Smooth Muscle Cell Arachidonic Acid Release, Migration, and Proliferation Are Markedly Attenuated in Mice Null for Calcium-independent Phospholipase A2β

Abstract

Pharmacologic evidence suggests that the lipid products generated by one or more calcium-independent phospholipases A(2) (iPLA(2)s) participate in the regulation of vascular tone through smooth muscle cell (SMC) Ca(2+) signaling and the release of arachidonic acid. However, the recent identification of new members of the iPLA(2) family, each inhibitable by (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one, has rendered definitive identification of the specific enzyme(s) mediating these processes difficult. Accordingly, we used iPLA(2)beta(-/-) mice to demonstrate that iPLA(2)beta is responsible for the majority of thapsigargin and ionophore (A23187)-induced arachidonic acid release from SMCs. Both thapsigargin and A23187 stimulated robust [(3)H]arachidonate (AA) release from wild-type aortic SMCs that was dramatically attenuated in iPLA(2)beta(-/-) mice (>80% reduction at 5 min; p < 0.01). Moreover, iPLA(2)beta(-/-) mice displayed defects in SMC Ca(2+) homeostasis and decreased SMC migration and proliferation in a model of vascular injury. Ca(2+)-store depletion resulted in the rapid entry of external Ca(2+) into wild-type aortic SMCs that was significantly slower in iPLA(2)beta-null cells (p < 0.01). Furthermore, SMCs from iPLA(2)beta-null mesenteric arterial explants demonstrated decreased proliferation and migration. The defects in migration and proliferation in iPLA(2)beta-null SMCs were restored by 2 mum AA. Remarkably, the cyclooxygenase-2-specific inhibitor, NS-398, prevented AA-induced rescue of SMC migration and proliferation in iPLA(2)beta(-/-) mice. Moreover, PGE(2) alone rescued proliferation and migration in iPLA(2)beta(-/-) mice. We conclude that iPLA(2)beta is an important mediator of AA release and prostaglandin E(2) production in SMCs, modulating vascular tone, cellular signaling, proliferation, and migration.