Regulation of pHi and Fluid Flux in Corneal Endothelium

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There are three major goals of this project period: 1) to demonstrate that the corneal endothelial PUMP is based on Lactate-Water coupled transport, 2) to determine the detailed physiological mechanism for the Lactate-Water coupled system, and 3) to begin to use this basic science knowledge to reverse corneal edema in Endothelial Dystrophy. The PUMP maintains corneal hydration and transparency. When the PUMP fails due to trauma, inflammation, ageing, or corneal dystrophy, corneal edema ensues, transparency is lost and vision is significantly degraded. The usual therapy is transplantation, which is not without significant compromises and complications. Knowing how the PUMP works is one approach to developing medical therapies that could delay or supplant the need for transplantation. Ion transport is a key feature of the PUMP. Over the previous 5-7 years we have provided strong evidence that the PUMP works by transporting lactate ions from the stroma to the anterior chamber. This lactate flux is facilitated by cellular and aqueous humor buffering power from CO2/HCO3- and the carbonic anhydrase system. Our data indicate that water flux is directly linked with lactate flux. We hypothesize that the endothelial cells create a standing [lactate] gradient that drives water osmotically from the stroma to the anterior chamber. Secondly, we show that lactate transport is compromised in a model of endothelial dystrophy. Therefore, we propose that enhancing lactate flux can reduce corneal edema in endothelial dystrophies. Using multiple in vitro, in vivo & ex vivo complementary approaches this will be tested in three aims. Aim #1 will provide experimental conditions that fill gaps in the evidence so that we can confirm the hypothesis that lactate flux, facilitated by active transport mechanisms, is the major contributor to the corneal endothelial PUMP. Aim 2 will determine the mechanism for coupling fluid flux to lactate flux by testing the hypothesis that a transendothelial [lactate] standing-gradient is present and examine the alternate hypothesis that water flux is linked directly to monocarboxylate cotransporter (MCT) flux. Aim 3 will test the hypothesis that Endothelial PUMP function, in normal and distressed cells, can be enhanced via Hypoxia Adaptation. If this hypothesis is correct, it will have the potential to be tested as a therapy for Fuchs Dystrophy.