Kidney International

Ciliogenesis associated kinase 1 (CILK1) deficiency in human and mice results in kidney developmental defects including cystogenesis. However, the biology of CILK1 in autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disease, remains to be investigated. Here, we show that CILK1 is overexpressed in dedifferentiated cells of renal tissue from ADPKD human patients in comparison to normal control tissue samples. We demonstrate that CILK1 overexpression results in protein accumulation in a non-phosphorylated inactive form. Using mouse polycystic kidney disease models, we reveal that inactive CILK1 accumulation is progressive over the course of disease progression. We show that genetic inactivation of the Polycystic Kidney Disease 1 (PKD1) gene is sufficient to trigger CILK1 accumulation. Altogether, these findings demonstrate that CILK1 regulation is altered in ADPKD and it represents a hallmark of disease progression.

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common genetic kidney disorder resulting in 10% of patients with renal failure. The molecular events responsible for the relentless growth of cysts are not defined. Thus, identification of novel drivers of ADPKD may lead to new therapies. Ankyrin Repeat and Single KH domain-1 (ANKHD1) controls cancer cell proliferation, yet its role in ADPKD is unexplored. Here, we present the first data that identify ANKHD1 as a driver of proliferative growth in cellular and mouse models of ADPKD. Using the first Ankhd1-deficient mice, we demonstrate that Ankhd1 heterozygosity potently reduces cystic growth and fibrosis, in a genetically orthologous mouse model of ADPKD. We performed transcriptome-wide profiling of patient-derived ADPKD cells with and without ANKHD1 siRNA silencing, revealing a major role for ANKHD1 in the control of cell proliferation and matrix remodelling. We validated the role of ANKHD1 in enhancing proliferation in patient-derived cells. Mechanistically ANKHD1 promotes STAT5 signalling in ADPKD mice. Hence, ANKHD1 is a novel driver of ADPKD, and its inhibition may be of therapeutic benefit.

BackgroundDespite MN being one of the most common causes of nephrotic syndrome worldwide, its biological and environmental determinants are poorly understood in large-part due to it being a rare disease. Making use of the UK Biobank, a unique resource holding a clinical dataset and stored DNA, serum and urine for [~]500,000 participants, this study aims to address this gap in understanding. MethodsThe primary outcome was putative MN as defined by ICD-10 codes occurring in the UK Biobank. Univariate relative risk regression modelling was used to assess the associations between the incidence of MN and related phenotypes with sociodemographic, environmental exposures, and previously described increased-risk SNPs. Results502,507 patients were included in the study of whom 100 were found to have a putative diagnosis of MN; 36 at baseline and 64 during the follow-up. Prevalence at baseline and last follow-up were 72 and 199 cases/million respectively. At baseline, as expected, the majority of those previously diagnosed with MN had proteinuria, and there was already evidence of proteinuria in patients diagnosed within the first 5 years of follow-up. The highest incidence rate for MN in patients was seen in those homozygous for the high-risk alleles (9.9/100,000 person-years). ConclusionIt is feasible to putatively identify patients with MN in the UK Biobank and cases are still accumulating. This study shows the chronicity of disease with proteinuria present years before diagnosis. Genetics plays an important role in disease pathogenesis, with the at-risk group providing a potential population for recall.

IntroductionGlomerulonephritis (GN) with crescents and IgA deposits on kidney biopsy poses a frequent diagnostic and therapeutic dilemma because of multiple possibilities. MethodsNative kidney biopsies showing IgA deposition and crescents (excluding lupus nephritis) were identified from our biopsy archives between January 2010 and December 2021. Detailed clinico-pathologic features were assessed. One-year clinical follow-up on a subset of cases was performed. ResultsA total of 285 cases were identified and these clustered into IgA nephropathy (IgAN, n=108), Staphylococcus or other infection-associated-GN (SAGN/IRGN, n=46), and anti-neutrophil cytoplasmic antibody associated-GN (ANCA-GN, n=24) based on constellation of clinico-pathologic features, but 101 cases (Group X) could not be definitively differentiated. The reasons have been elucidated, most important being atypical combination of clinico-pathologic features and lack of definitive evidence of active infection. Follow-up (on 72/101 cases), revealed that clinicians working diagnosis was IgAN in 42%, SAGN/IRGN in 24%, ANCA-GN in 24%, and others in 7% of the cases, but treatment approach varied from supportive/antibiotics to immunosuppression in each subgroup. Comparing these cases as "received immunosuppression" versus "no-immunosuppression", only two features - C3-dominant staining; and possibility of recent infection differed (higher in the no-immunosuppression group [p<0.05]). Renal loss was higher in the no-immunosuppression subgroup, but not statistically significant (p=0.11). ConclusionDiagnostic overlap may remain unresolved in a substantial number of kidney biopsies with glomerular crescents and IgA deposits. A case-by-case approach, appropriate antibiotics if infection is ongoing, and consideration for cautious immunosuppressive treatment for progressive renal dysfunction may be needed for best chance of renal recovery.

