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Afonso LG, Silva-Aguiar RP, Teixeira DE, Alves SAS, Schmaier AH, Pinheiro AAS, Peruchetti DB, Caruso-Neves C. The angiotensin II/type 1 angiotensin II receptor pathway is implicated in the dysfunction of albumin endocytosis in renal proximal tubule epithelial cells induced by high glucose levels. Biochim Biophys Acta Gen Subj 2024; 1868:130684. [PMID: 39084330 DOI: 10.1016/j.bbagen.2024.130684] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Revised: 07/09/2024] [Accepted: 07/25/2024] [Indexed: 08/02/2024]
Abstract
It is well-established that dysfunction of megalin-mediated albumin endocytosis by proximal tubule epithelial cells (PTECs) and the activation of the Renin-Angiotensin System (RAS) play significant roles in the development of Diabetic Kidney Disease (DKD). However, the precise correlation between these factors still requires further investigation. In this study, we aimed to elucidate the potential role of angiotensin II (Ang II), a known effector of RAS, as the mediator of albumin endocytosis dysfunction induced by high glucose (HG) in PTECs. To achieve this, we utilized LLC-PK1 and HK-2 cells, which are well-established in vitro models of PTECs. Using albumin-FITC or DQ-albumin as tracers, we observed that incubation of LLC-PK1 and HK-2 cells with HG (25 mM for 48 h) significantly reduced canonical receptor-mediated albumin endocytosis, primarily due to the decrease in megalin expression. HG increased the concentration of Ang II in the LLC-PK1 cell supernatant, a phenomenon associated with an increase in angiotensin-converting enzyme (ACE) expression and a decrease in prolyl carboxypeptidase (PRCP) expression. ACE type 2 (ACE2) expression remained unchanged. To investigate the potential impact of Ang II on HG effects, the cells were co-incubated with angiotensin receptor inhibitors. Only co-incubation with 10-7 M losartan (an antagonist for type 1 angiotensin receptor, AT1R) attenuated the inhibitory effect of HG on albumin endocytosis, as well as megalin expression. Our findings contribute to understanding the genesis of tubular albuminuria observed in the early stages of DKD, which involves the activation of the Ang II/AT1R axis by HG.
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Affiliation(s)
- Liz G Afonso
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Rodrigo P Silva-Aguiar
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Douglas E Teixeira
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sarah A S Alves
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Alvin H Schmaier
- Department of Medicine, Division of Hematology and Cell Therapy, Case Western Reserve University and University Hospitals Cleveland Medical Center, Cleaveland, USA
| | - Ana Acacia S Pinheiro
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Rio de Janeiro Innovation Network in Nanosystems for Health - NanoSAUDE/FAPERJ, Rio de Janeiro, Brazil
| | - Diogo B Peruchetti
- Departamento de Fisiologia e Biofísica, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil; Instituto Nacional de Ciência e Tecnologia em Nanofarmacêutica, INCT-NANOBiofar, CNPq/MCTI, Belo Horizonte, Brazil
| | - Celso Caruso-Neves
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil; Rio de Janeiro Innovation Network in Nanosystems for Health - NanoSAUDE/FAPERJ, Rio de Janeiro, Brazil; Instituto Nacional de Ciência e Tecnologia em Medicina Regenerativa, INCT-Regenera, CNPq/MCTI, Rio de Janeiro, Brazil.
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2
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Faivre A, Bugarski M, Rinaldi A, Sakhi IB, Verissimo T, Legouis D, Rutkowski JM, Correia S, Kaminska M, Dalga D, Malpetti D, Cippa PE, de Seigneux S, Hall AM. Spatiotemporal Landscape of Kidney Tubular Responses to Glomerular Proteinuria. J Am Soc Nephrol 2024; 35:854-869. [PMID: 38652545 PMCID: PMC11230716 DOI: 10.1681/asn.0000000000000357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Accepted: 04/12/2024] [Indexed: 04/25/2024] Open
Abstract
Key Points
Glomerular proteinuria induces large-scale changes in gene expression along the nephron.Increased protein uptake in the proximal tubule results in axial remodeling and injury.Increased protein delivery to the distal tubule causes dedifferentiation of the epithelium.
Background
Large increases in glomerular protein filtration induce major changes in body homeostasis and are associated with a higher risk of kidney functional decline and cardiovascular disease. We investigated how elevated protein exposure modifies the landscape of tubular function along the entire nephron, to understand the cellular changes that mediate these important clinical phenomena.
Methods
We conducted single-nucleus RNA sequencing, functional intravital imaging, and antibody staining to spatially map transport processes along the mouse kidney tubule. We then delineated how these were altered in a transgenic mouse model of inducible glomerular proteinuria (POD-ATTAC) at 7 and 28 days.
