Macrophage glucocorticoid receptors regulate Toll-like receptor 4–mediated inflammatory responses by selective inhibition of p38 MAP kinase

Abstract

To explore the role of glucocorticoids in regulation of kinase pathways during innate immune responses, we generated mice with conditional deletion of glucocorticoid receptor (GR) in macrophages (MGRKO). Activation of toll-like receptor 4 (TLR4) by lipopolysaccharide (LPS) caused greater mortality and cytokine production in MGRKO mice than in controls. Ex vivo, treatment with dexamethasone (Dex) markedly inhibited LPS-mediated induction of inflammatory genes in control but not GR-deficient macrophages. We show that Dex inhibits p38 MAPK, but not PI3K/Akt, ERK, or JNK, in control macrophages. Associated with p38 inhibition, Dex induced MAP kinase phosphatase-1 (MKP-1) in control, but not MGRKO, macrophages. Consistent with the ex vivo studies, treatment with a p38 MAPK–specific inhibitor resulted in rescue of MGRKO mice from LPS-induced lethality. Taken together, we identify p38 MAPK and its downstream targets as essential for GR-mediated immunosuppression in macrophages.

Anti-inflammatory functions of glucocorticoid-induced genes

“…It is expressed in response to GCs A Clark Anti-inflammatory functions of glucocorticoid-induced genes Page 18 of 53 in a wide variety of cell types including mast cells (Kassel et al, 2001), monocytes or macrophages (Abraham et al, 2006;Aeberli et al, 2006;Bhattacharyya et al, 2007;Chen et al, 2002;Zhao et al, 2005), microglia (Zhou et al, 2007), T lymphocytes , dermal, lung and synovial fibroblasts (Phillips et al, 2006;Toh et al, 2004;Yang et al, 2006), endothelial cells (Furst et al, 2007), osteoblasts (Engelbrecht et al, 2003;Leclerc et al, 2004), keratinocytes (Onda et al, 2006;Stojadinovic et al, 2006), adipocytes (Bazuine et al, 2004), lung epithelial cells (Chivers et al, 2006;Hermoso et al, 2004), airway smooth muscle cells (Issa et al, 2007) and HeLa cells (Imasato et al, 2002;Lasa et al, 2002). Typically expression is quite rapid (within one hour), sustained (up to 24 hours), requires relatively low concentrations of GC, and is blocked by the GR antagonist RU486.…”

“…Indeed, a variety of commonly prescribed GCs induced DUSP1 expression in alveolar macrophages in a manner roughly proportional to their anti-inflammatory efficacies . LPS-induced lethal endotoxic shock in mice was dependent on p38 MAPK activation and could be inhbited by GCs (Bhattacharyya et al, 2007). Macrophage specific knockout of GR expression increased susceptibility to LPS-induced lethal endotoxic shock, which was associated with failure of GCs to induce DUSP1 and inhibit p38 MAPK activation (Bhattacharyya et al, 2007).…”

“…LPS-induced lethal endotoxic shock in mice was dependent on p38 MAPK activation and could be inhbited by GCs (Bhattacharyya et al, 2007). Macrophage specific knockout of GR expression increased susceptibility to LPS-induced lethal endotoxic shock, which was associated with failure of GCs to induce DUSP1 and inhibit p38 MAPK activation (Bhattacharyya et al, 2007). This implies that the macrophage is an important site of action of GCs in one experimental model of acute inflammation, and that important anti-inflammatory effects are dependent on inhibition of p38 MAPK.…”

The role and regulation of 11β-hydroxysteroid dehydrogenase type 1 in the inflammatory response

“…In vitro, 11-dehydrocorticosterone (the 11β-HSD1 substrate in rodents) was equipotent with corticosterone in promoting Mφ phagocytosis of apoptotic PMN, but was without effect on Mφ from Hsd11b1 -/-mice . Glucocorticoid receptors in Mφ have been M a n u s c r i p t 9 implicated as the target for the protective effects of glucocorticoids against endotoxaemia (Bhattacharyya et al, 2007). Recent evidence suggests 11β-HSD1 in Mφ makes an important contribution to endogenous glucocorticoid action in the systemic response to endotoxin.…”

“…Endogenous glucocorticoids are essential to survive the lethal effects of pro-inflammatory mediators (IL-1, TNFα, LPS) (Bertini et al, 1988). Conversely, increased gene dosage of glucocorticoid receptor in mice enhances, whereas myeloid cell-specific disruption of the glucocorticoid receptor gene reduces, survival following endotoxic shock (Bhattacharyya et al, 2007;Reichardt et al, 2000). During inflammation, predominantly a response of the innate immune system, glucocorticoids restrain oedema, increase blood viscosity and alter leukocyte distribution/trafficking, haematopoietic differentiation programmes and gene transcription .…”