Publications by authors named "Christoph Kuppe"

32 Publications

Deep learning-based molecular morphometrics for kidney biopsies.

JCI Insight 2021 Apr 8;6(7). Epub 2021 Apr 8.

III. Department of Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Morphologic examination of tissue biopsies is essential for histopathological diagnosis. However, accurate and scalable cellular quantification in human samples remains challenging. Here, we present a deep learning-based approach for antigen-specific cellular morphometrics in human kidney biopsies, which combines indirect immunofluorescence imaging with U-Net-based architectures for image-to-image translation and dual segmentation tasks, achieving human-level accuracy. In the kidney, podocyte loss represents a hallmark of glomerular injury and can be estimated in diagnostic biopsies. Thus, we profiled over 27,000 podocytes from 110 human samples, including patients with antineutrophil cytoplasmic antibody-associated glomerulonephritis (ANCA-GN), an immune-mediated disease with aggressive glomerular damage and irreversible loss of kidney function. We identified previously unknown morphometric signatures of podocyte depletion in patients with ANCA-GN, which allowed patient classification and, in combination with routine clinical tools, showed potential for risk stratification. Our approach enables robust and scalable molecular morphometric analysis of human tissues, yielding deeper biological insights into the human kidney pathophysiology.
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http://dx.doi.org/10.1172/jci.insight.144779DOI Listing
April 2021

Causal integration of multi-omics data with prior knowledge to generate mechanistic hypotheses.

Mol Syst Biol 2021 01;17(1):e9730

Faculty of Medicine, and Heidelberg University Hospital, Institute for Computational Biomedicine, Heidelberg University, Heidelberg, Germany.

Multi-omics datasets can provide molecular insights beyond the sum of individual omics. Various tools have been recently developed to integrate such datasets, but there are limited strategies to systematically extract mechanistic hypotheses from them. Here, we present COSMOS (Causal Oriented Search of Multi-Omics Space), a method that integrates phosphoproteomics, transcriptomics, and metabolomics datasets. COSMOS combines extensive prior knowledge of signaling, metabolic, and gene regulatory networks with computational methods to estimate activities of transcription factors and kinases as well as network-level causal reasoning. COSMOS provides mechanistic hypotheses for experimental observations across multi-omics datasets. We applied COSMOS to a dataset comprising transcriptomics, phosphoproteomics, and metabolomics data from healthy and cancerous tissue from eleven clear cell renal cell carcinoma (ccRCC) patients. COSMOS was able to capture relevant crosstalks within and between multiple omics layers, such as known ccRCC drug targets. We expect that our freely available method will be broadly useful to extract mechanistic insights from multi-omics studies.
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http://dx.doi.org/10.15252/msb.20209730DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7838823PMC
January 2021

Experimental and computational technologies to dissect the kidney at the single-cell level.

Nephrol Dial Transplant 2020 Dec 17. Epub 2020 Dec 17.

Division of Nephrology, RWTH Aachen University, Aachen, Germany.

The field of single-cell technologies, in particular single-cell genomics with transcriptomics and epigenomics, and most recently single-cell proteomics, is rapidly growing and holds promise to advance our understanding of organ homoeostasis and disease, and facilitate the identification of novel therapeutic targets and biomarkers. This review offers an introduction to these technologies. In addition, as the size and complexity of the data require sophisticated computational methods for analysis and interpretation, we will also provide an overview of these methods and summarize the single-cell literature specifically pertaining to the kidney.
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http://dx.doi.org/10.1093/ndt/gfaa233DOI Listing
December 2020

Heterogeneous bone-marrow stromal progenitors drive myelofibrosis via a druggable alarmin axis.

Cell Stem Cell 2021 Apr 9;28(4):637-652.e8. Epub 2020 Dec 9.

Department of Hematology, Erasmus Medical Center, Rotterdam 3015GD, the Netherlands; Department of Cell Biology, Institute for Biomedical Engineering, Faculty of Medicine, RWTH Aachen University, Pauwelsstrasse 30, 52074 Aachen, Germany; Oncode Institute, Erasmus Medical Center, Rotterdam 3015GD, the Netherlands. Electronic address:

Functional contributions of individual cellular components of the bone-marrow microenvironment to myelofibrosis (MF) in patients with myeloproliferative neoplasms (MPNs) are incompletely understood. We aimed to generate a comprehensive map of the stroma in MPNs/MFs on a single-cell level in murine models and patient samples. Our analysis revealed two distinct mesenchymal stromal cell (MSC) subsets as pro-fibrotic cells. MSCs were functionally reprogrammed in a stage-dependent manner with loss of their progenitor status and initiation of differentiation in the pre-fibrotic and acquisition of a pro-fibrotic and inflammatory phenotype in the fibrotic stage. The expression of the alarmin complex S100A8/S100A9 in MSC marked disease progression toward the fibrotic phase in murine models and in patient stroma and plasma. Tasquinimod, a small-molecule inhibiting S100A8/S100A9 signaling, significantly ameliorated the MPN phenotype and fibrosis in JAK2V617F-mutated murine models, highlighting that S100A8/S100A9 is an attractive therapeutic target in MPNs.
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http://dx.doi.org/10.1016/j.stem.2020.11.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8024900PMC
April 2021

Decoding myofibroblast origins in human kidney fibrosis.

Nature 2021 01 11;589(7841):281-286. Epub 2020 Nov 11.

