BACKGROUND: Cyclophilin A can protect neurons against oxidative stress. OBJECTIVE: To investigate the effect of cyclophilin A on Bcl-2 and Bax protein expression in pheochro-mocytoma (PC12) cells treated with beta-amyloid fragment 25-35 (Aβ25-35), and to verify the protection pathway of cyclophilin A. DESIGN, TIME AND SETTING: The initial experiment was performed at the Laboratory of Department of Neurology, First Clinical College, China Medical University from November 2006 to July 2007. MATERIALS: PC12 cells were cultured at the Cell Center of Peking Union Medical College. Aβ25-35 (Sigma, USA), antibodies of Bcl-2 and Bax (Wuhan Boster, China), and recombinant human cyclophilin A (Biomol, USA) were used in this study. METHODS: PC12 cells were divided into three groups. Cells in the control group were incubated in culture medium. Cells in the Aβ25-35 injury group were incubated in medium containing a final concentration of 10 μmol/L of Aβ25-35. Cells in the cyclophilin A group were incubated in medium containing a final con-centration of 10 nmol/L of cyclophilin A for 30 minutes, and then treated with 10 μmol/L Aβ25-35. MAIN OUTCOME MEASURES: After 24 hours of culture, immunohistochemistry was used to detect Bcl-2 and Bax expression in PC12 cells. Annexin-V flow cytometry was employed to measure the apoptosis rate of PC12 cells. The MTT method was applied to examine the survival rate of PC12 cells. RESULTS: Bcl-2 expression decreased, whereas Bax expression increased in PC12 cells treated with Aβ25-35 (t = 2.277, 5.957, P < 0.05). However, in PC12 cells treated with Aβ25-35 and cyclophilin A, Bcl-2 expression increased and Bax expression decreased (t = 4.497, 2.531, P < 0.05). The survival rate of PC12 cells significantly decreased and the apoptosis rate increased (t=8.509, 22.886, P < 0.05) following Aβ25-35 treatment. Cyclophilin A enhanced the survival rate of PC12 cells to Aβ25-35-induced apoptosis (t = 4.895, 10.042, P < 0.05). CONCLUSION: Cyclophilin A can increase Bcl-2 expression and decrease Bax expression in PC12 cells treated with Aβ25-35, which indicates that cyclophilin A has a protective effect on Aβ25-35-induced injury to PC12 cells. BACKGROUND: Cyclophilin A can protect neurons against oxidative stress. OBJECTIVE: To investigate the effect of cyclophilin A on Bcl-2 and Bax protein expression in pheochro-mocytoma (PC12) cells treated with beta-amyloid fragment 25-35 (Aβ25-35) , and to verify the protection pathway of cyclophilin A. DESIGN, TIME AND SETTING: The initial experiment was performed at the Laboratory of Department of Neurology, First Clinical College, China Medical University from November 2006 to July 2007. MATERIALS: PC12 cells were cultured at the Cell Center of Peking Union Medical College. Aβ25-35 (Sigma, USA), antibodies of Bcl-2 and Bax (Wuhan Boster, China), and recombinant human cyclophilin A (Biomol, USA) were used in this study. Cells in the control group were incubated in culture medium. Cells in the Aβ25-35 injury group were incubated in medium containing a final concentration of 10 μmol / L of Aβ25-35. Cells in the cyclophilin A group we re incubated in medium containing a final con-centration of 10 nmol / L of cyclophilin A for 30 minutes, and then treated with 10 μmol / L Aβ 25-35. MAIN OUTCOME MEASURES: After 24 hours of culture, immunohistochemistry was used to detect Bcl -2 and Bax expression in PC12 cells. Annexin-V flow cytometry was employed to measure the apoptosis rate of PC12 cells. The MTT method was applied to examine the survival rate of PC12 cells. RESULTS: Bcl-2 expression decreased, whereas Bax expression increased in PC12 cells treated with Aβ25-35 (t = 2.277, 5.957, P <0.05). However, in PC12 cells treated with Aβ25-35 and cyclophilin A, Bcl- , P <0.05). The survival rate of PC12 cells significantly decreased and the apoptosis rate increased (t = 8.509, 22.886, P <0.05) following Aβ25-35 treatment. Cyclophilin A enhanced the survival rate of PC12 cells to Aβ25-35- induced apoptosis (t = 4.895, 10.042, P <0.05) CONCLUSION: Cyclophil in A can increase Bcl-2 expression and decrease Bax expression in PC12 cells treated with Aβ25-35, which indicates that cyclophilin A has a protective effect on Aβ25-35-induced injury to PC12 cells.