Beneficial Effects of <i>Myo</i>-Inositol Oxygenase Deficiency in Cisplatin-Induced AKI.

Abstract

Overexpression of the proximal tubular enzyme <i>myo</i>-inositol oxygenase (MIOX) induces oxidant stress <i>in vitro</i> However, the relevance of MIOX to tubular pathobiology remains enigmatic. To investigate the role of MIOX in cisplatin-induced tubular AKI, we generated conditional MIOX-overexpressing transgenic (MIOX-TG) mice and MIOX-knockout (MIOX^-/-) mice with tubule-specific MIOX overexpression or knockout, respectively. Compared with cisplatin-treated wild-type (WT) mice, cisplatin-treated MIOX-TG mice had even greater increases in urea, creatinine, and KIM-1 levels and more tubular injury and apoptosis, but these effects were attenuated in cisplatin-treated MIOX^-/- mice. Similarly, MIOX-TG mice had the highest and MIOX^-/- mice had the lowest renal levels of Bax, cleaved caspase-3, and NADPH oxidase-4 expression and reactive oxygen species (ROS) generation after cisplatin treatment. <i>In vitro</i>, cisplatin dose-dependently increased ROS generation in LLC-PK1 cells. Furthermore, MIOX overexpression in these cells accentuated cisplatin-induced ROS generation and perturbations in the ratio of GSH to oxidized GSH, whereas MIOX-siRNA or <i>N</i>-acetyl cysteine treatment attenuated these effects. Additionally, the cisplatin-induced enhancement of p53 activation, NF-<i>κ</i>B binding to DNA, and NF-<i>κ</i>B nuclear translocation in WT mice was exacerbated in MIOX-TG mice but absent in MIOX^-/- mice. <i>In vitro</i>, MIOX-siRNA or NAC treatment reduced the dose-dependent increase in p53 expression induced by cisplatin. We also observed a remarkable influx of inflammatory cells and upregulation of cytokines in kidneys of cisplatin-treated MIOX-TG mice. Finally, analysis of genomic DNA in WT mice revealed cisplatin-induced hypomethylation of the MIOX promoter. These data suggest that MIOX overexpression exacerbates, whereas MIOX gene disruption protects against, cisplatin-induced AKI.