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The XIII Banff meeting, held in conjunction the Canadian Society of Transplantation in Vancouver, Canada, reviewed the clinical impact of updates of C4d-negative antibody-mediated rejection (ABMR) from the 2013 meeting, reports from active Banff Working Groups, the relationships of donor-specific antibody tests (anti-HLA and non-HLA) with transplant histopathology, and questions of molecular transplant diagnostics. The use of transcriptome gene sets, their resultant diagnostic classifiers, or common key genes to supplement the diagnosis and classification of rejection requires further consensus agreement and validation in biopsies. Newly introduced concepts include the i-IFTA score, comprising inflammation within areas of fibrosis and atrophy and acceptance of transplant arteriolopathy within the descriptions of chronic active T cell-mediated rejection (TCMR) or chronic ABMR. The pattern of mixed TCMR and ABMR was increasingly recognized. This report also includes improved definitions of TCMR and ABMR in pancreas transplants with specification of vascular lesions and prospects for defining a vascularized composite allograft rejection classification. The goal of the Banff process is ongoing integration of advances in histologic, serologic, and molecular diagnostic techniques to produce a consensus-based reporting system that offers precise composite scores, accurate routine diagnostics, and applicability to next-generation clinical trials.

The XIII Banff meeting, held in conjunction the Canadian Society of Transplantation in Vancouver, Canada, reviewed the clinical impact of updates of C4d‐negative antibody‐mediated rejection (ABMR) from the 2013 meeting, reports from active Banff Working Groups, the relationships of donor‐specific antibody tests (anti‐HLA and non‐HLA) with transplant histopathology, and questions of molecular transplant diagnostics. The use of transcriptome gene sets, their resultant diagnostic classifiers, or common key genes to supplement the diagnosis and classification of rejection requires further consensus agreement and validation in biopsies. Newly introduced concepts include the i‐IFTA score, comprising inflammation within areas of fibrosis and atrophy and acceptance of transplant arteriolopathy within the descriptions of chronic active T cell–mediated rejection (TCMR) or chronic ABMR. The pattern of mixed TCMR and ABMR was increasingly recognized. This report also includes improved definitions of TCMR and ABMR in pancreas transplants with specification of vascular lesions and prospects for defining a vascularized composite allograft rejection classification. The goal of the Banff process is ongoing integration of advances in histologic, serologic, and molecular diagnostic techniques to produce a consensus‐based reporting system that offers precise composite scores, accurate routine diagnostics, and applicability to next‐generation clinical trials.

The XVIth Banff Meeting for Allograft Pathology was held in Banff, Alberta, Canada, from September 19 to 23, 2022, as a joint meeting with the Canadian Society of Transplantation. In addition to a key focus on the impact of microvascular inflammation and biopsy-based transcript analysis on the Banff Classification, further sessions were devoted to other aspects of kidney transplant pathology, in particular T cell-mediated rejection, activity and chronicity indices, digital pathology, xenotransplantation, clinical trials, and surrogate endpoints. Although the output of these sessions has not led to any changes in the classification, the key role of Banff Working Groups in phrasing unanswered questions, and coordinating and disseminating results of investigations addressing these unanswered questions was emphasized. This paper summarizes the key Banff Meeting 2022 sessions not covered in the Banff Kidney Meeting 2022 Report paper and also provides an update on other Banff Working Group activities relevant to kidney allografts., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: Cure Glomerulonephropathy (CureGN) is an observational cohort study of patients with minimal change disease (MCD), focal segmental glomerulosclerosis (FSGS), membranous nephropathy (MN), or IgA nephropathy. We developed a conventional, consensus-based scoring system to document pathologic features for application across multiple pathologists and herein describe the protocol, reproducibility, and correlation with clinical parameters at biopsy., Methods: Definitions were established for glomerular, tubular, interstitial, and vascular lesions evaluated semiquantitatively using digitized light microscopy slides and electron micrographs, and reported immunofluorescence. Cases with curated pathology materials as of April 2019 were scored by a randomly assigned pathologist, with at least 10% of cases scored by a second pathologist. Scoring reproducibility was assessed using Gwet's agreement coefficient (AC)1 statistic and correlations with clinical variables were performed., Results: Of 800 scored biopsies (134 MCD, 194 FSGS, 206 MN, 266 IgA), 94 were scored twice (11.8%). Of 60 pathology features, 46 (76.7%) demonstrated excellent (AC1>0.8), and 12 (20.0%) had good (AC1 0.6-0.8) reproducibility. Mesangial hypercellularity scored as absent, focal, or diffuse had moderate reproducibility (AC1 = 0.58), but good reproducibility (AC1 = 0.71) when scored as absent or focal versus diffuse. The percent glomeruli scored as no lesions had fair reproducibility (AC1 = 0.34). Strongest correlations between pathologic features and clinical characteristics at biopsy included interstitial inflammation, interstitial fibrosis, and tubular atrophy with estimated glomerular filtration rate, foot process effacement with urine protein/creatinine ratio, and active crescents with hematuria., Conclusions: Most scored pathology features showed excellent reproducibility, demonstrating consistency for these features across multiple pathologists. Correlations between certain pathologic features and expected clinical characteristics show the value of this approach for future studies on clinicopathologic correlations and biomarker discovery., Competing Interests: The authors declare that they have no relevant financial interests or conflicts of interest., (© 2023 The Author(s). Published by S. Karger AG, Basel.)

