Figure 6: Flow cytometry analysis of active caspase-3, caspase-8, and caspase-9 with FITC/PI double staining in HDFs (a). Quantitative analysis of apoptotic cells population for active caspase-3, caspase-8, and caspase-9. (b). Data are expressed as means SD, . adenotes compared to control young, b compared to GTT, c compared to SIPS, and d compared to control senescent cells.