The osteogenic potential of human mesenchymal stem cells: Novel markers and key factors for differentiation

Abstract: Mesenchymal stem cells are multipotent stem cells with ability to differentiate into cells of the connective tissue lineage, such as adipocytes, osteoblasts and chondrocytes, both in vitro and in vivo. The main objective of the present thesis was to study different aspects of the osteogenic potential of MSCs. By examining markers of differentiation, exploring approaches for enhanced osteogenesis through the use of small molecule substances, and studying the interactions between MSCs and inflammatory cells/signals, we aimed to gain new insights into factors and mechanisms involved in regulation of the osteogenic differentiation process. Through both a virtual ligand-based screening method combined with several in vitro screening steps, and a chemical inhibition of the PPAR-γ transcription factor, it was demonstrated that osteogenic differentiation of MSCs can be modulated by the use of a small molecule substance. Furthermore, a link between PPAR-γ, leptin and osteogenic differentiation was revealed. The surface markers CD10 and CD92, and intracellular protein CRYaB were demonstrated as suitable markers for monitoring and evaluating the differentiation of MSCs. CD10 and CD92 were shown to be markers of both osteogenic and adipogenic differentiation, whereas CRYaB was revealed as a marker specific for the osteogenic lineage. Activated human monocytes communicate pro-osteogenic signals to MSCs, independent of direct cell-cell contact. Furthermore, membrane vesicles isolated from gram-positive bacterial strains Staphylococcus aureus and Staphylococcus epidermidis also promote osteogenic differentiation of MSCs as well as modulate their secretion of signals related to inflammation and immune-modulation. In conclusion, the present thesis presents new and applicational knowledge regarding the phenotype of MSCs characteristic for osteogenic differentiation. Furthermore, through the results presented here insight is gained into several key factors, both of synthetic and biological origin, important in this process. This knowledge could be valuable in future strivings for enhanced osteogenic regeneration.