title: Intracellular transcytosis of albumin in glomerular endothelial cells after endocytosis through caveolae.
abstract: We previously described albumin endocytosis through caveolae in human renal glomerular endothelial cells (HRGECs). This suggested a new albumin transcytosis pathway, in addition to the fenestral pathway. As a next step, we investigated albumin transcytosis in HRGECs after caveolar endocytosis. HRGECs were incubated with Alexa Fluor 488-labeled bovine serum albumin from 0 to 360 min. Next, markers for endosomes, endoplasmic reticulum (ER), golgi apparatus (GA), lysosomes, and proteasomes and Fc receptors, microtubules, and actin were monitored by immunofluorescence. Labeled albumin co-localization with endosomes was gradually and significantly increased and it was significantly higher than with the other markers at any timepoint. Albumin, placed on inside of the Transwell membrane, diffused through HRGEC monolayers during a 360 min incubation period. This transportation of albumin through HRGECs was inhibited by methyl beta cyclodextrin (MBCD), a caveolae disrupting agent. MBCD also decreased albuminuria, causing decreased caveolin-1 (Cav-1) expression on glomerular capillaries, in puromycin aminonucleoside induced nephrotic mice. Albumin transcytosis depends on early endosomes, but not on other organelles, Fc receptors, or cytoskeletal components. Caveolae disruption prevented albumin transportation through HRGECs and decreased albuminuria in nephrotic mice. This newly described caveolae-dependent albumin pathway through glomerular endothelial cells is a potential pathogenetic mechanism for albuminuria, independent of the fenestrae.
authors.affiliation: Department of Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Takahito
authors.initials: T
authors.lastname: Moriyama
authors.affiliation: Department of Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Kayo
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: Department of Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Karasawa
authors.affiliation: Department of Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Uchida
authors.affiliation: Department of Medicine, Kidney Center, Tokyo Women's Medical University, Tokyo, Japan.
authors.forename: Kosaku
authors.initials: K
authors.lastname: Nitta
mesh_terms: D000419:Albuminuria / Q000139:chemically induced / Q000378:metabolism* / Q000517:prevention & control; D000818:Animals; D021941:Caveolae / Q000187:drug effects / Q000378:metabolism*; D051242:Caveolin 1 / Q000378:metabolism; D002478:Cells, Cultured; D004195:Disease Models, Animal; D004705:Endocytosis / Q000187:drug effects; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007678:Kidney Glomerulus / Q000098:blood supply*; D008297:Male; D008810:Mice, Inbred C57BL; D009401:Nephrosis / Q000139:chemically induced / Q000378:metabolism; D011692:Puromycin Aminonucleoside; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D013997:Time Factors; D057900:Transcytosis / Q000187:drug effects; D047392:beta-Cyclodextrins / Q000494:pharmacology
chemical_list: C495541:Cav1 protein, mouse; D051242:Caveolin 1; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D012710:Serum Albumin, Bovine; D011692:Puromycin Aminonucleoside
keywords: albumin; early endosomes; exocytosis; glomerular endothelial cells; transcytosis