RATIONALE: Airway hyperresponsiveness (AHR) is classically found in asthma, and persistent AHR is associated with poor asthma control. Although airway smooth muscle (ASM) cells play a critical pathophysiologic role in AHR, the paracrine contributions of surrounding cells such as fibroblasts to the contractile phenotype of ASM cells have not been examined fully. This study addresses the hypothesis that nicotine promotes a contractile ASM cell phenotype by stimulating fibroblasts to increase nerve growth factor (NGF) secretion into the environment. METHODS: Primary lung fibroblasts isolated from wild type and a7 nicotinic acetylcholine receptor (a7 nAChR) deficient mice were treated with nicotine (50 µg/ml) in vitro for 72 hours. NGF levels were measured in culture media and in bronchoalveolar lavage (BAL) fluid from asthmatic, smoking and non-smoking subjects by ELISA. The role of the NF?B pathway in nicotine-induced NGF expression was investigated by measuring NF?B nuclear translocation, transcriptional activity, chromatin immunoprecipitation assays, and si-p65 NF?B knockdown. The ability of nicotine to stimulate a fibroblast-mediated, contractile ASM cell phenotype was confirmed by examining expression of contractile proteins in ASM cells cultured with fibroblast-conditioned media or BAL fluid. RESULTS: NGF levels were elevated in the bronchoalveolar lavage fluid of nicotine-exposed mice, current smokers, and asthmatic children. Nicotine increased NGF secretion in lung fibroblasts in vitro in a dose-dependent manner and stimulated NF?B nuclear translocation, p65 binding to the NGF promoter, and NF?B transcriptional activity. These responses were attenuated in a7 nAChR deficient fibroblasts and in wild type fibroblasts following NF?B inhibition. Nicotine-treated, fibroblast-conditioned media increased expression of contractile proteins in ASM cells. CONCLUSION: Nicotine stimulates NGF release by lung fibroblasts through a7 nAChR and NF?B dependent pathways. These novel findings suggest that the nicotine-a7 nAChR-NF?B- NGF axis may provide novel therapeutic targets to attenuate tobacco smoke-induced AHR