Purinergic receptor inhibition prevents the development of smoke-induced lung injury and emphysema

Chlamydia persistence -- a tool to dissect chlamydia--host interactions

Under stress, chlamydiae can enter a non-infectious but viable state termed persistence. In the absence of a tractable genetic system, persistence induction provides an important experimental tool with which to study these fascinating organisms. This review will discuss examples of: i) persistence studies that have illuminated critical chlamydiae/host interactions; and ii) novel persistence models that will do so in the future.

Animal models of airway diseases

Over the past 20 years, the growing awareness that purinergic signaling events literally shape the immune and inflammatory responses to infection and allergic reactions warranted the development of animal models to assess their importance in vivo in acute lung injury and chronic airway diseases. The pioneer work conducted with the adenosine deaminase (ADA)-deficient mouse provided irrefutable evidence that excess adenosine (ADO) accumulating in the lungs of asthmatic patients, constitutes a powerful mediator of disease severity. These original studies launched the development of murine strains for the two major ectonucleotidases responsible for the generation of airway ADO from ATP release: CD39 and CD73. The dramatic acute lung injury and chronic lung complications, manifested by these knockout mice in response to allergens and endotoxin, demonstrated the critical importance of regulating the availability of ATP and ADO for their receptors. Therapeutic targets are currently evaluated using knockout mice and agonists/antagonists for each ADO receptor (A(1)R, A(2A)R, A(2B)R, and A(3)R) and the predominant ATP receptors (P2Y(2)R and P2X(7)R). This chapter provides an in-depth description of each in vivo study, and a critical view of the therapeutic potentials for the treatment of airway diseases.

The role of the NLRP3 inflammasome in the pathogenesis of airway disease

The incidences of respiratory diseases like asthma and Chronic Obstructive Pulmonary Disease (COPD) are increasing dramatically. Significantly, there are currently no treatments that can slow or prevent the relentless progression of COPD; and a sub-population of asthmatics are resistant to available therapies. What is more, currently prescribed medication has only minimal effect on the symptoms suffered in these patient groups. There is therefore an urgent need to develop effective drugs to treat these diseases. Whilst asthma and COPD are thought to be distinct diseases, it is currently believed that the pathogenesis of both is driven by the chronic inflammation present in the airways of these patients. It is thus hypothesised that if the inflammation could be attenuated, disease development would be slowed and symptoms reduced. It is therefore paramount to determine the pathways driving/propagating the inflammation. Recently there has been a growing body of evidence to suggest that the multimeric protein complex known as the Inflammasome may play key roles in the inflammation observed in respiratory diseases. The aim of this review is to discuss the role of the NLRP3 Inflammasome, and its associated inflammatory mediators (IL-1β and IL-18), in the pathogenesis of asthma and COPD.

Arsenic alters ATP-dependent Ca²+ signaling in human airway epithelial cell wound response

Arsenic is a natural metalloid toxicant that is associated with occupational inhalation injury and contaminates drinking water worldwide. Both inhalation of arsenic and consumption of arsenic-tainted water are correlated with malignant and nonmalignant lung diseases. Despite strong links between arsenic and respiratory illness, underlying cell responses to arsenic remain unclear. We hypothesized that arsenic may elicit some of its detrimental effects on the airway through limitation of innate immune function and, specifically, through alteration of paracrine ATP (purinergic) Ca²+ signaling in the airway epithelium. We examined the effects of acute (24 h) exposure with environmentally relevant levels of arsenic (i.e., < 4 μM as Na-arsenite) on wound-induced Ca²+ signaling pathways in human bronchial epithelial cell line (16HBE14o-). We found that arsenic reduces purinergic Ca²+ signaling in a dose-dependent manner and results in a reshaping of the Ca²+ signaling response to localized wounds. We next examined arsenic effects on two purinergic receptor types: the metabotropic P2Y and ionotropic P2X receptors. Arsenic inhibited both P2Y- and P2X-mediated Ca²+ signaling responses to ATP. Both inhaled and ingested arsenic can rapidly reach the airway epithelium where purinergic signaling is essential in innate immune functions (e.g., ciliary beat, salt and water transport, bactericide production, and wound repair). Arsenic-induced compromise of such airway defense mechanisms may be an underlying contributor to chronic lung disease.

Selective induction of endothelial P2Y6 nucleotide receptor promotes vascular inflammation

During a systemic inflammatory response endothelial-expressed surface molecules have been strongly implicated in orchestrating immune responses. Previous studies have shown enhanced extracellular nucleotide release during acute inflammatory conditions. Therefore, we hypothesized that endothelial nucleotide receptors could play a role in vascular inflammation. To address this hypothesis, we performed screening experiments and exposed human microvascular endothelia to inflammatory stimuli, followed by measurements of P2Y or P2X transcriptional responses. These studies showed a selective induction of the P2Y(6) receptor (> 4-fold at 24 hours). Moreover, studies that used real-time reverse transcription-polymerase chain reaction, Western blot analysis, or immunofluorescence confirmed time- and dose-dependent induction of P2Y(6) with tumor necrosis factor α or Lipopolysaccharide (LPS) stimulation in vitro and in vivo. Studies that used MRS 2578 as P2Y(6) receptor antagonist showed attenuated nuclear factor κB reporter activity and proinflammatory gene expression in human microvascular endothelial cells in vitro. Moreover, pharmacologic or genetic in vivo studies showed attenuated inflammatory responses in P2Y(6)(-/-) mice or after P2Y(6) antagonist treatment during LPS-induced vascular inflammation. These studies show an important contribution of P2Y(6) signaling in enhancing vascular inflammation during systemic LPS challenge and implicate the P2Y(6) receptor as a therapeutic target during systemic inflammatory responses.

Pannexin channels in ATP release and beyond: an unexpected rendezvous at the endoplasmic reticulum

The pannexin (Panx) family of proteins, which is co-expressed with connexins (Cxs) in vertebrates, was found to be a new GJ-forming protein family related to invertebrate innexins. During the past ten years, different studies showed that Panxs mainly form hemichannels in the plasma membrane and mediate paracrine signalling by providing a flux pathway for ions such as Ca²(+), for ATP and perhaps for other compounds, in response to physiological and pathological stimuli. Although the physiological role of Panxs as a hemichannel was questioned, there is increasing evidence that Panx play a role in vasodilatation, initiation of inflammatory responses, ischemic death of neurons, epilepsy and in tumor suppression. Moreover, it is intriguing that Panxs may also function at the endoplasmic reticulum (ER) as intracellular Ca²(+)-leak channel and may be involved in ER-related functions. Although the physiological significance and meaning of such Panx-regulated intracellular Ca²(+) leak requires further exploration, this functional property places Panx at the centre of many physiological and pathophysiological processes, given the fundamental role of intracellular Ca²(+) homeostasis and dynamics in a plethora of physiological processes. In this review, we therefore want to focus on Panx as channels at the plasma membrane and at the ER membranes with a particular emphasis on the potential implications of the latter in intracellular Ca²(+) signalling.