Effects of Chronic Oxidative Stress on TRPM2 and TRPC3 Channels: Potential Implications for Bipolar Disorder

Intracellular calcium and oxidative stress dyshomeostasis, which can be highly interactive, occur in bipolar disorder (BD), but the pathogenesis of these disturbances is unknown. The transient receptor potential (TRP) melastatin subtype 2 (TRPM2) and canonical subtype 3 (TRPC3) calcium-permeable non-selective ion channels, already implicated in BD, are involved in calcium and oxidative stress signalling. Thus, I sought to determine whether the expression and function of these channels are modulated by oxidative stress exposure in rat cortical neurons, astrocytes, and in human B lymphoblast cell lines (BLCLs), a cell model that reports diagnostically relevant abnormalities in BD. This thesis work demonstrated that TRPC3 expression and function are decreased after chronic, but not acute oxidative stress exposure in both human and rat cell models. TRPM2 expression, on the other hand, was increased after both acute and chronic stressor treatments in rat cortical neurons. In BLCLs, TRPM2-mediated calcium entry was blunted although no difference in TRPM2 mRNA expression was detected. Moreover, BLCLs from BD-I patients exhibited greater susceptibility to cell death and a differential sensitivity of TRPM2-mediated calcium influx to acute oxidative stress compared with healthy subjects, further supporting reduced cellular resilience in the pathophysiology of BD-I. I also demonstrated that TRPC3 protein is expressed in human brain from 8 days to 83 years old supporting an ongoing role in the developing and adult human brain. These findings support an important role for TRPM2 and TRPC3 in sensing and responding to oxidative stress, and in transducing oxidative stress signalling to intracellular calcium homeostatic and cellular stress responses, which have been implicated in the pathophysiology of BD. Finally, this work has highlighted an inherent difference in TRPM2 channel functionality in BD type I subjects compared with controls, adding functional evidence to the genetic and differential expression findings implicating TRPM2 dysfunction in BD.Ph