Fibrosis and progression of autosomal dominant polycystic kidney disease (ADPKD)

Novel Potential Therapeutic Targets in Autosomal Dominant Polycystic Kidney Disease from the Perspective of Cell Polarity and Fibrosis

Autosomal dominant polycystic kidney disease (ADPKD), a congenital genetic disorder, is a notable contributor to the prevalence of chronic kidney disease worldwide. Despite the absence of a complete cure, ongoing research aims for early diagnosis and treatment. Although agents such as tolvaptan and mTOR inhibitors have been utilized, their effectiveness in managing the disease during its initial phase has certain limitations. This review aimed to explore new targets for the early diagnosis and treatment of ADPKD, considering ongoing developments. We particularly focus on cell polarity, which is a key factor that influences the process and pace of cyst formation. In addition, we aimed to identify agents or treatments that can prevent or impede the progression of renal fibrosis, ultimately slowing its trajectory toward end-stage renal disease. Recent advances in slowing ADPKD progression have been examined, and potential therapeutic approaches targeting multiple pathways have been introduced. This comprehensive review discusses innovative strategies to address the challenges of ADPKD and provides valuable insights into potential avenues for its prevention and treatment.

Notch3 as a novel therapeutic target for the treatment of ADPKD by regulating cell proliferation and renal cyst development

Autosomal dominant polycystic kidney disease (ADPKD) is a common monogenic kidney disease. Emerging research indicates that the Notch signaling pathway plays an indispensable role in the pathogenesis of numerous kidney diseases, including ADPKD. Herein, we identified that Notch3 but not other Notch receptors was overexpressed in renal tissues from mice with ADPKD and ADPKD patients. Inhibiting Notch3 with γ-secretase inhibitors, which block a proteolytic cleavage required for Notch3 activation, or shRNA knockdown of Notch3 significantly delayed renal cyst growth in vitro and in vivo. Subsequent mechanistic study elucidated that the cleaved intracellular domain of Notch3 (N3ICD) and Hes1 could bind to the PTEN promoter, leading to transcriptional inhibition of PTEN. This further activated the downstream PI3K-AKT-mTOR pathway and promoted renal epithelial cell proliferation. Overall, Notch3 was identified as a novel contributor to renal epithelial cell proliferation and cystogenesis in ADPKD. We envision that Notch3 represents a promising target for ADPKD treatment.

Ultrastructure expansion microscopy (U-ExM) of mouse and human kidneys for analysis of subcellular structures

Ultrastructure expansion microscopy (U-ExM) involves the physical magnification of specimens embedded in hydrogels, which allows for super-resolution imaging of subcellular structures using a conventional diffraction-limited microscope. Methods for expansion microscopy exist for several organisms, organs, and cell types, and used to analyze cellular organelles and substructures in nanoscale resolution. Here, we describe a simple step-by-step U-ExM protocol for the expansion, immunostaining, imaging, and analysis of cytoskeletal and organellar structures in kidney tissue. We detail the critical modified steps to optimize isotropic kidney tissue expansion, and preservation of the renal cell structures of interest. We demonstrate the utility of the approach using several markers of renal cell types, centrioles, cilia, the extracellular matrix, and other cytoskeletal elements. Finally, we show that the approach works well on mouse and human kidney samples that were preserved using different fixation and storage conditions. Overall, this protocol provides a simple and cost-effective approach to analyze both pre-clinical and clinical renal samples in high detail, using conventional lab supplies and standard widefield or confocal microscopy.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cleavage of periostin by MMP9 protects mice from kidney cystic disease

The matrix metalloproteinase MMP9 influences cellular morphology and function, and plays important roles in organogenesis and disease. It exerts both protective and deleterious effects in renal pathology, depending upon its specific substrates. To explore new functions for MMP9 in kidney cysts formation and disease progression, we generated a mouse model by breeding juvenile cystic kidney (jck) mice with MMP9 deficient mice. Specifically, we provide evidence that MMP9 is overexpressed in cystic tissue where its enzymatic activity is increased 7-fold. MMP9 deficiency in cystic kidney worsen cystic kidney diseases by decreasing renal function, favoring cyst expansion and fibrosis. In addition, we find that periostin is a new critical substrate for MMP9 and in its absence periostin accumulates in cystic lining cells. As periostin promotes renal cyst growth and interstitial fibrosis in polycystic kidney diseases, we propose that the control of periostin by MMP9 and its associated intracellular signaling pathways including integrins, integrin-linked kinase and focal adhesion kinase confers to MMP9 a protective effect on the severity of the disease.

Cardiovascular Manifestations and Management in ADPKD

Cardiovascular disease (CVD) is the major cause of mortality in autosomal dominant polycystic kidney disease (ADPKD) and contributes to significant burden of disease. The manifestations are varied, including left ventricular hypertrophy (LVH), intracranial aneurysms (ICAs), valvular heart disease, and cardiomyopathies; however, the most common presentation and a major modifiable risk factor is hypertension. The aim of this review is to detail the complex pathogenesis of hypertension and other extrarenal cardiac and vascular conditions in ADPKD drawing on preclinical, clinical, and epidemiological evidence. The main drivers of disease are the renin-angiotensin-aldosterone system (RAAS) and polycystin-related endothelial cell dysfunction, with the sympathetic nervous system (SNS), nitric oxide (NO), endothelin-1 (ET-1), and asymmetric dimethylarginine (ADMA) likely playing key roles in different disease stages. The reported rates of some manifestations, such as LVH, have decreased likely due to the use of antihypertensive therapies; and others, such as ischemic cardiomyopathy, have been reported with increased prevalence likely due to longer survival and higher rates of chronic disease. ADPKD-specific screening and management guidelines exist for hypertension, LVH, and ICAs; and these are described in this review.

Abdominal Imaging in ADPKD: Beyond Total Kidney Volume

In the context of autosomal dominant polycystic kidney disease (ADPKD), measurement of the total kidney volume (TKV) is crucial. It acts as a marker for tracking disease progression, and evaluating the effectiveness of treatment strategies. The TKV has also been recognized as an enrichment biomarker and a possible surrogate endpoint in clinical trials. Several imaging modalities and methods are available to calculate the TKV, and the choice depends on the purpose of use. Technological advancements have made it possible to accurately assess the cyst burden, which can be crucial to assessing the disease state and helping to identify rapid progressors. Moreover, the development of automated algorithms has increased the efficiency of total kidney and cyst volume measurements. Beyond these measurements, the quantification and characterization of non-cystic kidney tissue shows potential for stratifying ADPKD patients early on, monitoring disease progression, and possibly predicting renal function loss. A broad spectrum of radiological imaging techniques are available to characterize the kidney tissue, showing promise when it comes to non-invasively picking up the early signs of ADPKD progression. Radiomics have been used to extract textural features from ADPKD images, providing valuable information about the heterogeneity of the cystic and non-cystic components. This review provides an overview of ADPKD imaging biomarkers, focusing on the quantification methods, potential, and necessary steps toward a successful translation to clinical practice.

Plant-derived compounds for treating autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD), the most common monogenic hereditary kidney disease, is the fourth leading cause of end-stage kidney disease worldwide. In recent years, significant progress has been made in delaying ADPKD progression with different kinds of chemical drugs, such as tolvaptan, rapamycin, and somatostatin. Meanwhile, numerous plant-derived compounds have been investigated for their beneficial effects on slowing ADPKD progression. Among them, saikosaponin-d, Ganoderma triterpenes, curcumin, ginkgolide B, steviol, resveratrol, Sparganum stoloniferum Buch.-Ham, Cordyceps sinensis, triptolide, quercitrin, naringin, cardamonin, gambogic acid, and olive leaf extract have been found to retard renal cyst development by inhibiting cell proliferation or promoting cell apoptosis in renal cyst-lining epithelial cells. Metformin, a synthesized compound derived from French lilac or goat's rue (Galega officinalis), has been proven to retard the progression of ADPKD. This review focuses on the roles and mechanisms of plant-derived compounds in treating ADPKD, which may constitute promising new therapeutics in the future.

