Reduced brain edema and infarct volume in aquaporin-4 deficient mice after transient focal cerebral ischemia

Abstract

Aquaporin-4 (AQP4) is a water channel expressed in astrocyte end-feet lining the blood-brain barrier. AQP4 deletion in mice is associated with improved outcomes in global cerebral ischemia produced by transient carotid artery occlusion, and focal cerebral ischemia produced by permanent middle cerebral artery occlusion (MCAO). Here, we investigated the consequences of 1-h transient MCAO produced by intraluminal suture blockade followed by 23 h of reperfusion. In nine AQP4(+/+) and nine AQP4(-/-) mice, infarct volume was significantly reduced by an average of 39 ± 4% at 24h in AQP4(-/-) mice, cerebral hemispheric edema was reduced by 23 ± 3%, and Evans Blue extravasation was reduced by 31 ± 2% (mean ± SEM). Diffusion-weighted magnetic resonance imaging showed greatest reduction in apparent diffusion coefficient around the occlusion site after reperfusion, with remarkably lesser reduction in AQP4(-/-) mice. The reduced infarct volume in AQP4(-/-) mice following transient MCAO supports the potential utility of therapeutic AQP4 inhibition in stroke.

Keywords: AQP4; Blood–brain barrier; Brain edema; Transient cerebral ischemia.

Figure 1. Infarct volume and hemispheric water content at 23-h reperfusion after 1-h MCA occlusion in AQP4^+/+ and AQP4^−/− mice

Brain slices of 2-mm thickness were sectioned at 1, 3, 5, and 7 mm distal from the frontal pole and stained with TTC. A. (top) Diagram of MCA occlusion model. (middle) Representative brain slices showing infarcted area (in white). (bottom) Infarct area (mean ± SEM, n=9, ** P < 0.01). B. Total infarct volume (from mice in A), **P < 0.01. C. Edema volume deduced from hemispheric enlargement comparing ipsilateral and contralateral brain of mice in A [24]. Edema volume = (Vi – Vc)/Vc*100%, where Vi is ipsilateral hemisphere volume and Vc is contralateral hemisphere volume. * P < 0.05.

Figure 2. ADC at indicated times during ischemia and reperfusion in AQP4^+/+ and AQP4^−/−mice

A. ADC maps calculated from three adjacent, 2-mm-thick slices, covering the majority of the brain. Representative of maps obtained from four AQP4^+/+ and four AQP4^−/− mice. B. Relative ADC values were calculated by normalizing to the contralateral hemisphere ADC values on a pixel-by-pixel basis, ** P < 0.01.

Figure 3. Evans Blue extravasation in AQP4^+/+ and AQP4^−/− mice at 23-h reperfusion after 1-h MCA occlusion

Evans blue dye was injected intraveneously 1 h before sacrifice. Dye extravasation was quantified following dye extraction from brain hemispheres after perfusion to remove intravascular dye (mean ± SEM, 4 mice per group, ** P < 0.01).