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Glucocorticoid- and Protein Kinase A–Dependent Transcriptome Regulation in Airway Smooth Muscle

¹ Department of Internal Medicine and Center for Human Genomics, Wake Forest University Health Sciences, Winston-Salem, North Carolina; and ² Laboratory of Pathology, National Cancer Institute, Bethesda, Maryland

Correspondence and requests for reprints should be addressed to Raymond B. Penn, Ph.D., Wake Forest University Health Sciences Center, Center for Human Genomics, Medical Center Blvd, Winston-Salem NC 27157. E-mail: rpenn{at}wfubmc.edu

Glucocorticoids (GCs) and protein kinase A (PKA)–activating agents (β-adrenergic receptor agonists) are mainstream asthma therapies based on their ability to prevent or reverse excessive airway smooth muscle (ASM) constriction. Their abilities to regulate another important feature of asthma—excessive ASM growth—are poorly understood. Recent studies have suggested that GCs render agents of inflammation such as IL-1β and TNF- mitogenic to ASM, via suppression of (antimitogenic) induced cyclooxygenase-2–dependent PKA activity. To further explore the mechanistic basis of these observations, we assessed the effects of epidermal growth factor and IL-1β stimulation, and the modulatory effects of GC treatment and PKA inhibition, on the ASM transcriptome by microarray analysis. Results demonstrate that ASM stimulated with IL-1β, in a manner that is often cooperative with stimulation with epidermal growth factor, exhibit a profound capacity to function as immunomodulatory cells. Moreover, results implicate an important role for induced autocrine/paracrine factors (many whose regulation was minimally affected by GCs or PKA inhibition) as regulators of both airway inflammation and ASM growth. Induction of numerous chemokines, in conjunction with regulation of proteases and agents of extracellular matrix remodeling, is suggested as an important mechanism promoting upregulated G protein–coupled receptor signaling capable of stimulating ASM growth. Additional functional assays suggest that intracellular PKA plays a critical role in suppressing the promitogenic effects of induced autocrine factors in ASM. Finally, identification and comparison of GC- and PKA-sensitive genes in ASM provide insight into the complementary effects of β-agonist/GC combination therapies, and suggest specific genes as important targets for guiding the development of new generations of GCs and adjunct asthma therapies.

Key Words: airway smooth muscle • protein kinase A • glucocorticoid • gene expression • G protein–coupled receptors

CLINICAL RELEVANCE Results from these studies help to understand how gene expression in human airway smooth muscle is regulated by inflammation and by the two principal asthma therapeutics: glucocorticoids and β-agonists. Changes in the airway smooth muscle transcriptome induced by glucocorticoids or protein kinase A inhibition provide insight into how glucocorticoid therapy may promote increased airway smooth muscle mass.