Joseph A. Bonanno - US grants

Corneal hydration is derived almost exclusively from the ion transport activities of the corneal endothelium. Numerous studies have shown that endothelial fluid transport, dehydration activity, and electrical potential are dependent on bathing solution pH and the presence of bicarbonate. In an environment of constant carbon dioxide concentration, extracellular and intracellular bicarbonate concentrations are exquisitely determined by extra- and intracellular pH (pHo and pHi), respectively. This suggest that elucidation of pHi regulatory mechanisms will be necessary to form any meaningful model for endothelial fluid transport. Preliminary observations have shown that endothelial pHi can be measured in fresh corneal explants by use of pH sensitive intracellular fluorescent probes. This one-year pilot project proposes to use this technique to: (1) identify the pHi regulatory mechanisms in fresh bovine corneal endothelium; (2) determine the relative activities of the bicarbonate transporters; and (3) determine the apical-basal polarity of the transporters by establishing cultures of bovine endothelium with the intent of growing monolayers onto tissue culture filters for independent perfusion of apical and basal membranes. Completion of these aims will provide data to formulate a working model of bicarbonate transport across a mammalian corneal endothelium. The long range goals of this line of study will be to: 1) correlate bicarbonate transporter activities with fluid transport and/or electrical potential; 2) measure bicarbonate transport activities in post-surgical diseased human endothelium to ascertain their role in the decline of endothelial function; and 3) determine the effects of contact lens induced acidosis on endothelial bicarbonate transport.

DESCRIPTION (provided by applicant): The cornea is the primary refractive element of the eye and therefore it must be smooth and transparent for good vision. Transparency is most affected by the hydration level of the stromal connective tissue. Hydration is dependent on the metabolic activities of the corneal epithelium and endothelium;however it is the endothelium that is primarily responsible for pumping ions and fluid that maintains the steady-state hydration of the stroma. The long-term goal of this project is to understand how the corneal endothelium does this job, so that medical therapies can be developed to enhance endothelial function in corneas that have been compromised by disease or trauma. The endothelial ion and fluid pump is most dependent on HCOa" for its function. Our approach has been to identify, characterize, and integrate the membrane pumps, transporters and channels into a model for transendothelial HCCV and fluid transport in a cultured endothelial cell system. In this period of the project we focus on understanding the mechanisms for apical HCOa'efflux, particularly the roles of carbonic anhydrases (CAs) and anion exchangers and how they may buffer and facilitate the transport of lactic acid. To do this, we will identify and localize lactate: H+ cotransporters and determine if lactate fluxes are reduced by pharmacological inhibitors for CAs and HCO3" transporters as well as following treatment with small interfering RNA to reduce CA or transporter expression. We also examine the roles of adenosine receptor stimulation and soluble adenylyl cyclase in setting cell [cAMP], which has a stimulatory effect on endothelial function. This will also use the siRNA approach and examine cAMP/PKA mediated phosphorylation of transporters, myosin light chain, and CREB transcription factor as well as the effects on net HCO3" transport as measures of relative PKA activity. Lastly, we will examine the model of HCOa" transport that is being built in vitro with cultured cells in the in vivo rabbit cornea. Our approach is to use lentiviral delivery of interfering RNA molecules to reduce specific transporter expression in vivo and examine the effect on corneal thickness and endothelial function. The results from this Aim will tell us the relative importance of the various transporters in maintaining corneal hydration in the in vivo cornea.

vision; biomedical equipment resource; biomedical facility;