The Thrombotic Microangiopathy Banff Working Group (TMA-BWG) was formed in 2015 to survey current practices and develop minimum diagnostic criteria (MDC) for renal transplant TMA (Tx-TMA). To generate consensus among pathologists and nephrologists, the TMA BWG designed a 3-Phase study. Phase I of the study is presented here. Using the Delphi methodology, 23 panelists with >3 years of diagnostic experience with Tx-TMA pathology listed their MDC suggesting light, immunofluorescence, and electron microscopy lesions, clinical and laboratory information, and differential diagnoses. Nine rounds (R) of consensus resulted in MDC validated during two Rs using online evaluation of whole slide digital images of 37 biopsies (28 TMA, 9 non-TMA). Starting with 338 criteria the process resulted in 24 criteria and 8 differential diagnoses including 18 pathologic, 2 clinical, and 4 laboratory criteria. Results show that 3/4 of the panelists agreed on the diagnosis of 3/4 of cases. The process also allowed definition refinement for 4 light and 4 electron microscopy lesions. For the first time in Banff classification, the Delphi methodology was used to generate consensus. The study shows that Delphi is a democratic and cost-effective method allowing rapid consensus generation among numerous physicians dealing with large number of criteria in transplantation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Afrouzian, Kozakowski, Liapis, Broecker, Truong, Avila-Casado, Regele, Seshan, Ambruzs, Farris, Buob, Chander, Cheraghvandi, Clahsen-van Groningen, de Almeida Araujo, Ertoy Baydar, Formby, Galesic Ljubanovic, Herrera Hernandez, Honsova, Mohamed, Ozluk, Rabant, Royal, Stevenson, Toniolo and Taheri.)

The Banff community summoned the TMA Banff Working Group to develop minimum diagnostic criteria (MDC) and recommendations for renal transplant TMA (Tx-TMA) diagnosis, which currently lacks standardized criteria. Using the Delphi method for consensus generation, 23 nephropathologists (panelists) with >3 years of diagnostic experience with Tx-TMA were asked to list light, immunofluorescence, and electron microscopic, clinical and laboratory criteria and differential diagnoses for Tx-TMA. Delphi was modified to include 2 validations rounds with histological evaluation of whole slide images of 37 transplant biopsies (28 TMA and 9 non-TMA). Starting with 338 criteria in R1, MDC were narrowed down to 24 in R8 generating 18 pathological, 2 clinical, 4 laboratory criteria, and 8 differential diagnoses. The panelists reached a good level of agreement (70%) on 76% of the validated cases. For the first time in Banff classification, Delphi was used to reach consensus on MDC for Tx-TMA. Phase I of the study (pathology phase) will be used as a model for Phase II (nephrology phase) for consensus regarding clinical and laboratory criteria. Eventually in Phase III (consensus of the consensus groups) and the final MDC for Tx-TMA will be reported to the transplantation community., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Afrouzian, Kozakowski, Liapis, Broecker, Truong, Avila-Casado, Regele, Seshan, Ambruzs, Farris, Buob, Chander, Cheraghvandi, Clahsen-van Groningen, de Almeida Araujo, Ertoy Baydar, Formby, Galesic Ljubanovic, Herrera Hernandez, Honsova, Mohamed, Ozluk, Rabant, Royal, Stevenson, Toniolo and Taheri.)

Kidney dysplasia is one of the most frequent causes of chronic kidney failure in children. While dysplasia is a histological diagnosis, the term 'kidney dysplasia' is frequently used in daily clinical life without histopathological confirmation. Clinical parameters of kidney dysplasia have not been clearly defined, leading to imprecise communication amongst healthcare professionals and patients. This lack of consensus hampers precise disease understanding and the development of specific therapies. Based on a structured literature search, we here suggest a common basis for clinical, imaging, genetic, pathological and basic science aspects of non-obstructive kidney dysplasia associated with functional kidney impairment. We propose to accept hallmark sonographic findings as surrogate parameters defining a clinical diagnosis of dysplastic kidneys. We suggest differentiated clinical follow-up plans for children with kidney dysplasia and summarize established monogenic causes for non-obstructive kidney dysplasia. Finally, we point out and discuss research gaps in the field., (© The Author(s) 2022. Published by Oxford University Press on behalf of the ERA.)

