Activation of calcium‐independent phospholipase A 2 following protease‐activated receptor cleavage in mouse cardiomyocytes

Abstract

Serine proteases such as thrombin and tryptase can regulate target cells by activating G-protein coupled protease-activated receptors (PAR). The role for PAR activation is not well defined and could be pro- or anti-inflammatory. We determined whether activation of calcium-independent phospholipase A2 (iPLA2) following PAR cleavage in cardiac myocytes contributes to PAF production and PGE2 release. We stimulated HL-1 mouse cardiomyocytes with thrombin or tryptase and measured arachidonic acid and prostaglandin E2 (PGE2) release, plus platelet-activating factor (PAF) production. Thrombin (0,1 IU/ml) or tryptase (20 ng/ml) stimulation resulted in a significant increase in arachidonic acid and PGE2 release that was maximal at 5 mins. Pretreatment of HL-1 cells with (R)-bromoenol lactone ((R)-BEL), a selective iPLA2γ inhibitor, completely blocked thrombin- and tryptase-stimulated arachidonic acid and PGE2 release. Similarly, increases in PAF production observed in HL-1 cells stimulated with thrombin (1 IU/ml, 10 mins) or tryptase (20 ng/ml, 10 mins) were inhibited by BEL pretreatment. These data suggest that there is an increase in iPLA2γ activity in mouse cardiac myocytes following PAR activation, that results in increased arachidonic acid and PGE2 release, and increased PAF production, mediators that may play a role in cardiac inflammation.