Extracellular signal-regulated kinase activation in airway smooth muscle cell proliferation in chronic asthmatic rats.

To investigate the regulatory effect of extracellular signal-regulated kinase (ERK) signaling pathway on airway smooth muscle cell (ASMC) proliferation in chronic asthmatic rats, the rat model of chronic asthma was established, and ERK agonist epidermal growth factor (EGF) and inhibitor PD98059 were used in the cell culture. ASMC proliferation was examined by flow cytometry analysis, methyl thiazolyl tetrazolium (MTT) colorimetric assay, [(3)H]-thymidine (TdR) incorporation and proliferating cell nuclear antigen (PCNA) immunocytochemical staining. The expressions of ERK mRNA, ERK protein, phosphorylated ERK1/2 (p-ERK1/2) protein were observed by RT-PCR and Western blot. The results showed that in chronic asthmatic group, compared with that in the control group, the percentage of cells at G(0)/G(1) phase was significantly decreased and the percentage of cells at S+G(2)/M phase was significantly increased. Absorbance (A(490)), DNA synthesis and the expression of PCNA protein in ASMCs in chronic asthmatic group were significantly increased. The expressions of ERK mRNA, ERK1/2 protein, p-ERK1/2 protein and the activation ratio of ERK in ASMCs in chronic asthmatic group were significantly increased compared with those in the control group. After treatment with PD98059, the percentage of cells at S+G(2)/M phase, A(490), DNA synthesis and the expression of PCNA protein in ASMCs in chronic asthmatic group were significantly decreased; the expressions of ERK mRNA, ERK1/2 protein, p-ERK1/2 protein and the activation ratio of ERK in ASMCs in chronic asthmatic group were significantly decreased compared with those in the control group. After treatment with EGF, the percentage of cells at S+G(2)/M phase, A(490), DNA synthesis and the expression of PCNA protein in ASMCs in chronic asthmatic group were significantly increased compared with those before treatment; and PD98059 markedly inhibited the effect of EGF. These results suggest that the endogenous proliferation activity of ASMCs in chronic asthmatic rats significantly increases compared with that in the control rats, and ERK1/2 participates in this process. The ERK signaling pathway might play an important role in regulating ASMC proliferation, leading to asthmatic airway remodeling.