Kidney lifespan is a patient-oriented outcome that provides much needed context for understanding chronic kidney disease (CKD). Nephron endowment, age-associated decline in nephron number, kidney injury history and the intrinsic capacity of nephrons to adapt to haemodynamic and metabolic overload vary widely within the population. Defining percentiles of kidney function might therefore help to predict individual kidney lifespan and distinguish healthy ageing from progressive forms of CKD. In response to nephron loss, the remaining nephrons undergo functional and structural adaptations to meet the ongoing haemodynamic and metabolic demands of the organism. When these changes are no longer sufficient to maintain kidney cell homeostasis, remnant nephron demise occurs and CKD progression ensues. An individual's trajectory of glomerular filtration rate and albuminuria reflects the extent of nephron loss and adaptation of the remaining nephrons. Nephron overload represents the final common pathway of CKD progression and is largely independent of upstream disease mechanisms. Thus, interventions that efficiently attenuate nephron overload in early disease stages can protect remnant kidney cells and nephrons, and delay CKD progression. This Review provides a conceptual framework for individualized diagnosis, monitoring and treatment of CKD with the goal of maximizing kidney lifespan., (© 2021. Springer Nature Limited.)

Mutations in LAMB2, encoding laminin β2, cause Pierson syndrome and occasionally milder nephropathy without extrarenal abnormalities. The most deleterious missense mutations that have been identified affect primarily the N-terminus of laminin β2. On the other hand, those associated with isolated nephropathy are distributed across the entire molecule, and variants in the β2 LEa-LF-LEb domains are exclusively found in cases with isolated nephropathy. Here we report the clinical features of mild isolated nephropathy associated with 3 LAMB2 variants in the LEa-LF-LEb domains (p.R469Q, p.G699R, and p.R1078C) and their biochemical characterization. Although Pierson syndrome missense mutations often inhibit laminin β2 secretion, the 3 recombinant variants were secreted as efficiently as WT. However, the β2 variants lost pH dependency for heparin binding, resulting in aberrant binding under physiologic conditions. This suggests that the binding of laminin β2 to negatively charged molecules is involved in glomerular basement membrane (GBM) permselectivity. Moreover, the excessive binding of the β2 variants to other laminins appears to lead to their increased deposition in the GBM. Laminin β2 also serves as a potentially novel cell-adhesive ligand for integrin α4β1. Our findings define biochemical functions of laminin β2 variants influencing glomerular filtration that may underlie the pathogenesis of isolated nephropathy caused by LAMB2 abnormalities.

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 ( 1 ) asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; ( 2 ) UA crystal granulomas may form due to pre-existing CKD; and ( 3 ) 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., (Copyright © 2020 by the American Society of Nephrology.)

Acute kidney injury (AKI) is the clinical term used for decline or loss of renal function. It is associated with chronic kidney disease (CKD) and high morbidity and mortality. However, not all causes of AKI lead to severe consequences and some are reversible. The underlying pathology can be a guide for treatment and assessment of prognosis. The Kidney Disease: Improving Global Outcomes guidelines recommend that the cause of AKI should be identified if possible. Renal biopsy can distinguish specific AKI entities and assist in patient management. This review aims to show the pathology of AKI, including glomerular and tubular diseases., (© The Author(s) 2020. Published by Oxford University Press on behalf of ERA-EDTA.)

The XV. Banff conference for allograft pathology was held in conjunction with the annual meeting of the American Society for Histocompatibility and Immunogenetics in Pittsburgh, PA (USA) and focused on refining recent updates to the classification, advances from the Banff working groups, and standardization of molecular diagnostics. This report on kidney transplant pathology details clarifications and refinements to the criteria for chronic active (CA) T cell-mediated rejection (TCMR), borderline, and antibody-mediated rejection (ABMR). The main focus of kidney sessions was on how to address biopsies meeting criteria for CA TCMR plus borderline or acute TCMR. Recent studies on the clinical impact of borderline infiltrates were also presented to clarify whether the threshold for interstitial inflammation in diagnosis of borderline should be i0 or i1. Sessions on ABMR focused on biopsies showing microvascular inflammation in the absence of C4d staining or detectable donor-specific antibodies; the potential value of molecular diagnostics in such cases and recommendations for use of the latter in the setting of solid organ transplantation are presented in the accompanying meeting report. Finally, several speakers discussed the capabilities of artificial intelligence and the potential for use of machine learning algorithms in diagnosis and personalized therapeutics in solid organ transplantation., (© 2020 The Authors. American Journal of Transplantation published by Wiley Periodicals LLC on behalf of The American Society of Transplantation and the American Society of Transplant Surgeons.)

