Mechanisms of pathogenicity and the quest for genetic modifiers of kidney disease in branchiootorenal syndrome

Backgound

Branchiootorenal (BOR) syndrome is an autosomal dominant disorder caused by pathogenic EYA1 variants and clinically characterized by auricular malformations with hearing loss, branchial arch anomalies, and congenital anomalies of the kidney and urinary tract. BOR phenotypes are highly variable and heterogenous. While random monoallelic expression is assumed to explain this phenotypic heterogeneity, the potential role of modifier genes has not yet been explored.

Methods

Through thorough phenotyping and exome sequencing, we studied one family with disease presentation in at least four generations in both clinical and genetic terms. Functional investigation of the single associated EYA1 variant c.1698+1G>A included splice site analysis and assessment of EYA1 distribution in patient-derived fibroblasts. The candidate modifier gene CYP51A1 was evaluated by histopathological analysis of murine Cyp51+/- and Cyp51-/- kidneys. As the gene encodes the enzyme lanosterol 14α-demethylase, we assessed sterol intermediates in patient blood samples as well.

Results

The EYA1 variant c.1698+1G>A resulted in functional deletion of the EYA domain by exon skipping. The EYA domain mediates protein-protein interactions between EYA1 and co-regulators of transcription. EYA1 abundance was reduced in the nuclear compartment of patient-derived fibroblasts, suggesting impaired nuclear translocation of these protein complexes. Within the affected family, renal phenotypes spanned from normal kidney function in adulthood to chronic kidney failure in infancy. By analyzing exome sequencing data for variants that potentially play roles as genetic modifiers, we identified a canonical splice site alteration in CYP51A1 as the strongest candidate variant.

Conclusion

In this study, we demonstrate pathogenicity of EYA1 c.1698+1G>A, propose a mechanism for dysfunction of mutant EYA1, and conjecture CYP51A1 as a potential genetic modifier of renal involvement in BOR syndrome.

Towards understanding policy design through text-as-data approaches: The policy design annotations (POLIANNA) dataset

Despite the importance of ambitious policy action for addressing climate change, large and systematic assessments of public policies and their design are lacking as analysing text manually is labour-intensive and costly. POLIANNA is a dataset of policy texts from the European Union (EU) that are annotated based on theoretical concepts of policy design, which can be used to develop supervised machine learning approaches for scaling policy analysis. The dataset consists of 20,577 annotated spans, drawn from 18 EU climate change mitigation and renewable energy policies. We developed a novel coding scheme translating existing taxonomies of policy design elements to a method for annotating text spans that consist of one or several words. Here, we provide the coding scheme, a description of the annotated corpus, and an analysis of inter-annotator agreement, and discuss potential applications. As understanding policy texts is still difficult for current text-processing algorithms, we envision this database to be used for building tools that help with manual coding of policy texts by automatically proposing paragraphs containing relevant information.

Claudin-10a Deficiency Shifts Proximal Tubular Cl- Permeability to Cation Selectivity via Claudin-2 Redistribution

Background The tight junction proteins claudin-2 and claudin-10a form paracellular cation and anion channels, respectively, and are expressed in the proximal tubule. However, the physiological role of claudin-10a in the kidney has been unclear. Methods To investigate the physiologic role of claudin-10a, we generated claudin-10a-deficient mice; confirmed successful knockout by Southern blot, Western blot, and immunofluorescence staining; and analyzed urine and serum of knockout and wild-type animals. We also used electrophysiologic studies to investigate the functionality of isolated proximal tubules, and studied compensatory regulation by pharmacologic intervention, RNA sequencing analysis, Western blot, immunofluorescence staining, and respirometry. Results Mice deficient in claudin-10a were fertile and without overt phenotypes. Upon knockout, claudin-10a was replaced by claudin-2 in all proximal tubule segments. Electrophysiology showed conversion from paracellular anion preference to cation preference and a loss of paracellular Cl^- over HCO3^- preference. As a consequence, there was tubular retention of calcium and magnesium, higher urine pH, and mild hypermagnesemia. A comparison of other urine and serum parameters under control conditions and sequential pharmacologic transport inhibition, as well as unchanged fractional lithium excretion, suggested compensative measures in proximal and distal tubular segments. Changes in proximal tubular oxygen handling and differential expression of genes regulating fatty acid metabolism indicated proximal tubular adaptation. Western blot and immunofluorescence revealed alterations in distal tubular transport. Conclusions Claudin-10a is the major paracellular anion channel in the proximal tubule and its deletion causes calcium and magnesium hyperreabsorption by claudin-2 redistribution. Transcellular transport in proximal and distal segments and proximal tubular metabolic adaptation compensate for loss of paracellular anion permeability.

