Imaging of N-linked glycans from formalin-fixed paraffin-embedded tissue sections using MALDI mass spectrometry.

Aberrant glycosylation is associated with most of the diseases. Direct imaging and profiling of N-glycans on tissue sections can reveal tissue-specific and/or disease-associated N-glycans, which not only could serve as molecular signatures for diagnosis but also shed light on the functional roles of these biomolecules. Mass spectrometry imaging (MSI) is a powerful tool that has been used to correlate peptides, proteins, lipids, and metabolites with their underlying histopathology in tissue sections. Here, we report an MSI technique for direct analysis of N-glycans from formalin-fixed paraffin-embedded (FFPE) tissues. This technique consists of sectioning FFPE tissues, deparaffinization, and rehydration of the sections, denaturing tissue proteins, releasing N-linked glycans from proteins by printing peptide-N-glycosidase F over the sections, spray-coating the tissue with matrix, and analyzing N-glycans by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Brain sections from a C57BL/6 mouse were imaged using this technique at a resolution of 100 μm. Forty-two N-glycans were analyzed from the mouse brain section. The mass spectrometry images were used to study the relative abundance of oligomannose, nonfucosylated, and fucosylated complex N-glycans in different brain areas including isocortex, hippocampal formation, and brainstem and specific glycans associated with different areas of the brain were identified. Furthermore, glioblastoma tumor xenografts in a NOD/SCID mouse were imaged. Several glycans with differential expression in tumor versus normal brain tissues were identified. The MSI technique allows for imaging of N-glycans directly from FFPE sections. This method can potentially identify tissue-specific and/or disease-associated glycans coexpressed with other molecular signatures or within certain histological structures.