Acute tissue injury causes DNA damage and repair processes involving increased cell mitosis and polyploidization, leading to cell function alterations that may potentially drive cancer development. Here, we show that acute kidney injury (AKI) increased the risk for papillary renal cell carcinoma (pRCC) development and tumor relapse in humans as confirmed by data collected from several single-center and multicentric studies. Lineage tracing of tubular epithelial cells (TECs) after AKI induction and long-term follow-up in mice showed time-dependent onset of clonal papillary tumors in an adenoma-carcinoma sequence. Among AKI-related pathways, NOTCH1 overexpression in human pRCC associated with worse outcome and was specific for type 2 pRCC. Mice overexpressing NOTCH1 in TECs developed papillary adenomas and type 2 pRCCs, and AKI accelerated this process. Lineage tracing in mice identified single renal progenitors as the cell of origin of papillary tumors. Single-cell RNA sequencing showed that human renal progenitor transcriptome showed similarities to PT1, the putative cell of origin of human pRCC. Furthermore, NOTCH1 overexpression in cultured human renal progenitor cells induced tumor-like 3D growth. Thus, AKI can drive tumorigenesis from local tissue progenitor cells. In particular, we find that AKI promotes the development of pRCC from single progenitors through a classical adenoma-carcinoma sequence., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Background: Serum oxalate levels suddenly increase with certain dietary exposures or ethylene glycol poisoning and are a well known cause of AKI. Established contributors to oxalate crystal-induced renal necroinflammation include the NACHT, LRR and PYD domains-containing protein-3 (NLRP3) inflammasome and mixed lineage kinase domain-like (MLKL) protein-dependent tubule necroptosis. These studies examined the role of a novel form of necrosis triggered by altered mitochondrial function., Methods: To better understand the molecular pathophysiology of oxalate-induced AIK, we conducted in vitro studies in mouse and human kidney cells and in vivo studies in mice, including wild-type mice and knockout mice deficient in peptidylprolyl isomerase F (Ppif) or deficient in both Ppif and Mlkl., Results: Crystals of calcium oxalate, monosodium urate, or calcium pyrophosphate dihydrate, as well as silica microparticles, triggered cell necrosis involving PPIF-dependent mitochondrial permeability transition. This process involves crystal phagocytosis, lysosomal cathepsin leakage, and increased release of reactive oxygen species. Mice with acute oxalosis displayed calcium oxalate crystals inside distal tubular epithelial cells associated with mitochondrial changes characteristic of mitochondrial permeability transition. Mice lacking Ppif or Mlkl or given an inhibitor of mitochondrial permeability transition displayed attenuated oxalate-induced AKI. Dual genetic deletion of Ppif and Mlkl or pharmaceutical inhibition of necroptosis was partially redundant, implying interlinked roles of these two pathways of regulated necrosis in acute oxalosis. Similarly, inhibition of mitochondrial permeability transition suppressed crystal-induced cell death in primary human tubular epithelial cells. PPIF and phosphorylated MLKL localized to injured tubules in diagnostic human kidney biopsies of oxalosis-related AKI., Conclusions: Mitochondrial permeability transition-related regulated necrosis and necroptosis both contribute to oxalate-induced AKI, identifying PPIF as a potential molecular target for renoprotective intervention., (Copyright © 2019 by the American Society of Nephrology.)

Mitotic catastrophe (MC) is a major cause of podocyte loss in vitro and in vivo. We evaluated urine samples (n = 184 urine samples from diabetic patients; n = 41 patients) from diabetic patients and determined the presence of podocytes in the urine and studied their characteristics, specifically asking whether apoptosis versus MC is present. We also evaluated diabetic glomeruli in renal biopsy specimens by electron microscopy (n = 54). A battery of stains including the antibody to podocalyxin (PCX) were used. PCX and podocytes (PCX+podo) showed nuclear morphologies such as a i) mononucleated normal shape (8.7%), ii) large and abnormal shape (3.8%), iii) multinucleated with or without micronucleoli (31.2%), iv) mitotic spindles (8.2%), v) single nucleus and denucleation combined (10.3%), and vi) denucleation only (37.0%). Large size/abnormal shape, multinucleation, mitotic spindles, and a combination of single nucleus and denucleation were considered features of MC (53.5%). Dual staining of PCX+podo was positive for Glepp 1 (50%), whereas none of PCX+podo were positive for nephrin, podocin, leukocyte, or parietal epithelial cell markers (cytokeratin 8), annexin V, cleaved caspase-3, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. Ten percent of PCX+podo were positive for phosphorylated vimentin. Electron microscopy identified cellular and nuclear podocyte changes characteristic of MC. The majority of urine podocytes in diabetic patients showed MC, not apoptosis. This noninvasive approach may be clinically useful in determining progressive diabetic nephropathy or response to therapeutic intervention., (Copyright © 2019 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.)

