Rosiglitazone attenuates development of polycystic kidney disease and prolongs survival in Han:SPRD rats

Renal ciliopathies: promising drug targets and prospects for clinical trials

INTRODUCTION

Renal ciliopathies represent a collection of genetic disorders characterized by deficiencies in the biogenesis, maintenance, or functioning of the ciliary complex. These disorders, which encompass autosomal dominant polycystic kidney disease (ADPKD), autosomal recessive polycystic kidney disease (ARPKD), and nephronophthisis (NPHP), typically result in cystic kidney disease, renal fibrosis, and a gradual deterioration of kidney function, culminating in kidney failure.

AREAS COVERED

Here we review the advances in basic science and clinical research into renal ciliopathies which have yielded promising small compounds and drug targets, within both preclinical studies and clinical trials.

EXPERT OPINION

Tolvaptan is currently the sole approved treatment option available for ADPKD patients, while no approved treatment alternatives exist for ARPKD or NPHP patients. Clinical trials are presently underway to evaluate additional medications in ADPKD and ARPKD patients. Based on preclinical models, other potential therapeutic targets for ADPKD, ARPKD, and NPHP look promising. These include molecules targeting fluid transport, cellular metabolism, ciliary signaling and cell-cycle regulation. There is a real and urgent clinical need for translational research to bring novel treatments to clinical use for all forms of renal ciliopathies to reduce kidney disease progression and prevent kidney failure.

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.

Metabolic Reprogramming and Reconstruction: Integration of Experimental and Computational Studies to Set the Path Forward in ADPKD

Metabolic reprogramming is a key feature of Autosomal Dominant Polycystic Kidney Disease (ADPKD) characterized by changes in cellular pathways occurring in response to the pathological cell conditions. In ADPKD, a broad range of dysregulated pathways have been found. The studies supporting alterations in cell metabolism have shown that the metabolic preference for abnormal cystic growth is to utilize aerobic glycolysis, increasing glutamine uptake and reducing oxidative phosphorylation, consequently resulting in ADPKD cells shifting their energy to alternative energetic pathways. The mechanism behind the role of the polycystin proteins and how it leads to disease remains unclear, despite the identification of numerous signaling pathways. The integration of computational data analysis that accompanies experimental findings was pivotal in the identification of metabolic reprogramming in ADPKD. Here, we summarize the important results and argue that their exploitation may give further insights into the regulative mechanisms driving metabolic reprogramming in ADPKD. The aim of this review is to provide a comprehensive overview on metabolic focused studies and potential targets for treatment, and to propose that computational approaches could be instrumental in advancing this field of research.

Rosiglitasone and ROCK Inhibitors Modulate Fibrogenetic Changes in TGF-β2 Treated Human Conjunctival Fibroblasts (HconF) in Different Manners

Purpose: The effects of Rho-associated coiled-coil containing protein kinase (ROCK) 1 and 2 inhibitor, ripasudil hydrochloride hydrate (Rip), ROCK2 inhibitor, KD025 or rosiglitazone (Rosi) on two-dimension (2D) and three-dimension (3D) cultured human conjunctival fibroblasts (HconF) treated by transforming growth factor (TGFβ2) were studied. Methods: Two-dimension and three-dimension cultured HconF were examined by transendothelial electrical resistance (TEER, 2D), size and stiffness (3D), and the expression of the extracellular matrix (ECM) including collagen1 (COL1), COL4 and COL6, fibronectin (FN), and α-smooth muscle actin (αSMA) by quantitative PCR (2D, 3D) in the presence of Rip, KD025 or Rosi. Results: TGFβ2 caused a significant increase in (1) the TEER values (2D) which were greatly reduced by Rosi, (2) the stiffness of the 3D organoids which were substantially reduced by Rip or KD025, and (3) TGFβ2 induced a significant up-regulation of all ECMs, except for COL6 (2D) or αSMA (3D), and down-regulation of COL6 (2D). Rosi caused a significant up-regulation of COL1, 4 and 6 (3D), and down-regulation of COL6 (2D) and αSMA (3D). Most of these TGFβ2-induced expressions in the 2D and αSMA in the 3D were substantially inhibited by KD025, but COL4 and αSMA in 2D were further enhanced by Rip. Conclusion: The findings reported herein indicate that TGFβ2 induces an increase in fibrogenetic changes on the plane and in the spatial space, and are inhibited by Rosi and ROCK inhibitors, respectively.

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.

Molecular Pathophysiology of Autosomal Recessive Polycystic Kidney Disease

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

Drug repurposing in autosomal dominant polycystic kidney disease: back to the future with pioglitazone

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of end-stage kidney failure. At present, only one drug, tolvaptan, has been approved for use to slow disease progression, but its use is limited by reduced tolerability and idiosyncratic liver toxicity. Thiazolidinediones were first developed as insulin-sensitizers but also regulate gene transcription in multiple tissues, leading to systemic effects on metabolism, inflammation and vascular reactivity. In this issue, Blazer-Yost et al. report the results of a single-centre Phase 1b double-blind placebo-controlled crossover study of the peroxisome proliferator-activated receptor γ (PPAR-γ) agonist pioglitazone in 18 ADPKD patients. Encouragingly, there were no major safety signals, although evidence of efficacy could not be demonstrated due to the small sample size. We review the preclinical evidence for the use of PPAR-γ agonists in ADPKD and speculate on the likely beneficial and adverse clinical effects of this interesting class of compounds in a future trial.

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.

