GLP-1R agonists as novel therapeutic option for ADPKD

Studies of patients with overweight or obesity and Autosomal Dominant Polycystic Kidney Disease (ADPKD) show that body mass index (BMI) or abdominal fat mass are an important predictor of the rate of kidney cysts growth. Also, we recently found that efficacy of tolvaptan decreases with increasing abdominal fat mass. Hence, achievement and/or maintenance of a healthy BMI appears to be an important clinical target in the management of ADPKD. However, behavioral interventions to reduce BMI often fail due to low efficacy and challenges in adherence or tolerability. Further, weight loss is not a viable therapeutic option for patients with normal BMI and ADPKD as it provokes health risks such as bone loss, decreased immune function, or anemia, to name a few. Long-acting glucagon-like peptide 1 receptor agonists (GLP-1Ra[s]) are a highly effective next generation therapy that is changing management of patients with chronic obesity and/or type 2 diabetes. Beyond their weight loss and their regulatory role in glucose metabolism, GLP-1Ras have also been described to lower systemic and organ inflammation as well as cellular stress caused by reactive oxygen species. Since kidney cyst growth has been shown to be modulated by dysregulated glucose metabolism, inflammation, kidney immune cell function, and oxidative stress, we hypothesize that GLP-1Ras are an attractive and plausible therapeutic approach in ADPKD. Critically, this is independent of their effect on reducing BMI; meaning, we believe that GLP-1Ras may present a novel therapeutic approach even in patients with a healthy BMI, low abdominal adiposity, and ADPKD. In our preliminary studies we have established a diet-induced-obesity (DIO) ADPKD model using mice with a mutation to Pkd1 resulting in ADPKD phenotypes that mimic human disease. This DIO ADPKD model has significantly increased body weight and fat mass as well as more severe cystic kidney disease, paralleling the clinical findings. In addition, we found that DIO drives an increase in numbers of kidney immune cells that have been implicated to augment kidney cyst growth. In this application, we will test the therapeutic potential of semaglutide, a well-tolerated, FDA-approved GLP-1Ra, in slowing PKD progression using our established DIO ADPKD1 model. In addition, we will test semaglutide efficacy in the same ADPKD1 model, however, with mice being of healthy body weight. We will also include a group of mice which will receive no drug, but whose food intake is matched to that of the semaglutide group to control for the secondary effect that reduced food intake, known to occur with GLP-1Ra use, has on PKD progression. At the end of study, we will assess various commonly used preclinical parameters that establish severity of PKD which include total kidney volume measured by magnetic resonance imaging, kidney fibrosis and cystic burden evaluated on tissues sections of dissected kidneys, and kidney function. As a secondary outcome, we will also evaluate changes to vascular function using ultrasound imaging approaches that measure aortic stiffness. This secondary outcome is being considered because oxidative stress is known to impact cardiovascular health, which is compromised in patients with ADPKD and presents the most common cause of mortality. In addition, we will use a multitude of sophisticated methods that will allow us to understand the mechanisms through which semaglutide may impact PKD severity. These include assessment of abdominal adipose tissue function and secretion of proinflammatory factors, systemic and kidney metabolism, as well as kidney immune cell function and kidney- as well as vascular cell oxidative stress. Together, our study will be the first, to our knowledge, that tests the efficacy of a GLP-1Ra to slow kidney cyst growth using a clinically relevant disease model with or without obesity, building the foundation for clinical translation. The mechanistic studies will provide additional insight into relevant pathways that are modulated by GLP-1R signaling and may identify new alternate targets for treatment approaches as well as biomarker studies. Finally, our study will provide novel insight into the role of adipose tissue remodeling in PKD progression, an organ that has been poorly studied to date in PKD. All in all, this study addresses the PKD Foundation special consideration areas of “lifestyle interventions”, “PKD drug discovery”, and “extra-renal manifestations of PKD”.

Dr. Katharina Hopp, Ph.D., is an Assistant Professor at the University of Colorado Anschutz Medical Campus, Department of Medicine, Division of Renal Diseases and Hypertension. She has researched PKD pathomechanisms for the last 15 years predominantly utilizing rodent models. She completed her graduate work in Biochemistry and Molecular Biology with a focus on PKD genetics under the guidance of Dr. Peter Harris, Mayo Clinic, Rochester, MN. Since her move to CU Anschutz, her research program has focused on understanding the interplay between immune cells and the cystic epithelium. In particular, she is interested in understanding whether dysregulated metabolism, as characteristic for PKD, impacts immune cell function and if dietary/metabolism-based approaches can prime immune cells in functioning to slow kidney cyst growth. In her free time, Dr. Hopp enjoys exploring the Rocky Mountains with her family via camping, hiking, and running.