Division of Nephrology and Clinical Immunology, RWTH Aachen University, Aachen, Germany.

Kidney fibrosis is the hallmark of chronic kidney disease progression; however, at present no antifibrotic therapies exist. The origin, functional heterogeneity and regulation of scar-forming cells that occur during human kidney fibrosis remain poorly understood. Here, using single-cell RNA sequencing, we profiled the transcriptomes of cells from the proximal and non-proximal tubules of healthy and fibrotic human kidneys to map the entire human kidney. This analysis enabled us to map all matrix-producing cells at high resolution, and to identify distinct subpopulations of pericytes and fibroblasts as the main cellular sources of scar-forming myofibroblasts during human kidney fibrosis. We used genetic fate-tracing, time-course single-cell RNA sequencing and ATAC-seq (assay for transposase-accessible chromatin using sequencing) experiments in mice, and spatial transcriptomics in human kidney fibrosis, to shed light on the cellular origins and differentiation of human kidney myofibroblasts and their precursors at high resolution. Finally, we used this strategy to detect potential therapeutic targets, and identified NKD2 as a myofibroblast-specific target in human kidney fibrosis.
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http://dx.doi.org/10.1038/s41586-020-2941-1DOI Listing
January 2021

Only Hyperuricemia with Crystalluria, but not Asymptomatic Hyperuricemia, Drives Progression of Chronic Kidney Disease.

J Am Soc Nephrol 2020 12 16;31(12):2773-2792. Epub 2020 Sep 16.

Division of Nephrology, Department of Medicine IV, Ludwig-Maximilian's-University Hospital, Munich, Germany

Background: The roles of asymptomatic hyperuricemia or uric acid (UA) crystals in CKD progression are unknown. Hypotheses to explain links between UA deposition and progression of CKD include that () asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; () UA crystal granulomas may form due to pre-existing CKD; and () proinflammatory granuloma-related M1-like macrophages may drive UA crystal-induced CKD progression.

Methods: MALDI-FTICR mass spectrometry, immunohistochemistry, 3D confocal microscopy, and flow cytometry were used to characterize a novel mouse model of hyperuricemia and chronic UA crystal nephropathy with granulomatous nephritis. Interventional studies probed the role of crystal-induced inflammation and macrophages in the pathology of progressive CKD.

Results: Asymptomatic hyperuricemia alone did not cause CKD or drive the progression of aristolochic acid I-induced CKD. Only hyperuricemia with UA crystalluria due to urinary acidification caused tubular obstruction, inflammation, and interstitial fibrosis. UA crystal granulomas surrounded by proinflammatory M1-like macrophages developed late in this process of chronic UA crystal nephropathy and contributed to the progression of pre-existing CKD. Suppressing M1-like macrophages with adenosine attenuated granulomatous nephritis and the progressive decline in GFR. In contrast, inhibiting the JAK/STAT inflammatory pathway with tofacitinib was not renoprotective.

Conclusions: Asymptomatic hyperuricemia does not affect CKD progression unless UA crystallizes in the kidney. UA crystal granulomas develop late in chronic UA crystal nephropathy and contribute to CKD progression because UA crystals trigger M1-like macrophage-related interstitial inflammation and fibrosis. Targeting proinflammatory macrophages, but not JAK/STAT signaling, can attenuate granulomatous interstitial nephritis.
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http://dx.doi.org/10.1681/ASN.2020040523DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7790211PMC
December 2020

A Functional Landscape of CKD Entities From Public Transcriptomic Data.

Kidney Int Rep 2020 Feb 13;5(2):211-224. Epub 2019 Nov 13.

Faculty of Medicine, RWTH Aachen University, Joint Research Centre for Computational Biomedicine (JRC-COMBINE), Aachen, Germany.

Introduction: To develop effective therapies and identify novel early biomarkers for chronic kidney disease, an understanding of the molecular mechanisms orchestrating it is essential. We here set out to understand how differences in chronic kidney disease (CKD) origin are reflected in gene expression. To this end, we integrated publicly available human glomerular microarray gene expression data for 9 kidney disease entities that account for most of CKD worldwide. Our primary goal was to demonstrate the possibilities and potential on data analysis and integration to the nephrology community.

Methods: We integrated data from 5 publicly available studies and compared glomerular gene expression profiles of disease with that of controls from nontumor parts of kidney cancer nephrectomy tissues. A major challenge was the integration of the data from different sources, platforms, and conditions that we mitigated with a bespoke stringent procedure.

Results: We performed a global transcriptome-based delineation of different kidney disease entities, obtaining a transcriptomic diffusion map of their similarities and differences based on the genes that acquire a consistent differential expression between each kidney disease entity and nephrectomy tissue. We derived functional insights by inferring the activity of signaling pathways and transcription factors from the collected gene expression data and identified potential drug candidates based on expression signature matching. We validated representative findings by immunostaining in human kidney biopsies indicating, for example, that the transcription factor FOXM1 is significantly and specifically expressed in parietal epithelial cells in rapidly progressive glomerulonephritis (RPGN) whereas not expressed in control kidney tissue. Furthermore, we found drug candidates by matching the signature on expression of drugs to that of the CKD entities, in particular, the Food and Drug Administration-approved drug nilotinib.

