Diverse regulation of retinal pigment epithelium phagocytosis of photoreceptor outer segments by calcium-independent phospholipase A₂, group VIA and secretory phospholipase A₂, group IB.

PURPOSE:To investigate the roles of the phospholipases A(2) (PLA(2)) subtypes, iPLA(2)-VIA and sPLA(2)-IB in retinal pigment epithelium (RPE) phagocytosis of photoreceptor outer segments (POS) and to explore a possible interaction between sPLA(2)-IB and iPLA(2)-VIA in the RPE. METHODS:To explore the role of iPLA(2)-VIA in RPE phagocytosis of POS, experiments with iPLA(2)-VIA vector transfection, iPLA(2)-VIA(-/-) knockout (KO) mice, and iPLA(2)-VIA inhibition by bromoenol lactone (BEL) were done. Exogenous addition of sPLA(2)-IB was used to investigate the role of sPLA(2)-IB in RPE phagocytosis. A Luciferase Reporter Vector containing the iPLA(2)-VIA promoter was used to study the effects of sPLA(2)-IB on the iPLA(2)-VIA and primary mouse RPE cells transfected with iPLA(2)-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 sPLA(2)-IB reduced phagocytosis in and primary mouse RPE cells. Finally, sPLA(2)-IB did not seem to affect the iPLA(2)-VIA promoter. CONCLUSION:The present study confirms the involvement of iPLA(2)-VIA in efficient RPE phagocytosis of POS, while exogenously added sPLA(2)-IB decreases phagocytosis regardless of enzymatic activity. No apparent interaction between iPLA(2)-VIA and sPLA(2)-IB was found.

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