Lin28B Regulates Angiotensin II-Mediated Let-7c/miR-99a MicroRNA Formation Consequently Affecting Macrophage Polarization and Allergic Inflammation.

Angiotensin-II (Ang-II) receptor plays a role in allergic airway inflammation; however, the underlying mechanism and role of macrophages need better understanding. In the present study, angiotensin-II infusion (1 μg/kg/min) in ovalbumin-induced airway inflammation mice model significantly decreased immune cell infiltration, goblet cell hyperplasia, and eosinophil numbers in lungs. Ang-II infusion increased M1 and decreased M2 macrophage population in bronchoalveolar lavage fluid and respective macrophage markers in lung macrophages. Similarly, in vitro Ang-II treatment in murine bone marrow-derived macrophages (BMDMs) induced M1 and reduced M2 macrophage phenotype with enhanced bactericidal activity. Mechanistically, Ang-II inhibits Let-7c and miR-99a expression in BMDMs and in vivo as well. Lentiviral overexpression of Let-7c and miR-99a miRNAs in BMDMs abrogated Ang-II-induced M1 phenotype activation and promoted M2 phenotype, which is governed by targeting TNFα by miR-99a. In lung macrophages, ovalbumin-induced TNFα inhibition was rescued after Ang-II treatment. In BMDMs, knockdown of TNFα abrogated Ang-II-induced M2 to M1 macrophage phenotype switch and associated bactericidal activity. Ang-II affects mature miRNA formation by enhancing Lin28B levels in macrophages in vivo and in vitro. Furthermore, Lin28B knockdown prevented Ang-II-mediated inhibition of mature Let-7c/miR-99a miRNA formation, M2 to M1 macrophage phenotype switch, and increased bactericidal activity. Therefore, present study suggests a role of Lin28B in Ang-II-induced Let-7c/miR-99a miRNA formation that consequently affects TNFα production, M1 phenotype activation, and allergic airway inflammation. Graphical Abstract Ovalbumin inhibits LIN28B expression thereby fails to inhibit premature to mature Let-7c/miR-99a miRNA formation. Mature miR-99a miRNA that inhibits TNFα consequently promotes M2 polarization and allergic airway inflammation. While Ang-II induces Lin28B, which inhibits Let-7c/miR-99a miRNA processing and mature miRNA formation, this results in increased TNFα levels that lead to M1 polarization and allergic airway inflammation inhibition.