Mutations In PKD1 Research Articles

The role of the co-chaperone DNAJB11 in polycystic kidney disease: Molecular mechanisms and cellular origin of cyst formation.

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2, encoding polycystin-1 (PC1) and polycystin-2 (PC2), which are required for the regulation of the renal tubular diameter. Loss of polycystin function results in cyst formation. Atypical forms of ADPKD are caused by mutations in genes encoding endoplasmic reticulum (ER)-resident proteins through mechanisms that are not well understood. Here, we investigate the function of DNAJB11, an ER co-chaperone associated with atypical ADPKD. We generated mouse models with constitutive and conditional Dnajb11 inactivation and Dnajb11-deficient renal epithelial cells to investigate the mechanism underlying autosomal dominant inheritance, the specific cell types driving cyst formation, and molecular mechanisms underlying DNAJB11-dependent polycystic kidney disease. We show that biallelic loss of Dnajb11 causes cystic kidney disease and fibrosis, mirroring human disease characteristics. In contrast to classical ADPKD, cysts predominantly originate from proximal tubules. Cyst formation begins in utero and the timing of Dnajb11 inactivation strongly influences disease severity. Furthermore, we identify impaired PC1 cleavage as a potential mechanism underlying DNAJB11-dependent cyst formation. Proteomic analysis of Dnajb11- and Pkd1-deficient cells reveals common and distinct pathways and dysregulated proteins, providing a foundation to better understand phenotypic differences between different forms of ADPKD.

Genetic analysis and counseling of ADPKD caused by novel heterozygous mutations of PKD1 in two Chinese families: Case report

Genetic analysis and counseling of ADPKD caused by novel heterozygous mutations of PKD1 in two Chinese families: Case report

Correlation between PKD1 Mutation Type and Height-Adjusted Total Kidney Volume in Chinese Patients with ADPKD: Genotype-Phenotype Analysis

Correlation between PKD1 Mutation Type and Height-Adjusted Total Kidney Volume in Chinese Patients with ADPKD: Genotype-Phenotype Analysis

Pkd1 Mutation Modulates Cognitive Function via N-methyl-D-aspartate Receptor-Mediated Synaptic Transmission and Autophagy

Pkd1 Mutation Modulates Cognitive Function via N-methyl-D-aspartate Receptor-Mediated Synaptic Transmission and Autophagy

Unusual familial cystic kidney disease: combining fine radiologic and genetic evaluation to solve the case

BackgroundAutosomal dominant polycystic kidney disease (ADPKD) is the most prevalent hereditary kidney disease, characterized by enlarged kidneys with numerous cysts, high blood pressure, and a variety of extrarenal complications. This disease is a significant cause of renal failure and requires accurate differentiation from other cystic kidney diseases, especially when family history does not clearly indicate ADPKD. This is crucial due to differences in prognosis, treatment, and familial implications. Advanced molecular genetics and imaging techniques are employed to diagnose and assess the prognosis of patients and their families.Case presentationThe case study revolves around three patients from the same family—two sisters and one daughter—referred to a nephrology department for ADPKD management. The initial proband, a 42-year-old woman, experienced abdominal discomfort leading to an ultrasound that suggested ADPKD. However, MRI findings indicated standard-sized kidneys with bilateral parapelvic cysts, and no genetic markers for ADPKD were found. Her sister, presenting with controlled hypertension and similar ultrasound findings, also had her initial ADPKD diagnosis refuted by MRI and genetic testing, which revealed no significant mutations. The daughter, however, exhibited a different scenario with enlarged kidneys and multiple cysts characteristic of early-stage ADPKD. Genetic testing confirmed a deleterious PKD1 mutation, suggesting a de novo mutation, as her father showed no signs of the disease.ConclusionThis study highlights the complexity and necessity of thorough diagnostic processes in suspected ADPKD cases to prevent misdiagnosis. The initial symptoms and imaging might misleadingly suggest ADPKD, as seen in the cases of the two older patients. Still, further detailed imaging and genetic analyses revealed no ADPKD, preventing inappropriate treatment and stress. In contrast, the younger patient's distinctive clinical and genetic profile confirmed ADPKD, illustrating the variability within even closely related individuals. Such detailed assessments are crucial in guiding correct treatment decisions and providing accurate familial counseling, emphasizing the importance of considering a broader spectrum of renal cystic disorders before confirming a diagnosis of ADPKD.

The Influence of Non-Pharmacological and Pharmacological Interventions on the Course of Autosomal Dominant Polycystic Kidney Disease.

Polycystic kidney disease (PKD) includes autosomal dominant (ADPKD) and autosomal recessive (ARPKD) forms, both of which are primary genetic causes of kidney disease in adults and children. ADPKD is the most common hereditary kidney disease, with a prevalence of 329 cases per million in Europe. This condition accounts for 5-15% of end-stage chronic kidney disease (ESKD) cases, and in developed countries such as Poland, 8-10% of all dialysis patients have ESKD due to ADPKD. The disease is caused by mutations in the PKD1 and PKD2 genes, with PKD1 mutations responsible for 85% of cases, leading to a more aggressive disease course. Recent research suggests that ADPKD involves a metabolic defect contributing to cystic epithelial proliferation and cyst growth. Aim: This review explores the interplay between metabolism, obesity, and ADPKD, discussing dietary and pharmacological strategies that target these metabolic abnormalities to slow disease progression. Conclusion: Metabolic reprogramming therapies, including GLP-1 analogs and dual agonists of GIP/GLP-1 or glucagon/GLP-1 receptors, show promise, though further research is needed to understand their potential in ADPKD treatment fully.

