Canonical Wnt inhibitors ameliorate cystogenesis in a mouse ortholog of human ADPKD

TRPV4-β-catenin axis is a novel therapeutic target for dry skin-induced chronic itch

Dry skin induced chronic pruritus is an increasingly common and debilitating problem, especially in the elderly. Although keratinocytes play important roles in innate and adaptive immunity and keratinocyte proliferation is a key feature of dry skin induced chronic pruritus, the exact contribution of keratinocytes to the pathogenesis of dry skin induced chronic pruritus is poorly understood. In this study, we generated the acetone-ether-water induced dry skin model in mice and found that epidermal hyperplasia induced by this model is partly dependent on the β-catenin signaling pathway. XAV939, an antagonist of β-catenin signaling pathway, inhibited epidermal hyperplasia in dry skin model mice. Importantly, dry skin induced chronic pruritus also dramatically reduced in XAV939 treated mice. Moreover, acetone-ether-water treatment-induced epidermal hyperplasia and chronic itch were decreased in Trpv4-/- mice. In vitro, XAV939 inhibited hypo-osmotic stress induced proliferation of HaCaT cells, and hypo-osmotic stress induced proliferation of in HaCaT cells and primary cultured keratinocytes were also significantly reduced by blocking TRPV4 function. Finally, thymic stromal lymphopoietin release was examined both in vivo and in vitro, which was significantly inhibited by XAV939 treatment and Trpv4 deficiency, and anti-TSLP antibody treatment significantly decreased AEW-induced scratching behavior. Overall, our study revealed a unique ability of TRPV4 expressing keratinocytes in the skin, which critically mediated dry skin induced epidermal hyperplasia and chronic pruritus, thus provided novel insights into the development of therapies for chronic pruritus in the elderly.

PKD2: An Important Membrane Protein in Organ Development

PKD2 was first identified as the pathogenic protein for autosomal dominant polycystic kidney disease (ADPKD) and is widely recognized as an ion channel. Subsequent studies have shown that PKD2 is widely expressed in various animal tissues and plays a crucial role in tissue and organ development. Additionally, PKD2 is conserved from single-celled organisms to vertebrates. Here, we provide an overview of recent advances in the function of PKD2 in key model animals, focusing on the establishment of left-right organ asymmetry, renal homeostasis, cardiovascular development, and signal transduction in reproduction and mating. We specifically focus on the roles of PKD2 in development and highlight future prospects for PKD2 research.

Two functional forms of the Meckel-Gruber syndrome protein TMEM67 generated by proteolytic cleavage by ADAMTS9 mediate Wnt signaling and ciliogenesis

TMEM67 mutations are the major cause of Meckel-Gruber syndrome. TMEM67 is involved in both ciliary transition zone assembly, and non-canonical Wnt signaling mediated by its extracellular domain. How TMEM67 performs these two separate functions is not known. We identify a novel cleavage motif in the extracellular domain of TMEM67 cleaved by the extracellular matrix metalloproteinase ADAMTS9. This cleavage regulates the abundance of two functional forms: A C-terminal portion which localizes to the ciliary transition zone regulating ciliogenesis, and a non-cleaved form which regulates Wnt signaling. By characterizing three TMEM67 ciliopathy patient variants within the cleavage motif utilizing mammalian cell culture and C. elegans, we show the cleavage motif is essential for cilia structure and function, highlighting its clinical significance. We generated a novel non-cleavable TMEM67 mouse model which develop severe ciliopathies phenocopying Tmem67 -/- mice, but in contrast, undergo normal Wnt signaling, substantiating the existence of two functional forms of TMEM67.

Clinical manifestation, epidemiology, genetic basis, potential molecular targets, and current treatment of polycystic liver disease

