The long-term goal of the laboratory has been to obtain basic information about the molecular and cellular biology of corneal wound healing. The studies in the current grant period demonstrated that epidermal growth factor receptor (EGFR) is the key receptor tyrosine kinase activated upon wounding, and the wound-induced activation of EGFR and its downstream signaling pathways, particularly ERK and PI3K, play a central role in mediating corneal epithelial wound healing. While in normal cornea an epithelial wound is usually healed in a timely fashion without any complications, epithelial wound healing is considerably delayed in the corneas of diabetic patients. The delayed healing of the epithelial defect (termed diabetic keratopathy) may result in sight threatening complications, such as persistent epithelial defect, recurrent erosion, and microbial keratitis. Preliminary studies using streptozotocin (SZT)-treated rats as a type 1 diabetes model and human diseased corneas revealed that EGFR signaling, in particular PI3K pathways, is compromised in the epithelia of diabetic rat corneas and of human diabetic, but not in normal and diet-controlled corneas. Our published and preliminary studies lead to the hypothesis that the tightly regulated EGFR signaling is abrogated by hyperglycemia in the epithelium and that strengthening of the weakened EGFR signaling, along with reducing oxidative stress, may preserve epithelial integrity and promote epithelial wound healing in the diabetic corneas.
Three specific aims are proposed to test this hypothesis. 1) To characterize EGFR signaling pathways and oxidative damage in SZT diabetic rat corneas. Alterations of EGFR signaling in the epithelia of SZT-induced and human diabetic corneas will be characterized and correlated to the epithelial abnormalities observed in these diseased corneas. 2) To determine how hyperglycemia affects EGFR signaling and epithelial integrity and function in the cornea. Cultured porcine corneas and primary human corneal epithelial cells will be used. The effects of high glucose that mimics hyperglycemia on the generation of reactive oxygen species, on EGFR signaling, and on epithelial integrity and function including barrier properties and wound healing will be assessed. 3) To determine how manipulation of EGFR-signaling pathways might be used to accelerate epithelial wound healing in diabetic corneas. EGFR ligands will be combined with antioxidant and their synergistic effects on promoting epithelial wound healing and barrier function will be elucidated. The results of these proposed studies should shed light on the mechanisms underlying pathogenesis of diabetic keratopathy and lead to the identification of effective treatments for the delayed diabetic corneal epithelial wound healing which currently are lacking.
This study will use animal models of diabetes, a unique ex vivo corneal organ culture model, cultured human corneal epithelial cells, and human diabetic corneas to study the mechanisms underlying pathogenesis of diabetic keratopathy, a disease with severe abnormalities in two thirds of patients. In the light of an ever-increasing patient population with diabetes and the lack of effective treatments for the disease, this study is of paramount importance and may lead to the development of therapeutics for treating the disease and for promoting delayed epithelial wound healing often associated with diabetic vitrectomy.
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