Idiopathic Pulmonary Fibrosis (IPF) is a lethal lung disease with progressive fibrosis and death within 2–3 years of diagnosis. IPF incidence and prevalence rates are increasing annually with few effective treatments available. Inhibition of interleukin 6 (IL-6) results in the attenuation of pulmonary fibrosis in mice. It is unclear whether this is due to blockade of classical signaling, mediated by membrane-bound IL-6 receptor alpha (mIL-6Rα), or trans signaling, mediated by soluble IL-6Rα (sIL-6Rα). Our study assessed the role of sL-6Rα in IPF. We demonstrated elevations of sIL-6Rα in IPF patients and in mice during the onset and progression of fibrosis. We demonstrated that protease-mediated cleavage from lung macrophages was important in production of sL-6Rα. In vivo neutralization of sIL-6Rα attenuated pulmonary fibrosis in mice as seen by reductions in myofibroblasts, fibronectin and collagen in the lung. In vitro activation of IL-6 trans signaling enhanced fibroblast proliferation and extracellular matrix protein production, effects relevant in the progression of pulmonary fibrosis. Together these findings demonstrate that the production of sL-6Rα from macrophages in the diseased lung contributes to IL-6 trans signaling that in turn influences events crucial in pulmonary fibrosis.

Idiopathic pulmonary fibrosis (IPF) is a lethal, fibroproliferative disease. Pulmonary hypertension (PH) can develop secondary to IPF and increase mortality. Alternatively, activated macrophages (AAMs) contribute to the pathogenesis of both IPF and PH. Here we hypothesized that adenosine signaling through the ADORA2B on AAMs impacts the progression of these disorders and that conditional deletion of ADORA2B on myeloid cells would have a beneficial effect in a model of these diseases. Conditional knockout mice lacking ADORA2B on myeloid cells (Adora2B f/f -LysM Cre ) were exposed to the fibrotic agent bleomycin (BLM; 0.035 U/g body weight, i.p.). At 14, 17, 21, 25, or 33 d after exposure, SpO 2 , bronchoalveolar lavage fluid (BALF), and histologic analyses were performed. On day 33, lung function and cardiovascular analyses were determined. Markers for AAM and mediators of fibrosis and PH were assessed. Adora2B f/f -LysM Cre mice presented with attenuated fibrosis, improved lung function, and no evidence of PH compared with control mice exposed to BLM. These findings were accompanied by reduced expression of CD206 and arginase-1, markers for AAMs. A 10-fold reduction in IL-6 and a 5-fold decrease in hyaluronan, both linked to lung fibrosis and PH, were also observed. These data suggest that activation of the ADORA2B on macrophages plays an active role in the pathogenesis of lung fibrosis and PH.-Karmouty-Quintana, H., Philip, K., Acero, L. F., Chen, N.-Y., Weng, T., Molina, J. G., Luo, F., Davies, J., Le, N.-B., Bunge, I., Volcik, K. A., Le, T.-T. T., Johnston, R. A., Xia, Y., Eltzschig, H. K., Blackburn, M. R. Deletion of ADORA2B from myeloid cells dampens lung fibrosis and pulmonary hypertension. FASEB J. 29, 50-60 (2015). www.fasebj.org

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Idiopathic pulmonary fibrosis (IPF) is a deadly chronic lung disease. Extracellular accumulation of adenosine and subsequent activation of the ADORA2B receptor play important roles in regulating inflammation and fibrosis in IPF. Additionally, alternatively activated macrophages (AAMs) expressing ADORA2B have been implicated in mediating adenosine's effects in IPF. Although hypoxic conditions are present in IPF, hypoxia's role as a direct modulator of macrophage phenotype and identification of factors that regulate ADORA2B expression on AAMs in IPF is not well understood. In this study, an experimental mouse model of pulmonary fibrosis and lung samples from patients with IPF were used to examine the effects and interactions of macrophage differentiation and hypoxia on fibrosis. We demonstrate that hypoxia-inducible factor 1-α (HIF1A) inhibition in late stages of bleomycin-induced injury attenuates pulmonary fibrosis in association, with reductions in ADORA2B expression in AAMs. Additionally, ADORA2B deletion or pharmacological antagonism along with HIF1A inhibition disrupts AAM differentiation and subsequent IL-6 production in cultured macrophages. These findings suggest that hypoxia, through HIF1A, contributes to the development and progression of pulmonary fibrosis through its regulation of ADORA2B expression on AAMs, cell differentiation, and production of profibrotic mediators. These studies support a potential role for HIF1A or ADORA2B antagonists in the treatment of IPF.-Philip, K., Mills, T. W., Davies, J., Chen, N.-Y., Karmouty-Quintana, H., Luo, F., Molina, J. G., Amione-Guerra, J., Sinha, N., Guha, A., Eltzschig, H. K., Blackburn, M. R. HIF1A up-regulates the ADORA2B receptor on alternatively activated macrophages and contributes to pulmonary fibrosis.