Pancreatic metastases after surgery for renal cell carcinoma: survival and pathways of progression.

PURPOSE: Metastatic ccRCC has peculiar tropism in the pancreas. We describe the characteristics and pathways of progression of patients with PM in a large multi-institutional consortium and compare them to patients with metastases from ccRCC at other sites. METHODS: Detailed clinical and histopathological data were collected. To account for differences in baseline characteristics between the two groups, IPTW was used to compare the two groups in terms of PFS and OS. RESULTS: Of the 182 patients, 33 (18%) had pancreatic, 94 (52%) pulmonary, 30 (16%) bone, 13 (7%) hepatic, and 12 (7%) brain metastases. Patients with PM had less aggressive ccRCC at baseline compared to those with progression at other sites in terms of tumour stage and grade. Median time from ccRCC surgery to PM was 8 (95%CI 5-10) vs. 1 year (95%CI 1-2) for progression to other sites (p < 0.001). Median IPTW-weighted time to second progression was 4.3 years (95%CI 2.4-not reached) for patients with PM vs 1.1 year (95%CI 0.8-2.3) for those with progression in other sites (p < 0.001). The most frequent second progression sites were pancreas (24%) and liver (15%) in patients with PM, while progression to the pancreas was rare (4%) in those with a different first progression site. Surgery alone (55%) or in combination with medical therapy (30%) was more frequent in the PM group than in other sites (p < 0.001). Median IPTW-OS time was longer for patients with PM [8.8 years (95%CI 6.5-not reached)] compared to those with first progression in other sites [2.8 years (95%CI 1.9-4.3), p < 0.001]. CONCLUSION: Pancreatic tropism is typical of ccRCC tumours with more indolent behaviour than those progressing to other sites. A long follow-up period is necessary to distinguish PM from ccRCC.

Von Hippel-Lindau disease-associated renal cell carcinoma: a call to action.

PURPOSE OF REVIEW: While the molecular and genetic bases of Von Hippel-Lindau (VHL) disease have been extensively investigated, limited evidence is available to guide diagnosis, local or systemic therapy, and follow-up. The aim of the current review is to summarize the ongoing trials both in preclinical and clinical setting regarding VHL disease management. RECENT FINDINGS: Although genotype/phenotype correlations have been described, there is considerable inter and intra-familiar heterogeneity in VHL disease. Genetic anticipation has been reported in VHL disease. From a clinical point of view, expert-opinion-based protocols suggest testing those patients with any blood relative of an individual diagnosed with VHL disease, those with at least 1 or more suggestive neoplasms or patients presenting with clear cell renal cell carcinoma (ccRCC) diagnosed at a less than 40 years old, and/or multiple ccRCC. Clinical research is focused on safety and efficacy of systemic agents for patients with VHL-related ccRCC, with the aim to possibly preserve kidney function and improve patient survival. SUMMARY: To date, preclinical and clinical research on the topic is scarce and clinical guidelines are not supported by strong validation studies.

Clinical, surgical, pathological and follow-up features of kidney cancer patients with Von Hippel-Lindau syndrome: novel insights from a large consortium.