Exploring the roles of axoneme polyglutamylation in the context of PKD

Inherited renal cystic diseases represent the most common human genetic diseases, including the ADPKD, ARPKD, the overlapping autosomal dominant polycystic liver diseases (ADPLD), and many syndromic forms of PKD, such as ciliopathies. ADPKD is the major form of PKD that mainly caused by mutations in PKD1/2 (encodes polycystin-1/2 or PC1/2) genes. Currently, tolvaptan, the only FDA-approved drug for ADPKD treatment, slows the disease by an indirect mechanism. However, it is only applicable for the patients with certain criteria and has substantial side effects. Optimal therapies capable of preventing diseases development or stopping their progression do not yet exist. Thus, drugs for treating PKD with wide spectrum of applicability and limited side effects are urgently needed.

Although the molecular mechanism of renal cystogenesis is still controversial, accumulating evidence suggest that the severity of PKD is closely correlates with the decreased functional dosage of polycystins. The primary cilium is a sensory antenna with central roles in sensing environmental cues and transduction of a variety of pivotal cellular signals. Polycystin complexes are hypothetically localize on primary cilia to inhibit renal cyst growth. Recent studies suggest that defective ciliary localization is one of the key mechanisms for decreased functional dosage of polycystins and cystogenesis in ADPKD, ARPKD, and PLD. Therefore, restoring the ciliary level of polycystins holds a strong therapeutic potential for these diseases but, unfortunately, without available molecular targets or drugs for that purpose.

Polyglutamylation (PG) is one of the tubulin posttranslational modifications that occur predominantly on cilia axoneme. Here, we propose that targeting axoneme PG could be a feasible and safe and therapeutic target for PKD for these reasons: 1) Axoneme PG controls the ciliary dosage of polycystins. 2) Increasing axoneme PG suppresses renal cyst growth in ex-vivo model of ADPKD. 3) Mouse genetic models with increased tubulin PG exhibit no noticeable physiological defects. 4) The proteins that control axoneme PG (enzymes, kinases, phosphatases) are conceptually druggable. However, there is no drug available to target axoneme PG and little is known about how axoneme PG is regulated.

Our preliminary studies identified a novel regulatory pathway for proper axoneme PG, targeting which increases ciliary polycystins and suppresses ex-vivo renal cystogenesis. Here, our proposed study aims to 1) further investigate the regulatory mechanism of axoneme PG. 2) screen small molecules, especially the existing clinical and preclinical drugs, to promote axoneme PG and increase ciliary polycystins. 3) determine the therapeutic effects of targeting axoneme PG in ADPKD. These studies will not only advance the knowledge of the regulatory mechanism of cilia function from basic science aspect, but also discover new targets and drugs to manipulate axoneme PG and ciliary polycystins. Importantly, completing the proposed studies could also discover a novel therapeutic strategy for PKD.

Kai He, Ph.D., is an Assistant Professor in the Department of Biochemistry and Molecular Biology at the Mayo Clinic. He received his Ph.D. in Biochemistry and Molecular Biology from the Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, and postdoctoral training at the Mayo Clinic. He has received fellowship from the PKD Foundation, and the Outstanding Trainee Award from the Chinese American Society of Nephrology. Cilia-related diseases (ciliopathies) are life-threatening disorders that affect multiple organs. Manifestations include polycystic kidney and liver, obesity and diabetes, skeletal malformation, cardiovascular diseases, and brain anomalies. Despite the importance of primary cilia in human health, how cilia and ciliopathy protein function remains poorly defined. Dr. He’s research program has focused on the molecular basis of tightly regulated cilia function and its implications in ciliopathies. Dr. He also dedicates to identify small molecules to specifically target primary cilia and assess their therapeutic potential in the context of ciliopathies, especially in PKD.