Conclusion: These results provide a foundation to comprehend the specific molecular mechanisms underlying different kidney disease entities that can pave the way to identify biomarkers and potential therapeutic targets. To facilitate further use, we provide our results as a free interactive Web application: https://saezlab.shinyapps.io/ckd_landscape/. However, because of the limitations of the data and the difficulties in its integration, any specific result should be considered with caution. Indeed, we consider this study rather an illustration of the value of functional genomics and integration of existing data.
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http://dx.doi.org/10.1016/j.ekir.2019.11.005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000845PMC
February 2020

The authors reply.

Kidney Int 2019 11;96(5):1241

Department of Pathology and Cell Biology, Renal Pathology Division, Columbia University Medical Center, New York, New York, USA.

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http://dx.doi.org/10.1016/j.kint.2019.08.016DOI Listing
November 2019

mTOR-mediated podocyte hypertrophy regulates glomerular integrity in mice and humans.

JCI Insight 2019 09 19;4(18). Epub 2019 Sep 19.

Development and Stem Cells Program, Monash Biomedicine Discovery Institute and Department of Anatomy and Developmental Biology, Monash University, Melbourne, Australia.

The cellular origins of glomerulosclerosis involve activation of parietal epithelial cells (PECs) and progressive podocyte depletion. While mammalian target of rapamycin-mediated (mTOR-mediated) podocyte hypertrophy is recognized as an important signaling pathway in the context of glomerular disease, the role of podocyte hypertrophy as a compensatory mechanism preventing PEC activation and glomerulosclerosis remains poorly understood. In this study, we show that glomerular mTOR and PEC activation-related genes were both upregulated and intercorrelated in biopsies from patients with focal segmental glomerulosclerosis (FSGS) and diabetic nephropathy, suggesting both compensatory and pathological roles. Advanced morphometric analyses in murine and human tissues identified podocyte hypertrophy as a compensatory mechanism aiming to regulate glomerular functional integrity in response to somatic growth, podocyte depletion, and even glomerulosclerosis - all of this in the absence of detectable podocyte regeneration. In mice, pharmacological inhibition of mTOR signaling during acute podocyte loss impaired hypertrophy of remaining podocytes, resulting in unexpected albuminuria, PEC activation, and glomerulosclerosis. Exacerbated and persistent podocyte hypertrophy enabled a vicious cycle of podocyte loss and PEC activation, suggesting a limit to its beneficial effects. In summary, our data highlight a critical protective role of mTOR-mediated podocyte hypertrophy following podocyte loss in order to preserve glomerular integrity, preventing PEC activation and glomerulosclerosis.
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http://dx.doi.org/10.1172/jci.insight.99271DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6795295PMC
September 2019

Heterogeneity and plasticity in healthy and atherosclerotic vasculature explored by single-cell sequencing.

Cardiovasc Res 2019 Oct;115(12):1705-1715

Pathology Department, CARIM School for Cardiovascular Diseases, MUMC Maastricht, P. Debyelaan 25, Maastricht, the Netherlands.

Cellular characteristics and their adjustment to a state of disease have become more evident due to recent advances in imaging, fluorescent reporter mice, and whole genome RNA sequencing. The uncovered cellular heterogeneity and/or plasticity potentially complicates experimental studies and clinical applications, as markers derived from whole tissue 'bulk' sequencing is unable to yield a subtype transcriptome and specific markers. Here, we propose definitions on heterogeneity and plasticity, discuss current knowledge thereof in the vasculature and how this may be improved by single-cell sequencing (SCS). SCS is emerging as an emerging technique, enabling researchers to investigate different cell populations in more depth than ever before. Cell selection methods, e.g. flow assisted cell sorting, and the quantity of cells can influence the choice of SCS method. Smart-Seq2 offers sequencing of the complete mRNA molecule on a low quantity of cells, while Drop-seq is possible on large numbers of cells on a more superficial level. SCS has given more insight in heterogeneity in healthy vasculature, where it revealed that zonation is crucial in gene expression profiles among the anatomical axis. In diseased vasculature, this heterogeneity seems even more prominent with discovery of new immune subsets in atherosclerosis as proof. Vascular smooth muscle cells and mesenchymal cells also share these plastic characteristics with the ability to up-regulate markers linked to stem cells, such as Sca-1 or CD34. Current SCS studies show some limitations to the number of replicates, quantity of cells used, or the loss of spatial information. Bioinformatical tools could give some more insight in current datasets, making use of pseudo-time analysis or RNA velocity to investigate cell differentiation or polarization. In this review, we discuss the use of SCS in unravelling heterogeneity in the vasculature, its current limitations and promising future applications.
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http://dx.doi.org/10.1093/cvr/cvz185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6873093PMC
October 2019

Novel 3D analysis using optical tissue clearing documents the evolution of murine rapidly progressive glomerulonephritis.

Kidney Int 2019 08 15;96(2):505-516. Epub 2019 Mar 15.