PURPOSE: To investigate the natural history and follow-up after kidney tumor treatment of Von Hippel-Lindau (VHL) patients. MATERIALS AND METHODS: A multi-institutional European consortium of patients with VHL syndrome included 96 non-metastatic patients treated at 9 urological departments (1987-2018). Descriptive and survival analyses were performed. RESULTS AND LIMITATIONS: Median age at VHL diagnosis was 34 years (IQR 25-43). Two patients (2.1%) showed only renal manifestations at VHL diagnosis. Concomitant involvement of Central Nervous System (CNS) vs. pancreas vs. eyes vs. adrenal gland vs. others were present in 60.4 vs. 68.7 vs. 30.2 vs. 15.6 vs. 15.6% of patients, respectively. 45% of patients had both CNS and pancreatic diseases alongside kidney. The median interval between VHL diagnosis and renal cancer treatment resulted 79 months (IQR 0-132), and median index tumor size leading to treatment was 35.5 mm (IQR 28-60). Of resected malignant tumours, 73% were low grade. Of high-grade tumors, 61.1% were large > 4 cm. With a median follow-up of 8 years, clinical renal progression rate was 11.7% and 29.3% at 5 and 10 years, respectively. Overall mortality was 4% and 7.5% at 5 and 10 years, respectively. During the follow-up, 50% of patients did not receive a second active renal treatment. Finally, 25.3% of patients had CKD at last follow-up. CONCLUSIONS: Mean period between VHL diagnosis and renal cancer detection is roughly three years, with significant variability. Although, most renal tumors are small low-grade, clinical progression and mortality are not negligible. Moreover, kidney function represents a key issue in VHL patients.

2-Deoxy-d-Glucose Ameliorates PKD Progression.

Autosomal dominant polycystic kidney disease (ADPKD) is an important cause of ESRD for which there exists no approved therapy in the United States. Defective glucose metabolism has been identified as a feature of ADPKD, and inhibition of glycolysis using glucose analogs ameliorates aggressive PKD in preclinical models. Here, we investigated the effects of chronic treatment with low doses of the glucose analog 2-deoxy-d-glucose (2DG) on ADPKD progression in orthologous and slowly progressive murine models created by inducible inactivation of the Pkd1 gene postnatally. As previously reported, early inactivation (postnatal days 11 and 12) of Pkd1 resulted in PKD developing within weeks, whereas late inactivation (postnatal days 25-28) resulted in PKD developing in months. Irrespective of the timing of Pkd1 gene inactivation, cystic kidneys showed enhanced uptake of (13)C-glucose and conversion to (13)C-lactate. Administration of 2DG restored normal renal levels of the phosphorylated forms of AMP-activated protein kinase and its target acetyl-CoA carboxylase. Furthermore, 2DG greatly retarded disease progression in both model systems, reducing the increase in total kidney volume and cystic index and markedly reducing CD45-positive cell infiltration. Notably, chronic administration of low doses (100 mg/kg 5 days per week) of 2DG did not result in any obvious sign of toxicity as assessed by analysis of brain and heart histology as well as behavioral tests. Our data provide proof of principle support for the use of 2DG as a therapeutic strategy in ADPKD.

Impaired glomerulogenesis and endothelial cell migration in Pkd1-deficient renal organ cultures.

The PKD1 gene is essential for a number of biological functions, and its loss-of-function causes autosomal dominant polycystic kidney disease (ADPKD). The gene is developmentally regulated and believed to play an essential role in renal development. Previous studies have shown that manipulating murine renal organ cultures with dominant-negative forms of the Pkd1 gene impaired ureteric bud (UB) branching. In the current study, we analyzed different stages of renal development in two distinct mouse models carrying either a null mutation or inactivation of the last two exons of Pkd1. Surprisingly, metanephric explants from Pkd1-deleted kidneys harvested at day E11.5 did not show defects of UB branching and elongation, estimated by cytokeratin staining on fixed tissues or by Hoxb7-GFP time-lapse imaging. However, renal explants from Pkd1-mutants isolated at day E14.5 showed impaired nephrogenesis. Notably, we observed cell migratory defects in the developing endothelial compartment. Previous studies had implicated the Pkd1 gene in controlling cell migration and collagen deposition through PI3 kinases. In line with these studies, our results show that wild-type explants treated with PI3-kinase inhibitors recapitulate the endothelial defects observed in Pkd1 mutants, whereas treatment with VEGF only partially rescued the defects. Our data are consistent with a role for the Pkd1 gene in the endothelium that may be required for proper nephrogenesis.

Defective metabolism in polycystic kidney disease: potential for therapy and open questions.

