Renal Pathology of Ciliopathies

Renal ciliopathies are a group of genetic disorders that affect the function of the primary cilium in the kidney, as well as other organs. Since primary cilia are important for regulation of cell signaling pathways, ciliary dysfunction results in a range of clinical manifestations, including renal failure, cyst formation, and hypertension. We summarize the current understanding of the pathophysiological and pathological features of renal ciliopathies in childhood, including autosomal dominant and recessive polycystic kidney disease, nephronophthisis, and Bardet-Biedl syndrome, as well as skeletal dysplasia associated renal ciliopathies. The genetic basis of these disorders is now well-established in many cases, with mutations in a large number of cilia-related genes such as PKD1, PKD2, BBS, MKS, and NPHP being responsible for the majority of cases. Renal ciliopathies are broadly characterized by development of interstitial fibrosis and formation of multiple renal cysts which gradually enlarge and replace normal renal tissue, with each condition demonstrating subtle differences in the degree, location, and age-related development of cysts and fibrosis. Presentation varies from prenatal diagnosis of congenital multisystem syndromes to an asymptomatic childhood with development of complications in later adulthood and therefore clinicopathological correlation is important, including increasing use of targeted genetic testing or whole genome sequencing, allowing greater understanding of genetic pathophysiological mechanisms.

Kidney Energetics and Cyst Burden in Autosomal Dominant Polycystic Kidney Disease: A Pilot Study

RATIONALE & OBJECTIVE

In this pilot study, we hypothesized that autosomal dominant polycystic kidney disease (ADPKD) is characterized by impaired kidney oxidative metabolism that associates with kidney size and cyst burden.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

Twenty adults with ADPKD (31±6 years of age, 65% women, BMI: 26.8 [22.7, 30.4] kg/m2, eGFR (2021 CKD-EPI Creatinine): 103±18 ml/min/1.73m2, height-adjusted total kidney volume [HtTKV]: 731±370 ml/m, Mayo Classifications: 1B [5%], 1C [42%], 1D [21%], 1E [32%]) and 11 controls in normal weight category (NWC; 25±3 years of age, 45% women, BMI: 22.5 [21.7, 24.2] kg/m2, eGFR: 113±15 ml/min/1.73m2, HtTKV: 159±31 ml/m) at the University of Colorado Anschutz Medical Campus.

PREDICTORS

ADPKD status (yes/no) and severity (Mayo Classifications).

OUTCOMES

HtTKV and cyst burden by MRI, kidney oxidative metabolism and perfusion by 11C-acetate PET/CT, insulin sensitivity by hyperinsulinemic-euglycemic clamps (presented as ratio of M-value of steady state insulin concentration [M/I]).

ANALYTICAL APPROACH

Chi-square/Fisher's exact tests used for categorical variables and t-tests/ Mann-Whitney U tests for continuous variables. Pearson correlation used to estimate the relationships between variables.

RESULTS

Compared to NWC, participants with ADPKD exhibited lower mean±SD M/I ratio (0.586±0.205 vs. 0.424±0.171 (mg/kg lean/min) / (μIU/mL), p=0.04), lower median [p25, p75] cortical perfusion (1.93 [1.80, 2.09 vs. 0.68 [0.47, 1.04] mL/min/g, p<0.001) and lower median [p25, p75] total kidney oxidative metabolism (0.17 [0.16,0.19] vs. 0.14 [0.12, 0.15] min-1, p=0.001) in voxel-wise models excluding cysts. HtTKV correlated inversely with cortical perfusion (r:-0.83, p<0.001), total kidney oxidative metabolism (r:-0.61, p<0.001) and M/I (r:-0.41, p=0.03).

LIMITATIONS

Small sample size and cross-sectional design.

CONCLUSION

Adults with ADPKD and preserved kidney function exhibited impaired renal perfusion and kidney oxidative metabolism across a wide range of cysts and kidney enlargements.

Mastigoneme structure reveals insights into the O-linked glycosylation code of native hydroxyproline-rich helices

Hydroxyproline-rich glycoproteins (HRGPs) are a ubiquitous class of protein in the extracellular matrices and cell walls of plants and algae, yet little is known of their native structures or interactions. Here, we used electron cryomicroscopy (cryo-EM) to determine the structure of the hydroxyproline-rich mastigoneme, an extracellular filament isolated from the cilia of the alga Chlamydomonas reinhardtii. The structure demonstrates that mastigonemes are formed from two HRGPs (a filament of MST1 wrapped around a single copy of MST3) that both have hyperglycosylated poly(hydroxyproline) helices. Within the helices, O-linked glycosylation of the hydroxyproline residues and O-galactosylation of interspersed serine residues create a carbohydrate casing. Analysis of the associated glycans reveals how the pattern of hydroxyproline repetition determines the type and extent of glycosylation. MST3 possesses a PKD2-like transmembrane domain that forms a heteromeric polycystin-like cation channel with PKD2 and SIP, explaining how mastigonemes are tethered to ciliary membranes.

Visceral Adiposity and Progression of ADPKD: A Cohort Study of Patients From the TEMPO 3:4 Trial

RATIONALE & OBJECTIVE

Body-mass index (BMI) is an independent predictor of kidney disease progression in individuals with autosomal dominant polycystic kidney disease (ADPKD). Adipocytes do not simply act as a fat reservoir but are active endocrine organs. We hypothesized that greater visceral abdominal adiposity would associate with more rapid kidney growth in ADPKD and influence the efficacy of tolvaptan.

STUDY DESIGN

A retrospective cohort study.

SETTING & PARTICIPANTS

1053 patients enrolled in the TEMPO 3:4 tolvaptan trial with ADPKD and high risk of rapid disease progression.

PREDICTOR

Estimates of visceral adiposity extracted from coronal plane MRIs using deep learning.

OUTCOME

Annual change in total kidney volume (TKV) and effect of tolvaptan on kidney growth.

ANALYTICAL APPROACH

Multinomial logistic regression and linear mixed models.

RESULTS

In fully adjusted models, the highest tertile of visceral adiposity was associated with greater odds of annual change in TKV of ≥7% vs. <5% (OR: 4.78 [3.03, 7.47]). The association was stronger in females than males (interaction p<0.01). In linear mixed models with an outcome of % change in TKV per year, tolvaptan efficacy (% change in TKV) was reduced with higher visceral adiposity (three-way interaction of treatment*time*visceral adiposity p=0.002). Visceral adiposity significantly improved classification performance of predicting rapid annual % change in TKV for individuals with a normal BMI (De-Long's test Z-score: -2.03; p=0.04). Greater visceral adiposity was not associated with estimated glomerular filtration rate (eGFR) slope in the overall cohort; however, visceral adiposity was associated with more rapid decline in eGFR slope (below the median) in females (fully adjusted OR 1.06 [1.01, 1.11] per 10 unit increase in visceral adiposity) but not males (0.98 [0.95, 1.02]).

LIMITATIONS

Retrospective; rapid progressors; computational demand of deep learning.

CONCLUSIONS

Visceral adiposity that can be quantified by MRI in the coronal plane using a deep learning segmentation model, independently associates with more rapid kidney growth, and improves classification of rapid progression in individuals with a normal BMI. Tolvaptan efficacy decreases with increasing visceral adiposity.

CFAP47 is a novel causative gene implicated in X-linked polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a well-described condition in which ~80% of cases have a genetic explanation, while the genetic basis of sporadic cystic kidney disease in adults remains unclear in ~30% of cases. This study aimed to identify novel genes associated with polycystic kidney disease (PKD) in patients with sporadic cystic kidney disease in which a clear genetic change was not identified in established genes. A next-generation sequencing panel analyzed known genes related to renal cysts in 118 sporadic cases, followed by whole-genome sequencing on 47 unrelated individuals without identified candidate variants. Three male patients were found to have rare missense variants in the X-linked gene Cilia And Flagella Associated Protein 47 (CFAP47). CFAP47 was expressed in primary cilia of human renal tubules, and knockout mice exhibited vacuolation of tubular cells and tubular dilation, providing evidence that CFAP47 is a causative gene involved in cyst formation. This discovery of CFAP47 as a newly identified gene associated with PKD, displaying X-linked inheritance, emphasizes the need for further cases to understand the role of CFAP47 in PKD.

