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.

Guiding protein delivery into live cells using DNA-programmed membrane fusion

“… 10 Previous work has indicated that treating cells with endocytosis inhibitors could effectively inhibit various endocytotic pathways, for example, endocytic chlorpromazine (CPZ, interfering with clathrin-dependent endocytosis) 33 , 34 and methyl-β-cyclodextrin (MβCD, disrupting caveola-dependent endocytosis). 35 , 36 We also found that CPZ or methyl-β-cyclodextrin could reduce the cellular uptake of liposomes by L1210 and HeLa cells (Fig. S14 † ).…”

Biodistribution, biocompatibility and targeted accumulation of magnetic nanoporous silica nanoparticles as drug carrier in orthopedics

“…Although MNPSNPs are negatively charged [96,97] and hydrophilic [98] due to PEG-coating, pinocytosis (< 500 nm size [99]) could occur, albeit more slowly. In addition, caveolae-mediated endocytosis which exists in muscles, among others [100], could have functioned as transcytosis pathway [101,102]. However, in the clinical scenario of implant infection, increased endothelial permeability is present [103,104] and therewith overcoming the first barrier, the transfer from blood vessel into the infected tissue surrounding the implant, should probably occur.…”

Albumin protects the liver from tumor necrosis factor α‐induced immunopathology

“…Indeed, intracellular albumin uptake has been demonstrated in hepatocytes and leukocytes as well as in endothelial and epithelial cell lines using fluorescently labeled albumin and confocal microscopy or flow cytometry approaches. 10,22,36,37 Importantly, in these cells, the intracellular albumin signal was shown to colocalize with markers of the endosome-lysosomal compartment. 10,37 In this subcellular compartment, albumin is not a mere bystander but rather is an effector molecule able to block endosomal TLR signaling and the production of cytokines by leukocytes in response to bacterial DNA.…”