Mass spectrometry imaging of kidney sections

MSI of kidney sections was performed as previously reported³⁰. Briefly, kidney tissues were sectioned to 8 μm in thickness with a cryostat and thaw-mounted onto indium tin oxide-coated glass slides. Using a 0.3 mm caliber nozzle airbrush (Procon boy FWA Platinum; Mr. Hobby), 9-AA (750 μL, 4.5 mg/mL in methanol) was sprayed on the slide. MALDI-MSI analysis was performed using iMScope (Shimadzu, Japan). Mass spectra of the designated areas on a specimen photographed before matrix application were acquired in the negative ion mode. Mass spectra were acquired under the condition of a laser frequency and scanning mass ranging from m/z 200 to m/z 220 and m/z 170 to m/z 189. The spatial interval of data points was 50 μm, giving 10,120 data points in total for each section. The data collected through the microscopic system were digitally processed using Imaging MS Solution analysis software (Shimadzu).