Development of mass spectrometry imaging methods to discern glycerophospholipid isomer distributions in tissue sections

• Applicant: Professor Dr.-Ing. Sven Heiles
• Subject Area: Analytical Chemistry
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 426062756

Mass spectrometry imaging (MSI) allows for a label-free, untargeted detection and localization of numerous compound classes such as metabolites, peptides and lipids in tissue sections. Glycerophospholipids (GPLs), important signalling molecules and the major component of most cell membranes, are of particular interest in many MSI investigations as numerous researchers have shown that GPL distributions and abundances can be used to tell healthy and infected tissue apart. Despite the impressive capabilities of current MSI technologies and their potential use for molecular histology and diagnosis, the origin of disease- and infection-associated GPL abundance changes is not clear, yet. This is in part due to the inability to resolve and locally track GPL structure changes in tissue sections and link GPLs to known enzymatic processes. Especially the position of C=C bonds and the location of fatty acids on the glycerol backbone of GPLs (stereospecific-numbering (sn) isomerism) cannot routinely be inferred from tandem MSI experiments. This hampers the ability to track structural GPL alterations and rationalize the changed GPL metabolism in infected tissue. The goal of the proposed research project is to develop matrix-assisted laser desorption/ionization (MALDI)-MSI workflows using the recently introduced concept of Paternò-Büchi (PB) reactive matrices to infer local C=C position and sn-isomer changes of GPLs in tissue sections. For this purpose, PB-reactive matrices will be tested in order to improve the coverage of GPL classes and increase the overall ion signal thereby allowing for high lateral resolution GPL structure-selective MALDI MSI investigations. Furthermore, adapted tandem mass spectrometry schemes will be employed to allow for local sn-isomer and simultaneous C=C position discrimination upon derivatization of unsaturated GPLs. In the first part of the project, new PB-reactive MALDI matrix materials will be synthesized and the performance will be compared to workflows that use established matrices. In the second part of the project, commercially available and newly synthesized matrices will be used to discern the distribution of C=C bond position and sn-isomers of GPLs in model tissues such as mouse brain and kidney sections. To demonstrate the capabilities of the best performing compounds, GPLs and their C=C position as well as sn-isomers will be investigated in xenograft melanoma tissue (primary tumour and metastasis). These experiments will be performed in close collaboration with Prof. Dr. Dr. Alpaslan Tasdogan (University Hospital Essen), who is an expert for cancer metabolism. The distribution of GPLs and their isomers will be compared to corresponding spatial distribution patterns in control tissue. The aim is to obtain first indications for dysregulated GPL metabolism in melanoma and link these changes to enzymes such as stearyl-CoA-desaturase, lysophosphatidylcholine-acyl-transferase or elongase.

• DFG Programme: Research Grants