Metabolic Reprogramming in Autosomal Dominant Polycystic Kidney Disease: Evidence and Therapeutic Potential

Autosomal dominant polycystic kidney disease is characterized by progressive development and enlargement of kidney cysts, leading to ESKD. Because the kidneys are under high metabolic demand, it is not surprising that mounting evidence suggests that a metabolic defect exists in in vitro and animal models of autosomal dominant polycystic kidney disease, which likely contributes to cystic epithelial proliferation and subsequent cyst growth. Alterations include defective glucose metabolism (reprogramming to favor aerobic glycolysis), dysregulated lipid and amino acid metabolism, impaired autophagy, and mitochondrial dysfunction. Limited evidence supports that cellular kidney metabolism is also dysregulated in humans with autosomal dominant polycystic kidney disease. There are notable overlapping features and pathways among metabolism, obesity, and/or autosomal dominant polycystic kidney disease. Both dietary and pharmacologic-based strategies targeting metabolic abnormalities are being considered as therapies to slow autosomal dominant polycystic kidney disease progression and are attractive, particularly given the slowly progressive nature of the disease. Dietary strategies include daily caloric restriction, intermittent fasting, time-restricted feeding, a ketogenic diet, and 2-deoxy-glucose as well as alterations to nutrient availability. Pharmacologic-based strategies include AMP-activated kinase activators, sodium glucose cotransporter-2 inhibitors, niacinamide, and thiazolidenediones. The results from initial clinical trials targeting metabolism are upcoming and anxiously awaited within the scientific and polycystic kidney disease communities. There continues to be a need for additional mechanistic studies to better understand the role of dysregulated metabolism in autosomal dominant polycystic kidney disease and for subsequent translation to clinical trials. Beyond single-intervention trials focused on metabolic reprograming in autosomal dominant polycystic kidney disease, great potential also exists by combining metabolic-focused therapeutic approaches with compounds targeting other signaling cascades altered in autosomal dominant polycystic kidney disease, such as tolvaptan.

Prioritization of novel ADPKD drug candidates from disease-stage specific gene expression profiles

Background

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is one of the most common causes of end-stage renal failure, caused by mutations in PKD1 or PKD2 genes. Tolvaptan, the only drug approved for ADPKD treatment, results in serious side-effects, warranting the need for novel drugs.

Methods

In this study, we applied RNA-sequencing of Pkd1cko mice at different disease stages, and with/without drug treatment to identify genes involved in ADPKD progression that were further used to identify novel drug candidates for ADPKD. We followed an integrative computational approach using a combination of gene expression profiling, bioinformatics and cheminformatics data.

Findings

We identified 1162 genes that had a normalized expression after treating the mice with drugs proven effective in preclinical models. Intersecting these genes with target affinity profiles for clinically-approved drugs in ChEMBL, resulted in the identification of 116 drugs targeting 29 proteins, of which several are previously linked to Polycystic Kidney Disease such as Rosiglitazone. Further testing the efficacy of six candidate drugs for inhibition of cyst swelling using a human 3D-cyst assay, revealed that three of the six had cyst-growth reducing effects with limited toxicity.

Interpretation

Our data further establishes drug repurposing as a robust drug discovery method, with three promising drug candidates identified for ADPKD treatment (Meclofenamic Acid, Gamolenic Acid and Birinapant). Our strategy that combines multiple-omics data, can be extended for ADPKD and other diseases in the future.

Funding

European Union's Seventh Framework Program, Dutch Technology Foundation Stichting Technische Wetenschappen and the Dutch Kidney Foundation.

ADPKD current management and ongoing trials

Among the diseases that require renal replacement therapy (RRT), ADPKD is the fourth for incidence and prevalence. In Italy, there are at least 32,000 patients affected by ADPKD, of which about 2900 in dialysis. The pure costs of dialysis treatment for the Italian National Health Service can be conservatively estimated at 87 million euros per year. Even a modest slowdown in the evolution of the disease would obtain an important result in terms of reduction of health expenditure. In recent years, many new or repurposed drugs have been evaluated in clinical trials for ADPKD. In this review we will mainly focus on advanced stage clinical trials (phase 2 and 3). We have grouped these studies according to the molecular pathway addressed by the experimental drug or the therapeutic strategy. More than 10 years after the start of the first Phase III clinical trials in ADPKD, the first drug active in slowing disease progression is finally available. It cannot be considered a goal but only the beginning of a journey because of the significant side effects and the high cost of Tolvaptan. An exuberant basic research activity in the field, together with the large number of ongoing protocols, keep the nephrologists and their patients positive with regard to the discovery of new and better therapies in a not-too-distant future.

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.

Metabolism and mitochondria in polycystic kidney disease research and therapy

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common, potentially lethal, monogenic diseases and is caused predominantly by mutations in polycystic kidney disease 1 (PKD1) and PKD2, which encode polycystin 1 (PC1) and PC2, respectively. Over the decades-long course of the disease, patients develop large fluid-filled renal cysts that impair kidney function, leading to end-stage renal disease in ~50% of patients. Despite the identification of numerous dysregulated pathways in ADPKD, the molecular mechanisms underlying the renal dysfunction from mutations in PKD genes and the physiological functions of the polycystin proteins are still unclear. Alterations in cell metabolism have emerged in the past decade as a hallmark of ADPKD. ADPKD cells shift their mode of energy production from oxidative phosphorylation to alternative pathways, such as glycolysis. In addition, the polycystins seem to play regulatory roles in modulating mechanisms and machinery related to energy production and utilization, including AMPK, PPARα, PGC1α, calcium signalling at mitochondria-associated membranes, mTORC1, cAMP and CFTR-mediated ion transport as well as the expression of crucial components of the mitochondrial energy production apparatus. In this Review, we explore these metabolic changes and discuss in detail the relationship between energy metabolism and ADPKD pathogenesis and identify potential therapeutic targets.

