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R. Li, P. McCourt, X. Liu, B. Smedsrød, K. Sørensen; Endocytosis of Advanced Glycation End Products in Bovine Retinal Pigment Epithelial Cells. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2206.
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© ARVO (1962-2015); The Authors (2016-present)
To study expression of stabilin receptors and endocytosis of macromolecules in RPE cells. The retinal pigment epithelial (RPE) cells have diverse features and serve as a versatile partner in vision. Besides phagocytosis of degenerated outer segments of the photoreceptor, the tight cellular junctions of the RPE form a barrier that prevents passage of large molecules, including proteins and lipids, in and out of the sub-retinal space. Therefore, the RPE cells must also serve as scavenger cells in the retina, responsible for clearance of waste macromolecules. Typical scavenger cells internalize modified macromolecules such as advanced glycation end products (AGEs), via scavenger receptor (SR) mediated endocytosis. In non-macrophagic scavenger cells, it has been reported that the novel SRs, stabilin 1 and 2, are the most important endocytic receptors for AGEs (Hansen et al., Exp Cell Res., 303:107-73, 2005). We therefore hypothesized that the RPE cells could have a similar phenotype.
Bovine RPE-choroid-sclera tissue cultures and primary RPE cell cultures were established and incubated with fluorescently labeled AGE modified bovine serum albumin (AGE-BSA) or formaldehyde-treated BSA (FSA) under serum free conditions. Immunocytochemistry and western blot analysis were done using polyclonal antibodies against human recombinant stabilin 1 and rat liver stabilin 2 (also named hyaluronan/scavenger receptor) (McCourt et al., Hepatology, 30:1276-1286, 1999; Politz et al. Biochem. J., 362:155-164, 2002).
Fluorescently labeled AGE-BSA and FSA were actively taken up by the RPE cells in the tissue cultures. Uptake was dose-dependent and was inhibited by excess amounts of non-labeled AGE-BSA and FSA, and fluorescently labeled FSA, respectively, but not by the non-SR ligand mannan. Specific fluorescence was also seen in vesicles in newly isolated RPE cell cultures. Immunolabeling of the RPE cultures showed positive staining with the anti-stabilin 1 and anti-stabilin 2 antibodies. The expression of stabilins was confirmed by western blot analysis.
We conclude that bovine RPE cells endocytose AGE-BSA and other modified macromolecules. The cells express the scavenger receptors stabilin 1 and stabilin 2, which may be involved in this uptake.
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