α7nAChR Prevents Premature Cervical Ripening by Inducing M2 Macrophage Polarization and Myofibroblast Differentiation

Clinical treatment of spontaneous preterm birth (sPTB) is usually dependent on drugs that inhibit uterine contractions. Such therapy is only effective in the short-term; inhibition of premature cervical maturation may represent a more effective approach to the prevention of sPTB. Cervical remodeling in sPTB is associated with invasion of macrophages, which produce proinflammatory cytokines. Activation of the alpha-7 nicotinic acetylcholine receptor (α7nAChR) alleviates the inflammatory response and prevents preterm labor, but the underlying mechanisms remain unclear. In our mouse model of lipopolysaccharide (LPS) induced preterm birth, α7nAChR expression on cervical macrophages was decreased, the number of M1 cervical macrophages was increased, and cervical collagen content was decreased compared to normal pregnant controls. Activation of α7nAchR by nicotine increased polarization of cervical macrophages toward the anti-inflammatory M2 phenotype, possibly by suppressing activation of the MAP kinases JNK and ERK1/2 and nuclear translocation of NF-κB and rescuing the inhibited JAK2/STAT3 and PI3K/AKT pathways. α7nAchR activation also maintained components of the cervical extracellular matrix, including collagen and α-smooth muscle actin; these actions were associated with upregulation of the TGF-β1/Smad3 pathway and myofibroblast differentiation. The effects of nicotine were reversed by the α7nAChR antagonist α-BGT. Findings from this study suggest that upregulating α7nAChR activity in macrophages strengthens crosstalk between macrophages and fibroblasts, and inhibits premature cervical ripening during preterm labor. Funding Statement: This study was supported by the National Natural Science Foundation of China (81971417, 81901568 and 81871181), the Guangdong Health and Family Planning Commission Project (A2017332), the Hospital fund project from Guangzhou Women and Children’s Medical Center (Pre-NSFC-2016-001), and the Guangzhou Science and Technology Project (2016A020218001). Declaration of Interests: The authors declare that they have no conflicts of interest. Ethics Approval Statement: This study was approved by the Ethics Committee of the Guangzhou Women and Children Medical Center (No. 2018041701 and No. 201922200), and all included patients provided written informed consent. All animal protocols were approved by the Committee on the Ethics of Animal Experiments of Guangzhou Medical University (Permit Number: 2012–50).