Metal-Stimulated Interleukin-6 Production Through a Proton-Sensing Receptor, Ovarian Cancer G Protein-Coupled Receptor 1, in Human Bronchial Smooth Muscle Cells: A Response Inhibited by Dexamethasone

Abstract

Purpose Human bronchial smooth muscle cells (BSMCs) contribute to airway obstruction and hyperresponsiveness in patients with bronchial asthma. BSMCs also generate cytokines and matricellular proteins in response to extracellular acidification through the ovarian cancer G protein-coupled receptor 1 (OGR1). Cobalt (Co) and nickel (Ni) are occupational agents, which cause occupational asthma. We examined the effects of Co and Ni on interleukin-6 (IL-6) secretion by human BSMCs because these metals may act as ligands of OGR1. Methods Human BSMCs were incubated in Dulbecco’s Modified Eagle Medium (DMEM) containing 0.1% bovine serum albumin (BSA) (0.1% BSA-DMEM) for 16 hours and stimulated for the indicated time by exchanging the medium with 0.1% BSA-DMEM containing any of the metals or pH-adjusted 0.1% BSA-DMEM. IL-6 mRNA expression was quantified via reverse transcription polymerase chain reaction (RT-PCR) using the real-time TaqMan technology. IL-6 was measured using an enzyme-linked immunosorbent assay. Dexamethasone (DEX) was added 30 minutes before each stimulation. To knock down the expression of OGR1 in BSMCs, small interfering RNA (siRNA) targeting OGR1 (OGR1-siRNA) was transfected to the cells and non-targeting siRNA (NT-siRNA) was used as a control. Results Co and Ni both significantly increased IL-6 secretion in human BSMCs at 300 μM. This significant increase in IL-6 mRNA expression was observed 5 hours after stimulation. BSMCs transfected with OGR1-siRNA produced less IL-6 than BSMCs transfected with NT-siRNA in response to either Co or Ni stimulation. DEX inhibited Co- and Ni-stimulated IL-6 secretion by human BSMCs as well as pH 6.3-stimulated IL-6 secretion in a dose-dependent manner. DEX did not decrease phosphorylation of ERK1/2, p38 MAP kinase, and NF-κB p65 induced by either Co or Ni stimulation. Conclusion Co and Ni induce secretion of IL-6 in human BSMCs through activation of OGR1. Co- and Ni-stimulated IL-6 secretion is inhibited by DEX.

Recent advances in acid sensing by G protein coupled receptors

“…OGR1 has been implicated in allergen-induced hyper-responsiveness and idiopathic pulmonary fibrosis [ 3 , 10 , 56 , 57 ] and was reported to be pro-inflammatory [ 29 , 56 ]. It is expressed in lung fibroblasts [ 3 , 56 ] and bronchial smooth muscle cells [ 10 , 29 ].…”

“…OGR1 has been implicated in allergen-induced hyper-responsiveness and idiopathic pulmonary fibrosis [ 3 , 10 , 56 , 57 ] and was reported to be pro-inflammatory [ 29 , 56 ]. It is expressed in lung fibroblasts [ 3 , 56 ] and bronchial smooth muscle cells [ 10 , 29 ]. Whilst OGR1 expression is increased in bronchial smooth muscle cells in an ovalbumin antigen-challenged murine asthma model [ 10 ], it is downregulated in fibroblasts from patients with idiopathic pulmonary fibrosis [ 65 ], which promotes myofibroblast differentiation, suggesting that OGR1 has anti-fibrotic effects in lung fibroblasts [ 56 ].…”