Research Report 2010 - MDC

TCF/Lef signaling in the kidney. One crucial aspect ofour future studies will be to elucidate the role of Wntsignaling in kidney disease, with an emphasis on thecanonical TCF/Lef-dependent pathway. For this purposewe are using different genetic and experimental mousemodels, which we analyze using genome-wide analysisof expression and transcription factor binding. We areworking in close collaboration with Thomas Willnow(MDC), Friedrich C. Luft (ECRC), and Jonathan Barasch(Columbia University, New York). We believe that adetailed elucidation of the transcriptional network controlledby TCF/Lef will yield fundamental insights intogrowth, remodeling, and regeneration in the kidney.CABTranscription factors involved in terminal renalepithelial differentiationWhile TCF/Lef-dependent signaling accounts for earlydevelopmental programs in renal epithelial progenitors,it may in fact be inhibitory to terminal differentiationof tubular epithelia. Therefore, we are seeking complementarytranscriptional regulators that induce theestablishment of epithelial polarity and the expressionof segment-specific markers. Using expression profiling,we identified two candidate transcriptional regulatorsof terminal differentiation, which belong to theCP2 group of transcription factors (Tcfcpl1 and Grhl2),which are highly and specifically expressed in the distalnephron. Characterization of Grhl2 is part of a DFGfundedproject (Schm 1730/3-1) within FG “Epithelialmechanisms of renal volume regulation” (Speaker:Sebastian Bachmann, Charité Berlin). The projects benefitfrom our close collaborations with JonathanBarasch (Columbia University, New York), ThomasWillnow (MDC), and Michael Bader (MDC).Biomarkers of Renal InjuryCharacterization of transcription factors in nephron epithelia.A. β-Galactosidase expressed from the Grhl2 locus displays an epithelialspecificpattern in the early postnatal kidney. B. Nuclear localization ofthe transcription factor Tcfcp2l1 (green) in a subset of nephron epithelia(red) as detected by confocal microscopy. C. Transcription factor bindingto genomic DNA in a renal epithelial cell line as determined by chromatinimmunoprecipitation followed by massively parallel sequencing.The frequency plot reveals strongly enriched transcription factor bindingto genomic DNA around transcriptional start sites (TSS).Re-expression of embryonic marker molecules is a commonfeature in disease states and is believed to participatein compensation and regeneration. Neutrophilgelatinase-associated lipocalin (NGAL) is a protein inthe developing kidney that is sufficient to induce differentiationin embryonic renal epithelial progenitors.NGAL is also markedly reactivated in tubular injury ofthe kidney and its urinary excretion is closely correlatedwith the temporal onset and severity of tubular injury.In collaboration with Jonathan Barasch (ColumbiaUniversity, New York), Friedrich C. Luft (ECRC) and RalphKettritz (ECRC), we are conducting clinical studies totest the performance of NGAL as a urinary and plasmabiomarker of acute kidney injury. We are aiming to optimizediagnostic algorithms that utilize NGAL measurementsto predict renal injury or to differentiate renalinjury from related clinical entities. This project servesas a prime example to illustrate the importance of anunderstanding of basic molecular mechanisms in theembryo to address the diagnosis of renal disease in theadult. Translational aspects of our research are markedlyenhanced by our close ties to the ‘Experimental andClinical Research Center’ (see ECRC section).Selected publicationsLi JY, Paragas N, Ned RM, Qiu A, Viltard M, Leete T, Drexler IR, Chen X,Sanna-Cherchi S, Mohammed F, Williams D, Lin CS, Schmidt-Ott KM,Andrews NC, Barasch J. (2009) Scara5 is a ferritin receptor mediatingnon-transferrin iron delivery. Dev Cell. 16:35-46.Schmidt-Ott KM, Barasch J. (2008) WNT/beta-catenin signaling innephron progenitors and their epithelial progeny. Kidney Int. 74:1004-8.Schmidt-Ott K.M., Masckauchan T.N., Chen X., Hirsh B.J., Sarkar A., Yang J.,Paragas N., Wallace V.A., Dufort D., Pavlidis P., Jagla B., Kitajewski J.,Barasch J. (2007) -Catenin/TCF/Lef Controls A Differentiation-AssociatedTranscriptional Program In Renal Epithelial Progenitors. Development.134(17):3177-90.Schmidt-Ott, K.M., Mori, K., Li, J.Y., Kalandadze, A., Cohen, D.J., Devarajan, P.,Barasch, J. (2007) Dual action of neutrophil gelatinase-associatedlipocalin. J Am Soc Nephrol. 18, 407-13.Schmidt-Ott, K.M., Chen, X., Paragas, N., Levinson, R.S., Mendelsohn, C.L.,Barasch,, J. (2006) c-kit delineates a distinct domain of progenitors in thedeveloping kidney. Dev Biol. 299, 238-49.Cardiovascular and Metabolic Disease Research 25