Polycystic liver disease (PLD) is a rare condition observed in three genetic diseases, including autosomal dominant polycystic liver disease (ADPLD), autosomal dominant polycystic kidney disease (ADPKD), and autosomal recessive polycystic kidney disease (ARPKD). PLD usually does not impair liver function, and advanced PLD becomes symptomatic when the enlarged liver compresses adjacent organs or increases intra-abdominal pressure. Currently, the diagnosis of PLD is mainly based on imaging, and genetic testing is not required except for complex cases. Besides, genetic testing may help predict patients' prognosis, classify patients for genetic intervention, and conduct early treatment. Although the underlying genetic causes and mechanisms are not fully understood, previous studies refer to primary ciliopathy or impaired ciliogenesis as the main culprit. Primarily, PLD occurs due to defective ciliogenesis and ineffective endoplasmic reticulum quality control. Specifically, loss of function mutations of genes that are directly involved in ciliogenesis, such as Pkd1, Pkd2, Pkhd1, and Dzip1l, can lead to both hepatic and renal cystogenesis in ADPKD and ARPKD. In addition, loss of function mutations of genes that are involved in endoplasmic reticulum quality control and protein folding, trafficking, and maturation, such as PRKCSH, Sec63, ALG8, ALG9, GANAB, and SEC61B, can impair the production and function of polycystin1 (PC1) and polycystin 2 (PC2) or facilitate their degradation and indirectly promote isolated hepatic cystogenesis or concurrent hepatic and renal cystogenesis. Recently, it was shown that mutations of LRP5, which impairs canonical Wnt signaling, can lead to hepatic cystogenesis. PLD is currently treated by somatostatin analogs, percutaneous intervention, surgical fenestration, resection, and liver transplantation. In addition, based on the underlying molecular mechanisms and signaling pathways, several investigational treatments have been used in preclinical studies, some of which have shown promising results. This review discusses the clinical manifestation, complications, prevalence, genetic basis, and treatment of PLD and explains the investigational methods of treatment and future research direction, which can be beneficial for researchers and clinicians interested in PLD.

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.

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.

Polycystin-2-dependent transcriptome reveals early response of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in polycystin genes, Pkd1 and Pkd2, but the underlying pathogenic mechanisms are poorly understood. To identify genes and pathways that operate downstream of polycystin-2 (PC2), a comprehensive gene expression database was created, cataloging changes in the transcriptome immediately following PC2 protein depletion. To explore cyst initiation processes, an immortalized mouse inner medullary collecting duct line was developed with the ability to knock out the Pkd2 gene conditionally. Genome-wide transcriptome profiling was performed using RNA sequencing in the cells immediately after PC2 was depleted and compared with isogenic control cells. Differentially expressed genes were identified, and a bioinformatic analysis pipeline was implemented. Altered expression of candidate cystogenic genes was validated in Pkd2 knockout mice. The expression of nearly 900 genes changed upon PC2 depletion. Differentially expressed genes were enriched for genes encoding components of the primary cilia, the canonical Wnt pathway, and MAPK signaling. Among the PC2-dependent ciliary genes, the transcription factor Glis3 was significantly downregulated. MAPK signaling formed a key node at the epicenter of PC2-dependent signaling networks. Activation of Wnt and MAPK signaling, concomitant with the downregulation of Glis3, was corroborated in Pkd2 knockout mice. The data identify a PC2 cilia-to-nucleus signaling axis and dysregulation of the Gli-similar subfamily of transcription factors as a potential initiator of cyst formation in ADPKD. The catalog of PC2-regulated genes should provide a valuable resource for future ADPKD research and new opportunities for drug development.NEW & NOTEWORTHY Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. Mutations in polycystin genes cause the disease, but the underlying mechanisms of cystogenesis are unknown. To help fill this knowledge gap, we created an inducible cell model of ADPKD and assembled a catalog of genes that respond in immediate proximity to polycystin-2 depletion using transcriptomic profiling. The catalog unveils a ciliary signaling-to-nucleus axis proximal to polycystin-2 dysfunction, highlighting Glis, Wnt, and MAPK signaling.

Prioritized polycystic kidney disease drug targets and repurposing candidates from pre-cystic and cystic mouse Pkd2 model gene expression reversion

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most prevalent monogenic human diseases. It is mostly caused by pathogenic variants in PKD1 or PKD2 genes that encode interacting transmembrane proteins polycystin-1 (PC1) and polycystin-2 (PC2). Among many pathogenic processes described in ADPKD, those associated with cAMP signaling, inflammation, and metabolic reprogramming appear to regulate the disease manifestations. Tolvaptan, a vasopressin receptor-2 antagonist that regulates cAMP pathway, is the only FDA-approved ADPKD therapeutic. Tolvaptan reduces renal cyst growth and kidney function loss, but it is not tolerated by many patients and is associated with idiosyncratic liver toxicity. Therefore, additional therapeutic options for ADPKD treatment are needed.

METHODS

As drug repurposing of FDA-approved drug candidates can significantly decrease the time and cost associated with traditional drug discovery, we used the computational approach signature reversion to detect inversely related drug response gene expression signatures from the Library of Integrated Network-Based Cellular Signatures (LINCS) database and identified compounds predicted to reverse disease-associated transcriptomic signatures in three publicly available Pkd2 kidney transcriptomic data sets of mouse ADPKD models. We focused on a pre-cystic model for signature reversion, as it was less impacted by confounding secondary disease mechanisms in ADPKD, and then compared the resulting candidates' target differential expression in the two cystic mouse models. We further prioritized these drug candidates based on their known mechanism of action, FDA status, targets, and by functional enrichment analysis.