Department of Nephrology and Clinical Immunology, RWTH Aachen University Clinic, Aachen, Germany; Interdisciplinary Centre for Clinical Research (IZKF Aachen), RWTH Aachen University Hospital, Aachen, Germany; Heisenberg Chair for Preventive and Translational Nephrology, Division of Nephrology, RWTH Aachen University, Aachen, Germany. Electronic address:

Recent developments in optical tissue clearing have been difficult to apply for the morphometric analysis of organs with high cellular content and small functional structures, such as the kidney. Here, we establish combinations of genetic and immuno-labelling for single cell identification, tissue clearing and subsequent de-clarification for histoimmunopathology and transmission electron microscopy. Using advanced light microscopy and computational analyses, we investigated a murine model of crescentic nephritis, an inflammatory kidney disease typified by immune-mediated damage to glomeruli leading to the formation of hypercellular lesions and the rapid loss of kidney function induced by nephrotoxic serum. Results show a graded susceptibility of the glomeruli, significant podocyte loss and capillary injury. These effects are associated with activation of parietal epithelial cells and formation of glomerular lesions that may evolve and obstruct the kidney tubule, thereby explaining the loss of kidney function. Thus, our work provides new high-throughput endpoints for the analysis of complex tissues with single-cell resolution.
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http://dx.doi.org/10.1016/j.kint.2019.02.034DOI Listing
August 2019

Novel parietal epithelial cell subpopulations contribute to focal segmental glomerulosclerosis and glomerular tip lesions.

Kidney Int 2019 07 27;96(1):80-93. Epub 2019 Feb 27.

Division of Nephrology and Clinical Immunology, Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University, Aachen, Germany. Electronic address:

Beside the classical flat parietal epithelial cells (PECs), we investigated proximal tubular epithelial-like cells, a neglected subgroup of PECs. These cells, termed cuboidal PECs, make up the most proximal part of the proximal tubule and may also line parts of Bowman's capsule. Additionally, a third intermediate PEC subgroup was identified at the junction between the flat and cuboidal PEC subgroups at the tubular orifice. The transgenic mouse line PEC-rtTA labeled all three PEC subgroups. Here we show that the inducible Pax8-rtTA mouse line specifically labeled only cuboidal and intermediate PECs, but not flat PECs. In aging Pax8-rtTA mice, cell fate mapping showed no evidence for significant transdifferentiation from flat PECs to cuboidal or intermediate PECs or vice versa. In murine glomerular disease models of crescentic glomerulonephritis, and focal segmental glomerulosclerosis (FSGS), intermediate PECs became more numerous. These intermediate PECs preferentially expressed activation markers CD44 and Ki-67, suggesting that this subgroup of PECs was activated more easily than the classical flat PECs. In mice with FSGS, cuboidal and intermediate PECs formed sclerotic lesions. In patients with FSGS, cells forming the tip lesions expressed markers of intermediate PECs. These novel PEC subgroups form sclerotic lesions and were more prone to cellular activation compared to the classical flat PECs in disease. Thus, colonization of Bowman's capsule by cuboidal PECs may predispose to lesion formation and chronic kidney disease. We propose that tip lesions originate from this novel subgroup of PECs in patients with FSGS.
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http://dx.doi.org/10.1016/j.kint.2019.01.037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7292612PMC
July 2019

Disruption of CUL3-mediated ubiquitination causes proximal tubule injury and kidney fibrosis.

Sci Rep 2019 03 14;9(1):4596. Epub 2019 Mar 14.

Division of Nephrology and Hypertension, Oregon Health and Science University, Portland, Oregon, USA.

Cullin 3 (CUL3) is part of the ubiquitin proteasomal system and controls several cellular processes critical for normal organ function including the cell cycle, and Keap1/Nrf2 signaling. Kidney tubule-specific Cul3 disruption causes tubulointerstitial fibrosis, but little is known about the mechanisms. Therefore, we tested the hypothesis that dysregulation of the cell cycle and Keap1/Nrf2 pathway play a role in initiating the kidney injury upon Cul3 disruption. Cul3 deletion increased expression of cyclin E and p21, associated with uncontrolled proliferation, DNA damage, and apoptosis, all of which preceded proximal tubule injury. The cdk2-cyclin E inhibitor roscovitine did not prevent the effects of Cul3 deletion, but instead exacerbated the kidney injury. Injury occurred despite accumulation and activation of CUL3 substrate Keap1/Nrf2, proposed to be protective in kidney injury. Cul3 disruption led to progressive interstitial inflammation, functionally relevant renal fibrosis and death. Finally, we observed reduced CUL3 expression in several AKI and CKD mouse models and in fibrotic human kidney tissue. These data establish CUL3 knockout mice as a novel genetic CKD model in which dysregulation of the cell cycle may play a primary role in initiating tubule injury, and that CUL3 dysregulation could contribute to acute and fibrotic kidney disease.
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http://dx.doi.org/10.1038/s41598-019-40795-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6418206PMC
March 2019

Identification of platelet-derived growth factor C as a mediator of both renal fibrosis and hypertension.

Kidney Int 2019 05 28;95(5):1103-1119. Epub 2019 Feb 28.

Division of Nephrology and Clinical Immunology, Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen University, Aachen, Germany.

