Protein kinase C-ε activation induces mitochondrial dysfunction and fragmentation in renal proximal tubules

Nowak G, Bakajsova D, Samarel AM. Protein kinase C-epsilon activation induces mitochondrial dysfunction and fragmentation in renal proximal tubules. Am J Physiol Renal Physiol 301: F197-F208, 2011. First published February 2, 2011; doi:10.1152/ajprenal.00364.2010.-PKC-epsilon activation mediates protection from ischemia-reperfusion injury in the myocardium. Mitochondria are a subcellular target of these protective mechanisms of PKC-epsilon. Previously, we have shown that PKC-epsilon activation is involved in mitochondrial dysfunction in oxidant-injured renal proximal tubular cells (RPTC; Nowak G, Bakajsova D, Clifton GL Am J Physiol Renal Physiol 286: F307-F316, 2004). The goal of this study was to examine the role of PKC-epsilon activation in mitochondrial dysfunction and to identify mitochondrial targets of PKC-epsilon in RPTC. The constitutively active and inactive mutants of PKC-epsilon were overexpressed in primary cultures of RPTC using the adenoviral technique. Increases in active PKC-epsilon levels were accompanied by PKC-epsilon translocation to mitochondria. Sustained PKC-epsilon activation resulted in decreases in state 3 respiration, electron transport rate, ATP production, ATP content, and activities of complexes I and IV and F(0)F(1)-ATPase. Furthermore, PKC-epsilon activation increased mitochondrial membrane potential and oxidant production and induced mitochondrial fragmentation and RPTC death. Accumulation of the dynamin-related protein in mitochondria preceded mitochondrial fragmentation. Antioxidants blocked PKC-epsilon-induced increases in the oxidant production but did not prevent mitochondrial fragmentation and cell death. The inactive PKC-epsilon mutant had no effect on mitochondrial functions, morphology, oxidant production, and RPTC viability. We conclude that active PKC-epsilon targets complexes I and IV and F(0)F(1)-ATPase in RPTC. PKC-epsilon activation mediates mitochondrial dysfunction, hyperpolarization, and fragmentation. It also induces oxidant generation and cell death, but oxidative stress is not the mechanism of RPTC death. These results show that in contrast to protective effects of PKC-epsilon activation in cardiomyocytes, sustained PKC-epsilon activation is detrimental to mitochondrial function and viability in RPTC.