Background: NFE2-related factor 2 (Nrf2) is a master regulatory transcription factor for antioxidant genes. Inhibition of its adaptor protein, Kelch-like ECH-associated protein 1 (Keap1), activates Nrf2. Podocyte injury triggers the progressive deterioration of glomerular damage toward glomerulosclerosis. We examined whether modulation of the Keap1-Nrf2 system has an impact on this process.
Methods: Nrf2 null-mutant (KO) and Keap1 hypomorphic knockdown (KD) mice were crossed with NEP25 mice, in which podocyte-specific injury can be induced by an immunotoxin.
Results: Thiobarbituric acid reactive substances, 8-hydroxydeoxyguanosine and phosphorylated JNK were increased in the injured NEP25 kidney. Real-time PCR revealed that Keap1 KD upregulated Nrf2 target genes, including Gclc, Gclm, Gstp1, Gstp2 and Nqo1 in the glomerulus. However, podocyte injury did not upregulate these genes in Keap1 wild-type mice, nor did it further increase the expression of those genes in Keap1 KD mice. Three weeks after the induction of podocyte injury, glomerulosclerosis was considerably more attenuated in Keap1 KD mice than in control mice (median sclerosis index, 0.27 versus 3.03, on a 0-4 scale). Keap1 KD mice also showed considerably preserved nephrin staining (median index, 6.76 versus 0.91, on a 0-8 scale) and decreased glomeruli containing desmin-positive injured podocytes (median percentage, 24.5% versus 85.8%), along with a decrease in mRNAs for Fn1, Tgfb1, Col4a4 and Col1a2.
Conclusions: Thus, podocyte injury cannot effectively activate Nrf2, but Nrf2 activation by Keap1 knockdown attenuates glomerulosclerosis. These results indicate that the Nrf2-Keap1 system is a promising drug target for the treatment of chronic kidney diseases.
Keywords: antioxidant genes; glomerulosclerosis; hypomorphic allele; oxidative stress.