Figure 1. Effect of age on the mitogenic response of human bmMSCs to IGF-I. BrdU incorporation analyses. Human bmMSCs were maintained in serum-free media for 24 h, and then subjected to BrdU incorporation analyses with or without concomitant treatment of 5, 50, and 250 ng/ml of IGF-I. (A) The correlation between the age and the IGF-I-triggered DNA synthesis was analyzed. (B) The average OD450 values of bmMSCs of adult (n=6), middle aged (n=8), and aged (n=17) groups cultured without IGF-I treatment are shown. The difference between the groups was analyzed by the Student’s t-test. (C) RT-qPCR analyses. The expression of IGF-IR and IGF-I mRNAs of the aged bmMSCs (n=17) were compared to those of the adult bmMSCs (n=6) (to which a value of 1 was assigned). Data represent the mean ± S.D. from three experiments. Student’s t-test was used to analyze the differences between the groups. (D) Western blot analyses. The protein levels of IGF-IR in the Aged-1, Aged-2, Adult-1, and Adult-2 cells are shown.