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Updated: Jul 6, 2026
In vitro Measurements of Tracheal Constriction Using Mice
Published on: June 25, 2012
Prolonged heterologous beta2-adrenoceptor desensitization promotes proasthmatic airway smooth muscle function via
Aihua Hu1, Gustavo Nino, Judith S Grunstein
1The Joseph Stokes Jr. Research Institute, Division of Pulmonary Medicine, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
Abstract:
Beta2-adrenergic receptor (beta2AR) agonists acutely relieve bronchoconstriction via cAMP-mediated relaxation of airway smooth muscle (ASM). Airway constrictor responsiveness may be significantly heightened, however, following protracted exposure to these agents, presumably reflecting the effects of beta2AR desensitization in ASM accompanying prolonged cAMP signaling. Because cAMP phosphodiesterase (PDE) activity can significantly modulate ASM contractility, we investigated the mechanism regulating PDE expression and its potential role in mediating changes in agonist-induced constrictor and relaxation responsiveness in ASM following its heterologous beta2AR desensitization by prolonged exposure to cAMP-elevating agents. Isolated rabbit ASM tissues and cultured human ASM cells treated for 24 h with the receptor- or nonreceptor-coupled cAMP-stimulating agent, prostaglandin E(2) (PGE(2)) or forskolin, respectively, exhibited constrictor hyperresponsiveness to acetylcholine and impaired beta2AR-mediated relaxation and cAMP accumulation. These proasthmatic-like changes in ASM function were associated with upregulated PDE4 activity, reflective of increased transcription of the PDE4D5 isoform, and were prevented by pretreatment of the ASM with a PDE4 inhibitor. Extended studies using gene silencing and pharmacological approaches to inhibit specific intracellular signaling molecules demonstrated that the mechanism underlying PGE(2)-induced transcriptional upregulation of PDE4D5 involves PKA-dependent activation of G(i) protein signaling via the betagamma-subunits, the latter eliciting downstream activation of ERK1/2 and its consequent induction of PDE4D5 transcription. Collectively, these findings identify that beta2AR desensitization in ASM following prolonged exposure to cAMP-elevating agents is associated with proasthmatic-like changes in ASM responsiveness that are mediated by upregulated PDE4 expression induced by activated cross talk between the PKA and ERK1/2 signaling pathways.
Insights
Prolonged use of beta2-adrenergic receptor (beta2AR) agonists can worsen asthma-like symptoms by desensitizing airways. This desensitization upregulates phosphodiesterase 4 (PDE4), increasing airway constriction and reducing relaxation.
Area of Science:
- Pharmacology
- Cellular Biology
- Respiratory Medicine
Background:
- Beta2-adrenergic receptor (beta2AR) agonists provide acute relief from bronchoconstriction through cAMP-mediated airway smooth muscle (ASM) relaxation.
- Prolonged beta2AR agonist exposure can lead to airway hyperresponsiveness, potentially due to beta2AR desensitization in ASM and altered cAMP signaling.
Purpose of the Study:
- To investigate the mechanisms regulating phosphodiesterase (PDE) expression in ASM following heterologous beta2AR desensitization.
- To determine the role of PDE activity in mediating changes in ASM responsiveness after prolonged exposure to cAMP-elevating agents.
Main Methods:
- Isolated rabbit ASM tissues and cultured human ASM cells were treated with prostaglandin E(2) (PGE(2)) or forskolin to induce desensitization.
- Assessed changes in ASM contractility, relaxation, cAMP accumulation, and PDE activity.
- Utilized gene silencing and pharmacological inhibitors to elucidate signaling pathways (PKA, G(i), ERK1/2) involved in PDE4D5 regulation.
Main Results:
- Prostaglandin E(2) or forskolin treatment resulted in constrictor hyperresponsiveness to acetylcholine and impaired beta2AR-mediated relaxation and cAMP accumulation.
- These functional changes were associated with upregulated PDE4 activity and increased transcription of the PDE4D5 isoform.
- The upregulation of PDE4D5 was dependent on PKA-mediated activation of G(i) protein signaling, leading to ERK1/2 activation and PDE4D5 transcription.
Conclusions:
- Beta2AR desensitization in ASM, induced by prolonged cAMP-elevating agents, leads to pro-asthmatic changes in ASM responsiveness.
- Upregulated PDE4 expression, specifically PDE4D5, mediated these functional alterations.
- Cross-talk between PKA and ERK1/2 signaling pathways is critical for the transcriptional induction of PDE4D5 during beta2AR desensitization.
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