Mass spectral profiling of glycosaminoglycans from histological tissue surfaces
Glycosaminoglycans (GAGs) are found in intracellular granules, cell surfaces, and extracellular matrices in a spatially and temporally regulated fashion, constituting the environment for cells to interact, migrate, and proliferate. Through binding with a great number of proteins, GAGs regulate many facets of biological processes from embryonic development to normal physiological functions. GAGs have been shown to be involved in pathologic changes and immunological responses including cancer metastasis and inflammation. Past analyses of GAGs have focused on cell lines, body fluids, and relatively large tissue samples. Structures determined from such samples reflect the heterogeneity of the cell types present. To gain an understanding of the roles played by GAG expression during pathogenesis, it is very important to be able to detect and profile GAGs at the histological scale so as to minimize cell heterogeneity to potentially inform diagnosis and prognosis. Heparan sulfate (HS) belongs to one major class of GAGs, characterized by dramatic structural heterogeneity and complexity. To demonstrate feasibility of analysis of HS, 15 μm frozen bovine brain stem, cortex, and cerebellum tissue sections were washed with a series of solvent solutions to remove lipids before applying heparin lyases I, II, and III on the tissue surfaces within 5 mm × 5 mm digestion spots. The digested HS disaccharides were extracted from tissue surfaces and then analyzed by using size exclusion chromatography/mass spectrometry (SEC-MS). The results from bovine brain stem, cortex, and cerebellum demonstrated the reproducibility and reliability of our profiling method. We applied our method to detect HS from human astrocytoma (WHO grade II) and glioblastoma (GBM, WHO grade IV) frozen slides. Higher HS abundances and lower average sulfation level of HS were detected in glioblastoma (GBM, WHO grade IV) slides compared to astrocytoma (WHO grade II) slides.