RESULTS

With this in-silico approach, we prioritized 29 unique drug targets differentially expressed in Pkd2 ADPKD cystic models and 16 prioritized drug repurposing candidates that target them, including bromocriptine and mirtazapine, which can be further tested in-vitro and in-vivo.

CONCLUSION

Collectively, these results indicate drug targets and repurposing candidates that may effectively treat pre-cystic as well as cystic ADPKD.

1-Indanone retards cyst development in ADPKD mouse model by stabilizing tubulin and down-regulating anterograde transport of cilia

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease. Cyst development in ADPKD involves abnormal epithelial cell proliferation, which is affected by the primary cilia-mediated signal transduction in the epithelial cells. Thus, primary cilium has been considered as a therapeutic target for ADPKD. Since ADPKD exhibits many pathological features similar to solid tumors, we investigated whether targeting primary cilia using anti-tumor agents could alleviate the development of ADPKD. Twenty-four natural compounds with anti-tumor activity were screened in MDCK cyst model, and 1-Indanone displayed notable inhibition on renal cyst growth without cytotoxicity. This compound also inhibited cyst development in embryonic kidney cyst model. In neonatal kidney-specific Pkd1 knockout mice, 1-Indanone remarkably slowed down kidney enlargement and cyst expansion. Furthermore, we demonstrated that 1-Indanone inhibited the abnormal elongation of cystic epithelial cilia by promoting tubulin polymerization and significantly down-regulating expression of anterograde transport motor protein KIF3A and IFT88. Moreover, we found that 1-Indanone significantly down-regulated ciliary coordinated Wnt/β-catenin, Hedgehog signaling pathways. These results demonstrate that 1-Indanone inhibits cystic cell proliferation by reducing abnormally prolonged cilia length in cystic epithelial cells, suggesting that 1-Indanone may hold therapeutic potential to retard cyst development in ADPKD.

Potential Application of Gambogic Acid for Retarding Renal Cyst Progression in Polycystic Kidney Disease

Abnormal cell proliferation and accumulation of fluid-filled cysts along the nephrons in polycystic kidney disease (PKD) could lead to a decline in renal function and eventual end-stage renal disease (ESRD). Gambogic acid (GA), a xanthone compound extracted from the brownish resin of the Garcinia hanburyi tree, exhibits various pharmacological properties, including anti-inflammation, antioxidant, anti-proliferation, and anti-cancer activity. However, its effect on inhibiting cell proliferation in PKD is still unknown. This study aimed to determine the pharmacological effects and detailed mechanisms of GA in slowing an in vitro cyst growth model of PKD. The results showed that GA (0.25-2.5 μM) significantly retarded MDCK cyst growth and cyst formation in a dose-dependent manner, without cytotoxicity. Using the BrdU cell proliferation assay, it was found that GA (0.5-2.5 μM) suppressed MDCK and Pkd1 mutant cell proliferation. In addition, GA (0.5-2.5 μM) strongly inhibited phosphorylation of ERK1/2 and S6K expression and upregulated the activation of phosphorylation of AMPK, both in MDCK cells and Pkd1 mutant cells. Taken together, these findings suggested that GA could retard MDCK cyst enlargement, at least in part by inhibiting the cell proliferation pathway. GA could be a natural plant-based drug candidate for ADPKD intervention.

Protein Kinase A Downregulation Delays the Development and Progression of Polycystic Kidney Disease

Background: Upregulation of cAMP-dependent and -independent PKA signaling is thought to promote cystogenesis in polycystic kidney disease (PKD). PKA-I regulatory subunit RIα is increased in kidneys of orthologous mouse models. Kidney-specific knockout of RIα upregulates PKA activity, induces cystic disease in wild-type mice, and aggravates it in Pkd1 ^RC/RC mice. Methods: PKA-I activation or inhibition was compared to EPAC activation or PKA-II inhibition using Pkd1 ^RC/RC metanephric organ cultures. The effect of constitutive PKA (preferentially PKA-I) downregulation in vivo was ascertained by kidney-specific expression of a dominant negative RIαB allele in Pkd1 ^RC/RC mice obtained by crossing Prkar1α ^R1αB/WT, Pkd1 ^RC/RC, and Pkhd1-Cre mice (C57BL/6 background). The effect of pharmacologic PKA inhibition using a novel, selective PRKACA inhibitor (BLU2864) was tested in mIMCD3 3D cultures, metanephric organ cultures, and Pkd1 ^RC/RC mice on a C57BL/6 x 129S6/Sv F1 background. Mice were sacrificed at 16 weeks of age. Results: PKA-I activation promoted and inhibition prevented ex vivo P-Ser133 CREB expression and cystogenesis. EPAC activation or PKA-II inhibition had no or only minor effects. BLU2864 inhibited in vitro mIMCD3 cystogenesis and ex vivo P-Ser133 CREB expression and cystogenesis. Genetic downregulation of PKA activity and BLU2864 directly and/or indirectly inhibited many pro-proliferative pathways and were both protective in vivo BLU2864 had no detectable on- or off-target adverse effects. Conclusions: PKA-I is the main PKA isozyme promoting cystogenesis. Direct PKA inhibition may be an effective strategy to treat PKD and other conditions where PKA signaling is upregulated. By acting directly on PKA, the inhibition may be more effective than or substantially increase the efficacy of treatments that only affect PKA activity by lowering cAMP.