Modulating inflammation with interleukin 37 treatment ameliorates murine Autosomal Dominant Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a leading cause of kidney failure and is associated with substantial morbidity and mortality. Interstitial inflammation is attributed to the action of infiltrating macrophages and is a feature thought to aggravate disease progression. Here, we investigated the therapeutic potential of the anti-inflammatory IL37b cytokine as a treatment for ADPKD using genetic mouse models, demonstrating that transgenic expression of human IL37b reduced collecting duct cyst burden in both early and adult-onset ADPKD rodent models. Moreover, injection of recombinant human IL37b could also reduce cyst burden in early onset ADPKD mice, an observation not associated with increased macrophage number at early stages of cyst formation. Interestingly, transgenic IL37b expression also did not alter macrophage numbers in advanced disease. Whole kidney RNA-seq highlighted an IL37b-mediated upregulation of the interferon signaling pathway and single-cell RNA-seq established that these changes originate at least partly from kidney resident macrophages. We further found that blocking type I interferon signaling in mice expressing IL37b resulted in increased cyst number, confirming this as an important pathway by which IL37b exerts its beneficial effects. Thus, our studies show that IL37b promotes interferon signaling in kidney resident macrophages which suppresses cyst initiation, identifying this protein as a potential therapy for ADPKD.

Endoscopic ultrasound-guided infectious liver cyst drainage associated with autosomal dominant polycystic kidney disease in which percutaneous approach is impossible

A man in his 70s on maintenance dialysis for autosomal dominant polycystic kidney disease was admitted with epigastralgia and a fever lasting for 1 week. Computed tomography showed a thickened liver cyst measuring 121 mm in the caudate lobe, suggesting infection. Percutaneous drainage was impossible because multiple liver cysts and ascites entered the puncture route. Endoscopic ultrasound (EUS) revealed a huge liver cyst with debris-like echoes. Transgastric EUS-guided drainage was performed, and internal and external drainage was performed without adverse events. After the procedure, the symptoms quickly improved, and the external drain was removed after 12 days. The internal drainage stent remained in place, and the patient was discharged from the hospital 53 days after the EUS-guided drainage. EUS-guided drainage is an effective alternative treatment for infected liver cysts where a percutaneous approach is impossible.

Pkd2 Deficiency in Embryonic Aqp2 + Progenitor Cells Is Sufficient to Cause Severe Polycystic Kidney Disease

SIGNIFICANCE STATEMENT

Autosomal dominant polycystic kidney disease (ADPKD) is a devastating disorder caused by mutations in polycystin 1 ( PKD1 ) and polycystin 2 ( PKD2 ). Currently, the mechanism for renal cyst formation remains unclear. Here, we provide convincing and conclusive data in mice demonstrating that Pkd2 deletion in embryonic Aqp2 + progenitor cells (AP), but not in neonate or adult Aqp2 + cells, is sufficient to cause severe polycystic kidney disease (PKD) with progressive loss of intercalated cells and complete elimination of α -intercalated cells, accurately recapitulating a newly identified cellular phenotype of patients with ADPKD. Hence, Pkd2 is a new potential regulator critical for balanced AP differentiation into, proliferation, and/or maintenance of various cell types, particularly α -intercalated cells. The Pkd2 conditional knockout mice developed in this study are valuable tools for further studies on collecting duct development and early steps in cyst formation. The finding that Pkd2 loss triggers the loss of intercalated cells is a suitable topic for further mechanistic studies.

BACKGROUND

Most cases of autosomal dominant polycystic kidney disease (ADPKD) are caused by mutations in PKD1 or PKD2. Currently, the mechanism for renal cyst formation remains unclear. Aqp2 + progenitor cells (AP) (re)generate ≥5 cell types, including principal cells and intercalated cells in the late distal convoluted tubules (DCT2), connecting tubules, and collecting ducts.

METHODS

Here, we tested whether Pkd2 deletion in AP and their derivatives at different developmental stages is sufficient to induce PKD. Aqp2Cre Pkd2f/f ( Pkd2AC ) mice were generated to disrupt Pkd2 in embryonic AP. Aqp2ECE/+Pkd2f/f ( Pkd2ECE ) mice were tamoxifen-inducted at P1 or P60 to inactivate Pkd2 in neonate or adult AP and their derivatives, respectively. All induced mice were sacrificed at P300. Immunofluorescence staining was performed to categorize and quantify cyst-lining cell types. Four other PKD mouse models and patients with ADPKD were similarly analyzed.

RESULTS

Pkd2 was highly expressed in all connecting tubules/collecting duct cell types and weakly in all other tubular segments. Pkd2AC mice had obvious cysts by P6 and developed severe PKD and died by P17. The kidneys had reduced intercalated cells and increased transitional cells. Transitional cells were negative for principal cell and intercalated cell markers examined. A complete loss of α -intercalated cells occurred by P12. Cysts extended from the distal renal segments to DCT1 and possibly to the loop of Henle, but not to the proximal tubules. The induced Pkd2ECE mice developed mild PKD. Cystic α -intercalated cells were found in the other PKD models. AQP2 + cells were found in cysts of only 13/27 ADPKD samples, which had the same cellular phenotype as Pkd2AC mice.

CONCLUSIONS

Hence, Pkd2 deletion in embryonic AP, but unlikely in neonate or adult Aqp2 + cells (principal cells and AP), was sufficient to cause severe PKD with progressive elimination of α -intercalated cells, recapitulating a newly identified cellular phenotype of patients with ADPKD. We proposed that Pkd2 is critical for balanced AP differentiation into, proliferation, and/or maintenance of cystic intercalated cells, particularly α -intercalated cells.

A de novo PKD1 mutation in a Chinese family with autosomal dominant polycystic kidney disease

BACKGROUND

PKD1, which has a relatively high mutation rate, is highly polymorphic, and the role of PKD1 is incompletely defined. In the current study, in order to determine the molecular etiology of a family with autosomal dominant polycystic kidney disease, the pathogenicity of an frameshift mutation in the PKD1 gene, c.9484delC, was evaluated.

METHODS

The family clinical data were collected. Whole exome sequencing analysis determined the level of this mutation in the proband's PKD1, and Sanger sequencing and bioinformatics analysis were performed. SIFT, Polyphen2, and MutationTaster were used to evaluate the conservation of the gene and pathogenicity of the identified mutations. SWISS-MODEL was used to predict and map the protein structure of PKD1 and mutant neonate proteins.

RESULTS

A novel c.9484delC (p.Arg3162Alafs*154) mutation of the PKD1 gene was identified by whole exome sequencing in the proband, which was confirmed by Sanger sequencing in his sister (II7). The same mutation was not detected in the healthy pedigree members. Random screening of 100 normal and end-stage renal disease patients did not identify the c.9484delC mutation. Bioinformatics analysis suggested that the mutation caused the 3162 nd amino acid substitution of arginine by alanine and a shift in the termination codon. As a result, the protein sequence was shortened from 4302 amino acids to 3314 amino acids, the protein structure was greatly changed, and the PLAT/LH2 domain was destroyed. Clustal analysis indicated that the altered amino acids were highly conserved in mammals.

CONCLUSION

A novel mutation in the PKD1 gene has been identified in an affected Chinese family. The mutation is probably responsible for a range of clinical manifestations for which reliable prenatal diagnosis and genetic counseling may be provided.

