The European Rare Kidney Disease Registry (ERKReg): objectives, design and initial results

Epidemiologia; Nefrologia pediàtrica; RegistreEpidemiología; Nefrología pediátrica; RegistroEpidemiology; Pediatric nephrology; RegistryBackground The European Rare Kidney Disease Reference Network (ERKNet) recently established ERKReg, a Web-based registry for all patients with rare kidney diseases. The main objectives of this core registry are to generate epidemiological information, identify current patient cohort for clinical research, explore diagnostic and therapeutic management practices, and monitor treatment performance and patient’s outcomes. The registry has a modular design that allows to integrate comprehensive disease-specific registries as extensions to the core database. The diagnosis (Orphacode) and diagnostic information (clinical, imaging, histopathological, biochemical, immunological and genetic) are recorded. Anthropometric, kidney function, and disease-specific management and outcome items informing a set of 61 key performance indicators (KPIs) are obtained annually. Data quality is ensured by automated plausibility checks upon data entry and regular offline database checks prompting queries. Centre KPI statistics and benchmarking are calculated automatically. Results Within the first 24 months since its launch, 7607 patients were enrolled to the registry at 45 pediatric and 12 specialized adult nephrology units from 21 countries. A kidney disease diagnosis had been established in 97.1% of these patients at time of enrolment. While 199 individual disease entities were reported by Orphacode, 50% of the cohort could be classified with 11, 80% with 43 and 95% with 92 codes. Two kidney diagnoses were assigned in 6.5% of patients; 5.9% suffered from syndromic disease. Whereas glomerulopathies (54.8%) and ciliopathies including autosomal dominant polycystic kidney disease (ADPKD) (31.5%) were the predominant disease groups among adults, the pediatric disease spectrum encompassed congenital anomalies of the kidney and urinary tract (CAKUT) (33.7%), glomerulopathies (30.7%), ciliopathies (14.0%), tubulopathies (9.2%), thrombotic microangiopathies (5.6%), and metabolic nephropathies (4.1%). Genetically confirmed diagnoses were reported in 24% of all pediatric and 12% adult patients, whereas glomerulopathies had been confirmed by kidney biopsy in 80.4% adult versus 38.5% pediatric glomerulopathy cases. Conclusions ERKReg is a rapidly growing source of epidemiological information and patient cohorts for clinical research, and an innovative tool to monitor management quality and patient outcomes.Open Access funding enabled and organized by Projekt DEAL. The ERKReg project was made possible by a European Union grant (Chafea #777303) within the Third Health Programme “ERN-2016—Framework Partnership Agreement 2017–2021”. Additional support was received by ERKNet within the same framework. Further support for the development of the registry was kindly provided by the ERA-EDTA Workgroup for Inherited Kidney Diseases (WGIKD)

Nephroprotective Efficacy of RAS Blockade in Mice Carrying R140Q Podocin Mutation

<p>INTRODUCTION:NPHS2 mutations cause hereditary nephrotic syndrome and progressive renal failure.We recently generated an inducible knock-in mouse model carrying R140Q,the analogue of the most common human mutation R138Q.These mice develop FSGS with nephrotic syndrome and progressive renal failure.Here we tested the efficacy of early and delayed RAS blockade in this model of hereditary podocyte disease.</p> <p>METHODS:In C57BL/6 mice with Nphs2Flox/R140Q/Cre+ genotype,hemizygosity for mutant podocin was induced by tamoxifen injection.Animals received combined high-dose ACE inhibition and AT1 receptor blockade(ramipril+candesartan 10mg/kg each,R+C)or remained untreated.Treatment was started either prophylactically(P)at time of induction or with a 4-week delay(D).Animals were either sacrificed after 5 wks(9 wks in D) or observed open-end.</p> <p>RESULTS:Induction of R140Q-podocin hemizygosity caused massive proteinuria peaking at 4 wks,followed by a gradual decrease as progressive renal failure developed.In the P animals,RAS blockade persistently inhibited proteinuria(13%of untreated animals at 4 wks,p<0.005).In the D group,proteinuria sharply decreased upon RAS blockade.Three-month survival was 31% in the untreated,67% in the D and 100% in the P group respectively(p<0.05).<br>Podocin protein abundance was almost totally lost in both untreated and treated animals,despite preserved or even increased mRNA expression.P group animals retained a higher number of podocytes per glomerulus and lower glomerulosclerosis and tubolointerstitial fibrosis indices than the untreated animals.In the D animals,histopathological lesions were slightly less marked at 9 wks than in the untreated animals at 5 wks.</p> <p>CONCLUSIONS:In mice carrying the most common human podocin mutation,RAS blockade attenatues proteinuria,podocyte loss and glomerulosclerosis despite persistently increased degradation of mutant podocin protein.Renal failure is delayed and survival prolonged.Treatment is more effective when applied prophylactically than when started in established nephropathy.Our findings indicate that early RAS blockade may provide effective nephroprotection in this hereditary podocytopathy.</p> <p> </p

