Objective:To observe the paracrine effects of mesenchymal stem cells(MSC)on the activated hepatic stellate cells Lx－2,and explore the possible mechanisms. Methods:A co－culture system was established by culturing bone marrow mesenchymal stem cell(BM－MSC)in the Transwell insert and Lx－2 on the plastic plates(6 well),which were placed on the upper and lower layer repectively,and set it as the experiment group. Normal Lx－2 was cultured alone as control. Cell apoptosis was determined by Hoechst 33342 staining and flow cytometry,respectively. The expressions of uncoupling protein 2(UCP2)mRNA and protein in Lx－2 were detected by quantitative real－time PCR(qRT－PCR)and Western blot,respectively. Intracellular and mitochondrial reactive oxygen species(ROS)levels of Lx－2 were measured by fluorescent probe method. The content of MDA in co－culture supernatant was determined by thiobarbituric acid(TBA)reaction. Results:Compared with the control group,Hoechst 33342 staining showed nuclear condensation,granular fluorescence and other typical features of apoptosis in parts of Lx－2 cells. The apoptotic rate of Lx－2 in the experiment group was 2.6 times of that in the control group(P < 0.05). The expressions of UCP2 mRNA and protein in Lx－2 were significantly inhibited compared with those in the control group(P < 0.05). The intracellular and mitochondrial ROS levels of Lx－2 in the experiment group were highly enhanced. The concentration of MDA in the co－culture supernatant in the experimental group was (0.43 ± 0.47)mmol/L,which was significantly higher than the control group with (0.16 ± 0.43)mmol/L(P < 0.05). Conclusion:The paracrine effects of MSC were capable of inducing Lx－2 apoptosis,which is supposed to be the result of the suppression of UCP2 and over－expression of intracellular and mitochondrial ROS in Lx－2.