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

Abstract

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.

Keywords::

• Glaucomatous optic neuropathy
• Optic nerve
• Aquaporin
• Astrocyte
• Lactate shuttle hypothesis

ACKNOWLEDGMENTS

This study was supported in part by Grants-in-Aid for Scientific Research Nos. 22390324 (A.N., M.N.) and 23592568 (M.N., A.N., A.K.) from the Ministry of Education, Culture, Sports, Science, and Technology of the Japanese Government. The authors thank Drs. Osamu Katsuta, Yuki Asai, and Atsushi Shimazaki of the Nara Research and Development Center and Santen Pharmaceutical Co., Ltd (Nara, Japan) for their preparation and supply of the control and ocular hypertensive monkey eyeballs and Ms. Tomoko Fukuda of the Cornea Center & Eye Bank, Tokyo Dental College, and Mr. Kazunori Watanabe of the Hyogo Eye Bank for their kind coordination in importing the human donor eyeballs from Sightlife.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.