Genetics and pathogenesis of polycystic kidney disease

Discovery of putative inhibitors of human Pkd1 enzyme: Molecular docking, dynamics and simulation, QSAR, and MM/GBSA

Polycystic kidney disease is the most prevalent hereditary kidney disease globally and is mainly linked to the overexpression of a gene called PKD1. To date, there is no effective treatment available for polycystic kidney disease, and the practicing treatments only provide symptomatic relief. Discovery of the compounds targeting the PKD1 gene by inhibiting its expression under the disease condition could be crucial for effective drug development. In this study, a molecular docking and molecular dynamic simulation, QSAR, and MM/GBSA-based approaches were used to determine the putative inhibitors of the Pkd1 enzyme from a library of 1379 compounds. Initially, fourteen compounds were selected based on their binding affinities with the Pkd1 enzyme using MOE and AutoDock tools. The selected drugs were further investigated to explore their properties as drug candidates and the stability of their complex formation with the Pkd1 enzyme. Based on the physicochemical and ADMET (Absorption, Distribution, Metabolism, Excretion, and Toxicity) properties, and toxicity profiling, two compounds including olsalazine and diosmetin were selected for the downstream analysis as they demonstrated the best drug-likeness properties and highest binding affinity with Pkd1 in the docking experiment. Molecular dynamic simulation using Gromacs further confirmed the stability of olsalazine and diosmetin complexes with Pkd1 and establishing interaction through strong bonding with specific residues of protein. High biological activity and binding free energies of two complexes calculated using 3D QSAR and Schrodinger module, respectively further validated our results. Therefore, the molecular docking and dynamics simulation-based in-silico approach used in this study revealed olsalazine and diosmetin as potential drug candidates to combat polycystic kidney disease by targeting Pkd1 enzyme.

HL156A, an AMP-Activated Protein Kinase Activator, Inhibits Cyst Growth in Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent genetic kidney disorder. While metformin has demonstrated the ability to inhibit cyst growth in animal models of ADPKD via activation of adenosine monophosphate-activated protein kinase (AMPK), its effectiveness in humans is limited due to its low potency. This study explored the impact of HL156A, a new and more potent AMPK activator, in a mouse model of ADPKD.

METHODS

To investigate whether HL156A inhibits the proliferation of renal cyst cells in ADPKD in vitro, exogenous human telomerase reverse transcriptase (hTERT)-immortalized renal cyst cells from ADPKD patients were treated with HL156A, and an MTT (dimethylthiazol-diphenyltetrazolium bromide) assay was performed. To assess the cyst-inhibitory effect of HL156A in vivo, we generated Pkd1 conditional knockout (KO) mice with aquaporin 2 (AQP2)-Cre, which selectively expresses Cre recombinase in the collecting duct. The effectiveness of HL156A in inhibiting cyst growth and improving renal function was confirmed by measuring the number of cysts and blood urea nitrogen (BUN) levels in the collecting duct-specific Pkd1 KO mice.

RESULTS

When cyst cells were treated with up to 20 µM of metformin or HL156A, HL156A reduced cell viability by 25% starting at a concentration of 5 µM, whereas metformin showed no effect. When AQP2-Cre male mice were crossed with Pkd1flox/flox female mice, and when AQP2-Cre female mice were crossed with Pkd1flox/flox male mice, the number of litters produced by both groups was comparable. In collecting duct-specific Pkd1 KO mice, HL156A was found to inhibit cyst growth, reducing both the number and size of cysts. Furthermore, it was confirmed that kidney function improved as HL156A treatment led to a reduction in elevated BUN levels. Lastly, it was observed that the increase in AMPK phosphorylation induced by HL156A decreased ERK phosphorylation and α-SMA expression.

CONCLUSION

HL156A has potential as a drug that can restore kidney function in ADPKD patients by inhibiting cyst growth.

Investigation of Basolateral Targeting Micelles for Drug Delivery Applications in Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a complex disorder characterized by uncontrolled renal cyst growth, leading to kidney function decline. The multifaceted nature of ADPKD suggests that single-pathway interventions using individual small molecule drugs may not be optimally effective. As such, a strategy encompassing combination therapy that addresses multiple ADPKD-associated signaling pathways could offer synergistic therapeutic results. However, severe off-targeting side effects of small molecule drugs pose a major hurdle to their clinical transition. To address this, we identified four drug candidates from ADPKD clinical trials, bardoxolone methyl (Bar), octreotide (Oct), salsalate (Sal), and pravastatin (Pra), and incorporated them into peptide amphiphile micelles containing the RGD peptide (GRGDSP), which binds to the basolateral surface of renal tubules via integrin receptors on the extracellular matrix. We hypothesized that encapsulating drug combinations into RGD micelles would enable targeting to the basolateral side of renal tubules, which is the site of disease, via renal secretion, leading to superior therapeutic benefits compared to free drugs. To test this, we first evaluated the synergistic effect of drug combinations using the 20% inhibitory concentration for each drug (IC20) on renal proximal tubule cells derived from Pkd1flox/-:TSLargeT mice. Next, we synthesized and characterized the RGD micelles encapsulated with drug combinations and measured their in vitro therapeutic effects via a 3D PKD growth model. Upon both IV and IP injections in vivo, RGD micelles showed a significantly higher accumulation in the kidneys compared to NT micelles, and the renal access of RGD micelles was significantly reduced after the inhibition of renal secretion. Specifically, both Bar+Oct and Bar+Sal in the RGD micelle treatment showed enhanced therapeutic efficacy in ADPKD mice (Pkd1fl/fl;Pax8-rtTA;Tet-O-Cre) with a significantly lower KW/BW ratio and cyst index as compared to PBS and free drug-treated controls, while other combinations did not show a significant difference. Hence, we demonstrate that renal targeting through basolateral targeting micelles enhances the therapeutic potential of combination therapy in genetic kidney disease.

Oral delivery of nanomedicine for genetic kidney disease

Chronic and genetic kidney diseases such as autosomal dominant polycystic kidney disease (ADPKD) have few therapeutic options, and clinical trials testing small molecule drugs have been unfavorable due to low kidney bioavailability and adverse side effects. Although nanoparticles can be designed to deliver drugs directly to the diseased site, there are no kidney-targeted nanomedicines clinically available, and most FDA-approved nanoparticles are administered intravenously which is not ideal for chronic diseases. To meet these challenges of chronic diseases, we developed a biomaterials-based strategy using chitosan particles (CP) for oral delivery of therapeutic, kidney-targeting peptide amphiphile micelles (KMs). We hypothesized that encapsuling KMs into CP would enhance the bioavailability of KMs upon oral administration given the high stability of chitosan in acidic conditions and mucoadhesive properties enabling absorption within the intestines. To test this, we evaluated the mechanism of KM access to the kidneys via intravital imaging and investigated the KM biodistribution in a porcine model. Next, we loaded KMs carrying the ADPKD drug metformin into CP (KM-CP-met) and measured in vitro therapeutic effect. Upon oral administration in vivo, KM-CP-met showed significantly greater bioavailability and accumulation in the kidneys as compared to KM only or free drug. As such, KM-CP-met treatment in ADPKD mice (Pkd1fl/fl;Pax8-rtTA;Tet-O-Cre which develops the disease over 120 days and mimics the slow development of ADPKD) showed enhanced therapeutic efficacy without affecting safety despite repeated treatment. Herein, we demonstrate the potential of KM-CP as a nanomedicine strategy for oral delivery for the long-term treatment of chronic kidney diseases.

