Intracellular Transcytosis of Albumin in Glomerular Endothelial Cells After Endocytosis Through Caveolae

Abstract

Background/Aims

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.

Methods and Results

HRGECs were incubated with Alexa Fluor 488-labeled bovine serum albumin from 0 to 360 minutes. 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 expression on glomerular capillaries, in puromycin aminonucleoside induced nephrotic mice.

Conclusion

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. This article is protected by copyright. All rights reserved

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