Pathogenesis Of Autosomal Dominant Polycystic Kidney Disease Research Articles

Inflammatory Cytokine Levels in Patients with Autosomal Dominant Polycystic Kidney Disease (ADPKD).

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic ciliopathy that causes adult-onset progressive renal failure. Inflammation and the resulting fibrosis play a crucial role in the pathogenesis. In recent years, an increasing number of inflammatory markers such as MCP-1 and TNF-α, that are associated with the development and progression of ADPKD have been identified. The objective of this study was to identify and evaluate potential proinflammatory biomarkers in patients with ADPKD from the German AD(H)PKD registry. In this exploratory pilot study, serum concentrations of IL-1β, IL-2, IL-6, IL-8, IL-10, IL-13, IFN-γ, MCP-1 and TNF-α were measured by multiplex immunoassay in 233 adults patients with ADPKD from the German AD(H)PKD registry and compared to an age- and sex-matched healthy control group (n = 30). IL-6, IL-8, MCP-1, TNF-α and IFN-γ concentrations were significantly higher in patients with ADPKD than in healthy controls. In addition, sex influenced the concentrations of MCP-1 and TNF-α in the ADPKD and control groups (MCP-1 male =134.8 pg/l, female=75.11pg/l; p = 0.0055; TNF-α male=26.22pg/l, female=21.08 pg/l; p = 0.0038). In conclusion, patients with ADPKD have significantly higher levels of IL-6, IL-8, MCP-1, TNF-α and IFN-γ compared to healthy individuals. These findings underline that inflammation may play a crucial role in the pathogenesis of ADPKD and may be a potential target, both as biomarkers and for therapeutic interventions.

MicroRNA and renal fibrosis in autosomal dominant polycystic kidney disease: a longitudinal study.

Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary kidney disorder that may progress to kidney failure, accounting for 5-10% of all patients with end-stage kidney disease (ESKD). Clinical data, as well as molecular genetics and advanced imaging techniques have provided surrogate prognostic biomarkers to predict rapid decline in kidney function, nonetheless enhanced tools for assessing prognosis for ADPKD are stillneeded. The aim of this study was to analyze specific microRNAs involved in the pathogenesis of ADPKD and in the development of renal fibrosis, evaluating their potential role as predictors of renal function loss. We evaluated kidney function by estimated glomerular filtration rate (eGFR) in 32 ADPKD patients in different stages of kidney disease at T0 and after a 24-month follow up (T1). Patients were divided into two groups: Rapid disease progression ([RP], n 15) and Non-rapid disease progression ([NRP], n 17), according to the Mayo Clinic classification criteria. At T0, ADPKD patients underwent plasma sampling for quantitative analysis of h-miR-17-5p, h-miR-21-5p and h-miR-199a-5p microRNA expression, using the quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) method and a 3T magnetic resonance imaging (MRI), using an advanced MRI imaging protocol, for the quantification of total kidney volume (TKV), total perfusion volume (TPV) and total fibrotic volume (TFV). The expression of h-miR17-5p was higher (p < 0.05) in ADPKD patients with rapid disease progression. h-miR-17-5p, h-miR-21-5p and h-mir-199-5p showed a positive and significant correlation with the eGFR slope (mL/min/1.73 m2/year) (p < 0.05) but not with the eGFR at both T0 and T1. Both total fibrotic volume (cm3) and height-adjusted total fibrotic volume (cm3/m) were positively and significantly correlated to h-miR 21-5p and h-miR 199-5p (p < 0.05), but not to total kidney volume (cm3) and height-adjusted total kidney volume (cm3/m). The microRNAs we studied were associated with fibrosis and renal damage, suggesting their possible role as biomarkers able to identify ADPKD patients at high risk of disease progression regardless of the degree of kidney function, and therefore suitable for medical therapy, and may help uncovering new molecular mechanisms underlying cystogenesis.