Myofibroblast depletion reduces kidney cyst growth and fibrosis in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) involves the development and persistent growth of fluid filled kidney cysts. In a recent study, we showed that ADPKD kidney cyst epithelial cells can stimulate the proliferation and differentiation of peri-cystic myofibroblasts. Although dense myofibroblast populations are often found surrounding kidney cysts, their role in cyst enlargement or fibrosis in ADPKD is unclear. To clarify this, we examined the effect of myofibroblast depletion in the Pkd1RC/RC (RC/RC) mouse model of ADPKD. RC/RC;αSMAtk mice that use the ganciclovir-thymidine kinase system to selectively deplete α-smooth muscle actin expressing myofibroblasts were generated. Ganciclovir treatment for four weeks depleted myofibroblasts, reduced kidney fibrosis and preserved kidney function in these mice. Importantly, myofibroblast depletion significantly reduced cyst growth and cyst epithelial cell proliferation in RC/RC;αSMAtk mouse kidneys. Similar ganciclovir treatment did not alter cyst growth or fibrosis in wild-type or RC/RC littermates. In vitro, co-culture with myofibroblasts from the kidneys of patients with ADPKD increased 3D microcyst growth of human ADPKD cyst epithelial cells. Treatment with conditioned culture media from ADPKD kidney myofibroblasts increased microcyst growth and cell proliferation of ADPKD cyst epithelial cells. Further examination of ADPKD myofibroblast conditioned media showed high levels of protease inhibitors including PAI1, TIMP1 and 2, NGAL and TFPI-2, and treatment with recombinant PAI1 and TIMP1 increased ADPKD cyst epithelial cell proliferation in vitro. Thus, our findings show that myofibroblasts directly promote cyst epithelial cell proliferation, cyst growth and fibrosis in ADPKD kidneys, and their targeting could be a novel therapeutic strategy to treat PKD.

Hypertrophic and fibrotic human PKD hearts are associated with macrophage infiltration and abnormal TGF-β(1) signaling

Autosomal dominant polycystic kidney disease (PKD) is a hereditary kidney disorder which can affect cardiovascular system. Cardiac hypertrophy and cardiomyopathy in PKD have been reported by echocardiography analyses, but histopathology analyses of human PKD hearts have never been examined. The current studies evaluated human heart tissues from five subjects without PKD (non-PKD) and five subjects with PKD. Our histopathology data of human PKD hearts showed an increased extracellular matrix associated with cardiac hypertrophy and fibrosis. Hypertrophy- and fibrosis-associated pathways involving abnormal cardiac structure were next analyzed. We found that human PKD myocardium was infiltrated by inflammatory macrophage M1 and M2; expression of transforming growth factor (TGF-β₁) and its receptor were upregulated with overexpression of pSmad3 and β-catenin. Because patients with PKD have an abnormal kidney function that could potentially affect heart structure, we used a heart-specific PKD mouse model to validate that cardiac hypertrophy and fibrosis were independent from polycystic kidney. In summary, our data show that hearts from human PKD were characterized by hypertrophy, interstitial fibrosis, perivascular fibrosis, and conduction system fibrosis with upregulated TGF-β₁ and its receptor. We suggest that such structural abnormalities may predispose to systolic and diastolic cardiac dysfunction in the PKD myocardium.

Ion channels as a therapeutic target for renal fibrosis

Renal ion channel transport and electrolyte disturbances play an important role in the process of functional impairment and fibrosis in the kidney. It is well known that there are limited effective drugs for the treatment of renal fibrosis, and since a large number of ion channels are involved in the renal fibrosis process, understanding the mechanisms of ion channel transport and the complex network of signaling cascades between them is essential to identify potential therapeutic approaches to slow down renal fibrosis. This review summarizes the current work of ion channels in renal fibrosis. We pay close attention to the effect of cystic fibrosis transmembrane conductance regulator (CFTR), transmembrane Member 16A (TMEM16A) and other Cl− channel mediated signaling pathways and ion concentrations on fibrosis, as well as the various complex mechanisms for the action of Ca2+ handling channels including Ca2+-release-activated Ca2+ channel (CRAC), purinergic receptor, and transient receptor potential (TRP) channels. Furthermore, we also focus on the contribution of Na+ transport such as epithelial sodium channel (ENaC), Na+, K+-ATPase, Na+-H+ exchangers, and K+ channels like Ca2+-activated K+ channels, voltage-dependent K+ channel, ATP-sensitive K+ channels on renal fibrosis. Proposed potential therapeutic approaches through further dissection of these mechanisms may provide new therapeutic opportunities to reduce the burden of chronic kidney disease.

Non-coding RNAs as potential biomarkers and therapeutic targets in polycystic kidney disease

Polycystic kidney disease (PKD) is a significant cause of end-stage kidney failure and there are few effective drugs for treating this inherited condition. Numerous aberrantly expressed non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), may contribute to PKD pathogenesis by participating in multiple intracellular and intercellular functions through post-transcriptional regulation of protein-encoding genes. Insights into the mechanisms of miRNAs and other ncRNAs in the development of PKD may provide novel therapeutic strategies. In this review, we discuss the current knowledge about the roles of dysregulated miRNAs and other ncRNAs in PKD. These roles involve multiple aspects of cellular function including mitochondrial metabolism, proliferation, cell death, fibrosis and cell-to-cell communication. We also summarize the potential application of miRNAs as biomarkers or therapeutic targets in PKD, and briefly describe strategies to overcome the challenges of delivering RNA to the kidney, providing a better understanding of the fundamental advances in utilizing miRNAs and other non-coding RNAs to treat PKD.

Restoration of atypical protein kinase C ζ function in autosomal dominant polycystic kidney disease ameliorates disease progression

Autosomal dominant polycystic kidney disease (ADPKD) affects more than 500,000 individuals in the United States alone. In most cases, ADPKD is caused by a loss-of-function mutation in the PKD1 gene, which encodes polycystin-1 (PC1). Previous studies reported that PC1 interacts with atypical protein kinase C (aPKC). Here we show that PC1 binds to the ζ isoform of aPKC (PKCζ) and identify two PKCζ phosphorylation sites on PC1's C-terminal tail. PKCζ expression is down-regulated in patients with ADPKD and orthologous and nonorthologous PKD mouse models. We find that the US Food and Drug Administration-approved drug FTY720 restores PKCζ expression in in vitro and in vivo models of polycystic kidney disease (PKD) and this correlates with ameliorated disease progression in multiple PKD mouse models. Importantly, we show that FTY720 treatment is less effective in PKCζ null versions of these PKD mouse models, elucidating a PKCζ-specific mechanism of action that includes inhibiting STAT3 activity and cyst-lining cell proliferation. Taken together, our results reveal that PKCζ down-regulation is a hallmark of PKD and that its stabilization by FTY720 may represent a therapeutic approach to the treat the disease.