Podocyte Purinergic P2X4 channels are mechanotransducers that mediate cytoskeletal disorganization

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X(4)) blocker 5-BDBD. Moreover, mechanical P2X(4) channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X(4) channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X(4) channels as mechanotransducers in podocytes

An inducible mouse model of podocin-mutation-related nephrotic syndrome

Mutations in the NPHS2 gene, encoding podocin, cause hereditary nephrotic syndrome. The most common podocin mutation, R138Q, is associated with early disease onset and rapid progression to end-stage renal disease. Knock-in mice carrying a R140Q mutation, the mouse analogue of human R138Q, show developmental arrest of podocytes and lethal renal failure at neonatal age. Here we created a conditional podocin knock-in model named NPHS2 R140Q/-, using a tamoxifen-inducible Cre recombinase, which permits to study the effects of the mutation in postnatal life. Within the first week of R140Q hemizygosity induction the animals developed proteinuria, which peaked after 4-5 weeks. Subsequently the animals developed progressive renal failure, with a median survival time of 12 (95% CI: 11-13) weeks. Foot process fusion was observed within one week, progressing to severe and global effacement in the course of the disease. The number of podocytes per glomerulus gradually diminished to 18% compared to healthy controls 12-16 weeks after induction. The fraction of segmentally sclerosed glomeruli was 25%, 85% and 97% at 2, 4 and 8 weeks, respectively. Severe tubulointerstitial fibrosis was present at later disease stage and was correlated quantitatively with the level of proteinuria at early disease stages. While R140Q podocin mRNA expression was elevated, protein abundance was reduced by more than 50% within one week following induction. Whereas miRNA21 expression persistently increased during the first 4 weeks, miRNA-193a expression peaked 2 weeks after induction. In conclusion, the inducible R140Q-podocin mouse model is an auspicious model of the most common genetic cause of human nephrotic syndrome, with a spontaneous disease course strongly reminiscent of the human disorder. This model constitutes a valuable tool to test the efficacy of novel pharmacological interventions aimed to improve podocyte function and viability and attenuate proteinuria, glomerulosclerosis and progressive renal failure

Bicarbonate buffered peritoneal dialysis fluid upregulates angiopoietin-1 and promotes vessel maturation

Background Ultrafiltration decline is a progressive issue for patients on chronic peritoneal dialysis (PD) and can be caused by peritoneal angiogenesis induced by PD fluids. A recent pediatric trial suggests better preservation of ultrafiltration with bicarbonate versus lactate buffered fluid; underlying molecular mechanisms are unknown. Methods Angiogenic cytokine profile, tube formation capacity and Receptor Tyrosine Kinase translocation were assessed in primary human umbilical vein endothelial cells following incubation with bicarbonate (BPDF) and lactate buffered (LPDF), pH neutral PD fluid with low glucose degradation product content and lactate buffered, acidic PD fluid with high glucose degradation product content (CPDF). Peritoneal biopsies from age-, PD-vintage- and dialytic glucose exposure matched, peritonitis-free children on chronic PD underwent automated histomorphometry and immunohistochemistry. Results In endothelial cells angiopoietin-1 mRNA and protein abundance increased 200% upon incubation with BPDF, but decreased by 70% with LPDF as compared to medium control; angiopoietin-2 remained unchanged. Angiopoietin-1/Angiopoietin-2 protein ratio was 15 and 3-fold increased with BPDF compared to LPDF and medium. Time-lapse microscopy with automated network analysis demonstrated less endothelial cell tube formation with BPDF compared to LPDF and CPDF incubation. Receptor Tyrosine Kinase translocated to the cell membrane in BPDF but not in LPDF or CPDF incubated endothelial cells. In children dialyzed with BPDF peritoneal vessels were larger and angiopoietin-1 abundance in CD31 positive endothelium higher compared to children treated with LPDF. Conclusion Bicarbonate buffered PD fluid promotes vessel maturation via upregulation of angiopoietin-1 in vitro and in children on dialysis. Our findings suggest a molecular mechanism for the observed superior preservation of ultrafiltration capacity with bicarbonate buffered PD fluid with low glucose degradation product content

