APC controls asymmetric Wnt/β-catenin signaling and cardiomyocyte proliferation gradient in the heart.
OBJECTIVE
Cardiomyocyte (CM) proliferation increases from the inner trabecular to outer compact myocardium in fetal hearts. We determined if canonical Wnt signaling has directional and graded activity to maintain this CM proliferation gradient. Moreover, we investigated whether perturbation of Wnt signaling intensity could modulate CM proliferative activity.


RESULTS
With confocal microscopy and image analysis we found that the Wnt effector, β-catenin, formed a signaling gradient which positively correlated with CM proliferative activity across ventricular walls of wild type (WT) embryos at embryonic day (E) 13.5 and 17.5. Negative Wnt regulators, adenomatosis polyposis coli (APC), had a reverse distribution pattern. The activation of canonical Wnt/β-catenin signaling by deletion of Apc in CMs led to ventricular hyperplasia with no adverse effects on fetal survival or CM differentiation. In contrast, cardiac deletion of β-catenin resulted in ventricular hypoplasia and fetal demise by E14.5. We further revealed differential distribution and regulation of three cyclin Ds in fetal hearts. Cyclin D1 was mainly expressed in endothelial cells. Although both cyclin D2 and D3 were present in CMs, only cyclin D2 was regulated by Wnt signaling perturbation: downregulation by β-catenin deletion and upregulation by Apc knockout.


CONCLUSIONS
Canonical Wnt signaling is asymmetrical and graded across ventricular walls and positively regulates CM proliferation via cyclin D2.
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA; Department of Laboratory Medicine and Pathology, University of Minnesota, Room 293, Dwan Variety Club Cardiovascular Research Center, 425 E River Pkwy, Minneapolis, MN 55455, USA.
Bo
B
Ye
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA.
Ning
N
Hou
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA.
Lu
L
Xiao
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA.
Yifan
Y
Xu
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA.
James
J
Boyer
Department of Pathology and Laboratory Medicine, UCLA Center for the Health Science, Room 13-145E, 10833 Le Conte Ave, Los Angeles, CA 90095, USA.
Haodong
H
Xu
Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA; Department of Laboratory Medicine and Pathology, University of Minnesota, Room 293, Dwan Variety Club Cardiovascular Research Center, 425 E River Pkwy, Minneapolis, MN 55455, USA. Electronic address: lif@umn.edu.
Faqian
F
Li
D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism*; D000818:Animals; D049109:Cell Proliferation; D048430:Cell Shape; D016213:Cyclins / Q000378:metabolism; D004622:Embryo, Mammalian / Q000378:metabolism; D004843:Epistasis, Genetic; D017353:Gene Deletion; D005786:Gene Expression Regulation; D051379:Mice; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D060449:Wnt Signaling Pathway; D051176:beta Catenin / Q000235:genetics / Q000378:metabolism
D025601:Adenomatous Polyposis Coli Protein; D016213:Cyclins; D051176:beta Catenin
Adenomatosis polyposis coli (APC); Development; Heart; Proliferation; Wnt; β-catenin