The role of phosphorylation of c-Jun NH2-terminal kinase in airway remodeling of asthmatic rats and the effect of glucocorticoids

Abstract

To study the role of phosphorylation of c-Jun NH2-terminal kinase (JNK) in asthmatic airway remodeling and to explore the effect of glucocorticoids on IL-1beta, JNK and airway remodeling. Forty-eight 4 - 6 week old male SD rats were randomly divided into 4 groups with 12 rats in each group: the control group, the asthma group, the budesonide (BUD) group, and the dexamethasone (DXM) group. The asthma airway remodeling models were made by intra-peritoneal injection of ovalbumin (OVA) on days 1 and 8 and inhalation of OVA every other day for 12 weeks since day 15. The BUD group underwent inhalation of BUD 30 min before every inhalation; the DXM group received intra-peritoneal injection of DXM 30 min before every inhalation; while the control group received normal saline instead of OVA. The histopathology and ultrastructural changes of pulmonary tissues were observed by light microscope and transmission electron microscope (TEM). The total bronchial wall thickness (Wat) and the airway smooth muscle thickness (Wam) were measured by image analysis system. The concentrations of IL-1beta in serum and BALF were tested by sandwich ELISA. The protein expressions of P-JNK and P-c-Jun were detected by immunohistochemistry technique. Lung tissue extracts were analyzed for phosphorylation of JNK by Western blot. Linear correlation analysis was used to evaluate correlations between Wat and P-JNK protein (mA), Wam and P-JNK protein (mA), P-JNK protein (mA) and levels of IL-1beta in serum, P-JNK protein (mA) and levels of IL-1beta in BALF. In the asthma group, HE-staining showed inflammatory cell infiltration around bronchi and mucous gland hyperplasia. TEM examination showed airway smooth muscle and collagen fiber proliferation, and widening of intercellular distance. The Wat and Wam of the asthma group were significantly higher than those of the control group, while the thickness of airway wall in the glucocorticoid intervention groups became significantly decreased. The concentrations of IL-1beta in serum and BALF of the asthma group [(81 +/- 4) ng/L, (331 +/- 15) ng/L] were significantly higher than those of the control group [(53 +/- 6) ng/L, (130 +/- 9) ng/L] (t = -8.62 and t = -24.10, both P < 0.01). Mean absorbance values (by immunohistochemistry) of P-JNK and P-c-Jun in the asthma group were significantly higher than those of the control group, and the mean absorbance values of P-JNK and P-c-Jun in the BUD and DXM groups were significantly lower than those of the asthma group, but higher than those of the control group (F = 223.59 and F = 76.53, both P < 0.01). Absorbance (by Western blot) of P-JNK in the control, asthma, BUD, and DXM groups were (1.00 +/- 0.00), (1.66 +/- 0.16), (1.18 +/- 0.12), and (1.29 +/- 0.14), respectively; that of the asthma group was significantly higher than that of the control group, while absorbance of P-JNK in the BUD and the DXM groups were significantly lower than that of the asthma group, but higher than that of the control group (F = 17.84, P < 0.05). Strong positive correlations were found between Wat or Wam and P-JNK (mA) (r = 0.700 and r = 0.769, P < 0.01, respectively, n = 48). Strong positive correlations were also found between P-JNK (mA) and concentration of IL-1beta in serum or BALF (r = 0.689 and r = 0.805, P < 0.01, respectively, n = 48). Phosphorylation of JNK is closely related to asthma airway remodeling. Glucocorticoids can inhibit phosphorylation of JNK, one mechanism of which may be down-regulation of IL-beta expression.