Signalling mechanisms mediating Zn-induced TRPM2 channel activation and cell death in microglial cells.

Excessive Zn causes brain damage via promoting ROS generation. Here we investigated the role of ROS-sensitive TRPM2 channel in HO/Zn-induced Ca signalling and cell death in microglial cells. HO/Zn induced concentration-dependent increases in cytosolic Ca concentration ([Ca]), which was inhibited by PJ34, a PARP inhibitor, and abolished by TRPM2 knockout (TRPM2-KO). Pathological concentrations of HO/Zn induced substantial cell death that was inhibited by PJ34 and DPQ, PARP inhibitors, 2-APB, a TRPM2 channel inhibitor, and prevented by TRPM2-KO. Further analysis indicate that Zn induced ROS production, PARP-1 stimulation, increase in the [Ca] and cell death, all of which were suppressed by chelerythrine, a protein kinase C inhibitor, DPI, a NADPH-dependent oxidase (NOX) inhibitor, GKT137831, a NOX1/4 inhibitor, and Phox-I2, a NOX2 inhibitor. Furthermore, Zn-induced PARP-1 stimulation, increase in the [Ca] and cell death were inhibited by PF431396, a Ca-sensitive PYK2 inhibitor, and U0126, a MEK/ERK inhibitor. Taken together, our study shows PKC/NOX-mediated ROS generation and PARP-1 activation as an important mechanism in Zn-induced TRPM2 channel activation and, TRPM2-mediated increase in the [Ca] to trigger the PYK2/MEK/ERK signalling pathway as a positive feedback mechanism that amplifies the TRPM2 channel activation. Activation of these TRPM2-depenent signalling mechanisms ultimately drives Zn-induced Ca overloading and cell death.