Human β-defensins differently affect proliferation, differentiation, and mineralization of osteoblast-like MG63 cells

Purpose of this study was to investigate whether human β-defensins (hBDs) affect maturation and proliferation of osteoblast-like MG63 cells in vitro. Osteoblast-like MG63 cells were stimulated with hBD-1, -2, and -3 under control conditions and with hBD-2 during experimental inflammation (induced by interleukin-1β, tumor necrosis factor-α, toll-like receptor-2 and -4 agonists). Expression of different osteogenic markers and hBDs were analyzed by real-time PCR, immunohistochemistry, and enzyme-linked immunosorbent assay. In addition, alkaline phosphatase (ALP) enzyme activity and biomineralization as markers for differentiation were monitored. All tested hBDs were expressed on mRNA and protein level in MG63 cells. Only stimulation with hBD-2 elevated the proliferation rate. hBD-2 and hBD-3 positively affected the differentiation of osteoblast-like cells provided by increased transcript levels of osteogenic markers, up-regulated ALP enzyme activity and enhanced mineralized nodule formation. All pro-inflammatory stimuli enhanced interleukin-6 and hBD-2 expression and down-regulated markers of osteoblastic differentiation. In accordance, inflammation increased transcript level of Notch-1 (an inhibitor of osteoblastic differentiation). hBD-2 was not able to revert effects of inflammation on differentiation. In bone cells human β-defensins exhibit further functions than antimicrobial peptide activity. These include stimulation of proliferation and differentiation. Differentiation arrest due to inflammation could not be overcome by hBD-2 alone.