Introduction: The Cure Glomerulonephropathy Network (CureGN) is a 66-center longitudinal observational study of patients with biopsy-confirmed minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, or IgA nephropathy (IgAN), including IgA vasculitis (IgAV). This study describes the clinical characteristics and treatment patterns in the IgA cohort, including comparisons between IgAN versus IgAV and adult versus pediatric patients., Methods: Patients with a diagnostic kidney biopsy within 5 years of screening were eligible to join CureGN. This is a descriptive analysis of clinical and treatment data collected at the time of enrollment., Results: A total of 667 patients (506 IgAN, 161 IgAV) constitute the IgAN/IgAV cohort (382 adults, 285 children). At biopsy, those with IgAV were younger (13.0 years vs. 29.6 years, P  < 0.001), more frequently white (89.7% vs. 78.9%, P  = 0.003), had a higher estimated glomerular filtration rate (103.5 vs. 70.6 ml/min per 1.73 m 2 , P  < 0.001), and lower serum albumin (3.4 vs. 3.8 g/dl, P  < 0.001) than those with IgAN. Adult and pediatric individuals with IgAV were more likely than those with IgAN to have been treated with immunosuppressive therapy at or prior to enrollment (79.5% vs. 54.0%, P  < 0.001)., Conclusion: This report highlights clinical differences between IgAV and IgAN and between children and adults with these diagnoses. We identified differences in treatment with immunosuppressive therapies by disease type. This description of baseline characteristics will serve as a foundation for future CureGN studies.

ER stress has emerged as a signaling platform underlying the pathogenesis of various kidney diseases. Thus, there is an urgent need to develop ER stress biomarkers in the incipient stages of ER stress-mediated kidney disease, when a kidney biopsy is not yet clinically indicated, for early therapeutic intervention. Cysteine-rich with EGF-like domains 2 (CRELD2) is a newly identified protein that is induced and secreted under ER stress. For the first time to our knowledge, we demonstrate that CRELD2 can serve as a sensitive urinary biomarker for detecting ER stress in podocytes or renal tubular cells in murine models of podocyte ER stress-induced nephrotic syndrome and tunicamycin- or ischemia-reperfusion-induced acute kidney injury (AKI), respectively. Most importantly, urinary CRELD2 elevation occurs in patients with autosomal dominant tubulointerstitial kidney disease caused by UMOD mutations, a prototypical tubular ER stress disease. In addition, in pediatric patients undergoing cardiac surgery, detectable urine levels of CRELD2 within postoperative 6 hours strongly associate with severe AKI after surgery. In conclusion, our study has identified CRELD2 as a potentially novel urinary ER stress biomarker with potential utility in early diagnosis, risk stratification, treatment response monitoring, and directing of ER-targeted therapies in selected patient subgroups in the emerging era of precision nephrology.

Collapsing glomerulopathy (CGP) is a pattern of kidney injury seen on renal biopsy with multiple associations and etiologies. It is most commonly described in African-Americans and others with recent African ancestry. The disease is rapidly progressive and often presents with abrupt onset of renal failure and nephrotic-range proteinuria. Since its description 30 years ago, this entity has transformed from a morphologic diagnosis typically seen in the setting of HIV infection to a complicated diagnosis with numerous etiologies, many of which are associated with underlying apolipoprotein L1 ( APOL1 )-risk variants or other genetic disorders. We review the evolution of CGP, and its history and proposed pathomechanisms. We also present the disease spectrum from our experience with emphasis on recognizing the lesion, distinguishing from mimics and linking the histopathological pattern to a specific cause. Our understanding continues to evolve as clinicians and scientists work toward a more complete understanding of the molecular pathways of injury in this disease and how these might be disrupted for therapeutic purposes. Much still remains to be discovered in CGP as the molecular underpinnings leading to disease are still not completely understood and no effective treatment exists despite the high morbidity. Based on this rapid evolution, CGP is a modern template of how we diagnose and think about kidney disease. The story of CGP represents the current shift in nephrology and nephropathology from morphology-alone-based diagnosis to a comprehensive approach including molecular diagnostics. We believe this new, holistic approach will lead to pathogenesis-centered diagnoses that will help to individualize risk stratification and treatment protocols.

Severe AKI is often associated with multiorgan dysfunction, but the mechanisms of this remote tissue injury are unknown. We hypothesized that renal necroinflammation releases cytotoxic molecules that may cause remote organ damage. In hypoxia-induced tubular epithelial cell necrosis in vitro , histone secretion from ischemic tubular cells primed neutrophils to form neutrophil extracellular traps. These traps induced tubular epithelial cell death and stimulated neutrophil extracellular trap formation in fresh neutrophils. In vivo , ischemia-reperfusion injury in the mouse kidney induced tubular necrosis, which preceded the expansion of localized and circulating neutrophil extracellular traps and the increased expression of inflammatory and injury-related genes. Pretreatment with inhibitors of neutrophil extracellular trap formation reduced kidney injury. Dual inhibition of neutrophil trap formation and tubular cell necrosis had an additive protective effect. Moreover, pretreatment with antihistone IgG suppressed ischemia-induced neutrophil extracellular trap formation and renal injury. Renal ischemic injury also increased the levels of circulating histones, and we detected neutrophil infiltration and TUNEL-positive cells in the lungs, liver, brain, and heart along with neutrophil extracellular trap accumulation in the lungs. Inhibition of neutrophil extracellular trap formation or of circulating histones reduced these effects as well. These data suggest that tubular necrosis and neutrophil extracellular trap formation accelerate kidney damage and remote organ dysfunction through cytokine and histone release and identify novel molecular targets to limit renal necroinflammation and multiorgan failure., (Copyright © 2017 by the American Society of Nephrology.)

