Nrf2-Dependent Adaptation to Oxidative Stress Protects Against Progression of Diabetic Nephropathy

Aims: Adaptation to oxidative stress is essential for maintaining protein and redox homeostasis in mammalian cells. Palmitic acid (PA) plays a central role in oxidative stress and immunoproteasome regulation in podocytes and diabetes, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have beneficial impact on diabetes. The role of Nrf2 in adaptation to oxidative stress and regulation of immunoproteasome by PA and EPA/DHA in podocytes and diabetic kidneys is not well defined. The present study describes the effect of PA- and EPA/DHA-induced oxidative stress in regulating Nrf2/immuoproteasome pathway in a model system relevant to diabetic nephropathy (DN). Results: Short PA exposure to podocytes promotes the upregulation of antioxidant proteins and immunoproteasome mediated by Nrf2, leading to acute transient oxidative stress adaptation. Both short- and long-term incubation of EPA or DHA in podocytes induced oxidative stress and activation of Nrf2, causing persistent oxidative stress adaptation. Long PA exposure to podocytes decreased the Nrf2 activity, and EPA/DHA attenuated these effects of PA. In db/db mice, feeding of EPA/DHA-rich fish oil increased oxidative stress in kidneys and induced renal cortical Nrf2 nuclear translocation and immunoproteasome overexpression, inhibiting the progression of DN. Innovation and Conclusion: We demonstrate an oxidative stress adaptation mechanism by PA and EPA/DHA regulated by Nrf2 in podocytes and kidneys of type 2 diabetes. This work provides an important insight into the pathogenetic mechanisms of DN by PA-induced oxidative stress. We conclude that activation of Nrf2-immunoproteasome signaling pathway by EPA/DHA plays a crucial role in abrogating the proteotoxic stress in DN. Antioxid. Redox Signal. 42, 751-766.