High Glucose Stimulation of Mitochondrial Metabolism and Superoxide Generation is Mediated by Thioredoxin-Interacting Protein (TXNIP)

Thioredoxin-interacting protein (TXNIP) is an endogenous inhibitor of thioredoxin (Trx), a thiol oxidoreductase that regulates cellular redox status. TXNIP is upregulated by high glucose (HG) and augments reactive oxygen species (ROS). We recently showed that a reduction of TXNIP inhibits HG-induced mitochondrial membrane potential and superoxide production in cultured renal mesangial cells (MCs) (JBC, 2013) and that TXNIP–/– mice are protected from diabetic nephropathy (DN) (JASN 2015). To investigate mechanisms, metabolic profiling and bioenergetics of HG-treated C3H (wild type) and Hcb-19 (TXNIP deficient) MCs were assessed. Metabolomic analysis revealed higher glycolytic, but significantly reduced citrate and isocitrate, TCA cycle intermediates, in HG-treated Hcb-19 compared to C3H. As well, a 2-fold increase in malonyl CoA was observed in Hcb-19 cells suggesting that acetylCoA was driven toward lipogenesis. These data were supported by a lower PDHE1α and citrate synthase protein and activity in these cells. Assessment with the Seahorse XF analyzer revealed that Hcb-19 cells displayed lower mitochondrial oxygen consumption and a reduced respiratory capacity. Furthermore, Hcb-19 cells displayed a markedly lower protein expression of electron transport chain complexes (ETC) I, II and III, the key generators of mitochondrial superoxide. These data indicate that TXNIP promotes mitochondrial glucose oxidation via the TCA cycle and ROS generation via the ETC, thereby stimulating a HG-oxidative stress pathway mediating DN.