Kidney Stones Account for Increased Imaging Studies in Autosomal Dominant Polycystic Kidney Disease

Key Points

Kidney stones are common in patients with autosomal dominant polycystic kidney disease compared with matched controls with CKD. The increase in imaging seen in patients with autosomal dominant polycystic kidney disease correlates with the kidney stone burden in these patients.

Background

Patients with autosomal dominant polycystic kidney disease (ADPKD) may have more imaging studies than patients with other forms of CKD. We characterized the imaging burden of patients with ADPKD relative to a CKD population to determine which factors lead to increased imaging in patients with ADPKD.

Methods

We retrospectively reviewed patients seen at Yale Nephrology between January 2012 and January 2021. We collected demographic, clinical, and imaging data through automated query and manual chart review. Eight hundred seven patients with ADPKD were matched to 4035 CKD controls on the basis of criteria of sex, race, ethnicity, CKD stage, hypertension, and diabetes, but not age. The number of abdominal imaging studies were compared between ADPKD and CKD groups, and the effect of kidney stone diagnosis was further evaluated. Chi-square and t tests were used to evaluate demographic variables, and Kruskal Wallis and negative binomial regression models were used to evaluate differences between abdominal imaging studies.

Results

Patients with ADPKD had a greater number of total abdominal imaging studies (P < 0.0001), ultrasounds (P < 0.0001), and magnetic resonance imagings (P = 0.02) compared with controls. In patients with preserved renal function (eGFR >60 ml/min per m2), these differences persisted. Kidney stones were significantly more common among patients with ADPKD (P < 0.0001). In multivariable assessment of imaging study counts using a negative binomial model controlling for kidney stones, ADPKD was no longer a significant predictor. In patients with ADPKD, pyelonephritis; cyst complications; lower eGFR; diabetes; coronary artery disease; kidney stones; lower body mass index; and being male, Black, and younger increased the likelihood of having more imaging studies.

Conclusions

The higher prevalence of abdominal imaging studies in patients with ADPKD correlated with the increased incidence of kidney stones observed in this population.

Update on the Application of Ultrasonography in Understanding Autosomal Dominant Polycystic Kidney Disease

With an estimated prevalence of 1 in 1000 individuals globally, autosomal dominant polycystic kidney disease (ADPKD) stands as the most prevalent inherited renal disorder. Ultrasonography (US) is the most widely used imaging modality in the diagnosis and monitoring of ADPKD. This review discusses the role of US in the evaluation of ADPKD, including its diagnostic accuracy, limitations, and recent advances. An overview of the pathophysiology and clinical manifestations of ADPKD has also been provided. Furthermore, the potential of US as a noninvasive tool for the assessment of disease progression and treatment response is examined. Overall, US remains an essential tool for the management of ADPKD, and ongoing research efforts are aimed at improving its diagnostic and prognostic capabilities.

Prevalence and outcomes of polycystic kidney disease in African populations: A systematic review

BACKGROUND

Polycystic kidney disease (PKD) is the most common genetic cause of kidney disease. It is a progressive and irreversible condition that can lead to end-stage renal disease and many other visceral complications. Current comprehensive data on PKD patterns in Africa is lacking.

AIM

To describe the prevalence and outcomes of PKD in the African population.

METHODS

A literature search of PubMed, African journal online, and Google Scholar databases between 2000 and 2023 was performed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses were followed to design the study. Clinical presentations and outcomes of patients were extracted from the included studies.

RESULTS

Out of 106 articles, we included 13 studies from 7 African countries. Ten of them were retrospective descriptive studies concerning 943 PKD patients with a mean age of 47.9 years. The accurate prevalence and incidence of PKD were not known but it represented the third causal nephropathy among dialysis patients. In majority of patients, the diagnosis of the disease was often delayed. Kidney function impairment, abdominal mass, and hypertension were the leading symptoms at presentation with a pooled prevalence of 72.1% (69.1-75.1), 65.8% (62.2-69.4), and 57.4% (54.2-60.6) respectively. Hematuria and infections were the most frequent complications. Genotyping was performed in few studies that revealed a high proportion of new mutations mainly in the PKD1 gene.

CONCLUSION

The prevalence of PKD in African populations is not clearly defined. Clinical symptoms were almost present with most patients who had kidney function impairment and abdominal mass at the diagnostic. Larger studies including genetic testing are needed to determine the burden of PKD in African populations.

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.

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.

Novel hits for autosomal dominated polycystic kidney disease (ADPKD) targeting derived by in silico screening on ZINC-15 natural product database

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetic kidney disorder that leads to growth cysts in the kidney, ultimately resulting in loss of function. Currently, no effective drug therapy can be safely used in the clinic. So, looking for effective therapeutic drugs is urgent for treating ADPKD. Our natural product library was prepared based on the ZINC-15 database. Lipinski's rule of five, drug-likeness, and toxicity screening of the designed library were evaluated. Swiss model online server was used for modeling of GANAB target. Finally, docking-based screening against ADPKD targets was done by MOE 2019 software. The top 14 favorable druglike and non-toxic hits were selected for docking studies. Our results showed that compound-10 (ZINC 6073947) as a sesquiterpene coumarin had more negative binding interaction into the active site of PPARG, OXSR1, GANAB, AVPR2, and PC2 with docking scores of -8.22, -7.52, -6.98, -6.61 and -6.05 kcal/mol, respectively, in comparison to Curcumin, as a natural product that is now in phase 4 clinical trial in ADPKD disease, with an affinity of -8.03, -6.42, -6.82, -5.84 and -5.10 kcal/mol, respectively. Furthermore, seven sesquiterpene coumarins similar to compound 10 were generated and docked. Farnesiferol B (16), compared to compound-10, showed binding affinity of -8.16, -6.4, -7.46, -6.92, and -6.11 kcal/mol against the above targets, respectively. Molecular dynamics, which was done on the compound-10 and 16 (Farnesiferol B) in complex with PPARG, GANAB, and AVPR2, showed more negative binding free-energy than Pioglitazone, Miglitol, and Tolvaptan as FDA-approved drugs for each target, respectively.Communicated by Ramaswamy H. Sarma.

Clinical findings, underlying pathogenetic processes and treatment of vascular dysfunction in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited disorder characterized by the development of fluid-filled cysts in the kidneys. The primary cause of ADPKD is mutations in the PKD1 (polycystic kidney disease 1) or PKD2 (polycystic kidney disease 2) gene. Patients with ADPKD often develop a variety of vascular abnormalities, which have a major impact on the structure and function of the blood vessels and can lead to complications such as hypertension, intracranial aneurysm (ICAN), and atherosclerosis. The progression of ADPKD involves intricate molecular and cellular processes that lead to the development of these vascular abnormalities. Our understanding of these processes remains incomplete, and available treatment options are limited. The aim of this review is to delve into the underlying mechanisms of these vascular abnormalities and to explore potential interventions.

