Primary open angle glaucoma, a major cause of irreversible blindness, is often associated with elevated intraocular pressure (IOP) due to increased aqueous humor outflow resistance at the trabecular meshwork (TM). The pathological mechanisms leading to increased outflow resistance and IOP elevation are poorly understood. We recently linked protein misfolding and endoplasmic reticulum (ER) stress to the development of glaucomatous TM damage and IOP elevation. TM cells activate protective unfolded protein response (UPR) pathway to eliminate abnormal protein accumulation. However chronic ER stress leads to induction of terminal UPR signals including ATF4 and CHOP that are known to induce cell death. Interestingly, human glaucomatous TM tissues also show significantly increased ATF4 and CHOP. Moreover, deletion of Chop protects from ER stress and IOP elevation in mouse models of glaucoma. It is not clear how ATF4 and CHOP cause TM dysfunction and IOP elevation. In our preliminary studies, we discovered that increased ATF4 or CHOP is associated with impaired autophagy, a lysosomal degradation pathway in the TM of human and murine glaucoma. Moreover, correction of impaired autophagy via specific activator of autophagy Tat-beclin1 peptide reduces elevated IOP in mouse model of glaucoma. Based on these findings, we hypothesize that during ocular chronic ER stress, the balance between pro-cell death ATF4 and CHOP and pro-survival corrective autophagic pathways determine glaucomatous TM disease progression.
The specific aims of this proposal are: (1) To determine whether ATF4 and CHOP impair autophagic function, induce TM cell death and elevate IOP in WT mice, (2) Determine whether ATF-4 or CHOP deficiency prevents IOP elevation by improving autophagic function in the TM of Tg-MYOCY437H mice, and (3) Determine whether enhancing autophagic flux by Tat-beclin 1 peptide reduces elevated IOP in mouse models of glaucoma and in the human anterior segment perfusion culture model. These studies will utilize cultured human TM cells, mouse models of glaucoma and human anterior segment organ culture model to examine the interactions between ATF4, CHOP and autophagy in TM mediated IOP regulation. The proposed study will provide a link between UPR and autophagy and investigate whether manipulation of these pathways can provide protection against glaucoma. These studies will further explore the possibility of treating glaucoma using Tat-beclin 1 peptide in degradation of abnormal protein accumulation.
The successful completion of this project will lead to insight into elevated intraocular pressure, a major risk factor of the human blinding disorder, primary open angle glaucoma. The results will potentially improve understanding of how protein misfolding regulates disease and provide novel therapeutic targets for treatment of this common disorder.