#339 Thyroid hormone levels critically contribute to ADPKD progression

Abstract Background and Aims Thyroid hormone (TH) signaling plays a crucial role in the regulation of the cell differentiation state, cell cycle and metabolism in various organs. Low TH levels are observed in most patients with chronic kidney disease, and correlate with cell de-differentiation and reactivation of the cell cycle. Despite this knowledge, possible alterations of TH signaling in Autosomal Dominant Polycystic Kidney Disease (ADPKD) and the capacity of TH to modulate anti-cystogenic and renoprotective pathways have not yet been studied. In this study we aimed to (i) investigate the role of TH signaling in the pathogenesis of ADPKD in patients and experimental models, and (ii) assess whether the pharmacological modulation of this pathway with TH (T3, T4) and TH analogs could arrest or reverse ADPKD progression. Method Ninety patients with a diagnosis of ADPKD based on renal ultrasonography findings or genetic testing were included in the study and divided into five subgroups of chronic kidney disease stages, according to the KDIGO classification. Serum TH was measured using ELISA and chemiluminescent immunoassays. The correlation between TH levels and renal function parameter (eGFR) in these patients was assessed using linear regression. 3D polycystic tubules were engineered from patient-derived cells as previously described (Benedetti et al. 2016). For the in vivo experiments, PCK rats—an animal model of ADPKD—were treated with T4 (10 μg/kg) or vehicle by gavage from 4 to 11 weeks of age. Age-matched SD rats were followed for the same length of time and used as controls. Results The analysis of patients’ data showed a strong linear correlation between the levels of FT3 and eGFR, and corresponding inverse correlation between rT3 (the inactivated form of T3) and eGFR. Treating patients-derived tubules with THs strongly inhibited cyst formation and growth. Interestingly, the results were validated in engineered polycystic tubules from three ADPKD patients with different mutations (missense, splice-site and stop-gain) in the PKD1 gene, further confirming that T4 plays an essential role in the cystogenesis and, presumably, progression of the disease in humans. Treating PCK rats—an animal model of ADPKD—with T4 resulted in a significant increase in T4 serum levels and a simultaneous reduction in the size of the macrocystic area compared to vehicle-treated PCK rats. Most importantly, T4 serum levels positively correlated with a reduction in both the size of the macrocystic area and loss of protein into the urine, indicating that TH signaling plays a role in the growth of cysts, and that exogenous T4 can slow down cystogenesis and improve renal function. Interestingly, our mechanistic studies revealed that T4 exerts its anti-cystogenic effects, at least partially, by binding to the membrane receptor αvβ3 and activating the MAPK cascade. Conclusion These results suggest that TH signaling plays a role in the progression of ADPKD and timely administration of T4, ideally at a relatively early stage of the disease, could delay progression or even reverse key clinical features of ADPKD.

The Link between Autosomal Dominant Polycystic Kidney Disease and Chromosomal Instability: Exploring the Relationship.

In autosomal dominant polycystic kidney disease (ADPKD) with germline mutations in a PKD1 or PKD2 gene, innumerable cysts develop from tubules, and renal function deteriorates. Second-hit somatic mutations and renal tubular epithelial (RTE) cell death are crucial features of cyst initiation and disease progression. Here, we use established RTE lines and primary ADPKD cells with disease-associated PKD1 mutations to investigate genomic instability and DNA damage responses. We found that ADPKD cells suffer severe chromosome breakage, aneuploidy, heightened susceptibility to DNA damage, and delayed checkpoint activation. Immunohistochemical analyses of human kidneys corroborated observations in cultured cells. DNA damage sensors (ATM/ATR) were activated but did not localize at nuclear sites of damaged DNA and did not properly activate downstream transducers (CHK1/CHK2). ADPKD cells also had the ability to transform, as they achieved high saturation density and formed colonies in soft agar. Our studies indicate that defective DNA damage repair pathways and the somatic mutagenesis they cause contribute fundamentally to the pathogenesis of ADPKD. Acquired mutations may alternatively confer proliferative advantages to the clonally expanded cell populations or lead to apoptosis. Further understanding of the molecular details of aberrant DNA damage responses in ADPKD is ongoing and holds promise for targeted therapies.

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

Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent monogenic renal disease progressing to end-stage renal disease. There is a pressing need for the identification of early ADPKD biomarkers to enable timely intervention and the development of effective therapeutic approaches. Here, we profiled human urinary extracellular vesicles small RNAs by small RNA sequencing in patients with ADPKD and compared their differential expression considering healthy control individuals to identify dysregulated small RNAs and analyze downstream interaction to gain insight about molecular pathophysiology. This is a cross-sectional study where urine samples were collected from a total of 23 PKD1-ADPKD patients and 28 healthy individuals. Urinary extracellular vesicles were purified, and small RNA was isolated and sequenced. Differentially expressed Small RNA were identified and functional enrichment analysis of the critical miRNAs was performed to identify driver genes and affected pathways. miR-320b, miR-320c, miR-146a-5p, miR-199b-3p, miR-671-5p, miR-1246, miR-8485, miR-3656, has_piR_020497, has_piR_020496 and has_piR_016271 were significantly upregulated in ADPKD patient urine extracellular vesicles and miRNA-29c was significantly downregulated. Five 'driver' target genes (FBRS, EDC3, FMNL3, CTNNBIP1 and KMT2A) were identified. The findings of the present study make significant contributions to the understanding of ADPKD pathogenesis and to the identification of novel biomarkers and potential drug targets aimed at slowing disease progression in ADPKD.