Background: Castleman's disease (CD) is an uncommon, heterogeneous lympho-proliferative disorder leading to high circulating levels of interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF). Renal involvement has been only described in a limited number of small studies. Herein, we report a rare case of renal thrombotic microangiopathy (TMA) associated with CD and investigate the podocyte expression of VEGF in the renal biopsy prior to initiation of treatment., Case Presentation: An 18-year-old male presented with fever, diarrhea, diffuse lymphadenopathy, ascites and acute kidney injury. Laboratory tests for hemolytic uremic syndrome and thrombotic thrombocytopenic purpura were negative. The kidney biopsy showed TMA. An excisional lymph node biopsy was consistent with CD, plasma cell variant. Immunofluorescence staining showed suppressed podocyte VEGF expression. Chemotherapy that inhibits production of inflammatory mediators including IL-6 and VEGF led to complete recovery of renal function., Conclusions: Our case illustrates a rare renal histological feature of CD. IL-6 and VEGF are postulated to suppress glomerular VEGF expression, thereby causing renal TMA. Therapy directed against these inflammatory mediators may have important therapeutic implications.

Murine double minute-2 (MDM2) is an E3-ubiquitin ligase and the main negative regulator of tumor suppressor gene p53. MDM2 has also a non-redundant function as a modulator of NF-kB signaling. As such it promotes proliferation and inflammation. MDM2 is highly expressed in the unchallenged tubular epithelial cells and we hypothesized that MDM2 is necessary for their survival and homeostasis. MDM2 knockdown by siRNA or by genetic depletion resulted in demise of tubular cells in vitro. This phenotype was completely rescued by concomitant knockdown of p53, thus suggesting p53 dependency. In vivo experiments in the zebrafish model demonstrated that the tubulus cells of the larvae undergo cell death after the knockdown of mdm2. Doxycycline-induced deletion of MDM2 in tubular cell-specific MDM2-knockout mice Pax8rtTa-cre; MDM2f/f caused acute kidney injury with increased plasma creatinine and blood urea nitrogen and sharp decline of glomerular filtration rate. Histological analysis showed massive swelling of renal tubular cells and later their loss and extensive tubular dilation, markedly in proximal tubules. Ultrastructural changes of tubular epithelial cells included swelling of the cytoplasm and mitochondria with the loss of cristae and their transformation in the vacuoles. The pathological phenotype of the tubular cell-specific MDM2-knockout mouse model was completely rescued by co-deletion of p53. Tubular epithelium compensates only partially for the cell loss caused by MDM2 depletion by proliferation of surviving tubular cells, with incomplete MDM2 deletion, but rather mesenchymal healing occurs. We conclude that MDM2 is a non-redundant survival factor for proximal tubular cells by protecting them from spontaneous p53 overexpression-related cell death.

Five hundred eighty renal biopsies from a pool of 27850 archived cases were identified in which a myoglobin stain was performed because of atypical casts. Two hundred and thirty-eight (41%) of these biopsies were found to be positive for myoglobin casts. The morphology of the myoglobin casts ranged from light, almost translucent and refractile, to pink, to dark red and slightly brown granular casts by hematoxylin and eosin, to beaded globular casts that stained brightly fuchsinophilic with Masson trichrome and partially argyrophilic with silver methenamine. All biopsies displayed acute tubular injury associated with intratubular debris and thinning and vacuolization of tubular epithelium. Approximately 20% of myoglobin-positive biopsies showed calcium oxalate or phosphate deposition. Positive myoglobin staining was present in casts, proximal tubular epithelial cells without casts, and also dehisced epithelial cells. Collecting ducts and occasionally the distal tubular epithelium also stained positive. One case showed concurrent myeloma cast nephropathy with "fractured" casts and translucent myoglobin-positive casts. Herein, we describe the morphologic spectrum of myoglobin-positive casts. We conclude that utilization of myoglobin immunohistochemistry is advantageous and, when not available, knowledge of the morphologic spectrum is important., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Endothelial dysfunction is a central pathomechanism in diabetes-associated complications. We hypothesized a pathogenic role in this dysfunction of cathepsin S (Cat-S), a cysteine protease that degrades elastic fibers and activates the protease-activated receptor-2 (PAR2) on endothelial cells. We found that injection of mice with recombinant Cat-S induced albuminuria and glomerular endothelial cell injury in a PAR2-dependent manner. In vivo microscopy confirmed a role for intrinsic Cat-S/PAR2 in ischemia-induced microvascular permeability. In vitro transcriptome analysis and experiments using siRNA or specific Cat-S and PAR2 antagonists revealed that Cat-S specifically impaired the integrity and barrier function of glomerular endothelial cells selectively through PAR2. In human and mouse type 2 diabetic nephropathy, only CD68(+) intrarenal monocytes expressed Cat-S mRNA, whereas Cat-S protein was present along endothelial cells and inside proximal tubular epithelial cells also. In contrast, the cysteine protease inhibitor cystatin C was expressed only in tubules. Delayed treatment of type 2 diabetic db/db mice with Cat-S or PAR2 inhibitors attenuated albuminuria and glomerulosclerosis (indicators of diabetic nephropathy) and attenuated albumin leakage into the retina and other structural markers of diabetic retinopathy. These data identify Cat-S as a monocyte/macrophage-derived circulating PAR2 agonist and mediator of endothelial dysfunction-related microvascular diabetes complications. Thus, Cat-S or PAR2 inhibition might be a novel strategy to prevent microvascular disease in diabetes and other diseases., (Copyright © 2016 by the American Society of Nephrology.)