Automatically Detecting Pancreatic Cysts in Autosomal Dominant Polycystic Kidney Disease on MRI Using Deep Learning.

Pancreatic cysts in autosomal dominant polycystic kidney disease (ADPKD) correlate with PKD2 mutations, which have a different phenotype than PKD1 mutations. However, pancreatic cysts are commonly overlooked by radiologists. Here, we automate the detection of pancreatic cysts on abdominal MRI in ADPKD. Eight nnU-Net-based segmentation models with 2D or 3D configuration and various loss functions were trained on positive-only or positive-and-negative datasets, comprising axial and coronal T2-weighted MR images from 254 scans on 146 ADPKD patients with pancreatic cysts labeled independently by two radiologists. Model performance was evaluated on test subjects unseen in training, comprising 40 internal, 40 external, and 23 test-retest reproducibility ADPKD patients. Two radiologists agreed on 52% of cysts labeled on training data, and 33%/25% on internal/external test datasets. The 2D model with a loss of combined dice similarity coefficient and cross-entropy trained with the dataset with both positive and negative cases produced an optimal dice score of 0.7 ± 0.5/0.8 ± 0.4 at the voxel level on internal/external validation and was thus used as the best-performing model. In the test-retest, the optimal model showed superior reproducibility (83% agreement between scan A and B) in segmenting pancreatic cysts compared to six expert observers (77% agreement). In the internal/external validation, the optimal model showed high specificity of 94%/100% but limited sensitivity of 20%/24%. Labeling pancreatic cysts on T2 images of the abdomen in patients with ADPKD is challenging, deep learning can help the automated detection of pancreatic cysts, and further image quality improvement is warranted.

Polycystin-1 loss of function increases susceptibility to atrial fibrillation through impaired DNA damage response.

The increasing prevalence of atrial fibrillation (AF) and chronic kidney diseases highlights the need for a deeper comprehension of the molecular mechanisms linking them. Mutations in PKD1, the gene encoding Polycystin-1 (PKD1 or PC1), account for 85% of autosomal dominant polycystic kidney disease (ADPKD) cases. This disease often includes cardiac complications such as AF. In cardiomyocytes, PC1 deletion reduces hypertrophic response to pressure overload but promotes baseline ventricular dysfunction, while deletion in fibroblasts ameliorates post-myocardial infarction fibrosis. Despite its known cardiac impact, the role of PC1 in atrial cardiomyocytes and arrhythmias is less understood. Here, we sought to investigate the role of PC1 in AF. We used intracardiac programmed stimulation and optical mapping to evaluate AF inducibility in two mouse models, Pkd1 R3277C, which recapitulates human ADPKD progression, and cardiomyocyte-specific Pkd1 deletion, and their respective controls. Isolated adult mouse atrial cardiomyocytes, human iPSC-derived atrial cardiomyocytes (hiPSC-aCM), and HL-1 cells served as in vitro cellular models. Molecular mechanisms were evaluated using optical mapping and molecular and biochemical approaches. Loss-of-function PC1 mutations significantly increased AF susceptibility in vivo and facilitated local reentry in ex vivo left atrial appendages. Comprehensive in vitro experiments supported a direct effect of PC1 in atrial cardiomyocytes. PC1-deficient monolayers exhibited increased arrhythmic events, escalating into reentrant spiral waves post-tachypacing. Transcriptomics analysis revealed PC1-dependent regulation of DNA repair, with PC1 deficiency leading to increased DNA damage under stress. PARP1 inhibitors or nicotinamide riboside, which counteract DNA damage-related metabolic consequences, reduced in vitro arrhythmias PC1-deficient monolayers. Overexpression of the C-terminus of PC1 had the opposite effects in DNA repair genes, suggesting its regulatory effects in atrial cardiomyocytes through retinoblastoma/E2F. Analyses of human atrial tissue from non-ADPKD patients showed reduced levels of mature PC1, suggesting a broader relevance of impaired PC1 in AF. Impaired PC1 increases in vivo AF inducibility under programmed electrical stimulation and promotes in vitro arrhythmias in hiPSC-aCM and HL-1 cells. Our findings indicate that PC1 protects against DNA damage to reduce AF susceptibility.

Decoupling shear stress and pressure effects in the biomechanics of autosomal dominant polycystic kidney disease using a perfused kidney-on-chip.

