Cell cycle protein profile of the hepatic stellate cells (HSCs) in dimethylnitrosamine-induced rat hepatic fibrosis

Cell cycle regulating proteins are known to have close relation with the proliferation of the mammalian cells. In injured liver, the number of HSCs is increased from proliferation. However, the expression of cell cycle proteins of HSCs during proliferation remains unevaluated. Therefore, cell cycle protein profiles of HSCs were studied in dimethyl-nitrosamine (DMN)-induced rat liver fibrosis model. Sprague-Dawley rats were intraperitoneally injected of DMN and the animals were sacrificed every week up to 4 weeks. HSCs were separated and the number of the cells in S phase was counted to evaluate the cell proliferation by flow cytometry. The expression of cyclin A, cyclin B, cyclin D1, cdk2, cdk4, cdc2, proliferating cell nuclear antigen (PCNA), p21(Cip.WAF1), and p27 was examined with immunoblotting analysis. Portion of S-phase cells peaked 7 days after DMN injection. At that time, cyclin A, and PCNA showed significant increase in HSCs compared to untreated HSCs 114% and 116%, respectively, P < 0.001). p21 (Cip/WAF1) was decreased significantly in DMN-treated HSCs compared to control cells (88%, P < 0.001). The increase of cyclin A, and PCNA and the decrease of p21(Cip/WAF1) seem to play important roles in the proliferation of HSCs during the early period of DMN treatment.