Emerging targeted strategies for the treatment of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a widespread genetic disease that leads to renal failure in the majority of patients. The very first pharmacological treatment, tolvaptan, received Food and Drug Administration approval in 2018 after previous approval in Europe and other countries. However, tolvaptan is moderately effective and may negatively impact a patient's quality of life due to potentially significant side effects. Additional and improved therapies are still urgently needed, and several clinical trials are underway, which are discussed in the companion paper Müller and Benzing (Management of autosomal-dominant polycystic kidney disease-state-of-the-art) Clin Kidney J 2018; 11: i2-i13. Here, we discuss new therapeutic avenues that are currently being investigated at the preclinical stage. We focus on mammalian target of rapamycin and dual kinase inhibitors, compounds that target inflammation and histone deacetylases, RNA-targeted therapeutic strategies, glucosylceramide synthase inhibitors, compounds that affect the metabolism of renal cysts and dietary restriction. We discuss tissue targeting to renal cysts of small molecules via the folate receptor, and of monoclonal antibodies via the polymeric immunoglobulin receptor. A general problem with potential pharmacological approaches is that the many molecular targets that have been implicated in ADPKD are all widely expressed and carry out important functions in many organs and tissues. Because ADPKD is a slowly progressing, chronic disease, it is likely that any therapy will have to continue over years and decades. Therefore, systemically distributed drugs are likely to lead to potentially prohibitive extra-renal side effects during extended treatment. Tissue targeting to renal cysts of such drugs is one potential way around this problem. The use of dietary, instead of pharmacological, interventions is another.

Concomitant use of rapamycin and rosiglitazone delays the progression of polycystic kidney disease in Han:SPRD rats: a study of the mechanism of action

Attributing to their antiproliferative effect, both rapamycin and peroxisome proliferator-activated receptor-γ (PPARγ) can halt the progression of autosomal dominant polycystic kidney disease (ADPKD). Whether combined use could enhance this effect is unknown. The present study used rapamycin and the PPARγ agonist rosiglitazone concomitantly to observe their combined effects on the proliferation of ADPKD cyst-lining epithelial cells and the progression of ADPKD in Han:SPRD rats. Concomitant use of the two drugs inhibited the proliferation of WT9-12 cells significantly through a superimposition effect. Rosiglitazone inhibited the phosphorylation of mammalian target of rapamycin p70S6K. Concomitant use of rosiglitazone and rapamycin further downregulated the p-p70S6K level. Rosiglitazone also inhibited the phosphorylation of Akt and antagonized the activation of Akt induced by rapamycin. Concomitant use of rosiglitazone and rapamycin significantly retarded the deterioration of renal function, decreased cyst cell proliferation and interstitial fibrosis in Han:SPRD rats. Rapamycin significantly increased cholesterol levels in the blood, whereas rosiglitazone mitigated rapamycin-induced hyperlipidemia. These results indicate that the effects of concomitant use of rosiglitazone and rapamycin in inhibiting the proliferation of WT9-12 cells and delaying the progression of ADPKD in Han:SPRD rats are stronger than those of either drug alone. The present study may provide a new strategy for the long-term treatment of ADPKD.

Peroxisome proliferator activating receptor-γ and the podocyte

Over the past two decades it has become clear that the glomerular podocyte is a key cell in preventing albuminuria, kidney failure and cardiovascular morbidity. Understanding the key pathways that protect the podocyte in times of glomerular stress, which can also be therapeutically manipulated, are highly attractive. In the following review we assess the evidence that the peroxisome proliferator activating receptor (PPAR) agonists are beneficial for podocyte and kidney function with a focus on PPAR-γ. We explain our current understanding of the mechanisms of action of these agonists and the evidence they are beneficial in diabetic and non-diabetic kidney disease. We also outline why these drugs have not been widely used for kidney disease in the past but they may be in the future.

Low density lipoprotein - rosiglitazone - chitosan-calcium alginate/nanoparticles inhibition of human tenon's fibroblasts activation and proliferation

Anti-fibrotic therapeutic methods with safety and efficiency after glaucoma filtration surgery (GFS) are desirable. In our previous study, by using Human Tenon's Fibroblasts (HTFs) as a model, we proved the expression of peroxisome proliferator activates receptor-γ (PPAR-γ) in HTFs; in addition, rosiglitazone (RSG), an agonist of PPAR-γ, can inhibit transforming growth factorsβ1 (TGF-β1)-induced reactivation of HTFs, thus to inhibit specifically scarring after GFS through intervening TGF-β/Smads signal pathway. However, a better drug delivery way of RSG, to prolong the duration of its function, and to reduce the toxicity of RSG to ocular tissue still remains challenges. Low density lipoprotein receptor (LDLr) is strongly expressed in hyper-proliferation HTFs after GFS. Therefore, we structured targeting LDL-RSG complexes and channel them into HTFs through LDL-LDLr pathway in order to promote anti-proliferation of HTFs and reduce the toxicity to ocular tissue. Meanwhile, in order to improve the release properties of LDL-RSG complexes, we structured slow release system of LDL-RSG/chitosan-calcium alginate - nanoparticles (CSNP), which effectively inhibited TGF-β1-induced HTFs proliferation, synthesis of extracellular matrix and activation of TGF-β1/SMAD pathway. These data suggested that LDL-RSG/CSNP can be a new anti-fibrotic therapeutic method on scarring after GFS and also a novelty administration of RSG.

