Kidney International

Key PointsO_LIRenin deficiency in renin-lineage cells worsened crescentic injury and impaired cell migration, revealing a protective role for renin in crescentic glomerulonephritis. C_LIO_LILoss of renin shifted renin-lineage cells signaling toward interferon/STAT1-driven C_LIO_LIRenin-lineage cell ablation in crescentic glomerulonephritis induced a less inflammatory disease time-course. C_LI BackgroundThe adult juxtaglomerular renin-lineage cell (RLC) niche contributes to intraglomerular repair after injury, but their role in highly inflammatory crescentic glomerulonephritis (cGN) remains unclear. While angiotensin II-AT1R signaling promotes fibrosis and inflammation, the contribution of the RLCs, and of renin expression within RLCs, to cGN outcome has not been investigated. MethodsWe used tdTomato lineage-tracing to track RLCs in wild-type (WT) and renin-knockout (RenKO) mice following cGN induction. RLC migration and glomerular injury were quantified histologically. Single-cell RNA sequencing was performed on isolated tdTomato-positive cells at day 10 and 21 after injury to characterize transcriptional programs. Disease progression was additionally examined in mice with diphtheria toxin A-mediated (DTA) RLC ablation. ResultsRLCs were detected within injured glomeruli during cGN, with sporadic localization to crescentic lesions. Genetic renin deletion in RLCs worsened cGN outcomes, with RenKO mice developing increased albuminuria (by 306%), crescent formation (by 50%) and podocyte loss (by 15%) by day 21 compared to WT controls. Renin-deficient RLCs exhibited a reduced intraglomerular migratory response with decreased colocalization with mesangial and podocytes cell markers. Single-cell transcriptomic analysis supports an immunomodulatory reparative phenotype in WT RLCs. In contrast, RenKO RLCs displayed enrichment of interferon-stimulated genes and pathways suppressing cell migration. RLC ablation reduced macrophage infiltration, but did not alter disease progression, suggesting compensatory cellular mechanisms. ConclusionsRenin expression supports the plasticity and injury-associated responses of RLCs during cGN. Loss of renin shifts RLCs toward an interferon-driven inflammatory and antimigratory phenotype that aggravates glomerular injury, while ablation of the RLCs may be compensated without major outcome changes.

Uromodulin, a protein made uniquely by the kidney, is protective against acute kidney injury. An integrated transcriptomic and multiplexed spatial protein imaging was used to uncover early cellular and molecular pathophysiological mechanisms following murine kidney ischemia and reperfusion injury (IRI) and better define the role of Uromodulin at the early stage of injury. Six hours following IRI, there was a pan-nephronal transcriptomic response with activation of common pathways but also unique gene expression signatures for each nephron segment. Cell-cell communications and epithelial-immune spatial interactions most prominently involved thick ascending limbs and distal nephron segments with distinct immune zonation in the inner stripe of the outer medulla. Uromodulin deficiency swayed the tubular transcriptomic signatures towards more severe injury and inflammation with altered macrophage communication. Uromodulin deficiency also caused partial loss of immune zonation and a shift towards broader epithelial-immune interactions in the outer stripe and cortex. Uromodulin inhibited activation of the Nlrc4-dependent alternative inflammasome pathway in macrophages, where the production of IL-1{beta} predominantly targets other immune and collecting duct (CD) cells. Indeed, Uromodulin deficiency induced the expression of CD8 in CD cells which acquire a proinflammatory phenotype linked to spatial niches containing immune cells. The presence of CD8+ CD cells was validated in human kidney biopsies. In conclusion, our findings support a role for Uromodulin in spatially confining the immune system around TAL cells in the inner stripe away from the vulnerable outer stripe in early injury. Uromodulin also inhibits the inflammasome-mediated macrophage-epithelial crosstalk that could induce collecting duct cells towards more inflammatory signaling.

Alport syndrome (AS) is a major cause of chronic kidney failure and affects millions of people worldwide. Pathogenic variants in COL4A3, COL4A4, and COL4A5, which encode the collagen IV 345 scaffold, compromise glomerular basement membrane (GBM) structure and function. However, the molecular mechanisms linking the >5,000 reported variants to disease pathology remain poorly understood. To address this gap, we previously examined a distinctive variant, an 8-amino acid "Z-appendage", added to the NC1 domain of the 3 chain. Knock-in mice carrying this variant developed GBM abnormalities and proteinuria, implicating the NC1 hexamer as a critical determinant of GBM function and suggesting that the hexamer surface contains bioactive sites that may mediate signaling and/or organization of macromolecular complexes. Given that approximately 80% of AS cases are associated with COL4A5 variants, including many within the NC1 hexamer, we asked whether relocating the Z-appendage from the 3 NC1 subunit to the 5 subunit produces similar pathology. Strikingly, Col4a5-Z mice did not develop proteinuria and showed only minor changes in GBM morphology. In contrast, the variant induced marked thickening of Bowmans capsule, accompanied by increased deposition of the collagen IV 121 scaffold, increased fibrillar collagen, and cellular deposits. Structural modeling predicts that the collagen IV 565-121 scaffold bearing two Z-appendages adopts an aberrant secondary structure that may stiffen the scaffold and occlude binding sites. Together, these findings reveal a bioactive role for the collagen IV 565-121 scaffold in the Bowmans capsule basement membrane, with potential implications for other 565-121containing tissues such as the aorta and bladder.

