REV-ERBα regulates cigarette smoke (CS)-induced macrophage polarization

Background: REV-ERBα (NR1D1) is a crucial clock gene that is decreased in smokers and COPD patients compared to nonsmokers. Depletion of Nr1d1 aggravated CS-induced airway epithelial inflammation. Distinct macrophage polarization phenotypes exhibit diverse functions, the disordered polarization of M1-like (pro-inflammatory) and M2-like (anti-inflammatory) phenotype plays a crucial role in CS-induced airway inflammation. However, the regulatory role of NR1D1 in CS-induced polarization of macrophages remains unclear. Methods: Bone marrow-derived macrophages (BMDM) from wild-type (WT) and Nr1d1 knockout (Nr1d1^-/-) mice were stimulated with CS extract (CSE). WT and Nr1d1^-/- mice were exposed to CS for 10 days. Cytokines related to M1 (iNOS, IL-1β, and CXCL2) and M2 phenotype (IL-10) in cells and bronchoalveolar lavage fluid (BALF) of mice were measured by RT-PCR/Western Blot and Luminex assay, respectively. Proportion of M1(CD86⁺IL-10⁻)and M2 phenotype (CD86⁻IL-10⁺) in lung homogenate (LH) was assessed by Flow cytometry. Results: We observed upregulation of both cytokines and proportion of M1 and M2 phenotype in CSE-treated WT BMDM and BALF/LH of CS-exposed WT mice (all p<0.05). Nr1d1 knockout further increased M1-related markers, but decreased M2-related marker in both in vitro and in vivo experiments (all p<0.05). After CS exposure, proportion of M2 phenotype in LH was downregulated in Nr1d1^-/- mice compared to WT mice (p<0.05), while no significant change was observed in M1-phenotype. Conclusion:Nr1d1 knockout promotes M1 macrophage polarization while inhibits M2 polarization in CS-induced airway inflammation. Targeting NR1D1 in macrophage may provide a novel therapeutic approach for CS-related airway inflammation.