Molecular and structural basis of the dual regulation of the polycystin-2 ion channel by small-molecule ligands

Mutations in the PKD2 gene, which encodes the polycystin-2 (PC2, also called TRPP2) protein, lead to autosomal dominant polycystic kidney disease (ADPKD). As a member of the transient receptor potential (TRP) channel superfamily, PC2 functions as a non-selective cation channel. The activation and regulation of the PC2 channel are largely unknown, and direct binding of small-molecule ligands to this channel has not been reported. In this work, we found that most known small-molecule agonists of the mucolipin TRP (TRPML) channels inhibit the activity of the PC2_F604P, a gain-of-function mutant of the PC2 channel. However, two of them, ML-SA1 and SF-51, have dual regulatory effects, with low concentration further activating PC2_F604P, and high concentration leading to inactivation of the channel. With two cryo-electron microscopy (cryo-EM) structures, a molecular docking model, and mutagenesis results, we identified two distinct binding sites of ML-SA1 in PC2_F604P that are responsible for activation and inactivation, respectively. These results provide structural and functional insights into how ligands regulate PC2 channel function through unusual mechanisms and may help design compounds that are more efficient and specific in regulating the PC2 channel and potentially also for ADPKD treatment.

Erratum: Regenerative calcium currents in renal primary cilia

[This corrects the article DOI: 10.3389/fphys.2022.894518.].

Leucine-Rich Repeat in Polycystin-1 Suppresses Cystogenesis in a Zebrafish (Danio rerio) Model of Autosomal-Dominant Polycystic Kidney Disease

Mutations of PKD1 coding for polycystin-1 (PC1) account for most cases of autosomal-dominant polycystic kidney disease (ADPKD). The extracellular region of PC1 contains many evolutionarily conserved domains for ligand interactions. Among these are the leucine-rich repeats (LRRs) in the far N-terminus of PC1. Using zebrafish (Danio rerio) as an in vivo model system, we explored the role of LRRs in the function of PC1. Zebrafish expresses two human PKD1 paralogs, pkd1a and pkd1b. Knockdown of both genes in zebrafish by morpholino antisense oligonucleotides produced phenotypes of dorsal-axis curvature and pronephric cyst formation. We found that overexpression of LRRs suppressed both phenotypes in pkd1-morphant zebrafish. Purified recombinant LRR domain inhibited proliferation of HEK cells in culture and interacted with the heterotrimeric basement membrane protein laminin-511 (α5β1γ1) in vitro. Mutations of amino acid residues in LRRs structurally predicted to bind laminin-511 disrupted LRR-laminin interaction in vitro and neutralized the ability of LRRs to inhibit cell proliferation and cystogenesis. Our data support the hypothesis that the extracellular region of PC1 plays a role in modulating PC1 interaction with the extracellular matrix and contributes to cystogenesis of PC1 deficiency.

Matrix Metalloproteinase-7 in Urinary Extracellular Vesicles Identifies Rapid Disease Progression in Autosomal Dominant Polycystic Kidney Disease

SIGNIFICANCE STATEMENT

There is an unmet need for biomarkers of disease progression in autosomal dominant polycystic kidney disease (ADPKD). This study investigated urinary extracellular vesicles (uEVs) as a source of such biomarkers. Proteomic analysis of uEVs identified matrix metalloproteinase 7 (MMP-7) as a biomarker predictive of rapid disease progression. In validation studies, MMP-7 was predictive in uEVs but not in whole urine, possibly because uEVs are primarily secreted by tubular epithelial cells. Indeed, single-nucleus RNA sequencing showed that MMP-7 was especially increased in proximal tubule and thick ascending limb cells, which were further characterized by a profibrotic phenotype. Together, these data suggest that MMP-7 is a biologically plausible and promising uEV biomarker for rapid disease progression in ADPKD.

BACKGROUND

In ADPKD, there is an unmet need for early markers of rapid disease progression to facilitate counseling and selection for kidney-protective therapy. Our aim was to identify markers for rapid disease progression in uEVs.

METHODS

Six paired case-control groups ( n =10-59/group) of cases with rapid disease progression and controls with stable disease were formed from two independent ADPKD cohorts, with matching by age, sex, total kidney volume, and genetic variant. Candidate uEV biomarkers were identified by mass spectrometry and further analyzed using immunoblotting and an ELISA. Single-nucleus RNA sequencing of healthy and ADPKD tissue was used to identify the cellular origin of the uEV biomarker.

RESULTS

In the discovery proteomics experiments, the protein abundance of MMP-7 was significantly higher in uEVs of patients with rapid disease progression compared with stable disease. In the validation groups, a significant >2-fold increase in uEV-MMP-7 in patients with rapid disease progression was confirmed using immunoblotting. By contrast, no significant difference in MMP-7 was found in whole urine using ELISA. Compared with healthy kidney tissue, ADPKD tissue had significantly higher MMP-7 expression in proximal tubule and thick ascending limb cells with a profibrotic phenotype.

CONCLUSIONS

Among patients with ADPKD, rapid disease progressors have higher uEV-associated MMP-7. Our findings also suggest that MMP-7 is a biologically plausible biomarker for more rapid disease progression.

Inspiring Tactics with the Improvement of Mitophagy and Redox Balance for the Development of Innovative Treatment against Polycystic Kidney Disease

Polycystic kidney disease (PKD) is the most common genetic form of chronic kidney disease (CKD), and it involves the development of multiple kidney cysts. Not enough medical breakthroughs have been made against PKD, a condition which features regional hypoxia and activation of the hypoxia-inducible factor (HIF) pathway. The following pathology of CKD can severely instigate kidney damage and/or renal failure. Significant evidence verifies an imperative role for mitophagy in normal kidney physiology and the pathology of CKD and/or PKD. Mitophagy serves as important component of mitochondrial quality control by removing impaired/dysfunctional mitochondria from the cell to warrant redox homeostasis and sustain cell viability. Interestingly, treatment with the peroxisome proliferator-activated receptor-α (PPAR-α) agonist could reduce the pathology of PDK and might improve the renal function of the disease via the modulation of mitophagy, as well as the condition of gut microbiome. Suitable modulation of mitophagy might be a favorable tactic for the prevention and/or treatment of kidney diseases such as PKD and CKD.

The Cyst Epithelium in Polycystic Kidney Disease Patients Displays Normal Apical-Basolateral Cell Polarity

The main characteristic of polycystic kidney disease is the development of multiple fluid-filled renal cysts. The discovery of mislocalized sodium-potassium pump (Na,K-ATPase) in the apical membrane of cyst-lining epithelia alluded to reversal of polarity as a possible explanation for the fluid secretion. The topic of apical Na,K-ATPase in cysts remains controversial. We investigated the localization of the Na,K-ATPase and assessed the apical-basolateral polarization of cyst-lining epithelia by means of immunohistochemistry in kidney tissue from six polycystic kidney disease patients undergoing nephrectomy. The Na,K-ATPase α1 subunit was conventionally situated in the basolateral membrane of all immunoreactive cysts. Proteins of the Crumbs and partitioning defective (Par) complexes were localized to the apical membrane domain in cyst epithelial cells. The apical targeting protein Syntaxin-3 also immunolocalized to the apical domain of cyst-lining epithelial cells. Proteins of the basolateral Scribble complex immunolocalized to the basolateral domain of cysts. Thus, no deviations from the typical epithelial distribution of basic cell polarity proteins were observed in the cysts from the six patients. Furthermore, we confirmed that cysts can originate from virtually any tubular segment with preserved polarity. In conclusion, we find no evidence of a reversal in apical-basolateral polarity in cyst-lining epithelia in polycystic kidney disease.

The Han:SPRD Rat: A Preclinical Model of Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) stands as the most prevalent hereditary renal disorder in humans, ultimately culminating in end-stage kidney disease. Animal models carrying mutations associated with polycystic kidney disease have played an important role in the advancement of ADPKD research. The Han:SPRD rat model, carrying an R823W mutation in the Anks6 gene, is characterized by cyst formation and kidney enlargement. The mutated protein, named Samcystin, is localized in cilia of tubular epithelial cells and seems to be involved in cystogenesis. The homozygous Anks6 mutation leads to end-stage renal disease and death, making it a critical factor in kidney development and function. This review explores the utility of the Han:SPRD rat model, highlighting its phenotypic similarity to human ADPKD. Specifically, we discuss its role in preclinical trials and its importance for investigating the pathogenesis of the disease and developing new therapeutic approaches.

