Long non-coding RNA NRIR inhibits osteogenesis in peri-implantitis by promoting NLRP3 inflammasome-mediated macrophage pyroptosis.

BACKGROUND

Peri-implantitis is an inflammatory bone disease that seriously affects the health of dental implants. Pyroptosis plays an important role in peri-implantitis and inhibition of pyroptosis may point out a new direction for treating the disease. The long non-coding RNA Negative Regulator of Interferon Response (lncRNA NRIR) is closely related to peri-implantitis and may be involved in the process of pyroptosis. The aim of this study was to explore the regulatory mechanism of NRIR in peri-implantitis.

METHODS

The expression levels of NRIR and its target gene Cytidine Monophosphate Kinase 2 (CMPK2) in the gingiva surrounding infected implants were explored using bioinformatics analysis. Lipopolysaccharide (LPS)-stimulated macrophage pyroptosis model and a rat model of LPS-induced peri-implantitis were constructed. We used small interfering RNA (siRNA) and plasmids to regulate the expression of NRIR and CMPK2 in macrophages. We used various ways to evaluate inflammation, pyroptosis, osteogenic differentiation, including RT-qPCR, Western blotting, ELISA, Immunofluorescence staining, ALP activity, ARS staining, and Immunohistochemical analysis.

RESULTS

Initially, we used bioinformatics method to identify high expression of NRIR and CMPK2 in the gingiva surrounding infected implants. Both the knockdown of NRIR and CMPK2 could markedly suppress the expression of NLRP3 inflammasome and the release of interleukin-1β (IL-1β) in LPS-stimulated THP-1-derived macrophages. Meanwhile, upregulation of CMPK2 reversed the negative effects of downregulation of NRIR on macrophage pyroptosis. Functionally, NRIR knockdown in macrophages promoted osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Notably, we identified that IL-1β protein could reverse this trend. Mechanistically, NRIR regulated NLRP3 inflammasome-mediated pyroptosis of macrophages through the NF-κB pathway. Furthermore, the in vivo experiments demonstrated that silencing NRIR inhibited the expression of NLRP3 inflammasome and IL-1β, but promoted the expression of osteogenic differentiation related factors in tissue surrounding the implants.

CONCLUSION

This study demonstrated that NRIR played a crucial role in the crosstalk between macrophage pyroptosis and BMSCs osteogenic differentiation, thus providing a possible therapeutic target against inflammatory bone disease including peri-implantitis.