Sensitization of H2O2-induced TRPM2 activation and subsequent interleukin-8 (CXCL8) production by intracellular Fe(2+) in human monocytic U937 cells.

Abstract Transient receptor potential melastatin 2 (TRPM2) is an oxidative stress-sensitive Ca 2+ -permeable channel. In monocytes/macrophages, H 2 O 2 -induced TRPM2 activation causes cell death and/or production of chemokines that aggravate inflammatory diseases. However, relatively high concentrations of H 2 O 2 are required for activation of TRPM2 channels in vitro. Thus, in the present study, factors that sensitize TRPM2 channels to H 2 O 2 were identified and subsequent physiological responses were examined in U937 human monocytes. Temperature increase from 30 °C to 37 °C enhanced H 2 O 2 -induced TRPM2-mediated increase in intracellular free Ca 2+ ([Ca 2+ ] i ) in TRPM2-expressing HEK 293 cells (TRPM2/HEK cells). The H 2 O 2 -induced TRPM2 activation enhanced by the higher temperature was dramatically sensitized by intracellular Fe 2+ -accumulation following pretreatment with FeSO 4 . Thus intracellular Fe 2+ -accumulation sensitizes H 2 O 2 -induced TRPM2 activation at around body temperature. Moreover, intracellular Fe 2+ -accumulation increased poly(ADP-ribose) levels in nuclei by H 2 O 2 treatment, and the sensitization of H 2 O 2 -induced TRPM2 activation were almost completely blocked by poly(ADP-ribose) polymerase inhibitors, suggesting that intracellular Fe 2+ -accumulation enhances H 2 O 2 -induced TRPM2 activation by increase of ADP-ribose production through poly(ADP-ribose) polymerase pathway. Similarly, pretreatment with FeSO 4 stimulated H 2 O 2 -induced TRPM2 activation at 37 °C in U937 cells and enhanced H 2 O 2 -induced ERK phosphorylation and interleukin-8 (CXCL8) production. Although the addition of H 2 O 2 to cells under conditions of intracellular Fe 2+ -accumulation caused cell death, concentration of H 2 O 2 required for CXCL8 production was lower than that resulting in cell death. These results indicate that intracellular Fe 2+ -accumulation sensitizes TRPM2 channels to H 2 O 2 and subsequently produces CXCL8 at around body temperature. It is possible that sensitization of H 2 O 2 -induced TRPM2 channels by Fe 2+ may implicated in hemorrhagic brain injury via aggravation of inflammation, since Fe 2+ is released by heme degradation under intracerebral hemorrhage.