Clinical and genetic characteristics of Dent's disease type 1 in Europe

Background. Dent's disease type 1 (DD1) is a rare X-linked nephropathy caused by CLCN5 mutations, characterized by proximal tubule dysfunction, including low molecular weight proteinuria (LMWP), hypercalciuria, nephrolithiasis- nephrocalcinosis, progressive chronic kidney disease (CKD) and kidney failure (KF). Current management is symptomatic and does not prevent disease progression. Here we describe the contemporary DD1 picture across Europe to highlight its unmet needs. Methods. A physician-based anonymous international e-survey supported by several European nephrology networks/societies was conducted. Questions focused on DD1 clinical features, diagnostic procedure and mutation spectra. Results. A total of 207 DD1 male patients were reported; clinical data were available for 163 with confrmed CLCN5 mutations. Proteinuria was the most common manifestation (49.1%). During follow-up, all patients showed LMWP, 66.4% nephrocalcinosis, 44.4% hypercalciuria and 26.4% nephrolithi- asis. After 5.5 years, ≈50% of patients presented with renal dysfunction, 20.7% developed CKD stage ≥3 and 11.1% developed KF. At the last visit, hypercalciuria was more frequent in paedi-atric patients than in adults (73.4% versus 19.0%). Conversely, nephrolithiasis, nephrocalcinosis and renal dysfunction were more prominent in adults. Furthermore, CKD progressed with age. Despite no clear phenotype/genotype correlation, decreased glomerular fltration rate was more frequent in subjects with CLCN5 mutations afecting the pore or CBS domains compared with those with early-stop mutations. Conclusions. Results from this large DD1 cohort confrm previous fndings and provide new insights regarding age and genotype impact on CKD progression. Our data strongly support that DD1 should be considered in male patients with CKD, nephrocalcinosis/hypercalciuria and non-nephrotic pro-teinuria and provide additional support for new research opportunities.</p

Podocyte Purinergic P2X 4

Podocytes are specialized, highly differentiated epithelial cells in the kidney glomerulus that are exposed to glomerular capillary pressure and possible increases in mechanical load. The proteins sensing mechanical forces in podocytes are unconfirmed, but the classic transient receptor potential channel 6 (TRPC6) interacting with the MEC-2 homolog podocin may form a mechanosensitive ion channel complex in podocytes. Here, we observed that podocytes respond to mechanical stimulation with increased intracellular calcium concentrations and increased inward cation currents. However, TRPC6-deficient podocytes responded in a manner similar to that of control podocytes, and mechanically induced currents were unaffected by genetic inactivation of TRPC1/3/6 or administration of the broad-range TRPC blocker SKF-96365. Instead, mechanically induced currents were significantly decreased by the specific P2X purinoceptor 4 (P2X(4)) blocker 5-BDBD. Moreover, mechanical P2X(4) channel activation depended on cholesterol and podocin and was inhibited by stabilization of the actin cytoskeleton. Because P2X(4) channels are not intrinsically mechanosensitive, we investigated whether podocytes release ATP upon mechanical stimulation using a fluorometric approach. Indeed, mechanically induced ATP release from podocytes was observed. Furthermore, 5-BDBD attenuated mechanically induced reorganization of the actin cytoskeleton. Altogether, our findings reveal a TRPC channel-independent role of P2X(4) channels as mechanotransducers in podocytes

Current management of transition of young people affected by rare renal conditions in the ERKNet

Transition in medical care is a high-risk period in adolescence and young adulthood. To date, data on transition policy, its application in practice, and transition procedures in patients with rare, hereditary kidney diseases in Europe is scarce. An online survey was developed and was distributed within the paediatric centres of the European Reference Network for Rare Kidney Diseases (ERKNet) aiming to assess the transition-relevant structures from the providers’ perspectives. Its items were based on the consensus statement on transition published by the International Society of Nephrology (ISN) and the International Paediatric Nephrology Association (IPNA) in 2011. Forty-six paediatric experts based at 28/32 ERKNet university hospitals participated. Annually, a median number of 14 patients (1–80) are transferred to adult based care. One centre continued to care for paediatric kidney transplant recipients throughout their entire lifespan. Choosing this option terminated the survey and no further data was obtained from this centre. 29/45 experts confirmed the application of an—at least unwritten—transition procedure (64%). Transition clinics are offered by 23 experts. Most physicians (40%) transfer patients at age 18–19, 10 experts at age <18. Most physicians transfer the patients to a university hospital and/or a community hospital. The transition guidelines have been implemented in ERKNet centres only partly and with huge heterogeneity. Implementation of transition tools and structures within ERKNet could improve health of children with hereditary kidney diseases. Adherence of experts to the transition-guidelines was significantly correlated with gross national income of their countries

Whereas mRNA expression of mutant <i>Nphs2</i> is elevated, podocin protein abundance is diminished.

<p>(A) <i>Nphs2</i>^{<i>R140Q/-</i>} animals showed an elevated expression level of mutated podocin mRNA during the first four weeks following induction (analysis is based on 4–6 animals per group and time point) WT: wild type. (B) Western blot analysis of total kidney extracts showing partial podocin protein loss during first two weeks, subtotal loss after 4–6 weeks and complete loss at attainment of end-stage renal disease (week 12–16) (analysis is based on 4–6 animals per group and time point; p<0.05).</p