The role of mitochondrial permeability transition pore in regulating the shedding of the platelet GPIbα ectodomain.

Agonists induce platelet activation or apoptosis with concomitant shedding of the platelet receptor glycoprotein Ibα (GPIbα) ectodomain in a disintegrin and metalloproteinase 17 (ADAM17)-dependent mechanism. Mitochondrial permeability transition pore (MPTP) plays a pivotal role in platelet activation or apoptosis. However, its impact on ADAM17-mediated GPIbα ectodomain shedding remains unclear. Here, we aimed to test the hypothesis that MPTP regulates ADAM17-dependent GPIbα ectodomain shedding. We showed that calcium ionophore A23187- or thrombin plus collagen-induced GPIbα ectodomain shedding was partially inhibited by a MPTP inhibitor, and a MPTP potentiator promoted A23187-induced GPIbα cleavage. Furthermore, A23187-induced elevation of mitochondrial Ca(2+) levels was blocked by the mitochondrial calcium uniporter (MCU) inhibitor Ru360 or treatment with the membrane-permeable Ca(2+) chelator BAPTA-AM. We also demonstrated that an increase in mitochondrial Ca(2+) levels triggered MPTP opening, as revealed by the examination of mitochondrial inner transmembrane potential depolarization. In addition, A23187 induced-mitochondrial reactive oxygen species (ROS) generation was blocked by the MPTP inhibitor or by treatment with the mitochondria-targeted ROS scavenger. Lastly, A23187-induced GPIbα shedding was partially blocked by inhibitors of either ROS or calpain, and was completely inhibited when platelets were exposed to both inhibitors. Therefore, these observations indicate that MPTP opening triggered mitochondrial ROS production, which plays an important role in regulating ADAM17-mediated shedding of the GPIbα ectodomain in A23187-treated platelets.