Results
Glomerular proteinuria activated large-scale and pleiotropic changes in gene expression in all major nephron sections. Extension of protein uptake from early (S1) to later (S2) parts of the proximal tubule initially triggered dramatic expansion of a hybrid S1/2 population, followed by injury and failed repair, with the cumulative effect of loss of canonical S2 functions. Proteinuria also induced acute injury in S3. Meanwhile, overflow of luminal proteins to the distal tubule caused transcriptional convergence between specialized regions and generalized dedifferentiation.
Conclusions
Proteinuria modulated cell signaling in tubular epithelia and caused distinct patterns of remodeling and injury in a segment-specific manner.
Podcast
This article contains a podcast at https://dts.podtrac.com/redirect.mp3/www.asn-online.org/media/podcast/JASN/2024_05_01_ASN0000000000000357.mp3
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Affiliation(s)
- Anna Faivre
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - Milica Bugarski
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Anna Rinaldi
- Laboratories for Translational Research, Ente Ospedaliero Cantonale, Bellinzona, Switzerland
- Division of Nephrology, Department of Medicine, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Imene B Sakhi
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Thomas Verissimo
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - David Legouis
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
- Division of Intensive Care, Department of Acute Medicine, University Hospital of Geneva, Geneva, Switzerland
| | | | - Sara Correia
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Monika Kaminska
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
| | - Delal Dalga
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
| | - Daniele Malpetti
- Istituto Dalle Molle di Studi sull'Intelligenza Artificiale (IDSIA), USI/SUPSI, Lugano, Switzerland
| | - Pietro E Cippa
- Laboratories for Translational Research, Ente Ospedaliero Cantonale, Bellinzona, Switzerland
- Division of Nephrology, Department of Medicine, Ente Ospedaliero Cantonale, Lugano, Switzerland
| | - Sophie de Seigneux
- Department of Medicine and Cell Physiology and Metabolism, University of Geneva, Geneva, Switzerland
- Department of Medicine, Service of Nephrology, Geneva University Hospitals, Geneva, Switzerland
| | - Andrew M Hall
- Institute of Anatomy, University of Zurich, Zurich, Switzerland
- Department of Nephrology, University Hospital Zurich, Zurich, Switzerland
- Zurich Kidney Center, Zurich, Switzerland
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3
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Edwards A. Renal handling of albumin in rats with early stage diabetes: A theoretical analysis. J Physiol 2024; 602:3575-3592. [PMID: 38857419 PMCID: PMC11250707 DOI: 10.1113/jp286245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2024] [Accepted: 05/20/2024] [Indexed: 06/12/2024] Open
Abstract
In early diabetic nephropathy (DN), recent studies have shown that albuminuria stems mostly from alterations in tubular function rather than from glomerular damage. Several factors in DN, including hyperfiltration, hypertrophy and reduced abundance of the albumin receptors megalin and cubilin, affect albumin endocytosis in the proximal tubule (PT). To assess their respective contribution, we developed a model of albumin handling in the rat PT that couples the transport of albumin to that of water and solutes. Our simulations suggest that, under basal conditions, ∼75% of albumin is retrieved in the S1 segment. The model predicts negligible uptake in S3, as observed experimentally. It also accurately predicts the impact of acute hyperglycaemia on urinary albumin excretion. Simulations reproduce observed increases in albumin excretion in early DN by considering the combined effects of increased glomerular filtration rate (GFR), osmotic diuresis, hypertrophy, and megalin and cubilin downregulation, without stipulating changes in glomerular permselectivity. The results indicate that in isolation, glucose-elicited osmotic diuresis and glucose transporter upregulation raise albumin excretion only slightly. Enlargement of PT diameter not only augments uptake via surface area expansion, but also reduces fluid velocity and thus shear stress-induced stimulation of endocytosis. Overall, our model predicts that downregulation of megalin and cubilin and hyperfiltration both contribute significantly to increasing albumin excretion in rats with early-stage diabetes. The results also suggest that acute sodium-glucose cotransporter 2 inhibition lowers albumin excretion only if GFR decreases sufficiently, and that angiotensin II receptor blockers mitigate urinary albumin loss in early DN in large part by upregulating albumin receptor abundance. KEY POINTS: The urinary excretion of albumin is increased in early diabetic nephropathy (DN). It is difficult to experimentally disentangle the multiple factors that affect the renal handling of albumin in DN. We developed a mathematical model of albumin transport in the rat proximal tubule (PT) to examine the impact of elevated plasma glucose, hyperfiltration, PT hypertrophy and reduced abundance of albumin receptors on albumin uptake and excretion in DN. Our model predicts that glucose-elicited osmotic diuresis per se raises albumin excretion only slightly. Conversely, increases in PT diameter and length favour reduced albumin excretion. Our results suggest that downregulation of the receptors megalin and cubilin in PT cells and hyperfiltration both contribute significantly to increasing albumin excretion in DN. The model helps to better understand the mechanisms underlying urinary loss of albumin in early-stage diabetes, and the impact of specific treatments thereupon.
