Agonist-Specific Desensitization of PGE2-Stimulated cAMP Signaling due to upregulated Phosphodiesterase Expression in Human Lung Fibroblasts

Authors

Francisco Nunez, Chapman UniversityFollow
Nancy A. Schulte, University of Nebraska
David M. Fogel, Chapman UniversityFollow
Joel Michalski, University of Nebraska
Stephen I. Rennard, University of Nebraska
Raymond B. Penn, Thomas Jefferson University
Myron L. Toews, University of Nebraska
Rennolds S. Ostrom, Chapman UniversityFollow

Document Type

Article

Publication Date

12-28-2019

Abstract

Pulmonary fibrosis is characterized by fibroblasts persisting in an activated form, producing excessive fibrous material that destroys alveolar structure. The second messenger molecule cyclic 3′,5′-adenosine monophosphate (cAMP) has antifibrotic properties, and prostaglandin E₂ (PGE₂) can stimulate cAMP production through prostaglandin E (EP)₂ and EP₄ receptors. Although EP receptors are attractive therapeutic targets, the effects of long-term exposure to PGE₂ have not been characterized. To determine the effects of long-term exposure of lung fibroblasts to PGE₂, human fetal lung (HFL)-1 cells were treated for 24 h with 100 nM PGE₂ or other cAMP-elevating agents. cAMP levels stimulated by acute exposure to PGE₂ were measured using a fluorescent biosensor. Pretreatment for 24 h with PGE₂ shifted the concentration-response curve to PGE₂ rightward by approximately 22-fold but did not affect responses to the beta-adrenoceptor agonist isoproterenol. Neither isoproterenol nor forskolin pretreatment altered PGE₂ responses, implying that other cAMP-elevating agents do not induce desensitization. Use of EP₂- and EP₄-selective agonists and antagonists suggested that PGE₂-stimulated cAMP responses in HFL-1 cells are mediated by EP₂ receptors. EP₂ receptors are resistant to classical mechanisms of agonist-specific receptor desensitization, so we hypothesized that increased PDE activity mediates the loss of signaling after PGE₂ pretreatment. PGE₂ treatment upregulated messenger RNA for PDE3A, PDE3B, PDE4B, and PDE4D and increased overall PDE activity. The PDE4 inhibitor rolipram partially reversed PGE2- mediated desensitization and PDE4 activity was increased, but rolipram did not alter responses to isoproterenol. The PDE3 inhibitor cilostazol had minimal effect. These results show that long-term exposure to PGE₂ causes agonist-specific desensitization of EP₂ receptor-stimulated cAMP signaling through the increased expression of PDE isozymes, most likely of the PDE4 family.

Comments

This article was originally published in Naunyn-Schmiedeberg's Archives of Pharmacology in 2019. https://doi.org/10.1007/s00210-019-01800-5

Recommended Citation

Nunez, F.J., Schulte, N.A., Fogel, D.M. et al. Agonist-specific desensitization of PGE2-stimulated cAMP signaling due to upregulated phosphodiesterase expression in human lung fibroblasts. Naunyn-Schmiedeberg's Arch Pharmacol. 2019. https://doi.org/10.1007/s00210-019-01800-5

Copyright

The authors

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This work is licensed under a Creative Commons Attribution 4.0 License.