Crosstalk between lysine methyltransferase Smyd2 and TGF-β-Smad3 signaling promotes renal fibrosis in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited genetic disorder, which is caused by mutations of PKD1 or PKD2 gene and is characterized by renal fluid-filled cyst formation and interstitial fibrosis. PKD1 gene mutation results in the upregulation of SET and MYND domain-containing lysine methyltransferase 2 (SMYD2) in Pkd1 mutant mouse and ADPKD patient kidneys. However, the role and mechanism of Smyd2 in the regulation of renal fibrosis in ADPKD remains elusive. In this study, we show that: 1) the expression of Smyd2 can be regulated by TGF-β-Smad3 in normal rat kidney 49F (NRK-49F) cells and mouse fibroblast NIH3T3 cells; 2) knockdown of Smyd2 and inhibition of Smyd2 with its specific inhibitor, AZ505, decreases TGF-β-induced expression of α-smooth muscle actin (α-SMA), fibronectin, collagens 1 and 3 and plasminogen activator inhibitor-1( PAI1) in NRK-49F cells; 3) Smyd2 regulates the transcription of fibrotic marker genes through binding on the promoters of those genes or through methylating histone H3 to indirectly regulate the expression of those genes; and 4) knockout and inhibition of Smyd2 significantly decreases renal fibrosis in Pkd1 knockout mice, supporting that targeting Smyd2 can not only delay cyst growth but also attenuate renal fibrosis in ADPKD. This study identifies a crosstalk between TGF-β signaling and Smyd2 in the regulation of fibrotic gene transcription and the activation of fibroblasts in cystic kidneys, suggesting that targeting Smyd2 with AZ505 is a potential therapeutic strategy for ADPKD treatment.

Pharmacological Effects of Panduratin A on Renal Cyst Development in In Vitro and In Vivo Models of Polycystic Kidney Disease

Renal cyst expansion in polycystic kidney disease (PKD) involves abnormalities in both cyst-lining-cell proliferation and fluid accumulation. Suppression of these processes may retard the progression of PKD. Evidence suggests that the activation of 5' AMP-activated protein kinase (AMPK) inhibits cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride secretion, leading to reduced progression of PKD. Here we investigated the pharmacological effects of panduratin A, a bioactive compound known as an AMPK activator, on CFTR-mediated chloride secretion and renal cyst development using in vitro and animal models of PKD. We demonstrated that AMPK was activated in immortalized normal renal cells and autosomal dominant polycystic kidney disease (ADPKD) cells following treatment with panduratin A. Treatment with panduratin A reduced the number of renal cyst colonies corresponding with a decrease in cell proliferation and phosphorylated p70/S6K, a downstream target of mTOR signaling. Additionally, panduratin A slowed cyst expansion via inhibition of the protein expression and transport function of CFTR. In heterozygous Han:Sprague-Dawley (Cy/+) rats, an animal model of PKD, intraperitoneal administration of panduratin A (25 mg/kg BW) for 5 weeks significantly decreased the kidney weight per body weight ratios and the cystic index. Panduratin A also reduced collagen deposition in renal tissue. Intraperitoneal administration of panduratin A caused abdominal bleeding and reduced body weight. However, 25 mg/kg BW of panduratin A via oral administration in the PCK rats, another non-orthologous PKD model, showed a significant decrease in the cystic index without severe adverse effects, indicating that the route of administration is critical in preventing adverse effects while still slowing disease progression. These findings reveal that panduratin A might hold therapeutic properties for the treatment of PKD.

Rapidly Progressing to ESRD in an Individual with Coexisting ADPKD and Masked Klinefelter and Gitelman Syndromes

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenetic hereditary renal disease, promoting end-stage renal disease (ESRD). Klinefelter syndrome (KS) is a consequence of an extra copy of the X chromosome in males. Main symptoms in KS include hypogonadism, tall stature, azoospermia, and a risk of cardiovascular diseases, among others. Gitelman syndrome (GS) is an autosomal recessive disorder caused by SLC12A3 variants, and is associated with hypokalemia, hypomagnesemia, hypocalciuria, normal or low blood pressure, and salt loss. The three disorders have distinct and well-delineated clinical, biochemical, and genetic findings. We here report a male patient with ADPKD who developed early chronic renal failure leading to ESRD, presenting with an intracranial aneurysm and infertility. NGS identified two de novo PKD1 variants, one known (likely pathogenic), and a previously unreported variant of uncertain significance, together with two SLC12A3 pathogenic variants. In addition, cytogenetic analysis showed a 47, XXY karyotype. We investigated the putative impact of this rare association by analyzing possible clinical, biochemical, and/or genetic interactions and by comparing the evolution of renal size and function in the proband with three age-matched ADPKD (by variants in PKD1) cohorts. We hypothesize that the coexistence of these three genetic disorders may act as modifiers with possible synergistic actions that could lead, in our patient, to a rapid ADPKD progression.

Activation of Notch3 in Renal Tubular Cells Leads to Progressive Cystic Kidney Disease

Background: Polycystic kidney disease (PKD) is a genetic disorder affecting millions of people worldwide that is characterized by fluid-filled cysts and leads to end-stage renal disease (ESRD). The hallmarks of PKD are proliferation and dedifferentiation of tubular epithelial cells, cellular processes known to be regulated by Notch signaling. Methods: We found increased Notch3 expression in human PKD and renal cell carcinoma biopsies. To obtain insight into the underlying mechanisms and the functional consequences of this abnormal expression, we developed a transgenic mouse model with conditional overexpression of the intracellular Notch3 (ICN3) domain specifically in renal tubules. We evaluated the alterations in renal function (creatininemia, BUN) and structure (cysts, fibrosis, inflammation) and measured the expression of several genes involved in Notch signaling and the mechanisms of inflammation, proliferation, dedifferentiation, fibrosis, injury, apoptosis and regeneration. Results: After one month of ICN3 overexpression, kidneys were larger with tubules grossly enlarged in diameter, with cell hypertrophy and hyperplasia, exclusively in the outer stripe of the outer medulla. After three months, mice developed numerous cysts in proximal and distal tubules. The cysts had variable sizes and were lined with a single- or multilayered, flattened, cuboid or columnar epithelium. This resulted in epithelial hyperplasia, which was observed as protrusions into the cystic lumen in some of the renal cysts. The pre-cystic and cystic epithelium showed increased expression of cytoskeletal filaments and markers of epithelial injury and dedifferentiation. Additionally, the epithelium showed increased proliferation with an aberrant orientation of the mitotic spindle. These phenotypic tubular alterations led to progressive interstitial inflammation and fibrosis. Conclusions: In summary, Notch3 signaling promoted tubular cell proliferation, the alignment of cell division, dedifferentiation and hyperplasia, leading to cystic kidney diseases and pre-neoplastic lesions.

Generation of heterozygous PKD1 mutant pigs exhibiting early-onset renal cyst formation

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease, manifesting as the progressive development of fluid-filled renal cysts. In approximately half of all patients with ADPKD, end-stage renal disease results in decreased renal function. In this study, we used CRISPR-Cas9 and somatic cell cloning to produce pigs with the unique mutation c.152_153insG (PKD1^insG/+). Pathological analysis of founder cloned animals and progeny revealed that PKD1^insG/+ pigs developed many pathological conditions similar to those of patients with heterozygous mutations in PKD1. Pathological similarities included the formation of macroscopic renal cysts at the neonatal stage, number and cystogenic dynamics of the renal cysts formed, interstitial fibrosis of the renal tissue, and presence of a premature asymptomatic stage. Our findings demonstrate that PKD1^insG/+ pigs recapitulate the characteristic symptoms of ADPKD.

