Abstract: SA-PO515
Thioredoxin-Interacting Protein (TXNIP) Promotes GAPDH Nuclear Translocation by High Glucose
Session Information
- Diabetic Kidney Disease: Basic - III
November 09, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Diabetic Kidney Disease
- 601 Diabetic Kidney Disease: Basic
Authors
- Zhong, Lexy (huize), University of Toronto, Toronto, Ontario, Canada
- Xia, Ling, Research Institute-McGill University Health Center(RI-MUHC), Montreal, Quebec, Canada
- Fantus, Ivan George, Metabolic Disorders and Complications Program (MeDiC), Montreal, Quebec, Canada
Background
Thioredoxin-interacting protein (TXNIP) is a multifunctional protein that regulates glucose metabolism and the cellular redox state, the latter by binding and inhibiting the endogenous antioxidant thioredoxin. TXNIP is markedly upregulated by high glucose and we previously showed that STZ-induced diabetic TXNIP-/- mice are protected from developing features of Diabetic Nephropathy (DN). The pathogenesis of diabetes complications involves the oxidative inhibition of the glycolytic enzyme GAPDH, resulting in aberrant glucose metabolism. However, nitrosylation and oxidation (N/O) of GAPDH was found in neuronal cells to cause its nuclear translocation by binding the E3 ligase Siah1, followed by activation of proapoptotic gene expression. We postulated that TXNIP would promote GAPDH N/O and nuclear translocation in HG by inhibiting redox balance.
Methods
To study TXNIP signalling in vitro, primary mesangial cells (MCs) from TXNIP+/+ (WT) and TXNIP-/- (KO) mice were cultured in normal (5mM) and high glucose (25mM; HG). GAPDH activity, GAPDH/Siah1 nuclear translocation, caspase-3 cleavage, and Bax/Bcl-2 expression were examined via immunoblotting. To test our hypothesis in vivo, STZ-induced diabetic DBA/2J mice were orally treated with deprenyl, a drug used in Parkinson’s disease and shown to inhibit GAPDH-Siah1 binding, or the vehicle as a control. Structural outcomes including glomerular mesangial expansion and fibrosis, basement membrane thickening, podocyte foot process effacement, and NOX4 expression were assessed by histology. Functional outcomes such as albuminuria were assessed by ELISA.
Results
In vitro, exposure of primary cultured WT MCs to HG significantly decreased GAPDH activity, caused nuclear localization of both GAPDH and Siah1 at 24h and 48h, and increased caspase-3 cleavage and the Bax/Bcl-2 ratio at 12h and 24h, while TXNIP-/- MC showed no HG-mediated effect. In vivo, deprenyl treatment significantly reduced diabetes-induced albuminuria, glomerular mesangial expansion and fibrosis, basement membrane thickening, podocyte foot process effacement, and NOX4 expression.
Conclusion
These data suggest that GAPDH has a direct pathogenic role in DN via the GAPDH-Siah1 signalling pathway and that TXNIP is a critical modulator of this pathway that promotes DN.
Funding
- Government Support - Non-U.S.