Global analysis of urinary extracellular vesicle small RNAs in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent monogenic renal disease progressing to end-stage renal disease. There is a pressing need for the identification of early ADPKD biomarkers to enable timely intervention and the development of effective therapeutic approaches. Here, we profiled human urinary extracellular vesicles small RNAs by small RNA sequencing in patients with ADPKD and compared their differential expression considering healthy control individuals to identify dysregulated small RNAs and analyze downstream interaction to gain insight about molecular pathophysiology.

METHODS

This is a cross-sectional study where urine samples were collected from a total of 23 PKD1-ADPKD patients and 28 healthy individuals. Urinary extracellular vesicles were purified, and small RNA was isolated and sequenced. Differentially expressed Small RNA were identified and functional enrichment analysis of the critical miRNAs was performed to identify driver genes and affected pathways.

RESULTS

miR-320b, miR-320c, miR-146a-5p, miR-199b-3p, miR-671-5p, miR-1246, miR-8485, miR-3656, has_piR_020497, has_piR_020496 and has_piR_016271 were significantly upregulated in ADPKD patient urine extracellular vesicles and miRNA-29c was significantly downregulated. Five 'driver' target genes (FBRS, EDC3, FMNL3, CTNNBIP1 and KMT2A) were identified.

CONCLUSIONS

The findings of the present study make significant contributions to the understanding of ADPKD pathogenesis and to the identification of novel biomarkers and potential drug targets aimed at slowing disease progression in ADPKD.

Monoallelic pathogenic IFT140 variants are a common cause of autosomal dominant polycystic kidney disease-spectrum phenotype

Background

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disorder, characterized by development and enlargement of kidney cysts, eventually leading to end-stage kidney disease (ESKD). Pathogenic variants in the PKD1 and PKD2 genes are the major cause of ADPKD; additional rare variants in the GANAB, DNAJB11, ALG5 and ALG9 genes have been found in a minority of ADPKD patients. More recently, a significant number of ADPKD families have been linked to monoallelic variants in the IFT140 gene.

Methods

In this retrospective study, we tested the prevalence of the known causative genes of ADPKD-spectrum phenotype, including the PKD1, PKD2, GANAB, DNAJB11, ALG5, ALG and IFT140 genes, in a cohort of 129 ADPKD patients who consecutively underwent genetic testing in a single centre in Italy. Genetic testing utilized a combination of targeted next-generation sequencing, long-range polymerase chain reaction, Sanger sequencing and multiplex ligation-dependent probe amplification. Clinical evaluation was conducted through renal function testing and imaging features, including ultrasonography, computer tomography and magnetic resonance imaging.

Results

Of the 129 enrolled patients, 86 (66.7%) had pathogenic variants in PKD1 and 28 (21.7%) in PKD2, loss of function pathogenic variants in the IFT140 gene were found in 3 unrelated patients (2.3%), no pathogenic variants were found in other ADPKD genes and 12 patients (9.3%) remained genetically unresolved (ADPKD-GUR). Familial clinical and genetic screening of the index patients with ADPKD due to an IFT140 pathogenic variant (ADPKD-IFT140) allowed identification of eight additional affected relatives. In the 11 ADPKD-IFT140 patients, the renal phenotype was characterized by mild and late-onset PKD, with large renal cysts and limited kidney insufficiency. Extrarenal manifestations, including liver cysts, were rarely seen.

Conclusion

Our data suggest the monoallelic pathogenic IFT140 variants are the third most common cause of the ADPKD-spectrum phenotype in Italy, usually associated with a mild and atypical renal cystic disease.

State of the Science and Ethical Considerations for Preimplantation Genetic Testing for Monogenic Cystic Kidney Diseases and Ciliopathies

There is a broad phenotypic spectrum of monogenic polycystic kidney diseases (PKDs). These disorders often involve cilia-related genes and lead to the development of fluid-filled cysts and eventual kidney function decline and failure. Preimplantation genetic testing for monogenic (PGT-M) disorders has moved into the clinical realm. It allows prospective parents to avoid passing on heritable diseases to their children, including monogenic PKD. The PGT-M process involves embryo generation through in vitro fertilization, with subsequent testing of embryos and selective transfer of those that do not harbor the specific disease-causing variant(s). There is a growing body of literature supporting the success of PGT-M for autosomal-dominant and autosomal-recessive PKD, although with important technical limitations in some cases. This technology can be applied to many other types of monogenic PKD and ciliopathies despite the lack of existing reports in the literature. PGT-M for monogenic PKD, like other forms of assisted reproductive technology, raises important ethical questions. When considering PGT-M for kidney diseases, as well as the potential to avoid disease in future generations, there are regulatory and ethical considerations. These include limited government regulation and unstandardized consent processes, potential technical errors, high cost and equity concerns, risks associated with pregnancy for mothers with kidney disease, and the impact on all involved in the process, including the children who were made possible with this technology.

Deletion of Aurora kinase A prevents the development of polycystic kidney disease in mice

Aurora Kinase A (AURKA) promotes cell proliferation and is overexpressed in different types of polycystic kidney disease (PKD). To understand AURKA's role in regulating renal cyst development we conditionally deleted the gene in mouse models of Autosomal Dominant PKD (ADPKD) and Joubert Syndrome, caused by Polycystin 1 (Pkd1) and Inositol polyphosphate-5-phosphatase E (Inpp5e) mutations respectively. We show that while Aurka is dispensable for collecting duct development and homeostasis, its deletion prevents cyst formation in both disease models. Cross-comparison of transcriptional changes implicated AKT signaling in cyst prevention and we show that (i) AURKA and AKT physically interact, (ii) AURKA regulates AKT activity in a kinase-independent manner and (iii) inhibition of AKT can reduce disease severity. AKT activation also regulates Aurka expression, creating a feed-forward loop driving renal cystogenesis. We find that the AURKA kinase inhibitor Alisertib stabilises the AURKA protein, agonizing its cystogenic functions. These studies identify AURKA as a master regulator of renal cyst development in different types of PKD, functioning in-part via AKT.

Variants in the WDR44 WD40-repeat domain cause a spectrum of ciliopathy by impairing ciliogenesis initiation

WDR44 prevents ciliogenesis initiation by regulating RAB11-dependent vesicle trafficking. Here, we describe male patients with missense and nonsense variants within the WD40 repeats (WDR) of WDR44, an X-linked gene product, who display ciliopathy-related developmental phenotypes that we can model in zebrafish. The patient phenotypic spectrum includes developmental delay/intellectual disability, hypotonia, distinct craniofacial features and variable presence of brain, renal, cardiac and musculoskeletal abnormalities. We demonstrate that WDR44 variants associated with more severe disease impair ciliogenesis initiation and ciliary signaling. Because WDR44 negatively regulates ciliogenesis, it was surprising that pathogenic missense variants showed reduced abundance, which we link to misfolding of WDR autonomous repeats and degradation by the proteasome. We discover that disease severity correlates with increased RAB11 binding, which we propose drives ciliogenesis initiation dysregulation. Finally, we discover interdomain interactions between the WDR and NH2-terminal region that contains the RAB11 binding domain (RBD) and show patient variants disrupt this association. This study provides new insights into WDR44 WDR structure and characterizes a new syndrome that could result from impaired ciliogenesis.

Ketogenic metabolic therapy for chronic kidney disease - the pro part

Ketogenic metabolic therapy (KMT) is a medical nutrition therapy to address certain health and disease conditions. It is increasingly used for many non-communicable diseases that are rooted in abnormal metabolic health. Since chronic kidney disease (CKD) is commonly caused by overnutrition leading to hyperglycemia, insulin resistance and diabetes mellitus, the carbohydrate restriction inherent in KMT may offer a therapeutic option. Numerous studies have found that various forms of KMT are safe for individuals with CKD and may lead to improvement of renal function. This is in contrast to the current standard pharmacological approach to CKD that only slows the relentless progression towards renal failure. Kidney care providers, including physicians and dietitians, are usually not aware of non-standard dietary interventions, including KMT, and often criticize KMT due to common misconceptions and uncertainty about the underlying science, including the common misconception that KMT must involve high protein or meat consumption. This review article discusses the rationales for using KMT, including plant-dominant KMT, for treatment of CKD, clarifies common misconceptions, summarizes the results of clinical studies and discusses why KMT is emerging as an effective medical nutrition therapy (MNT) to consider for patients with kidney disease. KMT, including its plant-dominant versions, can expand a practitioner's kidney health toolbox and will likely become a first-line therapy for CKD in certain CKD-associated conditions such as obesity, metabolic syndrome and polycystic kidney disease.

