PNPLA2 (Patatin-like Phospholipase Domain Containing Protein 2), a novel gene involved in lipid metabolism in the RPE

Authors

• F Polato
• M Abu-Asab
• SP Becerra

Abstract

Previously, we identified the PNPLA2 gene in mammalian retinal pigment epithelium (RPE). The PNPLA2 protein, PEDF-R, exhibits phospholipase and triglyceride lipase activities, both of which release fatty acids from phospholipids and triglycerides, respectively. Massive accumulation of lipids occurs in murine macrophages, adipocytes, cardiomyocytes and hepatocytes that lack Pnpla2. To understand the role of Pnpla2 in lipid biology of the murine RPE, we generated a conditional Pnpla2 knockout mouse model in RPE. Pnpla2 floxed (Pnpla2f/f) mice were crossed with the BEST1-cre transgenic mouse line that expresses the Cre gene specifically in the RPE. Pnpla2 transcript levels decreased in the RPE/Choroid RNA of knockout mice. Oil Red O staining of lipids increased in the RPE of Pnpla2-KO mice. Electron microscopy micrographs showed the accumulation of large lipid droplets in the Pnpla2-KO RPE, decreased thickness of the basal RPE infoldings, abnormal mitochondria, and disorganized localization of organelles (mitochondria and melanosomes). Pnpla2-KO RPE released similar levels of ß-hydroxybutyrate upon ingestion of outer segments compared to controls. The effects of lipid deposits in the RPE on homeostasis of photoreceptors were investigated. The morphology of the retina by optical coherence tomography showed no apparent differences in the structure and thickness of the outer nuclear layer between knockouts and controls. Retinal functionality evaluated by electroretinography, showed no differences in the amplitude of the scotopic a- and b-wave as well as the photopic b-wave in the knockout mice relative to controls. The data suggest that the Pnpla2 plays a role in fatty acid metabolism in the RPE.

Scientific Focus Area: Molecular Biology and Biochemistry

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