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Affiliation(s)
- Aurélie Edwards
- Department of Biomedical Engineering, Boston University, Boston, MA, USA
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4
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Ralph DL, Ha D, Lei H, Priver TS, Smith SD, McFarlin BE, Schwindt S, Pandya D, Koepsell H, Pastor-Soler NM, Edwards A, McDonough AA. Potassium-Alkali-Enriched Diet, Hypertension, and Proteinuria following Uninephrectomy. J Am Soc Nephrol 2024:00001751-990000000-00357. [PMID: 38913441 DOI: 10.1681/asn.0000000000000420] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 06/10/2024] [Indexed: 06/26/2024] Open
Abstract
Key Points
A K-alkali–enriched diet blunted post-uninephrectomy hypertension and facilitated acid clearance by suppressing Na+ reabsorption.Uninephrectomy-associated proteinuria could be attributed to elevated single-nephron GFR and downregulation of megalin, which reduced fractional protein endocytosis.
Background
Losing or donating a kidney is associated with risks of developing hypertension and albuminuria. Few studies address mechanisms or interventions. We investigate the potential benefits of a K+- alkali–enriched diet and the mechanisms underlying proteinuria.
Methods
Male Sprague Dawley rats were fed either a 2% NaCl+0.95% KCl diet (HNa-LK) or a 0.74% NaCl+3% K+-alkali diet (HK-alk) for 3 weeks before uninephrectomy and then maintained on respective diets for 12 weeks. BP (by tail-cuff), urine, blood, and kidney proteins were analyzed before and after uninephrectomy.
Results
Before uninephrectomy, HK-alk–fed versus HNa-LK–fed rats exhibited similar BPs and plasma [K+], [Na+], but lower proximal (NHE3, sodium bicarbonate cotransporter 1, NaPi2) and higher distal (NCC, ENaC, and pendrin) transporter abundance, a pattern facilitating K+ and HCO3
− secretion. After uninephrectomy, single-nephron GFR increased 50% and Li+ clearance doubled with both diets; in HK-alk versus HNa-LK, the increase in BP was less and ammoniagenesis was lower, abundance of proximal tubule transporters remained lower, ENaC-α fell, and NCCp increased, consistent with K+ conservation. After uninephrectomy, independent of diet, albuminuria increased eight-fold and abundance of endocytic receptors was reduced (megalin by 44%, disabled homolog 2 by 25%–35%) and kidney injury molecule-1 was increased.
Conclusions
The K-alkali–enriched diet blunted post-uninephrectomy hypertension and facilitated acid clearance by suppressing proximal Na+ transporters and increasing K+-alkali secretion. Furthermore, uninephrectomy-associated proteinuria could be attributed, at least in part, to elevated single-nephron GFR coupled with downregulation of megalin, which reduced fractional protein endocytosis and Vmax.
