Abstract WP314: Reduced Post-Ischemic Brain Tissue Injury Following Transient Focal Cerebral Ischemia in Transient Receptor Potential Vanilloid 4 Knockout Mice

Abstract

Background: In the acute phase of ischemia-reperfusion, post-ischemic delayed hypoperfusion in microvascular regions contributes to post-ischemic brain tissue injury. Transient receptor potential vanilloid 4 (TRPV4) is a nonselective cation channel expressed on astrocyte endfeet regulating vascular tone, which may contribute to ischemia-induced brain tissue injury. Objective: To clarify whether brain tissue injury following transient middle cerebral artery occlusion (tMCAO) is ameliorated by Trpv4 knockout ( Trpv4 -/- ). Methods: tMCAO was induced by an insertion of silicon-coated filament from right common carotid artery to occlude right MCA for 30 minutes for wild type (WT) and Trpv4 -/- mice aged 8-10 weeks (median [interquartile] weight: 23.3 [21.7-24.9] g for WT mice and 24.1 [20.8-26.2] g for Trpv4 -/- mice). Ischemia-induced lesion volume was evaluated by 2,3,5-Triphenyltetrazolium chloride staining at 24 hours post-tMCAO, and tissue water content and Evans blue leakage in the ipsilateral hemisphere alongside 18-point neurological score were evaluated at 48 hours post-tMCAO. Transmission electron microscopy (TEM) was performed to assess the morphological changes in the microvasculature in the ischemic lesions at 6 hours post-tMCAO. Results: Compared with WT mice, Trpv4 -/- mice showed reduced ischemia-induced lesion volumes (median 40 mm 3 vs. 53 mm 3 , p < 0.05) at 24 hours and reduced tissue water content by subtraction of the contralateral from the ipsilateral hemisphere (median 4.9% vs. 2.8%, p < 0.05) and Evans blue leakage by ratio of ipsilateral to contralateral hemisphere (median 2.3 vs. 3.2, p < 0.05) alongside milder neurological score (median 12 vs. 10, p < 0.01) at 48 hours post-tMCAO. TEM revealed that parenchymal microvessels in the ischemic lesion were compressed and narrowed by the swollen endfeet of astrocytes in a WT mouse, whereas those were markedly reduced in a Trpv4 -/ - mouse. Conclusions: Trpv4 -/- mice showed reduced post-ischemic brain tissue injury. Suppressing the astrocyte endfeet swelling shortly after reperfusion is one of the key neuroprotective mechanisms of TRPV4 inhibition, which is a promising target for the treatment of acute ischemic stroke.