Role of protein phosphatase 5 (PP5) in mediating corticosteroid insensitivity in airway smooth muscle (ASM) cells in severe asthma

Although the mechanisms mediating corticosteroid resistance in severe asthma are still unknown, recent evidence suggests ASM cells isolated from patients with severe asthma have a decreased insensitivity to dexamethasone (Dex) with respect to the inhibition of chemokine production. Here we investigated whether this corticosteroid insensitivity seen in ASM from severe asthmatics was due to an abnormal GR signalling pathway. We here observed that production of CCL5 and CCL11 by TNF in ASM cells from severe asthmatics (compared to healthy subjects and nonsevere asthma) was not affected by Dex or fluticasone (FP) pretreatment. Using immunoblot assays we found that the time 1-24hr dependent phosphorylation of GR on ser 211 residues induced by FP was significantly impaired in ASM cells from severe asthmatics when compared to cells from healthy subjects and nonsevere asthmatics. FP-induced expression of the GRE-inducible gene glucocorticoid-induced leucine zipper (GILZ) was also reduced in severe asthmatic ASM cells. Flow cytometry assays demonstrated a significant up-regulation of the serine/threonine protein phosphatase 5 (PP5) in ASM cells from severe asthmatics. More importantly, inhibiting PP5 using siRNA strategy restored the ability to inhibit TNF-induced CCL5 and CCL11 (assessed by ELISA) in ASM cells from severe asthma patients. The data show that ASM cells from severe asthmatics have a reduced sensitivity to corticosteroids that is in part due to an impaired GR phosphoryla...
Source: European Respiratory Journal - Category: Respiratory Medicine Authors: Tags: 3.2 Airway Cell Biology and Immunopathology Source Type: research