Neuronal localization of a novel mosaic apolipoprotein E receptor, LR11, in rat and human brain

A new type of mosaic protein was recently discovered as a new member of the low density lipoprotein receptor (LDLR) family, designated as LR11. The predominant expression of LR11 transcripts in brain tissue and the presence of elements found in neural adhesion molecules suggested a function(s) in the central nervous system (CNS). In order to gain insight about this complex receptor in the CNS, we raised a rabbit polyclonal antibody and examined immunohistochemically rat and human brain tissue. A strong LR11 immunoreactivity was found to be localized mainly in neurons throughout the brain in both species. A detailed mapping in the rat brain showed a distribution of LR11 immunoreactivity in a widespread population of neurons, though the intensity varied between different locations. The most prominent immunoreactivity was observed in neurons of the hippocampus, some nuclei of brain stem and Purkinje cells, whereas neurons of the thalamus and the hypothalamus showed weak staining. Uniquely, the single LR11 immunoreactive cytoplasmic puncta were observed in the proximity of apical dendrites, most conspicuously in the pyramidal neurons of hippocampus. In the human brain, one to four immunoreactive puncta were seen within individual neurons. The neuronal localization of LR11 and its unique association of cytoplasmic structure, presumably botrysome, may suggest the roles of LR11 in both the lipoprotein metabolism and intracellular trafficking in certain neuronal population of the CNS.