Browsing Department of Biochemistry and Molecular Biology Theses and Dissertations by Subjects
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MECHANISM OF 12/15 LIPOXYGENASE-INDUCED RETINAL MICROVASCULAR DYSFUNCTION IN DIABETIC RETINOPATHYOur earlier studies have established the role of 12/15-lipoxygenase (LO) in mediating the inflammatory reaction in diabetic retinopathy. However, the exact mechanism is still unclear. The goal of the current study was to identify the potential role of endoplasmic reticulum (ER) stress as a major cellular stress response in the 12/15-LO-induced retinal changes in diabetic retinopathy. We used in vivo and in vitro approaches. For in vivo studies, experimental diabetes was induced in wild-type (WT) mice and 12/15-Lo (also known as Alox15) knockout mice (12/15-Lo−/−); ER stress was then evaluated after 12-14 weeks of diabetes. We also tested the effect of intravitreal injection of 12-hydroxyeicosatetraenoic acid (HETE) on retinal ER stress in WT mice and in mice lacking the catalytic subunit of NADPH oxidase, encoded by Nox2 (also known as Cybb) (Nox2−/− mice). In vitro studies were performed using human retinal endothelial cells (HRECs) treated with 15-HETE (0.1 µmol/l) or vehicle, with or without ER stress or NADPH oxidase inhibitors. This was followed by evaluation of ER stress response, NADPH oxidase expression/activity and the levels of phosphorylated vascular endothelial growth factor receptor-2 (p-VEGFR2) by western blotting and immunoprecipitation assays. Moreover, real-time imaging of intracellular calcium (Ca2+) release in HRECs treated with or without 15-HETE was performed using confocal microscopy. Deletion of 12/15-Lo significantly attenuated diabetes-induced ER stress in mouse retina. In vitro, 15-HETE upregulated ER stress markers such as phosphorylated RNA-dependent protein kinase-like ER-regulated kinase (p-PERK), activating transcription factor 6 (ATF6) and protein disulfide isomerase (PDI) in HRECs. Inhibition of ER stress reduced 15-HETE-induced-leukocyte adhesion, VEGFR2 phosphorylation and NADPH oxidase expression/activity. However, inhibition of NADPH oxidase or deletion of Nox2 had no effect on ER stress induced by the 12/15-LO-derived metabolites both in vitro and in vivo. We also found that 15-HETE increases the intracellular calcium in HRECs. ER stress contributes to 12/15-LO-induced retinal inflammation in diabetic retinopathy via activation of NADPH oxidase and VEGFR2. Perturbation of calcium homeostasis in the retina might also play a role in linking 12/15-LO to retinal ER stress and subsequent microvascular dysfunction in diabetic retinopathy.
THE ROLE OF GPR109A IN REGULATION OF RETINAL ANGIOGENESIS AND BLOOD-RETINAL BARRIER AS A POTENTIAL THERAPEUTIC TARGET IN DIABETIC RETINOPATHYCurrently, treatments of diabetic retinopathy (DR) have limited therapeutic benefits and limited accessibility to the growing diabetic population at risk because of the high expenses and complicated procedures. Inflammation, endothelial dysfunction, and microvascular damage are common features of diabetic complications including DR. GPR109A is the metabolite sensing receptor of beta-hydroxybutyrate (BHB) the principal ketone body in humans. Our previous studies have shown the role of GPR109A expression in promoting anti-inflammatory response in retinal pigmented epithelial (RPE) cells and the relevance of the receptor in DR. Expression of the GPR109A in microvascular endothelial cells (ECs) has been reported recently. However, the relevance of GPR109A expression and activation to retinal EC functions are yet to be studied. Our goal in this study was to identify the role of GPR109A expression and activation in barrier and angiogenic functions of retinal ECs in context of diabetic retinopathy. We used electrical cell impedance sensing (ECIS) technology to evaluate barrier functions in primary human retinal endothelial cells (HRECs) which constitute the inner BRB. Knocking down GPR109A in HRECs with siRNA decreased the transendothelial electrical resistance (TEER) compared to scrambled siRNA. Treating HRECs with BHB increased their TEER and counteracted VEGF-induced barrier disruption through activation of GPR109A and increasing zonula occludens-1 (ZO-1) expression. Treatment of STZ-diabetic mice with exogenous BHB for one month protected against the pathologic albumin leakage induced by diabetes and improved the visual acuity of this animal model of diabetes. Using the mouse model of oxygen induced retinopathy (OIR), we showed that Gpr109a-/- mice had slower vascular recovery from pathologic angiogenesis compared to age matched wild type mice. Moreover, physiologic revascularization of vaso-oblitrated retinas was impaired by loss of GPR109a and associated with dysregulated inflammatory and angiogenic signaling. Collectively, these data point to a role for GPR109A in the regulation of barrier and angiogenic mechanisms in retinal ECs and, promote the receptor as a potential druggable target for impacting these mechanisms in microvascular retinal diseases such as DR.