MCTR1 enhances the resolution of lipopolysaccharide-induced lung injury through STAT6-mediated resident M2 alveolar macrophage polarization in mice

Acute respiratory distress syndrome (ARDS) is a fatal disease characterized by excessive infiltration of inflammatory cells. MCTR1 is an endogenously pro-resolution lipid mediator. We tested the hypothesis that MCTR1 accelerates inflammation resolution through resident M2 alveolar macrophage polarization. The mice received MCTR1 via intraperitoneal administration 3 days after LPS stimulation, and then, the bronchoalveolar lavage (BAL) fluid was collected 24 hours later to measure the neutrophil numbers. Flow cytometry was used to sort the resident and recruited macrophages. Post-treatment with MCTR1 offered dramatic benefits in the resolution phase of LPS-induced lung injury, including decreased neutrophil numbers, reduced BAL fluid protein and albumin concentrations and reduced histological injury. In addition, the expression of the M2 markers Arg1, FIZZ1, Remlα, CD206 and Dectin-1 was increased on resident macrophages in the LPS + MCTR1 group. Resident macrophage depletion abrogated the therapeutic effects of MCTR1, and reinjection of the sorted resident macrophages into the lung decreased neutrophil numbers. Finally, treatment with MCTR1 increased STAT6 phosphorylation. The STAT6 Inhibitor AS1517499 abolished the beneficial effects of MCTR1. In conclusion, MCTR1 promotes resident M2 alveolar macrophage polarization via the STAT6 pathway to accelerate resolution of LPS-induced lung injury.