Hyperpolarized 83Kr magnetic resonance imaging of alveolar degradation in a rat model of emphysema.

Hyperpolarized (83)Kr surface quadrupolar relaxation (SQUARE) generates MRI contrast that was previously shown to correlate with surface-to-volume ratios in porous model surface systems. The underlying physics of SQUARE contrast is conceptually different from any other current MRI methodology as the method uses the nuclear electric properties of the spin I = 9/2 isotope (83)Kr. To explore the usage of this non-radioactive isotope for pulmonary pathophysiology, MRI SQUARE contrast was acquired in excised rat lungs obtained from an elastase-induced model of emphysema. A significant (83)Kr T1 relaxation time increase in the SQUARE contrast was found in the elastase-treated lungs compared with the baseline data from control lungs. The SQUARE contrast suggests a reduction in pulmonary surface-to-volume ratio in the emphysema model that was validated by histology. The finding supports usage of (83)Kr SQUARE as a new biomarker for surface-to-volume ratio changes in emphysema.

The role of adenylyl cyclase isoform 6 in ß-adrenoceptor signalling in murine airways.

BACKGROUND AND PURPOSE: Adenylyl cyclase (AC) is a key signalling enzyme for many GPCRs and catalyses the conversion of ATP to cAMP which, in turn, is a crucial determinant of many biological responses. ß-Adrenoceptor agonists are prescribed as bronchodilators for asthma and chronic obstructive pulmonary disease, and it is commonly assumed that they elicit their actions via AC-dependent production of cAMP. However, empirical evidence in support of this is lacking and the exact mechanism by which these drugs acts remains elusive. This is partly due to the existence of at least 10 different isoforms of AC and the absence of any truly selective pharmacological inhibitors. Here, we have used genetically modified mice and model systems to establish the role of AC isoforms in the airway responses to ß-adrenoceptor agonists. EXPERIMENTAL APPROACH: Receptors mediating responses to ß-adrenoceptor agonists in airway smooth muscle (ASM) and sensory nerve were identified in isolated tissue systems. Expression of mRNA for the AC isoforms in ASM and neurones was determined by qPCR. Functional responses were assessed in AC isoform KO mice and wild-type controls. KEY RESULTS: Airway and vagal tissue expressed mRNA for various isoforms of AC. AC6 was the most prominent isoform. Responses to ß-adrenoceptor agonists in tissues from AC6 KO mice were virtually abolished. CONCLUSIONS AND IMPLICATIONS: AC6 played a critical role in relaxation of ASM to ß1 -adrenoceptor agonists and in modulation of sensory nerves by ß1-3 -adrenoceptor agonists. These results further unravel the signalling pathway of this extensively prescribed class of medicine.

Role of transient receptor potential and pannexin channels in cigarette smoke-triggered ATP release in the lung.

BACKGROUND: COPD is an inflammatory disease usually associated with cigarette smoking (CS) with an increasing global prevalence and no effective medication. Extracellular ATP is increased in the COPD affected lung and may play a key role in driving CS-induced airway inflammation, but the mechanism involved in ATP release has eluded researchers. Recently, the transient receptor potential (TRP) and pannexin-1 channels have been suggested to play a role in other experimental paradigms. Thus, the aim of this work is to investigate if these channels are involved in CS-induced ATP release in the lung. METHODS: Primary human cells were exposed to CS and extracellular ATP levels measured. Mice were exposed to mainstream CS and airway inflammation assessed. TRPV1/4 mRNA expression was assessed in human lung parenchyma. RESULTS: CS exposure caused a dose-related increase in ATP from primary airway bronchial epithelial cells. This was attenuated by blockers of TRPV1, TRPV4 and pannexin-1 channels. Parallel data was obtained using murine acute CS-driven model systems. Finally, TRPV1/4 mRNA expression was increased in lung tissue samples from patients with COPD. CONCLUSIONS: Extracellular ATP is increased in the COPD affected lung and may play a key role in driving disease pathophysiology. These experiments uncover a novel mechanism which may be responsible for CS-induced ATP release. These findings highlight novel targets that could lead to the development of medicine to treat this devastating disease.

