Examining the Roles of Membrane Lipids and Secreted Bioactive Lipids on Immune System Cell Function: Studies on Mast Cells and Platelets

Abstract

The central theme of this dissertation is application of sensitive analytical chemistry tools to further the fundamental understanding of the role of both secreted lipids that act as short-range hormones and structural lipids that play an active role in cellular signaling in the function of immune system cells. Lipids, both as the cell-secreted mediators of inflammation and as important structural components of all mammalian cell membranes, have critically important roles in the functions of cells in the immune system. As such, this dissertation focuses on developing and applying ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) methods to address the challenge of quantifying mast cell-secreted bioactive lipids in complex cell cultures as well as understanding the roles that membrane phospholipids play in platelet signaling. With the exception of red blood cells, every mammalian cell uses phospholipids as enzyme substrates to generate and secrete bioactive lipid species that act as short-range hormones. Similarly, the phospholipids that compose the cellular membrane participate in cellular signaling and many physiological functions. Despite their prevalence, detection of secreted and structural lipids has traditionally presented a significant analytical challenge. The advent of UPLC-MS/MS, however, enables rapid, sensitive, and selective analysis of multiple structurally diverse lipids simultaneously, which enables us to study critical cellular functions and the effects of secreted bioactive lipids. In this dissertation, UPLC-MS/MS methods are developed (Chapter 2) for the rapid and simultaneous analysis of secreted phospholipids and eicosanoids to characterize mast cell function in complex cell cultures (Chapters 2 and 3). UPLC-MS/MS methods are also applied to contribute to the fundamental understanding of exogenous phospholipids and their influence on platelet function (Chapters 4 and 5), both at the single platelet level and in the context of concerted activity between many platelets together in suspension. Both mast cells (Chapters 2 and 3) and platelets (Chapters 4 and 5) present interesting and challenging platforms for the application of new methods for studying secreted and structural lipid function. Overall, the work in this dissertation contributes to the development and application of UPLC-MS/MS for simultaneous determination of structurally diverse lipids and exploits this method to achieve new insights into the fundamental role of phospholipids in mast cells and platelets.