microRNA-17 family promotes polycystic kidney disease progression through modulation of mitochondrial metabolism

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent genetic cause of renal failure. Here we identify miR-17 as a target for the treatment of ADPKD. We report that miR-17 is induced in kidney cysts of mouse and human ADPKD. Genetic deletion of the miR-17∼92 cluster inhibits cyst proliferation and PKD progression in four orthologous, including two long-lived, mouse models of ADPKD. Anti-miR-17 treatment attenuates cyst growth in short-term and long-term PKD mouse models. miR-17 inhibition also suppresses proliferation and cyst growth of primary ADPKD cysts cultures derived from multiple human donors. Mechanistically, c-Myc upregulates miR-17∼92 in cystic kidneys, which in turn aggravates cyst growth by inhibiting oxidative phosphorylation and stimulating proliferation through direct repression of Pparα. Thus, miR-17 family is a promising drug target for ADPKD, and miR-17-mediated inhibition of mitochondrial metabolism represents a potential new mechanism for ADPKD progression.

Autosomal dominant polycystic kidney disease (ADPKD) is a life-threatening genetic disease that leads to renal failure. Here Hajarnis et al. show that miR-17 modulates cyst progression in ADPKD through metabolic reprogramming of mitochondria and its inhibition slows cyst development and improves renal functions.

Inhibition of cyst growth in PCK and Wpk rat models of polycystic kidney disease with low doses of peroxisome proliferator-activated receptor γ agonists

BACKGROUND AND OBJECTIVES

The studies were designed to test the efficacy of two peroxisome proliferator-activated receptor γ (PPARγ) agonists in two rodent models of polycystic kidney disease (PKD).

MATERIALS AND METHODS

The PCK rat is a slowly progressing cystic model while the Wpk^-/- rat is a rapidly progressing model. PCK rats were fed with a pharmacological (0.4 mg/kg body weight [BW]) and a sub-pharmacological (0.04 mg/kg BW) dose of rosiglitazone (week 4-28). Wpk^-/- rats were fed with pharmacological (2.0 mg/kg BW) and sub-pharmacologic (0.2 mg/kg BW) doses of pioglitazone from day 5 to 18. At termination, kidney weights of treated versus untreated cystic animals were used to determine efficacy. The current studies were also compared with previous studies containing higher doses of PPARγ agonists. The concentrations used in the animals were calculated with reference to equivalent human doses for both drugs.

RESULTS

The current studies demonstrate: 1) that low, pharmacologically relevant, doses of the PPARγ agonists effectively inhibit cyst growth; 2) there is a class action of the drugs with both commercially available PPARγ agonists, rosiglitazone, and pioglitazone, inhibiting cyst growth; 3) the drugs showed efficacy in two different preclinical cystic models. In the PCK rat, animals fed with a sub-pharmacological dose of rosiglitazone for 24 weeks had significantly lower kidney weights than untreated animals (3.68 ± 0.13 g vs. 4.17 ± 0. 11 g, respectively, P < 0.01) while treatment with a pharmacologic dose had no significant effect on kidney weight. The rapidly progressing Wpk^-/- rats were fed with pharmacological and sub-pharmacologic doses of pioglitazone from day 5 to 18 and the kidneys were compared with non-treated, cystic animals. Kidney weights on the pharmacologic dose were not statistically lower than the untreated animals while rats fed a sub-pharmacologic dose showed a significant decrease compared with untreated animals (3.35 ± 0.15 g vs. 4.55 ± 0.46 g, respectively, P = 0.045).

CONCLUSION

Concentrations of PPARγ agonists below the human equivalent diabetic doses are effective in slowing cyst growth in two rodent models of PKD.

Rosiglitazone inhibits TGF-β 1 induced activation of human Tenon fibroblasts via p38 signal pathway

Purpose

Transdifferentiation of human Tenon fibroblasts to myofibroblasts and subsequent deposition of extracellular matrix is a key step in the scarring after glaucoma filtration surgery. The p38 signaling pathway plays an important role in cell proliferation and differentiation, and its upstream regulators and downstream molecules are widely distributed in the eye. We aimed to investigate the role of p38 in the activation of Tenon fibroblasts and that of the anti-fibrotic mechanism of rosiglitazone in the modulation of the p38 signaling pathway.

Methods

Cultured Tenon fibroblasts were stimulated with transforming growth factor (TGF)-β1. Activation of p38 was examined by western blot analysis. Rosiglitazone and blocking of the p38 signaling pathway by SB203580 were used to antagonize stimulation by TGF-β1. Fibroblast motility was examined by wound closure assay; alpha-smooth muscle actin, connective tissue growth factor, and collagen type I were determined by qPCR and western blot. Expression and localization of alpha-smooth muscle actin were determined by immunofluorescence staining.

Results

Phosphorylated p38 was upregulated in fibroblasts stimulated with TGF-β1, and this effect was substantially inhibited by rosiglitazone. Proliferation and migration of fibroblasts were suppressed by rosiglitazone and SB203580. Expression of alpha-smooth muscle actin, connective tissue growth factor, and collagen type I were decreased at the mRNA and protein levels by rosiglitazone and SB203580. However, the inhibitory effect of SB203580 on transcription and protein expression was weaker than that of rosiglitazone. Similar phenomena were found on immunofluorescence microscopy of alpha-smooth muscle actin.

