Abstract： Objective To study the role of SIRT 1 in apoptosis of PC 12 neuronal cells induced by lipopolysaccharide (LPS). Methods PC12 cells were cultured with different concentrations of LS (50 μg/mL,500 μg/mL,750 μg/mL,1000 μg/mL and 1250 μg/mL),and some other PC12 cells were routinely cultured as controls. MTT assay was employed to identify the cell survival 24 h after the inducement,and accordingly,the suitable LPS concentration for subsequent experiments was determined based on MTT results. And then, cell apoptosis in the experimental groups under the suitable LPS concentration at different times (1/2,2,18,24,and 48 h) and control group was noted by flow cytometry and Hoechst 33258 staining; Western blotting was used to detect the SIRT1 level in PC12 cells. Results Hoechst 33258 staining indicated that a few apoptotic bodies were noted 1/2 h after inducement,expressing as karyopyknosis and karyorrhexis; apoptotic bodies began to increase 18 h after inducement,reaching their peak level 24 h after inducement; and a decreased trend was observed 48 h after inducement. Flow cytometry indicated that significantly higher apoptosis rate at each time point was noted as compared with that in the control group (P＜0.05); and Hoechst 33258 staining showed the same result. Western blotting revealed that the SIRT1 expression was (1.84±0.04) in the control group,decreasing to (1.17±0.09) 1/2 h after the inducement,and reaching the lowest level (0.62±0.03) 24 h after the inducement; and then, the expression was increased to (0.77±0.02) 48 h after the inducement;significant difference on the expression at each time point was noted as compared with that in the control group (P＜0.05). Conclusion LPS can induce PC12 cell apoptosis and SIRT1 protein expression is inhibited,indicating that SIRT1 may take part in the apoptosis and play a protective role to PC12 cells.