Real time analysis of β(2)-adrenoceptor-mediated signaling kinetics in human primary airway smooth muscle cells reveals both ligand and dose dependent differences

Management of COPD exacerbations: pharmacotherapeutics of medications

Chronic obstructive pulmonary disease (COPD) is widely established as a health challenge, with predictions that it will be the third leading cause of global mortality and reduced health status within the next 10 years. Exacerbations of COPD are now the second largest cause of emergency hospitalisation in the UK. The respiratory clinical nurse specialist has an active role in the acute management of COPD exacerbations in the hospital setting, and it is essential that prescribing decisions are made based on the best available evidence. This article critically evaluates the pharmacotherapeutics and evidence base for the use of two medications, salbutamol and amoxicillin, in treating unstable COPD, and discusses implications for clinical practice.

Phosphodiesterases as therapeutic targets for respiratory diseases

Chronic respiratory diseases, such as chronic obstructive pulmonary disease (COPD) and asthma, affect millions of people all over the world. Cyclic adenosine monophosphate (cAMP) which is one of the most important second messengers, plays a vital role in relaxing airway smooth muscles and suppressing inflammation. Given its vast role in regulating intracellular responses, cAMP provides an attractive pharmaceutical target in the treatment of chronic respiratory diseases. Phosphodiesterases (PDEs) are enzymes that hydrolyze cyclic nucleotides and help control cyclic nucleotide signals in a compartmentalized manner. Currently, the selective PDE4 inhibitor, roflumilast, is used as an add-on treatment for patients with severe COPD associated with bronchitis and a history of frequent exacerbations. In addition, other novel PDE inhibitors are in different phases of clinical trials. The current review provides an overview of the regulation of various PDEs and the potential application of selective PDE inhibitors in the treatment of COPD and asthma. The possibility to combine various PDE inhibitors as a way to increase their therapeutic effectiveness is also emphasized.

Cigarette smoke up-regulates PDE3 and PDE4 to decrease cAMP in airway cells

BACKGROUND AND PURPOSE

cAMP is a central second messenger that broadly regulates cell function and can underpin pathophysiology. In chronic obstructive pulmonary disease, a lung disease primarily provoked by cigarette smoke (CS), the activation of cAMP-dependent pathways, via inhibition of hydrolyzing PDEs, is a major therapeutic strategy. Mechanisms that disrupt cAMP signalling in airway cells, in particular regulation of endogenous PDEs, are poorly understood.

EXPERIMENTAL APPROACH

We used a novel Förster resonance energy transfer (FRET) based cAMP biosensor in mice in vivo, ex vivo precision cut lung slices (PCLS) and in human cell models, in vitro, to track the effects of CS exposure.

KEY RESULTS

Under fenoterol stimulation, FRET responses to cilostamide were significantly increased in in vivo, ex vivo PCLS exposed to CS and in human airway smooth muscle cells exposed to CS extract. FRET signals to rolipram were only increased in the in vivo CS model. Under basal conditions, FRET responses to cilostamide and rolipram were significantly increased in in vivo, ex vivo PCLS exposed to CS. Elevated FRET signals to rolipram correlated with a protein up-regulation of PDE4 subtypes. In ex vivo PCLS exposed to CS extract, rolipram reversed down-regulation of ciliary beating frequency, whereas only cilostamide significantly increased airway relaxation of methacholine pre-contracted airways.

CONCLUSION AND IMPLICATIONS

Exposure to CS, in vitro or in vivo, up-regulated expression and activity of both PDE3 and PDE4, which affected real-time cAMP dynamics. These mechanisms determine the availability of cAMP and can contribute to CS-induced pulmonary pathophysiology.