[Potter sequence in a newborn with polycystic kidney disease]

A rare clinical case of a newborn boy with a diagnosed Potter sequence is presented. The diagnosis was made based on polycystic dysplasia of the kidneys, cysts in the liver, hypoplasia of the lungs and characteristic external signs due to critical oligohydramnios. The child's parents were closely related, which suggested an autosomal recessive form of the disease. The newborn lived for 15 hours, after which the death, developed as a result of respiratory failure, was ascertained.

Prenatal diagnosis of polycystic renal diseases: diagnostic yield, novel disease-causing variants, and genotype-phenotype correlations

BACKGROUND

Polycystic renal disease is a frequent congenital anomaly of the kidneys, but research using chromosomal microarray analysis and exome sequencing in fetuses with polycystic renal disease remains sparse, with most studies focusing on the multisystem or genitourinary system.

OBJECTIVE

This study aimed to assess the detection rate of detectable genetic causes of fetal polycystic renal disease at different levels, novel disease-causing variants, and genotype-phenotype correlations.

STUDY DESIGN

This study included 220 fetal polycystic renal disease cases from January 2014 to June 2022. Cases were divided into the following 3 groups: isolated multicystic dysplastic kidneys, nonisolated multicystic dysplastic kidneys, and suspected polycystic kidney disease group. We reviewed data on maternal demographics, ultrasonographic results, chromosomal microarray analysis/exome sequencing results, and pregnancy outcomes.

RESULTS

In our cohort, chromosomal microarray analysis identified 19 (8.6%) fetuses carrying chromosomal abnormalities, and the most common copy number variation was 17q12 microdeletion (7/220; 3.2%). Furthermore, 94 families chose to perform trio-exome sequencing testing, and 21 fetuses (22.3%) were found to harbor pathogenic/likely pathogenic variants. There was a significant difference in the live birth rate among the 3 groups (91/130 vs 46/80 vs 1/10; P<.001). Among 138 live birth cases, 106 (78.5%) underwent postnatal ultrasound review, of which 95 (89.6%) had a consistent prenatal-postnatal ultrasound diagnosis.

CONCLUSION

For both isolated and nonisolated polycystic renal disease, our data showed high detection efficiency with both testing tools. The detection of novel pathogenic variants expands the known disease spectrum of polycystic renal disease-associated genes while enriching our understanding of the genotype-phenotype correlation. Therefore, we consider it feasible to perform chromosomal microarray analysis+exome sequencing testing in fetal polycystic renal disease. Moreover, prenatal-postnatal ultrasound concordance was greater, the live birth rate was higher, and prognosis was better when known genetic disorders were excluded, indicating that genetic testing results significantly influenced pregnancy decisions.

A rare case of fatal poisoning during long-term therapy with lithium carbonate - chronic poisoning, suicide or psychiatric malpractice?

The study aims to present a case of atypical poisoning with lithium carbonate in a 57-year-old woman treated for bipolar affective disorder with lithium carbonate for about 30 years. The patient was admitted to the hospital with significant agitation. An important finding obtained from the family interview was the patient's significant weight loss over the past year. In the hospital, the patient received haloperidol and clonazepam. Laboratory tests showed a very high blood lithium concentration of 3.79 mmol/l [N: 0.6─1.2 mmol/l] and elevated serum concentrations of creatinine (3.6 mg/dl) and urea (110 mg/dl). The patient was transferred to the toxicology department, where hemodialysis was performed and intensive treatment initiated. Despite the rapid decrease in lithium levels, her condition gradually deteriorated. The patient died on the fifth day of hospitalization. The autopsy revealed polycystic kidney disease (PKD). During the preparation of the medico-legal report on the correctness of the medical treatment, it was assumed that the cause of death was lithium carbonate poisoning in the course of advanced chronic kidney disease due to PKD, probably a consequence of long-term lithium therapy. The analysis of medical records revealed that despite her psychiatrist's recommendation, the patient had been refusing the monitoring of lithium levels for the past 18 years. This case demonstrates that both psychiatrists and toxicologists should be aware of possible lithium poisoning upon the deterioration of renal function. Therefore, assessment of renal function should be an integral part of monitoring lithium therapy.

Triple Genetic Diagnosis in a Patient with Late-Onset Leukodystrophy and Mild Intellectual Disability

We describe the complex case of a 44-year-old man with polycystic kidney disease, mild cognitive impairment, and tremors in the upper limbs. Brain MRI showed lesions compatible with leukodystrophy. The diagnostic process, which included clinical exome sequencing (CES) and chromosomal microarray analysis (CMA), revealed a triple diagnosis: autosomal dominant polycystic kidney disease (ADPKD) due to a pathogenic variant, c.2152C>T-p.(Gln718Ter), in the PKD1 gene; late-onset phenylketonuria due to the presence of two missense variants, c.842C>T-p.(Pro281Leu) and c.143T>C-p.(Leu48Ser) in the PAH gene; and a 915 Kb duplication on chromosome 15. Few patients with multiple concurrent genetic diagnoses are reported in the literature; in this ADPKD patient, genome-wide analysis allowed for the diagnosis of adult-onset phenylketonuria (which would have otherwise gone unnoticed) and a 15q11.2 duplication responsible for cognitive and behavioral impairment with incomplete penetrance. This case underlines the importance of clinical genetics for interpreting complex results obtained by genome-wide techniques, and for diagnosing concurrent late-onset monogenic conditions.

Polygenic risk alters the penetrance of monogenic kidney disease

Chronic kidney disease (CKD) is determined by an interplay of monogenic, polygenic, and environmental risks. Autosomal dominant polycystic kidney disease (ADPKD) and COL4A-associated nephropathy (COL4A-AN) represent the most common forms of monogenic kidney diseases. These disorders have incomplete penetrance and variable expressivity, and we hypothesize that polygenic factors explain some of this variability. By combining SNP array, exome/genome sequence, and electronic health record data from the UK Biobank and All-of-Us cohorts, we demonstrate that the genome-wide polygenic score (GPS) significantly predicts CKD among ADPKD monogenic variant carriers. Compared to the middle tertile of the GPS for noncarriers, ADPKD variant carriers in the top tertile have a 54-fold increased risk of CKD, while ADPKD variant carriers in the bottom tertile have only a 3-fold increased risk of CKD. Similarly, the GPS significantly predicts CKD in COL4A-AN carriers. The carriers in the top tertile of the GPS have a 2.5-fold higher risk of CKD, while the risk for carriers in the bottom tertile is not different from the average population risk. These results suggest that accounting for polygenic risk improves risk stratification in monogenic kidney disease.

Ouabain enhances renal cyst growth in a slowly progressive mouse model of autosomal dominant polycystic kidney disease

Renal cyst progression in autosomal dominant polycystic kidney disease (ADPKD) is highly dependent on agents circulating in blood. We have previously shown, using different in vitro models, that one of these agents is the hormone ouabain. By binding to Na+-K+-ATPase (NKA), ouabain triggers a cascade of signal transduction events that enhance ADPKD cyst progression by stimulating cell proliferation, fluid secretion, and dedifferentiation of the renal tubular epithelial cells. Here, we determined the effects of ouabain in vivo. We show that daily administration of ouabain to Pkd1RC/RC ADPKD mice for 1-5 mo, at physiological levels, augmented kidney cyst area and number compared with saline-injected controls. Also, ouabain favored renal fibrosis; however, renal function was not significantly altered as determined by blood urea nitrogen levels. Ouabain did not have a sex preferential effect, with male and female mice being affected equally. By contrast, ouabain had no significant effect on wild-type mice. In addition, the actions of ouabain on Pkd1RC/RC mice were exacerbated when another mutation that increased the affinity of NKA for ouabain was introduced to the mice (Pkd1RC/RCNKAα1OS/OS mice). Altogether, this work highlights the role of ouabain as a procystogenic factor in the development of ADPKD in vivo, that the ouabain affinity site on NKA is critical for this effect, and that circulating ouabain is an epigenetic factor that worsens the ADPKD phenotype.NEW & NOTEWORTHY This work shows that the hormone ouabain enhances the progression of autosomal dominant polycystic kidney disease (ADPKD) in vivo. Ouabain augments the size and number of renal cysts, the kidney weight to body weight ratio, and kidney fibrosis in an ADPKD mouse model. The Na+-K+-ATPase affinity for ouabain plays a critical role in these effects. In addition, these outcomes are independent of the sex of the mice.

