title: Continuous antagonism by Dkk1 counter activates canonical Wnt signaling and promotes cardiomyocyte differentiation of embryonic stem cells.
abstract: Embryonic stem (ES) cells give rise to mesodermal progenitors that differentiate to hematopoietic and cardiovascular cells. The wnt signaling pathway plays multiple roles in cardiovascular development through a network of intracellular effectors. To monitor global changes in wnt signaling during ES cell differentiation, we generated independent ES cell lines carrying the luciferase gene under promoters that uniquely respond to specific wnt pathway branches. Our results show that successive, mutually exclusive waves of noncanonical and canonical wnt signaling precede mesoderm differentiation. Blocking the initial noncanonical JNK/AP-1 signaling with SP60125 aborts cardiovascular differentiation and promotes hematopoiesis, whereas interference with the subsequent peak of canonical wnt signaling using Dkk1 has the opposite effect. Dkk1 blockade triggers counter mechanisms that lead to delayed and extended activation of canonical wnt signaling and mesoderm differentiation that appear to favor the cardiomyocytic lineage at the expense of hematopoietic cells. The cardiomyocytic yield can be further enhanced by overexpression of Wnt11 leading to approximately 95-fold enrichment in contracting cells. Our results suggest that the initial noncanonical wnt signaling is necessary for subsequent activation of canonical signaling and that the latter operates under a regulatory loop which responds to suppression with hyperactivation of compensatory mechanisms. This model provides new insights on wnt signaling during ES cell differentiation and points to a method to induce cardiomyocytic differentiation without precise timing of wnt signaling manipulation. Taking into account the heterogeneity of pluripotent cells, these findings might present an advantage to enhance the cardiogenic potential of stem cells.
authors.affiliation: Division of Cardiovascular Medicine, Department of Medicine, Vanderbilt University, Nashville, Tennessee 37232-6300, USA.
authors.forename: Meena
authors.initials: M
authors.lastname: Rai
authors.forename: Joel M
authors.initials: JM
authors.lastname: Walthall
authors.forename: Jianyong
authors.initials: J
authors.lastname: Hu
authors.forename: Antonis K
authors.initials: AK
authors.lastname: Hatzopoulos
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D053595:Embryonic Stem Cells / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D017930:Genes, Reporter; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology*; D049409:Luciferases, Firefly / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011401:Promoter Regions, Genetic; D060888:Real-Time Polymerase Chain Reaction; D015533:Transcriptional Activation; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism; D060449:Wnt Signaling Pathway
chemical_list: D000943:Antigens, Differentiation; C501127:Dkk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; D051153:Wnt Proteins; C508957:Wnt11 protein, mouse; D049409:Luciferases, Firefly