IK is essentially involved in ciliogenesis as an upstream regulator of oral-facial-digital syndrome ciliopathy gene, ofd1

BACKGROUND

The cilia are microtubule-based organelles that protrude from the cell surface. Abnormalities in cilia result in various ciliopathies, including polycystic kidney disease (PKD), Bardet-Biedl syndrome (BBS), and oral-facial-digital syndrome type I (OFD1), which show genetic defects associated with cilia formation. Although an increasing number of human diseases is attributed to ciliary defects, the functions or regulatory mechanisms of several ciliopathy genes remain unclear. Because multi ciliated cells (MCCs) are especially deep in vivo, studying ciliogenesis is challenging. Here, we demonstrate that ik is essential for ciliogenesis in vivo.

RESULTS

In the absence of ik, zebrafish embryos showed various ciliopathy phenotypes, such as body curvature, abnormal otoliths, and cyst formation in the kidney. RNA sequencing analysis revealed that ik positively regulated ofd1 expression required for cilium assembly. In fact, depletion of ik resulted in the downregulation of ofd1 expression with ciliary defects, and these ciliary defects in ik mutants were rescued by restoring ofd1 expression. Interestingly, ik affected ciliogenesis particularly in the proximal tubule but not in the distal tubule in the kidney.

CONCLUSIONS

This study demonstrates the role of ik in ciliogenesis in vivo for the first time. Loss of ik in zebrafish embryos displays various ciliopathy phenotypes with abnormal ciliary morphology in ciliary tissues. Our findings on the ik-ofd1 axis provide new insights into the biological function of ik in clinical ciliopathy studies in humans.

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.

Many lessons still to learn about autosomal dominant polycystic kidney disease

We are still learning the genetic basis for many rare diseases. Here we provide a commentary on the analysis of the genetic landscape of patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD), one of the most common genetic kidney diseases. Approaches including both phenotype first and genotype first allows some interesting and informative observations within this disease population. PKD1 and PKD2 are the most frequent genetic causes of ADPKD accounting for 78% and 15% respectively, whilst around 7-8% of cases have an alternative genetic diagnosis. These rarer forms include IFT140, GANAB, PKHD1, HNF1B, ALG8, and ALG9. Some previously reported likely pathogenic PKD1 and PKD2 alleles may have a reduced penetrance, or indeed may have been misclassified in terms of their pathogenicity. This recent data concerning all forms of ADPKD points to the importance of performing genetics tests in all families with a clinical diagnosis of ADPKD as well as those with more atypical cystic kidney appearances. Following allele identification, performing segregation analysis wherever possible remains vital so that we continue to learn about these important genetic causes of kidney failure.

Co-Inheritance of Pathogenic Variants in PKD1 and PKD2 Genes Determined by Parental Segregation and De Novo Origin: A Case Report

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease, and it is typically caused by PKD1 and PKD2 heterozygous variants. Nonetheless, the extensive phenotypic variability observed among affected individuals, even within the same family, suggests a more complex pattern of inheritance. We describe an ADPKD family in which the proband presented with an earlier and more severe renal phenotype (clinical diagnosis at the age of 14 and end-stage renal disease aged 24), compared to the other affected family members. Next-generation sequencing (NGS)-based analysis of polycystic kidney disease (PKD)-associated genes in the proband revealed the presence of a pathogenic PKD2 variant and a likely pathogenic variant in PKD1, according to the American College of Medical Genetics and Genomics (ACMG) criteria. The PKD2 nonsense p.Arg872Ter variant was segregated from the proband's father, with a mild phenotype. A similar mild disease presentation was found in the proband's aunts and uncle (the father's siblings). The frameshift p.Asp3832ProfsTer128 novel variant within PKD1 carried by the proband in addition to the pathogenic PKD2 variant was not found in either parent. This report highlights that the co-inheritance of two or more PKD genes or alleles may explain the extensive phenotypic variability among affected family members, thus emphasizing the importance of NGS-based techniques in the definition of the prognostic course.

Urinary Extracellular Vesicles in Chronic Kidney Disease: From Bench to Bedside?

Extracellular vesicles are a diverse group of particles that include exosomes, microvesicles, and apoptotic bodies and are defined by size, composition, site of origin, and density. They incorporate various bioactive molecules from their cell of origin during formation, such as soluble proteins, membrane receptors, nucleic acids (mRNAs and miRNAs), and lipids, which can then be transferred to target cells. Extracellular vesicles/exosomes have been extensively studied as a critical factor in pathophysiological processes of human diseases. Urinary extracellular vesicles could be a promising liquid biopsy for determining the pattern and/or severity of kidney histologic injury. The signature of urinary extracellular vesicles may pave the way for noninvasive methods to supplement existing testing methods for diagnosing kidney diseases. We discuss the potential role of urinary extracellular vesicles in various chronic kidney diseases in this review, highlighting open questions and discussing the potential for future research.

Single-Cell and CellChat Resolution Identifies Collecting Duct Cell Subsets and Their Communications with Adjacent Cells in PKD Kidneys

ADPKD is a genetic disorder with a molecular complexity that remains poorly understood. In this study, we sampled renal cells to construct a comprehensive and spatiotemporally resolved gene expression atlas in whole Pkd1 mutant polycystic mouse kidneys at single-cell resolution. We characterized cell diversity and identified novel collecting duct (CD) cell subtypes in cystic kidneys. We further found that CD cells appear to take different cell fate trajectories, and the first and the most important step might take place around day 14 in Pkd1 homozygous kidneys. After that day, increased numbers of CD cells showed highly proliferative and fibrotic characteristics, as detected in later-stage Pkd1 homozygous kidneys, both of which should contribute to cyst growth and renal fibrosis. With a newly developed modeling algorithm, called CellChat Explorer, we identify cell-to-cell communication networks mediated by the ligand receptor, such as MIF-CD44/CD74, in cystic kidneys, and confirm them via the expression patterns of ligands and receptors in four major cell types, which addresses the key question as to whether and how Pkd1 mutant renal epithelial cells affect their neighboring cells. The allele-specific gene expression profiles show that the secretion of cytokines by Pkd1 mutant epithelial cells may affect the gene expression profiles in recipient cells via epigenetic mechanisms, and vice versa. This study can be used to drive precision therapeutic targeting of ADPKD.

miR-20a is upregulated in serum from domestic feline with PKD1 mutation

Polycystic kidney disease (PKD), also known as autosomal dominant polycystic kidney disease (ADPKD) is a genetically heterogeneous condition characterized by cysts in renal parenchyma. It is the most prevalent inherited disease of domestic cats. MicroRNAs (miRNAs or ncRNA) are short, noncoding, single-stranded RNAs that may induce PKD cytogenesis by affecting numerous targets genes as well as by directly regulating PKD gene expression. We compared the relative expression profile of miR-20a, -192, -365, -15b-5p, and -16-5p from plasma and serum samples of nine domestic cats with PKD1 mutation, detected by polymerase chain reaction (PCR), and a control group (n = 10). Blood samples from cats with PKD1 mutation provide similar concentrations of microRNAs either from plasma or serum. Serum miR-20a is upregulated in PKD group with p < 0.005; Roc curve analysis showed an AUC of 90,1% with a cut-off value sensitivity of 77.8% and specificity of 100%. This data provides important information regarding renal miRNA expression in peripheral blood sampling.