Antioxidant enzyme peroxiredoxin 5 regulates cyst growth and ciliogenesis via modulating Plk1 stability

Oxidative stress is emerging as a contributing factor to the homeostasis in cystic diseases. However, the role antioxidant enzymes play in the pathogenesis of autosomal dominant polycystic kidney disease (ADPKD) remains elusive. Peroxiredoxin 5 (Prdx5) is an antioxidant enzyme that catalyzes the reduction of H2 O2 and alkyl hydroperoxide and plays an important role in different biological processes. In this study, we show that Prdx5 is downregulated in a PKD mutant mouse model and ADPKD patient kidneys. Knockdown of Prdx5 resulted in the formation of cysts in a three-dimensional mouse inner medullar collecting duct (IMCD) cell Matrigel culture system. The mechanisms of Prdx5 deficiency mediated cyst growth include: (1) induction of oxidative stress as indicated by increased mRNA expression of heme oxygenase-1, an oxidant stress marker; (2) activation of Erk, S6 and mTORC1, which contribute to cystic renal epithelial cell proliferation and cyst growth; (3) abnormal centrosome amplification and multipolar spindle formation which result in genome instability; (4) upregulation of Polo-like kinase 1 (Plk1) and Aurora kinase A, important mitotic kinases involved in cell proliferation and ciliogenesis; (5) impaired formation of primary cilia in mouse IMCD3 and retinal pigment epithelial cells, which could be rescued by inhibiting Plk1 activity; and (6) restraining the effect of Wnt3a and Wnt5a ligands on primary cilia in mouse IMCD3 cells, while regulating the activity of the canonical and non-canonical Wnt signaling in a separate cilia independent mechanism, respectively. Importantly, we found that targeting Plk1 with its inhibitor, volasertib, delayed cyst growth in Pkd1 conditional knockout mouse kidneys. Together, these findings indicate that Prdx5 is an important antioxidant that regulates cyst growth via diverse mechanisms, in particular, the Prdx5-Plk1 axis, and that induction and activation of Prdx5, alone or together with inhibition of Plk1, represent a promising strategy for combatting ADPKD.

Deletion of kif3a in CK19 positive cells leads to primary cilia loss, biliary cell proliferation and cystic liver lesions in TAA-treated mice

BACKGROUND & AIMS

Loss of primary cilia in epithelial cells is known to cause cystic diseases of the liver and kidney. We have previously shown that during experimental and human cirrhosis that primary cilia were predominantly expressed on biliary cells in the ductular reaction. However, the role of primary cilia in the pathogenesis of the ductular reaction is not fully understood.

METHODS

Primary cilia were specifically removed in biliary epithelial cells (BECs) by the administration of tamoxifen to Kif3a^f/f;CK19^CreERT mice at week 2 of a 20-week course of TAA treatment. Biliary progenitor cells were isolated and grown as organoids from gallbladders. Cells and tissue were analysed using histology, immunohistochemistry and Western blot assays.

RESULTS

At the end of 20 weeks TAA administration, primary cilia loss in liver BECs resulted in multiple microscopic cystic lesions within an unaltered ductular reaction. These were not seen in control mice who did not receive TAA. There was no effect of biliary primary cilia loss on the development of cirrhosis. Increased cellular proliferation was seen within the cystic structures associated with a decrease in hepatocyte lobular proliferation. Loss of primary cilia within biliary organoids was initially associated with reduced cell passage survival but this inhibitory effect was diminished in later passages. ERK but not WNT signalling was enhanced in primary cilia loss-induced cystic lesions in vivo and its inhibition reduced the expansion of primary cilia deficient biliary progenitor cells in vitro.

