A Preliminary Study of Reduced Expression of Aquaporin-9 in the Optic Nerve of Primate and Human Eyes with Glaucoma

Purpose: To preliminarily test whether aquaporin (AQP)-9 is expressed in the primate and human optic nerve and whether glaucoma reduces its expression. Methods: The expression of AQP-4 and AQP-9 was immunohistochemically studied in the optic nerves of monkey eyes (an angle-laser-induced ocular hypertensive (OH) eye and a control fellow eye) and of human donor eyes (one control eye and one glaucomatous eye). Results: AQP-9 was immunoreactive throughout the entire region of the optic nerve in the monkey and human control eyes and was co-labeled with glial fibrillary acidic protein. In both the monkey OH and human glaucomatous optic nerves, the level of AQP-9 immunoreactivity was substantially reduced. AQP-4 was immunoreactive only in the retrobulbar region in both the monkey and human control optic nerves, whereas neither OH nor glaucoma affected the AQP-4 expression pattern. Conclusions: As has been shown in rats, the optic nerve head in monkeys and humans expresses AQP-9 but not AQP-4. Elevated intraocular pressure or glaucoma reduces AQP-9 expression in the optic nerve. The decrease in the astrocytic expression of AQP-9 in the optic nerve could be implicated in the development of glaucomatous optic neuropathy.