Acute kidney injury (AKI) involves nephron injury leading to irreversible nephron loss, ie, chronic kidney disease (CKD). Both AKI and CKD are associated with distinct histological patterns of tissue injury, but kidney atrophy in CKD involves tissue remodeling with interstitial inflammation and scarring. No doubt, nephron atrophy, inflammation, fibrosis, and renal dysfunction are associated with each other, but their hierarchical relationships remain speculative. To better understand the pathophysiology, we provide an overview of the fundamental danger response programs that assure host survival upon traumatic injury from as early as the first multicellular organisms, ie, bleeding control by coagulation, infection control by inflammation, epithelial barrier restoration by re-epithelialization, and tissue stabilization by mesenchymal repair. Although these processes assure survival in the majority of the populations, their dysregulation causes kidney disease in a minority. We discuss how, in genetically heterogeneous population, genetic variants shift balances and modulate danger responses toward kidney disease. We further discuss how classic kidney disease entities develop from an insufficient or overshooting activation of these danger response programs. Finally, we discuss molecular pathways linking, for example, inflammation and regeneration or inflammation and fibrosis. Understanding the causative and hierarchical relationships and the molecular links between the danger response programs should help to identify molecular targets to modulate kidney injury and to improve outcomes for kidney disease patients.

Crystals cause injury in numerous disorders, and induce inflammation via the NLRP3 inflammasome, however, it remains unclear how crystals induce cell death. Here we report that crystals of calcium oxalate, monosodium urate, calcium pyrophosphate dihydrate and cystine trigger caspase-independent cell death in five different cell types, which is blocked by necrostatin-1. RNA interference for receptor-interacting protein kinase 3 (RIPK3) or mixed lineage kinase domain like (MLKL), two core proteins of the necroptosis pathway, blocks crystal cytotoxicity. Consistent with this, deficiency of RIPK3 or MLKL prevents oxalate crystal-induced acute kidney injury. The related tissue inflammation drives TNF-α-related necroptosis. Also in human oxalate crystal-related acute kidney injury, dying tubular cells stain positive for phosphorylated MLKL. Furthermore, necrostatin-1 and necrosulfonamide, an inhibitor for human MLKL suppress crystal-induced cell death in human renal progenitor cells. Together, TNF-α/TNFR1, RIPK1, RIPK3 and MLKL are molecular targets to limit crystal-induced cytotoxicity, tissue injury and organ failure.

Severe GN involves local neutrophil extracellular trap (NET) formation. We hypothesized a local cytotoxic effect of NET-related histone release in necrotizing GN. In vitro, histones from calf thymus or histones released by neutrophils undergoing NETosis killed glomerular endothelial cells, podocytes, and parietal epithelial cells in a dose-dependent manner. Histone-neutralizing agents such as antihistone IgG, activated protein C, or heparin prevented this effect. Histone toxicity on glomeruli ex vivo was Toll-like receptor 2/4 dependent, and lack of TLR2/4 attenuated histone-induced renal thrombotic microangiopathy and glomerular necrosis in mice. Anti-glomerular basement membrane GN involved NET formation and vascular necrosis, whereas blocking NET formation by peptidylarginine inhibition or preemptive anti-histone IgG injection significantly reduced all aspects of GN (i.e., vascular necrosis, podocyte loss, albuminuria, cytokine induction, recruitment or activation of glomerular leukocytes, and glomerular crescent formation). To evaluate histones as a therapeutic target, mice with established GN were treated with three different histone-neutralizing agents. Anti-histone IgG, recombinant activated protein C, and heparin were equally effective in abrogating severe GN, whereas combination therapy had no additive effects. Together, these results indicate that NET-related histone release during GN elicits cytotoxic and immunostimulatory effects. Furthermore, neutralizing extracellular histones is still therapeutic when initiated in established GN., (Copyright © 2015 by the American Society of Nephrology.)

Recent advances show that human focal segmental glomerulosclerosis (FSGS) is a primary podocytopathy caused by podocyte-specific gene mutations including NPHS1, NPHS2, WT-1, LAMB2, CD2AP, TRPC6, ACTN4 and INF2. This review focuses on genes discovered in the investigation of complex FSGS pathomechanisms that may have implications for the current FSGS classification scheme. It also recounts recent recommendations for clinical management of FSGS based on translational studies and clinical trials. The advent of next-generation sequencing promises to provide nephrologists with rapid and novel approaches for the diagnosis and treatment of FSGS. A stratified and targeted approach based on the underlying molecular defects is evolving.

