Background: Cerebral edema is an important initial event in cases of stroke among humans. Although hypertension is a major risk factor for endothelial injury, the precise mechanisms regulating brain microvascular changes are still unknown. To elucidate the pathogenesis of increases in vascular permeability in the cerebral cortex, we investigated the expression of glucose transporter-1 (GLUT-1) in endothelial cells and aquaporin-4 (AQP4) in astrocytes in relation to blood-brain barrier (BBB) function.
Methods: Using male stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY), the particular localization of both GLUT-1 and AQP4 was investigated by immunohistochemistry. Quantitative changes in these molecules were examined by Western blot analysis in these rats at 6 weeks and 20 weeks of age. Furthermore, to investigate the expression of these molecules at the mRNA level, reverse transcriptase-polymerase chain reaction (RT-PCR) analysis was carried out using 20-week-old SHRSP and age-matched WKY.
Results: We confirmed the localization of GLUT-1 in endothelial cells and that of AQP4 in the end feet of astrocytes around microvessels, as determined by electron immunohistochemistry. No significant differences were found in the expression of these molecules in rats at 6 weeks of age, whereas GLUT-1 expression was lower, but that of AQP4 was higher, in SHRSP after the establishment of hypertension. Furthermore, GLUT-1 mRNA expression was lower in SHRSP, and AQP4 mRNA expression was also lower in SHRSP than in WKY at 20 weeks of age.
Conclusions: These results indicate that AQP4 may play a much more important role in BBB function than GLUT-1, and thereby also in water distribution in the cerebral cortex of SHRSP with severe hypertension.