title: Glycoprotein 330/megalin: probable role in receptor-mediated transport of apolipoprotein J alone and in a complex with Alzheimer disease amyloid beta at the blood-brain and blood-cerebrospinal fluid barriers.
abstract: A soluble form of Alzheimer disease amyloid beta-protein (sA beta) is transported in the blood and cerebrospinal fluid mainly complexed with apolipoprotein J (apoJ). Using a well-characterized in situ perfused guinea pig brain model, we recently obtained preliminary evidence that apoJ facilitates transport of sA beta (1-40)-apoJ complexes across the blood-brain barrier and the blood-cerebrospinal fluid barrier, but the mechanisms remain poorly understood. In the present study, we examined the transport process in greater detail and investigated the possible role of glycoprotein 330 (gp330)/megalin, a receptor for multiple ligands, including apoJ. High-affinity transport systems with a Km of 0.2 and 0.5 nM were demonstrated for apoJ at the blood-brain barrier and the choroid epithelium in vivo, suggesting a specific receptor-mediated mechanism. The sA beta (1-40)-apoJ complex shared the same transport mechanism and exhibited 2.4- to 10.2-fold higher affinity than apoJ itself. Binding to microvessels, transport into brain parenchyma, and choroidal uptake of both apoJ and sA beta (1-40)-apoJ complexes were markedly inhibited (74-99%) in the presence of a monoclonal antibody to gp330/megalin and were virtually abolished by perfusion with the receptor-associated protein, which blocks binding of all known ligands to gp330. Western blot analysis of cerebral microvessels with the monoclonal antibody to gp330 revealed a protein with a mass identical to that in extracts of kidney membranes enriched with gp330/megalin, but in much lower concentration. The findings suggest that gp330/megalin mediates cellular uptake and transport of apoJ and sA beta (1-40)-apoJ complex at the cerebral vascular endothelium and choroid epithelium.
authors.affiliation: Department of Neurological Surgery, Childrens Hospital, Los Angeles, CA, USA.
authors.forename: B V
authors.initials: BV
authors.lastname: Zlokovic
authors.forename: C L
authors.initials: CL
authors.lastname: Martel
authors.forename: E
authors.initials: E
authors.lastname: Matsubara
authors.forename: J G
authors.initials: JG
authors.lastname: McComb
authors.forename: G
authors.initials: G
authors.lastname: Zheng
authors.forename: R T
authors.initials: RT
authors.lastname: McCluskey
authors.forename: B
authors.initials: B
authors.lastname: Frangione
authors.forename: J
authors.initials: J
authors.lastname: Ghiso
mesh_terms: D000595:Amino Acid Sequence; D016229:Amyloid beta-Peptides / Q000134:cerebrospinal fluid / Q000378:metabolism*; D000818:Animals; D000906:Antibodies; D001812:Blood-Brain Barrier; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D002199:Capillary Permeability; D002560:Cerebrovascular Circulation; D002831:Choroid Plexus / Q000378:metabolism; D051152:Clusterin; D004730:Endothelium, Vascular / Q000378:metabolism*; D005260:Female; D006023:Glycoproteins / Q000134:cerebrospinal fluid / Q000378:metabolism*; D006168:Guinea Pigs; D026541:Heymann Nephritis Antigenic Complex; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008562:Membrane Glycoproteins / Q000134:cerebrospinal fluid / Q000378:metabolism*; D008833:Microcirculation / Q000378:metabolism*; D018832:Molecular Chaperones; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000378:metabolism; D011973:Receptors, LDL / Q000378:metabolism*
chemical_list: D016229:Amyloid beta-Peptides; D000906:Antibodies; D051152:Clusterin; D006023:Glycoproteins; D026541:Heymann Nephritis Antigenic Complex; D007457:Iodine Radioisotopes; D008562:Membrane Glycoproteins; D018832:Molecular Chaperones; D010446:Peptide Fragments; D011973:Receptors, LDL