Glutathione Depletion and Parkinsonian Neurotoxin MPP+-Induced TRPM2 Channel Activation Play Central Roles in Oxidative Cytotoxicity and Inflammation in Microglia

Parkinson’s disease (PD) is one of most common neurodegenerative diseases. Environmental stressors such as oxidative stress (OS), calcium ion influx, apoptosis, and inflammation mechanisms are linked to activated microglia in patients with PD. The OS-dependent activated transient receptor potential melastatin 2 (TRPM2) channel is modulated in several neurons by glutathione (GSH). However, the cellular and molecular effects of GSH alteration on TRPM2 activation, OS, apoptosis, and inflammation in the microglia remain elusive. The microglia of TRPM2 wild-type (TRPM2-WT) and knockout (TRPM2-KO) mice were divided into control, PD model (MPP), l-buthionine sulfoximine (BSO), MPP + BSO and MPP + BSO + GSH groups. MPP-induced increases in apoptosis, death, OS, lipid peroxidation, PARP1, caspase-3 and caspase-9, inflammatory cytokines (IL-1β, TNF-α, IL-6), and intracellular free Zn2+ and Ca2+ levels in the microglia of TRPM2-WT mice were further increased by the BSO treatment, although they were diminished by the GSH treatment. Their levels were further reduced by PARP1 inhibitors (PJ34 and DPQ) and TRPM2 blockers (ACA and 2-APB). However, the effects of MPP and BSO were not observed in the microglia of TRPM2-KO mice. Taken together, our data demonstrate that maintaining GSH homeostasis is not only important for quenching OS in the microglia of patients with PD but also equally critical to modulating TRPM2, thus suppressing inflammatory responses elicited by environmental stressors.