Kidney tubular cells are submitted to two distinct mechanical forces generated by the urine flow: shear stress and hydrostatic pressure. In addition, the mechanical properties of the surrounding extracellular matrix modulate tubule deformation under constraints. These mechanical factors likely play a role in the pathophysiology of kidney diseases as exemplified by autosomal dominant polycystic kidney disease, in which pressure, flow and matrix stiffness have been proposed to modulate the cystic dilation of tubules with PKD1 mutations. The lack of in vitro systems recapitulating the mechanical environment of kidney tubules impedes our ability to dissect the role of these mechanical factors. Here we describe a perfused kidney-on-chip with tunable extracellular matrix mechanical properties and hydrodynamic constraints, that allows a decoupling of shear stress and flow. We used this system to dissect how these mechanical cues affect Pkd1 -/- tubule dilation. Our results show two distinct mechanisms leading to tubular dilation. For PCT cells (proximal tubule), overproliferation mechanically leads to tubular dilation, regardless of the mechanical context. For mIMCD-3 cells (collecting duct), tube dilation is associated with a squamous cell morphology but not with overproliferation and is highly sensitive to extracellular matrix properties and hydrodynamic constraints. Surprisingly, flow alone suppressed Pkd1 -/- mIMCD-3 tubule dilation observed in static conditions, while the addition of luminal pressure restored it. Our in vitro model emulating nephron geometrical and mechanical organization sheds light on the roles of mechanical constraints in ADPKD and demonstrates the importance of controlling intraluminal pressure in kidney tubule models.

PKD1 mutant clones within cirrhotic livers inhibit steatohepatitis without promoting cancer

Somatic mutations in non-malignant tissues are selected for because they confer increased clonal fitness. However, it is uncertain whether these clones can benefit organ health. Here, ultra-deep targeted sequencing of 150 liver samples from 30 chronic liver disease patients revealed recurrent somatic mutations. PKD1 mutations were observed in 30% of patients, whereas they were only detected in 1.3% of hepatocellular carcinomas (HCCs). To interrogate tumor suppressor functionality, we perturbed PKD1 in two HCC cell lines and six invivo models, in some cases showing that PKD1 loss protected against HCC, but in most cases showing no impact. However, Pkd1 haploinsufficiency accelerated regeneration after partial hepatectomy. We tested Pkd1 in fatty liver disease, showing that Pkd1 loss was protective against steatosis and glucose intolerance. Mechanistically, Pkd1 loss selectively increased mTOR signaling without SREBP-1c activation. In summary, PKD1 mutations exert adaptive functionality on the organ level without increasing transformation risk.

Improved predictions of total kidney volume growth rate in ADPKD using two-parameter least squares fitting

Mayo Imaging Classification (MIC) for predicting future kidney growth in autosomal dominant polycystic kidney disease (ADPKD) patients is calculated from a single MRI/CT scan assuming exponential kidney volume growth and height-adjusted total kidney volume at birth to be 150 mL/m. However, when multiple scans are available, how this information should be combined to improve prediction accuracy is unclear. Herein, we studied ADPKD subjects (n=36\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n = 36$$\\end{document}) with 8+ years imaging follow-up (mean = 11 years) to establish ground truth kidney growth trajectory. MIC annual kidney growth rate predictions were compared to ground truth as well as 1- and 2-parameter least squares fitting. The annualized mean absolute error in MIC for predicting total kidney volume growth rate was 2.1%±2%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$2.1\\% \\pm 2\\%$$\\end{document} compared to 1.1%±1%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.1\\% \\pm 1\\%$$\\end{document} (p=0.002\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p = 0.002$$\\end{document}) for a 2-parameter fit to the same exponential growth curve used for MIC when 4 measurements were available or 1.4%±1%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1.4\\% \\pm 1\\%$$\\end{document} (p=0.01\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p = 0.01$$\\end{document}) with 3 measurements averaging together with MIC. On univariate analysis, male sex (p=0.05\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p = 0.05$$\\end{document}) and PKD2 mutation (p=0.04\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$p = 0.04$$\\end{document}) were associated with poorer MIC performance. In ADPKD patients with 3 or more CT/MRI scans, 2-parameter least squares fitting predicted kidney volume growth rate better than MIC, especially in males and with PKD2 mutations where MIC was less accurate.

#174 Valvulopathies and left ventricular hypertrophy in ADPKD: prevalence and association with genotype and phenotype

