Activation of ERK1/2 pathway mediates oxidant-induced decreases in mitochondrial function in renal cells

Abstract

Previously, we showed that oxidant exposure in renal proximal tubular cells (RPTC) induces mitochondrial dysfunction mediated by PKC-epsilon. This study examined the role of ERK1/2 in mitochondrial dysfunction induced by oxidant injury and whether PKC-epsilon mediates its effects on mitochondrial function through the Raf-MEK1/2-ERK1/2 pathway. Sublethal injury produced by tert-butylhydroperoxide (TBHP) resulted in three- to fivefold increase in phosphorylation of ERK1/2 and p38 but not JNK. This was followed by decreases in basal and uncoupled respirations (41%), state 3 respiration and ATP production coupled to complex I (46%), and complex I activity (42%). Oxidant exposure decreased aconitase activity 30% but not pyruvate, alpha-ketoglutarate, and malate dehydrogenase activities. Inhibition of ERK1/2 restored basal and state 3 respirations, DeltaPsi(m), ATP production, and complex I activity but not aconitase activity. In contrast, activation of ERK1/2 by expression of constitutively active MEK1 suppressed basal, uncoupled, and state 3 respirations in noninjured RPTC to the levels observed in TBHP-injured RPTC. MEK1/2 inhibition did not change Akt or p38 phosphorylation, demonstrating that the protective effect of MEK1/2 inhibitor was not due to activation of Akt or inhibition of p38 pathway. Inhibition of PKC-epsilon did not block TBHP-induced ERK1/2 phosphorylation in whole RPTC or in mitochondria. We conclude that 1) oxidant-induced activation of ERK1/2 but not p38 or JNK reduces mitochondrial respiration and ATP production by decreasing complex I activity and substrate oxidation through complex I, 2) citric acid cycle dehydrogenases are not under control of the ERK1/2 pathway in oxidant-injured RPTC, 3) the protective effects of ERK1/2 inhibition are not due to activation of Akt, and 4) ERK1/2 and PKC-epsilon mediate oxidant-induced mitochondrial dysfunction through independent pathways.

Rapid Renal Regulation of Peroxisome Proliferator-activated Receptor γ Coactivator-1α by Extracellular Signal-Regulated Kinase 1/2 in Physiological and Pathological Conditions

“…However, ERK1/2 appears to regulate mitochondrial functions differently in various cell types, and the differences may be based on the level of oxidative phosphorylation that occurs in each cell type. RPTC used by Nowak et al (7) and in our studies derive all their energy from oxidative phosphorylation, similar to that found in kidney cortex.…”

“…In a study utilizing H 2 O 2 injury in human renal cells, ERK1/2 inhibition was shown to decrease necrosis and apoptosis (5), whereas in a cisplatin-induced cell injury model, ERK1/2 inhibition reduced caspase 3 activation and apoptosis (6). In renal proximal tubular cells (RPTC), phosphorylated ERK1/2 was shown to reduce mitochondrial respiration and ATP production by decreasing complex I electron transport chain activity in response to tert-butyl hydroperoxide (TBHP), a model oxidant (7). Nowak et al (7) also showed that expression of a constitutively active MEK1 increased ERK1/2 activation and decreased basal and uncoupled oxygen consumption, a measure of electron transport chain activity.…”

“…In renal proximal tubular cells (RPTC), phosphorylated ERK1/2 was shown to reduce mitochondrial respiration and ATP production by decreasing complex I electron transport chain activity in response to tert-butyl hydroperoxide (TBHP), a model oxidant (7). Nowak et al (7) also showed that expression of a constitutively active MEK1 increased ERK1/2 activation and decreased basal and uncoupled oxygen consumption, a measure of electron transport chain activity. Zhuang et al (8) demonstrated that H 2 O 2 treatment of RPTC led to a high level of ERK1/2 phosphorylation and loss of mitochondrial membrane potential, which was attenuated by treating with a MEK/ ERK1/2 inhibitor.…”

Mitochondrial calpain 10 activity and expression in the kidney of multiple species

“…Cells were grown to confluence and harvested for isolation of mitochondrial and cytosolic fractions as previously described [20].…”

6-Hydroxydopamine induces mitochondrial ERK activation

“…These results are consistent with reports from other laboratories where ERK activation lies downstream of mitochondrially-induced ROS [76][77][78][79], although , these studies did not examine ERK activation within mitochondria. Nowak et al have suggested that mitochondrially activated ERK suppresses mitochondrial respiration in oxidatively damaged tert-butylhydroperoxide treated renal epithelial cells [80]. Interestingly, while decreased mitochondrial respiration and ATP production were reversed by inhibition of the MEK/ERK pathway, these inhibitors did not restore mitochondrial aconitase activity [80].As mitochondrial aconitase inactivation is a sensitive indicator for mitochondrial superoxide, activation of the MEK/ERK pathway in this study was downstream of mitochondrial oxidative stress, but upstream of other aspects of mitochondrial dysfunction.…”