An optimized MALDI MSI protocol for spatial detection of tryptic peptides in fresh frozen prostate tissue

Therese S Høiem, Maria K Andersen, Marta Martin-Lorenzo, Rémi Longuespée, Britt S R Claes, Anna Nordborg, Frédéric Dewez, Benjamin Balluff, Marco Giampà, Animesh Sharma, Lars Hagen, Ron M A Heeren, Tone F Bathen, Guro F Giskeødegård, Sebastian Krossa, May-Britt Tessem*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

MALDI MS imaging (MSI) is a powerful analytical tool for spatial peptide detection in heterogeneous tissues. Proper sample preparation is crucial to achieve high quality, reproducible measurements. Here we developed an optimized protocol for spatially resolved proteolytic peptide detection with MALDI time-of-flight MSI of fresh frozen prostate tissue sections. The parameters tested included four different tissue washes, four methods of protein denaturation, four methods of trypsin digestion (different trypsin densities, sprayers, and incubation times), and five matrix deposition methods (different sprayers, settings, and matrix concentrations). Evaluation criteria were the number of detected and excluded peaks, percentage of high mass peaks, signal-to-noise ratio, spatial localization, and average intensities of identified peptides, all of which were integrated into a weighted quality evaluation scoring system. Based on these scores, the optimized protocol included an ice-cold EtOH+H2 O wash, a 5 min heating step at 95°C, tryptic digestion incubated for 17h at 37°C and CHCA matrix deposited at a final amount of 1.8 μg/mm2 . Including a heat-induced protein denaturation step after tissue wash is a new methodological approach that could be useful also for other tissue types. This optimized protocol for spatial peptide detection using MALDI MSI facilitates future biomarker discovery in prostate cancer and may be useful in studies of other tissue types.

Original languageEnglish
Article numbere2100223
Number of pages13
JournalProteomics
Volume22
Issue number10
Early online date16 Feb 2022
DOIs
Publication statusPublished - May 2022

Keywords

  • ADVANCEMENTS
  • CANCER
  • IDENTIFICATION
  • IMAGING MASS-SPECTROMETRY
  • MALDI mass spectrometry imaging
  • PARAFFIN-EMBEDDED TISSUE
  • PROTEIN
  • RESOLUTION
  • SAMPLE PREPARATION
  • SENSITIVITY
  • SOFTWARE
  • fresh frozen
  • peptides
  • prostate tissue
  • proteomics

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