Human podocytes perform polarized, caveolae-dependent albumin endocytosis

Dobrinskikh, Evgenia; Okamura, Koji; Kopp, Jeffrey B.; Doctor, R. Brian; Blaine, Judith

doi:10.1152/ajprenal.00532.2013

Cited by 70 publications

(95 citation statements)

References 47 publications

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“…6 We hypothesized that an increased flow of albumin across the filtration barrier may force the podocytes to clear the basement membrane and/or the subpodocyte space (SP) of accumulating albumin. In line with our hypothesis, cultured immortalized human podocytes were shown to perform caveolae-dependent endocytosis of albumin, 7 and albumin-containing vesicles could be observed by electron microscopy in mouse, rat, and human tissue. 8 Using intravital multiphoton microscopy (MPM) and electron microscopy, we found that Ang II infusion promotes the endocytosis of albumin by podocytes.…”

supporting

confidence: 84%

“…7 Our immunostainings confirmed the expression of caveolin-1 in the podocytes ( Figure 4A) of the Munich Wistar Froemter (MWF) rat and revealed that glomerular albumin colocalized with caveolin-1 ( Figure 4B). Because megalin colocalizes with caveolae in various cell types 10 and because the proximal tubular uptake of filtered albumin is mediated by the megalin/cubilin complex, [11][12][13] we hypothesized that megalin may be involved in the uptake of albumin by podocytes.…”

Section: Podocyte Albumin Endocytosis Is Megalin Dependentsupporting

confidence: 63%

“…Thus, cultured human podocytes performed caveolae-dependent albumin endocytosis and alternatively, lysosomal degradation or transcytosis. 7 In summary, Ang II increases the leakiness of the glomerular filtration barrier for albumin and initiates the endocytosis of albumin by podocytes in an AT1-and megalin-dependent manner. The increased movement of albumin across the filtration barrier is partly mediated by the transport of albumin along the transcellular pathway and likely facilitated by high albumin concentrations in the SP.…”

Section: Discussionmentioning

confidence: 97%

See 2 more Smart Citations

Intravital Imaging Reveals Angiotensin II–Induced Transcytosis of Albumin by Podocytes

Schießl¹,

Hammer²,

Kattler³

et al. 2016

Journal of the American Society of Nephrology

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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 (6SEM) of 3.762.2, 72.3618.6 (P,0.001), and 239.4634.6 mm 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.

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supporting

confidence: 84%

Section: Podocyte Albumin Endocytosis Is Megalin Dependentsupporting

confidence: 63%

Section: Discussionmentioning

confidence: 97%

See 1 more Smart Citation

Intravital Imaging Reveals Angiotensin II–Induced Transcytosis of Albumin by Podocytes

Schießl¹,

Hammer²,

Kattler³

et al. 2016

Journal of the American Society of Nephrology

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“…12 The growing number of studies showed that the SD is involved in the occurrence and transmission of signal transduction which maintained podocyte normal biological function, such as proliferation, differentiation, survival, endocytosis and cytoskeletal composition. [13][14][15] Therefore, SD which acts as a static molecular sieve and the highly dynamic complex, had a key effect on maintaining the normal structure of podocyte and functional integrity of the glomerular filtration barrier. 16 A recent report showed that glomerular mRNA level of CD2AP was significantly decreased in children with minimal change nephritic syndrome and primary IgA nephropathy.…”

Section: Discussionmentioning

confidence: 99%

Role of CD2-associated protein in podocyte apoptosis and proteinuria induced by angiotensin II

Huang

You

2014

Renal Failure

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Podocytes are highly differentiated epithelial cells that form interdigitating foot processes with bridging slit diaphragms (SDs) that regulate renal ultrafiltration. Proteinuria is the most common clinical manifestation of glomerular diseases. Losartan is the traditional reninangiotensin system (RAS). However; the precise mechanisms underlying the beneficial effects of Losartan on podocytes are still unknown. This study tested the hypothesis that podocytes were exposed to Angiotensin II (Ang II) to induce apoptosis and Proteinuria. Losartan directly reduces the rate of apoptotic podocytes induced by Ang II. Our results showed that apoptotic podocytes may be related to the decrease of CD2AP mRNA and protein expressions, Losartan reduced the apoptosis and Proteinuria by stabilizing the CD2AP mRNA and protein expressions. In this study, we explored the role of CD2-associated protein in podocyte apoptosis and Proteinuria induced by Ang II. Our findings provide some possible clues for further exploring the pharmacological targets to the proteinuria.

