Figure 6. Up-regulation of SIRT1 induced by 17β-E2 inhibited apoptosis in osteoblasts. (A) Cell apoptosis rates (%) were measured by using flow cytometry (FCM) analysis of Annexin V-FITC/PI dual staining in osteoblasts pretreated with or without SRT1720 and EX527 for 2 h prior to incubation with 17β-E2 (10-6 M) for 24 h. Q1, dead cells; Q2, later apoptotic cells; Q3, early apoptotic cells; Q4, living cells. The apoptotic rate was determined as the percentage of Q2+Q3. (B) The histogram showed the percentage of apoptosis rate in different groups. The results suggested that the apoptosis rates (Q2+Q3) were significantly decreased in 17β-E2 + SRT1720 group compared with those in the control group and 17β-E2 + EX527 group. (C) MTT assay was performed to detect the osteoblasts viability, and the histogram showed the cell viability (%) in different groups. The data were expressed as the means ± SD from 3 independent experiments. * P < 0.05 vs. the control group was considered significant.