Abstract
Purpose: :
RPE cells produce neuroprotectin D1 (NPD1) in response to oxidative stress, neurotrophins, and photoreceptor (PR) outer segment phagocytosis, which in turn elicits cell survival signaling. Here, we asked about the contribution of PRs to the synthesis of NPD1 in response to oxidative stress.
Methods: :
Rats were divided into two groups. One group kept in normal cyclic light (PR+), the other exposed to bright light (9h, 18 kLx) and recovery (>14d) (no PRs, PR-). PRs present in superior and inferior PR- retinas were 0% and <25%, respectively. Rats were dark adapted and retinas isolated from RPE after flat mounting on nitrocellulose membranes. Isolated retinas were incubated in DMEM/F12, with or without 100 µM H2O2 + 10 ng/mL TNF-α, for 0, 1, 2, 4, or 6 hours for PR+ and 2 hours for PR-, reactions quenched and tissue analyzed by LC-ESI-MSMS for NPD1 and other lipid mediators.
Results: :
Levels of free docosahexaenoic acid (DHA), arachidonic acid (AA), and 15S-HETE in PR+ showed superior to inferior differences, but no difference due to oxidative stress. In contrast, PR- showed higher levels of all three analytes in H2O2 vs. control treatment, but no superior to inferior difference. PR+ displayed a time dependent DHA increase; superior levels greater than inferior. AA release was seen in superior PR+, peaking between 1h and 2h, but inferior PR+ displayed no release. Similarly, a time dependent increase of 15S-HETE was seen in superior PR+, with no response from inferior PR+. Superior PR+ NPD1 displayed a large peak at 2h H2O2 treatment, not seen in inferior; superior control was also larger than inferior. PR- removed NPD1 H2O2 response at 2h, both treatments having levels similar to PR+ control levels.
Conclusions: :
The strong NPD1 peak from PR+ retina suggests active synthesis, of this lipid mediator, by PRs in the presence of oxidative stress. The change in NPD1 response due to loss of PRs indicates that PRs are more sensitive, by time, dose, or both, to oxidative stress than remaining neural retina. It also appears that superior retina responds differently, in regards to DHA and AA release and metabolism, than inferior retina. Since this differential response is lost in PR- retina, the effect seems attributable to PRs. Presumably, PRs produce NPD1 in response to oxidative stress, and superior PRs are either more sensitive, responding earlier, or can produce more NPD1 than inferior. One alternative to this is that other cell(s) produce NPD1 in response to signal(s) from PRs, superior PRs having more sensitivity, or greater response capacity than inferior PRs.