Cooperative Interaction of trp Melastatin Channel Transient Receptor Potential (TRPM2) With Its Splice Variant TRPM2 Short Variant Is Essential for Endothelial Cell ApoptosisNovelty and Significance

Rationale: Oxidants generated by activated endothelial cells are known to induce apoptosis, a pathogenic feature of vascular injury and inflammation from multiple pathogeneses. The melastatin-family transient receptor potential 2 (TRPM2) channel is an oxidant-sensitive Ca 2+ permeable channel implicated in mediating apoptosis; however, the mechanisms of gating of the supranormal Ca 2+ influx required for initiating of apoptosis are not understood. Objective: Here, we addressed the role of TRPM2 and its interaction with the short splice variant TRPM2 short variant (TRPM2-S) in mediating the Ca 2+ entry burst required for induction of endothelial cell apoptosis. Methods and Results: We observed that TRPM2-S was basally associated with TRPM2 in the endothelial plasmalemma, and this interaction functioned to suppress TRPM2-dependent Ca 2+ gating constitutively. Reactive oxygen species production in endothelial cells or directly applying reactive oxygen species induced protein kinase C-α activation and phosphorylation of TRPM2 at Ser 39. This in turn stimulated a large entry of Ca 2+ and activated the apoptosis pathway. A similar TRPM2-dependent endothelial apoptosis mechanism was seen in intact vessels. The protein kinase C-α–activated phosphoswitch opened the TRPM2 channel to allow large Ca 2+ influx by releasing TRPM2-S inhibition of TRPM2, which in turn activated caspase-3 and cleaved the caspase substrate poly(ADP-ribose) polymerase. Conclusions: Here, we describe a fundamental mechanism by which activation of the trp superfamily TRPM2 channel induces apoptosis of endothelial cells. The signaling mechanism involves reactive oxygen species–induced protein kinase C-α activation resulting in phosphorylation of TRPM2-S that allows enhanced TRPM2-mediated gating of Ca 2+ and activation of the apoptosis program. Strategies aimed at preventing the uncoupling of TRPM2-S from TRPM2 and subsequent Ca 2+ gating during oxidative stress may mitigate endothelial apoptosis and its consequences in mediating vascular injury and inflammation.