PhD Oral Exam - Stephanie He, Biology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

The prevalence of cardiovascular diseases, such as ischemia, underscores the need for innovative therapeutic strategies. Recent advances in the field of focused ultrasound offer a non-surgical, targeted, and promising technology to treat various life-threatening diseases, including brain disorders, inoperable cancers and some vascular diseases. This approach harnesses the therapeutic potential of ultrasound-stimulated microbubbles for the modulation of cellular and vascular permeability to guide the delivery of therapeutics. More recently, gene therapy has shown great potential as a less invasive approach in contrast to surgical interventions. In the context of cardiovascular diseases, microRNA-126 is a key target for therapeutic interventions, as it is abundant in endothelial cells that line blood vessels, and plays a pivotal role in promoting angiogenesis. This thesis explores the use of ultrasound-stimulated microbubbles as a non-viral and targeted approach for microRNA-126 delivery to endothelial cells in both in vitro and ex vivo models. First, I designed and characterized a cationic microbubble formulation that can carry a microRNA-126 payload on its surface. I then developed an ultrasound regimen to safely deliver microRNA-126 to endothelial cell suspensions and demonstrated its effect on blood vessel formation in vitro. My results indicate the increase of microRNA-126 in endothelial cells result in the modulation of key downstream proteins, notably PIK3R2 and SPRED1, and improves angiogenesis. Building on these findings, I then developed a more complex vascular model to study ultrasound-guided microRNA-126 delivery by isolating rat mesenteric arteries. This model allowed me to replicate a more physiologically relevant vascular environment ex vivo. By incorporating factors such as intralumenal pressure and fluid flow, this study investigated the effect of focused ultrasound on the vasoconstriction and vasodilation of an artery. My findings revealed a positive relationship between ultrasound-mediated cell permeabilization and increased flow rate, as well as an inverse relationship between the levels of microRNA-126 delivered and increased flow rate. These results suggest that understanding hemodynamic conditions in specific anatomic regions could enhance the effectiveness of gene delivery. Overall, this thesis highlights the potential to deliver microRNA-126 using focused ultrasound and microbubbles while minimizing cellular and vascular viability, with anticipation for its application in gene therapy for cardiovascular diseases.