Matrix-assisted laser desorption ionization-imaging mass spectrometry: a new methodology to study human osteoarthritic cartilage.

OBJECTIVE: Information about the distribution of proteins and the modulation that they undergo in the different phases of rheumatic pathologies is essential to understanding the development of these diseases. We undertook this study to demonstrate the utility of mass spectrometry (MS)-based molecular imaging for studying the spatial distribution of different components in human articular cartilage sections. METHODS: We compared the distribution of peptides and proteins in human control and osteoarthritic (OA) cartilage. Human control and OA cartilage slices were cut and deposited on conductive slides. After tryptic digestion, we performed matrix-assisted laser desorption ionization-imaging MS (MALDI-IMS) experiments in a MALDI-quadrupole time-of-flight mass spectrometer. Protein identification was undertaken with a combination of multivariate statistical methods and Mascot protein database queries. Hematoxylin and eosin staining and immunohistochemistry were performed to validate the results. RESULTS: We created maps of peptide distributions at 150-µm raster size from control and OA human cartilage. Proteins such as biglycan, prolargin, decorin, and aggrecan core protein were identified and localized. Specific protein markers for cartilage oligomeric matrix protein and fibronectin were found exclusively in OA cartilage samples. Their distribution displayed a stronger intensity in the deep area than in the superficial area. New tentative OA markers were found in the deep area of the OA cartilage. CONCLUSION: MALDI-IMS identifies and localizes disease-specific peptides and proteins in cartilage. All the OA-related peptides and proteins detected display a stronger intensity in the deep cartilage. MS-based molecular imaging is demonstrated to be an innovative method for studying OA pathology.