Predicting autosomal dominant polycystic kidney disease progression: review of promising Serum and urine biomarkers.

Autosomal dominant polycystic kidney disease (ADPKD) is one of the leading causes of end-stage renal disease. In spite of the recent tremendous progress in the understanding of ADPKD pathogenesis, the molecular mechanisms of the disease remain incompletely understood. Considering emerging new targeted therapies for ADPKD, it has become crucial to disclose easily measurable and widely available biomarkers for identifying patients with future rapid disease progression. This review encompasses all the research with a shared goal of identifying promising serum or urine biomarkers for predicting ADPKD progression or response to therapy. The rate of the ADPKD progress varies significantly between patients. The phenotypic variability is only partly explained by the underlying genetic lesion diversity. Considering significant decline in kidney function in ADPKD is not usually evident until at least 50% of the parenchyma has been destroyed, conventional kidney function measures, such as glomerular filtration rate (GFR), are not suitable for monitoring disease progression in ADPKD, particularly in its early stages. Since polycystic kidney enlargement usually precedes the decline in GFR, height-adjusted total kidney volume (ht-TKV) has been accepted as an early biomarker for assessing disease severity in ADPKD patients. However, since measuring ht-TKV is time-consuming and observer-dependent, the identification of a sensitive and quickly measurable biomarker is of a great interest for everyday clinical practice. Throughout the last decade, due to development of proteomic and metabolomic techniques and the enlightenment of multiple molecular pathways involved in the ADPKD pathogenesis, a number of urine and serum protein biomarkers have been investigated in ADPKD patients, some of which seem worth of further exploring. These include copeptin, angiotensinogen, monocyte chemoattractant protein 1, kidney injury molecule-1 and urine-to-plasma urea ratio among many others. The aim of the current review is to provide an overview of all of the published evidence on potentially clinically valuable serum and urine biomarkers that could be used for predicting disease progression or response to therapy in patients with ADPKD. Hopefully, this review will encourage future longitudinal prospective clinical studies evaluating proposed biomarkers as prognostic tools to improve management and outcome of ADPKD patients in everyday clinical practice.

Autosomal Dominant Polycystic Kidney Disease: Is There a Role for Autophagy?

Autosomal-Dominant Polycystic Kidney Disease (ADPKD) is a monogenic disorder initiated by mutations in either PKD1 or PKD2 genes, responsible for encoding polycystin 1 and polycystin 2, respectively. These proteins are primarily located within the primary cilia. The disease follows an inexorable progression, leading most patients to severe renal failure around the age of 50, and extra-renal complications are frequent. A cure for ADPKD remains elusive, but some measures can be employed to manage symptoms and slow cyst growth. Tolvaptan, a vasopressin V2 receptor antagonist, is the only drug that has been proven to attenuate ADPKD progression. Recently, autophagy, a cellular recycling system that facilitates the breakdown and reuse of aged or damaged cellular components, has emerged as a potential contributor to the pathogenesis of ADPKD. However, the precise role of autophagy in ADPKD remains a subject of investigation, displaying a potentially twofold impact. On the one hand, impaired autophagy may promote cyst formation by inducing apoptosis, while on the other hand, excessive autophagy may lead to fibrosis through epithelial to mesenchymal transition. Promising results of autophagy inducers have been observed in preclinical studies. Clinical trials are warranted to thoroughly assess the long-term safety and efficacy of a combination of autophagy inducers with metabolic and/or aquaferetic drugs. This research aims to shed light on the complex involvement of autophagy in ADPKD, explore the regulation of autophagy in disease progression, and highlight the potential of combination therapies as a promising avenue for future investigations.

Pkd2, mutations linking to autosomal dominant polycystic kidney disease, localizes to the endoplasmic reticulum and regulates calcium signaling in fission yeast.

Autosomal dominant polycystic kidney disease (ADPKD) is a renal disorder caused by mutations in the PKD2 gene, which encodes polycystin-2/Pkd2, a transient receptor potential channel. The precise role of Pkd2 in cyst formation remains unclear. The fission yeast Schizosaccharomyces pombe has a putative transient receptor potential channel, Pkd2, which shares similarities with human Pkd2. In this study, truncation analyses of fission yeast Pkd2 were conducted to investigate its localization and function. The results revealed that Pkd2 localizes not only to the plasma membrane but also to the endoplasmic reticulum (ER) in fission yeast. Furthermore, Pkd2 regulates calcium signaling in fission yeast, with the transmembrane domains of Pkd2 being sufficient for these processes. Specifically, the C-terminal region of Pkd2 plays a crucial role in the regulation of calcium signaling. Interestingly, human Pkd2 also localized to the ER and had some impact on calcium signaling in fission yeast. However, human Pkd2 failed to suppress the loss of fission yeast Pkd2. These findings indicate that hPkd2 may not completely substitute for cellular physiology of fission yeast Pkd2. This study provides insights into the localization and functional characteristics of Pkd2 in fission yeast, contributing to our understanding of the pathogenesis of ADPKD.

