Chronic Allergen Exposure Contributes to Steroid Resistance via Increased Phosphorylation of Glucocorticoid Receptors S226 and p38 MAPK in a Mouse Model of Asthma

Abstract

Chronic allergen exposure can significantly induce p38 mitogen-activated protein kinase (MAPK) activation in asthma. p38 MAPK is involved in steroid resistance through phosphorylation of glucocorticoid receptors (GR) at S226. This study aims to investigate whether chronic allergen exposure can induce steroid resistance and whether it is associated with p38 MAPK activation in asthma. A mouse model of asthma was prepared by sensitizing and challenging mice with chronic ovalbumin (OVA) exposure. Key features of allergic asthma, encompassing bronchial hyperresponsiveness, pathology of lung tissues, cytokine profiles of inflammation in bronchoalveolar lavage fluid (BALF), and serum immunoglobulin (Ig)E concentration were evaluated. Furthermore, suppressive effects of corticosteroid on the splenocytes under stimulation of lipopolysaccharides, glucocorticoid receptor (GR) DNA binding ability of splenocytes, expression of GRα and phosphorylation of GR s226 in splenocytes, and p38 MAPK phosphorylation in splenocytes and lung tissues were determined. Chronic OVA exposure substantially induced airway hypersensitivity, leading to increased inflammatory infiltration in lung tissues. Additionally, it resulted in elevated levels of interleukin (IL)-4, IL-5, and IL-6 in BALF, as well as heightened levels of IgE in serum. Furthermore, OVA exposure substantially enhanced p38 MAPK phosphorylation in lung tissues. It also weakened the suppressive impacts of corticosteroids on splenocytes, impaired the GR DNA binding ability, and led to an enhanced phosphorylated state of GR S226 and p38 MAPK in splenocytes. Taken together, chronic allergen exposure contributes to steroid resistance in asthma, which is linked to an increased phosphorylated state of GR S226 and p38 MAPK.