Glial cell aquaporin-4 overexpression in transgenic mice accelerates cytotoxic brain swelling - PubMed (original) (raw)

Glial cell aquaporin-4 overexpression in transgenic mice accelerates cytotoxic brain swelling

Baoxue Yang et al. J Biol Chem. 2008.

Abstract

Aquaporin-4 (AQP4) is a water transport protein expressed in glial cell plasma membranes, including glial cell foot processes lining the blood-brain barrier. AQP4 deletion in mice reduces cytotoxic brain edema produced by different pathologies. To determine whether AQP4 is rate-limiting for brain water accumulation and whether altered AQP4 expression, as occurs in various pathologies, could have functional importance, we generated mice that overexpressed AQP4 in brain glial cells by a transgenic approach using the glial fibrillary acid protein promoter. Overexpression of AQP4 protein in brain by approximately 2.3-fold did not affect mouse survival, appearance, or behavior, nor did it affect brain anatomy or intracranial pressure (ICP). However, following acute water intoxication produced by intraperitoneal water injection, AQP4-overexpressing mice had an accelerated progression of cytotoxic brain swelling, with ICP elevation of 20 +/- 2 mmHg at 10 min, often producing brain herniation and death. In contrast, ICP elevation was 14 +/- 2 mmHg at 10 min in control mice and 9.8 +/- 2 mmHg in AQP4 knock-out mice. The deduced increase in brain water content correlated linearly with brain AQP4 protein expression. We conclude that AQP4 expression is rate-limiting for brain water accumulation, and thus, that altered AQP4 expression can be functionally significant.

PubMed Disclaimer

Figures

FIGURE 1.

FIGURE 1.

Generation and initial characterization of glial cell-targeted, AQP4-overexpressing transgenic mice. A, schematic of GFAP-AQP4 transgene expression vector. Gray box, cytomegalovirus enhancer fragment. Open box, GFAP promoter fragment. Filled box, mouse AQP4 cDNA coding region. Striped box, AQP4 cDNA 3′-untranslated and poly-A sequences. The thin line represents pGEM3Z vector sequences. The arrows indicate the primer sites for genotyping. The numbers indicate the length of fragments. B, genomic PCR of four GFAP-AQP4 founder mice. C, relative AQP4 mRNA expression in brain quantified by real-time PCR, using as template cDNA reversed-transcribed from total brain RNA (S.E., n = 5, *, p < 0.01). D, AQP4 immunoblot of whole brain homogenates, 5 μg of protein/lane (top). The arrow indicates AQP4 protein monomer. β-actin immunoblot was used for normalization.

FIGURE 2.

FIGURE 2.

Brain anatomy and AQP4 expression in mice. A, brain histology in hematoxylin and eosin-stained sections from GFAP-AQP4 and wild-type (+/+) mice. Left, low magnification micrograph of cerebral cortex and hippocampus. Scale bar, 1 mm. Right, higher magnification micrographs of indicated regions. Scale bar, 100 μm. B, AQP4 (red, Cy3-labeled) and GFAP (green, fluorescein isothiocyanate-labeled) immunofluorescence, with cell nuclei-stained blue (4′,6-diamidino-2-phenylindole (DAPI)). Scale bar, 100 μm.

FIGURE 3.

FIGURE 3.

Accelerated brain water accumulation in AQP4-overexpressing mice in a water intoxication model of cytotoxic brain edema. A, baseline ICP in mice of indicated genotype. Data from individual mice are shown, with averaged data shown with error bars (S.E., differences not significant). B, original ICP curve for GFAP-AQP4 mouse. The arrow indicates the time of intraperitoneal administration of water (IP water, 10% body weight). The inset shows the time course of serum sodium after intraperitoneal administration of water (S.E., n = 4). C, representative ICP curves for two mice of each genotype. D, summary of ICP curve analysis: ΔICP at 10 and 20 min, d(ICP)/d_t_ at 10 min after water intoxication, maximal d(ICP)/d_t_, and time to reach maximal d(ICP)/d_t_ (S.E., 5–8 mice/group, *, p < 0.05, **, p < 0.01 when compared with +/+ mice).

FIGURE 4.

FIGURE 4.

Correlations between ICP parameters and brain AQP4 protein expression. A, ΔICP at 10 min (left) and maximal d(ICP)/d_t_ (right) determined from ICP curve analysis plotted against AQP4 protein expression determined by immunoblot analysis (S.E.). B, deduced increase in brain water at 10 min following intraperitoneal administration of water (Δ brain water, in μl), as a function of brain AQP4 expression. Δ brain water at 10 min is a measure of osmotic water permeability of the blood-brain barrier. Hypothetical curves (dashed) show predictions if AQP4 is rate-limiting for blood-brain barrier water permeability versus if the endothelium is rate-limiting for blood-brain water permeability.

Similar articles

Cited by

References

    1. Rash, J. E., Yasumura, T., Hudson, C. S., Agre, P., and Nielsen, S. (1998) Proc. Natl. Acad. Sci. U. S. A. 95 11981-11986 - PMC - PubMed
    1. Furman, C. S., Gorelick-Feldman, D. A., Davidson, K. G., Yasumura, T., Neely, J. D., Agre, P., and Rash, J. E. (2003) Proc. Natl. Acad. Sci. U. S. A. 100 13609-13614 - PMC - PubMed
    1. Ghabriel, M. N., Thomas, A., and Vink, R. (2006) Acta Neurochir. Suppl. 96 402-406 - PubMed
    1. Neal, C. J., Lee, E. Y., Gyorgy, A., Ecklund, J. M., Agoston, D. V., and Ling, G. S. (2007) J. Neurotrauma 24 1609-1617 - PubMed
    1. Saadoun, S., Papadopoulos, M. C., Davies, D. C., Krishna, S., and Bell, B. A. (2002) J. Neurol. Neurosurg. Psychiatry 72 262-265 - PMC - PubMed

Publication types

MeSH terms

Substances

Grants and funding

LinkOut - more resources