N-linked glycoproteomic analysis of formalin-fixed and paraffin-embedded tissues

Formalin-fixed, paraffin-embedded (FFPE) tissues have been used to discover disease-associated protein changes using mass spectrometry. Protein post-translational modifications such as glycosylation are known to associate with disease development. In this study, we investigated whether FFPE tissues preserve such modifications and therefore can be used as specimen of choice to identify the disease-associated modifications. We isolated the glycopeptides from the tryptic digest of frozen and FFPE lung tissues using solid-phase extraction of glycopeptides and analyzed them using mass spectrometry. The glycopeptides identified from FFPE lung tissue were compared to the ones from frozen lung tissue regarding their relative abundance, unique glycosylation sites, and subcellular locations. The results from our study confirmed that glycosylation in FFPE tissues are preserved and FFPE tissues can be used for discovery of new disease associated changes in protein modifications. Furthermore, we demonstrated the feasibility of applying the strategy of glycopeptide isolation from tryptic peptides of FFPE tissue to other tissues such as liver and heart.