NLRC5 modulates bone metabolism and plays a role in periodontitis.

INTRODUCTION: NOD-like receptor C5 (NLRC5) plays a significant role in the immune system, and is one of the largest members of the pattern recognition receptor family. Previous studies have found that NLRC5 might be involved in the regulation of various diseases, such as fibrotic diseases and cancers; however, its effect on bone metabolism-related diseases has not been reported. METHODS: Skeletons of Nlrc5-/- mice generated by CRISPR/Cas9 and wild-type (WT) mice were compared using X-ray, micro-computed tomography, double labeling, and histological examination. Tartrate-resistant acid phosphatase and pit-absorption assays were performed to evaluate the effect of NLRC5 on osteoclasts differentiation and osteoclastic capacity. The influence of NLRC5 on osteoblasts differentiation and bone formation were studied using alkaline phosphatase and alizarin red staining, respectively. Experimental periodontitis was induced by Porphyromonas gingivalis infection and ligature to investigate the role of NLRC5 in inflammatory periodontal bone loss. RESULTS: Adenovirus-mediated NLRC5 overexpression in human bone marrow mesenchymal stem cells regulated osteogenesis positively. The femoral osteogenesis ability was significantly weakened in Nlrc5-/- mice. Histology showed that the area of the femoral trabeculae in the Nlrc5-/- mice was less than that in the WT mice, and radiology suggested that the Nlrc5-/- mice had fewer trabeculae and a thinner bone cortex than those of the WT mice. Nlrc5 knockout decreased osteoblast mineralization and increased osteoclastogenesis in vitro. NLRC5 was downregulated in periodontitis and P. gingivalis infection. In the experimental periodontitis model, the alveolar bone loss, inflammatory cell infiltration, and inflammatory cytokines secretion (interleukin [IL]-1ß, IL-6, and tumor necrosis factor alpha [TNF-α]) in the Nlrc5-/- mice were significantly enhanced compared to WT mice. CONCLUSION: We verified a novel role of NLRC5 in bone metabolism by regulating both osteoclasts activity and osteoblasts activity. Our results revealed a protective effect of NLRC5 against periodontal inflammation and alveolar bone destruction. NLRC5 could be a novel treatment target to prevent periodontal bone destruction.