Prostaglandin E2, osmoregulation and disease progression in autosomal dominant polycystic kidney disease.

Prostaglandin E2 (PGE2) plays a physiological role in osmoregulation, a process that is affected early in autosomal dominant polycystic kidney disease (ADPKD). PGE2 has also been implicated in the pathogenesis of ADPKD in pre-clinical models, but human data are limited. Here, we hypothesized that urinary PGE2 excretion is associated with impaired osmoregulation, disease severity and disease progression in patients with ADPKD. Urinary excretions of PGE2 and its metabolite (PGEM) were measured in a prospective cohort of patients with ADPKD. Linear regression was used for the cross-sectional analysis of the associations between urinary PGE2 and PGEM excretions, markers of osmoregulation and disease severity. Cox regression and linear mixed models were used for the longitudinal analysis of the associations between urinary PGE2 and PGEM excretions and disease progression. In two separate intervention studies we quantified the effect of starting tolvaptan and adding hydrochlorothiazide to tolvaptan on urinary PGE2 and PGEM excretions. In 562 patients with ADPKD (61% female, eGFR 63 ± 28 ml/min/1.73 m2) higher urinary PGE2 or PGEM excretions were independently associated with higher plasma copeptin, lower urine osmolality, lower eGFR and greater total kidney volume. Patients with higher baseline urinary PGE2 and PGEM excretions had an increased risk of 40% eGFR loss or kidney failure (HR 1.28 and 1.47 for each doubling in urinary PGE2 or PGEM excretions) and a faster change in eGFR over time (-0.39 and -0.53 ml/min/1.73 m2/year for each doubling in urinary PGE2 or PGEM excretions). In the intervention studies, inducing polyuria by tolvaptan significantly increased urinary PGEM excretion, while reducing polyuria by adding hydrochlorothiazide to tolvaptan significantly increased urinary PGE2 excretion. Higher urinary PGE2 and PGEM excretions in patients with ADPKD are associated with parameters of osmoregulation, disease severity and progression.

Current and Advance Treatment Approaches of Autosomal Dominant Polycystic Kidney Disease

Polycystic kidney disease is a genetic or acquired disorder in which balloon-like structures called cysts which are filled with fluid are formed inside the kidneys. The most common type of PKD is autosomal dominant polycystic kidney disease (ADPKD). The major cause of ADPKD are found to be abnormalities in the genes, and these abnormalities are inherited within generations. Genetic mutations such as spontaneous mutations are observed in some cases of ADPKD. Other causes of ADPKD can be hypertension and proteinuria. ADPKD develops due to mutations in the genes PKD1 or PKD2. It is found that 85% of the ADPKD patients have mutated PKD1 and 15% of the ADPKD patients have mutated PKD2. It is the 4th common cause which results in End-Stage Renal Disease (ESRD). Different researches and studies are undergoing to find novel treatments for the diseases. There is a need to have a clear understanding of molecular and genetic pathogenesis of ADPKD to help build novel therapies. After the approval of Tolvaptan, an V2R antagonist, slow growth of cyst and less chances of kidney failure were observed in ADPKD patients. Some other therapies like mTOR pathways inhibitors, somatostatin therapies also help in halting the progression of disease. Complementary therapies such as ayurveda and homeopathy, yoga, acupuncture which can help prevent the progression and symptoms of ADPKD. More and more advancement of technologies, stem cell and nanoscience have emerged in finding solutions for renal replacement therapies and restoration of renal function. Keywords: Autosomal dominant polycystic kidney disease (ADPKD), complementary therapies, stem cell and nanoscience.

Large-scale epidemiological study on feline autosomal dominant polycystic kidney disease and identification of novel PKD1 gene variants.