Conclusions

The p38 signaling pathway mediates the TGF-β1-induced transdifferentiation of human Tenon fibroblasts to myofibroblasts. Rosiglitazone can exert anti-fibrotic activity by interfering with the TGF-β/p38 signaling pathway and might be useful for modulating scar formation after glaucoma filtration surgery.

New treatments for autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and results from mutations in PKD1 or PKD2. Cyst initiation and expansion arise from a combination of abnormal cell proliferation, fluid secretion and extracellular matrix defects and results in kidney enlargement and interstitial fibrosis. Since its first description over 200 years ago, ADPKD has been considered an untreatable condition and its management is limited to blood pressure reduction and symptomatic treatment of disease complications. Results of the recently reported TEMPO 3/4 trial thus represent a paradigm shift in demonstrating for the first time that cystic disease and loss of renal function can be slowed in humans. In this paper, we review the major therapeutic strategies currently being explored in ADPKD including a range of novel approaches in preclinical models. It is anticipated that the clinical management of ADPKD will undergo a revolution in the next decade with the translation of new treatments into routine clinical use.

Peroxisome proliferator-activated receptor agonists in a battle against the aging kidney

As aging is a complex phenomenon characterized by intraindividual and interindividual diversities in the maintenance of the homeostatic condition of cells and tissues, changes in renal function are not uniform and depend on associated diseases and environmental factors. Multiple studies have investigated the possible underlying mechanisms of age-related decline in kidney function. Evolutionary, molecular, cellular and systemic theories have been postulated to explain the primary disease independent age-related changes and adaptive responses. As peroxisome proliferator-activated receptors (PPARs) are involved in a broad spectrum of biological processes, PPAR activation might have an effect on the prevention of cell senescence. In this review, we will focus on the experimental and clinical evidence of PPAR agonists in a battle against the aging kidney.

Telmisartan ameliorates fibrocystic liver disease in an orthologous rat model of human autosomal recessive polycystic kidney disease

Human autosomal recessive polycystic kidney disease (ARPKD) produces kidneys which are massively enlarged due to multiple cysts, hypertension, and congenital hepatic fibrosis characterized by dilated bile ducts and portal hypertension. The PCK rat is an orthologous model of human ARPKD with numerous fluid-filled cysts caused by stimulated cellular proliferation in the renal tubules and hepatic bile duct epithelia, with interstitial fibrosis developed in the liver. We previously reported that a peroxisome proliferator activated receptor (PPAR)-γ full agonist ameliorated kidney and liver disease in PCK rats. Telmisartan is an angiotensin receptor blocker (ARB) used widely as an antihypertensive drug and shows partial PPAR-γ agonist activity. It also has nephroprotective activity in diabetes and renal injury and prevents the effects of drug-induced hepatotoxicity and hepatic fibrosis. In the present study, we determined whether telmisartan ameliorates progression of polycystic kidney and fibrocystic liver disease in PCK rats. Five male and 5 female PCK and normal control (+/+) rats were orally administered 3 mg/kg telmisartan or vehicle every day from 4 to 20 weeks of age. Treatment with telmisartan decreased blood pressure in both PCK and +/+ rats. Blood levels of aspartate amino transferase, alanine amino transferase and urea nitrogen were unaffected by telmisartan treatment. There was no effect on kidney disease progression, but liver weight relative to body weight, liver cystic area, hepatic fibrosis index, expression levels of Ki67 and TGF-β, and the number of Ki67- and TGF-β-positive interstitial cells in the liver were significantly decreased in telmisartan-treated PCK rats. Therefore, telmisartan ameliorates congenital hepatic fibrosis in ARPKD, possibly through the inhibition of signaling cascades responsible for cellular proliferation and interstitial fibrosis in PCK rats. The present results support the potential therapeutic use of ARBs for the treatment of fibrocystic liver disease in ARPKD patients.

Rosiglitazone inhibits insulin-like growth factor‑1-induced polycystic kidney disease cell growth and p70S6 kinase activation

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic kidney disorders. Thiazolidinediones (TZDs) are anti-diabetic drugs that have been shown to suppress polycystic kidney diseases (PKD) development. However, their underlying mechanism of action remains largely unknown. Insulin-like growth factor-1 (IGF-1) expression increases with the progression of cystic lesions in ADPKD and murine PKD, thus the increased expression of IGF-1 may contribute to the progression of cystic lesions. p70S6 kinase (p70S6K) is an important downstream signaling molecule of IGF-1 and is implicated in the regulation of cell cycle progression and cell proliferation. In the present study, we found that IGF-1 increased the growth of cyst-lining epithelial cells by 15-20% in a dose-dependent manner, while no effect on the proliferation of normal renal cortical tubular epithelial cells (RCTEC) was observed. Rosiglitazone, a TZD, was found to inhibit the IGF-1-induced growth of cyst-lining epithelial cells when applied at a dose of 50-200 µM. However, the IGF-1-induced growth of immortalized epithelial cells from >30 individual renal cysts obtained from 11 ADPKD patients (WT9-12 cells) was inhibited with a 12.5-µM dose of rosiglitazone. Moreover, rosiglitazone (at the same concentration) was shown to inhibit the IGF-1-induced activation of p70S6K. TZDs are known to exert antitumor properties via peroxisome proliferator-activated receptor (PPAR)γ-dependent and -independent mechanisms. The present study showed that PPARγ small interfering RNA (siRNA) did not block the effect of rosiglitazone in inhibiting the IGF-1-induced phosphorylation of p70S6K. In conclusion, cyst-lining epithelial cells were found to be more sensitive to IGF-1 compared with normal cells. Rosiglitazone inhibited the proliferation of cyst-lining epithelial cells; more specifically, it inhibited the proliferation-promoting activity of IGF-1 in these cells. This effect of rosiglitazone was demonstrated to be partially due to the inhibition of IGF-1-induced activation of p70S6K. Increased IGF-1 expression was identified in early-stage PKD, indicating that rosiglitazone is more suitable for the treatment of early-stage PKD.

