Paracrine effect of inflammatory cytokine-activated bone marrow mesenchymal stem cells and its role in osteoblast function

Mesenchymal stem cells (MSCs) have a crucial function in bone regeneration. Inflammation is a well-documented component of the osteogenic microenvironment. In the present study, we investigated whether stimulation of MSCs with inflammatory cytokines promotes osteogenesis through a paracrine mediator. MSCs were pre-stimulated with the inflammatory factors IFN-γ and TNF-α. After pre-stimulation, the MSC secretion levels of IL-6, HGF, VEGF, and TGF-β were significantly elevated (p < 0.01); however, the production of IL-2, IL-4, and IL-10 was not changed (p > 0.05). MG63, an osteoblast-like cell line, was cultured in different MSC-conditioned media. After treatment with conditioned media collected from MSCs pre-treated with cytokines, the proliferation and migration of MG63 cells were significantly improved, and the expression levels of the osteoblast differentiation markers ALP, COLI, OCN and OPN were significantly increased as revealed by a quantitative PCR analysis (p < 0.05). Furthermore, an immunofluorescence staining assay showed that more MG63 cells were OPN-positive, while an Alizarin red staining indicated the increased formation of calcium nodules in the IFN-γ and TNF-α combined pretreatment group. The results indicated that conditioned medium from inflammatory cytokine-activated MSCs can significantly promote osteoblast proliferation, migration, differentiation, and mineralization and ultimately enhance osteogenesis through paracrine mechanisms. These findings present a new direction for the clinical application of MSCs in the repair of bone defects.