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Affiliation(s)
- Donna L Ralph
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Darren Ha
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Hillmin Lei
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Taylor S Priver
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Scotti D Smith
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Brandon E McFarlin
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Seth Schwindt
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Drishti Pandya
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Hermann Koepsell
- Institute for Anatomy and Cell Biology, University of Würzburg, Würzburg, Germany
| | - Nuria M Pastor-Soler
- Division of Nephrology, Department of Medicine, Keck School of Medicine, University of Southern California, Los Angeles, California
| | - Aurelie Edwards
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts
| | - Alicia A McDonough
- Department of Physiology and Neuroscience, Keck School of Medicine, University of Southern California, Los Angeles, California
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Lackner EM, Cowan IA, Long KR, Weisz OA, Shipman KE. Fluid shear stress-induced changes in megalin trafficking enhance endocytic capacity in proximal tubule cells. Front Physiol 2024; 15:1404248. [PMID: 38948083 PMCID: PMC11211581 DOI: 10.3389/fphys.2024.1404248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Accepted: 05/29/2024] [Indexed: 07/02/2024] Open
Abstract
Proximal tubule (PT) cells maintain a high-capacity apical endocytic pathway to recover essentially all proteins that escape the glomerular filtration barrier. The multi ligand receptors megalin and cubilin play pivotal roles in the endocytic uptake of normally filtered proteins in PT cells but also contribute to the uptake of nephrotoxic drugs, including aminoglycosides. We previously demonstrated that opossum kidney (OK) cells cultured under continuous fluid shear stress (FSS) are superior to cells cultured under static conditions in recapitulating essential functional properties of PT cells in vivo. To identify drivers of the high-capacity, efficient endocytic pathway in the PT, we compared FSS-cultured OK cells with less endocytically active static-cultured OK cells. Megalin and cubilin expression are increased, and endocytic uptake of albumin in FSS-cultured cells is > 5-fold higher compared with cells cultured under static conditions. To understand how differences in receptor expression, distribution, and trafficking rates contribute to increased uptake, we used biochemical, morphological, and mathematical modeling approaches to compare megalin traffic in FSS- versus static-cultured OK cells. Our model predicts that culturing cells under FSS increases the rates of all steps in megalin trafficking. Importantly, the model explains why, despite seemingly counterintuitive observations (a reduced fraction of megalin at the cell surface, higher colocalization with lysosomes, and a shorter half-life of surface-tagged megalin in FSS-cultured cells), uptake of albumin is dramatically increased compared with static-grown cells. We also show that FSS-cultured OK cells more accurately exhibit the mechanisms that mediate uptake of nephrotoxic drugs in vivo compared with static-grown cells. This culture model thus provides a useful platform to understand drug uptake mechanisms, with implications for developing interventions in nephrotoxic injury prevention.
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Affiliation(s)
| | | | | | | | - Katherine E. Shipman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, United States
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6
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Satarug S. Is Chronic Kidney Disease Due to Cadmium Exposure Inevitable and Can It Be Reversed? Biomedicines 2024; 12:718. [PMID: 38672074 PMCID: PMC11048639 DOI: 10.3390/biomedicines12040718] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 03/09/2024] [Accepted: 03/21/2024] [Indexed: 04/28/2024] Open
Abstract
Cadmium (Cd) is a metal with no nutritional value or physiological role. However, it is found in the body of most people because it is a contaminant of nearly all food types and is readily absorbed. The body burden of Cd is determined principally by its intestinal absorption rate as there is no mechanism for its elimination. Most acquired Cd accumulates within the kidney tubular cells, where its levels increase through to the age of 50 years but decline thereafter due to its release into the urine as the injured tubular cells die. This is associated with progressive kidney disease, which is signified by a sustained decline in the estimated glomerular filtration rate (eGFR) and albuminuria. Generally, reductions in eGFR after Cd exposure are irreversible, and are likely to decline further towards kidney failure if exposure persists. There is no evidence that the elimination of current environmental exposure can reverse these effects and no theoretical reason to believe that such a reversal is possible. This review aims to provide an update on urinary and blood Cd levels that were found to be associated with GFR loss and albuminuria in the general populations. A special emphasis is placed on the mechanisms underlying albumin excretion in Cd-exposed persons, and for an accurate measure of the doses-response relationships between Cd exposure and eGFR, its excretion rate must be normalised to creatinine clearance. The difficult challenge of establishing realistic Cd exposure guidelines such that human health is protected, is discussed.
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Affiliation(s)
- Soisungwan Satarug
- Kidney Disease Research Collaborative, Translational Research Institute, Woolloongabba, Brisbane, QLD 4102, Australia
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7
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Lackner EM, Cowan IA, Long KR, Weisz OA, Shipman KE. Fluid Shear Stress-Induced Changes in Megalin Trafficking Enhance Endocytic Capacity in Proximal Tubule Cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.22.581213. [PMID: 38562767 PMCID: PMC10983855 DOI: 10.1101/2024.02.22.581213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Proximal tubule (PT) cells maintain a high-capacity apical endocytic pathway to recover essentially all proteins that escape the glomerular filtration barrier. The multiligand receptors megalin and cubilin play pivotal roles in the endocytic uptake of normally filtered proteins in PT cells but also contribute to the uptake of nephrotoxic drugs, including aminoglycosides. We previously demonstrated that opossum kidney (OK) cells cultured under continuous fluid shear stress (FSS) are superior to cells cultured under static conditions in recapitulating essential functional properties of PT cells in vivo. To identify drivers of the high-capacity, efficient endocytic pathway in the PT, we compared FSS-cultured OK cells with less endocytically active static-cultured OK cells. Megalin and cubilin expression are increased, and endocytic uptake of albumin in FSS-cultured cells is >5-fold higher compared with cells cultured under static conditions. To understand how differences in receptor expression, distribution, and trafficking rates contribute to increased uptake, we used biochemical, morphological, and mathematical modeling approaches to compare megalin traffic in FSS- versus static-cultured OK cells. Our model predicts that culturing cells under FSS increases the rates of all steps in megalin trafficking. Importantly, the model explains why, despite seemingly counterintuitive observations (a reduced fraction of megalin at the cell surface, higher colocalization with lysosomes, and a shorter half-life of surface-tagged megalin in FSS-cultured cells), uptake of albumin is dramatically increased compared with static-grown cells. We also show that FSS-cultured OK cells more accurately exhibit the mechanisms that mediate uptake of nephrotoxic drugs in vivo compared with static-grown cells. This culture model thus provides a useful platform to understand drug uptake mechanisms, with implications for developing interventions in nephrotoxic injury prevention.
