Thursday, May 9, 2024
5/9/2024
The lymphatic vascular system is essential for transporting interstitial fluid, dietary fat, and immune cells. Defects in these functions contribute to lymphedema, impaired lipid absorption, obesity, abnormal immune function, and cancer metastasis. During embryonic development, lymphangiogenesis is robust, primarily driven by vascular endothelial growth factor C (VEGF-C)-mediated activation of VEGFR-3, a main VEGF-C receptor on lymphatic endothelial cells (LECs). Emerging evidence has shown the metabolism of endothelial cells is critical for vascular development. Changes in EC metabolic pathways are found in pathologies such as cancer and diabetes as well. But most research has been focused on blood endothelial metabolic pathways. Despite a few recent pioneering studies, knowledge of LEC metabolism during lymphangiogenesis is limited. There is an unmet need to bridge the knowledge gap between cellular metabolism and lymphatic vascular development. Site-1 protease (S1P), encoded by membrane-bound transcription factor peptidase, site 1 (MBTPS1), is a serine protease in the Golgi apparatus. S1P is a key regulator of cholesterol biosynthesis by proteolytic activation of a membrane-bound latent transcription factor, sterol-regulatory element binding protein 2 (SREBP2). Recently, we found that mice with inducible endothelial cell- specific deficiency of S1P (iEC Mbtps1-/-, Mbtps1f/f;;Cdh5CreERT2) exhibited severe subcutaneous lymphedema and defective lymphatic vasculature during development. Our pilot experiments also showed that mice with LEC-specific deficiency of SREBP2 (LEC Srebf2-/-, Srebf2f/f;;Lyve1Cre) had a similar lymphatic vascular defect during development. These strong in vivo preliminary data support the central hypothesis that S1P/SREBP2-mediated cholesterol biosynthesis is required for lymphatic vascular development. We will test the central hypothesis through two Aims: 1) determine whether lymphatic endothelial S1P/SREBP2- mediated cholesterol biosynthesis is required for lymphatic vascular development. We will characterize LEC cellular defects, such as differentiation, migration, and proliferation, of S1P or SREBP2-deficient mice at different stages of embryonic development. These in vivo analyses will be complemented by in vitro assays using LECs isolated from wild-type (WT) or mutant mice as well as primary human LECs;; 2) determine mechanisms by which S1P/SREBP2- mediated cholesterol biosynthesis regulate lymphangiogenesis. Based on our preliminary results, we will primarily test the hypothesis S1P/SREBP2-mediated cholesterol biosynthesis is required for sustained VEGFR3 signaling mainly by in vitro assays using WT or mutant LECs as well as human LECs with knockdown of S1P/SREBP2 or functional inhibitors to S1P and SREBP2. Based on strong preliminary data, our proposed study will reveal novel insights into roles of S1P-mediated lipid metabolism in lymphatic vascular development. Our study may lead to novel therapeutic opportunities for pathologies with lymphatic vascular defects.
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