Effect of local mild hypothermia on expression of aquaporin-4 following intracerebral hemorrhage in rats

Abstract

To examined the effect of local mild hypothermia on the expression of aquaporin-4 (AQP-4) following intracerebral hemorrhage (ICH) in rats and clarified the mechanism of hypothermia on brain edema formation following ICH. Two hundreds and forty male Wistar rats were randomly divided into two groups: the intracerebral hemorrhage (ICH) group, in which autologous arterial blood were stereotaxically injected into right caudate nucleus; the local mild hypothermia (ICH + H) group, in which the rats were given 4 h local mild hypothermia after the injection of blood. Each group was divided into 6 subgroups: control, 6 h, 24 h, 72 h, 5 d and 7 d after operation; Brain water content was determined by dry-wet weight method and the permeability of BBB was measured by Evans-Blue extravasation. RT-PCR and Western blot were respectively used to evaluate AQP-4 mRNA and protein expression. In ICH group, compared with control, ICH significantly increased BWC, the permeability of BBB and the expression of AQP-4 mRNA, all began at 6 h and peaked at 72 h (P < 0.01), the increased protein expression of AQP-4 began at 24 h and also peaked at 72 h (P < 0.01). AQP-4 expression positively correlated, both at the mRNA and the protein level, with the permeability of BBB (r = 0.78 and r = 0.76 respectively). In ICH + H group, compared with ICH group, the elevation of BWC, BBB permeability and AQP-4 protein expression were strongly attenuated at all time point by hypothermia treatment (P < 0.01), while AQP-4 mRNA levels demonstrated a modest attenuation from 48 h. At 72 h, AQP-4 mRNA optical density (A) decreased from 1.25 +/- 0.03 (ICH group) to 1.04 +/- 0.02 (P < 0.01), AQP-4 protein expression (A) decreased from 0.77 +/- 0.08 (ICH group) to 0.25 +/- 0.04 (P < 0.01). This study indicates that BBB breakdown can increase the expression of AQP-4; local mild hypothermia can significantly reduce brain edema formation after ICH by suppressing the elevation of AQP-4 protein expression; Inhibition of BBB breakdown and the elevation of AQP-4 protein expression with local mild hypothermia appear to contribute to brain protection in this model.