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Affiliation(s)
- Emily M. Lackner
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Isabella A. Cowan
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Kimberly R. Long
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Ora A. Weisz
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
| | - Katherine E. Shipman
- Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA
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Long KR, Rbaibi Y, Kashlan OB, Weisz OA. Receptor-associated protein impairs ligand binding to megalin and megalin-dependent endocytic flux in proximal tubule cells. Am J Physiol Renal Physiol 2023; 325:F457-F464. [PMID: 37534387 DOI: 10.1152/ajprenal.00165.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2023] [Revised: 07/11/2023] [Accepted: 07/31/2023] [Indexed: 08/04/2023] Open
Abstract
Proximal tubule (PT) cells retrieve albumin and a broad array of other ligands from the glomerular ultrafiltrate. Efficient uptake of albumin requires PT expression of both megalin and cubilin receptors. Although most proteins engage cubilin selectively, megalin is required to maintain robust flux through the apical endocytic pathway. Receptor-associated protein (RAP) is a chaperone that directs megalin to the cell surface, and recombinant RAP dramatically inhibits the uptake of numerous megalin and cubilin ligands. The mechanism by which this occurs has been suggested to involve competitive inhibition of ligand binding and/or conformational changes in megalin that prevent interaction with ligands and/or with cubilin. To discriminate between these possibilities, we determined the effect of RAP on endocytosis of albumin, which binds to cubilin and megalin receptors with high and low affinity, respectively. Uptake was quantified in opossum kidney (OK) cells and in megalin or cubilin (Cubn) knockout (KO) clones. Surprisingly, RAP inhibited fluid-phase uptake in addition to receptor-mediated uptake in OK cells and Cubn KO cells but had no effect on endocytosis when megalin was absent. The apparent Ki for RAP inhibition of albumin uptake was 10-fold higher in Cubn KO cells compared with parental OK cells. We conclude that in addition to its predicted high-affinity competition for ligand binding to megalin, the primary effect of RAP on PT cell endocytosis is to globally dampen megalin-dependent endocytic flux. Our data explain the complex effects of RAP on binding and uptake of filtered proteins and reveal a novel role in modulating endocytosis in PT cells.NEW & NOTEWORTHY Receptor-associated protein inhibits binding and uptake of all known endogenous ligands by megalin and cubilin receptors via unknown mechanism(s). Here, we took advantage of recently generated knockout cell lines to dissect the effect of this protein on megalin- and cubilin-mediated endocytosis. Our study reveals a novel role for receptor-associated protein in blocking megalin-stimulated endocytic uptake of fluid-phase markers and receptor-bound ligands in proximal tubule cells in addition to its direct effect on ligand binding to megalin receptors.
