Respiratory syncytial virus induces insensitivity to β-adrenergic agonists in mouse lung epithelium in vivo

Abstract

Davis IC, Xu A, Gao Z, Hickman-Davis JM, Factor P, Sullender WM, Matalon S. Respiratory syncytial virus induces insensitivity to ␤-adrenergic agonists in mouse lung epithelium in vivo. Am J Physiol Lung Cell Mol Physiol 293: L281-L289, 2007. First published April 13, 2007; doi:10.1152/ajplung.00458.2006 is the most common cause of bronchiolitis in infants and children worldwide. We wished to determine whether intratracheal administration of ␤-agonists improved alveolar fluid clearance (AFC) across the distal respiratory epithelium of RSV-infected mice. Following intranasal infection with RSV strain A2, AFC was measured in anesthetized, ventilated BALB/c mice by instillation of 5% BSA into the dependent lung. We found that direct activation of protein kinase A by forskolin or 8-bromo-cAMP increased AFC at day 2 after infection with RSV. In contrast, short-and long-acting ␤-agonists had no effect at either day 2 or day 4. Insensitivity to ␤-agonists was not a result of elevated plasma catecholamines or lung epithelial cell ␤-adrenergic receptor degradation. Instead, RSV-infected mice had significantly higher levels of phosphorylated PKC in the membrane fractions of their lung epithelial cells. In addition, insensitivity to ␤-agonists was mediated in a paracrine fashion by KC (the murine homolog of CXCL8) and reversed by inhibition of either PKC or G protein-coupled receptor kinase 2 (GRK2). These results indicate that insufficient response to ␤-agonists in RSV may be caused, at least in part, by impaired ␤-adrenergic receptor signaling, as a consequence of GRK2-mediated uncoupling of ␤-adrenergic receptors from adenylyl cyclase. paramyxovirus; protein kinase C; G protein-coupled receptor kinase 2; CXCL8 RESPIRATORY SYNCYTIAL VIRUS (RSV) is the most common cause of lower respiratory tract disease in infants and children worldwide (44), is a frequent initiator of acute asthma exacerbations in young children, and has a disease impact comparable to that of nonpandemic influenza A in the elderly (8). Approximately 2-3% of all cases of RSV bronchiolitis result in severe hypoxia or a need for parenteral fluid supplementation that necessitates hospitalization (44). ␤-agonists are frequently used to treat RSV bronchiolitis, primarily because of their perceived ability to relax airway smooth muscle and cause bronchodilation, with the ultimate aim of alleviating hypoxemia. However, it is not clear that these drugs are clinically effective: meta-analyses have shown little or no overall benefit, regardless of viral bronchiolitis severity (15,20). Their lack of efficacy has not been explained, although it has often been ascribed to difficulties associated with drug delivery to the small airways of young infants, particularly in the presence of bronchoconstriction and inflammatory exudates or airway obstruction (28). ␤-agonists increase total body oxygen consumption, thereby increasing oxygen demands in infants hospitalized for respiratory compromise, and can potentially exacerbate ventilation-perfusion mismatch by inducing vaso...

α1-Antitrypsin Inhibits Epithelial Na+ Transport In Vitro and In Vivo

“…One difference between the studies of Planes and colleagues (1) and ours is the baseline values of AFC in C57BL/6 mice. Planes and colleagues reported values of 17% of instilled volume per 30 minutes, whereas our AFC values (consistent with our previous work [20,37,48]) are closer to 30% of instilled volume per 30 minutes. In our experiments, A1AT decreased AFC to 12%, which is similar to the baseline value of Planes and colleagues (1).…”

Inhibition of Lung Fluid Clearance and Epithelial Na+ Channels by Chlorine, Hypochlorous Acid, and Chloramines

“…A standard curve was prepared by assaying known concentrations of bovine serum albumin in 0.9% NaCl. AFC values were calculated as described before (24,32). In some cases mice were anesthetized with isoflurane 15 min post-Cl 2 exposure, and 100 l of saline containing either trypsin (5 M) or vehicle were instilled dropwise in their nostrils.…”

“…However, the effects of Cl 2 inhalation on Na ϩ -dependent alveolar fluid clearance (AFC) in vivo as well as the mechanisms by which Cl 2 and HOCl damage ENaC have not been investigated. This is an important area of research as damage to ENaC has been associated with abnormal fluid transport in various forms of lung injury (7,(21)(22)(23)(24)(25).…”

Alveolar Epithelial β2-Adrenergic Receptors

“…While initial studies of adrenalectomized animals (8,45) or desensitization of b-receptors (81, 82) note no net effect on lung water content or basal alveolar fluid clearance, a more recent study showed reduced basal alveolar fluid clearance in adrenelectomized mice (83). The differences between these studies may be due to inability to (9) similarly reveal normal water content when uninjured but decreased ability to clear excess water from the airspace and more pulmonary edema and decreased survival from acute lung injury (hyperoxia).…”