Elucidating the molecular changes of the outflow pathway extracellular matrix that regulate outflow facility in steroid-induced ocular hypertension and open angle glaucoma

Suny Downstate Medical Center, Brooklyn NY

Investigators

Abstract

Elevated intraocular pressure (IOP) is the only modifiable risk factor for open angle glaucoma (OAG). IOP is determined by the balance of aqueous humor production and outflow predominately through the conventional outflow tissues - the trabecular meshwork (TM) and Schlemm’s canal inner wall. TM cell dysfunction in OAG causes IOP elevation. Similar dysfunction and IOP elevation occur even in individuals without glaucoma when exposed to high enough concentrations of potent steroids for long enough periods of time. TM cells reside within a rich extracellular matrix (ECM) they synthesize and maintain. The TM ECM provides physical resistance to aqueous outflow but is also the source of cell attachment sites as well as signaling domains that affect the physiological state of TM cells and thereby can affect outflow facility. Our hypothesis is that because of exposure to steroids or because of genetic predisposition in OAG, TM cells do not properly maintain their ECM. Reversing critical ECM changes would thus help restoring healthy outflow and maintaining normal IOP. We have shown that tissue plasminogen activator (tPA) can reverse outflow facility reduction and IOP elevation in both steroid-induced glaucoma as well as in animals with mutant myocilin through upregulation of matrix metalloproteinase 9 (MMP9). MMP9 is known to participate degradation and ECM turnover of ECM components and the release of signaling molecules, e.g., VEGF, sequestered in the ECM. Using our biomimetic Artificial Conventional Outflow System (ACOS), we have identified differences in ECM molecules laid down by healthy human TM (HTM) and steroid-treated HTM cells which are known targets of MMP9. The overall objective of this project is to determine whether specific components of the ECM induced by steroids cause reduced outflow facility and whether they are also responsible for decreased outflow facility in other forms of OAG. To achieve this objective, we will initially employ the ACOS to maintain precise control of the experimental conditions. We will then confirm our findings using relevant animal models. Aim 1: Determine if ECM changes that lead to stiffening and reduced outflow facility are the same at the molecular level in OAG and steroid-induced IOP elevation. Aim 2: Determine if collagen II and elastin overproduction causes steroid-induced ECM stiffening and simulated outflow decrease in ACOS and the steroid-induced or OAG decrease in outflow leading to high IOP in mice. Aim 3: Determine if the tPA/MMP9 pathway affects outflow by releasing VEGF sequestered in the ECM or by inhibiting CXCL12 signaling. We will thus determine the contributions of specific ECM components in causing decreased outflow in steroid- induced ocular hypertension and OAG. These results can help us understand how changes in ECM composition affect tissue function and lead to development of novel therapeutics. The findings can have broader impact as many of the processes involved are hypothesized to be causative for fibrosis in various tissues and organs.