Docosahexaenoate phospholipids (DHA-PLs) are uniquely abundant in retinal and neuronal cells. Our basic research led to the discoveries that oxidation of DHA-PLs results in the generation of carboxyethylpyrrole (CEP) modifications of proteins and ethanolamine phospholipids whose levels are elevated in retinas and blood from individuals with age-related macular degeneration (AMD). Subsequent research revealed that CEPs stimulate angiogenesis found in the choroidal neovascularization of wet AMD through a vascular endothelial growth factor-independent mechanism involving Toll-like receptor (TLR)2 signaling. CEPs also contribute to the global retinal atrophy of dry AMD by IFN? and IL-17-producing CEP-specific T cells that promote M1 polarization of macrophages in the retina. Our most recent studies revealed that oxidized DHA-PLs release HOHA-lactone that can dissociate from cell membranes and react with proteins to generate CEPs, previously only known to be produced by direct reaction of an oxidized DHA-PLs with proteins. We now propose studies of HOHA-lactone chemistry and transport through cell membranes and monolayers to evaluate the likelihood that its escape from DHA-rich membranes of photoreceptor rod cell disks can produce CEPs in locations remote from the site of membrane oxidation. This may contribute to the clinically significant elevated levels of CEPs we discovered in the blood of individuals with AMD and it may account for CEP generation in the blood of rats upon light-induced oxidative injury of their retinas. We will examine the possibility that HOHA-lactone can enter cells and generate CEP modifications of intracellular proteins that can bind with and activate intracellular receptors such as platelet TLR9. Studies of HOHA-lactone glutathione (GSH) Michael adduct biochemistry will test the hypotheses that this adduct can serve as a Trojan horse that transports a CEP precursor out of cells, and that in conjunction with ALD-catalyzed reduction, can prevent CEP formation. Inspired by the biological activities found previously for adducts of other oxidized lipids with GSH, e.g. leukotrienes, pilot studies were conducted with GSH adducts of HOHA-lactone that revealed that submicromolar concentrations of GSH-HOHA-lactone and the alcohol produced by reduction of this aldehyde stimulate proliferation and tube formation by HUVEC cells. New cell biological studies are proposed to investigate the effects of HOHA-lactone, its GSH adducts and the CEP modifications of proteins and ethanol-amine phospholipids derived from the HOHA-lactone on primary human RPE cells, bone marrow-derived macrophages, and primary choroidal endothelial cells, including studies on the signaling pathways leading to the biological effects. The potential utility of the mechanistic information to be gleaned from the in vitro and in vivo studies proposed is exemplified by new insights recently developed suggesting that immunosuppressive therapy might be effective for ameliorating the retinal damage of dry AMD caused by a CEP-induced T-cell promoted invasion of the retina by inflammatory macrophages and their CEP-potentiated activation.
A new pathway for generating CEPs, protein and ethanolamine phospholipid modifications that contribute to the pathogenesis of both 'dry' and 'wet' age-related macular degeneration (AMD), will be studied. The ability of a reactive product of lipid oxidation, 'HOHA-lactone' to escape from cellular membranes in the retina and produce CEPs in locations remote from the site of membrane oxidation, including the blood, will be determined in a rat model of photooxidative injury. Investigations of the biological activities of HOHA-lactone, its interception by glutathione and the transformations and biological activities of the adducts will be extended, and the signaling pathways involved determined to provide a basis for the design of new therapeutic measures for the treatment of AMD.
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