Abstract Background and Aims Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited nephropathy due to mutations in PKD1 or PKD2 genes. In addition to kidney involvement, ADPKD is also characterized by extrarenal manifestations including the presence of cysts in other organs, intracranial aneurysms, arterial hypertension, valvulopathies and left ventricular hypertrophy (LVH). Cardiac abnormalities are an important cause of morbidity and mortality in ADPKD patients. Limited data on the association between these cardiovascular manifestations with phenotypic (both renal and systemic) and genotypic features of ADPKD are currently available. In this study we report the prevalence of the main cardiac abnormalities (valvulopathies, with a focus on aortic, mitral, tricuspid valve regurgitation, mitral prolapse, and LVH) observed in a large cohort of ADPKD patients, and investigated their association with renal diameter, renal function, other systemic manifestations such as pancreatic cysts, intracranial cysts, intracranial aneurysm and genotype. Method This retrospective study was conducted at the A. Gemelli Hospital, Rome in a single-center cohort of 129 ADPKD patients, who had previously undergone echocardiogram, abdominal ultrasound, brain MRI, and blood tests, between January 2018 and July 2023. Genetic testing was performed in 58 of the 129 patients. For the statistical analysis the average bilateral renal diameter of each patient was used. An interventricular septum cut-off thickness of 11 mm was used to define left ventricular hypertrophy. Non-parametric (Mann–Whitney and Spearman) and chi-square tests were applied as appropriate. Results In our cohort of 129 patients, the prevalence of valvulopathies was the following: 68% of mitral regurgitation, 22% of mitral prolapse, 20% of aortic regurgitation and 56% of tricuspid regurgitation. Left ventricular hypertrophy was identified in 28% of the entire cohort. We found that in ADPKD patients with aortic regurgitation, renal diameters are larger (p = 0.027) and the eGFR is lower (p < 0.01) than in patients without this echocardiographic abnormality (Fig. 1a,b). In the subset of genotyped ADPKD patients (58), mutations in PKD 1 were associated with mitral prolapse (p = 0.02). Interventricular septal thickness, regardless of the presence of hypertrophy was positively correlated (Fig. 1c) with renal diameter (p = 0.001 r = +0.289) and negatively (Fig. 2a) with eGFR (p < 0.001 r = −0.422). Both correlations, also adjusted for arterial hypertension, remained statistically significant (p = 0.008, coefficient r = +0.235 and p < 0.001, coefficient r = −0.304, respectively). In addition, patients with LVH featured a larger renal diameter (p = 0.03), and a lower eGFR (p < 0.001) (Fig. 2b-c). Moreover LVH was associated with the presence of PKD1 mutations (p = 0.03). Neither valvulopathies nor LVH were associated with other systemic manifestations of the disease. Conclusion We show for the first time an association of LVH with ADPKD genotype (specifically mutations in PKD1) and the association of a specific valvulopathy (aortic regurgitation) with the renal phenotype of ADPKD patients. To date only one study found an association of another valvulopathy, mitral regurgitation, with mutations in PKD1 [1]. Heart valves disease and LVH are risk factors for the subsequent development of further cardiovascular complications therefore understanding the pathogenetic mechanisms responsible for the higher incidence of these abnormalities in ADPKD would be useful to identify high-risk subgroups of patients and tailor personalised interventions.

#1049 Genetic characteristics of autosomal dominant polycystic kidney disease in a Greek population

Abstract Background and Aims Autosomal dominant polycystic kidney disease (ADPKD) is the predominant monogenic renal genetic disorder, and the fourth leading cause of end stage kidney disease. Confirmatory genetic testing defines the disease, provides prognostic information and may support therapeutic management. This study aims to investigate the genetic characteristics of a substantial cohort of ADPKD patients from a single Greek center. Method Ninety-three patients (46 females, 47 males with a mean age of 34 ± 15 years) were enrolled from 59 distinct families attending the outpatient ADPKD clinic at the Nephrology Department of the General Hospital of Athens “G. Gennimatas.” Genetic analysis included targeted next-generation sequencing (tNGS) of over 600 clinically relevant genes, Sanger sequencing, and Multiplex ligation-dependent probe amplification (MLPA). Whole exome and whole genome sequencing (WES and WGS) studies were conducted in 3 patients with negative results. Magnetic Resonance Imaging (MRI) was performed in 74 out of 93 patients, revealing more than 10 renal cysts in all but one patient. Children with a positive family history (FH) displayed at least one cyst in echography, while two without FH had multiple renal cysts. Results Genetic diagnosis was established in 88 of 93 patients (94.5%). Seventy patients (75%), demonstrated single nucleotide variants (SNVs) and large deletions (4 patients) in the PKD1 gene, whereas SNVs and large deletions (5 patients) in the PKD2 gene were identified in 15 (16%) patients. Additionally, mutations in genes other than PKD1 and PKD2 were identified in 3 patients (3.5%). Two cases, involving a father and son, revealed the presence of a SEC61B variant; the father exhibited more than 10 renal cysts and liver cysts in the MRI, while the son displayed only liver cysts. Additionally, a third patient, a woman with nephrolithiasis and over 10 renal cysts in the MRI, exhibited a SLC3A1 variant. Notably, 5 patients (5.5%) with ADPKD phenotype had negative genetic analyses, despite the application of both WES and WGS in three of these patients. Truncating mutations in PKD1 were observed in 43 of 70 cases, (61%), while the rest (39%) had non-truncating mutations. Detected variants were classified as Pathogenic (45.5%), Likely Pathogenic (36%), and Variants of Uncertain Significance (VUS-13.5%, 12 cases), according to the guidelines of the American College of Medical Genetics and Genomics. Reclassification to Likely Pathogenic could be proposed for 6 out of 12 cases with VUS variants for which family segregation was noted. Finally, 52% and 82% of the detected variants have not been previously reported in ClinVar and gnomAD databases, respectively. Conclusion In this ethnically homogenous population, truncating mutations in the PKD1 gene were the predominant genetic cause of ADPKD, followed by PKD1 non-truncating mutations, PKD2 gene variants and other rare or undefined genetic etiologies.

