Dramatic accumulation of triglycerides and precipitation of cardiac hemodynamic dysfunction during brief caloric restriction in transgenic myocardium expressing human calcium-independent phospholipase A ₂γ

Previously, we identified calcium-independent phospholipase A ₂γ(iPLA₂γ) with multiple translation initiation sites and dual mitochondrial and peroxisomal localization motifs. To determine the role of iPLA₂γ in integrating lipid and energy metabolism, we generated transgenic mice containing the α-myosin heavy chain promoter (αMHC) placed proximally to the human iPLA ₂γ coding sequence that resulted in cardiac myocyte-restricted expression of iPLA₂γ (TGiPLA₂γ). TGiPLA ₂γ mice possessed multiple phenotypes including: 1) a dramatic ∼35% reduction in myocardial phospholipid mass in both the fed and mildly fasted states; 2) a marked accumulation of triglycerides during brief caloric restriction that represented 50% of total myocardial lipid mass; and 3) acute fasting-induced hemodynamic dysfunction. Biochemical characterization of the TGiPLA₂γ protein expressed in cardiac myocytes demonstrated over 25 distinct isoforms by two-dimensional SDS-PAGE Western analysis. Immunohistochemistry identified iPLA₂γ in the peroxisomal and mitochondrial compartments in both wild type and transgenic myocardium. Electron microscopy revealed the presence of loosely packed and disorganized mitochondrial cristae in TGiPLA₂γ mice that were accompanied by defects in mitochondrial function. Moreover, markedly elevated levels of 1-hydroxyl-2-arachidonoyl-sn-glycero-3-phosphocholine and 1-hydroxyl-2- docosahexaenoyl-sn-glycero-3-phosphocholine were prominent in the TGiPLA ₂γ myocardium identifying the production of signaling metabolites by this enzyme in vivo. Collectively, these results identified the participation of iPLA₂γ in the remarkable lipid plasticity of myocardium, its role in generating signaling metabolites, and its prominent effects in modulating energy storage and utilization in myocardium in different metabolic contexts.