Platelet-derived growth factors (PDGF) have been implicated in kidney disease progression. We previously found that PDGF-C is upregulated at sites of renal fibrosis and that antagonism of PDGF-C reduces fibrosis in the unilateral ureteral obstruction model. We studied the role of PDGF-C in collagen 4A3 ("Alport") mice, a model of progressive renal fibrosis with greater relevance to human kidney disease. Alport mice were crossbred with PDGF-C mice or administered a neutralizing PDGF-C antibody. Both PDGF-C deficiency and neutralization reduced serum creatinine and blood urea nitrogen levels and mitigated glomerular injury, renal fibrosis, and renal inflammation. Unexpectedly, systolic blood pressure was also reduced in both Alport and wild-type mice treated with a neutralizing PDGF-C antibody. Neutralization of PDGF-C reduced arterial wall thickness in the renal cortex of Alport mice. Aortic rings isolated from anti-PDGF-C-treated wildtype mice exhibited reduced tension and faster relaxation than those of untreated mice. In vitro, PDGF-C upregulated angiotensinogen in aortic tissue and in primary hepatocytes and induced nuclear factor κB (NFκB)/p65-binding to the angiotensinogen promoter in hepatocytes. Neutralization of PDGF-C suppressed transcript expression of angiotensinogen in Alport mice and angiotensin II receptor type 1 in Alport and wildtype mice. Finally, administration of neutralizing PDGF-C antibodies ameliorated angiotensin II-induced hypertension in healthy mice. Thus, in addition to its key role in mediating renal fibrosis, we identified PDGF-C as a mediator of hypertension via effects on renal vasculature and on the renin-angiotensin system. The contribution to both renal fibrosis and hypertension render PDGF-C an attractive target in progressive kidney disease.
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http://dx.doi.org/10.1016/j.kint.2018.11.031DOI Listing
May 2019

Inverse correlation between vascular endothelial growth factor back-filtration and capillary filtration pressures.

Nephrol Dial Transplant 2018 09;33(9):1514-1525

Division of Nephrology and Immunology, RWTH Aachen University, Aachen, Germany.

Background: Vascular endothelial growth factor A (VEGF) is an essential growth factor during glomerular development and postnatal homeostasis. VEGF is secreted in high amounts by podocytes into the primary urine, back-filtered across the glomerular capillary wall to act on endothelial cells. So far it has been assumed that VEGF back-filtration is driven at a constant rate exclusively by diffusion.

Methods: In the present work, glomerular VEGF back-filtration was investigated in vivo using a novel extended model based on endothelial fenestrations as surrogate marker for local VEGF concentrations. Single nephron glomerular filtration rate (SNGFR) and/or local filtration flux were manipulated by partial renal mass ablation, tubular ablation, and in transgenic mouse models of systemic or podocytic VEGF overexpression or reduction.

Results: Our study shows positive correlations between VEGF back-filtration and SNGFR as well as effective filtration rate under physiological conditions along individual glomerular capillaries in rodents and humans.

Conclusion: Our results suggest that an additional force drives VEGF back-filtration, potentially regulated by SNGFR.
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http://dx.doi.org/10.1093/ndt/gfy057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6113640PMC
September 2018

Investigations of Glucocorticoid Action in GN.

J Am Soc Nephrol 2017 May 28;28(5):1408-1420. Epub 2016 Nov 28.

Division of Nephrology and Clinical Immunology, Rheinisch-Westfälische Technische Hochschule Aachen University, Aachen, Germany;

For several decades, glucocorticoids have been used empirically to treat rapid progressive GN. It is commonly assumed that glucocorticoids act primarily by dampening the immune response, but the mechanisms remain incompletely understood. In this study, we inactivated the glucocorticoid receptor (GR) specifically in kidney epithelial cells using Pax8-Cre/GR mice. Pax8-Cre/GR mice did not exhibit an overt spontaneous phenotype. In mice treated with nephrotoxic serum to induce crescentic nephritis (rapidly progressive GN), this genetic inactivation of the GR in kidney epithelial cells exerted renal benefits, including inhibition of albuminuria and cellular crescent formation, similar to the renal benefits observed with high-dose prednisolone in control mice. However, genetic inactivation of the GR in kidney epithelial cells did not induce the immunosuppressive effects observed with prednisolone. , prednisolone and the pharmacologic GR antagonist mifepristone each acted directly on primary cultures of parietal epithelial cells, inhibiting cellular outgrowth and proliferation. In wild-type mice, pharmacologic treatment with the GR antagonist mifepristone also attenuated disease as effectively as high-dose prednisolone without the systemic immunosuppressive effects. Collectively, these data show that glucocorticoids act directly on activated glomerular parietal epithelial cells in crescentic nephritis. Furthermore, we identified a novel therapeutic approach in crescentic nephritis, that of glucocorticoid antagonism, which was at least as effective as high-dose prednisolone with potentially fewer adverse effects.
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http://dx.doi.org/10.1681/ASN.2016010060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5407712PMC
May 2017

Focal segmental glomerulosclerosis: it may no longer be all about podocytes.

Kidney Int 2016 10;90(4):905

RWTH Aachen University, Nephrology and Immunology, Aachen, Germany. Electronic address:

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http://dx.doi.org/10.1016/j.kint.2016.07.025DOI Listing
October 2016

Adventitial MSC-like Cells Are Progenitors of Vascular Smooth Muscle Cells and Drive Vascular Calcification in Chronic Kidney Disease.

Cell Stem Cell 2016 11 8;19(5):628-642. Epub 2016 Sep 8.

Division of Nephrology, Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA.

