Imaging mass spectrometry enables molecular profiling of mouse and human pancreatic tissue

Abstract

Aims/hypothesis The molecular response and function of pancreatic islet cells during metabolic stress is a complex process. The anatomical location and small size of pancreatic islets coupled with current methodological limitations have prevented the achievement of a complete, coherent picture of the role that lipids and proteins play in cellular processes under normal conditions and in diseased states. Herein, we describe the development of untargeted tissue imaging mass spectrometry (IMS) technologies for the study of in situ protein and, more specifically, lipid distributions in murine and human pancreases. Methods We developed matrix-assisted laser desorption/ionisation (MALDI) IMS protocols to study metabolite, lipid and protein distributions in mouse (wild-type and ob/ob mouse models) and human pancreases. IMS allows for the facile discrimination of chemically similar lipid and metabolite isoforms that cannot be distinguished using standard immunohistochemical techniques. Coregistration of MS images with immunofluorescence images acquired from serial tissue sections allowed accurate cross-registration of cell types. By acquiring immunofluorescence images first, this serial section approach guides targeted high spatial resolution IMS analyses (down to 15 μm) of regions of interest and leads to reduced time requirements for data acquisition. Results MALDI IMS enabled the molecular identification of specific phospholipid and glycolipid isoforms in pancreatic islets with intra-islet spatial resolution. This technology shows that subtle differences in the chemical structure of phospholipids can dramatically affect their distribution patterns and, presumably, cellular function within the islet and exocrine compartments of the pancreas (e.g. 18:1 vs 18:2 fatty acyl groups in phosphatidylcholine lipids). We also observed the localisation of specific GM3 ganglioside lipids [GM3(d34:1), GM3(d36:1), GM3(d38:1) and GM3(d40:1)] within murine islet cells that were correlated with a higher level of GM3 synthase as verified by immunostaining. However, in human pancreas, GM3 gangliosides were equally distributed in both the endocrine and exocrine tissue, with only one GM3 isoform showing islet-specific localisation. Conclusions/interpretation The development of more complete molecular profiles of pancreatic tissue will provide important insight into the molecular state of the pancreas during islet development, normal function, and diseased states. For example, this study demonstrates that these results can provide novel insight into the potential signalling mechanisms involving phospholipids and glycolipids that would be difficult to detect by targeted methods, and can help raise new hypotheses about the types of physiological Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00125-019-4855-8) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

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“…S1, D and E ). This technology has been used previously to survey pancreatic cancer imaging MS to discriminate breast from pancreatic cancer metastasis in formalin-fixed, paraffin-embedded tissues ( Casadonte et al, 2014 ; Eberlin et al, 2014 ; Grüner et al, 2012 ) and to survey the molecular composition of multifunctional tissues such as the pancreas ( Prentice et al, 2019 ), but not to characterize the metabolic state ( Caprioli et al, 1997 ; Cornett et al, 2008 ). Fig.…”

β-Cell Dysfunction, Hepatic Lipid Metabolism, and Cardiovascular Health in Type 2 Diabetes: New Directions of Research and Novel Therapeutic Strategies

“…It could be used to determine the chemical structure of lipids within the lipid droplets inside the adipocytes, and within individual β-cells or acinar cells. MALDI (TOF/TOF) imaging could also be used for co-localization of lipid binding protein receptors (CD36) [ 214 ]. IMS data could be confirmed by high-resolution electron and confocal microscopy imaging.…”

Multifunctional Reactive MALDI Matrix Enabling High-Lateral Resolution Dual Polarity MSI and Lipid C=C Position-Resolved MS2I

“…MALDI-MSI distributions of lipids were largely in line with previous studies of pancreas tissue. 50 Multiple BzPy-derivatized lipid ion signals were subjected to MALDI-MS 2 I. Namely, protonated signals of PC 34:1+BzPy, PC 36:2+BzPy, PC 36:4+BzPy, and PC 34:2+BzPy were fragmented and αA ions were employed to visualize lateral DB position isomer distributions with 10 µm pixel size ( Figure 5, S21 and S22). To the best of our knowledge, this is the highest reported lateral resolution for DB position isomer imaging.…”