Hypoxia-responsive signaling regulates the apoptosis-dependent remodeling of the embryonic avian cardiac outflow tract.
We proposed a model in which myocardial hypoxia triggers the apoptosis-dependent remodeling of the avian outflow tract (OFT) in the transition of the embryo to a dual circulation. In this study, we examined hypoxia-dependent signaling in cardiomyocyte apoptosis and outflow tract remodeling. The hypoxia-inducible transcription factor HIF-1alpha was specifically present in the nuclei of OFT cardiomyocytes from stages 25-32, the period of hypoxia-dependent OFT remodeling. HIF-1alpha expression was sensitive to changes in ambient oxygen concentrations, while its dimerization partner HIF-1beta was constitutively expressed. There was not a simple relationship between HIF-1alpha expression and apoptosis. Apoptotic cardiomyocytes were detected in HIF-1alpha-positive and -negative regions, and a hypoxic stimulus sufficient to induce nuclear accumulation of HIF-1alpha did not induce cardiomyocyte apoptosis. The hypoxia-dependent expression of the vascular endothelial growth factor receptor (VEGFR2) in the distal OFT myocardium may be protective as cardiomyocyte apoptosis in the early stages (25-30) of OFT remodeling was absent from this region. Furthermore, recombinant adenoviral-mediated expression of dominant negative Akt, an inhibitor of tyrosine kinase receptor signaling, augmented cardiomyocyte apoptosis in the OFT and constitutively active Akt suppressed it. Adenovirus-mediated forced expression of VEGF165 induced conotruncal malformation such as double outlet right ventricle (DORV) and ventricular septal defect (VSD), similar to defects observed when apoptosis-dependent remodeling of the OFT was specifically targeted. We conclude that normal developmental remodeling of the embryonic avian cardiac OFT involves hypoxia/HIF-1-dependent signaling and cardiomyocyte apoptosis. Autocrine signaling through VEGF/VEGFR2 and Akt provides survival signals for the hypoxic OFT cardiomyocytes, and regulated VEGF signaling is required for the normal development of the OFT.
Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Yasuyuki
Y
Sugishita
David W
DW
Leifer
Faton
F
Agani
Michiko
M
Watanabe
Steven A
SA
Fisher
D000818:Animals; D030801:Animals, Genetically Modified; D017209:Apoptosis; D002642:Chick Embryo; D003370:Coturnix; D006321:Heart / Q000196:embryology*; D000860:Hypoxia / Q000473:pathology / Q000503:physiopathology; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics / Q000378:metabolism; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; C467484:VEGFA protein, human; D042461:Vascular Endothelial Growth Factor A; D040301:Vascular Endothelial Growth Factor Receptor-2; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt