MALDI Imaging for Proteomic Painting of Heterogeneous Tissue Structures

Abstract

Purpose To present matrix‐assisted laser desorption/ionization (MALDI) imaging as a powerful method to highlight various tissue compartments. Experimental design Formalin‐fixed paraffin‐embedded (FFPE) tissue of a uterine cervix, a pancreas, a duodenum, a teratoma, and a breast cancer tissue microarray (TMA) are analyzed by MALDI imaging and by immunohistochemistry (IHC). Peptide images are visualized and analyzed using FlexImaging and SCiLS Lab software. Different histological compartments are compared by hierarchical cluster analysis. Results MALDI imaging highlights tissue compartments comparable to IHC. In cervical tissue, normal epithelium can be discerned from intraepithelial neoplasia. In pancreatic and duodenal tissues, m/z signals from lymph follicles, vessels, duodenal mucosa, normal pancreas, and smooth muscle structures can be visualized. In teratoma, specific m/z signals to discriminate squamous epithelium, sebaceous glands, and soft tissue are detected. Additionally, tumor tissue can be discerned from the surrounding stroma in small tissue cores of TMAs. Proteomic data acquisition of complex tissue compartments in FFPE tissue requires less than 1 h with recent mass spectrometers. Conclusion and clinical relevance The simultaneous characterization of morphological and proteomic features in the same tissue section adds proteomic information for histopathological diagnostics, which relies at present on conventional hematoxylin and eosin staining, histochemical, IHC and molecular methods.

Proteomics in Pathology: The Special Issue

“…[15] Kriegsmann et al illustrated how MALDI imaging could highlight tissue compartments in a complementary fashion to immunohistochemistry. [16] The versatility of MALDI imaging regarding the nature of analyzable samples was demonstrated through the work of Piga et al who evaluated the time stability of thyroid fine-needle aspiration biopsies through their morphological and proteomic profile. [17] Schwamborn et al analyzed cytology microarrays of malignant peritoneal and pleural effusions from serous ovarian cancer and several non-ovarian carcinomas.…”

“…High‐resolution MALDI imaging was performed by Smith et al to highlight mass spectrometric signatures in glomeruli associated with the response of immunosuppressive treatment in membranous nephropathy . Kriegsmann et al illustrated how MALDI imaging could highlight tissue compartments in a complementary fashion to immunohistochemistry …”

Next-generation protein analysis in the pathology department

“…Tissue is digested during 1.5 hours at 37°C under 95% humidity. Enzyme application is a crucial preparation step for FFPE as different approaches can be used (different buffers, different concentrations of enzyme required, different digestion times and temperatures) in order to minimise the time and effort needed and maximise the spatial information 19–22…”

“…In the oncology field, publications have highlighted applications of MALDI IMS in lung cancer, breast cancer, brain tumours, gastrointestinal tract cancer, urogenital cancer, and head and neck cancer, among others 34–37. This technique has been experimentally applied for the detection of malignant tumour margins, tumour typing, grading37 and determination of cancer heterogeneity 21…”

Overview of Cytogenetic Technologies

“…It allows the study of fundamental biological questions, such as the nature of inherited syndromes, genomic alterations that are involved in tumorigenesis, and three-dimensional organization of the human genome [2]. Over the years, cytogenetic techniques have been used to unravel the three-dimensional organization of the genome and epigenetic features of higher-order chromatin structure [1,[3][4][5][6][7][8]. Throughout the history, various discoveries and techniques have revolutionized the field of human cytogenetics (Table 1) [1].…”