Rev-erb attenuates refractory periapical periodontitis via M1 polarization: An in vitro and in vivo study

Aim: Rev-erb alpha has been reported to regulate the healing of inflammatory lesions through its effect on the immune system in a variety of inflammatory disease. Moreover, the balance of macrophages polarization plays a crucial role in immune response and inflammatory progression. However, in refractory periapical periodontitis (RAP), the role of Rev-erb alpha in inflammatory response and bone resorption by regulating macrophage polarization remains unclarified. The aims of the present study were to investigate the expression of Rev-erb alpha in experimental RAP and to explore the relationship between Rev-erb alpha and macrophage polarization through the application of its pharmacological agonist SR9009 into the in vivo and in vitro experiments. Methodology: Enterococcus faecalis-induced RAP models were established in SD rats. Histological staining and micro-computed tomography scanning were used to evaluate osteoclastogenesis and alveolar bone resorption. The expression of Rev-erb alpha and macrophage polarization were detected in the periapical tissues from rats by immunofluorescence, flow cytometry, and western blots. Furthermore, immunohistochemical staining and enzyme-linked immunosorbent assay were performed to explore the relationship between Rev-erb alpha and inflammatory cytokines related to macrophage polarization. Result: Compared to healthy periapical tissue, the expression of Rev-erb alpha was significantly down-regulated in macrophages from inflammatory periapical area, especially in Enterococcus faecalis-induced periapical lesions, with obvious type-1 macrophage (M1)-like dominance and the production of pro-inflammatory cytokines. In addition, Rev-erb alpha activation by SR9009 could induce type-2 macrophage (M2)-like polarization in periapical tissue and THP1 cell line, followed by increased secretion of anti-inflammatory cytokines IL-10 and TGF-beta. Furthermore, intracanal application of SR9009 reduced the lesion size and promoted the repair of RAP by decreasing the number of osteoclasts and enhancing the formation of mineralized tissue in periapical inflammatory lesions. Conclusions: Rev-erb alpha played an essential role in the pathogenesis of RAP through its effect on macrophage polarization. Targeting Rev-erb alpha might be a promising and prospective therapy method for the prevention and management of RAP.