Features of diabetic retinopathy (DR) include leukocyte/endothelial interaction (leukostasis), breakdown of blood retinal barrier (BRB) and hyperpermeability. VEGF plays a crucial role in the development of hyperpermeability via activation of VEGF-R2 which subjected to negative control by oxidation of protein tyrosine phosphatases (PTPs). Despite the clinical evidence which shows that dyslipidemia may contribute to DR, its role has not been studied in detail. Diabetic dyslipidemia is characterized by an increase in arachidonic acid (AA) which is further metabolized by 12/15-lipoxygenase and other enzymatic pathways into proinflammatory lipid metabolites. Recently we demonstrated that upregulation of 12/15 lipoxygenase (12/15-LOX) and its lipid metabolites, 12-HETEs in DR contributes to retinal neovascularization via disrupting glial cells VEGF/PEDF balance. NADPH oxidase and endoplasmic reticulum (ER) are potential targets to the increased lipid metabolites of 12/15-LOX. The major goal of the current proposal is to investigate the hypothesis that activation of 12/15-LOX contributes to retinal inflammation during DR via NADPH oxidase-dependent mechanism which involves ER stress response, oxidation of PTPs and subsequent enhanced VEGF-R2 activity. Furthermore, VEGF-R2 activity is enhanced by VEGF produced by Muller cells which are activated by the excess lipid metabolites of 12/15-LOX in diabetic retina. Our hypothesis will be investigated via 3 specific aims 1) To determine whether 12/15-LOX pathway contributes to diabetes-induced retinal inflammation.
This aim will be tested in vivo and in vitro by examining the effect of pharmacological or molecular modulation of 12/15-LOX expression and activity on diabetes or high glucose-induced increases in inflammatory cytokines, leukostasis, hyperpermeability and alterations in tight junction proteins (TJPs). To characterize the role of retinal versus the circulating leukocyte 12/15-LOX in diabetes-induced retinal inflammation we will utilize bone marrow transplantation (BMT) studies to determine the effect of wild type leukocytes with 12/15-LOX knockout retinal endothelial cells, and vise versa, on inflammatory cell infiltration and subsequent leukostasis and hyperpermeability. 2) To determine whether NADPH oxidase-mediated ER stress contributes to retinal inflammation induced by lipid metabolites of 12/15-LOX. For this aim, the effect of inhibiting NADPH oxidase or ER stress response on 12/15-LOX and HG-mediated inflammatory response will be tested. The impact of intraocular injection of HETEs in NADPH oxidase catalytic subunit NOX2-deficient mice will be compared to the effect of HETEs in wild type mice. 3) To test the hypothesis that enhanced VEGF-R2 signaling pathway plays a role in 12/15-LOX-mediated retinal inflammation, we will test whether PTP agonist or VEGF-R2 inhibitors prevent the pro-inflammatory effect of 12/15-LOX lipid metabolites in cultured retinal endothelial cells. We will also examine the impact of adenoviral-mediated sFlt1 overexpression on 12/15-LOX mediated retinal inflammation in vivo. Our experiments should establish 12/15-LOX inflammatory pathway as a potential therapeutic target to prevent the early inflammatory response during DR and in turn halts the progress of the disease to the late stage of retinal neovascularization and vision loss.
Diabetic retinopathy (DR), the leading cause of blindness in working age Americans, is characterized by an initial period of inflammation followed by the formation of new blood vessels in the eye which ultimately leads to vision loss. The early inflammatory response is characterized by adhesion of the white blood cells (leukocyte) to the blood vessel wall and vascular leakage. We will test the hypothesis that 12/15-LOX enzymatic pathway of lipid metabolism in retina contributes to the initial period of retinal inflammation by inducing cellular stress response. This response includes oxidative stress and stress response in the endoplasmic reticulum (ER), an important cell organelle responsible for protein maturation and function. 12/15-LOX-mediated cellular stress leads to activation of inflammatory pathway mainly through the receptor of the vascular endothelium growth factor (VEGF-R2). The current proposal will establish the 12/15-LOX pathway as a novel therapeutic target to prevent the progression and development of DR.
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