Yang, Guang; (2018) The Roles of Lipids in Intercellular Adhesion and Cell Movement. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Cells actively regulate their lipid composition and localisation during cell division, with both signalling roles and structural roles likely. In this study, I investigate the specific roles of lipids in the formation and maintenance of cell-cell junctions, and in cell migration. Although massive membrane rearrangements occur during both processes and lipids are fundamental building blocks of cell membranes, the roles of lipids remain unclear. After perturbing lipid metabolism enzymes with an siRNA library targeting 260 lipid biosynthetic enzymes in HaCaT (immortalized human keratinocytes), junctions were visualised using the adherens junction (AJ) marker α-catenin, and the resultant junction morphologies were examined. The primary screen revealed a potential role for 16 enzymes with two distinct junctional phenotypes: intercellular gaps and abnormal junction morphology. A secondary migration screen based on wound healing assays was conducted with a subgroup of these hits. I found that depletion of some enzymes results in defects in migration speed and cohesiveness, which suggests potential important roles for those enzymes and the lipids they make in cell migration. AGPAT2 (1-Acylglycerol-3-Phosphate O-Acyltransferase 2) is one of the hits being prioritised for further experiments to understand the role of related lipids. The depletion of AGPAT2 changes cell-cell junction morphology dramatically. In HaCaT, AJs expand on the neighbouring cells, while in Caco-2 (human colorectal adenocarcinoma cells), tight junctions (TJs) show an undulating morphology. Lipidomic analysis conducted following AGPAT2 depletion identified increases in triacylglycerols (TAGs), decreases in ether phosphatidylcholines (PCs) and reduced membrane fluidity indices. Further experiments are being performed to better characterise the phenotypes and identify the exact roles of the lipids. Overall, my study provides evidence that lipids may be involved in cell migration and cell-cell junction formation and maintenance and suggests that proper lipid metabolism is essential for regulating cell-cell junction and migration.

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