Figure 6. SIRT1 siRNA-mediated downregulation exacerbates the development of senescence in normal human diploid fibroblasts. (A) Representative immunoblots for SIRT1 (upper panel) and β-actin (lower panel) proteins from IMR-90 cells (PDL 37) forty-eight hours after infection with either Ad-SIRT1 or an empty adenoviral vector as negative control (Ad-ctrl). (B) Representative phase-contrast photomicrographs showing SA β-gal staining of IMR-90 cells at PDL 50 forty-eight hours post-infection with either Ad-SIRT1 or Ad-ctrl (negative control). Original magnification: X100. (C) Quantification of the percentage of SA β-gal positive cells shown in (B).( D) Representative zymograms from early passage IMR-90 (PDL 29) cells seventy-two hours after transfection with Ad-SIRT1 siRNA or Ad-ctrl vector. Representative data from three independent experiments are shown. (E) Phase-contrast (photomicrographs of IMR-90 at PDL 37 infected with Ad-SIRT1, and subsequently incubated for 72 hours in media containing 10% of either CR (left panel) or AL (right panel) rat serum. Original magnification: X200.