Molecular Signaling in Cataracts

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Project Summary Cataract is one of the major causes of blindness worldwide. Following surgical removal of the cataractous lens, approximately 20% of cataract patients develop posterior capsular opacification (PCO) and significantly compromised quality of life. Given the prevalence of cataract and the relatively high rate of PCO following cataract surgery, especially among young patients who develop a more aggressive PCO as well as the increasing number of diabetics at higher risk to develop PCO, there is an urgent need for therapies to prevent cellular changes that lead to this blinding condition. There is currently no medical therapy to effectively prevent PCO and no alternative to capsulotomy for its treatment. Thus, the long-term impact of this work will address a currently unmet clinical need—the prevention of PCO using pharmaceutical agents to suppress growth factor signaling responsible for PCO development. Transforming growth factor-beta (TGF-β) is recognized as one of the major growth factors that drive PCO pathogenesis. TGF-β induces activation of Smad proteins, which then bring about transcription of a battery of genes involved in the shift of epithelial cells to a mesenchymal phenotype, known as epithelial-to-mesenchymal transition (EMT). In preliminary studies we showed that aldose reductase (AR), a polyol pathway enzyme linked to diabetic eye disease, facilitates Smad activation by TGF-β. Proposed studies seek to devise therapeutic strategies to interrupt the pathogenic signals that drive the PCO process. In Aim 1, we will use transgenic mouse models as a platform to test the hypothesis that AR facilitates EMT in PCO pathogensis. Comparative risk for PCO development will be measured in our AR-Tg mice, AR null mice (ARKO), and wild type C57BL6 mice, using immunostaining and quantitative PCR to measure EMT and structural markers in the lens at various times following surgery. In Aim 2, we will decipher the mechanism linking AR to TGFß-mediated signaling in PCO development. We will utilize mutant forms of AR and TGFß-receptor adaptor proteins to test the hypothesis that AR interferes with Smad-activation through its interactions with accessory proteins involved with Smad recruitment to the receptor complex. In Aim 3, we will explore two different therapeutic strategies to block EMT signaling in animal models of PCO. First we will test the hypothesis that pharmacological blockade of AR is sufficient to prevent cellular changes associated with PCO development. In a second arm of this study, we will test the ability of a membrane-permeable form of Smad7, an inhibitor of Smad signaling, to attenuate EMT in our mouse model of PCO. We will also investigate a combination therapy involving combined use of an AR inhibitor and Tat-Smad7. These studies aim to clarify molecular mechanisms leading to PCO and lead to therapeutic strategies for its prevention.