Human osteogenic protein-1 induces osteogenic differentiation of adipose-derived stem cells harvested from mice

Objective: Osteogenic protein-1 (OP-1) has been shown to stimulate undifferentiated cells to produce mineralized tissue. Adipose tissue is a rich source of undifferentiated cells for tissue engineering purposes. The purpose of this study was to investigate the effect of OP-1 on osteogenic differentiation of adipose-derived stem cells and the production of bony tissue in vitro. Design: Adipose-derived stem cells (ADSCs) were isolated from inguinal fat pads of adult mice. Following cell expansion the cells were plated in 8-well chambered slides. The cells received one of four treatments: Group 1 cells were maintained in control medium, Group 2 cells were cultured in a common osteogenic medium, Group 3 cells were cultured in osteogenic medium supplemented with 250 ng/mL of OP-1, and Group 4 cells were cultured with 250 ng/mL of OP-1 added to control medium. Osteogenic differentiation of ADSCs was determined by estimating the number and size of mineralized nodules, and the amount of extracellular osteopontin secreted into cell culture medium. Mineralized nodule production was assessed at day 21 with von Kossa staining. Extracellular osteopontin release was measured after 8 and 21 days by enzyme-linked immunosorbant assay (ELISA). ANOVA/Tukey tests were used to identify differences among the four treatment groups for mineralized nodule production and osteopontin release (p ≤ 0.05). Results: Deposition of calcified nodules and osteopontin secretion was significantly greater for cell cultures incubated with OP-1 (p ≤ 0.05). At day 21, no significant differences in osteopontin secretion were noted among groups incubated with osteogenic nutrients and/or OP-1 (p > 0.05), which were significantly higher than the group incubated in cell growth medium only (p ≤ 0.05). No significant differences in osteopontin secretion were noted between 8 and 21 days for any group (p > 0.05). Linear regression analysis demonstrated a linear relationship was present between the presence of calcified nodules and the amount of osteopontin released (p ≤ 0.05). Conclusions: OP-1 is a powerful inducer of osteogenic differentiation of adult adipose-derived stem cells.