Abstract
Aberrant protease activity has been implicated in the etiology of various prevalent diseases including neurodegeneration and cancer, in particular metastasis. Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) has recently been established as a key technology for bioanalysis of multiple biomolecular classes such as proteins, lipids, and glycans. However, it has not yet been systematically explored for investigation of a tissue's endogenous protease activity. In this study, we demonstrate that different tissues, spray-coated with substance P as a tracer, digest this peptide with different time-course profiles. Furthermore, we reveal that distinct cleavage products originating from substance P are generated transiently and that proteolysis can be attenuated by protease inhibitors in a concentration-dependent manner. To show the translational potential of the method, we analyzed protease activity of gastric carcinoma in mice. Our MSI and quantitative proteomics results reveal differential distribution of protease activity - with strongest activity being observed in mouse tumor tissue, suggesting the general applicability of the workflow in animal pharmacology and clinical studies.
Highlights
Spatial Distribution of Endogenous Tissue Protease Activity in Gastric Carcinoma Mapped by Matrix-assisted laser desorption/ionization (MALDI) Mass Spectrometry Imaging*□S
We reveal that distinct cleavage products originating from substance P are generated transiently and that proteolysis can be attenuated by protease inhibitors in a concentration-dependent manner
Monitoring of Endogenous Tissue Protease Activity Using MALDI MS Imaging—The pathophysiological importance of proteases has been known for a long time and current photonic tracer-based measurements in tissues may have limitations such as quenching, autofluorescence, and photo bleaching
Summary
It measures the decrease of a general tracer substrate, substance P, and the increase in digestion products in a time-dependent manner. We utilize a different analytical approach, matrix-assisted laser desorption ionization (MALDI) mass spectrometry imaging (MSI), for spatially-resolved analysis of endogenous protease activity in fresh-frozen tissue. We take this approach one step further and use spray-coating techniques for application of a protease substrate tracer, substance P, onto tissue for effective monitoring of endogenous enzyme activity and of the transient emergence of cleavage products over time at high spatial resolution. We utilize fast MALDI-TOF and high resolving power MALDI-Fourier Transform Ion Cyclotron Resonance (FTICR) MSI to visualize for the first time tissue protease activity in mouse gastric carcinoma using MALDI MSI
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