BackgroundTubulitis is a defining histologic feature of T cell-mediated rejection (TCMR), while glomerulitis is often characteristic of antibody mediated rejection (AMR). Histologic quantification of tubulitis and glomerulitis using Banff criteria is subject to interobserver variability. Bulk transcriptomic assays (e.g., MMDx) have introduced molecular correlations of tubulitis with TCMR and glomerulitis with AMR, but lack spatial resolution. MethodsWe applied a web-based platform, FUSION (Functional Unit State Identification in Whole Slide Images), to a cohort of 8 cases (n=2 per condition) with kidney allograft biopsy samples acute TCMR, active AMR, chronic active AMR, and no rejection (control). The machine-learning (ML) platform enabled integrated visualization and analysis of spatial transcriptomics (10x Genomics Visium v2) together with high-resolution whole-slide histology. ResultsTranscriptomics-derived immune cell proportions within AI-segmented tubular and glomerular regions were used to generate spatial Banff t- and g-scores. Derived t-scores showed full concordance with pathologist scores in both acute TCMR cases; g-scores showed concordance in 2 of 4 AMR cases, with discordant cases characterized by low absolute immune signal near the classification boundary. ConclusionsWe demonstrate the feasibility of using AI-based FTU segmentation integrated with spatial transcriptomics-derived immune cell proportions to generate spatially informed t- and g-scores aligned with Banff criteria, with full concordance in severe rejection and partial concordance in mild rejection. This approach lays the foundation for validated, spatial transcriptomics-augmented t-scores and g-scores that enhance diagnostic precision, reduces inter-observer variability among renal pathologists, and support potential clinical adoption.

BackgroundDistal renal tubular acidosis (dRTA) is a rare kidney disorder characterized by impaired urinary acidification due to defective proton secretion in type A intercalated cells of the collecting duct. Recently, pathogenic variants in the human gene encoding the WD Repeat Domain 72 protein (WDR72) have been reported in patients with dRTA, yet the physiological role of WDR72 in the kidney remains unknown. MethodsTo elucidate the renal function of Wdr72, we generated a kidney-specific knockout mouse model (Wdr72fl/fl;Pax8-Cre+) and assessed acid-base homeostasis under baseline, acute, and chronic acid loading. ResultsWdr72fl/fl;Pax8-Cre+ mice displayed persistently elevated urinary pH, reduced titratable acid and net acid excretion under basal and acid-loaded conditions, consistent with incomplete dRTA. While the systemic pH remained unchanged compared to controls under standard diet, chronic acid load led to mild hyperchloremic, hypokalemic metabolic acidosis. Notably, urinary NH excretion was increased upon acid loading accompanied by upregulation of key ammoniagenesis enzymes, which was detected even under basal conditions, consistent with a compensatory activation of proximal tubular acid excretion pathways. The total and membranous abundance of the V-ATPase B1 subunit decreased markedly within the kidney, despite unchanged transcript levels, suggesting a defect in V-ATPase trafficking or assembly. In addition, morphometric analyses revealed an increased proportion of type A intercalating cells that failed to expand upon acid loading, indicating defective adaptive plasticity. ConclusionsKidney-specific Wdr72 deletion impairs distal urinary acidification through reduced V-ATPase abundance and membranous targeting, altered intercalated cell morphology, and limited adaptive remodeling, resulting in incomplete dRTA. Upregulation of renal ammoniagenesis partially compensates the acidification defect. These findings highlight WDR72 as a key regulator of distal nephron acid-base homeostasis and offer mechanistic insight into WDR72-associated dRTA. Key PointsO_LIKidney-specific deletion of Wdr72 reduced Atp6v1b1 membranous localization in intercalated cells. C_LIO_LIKidney-specific Wdr72 knockout altered intercalated cell morphology, and limited their adaptive remodeling. C_LIO_LIThe lack of the renal Wdr72 resulted in incomplete dRTA, compensated partially by elevated ammoniagenesis. C_LI