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Affiliation(s)
- Kimberly R Long
- Renal-Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Youssef Rbaibi
- Renal-Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Ossama B Kashlan
- Renal-Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
| | - Ora A Weisz
- Renal-Electrolyte Division, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States
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9
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Satarug S, Vesey DA, Khamphaya T, Pouyfung P, Gobe GC, Yimthiang S. Estimation of the Cadmium Nephrotoxicity Threshold from Loss of Glomerular Filtration Rate and Albuminuria. TOXICS 2023; 11:755. [PMID: 37755765 PMCID: PMC10534899 DOI: 10.3390/toxics11090755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2023] [Revised: 09/04/2023] [Accepted: 09/05/2023] [Indexed: 09/28/2023]
Abstract
Cadmium (Cd) is a pervasive, toxic environmental pollutant that preferentially accumulates in the tubular epithelium of the kidney. Current evidence suggests that the cumulative burden of Cd here leads to the progressive loss of the glomerular filtration rate (GFR). In this study, we have quantified changes in estimated GFR (eGFR) and albumin excretion (Ealb) according to the levels of blood Cd ([Cd]b) and excretion of Cd (ECd) after adjustment for confounders. ECd and Ealb were normalized to creatinine clearance (Ccr) as ECd/Ccr and Ealb/Ccr. Among 482 residents of Cd-polluted and non-polluted regions of Thailand, 8.1% had low eGFR and 16.9% had albuminuria (Ealb/Ccr) × 100 ≥ 20 mg/L filtrate. In the low Cd burden group, (ECd/Ccr) × 100 < 1.44 µg/L filtrate, eGFR did not correlate with ECd/Ccr (β = 0.007) while an inverse association with ECd/Ccr was found in the medium (β = -0.230) and high burden groups (β = -0.349). Prevalence odds ratios (POR) for low eGFR were increased in the medium (POR 8.26) and high Cd burden groups (POR 3.64). Also, eGFR explained a significant proportion of Ealb/Ccr variation among those with middle (η2 0.093) and high [Cd]b tertiles (η2 0.132) but did not with low tertiles (η2 0.001). With an adjustment of eGFR, age and BMI, the POR values for albuminuria were increased in the middle (POR 2.36) and high [Cd]b tertiles (POR 2.74) and those with diabetes (POR 6.02) and hypertension (2.05). These data indicate that (ECd/Ccr) × 100 of 1.44 µg/L filtrate (0.01-0.02 µg/g creatinine) may serve as a Cd threshold level based on which protective exposure guidelines should be formulated.
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Affiliation(s)
- Soisungwan Satarug
- The Centre for Kidney Disease Research, Translational Research Institute, Brisbane 4102, Australia; (D.A.V.); (G.C.G.)
| | - David A. Vesey
- The Centre for Kidney Disease Research, Translational Research Institute, Brisbane 4102, Australia; (D.A.V.); (G.C.G.)
- Department of Kidney and Transplant Services, Princess Alexandra Hospital, Brisbane 4102, Australia
| | - Tanaporn Khamphaya
- Occupational Health and Safety, School of Public Health, Walailak University, Nakhon Si Thammarat 80160, Thailand; (T.K.); (P.P.); (S.Y.)
| | - Phisit Pouyfung
- Occupational Health and Safety, School of Public Health, Walailak University, Nakhon Si Thammarat 80160, Thailand; (T.K.); (P.P.); (S.Y.)
| | - Glenda C. Gobe
- The Centre for Kidney Disease Research, Translational Research Institute, Brisbane 4102, Australia; (D.A.V.); (G.C.G.)
- School of Biomedical Sciences, The University of Queensland, Brisbane 4072, Australia
- NHMRC Centre of Research Excellence for CKD QLD, UQ Health Sciences, Royal Brisbane and Women’s Hospital, Brisbane 4029, Australia
| | - Supabhorn Yimthiang
- Occupational Health and Safety, School of Public Health, Walailak University, Nakhon Si Thammarat 80160, Thailand; (T.K.); (P.P.); (S.Y.)
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Shipman KE, Baty CJ, Long KR, Rbaibi Y, Cowan IA, Gerges M, Marciszyn AL, Kashlan OB, Tan RJ, Edwards A, Weisz OA. Impaired Endosome Maturation Mediates Tubular Proteinuria in Dent Disease Cell Culture and Mouse Models. J Am Soc Nephrol 2023; 34:619-640. [PMID: 36758125 PMCID: PMC10103310 DOI: 10.1681/asn.0000000000000084] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2022] [Accepted: 01/03/2023] [Indexed: 02/11/2023] Open
Abstract
SIGNIFICANCE STATEMENT Loss of function of the 2Cl - /H + antiporter ClC-5 in Dent disease causes an unknown impairment in endocytic traffic, leading to tubular proteinuria. The authors integrated data from biochemical and quantitative imaging studies in proximal tubule cells into a mathematical model to determine that loss of ClC-5 impairs endosome acidification and delays early endosome maturation in proximal tubule cells, resulting in reduced megalin recycling, surface expression, and half-life. Studies in a Dent mouse model also revealed subsegment-specific differences in the effects of ClC-5 knockout on proximal tubule subsegments. The approach provides a template to dissect the effects of mutations or perturbations that alter tubular recovery of filtered proteins from the level of individual cells to the entire proximal tubule axis. BACKGROUND Loss of function of the 2Cl - /H + antiporter ClC-5 in Dent disease impairs the uptake of filtered proteins by the kidney proximal tubule, resulting in tubular proteinuria. Reduced posttranslational stability of megalin and cubilin, the receptors that bind to and recover filtered proteins, is believed to underlie the tubular defect. How loss of ClC-5 leads to reduced receptor expression remains unknown. METHODS We used biochemical and quantitative imaging data to adapt a mathematical model of megalin traffic in ClC-5 knockout and control cells. Studies in ClC-5 knockout mice were performed to describe the effect of ClC-5 knockout on megalin traffic in the S1 segment and along the proximal tubule axis. RESULTS The model predicts that ClC-5 knockout cells have reduced rates of exit from early endosomes, resulting in decreased megalin recycling, surface expression, and half-life. Early endosomes had lower [Cl - ] and higher pH. We observed more profound effects in ClC-5 knockout cells expressing the pathogenic ClC-5 E211G mutant. Alterations in the cellular distribution of megalin in ClC-5 knockout mice were consistent with delayed endosome maturation and reduced recycling. Greater reductions in megalin expression were observed in the proximal tubule S2 cells compared with S1, with consequences to the profile of protein retrieval along the proximal tubule axis. CONCLUSIONS Delayed early endosome maturation due to impaired acidification and reduced [Cl - ] accumulation is the primary mediator of reduced proximal tubule receptor expression and tubular proteinuria in Dent disease. Rapid endosome maturation in proximal tubule cells is critical for the efficient recovery of filtered proteins.