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by bilateral renal cyst formation. The disease is caused by mutations in either the PKD1 or the PKD2 gene. Progress has been made in understanding the molecular basis of the disease leading to the general agreement on ADPKD being a loss-of-function disease. Identification of signalling cascades dysfunctional in the cystic epithelia has led to several pre-clinical studies of animal models using a variety of inhibitors to slow disease progression. These were followed by clinical trials, some of which generated promising results, although an approved therapy is still lacking. Here, we summarize and discuss recent work providing evidence that metabolic alterations can be observed in ADPKD. In particular, we will focus our discussion on the potential role of glucose metabolism in the pathogenesis of ADPKD. These recent findings provide a new perspective for the understanding of the pathobiology of ADPKD and open potential new avenues for therapeutical approaches. At the same time, these studies also raise important and intriguing biological and medical questions that will need to be addressed experimentally prior to embracing a more enthusiastic view of the applicability of the results.

Centralization of care for rare genetic syndromes associated with cancer: improving outcomes and advancing research on VHL disease.

Von Hippel-Lindau (VHL) disease is a rare genetic syndrome caused by a germline pathogenic variant in one VHL allele. Any somatic event disrupting the other allele induces VHL protein (pVHL) loss of function, ultimately leading to patients developing multiple tumours in multiple organs at multiple timepoints, and reducing life expectancy. Treatment of this complex, rare disease is often fragmented, as patients visit specialist clinicians in isolation at different medical centres. Consequently, patients can receive sub-optimal treatment that results in decreased quality of life and a poor experience of health care systems. In 2021, we established a comprehensive clinical centre at San Raffaele Hospital, Milan, devoted to VHL disease. The centre provides a structured programme for the diagnosis, surveillance and treatment of patients alongside research into VHL disease and involves a multidisciplinary team of dedicated physicians. This programme demonstrates the benefits of care centralization, including concentration of knowledge and services, synergy and multidisciplinary management, improved networking and patient resources, reducing health care costs, and fostering research and innovation. VHL disease provides an ideal model to assess the advantages of centralizing care for rare disease and represents an unparalleled opportunity to broaden our understanding of cancer biology in general.

Differential Prognostic Value of Extrarenal Involvement in Patients With Non-Metastatic Renal Cell Cancer.

INTRODUCTION: A better definition of the prognostic significance of non-metastatic pT3a stage RCC subcategories is crucial to select the best candidate for adjuvant treatment. The aim of the study is to investigate the differential prognosis of extrarenal involvement in patients with non-metastatic pT3a RCC. MATERIALSAND METHODS: From a single institutional prospective database, 451 consecutive patients treated for pT3aN0/NxM0 RCC were selected and stratified according to pT3a subtypes (perirenal fat invasion, sinus fat invasion, segmental/renal vein thrombus, ≥ 2 features). Cancer specific survival (CSS), metastasis free survival (MFS) and relapse free survival (RFS) were primary endpoints of multivariable Cox regression models. RESULTS: Overall, 67 (15%) patients presented with renal/segmental vein thrombus only, 185 (41%) with perirenal fat invasion, 101 (22%) with sinus fat invasion and 98 (22%) with ≥ 2 features. The presence of ≥ 2 pT3a features was associated with a higher risk of metastasis (HR=2.36; 95%CI 1.30-4.27; P value = .005), recurrence (HR=2.41; 95%CI 1.36-4.28; P value=.003) and cancer specific mortality (HR=3.54; 95%CI 1.45-8.63; P value = .005) compared to only 1 pT3a feature. Moreover, the presence of perirenal fat invasion was associated with lower CSS (HR=2.82; 95% CI 1.19-6.69; P value = .02) compared to sinus fat invasion or tumoral thrombus only. CONCLUSION: The concurrent presence of ≥ 2 pT3a features is associated to a higher risk of distant progression, relapse and cancer specific mortality, implying potential role for adjuvant therapy or a more stringent follow-up. Moreover, perirenal fat invasion is associated with worse CSS compared to other pT3a patterns taken alone.

