title: Glomerular endothelial surface layer acts as a barrier against albumin filtration.
abstract: Glomerular endothelium is highly fenestrated, and its contribution to glomerular barrier function is the subject of debate. In recent years, a polysaccharide-rich endothelial surface layer (ESL) has been postulated to act as a filtration barrier for large molecules, such as albumin. To test this hypothesis, we disturbed the ESL in C57Bl/6 mice using long-term hyaluronidase infusion for 4 weeks and monitored albumin passage using immunolabeling and correlative light-electron microscopy that allows for complete and integral assessment of glomerular albumin passage. ESL ultrastructure was visualized by transmission electron microscopy using cupromeronic blue and by localization of ESL binding lectins using confocal microscopy. We demonstrate that glomerular fenestrae are filled with dense negatively charged polysaccharide structures that are largely removed in the presence of circulating hyaluronidase, leaving the polysaccharide surfaces of other glomerular cells intact. Both retention of native ferritin [corrected] in the glomerular basement membrane and systemic blood pressure were unaltered. Enzyme treatment, however, induced albumin passage across the endothelium in 90% of glomeruli, whereas this could not be observed in controls. Yet, there was no net albuminuria due to binding and uptake of filtered albumin by the podocytes and parietal epithelium. ESL structure and function completely recovered within 4 weeks on cessation of hyaluronidase infusion. Thus, the polyanionic ESL component, hyaluronan, is a key component of the glomerular endothelial protein permeability barrier.
authors.affiliation: Einthoven Laboratory for Vascular Medicine, Department of Nephrology, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Martijn J C
authors.initials: MJ
authors.lastname: Dane
authors.forename: Bernard M
authors.initials: BM
authors.lastname: van den Berg
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Avramut
authors.forename: Frank G A
authors.initials: FG
authors.lastname: Faas
authors.forename: Johan
authors.initials: J
authors.lastname: van der Vlag
authors.forename: Angelique L W M M
authors.initials: AL
authors.lastname: Rops
authors.forename: Raimond B G
authors.initials: RB
authors.lastname: Ravelli
authors.forename: Bram J
authors.initials: BJ
authors.lastname: Koster
authors.forename: Anton Jan
authors.initials: AJ
authors.lastname: van Zonneveld
authors.forename: Hans
authors.initials: H
authors.lastname: Vink
authors.forename: Ton J
authors.initials: TJ
authors.lastname: Rabelink
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D004727:Endothelium / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005453:Fluorescence; D050533:Glomerular Basement Membrane / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D005919:Glomerular Filtration Rate / Q000187:drug effects / Q000502:physiology*; D006736:Horses; D006821:Hyaluronoglucosaminidase / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000166:cytology / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D037102:Lectins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010539:Permeability / Q000187:drug effects; D050199:Podocytes / Q000166:cytology / Q000187:drug effects / Q000648:ultrastructure
chemical_list: D000418:Albumins; D037102:Lectins; D006821:Hyaluronoglucosaminidase