Regulation of Lymphangiogenesis by Thrombospondin 1

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Project Summary Atherosclerosis accounts for the majority of deaths in the United States and is characterized by excessive lipid accumulation in the arterial wall. Arterial lipid accumulation results from the imbalance of cellular lipoprotein uptake, removal of cholesterol and de novo cellular lipid synthesis. The lymphatic network is an indispensable player in the removal of cholesterol and inflammatory cells/cytokines from atherosclerotic lesions. Surgical and genetic disruption of lymphatic drainage leads to aggravated atherosclerotic lesion formation. However, the precise endogenous factors and mechanisms regulating lymphangiogenesis in atherosclerotic vessels remain unidentified. Previous studies have linked elevated matrix protein thrombospondin-1 (TSP1) levels with human atherosclerotic disease, however the mechanisms by which TSP1 contributes to atherosclerotic lesion formation and its effect on arterial lymphangiogenesis remain unknown. Our preliminary studies demonstrate that i) lymphatic endothelial cells (LEC) express high levels of TSP1 receptor, CD47; ii) TSP1 at pathophysiologically relevant concentrations inhibits lymphangiogenesis in vitro; and iii) global deletion of TSP1 and CD47 in hypercholesteremic mice attenuates atherosclerosis. Based on these results, I hypothesize that TSP1 impairs lymphangiogenesis via CD47-dependent mechanisms and induction of lymphangiogenesis via LEC CD47 deletion increases reverse cholesterol transport and decreases atherosclerosis development. The proposal will examine in vitro whether TSP1-mediated CD47 activation in LEC inhibits lymphangiogenesis via increased ROS generation, decreased NO bioavailability and attenuation of PI3K-Akt and ERK1/2 activation (Aim 1). The proposal will investigate whether inhibiting CD47 signaling specifically in LEC increases lymphangiogenesis, improves reverse cholesterol transport (Aim 2) and suppresses atherosclerosis development in vivo (Aim 3). Various molecular biology and imaging techniques, ROS/NO detection methods, lymphangiogenesis assays, PCSK9-AAV8-induced atherosclerosis model, in vivo reverse cholesterol transport, lymphatic function analysis and LEC-specific CD47 knockout mice will be employed to test the hypothesis. Successful completion of the proposed studies will contribute to a better understanding of the regulation of lymphangiogenesis and lymphatic vessel function in atherosclerosis. This grant will be critical for Dr. Singla to achieve the following short- and long- term objectives: 1) to acquire additional scientific training both methodologically and conceptually; 2) to merge the yet distinct matrix protein biology and lymphatics fields with the goals toward opening up new avenues of discovery; 3) to establish Dr. Singla’s independent research program; 4) publish high-impact corresponding author articles and develop a highly competitive R01 grant application. Dr. Singla has assembled a multidisciplinary team, including his mentors, consultants, and advisors to guide his career towards independence and assist with the completion of the proposed research study.