Contact lens wear is a safe and effective form of correction for refractive error. However, a significant number of people are unable to wear lenses because of chronic corneal edema. Previous studies have shown significant individual differences in the amount of corneal edema produced by contact lens-induced hypoxia. We will test the hypothesis that individual differences in corneal edema are associated with individual differences in metabolic activity of the cornea. In a large group of normal subjects we will measure corneal edema, oxygen consumption (Qc) and acid load produced by wearing contact lenses of high, medium and low oxygen transmissibility. Corneal edema will be determined by measuring corneal swelling following three hours of closed eye lens wear. Oxygen consumption will be determined by using a new non-invasive technique for measuring tear oxygen tension (PO2) under contact lenses of known oxygen transmissibility. Hypoxic acid load will be determined by measuring the change in corneal stromal pH during closed eye contact lens wear. Our hypothesis predicts that individuals with a relatively high Qc will have lower tear Po2 (i.e., relatively more hypoxia) for a given contact lens wearing condition. In order to maintain corneal energy levels, these individuals should have a greater dependence on glycolytic metabolism, which will lead to greater production of lactic acid. Thus, the hypothesis also predicts that individuals with high Qc will show the greatest drop in corneal pH. Since lactate is the osmotic agent for hypoxic corneal swelling, these individuals will show greater corneal swelling. An alternate hypothesis, that variability in corneal swelling is a function of the variability in endothelial function, will also be tested. If the primary hypothesis is accepted, then further studies will be initiated to determine if individuals with high metabolic demand have a greater propensity toward developing clinical complications while wearing contact lenses. If so, this could lead to the development of a provocative test for suitability of contact lens wear based on a quick and simple measure of corneal oxygen consumption.

[unreadable] DESCRIPTION (provided by applicant): Our broad, long-term objective is to support current and future vision research endeavors at Indiana University, Bloomington. This infrastructure grant would provide support for an Electronics module. The module will support an electronics engineer to concentrate on electronics design and programming support as well as a technician for fabrication of electronics interfaces. The application to our vision research projects is broad. They include advanced optics of the eye, visual displays for infant vision development, microscopic fluorimetry and imaging, and equipment repair support. [unreadable] [unreadable] [unreadable]

?SLC4A11 Mitochondrial Uncoupling and ROS Production in Corneal Endothelium? ABSTRACT Defects in the gene SLC4A11 cause Congenital Hereditary Endothelial Dystrophy and some forms of Fuchs Dystrophy. The goal of this study is to understand the role of this membrane transporter in normal corneal endothelial metabolism and how SLC4A11 deficiency leads to Corneal Dystrophy. The corneal endothelial ?pump? maintains corneal hydration and transparency. When the ?pump? fails due to trauma, inflammation, ageing, or 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. A hallmark of Corneal Endothelial Dystrophies is mitochondrial dysfunction. Our laboratory has shown that SLC4A11 is an NH3 dependent electrogenic H+ transporter. We have found that glutamine is actively metabolized by the endothelium producing NH3 and enhancing ATP formation. Slc4a11 knock out shows significant corneal edema, lactate accumulation, altered mitochondrial physiology, and ROS. These data have led to the overarching hypothesis that corneal endothelium actively metabolize glutamine and that the absence of SLC4A11 alters glutamine metabolism, leading to mitochondrial dysfunction, ROS, and eventual apoptosis. Preliminary data indicate that SLC4A11 is both a plasma membrane and a mitochondrial membrane protein, leading to the novel hypothesis that SLC4A11 is a mitochondrial uncoupler. Using multiple in vitro & in vivo complementary approaches these hypotheses will be tested in three aims. Aim 1 will determine how glutamine metabolism is facilitated in Corneal Endothelial mitochondria. The hypothesis is that Slc4a11 is an NH3 sensitive mitochondrial uncoupler that works in conjunction with Uncoupling Protein-2 and the potential mitochondrial buffer taurine to facilitate Glutamine catabolism. Aim 2 will examine the source of ROS and ROS as a stimulus to Apoptosis in Slc4a11 KO. Our hypothesis is that apoptosis is accelerated by ROS, which is generated by the interaction of NH3 with an energized electron transport chain and reduced by SLC4A11 uncoupling. Aim 3 will identify the cause of corneal edema in Slc4a11 KO Mice. We will test the hypothesis that loss of Slc4a11 secondarily induces downregulation of key proteins that facilitate lactate transport. Completion of this study will establish the role of SLC4A11 and glutamine in endothelial metabolism; provide new insight for mechanisms that facilitate glutamine metabolism yet alleviate NH3 induced ROS production that will be transferable to a wide array of glutamine metabolizing tissues; and provide insight for development of therapies for endothelial dystrophies.