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited disease in cats. In most cases, the responsible abnormality is a nonsense single nucleotide polymorphism in exon 29 of the PKD1 gene (chrE3:g.42858112C>A, the conventional PKD1 variant). The aim of this study was to conduct a large-scale epidemiological study of ADPKD caused by the conventional PKD1 variant in Japan and to search for novel polymorphisms by targeted resequencing of the PKD1 using a next-generation sequencer. A total of 1281 cats visiting the Veterinary Medical Center of the University of Tokyo were included in this study. DNA was extracted from the blood of each cat. We established a novel TaqMan real-time PCR genotyping assay for the conventional PKD1 variant, and all cases were examined for the presence of this variant. Targeted resequencing of all exons of the PKD1 was performed on the DNA of 23 cats with the conventional PKD1 variant, six cats diagnosed with cystic kidneys but without this variant, and 61 wild-type normal cats. Among the 1281 cats examined in this study, 23 (1.8%) harboured the conventional PKD1 variant. The odds of having the conventional PKD1 variant were significantly higher in Persian cats, Scottish Folds and Exotic Shorthairs than in the other breeds, although the number of cases in each breed was small. Furthermore, we identified four variants unique to cats with cystic kidneys that were not found in wild-type normal cats, all of which were in exon 15. In particular, two (chrE:g.42848725delC, pGly1641fs and chrE:g.42850283C>T, pArg2162Trp) were candidate variants. This study revealed that the conventional PKD1 variant was prevalent in Scottish Fold, Persian and Exotic Shorthair breeds in Japan, and variants in exon 15 of PKD1, in addition to the conventional variant in exon 29, would be key factors in the pathogenesis of ADPKD in cats.

Targeting the ADPKD methylome using nanoparticle-mediated combination therapy.

DNA methylation aberrancies are found in autosomal dominant polycystic kidney disease (ADPKD), which suggests the methylome to be a promising therapeutic target. However, the impact of combining DNA methylation inhibitors (DNMTi) and ADPKD drugs in treating ADPKD and on disease-associated methylation patterns has not been fully explored. To test this, ADPKD drugs, metformin and tolvaptan (MT), were delivered in combination with DNMTi 5-aza-2'-deoxycytidine (Aza) to 2D or 3D cystic Pkd1 heterozygous renal epithelial cells (PKD1-Het cells) as free drugs or within nanoparticles to enable direct delivery for future in vivo applications. We found Aza synergizes with MT to reduce cell viability and cystic growth. Reduced representation bisulfite sequencing (RRBS) was performed across four groups: PBS, Free-Aza (Aza), Free-Aza+MT (F-MTAza), and Nanoparticle-Aza+MT (NP-MTAza). Global methylation patterns showed that while Aza alone induces a unimodal intermediate methylation landscape, Aza+MT recovers the bimodality reminiscent of somatic methylomes. Importantly, site-specific methylation changes associated with F-MTAza and NP-MTAza were largely conserved including hypomethylation at ADPKD-associated genes. Notably, we report hypomethylation of cancer-associated genes implicated in ADPKD pathogenesis as well as new target genes that may provide additional therapeutic effects. Overall, this study motivates future work to further elucidate the regulatory mechanisms of observed drug synergy and apply these combination therapies in vivo.

Pleural Effusions on MRI in Autosomal Dominant Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) has cystic fluid accumulations in the kidneys, liver, pancreas, arachnoid spaces as well as non-cystic fluid accumulations including pericardial effusions, dural ectasia and free fluid in the male pelvis. Here, we investigate the possible association of ADPKD with pleural effusion. ADPKD subjects (n = 268) and age-gender matched controls without ADPKD (n = 268) undergoing body magnetic resonance imaging from mid-thorax down into the pelvis were independently evaluated for pleural effusion by 3 blinded expert observers. Subjects with conditions associated with pleural effusion were excluded from both populations. Clinical and laboratory data as well as kidney, liver and spleen volume, pleural fluid volume, free pelvic fluid and polycystic kidney disease genotype were evaluated. Pleural effusions were observed in 56 of 268 (21%) ADPKD subjects compared with 21 of 268 (8%) in controls (p < 0.0001). In a subpopulation controlling for renal function by matching estimated glomerular filtration rate (eGFR), 28 of 110 (25%) ADPKD subjects had pleural effusions compared to 5 of 110 (5%) controls (p < 0.001). Pleural effusions in ADPKD subjects were more prevalent in females (37/141; 26%) than males (19/127,15%; p = 0.02) and in males were weakly correlated with the presence of free pelvic fluid (r = 0.24, p = 0.02). ADPKD subjects with pleural effusions were younger (48 ± 14 years old vs. 43 ± 14 years old) and weighed less (77 vs. 70 kg; p ≤ 0.02) than those without pleural effusions. For ADPKD subjects with pleural effusions, the mean volume of fluid layering dependently in the posterior−inferior thorax was 19 mL and was not considered to be clinically significant. Pleural effusion is associated with ADPKD, but its role in the pathogenesis of ADPKD requires further evaluation.