Introduction: Podocyte injury is central to the pathogenesis of most glomerulonephritides (GN) and causes segmental glomerulosclerotic lesions that predict progression in IgA Nephropathy (IgAN). Recent advances in high-resolution microscopy and AI-assisted image analysis have enabled detailed quantification of podocyte foot process (FP) morphology. However, whether nanoscale podocyte morphometrics can predict disease progression or treatment response in GN has not been investigated. Aim: To evaluate whether nanoscale podocyte morphometric parameters predict clinical characteristics, disease progression, and treatment response in GN, with a focus on IgAN. Method: Podocyte morphometrics were analyzed in kidney biopsies from patients with GN using high-resolution microscopy and the deep learning-based tool Automatic Morphometric Analysis of Podocytes (AMAP). Four morphometric parameters were quantified: slit diaphragm length (SDL), FP area, FP circularity and FP perimeter. These parameters were correlated with clinical characteristics, conventional electron microscopy (EM) findings and longitudinal follow-up data. Results: The study included 37 patients with GN from Danderyd University Hospital (Stockholm, Sweden), with IgAN representing the largest diagnostic subgroup (n = 19). The median follow-up for the cohort was 3.0 years. SDL correlated significantly with urine albumin-to-creatinine ratio (uACR; p = 0.021), whereas conventional EM measurements did not (p = 0.22). Within the IgAN subgroup, lower SDL was associated with a steeper decline in eGFR, higher FP area with increased long-term proteinuria, and higher FP circularity with improvement in uACR during the first year. The association between lower SDL and eGFR decline remained as a trend in IgAN patients not treated with corticosteroids (p = 0.068) but was absent in the treatment group (p = 0.59). Conclusion: In this proof-of-concept study, nanoscale podocyte morphometrics demonstrated greater sensitivity than conventional EM in quantifying podocyte injury and predicting progression in IgAN. These findings suggest that high-resolution morphometrics may improve risk stratification in IgAN but require validation in larger, independent cohorts before clinical implementation.

Metabolic dysfunction-associated kidney disease (MDAKD) is closely linked to dietary excess, but models that capture early kidney injury without obesity are limited. We fed male C57BL/6J (6J) and C57BL/6N (6N) mice a high-fat, high-sodium (HF/HNa) or control diet for 16 weeks. HF/HNa feeding did not alter body weight, adiposity, or total food intake; however, it increased dietary energy and sodium exposure, kidney mass, water intake, and urine volume. GFR declined modestly in 6J mice, whereas 6N mice maintained or slightly increased GFR. Both substrains showed increased urinary albumin, creatinine, KIM-1, and NGAL, while cystatin C rose predominantly in 6N mice, indicating strain-dependent tubular injury. Whole-kidney trichrome staining revealed increased fibrotic area with HF/HNa, particularly in 6N mice, without significant changes in glomerular morphology. In isolated renal mitochondria, oxygen consumption was preserved, but ATP production and ATP:O ratios were reduced, with unchanged citrate synthase activity and OXPHOS protein abundance, consistent with early mitochondrial bioenergetic uncoupling. Exploratory urinary proteomics in 6J mice identified HF/HNa-associated changes in proteins linked to tubular stress and extracellular matrix remodeling. These findings define an early MDAKD-like renal phenotype with strain-specific functional responses, tubular injury, fibrosis, and impaired mitochondrial ATP efficiency. Translational StatementMetabolic Dysfunction-Associated Kidney Disease (MDAKD) is a leading driver of chronic kidney disease (CKD) in the world. In addition to obesity and related comorbidities, renal mitochondrial dysfunction is thought to be a key contributor to the development of CKD in patients with MDAKD; however, few models recapitulate the progression of MDAKD. We couple well-established mouse models of obesity, namely the C57Bl/6J and C57Bl/6N mouse lines, with a high-fat, high-salt diet to induce renal mitochondrial dysfunction, leading to early stages of MDAKD as indicated by widespread fibrosis and mild reduction in glomerular filtration rate, though these effects were strain-dependent. We identify diet-induced mitochondrial dysfunction as a common feature in both mouse strains, suggesting impairments in mitochondrial respiration and oxidative ATP production are indeed a contributing factor to the development of MDAKD. This study highlights the role of energetic impairments in the pathogenesis of MDAKD and may guide future therapies for CKD.

