Proteoform-selective imaging of tissues using mass spectrometry

Unraveling the complexity of biological systems relies on the development of new approaches for spatially resolved proteoform-specific analysis of the proteome. Top-down proteomics is a powerful tool, which has been used for the identification of thousands of proteoforms in biological samples. Herein, we present a first spatially resolved top-down proteomics analysis of biological tissues using nanospray desorption electrospray ionization mass spectrometry imaging (nano-DESI MSI). Nano-DESI generates multiply charged protein ions, which is advantageous for their structural characterization using tandem mass spectrometry (MS/MS). Proof-of-concept experiments demonstrate that the nano-DESI MSI combined with on-tissue top-down proteomics is ideally suited for the proteoform-selective imaging of thin tissue sections. Using rat brain tissue as a model system, we provide the first evidence of the differential proteoform expression in different regions of the brain.