title: Permeation of macromolecules into the renal glomerular basement membrane and capture by the tubules.
abstract: How the kidney prevents urinary excretion of plasma proteins continues to be debated. Here, using unfixed whole-mount mouse kidneys, we show that fluorescent-tagged proteins and neutral dextrans permeate into the glomerular basement membrane (GBM), in general agreement with Ogston's 1958 equation describing how permeation into gels is related to molecular size. Electron-microscopic analyses of kidneys fixed seconds to hours after injecting gold-tagged albumin, negatively charged gold nanoparticles, and stable oligoclusters of gold nanoparticles show that permeation into the lamina densa of the GBM is size-sensitive. Nanoparticles comparable in size with IgG dimers do not permeate into it. IgG monomer-sized particles permeate to some extent. Albumin-sized particles permeate extensively into the lamina densa. Particles traversing the lamina densa tend to accumulate upstream of the podocyte glycocalyx that spans the slit, but none are observed upstream of the slit diaphragm. At low concentrations, ovalbumin-sized nanoparticles reach the primary filtrate, are captured by proximal tubule cells, and are endocytosed. At higher concentrations, tubular capture is saturated, and they reach the urine. In mouse models of Pierson's or Alport's proteinuric syndromes resulting from defects in GBM structural proteins (laminin β2 or collagen α3 IV), the GBM is irregularly swollen, the lamina densa is absent, and permeation is increased. Our observations indicate that size-dependent permeation into the lamina densa of the GBM and the podocyte glycocalyx, together with saturable tubular capture, determines which macromolecules reach the urine without the need to invoke direct size selection by the slit diaphragm.
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525; lawrence_unc@outlook.com.
authors.forename: Marlon G
authors.initials: MG
authors.lastname: Lawrence
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Altenburg
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Ryan
authors.initials: R
authors.lastname: Sanford
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Julian D
authors.initials: JD
authors.lastname: Willett
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Bleasdale
authors.affiliation: The Molecular Biosenser and Imaging Center, Carnegie Mellon University, Pittsburgh, PA 15213.
authors.forename: Byron
authors.initials: B
authors.lastname: Ballou
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wilder
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Feng
authors.initials: F
authors.lastname: Li
authors.affiliation: Division of Nephrology, Washington University School of Medicine, St. Louis, MO 63110-1093.
authors.forename: Jeffrey H
authors.initials: JH
authors.lastname: Miner
authors.affiliation: Division of Pediatrics, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Karolinska University Hospital Huddinge, 14186 Stockholm, Sweden.
authors.forename: Ulla B
authors.initials: UB
authors.lastname: Berg
authors.affiliation: Department of Pathology and Laboratory Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7525.
authors.forename: Oliver
authors.initials: O
authors.lastname: Smithies
mesh_terms: D000818:Animals; D005260:Female; D050533:Glomerular Basement Membrane / Q000378:metabolism* / Q000648:ultrastructure; D006046:Gold; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007684:Kidney Tubules / Q000378:metabolism* / Q000648:ultrastructure; D007687:Kidney Tubules, Proximal / Q000378:metabolism; D046911:Macromolecular Substances / Q000378:metabolism*; D008297:Male; D053768:Metal Nanoparticles; D051379:Mice; D018613:Microscopy, Confocal; D010539:Permeability; D050199:Podocytes / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D006046:Gold
keywords: Alport's syndrome; Pierson's syndrome; gel permeation; gold nanoparticles; slit diaphragm