Mesenchymal stem cell (MSC)-like cells reside in the vascular wall, but their role in vascular regeneration and disease is poorly understood. Here, we show that Gli1 cells located in the arterial adventitia are progenitors of vascular smooth muscle cells and contribute to neointima formation and repair after acute injury to the femoral artery. Genetic fate tracing indicates that adventitial Gli1 MSC-like cells migrate into the media and neointima during athero- and arteriosclerosis in ApoE mice with chronic kidney disease. Our data indicate that Gli1 cells are a major source of osteoblast-like cells during calcification in the media and intima. Genetic ablation of Gli1 cells before induction of kidney injury dramatically reduced the severity of vascular calcification. These findings implicate Gli1 cells as critical adventitial progenitors in vascular remodeling after acute and during chronic injury and suggest that they may be relevant therapeutic targets for mitigation of vascular calcification.
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http://dx.doi.org/10.1016/j.stem.2016.08.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5097006PMC
November 2016

Role of mesenchymal stem cells in kidney injury and fibrosis.

Curr Opin Nephrol Hypertens 2016 07;25(4):372-7

Division of Nephrology, RWTH Aachen University, Aachen, Germany.

Purpose Of Review: Multiple studies have established the beneficial role of mesenchymal stem cell (MSC) therapy for kidney injury. In this review we will discuss the recent identification of Gli1 as a marker for perivascular MSC and the role of this cell population in kidney fibrosis.

Recent Findings: Recent studies demonstrate that expression of the hedgehog transcriptional activator Gli1 specifically marks perivascular MSC. Genetic fate tracing of MSC in kidney injury revealed their contribution to the myofibroblast pool whereas ablation of MSC reduced kidney fibrosis. Furthermore, strong evidence suggests that pharmacologically targeting Gli proteins inhibits cell-cycle progression of myofibroblasts in kidney fibrosis and is a promising therapeutic strategy in chronic kidney disease.

Summary: Although there is tremendous excitement about MSC as cellular therapy in kidney injury it has been shown that resident perivascular MSC are a major source of myofibroblasts and a novel therapeutic target in kidney fibrosis. While resident kidney MSC might also be involved in capillary rarefaction after injury and during fibrosis progression their potential role in kidney repair, angiogenesis, and regeneration remains unclear. Further studies are needed to identify the molecular pathways that control the profibrotic versus proregenerative role of resident MSC in kidney injury and repair.
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http://dx.doi.org/10.1097/MNH.0000000000000230DOI Listing
July 2016

The Authors Reply.

Kidney Int 2016 06;89(6):1404

RWTH Aachen University, Division of Nephrology and Immunology, Aachen, Germany; Interdisciplinary Centre for Clinical Research (IZKF Aachen), RWTH Aachen University Hospital, Aachen, Germany. Electronic address:

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http://dx.doi.org/10.1016/j.kint.2016.03.002DOI Listing
June 2016

Progress and controversies in unraveling the glomerular filtration mechanism.

Curr Opin Nephrol Hypertens 2015 May;24(3):208-16

Division of Nephrology and Immunology, RWTH Aachen University, Aachen, Germany *Turgay Saritas and Christoph Kuppe contributed equally to the writing of this article.

Purpose Of Review: At first sight, the glomerular filter appears like a problem that should be easily solved. The majority of researchers view the filter like an impermeable wall perforated by specialized and size-selective pores (pore model). However, the fact that this model is in conflict with many of the experimental findings suggests that it may not yet be complete.

Recent Findings: In the more recent electrokinetic model, we have proposed including electrical effects (streaming potentials). The present review investigates how this can provide a relatively simple mechanistic explanation for the great majority of the so far unexplained characteristics of the filter, for example why the filter never clogs.

Summary: Understanding how the glomerular filter functions is a prerequisite to investigate the pathogenesis of proteinuric glomerular diseases and the link between glomerular proteinuria and cardiovascular disease.
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http://dx.doi.org/10.1097/MNH.0000000000000116DOI Listing
May 2015

Common histological patterns in glomerular epithelial cells in secondary focal segmental glomerulosclerosis.

Kidney Int 2015 Nov 8;88(5):990-8. Epub 2015 Apr 8.

Department of Internal Medicine II, Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany.

Parietal epithelial cells (PECs) are involved in the development of sclerotic lesions in primary focal and segmental glomerulosclerosis (FSGS). Here, the role of PECs was explored in the more common secondary FSGS lesions in 68 patient biopsies, diagnosed with 11 different frequently or rarely encountered glomerular pathologies and additional secondary FSGS lesions. For each biopsy, one section was quadruple stained for PECs (ANXA3), podocytes (synaptopodin), PEC matrix (LKIV69), and Hoechst (nuclei), and a second was quadruple stained for activated PECs (CD44 and cytokeratin-19), PEC matrix, and nuclei. In all lesions, cellular adhesions (synechiae) between Bowman's capsule and the tuft were formed by cells expressing podocyte and/or PEC markers. Cells expressing PEC markers were detected in all FSGS lesions independent of the underlying glomerular disease and often stained positive for markers of activation. Small FSGS lesions, which were hardly identified on PAS sections previously, were detectable by immunofluorescent staining using PEC markers, potentially improving the diagnostic sensitivity to identify these lesions. Thus, similar patterns of cells expressing podocyte and/or PEC markers were found in the formation of secondary FSGS lesions independent of the underlying glomerular disease. Hence, our findings support the hypothesis that FSGS lesions follow a final cellular pathway to nephron loss that includes involvement of cells expressing PEC markers.
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http://dx.doi.org/10.1038/ki.2015.116DOI Listing
November 2015

Point: Proposing the electrokinetic model.

Perit Dial Int 2015 Jan-Feb;35(1):5-8

Division of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany.

