Low-Density Lipoprotein Receptor on Endothelium of Brain Capillaries

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.