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Pro-asthmatic cytokines regulate unliganded and ligand-dependent glucocorticoid receptor signaling in airway smooth muscle.

ABSTRACT: To elucidate the regulation of glucocorticoid receptor (GR) signaling under pro-asthmatic conditions, cultured human airway smooth muscle (HASM) cells were treated with proinflammatory cytokines or GR ligands alone and in combination, and then examined for induced changes in ligand-dependent and -independent GR activation and downstream signaling events. Ligand stimulation with either cortisone or dexamethsone (DEX) acutely elicited GR translocation to the nucleus and, comparably, ligand-independent stimulation either with the Th2 cytokine, IL-13, or the pleiotropic cytokine combination, IL-1β/TNFα, also acutely evoked GR translocation. The latter response was potentiated by combined exposure of cells to GR ligand and cytokine. Similarly, treatment with either DEX or IL-13 alone induced GR phosphorylation at its serine-211 residue (GR(Ser211)), denoting its activated state, and combined treatment with DEX+IL-13 elicited heightened and sustained GR(Ser211) phosphorylation. Interestingly, the above ligand-independent GR responses to IL-13 alone were not associated with downstream GR binding to its consensus DNA sequence or GR transactivation, whereas both DEX-induced GR:DNA binding and transcriptional activity were significantly heightened in the presence of IL-13, coupled to increased recruitment of the transcriptional co-factor, MED14. The stimulated GR signaling responses to DEX were prevented in IL-13-exposed cells wherein GR(Ser211) phosphorylation was suppressed either by transfection with specific serine phosphorylation-deficient mutant GRs or treatment with inhibitors of the MAPKs, ERK1/2 and JNK. Collectively, these novel data highlight a heretofore-unidentified homeostatic mechanism in HASM cells that involves pro-asthmatic cytokine-driven, MAPK-mediated, non-ligand-dependent GR activation that confers heightened glucocorticoid ligand-stimulated GR signaling. These findings raise the consideration that perturbations in this homeostatic cytokine-driven GR signaling mechanism may be responsible, at least in part, for the insensirtivity to glucocorticoid therapy that is commonly seen in individuals with severe asthma.

SUBMITTER: Hu A

PROVIDER: S-EPMC3617099 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background and objectiveAirway remodeling in asthma refers to numerous structural changes in the airway in asthmatic patients, with thickening of the airway smooth muscle layer as its core feature. However, the nature and sources of the abnormally increased airway smooth muscle cells (ASMCs) in airway remodeling remain unclear. ASMCs play a key role in the pathogenesis of fatal asthma; therefore, it is important to clarify the properties and sources of these ASMCs responsible for asthmatic airway remodeling, which may provide a new direction for the precise treatment for asthma.MethodsWe performed a narrative review of the literature on PubMed, Web of Science, and Google Scholar databases searching for the cellular sources of ASMCs in asthmatic airway remodeling and their clinical relevance.Key content and findingsIt has long been thought that ASMCs are the result of abnormal proliferation of the native ASMCs in asthma; however, increasing evidence suggests that increased "ASMCs" may be due to the differentiation/transdifferentiation of other cells including mesenchymal stem cells (MSCs), myofibroblasts (MYFs), pericytes, and epithelial-mesenchymal transition (EMT). Recently, several pharmacological and biological therapies aimed at "reducing asthmatic ASMCs" have been developed, among which gallopamil, JQ1 [an inhibitor of the bromodomain and extra-terminal domain (BET) protein family], and histone deacetylase (HDAC) inhibitors can alleviate asthma airway remodeling and hyperresponsiveness and improve asthma symptoms in both mouse models and preclinical experiments.ConclusionsAs one of the core features of asthma, ASMCs are an important effector of airway remodeling. It has become extremely important to develop therapies for the reduction and prevention of the "ASMCs" on the basis of the properties and sources of "ASMCs". Many studies have shown that epigenetic regulation is closely related to the abnormal increase of ASMCs in asthma, and interfering with epigenetic regulation factors can reduce the increased smooth muscle cells. Although the epigenetic regulation of asthma is still in its nascent stage, epigenetic therapy targeting "ASMCs" may become another new strategy for asthma prevention and treatment.

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Pro-asthmatic cytokines regulate unliganded and ligand-dependent glucocorticoid receptor signaling in airway smooth muscle.

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