CONCLUSIONS

TAA-treated kif3a BEC-specific knockout mice had an unaltered progression to cirrhosis, but developed cystic lesions that showed increased proliferation.

Metformin induces lactate accumulation and accelerates renal cyst progression in Pkd1-deficient mice

Metabolic reprogramming is a potential treatment strategy for autosomal dominant polycystic kidney disease (ADPKD). Metformin has been shown to inhibit the early stages of cyst formation in animal models. However, metformin can lead to lactic acidosis in diabetic patients with advanced chronic kidney disease, and its efficacy in ADPKD is still not fully understood. Here, we investigated the effect of metformin in an established hypomorphic mouse model of PKD that presents stable and heritable knockdown of Pkd1. The Pkd1 miRNA transgenic mice of both genders were randomized to receive metformin or saline injections. Metformin was administrated through daily intraperitoneal injection from postnatal day 35 for 4 weeks. Unexpectedly, metformin treatment at a concentration of 150 mg/kg increased disease severity, including kidney-to-body weight ratio, cystic index and plasma BUN levels, and was associated with increased renal tubular cell proliferation and plasma lactate levels. Functional enrichment analysis for cDNA microarrays from kidney samples revealed significant enrichment of several pro-proliferative pathways including β-catenin, hypoxia-inducible factor-1α, protein kinase Cα and Notch signaling pathways in the metformin-treated mutant mice. The plasma metformin concentrations were still within the recommended therapeutic range for type 2 diabetic patients. Short-term metformin treatment in a second Pkd1 hypomorphic model (Pkd1RC/RC) was however neutral. These results demonstrate that metformin may exacerbate late-stage cyst growth associated with the activation of lactate-related signaling pathways in Pkd1 deficiency. Our findings indicate that using metformin in the later stage of ADPKD might accelerate disease progression and call for the cautious use of metformin in these patients.

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 cellular pathways and potential therapeutics of Polycystic Kidney Disease

Polycystic Kidney Disease (PKD) refers to a group of disorders, driven by the formation of cysts in renal tubular cells and is currently one of the leading causes of end-stage renal disease. The range of symptoms observed in PKD is due to mutations in cilia-localising genes, resulting in changes in cellular signalling. As such, compounds that are currently in preclinical and clinical trials target some of these signalling pathways that are dysregulated in PKD. In this review, we highlight these pathways including cAMP, EGF and AMPK signalling and drugs that target them and may show promise in lessening the disease burden of PKD patients. At present, tolvaptan is the only approved therapy for ADPKD, however, it carries several adverse side effects whilst comparatively, no pharmacological drug is approved for ARPKD treatment. Aside from this, drugs that have been the subject of multiple clinical trials such as metformin, which targets AMPK signalling and somatostatins, which target cAMP signalling have shown great promise in reducing cyst formation and cellular proliferation. This review also discusses other potential and novel targets that can be used for future interventions, such as β-catenin and TAZ, where research has shown that a reduction in the overexpression of these signalling components results in amelioration of disease phenotype. Thus, it becomes apparent that well-designed preclinical investigations and future clinical trials into these pathways and other potential signalling targets are crucial in bettering disease prognosis for PKD patients and could lead to personalised therapy approaches.

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.

Limitations and opportunities in the pharmacotherapy of ciliopathies

Ciliopathies are a family of rather diverse conditions, which have been grouped based on the finding of altered or dysfunctional cilia, potentially motile, small cellular antennae extending from the surface of postmitotic cells. Cilia-related disorders include embryonically arising conditions such as Joubert, Usher or Kartagener syndrome, but also afflictions with a postnatal or even adult onset phenotype, i.e. autosomal dominant polycystic kidney disease. The majority of ciliopathies are syndromic rather than affecting only a single organ due to cilia being found on almost any cell in the human body. Overall ciliopathies are considered rare diseases. Despite that, pharmacological research and the strive to help these patients has led to enormous therapeutic advances in the last decade. In this review we discuss new treatment options for certain ciliopathies, give an outlook on promising future therapeutic strategies, but also highlight the limitations in the development of therapeutic approaches of ciliopathies.