Governing complex societal problems: The impact of private on public regulation through technological change

When addressing complex societal problems, public regulation is increasingly complemented by private regulation. Extant literature has provided valuable insights into the effectiveness of such complex governance structures, with most empirical studies focusing on how public regulation influences private regulation. Conversely, the impact of private on public regulation is less well studied. Here, we investigate this impact with a focus on technological change as possible mechanism. Based on a case study of energy efficiency in buildings in Switzerland, we find evidence of a symbiotic interaction between public and private regulation that leads to ratcheting-up of regulatory stringency. We identify technological change as the mechanism linking private and public regulation. We discuss the relevance of our findings for governance literature and regulators.

MO049FUNCTIONAL IMPORTANCE OF MAPKBP1 PROTEIN DOMAINS IN NEPHRONOPHTHISIS

Background and Aims

Nephronophthisis is an autosomal-recessive kidney disease that accounts for a significant proportion of end-stage renal disease (ESRD) in childhood, adolescence and early adulthood. Biallelic pathogenic variants in MAPKBP1, encoding the c-Jun N-terminale kinase (JNK)-binding protein 1, are associated with development of Nephronophthisis and subsequent chronic kidney disease (CKD) (Macia et al, AJHG, 2017). We recently characterized MAPKBP1 as microtubule-associated protein that is able to localize to centrioles and the base of primary cilia depending on dimerization via its C-terminal coiled-coil domain (Schönauer et al, Kidney Int, 2020). However, the physiological function of its N-terminal WD40 and intermediate JNK-binding domain is still poorly understood. By in vitro comparison of artificial domain deletions with known and novel patient variants, we aim at pinpointing functional consequences of pathogenic MAPKBP1 in cilia and cell cycle control.

Method

N-terminally GFP-tagged MAPKBP1 constructs with either full-domain deletions or patient-derived variants were expressed in non-ciliated HeLa and ciliated H69 cells for fluorescence microscopy studies. Furthermore, RNA-seq analysis using primary patient cells was conducted to investigate differentially regulated molecular pathways compared to healthy control individuals.

Results

Immunofluorescence microscopy revealed inappropriate intracellular localization upon single or combined deletion of any MAPKBP1 protein domain. Compared to wild type, all deletion variants showed reduced intensity at the centrosome and ciliary base. Despite preserved dimerization ability, loss of the intermediate JNK-binding domain (JBD) most effectively abolished centrosomal or ciliary targeting, whereas loss of the N-terminal WD40-domain induced strongest mitotic aberrations. Unlike wild type, both, artificial and patient-derived truncating variants were able to enter the nucleus. RNA-seq analysis using primary patient fibroblasts with varying C-terminal truncations will allow important insights into common gene expression profiles unveiling consequences of aberrant intracellular trafficking.

Conclusion

In the present work, we demonstrate that all protein domains are indispensable for appropriate MAPKBP1 intracellular localization and function. Most of clinically reported patient variants exhibiting C-terminal truncation of varying lengths resulted in comparable intracellular behavior in presence of an intact N-terminal WD40 domain. Surprisingly, deletion of the JNK-binding domain alone aggravated functional disturbances hinting at a prominent regulatory role of this protein part interdepending with dimerization. Further insights into domain-specific functions will explain molecular disease mechanisms of MAPKBP1.

P0071MOLECULAR ALTERATIONS AND THE SEARCH FOR GENETIC MODIFIERS IN BRANCHIOOTORENAL SYNDROME

Background and Aims

Branchiootorenal (BOR) syndrome (MIM# 113650) is an exceedingly rare disorder of autosomal-dominant inheritance that describes the combination of branchial anomalies, structurally defective ears with associated hearing loss, and congenital anomalies of the kidney and urinary tract (CAKUT). Pathogenic variants in the developmentally important gene EYA1 have been found to underlie most instances of BOR syndrome. Given the high inter- and intrafamilial variability of phenotypic traits in BOR syndrome, renal involvement varies significantly. However, distinct somatic, genetic, or environmental factors underlying this phenomenon remain elusive. Moreover, the precise role of EYA1 in renal development and pathogenesis of BOR related kidney disease remains ill-defined. Here, we sought to investigate molecular alterations as well as genetic modifiers of renal involvement in a family segregating a previously reported (Rodríguez-Soriano et al. Pediatr Nephrol 2001) heterozygous canonical splice site variant in EYA1 (c.1698 + 1G>A, NM_000503.5). Remarkably, structural kidney anomalies led to end-stage renal disease in a two-year old boy while his father exhibited normal renal function.