IntroductionThere remains considerable debate as to the cause of the epidemic of Mesoamerican Nephropathy (MeN). We have previously reported early loss of estimated glomerular filtration rate (eGFR) as a surrogate for disease onset in a population-representative cohort study of young-adults at risk of disease from Northwest Nicaragua. Using a nested case-control approach we analysed urine and serum proteins surrounding this timepoint with the aim of gaining insight into the primary disease aetiology. MethodsWe conducted label-free ultra high-performance liquid chromatography mass-spectrometry based proteomics using urine samples collected at the study visit before, and at, first observed eGFR loss amongst cases and compared results to matched controls. We then performed direct protein measurements in a discovery cohort followed by quantification of serum total immunoglobulin E (stIgE) at multiple timepoints in a replication cohort. ResultsProteomic analysis demonstrated no differences in the levels of any single protein between cases and controls (n=25 each), at either timepoint, after correction for multiple comparisons. However, functional enrichment analysis demonstrated upregulation of adaptive immune pathways amongst cases. Direct measurements in the discovery cohort using high-sensitivity PCR-based immunoassay (n=21 controls, 19 cases) demonstrated higher stIgE in cases at the study visit immediately prior to first observed eGFR loss (mean difference 810kU/L, 95% confidence interval (CI): 162-1457kU/L). In the replication cohort (n=22 cases, 21 controls) an stIgE level >500kU/L measured by electrochemiluminescence in study samples from any timepoint in the 3 years prior to the first observed loss of eGFR was independently associated with case status when compared to samples from controls at matched visits (adjusted Odds Ratio: 8.1, 95% CI: 1.4-47.8). DiscussionA high level of stIgE precedes loss of eGFR in those at risk of MeN. Understanding what leads to this rise is likely to be key to understanding the cause of the MeN epidemic. Lay SummaryMesoamerican nephropathy describes an epidemic-level chronic kidney disease impacting rural working age adults in Central America. Although a number of exposures, including occupational heat exposure, have been proposed the cause of the epidemic, there remains much debate as to the primary aetiology of the disease. In this study we interrogated urine and blood samples from individuals from affected communities at risk of disease both before and after they develop kidney dysfunction. Using two different approaches, analysis of both urine and blood samples provide evidence of upregulation of immunoglobulin-E (IgE) related pathways in the 2-3 years before individuals develop evidence of kidney disease. Infections (particularly those involving parasites) and allergic reactions, but not heat exposure, have been reported to increase IgE levels. Going forwards, understanding the cause of this increase in IgE in individuals at risk of disease is likely to provide insight into the cause of Mesoamerican Nephropathy epidemics.

Acute kidney injury (AKI) is a sudden episode of kidney failure linked to a wide range of health conditions. High mortality in AKI highlights the need to identify new therapeutic approaches. Homeostasis in multicellular organisms is exquisitely regulated by phagocytosis of apoptotic cells, also known as efferocytosis. Apoptotic cells are frequently observed at sites of inflammation, including in AKI. Engulfment and cell motility protein-1 (ELMO1) is a regulator of the actin cytoskeleton that promotes apoptotic cell removal by phagocytes during efferocytosis. Mutations in the human ELMO1 gene are linked with diabetic nephropathy and, in animal models of this disease, high ELMO1 levels promote renal dysfunction. However, the role of ELMO1 in AKI was not known. Here, we describe the links between ELMO1 and kidney pathology and test global and tissue-specific ELMO1-deficient mice in models of AKI. While global loss of Elmo1 expression did not impact the immediate loss of renal function after ischemia-reperfusion elicited AKI, ELMO1 deficiency resulted in increased tissue injury in AKI caused by cisplatin injection. Cisplatin induced robust renal cell apoptosis that was significantly elevated in mice with the global loss of ELMO1, but not in mice with the macrophage-specific Elmo1 deletion. Using primary cell culture and immunofluorescence approaches, we highlight the role of ELMO1 in efferocytosis by several renal cell types, suggesting possible additive effects during nephrotoxic injury.

Claudin-4 (CLDN4) is a key determinant of paracellular ion transport in the distal nephron, where it contributes to chloride permeability and transepithelial resistance. Although CLDN4 knockout mice exhibit hypercalciuria, the epithelial mechanism linking CLDN4 to calcium permeability and kidney stone disease remains unclear. We examined the molecular and functional effects of a kidney stone-associated CLDN4 variant P74L which was identified in two unrelated individuals with nephrolithiasis from the Bern Kidney Stone Registry. Using doxycycline-inducible epithelial cell models expressing human wild-type (WT) or mutant CLDN4, we show that the P74L variant displayed reduced protein stability, impaired junctional incorporation, and decreased surface expression. In contrast to WT CLDN4, whose overexpression increased transepithelial electrical resistance and restricted paracellular sodium, chloride, and calcium permeability, P74L CLDN4 failed to confer these effects. Expression of P74L CLDN4 was associated with reduced CLDN3 and CLDN7 messenger abundance without significant changes in CLDN8 or transcriptional regulation of other distal calcium (and other ion) transport genes. Together, these findings identify CLDN4 P74L as a loss-of-function variant that increases epithelial calcium permeability, possibly leading to increased calcium back-flux in the distal nephron relevant to nephrolithiasis.