Comparing Effects of Tolvaptan and Instruction to Increase Water Consumption in ADPKD: Post Hoc Analysis of TEMPO 3:4

Key Points

In a post hoc analysis, short-term reduction in spot urine osmolality (Uosm) was associated with decreased kidney volume growth in autosomal dominant polycystic kidney disease for both tolvaptan and instruction to increase hydration alone. For the same spot Uosm reduction, however, the kidney volume benefit was greater with tolvaptan, possibly because of greater cumulative 24-hour Uosm suppression by tolvaptan.

Background

In addition to decreasing water excretion and increasing urinary concentration, the antidiuretic hormone vasopressin plays a role in the pathophysiology of autosomal dominant polycystic kidney disease. It has been hypothesized that by suppressing vasopressin release, drinking large amounts of water might exert therapeutic effects in autosomal dominant polycystic kidney disease similar to those of tolvaptan, an antagonist of the vasopressin type 2 receptor, but evidence is lacking. We analyzed data from tolvaptan clinical trials to evaluate relationships among water intake, urine osmolality (Uosm), and change in total kidney volume (TKV).

Methods

Analysis of the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes 3:4 clinical trial in which participants were randomized to tolvaptan or placebo and instructed to drink large amounts of water. The relationship between change in spot Uosm from baseline to week 3 and change in TKV to month 12 was assessed using linear regression modeling. Two short-term tolvaptan trials were analyzed to explore relationships between intermittent Uosm sampling and 24-hour Uosm suppression.

Results

With both tolvaptan and placebo (i.e. , mandated high water intake alone), Uosm reduction at week 3 was associated with reduction in TKV growth at month 12. However, for the same decrease in spot Uosm, the corresponding reduction in TKV growth was greater for tolvaptan (e.g. , a −250 mOsm/kg reduction in Uosm at week 3 was associated with a −1% change in TKV at month 12 for tolvaptan versus +4.5% for placebo). In short-term trials, similar reductions in spot or trough Uosm values were achievable with tolvaptan and high water intake, but cumulative 24-hour suppression was greater with tolvaptan.

Conclusions

This analysis supports a relationship between effects on Uosm and inhibition of disease progression by tolvaptan and high water intake alone. The findings further suggest that 24-hour Uosm measurement is superior to spot Uosm for assessing suppression of vasopressin activity by tolvaptan.

Feasibility and impact of ketogenic dietary interventions in polycystic kidney disease: KETO-ADPKD-a randomized controlled trial

Ketogenic dietary interventions (KDIs) are beneficial in animal models of autosomal-dominant polycystic kidney disease (ADPKD). KETO-ADPKD, an exploratory, randomized, controlled trial, is intended to provide clinical translation of these findings (NCT04680780). Sixty-six patients were randomized to a KDI arm (ketogenic diet [KD] or water fasting [WF]) or the control group. Both interventions induce significant ketogenesis on the basis of blood and breath acetone measurements. Ninety-five percent (KD) and 85% (WF) report the diet as feasible. KD leads to significant reductions in body fat and liver volume. Additionally, KD is associated with reduced kidney volume (not reaching statistical significance). Interestingly, the KD group exhibits improved kidney function at the end of treatment, while the control and WF groups show a progressive decline, as is typical in ADPKD. Safety-relevant events are largely mild, expected (initial flu-like symptoms associated with KD), and transient. Safety assessment is complemented by nuclear magnetic resonance (NMR) lipid profile analyses.

Robotic bilateral nephrectomy for large polycystic kidney disease

Objective

This study aims to describe our technique and review our experience with synchronous robotic bilateral nephrectomy for large kidneys in ADPKD with the da Vinci XI and da Vinci Single Port platforms (Intuitive Surgical, Sunnyvale, CA).

Materials and Methods

We performed a retrospective review of all robotic bilateral nephrectomy cases from January 2020 to present at a high-volume robotic single centre. Demographic data and perioperative details including preoperative CT scans, indication for nephrectomy and renal function were collected. We also collected post-op course data and final specimen data details.

Results

Fourteen cases were included. Patient demographics, indications for surgery and specimen data are outlined in Table 1. The largest kidney removed has a measurement of 32 cm in the largest dimension on preoperative imaging. Median operating time from incision to closure was 299 min (IQR 260, 339). Median estimated blood loss was 75 cc (IQR 50, 187.5). Two patients were transfused intraoperatively. Median pre- and post-operative Hgb was 11.0 and 9.6, respectively. Median length of stay was 3 days (IQR 2, 3.5). There were no intraoperative complications and no open conversions. Post-operative complications included one incisional hematoma and one superficial wound infection. One patient was admitted to the surgical ICU post operatively for ventilatory support. Two patients were readmitted within 30 days of surgery.

Conclusion

The robotic approach to bilateral native nephrectomy for ADPKD should be considered when native nephrectomies are indicated. The operative times and outcomes are favourable compared with prior series, and this technique works even for very large kidneys.

Certain heterozygous variants in the kinase domain of the serine/threonine kinase NEK8 can cause an autosomal dominant form of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) resulting from pathogenic variants in PKD1 and PKD2 is the most common form of PKD, but other genetic causes tied to primary cilia function have been identified. Biallelic pathogenic variants in the serine/threonine kinase NEK8 cause a syndromic ciliopathy with extra-kidney manifestations. Here we identify NEK8 as a disease gene for ADPKD in 12 families. Clinical evaluation was combined with functional studies using fibroblasts and tubuloids from affected individuals. Nek8 knockout mouse kidney epithelial (IMCD3) cells transfected with wild type or variant NEK8 were further used to study ciliogenesis, ciliary trafficking, kinase function, and DNA damage responses. Twenty-one affected monoallelic individuals uniformly exhibited cystic kidney disease (mostly neonatal) without consistent extra-kidney manifestations. Recurrent de novo mutations of the NEK8 missense variant p.Arg45Trp, including mosaicism, were seen in ten families. Missense variants elsewhere within the kinase domain (p.Ile150Met and p.Lys157Gln) were also identified. Functional studies demonstrated normal localization of the NEK8 protein to the proximal cilium and no consistent cilia formation defects in patient-derived cells. NEK8-wild type protein and all variant forms of the protein expressed in Nek8 knockout IMCD3 cells were localized to cilia and supported ciliogenesis. However, Nek8 knockout IMCD3 cells expressing NEK8-p.Arg45Trp and NEK8-p.Lys157Gln showed significantly decreased polycystin-2 but normal ANKS6 localization in cilia. Moreover, p.Arg45Trp NEK8 exhibited reduced kinase activity in vitro. In patient derived tubuloids and IMCD3 cells expressing NEK8-p.Arg45Trp, DNA damage signaling was increased compared to healthy passage-matched controls. Thus, we propose a dominant-negative effect for specific heterozygous missense variants in the NEK8 kinase domain as a new cause of PKD.

The genetic spectrum of polycystic kidney disease in children

OBJECTIVE

Autosomal dominant polycystic kidney disease is an inherited kidney disorder with mutations in polycystin-1 or polycystin-2. Autosomal recessive polycystic kidney disease is a severe form of polycystic kidney disease that is characterized by enlarged kidneys and congenital hepatic fibrosis. Mutations at PKHD1 are responsible for all typical forms of autosomal recessive polycystic kidney disease.