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Affiliation(s)
- Katherine E. Shipman
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Catherine J. Baty
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Kimberly R. Long
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Youssef Rbaibi
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Isabella A. Cowan
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Mona Gerges
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Allison L. Marciszyn
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Ossama B. Kashlan
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Roderick J. Tan
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
| | - Aurélie Edwards
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts
| | - Ora A. Weisz
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania
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Cadmium-Induced Proteinuria: Mechanistic Insights from Dose-Effect Analyses. Int J Mol Sci 2023; 24:ijms24031893. [PMID: 36768208 PMCID: PMC9915107 DOI: 10.3390/ijms24031893] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 01/16/2023] [Accepted: 01/17/2023] [Indexed: 01/21/2023] Open
Abstract
Cadmium (Cd) is a toxic metal that accumulates in kidneys, especially in the proximal tubular epithelial cells, where virtually all proteins in the glomerular ultrafiltrate are reabsorbed. Here, we analyzed archived data on the estimated glomerular filtration rate (eGFR) and excretion rates of Cd (ECd), total protein (EProt), albumin (Ealb), β2-microglobulin (Eβ2M), and α1-microglobulin (Eα1M), which were recorded for residents of a Cd contamination area and a low-exposure control area of Thailand. Excretion of Cd and all proteins were normalized to creatinine clearance (Ccr) as ECd/Ccr and EProt/Ccr to correct for differences among subjects in the number of surviving nephrons. Low eGFR was defined as eGFR ≤ 60 mL/min/1.73 m2, while proteinuria was indicted by EPro/Ccr ≥ 20 mg/L of filtrate. EProt/Ccr varied directly with ECd/Ccr (β = 0.263, p < 0.001) and age (β = 0.252, p < 0.001). In contrast, eGFR values were inversely associated with ECd/Ccr (β = -0.266, p < 0.001) and age (β = -0.558, p < 0.001). At ECd/Ccr > 8.28 ng/L of filtrate, the prevalence odds ratios for proteinuria and low eGFR were increased 4.6- and 5.1-fold, respectively (p < 0.001 for both parameters). Thus, the eGFR and tubular protein retrieval were both simultaneously diminished by Cd exposure. Of interest, ECd/Ccr was more closely correlated with EProt/Ccr (r = 0.507), Eβ2M (r = 0.430), and Eα1M/Ccr (r = 0.364) than with EAlb/Ccr (r = 0.152). These data suggest that Cd may differentially reduce the ability of tubular epithelial cells to reclaim proteins, resulting in preferential reabsorption of albumin.
