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.
Sugishita
Yasuyuki
Y
Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA.
Leifer
David W
DW
Agani
Faton
F
Watanabe
Michiko
M
Fisher
Steven A
SA
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