Deciphering the role of the long noncoding RNA Pvt1 in ADPKD

Despite remarkable advances in our understanding of ADPKD in the last few decades, the disease still has a devastating impact on affected families and society in general. Every year, thousands of people are diagnosed with ADPKD worldwide; therefore, there is an urgent need to further investigate the molecular mechanisms and develop more effective therapies that can positively impact the life and health of individuals with ADPKD. Long noncoding RNAs (LncRNAs) are a class of non-protein coding RNAs with pivotal functions in development and disease. They have emerged as an exciting new drug target category for many common conditions. However, the role of lncRNAs in ADPKD has been understudied. This proposal will determine the impact of a known, highly conserved, and pathogenic lncRNA, called PVT1, on ADPKD pathogenesis. Our proposed assays are based on strong preliminary data showing that Pvt1 silencing reduces cyst growth in cultured kidneys from Pkd1-null mouse embryos. We will utilize pre-clinical models of mouse and human ADPKD to determine whether inhibition of PVT1 ameliorates cystogenesis. One protein that is known to be regulated by PVT1 and plays a critical role in advancing ADPKD is c-MYC. c-MYC is an attractive drug candidate; however, targeting c-MYC remains a challenge. Our proposal provides a complementary approach to traditional drug development in ADPKD. This approach focuses on targeting a single lncRNA to manipulate multiple genes, proteins, and pathways. Should we succeed, it would open the door for exploring the therapeutic potential of inhibiting PVT1 and reducing c-MYC levels to ameliorate cystogenesis in ADPKD.

Karam Aboudehen is an Assistant Professor in the Department of Medicine, Division of Nephrology, at Stony Brook University (SBU). In 2012, he completed his graduate training at Tulane University under the guidance of Dr. Samir El-Dahr in Pediatric Nephrology. He then joined Dr. Peter Igarashi laboratory as a post-doctoral fellow at the University of Texas Southwestern Medical Center in Dallas. In 2016, Dr. Aboudehen was appointed to a faculty position at the University of Minnesota before recently joining the Nephrology Division at SBU in 2022. Research in Aboudehen’s lab focus on investigating the role of long noncoding RNAs (lncRNAs) in polycystic kidney disease (PKD). The long-term objective is to discover therapeutically targetable lncRNAs that prevent or mitigate cyst formation and/or progression in PKD. His lab utilizes cutting edge technologies that include mouse molecular genetics, next generation sequencing and mass spectrometry, genetic engineering, RNA pulldown assays, and viral gene delivery.

Renal Innervation and Nerve Activity Influence on Cystic Progression in ARPKD

Polycystic kidney disease (PKD), both autosomal dominant (AD) and autosomal recessive (AR) forms, remains the leading cause of inheritable kidney disease in adults and children throughout the world. PKD is defined by the development of non-cancerous neoplasms (i.e. fluid-filled sacs) that grow overtime and progressively cause kidney failure. Though the cause of renal cyst formation is well-understood to be primarily driven by an inherited or spontaneous genetic mutation, there remains no cure beyond kidney transplantation. Since access to kidney transplantation is extremely limited, it is vital to this patient population to study alternative strategies for treatment. In recent years, there has been a very important advancement in drug therapy, known as Tolvaptan, that interrupts the vasopressin type 2 receptor (V2R) in the kidney. This receptor contributes to cyst growth in PKD, and Tolvaptan has been shown to slow cyst progression and, in turn, kidney failure. While promising Tolvaptan serves as an excellent intervention currently, there are notable side effects that decrease a patient’s quality of life, such as excessive thirst (polydipsia) and urination (polyuria) – all day and all night. Our laboratory is focused on targeting the same pathway through the kidney’s nervous system, which is known to regulate kidney function and potentially V2R signaling.
The kidney is innervated with many nerves that relay signals to the kidney from the brain (efferent nerves), and from the kidney to the brain (afferent nerves). In several preclinical studies in other models of kidney disease, the activity of these kidney nerves is increased compared to healthy controls. If these signals are disrupted by surgically cutting these nerves, many models of kidney disease are improved. This procedure is referred to as renal (i.e. kidney) denervation (RDNx). Most excitingly, our lab has recently reported that performing the RDNx procedure in a rat model of PKD slows cyst growth. Notably, there were no effects on water intake or urination volumes, which may be preferential to the side effects noted earlier with Tolvaptan. While these early results are promising indeed, further research is required to understand the molecular pathways affected by the RDNx procedure before advancing this new treatment to clinical trials.
A few outstanding questions remain regarding the effect of RDNx. Firstly, it remains unknown if there are direct effects on the V2R signaling in the kidney. The experiments outlined in our proposal directly test this to see if this receptor is involved in the effects of RDNx. Secondly, it is unknown if kidney nerve activity is increased progressively as the cysts grow. We have carefully designed experiments to quantify the nerve signaling to determine when and if nerve activity is altered. This would be very valuable in determining when the RDNx procedure would be most effective. Finally, we will determine the if the beneficial effects of RDNx are dependent on the removal of the local proteins that are released at the ends of these nerves (i.e. neurotransmitters). This will determine whether the signal relayed to the brain is more important, or if the neurotransmitters contribute to the cyst progression.
Overall, Dr. Banek’s laboratory is well-experienced and equipped to run these studies at the University of Arizona and Sarver Heart Center. These studies are carefully designed to reveal the underlying mechanisms of the kidney’s nervous system and its contribution to PKD progression. If successful, RDNx and/or the underlying mechanistic targets may be quickly launched to the next stage for clinical translation to complement the severely limited tool chest for PKD treatment.

Christopher Banek, PhD is an Assistant Professor in the Department of Physiology at the University of Arizona College of Medicine in Tucson, AZ. Dr. Banek has an expansive training background in neuro, cardiovascular, and renal physiology, with a specific emphasis on hypertension and renal injury/inflammation. He received his PhD in Human Physiology from the University of Oregon, and completed a postdoctoral fellowship in cardiovascular physiology at the University of Minnesota Medical School. Throughout his career, Dr. Banek has focused on the physiological underpinnings of cardiovascular and renal disease – largely in the context of high blood pressure (i.e. hypertension) and kidney dysfunction. His recent studies have largely focused on the contributions of the kidney’s nervous system to the development and progression of polycystic kidney disease. Dr. Banek’s team recently published a study on the novel application of a targeted nerve ablation technique (renal denervation; RDNx) that disrupts the kidney’s nervous system in a model of autosomal recessive PKD, which reduced kidney cystic progression and blood pressure. Dr. Banek and his team are now focused on elucidating the underlying mechanisms and role of renal nerves in the progression of renal cysts, as well as the potential for RDNx as a novel therapeutic modality for PKD intervention. 

Developing a New Therapeutic Approach for Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease (ARPKD), caused by mutations in the PKHD1 gene (2,3), is a debilitating genetic disorder causing newborn morbidity and mortality. The most severe disease occurs when the fetus develops abnormal kidneys and a deficit in fluid surrounding the fetus (4). Those who survive to birth face a myriad of symptoms, including increased blood pressure and changes in the fine structure of the liver; they also develop dilations in portions of the kidney ultimately leading to its destruction (5). Management of the disease in infants who survive the first weeks of life is difficult, requiring extreme measures including kidney and/or liver transplant (6). Clearly, there is a critical need to develop treatments for ARPKD. We provide compelling data showing that an approved drug for cystic fibrosis, VX-809, reduces abnormal cyst growth in liver cells from ARPKD model mice. We propose the novel hypothesis that drugs used to treat cystic fibrosis can be used as a treatment for ARPKD and (7) can be fast-tracked for ARPKD treatment. The goal here is to provide a strong proof-of-principle and mechanistic background that will allow the drugs to move forward as a treatment for ARPKD and to establish a new paradigm based on restoring key mechanisms to reduce disease in the lungs, kidneys, and liver. Aim 1 will address the therapeutic potential of cystic fibrosis drugs by determining how they restore function in multiple models of ARPKD. Here we will evaluate a new therapeutic paradigm, using two mouse models to assess the ability of drugs to restore liver and kidney function to these animals. These experiments in rat and mouse models will provide the proof-of-principle that can be used to develop modulators into approved drugs for the treatment of ARPKD. Aim 2 will uncover novel mechanisms that lead to multiorgan disease in ARPKD. We have found three profound bodily functions that misfunction in ARPKD, which together may be targets for therapeutic intervention. In this Aim, we will address the contributions of each of these to the pathology associated with ARPKD. The goal is to define pathways in the body that lead to disease, thereby providing a mechanistic understanding of how modulator drugs work to reduce the dis-ease. An understanding of drug mechanism is not only important for clinical development but also for the development of additional medicines that might work even better.

