Molecular Mechanisms of Outflow Segmentation and Intraocular Pressure Homeostasis

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Project Summary Glaucoma is a major blinding disease. The primary risk factor and only current treatment target for all types of glaucoma is elevated intraocular pressure (IOP). We have identified a robust IOP homeostatic mechanism in which sustained pressure deviations are sensed as mechanical stretching/distortion by cells within the juxtacanalicular (JCT) region of the outflow pathway and corrective adjustments are made to the outflow resistance which restore IOP to appropriate levels. This appears to be a key reason that most people do not develop glaucoma. We recently showed that glaucomatous anterior segments cannot execute a normal IOP homeostatic response. Outflow is segmental around the circumference of the eye with regions of high flow (HF) intermediate flow (IF) and low flow (LF). We recently showed that glaucomatous eyes have more LF regions than normal eyes. This proposal is directed at understanding these two phenomena, IOP homeostasis and outflow segmentation, and exploiting this understanding to correct the glaucomatous deficiencies in them. To begin understanding the IOP homeostatic process and outflow segmentation, we evaluated molecular distribution differences between HF and LF regions of human anterior segments that had been perfused at 1x (normal) or 2x (homeostatic response) pressures. We selected a subset of the molecular differences that seemed most relevant to these processes; they were mostly extracellular matrix (ECM) proteins that function in ECM organization and remodeling. We will refine their distributions, evaluate their regional biosynthesis/dynamics rates, use RNAi silencing to knockdown their levels, interfere directly with their binding interactions, and conduct a few select protein overexpression studies. Primary readouts will be outflow segmentation changes and outflow facility changes in perfused human anterior segment organ culture. Next we will obtain the same molecular distribution data for glaucomatous eyes and using the most effective RNAi silencing and binding interaction perturbations from normal and apply them to glaucomatous eyes. The point will be to modify outflow segmentation and IOP homeostatic responsiveness in diseased tissue to restore function.