Increased expression of the chronic ER stress-induced transcriptional factor, ATF4 leads to glaucoma by promoting protein synthesis and ER client protein load

Abstract

Purpose : The underlying pathological mechanisms of glaucomatous damage to the trabecular meshwork (TM) and elevation of intraocular pressure (IOP) are not completely understood. We have previously shown that chronic endoplasmic reticulum (ER) stress is associated with glaucomatous TM damage and IOP elevation. However, it is not understood whether and how chronic ER stress leads to TM dysfunction and IOP elevation. The purpose of this study is to investigate the exact molecular signaling cascades of chronic ER stress responsible for TM damage and IOP elevation

Methods : Intraocular pressures were monitored using a rebound tonometer. Aqueous humor outflow was measured using the constant flow infusion technique. RGC function was analyzed using binocular snout pattern ERG. The total number of RBPMS-positive RGCs in whole-mount retinas were counted using Image J software. Axonal degeneration in the optic nerve was examined by PPD staining. De novo protein synthesis in the cells was assessed using the SUnSET assay.

Results : We show that the chronic ER stress-induced ATF4-CHOP-GADD34 signaling pathway is increased in glaucomatous human and mouse TM. Expression of ATF4 in the TM reduces aqueous humor outflow facility and elevates IOP significantly in mice. Sustained ATF4-induced IOP elevation leads to glaucomatous neurodegeneration similar to human glaucoma. Interestingly, ATF4 interacts with CHOP and this interaction is essential for IOP elevation. Expression of ATF4 in the TM promotes aberrant protein synthesis and induces ER client protein load and ER stress, leading to TM dysfunction and cell death, thereby elevating IOP. Notably, inhibition of protein synthesis by treatment with cycloheximide or genetic depletion of GADD34 prevents ATF4-induced TM cell death. Also, genetic depletion or pharmacological inhibition of the ATF4-CHOP-GADD34 pathway rescues mouse models of glaucoma by reducing protein synthesis and ER client protein load in TM cells. Importantly, we show that glaucomatous TM cells exhibit significantly increased protein synthesis, which is associated with induction of ATF4, CHOP and GADD34 levels.

Conclusions : Our studies indicate that induction of ATF4-CHOP-GADD34 signaling in glaucoma contributes to TM dysfunction and IOP elevation by promoting aberrant protein synthesis, thus providing a novel target for the treatment of glaucoma.

This is a 2020 ARVO Annual Meeting abstract.