PORTEFEUILLE

Uromodulin was described decades ago as the most abundant protein in urine. Recent studies linked uromodulin with a set of rare, uromodulin-associated kidney disorders (UAKD). UAKD are autosomal dominant disorders characterised by hyperuricemia and gout early in life, alteration of urinary concentrating ability, and development of tubulo-interstitial fibrosis invariably leading to chronic renal failure and end-stage renal disease in young adults. The care of patients with UAKD is hampered by unresolved issues concerning the causal and modifying genes, the underlying molecular mechanisms, the variable phenotype and the risk of developing kidney failure or multi-systemic complications.

In a collaborative effort, we will have access to a large, well-characterized existing patient cohort and biomaterial, complemented by cutting-edge cellular and mouse models, to pursue three major aims:
Aim 1: To develop a new ontology of UAKD and characterize the clinical and genetic features of hyperuricemic nephropathies. We will use a comprehensive approach to develop a new classification system of these rare nephropathies, based on a registry that will integrate deep phenotyping with genetic, biochemical, histopathological and clinical informations.

Aim 2: To identify new genes involved in UAKD and hyperuricemic nephropathy. We will identify new genes causing UAKD, and characterize the functional consequences of mutations.

Aim 3: To decipher the molecular mechanisms of UAKD. We will perform in vivo and in vitro studies to understand the link between defective uromodulin (intracellular accumulation) and modifications in tubular functions, handling of uric acid, and subsequent renal damage leading to chronic kidney disease.

Overall, this project will help to better understand the clinical presentation, the genetic causes and the mechanisms of UAKD and improve the care of patients suffering from these rare inherited kidney disorders. These insights may also be relevant for the mechanisms of renal disease progression and for conformational and endoplasmic reticulum storage diseases.

To date, more than 200 different rare renal diseases have been described, with an overall prevalence of about 60-80 cases per 100,000 total population in Europe. In contrast to many other rare diseases, patients with kidney disorders rarely die when their disease progresses but - thanks to organ replacement therapy - may remain alive for many years. However, this apparent advantage is frequently brought at the expense of severely compromised health with poor quality of life, causing a tremendous cumulative cost burden to health care systems. In particular, patients born with congenital nephropathies face decades of life with chronic kidney disease (CKD) leading to end-stage renal disease (ESRD) with a high likelihood of altered physical, cognitive and psychosocial development.

The current diagnostic and treatment of rare kidney diseases is highly unsatisfactory and progress is needed in priority areas of research including:
- Refining disease ontology beyond phenotypic or morphological description;
- Identification of genetic initiators and modifiers of disease and their molecular pathways;
- Development and application of disease models suitable to screen for novel therapies.
In this project, we will focus on uromodulin-associated kidney disorders as a paradigm of these difficulties, with need and potential for diagnostic and therapeutic progress.

This project is the first kidney disease-related program to be supported by Gebert Rüf Stiftung. Chronic kidney disease is a growing burden worldwide, and inherited kidneys disorders present particular challenges to overcome. Based on pre-existing cohorts, biobanks and models, as well as strong interactions and networking, the project addresses several priorities outlined in the Orphanet plan for rare diseases research in Europe (2011). The support of the Foundation will also strength translational research on rare kidney disorders in Switzerland.

Completion of the project: April 2016
We have used a comprehensive approach to classify these rare nephropathies, based on a registry that integrates deep phenotyping with genetic, biochemical, histopathological and clinical informations. The current registry includes more than 100 families, with 25 originating from various regions of Switzerland. The results have been presented at the Swiss Society of Nephrology (E. Olinger et al. Interlaken, 12/2014).

We organized a Kidney Disease: Improving Global Outcomes (KDIGO) Conference that adopted diagnostic criteria and a new terminology for UMOD-associated kidney diseases using the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' (ADTKD) appended by a gene-based subclassification. Implementation of these recommendations will facilitate recognition and characterization of these diseases. These recommendations have been published in Eckardt et al. 2015.

On the basis of the registry described above, we have identified a set of 5 families with typical UAKD but no mutation evidenced in the UMOD, HNF1B and REN, i.e. the genes that have been associated with UAKD thus far. These families are currently screened in order to identify new genes causing UAKD (coll. BROAD Institute, Boston, USA; University of Oxford, UK).

