Molecular Regulation of Vascular System Development and Angiogenesis.
Establishment of a functional circulatory system during development is crucial for delivery of nutrients and oxygen to the embryo. Defects in the development of blood vessels result in death before birth or in congenital cardiovascular abnormalities. Our main focus is to examine the molecular and genetic pathways that regulate the three principal processes of vascular development and homeostasis: endothelial cell lineage determination, vasculogenesis and angiogenesis. More recently, we have extended our studies to investigating the molecular underpinning of certain vascular diseases. We focus on the mouse model and the embryonic stem cell (ESC) in vitro differentiation system because of the ready availability of genetic and experimental tools, and because of physiological similarities between mice and humans. Using an expression-based "gene trap" screen in mouse ESCs and embryos, we previously identified two novel genes that are involved in vascular system development, Vezf1 and Egfl7.
Transcriptional control of blood vascular and lymphatic development.
Vascular endothelial zinc finger 1 (Vezf1) encodes a Zn finger transcription factor with prominent expression in vascular endothelial cells. Using a loss-of-function approach, we showed that Vezf1 plays an essential and dosage-dependent role in the proliferation, remodeling, and integrity of the developing blood vasculature. Strikingly, mutant embryos also display lymphatic vessel abnormalities with a phenotype reminiscent of the human congenital malformation syndrome, nuchal edema.
We presently focus on dissecting the genetic pathways that Vezf1 participates in during embryogenesis and in adults. Collaborative studies on Vezf1 null ESCs with Dr. Gary Felsenfeld indicate that Vezf1 is involved in the epigenetic regulation of gene expression through regulating the DNA methyltransferase Dnmt3b. In addition, VEZF1 binds to the Rho GTPase RhoB, and the two genes genetically interact in formation and maintenance of the blood and lymphatic vasculature. A microarray screen for Vezf1 targets in Vezf1KO embryos identified several candidate genes involved in pathways that are relevant to blood coagulation, platelet activation, lipoprotein transport and vascular homeostasis. These studies implicate Hnf4a as a critical mediator of Vezf1 function. Future studies will provide a detailed understanding how Vezf1 modulates these pathways during development and angiogenesis. Another recent focus is on identifying genetic factors underlying a class of developmental lymphatic malformation termed nuchal edemas. These studies are undertaken in collaboration with colleagues in the Fetal-Maternal Medicine Division at New York Presbyterian/Weill Cornell Medical College.
Signaling pathways in vascular development and disease.
A second endothelial gene identified in our screen, EGF-like domain 7 (Egfl7), is an early marker for endothelial cells and their progenitors in the yolk sac blood islands. Endothelial Egfl7 expression is high during vascular development and during physiological and pathological angiogenesis. Importantly, EGFL7 has the hallmarks of an angiogenic factor: it is secreted, acts as a chemoattractant for endothelial cells and binds to components of the extracellular matrix. Using lentivirus-mediated knock-down and transgenic overexpression approaches, we showed that Egfl7 function is required during vascular patterning and integrity. We also showed that EGFL7 interacts with endothelial Notch and modulates Notch signaling.
Our present research uses loss- and gain-of-function approaches to understand these interactions on a molecular, cellular and genetic level in primary endothelial cells, in embryos and in the vascular niche of the adult bone marrow. We are also testing our hypothesis that EGFL7 responds to ischemia and vascular injury to regulate neoangiogenesis through cross-talk with HIF-1alpha, VEGF and Notch. We are also exploring the identity and developmental potential of Egfl7-positive progenitor cells by marking these cells with a fluorescent marker. Finally, we are investigating the role Egfl7 in pre-eclampsia, a pregnancy-specific disease that is defined by sudden onset of hypertension and proteinuria in the last trimester.