Small hairpin inhibitory RNA delivery in the metanephric organ culture identifies long noncoding RNA Pvt1 as a modulator of cyst growth

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic disorder characterized by the formation of kidney cysts that originate from the epithelial tubules of the nephron and primarily results from mutations in polycystin-1 (PKD1) and polycystin-2 (PKD2). The metanephric organ culture (MOC) is an ex vivo system in which explanted embryonic kidneys undergo tubular differentiation and kidney development. MOC has been previously used to study polycystic kidney disease as treatment with 8-bromo-cAMP induces the formation of kidney cysts. However, the inefficiency of manipulating gene expression in MOC has limited its utility for identifying genes and pathways that are involved in cystogenesis. Here, we used a lentivirus and three serotypes of self-complementary adeno-associated viral (scAAV) plasmids that express green fluorescent protein and found that scAAV serotype D/J transduces the epithelial compartment of MOC at an efficiency of 68%. We used scAAV/DJ to deliver shRNA to knockdown Pvt1, a long noncoding RNA, which was upregulated in kidneys from Pkd1 and Pkd2 mutant mice and humans with ADPKD. shRNA delivery by scAAV/DJ downregulated expression of Pvt1 by 45% and reduced the cyst index by 53% in wild-type MOCs and 32% in Pkd1-null MOCs. Knockdown of Pvt1 decreased the level of c-MYC protein by 60% without affecting Myc mRNA, indicating that Pvt1 regulation of c-MYC was posttranscriptional. These results identify Pvt1 as a long noncoding RNA that modulates cyst progression in MOC.NEW & NOTEWORTHY This study identified scAAV/DJ as effective in transducing epithelial cells of the metanephric organ culture (MOC). We used scAAV/DJ shRNA to knockdown Pvt1 in cystic MOCs derived from Pkd1-null embryos. Downregulation of Pvt1 reduced cyst growth and decreased levels of c-MYC protein. These data suggest that suppression of Pvt1 activity in autosomal dominant polycystic kidney disease might reduce cyst growth.

Channel Function of Polycystin-2 in the Endoplasmic Reticulum Protects against Autosomal Dominant Polycystic Kidney Disease

BACKGROUND

Mutations of PKD2, which encodes polycystin-2, cause autosomal dominant polycystic kidney disease (ADPKD). The prevailing view is that defects in polycystin-2-mediated calcium ion influx in the primary cilia play a central role in the pathogenesis of cyst growth. However, polycystin-2 is predominantly expressed in the endoplasmic reticulum (ER) and more permeable to potassium ions than to calcium ions.

METHODS

The trimeric intracellular cation (TRIC) channel TRIC-B is an ER-resident potassium channel that mediates potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium ion release. Using TRIC-B as a tool, we examined the function of ER-localized polycystin-2 and its role in ADPKD pathogenesis in cultured cells, zebrafish, and mouse models.

RESULTS

Agonist-induced ER calcium ion release was defective in cells lacking polycystin-2 and reversed by exogenous expression of TRIC-B. Vice versa, exogenous polycystin-2 reversed an ER calcium-release defect in cells lacking TRIC-B. In a zebrafish model, expression of wild-type but not nonfunctional TRIC-B suppressed polycystin-2-deficient phenotypes. Similarly, these phenotypes were suppressed by targeting the ROMK potassium channel (normally expressed on the cell surface) to the ER. In cultured cells and polycystin-2-deficient zebrafish phenotypes, polycystin-2 remained capable of reversing the ER calcium release defect even when it was not present in the cilia. Transgenic expression of Tric-b ameliorated cystogenesis in the kidneys of conditional Pkd2-inactivated mice, whereas Tric-b deletion enhanced cystogenesis in Pkd2-heterozygous kidneys.

CONCLUSIONS

Polycystin-2 in the ER appears to be critical for anticystogenesis and likely functions as a potassium ion channel to facilitate potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium release. The results advance the understanding of ADPKD pathogenesis and provides proof of principle for pharmacotherapy by TRIC-B activators.

Cilia-Localized Counterregulatory Signals as Drivers of Renal Cystogenesis

Primary cilia play counterregulatory roles in cystogenesis—they inhibit cyst formation in the normal renal tubule but promote cyst growth when the function of polycystins is impaired. Key upstream cilia-specific signals and components involved in driving cystogenesis have remained elusive. Recent studies of the tubby family protein, Tubby-like protein 3 (TULP3), have provided new insights into the cilia-localized mechanisms that determine cyst growth. TULP3 is a key adapter of the intraflagellar transport complex A (IFT-A) in the trafficking of multiple proteins specifically into the ciliary membrane. Loss of TULP3 results in the selective exclusion of its cargoes from cilia without affecting their extraciliary pools and without disrupting cilia or IFT-A complex integrity. Epistasis analyses have indicated that TULP3 inhibits cystogenesis independently of the polycystins during kidney development but promotes cystogenesis in adults when polycystins are lacking. In this review, we discuss the current model of the cilia-dependent cyst activation (CDCA) mechanism in autosomal dominant polycystic kidney disease (ADPKD) and consider the possible roles of ciliary and extraciliary polycystins in regulating CDCA. We then describe the limitations of this model in not fully accounting for how cilia single knockouts cause significant cystic changes either in the presence or absence of polycystins. Based on available data from TULP3/IFT-A-mediated differential regulation of cystogenesis in kidneys with deletion of polycystins either during development or in adulthood, we hypothesize the existence of cilia-localized components of CDCA (cCDCA) and cilia-localized cyst inhibition (CLCI) signals. We develop the criteria for cCDCA/CLCI signals and discuss potential TULP3 cargoes as possible cilia-localized components that determine cystogenesis in kidneys during development and in adult mice.

A MRI-based radiomics nomogram for evaluation of renal function in ADPKD

OBJECTIVES

This study is aimed to establish a fusion model of radiomics-based nomogram to predict the renal function of autosomal dominant polycystic kidney disease (ADPKD).

METHODS

One hundred patients with ADPKD were randomly divided into training group (n = 69) and test group (n = 31). The radiomics features were extracted from T1-weighted fat suppression images (FS-T1WI) and T2-weighted fat suppression images (FS-T2WI). Decision tree algorithm was employed to build radiomics model to get radiomics signature. Then multivariate logistic regression analysis was used to establish the radiomics nomogram based on independent clinical factors, conventional MR imaging variables and radiomics signature. The receiver operating characteristic (ROC) analysis and Delong test were used to compare the performance of radiomics model and radiomics nomogram model, and the decision curve to evaluate the clinical application value of radiomics nomogram model in the evaluation of renal function in patients with ADPKD.

RESULTS

Fourteen radiomics features were selected to establish radiomics model. Based on FS-T1WI and FS-T2WI sequences, the radiomics model showed good discrimination ability in training group and test group [training group: (AUC) = 0.7542, test group (AUC) = 0.7417]. The performance of radiomics nomogram model was significantly better than that of radiomics model in all data sets [radiomics model (AUC) = 0.7505, radiomics nomogram model (AUC) = 0.8435, p value = 0.005]. The analysis of calibration curve and decision curve showed that radiomics nomogram model had more clinical application value.

CONCLUSION

radiomics analysis of MRI can be used for the preliminary evaluation and prediction of renal function in patients with ADPKD. The radiomics nomogram model shows better prediction effect in renal function evaluation, and can be used as a non-invasive renal function prediction tool to assist clinical decision-making. Trial registration ChiCTR, ChiCTR2100046739. Registered 27 May 2021-retrospectively registered, http://www.ChiCTR.org.cn/showproj.aspx?proj=125955.

