Neuroprotectin D1: A docosahexaenoic acid-derived docosatriene protects human retinal pigment epithelial cells from oxidative stress

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Abstract
Docosahexaenoic acid (DHA) is a lipid peroxidation target in oxidative injury to retinal pigment epithelium (RPE) and retina. Photoreceptor and synaptic membranes share the highest content of DHA of all cell membranes. This fatty acid is required for RPE functional integrity; however, it is not known whether specific mediators generated from DHA contribute to its biological significance. We used human ARPE-19 cells and demonstrated the synthesis of 10,17S-docosatriene [neuroprotectin D1 (NPD1)]. This synthesis was enhanced by the calcium ionophore A-23187, by IL-1β, or by supplying DHA. Under these conditions, there is a time-dependent release of endogenous free DHA followed by NPD1 formation, suggesting that phospholipase A2releases the mediator's precursor. Added NPD1 potently counteracted H2O2/tumor necrosis factor α oxidative-stress-triggered apoptotic RPE DNA damage. NPD1 also up-regulated the antiapoptotic proteins Bcl-2 and Bcl-xLand decreased proapoptotic Bax and Bad expression. Moreover, NPD1 (50 nM) inhibited oxidative-stress-induced caspase-3 activation. NPD1 also inhibited IL-1β-stimulated expression of cyclooxygenase 2 promoter transfected into ARPE-19 cells. Overall, NPD1 protected RPE cells from oxidative-stress-induced apoptosis, and we predict that it will similarly protect neurons. This lipid mediator therefore may indirectly contribute to photoreceptor cell survival as well. Because both RPE and photoreceptor cells die in retinal degenerations, our findings contribute to the understanding of retinal cell survival signaling and potentially to the development of new therapeutic strategies.

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