title: Disruption of glomerular basement membrane charge through podocyte-specific mutation of agrin does not alter glomerular permselectivity.
abstract: Glomerular charge selectivity has been attributed to anionic heparan sulfate proteoglycans (HSPGs) in the glomerular basement membrane (GBM). Agrin is the predominant GBM-HSPG, but evidence that it contributes to the charge barrier is lacking, because newborn agrin-deficient mice die from neuromuscular defects. To study agrin in adult kidney, a new conditional allele was used to generate podocyte-specific knockouts. Mutants were viable and displayed no renal histopathology up to 9 months of age. Perlecan, a HSPG normally confined to the mesangium in mature glomeruli, did not appear in the mutant GBM, which lacked heparan sulfate. Moreover, GBM agrin was found to be derived primarily from podocytes. Polyethyleneimine labeling of fetal kidneys revealed anionic sites along both laminae rarae of the GBM that became most prominent along the subepithelial aspect at maturity; labeling was greatly reduced along the subepithelial aspect in agrin-deficient and conditional knockout mice. Despite this severe charge disruption, the glomerular filtration barrier was not compromised, even when challenged with bovine serum albumin overload. We conclude that agrin is not required for establishment or maintenance of GBM architecture. Although agrin contributes significantly to the anionic charge to the GBM, both it and its charge are not needed for glomerular permselectivity. This calls into question whether charge selectivity is a feature of the GBM.
authors.affiliation: Washington University School of Medicine, Renal Division, St Louis, MO 63110, USA.
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Harvey
authors.forename: George
authors.initials: G
authors.lastname: Jarad
authors.forename: Jeanette
authors.initials: J
authors.lastname: Cunningham
authors.forename: Angelique L
authors.initials: AL
authors.lastname: Rops
authors.forename: Johan
authors.initials: J
authors.lastname: van der Vlag
authors.forename: Jo H
authors.initials: JH
authors.lastname: Berden
authors.forename: Marcus J
authors.initials: MJ
authors.lastname: Moeller
authors.forename: Lawrence B
authors.initials: LB
authors.lastname: Holzman
authors.forename: Robert W
authors.initials: RW
authors.lastname: Burgess
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Miner
mesh_terms: D018171:Agrin / Q000235:genetics / Q000502:physiology*; D000818:Animals; D027321:Anion Transport Proteins / Q000378:metabolism; D002463:Cell Membrane Permeability; D004594:Electrophysiology; D050533:Glomerular Basement Membrane / Q000502:physiology*; D007668:Kidney / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D007678:Kidney Glomerulus / Q000033:anatomy & histology / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation; D050199:Podocytes / Q000378:metabolism*; D014463:Ultrasonography
chemical_list: D018171:Agrin; D027321:Anion Transport Proteins