[The role of external signal regulated kinase and transforming growth factor beta(1) in asthma airway remodeling and regulation of glucocorticoids].

Objective: To study role of external signal regulated kinase (ERK) and transforming growth factor beta(1) (TGF-beta1) in asthma airway remodeling and to explore the regulation of glucocorticoids on ERK, TGF-beta1, and airway remodeling.

Methods: Thirty SD rats were randomly divided into 3 equal groups: control group; asthma group, undergoing intra-peritoneal injection of ovalbumin (OVA) on days 1 and 8 and inhalation of OVA every other day for 8 weeks since day 15 to establish chronic asthma models; dexamethasone (DM) intervention group, undergoing intra-peritoneal injection of DM 30 min before every inhalation instigation; and control group, receiving normal saline instead of DM. 1 - 2 hours after the last instigation the left lungs were taken out. The total bronchial wall thickness (Wat) and smooth muscle thickness (Wam) were measured by image analysis system. Phosphorylated ERK (P-ERK) was detected by immunohistochemistry. 1 - 2 hours after the last instigation blood samples were collected from the femoral artery. The concentration of transforming growth factor (TGF)-beta1 in the serum was measured by sandwich ELISA. Rat airway epithelial cells were cultured, stimulated with platelet-derived growth factor-BB (PDGF-BB, 1, 10, 25, or 50 microg/L), U0126 (specific inhibitor of phosphorylation of ERK), or budesonide (BUD). Western blotting was used to detect the P-ERK level. The level of TGF-beta1 in the cell culture supernatant was detected by sandwich ELISA.

Results: The Wat and Wam of the asthma group was significantly higher than those of the control group (both P < 0.01), and the Wat and Wam of the DM group were both significantly lower than those of the asthma group (both P < 0.01). The mean optical density of P-ERK and concentration of TGF-beta1 in the serum of the asthma group were 31.1 +/- 2.2 and 28.1 +/- 7.4 microg/L respectively, both significantly higher than those of the control group (12.8 +/- 2.4 and 13.6 +/- 2.7 microg/L respectively, both P < 0.01), and the mean optical density of P-ERK and concentration of TGF-beta1 in the serum of the DM group were 18.7 +/- 3.1 and 15.0 +/- 3.2 microg/L respectively, both significantly lower than those asthma group (both P < 0.01). In the PDGF-BB (25 microg/L) stimulated cells marked phosphorylation of ERK occurred 15 min later, the level of P-ERK remained high up to 8 hour later, and the maximal activation occurred at the period of 2 h - 4 h later, 6.5 +/- 0.4 times that of the control value (P < 0.01). The phosphorylation levels of ERK depended on the concentration of PDGF-BB and the maximal level phosphorylation was detected with the concentration of PDGF-BB of 50 microg/L, which was 4.1 +/- 0.3 times that of the control value (P < 0.01). U0126 and BUD inhibited the phosphorylation of ERK in the cells stimulated by PDGF-BB of the concentration of 25 microg/L. there was no difference in the level of TGF-beta1 in the cell culture supernatant among different groups.

Conclusion: Phosphorylation of ERK and TGF-beta1 have an important role in asthma airway remodeling; PDGF-BB does not induce normal rat airway epithelial cells to product or release TGF-beta1 by phosphorylation of ERK. Glucocorticoids can inhibit phosphorylation of ERK.