MALDI imaging mass spectrometry to investigate compartments of synovial tissue of patients with rheumatoid arthritis MALDI IMS zur Untersuchung von Synovial Gewebe bei Rheumatoider Arthritis

Aim: Rheumatoid arthritis (RA) is an autoimmune disease with proliferation of lymphocytes, fibroblasts and synovial lining causing cartilage and bone destruction. The etiology and pathogenesis of this disease are still unknown. Early and precise diagnosis is mandatory to choose the appropriate therapy. Diagnosis of RA is made according to the (American Congress of Rheumatology) ACR-criteria. Personalized medicine requires exact description of synovial pathology to target the appropriate cell population in various RA subtypes or stages. The aim of this study is to identify differences in peptide patterns in two compartments of synovial tissue by MALDI TOF Mass Spectrometry (MS) profiling and imaging. Methods: Patients were classified according to the American College of Rheumatology (ACR) criteria for RA. Adjacent serial FFPE sections were stained with H&E and were reviewed by a pathologist. Areas of interest (synovial lining and sublining layer, 10 discrete areas per compartment) were marked digitally and the histology annotated images were merged with a photomicrograph of the section taken before the MALDI MS measurement. For MALDI MS analysis, trypsin and matrix solution were applied to discrete regions of interest using a robotic spotter. Pixel coordinates of these areas were transferred to a mass spectrometer for spectral acquisition in reflector mode. Generated data were then subjected to biocomputational analysis to reveal biomarker candidates. In total, 20 tissue sections were analyzed. Some tissue sections were chosen for MALDI MS imaging of the whole tissue sections to show the distribution of the m/z values of interest. Results: Various m/z values representing different peptide profiles were demonstrated in the two tissue compartments. Several peptides were found to be expressed at higher levels in the synovial lining compared to the sublining layer, with a 99.5% confidence level and a 1.7 fold change. Other peptides were more pronounced in the sublining areas. Conclusion: We clearly show different peptide patterns in synovial lining layer and sublining areas by MALDI MS profiling and imaging. Further studies are required to to provide greater statistical power and to identify subtypes or different disease stages that are directly applicable to personalized medicine.