Arrhythmogenic Hearts in PKD2 Mutant Mice Are Characterized by Cardiac Fibrosis, Systolic, and Diastolic Dysfunctions

Autosomal dominant polycystic kidney disease (PKD) is a hereditary disorder affecting multiple organs, including the heart. PKD has been associated with many cardiac abnormalities including the arrhythmogenic remodeling in clinical evaluations. In our current study, we hypothesized that Pkd2 gene mutation results in structural and functional defects in the myocardium. The structural and functional changes of Pkd2 mutant hearts were analyzed in the myocardial-specific Pkd2 knockout (KO) mouse. We further assessed a potential role of TGF-b₁ signaling in the pathology of Pkd2-KO hearts. Hearts from age-matched 6-month-old MyH6•Pkd2 ^wt/wt (control or wild-type) and MyH6•Pkd2 ^flox/flox (mutant or Pkd2-KO) mice were used to study differential heart structure and function. Cardiac histology was used to study structure, and the "isolated working heart" system was adapted to mount and perfuse mouse heart to measure different cardiac parameters. We found that macrophage1 (M1) and macrophage 2 (M2) infiltration, transforming growth factor (TGF-b₁) and TGF-b₁ receptor expressions were significantly higher in Pkd2-KO, compared to wild-type hearts. The increase in the extracellular matrix in Pkd2-KO myocardium led to cardiac hypertrophy, interstitial and conduction system fibrosis, causing cardiac dysfunction with a predisposition to arrhythmia. Left ventricular (LV) expansion or compliance and LV filling were impaired in fibrotic Pkd2-KO hearts, resulted in diastolic dysfunction. LV systolic contractility and elastance decreased in fibrotic Pkd2-KO hearts, resulted in systolic dysfunction. Compared to wild-type hearts, Pkd2-KO hearts were less responsive to the pharmacological stress-test and changes in preload. In conclusion, Pkd2-KO mice had systolic and diastolic dysfunction with arrhythmogenic hearts.

Heterogeneity of cell composition and origin identified by single-cell transcriptomics in renal cysts of patients with autosomal dominant polycystic kidney disease

Rationale: Renal cysts in patients with autosomal dominant polycystic kidney disease (ADPKD) can originate from any nephron segments, including proximal tubules (PT), the loop of Henle (LOH), distal tubules (DT), and collecting ducts (CD). Previous studies mostly used limited cell markers and failed to identify cells negative for these markers. Therefore, the cell composition and origin of ADPKD cyst are still unclear, and mechanisms of cystogenesis of different origins await further exploration.

Methods: We performed single-cell RNA sequencing for the normal kidney tissue and seven cysts derived from superficial or deep layers of the polycystic kidney from an ADPKD patient.

Results: Twelve cell types were identified and analyzed. We found that a renal cyst could be derived either from CD or both PT and LOH. Gene set variation analysis (GSVA) showed that epithelial mesenchymal transition (EMT), TNFA signaling via the NFKB pathways, and xenobiotic metabolism were significantly activated in PT-derived cyst epithelial cells while robust expression of genes involved in G2M Checkpoint, mTORC1 signaling, E2F Targets, MYC Targets V1, MYC Targets V2 were observed in CD-derived cells.

Conclusion: Our results revealed that a single cyst could originate from CD or both PT and LOH, suggesting heterogeneity of polycystic composition and origin. Furthermore, cyst epithelial cells with different origins have different gene set activation.

The tyrosine-kinase inhibitor Nintedanib ameliorates autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and is characterized by progressive growth of fluid-filled cysts. Growth factors binding to receptor tyrosine kinases (RTKs) stimulate cell proliferation and cyst growth in PKD. Nintedanib, a triple RTK inhibitor, targets the vascular endothelial growth-factor receptor (VEGFR), platelet-derived growth-factor receptor (PDGFR), and fibroblast growth-factor receptor (FGFR), and is an approved drug for the treatment of non-small-cell lung carcinoma and idiopathic lung fibrosis. To determine if RTK inhibition using nintedanib can slow ADPKD progression, we tested its effect on human ADPKD renal cyst epithelial cells and myofibroblasts in vitro, and on Pkd1f/fPkhd1Cre and Pkd1RC/RC, orthologous mouse models of ADPKD. Nintedanib significantly inhibited cell proliferation and in vitro cyst growth of human ADPKD renal cyst epithelial cells, and cell viability and migration of human ADPKD renal myofibroblasts. Consistently, nintedanib treatment significantly reduced kidney-to-body-weight ratio, renal cystic index, cystic epithelial cell proliferation, and blood-urea nitrogen levels in both the Pkd1f/fPkhd1Cre and Pkd1RC/RC mice. There was a corresponding reduction in ERK, AKT, STAT3, and mTOR activity and expression of proproliferative factors, including Yes-associated protein (YAP), c-Myc, and Cyclin D1. Nintedanib treatment significantly reduced fibrosis in Pkd1RC/RC mice, but did not affect renal fibrosis in Pkd1f/fPkhd1Cre mice. Overall, these results suggest that nintedanib may be repurposed to effectively slow cyst growth in ADPKD.

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.

Natural-derived compounds and their mechanisms in potential autosomal dominant polycystic kidney disease (ADPKD) treatment

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a monogenic kidney disorder that impairs renal functions progressively leading to kidney failure. The disease affects between 1:400 and 1:1000 ratio of the people worldwide. It is caused by the mutated PKD1 and PKD2 genes which encode for the defective polycystins. Polycystins mimic the receptor protein or protein channel and mediate aberrant cell signaling that causes cystic development in the renal parenchyma. The cystic development is driven by the increased cyclic AMP stimulating fluid secretion and infinite cell growth. In recent years, natural product-derived small molecules or drugs targeting specific signaling pathways have caught attention in the drug discovery discipline. The advantages of natural products over synthetic drugs enthusiast researchers to utilize the medicinal benefits in various diseases including ADPKD.

CONCLUSION

Overall, this review discusses some of the previously studied and reported natural products and their mechanisms of action which may potentially be redirected into ADPKD.

Methamphetamine-induced changes in myocardial gene transcription are sex-dependent

BACKGROUND

Prior work demonstrated that female rats (but not their male littermates) exposed to methamphetamine become hypersensitive to myocardial ischemic injury. Importantly, this sex-dependent effect persists following 30 days of subsequent abstinence from the drug, suggesting that it may be mediated by long term changes in gene expression that are not rapidly reversed following discontinuation of methamphetamine use. The goal of the present study was to determine whether methamphetamine induces sex-dependent changes in myocardial gene expression and whether these changes persist following subsequent abstinence from methamphetamine.

RESULTS

Methamphetamine induced changes in the myocardial transcriptome were significantly greater in female hearts than male hearts both in terms of the number of genes affected and the magnitude of the changes. The largest changes in female hearts involved genes that regulate the circadian clock (Dbp, Per3, Per2, BMal1, and Npas2) which are known to impact myocardial ischemic injury. These genes were unaffected by methamphetamine in male hearts. All changes in gene expression identified at day 11 returned to baseline by day 30.

CONCLUSIONS

These data demonstrate that female rats are more sensitive than males to methamphetamine-induced changes in the myocardial transcriptome and that methamphetamine does not induce changes in myocardial transcription that persist long term after exposure to the drug has been discontinued.

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.

Urinary exosome proteomic profiling defines stage-specific rapid progression of autosomal dominant polycystic kidney disease and tolvaptan efficacy

ADPKD is the most common genetic disease of the kidney leading to end-stage renal disease necessitating renal replacement therapy at any time between the 1^st and 8^th decades of life due to widely variable rates of disease progression. This presents significant patient anxiety and a significant prognostic and therapeutic challenge. Tolvaptan is the only approved drug licensed to slow ADPKD progression by reducing renal cystic expansion but side-effects can limit its efficacy. To address the need to identify new biomarkers to monitor progression of ADPKD and to evaluate the therapeutic effects of Tolvaptan, proteomic analysis was conducted on defined (40-100nm) urinary exosomes isolated from ADPKD patients phenotyped and clinically monitored over a 10-year period. Comparative Gene Ontology analysis of Tandem Mass Tag labelled mass spectrometry-derived protein profiles from urinary exosomes from ADPKD patients with rapid (>10ml/min/5 years decline in estimated glomerular filtration rate) versus slow progression showed distinctive patterns of pathway up-regulation. Clear discrimination between rapid and slowly-progressive profiles were seen in all stages functional decline in ADPKD patients whether with mild (>70ml/min), moderate (50-69ml/min) or severe (<49ml/min) disease at onset. Discriminatory pathways and proteins included Notch-, integrin- and growth factor-signalling; microtubular kinase, vesicular proteins and epidermal growth factor substrates. Confocal microscopy of fluorescently-labelled normal versus ADPKD epithelial cell-derived exosomes in vitro also identified ADPKD-dependent abnormalities in intracellular vesicular trafficking and implicated changes in ADPKD-dependent exosome secretion and target cell uptake as factors underlying urinary exosome excretion biomarker properties. Comparative proteomic analysis of urinary exosomal proteins in individual patients before and after treatment with Tolvaptan for 4 years also identified distinct patterns of pathway modification dependent on the degree of effectiveness of the therapeutic response. Up-regulation of Wnt-pathway and vesicular proteins were characteristic of urinary exosomes from ADPKD patients with good responses to Tolvaptan while upregulation of angiogenesis pathways and additional molecular forms of vasopressin receptor AVPR2 were characteristic in urinary exosomes of ADPKD patients with poor responses. Taken together, these studies conclude that proteomic profiling of urinary exosome biomarkers provides a specific, sensitive and practical non-invasive method to identify and monitor the rate of disease progression and the effects of Tolvaptan therapy in individual ADPKD patients. This provides a means to identify those patients most likely to benefit maximally from therapy and to progress towards a personalization of ADPKD prognosis and management.

