Abstract: Objective To study the effects of Aβ25-35 on the expression of gene P21，CDK4，E2F1 and BAX in the cultured PC12 cells. Methods PC12 cells were treated with 25?mol/L Aβ25-35，the relation between cell cycle redistribution and apoptosis was analyzed by flow cytometry（FCM）.Protein and mRNA expression of P21，CDK4，E2F1 and BAX were detected by RT-PCR and Western-blot respectively. Results About 90% PC12 cells were found arrest on G0/G1 by FCM being deprived serum. Treated with 25?mol/L Aβ25-35 for 8，16，24h，the percent of S phase cells was raised remarkably (P<0.01) at 8h, but the percent of S phase cells was declined gradually after treated for 16h. Meanwhile apoptotic rate was increased obviously between 16 h and 24 h(P＜0.01), the hypodiploid peak could be observed ahead of G0/G1 phase(Ap).After synchronized PC12 cells being treated with 25?mol/L Aβ25-35 from 0 to 20h, the mRNA and protein expression of P21 gene were downregulated, while CDK4，E2F1 and BAX gene were upregulated. Conclusion Aβ25-35 induces the synchronized PC12 cells attempting to re-enter cell cycle，which appear the apoptotic peak subsequently. This is likely related to decreasing the mRNA and protein expression of P21 gene, and increasing the mRNA and protein expression of CDK4，E2F1 and BAX gene.

Key words: Aβ25-35, PC12 cell, P21, CDK4, E2F1, Bax, gene expression