Abstract 93: Androgen Regulation of Protection Provided by Inhibition of TRPM2 Channels against Experimental Stroke in Mice

Abstract

Introduction: Stroke is a sexually dimorphic disease that affects men more severely than women. Transient receptor potential (TRP) channels have been implicated in ischemia-induced neuronal damage. We recently demonstrated that pharmacological and genetic inhibition of TRPM2, a member of the TRP channel superfamily, protects against cerebral ischemia in male mice, while having no effect in females. In addition, TRPM2 channels are activated by adenine dinucleotide phosphate ribose (ADPr) generated by poly(ADPr) polymerase (PARP). In this study, we examined the role of male sex steroids in TRPM2 engagement following experimental stroke. Methods: Focal ischemia was induced by 60 min of middle cerebral artery occlusion in male C57Bl/6 mice. To assess the efficacy of post-insult administration of TRPM2 inhibitor clotrimazole (CTZ), intact mice were treated with either CTZ (30 mg/kg) or vehicle 1 h after reperfusion. Mice were castrated (CAST) in order to remove sex steroids and either dihydrotestosterone (DHT) or vehicle was implanted. Then, animals were treated with either CTZ or vehicle 1 hr after reperfusion. The infarct sizes were evaluated in TRPM2 -/- mice to confirm TRPM2 engagement. We further compared the PARP activity in intact male and female brain to that in ischemic brain. Results: Animals treated with CTZ had significantly smaller infarcts compared to vehicle treated animals (46.2±3.1% (n=8) in vehicle vs. 32.5±3.6% (n=8; P<0.05) in CTZ). Removal of sex steroids resulted in loss of protection by CTZ (44.6±3.1% (n=9) in vehicle treated CAST vs. 35.8±3.6% (n=11) in CTZ treated CAST). Androgen replacement with DHT (CAST+DHT) resulted in recovery of CTZ protection (40.4±2.3% (n=12) in vehicle vs. 31.5±2.8% (n=11; P<0.05) in CTZ). TRPM2 -/- mice had smaller infarcts compared to wild type (28.4±7.0 (n=5) vs. 49.0±1.2 (n=5); P<0.05). We found higher PARP activity in male penumbral tissues compared to male normal tissues (P<0.05), while having no difference in females. Conclusions: These data indicate that TRPM2 inhibition provides protection from ischemic stroke in male animals in an androgen-dependent manner. Therefore, androgen status must be considered when considering inhibition of TRPM2 channels as a potential therapeutic strategy in men.