title: Cellular specificity of the blood-CSF barrier for albumin transfer across the choroid plexus epithelium.
abstract: To maintain the precise internal milieu of the mammalian central nervous system, well-controlled transfer of molecules from periphery into brain is required. Recently the soluble and cell-surface albumin-binding glycoprotein SPARC (secreted protein acidic and rich in cysteine) has been implicated in albumin transport into developing brain, however the exact mechanism remains unknown. We postulate that SPARC is a docking site for albumin, mediating its uptake and transfer by choroid plexus epithelial cells from blood into cerebrospinal fluid (CSF). We used in vivo physiological measurements of transfer of endogenous (mouse) and exogenous (human) albumins, in situ Proximity Ligation Assay (in situ PLA), and qRT-PCR experiments to examine the cellular mechanism mediating protein transfer across the blood-CSF interface. We report that at all developmental stages mouse albumin and SPARC gave positive signals with in situ PLAs in plasma, CSF and within individual plexus cells suggesting a possible molecular interaction. In contrast, in situ PLA experiments in brain sections from mice injected with human albumin showed positive signals for human albumin in the vascular compartment that were only rarely identifiable within choroid plexus cells and only at older ages. Concentrations of both endogenous mouse albumin and exogenous (intraperitoneally injected) human albumin were estimated in plasma and CSF and expressed as CSF/plasma concentration ratios. Human albumin was not transferred through the mouse blood-CSF barrier to the same extent as endogenous mouse albumin, confirming results from in situ PLA. During postnatal development Sparc gene expression was higher in early postnatal ages than in the adult and changed in response to altered levels of albumin in blood plasma in a differential and developmentally regulated manner. Here we propose a possible cellular route and mechanism by which albumin is transferred from blood into CSF across a sub-population of specialised choroid plexus epithelial cells.
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia; Department of Neurobiology, Stanford University, Stanford, California, United States of America.
authors.forename: Shane A
authors.initials: SA
authors.lastname: Liddelow
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
authors.forename: Katarzyna M
authors.initials: KM
authors.lastname: Dzięgielewska
authors.affiliation: Institute of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Kjeld
authors.initials: K
authors.lastname: Møllgård
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
authors.forename: Sophie C
authors.initials: SC
authors.lastname: Whish
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
authors.forename: Natassya M
authors.initials: NM
authors.lastname: Noor
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Wheaton
authors.affiliation: Institute of Tendon and Bone Regeneration, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Renate
authors.initials: R
authors.lastname: Gehwolf
authors.affiliation: Department of Organismic Biology, University of Salzburg, Salzburg, Austria; Institute of Tendon and Bone Regeneration, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Andrea
authors.initials: A
authors.lastname: Wagner
authors.affiliation: Institute of Tendon and Bone Regeneration, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Andreas
authors.initials: A
authors.lastname: Traweger
authors.affiliation: Department of Organismic Biology, University of Salzburg, Salzburg, Austria.
authors.forename: Hannelore
authors.initials: H
authors.lastname: Bauer
authors.affiliation: Institute of Tendon and Bone Regeneration, Paracelsus Medical University, Salzburg, Austria.
authors.forename: Hans-Christian
authors.initials: HC
authors.lastname: Bauer
authors.affiliation: Department of Pharmacology & Therapeutics, University of Melbourne, Melbourne, Australia.
authors.forename: Norman R
authors.initials: NR
authors.lastname: Saunders
mesh_terms: D000818:Animals; D001812:Blood-Brain Barrier / Q000378:metabolism*; D002831:Choroid Plexus / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D004848:Epithelium / Q000098:blood supply / Q000378:metabolism; D006801:Humans; D051379:Mice; D015676:Osteonectin / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics; D012709:Serum Albumin / Q000134:cerebrospinal fluid / Q000378:metabolism*
chemical_list: D015676:Osteonectin; C577241:SPARC protein, human; D012709:Serum Albumin