Lack of Phospholipase A 2 Receptor Increases Susceptibility to Cardiac Rupture After Myocardial Infarction

Abstract

Recent evidence indicates that the biological effects of secretory phospholipase A2 (sPLA2) cannot be fully explained by its catalytic activity. A cell surface receptor for sPLA2 (PLA2 receptor 1 [PLA2R]) and its high-affinity ligands (including sPLA2-IB, sPLA2-IIE, and sPLA2-X) are expressed in the infarcted myocardium. This study asked whether PLA2R might play a pathogenic role in myocardial infarction (MI) using mice lacking PLA2R (PLA2R(-/-)). MI was induced by permanent ligation of the left coronary artery. PLA2R(-/-) mice exhibited higher rates of cardiac rupture after MI compared with PLA2R wild-type (PLA2R(+/+)) mice (46% versus 21%, respectively; P=0.015). PLA2R(-/-) mice had a 31% decrease in collagen content and a 45% decrease in the number of α-smooth muscle actin-positive fibroblasts in the infarcted region compared with PLA2R(+/+) mice. PLA2R was primarily found in myofibroblasts in the infarcted region. PLA2R(-/-) myofibroblasts were impaired in collagen-dependent migration, proliferation, and activation of focal adhesion kinase in response to sPLA2-IB. Binding of sPLA2-IB to PLA2R promoted migration and proliferation of myofibroblasts through functional interaction with integrin β1, independent of the catalytic activity of sPLA2-IB. In rescue experiments, the injection of PLA2R(+/+) myofibroblasts into the infarcted myocardium prevented post-MI cardiac rupture and reversed the decrease in collagen content in the infarcted region in PLA2R(-/-) mice. PLA2R deficiency increased the susceptibility to post-MI cardiac rupture through impaired healing of the infarcted region. This might be partly explained by a reduction in integrin β1-mediated migratory and proliferative responses of PLA2R(-/-) myofibroblasts.