Colocalization of SR–BI receptor and the Steroidogenic Acute regulatory (StAR) protein in rat ocular tissues

Abstract

Abstract: : Purpose : The class B type I scavenger receptor (SR–BI) plays a key role in HDL metabolism, it mediates the selective uptake of lipoprotein cholesterol to steroidogenic tissues. In this study, the expression of SR–BI was investigated in normal rat eyes and compared with the expression of the steroidogenic acute regulatory protein (StAR) involved in the rate–limiting step of steroid production. Methods : mRNA expression of SR–BI was semi–quantified by reverse transcription–polymerase chain reaction (RT–PCR) in control tissues, and retina. Its ocular cellular localization was performed by in–situ hybridization. We performed SR–BI western blot analysis in retinal proteins extracts. SR–BI and StAR proteins localization in the normal eye rat have been determined by imunohistochemistry. Results :RT–PCR analysis shows that SR–BI mRNAs are highly expressed in retinal pigment epithelial cells (RPE), and neuroretina. These results are confirmed by western blot analysis. SR–BI mRNAs are detected in different cells types by in situ hybridization on rat eye tissue sections: in corneal, lens, ciliary epithelial, retinal, choriocapillary and endothelial cells. SR–BI proteins are localized by imunohistochemistry in the same cells as their mRNAs. They are especially expressed in rod inner segment (RIS), plexiform layers and ganglionic cells on eye slides. Immunohistochemistry of StAR protein showed the same expression pattern than SR–BI in rat eye. Conclusions : The high expression of SR–BI and StAR in the eye may suggest a key role of these genes in the ocular cholesterol metabolism and strengthens the hypothesis of the SR–BI involvement in ocular membranes biosynthesis and neurosteroidogenesis.

Keywords: gene/expression • immunohistochemistry • retina