Dr. Liudmila Cebotaru’s training in medicine began at the age of 18, when she received a R.N. degree from Medical College of Balti, Moldova. She continued her medical training by obtaining an M.D. degree from University of “Carol Davila” School of Medicine and Pharmacy of Bucharest, Romania, and then obtained further training in the areas of pathology. While studying medicine, she also successfully achieved a J.D. degree from the University of Bucharest, Law School and continued in the US, where she later received a Master’s Degree in US Law from the University of Baltimore. Her training in the U.S. began as a post-doctoral fellow at Johns Hopkins University in Gastroenterology and Physiology. She remained at JHU and was promoted to Associate Professor in 2017. In keeping with her training in both medicine and basic science, her passion is to understand the molecular basis of the disease process and to restore normal function to disease-causing mutant proteins. She strongly believes that by understanding the mechanism of the disease process at a basic level, we can devise strategies to correct or at least, bypass defective proteins and restore function. She is currently conducting extensive studies in developing gene therapies for Cystic Fibrosis and in the role of CFTR in Autosomal Dominant Polycystic Kidney Disease. As a result of her past studies on the mechanism of how the cell handles defective proteins and how to rescue function using CFTR modulators, she uncovered a potential new strategy for reducing liver and kidney disease in Autosomal Recessive Polycystic Kidney Disease.

Accurate assessment of intrarenal perfusion in ADPKD using quantitative DCE-MRI

To date, the best methods of identifying high-risk patients for rapidly progressive ADPKD are based on total kidney volume (TKV). However, TKV trajectories are typically not smooth even when followed yearly, and an accurate assessment of therapeutic response based on TKV may require several-year follow-ups. Thus, there is an urgent need to develop a more sensitive alternative for disease activity monitoring.

Intrarenal perfusion may serve as a robust indicator of ADPKD severity. ADPKD causes polycystin impairment in the renal endothelial cells, leading to vascular remodeling, ischemia, fibrosis, and, consequently, perfusion decrease. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can non-invasively assess tissue perfusion by monitoring the dynamic change of MRI contrast agents. Macrocyclic gadolinium-based MRI contrast agents (e.g., gadoteridol) are known to be safe even in patients with stages 4 and 5 of chronic kidney diseases. The volume transfer constant (Ktrans), one of the quantitative DCE-MRI (qDCE) parameters, measures tissue perfusion.

However, the measurement variability across different MRI scanners remains a concern for the reproducible application of qDCE across various clinics. Each MRI vendor provides unique hardware configurations, pulse sequences, and reconstruction algorithms, which cause variations in quantitating tissue contrast agent concentration and DCE-MRI parameters. An external phantom with a known contrast agent concentration may allow us to detect and correct the variation. Furthermore, if the phantom is miniaturized to be imaged concurrently in the bore of a standard MRI scanner with a patient, the intra-scanner variability due to hardware instability can also be reduced.

We developed a point-of-care perfusion phantom named P4 (Point-of-care Portable Perfusion Phantom). The P4 phantom can be imaged with a human subject in a standard MRI scanner to reduce inter/intra-scanner variabilities. In our recent study, the intraclass correlation coefficient (ICC) of Ktrans measurement across three 3T MRI scanners in two clinics was improved from 0.38 to 0.99 after the P4-based error correction. The P4 phantom is inexpensive and ready to use in any commercially available MRI system without needing adjustment. Therefore, the P4 phantom is ideal for highly reproducible qDCE measurement of intrarenal perfusion.

We hypothesize that the intrarenal perfusion measurement using qDCE is highly reproducible when a P4-based error correction scheme is employed. We aim to test this hypothesis with an ADPKD patient cohort at the University of Alabama at Birmingham (UAB). The anticipated high reproducibility of the P4-based qDCE measurement will provide strong evidence for integrating this method into ADPKD clinical trials as a novel phenotypic readout. If successful, this technology will: a) improve precision in ADPKD risk stratification and prediction of outcomes, allowing more timely dose adjustment of therapeutics, and b) enable accurate data comparison across different MRI scanners, facilitating collaboration among institutes to develop advanced treatments for this devastating disease.

I am a professor in the Department of Radiology for the Division of Advanced Medical Imaging Research at the University of Alabama at Birmingham (UAB). My research vision is to globally standardize quantitative imaging of various diseases including polycystic kidney disease (PKD), which will facilitate automatic prognosis and therapy monitoring for patients. Automatic clinical decisions will drastically reduce the turnaround time and medical expenses for patients. My research mission is to develop hardware and software tools along with this initiative and validate those tools in multi-institutional clinical trials. In the proposed study, I will develop a novel prognostic imaging biomarker for PKD, which will be used for early therapy adjustment.

