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Abstract: SA-PO531

Hyperglycemia Reduced DUSP4 Expression Leads to JNK MAPK Activation, Increased NOX4 Expression, and Insulin Resistance in Podocytes and Diabetic Nephropathy

Session Information

Category: Diabetic Kidney Disease

  • 601 Diabetic Kidney Disease: Basic

Authors

  • Rousseau, Marina, University of Sherbrooke, Compton, Quebec, Canada
  • Denhez, Benoit, University of Sherbrooke, Compton, Quebec, Canada
  • Lizotte, Farah, University of Sherbrooke, Compton, Quebec, Canada
  • Geraldes, Pedro Miguel, University of Sherbooke, Sherbrooke, Quebec, Canada
Background

Podocyte dysfunction is an early event in the development of diabetic nephropathy (DN) with multiple causes including insulin resistance and increased oxidative stress (ROS via NOX4) which lead to the activation of p38 and JNK MAPK pathways. A previous study has shown that JNK activation leads to serine 307 (ser307) phosphorylation of IRS1 (inhibitory phosphorylation) in insulin-resistant ob/ob mice. Our laboratory recently reported a decrease in the expression of DUSP4, a dual specificity phosphatase known to inhibit the MAPKs, which was associated with elevated JNK activation and NOX4 expression in podocytes exposed to high glucose. Thus, we hypothesized that hyperglycemia-induced DUSP4 expression reduction leads to insulin resistance in podocytes and DN via JNK activation and NOX4 expression.

Methods

Cultured podocytes were exposed to normal (5.6 mM) or high (HG; 25 mM) levels of glucose for 72h with either an overexpression of DUSP4 (adenovirus) or an inhibition of JNK (JNK inhibitor SP600125). In vivo, insulin injection was performed 15min prior to euthanasia where renal cortex was extracted from nondiabetic and diabetic (Ins2+/C96Y) mice, with or without a deletion of DUSP4 (Dusp4-/-).

Results

Podocytes exposed to HG showed reduced DUSP4 expression, increased JNK activation and increased ser307 phosphorylation of IRS1, which contributed to a decrease in the phosphorylation of Akt after insulin stimulation. Both DUSP4 overexpression and JNK inhibition blocked ser307 phosphorylation of IRS1 induced by HG and reestablished downstream insulin signaling cascade (tyrosine 612 phosphorylation of IRS1 and Akt phosphorylation). HG reduced DUSP4 expression was prevented using antioxidant N-acetyl cysteine and HG increased NOX4 expression was diminished with DUSP4 overexpression and JNK inhibition in podocytes. In vivo, DUSP4 reduction in renal cortex of Ins2+/C96Y mice correlated with JNK activation, increased ser307 phosphorylation of IRS1 and reduced Akt phosphorylation, reduction exacerbated in Ins2+/C96Y mice deficient for DUSP4.

Conclusion

HG induced JNK activation by reduced DUSP4 expression mediates an increase in the production of ROS via NOX4 as well as insulin resistance in DN.

Funding

  • Government Support - Non-U.S.