The Controversial Role of Fibrosis in Autosomal Dominant Polycystic Kidney Disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is characterized by the progressive growth of cysts but it is also accompanied by diffuse tissue scarring or fibrosis. A number of recent studies have been published in this area, yet the role of fibrosis in ADPKD remains controversial. Here, we will discuss the stages of fibrosis progression in ADPKD, and how these compare with other common kidney diseases. We will also provide a detailed overview of some key mechanistic pathways to fibrosis in the polycystic kidney. Specifically, the role of the 'chronic hypoxia hypothesis', persistent inflammation, Transforming Growth Factor beta (TGFβ), Janus Kinase/Signal Transducers and Activators of Transcription (JAK/STAT) and microRNAs will be examined. Evidence for and against a pathogenic role of extracellular matrix during ADPKD disease progression will be provided.

Clinical characteristics associated with 1-year tolvaptan efficacy in autosomal dominant polycystic kidney disease with a wide range of kidney functions

Autosomal dominant polycystic kidney disease (ADPKD) develops into end-stage kidney disease by 65 years of age in an estimated 45%-70% of patients. Recent trials revealed that tolvaptan inhibits disease progression both in early-stage or late-stage ADPKD ; however, stratified analysis showed a difference of favorable factors correlated with tolvaptan efficacy between early-stage and late-stage ADPKD. Thus, we examined the efficacy of tolvaptan in ADPKD with a wide range of estimated glomerular filtration rates (eGFR). We enrolled 24 patients with eGFR 35.3 (28.0-65.5) ml / min / 1.73m2 and evaluated treatment effect as ΔΔeGFR (ml / min / 1.73m2 / year) or ΔΔtotal kidney volume (TKV) (% / year) that was calculated as post-treatment annual change - pre-treatment annual change. Pre ΔeGFR was significantly low in eGFR responders, defined as ΔΔeGFR > 0 ml / min / 1.73m2 / year. In eGFR responders, pre ΔeGFR, post ΔeGFR, eGFR, TKV, and proteinuria were significantly correlated with ΔΔeGFR. In TKV responders defined as ΔΔTKV > 5 % / year, we identified hypertension history, proteinuria, TKV, and post ΔTKV as significantly correlated factors with ΔΔTKV. In conclusion, pre ΔeGFR may be a predictive factor of therapeutic efficacy on kidney function. Tolvaptan may have greater efficacy in early-stage ADPKD with rapid GFR decline or with well-controlled blood pressure. J. Med. Invest. 67 : 315-320, August, 2020.

MicroRNAs and Polycystic Kidney Disease

Important advances have been made regarding the diagnosis and management of polycystic kidney diseases. Care of patients with polycystic kidney diseases has moved beyond supportive care for complications and chronic kidney disease to new potentially disease-modifying therapies. Recently, the role of noncoding RNAs, in particular microRNAs, has been described in polycystic kidney diseases. microRNAs are involved in the regulation of gene expression, in which PKD1, PKD2, and other genes that contribute to the pathogenesis of polycystic kidney diseases are considerable participants. Seminal studies have highlighted the potential importance of microRNAs as new therapeutic targets and innovative diagnostic and/or prognostic biomarkers. Furthermore, an anti-miR-17 drug has advanced through preclinical autosomal dominant polycystic disease studies, and an anti-miR-21 drug has already cleared a phase 1 clinical trial. Most probably, new drugs in the microRNA research field will be yielded as a result of ongoing and planned therapeutic trials. To provide a foundation for understanding microRNA functions as a disease-modifying therapeutic drug in novel targeted therapies, in this narrative review we present an overview of the current knowledge of microRNAs in the pathogenesis of polycystic kidney diseases.

Association between urinary biomarkers and disease progression in adults with autosomal dominant polycystic kidney disease

Background

Height-adjusted total kidney volume (htTKV) is considered as the best predictor of kidney function in patients with autosomal dominant polycystic kidney disease (ADPKD), but its limited predictive capacity stresses the need to find new biomarkers of ADPKD progression. The aim of this study was to investigate urinary biomarkers of ADPKD progression.

Methods

This observational study included ADPKD patients, and two comparator groups of ischaemic and non-ischaemic kidney injury: benign nephroangiosclerosis patients and non-ischaemic chronic kidney disease (CKD) patients. Proteinuria, htTKV and urinary levels of molecules are associated with ischaemia and/or tubular injury. The slope of estimated glomerular filtration rate (eGFR) was used as a dependent variable in univariate and multivariate models of kidney function decline.

Results

The study included 130 patients with ADPKD, 55 with nephroangiosclerosis and 40 with non-ischaemic CKD. All patients had increased urinary concentrations of biomarkers associated with tubular lesions (liver fatty acid-binding protein, kidney injury molecule-1, β2-microglobulin) and molecules overexpressed under ischaemic conditions [hypoxia-inducible factor-1α, vascular endothelial growth factor (VEGF) and monocyte chemoattractant protein-1 (MCP-1)]. These biomarkers correlated positively with htTKV and negatively with the eGFR slope. htTKV was the single best predictor of the eGFR slope variability in univariate analyses. However, a multivariate model including urinary levels of β2-microglobulin, MCP-1 and VEGF improved the capacity to predict the decline of eGFR in ADPKD patients compared with htTKV alone.

Conclusions

The urinary levels of molecules associated with either renal ischaemia (VEGF and MCP-1) or tubular damage (β2-microglobulin) are associated with renal function deterioration in ADPKD patients, and are, therefore, candidates as biomarkers of ADPKD progression.

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.

RNA helicase p68 inhibits the transcription and post-transcription of Pkd1 in ADPKD

Background: Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations of the PKD1 and PKD2 genes. Dysregulation of the expression of PKD genes, the abnormal activation of PKD associated signaling pathways, and the expression and maturation of miRNAs regulates cyst progression. However, the upstream factors regulating these abnormal processes in ADPKD remain elusive.

Methods: To investigate the roles of an RNA helicase, p68, in ADPKD, we performed Western blot and qRT-PCR analysis, immunostaining and ChIP assay in cystic renal epithelium cells and tissues.

Results: We found that p68 was upregulated in cystic renal epithelial cells and tissues. p68 represses Pkd1 gene expression via transcriptional and posttranscriptional mechanisms in renal epithelial cells, in that 1) p68 binds to the promoter of the Pkd1 gene together with p53 to repress transcription; and 2) p68 promotes the expression and maturation of miR-17, miR-200c and miR-182 and via these miRNAs, post-transcriptionally regulates the expression of Pkd1 mRNA. Drosha is involved in this process by forming a complex with p68. p68 also regulates the phosphorylation and activation of PKD proliferation associated signaling and the expression of fibrotic markers in Pkd1 mutant renal epithelial cells. Silence of p68 delays cyst formation in collecting duct cell mediated 3D cultures. In addition, the expression of p68 is induced by H₂O₂-dependent oxidative stress and DNA damage which causes downregulation of Pkd1 transcription in cystic renal epithelial cells and tissues.

