Browsing by Author "Childs, Sarah J"

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    Characterizing the role of Rasa1 in vascular development in zebrafish
    (2015-04-20) Davari, Paniz; Childs, Sarah J
    Vascular malformation syndromes arise during embryonic development and can have devastating effects on the quality of life of patients. Capillary malformations present with the overgrowth and permanent dilation of the capillaries under the skin but are often accompanied by fast-flow arteriovenous malformations in other internal organs. Recently, mutations in the GTPase activating protein RASA1 were found to be one cause of capillary malformation- arteriovenous malformation (CM-AVM). I set out to model CM-AVM in the zebrafish and found that loss of rasa1 leads to a large arteriovenous malformation that connects the artery and vein without intervening capillaries. In wild-type zebrafish embryos, a distinct aorta and a caudal vein plexus are visible in the tail region. However, in rasa1a morphants, there is an enlarged single vessel instead of a plexus, and this vessel fails to develop sprouts. Arteriovenous shunts develop commonly in this region. I next examined the mechanism by which rasa1 functions. I found that rasa1a genetically interacts with rras but not farnesyl- modified ras (rat sarcoma) genes. rasa1a also functions in parallel pathway to rras2. Finally, I showed misregulation of vegfc (vascular growth factor c) and vegfr3 (vascular growth factor receptor 3) in rasa1a morphants, suggesting rasa1a loss leads to misregulation of venous signaling pathways.
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    Fine-tuning blood vessel development
    (2020-09-11) Watterston, Charlene; Childs, Sarah J; Brook, William J; Huang, Peng; Bonni, Shirin; Yelon, Deborah
    Blood vessel development is typically characterized by stages marking the growth and gradual refinement of vascular networks. Understanding how these stages integrate is essential to our understanding of how the early signals which control vessel growth can influence later stages of vessel stabilization. In this thesis, I use a zebrafish model (Danio rerio) to explore the roles of two negative regulators that modulate key signaling pathways controlling vessel growth. At the early stages, the initial growth of vessels is carefully controlled by distinct gene expression patterns. As a vessel forms, in response to the attractive Vascular endothelial growth factor (Vegf) pathway, its sprouting is often opposed by repulsive Semaphorins (Semas) which limit directional growth. I investigated the role of semaphorin3fb (sema3fb) which I found to be expressed within developing endothelial cells of the zebrafish embryo. I found that sema3fb likely acts through auto-secretory feedback to modulate Vegf responses to promote appropriate vessel growth. At later stages, a supportive layer of vascular smooth muscle cells (vSMCs) is recruited to form the contractile layer of the vessel wall. Bone morphogenic protein (Bmp) signaling is implicated in cellular crosstalk from the underlying endothelium to vSMCs which is critical to the structural integrity of a blood vessel. I investigated the microRNA26a (miR26a), which I found enriched in the endothelial lining of the blood vessel. I identified a non-autonomous role for miR26a in regulating Bmp signaling through its effector Smad1 to control vSMC maturation. Together my work offers mechanistic insight into the cellular communication pathways that regulate blood vessel formation and focuses on how both internal and external signaling pathways communicate to promote vessel formation.
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    Quantum dot interactions and flow effects in angiogenic zebrafish (Danio rerio) vessels and human endothelial cells
    (Elsevier, 2017-01) Jiang, Xiao-Yu; Sarsons, Christopher D; Gomez-Garcia, M Juliana; Cramb, David T; Rinker, Kristina D; Childs, Sarah J
    Nanoparticle (NP) interactions with biological tissues are affected by the size, shape and surface chemistry of the NPs. Here we use in vivo (zebrafish) and in vitro (HUVEC) models to investigate association of quantum dots (QDs) with endothelial cells and the effect of fluid flow. After injection into the developing zebrafish, circulating QDs associate with endothelium and penetrate surrounding tissue parenchyma over time. Amino-functionalized QDs cluster, interact with cells, and clear more rapidly than carboxy-functionalized QDs in vivo, highlighting charge influences. QDs show stronger accumulation in slow-flowing, small caliber venous vessels than in fast-flowing high caliber arterial vessels. Parallel-plate flow experiments with HUVEC support these findings, showing reduced QD-EC association with increasing flow. In vivo, flow arrest after nanoparticle injection still results in venous accumulation at 18 h. Overall our results suggest that both QD charge and blood flow modulate particle-endothelial cell interactions.
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    The use of small molecules to illuminate vascular development
    (2017) Goi, Michela; Childs, Sarah J
    Development of the vascular system is a multifactorial process. Its proper establishment has a big impact on life. Not only is this process essential for organismal growth but abnormal blood vessel formation leads to several pathologies. In some cases the disease itself triggers changes to the vascular system. I have worked on three aspects regarding the development of the vascular system: drugs inhibiting the formation of new sprouting vessels (angiogenic vessels), vascular patterning, and its stability. I have used small molecules to probe these processes. First, I showed the advantage of using zebrafish as a model system for efficiently screening anti-angiogenic small molecule compounds designed for cancer therapy. Treating cancer by inhibiting its recruitment of new blood vessels prevents nutrients from reaching the growing tumor. Of 11 novel potential compounds tested, I identified 5 with anti-angiogenic properties, all likely inhibiting the Vascular endothelial growth factor (Vegf) pathway, and showed that these compounds have different effects and efficacies. However, blood vessel patterning cues and mechanisms differ in different organs. In order to design more effective therapies, I next investigated the development of the intestinal vasculature, a poorly characterized vascular bed. By using small molecule inhibitors, I found that both Vegf and Bone morphogenetic protein (Bmp) signaling drive the growth and patterning of this plexus. A genetic mutant with overgrowth of the intestinal vasculature follows similar growth cues, but development is faster and unrestricted. Finally, I have investigated a later aspect of blood vessel development: vascular stability. By interacting with mural cells, endothelial cells mature into a functional apparatus that delivers nutrients, collects waste, responds to inflammation, and regulates blood pressure. The nkx3.2 transcription factor was downregulated in two models of vascular instability. I found that Nkx3.2 contributes to vascular stability as its knockout reduces the number of mural cells, and that mutant embryos are more likely to hemorrhage after treatment with a drug affecting mural-endothelial cell contact. Through this work I have increased our knowledge of vascular development and stabilization through detailed understanding of early vessel formation and the use of small molecules.