Mass Spectrometry-Based Spatial Imaging of the Cochlea

Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI) is transforming spatial molecular studies. However, applying MALDI-MSI to small, anatomically complex tissues remains challenging. One such structure is the cochlea, the auditory part of the inner ear that is critical for hearing. To address these challenges, we developed and implemented a streamlined workflow for sample preparation and processing to obtain MALDI-MSI data on mouse cochlea. Sample acquisition was optimized to minimize time and processing steps, allowing use of flash-frozen neonatal mouse heads. This workflow enabled high spatial resolution metabolomic and lipidomic imaging of the sagittally cryosectioned mouse cochlea using N-(1-naphthyl) ethylenediamine dihydrochloride (NEDC) matrix via sublimation. Optimized NEDC sublimation allowed high signal-to-noise, reduced delocalization, and salt tolerance, allowing acquisition of 5 μm-resolution imaging data on a MALDI-MSI instrument. Sublimation was found to be superior to spraying as a method for matrix application due to its higher signal-to-noise, particularly for lipids and fatty acids, and improved spatial resolution. Diverse metabolites and lipids were measured throughout the cochlear region, revealing distinct spatial distributions. Clustering identified reproducible physiological regions, including the otic capsule and spiral ducts. High spatial resolution imaging revealed distinct tissues, cell types, and molecular signatures within the cochlea. These findings establish the utility of high spatial resolution MALDI-MSI for auditory research, enabling molecular mapping of cochlear function and dysfunction.