#2048 Exploring somatic mutation mechanisms in pre-cystic renal cells of autosomal dominant polycystic kidney disease patients

Abstract Background and Aims Genetic changes accumulate in our cells during a lifetime, at a rate that varies according to cell type and mutagen exposure [1]. Somatic mutations are the driving force of cancer and contribute to “second hit” disorders, such as Autosomal Dominant Polycystic Kidney Disease (ADPKD). ADPKD is caused by inherited mutations that disrupt one allele of PKD1 or PKD2 genes. Somatic loss of the second allele triggers tubule cell clonal expansion and the formation of renal cysts. Given the high number of cysts that form during a lifetime, somatic mutation rates may be abnormally high in the kidney of ADPKD patients. The identification of factors enhancing somatic mutation rates can lead to preventive strategies to limit cyst formation. Metabolic alterations, i.e. increased glutamine utilization and reduced urea cycle, have been shown to induce somatic mutations in cancer [2]. Loss of urea cycle increases pyrimidine synthesis, which unbalances the nucleotide pools and results in a distinct signature of single base substitutions (SBSs) [1]. Similar metabolic changes have been observed in ADPKD [3, 4]. Thus, we sought to test metabolism-driven somatic mutagenesis in pre-cystic kidneys and its contribution to second hit mutations in ADPKD. Method We clonally expanded normal kidney cells from human urine samples and performed a gene expression study by qPCR. We studied 31 clones from 4 ADPKD patients (age range: 25-45) with truncating mutations in PKD1 and normal kidney function, despite a clear cystic phenotype. ADPKD cells were compared to 55 clones from 5 healthy volunteers (age range: 24-53), and 32 clones from 6 patients with another cystic kidney disease, Von Hippel Lindau disease (VHL; age range: 29-56). A subset of clones (n = 19 controls, n = 12 ADPKD) was subjected to whole genome sequencing and somatic mutation analysis. Results Urines of ADPKD patients contained higher numbers of cells that expanded in vitro, compared to both control (p = 0.0008) and VHL individuals (p = 0.01). Gene expression analyses showed that irrespective of genetic background, all cultured clones originated from the kidney tubule epithelium (high PAX2 and PAX8), and some originated from damaged tubules (VCAM1, KIM1). We tested the hypothesized metabolic rewiring by analyzing expression levels of enzymes involved in glutamine utilization, urea cycle, and pyrimidine biosynthesis. Except for ASNS (Asparagine Synthetase), which was higher in ADPKD vs control clones (p = 0.0098), no gene-expression differences were observed. However, clones from ADPKD patients showed signs of the metabolic rewiring responsible for increased pyrimidine production, i.e. a positive correlation (r = 0.691; p < 0.0001) between urea cycle enzymes downregulation and upregulation of the pyrimidine synthesis enzyme CAD. Since excessive pyrimidines lead to mutation [2], we analyzed the number of somatic SBSs per genome, after filtering for germline variants. We did not find increased mutation rates in ADPKD compared to controls, but an analogous, linear increase of mutations with age and similar levels of the pyrimidine-rich mutational signature. Conclusion Urine-derived kidney tubule epithelial cells with heterozygous truncating mutations in PKD1 exhibit certain characteristics of metabolic reprogramming typical of kidneys from ADPKD patients with advanced pathology. Nevertheless, in the limited number of pre-cystic cells that we have analyzed, this metabolic reprogramming did not translate into an excess of somatic mutations.

#1428 Rnd3, a novel gene involved in ADPKD

Abstract Background and Aims Autosomal dominant polycystic kidney disease (ADPKD) is an adult-onset, multi-systemic disorder, that affects ∼12.5 million people worldwide. ADPKD is characterised by progressive kidney enlargement caused by uncontrollable growth of cysts, alongside extra-renal phenotypes such as cysts in the liver, pancreas, and hypertension. Truncated mutations in PKD1 and PKD2 that encode for PC1 and PC2, respectively, are responsible for 85% and 15% of reported cases. Mutations in PKD1 are associated with the more severe form of ADPKD and earlier mean age of onset. The phenotypic variability of ADPKD can be attributed to genic, allelic and gene modifier effects. Modifier genes influence the molecular and/or phenotypic expression of other genes, altering the range of symptoms and the severity of the disease. In mice with a single gene mutation, modifier genes reduce the penetrance, dominance modification, expressivity, and phenotypic pleiotropy. To understand the involvement of modifier genes in the ADPKD kidney phenotype, a novel mouse model Rnd3tm1b(EUCOMM)Hmgu was generated, and in adult and aged Rnd3tm1b/+ mice, a kidney phenotype characteristic of ADPKD was evident. Rnd3 is an atypical member of the Rnd subgroup of the Rho family of GTPases and has a role in actin cytoskeleton reorganisation, cell cycle progression, and cell migration. Method 5 and 9-month-old kidneys from Rnd3tm1b/+ and age-matched wildtype mice were studied. In the Rnd3tm1b (EUCOMM)Hmgu mouse model, the TB1B mutation causes an inactivation of Rnd3 via the deletion of Exon 2 in C57BL/6N mice. RT-qPCR and SDS-Page Westerns were performed as well as staining for markers associated with Polycystic Kidney Disease. Results The onset of cyst formation in the cortex is apparent in 5-month-old Rnd3tm1b/+ kidneys compared to age-matched wildtype kidneys (Fig. 1a). A statistically significant 10% (p < 0.0465) increase in the proliferative index was observed in 5-month-old Rnd3tm1b/+ mice (Fig. 1e,f). Vimentin expression was also increased in podocytes and confirmed by a statistically significant 25% (p < 0.0461) increase in Rnd3tm1b/+ kidneys (Fig. 1g,h). Aquaporin-2 (Aqp2) expression was decreased in collecting ducts and verified by a statistically significant 0.4-fold-change (p < 0.0451) decrease in protein level in kidneys of 5-month-old Rnd3tm1b/+ mice (Fig. 1i-k). A statistically significant 0.75-fold (p < 0.0006) and 1.5-fold-increase (p < 0.02) in Pkd1 and Pkd2 expression was observed in 5-month-old Rnd3tm1b/+ kidneys, respectively (Fig. 1c). Kidneys of 9-month-old Rnd3tm1b/+mice presented with multiple cysts in the cortex, mimicking the ADPKD kidney phenotype (Fig. 1b). Vimentin staining in podocytes was increased and confirmed by a statistically significant 14% (p < 0.0419) increase in Rnd3tm1b/+mice (Fig. 1l,m). Expression of Pkd1 and Pkd2 was downregulated by a statistically significant 0.39-fold (p < 0.0001) and 0.2-fold-change (p < 0.004) in Rnd3tm1b/+mice (Fig. 1d). Conclusion Together, these findings highlight the importance of Rnd3 as a potential modifier in the onset of ADPKD by mediating the expression of Pkd1 and Pkd2. Interestingly, there is a critical window where Pkd1 and Pkd2 expression is altered, exacerbating the phenotype between 5 and 9-month-old Rnd3tm1b/+ mice. In addition to this, by understanding how modifiers are involved in triggering the onset of phenotypes in ADPKD, potential diagnostic and therapeutic measures can be discovered to ultimately aid in diagnosing ADPKD at a much earlier stage.

