Endothelial TRPA1 Channels Are Activated by Hypoxia in Cerebral Arteries and Protect Against Ischemic Damage

Abstract

Acute drops in cerebral perfusion can lead to rapid neuronal death, as seen during transient ischemic attacks and ischemic strokes. The extent of brain damage following hypoxia is linked to the ability of collateral blood vessels to adequately supply blood to the peri‐infarct region and thus prevent neuronal loss and infarct expansion. During hypoxia, reactive oxygen species (ROS) are increased and may activate the Ca2+‐permeable transient receptor potential ankyrin 1 (TRPA1) in endothelial cells, promoting vasodilation. Here, we tested the hypothesis that TRPA1 channels in endothelial cells are activated by hypoxia‐derived ROS, leading to cerebral artery dilation and reduced ischemic damage. Using a novel mouse model expressing the Ca2+ indicator GCaMP6f in endothelial cells (Tek:GCaMP6f), we show that 4‐hydroxynonenal (4‐HNE), a lipid peroxide, increased TRPA1 channel activity, detected as elementary Ca2+ influx events (TRPA1 sparklets). The TRPA1 inhibitor A967079 prevented 4‐HNE induction of TRPA1 sparklets in endothelial cells. Acute exposure of cerebral arteries to hypoxia (5% O2, 6% CO2, 89% N2) significantly increased 4‐HNE accumulation in cerebral arteries, which was linked to an increase in TRPA1 sparklets. Hypoxia induction of TRPA1 sparklets was blocked by the TRPA1 inhibitor A967079, and by PEGylated superoxide dismutase (PEG‐SOD), suggesting a role for intracellular generation of ROS. Incubation of arteries with the mitochondria‐targeted antioxidant mitoTEMPO prevented the hypoxia‐induced increase in TRPA1 sparklets, whereas extracellular SOD or the NADPH oxidase inhibitor apocynin had no effect. In pressure myography studies, hypoxia caused endothelium‐dependent dilation of isolated cerebral arteries, an effect that was prevented by the membrane‐permeable SOD mimetic tempol and by mitoTEMPO. Hypoxia‐induced dilation of cerebral arteries was partially inhibited by the TRPA1 antagonist A967079 and was reduced in arteries isolated from endothelial cell‐specific TRPA1 knockout mice (eTRPA1−/− mice). In vivo, loss of TRPA1 channels in endothelial cells increased infarct size following middle cerebral occlusion, a model of ischemic strokes. Reversely, TRPA1 activation with cinnamaldehyde (50 mg/kg) reduced infarct size in wildtype, but not eTRPA1−/−, mice. Together, these data suggest that TRPA1 channels in cerebral artery endothelial cells are early sensors of hypoxia and orchestrate a response that culminates with vasodilation, thereby reducing ischemic damage. Further, pharmacological activation of TRPA1 channels may be a putative therapeutic target to reduce cerebral ischemic damage.Support or Funding InformationSupported by the National Institutes of Health (R01HL091095 to SE) and the American Heart Association (15POST2472002 to PWP)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.