Myofiber metabolic type determination by mass spectrometry imaging
Résumé
In muscle imaging, myofiber type determination is of great importance to better understand biological mechanisms related to skeletal muscle changes associated with pathologies. However, reference methods (histo-enzymology and immunohistochemistry) require serial-cross sections, and several days from the sampling to the results of image analysis. In this work, a strategy based on MALDI-Mass Spectrometry Imaging was developed as an alternative to the classical methods for myofiber metabolic type determination. The spectra were acquired on an Autoflex Speed MALDI-TOF/TOF mass spectrometer with a Smartbeam laser (Bruker Daltonics) in positive linear mode at a mass range of m/z 2,000 – 20,000 and a rastering of 100 mm. Spectra were baseline-subtracted, smoothed and peak picking was applied to the TIC spectra. The different tissue classes were determined so that every myofiber was correctly assigned: oxidative (OM) versus glycolytic metabolic (GM) type myofibers, accordingly to the immunofluorescence typology. A predictive model was then built in SCILS Lab software to discriminate the metabolic myofiber types using the MALDI spectral data, and used to classify spectral data acquired on tibialis muscle sections (intermediate metabolism). The performance of the model was evaluated through the percentage of correct assignment into each myofiber metabolic type class (internal validation of 96%). Myofiber type determination using MALDI-MSI tibialis spectra revealed that 11% of the myofibers belonged to the OM class and 89% of the myofibers belonged to the GM one. The successful classification of MALDI spectra acquired on tibialis muscle section was confirmed since the myofiber type determination using immunohistofluorescence showed that 9% of the myofibers belonged to theOM class and 91% of the myofibers belonged to theGM one. This approach can be successfully applied to any organisms, to perform both MALDI-MSI of proteins and myofiber type determination, saving considerable time and expenses.
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