Molecular Morphology of the Chick Heart Visualized by MALDI Imaging Mass Spectrometry

Abstract

Utilization of MALDI-MS (matrix-assisted laser desorption/ionization mass spectrometry) for tissue imaging is a relatively new proteomic technique that simultaneously maps the spatial distribution of multiple proteins directly within a single frozen tissue section. Here we report the development of a methodology to apply MALDI tissue imaging to chick heart tissue sections acquired from fixed and paraffin-embedded samples. This protocol produces molecular images that can be related to the high quality histological tissue sections. Perfused term chick hearts were fixed in acidic ethanol and embedded in paraffin wax. Tissue sections (15 μm) were collected onto conductive slides, deparaffinized with xylene and transitioned into water with graded ethanol washes and allowed to air dry. In separate experiments three different MALDI matrices were applied to chick heart tissue sections through repeated cycles from a glass nebulizer. Tissue sections were then analyzed by MALDI mass spectrometry using a raster step-size of 75–100 μm, and molecular images for specific m/z ratios reconstituted. MALDI tissue imaging revealed spatially-resolved protein signals within single heart sections that are specific to structures or regions of the heart, e.g., vessels, valves, endocardium, myocardium, or septa. Moreover, no prior knowledge of protein expression is required as is the case for immunohistochemistry and in situ hybridization methodologies. The ability to simultaneously localize a large number of unique protein signals within a single tissue section, with good preservation of histological features, provides cardiovascular researchers a new tool to give insight into the molecular mechanisms underlying normal and pathological conditions.

MALDI Mass Spectrometric Imaging of Lipids in Rat Brain Injury Models

“…Perhaps not unexpectedly, the most abundant ions observed below m/z 1500 in the MALDI IMS experiment of tissues such as brain (6), kidney (7), liver (8), eye (9), and blood vessels (10) were derived from those lipids that make up the various membranes of the living cell (phospholipids and sphingolipids) as well as lipid storage vesicles found in abundance in certain cell types. The most abundant positive ions typically observed are derived from a single class of lipid called phosphatidylcholine (PC), but within that class are numerous molecular species that differ from each other by fatty acyl group esterification to the glycerophosphocholine backbone.…”

Imaging Mass Spectrometry of Proteins and Peptides

“…The distributions obtained for ubiquitin, calcyclin, calgizzarin, and transthyretin were found to be similar to their respective mrnA expressions by in situ hybridization experiments, thus validating the approach [46]. grey et al [47] reported on the visualization of the molecular morphology of the chick heart using IMS. Tissue sections from term chicks were obtained and coated with either chcA, DhB, or SA.…”

Advances in MALDI imaging mass spectrometry of proteins in cardiac tissue, including the heart valve

“…One fixation approach that has worked well for obtaining signal from cardiac tissue is fixation by acidified ethanol prior to sectioning [26]. Fresh cardiac tissue is incubated overnight in a cold, acidic solution of ethanol.…”

“…Evaluation of chicken heart treated in this manner showed that heart tissue has significant protein gradients throughout the heart with unique proteins found in ventricles, vessels or heart valves. This was one of the first illustrations of the use of MALDI IMS to detect proteomic content from a cross section of heart tissue while retaining localization to histological features [26]. …”