Testosterone in males with COVID-19: a 12-month cohort study.

BACKGROUND: Male patients with COVID-19 have been found with reduced serum total testosterone (tT) levels and with more severe clinical outcomes. OBJECTIVES: To assess total testosterone (tT) levels and the probability of recovering eugonadal tT levels during a minimum 12-month timespan in a cohort of men who have been followed over time after the recovery from laboratory-confirmed COVID-19. MATERIALS AND METHODS: Demographic, clinical and hormonal values were collected for the overall cohort. Hypogonadism was defined as tT ≤9.2 nmol/l. The Charlson Comorbidity Index was used to score health-significant comorbidities. Descriptive statistics was used to compare hormonal levels at baseline versus 7-month (FU1) versus 12-month (FU2) follow-up, respectively. Multivariate cox proportional hazards regression model was used to identify the potential predictors of eugonadism recovery over time among patients with hypogonadism at the time of infection. RESULTS: Of the original cohort of 286 patients, follow-up data were available for 121 (42.3%) at FU1 and 63 (22%) patients at FU2, respectively. Higher median interquartile range (IQR) tT levels were detected at FU2 (13.8 (12.3-15.3) nmol/L) versus FU1 (10.2 [9.3-10.9] nmol/L) and versus baseline (3.6 [3.02-4.02] nmol/L) (all p < 0.0001), whilst both LH and E2 levels significantly decreased over the same time frame (all p ≤ 0.01). Circulating IL-6 levels further decreased at FU2 compared to FU1 levels (19.3 vs. 72.8 pg/ml) (p = 0.02). At multivariable cox regression analyses, baseline tT level (HR 1.19; p = 0.03 [1.02-1.4]) was independently associated with the probability of tT level normalization over time, after adjusting for potential confounders. CONCLUSIONS: Circulating tT levels keep increasing over time in men after COVID-19. Still, almost 30% of men who recovered from COVID-19 had low circulating T levels suggestive for a condition of hypogonadism at a minimum 12-month follow-up.

Pembrolizumab in advanced renal cell carcinoma: a meta-analysis providing level 1a evidence.

The recent introduction of immunotherapy in the first line setting of advanced renal cell carcinoma (aRCC) has dramatically improved patients' prognosis. The aim of the current meta-analysis was to provide level 1a evidence supporting the use of pembrolizumab plus tyrosine kinase inhibitors (TKI) as first-line treatment for advanced RCC. All published randomized prospective trials including patients with advanced RCC treated with pembrolizumab in combination with TKIs vs Sunitinib were included in this meta-analysis. An algorithm was used to reconstruct survival data from the published Kaplan-Meier curves of overall survival (OS), progression free survival (PFS) and duration of response (DoR) from the included trials. Restricted mean survival time (RMST) with 95% confidence interval (CI) for comparison among the different regimens was calculated. Main outcomes were differences in RMST for OS, PFS and DoR for pembrolizumab plus TKIs vs sunitinib arm. Reconstructed survival data from 1,573 patients were retrieved from 2 trials (KEYNOTE-581 and KEYNOTE-426) comparing pembrolizumab plus TKI (lenvatinib or axitinib, respectively) to sunitinib. Patients who received pembrolizumab-lenvatinib or pembrolizumab-axinitinib had better OS (24-month ΔRMST of 1.79 months [95% CI: 0.12-2.50; P < 0.001]), PFS (24-month ΔRMST of 3.83 months [95% CI: 2.93-4.74; P < 0.001]) and DoR (24-month ΔRMST of 2.32 months [95% CI: 0.97-3.67; P < 0.001]) relative to sunitinib. Pembrolizumab-lenvatinib combination gave a marginal benefit in terms of OS, PFS and DoR relative to pembrolizumab-axitinib group. By relying on individual survival data, we provided a level-1a evidence supporting the use of pembrolizumab plus TKI for first-line aRCC treatment.