Background: Lower urine pH has been associated with reduced kidney function and an increased risk of kidney disease; however, its prognostic and pathological significance in biopsy-proven kidney disease remains unclear. A recent study demonstrated that medullary cast formation is independently associated with adverse renal outcomes beyond established predictors such as interstitial fibrosis and tubular atrophy (IFTA), yet its clinical determinants are not fully elucidated. Urine pH reflects the intratubular acid-base microenvironment and may contribute to tubular obstruction through cast formation. In this study, we examined kidney outcomes in patients undergoing native kidney biopsy, and the associations of urine pH with medullary cast formation. Methods: Among 1167 adults who underwent native kidney biopsy between 2011 and 2024, 503 patients with evaluable medullary tissue were included in this retrospective observational cohort study. Urine pH was analyzed in relation to clinical and histological variables and kidney outcomes. The primary outcome was a 40% decline in estimated glomerular filtration rate (eGFR) or initiation of renal replacement therapy. Results: The mean baseline eGFR was 54.3 mL/min/1.73 m2, the mean urine pH was 6.15, and the median urinary protein excretion was 1.1 g/gCr. During a median follow-up of 2.11 years, 113 patients (22.5%) reached the kidney outcome. Kaplan-Meier analysis showed that lower urine pH was associated with a higher risk of kidney outcomes. In Cox proportional hazards models adjusted for proteinuria, baseline eGFR, and IFTA score, urine pH remained independently associated with kidney outcomes (hazard ratio, 0.69; 95% confidence interval, 0.51-0.91). Inclusion of urine pH improved prognostic discrimination beyond established risk factors (Harrell C-index, 0.642 to 0.654). Lower urine pH was also associated with greater medullary cast formation. Conclusion: In patients undergoing native kidney biopsy, lower urine pH was independently associated with adverse kidney outcomes and greater medullary cast formation.

BackgroundRenal biopsy provides important prognostic information for patients with chronic kidney disease (CKD), primarily through evaluation of cortical histopathological lesions, including interstitial fibrosis and tubular atrophy (IFTA). However, the prognostic significance of renal medullary lesions remains poorly understood. We investigated whether medullary pathological findings are independently associated with renal outcomes and whether they improve prognostic discrimination beyond conventional cortical assessments. MethodsThis single-center retrospective cohort study screened 1,136 adult patients who underwent native kidney biopsy between 2011 and 2023. After applying predefined inclusion and exclusion criteria, 488 patients with adequate medullary tissue were included in the final analysis. Medullary fibrosis, inflammatory cell infiltration, and cast formation were semi-quantitatively graded and evaluated as predictors of renal outcomes. The primary outcome was a composite of [≥]40% decline in estimated glomerular filtration rate (eGFR) or initiation of renal replacement therapy. Associations were assessed using Cox proportional hazards models with sequential adjustment for demographic factors, baseline eGFR, proteinuria, and cortical IFTA. Model discrimination was evaluated using Harrells concordance-index (C-index). ResultsDuring a median follow-up of 2.3 years, 112 patients (23.0%) reached the composite renal outcome. In multivariable analysis adjusted for age, sex, baseline eGFR, and proteinuria, medullary cast formation was significantly associated with adverse renal outcomes (hazard ratio [HR] 1.70, 95% confidence interval [CI] 1.28-2.24). This association remained significant after additional adjustment for IFTA (HR 1.64, 95% CI 1.21-2.21), whereas medullary fibrosis lost significance after IFTA adjustment. Addition of medullary cast formation improved C-index by 0.016, indicating incremental prognostic value beyond conventional predictors. ConclusionMedullary cast formation is independently associated with renal outcomes and improves prognostic discrimination beyond established cortical parameters. Systematic evaluation of medullary lesions during routine kidney biopsy may enhance risk stratification in CKD. Prospective studies are warranted to clarify the causal role of medullary pathology in CKD progression.