Activation of liver X receptors reduces CFTR-mediated Cl(-) transport in kidney collecting duct cells

Liver X receptors (LXRs) are transcription factors belonging to the nuclear receptor super family, which act as regulators of lipid and glucose metabolism. However, LXRs have been shown to regulate the function of transporters in the kidney, including the Na-Pi cotransporter, organic anion transporter, and epithelial Na(+) channel. In this report, we demonstrated the ability of LXR ligands, both endogenous [22 (R)-hydroxycholesterol] and synthetic (T0901317 and GW3965), to reduce CFTR-mediated Cl(-) secretion in a type I Madin-Darby canine kidney (MDCK) cell line and in murine primary inner medullary collecting duct (IMCD) cells, based on measurements of [Arg(8)]-vasopressin-induced Cl(-) current. However, treatment of MDCK cell monolayers with 5 μM T0901317 for 24 h did not alter ouabain-senstive current or Na(+)-K(+)-ATPase-α protein content. Furthermore, basolateral membranes permeabilization of MDCK cell monolayers still resulted in a decrease in apical Cl(-) current stimulated by both [Arg(8)]-vasopressin and 8-cholorophenyl-thio-cAMP, indicating that the factor(s) encoded by the target gene(s) of agonist-activated LXRs might be located at the apical membrane. Western blot analysis revealed that inhibition of Cl(-) secretion occurred via a decrease in CFTR protein, which was not due to downregulation of its mRNA expression. In addition, both synthetic LXR agonists significantly retarded the growth of forskolin-induced cysts formed in MDCK cells cultured in collagen gel. This is the first evidence showing that ligand-activated LXRs are capable of downregulating CFTR-mediated Cl(-) secretion of kidney cells and of retarding cyst growth in a MDCK cell model.

Experimental therapies and ongoing clinical trials to slow down progression of ADPKD

The improvement of imaging techniques over the years has contributed to the understanding of the natural history of autosomal dominant polycystic kidney disease, and facilitated the observation of its structural progression. Advances in molecular biology and genetics have made possible a greater understanding of the genetics, molecular, and cellular pathophysiologic mechanisms responsible for its development and have laid the foundation for the development of potential new therapies. Therapies targeting genetic mechanisms in ADPKD have inherent limitations. As a result, most experimental therapies at the present time are aimed at delaying the growth of the cysts and associated interstitial inflammation and fibrosis by targeting tubular epithelial cell proliferation and fluid secretion by the cystic epithelium. Several interventions affecting many of the signaling pathways disrupted in ADPKD have been effective in animal models and some are currently being tested in clinical trials.

The role of the cilium in normal and abnormal cell cycles: emphasis on renal cystic pathologies

The primary cilium protrudes from the cell surface and acts as a sensor for chemical and mechanical growth cues, with receptors for a number of growth factors (PDGFα, Hedgehog, Wnt, Notch) concentrated within the ciliary membrane. In normal tissues, the cilium assembles after cells exit mitosis and is resorbed as part of cell cycle re-entry. Although regulation of the cilium by cell cycle transitions has been appreciated for over 100 years, only recently have data emerged to indicate the cilium also exerts influence on the cell cycle. The resorption/protrusion cycle, regulated by proteins including Aurora-A, VHL, and GSK-3β, influences cell responsiveness to growth cues involving cilia-linked receptors; further, resorption liberates the ciliary basal body to differentiate into the centrosome, which performs discrete functions in S-, G2-, and M-phase. Besides these roles, the cilium provides a positional cue that regulates polarity of cell division, and thus directs cells towards fates of differentiation versus proliferation. In this review, we summarize the specific mechanisms mediating the cilia-cell cycle dialog. We then emphasize the examples of polycystic kidney disease (PKD), nephronopthisis (NPHP), and VHL-linked renal cysts as cases in which defects of ciliary function influence disease pathology, and may also condition response to treatment.

Global Gene Expression Profiling in PPAR-γ Agonist-Treated Kidneys in an Orthologous Rat Model of Human Autosomal Recessive Polycystic Kidney Disease

Kidneys are enlarged by aberrant proliferation of tubule epithelial cells leading to the formation of numerous cysts, nephron loss, and interstitial fibrosis in polycystic kidney disease (PKD). Pioglitazone (PIO), a PPAR-γ agonist, decreased cell proliferation, interstitial fibrosis, and inflammation, and ameliorated PKD progression in PCK rats (Am. J. Physiol.-Renal, 2011). To explore genetic mechanisms involved, changes in global gene expression were analyzed. By Gene Set Enrichment Analysis of 30655 genes, 13 of the top 20 downregulated gene ontology biological process gene sets and six of the top 20 curated gene set canonical pathways identified to be downregulated by PIOtreatment were related to cell cycle and proliferation, including EGF, PDGF and JNK pathways. Their relevant pathways were identified using the Kyoto Encyclopedia of Gene and Genomes database. Stearoyl-coenzyme A desaturase 1 is a key enzyme in fatty acid metabolism found in the top 5 genes downregulated by PIO treatment. Immunohistochemical analysis revealed that the gene product of this enzyme was highly expressed in PCK kidneys and decreased by PIO. These data show that PIO alters the expression of genes involved in cell cycle progression, cell proliferation, and fatty acid metabolism.