Testosterone in males with COVID-19: A 7-month cohort study.

BACKGROUND: Circulating testosterone levels have been found to be reduced in men with severe acute respiratory syndrome coronavirus 2 infection, COVID-19, with lower levels being associated with more severe clinical outcomes. OBJECTIVES: We aimed to assess total testosterone levels and the prevalence of total testosterone still suggesting for hypogonadism at 7-month follow-up in a cohort of 121 men who recovered from laboratory-confirmed COVID-19. MATERIALS AND METHODS: Demographic, clinical, and hormonal values were collected for all patients. Hypogonadism was defined as total testosterone ≤9.2 nmol/L. The Charlson Comorbidity Index was used to score health-significant comorbidities. Descriptive statistics and multivariable linear and logistic regression models tested the association between clinical and laboratory variables and total testosterone levels at follow-up assessment. RESULTS: Circulating total testosterone levels increased at 7-month follow-up compared to hospital admittance (p < 0.0001), while luteinizing hormone and 17ß-estradiol levels significantly decreased (all p ≤ 0.02). Overall, total testosterone levels increased in 106 (87.6%) patients, but further decreased in 12 (9.9%) patients at follow-up, where a total testosterone level suggestive for hypogonadism was still observed in 66 (55%) patients. Baseline Charlson Comorbidity Index score (OR 0.36; p = 0.03 [0.14, 0.89]) was independently associated with total testosterone levels at 7-month follow-up, after adjusting for age, BMI, and IL-6 at hospital admittance. CONCLUSIONS: Although total testosterone levels increased over time after COVID-19, more than 50% of men who recovered from the disease still had circulating testosterone levels suggestive for a condition of hypogonadism at 7-month follow-up. In as many as 10% of cases, testosterone levels even further decreased. Of clinical relevance, the higher the burden of comorbid conditions at presentation, the lower the probability of testosterone levels recovery over time.

Multidisciplinary management of patients diagnosed with von Hippel-Lindau disease: A practical review of the literature for clinicians.

Objective: The aim of the current review is to summarize the available evidence to aid clinicians in the surveillance, treatment and follow-up of the different primary tumors developed by patients diagnosed with von Hippel-Lindau (VHL) syndrome. Methods: A non-systematic narrative review of original articles, meta-analyses, and randomized trials was conducted, including articles in the pre-clinical setting to support relevant findings. Results: VHL disease is the most common rare hereditary disorder associated with clear cell renal cell carcinoma. Affected individuals inherit a germline mutation in one VHL allele, and any somatic event that disrupt the other allele can trigger mutations, chromosomal rearrangements, or epigenetic regulations leading to oncogenesis. From a clinical perspective, patients continuously develop multiple primary tumors. Conclusion: Because VHL is considered a rare disease, very limited evidence is available for diagnosis, surveillance, active treatment with local or systemic therapy and follow-up.

Severely low testosterone in males with COVID-19: A case-control study.