It is still not fully resolved how the glomerular filter works and why it never clogs. Several models have been proposed. In this review, we will compare the most widely used "pore model" to the more recent and refined "electrokinetic model" of glomerular filtration. The pore model assumes the existence of highly ordered regular pores, but it cannot provide a mechanistic explanation for several of the inherent characteristics of the glomerular filter. The electrokinetic model assumes that streaming potentials generate an electrical field along the filter surface which repels the negatively charged plasma proteins, preventing them from passing across the filter. The electrokinetic model can provide elegant mechanistic solutions for most of the unresolved riddles about the glomerular filter.
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http://dx.doi.org/10.3747/pdi.2014.00189DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4335921PMC
November 2015

Renal lipidosis in patients enrolled in a methadone substitution program.

Arch Pathol Lab Med 2014 May;138(5):689-93

From the Department of Cellular and Molecular Pathology, German Cancer Research Center, Heidelberg, Germany (Drs Porubsky and Gröne); the Institute of Pathology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany (Dr Porubsky); the Department of Nephrology and Clinical Immunology, RWTH Aachen University Hospital, Aachen, Germany (Drs Kuppe, Moeller, and Floege); the Department of Internal Medicine, University Hospital Giessen and Marburg, Marburg, Germany (Dr Maier); the Department of Internal Medicine, University Hospital Giessen and Marburg, Giessen, Germany (Dr Birk); and the Medical Clinic and Policlinic, University Hospitals LMU, Munich, Germany (Dr Wörnle). Drs Porubsky and Kuppe contributed equally to the manuscript.

Kidney biopsies often show accumulation of lipids or lipidlike material. Evidence has been provided that lipids can directly initiate and contribute to the progression of glomerular and tubulointerstitial lesions. In this study we describe a renal lipidosis occurring in patients with a positive history of narcotic abuse who were enrolled in a methadone substitution program. All 3 patients presented with proteinuria (2.5-20 g/d) and impaired renal function. Renal biopsy revealed a pronounced extracellular and intracellular deposition of lipidlike material in the glomerular, interstitial, and tubular compartments. Known causes of lipid storage could be excluded clinically and morphologically. We consider this to be a distinct renal lipidosis associated with narcotic abuse, methadone intake, or intravenous abuse thereof.
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http://dx.doi.org/10.5858/arpa.2013-0075-CRDOI Listing
May 2014

The regenerative potential of parietal epithelial cells in adult mice.

J Am Soc Nephrol 2014 Apr 9;25(4):693-705. Epub 2014 Jan 9.

Department of Nephrology and Immunology and.

Previously, we showed that some podocytes in juvenile mice are recruited from cells lining Bowman's capsule, suggesting that parietal epithelial cells (PECs) are a progenitor cell population for podocytes. To investigate whether PECs also replenish podocytes in adult mice, PECs were genetically labeled in an irreversible fashion in 5-week-old mice. No significant increase in labeled podocytes was observed, even after 18 months. To accelerate a potential regenerative mechanism, progressive glomerular hypertrophy was induced by progressive partial nephrectomies. Again, no significant podocyte replenishment was observed. Rather, labeled PECs exclusively invaded segments of the tuft affected by glomerulosclerosis, consistent with our previous findings. We next reassessed PEC recruitment in juvenile mice using a different reporter mouse and confirmed significant recruitment of labeled PECs onto the glomerular tuft. Moreover, some labeled cells on Bowman's capsule expressed podocyte markers, and cells on Bowman's capsule were also directly labeled in juvenile podocyte-specific Pod-rtTA transgenic mice. In 6-week-old mice, however, cells on Bowman's capsule no longer expressed podocyte-specific markers. Similarly, in human kidneys, some cells on Bowman's capsule expressed the podocyte marker synaptopodin from 2 weeks to 2 years of age but not at 7 years of age. In summary, podocyte regeneration from PECs could not be detected in aging mice or models of glomerular hypertrophy. We propose that a small fraction of committed podocytes reside on Bowman's capsule close to the vascular stalk and are recruited onto the glomerular tuft during infancy to adolescence in mice and humans.
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http://dx.doi.org/10.1681/ASN.2013050481DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3968497PMC
April 2014

Glomerular disease: the role of parietal epithelial cells in hyperplastic lesions.

Nat Rev Nephrol 2014 Jan 26;10(1):5-6. Epub 2013 Nov 26.

Department of Nephrology and Clinical Immunology, RWTH University Hospital, Aachen University, Pauwelsstrasse 30, D-52074 Aachen, Germany.

Parietal epithelial cells (PECs) are increasingly recognized as key players in the pathogenesis of proliferative glomerular diseases. A new study by Rizzo and colleagues contributes to this emerging concept and identifies potential novel signalling pathways that might mediate the activation of PECs. However, the functional role of PECs remains controversial.
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http://dx.doi.org/10.1038/nrneph.2013.252DOI Listing
January 2014

Bioengineered kidneys: new sights on a distant horizon.

Int Urol Nephrol 2014 Feb 5;46(2):477-80. Epub 2013 Oct 5.

Department of Nephrology and Immunology, RWTH Aachen University, Pauwelsstrasse 30, 52074, Aachen, Germany.