PPARγ as a therapeutic target in diabetic nephropathy and other renal diseases

PURPOSE OF REVIEW

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated nuclear transcription factor that regulates many important physiological processes including glucose and lipid metabolism, energy homeostasis, cell proliferation, inflammation, immunity and reproduction. The current review aims to summarize and discuss recent findings evaluating the protective effects of PPARγ against kidney diseases with a focus on diabetic nephropathy. We will also delineate the potential underlying mechanisms.

RECENT FINDINGS

PPARγ plays important roles in renal physiology and pathophysiology. Agonists of PPARγ exert protective effects against various kidney diseases including diabetic nephropathy, ischemic renal injury, IgA nephropathy, chemotherapy-associated kidney damage, polycystic kidney diseases and age-related kidney diseases via both systemic and renal actions.

SUMMARY

PPARγ agonists are effective in delaying and even preventing the progression of many renal diseases, especially diabetic nephropathy. PPARγ may represent a promising target for the treatment of renal diseases.

Glitazones in chronic kidney disease: potential and concerns

AIMS

Glitazones rank now among the most used hypoglycemic agents in patients with type-2 diabetes. This systematic review focuses on the cardiovascular and renal outcomes in chronic kidney disease (CKD) patients treated with these drugs.

DATA SYNTHESIS

Data from randomized clinical trials and a meta-analysis indicate that glitazones (particularly rosiglitazone) may increase the risk of myocardial infarction, heart failure and cardiovascular death in type-2 diabetics. Observational studies looking at survival and cardiovascular outcomes in diabetic patients with kidney failure show controversial results. Studies in experimental models and clinical studies suggest that glitazones may have favorable effects on renal disease progression, because these drugs coherently reduce urinary albumin excretion and proteinuria in diabetic and non-diabetic nephropathies. No clinical trial based on clinical end-points like kidney failure has until now tested the effect of glitazones on the evolution of chronic renal failure in these patients.

CONCLUSIONS

Whether the use of glitazones has a positive or a negative impact upon major cardiovascular and renal outcomes in diabetic patients remains an open, unanswered question. Specific studies are needed to assess the efficacy and safety of glitazones in a high risk population like type-2 diabetics with chronic kidney disease.

Mechanism-based therapeutics for autosomal dominant polycystic kidney disease: recent progress and future prospects

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease, accounting for up to 10% of patients on renal replacement therapy. There are presently no proven treatments for ADPKD and an effective disease-modifying drug would have significant implications for patients and their families. Since the identification of PKD1 and PKD2, there has been an explosion in knowledge identifying new disease mechanisms and testing new drugs. Currently, the three major treatment strategies are to: (1) reduce cAMP levels; (2) inhibit cell proliferation, and (3) reduce fluid secretion. Several compounds shown to be effective in preclinical models have already undergone clinical trials and more are planned. In addition, a whole raft of other compounds have been developed from preclinical studies. The purpose of this paper is to evaluate the results of recent published trials, review current trials and highlight the most promising compounds in the pipeline. There appears to be no shortage of potential candidates, but several key issues need to be addressed to facilitate clinical translation.

Rosiglitazone inhibits transforming growth factor-β1 mediated fibrogenesis in ADPKD cyst-lining epithelial cells

Background

Interstitial fibrosis plays an important role in progressive renal dysfunction in autosomal dominant polycystic kidney disease (ADPKD). In our previous studies, we confirmed that PPAR-γ agonist, rosiglitazone could protect renal function and prolong the survival of a slowly progressive ADPKD animal model by reducing renal fibrosis. However, the mechanism remains unknown.

Methods

Primary culture epithelial cells pretreated with TGF-β1 were incubated with rosiglitazone. Extracellular matrix proteins were detected using real-time PCR and Western blotting. MAPK and Smad2 phosphorylation were measured with western blot. ERK1/2 pathway and P38 pathway were inhibited with the specific inhibitors PD98059 and SB203580. The Smad2 pathway was blocked with the siRNA. To address whether PPAR-γ agonist-mediated inhibition of TGF-β1–induced collagen type I expression was mediated through a PPAR-γ dependent mechanism, genetic and pharmaceutical approaches were used to block the activity of endogenous PPARγ.

Results

TGF-β1-stimulated collagen type I and fibronectin expression of ADPKD cyst-lining epithelia were inhibited by rosiglitazone in a dosage-dependent manner. Smad2, ERK1/2 and P38 pathways were activated in response to TGF-β1; however, TGF-β1 had little effect on JNK pathway. Rosiglitazone suppressed TGF-β1 induced Smad2 activation, while ERK1/2 and P38MAPK signals remained unaffected. Rosiglitazone could also attenuate TGF-β1-stimulated collagen type I and fibronectin expression in primary renal tubular epithelial cells, but had no effect on TGF-β1–induced activation of Smad2, ERK1/2 and P38 pathways. There was no crosstalk between the Smad2 and MAPK pathways in ADPKD cyst-lining epithelial cells. These inhibitory effects of rosiglitazone were reversed by the PPARγ specific antagonist GW9662 and PPARγ siRNA.

Conclusion

ADPKD cyst-lining epithelial cells participate in TGF-β1 mediated fibrogenesis. Rosiglitazone could suppress TGF-β1–induced collagen type I and fibronectin expression in ADPKD cyst-lining epithelia through modulation of the Smad2 pathway. Our study may provide therapeutic basis for clinical applications of rosiglitazone in retarding the progression of ADPKD.

