(VP072) LOSS OF THIOREDOXIN-INTERACTING PROTEIN (TXNIP) MEDIATES SENESCENCE IN RENAL MESANGIAL CELLS ASSOCIATED WITH HYPERACTIVATION OF AKT AND RAS; A POTENTIAL ADVERSE EFFECT OF THERAPEUTIC TARGETING.

Background: Thioredoxin-interacting protein (TXNIP) is an α-arrestin family member that is ubiquitously expressed. TXNIP is the only α-arrestin protein that binds and inhibits thioredoxin (Trx), an endogenous antioxidant. In the context of diabetes, TXNIP upregulation by high glucose mediates beta cell oxidative stress and apoptosis that underlies diabetes progression and similarly contributes to diabetic kidney disease. However, TXNIP is also a tumor suppressor and TXNIP-/- mice develop hepatocellular carcinoma. While loss of TXNIP is associated with enhances insulin sensitivity and directs cellular metabolism toward glycolysis and lactate accumulation, the Warburg effect, a major energy utilization pathway in cancer cells.

METHODS AND RESULTS: In studies of glomerular mesangial cells (MC), we found that development of senescence with cell passaging (25 passages) was associated with a loss of TXNIP. To investigate its role, primary mouse MC obtained from WT and TXNIP KO mice were compared at early passage (5-7). TXNIP KO MCs showed significantly increased expression of senescence markers P53 and P16 (p < 0.05), and beta-galactosidase staining (13-fold). Additionally, KO MCs showed significantly lower PTEN activity and consequently, higher activation of Akt versus WT MCs (p < 0.05). To investigate the role of Akt, cells were exposed to Akt inhibitor (GSK690693). Inhibition of Akt rescued the senescence phenotype with significant reduction of senescence markers (P53, P16 and beta-galactosidase staining). Akt activation induces reactive oxygen species (ROS). KO MCs showed significantly increased total cellular ROS (p < 0.05). However, there was no difference in mitochondrial ROS generation detected by Mitosox but KO MCs showed significantly increased NADPH oxidase 4 (NOX4) expression (p < 0.05). In addition, KO MCs also showed significantly more activated oncogene RAS (p < 0.05) and reduced apoptosis (p < 0.05). Akt inhibition significantly reduced total ROS and NOX4 expression (p < 0.05).

Conclusion: Collectively, these data showed for the first time that loss of TXNIP contributes to cellular senescence via mechanisms consistent with oncogene-induced senescence mediated by reduced PTEN and increased Akt and RAS activation. TXNIP has been proposed as a therapeutic target to prevent glucose toxicity and progression of diabetes and its complications. These data indicate that adverse health consequences can occur with over- or under-expression of TXNIP.