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Background: Marked podocyte depletion is an established key feature of glomerulosclerosis (FSGS). However, little is known about the consequences of mild podocyte loss. In addition, activation of parietal epithelial cells (PECs) has been proposed as a major effector in FSGS. This study investigates the consequences of graded podocyte depletion, the hypertrophic response of podocytes and associations with PEC activation and thereby glomerulosclerosis. Method(s): We induced selective podocyte depletion in PodCreiDTR mice by injection of diphtheria toxin (DT) at different doses. L-NAME induced hypertension was used as a second hit challenge after mild podocyte loss. The mammalian target of rapamycin (mTOR) signalling pathway was manipulated using mTOR inhibitors (RAD001 and INK128). Podocyte depletion and hypertrophy were examined by 3D analysis of whole glomeruli in optically-cleared kidney slices. Result(s): PodCreiDTR mice injected with a low dose of DT presented mild podocyte depletion, compensatory podocyte hypertrophy and reversible albuminuria without PEC activation or glomerulosclerosis, even following a second hit challenge (high blood pressure), suggesting a protective role of podocyte hypertrophy. Injection of a higher dose of DT in PodCreiDTR mice led to greater podocyte loss and hypertrophy. However, these mice showed PEC activation, glomerulosclerosis and persistent albuminuria, suggesting there is a limit for the protective role of podocyte hypertrophy. Pharmacological inhibition of mTOR during the induction of mild podocyte depletion led to persistent and exacerbated albuminuria, impairment of podocyte hypertrophy, PEC activation and glomerulosclerosis. Conclusion(s): Podocyte hypertrophy via mTOR signalling is required for the adaptive hypertrophic response of remaining podocytes after mild podocyte depletion. These results are relevant for the use of mTOR inhibitors in the context of FSGS and CKD.

Background: Podocyte depletion is a common feature of glomerulosclerosis (FSGS), but its role in crescentic nephritis remains unclear. This study combined genetic tagging of podocytes with three different optical clearing techniques to determine podocyte depletion in whole glomeruli from mice with crescentic nephritis. Method(s): Podocyte nuclei were labeled by eGFP-histone in of adult male Pod-rtTA/ H2B-eGFP mice by oral doxycycline, followed by a 7-day wash out period, and a single intra-peritoneal injection of nephrotoxic serum (NTS; 5mg/g). Experimental mice were killed 10 days after NTS injection, and compared to age-matched controls. Kidney slices were optically cleared with SCALE-A4, CLARITY and Ethyl Cinnamate (ECi). Highresolution serial optical images were obtained by confocal and two-photon microscopy. Result(s): Mean podocyte number per mouse showed very low variability within controls (1-5% variability, P>0.05) and within NTS-injected mice (1-9% variability, P>0.05) independent of the clearing technique. In NTS-injected mice, a similar degree of average podocyte depletion per mouse was identified with all clearing methods (60-63%, P<0.001). The technical (dis-)advantages of each clearing protocol were also analysed, including optimal penetration depth and resolution, compatibility with immunofluorescence, microscopy set-ups, and cost-efficiency. Importantly, total podocyte number per glomerulus showed great variability: controls (mean: 78,81; ranging from 49 to 128 podocytes per glomerulus) and in NTS-injected mice (mean: 29,99; ranging from 1 to 95 podocytes per glomerulus). Using the lowest value for podocyte number in controls as a cut-off reference, only 78% of analysed glomeruli (141 of 180) from NTS-injected mice had a certain degree of podocyte depletion. While deposition of the NTS within glomeruli occurred in a global and homogeneous fashion, podocyte loss was focal. Conclusion(s): This study has identified early focal podocyte depletion in mic