BackgroundRenal Ischaemia Reperfusion Injury (R-IRI) can cause Acute Kidney Injury (AKI) and Chronic Kidney Disease (CKD), resulting in significant morbidity and mortality. To understand the underlying mechanisms, reproducible small-animal models of AKI and CKD are needed. We describe how innovative technologies for measuring kidney function non-invasively in small rodents allow successful refinement of the R-IRI models, and offer the unique opportunity to monitor longitudinally in individual animals the transition from AKI to CKD. MethodsMale BALB/c mice underwent bilateral renal pedicle clamping (AKI) or unilateral renal pedicle clamping with delayed contralateral nephrectomy (CKD) under isoflurane anaesthetic. Transdermal GFR monitoring and multi-spectral optoacoustic tomography in combination with statistical analysis were used to identify and standardise variables within these models. ResultsPre-clamping anaesthetic time was one of the most important predictors of AKI severity after R-IRI. Standardising pre-clamping time resulted in a more predictably severe AKI model. In the CKD model, initial improvement in renal function was followed by significant progressive reduction in function between weeks 2 and 4. Performing contralateral nephrectomy on day 14 enabled the development of CKD in a survivable way. ConclusionsNon-invasive monitoring of global and individual renal function after R-IRI is feasible, reproducible and correlates well with classical markers of injury. This facilitates refinement of kidney injury models and enables the degree of injury seen in pre-clinical models to be translated to those seen in the clinical setting. Thus, future therapies can be tested in a clinically relevant, non-invasive manner. What is already knownThe severity of Renal Ischaemia Reperfusion injury (R-IRI) varies between animal strain, gender and age. Experimental variables including temperature and clamping time are usually tightly controlled but significant variability still exists. Classically, small rodent experiments depend on endpoint evaluation of serum and histological features of disease. However, new technologies including transdermal glomerular filtration rate (GFR) monitoring and Multispectral Optoacoustic Tomography (MSOT) may enable renal function to be accurately monitored longitudinally, enabling better refinement of these models. What this study addsThis study shows that transdermal GFR measurements have reliably enabled refinement of the R-IRI model by standardisation of the duration of isoflurane prior to commencing surgery. Individual kidney function can be assessed in-vivo after unilateral R-IRI using MSOT imaging. The excretion tmax of IRDye-800 reliably represents the relative function of the injured kidney, permitting longitudinal in-vivo assessment of differential kidney function. What impact this may have on practiceThis study demonstrates the utility of two minimally-invasive in-vivo methods of monitoring kidney function which have advantages over classical methods and potentially enable fewer animals to be used in future studies. The study demonstrates refinement of bilateral and unilateral R-IRI models which will also enable a reduction in the number of animals needed for experimentation.

Autosomal dominant polycystic kidney disease (ADPKD) causes the slow, progressive formation of fluid-filled cysts within the kidney that ultimately leads to renal failure. Despite being the most common genetic kidney disease, the range of therapies for ADPKD is limited. Ureteric bud (UB) organoids derived from human pluripotent stem cells (hPSCs) have been used to model ADPKD. Here, we describe a protocol to generate UB organoids in large-scale suspension culture that is amenable to drug discovery. When differentiated from PKD2-deficient hPSCs, the UB organoids robustly form cysts within 7 days and reach nearly 100% cyst efficiency within [~]20 days. Cystic UB organoids express ADPKD markers and are responsive to cyst-reducing compounds, such as the BET inhibitor JQ1 and the NF-{kappa}B inhibitor QNZ, but not tolvaptan. As proof-of-principle of the platform as a drug discovery tool, we screened a small molecule library comprised of nutrient conjugates and identified M1, a palmitate-glucosamine-glycine conjugate, that reduced cyst formation. These results demonstrate that our scalable method of cystic UB organoid production provides a simple and highly efficient platform for ADPKD drug discovery. TRANSLATIONAL STATEMENTAutosomal dominant polycystic kidney disease (ADPKD) affects over 12 million people worldwide, yet the currently available therapy tolvaptan only moderately delays disease progression and is burdened with adverse effects. Improved treatments that are well tolerated and effective are urgently needed. We established a human ureteric bud organoid platform that enables ADPKD-like cysts to be cultured at large scale and low cost. These cystic organoids resemble human ADPKD cysts and are suitable for drug discovery. Identification of the nutrient conjugate M1 as a new lead molecule for reducing cyst formation highlights the clinical relevance of this model.

