Effects of vaspin on the AKT signaling pathway during the first 24 h of differentiation. Vaspin (200 ng/mL) was added to the differentiation medium, and the cells were harvested after 2, 6, 12, or 24 h of culture. Western blot analyses were used to assess the protein levels of p-AKT and AKT, **P < 0.01 compared with the control group