#1040 Correlation of genotype to disease onset age and hypertension diagnosis in autosomal dominant polycystic kidney disease

Abstract Background and Aims Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the predominant genetic disease leading to End Stage Kidney Disease (ESKD). Genetic identity could correlate to the disease profile. Correlations between genetic and phenotype characteristics in a cohort of ADPKD patients are investigated. Method Genetic analysis was conducted in 85 patients with an ADPKD phenotype, employing targeted Next Generation (tNGS) or Sanger Sequencing and Multiplex ligation-dependent probe amplification (MLPA). Medical history, clinical and laboratory data, including Renal Magnetic Resonance Imaging (MRI) for Total Kidney Volume (TKV) measurement (in 66 patients), were recorded and subsequently correlated to the respective genotypes. Results Eighty-five patients (43 females, 42 males, 33 ± 16 years old) were included in the study. The mean age at diagnosis of the disease was at 21.5 ± 13 (0.6-69) years. Fifty-eight out of 85 patients (68%) had a familial history of ADPKD. The mean age at which the affected parent reached ESKD was 53.0 ± 9 years. Hypertension was diagnosed in 60 individuals (71%) within the study cohort. The mean age at hypertension diagnosis was 31 ± 11 years. In the assessment based on height-adjusted TKV and age, the Mayo Clinic Imaging Categories revealed that 9% of patients were classified as 1A, 20% as 1B, 29% as 1C, 29% as 1D, and 13% as 1E. Mutations in PKD1 gene were detected in 70 patients (82%), with 61% exhibiting truncating mutations and 39% non-truncating mutations, while PKD2 mutations were identified in 15 patients (18%). The average age of ADPKD diagnosis differed among genetic subgroups. Patients carrying PKD1-truncating mutations were diagnosed at 17.6 ± 11 years, those with PKD1-non-truncating mutations at 24.5 ± 12 years, and those with PKD2 mutations at 27.3 ± 16 years (p = 0.01). Moreover, the mean age at which the affected parent reached ESKD was 50 ± 8 years, 55 ± 10 and 60 ± 7 years in PKD1-truncating, PKD1-non-truncating and PKD2 patients respectively (p = 0.04). Additionally, the mean age of hypertension diagnosis was 29 ± 12 years in PKD1-truncating, 30 ± 10 years in PKD1-non-truncating and 40 ± 7 years in PKD2 patients (p = 0.05). Conclusion Mutation type correlates with the age of ADPKD diagnosis, the renal survival within families and the hypertension onset. Patients with PKD1-truncating mutations manifest an earlier onset of both the disease and hypertension compared to those with PKD2 gene mutations.