BackgroundFGF23 excess is associated with morbidity and mortality, but the role of excessive circulating FGF23 concentrations as a mere biomarker or causative factor of pathology is controversial. Here, we investigated the consequences of FGF23 excess in kidney disease. MethodsThis study used three independent disease models: i) anti-glomerular basement membrane (Anti-GBM) disease in male C57BL/6 mice, ii) Adriamycin (doxorubicin)-induced nephropathy in female BALB/c mice, and iii) male DBA/2J mice fed an adenine-containing diet. Anti-GBM and Adriamycin mice and matched control mice received intravenous injections of recombinant FGF23 1{micro}g or vehicle for six consecutive days (Anti-GBM) or once (Adriamycin model), with dissection 24h after the last injection. Adenine mice underwent organ harvesting after 15 weeks to establish ex vivo precision-cut kidney slices (PCKS) and 24h treatment with recombinant FGF23 or vehicle. In addition to histological and biochemical profiling, we assessed serum cytokines, biochemistry and renal transcriptomes and histology of mice and patients with IgA nephropathy. RNAseq data and published transcriptomes underwent gene set enrichment, bulk ligand-receptor interaction analysis and cell-type decomposition. ResultsMice with Anti-GBM disease showed decreased glomerular filtration rate, albuminuria and renal tubular casts. FGF23 treatment increased phosphaturia, but also circulating soluble TNF receptor-1. Renal transcriptomes revealed FGF23-driven proinflammatory transcriptional signatures in murine Anti-GBM and also adverse Vcam1, Pdgfrb and chemokine ligand-receptor signaling in Anti-GBM but not in healthy mice. FGF23 increased transcriptome-inferred renal macrophage content in Anti-GBM mice. Findings were confirmed by immunofluorescence. In Adriamycin-induced nephropathy and in PCKS from the adenine nephropathy model, a short-term FGF23 excess caused expression of proinflammatory transcripts. Finally, human data revealed associations between histopathological or transcriptome-inferred renal immune cell infiltration and circulating FGF23 concentrations. ConclusionFGF23-driven patterns of proinflammatory gene and protein expression or leukocyte overabundance in the kidney were observed in several different models or states of FGF23 excess. The present data provide evidence that excess FGF23 directly drives inflammation in kidney disease and may serve as a therapeutic target.

IntroductionAntibody-mediated rejection (AMR) remains a leading cause of kidney allograft failure, with both HLA and non-HLA antibodies implicated in its pathogenesis. The contribution of non-HLA antibodies (non-HLA Abs) to microvascular inflammation (MVI) and graft outcome, particularly in cases lacking donor-specific anti-HLA antibodies (HLA-DSAs), remains incompletely understood. MethodsWe analyzed 571 post-transplant serum samples from 326 patients with histological features of AMR (AMRh) and 164 stable controls. Non-HLA Abs were detected using the previously developed Non-HLA Antibody Detection Immunoassay (NHADIA), and associations were examined with histological lesions, AMRh persistence, and graft outcomes. Biopsies were scored according to Banff 2022 criteria, and patients were stratified by HLA-DSA and NHADIA status. ResultsNHADIA values were significantly higher in AMRh patients compared to controls (P=0.0001), regardless of HLA-DSA status. NHADIA values correlated with the severity of glomerulitis, peritubular capillaritis and global MVI scores. In AMRh patients with HLA-DSAs, non-HLA Abs remained independently associated with MVI severity. Follow-up biopsies revealed persistent AMR lesions in patients with both HLA-DSAs and non-HLA Abs. Allograft survival was lowest in double-positive patients, and NHADIA positivity independently predicted graft loss (HR=2.25, 95% CI: 1.03-4.92, P=0.042). Incorporating NHADIA into the Banff classification reclassified 61% of AMRh cases as "double-positive AMRh," and identified new subgroups with significant prognostic differences. ConclusionPost-transplant detection of non-HLA antibodies identifies a distinct subset of AMR with more severe histology and worse graft prognosis, particularly when coexisting with HLA-DSAs. Integrating non-HLA Ab testing into current diagnostic frameworks may refine AMR classification and improve risk stratification. TRANSLATIONAL STATEMENTThis study highlights the clinical relevance of non-HLA antibodies, identified using our innovative endothelial cell-based assay (NHADIA), in kidney transplant recipients. Their presence is associated with more severe antibody-mediated rejection (AMR) and poorer graft outcomes, even in the absence of donor-specific HLA antibodies. Incorporating non-HLA antibody detection into routine post-transplant evaluation may allow clinicians to better identify high-risk patients, including those previously classified as DSA-negative AMR. This expanded immunological profiling refines AMR diagnosis, improves risk stratification, and opens new avenues for personalized immunosuppressive strategies, ultimately enhancing long-term graft survival and patient care.