LGK974 suppresses lipopolysaccharide-induced endotoxemia in mice by modulating the crosstalk between the Wnt/β-catenin and NF-κB pathways

Endotoxemia, a type of sepsis caused by gram-negative bacterial endotoxin [i.e., lipopolysaccharide (LPS)], is associated with manifestations such as cytokine storm; failure of multiple organs, including the liver; and a high mortality rate. We investigated the effect and mechanism of action of LGK974, a Wnt signaling inhibitor, in mice with LPS-induced endotoxemia, an animal model of sepsis. LGK974 significantly and dose-dependently increased the survival rate and reduced plasma cytokine levels in mice with LPS-induced endotoxemia. Transcriptome analysis of liver tissues revealed significant changes in the expression of genes associated with the Wnt pathway as well as cytokine and NF-κB signaling during endotoxemia. LGK974 treatment suppressed the activation of NF-κB signaling and cytokine expression as well as the Wnt/β-catenin pathway in the livers of endotoxemic mice. Coimmunoprecipitation of phospho-IκB and β-transducin repeat-containing protein (β-TrCP) was increased in the livers of endotoxemic mice but was reduced by LGK974 treatment. Moreover, LGK974 treatment decreased the coimmunoprecipitation and colocalization of β-catenin and NF-κB, which were elevated in the livers of endotoxemic mice. Our results reveal crosstalk between the Wnt/β-catenin and NF-κB pathways via interactions between β-TrCP and phospho-IκB and between β-catenin and NF-κB during endotoxemia. The results of this study strongly suggest that the crosstalk between the Wnt/β-catenin and NF-κB pathways contributes to the mutual activation of these two pathways during endotoxemia, which results in amplified cytokine production, liver damage and death, and that LGK974 suppresses this vicious amplification cycle by reducing the crosstalk between these two pathways.

Combination of curcumin and ginkgolide B inhibits cystogenesis by regulating multiple signaling pathways

Autosomal dominant polycystic kidney disease (ADPKD), a common disease with a high incidence ratio of between 1/400 and 1/1,000 individuals, often results in kidney failure and even mortality. However, there are relatively few effective treatments available, and treatment is limited to lifelong hemodialysis or kidney transplant. Our previous studies have reported that curcumin (Cur) and ginkgolide B (GB) inhibited cystogenesis by regulating the Ras/ERK MAPK signaling pathway. In the present study, it was hypothesized that Cur and GB may have a synergistic effect on the inhibition of cystogenesis, and their synergistic effect may be the result of regulation of multiple signaling pathways. To assess this hypothesis, an in vitro Madin‑Darby canine kidney (MDCK) cyst model and an in vivo kidney‑specific polycystin 1 transient receptor potential channel interacting (Pkd1) knockout mouse model were established to observe the effects of the combination of Cur and GB. The cysts exposed to Cur, GB and Cur combined with GB became small thick‑walled cysts, small thin‑walled cysts and round shaped cell colonies, respectively. The combination of Cur and GB was more effective compared with either treatment alone in inhibiting cystogenesis. Additionally, to the best of our knowledge, the present study was the first to demonstrate the synergistic effect of Cur and GB on the inhibition of cystogenesis in Pkd1 knockout mice. Cur may have mediated its anti‑cyst effects by blocking EGFR/ERK1/2, JNK and PI3K/mTOR signaling pathways, while GB may have inhibited cystogenesis via the downregulation of the EGFR/ERK1/2, JNK and p38 signaling pathways. These results provide a proof‑of‑concept for application of the combination of Cur and GB in inhibiting cystogenesis in ADPKD.

Aquatic models of human ciliary diseases

Cilia are microtubule-based structures that either transmit information into the cell or move fluid outside of the cell. There are many human diseases that arise from malfunctioning cilia. Although mammalian models provide vital insights into the underlying pathology of these diseases, aquatic organisms such as Xenopus and zebrafish provide valuable tools to help screen and dissect out the underlying causes of these diseases. In this review we focus on recent studies that identify or describe different types of human ciliopathies and outline how aquatic organisms have aided our understanding of these diseases.

TAZ/Wnt-β-catenin/c-MYC axis regulates cystogenesis in polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, primarily caused by germline mutation of PKD1 or PKD2, leading to end-stage renal disease. There are few cures for ADPKD, although many researchers are trying to find a cure. The Hippo signaling pathway regulates organ growth and cell proliferation. Transcriptional coactivator with PDZ-binding motif (TAZ) is a Hippo signaling effector. In this study, we demonstrated that the PKD1–TAZ–Wnt–β-catenin–c-MYC signaling axis plays a critical role in cystogenesis. Endo IWR1 treatment, which inhibited β-catenin activity via AXIN stabilization, reduced cyst growth in an ADPKD model. Our findings provide a potential therapeutic target against ADPKD and would be important for clinical translation.