Polycystic kidney disease and therapeutic approaches

Polycystic kidney disease (PKD) is a common genetic disorder in which extensive epithelial-lined cysts develop in the kidneys. In previous studies, abnormalities of polycystin protein and its interacting proteins, as well as primary cilia, have been suggested to play critical roles in the development of renal cysts. However, although several therapeutic targets for PKD have been suggested, no early diagnosis or effective treatments are currently available. Current developments are active for treatment of PKD including inhibitors or antagonists of PPAR-γ, TNF-α, CDK and VEGF. These drugs are potential therapeutic targets in PKD, and need to be determined about pathological functions in human PKD. It has recently been reported that the alteration of epigenetic regulation, as well as gene mutations, may affect the pathogenesis of PKD. In this review, we will discuss recent approaches to PKD therapy. It provides important information regarding potential targets for PKD.

Drug discovery for polycystic kidney disease

In polycystic kidney disease (PKD), a most common human genetic diseases, fluid-filled cysts displace normal renal tubules and cause end-stage renal failure. PKD is a serious and costly disorder. There is no available therapy that prevents or slows down the cystogenesis and cyst expansion in PKD. Numerous efforts have been made to find drug targets and the candidate drugs to treat PKD. Recent studies have defined the mechanisms underlying PKD and new therapies directed toward them. In this review article, we summarize the pathogenesis of PKD, possible drug targets, available PKD models for screening and evaluating new drugs as well as candidate drugs that are being developed.

Thiazolidinediones inhibit MDCK cyst growth through disrupting oriented cell division and apicobasal polarity

Thiazolidinediones have been reported to retard cystic disease in rodent models by uncertain mechanisms. We hypothesized that their major effect in retarding cystogenesis was through inhibiting cell proliferation or stimulating apoptosis. In the Madin-Darby canine kidney cell (MDCK) model, rosiglitazone inhibited cyst growth in a time- and dose-dependent manner and this was accompanied by a reduction in basal proliferation and an increase in apoptosis. Unexpectedly, we also observed a striking abnormality in lumen formation resulting in a characteristic multiple lumen or loss of lumen phenotype in treated cells at doses which did not inhibit cell proliferation. These changes were preceded by mislocalization of gp135 and Cdc42, misorientation of the mitotic spindle, and retardation in centrosome reorientation with later changes in primary cilia length and mislocalization of E-cadherin. Cdc42 activation was unaffected by rosiglitazone in monolayer culture but was profoundly inhibited in three-dimensional culture. MDCK cells stably expressing mutant Cdc42 showed a similar mislocalization of gp135 expression and multilumen phenotype in the absence of rosiglitazone. We conclude that rosiglitazone influences MDCK cyst growth by multiple mechanisms involving dosage-dependent effects on proliferation, spindle orientation, centrosome migration, and lumen formation. Correct spatial Cdc42 activation is critical for lumen formation, but the effect of rosiglitazone is likely to involve both Cdc42 and non-Cdc42 pathways.

PPAR-gamma agonist ameliorates kidney and liver disease in an orthologous rat model of human autosomal recessive polycystic kidney disease

In autosomal recessive polycystic kidney disease (ARPKD), progressive enlargement of fluid-filled cysts is due to aberrant proliferation of tubule epithelial cells and transepithelial fluid secretion leading to extensive nephron loss and interstitial fibrosis. Congenital hepatic fibrosis associated with biliary cysts/dilatations is the most common extrarenal manifestation in ARPKD and can lead to massive liver enlargement. Peroxisome proliferator-activated receptor γ (PPAR-γ), a member of the ligand-dependent nuclear receptor superfamily, is expressed in a variety of tissues, including the kidneys and liver, and plays important roles in cell proliferation, fibrosis, and inflammation. In the current study, we determined that pioglitazone (PIO), a PPAR-γ agonist, decreases polycystic kidney and liver disease progression in the polycystic kidney rat, an orthologous model of human ARPKD. Daily treatment with 10 mg/kg PIO for 16 wk decreased kidney weight (% of body weight), renal cystic area, serum urea nitrogen, and the number of Ki67-, pERK1/2-, and pS6-positive cells in the kidney. There was also a decrease in liver weight (% of body weight), liver cystic area, fibrotic index, and the number of Ki67-, pERK1/2-, pERK5-, and TGF-β-positive cells in the liver. Taken together, these data suggest that PIO inhibits the progression of polycystic kidney and liver disease in a model of human ARPKD by inhibiting cell proliferation and fibrosis. These findings suggest that PPAR-γ agonists may have therapeutic value in the treatment of the renal and hepatic manifestations of ARPKD.

Pioglitazone Attenuates Cystic Burden in the PCK Rodent Model of Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a genetic disorder characterized by growth of fluid-filled cysts predominately in kidney tubules and liver bile ducts. Currently, the clinical management of PKD is limited to cyst aspiration, surgical resection or organ transplantation. Based on an observation that PPARγ agonists such as pioglitazone and rosiglitazone decrease mRNA levels of a Cl⁻ transport protein, CFTR (cystic fibrosis transmembrane conductance regulator), and the Cl⁻ secretory response to vasopressin in cultured renal cells, it is hypothesized that PPARγ agonists will inhibit cyst growth. The current studies show that a 7- or 14-week pioglitazone feeding regimen inhibits renal and hepatic bile duct cyst growth in the PCK rat, a rodent model orthologous to human PKD. These studies provide proof of concept for the mechanism of action of the PPARγ agonists and suggest that this class of drugs may be effective in controlling both renal and hepatic cyst growth and fibrosis in PKD.