Mass Spectrometry Imaging is a developmental technique that is gaining relevance in molecular biology for its promise of providing spatial distribution and identification capabilities through untargeted mass spectrometry means, eliminating the need for antibodies and histological staining, and dramatically increasing diagnostic efficiency in the context of heterogenous disorders.
Mass-spec imaging utilises specialised instrumental acquisition methods to provide mass-spec data in a spatial format. The foremost method for proteomics is MALDI. (Matrix-Assisted Laser-Desorption/Ionisation), where an organic matrix is added to the sample to assist in ablation of the sample. This is either done via a sprayer simply, or via sublimation. Sublimation minimises delocalisation of molecules whilst also providing the most uniform layer of matrix. Because sublimation is more complex however, results have not been reproducible across the literature. Here we demonstrate a reliable matrix sublimation workflow, as part of a larger spatial proteomics analysis of a murine colon cancer model, using mass spectrometry imaging.
Formalin Fixed Paraffin Embedded “Swiss roll” murine colon blocks were sectioned at 5µm before undergoing deparaffinization, a graded alcohol wash series, followed by tryptic digestion. Samples slides were then coated in CHCA via sublimation and allowed to recrystallise with TFA in a custom apparatus. Acquisition was then performed on a Waters Synapt XS MALDI, which maps the spatial distribution of peptides. The bioinformatics toolbox, ‘HiTMaP’ was then used to process the imaging data using the mus musculus (common house mouse) FASTA file to identify peptides. We identified at least 30 peptides of interest at a spatial resolution of 20µm. We conclude that by optimising matrix sublimation procedure, we can perform high-throughput, valid and reliable spatial proteomics analysis using MALDI mass spectrometry imaging.