Abstract 15154: Interaction of Krueppel-Like Factor (klf) 15 and Wnt-Signaling Pathway and its Role in Adult Cardiac Precursor Cell Regulation
Wnt/β-catenin signaling controls early cardiac development as well as adult heart remodeling in part via regulation of cardiac progenitor cell (CPC) differentiation. We characterized the effect of an identified β-catenin interaction partner, the Krüppel like factor 15 (KLF15), on Wnt/β-catenin signaling and adult CPC biology. An in vitro reporter assay showed KLF15 to significant repress β-catenin-dependent gene transcription in a concentration-dependent manner. Mutagenesis and co-immunoprecipitation analysis showed both, the KLF15-N-terminus (amino acids 45 to 152), and the KLF15-C-terminus, to be necessary for transcription repression. The analysis of Klf15 knock-out (KO) mice showed a cardiac KLF15-dependent repression of β-catenin transcription demonstrated by significant increase of its target genes TCF4 and c-Myc in KO mice at the protein and RNA level. This was associated with cardiac dysfunction as demonstrated by impaired fractional shortening (n=10). Flow cytometry analysis of the CPC enriched-population revealed a significant reduction of cardiogenic-committed precursors identified as Sca1/αMHC (WT 1.75±0.08% vs KO 0.83±0.19%) and Tbx5 (WT 5.23±0.48% vs KO 3.47±0.26%). In contrast, endothelial Sca1/CD31 cells were significantly higher in KO mice (WT 8.60±0.36% vs KO 11.25±0.39% n≥9). Mice with a cardiac β-catenin deletion showed decreased endothelial CD31 cells in the CPC fraction (WT 18.01±0.84% vs KO 15.06±0.76% n≥6). klf15 KO mice showed increased RNA expression of endothelial markers: von Willebrand Factor and CD105 (n=10). CPCs co-cultured on adult fibroblast resulted in increased endothelial Flk1 cells and reduction of αMHC and Hand1 cardiogenic cells in KO CPCs at day 10 of culture (n=6). Treating the co-cultures with Quercetin, an inhibitor of β-catenin transcription, resulted in partial abrogation of Flk1 cell increase and αMHC and Hand1 cell reduction. We conclude that KLF15-dependent β-catenin repression favors vascular differentiation and antagonizes cardiogenic cell differentiation similar to what has been observed in embryonic development. This work may have identified a novel molecular switch to therapeutically modulate CPC fate and unlock the regenerative potential of the adult heart.
- © 2011 by American Heart Association, Inc.