Multimodal Mass Spectrometry Imaging of Rat Brain Using IR-MALDESI and NanoPOTS-LC-MS/MS

Multimodal mass spectrometry imaging
(MSI) is a critical technique
used for deeply investigating biological systems by combining multiple
MSI platforms in order to gain the maximum molecular information about
a sample that would otherwise be limited by a single analytical technique.
The aim of this work was to create a multimodal MSI approach that
measures metabolomic and proteomic data from a single biological organ
by combining infrared matrix-assisted laser desorption electrospray
ionization (IR-MALDESI) for metabolomic MSI and nanodroplet processing
in one pot for trace samples (nanoPOTS) LC-MS/MS for spatially resolved
proteome profiling. Adjacent tissue sections of rat brain were analyzed
by each platform, and each data set was individually analyzed using
previously optimized workflows. IR-MALDESI data sets were annotated
by accurate mass and spectral accuracy using HMDB, METLIN, and LipidMaps
databases, while nanoPOTS-LC-MS/MS data sets were searched against
the rat proteome using the Sequest HT algorithm and filtered with
a 1% FDR. The combined data revealed complementary molecular profiles
distinguishing the corpus callosum against other sampled regions of
the brain. A multiomic pathway integration showed a strong correlation
between the two data sets when comparing average abundances of metabolites
and corresponding enzymes in each brain region. This work demonstrates
the first steps in the creation of a multimodal MSI technique that
combines two highly sensitive and complementary imaging platforms.
Raw data files are available in METASPACE (https://metaspace2020.eu/project/pace-2021) and MassIVE (identifier: MSV000088211).