#2416 Bicc1 and PKD: linking RNA metabolism to kidney disease

Abstract Background and Aims Mutations in PKD1 or PKD2 lead to autosomal dominant polycystic kidney disease (PKD) by allowing urine flow-sensing primary cilia to activate tissue growth signals. However, the responsible cilia-associated factors and a strategy to block them and cure PKD are elusive. Cilia also specify organ laterality. In this process, flow-stimulated cilia activate the cytosolic protein Bicaudal-C (Bicc1) to curb the translation and/or the stability of specific target mRNAs. To identify candidate regulatory factors, we investigated if Bicc1 ribonucleoprotein particle (RNP) formation involves known proteins linked to cilia and cystic kidney diseases. Method To address this question, we here used AlphaFold structure modeling of protein complexes, combined with in vitro reconstitution assays and live imaging of Bicc1 RNP assembly. To begin to validate these interactions, we tested by genetic approaches if specific interacting factors also regulate Bicc1 targets in cells and mice. Results We found that multivalent interactions with structured domains of the ankyrin repeat and SAM domain containing (ANKS) 3 and their allosteric regulation by the related ANKS6 protein inhibit or restore Bicc1 access to target mRNAs, respectively. Concomitantly, ANKS3 alone increased the solubility and fluidity of Bicc1, whereas co-recruitment of ANKS6 had the opposite effect, liberating Bicc1 to self-polymerize and to induce phase-transitioning of target mRNAs in gel-like meshworks. Conclusion Perturbations in Bicc1-ANKS3-ANKS6 RNP dynamics and altered translation of Bicc1 target mRNAs emerge as likely culprits regulating cyst formation downstream of ciliary defects. ANKS6 can be sequestered in cilia by inversin, and mutations in these proteins provoke kidney cysts in nephronophthisis patients. Therefore, besides systematically profiling Bicc1 RNPs, future studies should test if ANKS6 mediates their dynamic regulation by flow-stimulated cilia.

#1790 Metformin versus standard of care in slowing progression of autosomal dominant polycystic kidney disease and correlation with total kidney volume

Abstract Background and Aims Autosomal dominant kidney disease (ADPKD) is the most common monogenic disorder leading to renal failure with very limited therapeutic options. Apart from lifestyle modifications and control of hypertension, tolvaptan is the only Food and Drug Administration (FDA) approved disease modifying drug. Although, it has proven therapeutic benefit in slowing disease progression in high risk Mayo Class (Mayo Class 1C-E), the aquaretic potential, potential hepatotoxicity and the cost limits its widespread use especially in resource constrained country. Metformin has been shown to be effective in ADPKD in preclinical studies and is also well tolerated by the general population. We planned this study to assess the efficacy and safety of metformin in non diabetic ADPKD patients. Method Our study is a prospective, randomized controlled, open labelled clinical trial of 52 non diabetic adults 18 to 60 years of age with typical ADPKD, estimated glomerular filtration rate (eGFR) > 45 ml/min/m2 and no risk factors of rapid progression. Participants were randomized in a 1:1 ratio by a computer-generated random number table into Metformin + standard of care group (Metformin arm) and standard of care group (Placebo arm). Primary outcome of the study was to evaluate the effects of metformin versus placebo arm on the percentage and absolute change in eGFR over 6-month period. Secondary outcomes were to study the effect of metformin versus placebo arm on the percentage and absolute change in height adjusted total kidney volume (htTKV ml/m) at 6 months, to evaluate the effect of baseline plasma copeptin levels with percentage change in htTKV and eGFR over 6 months, to evaluate metformin tolerability, to evaluate the effects of metformin versus placebo on the changes in body weight, BMI, blood pressure and urine protein excretion at 6 months period. Results Mean (SD) age of the cohort was 37.15 (10.16) years with half of them being females. The mean (SD) baseline htTKV and eGFR was 335.67 (153.3) ml/m and 100.23 (25.95) ml/min/m2. Clinical exome sequencing was available in 9 (17.3%) patients of which two third had PKD1 mutation. Baseline characteristics were distributed equally across randomized groups. Baseline proteinuria was significantly higher in the Metformin arm (p = 0.014). The eGFR difference and percentage change in eGFR was not different between the groups at 6 months (p = 0.535, 0.483). There was no statistically significant difference in htTKV difference and percentage change in htTKV at 6 months between the groups although increase in htTKV was numerically smaller in the metformin group (p = 0.769, 0.805). Blood pressure, weight, body mass index (BMI) and proteinuria also did not differ between two groups. Half of the cohort tolerated the maximum dose of metformin. Around 2/3rd patients reported adverse effects most commonly asthenia. There was no lactic acidosis or significant gastrointestinal side effects as assessed by gastrointestinal rating scale (GSRS) scale. Baseline copeptin levels did not correlate with eGFR or htTKV difference at 6 months. Conclusion Metformin appears to be safe and tolerable in non diabetic ADPKD patients over 6 months. However larger clinical trials are needed to conclude regarding the efficacy in terms of eGFR decline or htTKV progression.

#2715 Towards precise prediction of prognosis in ADPKD: a comprehensive biomarker analysis

