ABSTRACT
The identification of neuroprotectin D1 (NPD1), a biosynthetic product of docosahexaenoic acid (DHA), in brain and retina as well as the characterization of its bioactivity, is generating a renewed interest in the functional role and pathophysiological significance of omega-3 fatty acids in the central nervous system. Neurotrophins, particularly pigment epithelium-derived factor (PEDF), induce NPD1 synthesis and its polarized apical secretion, implying paracrine and autocrine bioactivity of this lipid mediator. Also, DHA and PEDF synergistically activate NPD1 synthesis and antiapoptotic protein expression and decreased proapoptotic Bcl-2 protein expression and caspase 3 activation during oxidative stress. In experimental stroke, endogenous NPD1 synthesis was found to be upregulated, and the infusion of the lipid mediator into the brain under these conditions revealed neuroprotective bioactivity of NPD1. The hippocampal CA1 region from Alzheimer's disease (AD) patients (rapidly sampled) shows a major reduction in NPD1. The interplay of DHA-derived neuroprotective signaling aims to counteract proinflammatory, cell-damaging events triggered by multiple, converging cytokine and amyloid peptide factors, as in the case of AD. Generation of NPD1 from DHA thereby appears to redirect cellular fate toward successful preservation of retinal pigment epithelial (RPE)-photoreceptor cell integrity and brain cell aging. The Bcl-2 pro- and antiapoptotic proteins, neurotrophins, and NPD1, lie along a cell fate-regulatory pathway whose component members are highly interactive, and have potential to function cooperatively in cell survival. Agents that stimulate NPD1 biosynthesis, NPD1 analogs, or dietary regimens may be useful as new preventive/therapeutic strategies for neurodegenerative diseases.