Kidney Cancer and Chronic Kidney Disease: Too Close for Comfort

Kidney cancer and chronic kidney disease are two renal pathologies with very different clinical management strategies and therapeutical options. Nonetheless, the cellular and molecular mechanisms underlying both conditions are closely related. Renal physiology is adapted to operate with a limited oxygen supply, making the kidney remarkably equipped to respond to hypoxia. This tightly regulated response mechanism is at the heart of kidney cancer, leading to the onset of malignant cellular phenotypes. Although elusive, the role of hypoxia in chronic kidney diseases is emerging as related to fibrosis, a pivotal factor in decaying renal function. The present review offers a perspective on the common biological traits shared between kidney cancer and chronic kidney disease and the available and prospective therapies for both conditions.

Structural Pharmacology of TRP Channels

Transient receptor potential (TRP) ion channels are a super-family of ion channels that mediate transmembrane cation flux with polymodal activation, ranging from chemical to physical stimuli. Furthermore, due to their ubiquitous expression and role in human diseases, they serve as potential pharmacological targets. Advances in cryo-EM TRP channel structural biology has revealed general, as well as diverse, architectural elements and regulatory sites among TRP channel subfamilies. Here, we review the endogenous and pharmacological ligand-binding sites of TRP channels and their regulatory mechanisms.

Extracellular vesicles and exosomes generated from cystic renal epithelial cells promote cyst growth in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is caused by germline mutations of PKD1 or PKD2 on one allele and a somatic mutation inactivating the remaining normal allele. However, if and how null ADPKD gene renal epithelial cells affect the biology and function of neighboring cells, including heterozygous renal epithelial cells, fibroblasts and macrophages during cyst initiation and expansion remains unknown. Here we address this question with a "cystic extracellular vesicles/exosomes theory". We show that cystic cell derived extracellular vesicles and urinary exosomes derived from ADPKD patients promote cyst growth in Pkd1 mutant kidneys and in 3D cultures. This is achieved by: 1) downregulation of Pkd1 gene expression and upregulation of specific miRNAs, resulting in the activation of PKD associated signaling pathways in recipient renal epithelial cells and tissues; 2) the activation of fibroblasts; and 3) the induction of cytokine expression and the recruitment of macrophages to increase renal inflammation in cystic kidneys. Inhibition of exosome biogenesis/release with GW4869 significantly delays cyst growth in aggressive and milder ADPKD mouse models, suggesting that targeting exosome secretion has therapeutic potential for ADPKD.

The vasopressin-aquaporin-2 pathway syndromes

Vasopressin is the key hormone involved in water conservation and regulation of water balance, essential for life. In the renal collecting duct, vasopressin binds to the V2 receptor, increasing water permeability through activation of aquaporin-2 redistribution to the luminal membrane. This mechanism promotes rapid water reabsorption, important for immediate survival; however, only recently it has become clear that long-term adverse effects are associated with alterations of the vasopressin-aquaporin-2 pathway, leading to several syndromes associated with water balance disorders. The kidney resistance to the vasopressin action may cause severe dehydration for patients and, conversely, nonosmotic release of vasopressin is associated with water retention and increasing the circulatory blood volume. This chapter discusses the relevance of the altered vasopressin-aquaporin-2 pathway in some diseases associated with water balance disorders, including congenital nephrogenic diabetes insipidus, syndrome of inappropriate secretion of antidiuretic hormone, nephrogenic syndrome of inappropriate antidiuresis, and autosomal dominant polycystic kidney disease. The emerging picture suggests that targeting the vasopressin-AQP2 axis can provide therapeutic benefits in those patients.

Laparoscopic Nephrectomy for Massive Kidneys in Polycystic Kidney Disease

Background and Objectives:

Laparoscopic nephrectomy is now considered a feasible surgical approach, even for large kidneys. In the case of massive kidneys, laparoscopy can be problematic, so that some authors suggest an open approach. However, previous studies have shown that hand-assisted laparoscopic nephrectomy (HALN) may represent a useful compromise.

We describe our hand-assisted laparoscopic technique for nephrectomy of large kidneys (> 2500 g) to encourage the use of laparoscopy for nephrectomy in autosomal dominant polycystic kidney disease.

Methods:

We retrospectively analyzed data from 26 nephrectomies in 17 patients who underwent HALN for ADPKD and compared them to a group of 22 nephrectomies in 18 patients with open surgical technique.

Results:

The duration of the procedure was significantly longer in the laparoscopic group, with a median of 180 minutes versus 90 minutes for the unilateral nephrectomies, and 240 minutes versus 122 minutes for the bilateral procedures. The median kidney weight in the open group was 2500 g (range 1300 – 4500 g), while the median weight in the HALN group was 2375 g (range 1000 – 4700 g). The median hospital stay was comparable. No significant differences were recorded in the intra- and postoperative complication rate.

Conclusion:

Hand-assisted laparoscopic nephrectomy can be considered a technique of choice for patients suffering from ADPKD requiring nephrectomy, also with massive kidneys weighing more than 3500 g. Compared to open nephrectomy, HALN can be performed safely, with reasonably longer operating times and without major complications, and offers a significant reduction in hospitalization time, pain and postoperative discomfort.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD) is a rare disorder and one of the most severe forms of polycystic kidney disease, leading to end-stage renal disease (ESRD) in childhood. PKHD1 is the gene that is responsible for the vast majority of ARPKD. However, some cases have been related to a new gene that was recently identified (DZIP1L gene), as well as several ciliary genes that can mimic a ARPKD-like phenotypic spectrum. In addition, a number of molecular pathways involved in the ARPKD pathogenesis and progression were elucidated using cellular and animal models. However, the function of the ARPKD proteins and the molecular mechanism of the disease currently remain incompletely understood. Here, we review the clinics, treatment, genetics, and molecular basis of ARPKD, highlighting the most recent findings in the field.

A chalcone derivative retards renal cyst enlargement by inhibiting fluid secretion and cell proliferation in an in vitro model of polycystic kidney disease

BACKGROUND

Renal bilateral fluid filled-cyst in polycystic kidney disease (PKD) is associated with abnormal epithelial cell proliferation and transepithelial fluid secretion which leads to end-stage renal disease (ESRD). A chalcone derivative, isoliquiritigenin (ISLQ), has been shown to have various pharmacological properties. Since several studies have shown that ISLQ could inhibit CFTR channel activity, it is interesting to see whether it can inhibit renal cyst enlargement. The present study was aimed to determine an inhibitory effect and the mechanism of chalcone derivatives on MDCK cyst progression and Pkd1 mutant cells.

METHODS

MDCK cyst growth and cyst formation experiments, MTT assay, Ussing chamber experiment, BrdU cell proliferation assay and western blot analysis were performed in this study.

RESULTS

Among four compounds of chalcone derivatives tested, CHAL-005 (100 µM) was found to inhibit MDCK cyst growth in a dose-dependent manner without cytotoxicity. It inhibited short-circuit current of chloride secretion as well as CFTR protein expression in MDCK cells. CHAL-005 significantly suppressed cell proliferation. In addition, CHAL-005 strongly reduced phosphorylation ERK1/2 and phosphorylation S6 kinase in MDCK and Pkd1 mutant cells. Interestingly, CHAL-005 activated phosphorylation of AMP kinase protein expression in MDCK and Pkd1 mutant cells.

CONCLUSION

CHAL-005 slowed MDCK cyst progression by inhibiting CFTR expression and reducing ERK1/2 and mTOR/S6K signaling pathways as well as activating AMPK expression. Therefore, a chalcone derivative could represent as a promising drug candidate for polycystic kidney disease intervention.