METHODS

We evaluated the children diagnosed with polycystic kidney disease between October 2020 and May 2022. The diagnosis was established by family history, ultrasound findings, and/or genetic analysis. The demographic, clinical, and laboratory findings were evaluated retrospectively.

RESULTS

There were 28 children (male/female: 11:17) evaluated in this study. Genetic analysis was performed in all patients (polycystin-1 variants in 13, polycystin-2 variants in 7, and no variants in 8 patients). A total of 18 variants in polycystin-1 and polycystin-2 were identified and 9 (50%) of them were not reported before. A total of eight novel variants were identified as definite pathogenic or likely pathogenic mutations. There was no variant detected in the PKDH1 gene.

CONCLUSION

Our results highlighted molecular features of Turkish children with polycystic kidney disease and demonstrated novel variations that can be utilized in clinical diagnosis and prognosis.

Double Heterozygous Pathogenic Variants in the LOX and PKD1 Genes in a 5-Year-Old Patient with Thoracic Aortic Aneurysm and Polycystic Kidney Disease

Familial thoracic aortic aneurysms and dissections may occur as an isolated hereditary trait or as part of connective tissue disorders with Mendelian inheritance, but severe cardiovascular disease in pediatric patients is extremely rare. There is growing knowledge on pathogenic variants causing the disease; however, much of the phenotypic variability and gene-gene interactions remain to be discovered. We present a case report of a 5.5-year-old girl with an aortic aneurysm and concomitant polycystic kidney disease. Whole exome sequencing was performed, followed by family screening by amplicon deep sequencing and diagnostic imaging studies. In the proband, two pathogenic variants were identified: p.Tyr257Ter in the LOX gene inherited from her mother, and p.Thr2977Ile in the PKD1 gene inherited from her father. All adult carriers of either of these variants showed symptoms of aortic disease. We conclude that the coexistence of two independent genetic variants in the proband may be the reason for an early onset of disease.

Fibrocystin/Polyductin releases a C-terminal fragment that translocates into mitochondria and suppresses cystogenesis

Fibrocystin/Polyductin (FPC), encoded by PKHD1, is associated with autosomal recessive polycystic kidney disease (ARPKD), yet its precise role in cystogenesis remains unclear. Here we show that FPC undergoes complex proteolytic processing in developing kidneys, generating three soluble C-terminal fragments (ICDs). Notably, ICD15, contains a novel mitochondrial targeting sequence at its N-terminus, facilitating its translocation into mitochondria. This enhances mitochondrial respiration in renal epithelial cells, partially restoring impaired mitochondrial function caused by FPC loss. FPC inactivation leads to abnormal ultrastructural morphology of mitochondria in kidney tubules without cyst formation. Moreover, FPC inactivation significantly exacerbates renal cystogenesis and triggers severe pancreatic cystogenesis in a Pkd1 mouse mutant Pkd1V/V in which cleavage of Pkd1-encoded Polycystin-1 at the GPCR Proteolysis Site is blocked. Deleting ICD15 enhances renal cystogenesis without inducing pancreatic cysts in Pkd1V/V mice. These findings reveal a direct link between FPC and a mitochondrial pathway through ICD15 cleavage, crucial for cystogenesis mechanisms.

Vascular polycystin proteins in health and disease

PKD1 (polycystin 1) and PKD2 (polycystin 2) are expressed in a variety of different cell types, including arterial smooth muscle and endothelial cells. PKD1 is a transmembrane domain protein with a large extracellular N-terminus that is proposed to act as a mechanosensor and receptor. PKD2 is a member of the transient receptor potential (TRP) channel superfamily which is also termed TRPP1. Mutations in the genes which encode PKD1 and PKD2 lead to autosomal polycystic kidney disease (ADPKD). ADPKD is one of the most prevalent monogenic disorders in humans and is associated with extrarenal and vascular complications, including hypertension. Recent studies have uncovered mechanisms of activation and physiological functions of PKD1 and PKD2 in arterial smooth muscle and endothelial cells. It has also been found that PKD function is altered in the vasculature during ADPKD and hypertension. We will summarize this work and discuss future possibilities for this area of research.

Case report: A novel occurrence of persistent left cranial vena cava coexisting with polycystic kidney disease in a cat

A 7-year-old castrated male Munchkin cat was presented with anorexia. This cat had been diagnosed with chronic kidney disease due to polycystic kidney disease. Tachycardia with a systolic murmur (grade III/VI) was auscultated and for further diagnosis, echocardiography was performed. Based on echocardiography, persistent left cranial vena cava (PLCVC) was suspected due to enlargement of the coronary sinus and confirmed by saline contrast echocardiography. The dilated coronary sinus compressed the left atrium, and left ventricular hypertrophy with the systolic anterior motion of the mitral valve, aortic regurgitation, and mitral regurgitation were identified. After medical management using atenolol, left atrial function and other hemodynamics of the heart were improved, including the disappearance of regurgitation and normalization of left ventricular wall thickness. This case report describes the echocardiographic characteristics, diagnostic procedures, and disease progression in a cat with PLCVC after medical management using atenolol. Additionally, this is the first report of a cat with PLCVC, coexisting with polycystic kidney disease.

Super-giant fusiform basilar artery aneurysm

Intracranial aneurysms are focal pathological dilatation of the arteries with a prevalence of 3.2%. Fusiform aneurysms are rare and mainly due to dissection or atherosclerosis. They may manifestas as stroke, cranial nerve palsies, brainstem compression and Sub-arachnoid hemorrhage. A diameter greater than 10 mm is a risk factor for rupture and warrants early intervention.

Cleavage fragments of the C-terminal tail of polycystin-1 are regulated by oxidative stress and induce mitochondrial dysfunction

Mutations in the gene encoding polycystin-1 (PC1) are the most common cause of autosomal dominant polycystic kidney disease (ADPKD). Cysts in ADPKD exhibit a Warburg-like metabolism characterized by dysfunctional mitochondria and aerobic glycolysis. PC1 is an integral membrane protein with a large extracellular domain, a short C-terminal cytoplasmic tail and shares structural and functional similarities with G protein-coupled receptors. Its exact function remains unclear. The C-terminal cytoplasmic tail of PC1 undergoes proteolytic cleavage, generating soluble fragments that are overexpressed in ADPKD kidneys. The regulation, localization, and function of these fragments is poorly understood. Here, we show that a ∼30 kDa cleavage fragment (PC1-p30), comprising the entire C-terminal tail, undergoes rapid proteasomal degradation by a mechanism involving the von Hippel-Lindau tumor suppressor protein. PC1-p30 is stabilized by reactive oxygen species, and the subcellular localization is regulated by reactive oxygen species in a dose-dependent manner. We found that a second, ∼15 kDa fragment (PC1-p15), is generated by caspase cleavage at a conserved site (Asp-4195) on the PC1 C-terminal tail. PC1-p15 is not subject to degradation and constitutively localizes to the mitochondrial matrix. Both cleavage fragments induce mitochondrial fragmentation, and PC1-p15 expression causes impaired fatty acid oxidation and increased lactate production, indicative of a Warburg-like phenotype. Endogenous PC1 tail fragments accumulate in renal cyst-lining cells in a mouse model of PKD. Collectively, these results identify novel mechanisms regarding the regulation and function of PC1 and suggest that C-terminal PC1 fragments may be involved in the mitochondrial and metabolic abnormalities observed in ADPKD.