ImportanceMost studies of ADPKD genetics have used select cohorts, focusing on PKD1 and PKD2 and more recently several other cystic genes. However, the population prevalence of ADPKD and the contribution of each cystic gene to ADPKD are not well understood. ObjectiveDetermine the prevalence of ADPKD, contribution of PKD1, PKD2, and other cystic genes to ADPKD in a large, unselected cohort. Design, Setting, and ParticipantsWe determined the prevalence of ADPKD In an unselected health system-based cohort of 173,954 subjects with the existing exome sequencing and extensive electronic health records, including abdominal imaging. The presence of genetic variants in PKD1, PKD2, and eleven other cystic genes was evaluated. Rare genetic variants were identified in patients with chart review confirmed diagnosis of ADPKD. Main OutcomesDiagnosis of ADPKD and presences of rare (AF<0.0001) missense, protein-truncating variants (PTVs), or copy number variants deletions (CNV) in PKD1, PKD2, or PTVs and CNVs in the following 11 genes: ALG8, ALG9, DNAJB11, GANAB, HNF1B, IFT140, LRP5, PKHD1, PRKCSH, SEC61B, and SEC63. ResultsAmong 173,954 patients, there were 235 patients with chart review confirmed ADPKD (0.135%). Among patients with PTV or CNV in PKD1, 66/70 (94.2%) had ADPKD and 43/44 (97.7%) of patients with PTV or CNV in PKD2 had ADPKD. In contrast, only 24/77 (31.2%) patients with a PKD1 missense variant previously classified as "likely pathogenic" had ADPKD. A rare variant was identified in a cystic gene in 180/235 (76.6%) of ADPKD patients, with the most common genes implicated PKD1 (127) and PKD2 (34) and then IFT140 (7), PKHD1 (3), GANAB (4), HNF1B (2), ALG8 (1), ALG9 (1), IFT140+PKHD1 (1). The yield for a genetic determinant of ADPKD was 91.3% among those with a family history compared to 50.6% among those without a family history (p<0.0001). We report several previously unreported variants where pedigree data suggest pathogenicity. Atypical cystic genes ALG8, ALG9, GANAB, HNF1B, IFT140, and SEC63 were associated with having any kidney or liver cystic ICD code, but not diagnosed ADPKD. ConclusionsExome sequencing established the molecular diagnosis for the vast majority of patients with ADPKD, revealed a wider range of ADPKD with atypical cystic genes. Additional population-based research cohorts are needed to carefully curate missense PKD1 variants and variants in atypical cystic genes.

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.

BackgroundUnexplained kidney failure (uKF) affects 15% of individuals requiring kidney replacement therapy. Absence of a diagnosis creates uncertainty around recurrence after transplantation, familial risk, and participation in therapeutic trials. Whole genome sequencing (WGS) was used to identify genetic variants contributing to uKF. Methods218 patients who presented with uKF < 50 years old were recruited to the UKs 100,000 Genomes Project. Candidate variants in 183 genes were reviewed for pathogenicity by a multidisciplinary team. Gene-based association testing, structural variant analyses, and assessment of high-risk APOL1 genotypes were performed. Polygenic risk scores (PRS) were calculated for chronic kidney disease (CKD), and various glomerulonephritides. HLA associations in those with APOL1 high-risk genotype were also investigated. ResultsA positive genetic diagnosis was made in 17% (38/218) of patients. The median age of uKF onset was 36 years. Fewer genetic diagnoses were found in those aged [&ge;] 36 years compared to younger individuals, both with (11% vs. 35%, P=0.03) and without (5% vs. 19%, P=0.05) a family history. Three patients [&ge;] 36 years without a family history had pathogenic variants in type IV collagen genes. High-risk APOL1 genotypes were enriched in patients with recent African ancestry (52% vs 8.4%, P=5.97x10-8). Dividing the uKF cohort by subsequent identification of monogenic diagnosis, High-risk APOL1 genotype, or neither, we found that the SSNS PRS was higher in those with High-risk APOL1 (P=0.048), driven by differences at HLA-DQB1*03:19 (P=0.001). ConclusionsThese findings estimate the likelihood of a genetic diagnosis using WGS in uKF patients, showing fewer diagnoses in older patients without a family history. APOL1 contributes significantly to uKF in those with recent African ancestry, potentially interacting with HLA-DQB1. The lack of PRS signal for CKD suggests distinct biology between uKF and more common causes of CKD.

