Genetic ablation of calcium-independent phospholipase A₂γ (iPLA₂γ) attenuates calcium-induced opening of the mitochondrial permeability transition pore and resultant cytochrome c release

Herein, we demonstrate that calcium-independent phospholipase A ₂γ (iPLA₂γ) is a critical mechanistic participant in the calcium-induced opening of the mitochondrial permeability transition pore (mPTP). Liver mitochondria from iPLA₂γ ^-/-mice were markedly resistant to calcium-induced swelling in the presence or absence of phosphate in comparison with wild-type littermates. Furthermore, the iPLA₂γ enantioselective inhibitor (R)-(E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one ((R)-BEL) was markedly more potent than (S)-BEL in inhibiting mPTP opening in mitochondria from wildtype liver in comparison with hepatic mitochondria from iPLA₂γ^-/- mice. Intriguingly, low micromolar concentrations of long chain fatty acyl-CoAs and the non-hydrolyzable thioether analog of palmitoyl-CoA markedly accelerated Ca²⁺-induced mPTP opening in liver mitochondria from wild-type mice. The addition of L-carnitine enabled the metabolic channeling of acyl-CoA through carnitine palmitoyltransferases (CPT-1/2) and attenuated the palmitoyl-CoA-mediated amplification of calcium-induced mPTP opening. In contrast, mitochondria from iPLA₂γ^-/- mice were insensitive to fatty acyl- CoA-mediated augmentation of calcium-induced mPTP opening. Moreover, mitochondria from iPLA₂γ^-/- mouse liver were resistant to Ca²⁺/t-butyl hydroperoxide-induced mPTP opening in comparison with wild-type littermates. In support of these findings, cytochrome c release from iPLA₂γ^-/- mitochondria was dramatically decreased in response to calcium in the presence or absence of either t-butyl hydroperoxide or phenylarsine oxide in comparison with wild-type littermates. Collectively, these results identify iPLA₂γ as an important mechanistic component of the mPTP, define its downstream products as potent regulators of mPTP opening, and demonstrate the integrated roles of mitochondrial bioenergetics and lipidomic flux in modulating mPTP opening promoting the activation of necrotic and necroapoptotic pathways of cell death.