Gene interference regulates aquaporin-4 expression in swollen tissue of rats with cerebral ischemic edema Correlation with variation in apparent diffusion coefficient

To investigate the effects of mRNA interference on aquaporin-4 expression in swollen tissue of rats with ischemic cerebral edema, and diagnose the significance of diffusion-weighted MRI, we injected 5 pL shRNA- aquaporin-4 （control group） or siRNA- aquaporin-4 solution （1：800） （RNA interference group） into the rat right basal ganglia immediately before occlusion of the middle cerebral artery. At 0.25 hours after occlusion of the middle cerebral artery, diffusion-weighted MRI displayed a high signal; within 2 hours, the relative apparent diffusion coefficient decreased markedly, aquaporin-4 expression increased rapidly, and intracellular edema was obviously aggravated; at 4 and 6 hours, the relative apparent diffusion coefficient slowly returned to control levels, aquaporin-4 expression slightly increased, and angioedema was observed. In the RNA interference group, during 0.25- 6 hours after injection of siRNA- aquaporin-4 solution, the relative apparent diffusion coefficient slightly fluctuated and aquaporin-4 expression was upregulated; during 0.5 4 hours, the relative apparent diffusion coefficient was significantly higher, while aquaporin-4 expression was significantly lower when compared with the control group, and intracellular edema was markedly reduced; at 0.25 and 6 hours, the relative apparent diffusion coefficient and aquaporin-4 expression were similar when compared with the control group; obvious angioedema remained at 6 hours. Pearson＇s correlation test results showed that aquaporin-4 expression was negatively correlated with the apparent diffusion coefficient （r = -0.806, P 〈 0.01）. These findings suggest that upregulated aquaporin-4 expression is likely to be the main molecular mechanism of intracellular edema and may be the molecular basis for decreased relative apparent diffusion coefficient. Aquaporin-4 gene interference can effectively inhibit the upregulation of aquaporin-4 expression during the stage of intracelfular edema with time-effectiveness. Moreover, diffusion-weighted MRI can accurately detect intracellular edema.

Relationship between AQP4 expression and DWI of the cerebral ischemic edema in rats

Objective: To study the correlation between aquaporin-4 ( AQP4) expression and diffusion-weighted imaging ( DWI) in the process of ischemic brain edema for the molecular biologic mechanism of DWI. Methods: A total of 34 Wistar rats were divided into 8 groups randomly: Non-operated group (n = 4) , sham-operated group (n = 6) , and operated group, receiving right middle cerebral artery occlusion ( MCAO) for 15 and 30 min, and 1,3,6 and 24 h respectively (6 subgroups, n =4). All groups were imaged with DWI and T2WI. The apparent diffusion coefficient (ADC) , relevant density (rd) and relevant area (rs) of hyperintensity of the lesions on DWI and T2WI were measured. Relevant ADC (rADC) , relevant area of immunohistochemical staining for AQP4 (rS) , optical density of AQP4 hybridization (a) were calculated. After that the animals were sacrificed and perfused at different time intervals, correlations between DWI, ADC, and AQP4 expression (rS, a) in ischemic tissue was made. Results: There was a significant correlation between rS and a ( r = 0. 949 ). The abnormal high intensity was found in DWI of the ipsilateral MAC territory at 15 min after MCAO. The ADC value decreased quickly within 1 h after MCAO, the rd and rs of DWI increased rapidly and the expression of AQP4 increased quickly, too. However, there was no change on the T2WI. In the period of time (15 min - 1 h) , the AQP4 expression( a) had a strong relation to the rd and rs( r = 0. 914, 0. 895). With the progress of the time, the ADC value of MCAO decreased further to (2.1±0.6)×10-4 mm2/s at 3 h, and then followed an increased slowly till 24 h, but the rd and the rs as well as the expression of AQP4 continuously increased during the stage. The T2WI detected the lesion at the average time (1.4 h) after MCAO, and the rs of T2WI was less than that of DWI at the same time in the same layer (P < 0.05). Conclusion: The results imply that high expression of AQP4 may play a key role in ischemic brain edema. It is, certainly, one of the important reasons of the DWI molecular biologic mechanism in the cerebral ischemia.