Poor outcomes in proteinuric kidney diseases are challenging to successfully manage therapeutically due to the heterogeneity of underlying disease pathogenesis and associated risk for progression. The role of cytoskeleton-associated proteins, including the scaffolding protein Anillin (ANLN), are of specific interest in kidney disease given the importance of actin dynamics in the kidneys specialized epithelial cell types. In this study, we identify the prevalence of genetic variants in ANLN, the gene encoding ANLN, in a cohort of deeply phenotyped individuals with non-diabetic proteinuric kidney disease. Thirty-one individuals (of 864 genotyped) harbor heterozygously expressed variants in ANLN; 7 unrelated individuals shared the same variant (I1109V) in the C-terminal pleckstrin homology (PH) domain, a region necessary for interaction with the plasma membrane. Kidney organoids generated from I1109V induced pluripotent stem cells from 1 of these individuals showed increased epithelial cell mitogen-activated protein kinase 8 network activity and apoptosis, which was enhanced by tumor necrosis factor alpha (TNF-) and phenocopied by actin polymerization inhibition. TNF--treated I1109V organoids also exhibited tubular lumen expansion. Knockdown and re-expression of the analogous ANLN variant in Xenopus laevis embryonic epithelia resulted in defects in cell-cell junction dynamics including wavy cell membranes exhibiting increased transverse movements as well as abnormal junctional F-actin remodeling in response to mechanical stress and leaky barrier function. Taken together, these results indicate that enhanced tubular epithelial cell death, perturbed cell-cell contacts and barrier function defects are associated with a novel ANLN variant discovered in individuals with non-diabetic proteinuric kidney disease. ONE SENTENCE SUMMARYEnhanced tubular epithelial cell death and perturbed cell-cell junction integrity and barrier function are associated with a novel Anillin coding variant discovered in a cohort of individuals with proteinuric kidney disease.

Intercalated cells (ICs) of the renal collecting duct are traditionally recognized for their role in acid-base homeostasis, but growing evidence suggests they also participate in innate immune defense. Although ICs have been implicated in renal antimicrobial function, their specific role in coordinating immune responses during urinary tract infection (UTI) remains unclear. Using Ae1 R607H knock-in mice, a distal renal tubular acidosis (dRTA) model with A-intercalated cell (A-IC) dysfunction, we examined the renal response to uropathogenic Escherichia coli (UPEC). Mice with A-IC dysfunction exhibited higher bacterial loads 24 h post-infection and increased renal expression of antimicrobial peptides lipocalin-2 (Lcn2), galectin-3 (Lgals3), and cathelicidin-related antimicrobial peptide (Camp). Pro-inflammatory cytokines interleukin-6 (IL-6) and interleukin-1{beta} (IL-1{beta}) were elevated at both transcript and protein levels, whereas tumor necrosis factor- (TNF-) increased only at the protein level. Interleukin-10 (IL-10) showed a modest rise in mRNA. Chemokines C-X-C motif chemokine ligand 2 (Cxcl2) and C-C motif chemokine ligand 2 (Ccl2) were also upregulated, accompanied by excessive neutrophil infiltration and a marked shift in renal myeloid-cell composition. A-IC dysfunction therefore disrupts epithelial-immune homeostasis, resulting in exaggerated inflammation and impaired immune resolution. These findings identify A-ICs as essential epithelial immunomodulators that integrate antimicrobial defense, cytokine regulation, and immune-cell recruitment during UTI.

The glomerulus, a unique capillary network in the nephron, filters an entire blood volume approximately 300 times a day. Specialized epithelial cells known as podocytes form a critical component of the glomerular filtration barrier, and diseases linked to podocyte injury include minimal change disease, focal segmental glomerulosclerosis, and diabetic kidney disease. Because podocytes are terminally differentiated, their ability to respond to external stress is critical. The unfolded protein response (UPR), a cellular stress pathway, is associated with glomerular injury, although the role of the UPR in glomerular injury is undefined. The UPR is initially protective, leading to upregulation of molecular chaperones, a class of proteins that promote protein folding and are required to survive oxidative and ischemic injury. An unresolved UPR, however, leads to apoptosis. We previously found that one molecular chaperone, GRP170, provides protection against acute kidney injury since GRP170 depletion led to UPR induction and widespread kidney injury. Here we generated a new podocyte specific GRP170 knock out mouse (GRP170Pd-/-). Surprisingly, GRP170Pd-/- mice were born healthy, and podocyte development appeared normal. Within a month, however, the knockout mice exhibited profound glomerular injury manifesting as proteinuria, hypoalbuminemia, hyperlipidemia, and kidney injury. Concomitant with glomerular injury, we observed increased expression of the pro-apoptotic UPR target, CHOP, in podocytes. Together, our new model not only defines a protective role for GRP170 against glomerular injury but also provides a new model to test the therapeutic potential of small molecule UPR modulators to treat glomerular injury.

