NSUN2 methylates IRF4 to affect the capacity of macrophages attached to titanium implant on osteogenic differentiation of PDLSCs and angiogenesis of HUVECs in vitro

We aimed to investigate the effect and underlying mechanism of titanium (Ti) implant on the polarization of macrophages and subsequent effects on the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) and angiogenesis of human umbilical vein endothelial cells (HUVECs) affected by macrophages. Firstly, the regulatory effect of Ti implant on macrophage polarization was investigated. Levels of M1 polarization markers and M2 polarization markers in macrophages were evaluated by immunofluorescence staining method and qPCR analysis. The osteogenic differentiation capacity of PDLSCs cultured with supernatants of macrophages of each group was evaluated by the Alizarin Red S (ARS) staining method and qPCR. Angiogenesis related genes were also evaluated in HUVECs cultured in supernatants of macrophages. To explore whether RNA m5C modification can modulate the effects of Ti implant on macrophage regulation of osteogenic differentiation and angiogenesis, we analyzed the main genes related to m5C in macrophages using RNA m5C dot blotting and qPCR methods. The interaction between NSUN2 and IRF4 was verified by m5C-RIP, RIP, and double-luciferase gene report experiments. Macrophages were activated as M1 macrophages under the interference of LPS, and macrophages attached to Ti implants were more easily activated as M2 macrophages under the action of LPS. Macrophages activated by Ti implant enhanced osteogenic differentiation of PDLSCs and angiogenesis of HUVECs. NSUN2 level was up-regulated in macrophages treated with LPS and was down-regulated by Ti implant. Over-expression of NSUN2 attenuated the effect of Ti implant on M1 polarization promotion of macrophages and enhanced the M2 polarization promotion of macrophages. Up-regulation of NSUN2 weakened the effects of Ti implant on promotion the capacity of macrophages on osteogenic differentiation of PDLSCs and angiogenesis of HUVECs. The KEGG analysis suggested that IRF4 was enriched in several inflammatory signaling pathways. Moreover, NSUN2 methylates IRF4 to affect the capacity of macrophages on osteogenic differentiation of PDLSCs and angiogenesis of HUVECs. Taken together, macrophages of M1 type can be stimulated by Ti implants in vitro, promoting osteogenic differentiation of PDLSCs and angiogenesis in HUVECs through NSUN2-mediated methylation of IRF4.