Diverse Regulation of Retinal Pigment Epithelium Phagocytosis of Photoreceptor Outer Segments by Calcium-Independent Phospholipase A2, Group VIA and Secretory Phospholipase A2, Group IB

Abstract

Purpose: To investigate the roles of the phospholipases A2 (PLA2) subtypes, iPLA2-VIA and sPLA2-IB in retinal pigment epithelium (RPE) phagocytosis of photoreceptor outer segments (POS) and to explore a possible interaction between sPLA2-IB and iPLA2-VIA in the RPE.Methods: To explore the role of iPLA2-VIA in RPE phagocytosis of POS, experiments with iPLA2-VIA vector transfection, iPLA2-VIA−/− knockout (KO) mice, and iPLA2-VIA inhibition by bromoenol lactone (BEL) were done. Exogenous addition of sPLA2-IB was used to investigate the role of sPLA2-IB in RPE phagocytosis. A Luciferase Reporter Vector containing the iPLA2-VIA promoter was used to study the effects of sPLA2-IB on the iPLA2-VIA promoter.Results: ARPE-19 and primary mouse RPE cells transfected with iPLA2-VIA showed increased phagocytosis. Phagocytosis was reduced in primary mouse RPE inhibited with BEL and in RPE from KO mice. Exogenous addition of enzymatically active and inactive sPLA2-IB reduced phagocytosis in ARPE-19 and primary mouse RPE cells. Finally, sPLA2-IB did not seem to affect the iPLA2-VIA promoter.Conclusion: The present study confirms the involvement of iPLA2-VIA in efficient RPE phagocytosis of POS, while exogenously added sPLA2-IB decreases phagocytosis regardless of enzymatic activity. No apparent interaction between iPLA2-VIA and sPLA2-IB was found.