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A2083 - Macrophages Increase the Bone Morphogenetic Protein Antagonist Gremlin-1 in Response to Hypoxia
Author Block: L. Mthunzi, U. Knaus, P. McLoughlin; Medicine, University College Dublin, Dublin, Ireland.
Background Chronic lung diseases are the third most common cause of death worldwide and are frequently complicated by pulmonary hypertension (PH). We have previously demonstrated that gremlin-1 a bone morphogenetic protein (BMP) antagonist plays a key role in the development of PH1. Additionally, alveolar macrophage (AM) accumulation and their M2 polarization have been shown to play critical roles in the development of PH2. However, the mechanism by which AMs contribute to the development of PH remains to be elucidated. Preliminary studies (unpublished data) suggest AMs may be an important source of gremlin-1 in the hypoxic lung. In this study we assessed macrophage activation and gremlin-1 expression using bone marrow-derived macrophages (BMDMs). Methods The Animal Research Ethics Committee of University College Dublin approved all animal procedures. Mice were euthanized by cervical dislocation. BMDMs were generated using a standard protocol with L929-cell conditioned medium. LPS and IL-4+IL-13 were used for polarization studies. For hypoxia studies, BMDMs were maintained in normoxia (21% O2) or hypoxia (1% O2) for two days. Results Immunostaining and mRNA expression established BMDMs as a novel source of gremlin-1. Stimulation of macrophages with LPS induced M1-like polarization. Stimulation of macrophages with IL-4+IL-13 induced M2-like polarization. M1 or M2 polarization of macrophages in normoxia did not alter gremlin-1 expression. Interestingly, stimulation of macrophages with recombinant BMP2 augmented M2 polarization but did not change gremlin-1 expression. Maintenance of macrophages in hypoxia promoted increased expression of gremlin-1. Conclusions These findings suggest that polarization of macrophages in the absence of hypoxia does not increase gremlin-1. However, hypoxia stimulates increased gremlin-1 in macrophages suggesting that macrophage-derived gremlin-1 may act in an autocrine manner to influence polarization and in a paracrine manner to modify BMP signaling in nearby cells in the hypoxic lung. References 1. Cahill E, Costello CM, Rowan SC, Harkin S, Howell K, Leonard MO, et al. Gremlin plays a key role in the pathogenesis of pulmonary hypertension. Circulation. 2012;125(7):920-30. 2. Vergadi E, Chang MS, Lee C, Liang OD, Liu X, Fernandez-Gonzalez A, et al. Early macrophage recruitment and alternative activation are critical for the later development of hypoxia-induced pulmonary hypertension. Circulation. 2011;123(18):1986-95.