The need for renal replacement therapy is currently rising at an annually increasing rate. Current treatment options for patients with end-stage kidney disease include dialysis or organ transplantation. Yet, even though transplant survival has increased due to refined immunosuppressive therapy, morbidity remains high because of organ shortage. Here we discuss a recent publication that describes the transplantation of a bioengineered biocompatible kidney from a decellularized organ scaffold, thus possibly providing a solution to both transplant organ shortage and morbidity associated with long-term immunosuppression.
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http://dx.doi.org/10.1007/s11255-013-0570-4DOI Listing
February 2014

Macrophage activation syndrome in a patient with pulmonary inflammatory myofibroblastic tumour.

Allergy Asthma Clin Immunol 2012 May 20;8(1). Epub 2012 May 20.

Department of Nephrology and Clinical Immunology, University Hospital of the Aachen University of Technology (RWTH), Aachen, Germany.

We describe for the first time a case of macrophage activation syndrome (MAS) in a patient with a history of inflammatory myofibroblastic tumour (inflammatory pseudotumour, IPT) of the lung and thoracic spine. The patient was admitted to the intensive care unit with a history of prolonged remitting fever, hepatosplenomegaly, bilaterally enlarged thoracic lymph nodes and an acute severe inflammatory response syndrome (SIRS). Up-regulated cytokine production (e.g. IL-1ß and IL-6), increased levels of ferritin and circulating soluble interleukin-2 receptor (sIL-2R, sCD25) led to the differential diagnosis of MAS. Bone marrow aspiration, the main tool for a definite diagnosis, revealed macrophages phagocytosing haematopoietic cells. Immunosuppressive therapy with corticosteroids and cyclosporine was an effective treatment in this patient.
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http://dx.doi.org/10.1186/1710-1492-8-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3473307PMC
May 2012

Primary cultures of glomerular parietal epithelial cells or podocytes with proven origin.

PLoS One 2012 18;7(4):e34907. Epub 2012 Apr 18.

Division of Nephrology and Immunology, University Hospital of the Aachen University of Technology, Aachen, Germany.

Parietal epithelial cells (PECs) are crucially involved in the pathogenesis of rapidly progressive glomerulonephritis (RPGN) as well as in focal and segmental glomerulosclerosis (FSGS). In this study, transgenic mouse lines were used to isolate pure, genetically tagged primary cultures of PECs or podocytes using FACsorting. By this approach, the morphology of primary glomerular epithelial cells in culture could be resolved: Primary podocytes formed either large cells with intracytoplasmatic extensions or smaller spindle shaped cells, depending on specific culture conditions. Primary PECs were small and exhibited a spindle-shaped or polygonal morphology. In the very early phases of primary culture, rapid changes in gene expression (e.g. of WT-1 and Pax-2) were observed. However, after prolonged culture primary PECs and podocytes still segregated clearly in a transcriptome analysis--demonstrating that the origin of primary cell cultures is important. Of the classical markers, synaptopodin and podoplanin expression were differentially regulated the most in primary PEC and podocyte cultures. However, no expression of any endogenous gene allowed to differentiate between the two cell types in culture. Finally, we show that the transcription factor WT1 is also expressed by PECs. In summary, genetic tagging of PECs and podocytes is a novel and necessary tool to derive pure primary cultures with proven origin. These cultures will be a powerful tool for the emerging field of parietal epithelial cell biology.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0034907PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3329559PMC
November 2012

Chemokine Cxcl9 attenuates liver fibrosis-associated angiogenesis in mice.

Hepatology 2012 May;55(5):1610-9

Medical Department III, University Hospital Aachen, Aachen, Germany.

Unlabelled: Recent data suggest that the chemokine receptor CXCR3 is functionally involved in fibroproliferative disorders, including liver fibrosis. Neoangiogenesis is an important pathophysiological feature of liver scarring, but a functional role of angiostatic CXCR3 chemokines in this process is unclear. We therefore investigated neoangiogenesis in carbon tetrachloride (CCl(4))-induced liver fibrosis in Cxcr3(-/-) and wildtype mice by histological, molecular, and functional imaging methods. Furthermore, we assessed the direct role of vascular endothelial growth factor (VEGF) overexpression on liver angiogenesis and the fibroproliferative response using a Tet-inducible bitransgenic mouse model. The feasibility of attenuation of angiogenesis and associated liver fibrosis by therapeutic treatment with the angiostatic chemokine Cxcl9 was systematically analyzed in vitro and in vivo. The results demonstrate that fibrosis progression in Cxcr3(-/-) mice was strongly linked to enhanced neoangiogenesis and VEGF/VEGFR2 expression compared with wildtype littermates. Systemic VEGF overexpression led to a fibrogenic response within the liver and was associated with a significantly increased Cxcl9 expression. In vitro, Cxcl9 displayed strong antiproliferative and antimigratory effects on VEGF-stimulated endothelial cells and stellate cells by way of reduced VEGFR2 (KDR), phospholipase Cγ (PLCγ), and extracellular signal-regulated kinase (ERK) phosphorylation, identifying this chemokine as a direct counter-regulatory molecule of VEGF signaling within the liver. Accordingly, systemic administration of Cxcl9 led to a strong attenuation of neoangiogenesis and experimental liver fibrosis in vivo.

Conclusion: The results identify direct angiostatic and antifibrotic effects of the Cxcr3 ligand Cxcl9 in a model of experimental liver fibrosis. The amelioration of liver damage by systemic application of Cxcl9 might offer a novel therapeutic approach for chronic liver diseases associated with increased neoangiogenesis.
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http://dx.doi.org/10.1002/hep.25545DOI Listing
May 2012