Uptake of cholesterol by the retina occurs primarily via a lowdensity lipoprotein receptor-mediated process

[摘要] Purpose: In this study we examined the uptake of circulatinglipoproteins into the retina, using a naturally fluorescent cholesterolanalog for imaging and deuterated cholesterol for quantification by massspectroscopy. The purpose of this study was to better understandcholesterol uptake, transport and homeostasis in the retina.Methods: Human low density lipoprotein (LDL) and high densitylipoprotein (HDL) were labeled with the fluorescent cholesterol analogcholesta-5,7,9(11)-trien-3βol (CTL) and deuterated cholesterol(25,26,26,26,27,27,27-[2H]cholesterol, D7Ch). Rats were injectedintravenously with CTL-LDL, CTL-HDL and D7Ch-LDL. Fluorescent confocalmicroscopy was used to image the uptake of CTL and mass spectroscopy wasused to quantify D7Ch. Immunohistochemistry and fluorescent confocalmicroscopy were used to localize apoB (an LDL marker protein) and LDLreceptor (LDLR) protein in rat and monkey retinas.Results: CTL-specific fluorescence was imaged by confocal microscopyin the retinal pigment epithelium (RPE), choriocapillaris and parts ofthe neural retina within 2 h post-injection and was visualized in thephotoreceptor outer segments by 4 h. Replacing LDL with HDL as the CTLcarrier gave a less robust and more delayed labeling of retinal layers.Human apolipoprotein B (apoB) was also localized in the ratchoriocapillaris and RPE by 4 h post-injection. Human apoB was detectedby immunoblot analysis in the rat retina primarily as a about 70 kDaprotein, suggesting proteolytic degradation. LDL-mediated uptake ofcholesterol was quantified by mass spectroscopy using deuteratedcholesterol in place of CTL. In addition, apoB and LDLR were localizedin monkey retina by immunohistochemistry.Conclusions: The retina is capable of rapid uptake of circulatingLDL via an LDLR-mediated process primarily occurring in the RPE and alsopossibly Müller cells. Despite the dominance of HDL over LDL in ratserum, LDL appears to be the preferred carrier for cholesterol transportto and uptake by the retina. The results also suggest that blood-borneLDL represents a significant contributor to the steady-state levels ofcholesterol and possibly other lipids in the retina.

[学科分类] 生物化学/生物物理