Glycocalyx Syndecan-1 in Trophoblast Lipid Transport

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 DESCRIPTION (provided by applicant): The syncytiotrophoblast (STB) has critical functions including transport of gases and nutrients to the fetus. Maternal very low-density lipoproteins (VLDL) provide a significant source of free fatty acids (FFA), important for fetal growth and development. VLDL triglycerides are hydrolyzed to FFA by lipases expressed on the STB microvillous membrane (MVM), with FFA transferred to the fetus. Alternatively, however, maternal lipoproteins interact with receptors on the STB MVM, with endocytosis and intracellular hydrolysis. However, relatively little is known about the function of lipoprotein receptors on the trophoblast microvillous membrane, especially with regard to VLDL transport. Disruption of the overall system of placental lipid transfer can have a negative impact on the development of the fetus. The cell surface heparan sulfate proteoglycan (HSPG), syndecan-1 (SDC-1) functions as a receptor for various macromolecular cargo. On microvilli of hepatocytes, SDC-1 mediates cellular internalization of VLDL and remnant lipoproteins. Our preliminary data suggest that trophoblasts likewise bind and internalize VLDL by an HSPG-dependent mechanism, and that trophoblast expression of SDC-1 is significantly reduced in preeclamptic pregnancies. The hypothesis of this R03 proposal is that trophoblasts bind and internalize VLDL by an HSPG-dependent mechanism, and SDC-1 is the primary HSPG effecting this uptake. This will be tested using cells in culture, primarily 1) the human HTR-8/SVneo trophoblast cell line (HTR-8); 2) human Hep3B hepatocarcinoma cells as a positive control for SDC-1 -mediated VLDL uptake; and 3) a line of human fibroblasts (GM00701) that do not express the low-density lipoprotein (LDL) receptor and do not express SDC-1, but express high levels of functional LRP1 (multifunctional member of the LDL receptor superfamily). Aim 1, which builds upon our preliminary data, is to ascertain the role of trophoblast cell surface HSPGs in VLDL binding/uptake. Aim 2 is to determine whether the HSPG-dependent VLDL binding/uptake is primarily accomplished by SDC-1. Aim 3 is to rule out involvement of LRP1 in trophoblast internalization of VLDL. Aim 4 is to measure VLDL binding/uptake by placental villi in explant culture, comparing villi from women with preeclampsia versus uncomplicated pregnancy. The proposed work will further our understanding of lipoprotein handling by STB, and HSPG function in this regard. The research has important clinical implications given the vital importance of placental nutrient transport.