MALDI imaging mass spectrometry of N-linked glycans on formalin-fixed paraffin-embedded murine kidney
Recent developments in spatial proteomics have paved the way for retrospective in situ mass spectrometry (MS) analyses of formalin-fixed paraffin-embedded clinical tissue samples. This type of analysis is commonly referred to as matrix-assisted laser desorption/ionization (MALDI) imaging. Recently, formalin-fixed paraffin-embedded MALDI imaging analyses were augmented to allow in situ analyses of tissue-specific N-glycosylation profiles. In the present study, we outline an improved automated sample preparation method for N-glycan MALDI imaging, which uses in situ PNGase F-mediated release and measurement of N-linked glycans from sections of formalin-fixed murine kidney. The sum of the presented data indicated that N-glycans can be cleaved from proteins within formalin-fixed tissue and characterized using three strategies: (i) extraction and composition analysis through on-target MALDI MS and liquid chromatography coupled to electrospray ionization ion trap MS; (ii) MALDI profiling, where N-glycans are released and measured from large droplet arrays in situ; and (iii) MALDI imaging, which maps the tissue specificity of N-glycans at a higher resolution. Thus, we present a complete, straightforward method that combines MALDI imaging and characterization of tissue-specific N-glycans and complements existing strategies.Graphical AbstractMALDI imaging MS of N-linked glycans released from formalin-fixed paraffin-embedded murine kidney sections. Ion intensity maps for (Hex)2(HexNAc)3(Deoxyhexose)3+(Man)3(GlcNAc)2 (m/z 2304.932, red), (Hex)6+(Man)3(GlcNAc)2 (m/z 1905.742, green) and (Hex)2(HexNAc)2+(Man)3(GlcNAc)2 (m/z 1663.756, blue)Electronic supplementary materialThe online version of this article (doi:10.1007/s00216-014-8293-7) contains supplementary material, which is available to authorized users.