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common genetic renal disease, primarily caused by germline mutation of PKD1 or PKD2, leading to end-stage renal disease. The Hippo signaling pathway regulates organ growth and cell proliferation. Herein, we demonstrate the regulatory mechanism of cystogenesis in ADPKD by transcriptional coactivator with PDZ-binding motif (TAZ), a Hippo signaling effector. TAZ was highly expressed around the renal cyst-lining epithelial cells of Pkd1-deficient mice. Loss of Taz in Pkd1-deficient mice reduced cyst formation. In wild type, TAZ interacted with PKD1, which inactivated β-catenin. In contrast, in PKD1-deficient cells, TAZ interacted with AXIN1, thus increasing β-catenin activity. Interaction of TAZ with AXIN1 in PKD1-deficient cells resulted in nuclear accumulation of TAZ together with β-catenin, which up-regulated c-MYC expression. Our findings suggest that the PKD1–TAZ–Wnt–β-catenin–c-MYC signaling axis plays a critical role in cystogenesis and might be a potential therapeutic target against ADPKD.

The Role of Wnt Signalling in Chronic Kidney Disease (CKD)

Chronic kidney disease (CKD) encompasses a group of diverse diseases that are associated with accumulating kidney damage and a decline in glomerular filtration rate (GFR). These conditions can be of an acquired or genetic nature and, in many cases, interactions between genetics and the environment also play a role in disease manifestation and severity. In this review, we focus on genetically inherited chronic kidney diseases and dissect the links between canonical and non-canonical Wnt signalling, and this umbrella of conditions that result in kidney damage. Most of the current evidence on the role of Wnt signalling in CKD is gathered from studies in polycystic kidney disease (PKD) and nephronophthisis (NPHP) and reveals the involvement of β-catenin. Nevertheless, recent findings have also linked planar cell polarity (PCP) signalling to CKD, with further studies being required to fully understand the links and molecular mechanisms.

c-Myc is a regulator of the PKD1 gene and PC1-induced pathogenesis

Autosomal dominant polycystic kidney disease (ADPKD) is among the most common monogenic disorders mainly associated with PKD1/PC1 mutations. We show herein that renal regulation in Pc1 dosage-reduced and -increased mouse models converge toward stimulation of c-Myc expression along with β-catenin, delineating c-Myc as a key Pkd1 node in cystogenesis. Enhanced renal c-Myc-induced ADPKD in SBM transgenic mice lead conversely to striking upregulation of Pkd1/Pc1 expression and β-catenin activation, lending credence for reciprocal crosstalk between c-Myc and Pc1. In adult SBM kidneys, c-Myc is strongly enriched on Pkd1 promoter with RNA pol II, consistent with Pkd1 upregulation during cystogenesis. Similar c-Myc direct binding at birth uncovers an equivalent role on Pkd1 regulation during renal developmental program. Concurrent with enriched c-Myc binding, recruitment of active chromatin modifying co-factors by c-Myc at the Pkd1 regulatory region probably opens chromatin to stimulate transcription. A similar transcriptional activation by c-Myc is also likely operant on endogenous human PKD1 gene from our transactivation analysis in response to human c-MYC upregulation. Genetic ablation of c-Myc in Pc1-reduced and -increased mouse models significantly attenuates cyst growth, proliferation and PKD progression. Our study determined a dual role for c-Myc, as a major contributor in Pc1-induced cystogenesis and in a feed-forward regulatory Pkd1-c-Myc loop mechanism that may also prevail in human ADPKD.

Cardamonin retards progression of autosomal dominant polycystic kidney disease via inhibiting renal cyst growth and interstitial fibrosis

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic inherited kidney disease characterized by renal progressive fluid-filled cysts and interstitial fibrosis. Inhibiting renal cyst development and interstitial fibrosis has been proven effective in delaying the progression of ADPKD. The purpose of this study was to discover effective drugs from natural products for preventing and treating ADPKD. Candidate compounds were screened from a natural product library by virtual screening. The Madin-Darby canine kidney (MDCK) cyst model, embryonic kidney cyst model, and orthologous mouse model of ADPKD were utilized to determine the pharmacological activities of the candidate compounds. Western blot and morphological analysis were used to investigate underlying mechanisms. The experimental results showed that 0.625, 2.5, and 10 μM cardamonin dose-dependently reduced formation and enlargement in MDCK cyst model. Cardamonin also significantly attenuated renal cyst enlargement in ex vivo mouse embryonic kidneys and PKD mouse kidneys. We found that cardamonin inhibited renal cyst development and interstitial fibrosis by downregulating the MAPK, Wnt, mTOR, and transforming growth factor-β/Smad2/3 signaling pathways. Cardamonin significantly inhibits renal cyst development and interstitial fibrosis, suggesting that cardamonin shows promise as a potential therapeutic drug for preventing and treating ADPKD.