We used Digital Spatial Profiling to localize transcripts in glomeruli and tubulointerstitial compartments in a series of 4 biopsies from a patient diagnosed with acute antibody-mediated rejection (AMR). The 4 biopsies included: a baseline protocol biopsy 25 days after transplantation; a 3 month biopsy diagnosed as acute AMR; a biopsy 4 months after treatment with intravenous immunoglobulin (IVIg) showing ongoing AMR with a mild increase in tubulointerstitial fibrosis; and a biopsy 7 months later with resolution of glomerulitis. Glomeruli were captured in regions of interest (ROIs) for whole exome sequencing. Compared to baseline glomeruli, 17 transcripts were increased and 39 decreased in the 3 subsequent biopsies (> 2-fold and p < 0.005). Increased signatures for macrophages correlated with increased numbers of CD68 positive cells imaged in the corresponding glomeruli. The Human Cell Atlas classified the 39 transcripts decreased during the initial rejection as characteristic of podocytes and this gene signature did not recover in the subsequent 2 biopsies. Additional ROIs encompassing areas of tubulointerstitial fibrosis disclosed signatures for memory B cells in the acute AMR sample. Treatment with IVIg did not eliminate the B cell signal in the subsequent biopsy. Collectively these data demonstrate a compartmentalization of injury processes. Innate immune cells including macrophages were located in glomerular and tubulointerstitial compartments, whereas, adaptive immune cells including memory B cells localized to the tubulointerstitial compartment. Furthermore, podocyte transcripts were decreased in glomeruli and did not recover with treatment indicating a vulnerability of these cells to acute AMR.

BackgroundCongenital anomalies of the kidney and urinary tract (CAKUT) are the predominant cause for chronic kidney disease below 30 years of age. Many monogenic forms have been discovered mainly due to comprehensive genetic testing like exome sequencing (ES). However, disease-causing variants in known disease-associated genes still only explain a proportion of cases. Aim of this study was to unravel the underlying molecular mechanism of syndromic CAKUT in two multiplex families with presumed autosomal recessive inheritance. Methods and ResultsES in the index individuals revealed two different rare homozygous variants in FOXD2, a transcription factor not previously implicated in CAKUT in humans: a frameshift in family 1 and a missense variant in family 2 with family segregation patterns consistent with autosomal-recessive inheritance. CRISPR/Cas9-derived Foxd2 knock-out (KO) mice presented with bilateral dilated renal pelvis accompanied by renal papilla atrophy while extrarenal features included mandibular, ophthalmologic, and behavioral anomalies, recapitulating the phenotype of humans with FOXD2 dysfunction. To study the pathomechanism of FOXD2-dysfunction-mediated developmental renal defects, in a complementary approach, we generated CRISPR/Cas9-mediated KO of Foxd2 in ureteric-bud-induced mouse metanephric mesenchyme cells. Transcriptomic analyses revealed enrichment of numerous differentially expressed genes important in renal/urogenital development, including Pax2 and Wnt4 as well as gene expression changes indicating a cell identity shift towards a stromal cell identity. Histology of Foxd2 KO mouse kidneys confirmed increased fibrosis. Further, GWAS data (genome-wide association studies) suggests that FOXD2 could play a role for maintenance of podocyte integrity during adulthood. ConclusionsIn summary, our data implicate that FOXD2 dysfunction is a very rare cause of autosomal recessive syndromic CAKUT and suggest disturbances of the PAX2-WNT4 cell signaling axis contribute to this phenotype.

