ISGF3 with reduced phosphorylation is associated with constitutive expression of interferon-induced genes in aging cells

In vitro aging of NHDFs after serial passages. a NHDFs isolated from normal human dermal fibroblasts were obtained at passage 2. After starting the cultures, cells were passaged every 3 days. Early passage cells, passages 3 (p3) to 6 (p6); senescent cells, passage？>？20. b Confirmation of the aging of NHDFs at later passages. SA-β-gal, a senescence marker, was stained in cells at passages 3 (p3) and 21 (p21). Staining was denser in cells at later passages. Representative results from three independent experiments are shown. Bar, 10？μm. Positive cells were determined by counting 20 cells in every fifth field of view from three experiments in each group. Data are expressed as means？±？standard errors (s.e.). *p？<？0.05. c Higher p16INK4A protein levels and lower SIRT1 levels were detected in HNDFs at passage 23 (p23) compared with at passage 5 (p5), as determined by western blotting. Representative results from three independent experiments are show