0BackgroundA Disintegrin and Metalloprotease 17 (ADAM17) is a key sheddase regulating multiple inflammatory and growth factor-related pathways implicated in diabetic kidney disease (DKD). While cell-specific deletion of ADAM17 has shown renoprotective effects, the impact of global ADAM17 ablation in the context of diabetes remains incompletely understood. MethodsWe investigated the effects of tamoxifen-induced global Adam17 deletion in a murine model of type 1 diabetes induced by streptozotocin. Renal function, structural injury, inflammatory responses, stress-related signalling pathways, and fibrotic remodelling were comprehensively assessed and compared between diabetic Adam17 knockout and control mice. ResultsDespite persistent hyperglycaemia and albuminuria, diabetic Adam17 knockout mice exhibited preservation of glomerular filtration rate and marked attenuation of diabetes-associated renal injury. Global Adam17 deletion reduced mesangial expansion and structural damage, limited macrophage infiltration and chemokine expression, and significantly attenuated fibrotic remodelling. At the molecular level, Adam17 deficiency was associated with selective modulation of stress-related signalling pathways, including reduced activation of the PI3K/Akt axis and partial preservation of mitochondrial stress regulators, without evidence of a generalized suppression of cellular stress responses. ConclusionsOur findings demonstrate that global deletion of ADAM17 confers robust protection against diabetes-induced kidney injury through coordinated attenuation of inflammatory activation, stress-related signalling, and fibrotic progression. These results highlight the context-dependent role of ADAM17 in diabetic kidney disease and support the concept that therapeutic strategies targeting ADAM17-related pathways may require tissue- and disease-specific modulation to achieve renoprotective effects.

Background and objectivesDiagnostic disclosure practices for autosomal dominant polycystic kidney disease (ADPKD) vary and may influence patient experience and linkage to nephrology care. We characterized patient-reported diagnostic pathways, perceived timing, and disclosure experiences in the PK-DIAG survey. Design, setting, participants, and measurementsCross-sectional web-based survey in France (February 2019-August 2024) among adults with self-reported ADPKD, disseminated via patient organizations. Primary outcomes were poor tact (tact score 0-1 on a 0-5 scale) and very negative diagnostic disclosure experience (overall score 0-1 on a 0-5 scale). Multivariable logistic regression used complete-case analyses. ResultsAmong 1,021 respondents, diagnosis was commonly disclosed outside nephrology care; 49% reported disclosure by a radiologist. Poor tact was reported by 25% and was associated with radiologist (vs nephrologist) disclosure (adjusted odds ratio 2.50; 95% confidence interval 1.57-3.98). Very negative experience was reported by 29% and was associated with poor tact (adjusted odds ratio 4.55; 95% confidence interval 2.90-7.12) and information perceived as insufficient/unclear/inaccurate (adjusted odds ratio 2.52; 95% confidence interval 1.53-4.15). Most participants perceived diagnosis as timely (67%), while 18% perceived it as too early and 15% as too late. Distress (36%) or unmet psychological needs (40%) in the immediate post-disclosure period was common. ConclusionsADPKD diagnostic disclosure often occurred outside dedicated nephrology consultations and was frequently associated with poor tact and inadequate information. These findings support structured, guideline-aligned disclosure pathways incorporating timely counseling, psychosocial support, and rapid linkage to nephrology care. Key PointsO_LIIn PK-DIAG, initial disclosure of ADPKD frequently occurred outside nephrology care, most often by radiologists in radiology settings. C_LIO_LIAbout one quarter of respondents reported poor tact and 29% reported a very negative overall diagnostic disclosure experience. C_LIO_LIPoor tact and information perceived as insufficient/unclear/inaccurate were strongly associated with a very negative diagnostic experience. C_LI

Chronic kidney disease (CKD) affects over 850 million people worldwide and is characterized by progressive renal fibrosis driven by activated interstitial fibroblasts. Signaling by extracellular nucleotides and P2 receptors plays an important role in renal pathophysiology, yet its contribution to fibroblast activation and fibrosis remains poorly understood. Here, we investigated the expression and function of Gq/11-coupled P2Y receptors in renal interstitial fibroblasts and their involvement in experimental kidney fibrosis. Using highly selective RNA in situ hybridization, we detected P2Y1 (P2ry1) and P2Y6 (P2ry6) receptor expression in interstitial fibroblasts. Notably, P2Y6 expression was markedly upregulated in several experimental mouse models of renal fibrosis. Functional assays in primary cultured renal fibroblasts confirmed Gq/11-coupled P2Y receptor activity, as evidenced by transient intracellular Ca2+ elevations upon nucleotide stimulation. Primary cultured renal fibroblasts exhibited enhanced migration in response to extracellular uridine diphosphate (UDP). To assess the contribution of interstitial P2Y6 receptors to fibrosis progression, we employed an adenine-induced nephropathy model with or without the selective P2Y6 antagonist MRS2578. Pharmacological inhibition of P2Y6 significantly reduced the mRNA expression of the myofibroblast marker -smooth muscle actin and collagen I. Collectively, these findings suggest that upregulated P2Y6 receptor signaling promotes the transition of resident interstitial cells into myofibroblasts during renal fibrosis, likely by modulating fibroblast migration. Inhibition of P2Y6 signaling could represent a new strategy for reducing excessive renal fibrosis. TRANSLATIONAL STATEMENTThis study reveals the role of the P2Y6 receptor (P2ry6) in fibrotic processes in the kidney. P2Y6, a Gq/11 protein-coupled UDP-sensitive receptor, is expressed in renal interstitial PDGFR-{beta}-positive cells and macrophages. Its pharmacological inhibition significantly reduces fibrosis in the mouse adenine nephropathy model. Blocking P2Y6 therefore represents a promising therapeutic strategy for kidney diseases characterized by excessive scarring.