Multiple facets of cAMP signalling and physiological impact: cAMP compartmentalization in the lung

Therapies involving elevation of the endogenous suppressor cyclic AMP (cAMP) are currently used in the treatment of several chronic inflammatory disorders, including chronic obstructive pulmonary disease (COPD). Characteristics of COPD are airway obstruction, airway inflammation and airway remodelling, processes encompassed by increased airway smooth muscle mass, epithelial changes, goblet cell and submucosal gland hyperplasia. In addition to inflammatory cells, airway smooth muscle cells and (myo)fibroblasts, epithelial cells underpin a variety of key responses in the airways such as inflammatory cytokine release, airway remodelling, mucus hypersecretion and airway barrier function. Cigarette smoke, being next to environmental pollution the main cause of COPD, is believed to cause epithelial hyperpermeability by disrupting the barrier function. Here we will focus on the most recent progress on compartmentalized signalling by cAMP. In addition to G protein-coupled receptors, adenylyl cyclases, cAMP-specific phospho-diesterases (PDEs) maintain compartmentalized cAMP signalling. Intriguingly, spatially discrete cAMP-sensing signalling complexes seem also to involve distinct members of the A-kinase anchoring (AKAP) superfamily and IQ motif containing GTPase activating protein (IQGAPs). In this review, we will highlight the interaction between cAMP and the epithelial barrier to retain proper lung function and to alleviate COPD symptoms and focus on the possible molecular mechanisms involved in this process. Future studies should include the development of cAMP-sensing multiprotein complex specific disruptors and/or stabilizers to orchestrate cellular functions. Compartmentalized cAMP signalling regulates important cellular processes in the lung and may serve as a therapeutic target.

Distinct PKA and Epac compartmentalization in airway function and plasticity

Asthma and chronic obstructive pulmonary disease (COPD) are obstructive lung diseases characterized by airway obstruction, airway inflammation and airway remodelling. Next to inflammatory cells and airway epithelial cells, airway mesenchymal cells, including airway smooth muscle cells and (myo)fibroblasts, substantially contribute to disease features by the release of inflammatory mediators, smooth muscle contraction, extracellular matrix deposition and structural changes in the airways. Current pharmacological treatment of both diseases intends to target the dynamic features of the endogenous intracellular suppressor cyclic AMP (cAMP). This review will summarize our current knowledge on cAMP and will emphasize on key discoveries and paradigm shifts reflecting the complex spatio-temporal nature of compartmentalized cAMP signalling networks in health and disease. As airway fibroblasts and airway smooth muscle cells are recognized as central players in the development and progression of asthma and COPD, we will focus on the role of cAMP signalling in their function in relation to airway function and plasticity. We will recapture on the recent identification of cAMP-sensing multi-protein complexes maintained by cAMP effectors, including A-kinase anchoring proteins (AKAPs), proteins kinase A (PKA), exchange protein directly activated by cAMP (Epac), cAMP-elevating seven-transmembrane (7TM) receptors and phosphodiesterases (PDEs) and we will report on findings indicating that the pertubation of compartmentalized cAMP signalling correlates with the pathopysiology of obstructive lung diseases. Future challenges include studies on cAMP dynamics and compartmentalization in the lung and the development of novel drugs targeting these systems for therapeutic interventions in chronic obstructive inflammatory diseases.

Novel cAMP signalling paradigms: therapeutic implications for airway disease

Since its discovery over 50 years ago, cAMP has been the archetypal second messenger introducing students to the concept of cell signalling at the simplest level. As explored in this review, however, there are many more facets to cAMP signalling than the path from Gs-coupled receptor to adenylyl cyclase (AC) to cAMP to PKA to biological effect. After a brief description of this canonical cAMP signalling pathway, a snapshot is provided of the novel paradigms of cAMP signalling. As in the airway the cAMP pathway relays the major bronchorelaxant signal and as such is the target for frontline therapy for asthma and COPD, particular emphasis is given to airway disease and therapy. Areas discussed include biased agonism, continued signalling following internalization, modulation of cAMP by AC, control of cAMP degradation, cAMP and calcium crosstalk, Epac-mediated signalling and finally the implications of altered genotypes will be considered. LINKED ARTICLES This article is part of a themed section on Novel cAMP Signalling Paradigms. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.166.issue-2.