Activation of adenosine A3 receptors (A3

The tachykinin neuropeptides substance P and neurokinin (NK) A have been postulated to participate in the inflammatory reaction in airways of smokers and asthmatics. We have examined the hypothesis that the expression of one or more of the three cloned tachykinin receptors (NK1, NK2, and NK3) is increased in inflammatory airway disorders, which could result in augmentation of the effect of released tachykinin neuropeptides. NK1 receptor and NK2 receptor but not NK3-receptor mRNA were detected by ribonuclease protection assay in RNA from both cartilaginous and membranous bronchi and subpleural lung. In lung samples containing membranous airways, NK2-receptor mRNA expression was increased fourfold in asthmatics compared with nonsmoking controls, whereas NK1-receptor mRNA levels were similar in the two groups. NK1- and NK2-receptor mRNA expression was increased twofold in smokers without airflow obstruction compared with nonsmokers, whereas NK1-receptor mRNA expression was significantly lower in patients with chronic obstructive pulmonary disease compared with smoking controls. In situ hybridization indicated NK1-receptor mRNA was expressed in submucosal glands and airway epithelial cells, whereas NK2-receptor and NK3-receptor mRNA were not detected. These observations have implications for the pathophysiology and treatment of both asthma and tobacco smoke-induced airway inflammation.

Endothelin-1 (ET-1), a G protein-coupled receptor-activating peptide, is increased in airway epithelium, plasma, and bronchoalveolar lavage fluid of asthmatic patients. We hypothesized that ET-1 may contribute to the increased airway smooth muscle mass found in severe asthma by inducing hypertrophy and inhibiting apoptosis of smooth muscle cells. To investigate this hypothesis, we determined that treatment of primary human bronchial smooth muscle cells with ET-1 dose dependently [10(-11)-10(-7) M] inhibited the apoptosis induced by serum withdrawal. ET-1 treatment also resulted in a significant increase in total protein synthesis, mediated through both ET(A) and ET(B) receptors, cell size, as well as increased expression of myosin heavy chain, alpha-smooth muscle actin, and calponin. ET-1-induced hypertrophy was accompanied by activation of JAK1/STAT-3 and MAPK1/2 (ERK1/2) cell signaling pathways. Inhibition of JAK1/STAT-3 pathways by piceatannol or ERK1/2 by the MAPK/ERK kinase 1/2 inhibitor U0126 blunted the increase in total protein synthesis. The hypertrophic effect of ET-1 was equivalent to that of the gp130 cytokine oncostatin M and greater than that induced by cardiotrophin-1. ET-1 induced release of IL-6 but not IL-11, leukemia inhibitory factor, oncostatin M, or cardiotrophin-1, although treatment of cells with IL-6 alone did not induce hypertrophy. These results suggest that ET-1 is a candidate mediator for the induction of increased smooth muscle mass in asthma and identify signaling pathways activated by this mediator.

The distribution and regulation of leukemia inhibitory factor (LIF) and its receptor (LIFR) in human lung tissue is unknown. We recently found that LIF was immunolocalized to several cell types in human airways, and that exogenous LIF modulated neural and contractile responses of explanted airways. The present study aimed to determine the cellular distribution and regulation of gene transcripts for LIF and LIFR in human lung, and measured the release of LIF in response to anti-immunoglobulin (Ig)E, interleukin (IL)-1beta, and IL-6. Exposure of human lung to IL-1beta (100 pg/ml) resulted in the rapid induction of LIF messenger RNA (mRNA) (1 h) and subsequent protein release (6 h). Similar results were observed when lung tissue was exposed to anti-IgE (6 U/ml). Gene transcripts for LIF were observed in nine pulmonary cell types, with the greatest expression occurring in fibroblasts. LIFR transcripts were also widely expressed in these cell types. In cultures of nontransformed epithelial cells, lung fibroblasts, and airway smooth-muscle cells, IL-1beta (100 pg/ml) induced the rapid accumulation of LIF mRNA and protein release, with fibroblasts liberating the greatest amount. IL-6 also induced the expression of LIF mRNA and release of LIF in airway smooth-muscle cells, whereas exogenous LIF itself had no effect. Expression of LIFR mRNA was not influenced by exposure to IL-1beta or LIF in any of the cell lines used. These results highlight the widespread distribution and rapid release of LIF in human lung tissue and, in conjunction with our previous report, suggest that this cytokine may play an important role in lung inflammatory processes and neuroimmune interactions.