Rare kidney diseases are not well characterised, despite making a significant contribution to the burden of kidney disease globally. The National Registry of Rare Kidney Diseases (RaDaR) collects longitudinal disease and treatment-related data from people living with rare kidney diseases across the UK, and is the largest rare kidney disease registry in the world. We present the clinical demographics and renal function of 25,880 prevalent patients and evaluate for any potential recruitment bias to RaDaR. RaDaR has automatic linkage with the UK Renal Registry (UKRR, with which all UK patients receiving Kidney Replacement Therapy (KRT) are registered). To assess for recruitment bias to RaDaR, ethnicity and socioeconomic status of 1) prevalent RaDaR patients receiving KRT were compared with patients with eligible rare disease diagnoses receiving KRT in the UKRR 2) patients recruited to RaDaR and all eligible unrecruited patients at two renal centres were compared 3) the age-stratified ethnicity distribution of RaDaR patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD) was compared to the English Census. We found evidence of some disparities in ethnicity and social deprivation in recruitment to RaDaR, however these were not consistent across all comparisons. Predominant rare kidney diseases in adults were ADPKD (29.2%), Vasculitis (15.8%) and IgA nephropathy (15.7%), compared to Idiopathic nephrotic syndrome (43.6%), Vasculitis (10.8%) and Alport Syndrome (5.9%) in children. Compared with either adults recruited to RaDaR or the English population, children recruited to RaDaR were more likely to be of Asian ethnicity and live in more socially deprived areas. Lay SummaryRare kidney diseases make a significant contribution to the number of people living with kidney disease globally: >25% of adults and >50% of children with kidney failure have a rare disease. However, there is a lack of high-quality published data on how these conditions present, and in which patient groups. Patients often face delays in diagnosis and lack of reliable information on their condition once diagnosed. The UK National Registry of Rare Kidney Diseases (RaDaR) was formed in 2010 to address this knowledge gap. It collects long-term data for UK patients with rare kidney conditions, and is the largest rare kidney disease registry in the world. Here, we present information about 25,880 adults and children recruited to RaDaR, including ethnicity, socioeconomic status, and kidney function, and investigate whether there is any bias in recruitment to RaDaR. To our knowledge, this is the largest epidemiological description of rare kidney diseases worldwide.

BackgroundPhospholipase A2 receptor-associated membranous nephropathy (PLA2R-MN) is an anti-PLA2R antibody (PLA2R-Ab) mediated autoimmune kidney disease. Although antibody titer correlates closely with disease activity, whether it can provide longer-term predictions on disease course and progression is unclear. Rituximab, a B-cell depletion therapy, has become the first-line treatment option for PLA2R-MN; however, the response to Rituximab varies among patients. MethodsWe developed a flow cytometry-based test that detects and quantifies PLA2R antigen-specific memory B cells (PLA2R-MBCs) in peripheral blood, the primary source for PLA2R-Ab production upon disease relapse. We applied the test to 159 blood samples collected from 28 patients with PLA2R-MN (at diagnosis, during and after immunosuppressive treatment, immunological remission, and relapse) to evaluate the relationship between circulating PLA2R-MBC levels and disease activity. ResultsThe level of PLA2R-MBCs in healthy controls (n=56) is less than or equal to 1.5% of the total MBC compartment. High circulating PLA2R-MBC levels were detected in two patients post-Rituximab despite achieving immunologic and proteinuric remission, as well as in two patients with negative serum autoantibody but increasing proteinuria. Elimination of these cells with Rituximab improved clinical outcomes. Moreover, five patients exhibited elevated PLA2R-MBC levels before disease relapse, followed by a rapid decline to baseline when relapse became clinically evident. COVID-19 vaccination or SARS-CoV-2 infection significantly affected the dynamics of circulating PLA2R-MBCs. ConclusionsThis study suggests that monitoring PLA2R-MBC levels in patients with PLA2R-MN may help refine and individualize immunosuppressive therapy and predict disease course and progression. The technology and findings may also have broader applications in the clinical management of other autoimmune diseases.

BackgroundHeterozygous ALG8 variants have previously been associated with polycystic liver disease (PLD) with or without kidney cysts. A clear-cut relationship between application of PKD diagnostic criteria and kidney manifestations of ALG8 variants remains to be described. We therefore sought to determine whether ALG8 protein-truncating variant (PTV) heterozygotes are at increased risk of polycystic kidney disease (PKD). MethodsWe identified participants heterozygous for pathogenic (P) and likely pathogenic (LP) ALG8 (NM_024079.5) PTVs described in ClinVar from the Geisinger-Regeneron DiscovEHR MyCode study, an unselected health system-based cohort linked to electronic health records. ALG8 PTV heterozygotes were matched 1:1 to non-heterozygote family members by age at time of imaging (within 10 years) and sex. Phenotypes were assessed by International Classification of Disease (ICD) codes, chart review, and imaging, which was reviewed by a blinded radiologist. Imaging diagnosis of PKD was defined as [&ge;]4 kidney cysts on an abdominal ultrasound or computed tomography. Secondary outcomes included bilateral renal cysts, and [&ge;]1 liver cyst. ResultsOut of 174,418 participants in MyCode,103 participants (mean age 56.7 years) were heterozygous for an ALG8 P/LP variant: p.Arg364Ter (n=86), p.Arg41Ter (n=7), p.Arg179Ter (n=9), and c.368+2T>G (n=2). None of the ALG8 P/LP variant heterozygotes had an ICD diagnosis of PKD or PLD. Out of 51 participants [&ge;]40 years of age with available imaging, 51% had [&ge;]4 renal cysts and 14% had [&ge;]1 liver cyst. After matching 23 ALG8 P/LP variant heterozygotes with 23 related non-heterozygotes by age and imaging modality, ALG8 P/LP heterozygotes had higher prevalence of 4+ kidney cysts (48% versus 9% in non-heterozygotes; p=0.007) and bilateral kidney cysts (61% vs. 17%; p=0.006). ConclusionsOur study demonstrates that patients heterozygous for ALG8 P/LP variants are at increased risk of PKD on imaging but not by ICD diagnosis codes. Additional studies are needed to determine whether ALG8 P/LP heterozygotes are at increased risk of kidney failure.