BackgroundThe effects of Banff histological diagnoses on kidney transplant outcome have been well characterized. However, repeated observation of such histological injury across multiple biopsies in kidney transplant recipients remains insufficiently explored. MethodsIn an observational cohort (N=1819 transplantations with 5736 post-transplant biopsies, recurrent event survival models quantified transitions between diagnoses of T-cell mediated rejection (TCMR), antibody-mediated rejection (AMR), DSA-negative C4d-negative microvascular inflammation (MVIDSA-/C4d-), BK polyomavirus nephropathy (BKPyVAN), borderline TCMR (bTCMR), and probable AMR (pAMR), revealing patterns in the disease trajectories. In two observational cohorts (N=1818 transplantations with 5732 biopsies, N=853 transplantations with 975 biopsies), time-dependent cumulative covariates were constructed for TCMR, AMR, MVIDSA-/C4d- and BKPyVAN, enabling estimation of associations of repeated diagnoses with graft failure using multivariable cause-specific Cox models. ResultsThe incidence rate of a diagnosis was most strongly associated with earlier diagnosis of the same type, but associations between different types of diagnoses also occurred. The hazard of kidney graft failure was significantly increased by repeated observation of TCMR in multiple biopsies (HR 7.97, 95% CI 4.94 - 12.86), as well as by repeated AMR (HR 6.19, 95% CI 3.15 - 12.17), repeated MVIDSA-/C4d- (HR 4.53, 95% CI 2.15-9.54) and repeated BKPyVAN (HR 10.90, 95% CI 5.83 - 20.35). The hazard of graft failure was increased more after repeated diagnoses in transplants than after first diagnoses. The effects of repeated TCMR and repeated AMR remained significant even when observed in protocol biopsies in the absence of graft dysfunction. Repeated observation of BKPyVAN was the most detrimental of all diagnoses when observed in indication biopsies, but it was the least harmful when observed in protocol biopsies. ConclusionIncidence of Banff histological diagnoses appears to be affected by earlier diagnoses, especially those of the same type. These repeated observations of a specific diagnosis have an additional effect on the hazard of graft failure, underscoring a critical unmet need for adequate treatment strategies for these recurrent or persistent injury processes. Lay summaryIn two observational cohorts of 1819 and 750 kidney transplant recipients, kidney transplant biopsies were taken at multiple time points after transplantation. Based on the Banff classification for transplant pathology, various post-transplant diseases were diagnosed, often at more than one time point during follow-up. We assessed patterns in the occurrence of diagnoses over time, and related these diagnoses to survival of the kidney grafts using survival models with time-dependent cumulative diagnoses. We found that repeated observation of the same diagnosis was much more common than consecutive observations of different diagnoses. Repeated diagnoses of tissue injury also decreased kidney graft survival more compared to single diagnoses. This indicates that treatment options for patients with repeated or persistent diagnoses are currently inadequate and novel strategies are needed.

BackgroundSubclinical kidney allograft acute rejection (SCR) corresponds to "the unexpected histological evidence of acute rejection in a stable patient". The diagnosis of SCR relies on surveillance biopsy. Positron emission tomography (PET/CT) after injection of F18-fluorodeoxyglucose ([18F]FDG) has been proposed as a non-invasive screening approach. In the present multicenter prospective study, we assess the diagnostic yield [18F]FDGPET/CT to rule out SCR in stable KTR at 3 months post KTx. MethodsFrom 01/2021 to 03/2025, we prospectively combined surveillance biopsy and [18F]FDGPET/CT at [~]3 months post transplantation in adult kidney transplant recipients from 4 independent imaging centers. The mean standardized uptake value (mSUV) was measured in kidney cortex and referenced as a ratio to psoas muscle mSUV (mSUVR). ResultsOur multicentric 185-patient cohort was categorized upon Banff-2022: normal (n=158); borderline (n=18); SCR (n=9, including 6 T-cell-mediated rejection and 3 microvascular inflammation). No significant correlation was observed between the mSUVR and ti score (R=0.032, p-value=0.67). The mSUVR reached 2.33 [1.97-2.93], 2.71 [2.50-3.33] and 2.42 [2.27-3.14] in normal, borderline and SCR groups, respectively. In multivariate models stratified by center, the risk of non-normal histology (n=27, including borderline and SCR) increased with donor age (OR=1.05 [1.01-1.1], p=0.02) but not with the mSUVR (OR=4.11 [0.91-18.48], p=0.07). The risk of biopsy-proven SCR (n=9) was not significantly associated with mSUVR. ConclusionsThe mSUVR of [18F]FDG PET/CT does not reliably rule out SCR on surveillance biopsy.

