Figure 2. Knockdown of SIRT6 expression induces endothelial cell senescence. (A) Western blot analysis showing the knockdown expression of SIRT1, SIRT3, and SIRT6 in HUVECs treated with SIRT1, SIRT3, and SIRT6 siRNAs, respectively. Total protein was extracted from cells 1 and 3 d after siRNA treatment. (B) The representative images obtained from SA β-gal-stained HUVECs. The cells transfected with the indicated siRNA (25 nM) were re-transfected with the siRNA 3 d after the first siRNA treatment. After 6 d from the first transfection, cells were stained for SA β-gal. (C) The percentage of SA β-gal-positive senescent cells at 6 d after siRNA transfection. The data are shown as the mean ± SD (n = 3). *P < 0.05 vs. control siRNA.