Cardiac Involvement in Autosomal Dominant Polycystic Kidney Disease

Cardiovascular disorders are the main complication in autosomal dominant polycystic kidney disease (ADPKD). contributing to both morbidity and mortality. This review considers clinical studies unveiling cardiovascular features in patients with ADPKD. Additionally, it focuses on basic science studies addressing the dysfunction of the polycystin proteins located in the cardiovascular system as a contributing factor to cardiovascular abnormalities. In particular, the effects of polycystin proteins’ deficiency on the cardiomyocyte function have been considered.

Histomorphology and Immunohistochemistry of a Congenital Nephromegaly Demonstrate Concurrent Features of Heritable and Acquired Cystic Nephropathies in a Girgentana Goat (Capra falconeri)

Polycystic kidney diseases (PKD) represent frequent congenital and adult nephropathies in humans and domestic animals. This report illustrates an uncommon state of congenital PKD in a girgentana goat (Capra falconeri). A stillborn female goat kid was submitted for postmortem examination and underwent macroscopic and microscopic examination. The kidneys showed a bilateral nephromegaly and a perpendicular polycystic altered texture of the renal parenchyma. Renal tissue sections were comprehensively investigated by histopathology (overview and special stains), immunohistochemistry (CD10, CD117, pan-cytokeratin, cytokeratin 7, E-cadherin, Pax2, Pax8, and vimentin), and electron microscopy (SEM, TEM). Histopathology of renal tissue sections revealed polycystic alterations of the renal parenchyma as well as conspicuous polypoid proliferates/projections of the renal tubular epithelium, which showed clear cell characteristics. Furthermore, epithelial projections were indicative for epithelio-mesenchymal-transition, cellular depolarization, and strong expression of differentiation markers Pax2, Pax8, and CD10. Ultrastructural morphology of the projections was characterized by numerous diffusely distributed, demarked round cytoplasmic structures and several apico-lateral differentiations. Additionally, hepatic malformations comprising biliary duct proliferation with saccular dilation and bridging fibrosis were observed. Notably, this report describes the first case of a congenital cystic nephropathy with overlapping features of heritable and acquired nephropathies in any species. Epithelio-mesenchymal-transition and altered cadherin expression seem to be crucial components of a suspected pathomechanism during cystogenesis.

Complications in Patients With Autosomal Dominant Polycystic Kidney Disease Undergoing Ureteroscopy: A Cohort Study

BACKGROUND

Ureteroscopy is a minimally invasive treatment option for upper tract stones. The distorted kidney anatomy in patients with autosomal dominant polycystic kidney disease (ADPKD) may place them at higher risk for ureteroscopic complications.

OBJECTIVE

To compare the 30-day risk of ureteroscopic complications between patients with and without ADPKD.

DESIGN

Retrospective cohort study.

SETTING

Ontario, Canada.

PATIENTS

Seventy three patients with ADPKD and 81 445 patients without ADPKD who underwent ureteroscopy for upper urinary tract stones between April 1, 2002, and March 1, 2018.

MEASUREMENTS

A 30-day risk of (1) hospital presentation with ureteroscopic complications (which was a composite outcome of either emergency department visit or hospital admission with acute kidney injury, urinary tract infection, or sepsis); (2) all-cause hospital presentation; (3) all-cause hospital admission; and (4) all-cause emergency department visit.

METHODS

We regressed outcomes on demographic variables, health care use in the prior 1-year, various procedures and comorbidities related to the outcome in the prior 5 years, and prescribed medications filled in the past 120 days using modified Poisson regression to compare the risk ratio (RR) of each outcome between patients with and without ADPKD.

RESULTS

The median (interquartile, IQR) age was 44 (38-60 years) in the ADPKD group and 53 (42-64) in the control group. About 40% were women in both groups. The risk of ureteroscopic complications was not significantly different in patients with versus without ADPKD (8.2% vs 4.3%; adjusted RR = 1.5, 95% confidence interval [CI] = 0.7-3.2). Patients with versus without ADPKD were more likely to present to hospital after their procedure (35.6% vs. 20.0%; adjusted RR = 1.6, 95% CI = 1.2-2.2), which included a statistically significant increase in the risk of presenting to the emergency department (32.9% vs. 19.0%; adjusted RR = 1.6, 95% CI = 1.1-2.2) but not hospital admissions (10.9% vs. 5.0%; adjusted RR = 1.8, 95% CI = 0.9-3.4).

LIMITATIONS

The low numbers of events led to imprecision around the estimates.

CONCLUSION

Patients with ADPKD have a higher risk of return to the hospital within 30 days of ureteroscopy for stone disease.

TRIAL REGISTRATION

We did not register this study.

Quantitative Systems Toxicology Modeling Predicts that Reduced Biliary Efflux Contributes to Tolvaptan Hepatotoxicity

Patients with autosomal dominant polycystic kidney disease (ADPKD) exhibit enhanced susceptibility to tolvaptan hepatotoxicity relative to other patient populations. In a rodent model of ADPKD, the expression and function of the biliary efflux transporter Mrp2 was reduced, and biliary excretion of a major tolvaptan metabolite (DM-4103) was decreased. The current study investigated whether reduced biliary efflux could contribute to increased susceptibility to tolvaptan-associated hepatotoxicity using a quantitative systems toxicology (QST) model (DILIsym). QST simulations revealed that decreased biliary excretion of DM-4103, but not tolvaptan, resulted in substantial hepatic accumulation of bile acids, decreased electron transport chain activity, reduced hepatic adenosine triphosphate concentrations, and an increased incidence of hepatotoxicity. In vitro experiments (C-DILI) with sandwich-cultured human hepatocytes and HepaRG cells were performed to assess tolvaptan-associated hepatotoxic effects when MRP2 was impaired by chemical inhibition (MK571, 50 µM) or genetic knockout, respectively. Tolvaptan (64 µM, 24-hour) treatment of these cells increased cytotoxicity markers up to 27.9-fold and 1.6-fold, respectively, when MRP2 was impaired, indicating that MRP2 dysfunction may be involved in tolvaptan-associated cytotoxicity. In conclusion, QST modeling supported the hypothesis that reduced biliary efflux of tolvaptan and/or DM-4103 could account for increased susceptibility to tolvaptan-associated hepatotoxicity; in vitro experiments implicated MRP2 dysfunction as a key factor in susceptibility. QST simulations revealed that DM-4103 may contribute to hepatotoxicity more than the parent compound. ADPKD progression and gradual reduction in MRP2 activity may explain why acute liver events can occur well after one year of tolvaptan treatment.

What about the males? the C. elegans sexually dimorphic nervous system and a CRISPR-based tool to study males in a hermaphroditic species

Sexual dimorphism is a device that supports genetic diversity while providing selective pressure against speciation. This phenomenon is at the core of sexually reproducing organisms. Caenorhabditis elegans provides a unique experimental system where males exist in a primarily hermaphroditic species. Early works of John Sulston, Robert Horvitz, and John White provided a complete map of the hermaphrodite nervous system, and recently the male nervous system was added. This addition completely realized the vision of C. elegans pioneer Sydney Brenner: a model organism with an entirely mapped nervous system. With this 'connectome' of information available, great strides have been made toward understanding concepts such as how a sex-shared nervous system (in hermaphrodites and males) can give rise to sex-specific functions, how neural plasticity plays a role in developing a dimorphic nervous system, and how a shared nervous system receives and processes external cues in a sexually-dimorphic manner to generate sex-specific behaviors. In C. elegans, the intricacies of male-mating behavior have been crucial for studying the function and circuitry of the male-specific nervous system and used as a model for studying human autosomal dominant polycystic kidney disease (ADPKD). With the emergence of CRISPR, a seemingly limitless tool for generating genomic mutations with pinpoint precision, the C. elegans model system will continue to be a useful instrument for pioneering research in the fields of behavior, reproductive biology, and neurogenetics.

