Akt activation improves oxidative phosphorylation in renal proximal tubular cells following nephrotoxicant injury.

Previously, we showed that protein kinase B (Akt) activation increases intracellular ATP levels and decreases necrosis in renal proximal tubular cells (RPTC) injured by the nephrotoxicant S-(1, 2-dichlorovinyl)-l-cysteine (DCVC) (Shaik ZP, Fifer EK, Nowak G. Am J Physiol Renal Physiol 292: F292-F303, 2007). This study examined the role of Akt in improving mitochondrial function in DCVC-injured RPTC. Our data show a novel observation that phosphorylated (active) Akt is localized in mitochondria of noninjured RPTC, both in mitoplasts and the mitochondrial outer membrane. Mitochondrial levels of active Akt decreased in nephrotoxicant-injured RPTC, and this decrease was associated with mitochondrial dysfunction. DCVC decreased basal, uncoupled, and state 3 respirations; ATP production; activities of complexes I, II, and III; the mitochondrial membrane potential (DeltaPsi(m)); and F(0)F(1)-ATPase activity. Expressing constitutively active Akt in DCVC-injured RPTC increased the levels of phosphorylated Akt in mitochondria, reduced the decreases in basal and uncoupled respirations, increased complex I-coupled state 3 respiration and ATP production, enhanced activities of complex I, complex III, and F(0)F(1)-ATPase, and improved DeltaPsi(m). In contrast, inhibiting Akt activation by expressing dominant negative (inactive) Akt or using 20 microM LY294002 exacerbated decreases in electron transport rate, state 3 respiration, ATP production, DeltaPsi(m), and activities of complex I, complex III, and F(0)F(1)-ATPase. In conclusion, our data show that Akt activation promotes mitochondrial respiration and ATP production in toxicant-injured RPTC by 1) improving integrity of the respiratory chain and maintaining activities of complex I and complex III, 2) reducing decreases in DeltaPsi(m), and 3) restoring F(0)F(1)-ATPase activity.