Cytosolic phospholipase A₂-α is an early apoptotic activator in PEDF-induced endothelial cell apoptosis

Pigment epithelium-derived factor (PEDF) is an intrinsic antiangiogenic factor and a potential therapeutic agent. Previously, we discovered the mechanism of PEDF-induced apoptosis of human umbilical vein endothelial cells (HUVECs) as sequential induction/activation of p38 mitogen-activated protein kinase (MAPK), peroxisome proliferator-activated receptor gamma (PPAR-7), and p53. In the present study, we investigated the signaling role of cytosolic calcium-dependent phospholipase A₂-α (cPLA₂-α) to bridge p38 MAPK and PPAR-7 activation. PEDF induced cPLA₂-α activation in HUVECs and in endothelial cells in chemical burn-induced vessels on mouse cornea. The cPL₂-αactivation is evident from the phosphorylation and nuclear translocation of cPL₂-αas well as arachidonic acid release and the cleavage of PED6, a synthetic PLA₂ substrate. Such activation can be abolished by p38 MAPK inhibitor. The PEDF-induced PPAR-γ activation, p53 expression, caspase-3 activity, and apoptosis can be abolished by both cPLA2 inhibitor and small interfering RNA targeting cPL₂-α. Our observation not only establishes the signaling role of cPL₂-αbut also for the first time demonstrates the sequential activation of p38 MAPK, cPLA₂-α PPAR-γ, and p53 as the mechanism of PEDF- induced endothelial cell apoptosis.