CFTR and PC2, partners in the primary cilia in autosomal dominant polycystic kidney disease

Defects in the primary cilium are associated with autosomal dominant polycystic kidney disease (ADPKD). We used a combination of animal models, Western blotting, and confocal microscopy and discovered that CFTR and polycystin 2 (PC2) are both colocalized to the cilium in normal kidneys, with the levels of both being decreased in cystic epithelia. Cilia were longer in CFTR-null mice and in cystic cells in our ADPKD animal models. We examined septin 2, known to play a role in cilia length, to act as a diffusion barrier and to serve as an enhancer of proliferation. We found that septin 2 protein levels were upregulated and colocalized strongly with CFTR in cystic cells. Application of VX-809, the CFTR corrector, restored CFTR and PC2 toward normal in the cilia, decreased the protein levels of septin 2, and drastically reduced septin 2 colocalization with CFTR. Our data suggest that CFTR is present in the cilia and plays a role there, perhaps through its conductance of Cl-. We also postulate that septin 2 is important for localizing CFTR to the apical membrane in cystic epithelia.NEW & NOTEWORTHY CFTR is present in the primary cilia together with polycystin 2 (PC2). Ablation of CFTR makes cilia longer suggesting that CFTR plays a role there, perhaps through its conductance of Cl.

Utility of new image-derived biomarkers for autosomal dominant polycystic kidney disease prognosis using automated instance cyst segmentation

New image-derived biomarkers for patients affected by autosomal dominant polycystic kidney disease are needed to improve current clinical management. The measurement of total kidney volume (TKV) provides critical information for clinicians to drive care decisions. However, patients with similar TKV may present with very different phenotypes, often requiring subjective decisions based on other factors (e.g., appearance of healthy kidney parenchyma, a few cysts contributing significantly to overall TKV, etc.). In this study, we describe a new technique to individually segment cysts and quantify biometric parameters including cyst volume, cyst number, parenchyma volume, and cyst parenchyma surface area. Using data from the Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease (CRISP) study the utility of these new parameters was explored, both quantitatively as well as visually. Total cyst number and cyst parenchyma surface area showed superior prediction of the slope of estimated glomerular filtration rate decline, kidney failure and chronic kidney disease stages 3A, 3B, and 4, compared to TKV. In addition, presentations such as a few large cysts contributing significantly to overall kidney volume were shown to be much better stratified in terms of outcome predictions. Thus, these new image biomarkers, which can be obtained automatically, will have great utility in future studies and clinical care for patients affected by autosomal dominant polycystic kidney disease.

Experimental Models of Polycystic Kidney Disease: Applications and Therapeutic Testing

Polycystic kidney diseases (PKDs) are genetic disorders characterized by the formation and expansion of numerous fluid-filled renal cysts, damaging normal parenchyma and often leading to kidney failure. Although PKDs comprise a broad range of different diseases, with substantial genetic and phenotypic heterogeneity, an association with primary cilia represents a common theme. Great strides have been made in the identification of causative genes, furthering our understanding of the genetic complexity and disease mechanisms, but only one therapy so far has shown success in clinical trials and advanced to US Food and Drug Administration approval. A key step in understanding disease pathogenesis and testing potential therapeutics is developing orthologous experimental models that accurately recapitulate the human phenotype. This has been particularly important for PKDs because cellular models have been of limited value; however, the advent of organoid usage has expanded capabilities in this area but does not negate the need for whole-organism models where renal function can be assessed. Animal model generation is further complicated in the most common disease type, autosomal dominant PKD, by homozygous lethality and a very limited cystic phenotype in heterozygotes while for autosomal recessive PKD, mouse models have a delayed and modest kidney disease, in contrast to humans. However, for autosomal dominant PKD, the use of conditional/inducible and dosage models have resulted in some of the best disease models in nephrology. These have been used to help understand pathogenesis, to facilitate genetic interaction studies, and to perform preclinical testing. Whereas for autosomal recessive PKD, using alternative species and digenic models has partially overcome these deficiencies. Here, we review the experimental models that are currently available and most valuable for therapeutic testing in PKD, their applications, success in preclinical trials, advantages and limitations, and where further improvements are needed.

Accelerated cystogenesis by dietary protein load is dependent on, but not initiated by kidney macrophages

Background

Disease severity of autosomal dominant polycystic kidney disease (ADPKD) is influenced by diet. Dietary protein, a recognized cyst-accelerating factor, is catabolized into amino acids (AA) and delivered to the kidney leading to renal hypertrophy. Injury-induced hypertrophic signaling in ADPKD results in increased macrophage (MФ) activation and inflammation followed by cyst growth. We hypothesize that the cystogenesis-prompting effects of HP diet are caused by increased delivery of specific AA to the kidney, ultimately stimulating MФs to promote cyst progression.

Methods

Pkd1flox/flox mice with and without Cre (CAGG-ER) were given tamoxifen to induce global gene deletion (Pkd1KO). Pkd1KO mice were fed either a low (LP; 6%), normal (NP; 18%), or high (HP; 60%) protein diet for 1 week (early) or 6 weeks (chronic). Mice were then euthanized and tissues were used for histology, immunofluorescence and various biochemical assays. One week fed kidney tissue was cell sorted to isolate tubular epithelial cells for RNA sequencing.

Results

Chronic dietary protein load in Pkd1KO mice increased kidney weight, number of kidney infiltrating and resident MФs, chemokines, cytokines and cystic index compared to LP diet fed mice. Accelerated cyst growth induced by chronic HP were attenuated by liposomal clodronate-mediated MФ depletion. Early HP diet fed Pkd1KO mice had larger cystic kidneys compared to NP or LP fed counterparts, but without increases in the number of kidney MФs, cytokines, or markers of tubular injury. RNA sequencing of tubular epithelial cells in HP compared to NP or LP diet group revealed increased expression of sodium-glutamine transporter Snat3, chloride channel Clcnka, and gluconeogenesis marker Pepck1, accompanied by increased excretion of urinary ammonia, a byproduct of glutamine. Early glutamine supplementation in Pkd1KO mice lead to kidney hypertrophy.

Conclusion

Chronic dietary protein load-induced renal hypertrophy and accelerated cyst growth in Pkd1KO mice is dependent on both infiltrating and resident MФ recruitment and subsequent inflammatory response. Early cyst expansion by HP diet, however, is relient on increased delivery of glutamine to kidney epithelial cells, driving downstream metabolic changes prior to inflammatory provocation.

Tuberous Sclerosis Complex Kidney Lesion Pathogenesis: A Developmental Perspective

The phenotypic diversity of tuberous sclerosis complex (TSC) kidney pathology is enigmatic. Despite a well-established monogenic etiology, an incomplete understanding of lesion pathogenesis persists. In this review, we explore the question: How do TSC kidney lesions arise? We appraise literature findings in the context of mutational timing and cell-of-origin. Through a developmental lens, we integrate the critical results from clinical studies, human specimens, and genetic animal models. We also review novel insights gleaned from emerging organoid and single-cell sequencing technologies. We present a new model of pathogenesis which posits a phenotypic continuum, whereby lesions arise by mutagenesis during development from variably timed second-hit events. This model can serve as a conceptual framework for testing hypotheses of TSC lesion pathogenesis, both in the kidney and in other affected tissues.

Cystic Kidney Diseases in Children and Adults: Differences and Gaps in Clinical Management

Cystic kidney diseases, when broadly defined, have a wide differential diagnosis extending from recessive diseases with a prenatal or pediatric diagnosis, to the most common autosomal-dominant polycystic kidney disease primarily affecting adults, and several other genetic or acquired etiologies that can manifest with kidney cysts. The most likely diagnoses to consider when assessing a patient with cystic kidney disease differ depending on family history, age stratum, radiologic characteristics, and extrarenal features. Accurate identification of the underlying condition is crucial to estimate the prognosis and initiate the appropriate management, identification of extrarenal manifestations, and counseling on recurrence risk in future pregnancies. There are significant differences in the clinical approach to investigating and managing kidney cysts in children compared with adults. Next-generation sequencing has revolutionized the diagnosis of inherited disorders of the kidney, despite limitations in access and challenges in interpreting the data. Disease-modifying treatments are lacking in the majority of kidney cystic diseases. For adults with rapid progressive autosomal-dominant polycystic kidney disease, tolvaptan (V2-receptor antagonist) has been approved to slow the rate of decline in kidney function. In this article, we examine the differences in the differential diagnosis and clinical management of cystic kidney disease in children versus adults, and we highlight the progress in molecular diagnostics and therapeutics, as well as some of the gaps meriting further attention.