TLR4 activation induces IL-1ß release via an IPAF dependent but caspase 1/11/8 independent pathway in the lung.

BACKGROUND: The IL-1 family of cytokines is known to play an important role in inflammation therefore understanding the mechanism by which they are produced is paramount. Despite the recent plethora of publications dedicated to the study of these cytokines, the mechanism by which they are produced in the airway following endotoxin, Lipopolysaccharide (LPS), exposure is currently unclear. The aim was to determine the mechanism by which the IL-1 cytokines are produced after LPS inhaled challenge. METHODS: Mice were challenged with aerosolised LPS, and lung tissue and bronchiolar lavage fluid (BALF) collected. Targets were measured at the mRNA and protein level; caspase activity was determined using specific assays. RESULTS: BALF IL-1b/IL-18, but not IL-1a, was dependent on Ice Protease-Activating Factor (IPAF), and to a lesser extent Apoptosis-associated Speck-like protein containing a CARD (ASC). Interestingly, although we measured an increase in mRNA expression for caspase 1 and 11, we could not detect an increase in lung enzyme activity or a role for them in IL-1a/b production. Further investigations showed that whilst we could detect an increase in caspase 8 activity at later points in the time course (during resolution of inflammation), it appeared to play no role in the production of IL-1 cytokines in this model system. CONCLUSIONS: TLR4 activation increases levels of BALF IL-1b/IL-18 via an IPAF dependent and caspase 1/11/8 independent pathway. Furthermore, it would appear that the presence of IL-1a in the BALF is independent of these pathways. This novel data sheds light on innate signalling pathways in the lung that control the production of these key inflammatory cytokines.

Is intrinsic aerobic exercise capacity a determinant of COPD susceptibility?

Chronic obstructive pulmonary disease is a leading cause of morbidity and mortality, which is most commonly associated with smoking or exposure to environmental pollutants. Unfortunately, there is an inadequate understanding of the molecular and physiological determinants governing one's susceptibility for developing COPD. Here, we describe a novel hypothesis: Individuals with intrinsically low aerobic exercise capacity are more likely to develop COPD after exposure to key risk factors. The hypothesis is based on observations that aerobic exercise capacity is tightly associated with mortality across many complex diseases. The premise is supported by recent studies demonstrating that smokers who exercise regularly are less likely to develop or be hospitalized for COPD. Herein, we describe the evolutionary and molecular basis for this hypothesis and how it is a natural extension of previous theories explaining COPD susceptibility.

Sodium-dependent regulation of renal amiloride-sensitive currents by apical P2 receptors.

The epithelial sodium channel (ENaC) plays a major role in the regulation of sodium balance and BP by controlling Na(+) reabsorption along the renal distal tubule and collecting duct (CD). ENaC activity is affected by extracellular nucleotides acting on P2 receptors (P2R); however, there remain uncertainties over the P2R subtype(s) involved, the molecular mechanism(s) responsible, and their physiologic role. This study investigated the relationship between apical P2R and ENaC activity by assessing the effects of P2R agonists on amiloride-sensitive current in the rat CD. Using whole-cell patch clamp of principal cells of split-open CD from Na(+)-restricted rats, in combination with immunohistochemistry and real-time PCR, we found that activation of metabotropic P2R (most likely the P2Y(2) and/or (4) subtype), via phospholipase C, inhibited ENaC activity. In addition, activation of ionotropic P2R (most likely the P2X(4) and/or (4/6) subtype), via phosphatidylinositol-3 kinase, either inhibited or potentiated ENaC activity, depending on the extracellular Na(+) concentration; therefore, it is proposed that P2X(4) and/or (4/6) receptors might function as apical Na(+) sensors responsible for local regulation of ENaC activity in the CD and could thereby help to regulate Na(+) balance and systemic BP.