Method

For analysis of the splice site EYA1 variant, cDNA was obtained from primary patient fibroblasts. Immunofluorescence microscopy was employed to assess the intracellular distribution of EYA1 in both patient and control fibroblasts. Semiquantitative data on cellular EYA1 abundance were obtained from immunoblotting of whole protein extracts from patient and control fibroblast cultures. As for the investigation of genetic modifiers of renal involvement in BOR syndrome, identification of candidate genes was based upon whole exome sequencing data in all four family members (the parental couple and both affected children). Analysis of variants was restricted to de novo variants and those inherited from the non-affected mother.

Results

The splice site EYA1 variant that was assumed to be disease-causing turned out to be pathogenic. Mutant transcript variants result from exon skipping, leading to the translation of an aberrant C-terminus. This affects the highly conserved C-terminal EYA domain that is crucial for interaction with several transcription factors (e.g., from the SIX family). In line with these findings, our imaging data demonstrate a reduced nuclear enrichment of EYA1 in the mutant case, suggesting an impaired nuclear translocation process. Immunoblotting showed an increased EYA1 abundance in mutant fibroblasts, possibly indicating compensation of gene dose effects. Data from immunofluorescence microscopy and immunoblotting are preliminary. Finally, our search for genetic modifiers of renal involvement in BOR syndrome yielded a promising candidate variant in CYP51A1 in both affected children and their mother. CYP51A1 is an essential enzyme of cholesterol synthesis and has been shown to be indispensable for embryonic development.

Conclusion

Here, we sought to define the molecular basis of BOR syndrome in a family segregating a canonical splice site variant in EYA1. Analysis of the splice site demonstrates pathogenicity of this very variant. Further in vitro functional analyses show reduced nuclear localization of EYA1 in mutant fibroblasts, albeit we detected an increase in EYA1 abundance. Our findings are compatible with the notion that the interaction of mutant EYA1 with various transcription factors in the cytosol is impaired, preventing nuclear translocation of the protein complex. We propose that an increase in EYA1 abundance in mutant cells constitutes a compensatory mechanism. In searching for genetic modifiers of renal involvement in BOR syndrome, we identified a candidate variant in CYP51A1. Both CYP51A1 and EYA1 are developmentally important and concurrence of pathogenic variants in both genes may impair normal renal development.

Matching clinical and genetic diagnoses in autosomal dominant polycystic kidney disease reveals novel phenocopies and potential candidate genes

Purpose

Autosomal dominant polycystic kidney disease (ADPKD) represents the most common hereditary nephropathy. Despite growing evidence for genetic heterogeneity, ADPKD diagnosis is still primarily based upon clinical imaging criteria established before discovery of additional PKD genes. This study aimed at assessing the diagnostic value of genetic verification in clinical ADPKD.

Methods

In this prospective, diagnostic trial, 100 families with clinically diagnosed ADPKD were analyzed by PKD gene panel and multiplex ligation-dependent probe amplification (MLPA); exome sequencing (ES) was performed in panel/MLPA-negative families.

Results

Diagnostic PKD1/2 variants were identified in 81 families (81%), 70 of which in PKD1 and 11 in PKD2. PKD1 variants of unknown significance were detected in another 9 families (9%). Renal survival was significantly worse upon PKD1 truncation versus nontruncation and PKD2 alteration. Ten percent of the cohort were PKD1/2-negative, revealing alternative genetic diagnoses such as autosomal recessive PKD, Birt–Hogg–Dubé syndrome, and ALG9-associated PKD. In addition, among unsolved cases, ES yielded potential novel PKD candidates.

Conclusion

By illustrating vast genetic heterogeneity, this study demonstrates the value of genetic testing in a real-world PKD cohort by diagnostic verification, falsification, and disease prediction. In the era of specific treatment for fast progressive ADPKD, genetic confirmation should form the basis of personalized patient care.

Enhancing the effect of repetitive I-wave paired-pulse TMS (iTMS) by adjusting for the individual I-wave periodicity

BACKGROUND

Repeated application of paired-pulse TMS over the primary motor cortex (M1) in human subjects with an inter-pulse interval (IPI) of 1.5 ms (iTMS(1.5 ms)) has been shown to significantly increase paired-pulse MEP (ppMEP) amplitudes during the stimulation period and increased single-pulse MEP amplitudes for up to 10 minutes after termination of iTMS.

RESULTS

Here we show in a cross-over design that a modified version of the iTMS(1.5 ms) protocol with an I-wave periodicity adjusted to the individual I1-peak wave latency (iTMS(adj)) resulted in a stronger effect on ppMEPs relative to iTMS(1.5 ms).

CONCLUSIONS

Based on these findings, our results indicate that the efficiency of iTMS strongly depends on the individual choice of the IPI and that parameter optimization of the conventional iTMS(1.5 ms) protocol might improve the outcome of this novel non-invasive brain stimulation technique.