The Ca2+-calmodulin-Ca2+/calmodulin-dependent protein kinase II pathway is involved in oxidative stress-induced mitochondrial permeability transition and apoptosis in rat hepatocytes

Oxidative stress is a common event in most hepatopathies, leading to mitochondrial permeability transition pore (MPTP) formation and further exacerbation of both oxidative stress from mitochondrial origin and cell death. Intracellular Ca2+ elevations play a permissive role in these events, but the underlying mechanisms are poorly known. We examined in primary cultured rat hepatocytes whether the Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII) signalling pathway is involved in this process, by using tert-butyl hydroperoxide (tBOOH) as a pro-oxidizing, model compound. tBOOH (500 µM, 15 min) induced MPTP formation, as assessed by measuring mitochondrial membrane depolarization as a surrogate marker, and increased lipid peroxidation in a clyclosporin A (CsA)-sesitive manner, revealing the involvement of MPTPs in tBOOH-induced ROS formation. Intracellular Ca2+ sequestration with BAPTA/AM, CaM blockage with W7 or trifluoperazine, and CaMKII inhibition with KN-62 all fully prevented tBOOH-induced MPTP opening and reduced tBOOH-induced lipid peroxidation to a similar extent to CsA, suggesting that Ca2+/CaM/CaMKII signaling pathway fully mediates MPTP-mediated mitochondrial ROS generation. tBOOH induced apoptosis, as shown by flow cytometry of annexin V/propidium iodide, mitochondrial release of cytochrome c, activation of caspase-3 and increase in the Bax-to-Bcl-xL ratio, and the Ca2+/CaM/CaMKII signaling antagonists fully prevented these effects. Intramitochondrial CaM and CaMKII were partially involved in tBOOH-induced MPTP formation, since W7 and KN-62 both attenuated the tBOOH-induced, MPTP-mediated swelling of isolated mitochondria. We concluded that Ca2+/CaM/CaMKII signaling pathway is a key mediator of oxidative stress-induced induced MPTP formation, and the subsequent exacerbation of oxidative stress from mitochondrial origin and apoptotic cell death.