Cardiac-driven hypertension in Autosomal Dominant Polycystic Kidney Disease

Heart failure is the main cause of death in patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD). One of the most significant preventative measures to reduce heart failure is to lower blood pressure. This is because the heart is a pump, and when the hose (blood vessels) become too tight, the buildup in pressure causes the pump to fail (i.e.: heart failure). High blood pressure (hypertension) affects over 70% of all ADPKD patients and is one of the earliest detectable symptoms of ADPKD.

Almost all ADPKD patients take medications that reduce blood pressure. However, many factors cause hypertension. These include things we can put into our body, like a high salt diet, or things inside our bodies, like a cystic kidney pushing on the kidney blood vessels. The kidney cysts start a vicious cycle where the kidneys release of a substance called renin. Renin causes the production of substances that cause the body to hold onto more salt, resulting in an even higher blood pressure. Most ADPKD patients receive medications called ACE inhibitors or ARBs that try to break the renin cycle and lower blood pressure. However, the heart can also release helpful factors, called natriuretic peptides, that lower a patient’s blood pressure. Natriuretic peptides are the body’s own way of trying to fix hypertension as they allow the heart and blood vessels to relax (thus reducing blood pressure) and cause the kidneys to excrete more salt in the urine. These combined effects of relaxation and decreased salt all reduce blood pressure. Our end goal is to see if we can help the hearts of ADPKD patients help their kidneys by producing more beneficial natriuretic peptides and ultimately reduce hypertension and heart failure.

Our mice which do not have polycystin 2 (one of the two genes which when mutated result in ADPKD) in the heart but have normal kidneys have profound hypertension. Excitingly, our studies suggest that the hypertension happens because the mice without polycystin 2 in the heart cannot produce natriuretic peptides. In this proposal, we have two goals that will help us better understand how loss of polycystins in the heart leads to hypertension and if existing FDA approved treatments that preserve natriuretic peptides can reduce hypertension in ADPKD.

Our first goal is to better understand how loss of polycystin proteins prevent the production of natriuretic peptides. We will test if polycystin 1 and polycystin 2 (the two genes which when mutated cause the majority of ADPKD) both contribute to the production of natriuretic peptides. Using modified heart cells grown in the laboratory, we will test different mutations to polycystin 1 and 2 that occur in ADPKD patients for their ability to produce natriuretic peptides. The impact of completing this goal is that we will know if patients with polycystin 1 or polycystin 2 mutations both have reduced natriuretic peptide production. This may help inform how a patient’s hypertension is developing and provide clinicians with opportunities to intervene.

Our second goal is to test in our hypertensive mouse if an already approved heart failure FDA drug (sacubitril/valsartan; marketed by Novatis as Entresto) reduces blood pressure. Entresto is a dual formation drug that keeps natriuretic peptides from breaking down in the body (sacubitril) and an ARB that targets the renin pathway (valsartan). This dual combination treatment may be more effective than the renin pathway drugs that are commonly prescribed to ADPKD patients.

For the ADPKD patient, these studies will be the first scientific test of how the polycystin proteins decrease natriuretic peptide production, and second, these studies will test an already approved FDA natriuretic peptide drug to reduce blood pressure. Ultimately, the hope is that we will have better hypertension treatments that also reduces heart failure in the ADPKD patient.

Dr. Ivana Kuo is an Assistant Professor in the Department of Cell and Molecular Physiology at Loyola University Chicago. She obtained her PhD in Neuroscience at the Australian National University, before studying the function of polycystin proteins in her postdoctoral work at Yale University in the Department of Pharmacology under the mentorship of Dr. Barbara Ehrlich. Dr. Kuo’s laboratory uses cell and mouse models to understand the cardiovascular manifestations within ADPKD, with a particular emphasis on how polycystin proteins in cardiomyocytes contribute to cardiac function.

Identifying clinical and biochemical risk markers of ARPKD liver disease

Autosomal recessive polycystic kidney disease (ARPKD) is a disorder, that typically presents with symptoms in childhood. The two organs that are mainly affected are the kidneys and the liver. Kidney disease in ARPKD results in enlarged cystic kidneys and impaired kidney function. Liver disease in ARPKD is characterized by inborn fibrotic changes of the liver and dilated bile ducts. While the fibrotic changes lead to congestion of the blood flow through the liver, the dilated bile ducts result in an increased risk of severe infection and inflammation for patients. Liver disease in ARPKD may result in a need for patient to undergo liver transplantation or combined liver and kidney transplantation. ARPKD is one of the two main reasons for combined liver and kidney transplantation in childhood.

