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Rationale: In skeletal muscles, there are four myofiber types, Types I, IIa, IIx, and IIb, which show different contraction characteristics and have different metabolic statuses. To understand muscle function, it is necessary to analyze myofiber-specific metabolic changes. However, these fibers are heterogeneous and are hard to discriminate by conventional analyses using tissue extracts. In this study, we found myofiber-specific molecules and molecular markers of other cells such as smooth muscle cells, fat cells, and motor neurons, and visualized them within muscle sections., Methods: We used three different muscle tissues, namely extensor digitorum longus, soleus, and gastrocnemius tissues, from ICR mice. After the muscles had been harvested, cross-sections were prepared using a cryostat and analyzed using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI), and conventional immunofluorescence imaging., Results: By comparing the MALDI MSI results with the immunofluorescence imaging results, we were able to identify each fiber and cell-specific ion. It was especially important that we could find Type IIa and IIb specific ions, because these were difficult to distinguish., Conclusions: Through MSI analyses, we performed a comprehensive survey to identify cell- and myofiber-specific molecular markers. In conclusion, we assigned muscle fiber Type I, IIa, and IIb-specific molecular ions at m/z 856.6, 872.6, and 683.8, respectively. These molecular markers might be useful for verifying changes that occur due to exercise and/or disease., (© 2018 John Wiley & Sons, Ltd.)

Rice is one of the most important food crops in the world and new varieties have been bred for specific purposes, such as the development of drought-resistance, or the enrichment of functional food factors. The localization and composition of metabolites in such new varieties must be investigated because all artificial interventions are expected to change the metabolites of rice. Imaging mass spectrometry using matrix-assisted laser desorption/ionization (MALDI-IMS) is a suitable tool for investigating the localization and composition of metabolites; however, suitable methodologies for the MALDI-IMS analysis of rice have not yet been established. In this study, we optimized the methods for analyzing rice grains by MALDI-IMS using adhesive film and found the characteristic distribution of metabolites in rice. Lysophosphatidylcholine (LPC) was localized in the endosperm. Phosphatidylcholine (PC), gamma-oryzanol and phytic acid were localized in the bran (germ and seed coat), and alpha-tocopherol was distributed in the germ (especially in the scutellum). In addition, MALDI-IMS revealed the LPC and PC composition of the rice samples. The LPC composition, LPC (1-acyl 16:0), LPC (1-acyl 18:2), LPC (1-acyl 18:1) and LPC (1-acyl 18:0), was 59.4 +/- 4.5%, 19.6 +/- 2.5%, 14.2 +/- 4.5% and 6.8 +/- 1.4%. The PC composition, PC (diacyl 16:0/18:2), PC (diacyl 16:0/18:1), PC (diacyl 18:1/18:3), PC (diacyl 18:1/18:2) and PC (diacyl 18:1/18:2), was 19.6 +/- 1.0%, 21.0 +/- 1.0%, 15.0 +/- 1.4%, 26.7 +/- 0.7% and 17.8 +/- 1.9%. This approach can be applied to the assessment of metabolites not only in rice, but also in other foods for which the preparation of sections is a challenging task., (2010 John Wiley & Sons, Ltd.)

We recently developed a matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight (MALDI-QIT-TOF)-based imaging mass spectrometry (IMS) system. This system enables us to perform structural analyses using tandem mass spectrometry (MS/MS), as well as to visualize phospholipids and peptides in frozen sections. In the retina, phototransduction is regulated by the light-sensitive interaction between visual pigment-coupled receptor proteins, such as rhodopsin, and G proteins, such as transducin. There are some reports that the conformation of rhodopsin is influenced by the composition of phospholipids in the lipid bilayer membrane. However, these results were based on in vitro experiments and have not been analyzed in vivo. In this study, we visualized and identified phospholipids in mouse retinal sections with the MALDI-QIT-TOF-based IMS system. From a spectrum obtained by raster-scanned analysis of the sections, ions with high signal intensities were selected and analyzed by MS/MS. As a result, sixteen ions were identified as being from four diacyl-phosphatidylcholine (PC) species, i.e., PC (16:0/16:0), PC (16:0/18:1), PC (16:0/22:6), and PC (18:0/22:6), with different ion forms. The ion images revealed different distributions on the retinal sections: PC (16:0/18:1) was distributed in the inner nuclear layer and outer plexiform layer, PC (16:0/16:0) in the outer nuclear layer and inner segment, and both PC (16:0/22:6) and PC (18:0/22:6) in the outer segment and pigment epithelium. In conclusion, our in vivo IMS analyses demonstrated a three-zone distribution of PC species on the retinal sections. This approach may be useful for analyzing lipid changes and their contribution to phototransduction in the retina.