c-Jun N-terminal kinase regulates mitochondrial bioenergetics by modulating pyruvate dehydrogenase activity in primary cortical neurons

Abstract

This study examines the role of c-jun N-terminal kinase (JNK) in mitochondrial signaling and bioenergetics in primary cortical neurons and isolated rat brain mitochondria. Exposure of neurons to either anisomycin (an activator of JNK/p38 mitogen-activated protein kinases) or H2O 2 resulted in activation (phosphorylation) of JNK (mostly p46 JNK1) and its translocation to mitochondria. Experiments with mitochondria isolated from either rat brain or primary cortical neurons and incubated with proteinase K revealed that phosphorylated JNK was associated with the outer mitochondrial membrane; this association resulted in the phosphorylation of the E1α subunit of pyruvate dehydrogenase, a key enzyme that catalyzes the oxidative decarboxylation of pyruvate and that links two major metabolic pathways: glycolysis and the tricarboxylic acid cycle. JNK-mediated phosphorylation of pyruvate dehydrogenase was not observed in experiments carried out with mitoplasts, thus suggesting the requirement of intact, functional mitochondria for this effect. JNK-mediated phosphorylation of pyruvate dehydrogenase was associated with a decline in its activity and, consequently, a shift to anaerobic pyruvate metabolism: the latter was confirmed by increased accumulation of lactic acid and decreased overall energy production (ATP levels). Pyruvate dehydrogenase appears to be a specific phosphorylation target for JNK, for other kinases, such as protein kinase A and protein kinase C did not elicit pyruvate dehydrogenase phosphorylation and did not decrease the activity of the complex. These results suggest that JNK mediates a signaling pathway that regulates metabolic functions in mitochondria as part of a network that coordinates cytosolic and mitochondrial processes relevant for cell function. © 2007 The Authors.