RNA interference (RNAi) is gaining increasing popularity both as a molecular biology tool and as a potential therapeutic agent. RNAi is a naturally occurring gene regulatory mechanism, which has a number of advantages over other gene/antisense therapies including specificity of inhibition, potency, the small size of the molecules and the diminished risk of toxic effects, e.g., immune responses. Targeted, local delivery of RNAi to the lungs via inhalation offers a unique opportunity to treat a range of previously untreatable or poorly controlled respiratory conditions. In this timely review we look at the potential applications of RNAi in the lungs for the treatment of a range of diseases including inflammatory and immune conditions, cystic fibrosis, infectious disease and cancer. In 2006 Alnylam initiated the first phase 1 clinical study of an inhaled siRNA for the treatment of respiratory syncytial virus. If its potential as a therapeutic is to be realized, then safe and efficient means of targeted delivery of small interfering RNA (siRNA) to the lungs must be developed. Therefore in this review we also present the latest developments in siRNA delivery to airway cells in vitro and the work to date on in vivo delivery of siRNA to the lungs for the treatment of a range of diseases.

Eosinophil localization to cholinergic nerves occurs in a variety of inflammatory conditions, including asthma. This localization is mediated by interactions between eosinophil integrins and neuronal vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1). Eosinophil-nerve cell interactions lead to generation of neuronal reactive oxygen species and release of eosinophil proteins. The effects of eosinophil adhesion on neuronal intracellular signaling pathways were investigated. Eosinophil adhesion to IMR32 cholinergic nerves led to a rapid and sustained activation of the nuclear transcription factors nuclear factor (NF)-kappaB and activator protein (AP)-1 in the nerve cells. Eosinophil binding to neuronal ICAM-1 led to a rapid activation of ERK1/2 in nerve cells. Inhibition of ERK1/2 prevented NF-kappaB activation. Eosinophil adhesion to VCAM-1 resulted in AP-1 activation, mediated partially by rapid activation of the p38 mitogen-activated protein kinase. These data show that adhesion of eosinophils induces mitogen-activated protein kinase-dependent activation of the transcription factors NF-kappaB and AP-1 in nerve cells, indicating that eosinophil adhesion may control nerve growth and phenotype.

Activated eosinophils release potentially toxic cationic granular proteins, including the major basic proteins (MBP) and eosinophil-derived neurotoxin (EDN). However, in inflammatory conditions including asthma and inflammatory bowel disease, localization of eosinophils to nerves is associated with nerve plasticity, specifically remodeling. In previous in vitro studies, we have shown that eosinophil adhesion to IMR-32 nerve cells, via nerve cell intercellular adhesion molecule-1, results in an adhesion-dependent release of granule proteins. We hypothesized that released eosinophil granule proteins may affect nerve cell signaling and survival, leading to nerve cell remodeling. Culture in serum-deprived media induced apoptosis in IMR-32 cells that was dose-dependently abolished by inclusion of MBP1 but not by EDN. Both MBP1 and EDN induced phosphorylation of Akt, but with divergent time courses and intensities, and survival was independent of Akt. MBP1 induced activation of neural nuclear factor (NF)-kappaB, from 10 min to 12 h, declining by 24 h, whereas EDN induced a short-lived activation of NF-kappaB. MBP1-induced protection was dependent on phosphorylation of ERK 1/2 and was related to a phospho-ERK-dependent upregulation of the NF-kappaB-activated anti-apoptotic gene, Bfl-1. This signaling pathway was not activated by EDN. Thus, MBP1 released from eosinophils at inflammatory sites may regulate peripheral nerve plasticity by inhibiting apoptosis.