The link between uromodulin, tubular functions and renal damage leading to chronic kidney disease (CKD) has been particularly investigated using a translational approach. We have demonstrated that UMOD risk variants directly increase UMOD expression in vitro and in vivo. This very mechanism is relevant in humans, as pharmacological inhibition of NKCC2 is more effective in lowering BP in hypertensive patients homozygous for UMOD risk variants. These findings point to uromodulin as a novel therapeutic target to lower BP and preserve renal function. These results have been presented during the ASN Meetings in Atlanta (2013) and Philadelphia (2014) and detailed in several publications : Trudu M et al. 2013; Eckardt et al. 2015, Labriola et al. 2014, Olden et al. 2014.

To overcome limitations of culture systems in terms of terminal differentiation, we developed a primary culture system based on pure TAL segments microdissected from mouse kidney and grown on permeable filters. These polarized monolayers display morphological features and critical functions of TAL cells in vivo, including electrophysiological properties and processing of uromodulin. These results have been detailed in Glaudemans et al. 2014.

We developed and characterized a robust ELISA for uromodulin, and used this new assay to show the value of uromodulin as a biomarker for renal function and risk of CKD. The results have been detailed in Youhanna S, et al. 2014, Pruijm et al. 2016, Troyanov et al. 2016.

We recently used a multi-level approach to demonstrate that a common variant of the UMOD gene, driving higher urinary excretion of uromodulin, has been kept at a high frequency because of its protective effect against urinary tract infections (detailed in Ghirotto et al. 2016).

In order to establish the precise role of hyperuricemia in UAKD we created a humanized mouse model by genetic deletion of the uricase. Viable uricase knockout mice (Uox KO mice) were obtained and characterized at the University of Lausanne. Homozygous Uox KO mice display a severe renal phenotype with high mortality - preventing detailed analyses of the kidney. Treatment with allopurinol rescued the mortality in this model, but not the severity of renal damage. We will thus develop a floxed Uox line allowing a conditional invalidation of the gene. The Uox mouse model is anyway useful to better understand the uric acid homeostasis, and will be useful in other studies.

We have generated two new lines of Umod knock-in (KI) mouse harbouring the C170Y and R185S human mutations. Characterization of these mice revealed key features observed in the human disease, opening important perspective for mechanistic studies.