Organelle Stress and Crosstalk in Kidney Disease

Organelles play important roles in maintaining cellular homeostasis. Organelle stress responses, especially in mitochondria, endoplasmic reticula (ER), and primary cilia, are deeply involved in kidney disease pathophysiology. Mitochondria are the center of energy production in most eukaryotic cells. Renal proximal tubular cells are highly energy demanding and abundant in mitochondria. Mitochondrial dysfunctions in association with energy metabolism alterations produce reactive oxygen species and promote inflammation in proximal tubular cells, resulting in progression of kidney disease. The ER play critical roles in controlling protein quality. Unfolded protein response (UPR) pathways are the adaptive response to ER stress for maintaining protein homeostasis. UPR pathway dysregulation under pathogenic ER stress often occurs in glomerular and tubulointerstitial cells and promotes progression of kidney disease. The primary cilia sense extracellular signals and maintain calcium homeostasis in cells. Dysfunction of the primary cilia in autosomal dominant polycystic kidney disease reduces the calcium concentration in proximal tubular cells, leading to increased cell proliferation and retention of cyst fluid. In recent years, the direct interaction at membrane contact sites has received increased attention in association with the development of imaging technologies. The part of the ER that is directly connected to mitochondria is termed the mitochondria-associated ER membrane (MAM), which regulates calcium homeostasis and phospholipid metabolism in cells. Disruption of MAM integrity collapses cellular homeostasis and leads to diseases such as diabetes and Alzheimer disease. This review summarizes recent research on organelle stress and crosstalk, and their involvement in kidney disease pathophysiology. In addition, potential treatment options that target organelle stress responses are discussed.

A cut above (and below): Protein cleavage in the regulation of polycystin trafficking and signaling

The polycystin-1 and 2 proteins, encoded by the genes mutated in Autosomal Dominant Polycystic Kidney Disease, are connected to a large number of biological pathways. While the nature of these connections and their relevance to the primary functions of the polycystin proteins have yet to be fully elucidated, it is clear that many of them are mediated by or depend upon cleavage of the polycystin-1 protein. Cleavage of polycystin-1 at its G protein coupled receptor proteolytic site is an obligate step in the protein's maturation and in aspects of its trafficking. This cleavage may also serve to prime polycystin-1 to play a role as a non-canonical G protein coupled receptor. Cleavage of the cytoplasmic polycystin-1C terminal tail releases fragments that are able to enter the nucleus and the mitochondria and to influence their activities. Understanding the nature of these cleavages, their regulation and their consequences is likely to provide valuable insights into both the physiological functions served by the polycystin proteins and the pathological consequences of their absence.

Hypoxia and Endothelial Dysfunction in Autosomal-Dominant Polycystic Kidney Disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited kidney disease, characterized by growth of bilateral renal cysts, hypertension, and multiple extrarenal complications that eventually can lead to renal failure. It is caused by mutations in PKD1 or PKD2 genes encoding the proteins polycystin-1 and polycystin-2, respectively. Over the past few years, studies investigating the role of primary cilia and polycystins, present not only on the surface of renal tubular cells but also on vascular endothelial cells, have advanced our understanding of the pathogenesis of ADPKD and have shown that mechanisms other than cyst formation also contribute to renal functional decline in this disease. Among them, increased oxidative stress, endothelial dysfunction, and hypoxia may play central roles because they occur early in the disease process and precede the onset of hypertension and renal functional decline. Endothelial dysfunction is linked to higher asymmetric dimethylarginine levels and reduced nitric oxide bioavailability, which would cause regional vasoconstriction and impaired renal blood flow. The resulting hypoxia would increase the levels of hypoxia-inducible-transcription factor 1α and other angiogenetic factors, which, in turn, may drive cyst growth. In this review, we summarize the existing evidence for roles of endothelial dysfunction, oxidative stress, and hypoxia in the pathogenesis of ADPKD.

GDNF drives rapid tubule morphogenesis in a novel 3D in vitro model for ADPKD

Cystogenesis is a morphological consequence of numerous genetic diseases of the epithelium. In the kidney, the pathogenic mechanisms underlying the program of altered cell and tubule morphology are obscured by secondary effects of cyst expansion. Here, we developed a new 3D tubuloid system to isolate the rapid changes in protein localization and gene expression that correlate with altered cell and tubule morphology during cyst initiation. Mouse renal tubule fragments were pulsed with a cell differentiation cocktail including glial-derived neurotrophic factor (GDNF) to yield collecting duct-like tubuloid structures with appropriate polarity, primary cilia, and gene expression. Using the 3D tubuloid model with an inducible Pkd2 knockout system allowed the tracking of morphological, protein, and genetic changes during cyst formation. Within hours of inactivation of Pkd2 and loss of polycystin-2, we observed significant progression in tubuloid to cyst morphology that correlated with 35 differentially expressed genes, many related to cell junctions, matrix interactions, and cell morphology previously implicated in cystogenesis.This article has an associated First Person interview with the first author of the paper.

An Overview of In Vivo and In Vitro Models for Autosomal Dominant Polycystic Kidney Disease: A Journey from 3D-Cysts to Mini-Pigs

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inheritable cause of end stage renal disease and, as of today, only a single moderately effective treatment is available for patients. Even though ADPKD research has made huge progress over the last decades, the precise disease mechanisms remain elusive. However, a wide variety of cellular and animal models have been developed to decipher the pathophysiological mechanisms and related pathways underlying the disease. As none of these models perfectly recapitulates the complexity of the human disease, the aim of this review is to give an overview of the main tools currently available to ADPKD researchers, as well as their main advantages and limitations.

Detection of a novel mutation in a Tunisian child with polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the most common monogenic disease that has an adverse impact on the patients' health and quality of life. ADPKD is usually known as "adult-type disease," but rare cases have been reported in pediatric patients. We present here a 2-year-old Tunisian girl with renal cyst formation and her mother with adult onset ADPKD. Disease-causing mutation has been searched in PKD1 and PKD2 using Long-Range and PCR followed by sequencing. Molecular sequencing displayed us to identify a novel likely pathogenic mutation (c.696 T > G; p.C232W, exon 5) in PKD1. The identified PKD1 mutation is inherited and unreported variant, which can alter the formation of intramolecular disulfide bonds essential for polycystin-1 function. We report here the first mutational study in pediatric patient with ADPKD in Tunisia.

The role of PPARα in autosomal dominant polycystic kidney disease

PURPOSE OF REVIEW

Metabolic reprogramming is a prominent feature of cyst epithelial cells in autosomal dominant polycystic kidney disease (ADPKD). Peroxisome proliferator activated receptor alpha (PPARα) is a transcription factor that regulates many aspects of cellular metabolism. The purpose of this review is to understand the role of PPARα in ADPKD.

