Low‐Density Lipoprotein Receptor on Endothelium of Brain Capillaries

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Abstract
The presence of lipoproteins, apolipoproteins, and their receptors in the brain could provide a system for cholesterol homeostasis, as they do in other tissues. This study was undertaken to determine whether plasma low‐density lipoprotein, the major carrier of cholesterol, is involved in the delivery of lipids through the blood‐brain barrier. 125I‐Labeled low‐density lipoprotein bound to a specific receptor on the endothelium of brain capillaries when it was injected immediately postmortem into bovine brain circulation. In contrast, no specific binding of 125I‐low density lipoprotein was found when the incubations were performed with isolated capillaries. Incubations of endothelial or basement membranes of brain capillaries with 125I‐low density lipoprotein demonstrated a high‐affinity association of low‐density lipoprotein with the membranes of bovine cerebral endothelial cells. The specificity of the low‐density lipoprotein binding was determined in several ways using a dot blot assay. This receptor shows the same characteristics as the low‐density lipoprotein receptor on human fibroblasts. The molecular weight of the bovine brain capillary low‐density lipoprotein receptor (132,000) was determined by ligand blotting. These results demonstrated the occurrence of a low‐density lipoprotein receptor on the endothelial cells of brain capillaries.

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