Sporadic obstructive hydrocephalus in Aqp4 null mice

Abstract

Aquaporin-4 (Aqp4) is a water transport protein expressed in glia and ependymocytes in brain. We report here the unexpected occurrence of severe obstructive hydrocephalus in a random subset of Aqp4 knockout mice. Of 612 Aqp4 knockout mice produced by heterozygote-heterozygote or knockout-knockout breedings, 9.6% of offspring manifested progressive encephalomegaly. Encephalomegaly was never seen in wild-type or Aqp4 heterozygous mice. Examination of the subset encephalomegalic mice revealed marked triventricular hydrocephalus (lateral ventricle size approximately 500 mm(3)), elevated intracranial pressure (19 +/- 3 vs. 6.1 +/- 0.6 mm Hg), and death by age 6 weeks, with a median survival of 28 days. Intraventricular dye injection studies revealed total obstruction of the cerebral aqueduct. Evans blue extravasation studies indicated an intact blood-brain barrier in the hydrocephalic mice. Brain histology revealed reduced ventricular size and ependymocyte disorganization in some nonhydrocephalic Aqp4 null mice. Our studies establish Aqp4 deletion as a predisposing factor for the development of congenital obstructive hydrocephalus in mice. We suggest that AQP4 polymorphisms might also contribute to the development of aqueduct stenosis in humans.

Fig 1

Spontaneous hydrocephalus in Aqp4 null mice. A: External appearance of an Aqp4^+/+, a nonhydrocephalic Aqp4^−/−, and a hydrocephalic Aqp4^−/− (H) mouse. B: Whole brain (top) and coronal sections (bottom) of brains from a hydrocephalic Aqp4^−/− (H), a non-hydrocephalic Aqp4^−/−, and an Aqp4^+/+ mouse. Scale in centimeters. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Fig 2

Survival of Aqp4 null mice. Curve labeled Aqp4^−/− represents nonhydrocephalic Aqp4^−/− mice, and curve labeled Aqp4^−/−(H) represents mice with visible encephalomegaly by age 3 weeks.

Fig 3

ICP measurements. ICP of hydrocephalic Aqp4^−/− (H) mice was significantly higher than Aqp4^+/+ or nonhydrocephalic Aqp4^−/− mice. Mean ± SD, n = 8 per group. ^★P < 0.001.

Fig 4

Aqueduct stenosis in Aqp4 null hydrocephalic mice. A: Serial coronal sections of the brains from a hydrocephalic Aqp4^−/− (H) and an Aqp4^+/+ mouse after injection of Evans blue dye into a lateral ventricle. Note absence of dye from the fourth ventricle of the Aqp4^−/− (H) mouse. L, lateral ventricle; 3rd, third ventricle; Aq, aqueduct; 4th, fourth ventricle. B: Hematoxylin–eosin–stained sections through the aqueduct in a hydrocephalic Aqp4^−/− (left) and an Aqp4^+/+ (right) mouse. Green arrows show nuclei of ependymal cells arranged as a cuboidal/columnar epithelium. Red arrows indicate region with paucity of ependymal cells. Black arrow shows an abnormal-looking (pyknotic) ependymal cell nucleus forming a multilayered epithelium. C: Analysis of aqueduct shape (as major:minor axis ratio) and size (as area). Mean ± SD, n = 12 per group. ^★P < 0.02. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Fig 5

Blood–brain barrier integrity in Aqp4 null hydrocephalic mice. A: Serial coronal brain sections from a hydrocephalic Aqp4^−/− (H) and an Aqp4^+/+ mouse after intravenous Evans blue dye infusion and intravascular washout. B: Amount of extravasated Evans blue dye was not different in the three groups. Mean ± SD, n = 8 per group. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Fig 6

Ependymal abnormalities in selected Aqp4 null mice. Magnified view of ependyma in Aqp4^+/+ mice and selected nonhydrocephalic Aqp4^−/− mice where ependymal disorganization was seen. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]