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Development and application of global lipidomic arrays to inflammatory vascular disease

Final Report Summary - LIPIDARRAY (Development and application of global lipidomic arrays to inflammatory vascular disease.)

Lipids (fats) comprise large diverse families of molecules that are essential for all aspects of health and disease. Their dysregulation is a defining feature of inflammatory disease. Many remain undiscovered, we estimate around 50 %, meaning that new methods for the discovery and characterization of lipids are essential.

The overarching aim of LipidArrays was to develop and apply new approaches for discovery and characterisation of lipids that are generated in inflammatory diseases such as cardiovascular disease and dementia. At the time we started, interest was growing in the use of “untargeted” mass spectrometry (MS), to map all metabolites/lipids in samples, but significant barriers were becoming apparent. These included the fact that data from MS contains around 10-fold more noise than real data, thus identifying new lipids was virtually impossible. Robust informatics tools to clean up MS data based on intelligent principles were unavailable, or not fit-for-purpose, for analysing lipids.

Our planned approach was to apply “untargeted” MS to all lipids in a sample and then generate new software to clean up the huge numbers of artefacts, leaving only real lipids for analysis. For this, we designed the software LipidFinder, and made it available on LIPID MAPS through a dedicated interface and via GitHub. A second version, linked with the popular XCMS metabolomics tool is about to be released.

Using LipidFinder, we mapped lipids in various samples from plasma to cultured cells, and uncovered new information on how lipids, particularly those generated by blood cells can regulate health and disease. First, with plasma cohort samples from healthy men, taken around 25 yrs ago, we identified a unique signature of inflammatory lipids that define a common genetic form of cardiovascular disease (linked with chromosome 9p21), that up to now had no known metabolic alterations. We found that metabolism of lipids called lysophospholipids is dysregulated in people at risk of this form of vascular disease and we are now researching the biological basis of this observation in circulating blood cells. We also found that other less common forms of vascular disease appear to have gene-specific changes in metabolism of specialized lipids called sphingolipids (important lipids in cancer, inflammation and many other processes).

We conducted several studies on lipid metabolism in macrophages (a specialized immune cell). In macrophages missing a key protein required for their development (GATA6), we identified an alteration in sphingolipids that appears to lead to a form of lysosomal storage disease. Separately we used lipidomics to research the metabolic fate of specialized lipids called oxylipins, and found that macrophages consume large amounts of these in a manner that can potentially limit their bioactions during inflammation. We particularly focused on determining how macrophage mitochondria (essential organelles in cells that generate energy) metabolise oxylipins and found that this process is itself upregulated during inflammation in vitro and in vivo. Last, we uncovered using our lipidomic screen that lipids called cardiolipins are upregulated when macrophages differentiate to specialized subpopulations, called M2 cells. This appears to be required for their differentiation, thus manipulating it could provide a way to promote or prevent macrophage driven immune responses in vivo.

With platelets (circulating blood cells required for clotting), we estimated the total number of lipids present, and defined how many of these change on activation and during inhibition with aspirin. The diversity of membrane lipids that drive blood clotting (enzymatically-oxidized phospholipids) was mapped. We identified a new metabolic switch for energy generation by these cells involving lipids. This work led to new insights into how platelets regulate blood clotting, a process essential for life, and of key importance in virtually all human diseases.