Airway smooth muscle prostaglandin-EP1 receptors directly modulate β2–adrenergic receptors within a unique heterodimeric complex

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Abstract

Multiple and paradoxical effects of airway smooth muscle (ASM) 7-transmembrane–spanning receptors activated during asthma, or by treatment with bronchodilators such as β2–adrenergic receptor (β2AR) agonists, indicate extensive receptor crosstalk. We examined the signaling of the prostanoid-EP1 receptor, since its endogenous agonist prostaglandin E2 is abundant in the airway, but its functional implications are poorly defined. Activation of EP1 failed to elicit ASM contraction in mouse trachea via this Gαq-coupled receptor. However, EP1 activation markedly reduced the bronchodilatory function of β2AR agonist, but not forskolin, indicating an early pathway interaction. Activation of EP1 reduced β2AR-stimulated cAMP in ASM but did not promote or augment β2AR phosphorylation or alter β2AR trafficking. Bioluminescence resonant energy transfer showed EP1 and β2AR formed heterodimers, which were further modified by EP1 agonist. In cell membrane [35S]GTPγS binding studies, the presence of the EP1 component of the dimer uncoupled β2AR from Gαs, an effect accentuated by EP1 agonist activation. Thus alone, EP1 does not appear to have a significant direct effect on airway tone but acts as a modulator of the β2AR, altering Gαs coupling via steric interactions imposed by the EP1:β2AR heterodimeric signaling complex and ultimately affecting β2AR-mediated bronchial relaxation. This mechanism may contribute to β-agonist resistance found in asthma.

Authors

Dennis W. McGraw, Kathryn A. Mihlbachler, Mary Rose Schwarb, Fahema F. Rahman, Kersten M. Small, Khalid F. Almoosa, Stephen B. Liggett

Elastin fragments drive disease progression in a murine model of emphysema

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Abstract

Mice lacking macrophage elastase (matrix metalloproteinase-12, or MMP-12) were previously shown to be protected from the development of cigarette smoke–induced emphysema and from the accumulation of lung macrophages normally induced by chronic exposure to cigarette smoke. To determine the basis for macrophage accumulation in experimental emphysema, we now show that bronchoalveolar lavage fluid from WT smoke-exposed animals contained chemotactic activity for monocytes in vitro that was absent in lavage fluid from macrophage elastase–deficient mice. Fractionation of the bronchoalveolar lavage fluid demonstrated the presence of elastin fragments only in the fractions containing chemotactic activity. An mAb against elastin fragments eliminated both the in vitro chemotactic activity and cigarette smoke–induced monocyte recruitment to the lung in vivo. Porcine pancreatic elastase was used to recruit monocytes to the lung and to generate emphysema. Elastin fragment antagonism in this model abrogated both macrophage accumulation and airspace enlargement.

Authors

A. McGarry Houghton, Pablo A. Quintero, David L. Perkins, Dale K. Kobayashi, Diane G. Kelley, Luiz A. Marconcini, Robert P. Mecham, obert M. Senior,, Steven D. Shapiro

Maturational differences in lung NF-κB activation and their role in tolerance to hyperoxia

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Abstract

Neonatal rodents are more tolerant to hyperoxia than adults. We determined whether maturational differences in lung NF-κB activation could account for the differences. After hyperoxic exposure (O2 > 95%), neonatal (<12 hours old) lung NF-κB binding was increased and reached a maximum between 8 and 16 hours, whereas in adults no changes were observed. Additionally, neonatal NF-κB/luciferase transgenic mice (incorporating 2 NF-κB consensus sequences driving luciferase gene expression) demonstrated enhanced in vivo NF-κB activation after hyperoxia in real time. In the lungs of neonates, there was a propensity toward NF-κB activation as evidenced by increased lung I-κB kinase protein levels, I-κBα phosphorylation, β-transducin repeat–containing protein levels, and total I-κBα degradation. Increased lung p-JNK immunoreactive protein was observed only in the adult lung. Inhibition of pI-κBα by BAY 11-7085 resulted in decreased Bcl-2 protein levels in neonatal lung homogenates and decreased cell viability in lung primary cultures after hyperoxic exposure. Furthermore, neonatal p50-null mutant (p50–/–) mice showed increased lung DNA degradation and decreased survival in hyperoxia compared with WT mice. These data demonstrate that there are maturational differences in lung NF-κB activation and that enhanced NF-κB may serve to protect the neonatal lung from acute hyperoxic injury via inhibition of apoptosis.

Authors

Guang Yang, Aida Abate, Adia G. George, Yi-Hao Weng, Phyllis A. Dennery

PKCβ regulates ischemia/reperfusion injury in the lung

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Abstract

Activation of PKCβII is associated with the response to ischemia/reperfusion (I/R), though its role, either pathogenic or protective, has not been determined. In a murine model of single-lung I/R, evidence linking PKCβ to maladaptive responses is shown in the following studies. Homozygous PKCβ-null mice and WT mice fed the PKCβ inhibitor ruboxistaurin subjected to I/R displayed increased survival compared with controls. In PKCβ-null mice, phosphorylation of extracellular signal–regulated protein kinase-1 and -2 (ERK1/2), JNK, and p38 MAPK was suppressed in I/R. Expression of the immediate early gene, early growth response-1 (Egr-1), and its downstream target genes was significantly increased in WT mice in I/R, particularly in mononuclear phagocytes (MPs), whereas this expression was attenuated in PKCβ-null mice or WT mice fed ruboxistaurin. In vitro, hypoxia/reoxygenation-mediated induction of Egr-1 in MPs was suppressed by inhibition of PKCβ, ERK1/2, and JNK, but not by inhibition of p38 MAPK. These findings elucidate key roles for PKCβII activation in I/R by coordinated activation of MAPKs (ERK1/2, JNK) and Egr-1.

Authors

Tomoyuki Fujita, Tomohiro Asai, Martin Andrassy, David M. Stern, David J. Pinsky, Yu Shan Zou, Morihito Okada, Yoshifumi Naka, Ann Marie Schmidt, Shi-Fang Yan

T cell activation causes diarrhea by increasing intestinal permeability and inhibiting epithelial Na⁺/K⁺-ATPase

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Abstract

Research Article

Authors

Mark W. Musch, Lane L. Clarke, Daniel Mamah, Lara R. Gawenis, Zheng Zhang, William Ellsworth, David Shalowitz, Navdha Mittal, Petros Efthimiou, Ziad Alnadjim, Steve D. Hurst, Eugene B. Chang, Terrence A. Barrett

The gene encoding the iron regulatory peptide hepcidin is regulated by anemia, hypoxia, and inflammation

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Abstract

Research Article

Authors

Gaël Nicolas, Caroline Chauvet, Lydie Viatte, Jean Louis Danan, Xavier Bigard, Isabelle Devaux, Carole Beaumont, Axel Kahn, Sophie Vaulont

TNF-α mediates chemokine and cytokine expression and renal injury in cisplatin nephrotoxicity

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Abstract

Research Article

Authors

Ganesan Ramesh, W. Brian Reeves