BACKGROUND: Circulating androgens could have a relevant pathobiological role in clinical outcomes in men with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection (COVID-19). OBJECTIVES: We aimed to assess: (a) circulating sex steroids levels in a cohort of 286 symptomatic men with laboratory-confirmed COVID-19 at hospital admission compared to a cohort of 281 healthy men; and (b) the association between serum testosterone levels (tT), COVID-19, and clinical outcomes. MATERIALS AND METHODS: Demographic, clinical, and hormonal values were collected for all patients. Hypogonadism was defined as tT ≤9.2 nmol/l. The Charlson Comorbidity Index (CCI) was used to score health-significant comorbidities. Severe clinical outcomes were defined as patients either transferred to intensive care unit (ICU) or death. Descriptive statistics and multivariable linear and logistic regression models tested the association between clinical and laboratory variables and tT levels. Univariable and multivariable logistic regression models tested the association between tT and severe clinical outcomes. RESULTS: Overall, a significantly lower levels of LH and tT were found in patients with COVID-19 compared to healthy controls (all p < 0.0001); conversely, healthy controls depicted lower values of circulating E2 (p < 0.001). Testosterone levels suggestive for hypogonadism were observed in 257 (89.8%) patients at hospital admission. In as many as 243 (85%) cases, hypogonadism was secondary. SARS-CoV-2 infection status was independently associated with lower tT levels (p < 0.0001) and greater risk of hypogonadism (p < 0.0001), after accounting for age, BMI, CCI, and IL-6 values. Lower tT levels were associated with higher risk of ICU admission and death outcomes (all p ≤ 0.05), after accounting for clinical and laboratory parameters. CONCLUSIONS: We unveil an independent association between SARS-CoV-2 infection status and secondary hypogonadism already at hospital admission, with lower testosterone levels predicting the most severe clinical outcomes.

Dissection of metabolic reprogramming in polycystic kidney disease reveals coordinated rewiring of bioenergetic pathways.

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a genetic disorder caused by loss-of-function mutations in PKD1 or PKD2. Increased glycolysis is a prominent feature of the disease, but how it impacts on other metabolic pathways is unknown. Here, we present an analysis of mouse Pkd1 mutant cells and kidneys to investigate the metabolic reprogramming of this pathology. We show that loss of Pkd1 leads to profound metabolic changes that affect glycolysis, mitochondrial metabolism, and fatty acid synthesis (FAS). We find that Pkd1-mutant cells preferentially use glutamine to fuel the TCA cycle and to sustain FAS. Interfering with either glutamine uptake or FAS retards cell growth and survival. We also find that glutamine is diverted to asparagine via asparagine synthetase (ASNS). Transcriptional profiling of PKD1-mutant human kidneys confirmed these alterations. We find that silencing of Asns is lethal in Pkd1-mutant cells when combined with glucose deprivation, suggesting therapeutic approaches for ADPKD.

Polycystin-1 binds Par3/aPKC and controls convergent extension during renal tubular morphogenesis.

Several organs, including the lungs and kidneys, are formed by epithelial tubes whose proper morphogenesis ensures correct function. This is best exemplified by the kidney, where defective establishment or maintenance of tubular diameter results in polycystic kidney disease, a common genetic disorder. Most polycystic kidney disease cases result from loss-of-function mutations in the PKD1 gene, encoding Polycystin-1, a large receptor of unknown function. Here we demonstrate that PC-1 has an essential role in the establishment of correct tubular diameter during nephron development. Polycystin-1 associates with Par3 favouring the assembly of a pro-polarizing Par3/aPKC complex and it regulates a programme of cell polarity important for oriented cell migration and for a convergent extension-like process during tubular morphogenesis. Par3 inactivation in the developing kidney results in defective convergent extension and tubular morphogenesis, and in renal cyst formation. Our data define Polycystin-1 as central to cell polarization and to epithelial tube morphogenesis and homeostasis.

Defective glucose metabolism in polycystic kidney disease identifies a new therapeutic strategy.

Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disorder characterized by bilateral renal cyst formation. Recent identification of signaling cascades deregulated in ADPKD has led to the initiation of several clinical trials, but an approved therapy is still lacking. Using a metabolomic approach, we identify a pathogenic pathway in this disease that can be safely targeted for therapy. We show that mutation of PKD1 results in enhanced glycolysis in cells in a mouse model of PKD and in kidneys from humans with ADPKD. Glucose deprivation resulted in lower proliferation and higher apoptotic rates in PKD1-mutant cells than in nondeprived cells. Notably, two distinct PKD mouse models treated with 2-deoxyglucose (2DG), to inhibit glycolysis, had lower kidney weight, volume, cystic index and proliferation rates as compared to nontreated mice. These metabolic alterations depend on the extracellular signal-related kinase (ERK) pathway acting in a dual manner by inhibiting the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) axis on the one hand while activating the mTOR complex 1 (mTORC1)-glycolytic cascade on the other. Enhanced metabolic rates further inhibit AMPK. Forced activation of AMPK acts in a negative feedback loop, restoring normal ERK activity. Taken together, these data indicate that defective glucose metabolism is intimately involved in the pathobiology of ADPKD. Our findings provide a strong rationale for a new therapeutic strategy using existing drugs, either individually or in combination.

