proteins（P<0.05）.2.The activation of autophagy contributes to GP-induced ferroptosis resistance in MIN6 cells:GP and CQ significantly decreased cell viability,decreased SOD and GSH contents and mitochondrial membrane potential,increased MDA content,ROS fluorescence intensity and Fe²⁺content（P<0.05）,down-regulated GPX4 and NCOA4 proteins,and up-regulated ACSL4,FE,LC3Ⅱand P62 proteins（P<0.05）.Compared with GP group,autophagy agonist RAPA significantly increased cell viability,SOD and GSH contents and mitochondrial membrane potential,decreased MDA content,ROS fluorescence intensity and Fe²⁺content（P<0.05）,up-regulated GPX4,NCOA4 and LC3Ⅱproteins,and down-regulated ACSL4,FE and P62 proteins（P<0.05）.3.The inhibition of ferroptosis helps to improve GP-induced autophagy in MIN6 cells:GP group up-regulated the expression of LC3Ⅱand P62 protein（P<0.05）.Compared with GP group,Fer-1 down-regulated the expression of LC3Ⅱand P62 protein（P<0.05）,while erastin up-regulated the expression of LC3Ⅱand P62 protein（P<0.05）.4.GSPE protects GP-induced MIN6 cell injury by enhancing autophagy and inhibiting ferroptosis:Compared with GP group,GSPE intervention increased cell viability,decreased ferrous ions,MDA and ROS levels,increased GSH,SOD activity and mitochondrial membrane potential,increased GPX4,NCOA4,LC3Ⅱ,Nrf2 and HO-1 protein expression,and decreased ACSL4,FE,and P62 protein expression（P<0.05）.5.GSPE improves autophagy and inhibits ferroptosis in MIN6 cells by activating the Nrf2 pathway:After si-Nrf2 transfected MIN6 cells for 4h,GSPE intervened in the cells for 24h.Compared with GSPE,after si-Nrf2,GSPE intervention decreased Nrf2,HO-1,GPX4 and NCOA4 protein expression,and increased ACSL4 and LC3Ⅱ（P<0.05）.There was no significant change in P62 and FE（P>0.05）.Conclusion:Ferroptosis and autophagic flux blockage are involved in glucolipotoxicity-induced MIN6 cell damage,and autophagy and ferroptosis promote each other,leading toβ-cell damage.GSPE may enhance autophagy and inhibit ferroptosis by activating Nrf2 signaling pathway,thereby alleviating pancreaticβ-cell damage.