Abstract Background and Aims Determining prognosis in patients with autosomal dominant polycystic kidney disease (ADPKD) heavily relies on the height-adjusted total kidney volume (HtTKV) Mayo classification. This classification predicts kidney outcomes on a group level but lacks precision in individual patients. Recently, several urine and blood biomarkers have demonstrated prognostic value in ADPKD, independent of HtTKV and baseline eGFR. This study compares the prognostic value of various biomarkers to aid selection when developing novel risk stratification tools. Method Included were participants of the DIPAK studies with a follow-up duration of >1 year and ≥3 eGFR measurements. We excluded patients with diabetes mellitus and patients using tolvaptan or somatostatin analogues. At baseline, urine samples were analyzed for albumin, urea, creatinine, β2-microglobulin (β2-MG), monocyte chemotactic protein-1 (MCP-1), TmP/GFR (tubular maximum reabsorption rate of phosphate to GFR), and blood was drawn to measure creatinine, urea (for assessment of urinary-to-plasma urea ratio; UP urea), glucagon, fibroblast growth factor 23 (FGF-23) and copeptin. Albumin, β2-MG and MCP-1 were divided by urinary creatinine concentration to account for concentration effects. The cross-sectional and longitudinal association with baseline eGFR and eGFR decline over time was analyzed using multivariate linear regression and repeated measures linear mixed model regression. Furthermore, logistic regression models were tested to identify patients with rapidly-progressive disease (eGFR slope ≤ −3.0 ml/min/1.73 m2/year). Lastly, multivariate Cox regression analysis was conducted to evaluate the time to the combined endpoint of 30% decline in eGFR, reaching an eGFR ≤ 15 ml/min/1.73 m2, initiation of dialysis or receiving a kidney transplant. Results 565 patients were included with a mean age of 47 ± 11 years, eGFR of 64 ± 27 ml/min/1.73 m2 and HtTKV of 858 [IQR: 540, 1305] ml/m. During a mean follow-up of 5.2 ± 2.2 years, the mean eGFR decline was −3.38 ± 2.37 mL/min/1.73 m2/year. Of these patients, 283 (50.1%) had rapidly progressive disease and 267 (47.3%) reached the combined kidney endpoint. All biomarkers except glucagon were associated with baseline eGFR and eGFR decline over time after adjustment for established clinical risk factors for disease progression (sex, PKD mutation and baseline age and eGFR). After adjustment for the same covariates, albumin/creatinine, MCP-1/creatinine, FGF-23, UP-urea and copeptin were predictive of rapid disease progression. The area under the curve (AUC) value for predicting rapidly progressive disease for the Mayo HtTKV classification alone was 0.694, which could be improved to 0.766 (P < .001) by a risk prediction model that also included the aforementioned predictive clinical risk factors. The introduction of several biomarkers further improved this clinical model, including albumin/creatinine (AUC 0.794, p = 0.03), MCP-1/creatinine (AUC 0.804, p = 0.04) and copeptin (AUC 0.789, p = 0.05). Similar results were seen in multivariate Cox regression models after adjustment for covariates, with independent predictors of the combined endpoint being again albumin/creatinine (P < .001), MCP-1 creatinine (P < .001), copeptin (p = 0.012), but now also UP-urea (p = 0.008) and FGF-23 (P < .001). These findings appeared robust in subgroup analyses of 200 patients with Mayo HtTKV class 1C and 122 patients with early disease (age ≤ 40 years and eGFR ≥ 60 ml/min/1.73 m2 at baseline), in whom predicting prognosis is most challenging. Conclusion In patients with ADPKD, albumin/creatinine, MCP-1/creatinine, FGF-23 and copeptin are consistent predictors of kidney outcomes after adjustment for established clinical risk factors. Our data suggest that these biomarkers should be prioritized when developing novel multimarker models to enhance precision of risk prediction in ADPKD.

Kidney Measurement and Glomerular Filtration Rate Evolution in Children with Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited disorder characterized by renal tubular cystic dilatations. The cysts can develop anywhere along the nephron, and over time the cystic dilatation leads to kidney enlargement. On the other hand, the cysts begin to reduce the number of functional nephrons as a consequence of cystic expansion that further contributes to the decline in renal function over the years. The pressure exerted by the dilated cysts leads to compensatory mechanisms that further contribute to the decline in renal function. These structural changes are responsible of glomerular hyperfiltration states, albuminuria, proteinuria, and hematuria. However, the presentation of ADPKD varies in children, from a completely asymptomatic child with incidental ultrasound detection of cysts to a rapidly progressive disease. There have been reports of early onset ADPKD in children younger than 2 years that showed a more rapid decline in renal function. ADPKD is caused by a mutation in PKD1 and PKD2 genes. Today, the PKD1 gene mutation seems to account for up to 85% of the cases worldwide, and it is associated with worse renal outcomes. Individuals with PKD2 gene mutation seem to present a milder form of the disease, with a more delayed onset of end-stage kidney disease. The cardinal sign of ADPKD is the presence of renal cysts during renal ultrasound. The current guidelines provide clinicians the recommendations for genetic testing in children with a positive family history. Given that the vast majority of children with ADPKD present with normal or supra-normal kidney function, we explored the glomerular filtration rates dynamics and the renal ultrasound-adjusted percentiles. In total, 14 out of 16 patients had kidney percentiles over 90%. The gene mutations were equally distributed among our cohort. In addition, we compared the modified Schwartz formula to the quadratic equation after adjusting the serum creatinine measurements. It seems that even though children with ADPKD have enlarged kidneys, the renal function is more likely normal or near normal when the quadratic estimation of glomerular filtration rate is used (qGFR tended to be lower, 111.95 ± 12.43 mL/min/1.73 m2 when compared to Schwartz eGFR 126.28 ± 33.07 mL/min/1.73 m2, p = 0.14). Also, when the quadratic equation was employed, not even a single patient reached the glomerular hyperfiltration threshold. The quadratic formula showed that glomerular filtration rates are linear or slightly decreasing after 1 year of follow-up (quadratic ΔeGFR = -0.32 ± 5.78 mL/min/1.73 m2), as opposed to the Schwartz formula that can falsely classify children in a hyperfiltration state (ΔeGFR = 7.51 ± 19.46 mL/min/1.73 m2), p = 0.019.