Role of PKD2 in the endoplasmic reticulum calcium homeostasis.

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in the PKD1 or PKD2 gene which encodes membrane receptor PKD1 and cation channel PKD2, respectively. PKD2, also called transient receptor potential polycystin-2 (TRPP2), is a Ca2+-permeable channel located on the membrane of cell surface, primary cilia, and endoplasmic reticulum (ER). Ca2+ is closely associated with diverse cellular functions. While ER Ca2+ homeostasis depends on different Ca2+ receptors, channels and transporters, the role of PKD2 within the ER remains controversial. Whether and how PKD2-mediated ER Ca2+ leak relates to ADPKD pathogenesis is not well understood. Here, we reviewed current knowledge about the biophysical and physiological properties of PKD2 and how PKD2 contributes to ER Ca2+ homeostasis.

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

Mutations of PKD2, which encodes polycystin-2, cause autosomal dominant polycystic kidney disease (ADPKD). The prevailing view is that defects in polycystin-2-mediated calcium ion influx in the primary cilia play a central role in the pathogenesis of cyst growth. However, polycystin-2 is predominantly expressed in the endoplasmic reticulum (ER) and more permeable to potassium ions than to calcium ions. The trimeric intracellular cation (TRIC) channel TRIC-B is an ER-resident potassium channel that mediates potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium ion release. Using TRIC-B as a tool, we examined the function of ER-localized polycystin-2 and its role in ADPKD pathogenesis in cultured cells, zebrafish, and mouse models. Agonist-induced ER calcium ion release was defective in cells lacking polycystin-2 and reversed by exogenous expression of TRIC-B. Vice versa, exogenous polycystin-2 reversed an ER calcium-release defect in cells lacking TRIC-B. In a zebrafish model, expression of wild-type but not nonfunctional TRIC-B suppressed polycystin-2-deficient phenotypes. Similarly, these phenotypes were suppressed by targeting the ROMK potassium channel (normally expressed on the cell surface) to the ER. In cultured cells and polycystin-2-deficient zebrafish phenotypes, polycystin-2 remained capable of reversing the ER calcium release defect even when it was not present in the cilia. Transgenic expression of Tric-b ameliorated cystogenesis in the kidneys of conditional Pkd2-inactivated mice, whereas Tric-b deletion enhanced cystogenesis in Pkd2-heterozygous kidneys. Polycystin-2 in the ER appears to be critical for anticystogenesis and likely functions as a potassium ion channel to facilitate potassium-calcium counterion exchange for inositol trisphosphate-mediated calcium release. The results advance the understanding of ADPKD pathogenesis and provides proof of principle for pharmacotherapy by TRIC-B activators.

MO016: Feasibility and Effectiveness of Short-Term Ketogenic Interventions in Autosomal Dominant Polycystic Kidney Disease (ADPKD): Results from the Reset-Pkd Study

