Inhibition of heat shock protein 90 lowered intraocular pressure without affecting the production of aqueous humor in rabbits

<b><i>Introduction:</i></b> Heat shock protein (Hsp) 90 is one of the most abundant proteins in unstressed cells and regulates stability and functional maintenance of client proteins. In ocular tissue, Hsp90 is widely expressed in the cornea and retina and has multiple roles in these tissues. The expression of HSPs was induced in the retinas of glaucomatous patients and laser-induced glaucoma in monkey while their mechanisms remain to be elucidated. For this reason, we tried to elucidate the role of Hsp90 in intraocular pressure (IOP) regulation in rabbits. <b><i>Methods:</i></b> IOP was measured by a pneumatonometer before and after intracameral injection of Hsp90 inhibitors. The aqueous flow rate was measured by fluorophotometry. Trans-epithelial electrical resistance was measured in primary human trabecular meshwork cells. <b><i>Results:</i></b> 17-AAG, a specific Hsp90 inhibitor, significantly lowered IOP at concentrations of more than 30 μ<sc>m</sc> in normotensive rabbits. Other Hsp90 inhibitors also significantly lowered IOP in normotensive rabbits at a dose of 100 μ<sc>m</sc>. No reduction of aqueous humor production was observed by injection of 17-AAG in rabbits. Topical administration of pilocarpine tended to attenuate the IOP-lowering effects induced by the Hsp90 inhibitor. No reduction of trans-epithelial electrical resistance was observed by inhibition of Hsp90 in culture cells. <b><i>Conclusions:</i></b> These results indicated that intraocular Hsp90 regulates IOP, and the inhibition of Hsp90 by Hsp90 inhibitor decreases IOP without affecting aqueous humor production in rabbits. Further research in elucidating the mechanism of Hsp90 inhibitors will result in a better understanding of the role of Hsp90 in the regulation of IOP.