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Satarug S, Vesey DA, Gobe GC, Yimthiang S, Buha Đorđević A. Health Risk in a Geographic Area of Thailand with Endemic Cadmium Contamination: Focus on Albuminuria. TOXICS 2023; 11:68. [PMID: 36668794 PMCID: PMC9866753 DOI: 10.3390/toxics11010068] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2022] [Revised: 01/10/2023] [Accepted: 01/10/2023] [Indexed: 06/17/2023]
Abstract
An increased level of cadmium (Cd) in food crops, especially rice is concerning because rice is a staple food for over half of the world’s population. In some regions, rice contributes to more than 50% of the total Cd intake. Low environmental exposure to Cd has been linked to an increase in albumin excretion to 30 mg/g creatinine, termed albuminuria, and a progressive reduction in the estimated glomerular filtration rate (eGFR) to below 60 mL/min/1.73 m2, termed reduced eGFR. However, research into albuminuria in high exposure conditions is limited. Here, we applied benchmark dose (BMD) analysis to the relevant data recorded for the residents of a Cd contamination area and a low-exposure control area. We normalized the excretion rates of Cd (ECd) and albumin (Ealb) to creatinine clearance (Ccr) as ECd/Ccr and Ealb/Ccr to correct for differences among subjects in the number of surviving nephrons. For the first time, we defined the excretion levels of Cd associated with clinically relevant adverse kidney health outcomes. Ealb/Ccr varied directly with ECd/Ccr (β = 0.239, p < 0.001), and age (β = 0.203, p < 0.001), while normotension was associated with lower Ealb/Ccr (β = −0.106, p = 0.009). ECd/Ccr values between 16.5 and 35.5 ng/L of the filtrate were associated with a 10% prevalence of albuminuria, while the ECd/Ccr value of 59 ng/L of the filtrate was associated with a 10% prevalence of reduced eGFR. Thus, increased albumin excretion and eGFR reduction appeared to occur at low body burdens, and they should form toxicity endpoints suitable for the calculation of health risk due to the Cd contamination of food chains.
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Affiliation(s)
- Soisungwan Satarug
- Kidney Disease Research Collaborative, Translational Research Institute, Brisbane 4102, Australia
| | - David A. Vesey
- Kidney Disease Research Collaborative, Translational Research Institute, Brisbane 4102, Australia
- Department of Nephrology, Princess Alexandra Hospital, Brisbane 4102, Australia
| | - Glenda C. Gobe
- Kidney Disease Research Collaborative, Translational Research Institute, Brisbane 4102, Australia
- School of Biomedical Sciences, The University of Queensland, Brisbane 4072, Australia
- NHMRC Centre of Research Excellence for CKD QLD, UQ Health Sciences, Royal Brisbane and Women’s Hospital, Brisbane 4029, Australia
| | - Supabhorn Yimthiang
- Occupational Health and Safety, School of Public Health, Walailak University, Nakhon Si Thammarat 80160, Thailand
| | - Aleksandra Buha Đorđević
- Department of Toxicology “Akademik Danilo Soldatović”, University of Belgrade-Faculty of Pharmacy, 11000 Belgrade, Serbia
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Shipman KE, Long KR, Cowan IA, Rbaibi Y, Baty CJ, Weisz OA. An Adaptable Physiological Model of Endocytic Megalin Trafficking in Opossum Kidney Cells and Mouse Kidney Proximal Tubule. FUNCTION 2022; 3:zqac046. [PMID: 36325513 PMCID: PMC9614980 DOI: 10.1093/function/zqac046] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 08/30/2022] [Accepted: 08/31/2022] [Indexed: 01/11/2023] Open
Abstract
The cells that comprise the proximal tubule (PT) are specialized for high-capacity apical endocytosis necessary to maintain a protein-free urine. Filtered proteins are reclaimed via receptor-mediated endocytosis facilitated by the multiligand receptors megalin and cubilin. Despite the importance of this pathway, we lack a detailed understanding of megalin trafficking kinetics and how they are regulated. Here, we utilized biochemical and quantitative imaging methods in a highly differentiated model of opossum kidney (OK) cells and in mouse kidney in vivo to develop mathematical models of megalin traffic. A preliminary model based on biochemically quantified kinetic parameters was refined by colocalization of megalin with individual apical endocytic compartment markers. Our model predicts that megalin is rapidly internalized, resulting in primarily intracellular distribution of the receptor at steady state. Moreover, our data show that early endosomes mature rapidly in PT cells and suggest that Rab11 is the primary mediator of apical recycling of megalin from maturing endocytic compartments. Apical recycling represents the rate-limiting component of endocytic traffic, suggesting that this step has the largest impact in determining the endocytic capacity of PT cells. Adaptation of our model to the S1 segment of mouse PT using colocalization data obtained in kidney sections confirms basic aspects of our model and suggests that our OK cell model largely recapitulates in vivo membrane trafficking kinetics. We provide a downloadable application that can be used to adapt our working parameters to further study how endocytic capacity of PT cells may be altered under normal and disease conditions.
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Affiliation(s)
- Katherine E Shipman
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Kimberly R Long
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Isabella A Cowan
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Youssef Rbaibi
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Catherine J Baty
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
| | - Ora A Weisz
- Renal Electrolyte Division, Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
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Weinstein AM. Assessing proteinuria: value added from a mathematical model. J Physiol 2022; 600:1817-1818. [PMID: 35234287 DOI: 10.1113/jp282967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Alan M Weinstein
- Department of Medicine, Department of Physiology and Biophysics, Weill Medical College of Cornell University
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