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Raji Shyam, Preejith P Vachali, Kelly Nelson, Aruna Gorusupudi, Paul S Bernstein; Scavenger Receptor Class B Proteins Mediate Carotenoid Uptake into the Primate Retina. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3577.
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© ARVO (1962-2015); The Authors (2016-present)
Carotenoid transport into the primate retina is not well characterized. Several studies have pointed to the role of Class B scavenger receptors as carotenoid transporters. In this study, we undertook a systematic approach to study the presence and function of all three Class B scavenger receptor proteins in the primate eye.
Total RNA was isolated from human donor eye tissues and q-PCR was carried out to determine the transcript levels of scavenger receptors. Protein was isolated from human donor eye tissues and western blotting was conducted using antibodies against SCARB1, SCARB2, and CD36 to determine their protein levels. Immunostaining was carried out in sections of macaque eye using the above mentioned antibodies to determine the expression pattern of scavenger receptors in the primate eye. In order to determine the function of these proteins as carotenoid transporters, overexpression was carried out in HEK-293T cells followed by treatment with various concentrations and types of carotenoids. Surface plasmon resonance experiments were conducted to determine the binding affinity of carotenoids with scavenger receptor proteins.
We detected the presence of various isoforms of all three Class B scavenger receptors in the primate eye. Relative abundance of SCARB2 transcripts and protein was higher than that observed for SCARB1 and CD36. Expression of scavenger receptors in the primate eye sections showed no overlap in their pattern, suggestive of non-redundant roles in carotenoid uptake. Overexpression of these proteins resulted in the increase carotenoid uptake. The carotenoid uptake efficiency by these receptors, however, was dependent on the concentration of carotenoids. For example – SCARB1 overexpressed cells showed significant increase in the uptake of lutein at concentrations between 1 and 10 μM, whereas SCARB2 overexpressed cells took up more lutein at lower concentrations. Surface plasmon resonance studies determined the <i abp="902">K<sub abp="900">D of scavenger receptor proteins to bind carotenoids to be around 1 μM, typical of transport proteins
Our data suggest that all three Class B scavenger receptors can function as carotenoid transporters in the vertebrate eye. In addition, the interaction of Class B scavenger receptors with carotenoids is dependent on the type and concentration of the ligand.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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