The master regulators Myc and p53 cellular signaling and functions in polycystic kidney disease

The transcription factors Myc and p53 associated with oncogenesis play determinant roles in a human genetic disorder, autosomal dominant polycystic kidney disease (ADPKD), that was coined early in ADPKD etiology a «neoplasia in disguise ». These factors are interdependent master cell regulators of major biological processes including proliferation, apoptosis, cell growth, metabolism, inflammation, fibrosis and differentiation that are all modulated in ADPKD. Myc and p53 proteins evolved to respond and carry out overlapping functions via opposing mechanisms of action. Studies in human ADPKD kidneys, caused by mutations in the PKD1 or PKD2 genes, reveal reduced p53 expression and high expression of Myc in the cystic tubular epithelium. Myc and p53 via direct interaction act respectively, as transcriptional activator and repressor of PKD1 gene expression, consistent with increased renal PKD1 levels in ADPKD. Mouse models generated by Pkd1 and Pkd2 gene dosage dysregulation reproduce renal cystogenesis with activation of Myc expression and numerous signaling pathways, strikingly similar to those determined in human ADPKD. In fact, upregulation of renal Myc expression is also detected in virtually all non-orthologous animal models of PKD. A definitive causal connection of Myc with cystogenesis was established by renal overexpression of Myc in transgenic mice that phenocopies human ADPKD. The network of activated signaling pathways in human and mouse cystogenesis individually or in combination can target Myc as a central node of PKD pathogenesis. One or many of the multiple functions of Myc upon activation can play a role in every phases of ADPKD development and lend credence to the notion of "Myc addiction" for cystogenesis. We propose that the residual p53 levels are conducive to an ADPKD biological program without cancerogenesis while a "p53 dependent annihilation" mechanism would be permissive to oncogenesis. Of major importance, Myc ablation in orthologous mouse models or direct inhibition in non-orthologous mouse model significantly delays cystogenesis consistent with pharmacologic or genetic inhibition of Myc upstream regulator or downstream targets in the mouse. Together, these studies on PKD proteins upon dysregulation not only converged on Myc as a focal point but also attribute to Myc upregulation a causal and « driver » role in pathogenesis. This review will present and discuss our current knowledge on Myc and p53, focused on PKD mouse models and ADPKD.

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.

Role of the RNA-binding protein Bicaudal-C1 and interacting factors in cystic kidney diseases

Polycystic kidneys frequently associate with mutations in individual components of cilia, basal bodies or centriolar satellites that perturb complex protein networks. In this review, we focus on the RNA-binding protein Bicaudal-C1 (BICC1) which was found mutated in renal cystic dysplasia, and on its interactions with the ankyrin repeat and sterile α motif (SAM)-containing proteins ANKS3 and ANKS6 and associated kinases and their partially overlapping ciliopathy phenotypes. After reviewing BICC1 homologs in model organisms and their functions in mRNA and cell metabolism during development and in renal tubules, we discuss recent insights from cell-based assays and from structure analysis of the SAM domains, and how SAM domain oligomerization might influence multivalent higher order complexes that are implicated in ciliary signal transduction.

Hepatocyte nuclear factor-1β regulates Wnt signaling through genome-wide competition with β-catenin/lymphoid enhancer binding factor

Hepatocyte nuclear factor-1β (HNF-1β) is a tissue-specific transcription factor that is essential for normal kidney development and renal tubular function. Mutations of HNF-1β produce cystic kidney disease, a phenotype associated with deregulation of canonical (β-catenin-dependent) Wnt signaling. Here, we show that ablation of HNF-1β in mIMCD3 renal epithelial cells produces hyperresponsiveness to Wnt ligands and increases expression of Wnt target genes, including Axin2, Ccdc80, and Rnf43 Levels of β-catenin and expression of Wnt target genes are also increased in HNF-1β mutant mouse kidneys. Genome-wide chromatin immunoprecipitation sequencing (ChIP-seq) in wild-type and mutant cells showed that ablation of HNF-1β increases by 6-fold the number of sites on chromatin that are occupied by β-catenin. Remarkably, 50% of the sites that are occupied by β-catenin in HNF-1β mutant cells colocalize with HNF-1β-occupied sites in wild-type cells, indicating widespread reciprocal binding. We found that the Wnt target genes Ccdc80 and Rnf43 contain a composite DNA element comprising a β-catenin/lymphoid enhancer binding factor (LEF) site overlapping with an HNF-1β half-site. HNF-1β and β-catenin/LEF compete for binding to this element, and thereby HNF-1β inhibits β-catenin-dependent transcription. Collectively, these studies reveal a mechanism whereby a transcription factor constrains canonical Wnt signaling through direct inhibition of β-catenin/LEF chromatin binding.