BackgroundMembranous nephropathy (MN) is caused by autoantibody binding to podocyte foot process antigens such as THSD7A and PLA2R1. The mechanisms of the glomerular antigen/autoantibody deposition and clearance are unknown. MethodsWe explore the origin and significance of glomerular accumulations in (1) diagnostic and follow-up biospecimens from THSD7A+ and PLA2R1+-MN patients compared to nephrotic non-MN patients, and (2) in experimental models of THSD7A+-MN. ResultsWe discovered podocyte exophers as correlates of histological antigen/autoantibody aggregates found in the glomerular urinary space of MN patients. Exopher vesicle formation represents a novel form of toxic protein aggregate removal in Caenorhabditis elegans neurons. In MN patients, podocytes released exophers to the urine. Enrichment of exophers from MN patient urines established them as a glomerular exit route for antigens and bound autoantibody. Exophers also carried disease-associated proteins such as complement and provided a molecular imprint of podocyte injury pathways. In experimental THSD7A+-MN, exophers were formed from podocyte processes and cell body. Their formation involved the translocation of antigen/autoantibody from the subepithelial to the urinary side of podocyte plasma membranes. Urinary exopher-release correlated with lower albuminuria and lower glomerular antigen/autoantibody burden. In MN patients the prospective monitoring of urinary exopher abundance and of exopher-bound autoantibodies was additive in the assessment of immunologic MN activity. ConclusionsExopher-formation and release is a novel pathomechanism in MN to remove antigen/autoantibody aggregates from the podocyte. Tracking exopher-release will add a non-invasive diagnostic tool with prognostic potential to clinical diagnostics and follow-up of MN patients.

Introduction Acute interstitial nephritis is an important differential diagnosis in patients with deteriorating kidney function. Diagnosis currently requires kidney biopsy, an invasive procedure associated with risks. We hypothesized that urinary T cells may serve as a non-invasive biomarker for acute interstitial nephritis. Methods A total of 320 patients undergoing clinically indicated kidney biopsy were enrolled in a discovery cohort at Charite Berlin (n = 80), an internal validation cohort at Charite (n = 100), and an external validation cohort at The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou (n = 140). Urinary immune cells were assessed by flow cytometry. Renal T cell infiltration was evaluated by immunofluorescence in kidney biopsy specimens from the discovery and internal validation cohorts, including 16 patients with acute interstitial nephritis and 9 patients without acute interstitial nephritis. Additionally, CXCL9 was measured by ELISA in 102 urine samples from these cohorts. Results Across all cohorts, 27 patients (8.4%) were diagnosed with acute interstitial nephritis. In the discovery cohort, multiple urinary T cell subsets were increased in acute interstitial nephritis, with activated CD4+ effector memory T cells expressing CD38 and HLA-DR showing the strongest diagnostic performance. This marker outperformed urinary monocytes, eosinophils, and CXCL9 and was validated in both independent cohorts. Across all cohorts, the area under the receiver operating characteristic curve was 0.84 and increased to 0.91 after exclusion of 8 patients receiving corticosteroids. A cutoff of 211 activated CD4+ effector memory T cells per 100 mL urine yielded a sensitivity of 78% and a specificity of 81%. Urinary activated CD4+ effector memory T cell counts correlated with renal CD4+ and CD4+ CD38+ T cell infiltration in acute interstitial nephritis. Conclusions Urinary activated CD4+ effector memory T cells expressing CD38 and HLA-DR represent a promising non-invasive biomarker for the diagnosis of acute interstitial nephritis.