In testing the hypothesis that interleukin-4 receptor alpha-subunit (IL-4R alpha)-coupled signaling mediates altered airway smooth muscle (ASM) responsiveness in the atopic sensitized state, isolated rabbit tracheal ASM segments were passively sensitized with immunoglobulin E (IgE) immune complexes, both in the absence and presence of an IL-4R alpha blocking antibody (anti-IL-4R alpha Ab). Relative to control ASM, IgE-sensitized tissues exhibited enhanced isometric constrictor responses to administered ACh and attenuated relaxation responses to isoproterenol. These proasthmatic-like effects were prevented in IgE-sensitized ASM that were pretreated with anti-IL-4R alpha Ab. In complementary experiments, IgE-sensitized cultured human ASM cells exhibited upregulated expression of IL-13 mRNA and protein, whereas IL-4 expression was undetected. Moreover, extended studies demonstrated that 1) exogenous IL-13 administration to naïve ASM elicited augmented contractility to ACh and impaired relaxation to isoproterenol, 2) these effects of IL-13 were prevented by pretreating the tissues with an IL-5 receptor blocking antibody, and 3) IL-13 administration induced upregulated mRNA expression and release of IL-5 protein from cultured ASM cells. Collectively, these findings provide new evidence demonstrating that the altered responsiveness of IgE-sensitized ASM is largely attributed to activation of an intrinsic Th2-type autocrine mechanism involving IL-13/IL-4R alpha-coupled release and action of IL-5 in the sensitized ASM itself.

Nino G, Hu A, Grunstein JS, Grunstein MM. Mechanism regulating proasthmatic effects of prolonged homologous ␤ 2-adrenergic receptor desensitization in airway smooth muscle. Am J Physiol Lung Cell Mol Physiol 297: L746 -L757, 2009. First published August 7, 2009; doi:10.1152/ajplung.00079.2009.-Use of long-acting ␤ 2-adrenergic receptor (␤2AR) agonists to treat asthma incurs an increased risk of asthma morbidity with impaired bronchodilation and heightened bronchoconstriction, reflecting the adverse effects of prolonged homologous ␤2AR desensitization on airway smooth muscle (ASM) function. Since phosphodiesterase 4 (PDE4) regulates ASM relaxation and contractility, we examined whether the changes in ASM function induced by prolonged homologous ␤2AR desensitization are attributed to altered expression and action of PDE4. Cultured human ASM cells and isolated rabbit ASM tissues exposed for 24 h to the long-acting ␤2AR agonist salmeterol exhibited impaired acute ␤2AR-mediated cAMP accumulation and relaxation, respectively, together with ASM constrictor hyperresponsiveness. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity due to enhanced expression of the PDE4D5 isoform and were prevented by pretreating the ASM preparations with the PDE4 inhibitor rolipram or with inhibitors of either PKA or ERK1/2 signaling. Extended studies using gene silencing and pharmacological approaches demonstrated that: 1) the mechanism underlying upregulated PDE4D5 expression following prolonged ␤2AR agonist exposure involves PKA-dependent activation of Gi protein signaling via its ␤␥-subunits, which elicits downstream activation of ERK1/2 and its induction of PDE4D5 transcription; and 2) the induction of PDE4 activity and consequent changes in ASM responsiveness are prevented by pretreating the ␤2AR agonist-exposed ASM preparations with inhibitors of Gi-␤␥ signaling. Collectively, these findings identify that the proasthmatic changes in ASM function resulting from prolonged homologous ␤2AR desensitization are attributed to upregulated PDE4 expression induced by Gi-␤␥-mediated cross-talk between the PKA and ERK1/2 signaling pathways. asthma; long-acting ␤2-agonists; salmeterol; cAMP signaling; G proteins; phosphodiesterase-4 CHRONIC USE OF LONG-ACTING ␤ 2 -adrenergic receptor (␤2AR) agonists to treat asthma has been associated with loss of bronchodilator effect, worsening of airway hyperreactivity, and an increased incidence of asthma-related morbidity and mortality (1, 24, 28). These adverse effects on the asthmatic phenotype are thought to result from the development of airway tolerance to ␤2AR stimulation due, in large part, to prolonged homologous (agonist-specific) ␤2AR desensitization of the airway smooth muscle (ASM) (10). Investigations into the etiology of homologous ␤2AR desensitization have largely focused on the roles played by G protein-coupled receptor (GPCR) kinases (GRKs) and cAMP-dependent PKA in mediating phosphorylation of the ␤2AR. While these studies have provided valuable...