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“…Therefore, in this work, we sought to determine the functional significance of RalA recruitment and association with FilA and Cav-1 in human lung microvascular endothelial cells (HLMVECs). We observed RalA activation and recruitment to EC caveolae upon stimulation of albumin, perhaps the best studied macromolecular cargo of endothelial caveolae (24), and demonstrated that FilA is not required for RalA activation by albumin, but rather that it is essential for RalA association with caveolae. Furthermore, a significant decrease in caveolae-mediated internalization of albumin was detected in cells treated with RalA siRNA, suggesting that RalA activation is critical for efficient caveolae-mediated transport.…”

mentioning

confidence: 80%

Phosphatidic Acid Produced by RalA-activated PLD2 Stimulates Caveolae-mediated Endocytosis and Trafficking in Endothelial Cells

Jiang

Sverdlov²,

Tóth³

et al. 2016

Journal of Biological Chemistry

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Caveolae are the primary route for internalization and transendothelial transport of macromolecules, such as insulin and albumin. Caveolae-mediated endocytosis is activated by Src-dependent caveolin-1 (Cav-1) phosphorylation and subsequent recruitment of dynamin-2 and filamin A (FilA), which facilitate vesicle fission and trafficking, respectively. Here, we tested the role of RalA and phospholipase D (PLD) signaling in the regulation of caveolae-mediated endocytosis and trafficking. The addition of albumin to human lung microvascular endothelial cells induced the activation of RalA within minutes, and siRNAmediated down-regulation of RalA abolished fluorescent BSA uptake. Co-immunoprecipitation studies revealed that albumin induced the association between RalA, Cav-1, and FilA; however, RalA knockdown with siRNA did not affect FilA recruitment to Cav-1, suggesting that RalA was not required for FilA and Cav-1 complex formation. Rather, RalA probably facilitates caveolae-mediated endocytosis by activating downstream effectors. PLD2 was shown to be activated by RalA, and inhibition of PLD2 abolished Alexa-488-BSA uptake, indicating that phosphatidic acid (PA) generated by PLD2 may facilitate caveolaemediated endocytosis. Furthermore, using a PA biosensor, GFP-PASS, we observed that BSA induced an increase in PA co-localization with Cav-1-RFP, which could be blocked by a dominant negative PLD2 mutant. Total internal reflection fluorescence microscopy studies of Cav-1-RFP also showed that fusion of caveolae with the basal plasma membrane was dependent on PLD2 activity. Thus, our results suggest that the small GTPase RalA plays an important role in promoting invagination and trafficking of caveolae, not by potentiating the association between Cav-1 and FilA but by stimulating PLD2-mediated generation of phosphatidic acid.Caveolae-mediated transcellular transport of macromolecules through endothelial cells (ECs) 2 lining blood vessels is a highly selective and regulated process (1). Although the signaling mechanisms regulating the invagination and internalization (endocytosis) of caveolae have not been fully characterized, it was shown that Src-dependent phosphorylation of the large GTPase dynamin-2 (2, 3) and its recruitment to the neck of caveolae (4), phosphorylation of caveolin-1 Tyr-14 (5) and subsequent recruitment of actin cross-linking protein filamin A (FilA) to caveolae (6), and dynamic actin remodeling (7) are some of the general requirements (8).In addition to the large GTPase dynamin-2, which is required for fission of caveolae from the plasma membrane, several small GTPases detected in caveolin-enriched membrane fractions have been proposed to participate in caveolae-mediated transport. For example, Cdc42, a small GTPase of the Rho family, was detected in caveolae (9), where it is thought to control caveolae-mediated endocytosis by regulating actin polymerization and interactions between the actin cytoskeleton and intersectin, a scaffolding protein required for efficient fission and internalization of ...

show abstract

Human podocytes perform polarized, caveolae-dependent albumin endocytosis

Cited by 70 publications

References 47 publications

Intravital Imaging Reveals Angiotensin II–Induced Transcytosis of Albumin by Podocytes

Intravital Imaging Reveals Angiotensin II–Induced Transcytosis of Albumin by Podocytes

Role of CD2-associated protein in podocyte apoptosis and proteinuria induced by angiotensin II

Phosphatidic Acid Produced by RalA-activated PLD2 Stimulates Caveolae-mediated Endocytosis and Trafficking in Endothelial Cells

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