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ABSTRACT NF‐E2 p45‐related factor 2 (Nrf2), is a major redox sensitive transcription factor that plays an essential role in regulating glucose metabolism. Inactivation of Nrf2 has been associated with diabetic… Click to show full abstract
ABSTRACT NF‐E2 p45‐related factor 2 (Nrf2), is a major redox sensitive transcription factor that plays an essential role in regulating glucose metabolism. Inactivation of Nrf2 has been associated with diabetic complications however, mechanisms warranting Nrf2 suppression are incompletely understood. We hypothesized that PHLPP1 activates GSK3&bgr; to induce &bgr;‐TrCP mediated Nrf2 phosphorylation and degradation. In vivo study was carried out in STZ‐NA induced type 2 diabetic male Wistar rats. GSK3&bgr; mediated Nrf2 ubiquitination was confirmed by administration of GSK3&bgr; inhibitor (LiCl; 60mg/kg bwt.) which rapidly enhanced Nrf2 protein levels in STZ‐NA treated diabetic rats. In addition, high glucose (30mM; 48h) treated renal proximal tubular cells NRK52E showed decreased Nrf2 nuclear localization, enhanced oxidative stress and caspase3 activation. While specific inhibition with GSK3&bgr; inhibitor SB216763 in vitro restored cellular homeostasis, glucose uptake and decreased apoptotic cell death. Immunoblotting and immunocytochemistry data demonstrated that aberrant renal glucose fluxes are associated with p53 mediated modulation in glucose transporter levels where expression of p53 is indirectly targeted through Nrf2 responsive MDM2 protein. Gene knockdown of PHLPP1 in NRK52E cells enhanced Nrf2‐responsive antioxidant enzymes HO‐1 and NQO‐1 which suggested that PHLPP1 up‐regulation during hyperglycemia lowers Nrf2 stability via GSK3&bgr; activation. More significantly, GSK3&bgr; inhibition enhanced Nrf2‐ARE binding compared to diabetic rats, providing further confirmation for GSK3&bgr;/&bgr;‐TrCP pathway in suppressing Nrf2 activation during diabetic renal injury. Taken together, our results indicate that PHLPP1 up‐surged Nrf2 nuclear instability by promoting Nrf2/&bgr;‐TrCP association and its inhibition may be critical in the management of diabetic nephropathy. HIGHLIGHTSDeficient Nrf2 signaling negatively impacts cell survival during hyperglycemia.Up‐regulation of PHLPP1 limits Akt signaling which subsequently down regulate Nrf2 expression through GSK3&bgr; activation.Hyperglycemia induced PHLPP1 promotes Nrf2 ubiquitination via GSK3&bgr;/&bgr;‐TrCP axis.Specific inhibition of PHLPP1 and GSK3&bgr; promotes Nrf2 stability in hyperglycemic renal cells.