Different from kidney disease in ARPKD, first symptoms associated with liver disease in ARPKD tend to present a bit later in childhood and may show progression until adulthood. For some patients the involvement of the liver may then even be more severe than kidney disease. However, it is not well-known why some patients with ARPKD develop a more pronounced form of liver disease than others and if there are early clinical, imaging or laboratory findings or disease patterns that could indicate a high risk to patients and caregivers at an early timepoint in life. It is also not well-understood, how different variants in the ARPKD-causing gene PKHD1 lead to liver disease.
In the past we have mainly studied risk factors of kidney disease progression in ARPKD. We identified first risk markers of rapid progression of kidney disease n childhood. These studies have facilitated the establishment of first clinical trials.

In the current project we aim to follow the same path for liver disease. We will use the existing data of more than 700 patients in the European ARegPKD registry, the largest clinical dataset on clinical longterm courses of patients with ARPKD collected so far. Using complex statistical workup methods we aim to identify risk markers at an early timepoint in young childhood that could help to predict the progression of liver disease. This could include ultrasound or other imaging findings, laboratory values, specific genetic variants or a combination of different markers.

In addition to the statistical workup of the clinical findings, we aim to identify blood markers of liver disease in ARPKD. In previous ARegPKD analyses we identified PKHD1 variants that are associated with variable degree of liver disease. We have used the novel molecular technique of CRISPR/Cas9 and have generated corresponding mouse models carrying exactly the same variants. We will characterize disease progression in these mouse models by studying liver tissue structure and protein expression profiles at different time points in an independent project. Bridging the work between clinical markers and laboratory studies we will now study potential novel serum biomarkers in the here suggested study. We have successfully established the technique of unbiased serum proteome analyses in Cologne and have deep pre-existing data on typical patterns in children with chronic kidney disease. For these studies a volume of 5µl is enough to perform the highly-specific analyses of around 300 proteins in serum at the same time. Serum proteins serve as biomarkers for many diseases and we hypothesize that there may be specific changes of serum markers due to liver disease in ARPKD that we can identify through this unbiased approach. We also hypothesize that early markers can differentiate between the disease patterns and that they can be helpful add-ons to clinical markers. Using the newly developed mouse models, we will analyse how serum proteome patterns change over time in mice with liver disease and/or kidney disease. In addition to studying the more clearly defined mouse models we will also perform proteome analyses of patient samples and will study associations with the clinical extent of liver and/or kidney disease documented in ARegPKD. In complex bioinformatical approaches we will integrate the findings from clinical observations and serum proteome measurements in a joint model that will help to improve prediction profiles for individual patients at a young age childhood.

This project could have impact for ARPKD research in multiple ways. It could help to identify subgroups of patients with liver disease that could be studied and compared more precisely in clinical trials. Here, clinical and biochemical markers could be combined and the risk for severe liver disease may be predicted more precisely thus supporting clinical decision-making. The project could also help to establish novel models to specifically study molecular mechanisms of liver disease development and progression in ARPKD, which could be helpful for future studies of therapeutic approaches.

Max C. Liebau, MD, is a clinical consultant pediatric nephrologist at the Department of Pediatrics at the University Hospital Cologne, Germany, where he holds positions as Head of the Social Pediatric Center for Chronically Ill Children and Head of Translational Pediatric Nephrology. Dr Liebau combines his clinical training as a pediatric nephrologist with his experience in cellular and molecular biology obtained in the Nephrology Research Laboratories in Freiburg and Cologne, Germany and at the University of California, Santa Barbara. His group follows a translational research approach to study genetic kidney diseases with a special focus on Autosomal Recessive Polycystic Kidney Disease (ARPKD). The group aims to understand the molecular function of the ARPKD protein fibrocystin and to characterize clinical long-term courses of ARPKD as a basis for the identification of clinical and/or biochemical risk markers of disease progression. Dr Liebau initiated and is currently leading the international ARPKD registry study ARegPKD and is a co-initiator of the pediatric ADPKD registry study ADPedKD. His research is funded by the German Research Council and the German Federal Ministry for Education and Research amongst others.