Abstract BACKGROUND AND AIMS Over the last years, there has been increasing evidence that defects in the energy metabolism of polycystic kidney disease (PKD) cyst lining cells, especially increased glucose dependency and defects in fatty acid oxidation, may underlie the pathogenesis of ADPKD, Rowe et al. (Defective glucose metabolism in polycystic kidney disease identifies a new therapeutic strategy. Nat Med 2013; 19(4): 488–493). Based on these data, ketogenic dietary interventions have effectively been used in PKD animal models, Kipp et al. (A mild reduction of food intake slows disease progression in an orthologous mouse model of polycystic kidney disease. Am J Physiol Renal Physiol 2016;310(8):F726-F31), Torres et al. (Ketosis ameliorates renal cyst growth in polycystic kidney disease. Cell Metab 2019;30(6):1007–23 e5) and Warner et al. (Food restriction ameliorates the development of polycystic kidney disease. J Am Soc Nephrol 2016;27(5):1437–1447). As a first-in-human pilot study, the RESET-PKD study now strives to translate these promising results in the clinical setting. METHOD The present study enrolled 10 ADPKD patients with rapid disease progression. After a screening visit (V1), patients followed their usual carbohydrate-rich diet for up to 4 weeks. In a second visit (V2), patients chose to either perform a 3-day water fast (WF) or a 14-day ketogenic diet (KD) until a third study visit (V3), after which they returned to their normal high-carbohydrate diet for 3–6 weeks until a final visit (V4). At all visits, total kidney volume (TKV) and total liver volume (TLV) were monitored using MRI; anthropometric parameters, body composition and biochemical parameters (i.e. serum creatinine, complete blood cell count, glucose, β-hydroxybutyrate in fingerstick blood and acetone in breath) were measured. Ketone bodies were evaluated at all visits and in between. Feasibility was examined using respective questionnaires. Undesirable effects such as feelings of hunger and discomfort were documented in a study diary. RESULTS All participants (KD: n = 5, WF: n = 5; age: 39.8 ± 11.6 years; eGFR: 82 ± 23.5 mL/min; TKV: 2224 ± 1156 mL) were classified as Mayo Class 1C to 1E. Serum creatinine values were not altered by the ketogenic dietary interventions (V2: 1.17 ± 0.33 mg/dL versus V3: 1.20 ± 0.35 mg/dL, P = 0.826), but serum glucose levels decreased significantly (V2: 84 ± 3 mg/dL, V3: 70 ± 13 mg/dL, P = 0.004). BHB blood levels as well as acetone levels in breath increased in both study arms (V1 to V2 average acetone: 2.6 ± 1.18 ppm, V2 to V3: 22.8 ± 11.9 ppm, P &amp;lt; 0.0001; V1 to V2 average BHB: 0.22 ± 0.08 mmol/L, V2 to V3: 1.89 ± 0.92 mmol/L, P &amp;lt; 0.0001). Nine out of 10 patients reached a ketogenic state during the intervention and 90% evaluated ketogenic interventions as being feasible while 80% of patients both reached the metabolic endpoint and rated ketogenic dietary interventions as feasible. TKV changes during KD and WF did not show any significant differences compared to the period on carbohydrate-rich diet (ΔTKV V1 to V2: 0.75 ± 0.54%, ΔTKV V2 to V3: −1.06 ± 1.16%). CONCLUSION The RESET-PKD study demonstrates feasibility of short-term ketogenic interventions both regarding reliable attainment of ketosis and patient-reported feasibility of this intervention in everyday life. In this proof of principle study, short-term ketogenic interventions could not show a significant reduction in TKV. However, this endpoint is likely to require long-term exposure to ketogenesis. Future large-scale clinical trials examining such long-term dietary interventions—e.g. the KETO-ADPKD study—will be of great importance to further evaluate long-term feasibility and the therapeutic potential of ketogenic diets in ADPKD.

Autosomic dominant polycystic kidney disease and metformin: Old knowledge and new insights on retarding progression of chronic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common congenital kidney disorder, generally caused by mutations in the PKD1 and PKD2 genes, coding for polycystins 1 and 2. Its pathogenesis is accompanied by alterations of the cAMP, mTOR, MAPK/ERK, and JAK/STAT pathways. ADPKD is clinically characterized by the formation of many growing cysts with kidney enlargement and a progressive damage to the parenchyma, up to its complete loss of function, and the onset of end-stage renal disease (ESRD). The current aim of ADPKD therapy is the inhibition of cyst development and retardation of chronic kidney disease progression. Several drugs have been recently included as potential therapies for ADPKD including metformin, the drug of choice for the treatment of type 2 diabetes mellitus, according to its potential inhibitory effects on cystogenesis. In this review, we summarize preclinical and clinical evidence endorsing or rejecting metformin administration in ADPKD evolution and pathological mechanisms. We explored the biology of APDKD and the role of metformin in slowing down cystogenesis searching PubMed and Clinical Trials to identify relevant data from the database inception to December 2020. From our research analysis, evidence for metformin as emerging cure for ADPKD mainly arise from preclinical studies. In fact, clinical studies are still scanty and stronger evidence is awaited. Its effects are likely mediated by inhibition of the ERK pathway and increase of AMPK levels, which are both linked to ADPKD pathogenesis.

SNX9 Inhibits Cell Proliferation and Cyst Development in Autosomal Dominant Polycystic Kidney Disease via Activation of the Hippo-YAP Signaling Pathway.

Autosomal dominant polycystic kidney disease (ADPKD) is a complex process, involving the alteration of multiple genes and signaling pathways, and the pathogenesis of ADPKD remains largely unknown. Here, we demonstrated the suppressive role of sorting nexin 9 (SNX9) during ADPKD development. Sorting nexin 9 expression was detected in the kidney tissues of ADPKD patients, for the first time, and SNX9 expression was also detected in Pkd1 knockout (Pkd1–/–) and control mice. Subsequently, a series of gain- and loss-of-function studies were performed, to explore the biological roles and underlying molecular mechanisms of SNX9 in ADPKD progression. The expression of SNX9 was significantly downregulated in ADPKD patients and Pkd1–/– mice compared with control individuals and wild-type mice (Pkd1+/+), respectively. The ectopic expression of SNX9 significantly inhibited ADPKD cell proliferation, renal cyst formation and enlargement, whereas these effects were promoted by SNX9 silencing. Mechanistically, we found that SNX9 interacted directly with yes-associated protein (YAP) and increased the large tumor suppressor kinase 1-mediated phosphorylation of YAP, resulting in the cytoplasmic retention of YAP, the decreased transcriptional activity of the YAP/TEA domain transcription factor 4 complex, and, consequently, the inhibition of Hippo target gene expression and ADPKD development. Taken together, our findings provided novel insights into the role played by SNX9 during ADPKD pathogenesis and may reveal novel therapeutic approaches for ADPKD and related kidney diseases.

