Characterization of lipidic markers of chondrogenic differentiation using mass spectrometry imaging

Mesenchymal stem cells (MSC) are an interesting alternative for cell-based therapy of cartilage defects attributable to their capacity to differentiate towards chondrocytes in the process termed chondrogenesis. The metabolism of lipids has recently been associated with the modulation of chondrogenesis and also with the development of pathologies related to cartilage degeneration. Information about the distribution and modulation of lipids during chondrogenesis could provide a panel of putative chondrogenic markers. Thus, the discovery of new lipid chondrogenic markers could be highly valuable for improving MSC-based cartilage therapies. In this work, mass spectrometry imaging (MSI) was used to characterize the spatial distribution of lipids in human bone marrow MSCs (hBMSCs) during the first steps of chondrogenic differentiation. The analysis of MSC micromasses at days 2 and 14 of chondrogenesis by matrix-assisted laser desorption ionization-mass spectrometry imaging (MALDI-MSI) led to the identification of 20 different lipid species, including fatty acids (FA), sphingolipids (SLs) and phospholipids (PLs). Phosphocholine, several sphingomyelins (SMs) and phosphatidylcholines (PCs) were found to increase during the undifferentiated chondrogenic stage. A particularly detected lipid profile was verified by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Using this technology, a higher intensity of phosphocholine-related ions was observed in the peripheral region of the micromasses collected at day 14.