Potential role for Nrf2 activation in the therapeutic effect of MG132 on diabetic nephropathy in OVE26 diabetic mice

Cui W, Li B, Bai Y, Miao X, Chen Q, Sun W, Tan Y, Luo P, Zhang C, Zheng S, Epstein PN, Miao L, Cai L. Potential role for Nrf2 activation in the therapeutic effect of MG132 on diabetic nephropathy in OVE26 diabetic mice. Am J Physiol Endocrinol Metab 304: E87-E99, 2013. First published November 6, 2012; doi:10.1152/ajpendo.00430.2012.-Oxidative stress is a major cause of diabetic nephropathy. Upregulation of the key antioxidative transcription factor, nuclear factor-erythroid 2-related factor 2 (Nrf2), was found to prevent the development of diabetic nephropathy. The present study was designed to explore the therapeutic effect of Nrf2 induced by proteasomal inhibitor MG132 at a low dose (10 mu g/kg) on diabetic nephropathy. Transgenic type 1 diabetic (OVE26) mice displayed renal dysfunction with albuminuria by 3 mo of age, at which time MG132 treatment was started. After 3-mo treatment with MG132, renal function, morphology, and biochemical changes were examined with real-time PCR, Western blotting, and immunohistochemical examination. Compared with age-matched, nontreated diabetic mice, MG132-treated diabetic mice showed significant improvements in terms of renal structural and functional alterations. These therapeutic effects were associated with increased Nrf2 expression and transcriptional upregulation of Nrf2-regulated antioxidants. Mechanistic study using human renal tubular HK11 cells confirmed the role of Nrf2, as silencing the Nrf2 gene with its specific siRNA abolished MG132 prevention of high-glucose-induced profibrotic response. Furthermore, diabetes was found to significantly increase proteasomal activity in the kidney, an effect that was significantly attenuated by 3 mo of treatment with MG132. These results suggest that MG132 upregulates Nrf2 function via inhibition of diabetes-increased proteasomal activity, which can provide the basis for the therapeutic effect of MG132 on the kidney against diabetes-induced oxidative damage, inflammation, fibrosis, and eventual dysfunction.