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N. Tserentsoodol, N.V. Gordiyenko, J.W. Lee, I.R. Rodriguez; Localization of Scavenger Receptors Class B (SRBI.1 and SRBI.2) Responsible for Lipid Transport in the Retina . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2992.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To determine the localization of the class B type I scavenger receptors SRBI.1 and SRBI.2 in the monkey retina. These receptors originate from the same gene and are alternatively spliced to generate unique C–termini. These receptors mediate the uptake of HDL and are known to be involved in reverse cholesterol transport by facilitating cholesterol efflux from peripheral tissues to the liver. Methods: Fresh monkey (Macaca mulatta) retina specimens were isolated and fixed in 4% paraformaldehyde. Cryostat sections (10µm thick) and vibrotome sections (100µm thick) were used for immunofluorscence labeling. Rabbit polyclonal antibodies to peptides specific to human SRBI.1 and SRBI.2 were purchased from Novus Biologicals (Coralville, IA). Mouse anti–rhodopsin was purchased from Chemicon International (Temecula, CA), goat anti–rabbit Cy5 was purchased from Jackson ImmunoResearch (West Grove, PA) and Alexa–488–labeled goat anti–mouse was purchased from Molecular Probes (Eugene, OR). Nuclei were stained with 4', 6–diamidino–2–phenylindole dihydrochloride (DAPI). Specimens were examined with a SP2 laser confocal microscope (Leica Microsystems, Exton PA). Results: Immunofluorescence staining of sections with anti–SRBI.1 showed localization mainly to Müller cells and its processes but also to the RPE. Anti–SRBI.2 labeled the apical RPE and microvilli as well as the rod outer segments (ROS) and the choriocapillaris. To distinguish the localization of SRBI.2 between the ROS and the RPE microvilli, the retina was sectioned across the ROS. The ROS cross sections were double–labeled with anti–SRBI.2 (Cy5) and anti–rhodopsin (Alexa 488). SRBI.2 colocalized with rhodopsin in the outer membrane of the ROS but not inside the disks. Immunofluorescence staining of SRBI.1 and SRBI.2 in cultured RPE cells showed punctuate staining to the cell surface. No co–localization or movement was observed when cells internalized fluorescent labeled LDL. Conclusions: SRBI.1 localized to Müller cells and SRBI.2 localized to the apical surface of the RPE, choriocapillaris and the ROS. The localization of these receptors in the retina suggests they may be involved in the movement of lipids within the retina. SRBI.2 may also be involved in processing of lipids during ROS phagocytosis. Other scavenger receptors are also under investigation.
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