THU0003 CRYSTALLINE SILICA IMPAIRS EFFEROCYTOSIS CAPACITIES OF HUMAN MONOCYTE-DERIVED MACROPHAGES THROUGH RHOA-ROCK ACTIVATION
Authors: Lescoat Alain, Alice Ballerie, Marie Lelong, Marie LelongYu Augagneur, Claudie Morzadec, Stéphane Jouneau, Patrick Jégo, Olivier Fardel, Laurent Vernhet, Valérie Lecureur
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Inhalation of crystalline silica can lead to pulmonary diseases and systemic autoimmune disorders, such as systemic sclerosis (SSc), systemic lupus erythematosus or rheumatoid arthritis (1). A failure of apoptotic cell clearance, also called efferocytosis, is reported in autoimmune diseases and, impaired efferocytosis in macrophages from SSc patients has especially been described recently (2). However, the precise mechanisms linking crystalline silica exposure and autoimmune disorders is still to be determined. <h3>Objectives:</h3> This study explored the effects of crystalline silica on efferocytosis abilities of human macrophages. <h3>Methods:</h3> Monocyte-derived macrophages (MDM) were exposed <i>in vitro</i> to crystalline silica for 4 hours. Their ability to phagocyte CFSE-positive apoptotic and non-apoptotic Jurkat cells and their polarization profile after silica exposure were assessed by flow cytometry. Efferocytosis capacities of MDM from SSc were also evaluated using the same methods. <h3>Results:</h3> Crystalline silica exposure impaired efferocytosis capacities of human MDM in a specific and dose-dependent manner. This effect of silica required the expression of SR-B1 and, was associated with a decreased membrane expression of the M2 polarization markers CD206, CD204 and CD163. Their expressions after silica exposure were similar to those of M1 polarized MDM. Silica increased F-actin staining, RhoA activation and phosphorylation of myosin phosphatase subunit 1 (MYPT1), a known ROCK target. Y27632, a Rho kinase (ROCK) inhibitor, reversed the F-actin staining, the phosphorylation of MYPT1 and, at least in part, the silica-induced impairment of efferocytosis. Moreover, efferocytosis abilities of MDM from SSc patients were similar to those of silica-exposed MDM and, a treatment of SSc-MDM with Y27632 significantly increase their efferocytosis capacities, suggesting an activation of the RhoA/ROCK pathway in SSc MDM also. <h3>Conclusion:</h3> These findings demonstrate that silica impairs efferocytosis in MDM via an activation of RhoA/ROCK pathway<b> (Figure 1)</b>. These results also suggest a therapeutic potential of drugs targeting this pathway and advance the hypothesis that silica exposure may contribute to the impaired efferocytosis capacities of macrophages from SSc patients, a silica-associated systemic disorder still without curative treatment to date. <h3>References:</h3> [1] Blanc PD, Järvholm B, Torén K. Prospective risk of rheumatologic disease associated with occupational exposure in a cohort of male construction workers. Am J Med. 2015 Oct;128(10):1094-101. [2] Ballerie A, Lescoat A, Augagneur Y, Lelong M, Morzadec C, Cazalets C, Jouneau S, Fardel O, Vernhet L, Jégo P, Lecureur V. Efferocytosis capacities of blood monocyte-derived macrophages in systemic sclerosis. Immunol Cell Biol. 2018 Nov 13. <h3>Acknowledgement:</h3> This work was supported by the "Groupe Francophone de la Recherche sur la Sclerodermie". <h3>Disclosure of Interests:</h3> None declared