A novel nutrient sensor pathway in ADPKD

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is among the most common, life-threatening hereditary kidney diseases affecting approximately 1:1000 individuals worldwide. ADPKD causes progressive growth of large fluid-filled renal cysts, which causes kidney injury and can lead to end-stage renal disease. The disease also causes pain, hypertension, bladder infection, vascular complications and liver cysts. As such, the medical burden of ADPKD affects quality of life. There is one FDA-approved therapy, but it has variable effectiveness and multiple side effects. Thus, there is a need to increase our understanding of the mechanisms that drive ADPKD progression to devise new therapeutic strategies. The molecular etiology of renal cystogenesis is complex, but studies indicate the disease mechanism originates from a defect in the primary cilium. The primary cilium is a sensory organelle that converts chemical and mechanical cues into pathways that regulate cell homeostasis. Altered cellular metabolism has emerged as an important contributor to ADPKD pathogenesis, and studies suggest primary cilia and cellular metabolism connect. We propose that a nutrient sensor pathway acts both as a novel potential therapeutic target and molecular link between the ciliary and metabolic defects in ADPKD. Using a mouse model that mimics the slowly-progressive nature of the disease as well as our recently developed cell culture device that enables formation of in vitro 3D renal tubules comprised of patient-derived cells to evaluate the chemosensory function of ADPKD primary cilia, we anticipate our experiments will show that ADPKD renal cystogenesis is mitigated by inhibition of this nutrient sensor, and that novel regulatory mechanisms, feedback loops, and in turn, additional therapeutic targets will be revealed. Our 3D renal tubule mimetic creates a more physiologically relevant environment and can be used for future screening of pharmacological compounds. Thus, completion of this proposal will present a new therapeutic target and novel avenues to identify additional therapeutic strategies against ADPKD. This will contribute toward alleviating the immense medical burdens of this common genetic disease.

Pamela Tran, PhD, is an Associate Professor in the Department of Cell Biology and Physiology and in the Jared Grantham Kidney Institute at the University of Kansas Medical Center (KUMC). She is Co-Director of the In Vivo Models Core of the PKD-Research Resource Consortium at KUMC. For 20 years, she has been using genetic mouse models to investigate the role of primary cilia dysfunction in various diseases, such as PKD, obesity and skeletal disorders. In collaboration with other investigators at KUMC, her laboratory has found that a post-translational modification and regulator of metabolism, O-GlcNAcylation, is upregulated in ADPKD. This proposal seeks to explore a possible connection between increased O-GlcNAcylation and the ciliary defects in ADPKD.

The role of high mobility group box 1-induced NF-kappa B activation in polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the formation and growth of numerous fluid-filled cysts and the development of tissue inflammation and fibrosis. Inflammation is a key driving force for cyst growth and tissue fibrosis of ADPKD. This study will help to understand the molecular mechanisms for the inflammation development of ADPKD and will test resolvins, newly discovered anti-inflammatory molecules, as a potential therapeutic approach to slow the disease.

Yan Zhang is a Research Assistant Professor in the Department of Biological Science at Michigan Technological University. Dr. Zhang earned her PhD in Pharmacology and Toxicology from the University of Missouri-Kansas City, and her work investigated the molecular mechanisms mediating “sterile” inflammation, demonstrating that toll-like receptors are required for endogenous damage-associated molecular patterns-mediated activation of innate immunity. After that, Dr. Zhang completed her postdoc training in Dr. Darren Wallace’s laboratory of Jared Grantham Kidney Institute at the University of Kansas Medical Center. Her research has focused extensively on identifying key regulators for cyst growth, interstitial inflammation, and fibrosis in PKD and novel therapeutic approaches to slow the disease. Her work showed that conditional overexpression of transforming growth factor-beta1 in collecting ducts increased cell proliferation, accelerated renal fibrosis and the decline of renal function, and shortened the lifespan of PKD mice. Her work also demonstrated that elevated Ca/Calmodulin-dependent kinase 4 in cystic epithelial cells is a novel upstream regulator of mTOR, a key regulator of cell proliferation and cyst growth in ADPKD. In addition, she examined the role of liver kinase B1 (LKB1), the primary upstream regulator of AMP kinases, in the disease progression of ADPKD and found that LKB1 is an important regulator of key pathways involved in cyst growth and fibrosis, and activation of LKB1 slows disease progression of PKD mice.