Circular RNA ACTR2 activates M2 polarization of macrophages through activating Yes-associated protein signalling and contributes to renal fibrosis

Macrophages, associated with their heterogenous and dynamic polarization status, actively shape the development of renal fibrosis (RF). In this study, we revealed the significance of a signalling axis, circular RNA ACTR2 (circACTR2)/miR-200c/Yes-associated protein (YAP), in regulating macrophage polarization and the development of RF. A unilateral urethral obstruction (UUO)-induced RF model was established in vivo. In vitro, interferon-γ (IFNγ) and interleukin (IL)-4 were applied to induce M1 and M2 polarization, respectively. The abundance of M1 and M2 macrophages were examined by immunofluorescence (IF) or flow cytrometry on markers specific for each subtype. Expressions of circACTR2, miR-200c and YAP were measured by quantitative real-time-polymerase chain reaction and/or Western blotting. Interactions between circACTR2, miR-200c and YAP were examined by combining luciferase assay, RNA immunoprecipitation and IF. Impact of targeting circACTR2 on RF and macrophage polarization was also examined in vivo. UUO-induced RF was associated with increased M1 and M2 macrophages, up-regulations of circACTR2 and YAP and the down-regulation of miR-200c in the obstructed kidney. circACTR2 was essential for IL-4-induced M2 polarization, but not IFNγ-induced M1 polarization. This activity of circACTR2 was mediated by sponging miR-200c and activating the downstream YAP signalling. In vivo, knocking down circACTR2 boosted miR-200c expression, reduced YAP level, lowered M2 macrophages in obstructed kidney and ameliorated UUO-induced RF. circACTR2, by targeting and sponging miR-200c, activates YAP signalling, stimulates M2 macrophage polarization and promotes the development of RF. Therefore, targeting circACTR2 may benefit the treatment of RF.