Conclusions: p68 plays a critical role in negatively regulating the expression of the PKD1 gene along with positively regulating the expression and maturation of miRNAs and activation of PKD associated signaling pathways to cause renal cyst progression and fibrosis in ADPKD.

Suspected Pulmonary Embolism Postcesarean Section in a Patient with Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common genetically inherited kidney disease worldwide. It is however relatively underdiagnosed in Africans because its diagnosis is often incidental. During pregnancy, ADPKD is associated with increased risk of preeclampsia and venous thromboembolism. The case of a 33-year-old lady incidentally diagnosed with ADPKD during pregnancy is presented. She developed preeclampsia at term and had cesarean delivery of twins. She however suffered cardiopulmonary arrest postoperatively and this created a treatment dilemma because therapeutic anticoagulation which was the primary treatment for her suspected pulmonary embolism was absolutely contraindicated if the actual cause of her collapse was ruptured cerebral aneurysm which was also a feature of ADPKD. We decided to resuscitate aggressively and perform an urgent cranial computed tomography which ruled out intracranial hemorrhage. We then commenced anticoagulation and she made an excellent recovery. This case illustrates the importance of a timely multidisciplinary approach to patient management.

Epithelial Vasopressin Type-2 Receptors Regulate Myofibroblasts by a YAP-CCN2-Dependent Mechanism in Polycystic Kidney Disease

BACKGROUND

Fibrosis is a major cause of loss of renal function in autosomal dominant polycystic kidney disease (ADPKD). In this study, we examined whether vasopressin type-2 receptor (V2R) activity in cystic epithelial cells can stimulate interstitial myofibroblasts and fibrosis in ADPKD kidneys.

METHODS

We treated Pkd1 gene knockout (Pkd1KO) mice with dDAVP, a V2R agonist, for 3 days and evaluated the effect on myofibroblast deposition of extracellular matrix (ECM). We also analyzed the effects of conditioned media from primary cultures of human ADPKD cystic epithelial cells on myofibroblast activation. Because secretion of the profibrotic connective tissue growth factor (CCN2) increased significantly in dDAVP-treated Pkd1KO mouse kidneys, we examined its role in V2R-dependent fibrosis in ADPKD as well as that of yes-associated protein (YAP).

RESULTS

V2R stimulation using dDAVP increased the renal interstitial myofibroblast population and ECM deposition. Similarly, conditioned media from human ADPKD cystic epithelial cells increased myofibroblast activation in vitro, suggesting a paracrine mechanism. Renal collecting duct-specific gene deletion of CCN2 significantly reduced cyst growth and myofibroblasts in Pkd1KO mouse kidneys. We found that YAP regulates CCN2, and YAP inhibition or gene deletion reduces renal fibrosis in Pkd1KO mouse kidneys. Importantly, YAP inactivation blocks the dDAVP-induced increase in myofibroblasts in Pkd1KO kidneys. Further in vitro studies showed that V2R regulates YAP by an ERK1/2-dependent mechanism in human ADPKD cystic epithelial cells.

CONCLUSIONS

Our results demonstrate a novel mechanism by which cystic epithelial cells stimulate myofibroblasts in the pericystic microenvironment, leading to fibrosis in ADPKD. The V2R-YAP-CCN2 cell signaling pathway may present a potential therapeutic target for fibrosis in ADPKD.

Extracellular matrix, integrins, and focal adhesion signaling in polycystic kidney disease

In autosomal dominant polycystic kidney disease (ADPKD), the inexorable growth of numerous fluid-filled cysts leads to massively enlarged kidneys, renal interstitial damage, inflammation, and fibrosis, and progressive decline in kidney function. It has long been recognized that interstitial fibrosis is the most important manifestation associated with end-stage renal disease; however, the role of abnormal extracellular matrix (ECM) production on ADPKD pathogenesis is not fully understood. Early evidence showed that cysts in end-stage human ADPKD kidneys had thickened and extensively laminated cellular basement membranes, and abnormal regulation of gene expression of several basement membrane components, including collagens, laminins, and proteoglycans by cyst epithelial cells. These basement membrane changes were also observed in dilated tubules and small cysts of early ADPKD kidneys, indicating that ECM alterations were early features of cyst development. Renal cystic cells were also found to overexpress several integrins and their ligands, including ECM structural components and soluble matricellular proteins. ECM ligands binding to integrins stimulate focal adhesion formation and can promote cell attachment and migration. Abnormal expression of laminin-332 (laminin-5) and its receptor α₆β₄ stimulated cyst epithelial cell proliferation; and mice that lacked laminin α₅, a component of laminin-511 normally expressed by renal tubules, had an overexpression of laminin-332 that was associated with renal cyst formation. Periostin, a matricellular protein that binds α_Vβ₃- and α_Vβ₅-integrins, was found to be highly overexpressed in the kidneys of ADPKD and autosomal recessive PKD patients, and several rodent models of PKD. α_Vβ₃-integrin is also overexpressed by cystic epithelial cells, and the binding of periostin to α_Vβ₃-integrin activates the integrin-linked kinase and downstream signal transduction pathways involved in tissue repair promoting cyst growth, ECM synthesis, and tissue fibrosis. This chapter reviews the roles of the ECM, integrins, and focal adhesion signaling in cyst growth and fibrosis in PKD.

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.

Regulation of the Extracellular Matrix by Ciliary Machinery

The primary cilium is an organelle involved in cellular signalling. Mutations affecting proteins involved in cilia assembly or function result in diseases known as ciliopathies, which cause a wide variety of phenotypes across multiple tissues. These mutations disrupt various cellular processes, including regulation of the extracellular matrix. The matrix is important for maintaining tissue homeostasis through influencing cell behaviour and providing structural support; therefore, the matrix changes observed in ciliopathies have been implicated in the pathogenesis of these diseases. Whilst many studies have associated the cilium with processes that regulate the matrix, exactly how these matrix changes arise is not well characterised. This review aims to bring together the direct and indirect evidence for ciliary regulation of matrix, in order to summarise the possible mechanisms by which the ciliary machinery could regulate the composition, secretion, remodelling and organisation of the matrix.

Plasma copeptin as a predictor of kidney disease

Background

Plasma copeptin, a marker of vasopressin, is associated with renal function decline in the general population. Our aim was to study the links between elevated copeptin and future risk of kidney disease.

Methods

Copeptin was measured in a sample of the Malmö Preventive Project (MPP) Reinvestigation (n = 5158) and in the Malmö Diet and Cancer Cardiovascular Cohort (MDC-CC) (n = 5162). According to national registers, 89 subjects in MPP and 180 in MDC-CC developed chronic kidney disease (CKD) during follow-up (8.7 and 19.6 years, respectively).

Results

After multivariate adjustment (gender, age, body mass index, smoking status, estimated glomerular filtration rate, prevalent diabetes, systolic blood pressure and prevalent antihypertensive treatment), copeptin (beta-coefficient per 1 standard deviation increment of ln copeptin) was independently associated with increased risk of CKD during follow-up in both cohorts (MPP: (HR) 1.46, 95% confidence interval (CI) 1.18–1.80, P < 0.001; MDC-CC: HR 1.25, 95% CI 1.02–1.54, P = 0.03) among subjects free from prevalent kidney disease at baseline. Furthermore, in MPP, elevated copeptin predicted a specified diagnosis of kidney disease other than CKD (HR 1.31, 95% CI 1.08–1.59, P = 0.006) after multivariate adjustment. In a corresponding analysis in MDC-CC, copeptin was associated with a 10% increased risk, which, however, was non-significant (P = 0.25). A meta-analysis of the MPP and MDC-CC data showed significant association between elevated copeptin and a specified diagnosis of kidney disease other than CKD (HR 1.18, 95% CI 1.05–1.34, P = 0.008).