Murine double minute-2 (MDM2), an E3 ligase that regulates the cell cycle and inflammation, is highly expressed in podocytes. In podocyte injury, MDM2 drives podocyte loss by mitotic catastrophe, but the function of MDM2 in resting podocytes has not been explored. Here, we investigated the effects of podocyte MDM2 deletion in vitro and in vivo. In vitro, MDM2 knockdown by siRNA caused increased expression of p53 and podocyte death, which was completely rescued by coknockdown of p53. Apoptosis, pyroptosis, pyronecrosis, necroptosis, ferroptosis, and parthanatos were excluded as modes of occurrence for this p53-overactivation-related cell death (here referred to as podoptosis). Podoptosis was associated with cytoplasmic vacuolization, endoplasmic reticulum stress, and dysregulated autophagy (previously described as paraptosis). MDM2 knockdown caused podocyte loss and proteinuria in a zebrafish model, which was consistent with the phenotype of podocyte-specific MDM2-knockout mice that also showed the aforementioned ultrastructual podocyte abnormalities before and during progressive glomerulosclerosis. The phenotype of both animal models was entirely rescued by codeletion of p53. We conclude that MDM2 maintains homeostasis and long-term survival in podocytes by preventing podoptosis, a p53-regulated form of cell death with unspecific features previously classified as paraptosis., (Copyright © 2015 by the American Society of Nephrology.)

Purpose: Congenital urinary tract obstruction is a leading cause of renal maldevelopment and pediatric kidney disease. Nonetheless, few groups have examined its molecular pathogenesis in humans. We evaluated the role of BMP-7, a protein required for renal injury repair and nephrogenesis, in disease progression in patients with obstructive uropathy., Materials and Methods: Whole kidney and cell specific BMP-7 expression was examined in a murine model of unilateral ureteral obstruction and in patients with congenital ureteropelvic junction obstruction. Findings were correlated with molecular markers of renal injury and clinical parameters., Results: Unilateral ureteral obstruction led to a dramatic decrease in BMP-7 expression in the proximal and distal tubules before the onset of significant loss of renal architecture and fibrosis, suggesting that this is a critical molecular event that drives early stage disease progression. Loss of BMP-7 expression then extended to the collecting ducts and glomeruli in end stage kidney disease. When translating these findings to patients with ureteropelvic junction obstruction, global loss of BMP-7 expression correlated with a decreased number of nephrons, loss of renal architecture, severe renal fibrosis and loss of kidney function., Conclusions: Given that BMP-7 has a critical role in renal injury repair and nephrogenesis, these findings show that cell specific changes in BMP-7 expression contribute to the onset of irreversible renal injury and impaired kidney development secondary to congenital urinary tract obstruction. Accordingly therapies that target these cell populations to restore BMP-7 activity may limit disease progression in patients with obstructive uropathy., (Copyright © 2015 American Urological Association Education and Research, Inc. Published by Elsevier Inc. All rights reserved.)

Background: Recurrent focal segmental glomerular sclerosis (rFSGS) in renal transplant recipients (RTR) is difficult to predict and treat. Early rFSGS is likely from circulating factors and preformed antibodies., Methods: We present the case of a 23-year-old white man who presented with rFSGS and acute renal failure, requiring dialysis 9-months after a 1-haplotype matched living-related transplant. We retrospectively analyzed serum samples from various clinical stages for rFSGS biomarkers: serum glomerular albumin permeability (Palb), soluble urokinase-type plasminogen activator receptor (suPAR) serum level with suPAR-β3 integrin signaling on human podocytes, and angiotensin II type I receptor-antibody (AT1R-Ab) titer., Results: All biomarkers were abnormal at 1-year pre-transplant prior to initiation of dialysis and at the time of transplant. After initiation of hemodialysis, β3 integrin activity on human podocytes, in response to patient serum, as well as AT1R-Ab were further elevated. At the time of biopsy-proven recurrence, all biomarkers were abnormally high. One week after therapy with aborted plasmapheresis (secondary to intolerance), and high dose steroids, the Palb and suPAR-β3 integrin activity remained significantly positive. After 12-weeks of treatment with high-dose steroids, rituximab, and galactose, the patient remained hemodialysis-dependent. Three-months after his initial presentation, we commenced adrenocorticotropic hormone (ACTH, Acthar(®) Gel), 80 units subcutaneously twice weekly. Four-weeks later, he was able to discontinue dialysis. After 8-months of maintenance ACTH therapy, his serum creatinine stabilized at 1.79 mg/dL with <1 g of proteinuria., Conclusion: ACTH therapy was associated with improvement in renal function within 4 weeks. The use of rFSGS biomarkers may aid in predicting development of rFSGS.