Abstract
In the brain, aquaporin-1 (AQP-1), a water channel for high osmotic water permeability, is mainly expressed in the apical membrane of the ventricular choroid plexus and regulates formation of cerebrospinal fluid (CSF). Although the physiology of AQP-1 has been the subject of several publications, much less is known about the trans-acting factors involved in the control of AQP-1 gene expression. Here we report that TTF-1, a homeodomain-containing transcriptional regulator, is coexpressed with AQP-1 in the rat brain choroid plexus and enhances AQP-1 gene transcription by binding to conserved core TTF-1-binding motifs in the 5'-flanking region of the AQP-1 gene. Intracerebroventricular administration of an antisense TTF-1 oligodeoxynucleotide significantly decreased AQP-1 synthesis and reduced CSF formation. In addition, blockade of TTF-1 synthesis increased survival of the animals following acute water intoxication-induced brain edema. These results suggest that TTF-1 is physiologically involved in the transcriptional control of AQP-1, which is required for CSF formation.
Highlights
Including the choroid plexus and circumventricular organs of the lateral, third, and fourth ventricles
Previous reports have shown that AQP-1 is exclusively expressed in the apical membrane of the choroid plexus epithelium [25]
We used fluorescence in situ hybridization (FISH) to determine the localization of transcription factor-1 (TTF-1) and AQP-1 mRNAs in the choroid plexus
Summary
Animals and Tissue Preparation—Two-month-old male Sprague-Dawley rats (Daehan Animal Breeding Co., Chungwon, Korea) were used in this study. After washing three times in TNT buffer for 5 min each, mRNA signals of TTF-1 and AQP-1 were detected by using a Cy3-labeled and FITC-labeled tyramide signal amplification system, respectively (PerkinElmer Life Sciences). After incubation with Cy3-coupled tyramide to detect the DIG-labeled TTF-1 probe, the sections were washed three times in TNT buffer for 5 min each. To detect fluoresceinlabeled AQP-1 probe, sections were placed in TNB blocking buffer for 1 h at room temperature and incubated with HRP-conjugated anti-fluorescein antibody for 1 h. Measurements of Survival Rate of Animals and Brain Water Content after Acute Water Intoxication—To determine the effect of TTF-1 AS ODN on the survival rate of animals subjected to acute water intoxication, rats were given distilled water containing 1-deamino-8-D-arginine vasopressin (dDAVP, 0.4 g/kg body weight; Sigma) equal to a 25% of body weight by intraperitoneal injection, as reported previously [24], 12 h after the second ODN injection. Student’s t test was used for the comparison of two groups
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