Submitted to: Genes and Development
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/9/2004
Publication Date: 7/1/2004
Citation: Bohnsack, B.L., Lai, L., Dolle, P., Hirschi, K.K. 2004. Signaling heirarchy downstream of retinoic acid that independently regulates vascular remodeling and endothelial cell proliferation. Genes and Development. 18(11):1345-1358. Interpretive Summary: Retinoic acid is crucial in the control of endothelial cell growth and proliferation during embryonic blood vessel growth. Employing an embryo culture system, we examined retinoic acid regulation of blood vessel development in the yolk sac of mice embryos. Study of mice engineered to be deficient in the enzyme that produces retinoic acid showed that various cell factors derived from the endoderm layer of the embryos do not independently promote blood vessel growth, but do so collectively. Our results suggest that downstream signaling of retinoic acid is an important factor in vascular remodeling.
Technical Abstract: We previously demonstrated that during vascular morphogenesis, retinoic acid (RA) is required for the control of endothelial cell proliferation and capillary plexus remodeling. Herein, we investigate the mechanisms by which RA regulates these processes in the yolk sac. We found that although the enzyme required for RA production during early embryogenesis, retinaldehyde dehydrogenase-2 (Raldh2), was expressed in the visceral endoderm, RA receptors alpha1 and alpha2 were expressed in endothelial cells in the mesoderm, indicating that they are direct targets of RA. In Raldh2(-/-) embryos, there was down-regulation of TGF-beta1, fibronectin (Fn) and integrin alpha5, which was associated with decreased visceral endoderm survival and production of VEGF-A, Indian hedgehog (IHH), and bFGF. Exogenous provision of RA or Fn to Raldh2(-/-) explants in whole mouse embryo culture restored vascular remodeling, visceral endoderm survival, as well as integrin alpha5 expression and its downstream signaling that controls endothelial growth. Exogenous provision of visceral endoderm-derived factors (VEGF-A, IHH, and bFGF) failed to rescue endothelial cell proliferative control but collectively promoted vascular remodeling, suggesting that these processes are independently regulated via a signaling hierarchy downstream of RA.