Investigation of Phosphatidylinositols and Phosphoinositides Using Matrix- Assisted Laser Desorption/Ionization Mass Spectrometry Imaging

Abstract

Matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is a powerful analytical technique that captures the spatial distribution of biomolecules directly from tissue surfaces. Widely used in lipidomics, MALDI-MSI provides label-free, high-resolution imaging of lipid species in situ, making it invaluable for studying lipid dynamics in health and disease. This thesis focuses on phosphatidylinositols (PIs) and their phosphorylated forms, phosphoinositides (PIPs), which are critical regulators of cellular signaling, membrane dynamics, and cytoskeletal organization. Dysregulation of PIs and PIPs are implicated in various diseases, including atypical hemolytic uremic syndrome (aHUS), necessitating a deeper understanding of their spatial distribution and abundance.

Given the low concentration of PIs and PIPs, the study aimed to optimize MALDI-MSI for their detection. Thus, various chemical matrices necessary for the desorption and subsequent ionization processes in MALDI, were systematically evaluated to enhance the ionization and improve the detectability of these species, identifying 2,5-dihydroxyacetophenone and 1,5-diaminonaphthalene as optimal matrices. Additionally, we explored the limitation of MALDI-MS, specifically investigating the in-source fragmentation (ISF) of phosphatidylinositol triphosphate using the survival yield method, confirming that ISF occurs within the high energy conditions of MALDI.