Rolle von beta-Catenin im Rahmen des myokardialen Remodeling bei linksventrikulärer Druckbelastung und nach Myokardinfarkt
Zusammenfassung der Projektergebnisse
The project analyzed cellular and molecular pathways of LV remodeling in order to identify new targets and possibly new treatment options aiming at adult LV muscular tissue regeneration. Functional characterization by echocardiography of transgenic mice with conditional, cardiac-specific gain- and loss-off-function β-catenin mutations demonstrated increased nuclear activity of β-catenin to be deleterious for cardiac remodeling whereas conditional, β-catenin loss-off-function appeared to be protective. FACS analysis of whole-cell myocardial lysates was suggestive of cardiac precursor cell differentiation regenerating cardiac muscular tissue in the absence of increased cell proliferation. As β-catenin is ubiquitously expressed and is also involved in several other cellular proliferation and differentiation processes including tumor growth, heart-specific β-catenin regulation would need to be understood prior to exploit this pathway for therapeutic purposes. We therefore analyzed specific β-catenin interaction partners that would possibly allow for cardiac specific β-catenin modulation, namely KLF15 and FHL2 both identified by a yeast-two-hybrid screen with a cardiac-specific cDNA library and β-catenin as the bait. The effects of KLF15 were analyzed by various experiments including functional and cellular characterization of a global KLF15 null-mutant. We found KLF15 to inhibit cardiac β-catenin activation by activating the nemo-like kinase (NLK), which in turn phosphorylates Tcf4 targeting it for proteasom degradation. Tcf4 is the DNA-binding partner of β-catenin in the nucleus. KLF15 null-mutants exhibit an increased β-catenin dependent transcription and a phenotype similar to conditional β-catenin gain-of-function mutants: upon aging, cardiac function deteriorated and increased afterload lead to rapid ventricular dilation and reduced ejection fraction as measured by echocardiography. This was again associated with impaired differentiation of cardiac precursor cells (CPC) both in vitro and in vivo: adult cardiac CPC's differentiated towards an endothelial but not myocardial lineage both in vitro as well as in vivo. Similarly to KLF15, the four-and-a-half-LIM-domain 2 (FHL2) protein was found to regulate embryonic cardiac precursor cells in different in vivo models. Downstream of β-catenin regulation, we found the Tbx5 transcription factor specific for the first heart field giving rise to the left ventricle to be upregulated. Thus in the final part of the project, we performed a large scale screening assay to identify small molecules that would upregulate Tbx5. These small molecules are currently tested in dose-response experiments. If a powerful Tbx5 regulator (possibly in parallel found to be a β-catenin inhibitor) can be identified, such a molecule should be able to enhance endogenous cardiac regeneration following injury. Mechanistically, we will test the hypothesis that Tbx5 activators would reprogram non-cardiomyocytes to differentiate towards a cardiomyocyte lineage. Such a molecule and mechanism could be patented if modified to be as specific and effective as possible. The project newly idnetified the molecular role of FHL2, KLF15 and β-catenin in adult cardiac remodeling. Ongoing studies aim to mimick this effect with small molecules targeting Tbx5 and p-catenin.
Projektbezogene Publikationen (Auswahl)
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Beta-catenin downregulation is required for adaptive cardiac remodeling. Circ Res 2007;100(9):1353-62
Baurand A, Zelarayan L, Betney R, Gehrke C, Dunger S, Noack C, Busjahn A, Huelsken J, Taketo MM, Birchmeier W, Dietz R, Bergmann MW
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Beta-Catenin downregulation attenuates ischemic cardiac remodeling through enhanced resident precursor cell differentiation. Proc Natl Acad Sci USA 2008;105(50): 19762-7
Zelarayan LC, Noack C, Sekkali B, Kmecova J, Gehrke C, Renger A, Zafiriou MP, van der Nagel R, Dietz R, de Windt LJ, Balligand JL, Bergmann MW
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WNT signaling in adult cardiac hypertrophy and remodeling: lessons learned from cardiac development. Circ Res 2010;107(10):1198-208
Bergmann MW
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Krueppel-like factor 15 regulates Wnt/beta-catenin transcription and controls cardiac progenitor cell fate in the postnatal heart. EMBO Mol Med 2012;4(9):992-1007
Noack C, Zafiriou MP, Schaeffer HJ, Renger A, Pavlova E, Dietz R, Zimmermann WH, Bergmann MW, Zelarayan LC
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The four and a half LIM-domain 2 controls early cardiac cell commitment and expansion via regulating beta-catenin-dependent transcription. Stem Cells 2013;31(5):928-40
Renger A, Zafiriou MP, Noack C, Pavlova E, Becker A, Sharkova K, Bergmann MW, El-Armouche A, Zimmermann WH, Zelarayan LC
