Targeting ER Stress for the Treatment of Steroid and Myocilin Glaucoma

Elevation of eye pressure can lead to blindness in humans. The trabecular meshwork (TM) tissue, which drains the eye and controls eye pressure, is damaged in glaucoma, thus raising eye pressure. Our recent work identified that endoplasmic reticulum (ER) stress to the TM cells is involved in elevation of eye pressure. Specifically, we discovered that two molecules, ATF4 and CHOP, are involved in this process. In this proposal, we will test whether inhibition of these molecules via a new type of drug known as an integrated stress response inhibitor (ISRIB) that lowers eye pressure in mice and cultured TM cells.

Primary open angle glaucoma (POAG), a second leading cause of blindness in the United States, is often accompanied by elevated intraocular pressure (IOP) resulting from increased resistance to aqueous humor outflow through the trabecular meshwork (TM). It is known that chronic IOP elevation leads to loss of retinal ganglion axons and blindness. Therefore, it is important to understand the pathological mechanisms leading to IOP elevation. Although glaucomatous damage to TM is known to elevate IOP, none of the current treatments target this pathway. There is a critical need to develop novel treatments targeted at glaucomatous TM damage.

We have shown that progressive accumulation of misfolded proteins is associated with the glaucomatous TM damage and IOP elevation. Specifically, we discovered that chronic endoplasmic reticulum (ER) stress-induced ATF4/CHOP in the TM is associated with IOP elevation. Expression of ATF4 in the TM leads to significant IOP elevation and reduces outflow facility in wild type mice. In this proposal, we propose to examine whether inhibition of ATF4/CHOP pathway using an integrated stress response inhibitor (ISRIB), a selective and potent inhibitor of ATF4/CHOP pathway, reduces unfolded protein load in TM cells and prevents IOP elevation in mouse models of glaucoma.

The proposed study will directly test the therapeutic effectiveness of ISRIB on protein misfolding and reduction of elevated IOP using human TM cells and mouse models of glaucoma. This study takes advantage of recently developed mouse models of glaucoma that faithfully replicate the human disease. Tg-MYOCY437H mice developed in our laboratory provide an excellent model to discover in vivo mechanisms of protein misfolding. Using dexamethasone-induced glaucoma models (eg, steroid-induced glaucoma), we will examine whether ISRIB reduces normal (not mutant) protein accumulation in TM and prevents IOP elevation. The proposed experiments are likely to provide mechanistic insights into how inhibition of ATF4/CHOP signaling (ie, a pro-death signaling cascade) prevents unfolded protein load, which can be further explored for development of novel drug targets.