Ghirotto S, Tassi F, Barbujani G, Pattini L, Hayward C, Vollenweider P, Bochud M, Rampoldi L, Devuyst O. The Uromodulin Gene Locus Shows Evidence of Pathogen Adaptation through Human Evolution. J Am Soc Nephrol 2016 Mar 10. pii: ASN.2015070830. PMID: 26966016:
Pruijm M, Ponte B, Ackermann D, Paccaud F, Guessous I, Ehret G, Pechère-Bertschi A, Vogt B, Mohaupt MG, Martin PY, Youhanna SC, Nägele N, Vollenweider P, Waeber G, Burnier M, Devuyst O*, Bochud M*. Associations of Urinary Uromodulin with Clinical Characteristics and Markers of Tubular Function in the General Population. Clin J Am Soc Nephrol 11: 70-80, 2016 (* Equal senior authorship);
Troyanov S, Delmas-Frenette C, Bollée G, Youhanna S, Bruat V, Awadalla P, Devuyst O*, Madore F*. Clinical, Genetic, and Urinary Factors Associated with Uromodulin Excretion. Clin J Am Soc Nephrol 11: 62-69, 2016. (* Corresponding authors):
Devuyst O, Bochud M. Uromodulin, kidney function, cardiovascular disease, and mortality. Kidney Int 88: 944-946, 2015;
Brunati M, Perucca S, Han L, Cattaneo A, Consolato F, Andolfo A, Schaeffer C, Olinger E, Peng J, Santambrogio S, Perrier R, Li S, Bokhove M, Bachi A, Hummler E, Devuyst O, Wu Q, Jovine L, Rampoldi L. The serine protease hepsin mediates urinary secretion and polymerisation of Zona Pellucida domain protein uromodulin. Elife 4: e08887, 2015;
Eckardt KU, Alper SL, Antignac C, Bleyer AJ, Chauveau D, Dahan K, Deltas C, Hosking A, Kmoch S, Rampoldi L, Wiesener M, Wolf MT, Devuyst O. Autosomal dominant tubulointerstitial kidney disease: diagnosis, classification, and management--A KDIGO consensus report. Kidney Int 88: 676-683, 2015;
Labriola L, Olinger E, Belge H, Pirson Y, Dahan K, Devuyst O. Paradoxical response to furosemide in uromodulin-associated kidney disease. Nephrol Dial Transplant 30: 330-335, 2015;
Bonny O, Bochud M. Genetics of calcium homeostasis in humans: continuum between monogenic diseases and continuous phenotypes, Nephrol Dial Transplant 29: iv55–iv62, 2014;
Demoulin N, Aydin S, Cosyns JP, Dahan K, Cornet G, Auberger I, Loffing J, Devuyst O. Gitelman syndrome and glomerular proteinuria: a link between loss of sodium-chloride cotransporter and podocyte dysfunction ? Nephrol Dial Transplant 29 Suppl 4:iv117-20, 2014;
Devuyst O, Knoers NV, Remuzzi G, Schaefer F; Board of the Working Group for Inherited Kidney Diseases of the European Renal Association and European Dialysis and Transplant Association. Rare inherited kidney diseases: challenges, opportunities, and perspectives. Lancet 383:1844-59, 2014;
Olden M, Corre T, Hayward C, Toniolo D, Ulivi S, Gasparini P, Pistis G, Hwang SJ, Bergmann S, Campbell H, Cocca M, Gandin I, Girotto G, Glaudemans B, Hastie ND, Loffing J, Polasek O, Rampoldi L, Rudan I, Sala C, Traglia M, Vollenweider P, Vuckovic D, Youhanna S, Weber J, Wright AF, Kutalik Z, Bochud M, Fox CS, Devuyst O. Common Variants in UMOD Associate with Urinary Uromodulin Levels: A Meta-Analysis. J Am Soc Nephrol 25:1869-82, 2014;
Gailly P, Szutkowska M, Olinger E, Debaix H, Seghers F, Janas S, Vallon V, Devuyst O. P2Y2 receptor activation inhibits the expression of the sodium-chloride cotransporter NCC in distal convoluted tubule cells. Pflugers Arch 466:2035-47, 2014;
Youhanna S, Weber J, Beaujean V, Glaudemans B, Sobek J, Devuyst O. Determination of uromodulin in human urine: influence of storage and processing. Nephrol Dial Transplant 29:136-45, 2014;
Glaudemans B, Terryn S, Gölz N, Brunati M, Cattaneo A, Bachi A, Al-Qusairi L, Ziegler U, Staub O, Rampoldi L, Devuyst O. A primary culture system of mouse thick ascending limb cells with preserved function and uromodulin processing. Pflugers Arch 466:343-56, 2014;
Trudu M, Janas S, Lanzani C, Debaix H, Schaeffer C, Ikehata M, Citterio L, Demaretz S, Trevisani F, Ristagno G, Glaudemans B, Laghmani K, Dell'antonio G; the Swiss Kidney Project on Genes in Hypertension (SKIPOGH) team, Bochud M, Burnier M, Martin PY, Mohaupt M, Paccaud F, Pechère-Bertschi A, Vogt B, Ackermann D, Ehret G, Guessous I, Ponte B, Pruijm M, Loffing J, Rastaldi MP, Manunta P, Devuyst O*, Rampoldi L*. Common noncoding UMOD gene variants induce salt-sensitive hypertension and kidney damage by increasing uromodulin expression. Nat Med 19: 1655-60, 2013 (*Olivier Devuyst & Luca Rampolid contributed equally to this work);
Köttgen A, Albrecht E, Teumer A, ..., Devuyst O, ..., Fox CS, Caulfield M, Bochud M, Gieger C. Genome-wide association analyses identify 18 new loci associated with serum urate concentrations. Nat Genet 2012 Dec 23. doi: 10.1038/ng.2500;
Bollée G, Dahan K, Flamant M, Morinière V, Pawtowski A, Heidet L, Lacombe D, Devuyst O, Pirson Y, Antignac C, Knebelmann B. Phenotype and outcome in hereditary tubulointerstitial nephritis secondary to UMOD mutations. Clin J Am Soc Nephrol. 2011 Oct;6(10):2429-38;
Rampoldi L, Scolari F, Amoroso A, Ghiggeri G, Devuyst O. The rediscovery of uromodulin (Tamm-Horsfall protein): from tubulointerstitial nephropathy to chronic kidney disease. Kidney Int. 2011 Aug;80(4):338-47;
Bernascone I, Janas S, Ikehata M, Trudu M, Corbelli A, Schaeffer C, Rastaldi MP, Devuyst O, Rampoldi L. A transgenic mouse model for uromodulin-associated kidney diseases shows specific tubulo-interstitial damage, urinary concentrating defect and renal failure. Hum Mol Genet 19: 2998-3010, 2010;
Dahan K*, Devuyst O*, Smaers M, et al. A cluster of mutations in the UMOD gene causes familial juvenile hyperuricemic nephropathy with abnormal expression of uromodulin. J Am Soc Nephrol. 2003 Nov;14(11):2883-93. (* Equal contribution).