Nephrocystin-1 forms a complex with polycystin-1 via a polyproline motif/SH3 domain interaction and regulates the apoptotic response in mammals.

Mutations in PKD1, the gene encoding for the receptor Polycystin-1 (PC-1), cause autosomal dominant polycystic kidney disease (ADPKD). The cytoplasmic C-terminus of PC-1 contains a coiled-coil domain that mediates an interaction with the PKD2 gene product, Polycystin-2 (PC-2). Here we identify a novel domain in the PC-1 C-terminal tail, a polyproline motif mediating an interaction with Src homology domain 3 (SH3). A screen for interactions using the PC-1 C-terminal tail identified the SH3 domain of nephrocystin-1 (NPHP1) as a potential binding partner of PC-1. NPHP1 is the product of a gene that is mutated in a different form of renal cystic disease, nephronophthisis (NPHP). We show that in vitro pull-down assays and NMR structural studies confirmed the interaction between the PC-1 polyproline motif and the NPHP1 SH3 domain. Furthermore, the two full-length proteins interact through these domains; using a recently generated model system allowing us to track endogenous PC-1, we confirm the interaction between the endogenous proteins. Finally, we show that NPHP1 trafficking to cilia does not require PC-1 and that PC-1 may require NPHP1 to regulate resistance to apoptosis, but not to regulate cell cycle progression. In line with this, we find high levels of apoptosis in renal specimens of NPHP patients. Our data uncover a link between two different ciliopathies, ADPKD and NPHP, supporting the notion that common pathogenetic defects, possibly involving de-regulated apoptosis, underlie renal cyst formation.

A novel mouse model reveals that polycystin-1 deficiency in ependyma and choroid plexus results in dysfunctional cilia and hydrocephalus.

Polycystin-1 (PC-1), the product of the PKD1 gene, mutated in the majority of cases of Autosomal Dominant Polycystic Kidney Disease (ADPKD), is a very large (approximately 520 kDa) plasma membrane receptor localized in several subcellular compartments including cell-cell/matrix junctions as well as cilia. While heterologous over-expression systems have allowed identification of several of the potential biological roles of this receptor, its precise function remains largely elusive. Studying PC-1 in vivo has been a challenging task due to its complexity and low expression levels. To overcome these limitations and facilitate the study of endogenous PC-1, we have inserted HA- or Myc-tag sequences into the Pkd1 locus by homologous recombination. Here, we show that our approach was successful in generating a fully functional and easily detectable endogenous PC-1. Characterization of PC-1 distribution in vivo showed that it is expressed ubiquitously and is developmentally-regulated in most tissues. Furthermore, our novel tool allowed us to investigate the role of PC-1 in brain, where the protein is abundantly expressed. Subcellular localization of PC-1 revealed strong and specific staining in ciliated ependymal and choroid plexus cells. Consistent with this distribution, we observed hydrocephalus formation both in the ubiquitous knock-out embryos and in newborn mice with conditional inactivation of the Pkd1 gene in the brain. Both choroid plexus and ependymal cilia were morphologically normal in these mice, suggesting a role for PC-1 in ciliary function or signalling in this compartment, rather than in ciliogenesis. We propose that the role of PC-1 in the brain cilia might be to prevent hydrocephalus, a previously unrecognized role for this receptor and one that might have important implications for other genetic or sporadic diseases.