Figure 5. Antioxidant NAC alleviated postprandial TRL-induced AMSC senescence and ROS production. (A) AMSCs reached approximately 30%-40% culture-confluence were treated with PBS, NAC (10 nM), TRL (100 μg/mL), or TRL (100 μg/mL) with pretreatment of 5 or 10 nM NAC for 8 d. Subsequently, the intracellular ROS production and the number of senescent cells were evaluated using the fluorescent probe, DCFA-DA (green under fluorescence microscope), and SA-β-Gal staining (blue under the light microscope), respectively. Nuclei were stained using DAPI (blue under the fluorescence microscope). Images were obtained under a microscope (×200 magnification). (B) The fluorescence intensity analysis of ROS production. (C) SA-β-Gal positive cells were counted manually by scanning a total of 200 cells in each sample. (D–F) the protein levels of p21 and SIRT1 were detected using western blotting (D), and then the relative protein levels of p21 (E) and SIRT1 (F) were analyzed using ImageJ. Data are expressed as the mean ± SD (n ≥ 3). *P < 0.05, **P < 0.01 when compared with the PBS group. (G) A schematic illustration of the proposed mechanism of AMSC premature senescence induced by postprandial TRL. Postprandial TRL increased intracellular oxidative stress, downregulated SIRT1 level, and activated the p53/Ac-p53/p21 pathway, which ultimately promoted the premature senescence of undifferentiated and differentiating AMSCs.