"Imaging Mass Spectrometry is a rapidly developing technique that uses spatially resolved proteomic techniques to investigate a tissue’s biomolecular content. Imaging MS of pharmaceuticals has demonstrated that relative quantitation can be obtained if the MS response factors are known. However MS response factors for peptides and proteins are highly dependent on their exact nature. Despite it being acknowledged as the single biggest factor limiting the clinical application of the technique, to date it has remained an enigma how imaging MS analyses may be explicitly normalized to enable relative quantitation because it would require the relative response factors to be determined for every peptide/protein.
Here I will develop a methodology for the explicit normalization of every protein detected during imaging MS experiments. This will utilize the recently released SILAC mouse to create a reference standard in which all lysine residues are replaced with 13C6-lysine. Tryptic digestion of SILAC protein extract creates tryptic peptides containing a single 13C6-lysine, which can be used as a reference standard for the 12C6-lysine containing peptides created by on-tissue digestion of normal mouse tissue.
Ultrahigh mass resolution imaging MS will be used to ensure all tryptic peptides, and their 13C6-lysine reference standards, are resolved enabling the images of all tryptic peptides to be normalized using their own isotopically labelled analogues. The quantitative capabilities will be determined for every tryptic peptide ion detected from mouse brain tissue.
The capabilities of this ENIGMAS strategy (Explicitly Normalized ImaGing Mass Spectrometry) will be used to investigate the spatial and temporal evolution of the proteome perturbations that follow migraine. Multiple measurement repeats and multiple animals in each group will provide the first measure of statistical significance for imaging MS based molecular histology, a crucial step toward its clinical application."
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