Objective     To study the effects of low-dose lipopolysaccharide (LPS) on nuclear factor-erythroid 2-related factor-2 (Nrf2) expression and reactive oxygen species (ROS) level in PC12 cells.     Methods     LPS solutions with concentrations of 0.01

0.025

0.05

0.1

0

.25

0.5 and 1 μg/μl were used to treat PC12 cells for 24 h

and then cell viability was tested by MTT assay to determine the maximum safe dose. PC12 cells treated by LPS of the determined dose were subjected to detection of Nrf2 mRNA and protein expression in whole cell and Nrf2 protein expression in cytoplasm and nuclei through RT-PCR and Western blotting. The average fluorescence intensity of ROS in the cells was tested by   flow cytometry   as well.     Results     LPS with a concentration lower than 0.1 μg/μl had no obvious toxicity to PC12 cells (

P

>0.05). In PC12 cells treated by 0.1 μg/μl LPS for 24 h

the expression of Nrf2 mRNA and protein in whole cell increased gradually. During the process

there were significant differences for mRNA expression at 18 h as well as mRNA and total protein expression at 24 h

as compared with those of the control group (

P

<

0.01). In PC12 cells treated by 0.1 μg/μl LPS for 1

3

6 and 12 h

the Nrf2 protein expression in  cytoplasm  decreased gradually and then recovered slightly

with the lowest expression at 6 h

as compared with that of the control group (

P

<

0.01). The Nrf2 protein expression in the nuclei increased

with a significant difference from that of the control group (

P

<

0.01)

and showed an expression peak at 3 h. In PC12 cells treated by 0.1 μg/μl LPS for 8 h

the average fluorescence intensity of ROS decreased significantly (

P

<

0.01).     Conclusion      Low-dose LPS can promote the transcription

translation and nuclear translocation of Nrf2 in PC12 cells with time dependence and reduce ROS level

and probably participates in stress tolerance.