Effects of inflammation on the aged periodontium via NF-κB/FOXO3a/c-JUN signalling

Abstract

Ageing is widely recognised as a major risk factor for numerous chronic inflammatory diseases. Elevated levels of pro-inflammatory markers in older individuals have been linked to an increased risk of age-related diseases and various chronic conditions. Coinciding with other chronic diseases, periodontal disease increases in prevalence and severity with ageing. The periodontal ligament (PDL) is a key component of the periodontium, and PDL cells (PDLCs) are of critical important in the process of periodontal remodelling. However, the specific mechanisms that connect inflammation with ageing in the periodontium remain unclear. This study aims to investigate the impact of inflammation on the senescence phenotype and bone metabolism of the aged periodontium, as well as to explore the molecular mechanisms that underlie this effect. First, to investigate the effect of inflammation on the aged periodontium, we conducted an in vivo study to assess the senescence phenotype and alveolar bone loss of young and aged mice with inflammation. Inflammation was observed to induce increased senescence of PDL tissue, while the senescence phenotype was more aggravated in aged mice. Moreover, alveolar bone loss and disordered bone trabeculae were observed in both young and aged mice with inflammation, but these symptoms were more severe in aged mice. Second, we attempted to explore the mechanism responsible for the effect of inflammation on the aged periodontium. We conducted an in vitro study to investigate the osteogenic differentiation potential of aged PDLCs in response to an inflammatory challenge and examined the expression levels of nuclear factor kappa B (NF-κB) and related proteins in aged PDLCs under inflammatory conditions. Our results unveiled a notable increase in the senescence phenotype for both young and aged PDLCs after inflammatory stimulation, and this inflammation inhibited the osteogenic differentiation ability of aged PDLCs. Furthermore, in the physiological ageing process, NF-κB signalling downregulated the osteogenic differentiation of aged PDLCs by suppressing forkhead box (FOXO)3a and c-JUN. However, after exogenous inflammatory stimulation, NF-κB signalling inhibited the osteogenic differentiation of aged PDLCs by increasing FOXO3a phosphorylation and c-JUN expression. During this process, p21 had a synergistic inhibitory effect on the osteogenesis of aged PDLCs. Therefore, the NF-κB/FOXO3a/c-JUN signalling pathway was demonstrated to play an essential role in inhibiting the osteogenic differentiation of aged PDLCs under an inflammatory microenvironment and different mechanisms were observed for the intrinsic pro-inflammatory environment caused by ageing versus an exogenous inflammatory microenvironment. To verify the role of the NF-κB signalling pathway in regulating alveolar bone metabolism in the aged periodontium in the presence of inflammation, we conducted in vivo tests to examine alveolar bone and senescence phenotypes in young and aged mice treated with an NF-κB inhibitor. The results verified that inflammation enhanced bone loss in the aged periodontium by activating the NF-κB/FOXO3a/c-JUN signalling pathway. In summary, we find that inflammation aggravates senescence of the periodontium, inhibits osteogenesis, and enhances bone loss in the aged periodontium through the NF-κB/FOXO3a/c-JUN signalling pathway. These findings offer valuable insights into the underlying mechanisms of inflammation and ageing and their interactions in the periodontium.