Figure 6. SIRT6 knockdown significantly induces cell proliferation in endothelial cells. (A) MTT assay showing the effect of SIRT6 knockdown on endothelial cell proliferation. HUVECs were transfected with 25 nM control or SIRT6 siRNA and incubated for the indicated number of days. *P < 0.01 vs. control siRNA. (B) Cell cycle analysis indicating that SIRT6 siRNA induces cell cycle arrest in endothelial cells. HUVECs were transfected with 25 nM control or SIRT6 siRNA. After 3 d, cells were stained with PI and analyzed using flow cytometry. Graphs show the mean percentage ± SD of cells in G0/G1, S, and G2/M phases. *P < 0.05 vs. control siRNA. **P < 0.01 vs. control siRNA. (C) Western blot analysis to determine the effect of SIRT6 knockdown on the expression of cell cycle regulators. β-Actin was used as a loading control.