A MALDI Imaging Mass Spectrometry Workflow for Spatial Profiling Analysis of N-linked Glycan Expression in Tissues

A new Matrix Assisted Laser Desorption Ionization Imaging Mass Spectrometry (MALDI-IMS) method to spatially profile the location and distribution of multiple N-linked glycan species in tissues is described. Application of an endoglycosidase, peptide N-glycosidase F (PNGaseF), directly on tissues followed by incubation releases N-linked glycan species amenable to detection by MALDI-IMS. The method has been designed to simultaneously profile the multiple glycan species released from intracellular organelle and cell surface glycoproteins, while maintaining histopathology compatible preparation workflows. A recombinant PNGaseF enzyme was sprayed uniformly across mouse brain tissue slides, incubated for two hours, then sprayed with 2,5-dihydroxybenzoic acid matrix for MALDI-IMS analysis. Using this basic approach, global snapshots of major cellular N-linked glycoforms were detected, including their tissue localization and distribution, structure and relative abundance. Off-tissue extraction and modification of glycans from similarly processed tissues and further mass spectrometry or HPLC analysis was done to assign structural designations. MALDI-IMS has primarily been utilized to spatially profile proteins, lipids, drug and small molecule metabolites in tissues, but it has not been previously applied to N-linked glycan analysis. The translatable MALDI-IMS glycan profiling workflow described herein can readily be applied to any tissue type of interest. From a clinical diagnostics perspective, the ability to differentially profile N glycans and correlate their molecular expression to histopathological changes can offer new approaches to identifying novel disease related targets for biomarker and therapeutic applications.