p38 Mitogen-Activated Protein Kinase-γ Inhibition by Long-Acting β₂Adrenergic Agonists Reversed Steroid Insensitivity in Severe Asthma

Abstract

Corticosteroid insensitivity (CI) is a major barrier to treating severe asthma. Despite intensive research, the molecular mechanism of CI remains uncertain. The aim of this study was to determine abnormality in corticosteroid action in severe asthma and to identify the molecular mechanism of the longacting ␤ 2 -adrenergic agonists (LABAs) formoterol and salmeterol on restoration of corticosteroid sensitivity in severe asthma in vitro. Peripheral blood mononuclear cells (PBMCs) were obtained from 16 subjects with severe corticosteroid-insensitive asthma, 6 subjects with mild corticosteroid-sensitive asthma, and 11 healthy volunteers. Corticosteroid (dexamethasone) sensitivity was determined on tumor necrosis factor-␣ (TNF-␣)-induced interleukin (IL)-8 production. Glucocorticoid receptor (GR) phosphorylation and kinase phosphorylation were evaluated by immunoprecipitation-Western blotting analysis and kinase phosphorylation array in IL-2/IL-4-treated corticosteroid insensitive model in PBMCs. In vitro corticosteroid sensitivity on TNF-␣-induced IL-8 production was significantly lower in patients with severe asthma than in healthy volunteers and patients with mild asthma. This CI seen in severe asthma was associated with reduced GR nuclear translocation and with hyperphosphorylation of GR, which were reversed by LABAs. In IL-2/IL-4-treated PBMCs, LABAs inhibited phosphorylation of Jun-NH 2 -terminal kinase and p38 mitogen-activated protein kinase-␥ (p38MAPK-␥) as well as GR. In addition, cells with p38MAPK-␥ knockdown by RNA interference did not develop CI in the presence of IL-2/IL-4. Furthermore, p38MAPK-␥ protein expression was up-regulated in PBMCs from some patients with severe asthma. In conclusion, p38 MAPK-␥ activation impairs corticosteroid action and p38 MAPK-␥ inhibition by LABAs has potential for the treatment of severe asthma.

Basal p38 Mitogen-Activated Protein Kinase Regulates Unliganded Glucocorticoid Receptor Function in Airway Smooth Muscle Cells

“…In severe asthma, there appear to be multiple mechanisms that affect GR phosphorylation status, which could explain GC insensitivity seen in these patients. Increased p38 MAPK expression in PBMCs (24) or activity in PBMCs and alveolar macrophages (23,49) is associated with reduced patient sensitivity to GC therapy, possibly by driving GR phosphorylation on S226. The same group raised the hypothesis that decreased PP2A function could serve as a mechanism leading to GC insensitivity, in part via its failure to dephosphorylate GR on S226 residues (50).…”

“…Earlier studies in immune cells suggested that the p38 MAPK-GR interaction acts as a novel mechanism driving GC resistance in patients with severe asthma (11). Indeed, the blockade of p38 MAPK pathways by soluble inhibitors (20,23) or by the longacting b agonists (LABAs) formoterol and salmeterol (24) was associated with a restoration of cell sensitivity to GC. Those reports identified p38 MAPK as an important kinase in peripheral blood mononuclear cells (PBMCs) that reduces GR functions by impairing GR nuclear translocation and/or DNA binding affinity.…”

“…p38 MAPK is activated by upstream MAPK kinases (MKK3 or MKK6) in response to a number of inflammatory or environmental signals (17)(18)(19). Different reports have convincingly implicated p38 MAPK pathways in the pathogenesis of patients with asthma, in particular those with severe disease (20)(21)(22)(23)(24). The exact role of p38 MAPK in GR functions in human diseases has just started to emerge.…”

Addressing corticosteroid insensitivity in adults with asthma

“…A PI3Kδ/γ inhibitor RV1729 has undergone early stage clinical evaluation in COPD, although no results are published (ClinicalTrials.gov Identifier: NCT02140346). The tricyclic antidepressant nortriptyline reverses corticosteroid insensitivity induced by oxidative stress in vitro by inhibition of PI3K-δ and it has been proposed as a potential treatment for corticosteroidinsensitivity in severe asthma, smokers with asthma and COPD [131]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 inhaled dual PDE 3 and PDE 4 inhibitor, RPL554 has bronchodilator effects and is well tolerated in patients with asthma and COPD [140].…”

“…A PI3Kδ/γ inhibitor RV1729 has undergone early stage clinical evaluation in COPD, although no results are published (ClinicalTrials.gov Identifier: NCT02140346). The tricyclic antidepressant nortriptyline reverses corticosteroid insensitivity induced by oxidative stress in vitro by inhibition of PI3K-δ and it has been proposed as a potential treatment for corticosteroidinsensitivity in severe asthma, smokers with asthma and COPD [131]. …”