In Situ Cell-by-Cell Imaging and Analysis of Small Cell Populations by Mass Spectrometry

摘要

ABSTRACT:Molecular imaging bymass spectrometry (MS) isnemerging as a tool to determine the distribution of proteins,nlipids, andmetabolites in tissues. The existing imagingmethods,nhowever, mostly rely on predefined rectangular grids fornsampling that ignore the natural cellular organization of thentissue. Here we demonstrate that laser ablation electrospraynionization (LAESI) MS can be utilized for in situ cell-by-cellnimaging of plant tissues. The cell-by-cell molecular image of thenmetabolite cyanidin, the ion responsible for purple pigmenta-ntion in onion (Allium cepa) epidermal cells, correlated well withnthe color of cells in the tissue. Chemical imaging using single-cells as voxels reflects the spatial distribution of biochemical differencesnwithin a tissue without the distortion stemming from sampling multiple cells within the laser focal spot. Microsampling by lasernablation also has the benefit of enabling the analysis of very small cell populations for biochemical heterogeneity. For example, with an∼30 μmablation spot we were able to analyze 3-4 achlorophyllous cells within an oil gland on a sour orange (Citrus aurantium) leaf.nTo explore cell-to-cell variations within and between tissues, multivariate statistical analysis on LAESI-MS data from epidermal cellsnof an A. cepa bulb and a C. aurantium leaf and from human buccal epithelial cell populations was performed using the method ofnorthogonal projections to latent structures discriminant analysis (OPLS-DA). The OPLS-DA analysis of mass spectra, containingnover 300 peaks each, provided guidance in identifying a small number of metabolites most responsible for the variance between thencell populations. Thesemetabolites can be viewed as promising candidates for biomarkers that, however, require further verification.