BackgroundThe Kidney Precision Medicine Project (KPMP) consortium aims to redefine chronic kidney disease (CKD) by integrating clinical, pathological, and molecular tissue data from kidney biopsies. Here, we demonstrate how biopsy data in CKD can clarify disease etiology and contribute to understandings of disease pathophysiology and clinical prognosis. MethodsThe KPMP is obtaining research kidney biopsies from individuals with CKD (defined as an estimated glomerular filtration rate [eGFR] < 60 mL/min/1.73m2 and/or albuminuria [&ge;]30 mg/g creatinine) and diabetes (enrolled as diabetes and CKD or DKD) or hypertension (enrolled as hypertension and CKD or HCKD). A team of kidney pathologists and nephrologists adjudicated the primary clinico-pathological diagnosis for 258 participants with CKD. We compared pathological features and kidney transcriptional signatures between participants with a primary adjudicated diagnosis of diabetic nephropathy and those with other causes of CKD. We developed a model using clinical and biomarker data that predicted the probability of diabetic nephropathy and tested associations of the signature with CKD progression among Chronic Renal Insufficiency Cohort (CRIC) participants with diabetes (n=229). ResultsAmong 183 participants enrolled as DKD, 102 (56%) had a primary adjudicated clinico-pathologic diagnosis of diabetic nephropathy. Among 75 participants enrolled as HCKD, 42 (56%) had a primary diagnosis of hypertension-associated kidney disease. Those with diabetic nephropathy, compared with other diagnoses, had more severe interstitial fibrosis, tubular atrophy, tubular injury, segmental sclerosis, and severe arteriolar hyalinosis, and single-nucleus and single-cell transcriptional analyses revealed upregulation of immune and inflammatory pathways and downregulation of oxidative phosphorylation. A combination of age, hemoglobin A1c, urine albumin-creatinine ratio, and serum KIM-1 and sTNFR1 predicted a clinico-pathologic diagnosis of diabetic nephropathy in the KPMP (AUC 0.82, 95% CI 0.75-0.89) and was associated with an increased risk of CKD progression among patients with diabetes enrolled in CRIC (HR 1.48 [95% CI 1.27-1.73] per 10% higher predicted probability of diabetic nephropathy). ConclusionIn common presentations of CKD, kidney biopsies may alter a priori impressions, reveal a diversity of diagnosis, structure, and function that is associated with clinical outcomes and can impact therapeutic decisions.

Background: Single-nephron glomerular filtration rate (GFR) represents a nephron-level functional index that may reveal key pathophysiological mechanisms driving progression in patients with diabetic nephropathy. However, its clinical relevance remains incompletely understood. This cross-sectional study assessed single-nephron estimated GFR (eGFR) across different chronic kidney disease (CKD) stages in patients with advanced diabetic nephropathy. Methods: Nephron number was estimated as the number of nonglobally sclerotic glomeruli per kidney using computed tomography-derived cortical volume combined with biopsy stereology. Single-nephron eGFR was calculated by dividing eGFR by the nephron number of both kidneys. Patients were stratified according to CKD stage at kidney biopsy. Associations between CKD stages and single-nephron eGFR were evaluated using multivariable linear regression models adjusted for age, sex, urinary protein excretion, and eGFR. Results: The study included 105 patients with biopsy-proven diabetic nephropathy and overt proteinuria (median age 59 years, 83% male, HbA1c 6.6%, 57% had nephrotic range proteinuria). The percentage of globally sclerotic glomeruli, mesangial expansion score, and prevalence of nodular lesions increased significantly with advancing CKD stage. Median nephron number declined from 529,178 to 224,458 per kidney, whereas glomerular volume remained constant. Single-nephron eGFR decreased markedly with CKD stage and remained significantly inversely associated with CKD stage after adjustment for clinicopathologic covariates (P for trend <0.001). Conclusion: In overt diabetic nephropathy, single-nephron eGFR decreased with advancing CKD stage, despite relatively preserved glomerular volume. At this stage of disease, structural alterations specific to diabetic nephropathy may impair effective single-nephron filtration capacity.