Research Paper Volume 14, Issue 20 pp 8167—8178

Figure 1. Aging human skin fibroblasts express SFRP4. (A) SA-β-gal staining of proliferating and senescent cells. Senescent cells profusely express SA-β-gal in the cytoplasm. Bar = 50 μm. (B) BrdU absorption by proliferating and senescent cells. Senescent cells have decreased BrdU absorption due to decreased mitotic activity. (C) RT-PCR analysis of SASP gene expression by cell extracts. GAPDH was used as the housekeeping gene. (D) ELISA for protein expression of IL6 and IL8. (E) Western blot analysis of cell extract proteins. GAPDH was used as the housekeeping protein. (F) Immunostaining of p16^ink4a and SFRP4 in proliferating and senescent cells. SFRP4 expression is observed in the cytoplasm in senescent cells consistent with p16ink4a positivity. Bar = 20 μm. P: Proliferating cells. S: Senescent cells. *; P < 0.05. Mann–Whitney U test was used to analyze differences between two groups. All experiments were repeated in triplicate.