RECENT FINDINGS

PPARα expression is reduced in ADPKD kidneys of mice and humans. This downregulation is in part secondary to microRNA mediated translational repression and leads to impairment of fatty acid metabolism. Genetic studies demonstrate that deletion of Pparα aggravates cyst growth in a slowly progressive mouse model of ADPKD. Recent studies also show that administration of Pparα agonists ameliorates cyst burden in mice.

SUMMARY

Abnormal reduction of PPARα affects cellular metabolism in ADPKD. Pparα is a modulator of cyst progression in mouse models of ADPKD. These studies establish PPARα as an exciting new drug target for the treatment of individuals with ADPKD.

The centrosomal/basal body protein OFD1 is required for microtubule organization and cell cycle progression

Oral-Facial-Digital type I (OFD1) is a rare inherited form of renal cystic disease associated with ciliary dysfunction. This disorder is due to mutations in the OFD1 gene that encodes a protein localized to centrosomes and basal bodies in different cell types. Immunofluorescence analysis demonstrated that OFD1 displays a dynamic distribution during cell cycle. High-content microscopy analysis of Ofd1-depleted fibroblasts revealed impaired cell cycle progression. Immunofluorescence analysis and cell proliferation assays also indicated the presence of a variety of defects such as centrosome accumulation, nuclear abnormalities and aneuploidy. In addition, Ofd1-depleted cells displayed an abnormal microtubule network that may underlie these defects. All together our results suggest that OFD1 contributes to the function of the microtubule organizing center (MTOC) in the cell, controlling cell cycle progression both in vitro and in vivo.

Molecular pathways involved in injury-repair and ADPKD progression

The major hallmark of Autosomal Dominant Polycystic Kidney Disease (ADPKD) is the formation of many fluid-filled cysts in the kidneys, which ultimately impairs the normal renal structure and function, leading to end-stage renal disease (ESRD). A large body of evidence suggests that injury-repair mechanisms are part of ADPKD progression. Once cysts have been formed, proliferation and fluid secretion contribute to the cyst size increase, which eventually causes stress on the surrounding tissue resulting in local injury and fibrosis. In addition, renal injury can cause or accelerate cyst formation. In this review, we will describe the various mechanisms activated during renal injury and tissue repair and show how they largely overlap with the molecular mechanisms activated during PKD progression. In particular, we will discuss molecular mechanisms such as proliferation, inflammation, cell differentiation, cytokines and growth factors secretion, which are activated following the renal injury to allow the remodelling of the tissue and a proper organ repair. We will also underline how, in a context of PKD-related gene mutations, aberrant or chronic activation of these developmental pathways and repair/remodelling mechanisms results in exacerbation of the disease.

Advances in Autosomal Dominant Polycystic Kidney Disease: A Clinical Review

Polycystic kidney disease (PKD) is a multiorgan disorder resulting in fluid-filled cyst formation in the kidneys and other systems. The replacement of kidney parenchyma with an ever-increasing volume of cysts eventually leads to kidney failure. Recently, increased understanding of the pathophysiology of PKD and genetic advances have led to new approaches of treatment targeting physiologic pathways, which has been proven to slow the progression of certain types of the disease. We review the pathophysiologic patterns and recent advances in the clinical pharmacotherapy of autosomal dominant PKD. A multipronged approach with pharmacologic and nonpharmacologic treatments can be successfully used to slow down the rate of progression of autosomal dominant PKD to kidney failure.

Role of transcription factor hepatocyte nuclear factor-1β in polycystic kidney disease

Hepatocyte nuclear factor-1β (HNF-1β) is a DNA-binding transcription factor that is essential for normal kidney development. Mutations of HNF1B in humans produce cystic kidney diseases, including renal cysts and diabetes, multicystic dysplastic kidneys, glomerulocystic kidney disease, and autosomal dominant tubulointerstitial kidney disease. Expression of HNF1B is reduced in cystic kidneys from humans with ADPKD, and HNF1B has been identified as a modifier gene in PKD. Genome-wide analysis of chromatin binding has revealed that HNF-1β directly regulates the expression of known PKD genes, such as PKHD1 and PKD2, as well as genes involved in PKD pathogenesis, including cAMP-dependent signaling, renal fibrosis, and Wnt signaling. In addition, a role of HNF-1β in regulating the expression of noncoding RNAs (microRNAs and long noncoding RNAs) has been identified. These findings indicate that HNF-1β regulates a transcriptional and post-transcriptional network that plays a central role in renal cystogenesis.

A case of cerebral infarction caused by painless acute aortic dissection in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder, characterized by the progressive formation of renal cysts. Although ADPKD is strongly associated with cerebral and cardiovascular complications, cerebral ischemia caused by dissection of thoracic and carotid arteries has rarely been reported. We report the case of a 71-year-old Japanese woman who complained of hemiparesis. She required maintenance hemodialysis therapy with a background of ADPKD. Cerebral infarction was initially diagnosed by excluding intracranial hemorrhage and aneurysm rupture that are recognized as common complications of ADPKD and thereby anticoagulation therapy was initiated. However, the patient was suspected as having painless aortic dissection because a chest X-ray examination showed expanded upper mediastinum. Sequential vascular imagings revealed dissection of the aorta, originating from brachiocephalic trunk to the right common carotid artery with mediastinal hematoma. The patient died from progression of dissection. Herein, we described a case of the ADPKD patient that an acute aortic dissection without any pain induced the occlusion of supplying vessels to the brain, resulting in cerebral ischemic symptoms. A high level of clinical vigilance for an acute aortic dissection should be maintained in the ADPKD population with sudden onset of neurological symptoms even in the absence of pain. Furthermore, the initiation of anticoagulation treatment for cerebral ischemia which may aggravate the risk of further dissection requires careful consideration.

The emerging role of cellular senescence in renal diseases

Cellular senescence represents the state of irreversible cell cycle arrest during cell division. Cellular senescence not only plays a role in diverse biological events such as embryogenesis, tissue regeneration and repair, ageing and tumour occurrence prevention, but it is also involved in many cardiovascular, renal and liver diseases through the senescence-associated secretory phenotype (SASP). This review summarizes the molecular mechanisms underlying cellular senescence and its possible effects on a variety of renal diseases. We will also discuss the therapeutic approaches based on the regulation of senescent and SASP blockade, which is considered as a promising strategy for the management of renal diseases.

Monkeys mutant for PKD1 recapitulate human autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) caused by PKD1 mutations is one of the most common hereditary disorders. However, the key pathological processes underlying cyst development and exacerbation in pre-symptomatic stages remain unknown, because rodent models do not recapitulate critical disease phenotypes, including disease onset in heterozygotes. Here, using CRISPR/Cas9, we generate ADPKD models with PKD1 mutations in cynomolgus monkeys. As in humans and mice, near-complete PKD1 depletion induces severe cyst formation mainly in collecting ducts. Importantly, unlike in mice, PKD1 heterozygote monkeys exhibit cyst formation perinatally in distal tubules, possibly reflecting the initial pathology in humans. Many monkeys in these models survive after cyst formation, and cysts progress with age. Furthermore, we succeed in generating selective heterozygous mutations using allele-specific targeting. We propose that our models elucidate the onset and progression of ADPKD, which will serve as a critical basis for establishing new therapeutic strategies, including drug treatments.