title: Intravital Imaging Reveals Angiotensin II-Induced Transcytosis of Albumin by Podocytes.
abstract: Albuminuria is a hallmark of kidney disease of various etiologies and usually caused by deterioration of glomerular filtration barrier integrity. We recently showed that angiotensin II (Ang II) acutely increases albumin filtration in the healthy kidney. Here, we used intravital microscopy to assess the effects of Ang II on podocyte function in rats. Acute infusion of 30, 60, or 80 ng/kg per minute Ang II enhanced the endocytosis of albumin by activation of the type 1 Ang II receptor and resulted in an average (±SEM) of 3.7±2.2, 72.3±18.6 (P<0.001), and 239.4±34.6 µm(3) (P<0.001) albumin-containing vesicles per glomerulus, respectively, compared with none at baseline or 10 ng/kg per minute Ang II. Immunostaining of Ang II-infused kidneys confirmed the presence of albumin-containing vesicles, which colocalized with megalin, in podocin-positive cells. Furthermore, podocyte endocytosis of albumin was markedly reduced in the presence of gentamicin, a competitive inhibitor of megalin-dependent endocytosis. Ang II infusion increased the concentration of albumin in the subpodocyte space, a potential source for endocytic protein uptake, and gentamicin further increased this concentration. Some endocytic vesicles were acidified and colocalized with LysoTracker. Most vesicles migrated from the capillary to the apical aspect of the podocyte and were eventually released into the urinary space. This transcytosis accounted for approximately 10% of total albumin filtration. In summary, the transcellular transport of proteins across the podocyte constitutes a new pathway of glomerular protein filtration. Ang II enhances the endocytosis and transcytosis of plasma albumin by podocytes, which may eventually impair podocyte function.
authors.affiliation: Institutes of Physiology and.
authors.forename: Ina Maria
authors.initials: IM
authors.lastname: Schießl
authors.affiliation: Institutes of Physiology and.
authors.forename: Anna
authors.initials: A
authors.lastname: Hammer
authors.affiliation: Institutes of Physiology and.
authors.forename: Veronika
authors.initials: V
authors.lastname: Kattler
authors.affiliation: Institutes of Physiology and.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Gess
authors.affiliation: Department of Medicine, University of Fribourg, Fribourg, Switzerland.
authors.forename: Franziska
authors.initials: F
authors.lastname: Theilig
authors.affiliation: Molecular and Cellular Anatomy, University of Regensburg, Regensburg, Germany; and.
authors.forename: Ralph
authors.initials: R
authors.lastname: Witzgall
authors.affiliation: Institutes of Physiology and hayo@castrop.com.
authors.forename: Hayo
authors.initials: H
authors.lastname: Castrop
mesh_terms: D000418:Albumins / Q000378:metabolism*; D000588:Amines; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D005260:Female; D005839:Gentamicins / Q000494:pharmacology; D000069416:Intravital Microscopy; D007678:Kidney Glomerulus / Q000187:drug effects / Q000502:physiology*; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000378:metabolism; D008854:Microscopy, Electron; D036641:Microscopy, Fluorescence, Multiphoton; D050199:Podocytes / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D057900:Transcytosis / Q000187:drug effects*; D022161:Transport Vesicles; D014556:Urine; D014662:Vasoconstrictor Agents / Q000494:pharmacology*
chemical_list: D000418:Albumins; D000588:Amines; D005839:Gentamicins; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D011500:Protein Synthesis Inhibitors; D044140:Receptor, Angiotensin, Type 1; C493330:Red DND-99; D014662:Vasoconstrictor Agents; D000804:Angiotensin II
keywords: angiotensin; podocyte; proteinuria