Allergen-induced inflammation and airway epithelial and smooth muscle cell proliferation: role of Jun N-terminal kinase

Abstract

Chronic cellular inflammation and airway wall remodelling with subepithelial fibrosis and airway smooth muscle (ASM) cell hyperplasia are features of chronic asthma. Jun N-terminal kinase (JNK) may be implicated in these processes by regulating the transcriptional activity of activator protein (AP)-1. We examined the effects of an inhibitor of JNK, SP600125 (anthra [1,9-cd] pyrazole-6 (2 H)-one), in a model of chronic allergic inflammation in the rat. Rats sensitised to ovalbumin (OA) were exposed to OA-aerosol every third day on six occasions and were treated with SP600125 (30 mg kg-1 b.i.d; 360 mg in total) for 12 days, starting after the second through to the sixth OA exposure. We measured eosinophilic and T-cell inflammation in the airways, proliferation of ASM cells and epithelial cells by incorporation of bromodeoxyuridine (BrdU), and bronchial responsiveness to acetylcholine. SP600125 significantly reduced the number of eosinophils (P<0.05) and lymphocytes (P<0.05) in bronchoalveolar lavage fluid, suppressed eosinophilic (P<0.05) and CD2+ T-cell (P<0.05) infiltration within the bronchial submucosa, and the increased DNA incorporation in ASM (P<0.05) and epithelial cell incorporation (P<0.05). SP600125 did not alter bronchial hyper-responsiveness observed after chronic allergen exposure. Pathways regulated by JNK positively regulate ASM cell proliferation and allergic cellular inflammation following chronic allergen exposure.

Figure 1

Mean −logPC₂₀₀, which is the negative logarithm of the provocative concentration of ACh needed to increase baseline lung resistance by 200%, after saline, ovalbumin (OA) and after OA with SP600125 administration. There was a significant increase in −logPC₂₀₀ after chronic OA exposure, indicating BHR. (^*P<0.05 as compared to group saline); SP600125 did not alter BHR. Horizontal bars represent the mean values for each group with the bars representing the 95% CI.

Figure 2

Effect of SP600125 on (a) airway smooth muscle cell BrdU incorporation, and (b) epithelial cell BrdU incorporation. Treatment with SP600125 attenuated the increase in ASM BrdU index observed after allergen exposure (^***P<0.001, as compared to group saline; #P<0.05 as compared to group OA). Similar results were obtained for BrdU immunoreactive epithelial cells (^**P<0.01, compared to group saline; #P<0.05 as compared to group OA). Horizontal bars represent the mean values for each group with the bars representing the 95% CI.

Figure 3

Effect of SP600125 on the phosphorylation of c-jun. (a) Western blot analysis of c-jun and phospho-c-jun in lung tissue from sensitised rats exposed to saline (saline control) or to OA exposed or to OA exposed, pretreated with SP600125 (OA exposed+SP600125). Phospho-c-jun expression was observed in OA-exposed rats and was inhibited in SP600125-treated rats. Results of four rats in each group are shown (labelled 1–4). c-jun expression was not changed. There were also no changes in β-actin. (b) Mean density of phospho-c-jun in the three groups of rats. ^*P<0.05, as compared to group saline; ^#P<0.05 as compared to group OA exposed. Data shown as mean±s.e.m.