Background: Optical clearing and advanced light microscopy have revolutionised three-dimensional quantification in cell biology. Here, we present a Systematic Pipeline of Enhanced Clarification for Three-dimensional Rendering and Unbiased Morphometrics (SPECTRUM) as a unique tool for the comprehensive analysis of glomerular health and disease. Method(s): SPECTRUM is based on a combination of single cell identification (ie. lineage tracing), optical clearing, advanced light microscopy with single cell resolution, and 3D morphometrics. Podocytes and parietal epithelial cells (PECs) were genetically labelled with eGFP using inducible mouse systems (POD or PEC -rtTA/H2B-eGFP). Crescentic nephritis was used as a validation model. Several optical clearing protocols were optimized for kidney tissue, including aqueous, hydrogel, and solvent-based approaches. Image acquisition was based on whole structures (ie. glomeruli and lesions) using light sheet, confocal and two-photon microscopy. Subsequent tissue de-clarification with immunolabelling and classical histopathology allowed the combination of 3D and 2D analyses. Result(s): While IgG deposition showed a homogeneous distribution among all analysed glomeruli, only 80 showed signs of podocyte loss (podocyte loss per glomerulus of about 60). Only glomerular lesions showed significant increases in numbers of PECs (sign of PEC activation) in close association with reductions in glomerular capillary volume (sign of capillary injury). PEC activation was confirmed via immunofluorescence in recycled tissue samples (ie. de-novo CD44 expression). Based on 3D analysis of intraglomerular lesion location, we identified a progressive pattern from localised tubular lesions to segmental lesions and development of atubular glomeruli. Conclusion(s): SPECTRUM provides new roadmap for morphometrics in the kidney. In crescentic nephritis, SPECTRUM revealed that despite of uniform IgG deposition, there was focal lesion development and podocyte

Contains fulltext : 203024.pdf (publisher's version ) (Open Access), In November 2017, the Kidney Disease: Improving Global Outcomes (KDIGO) initiative brought a diverse panel of experts in glomerular diseases together to discuss the 2012 KDIGO glomerulonephritis guideline in the context of new developments and insights that had occurred over the years since its publication. During this KDIGO Controversies Conference on Glomerular Diseases, the group examined data on disease pathogenesis, biomarkers, and treatments to identify areas of consensus and areas of controversy. This report summarizes the discussions on primary podocytopathies, lupus nephritis, anti-neutrophil cytoplasmic antibody-associated nephritis, complement-mediated kidney diseases, and monoclonal gammopathies of renal significance.

The cellular origins of glomerulosclerosis involve activation of parietal epithelial cells (PECs) and progressive podocyte depletion. While mammalian target of rapamycin-mediated (mTORmediated) 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.Copyright © 2019, American Society for Clinical Investigation.

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.Copyright © 2019 International Society of Nephrology

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.Copyright © 2019 International Society of Nephrology

Chronic kidney disease can be understood as a pathological reduction in the number of functional glomeruli. It is a frequent medical problem and one of the major independent risk factors for cardiovascular morbidity and mortality. In humans, glomeruli/nephrons are generated during the prenatal period (glomerular endowment), which may be impaired by multiple conditions. After birth, glomeruli are progressively lost - mostly due to glomerular scarring (focal segmental glomerulosclerosis; FSGS). Multiple independent studies have shown that significant loss of glomerular visceral epithelial cells (podocytes) is sufficient to induce FSGS. It is generally believed that podocytes cannot renew themselves and it has been generally assumed that their number is determined at birth (podocyte endowment). However, there are several lines of experimental evidence showing that podocytes can be replenished in the postnatal period. First, a limited reserve of podocytes has been reported on Bowman's capsule, which may be associated with body growth and increases in glomerular size between childhood and adulthood. Second, two intrinsic progenitor cell niches have been proposed to replenish podocytes throughout adult life and in association with glomerular injury and podocyte loss: parietal epithelial cells and/or cells of the renin lineage. While there is increasing evidence supporting postnatal podocyte gain, controversy remains about the involved signalling pathways and the efficiency of these sources to prevent nephron loss.Copyright © 2018 Elsevier Ltd

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Item does not contain fulltext, 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/GRfl/fl mice. Pax8-Cre/GRfl/fl 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. In vitro, 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.

Item does not contain fulltext, Minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS) are the key histological findings in patients with idiopathic nephrotic syndrome (INS). Although MCD and idiopathic FSGS are often considered to represent separate entities based on differences in their presenting characteristics, histology and outcomes, little evidence exists for this separation. We propose that MCD and idiopathic FSGS are different manifestations of the same progressive disease. The gradual development of FSGS in patients with non-remitting or relapsing INS has been well documented. Moreover, FSGS is the uniform result of substantial podocyte loss in animal models, and a common feature of virtually all progressive human glomerulopathies. As evidence suggests a common aetiology, the pathogenesis of MCD and idiopathic FSGS should be studied together. In clinical trials, idiopathic FSGS should be considered to represent an advanced stage of disease progression that is less likely to respond to treatment than the earlier stage of disease, which is usually defined as MCD.