Conclusion

An increased level of copeptin independently predicts development of both CKD and other specified kidney diseases, suggesting that copeptin can be used to identify individuals at risk for kidney disease development.

Ketosis Ameliorates Renal Cyst Growth in Polycystic Kidney Disease

Mild reduction in food intake was recently shown to slow polycystic kidney disease (PKD) progression in mouse models, but whether the effect was due to solely reduced calories or some other aspect of the diet has been unclear. We now show that the benefit is due to the induction of ketosis. Time-restricted feeding, without caloric reduction, strongly inhibits mTOR signaling, proliferation, and fibrosis in the affected kidneys in a PKD rat model. A ketogenic diet had a similar effect and led to regression of renal cystic burden. Acute fasting in rat, mouse, and feline models of PKD results in rapid reduction of cyst volume, while oral administration of the ketone β-hydroxybutyrate (BHB) in rats strongly inhibits PKD progression. These results suggest that cystic cells in PKD are metabolically inflexible, which could be exploited by dietary interventions or supplementation with BHB, representing a new therapeutic avenue to treat PKD.

Polycystic Kidney Disease and Renal Fibrosis

Polycystic kidney disease (PKD) is a common genetic disorder characterized by formations of numerous cysts in kidneys and most caused by PKD1 or PKD2 mutations in autosomal dominant polycystic kidney disease (ADPKD). The interstitial inflammation and fibrosis is one of the major pathological changes in polycystic kidney tissues with an accumulation of inflammatory cells, chemokines, and cytokines. The immune response is observed across different stages and occurs prior to or coincident with cyst formation in ADPKD. Evidence for inflammation as an important contributor to cyst growth and fibrosis includes increased interstitial macrophages, upregulated expressions of pro-inflammatory cytokines, activated complement system, and activated pathways including NF-κB and JAK-STAT signaling in polycystic kidney tissues. Inflammatory cells are responsible for overproduction of several pro-fibrotic growth factors which promote renal fibrosis in ADPKD. These growth factors trigger epithelial mesenchymal transition and myofibroblast/fibrocyte activation, which stimulate the expansion of extracellular matrix (ECM) including collagen I, III, IV, V, and fibronectin, leading to renal fibrosis and reduced renal function. Besides, there are imbalanced ECM turnover regulators which lead to the increased ECM production and inadequate degradation in polycystic kidney tissues. Several fibrosis associated signaling pathways, such as TGFβ-SMAD, Wnt, and periostin-integrin-linked kinase are also activated in polycystic kidney tissues. Although the effective anti-fibrotic treatments are limited at the present time, slowing the cyst expansion and fibrosis development is very important for prolonging life span and improving the palliative care of ADPKD patients. The inhibition of pro-fibrotic cytokines involved in fibrosis might be a new therapeutic strategy for ADPKD in the future.

Angiotensinogen and interleukin 18 in serum and urine of children with kidney cysts

BACKGROUND

The most common disease associated with the presence of kidney cysts in the population is autosomal dominant polycystic kidney disease (ADPKD), which finally leads to end-stage renal disease.

METHOD

The study evaluated serum and urinary concentration of angiotensinogen (AGT) and interleukin 18 (IL-18) in a group of 39 children with renal cysts of different aetiology.

RESULTS

Serum and urinary AGT concentration in children with renal cysts was higher compared to controls, regardless of the underlying background and gender. Serum IL-18 concentration was lower, in contrast, and the concentration of IL-18 in the urine did not differ between affected and healthy children. Negative correlation between urinary IL-18 concentration and systolic and mean arterial blood pressure was noted.

CONCLUSIONS

Higher AGT levels in serum and urine in children with renal cysts may indicate the activation of the renin-angiotensin-aldosterone system, including its intrarenal part, even before the onset of hypertension. Lower serum concentration of IL-18 in children with kidney cysts may indicate the loss of the protective role of this cytokine with the occurrence of hypertension.

Four-jointed knock-out delays renal failure in an ADPKD model with kidney injury

Autosomal Dominant Polycystic Kidney Disease is characterised by the development of fluid‐filled cysts in the kidneys which lead to end‐stage renal disease (ESRD). In the majority of cases, the disease is caused by a mutation in the Pkd1 gene. In a previous study, we demonstrated that renal injury can accelerate cyst formation in Pkd1 knock‐out (KO) mice. In that study, we found that after injury four‐jointed (Fjx1), an upstream regulator of planar cell polarity and the Hippo pathway, was aberrantly expressed in Pkd1 KO mice compared to WT. Therefore, we hypothesised a role for Fjx1 in injury/repair and cyst formation. We generated single and double deletion mice for Pkd1 and Fjx1, and we induced toxic renal injury using the nephrotoxic compound 1,2‐dichlorovinyl‐cysteine. We confirmed that nephrotoxic injury can accelerate cyst formation in Pkd1 mutant mice. This caused Pkd1 KO mice to reach ESRD significantly faster; unexpectedly, double KO mice survived significantly longer. Cyst formation was comparable in both models, but we found significantly less fibrosis and macrophage infiltration in double KO mice. Taken together, these data suggest that Fjx1 disruption protects the cystic kidneys against kidney failure by reducing inflammation and fibrosis. Moreover, we describe, for the first time, an interesting (yet unidentified) mechanism that partially discriminates cyst growth from fibrogenesis. © 2019 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Connective Tissue Growth Factor Is Related to All-cause Mortality in Hemodialysis Patients and Is Lowered by On-line Hemodiafiltration: Results from the Convective Transport Study

Connective tissue growth factor (CTGF) plays a key role in the pathogenesis of tissue fibrosis. The aminoterminal fragment of CTGF is a middle molecule that accumulates in chronic kidney disease. The aims of this study are to explore determinants of plasma CTGF in hemodialysis (HD) patients, investigate whether CTGF relates to all-cause mortality in HD patients, and investigate whether online-hemodiafiltration (HDF) lowers CTGF. Data from 404 patients participating in the CONvective TRAnsport STudy (CONTRAST) were analyzed. Patients were randomized to low-flux HD or HDF. Pre-dialysis CTGF was measured by sandwich ELISA at baseline, after six and 12 months. CTGF was inversely related in multivariable analysis to glomerular filtration rate (GFR) (p < 0.001) and positively to cardiovascular disease (CVD) (p = 0.006), dialysis vintage (p < 0.001), interleukin-6 (p < 0.001), beta-2-microglobulin (p = 0.045), polycystic kidney disease (p < 0.001), tubulointerstitial nephritis (p = 0.002), and renal vascular disease (p = 0.041). Patients in the highest quartile had a higher mortality risk compared to those in the lowest quartile (HR 1.7, 95% CI: 1.02-2.88, p = 0.043). HDF lowered CTGF with 4.8% between baseline and six months, whereas during HD, CTGF increased with 4.9% (p < 0.001). In conclusion, in HD patients, CTGF is related to GFR, CVD and underlying renal disease and increased the risk of all-cause mortality. HDF reduces CTGF.

Determinants of Progression in Early Autosomal Dominant Polycystic Kidney Disease: Is it Blood Pressure or Renin-Angiotensin-Aldosterone-System Blockade?

Background

The HALT PKD trial in early autosomal dominant polycystic kidney disease (ADPKD) showed that intensive control of systolic blood pressure to 95-110 mmHg was associated with a 14% slower rate of kidney volume growth compared to standard control. It is unclear whether this result was due to greater blockade of the renin-angiotensin-aldosterone system (RAAS) by allowing the use of higher drug doses in the low blood pressure arm, or due to the lower blood pressure per se.

