Abstract P208: Depletion of Dapper-1 Acts Antihypertrophic on Cardiomyocytes and Inhibits Wnt3a- and Wnt5a-Mediated Activation of the Wnt Signaling Pathway
Background: Cardiac development is regulated by the evolutionary conserved Wnt signaling pathway. While Wnt activity is silenced in the adult heart under normal conditions this pathway is activated during myocardial remodeling following pathological injury such as myocardial infarction. Among other members of this pathway Dapper-1 was suggested to antagonize Wnt activation but its role in Wnt signaling is poorly understood. In a murine myocardial infarction model as well as in a cardiomyocyte hypoxia model we found a robust over-expression of Dapper-1. To elucidate its function in cardiomyocytes we performed Dapper-1 specific siRNA mediated knockdown experiments.
Results: Depletion of Dapper-1 leads to reduction of cardiomyocyte surface area (-10% ± 4%, p<0.001 vs. control), attenuation of global protein content (-20% ± 3%, p<0.02 vs. control) and diminishes global protein synthesis (-27% ± 10%, p<0.02 vs. control). Augmentation of protein synthesis by β-adrenic Isoproterenol stimulation is widely inhibited. Wnt3a induced stimulation of protein synthesis and enlargement of cardiomyocyte surface area is blocked in Dapper-1 knockdown cardiomyocytes. Furthermore, we observed reduced total- and active-β-catenin protein levels. Moreover, Dapper-1 knockdown inhibits β-catenin from translocation to the nucleus following Wnt3a stimulation. TCF/LEF reporter activity was reduced in Dapper-1-diminished -and elevated in Dapper-1-overexpressed cardiomyocytes after Wnt3a treatment. Robust Ser9 -and weak Tyr216 phosphorylation of GSK3β suggested a GSK3β independent inhibition of canonical Wnt signaling. In addition, activation of non-canonical Wnt/JNK pathway by Wnt5a conditioned medium was completely inhibited in Dapper-1 knockdown cells.
Summary: Dapper1 is an essential modulator for global protein synthesis. Furthermore, Dapper-1 is required to activate canonical and noncanonical Wnt signaling pathways in cardiomyocytes.
- © 2011 by American Heart Association, Inc.