Abstract 15763: FoxO1 Drives VCAM1 Expression to Govern Chorioallantoic Fusion and Early Cardiac and Vascular Development
Introduction: Targeted disruption of FoxO1, a member of the Forkhead box-containing O family of transcription factors, leads to embryonic lethality on embryonic day 10.5 (E10.5) due to abnormal cardiac and vascular development. However, underlying mechanisms remain elusive.
Methods and Results: To explore this further, FoxO1-null (FoxO1-/-) and FoxO1 wild- type (WT) embryos were isolated at distinct developmental stages (∼E8.0-E10.5). Consistent with previous reports, FoxO1-inactivation was lethal at E10.5, and growth retardation with cardiac and vascular malformation were detected at E9.5. Although FoxO1-null and WT littermates were indistinguishable between E8.0-E9.0, null embryos manifested a misshapen allantois which remained unfused to surrounding placenta. As a similar phenotype underlies embryonic lethality in VCAM1-null embryos, we hypothesized that FoxO1 is an upstream element driving VCAM1-dependent chorioallantoic fusion and subsequent vascular/cardiovascular development. Vcam1 expression was significantly decreased in null embryos (immunohistochemical and biochemical markers), and TUNEL assays revealed age-dependent increases in apoptotic cells in FoxO1-null allantois as compared to WT littermates. By contrast, at this stage of development, expression of α-endomucin, an endothelium-specific protein, was not affected, suggesting that vascular malformation had not yet occurred at this stage. Sequence analysis revealed evolutionarily conserved FoxO-responsive elements (FREs) in the upstream promoter region (UPR) of the VCAM1 gene. To test their functional significance, we studied transiently transfected reporter constructs (COS cells), detecting dose-dependent induction of luciferase activity in both FoxO1 and Vcam1-UPR luciferase constructs harboring WT, but not mutated, FREs.
Conclusions: VCAM1 is a previously undescribed FoxO1 downstream target. Transcriptional regulation of VCAM1 gene expression by FoxO1 is essential for chorioallantoic fusion, cell survival, and proper cardiac and vascular development during early embryogenesis.
- © 2010 by American Heart Association, Inc.