Methods

In this secondary analysis of HALT PKD Study A, we categorized participants into high and low dose groups based on the median daily equivalent dose of RAAS blocking drugs used after the initial dose titration period. Using linear mixed models, we compared the percent change in total kidney volume and the slope of estimated glomerular filtration rate (eGFR) between the 2 groups. We also assessed the effects of time-varying dose and time-varying blood pressure parameters on these outcomes.

Results

Subjects in the high dose group (n=252) did not experience a slower increase in total kidney volume than those in the low-dose (n=225) group, after adjustment for age, sex, genotype, and BP arm. The chronic slope of eGFR decline was similar in the 2 groups. Higher time-varying systolic blood pressure was associated with a steeper decline in eGFR.

Conclusion

ADPKD progression (as detected by eGFR decline and TKV increase) was ameliorated by intense blood pressure control as opposed to pharmacologic intensity of RAAS blockade.

Effect of Statin Therapy on the Progression of Autosomal Dominant Polycystic Kidney Disease. A Secondary Analysis of the HALT PKD Trials

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) commonly results in end-stage renal disease (ESRD), yet a long-term treatment that is well tolerated is still lacking. In a small randomized trial in children and adolescents pravastatin administration for 3 years was associated with reduced renal cyst growth, but no large trial has tested the effect of statins in adults.

METHODS

We performed a post-hoc analysis of the HALT PKD trials to compare outcomes of participants who never used statins with those who used statin for at least 3 years. Because statins were not randomly allocated, we used propensity score models with inverse probability of treatment weighting to account for imbalances between the groups. For subjects in Study A (preserved renal function, n=438) relevant outcomes were percent change in total kidney and liver volume and the rate of decline in estimated glomerular filtration rate (eGFR); for those in Study B (reduced renal function, n=352) we compared time to the composite endpoint of death, ESRD or 50% decline in eGFR. Follow-up was 5-8 years.

RESULTS

There was no difference in any outcome between the 2 groups. However, limitations of this analysis are the small number of statin users in Study A, different statin drugs and doses used, non-randomized allocation and advanced disease stage in Study B.

CONCLUSION

Although this post-hoc analysis of the HALT PKD trials does not demonstrate a benefit of statin therapy, conclusions remain preliminary. A larger randomized trial in young people with ADPKD is necessary to answer the question whether statins can slow renal cyst growth and preserve kidney function.

Urinary proteome signature of Renal Cysts and Diabetes syndrome in children

Renal Cysts and Diabetes Syndrome (RCAD) is an autosomal dominant disorder caused by mutations in the HNF1B gene encoding for the transcriptional factor hepatocyte nuclear factor-1B. RCAD is characterized as a multi-organ disease, with a broad spectrum of symptoms including kidney abnormalities (renal cysts, renal hypodysplasia, single kidney, horseshoe kidneys, hydronephrosis), early-onset diabetes mellitus, abnormal liver function, pancreatic hypoplasia and genital tract malformations. In the present study, using capillary electrophoresis coupled to mass spectrometry (CE-MS), we investigated the urinary proteome of a pediatric cohort of RCAD patients and different controls to identify peptide biomarkers and obtain further insights into the pathophysiology of this disorder. As a result, 146 peptides were found to be associated with RCAD in 22 pediatric patients when compared to 22 healthy age-matched controls. A classifier based on these peptides was generated and further tested on an independent cohort, clearly discriminating RCAD patients from different groups of controls. This study demonstrates that the urinary proteome of pediatric RCAD patients differs from autosomal dominant polycystic kidney disease (PKD1, PKD2), congenital nephrotic syndrome (NPHS1, NPHS2, NPHS4, NPHS9) as well as from chronic kidney disease conditions, suggesting differences between the pathophysiology behind these disorders.

Periostin in the Kidney

Periostin is a matricellular protein that is expressed in several tissues during embryonic development; however, its expression in adults is mostly restricted to collagen-rich connective tissues. Periostin is expressed only briefly during kidney development, but it is not normally detected in the adult kidney. Recent evidence has revealed that periostin is aberrantly expressed in several forms of chronic kidney disease (CKD), and that its expression correlates with the degree of interstitial fibrosis and the decline in renal function. Polycystic kidney disease (PKD), a genetic disorder, is characterized by the formation of numerous fluid-filled cysts in the kidneys. Periostin is secreted by the cyst epithelial cells and accumulates within the extracellular matrix adjacent to the cysts. In PKD mice, periostin overexpression accelerates cyst growth and contributes to structural changes in the kidneys, including interstitial fibrosis. Recent evidence suggests that periostin is a tissue repair molecule; however, its role in repair following acute kidney injury has not been investigated. It is thought that persistent expression of this protein in CKD contributes importantly to tubulointerstitial fibrosis and the progressive decline in renal function. Future studies to define the diverse actions of periostin during kidney injury may lead to effective therapies to slow PKD progression and possibly prevent the development of CKD. This chapter reviews the current literature on the expression of periostin in PKD and other forms of CKD, mechanisms for periostin stimulated cyst growth, its potential role in extracellular matrix production and renal fibrosis, and the evidence for periostin as a novel biomarker for kidney disease.

Prevalence of polycystic kidney disease in Persian and Persian related-cats referred to Small Animal Hospital, University of Tehran, Iran

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the most prevalent inherited genetic disease of cats, predominantly affecting Persians and Persian-related cats.

AIMS

The purpose of this study was to determine prevalence of polycystic kidney disease (PKD) in Persian cats in Iran, and also to assess the relationships between PKD and gender, age as well as clinical and paracilinical manifestations.

METHODS

Sonographic screening examination was performed on all healthy and unhealthy Persian and Persian-related cats referred to Small Animal Hospital of Faculty of Veterinary Medicine, University of Tehran, from April 2014 to May 2015. Cats were classified as positive when at least one anechoic cavity was found in at least one kidney.

RESULTS

Of 76 Persian and Persian-related cats submitted for PKD ultrasound screening, 36.8% were found to have the disease and 63.2% were negative. Therefore, the prevalence of PKD was estimated 36.8% in Persian and Persian related cats in Tehran, Iran, which is approximately similar to prevalence in other parts of the world. Furthermore, there was a significant correlation between PKD and age, as in affected cats the detection probability of renal cysts in sonography was increased in older animals. For each year increase in age, the detection probability of PKD in sonography was increased about 2.62 times.

CONCLUSION

The prevalence of the PKD amongst Persian cats in Iran is relatively high, and insufficient attention to incidence and prevalence of PKD especially in breeding programs, would spread the disease throughout in Persian cats.

Morphology and Evaluation of Renal Fibrosis

With continuing damage, both the indigenous cells of the cortex and medulla, and inflammatory cells are involved in the formation and development of renal fibrosis. Furthermore, interactions among the glomerular, tubular, and interstitial cells contribute to the process by excessive synthesis and decreased degradation of extracellular matrix. The morphology of kidney is different from pathological stages of diseases and changes with various causes. At the end stage of the disease, the kidneys are symmetrically contracted with diffuse granules. Most glomeruli show diffuse fibrosis and hyaline degeneration, and intervening tubules become atrophied. Renal interstitium shows obvious hyperplasia of fibrous tissues with marked infiltration of lymphocytes, mononuclear cells, and plasma cells. The renal arterioles are wall thickening frequently because of hyaline degeneration. Morphologic analysis based on Masson staining of the kidney tissues has been regarded as the golden standard to evaluate the visual fibrosis. However, the present studies have found that the evaluation system has poor repeatability. Several computer-aided image analysis techniques have been used to assess interstitial fibrosis. It is possible that the evaluation of renal fibrosis is carried out by the artificial intelligence renal biopsy pathological diagnosis system in the near future.