Heart failure-induced activation of phospholipase iPLAγ generates hydroxyeicosatetraenoic acids opening the mitochondrial permeability transition pore.

Congestive heart failure typically arises from cardiac myocyte necrosis/apoptosis, associated with the pathological opening of the mitochondrial permeability transition pore (mPTP). mPTP opening decreases the mitochondrial membrane potential leading to the activation of Ca-independent phospholipase Aγ (iPLAγ) and the production of downstream toxic metabolites. However, the array of enzymatic mediators and the exact chemical mechanisms responsible for modulating myocardial mPTP opening remain unclear. Herein, we demonstrate that human heart failure activates specific myocardial mitochondrial phospholipases that increase Ca-dependent production of toxic hydroxyeicosatetraenoic acids (HETEs) and attenuate the activity of phospholipases that promote the synthesis of protective epoxyeicosatrienoic acids (EETs). Mechanistically, HETEs activated the Ca-induced opening of the mPTP in failing human myocardium, and the highly selective pharmacological blockade of either iPLAγ or lipoxygenases attenuated mPTP opening in failing hearts. In contrast, pharmacological inhibition of cytochrome P450 epoxygenases opened the myocardial mPTP in human heart mitochondria. Remarkably, the major mitochondrial phospholipase responsible for Ca-activated release of arachidonic acid (AA) in mitochondria from non-failing hearts was calcium-dependent phospholipase Aζ (cPLAζ) identified by sequential column chromatographies and activity-based protein profiling. In contrast, iPLAγ predominated in failing human myocardium. Stable isotope kinetics revealed that in non-failing human hearts, cPLAζ metabolically channels arachidonic acid into EETs, whereas in failing hearts, increased iPLAγ activity channels AA into toxic HETEs. These results mechanistically identify the sequelae of pathological remodeling of human mitochondrial phospholipases in failing myocardium. This remodeling metabolically channels AA into toxic HETEs promoting mPTP opening, which induces necrosis/apoptosis leading to further progression of heart failure.