Mimetic tissue models for accurate lipid quantitation in fibrotic mouse heart by MALDI-MSI

Accurate spatial quantitation of endogenous biomolecules is paramount to rationalize disease progression in tissues and translate findings into clinical use. In this contribution, we present a streamlined and quality-controlled spatial quantitation pipeline for accurate quantitative mass spectrometry imaging (MSI) of lipids. By creating miniaturized mimetic tissue models (MTM) spiked with stable isotope labelled standards (SILS) matching the tissue used for MSI, calibration and MSI experiments are performed from the same sample slide minimizing measurement variabilities. By determining the absolute SILS concentrations and lipid annotations via LC-MS/MS in the same MTMs as used for MSI, measurements are intrinsically quality controlled and quantitation results via MSI can be reported in units of µglipid/mgprotein commonly employed in lipidomics. We present an in-depth comparison of spatial quantitation via MSI and bulk LC-MS/MS for the same samples, i.e. mouse heart tissue, yielding good overall agreement between both quantification modalities for 95 endogenous lipids. Furthermore, we demonstrate the capability to capture heterogenous lipid expressions during disease progression quantitatively by charting lipidomic changes upon myocardial infarction-induced tissue remodeling. Our workflow reports absolute spatial quantitation results for 10 lipid classes and identifies 19 regulated lipids that are in line with known cellular remodeling events in fibrotic heart tissue.