Polycystin-1 regulates ARHGAP35-dependent centrosomal RhoA activation and ROCK signaling.

Mutations in PKD1 (encoding for polycystin-1 [PC1]) are found in 80%–85% of patients with autosomal dominant polycystic kidney disease (ADPKD). We tested the hypothesis that changes in actin dynamics result from PKD1 mutations through dysregulation of compartmentalized centrosomal RhoA signaling mediated by specific RhoGAP (ARHGAP) proteins resulting in the complex cellular cystic phenotype. Initial studies revealed that the actin cytoskeleton was highly disorganized in cystic cells derived from patients with PKD1 and was associated with an increase in total and centrosomal active RhoA and ROCK signaling. Using cilia length as a phenotypic readout for centrosomal RhoA activity, we identified ARHGAP5, -29, and -35 as essential regulators of ciliation in normal human renal tubular cells. Importantly, a specific decrease in centrosomal ARHGAP35 was observed in PKD1-null cells using a centrosome-targeted proximity ligation assay and by dual immunofluorescence labeling. Finally, the ROCK inhibitor hydroxyfasudil reduced cyst expansion in both human PKD1 3D cyst assays and an inducible Pkd1 mouse model. In summary, we report a potentially novel interaction between PC1 and ARHGAP35 in the regulation of centrosomal RhoA activation and ROCK signaling. Targeting the RhoA/ROCK pathway inhibited cyst formation in vitro and in vivo, indicating its relevance to ADPKD pathogenesis and for developing new therapies to inhibit cyst initiation.

Cux1 regulates cilia length in polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is one of the most common inherited disorders affecting the kidney. Renal cyst development in ADPKD results from mutations in the PKD1 or PKD2 genes, which encode the proteins polycstin1 (PC1) and polycystin2 (PC2), respectively. PC1 and PC2 proteins are localized to primary cilia where they are proposed to form a receptor channel complex that detects flow transmitting a calcium‐mediated signal. Primary cilia are critical to the pathogenesis of ADPKD, which is one of many ciliopathies that exhibit renal cystic disease. Cux1, a murine homolog of the Drosophila gene Cut, is a cell cycle dependent transcriptional repressor that regulates expression of the cyclin kinase inhibitor p27. Cux1 is highly and ectopically expressed in mice carrying a collecting duct specific mutation of Pkd1 (Pkd1CD) and in human ADPKD cells where it promotes cell proliferation. Mice carrying mutations in both Cux1 and Pkd1 have reduced cystic disease and an increased life span. A role for Cux1 in regulating genes involved in cilia assembly and function has recently been identified in the Galapagos cormorant, however, the role of Cux1 in cilia in the mammalian kidney is not known. To begin to determine whether Cux1 regulates ciliogenesis we evaluated cilia morphology and the expression of the ciliary protein, OFD1 (oral‐facial‐digital‐1), identified as a target of Cux1 in the Galapagos cormorant. Cilia analysis was performed on kidneys isolated from wild type, Cux1 transgenic, Pkd1CD, and Pkd1CD/Cux1 double mutant mice. Cilia morphology was assessed by immunofluorescence labeling of alpha‐tubulin and the collecting duct marker dolichos biflorus agglutinin (DBA) to identify cells in which Pkd1 was deleted. Cilia in Pkd1/Cux1 double knockout kidneys were significantly shorter than cilia in the Pkd1CD kidneys, consistent with previous studies showing that decreased cilia length corresponds to decreased cystic disease. OFD1 is an inhibitor of ciliogenesis and OFD1 expression in the various mouse models demonstrate that OFD1 expression corresponds to Cux1 expression. OFD1 protein levels were the lowest in the kidneys of mice constitutively expressing Cux1 and were highest in mice with deletions of Cux1. Taken together, our results reveal a novel role for Cux1 in regulating ciliogenesis in the kidney and suggest that the reduced cystic disease in the Pkd1/Cux1 double mutant mice results from reduced cilia length.Support or Funding InformationAmerican Association of Anatomy FGAP, Western Michigan University Homer Stryker MD School of Medicine