CDKN1A Mediates Regulated Cell Death in Osteoblasts and Exacerbates Periapical Bone Destruction in Apical Periodontitis

BACKGROUND: Apical periodontitis is a chronic inflammatory bone-destructive disease driven by intracanal microbial infection and host immune-inflammatory responses. Periapical bone destruction arises not only from excessive osteoclastic resorption but also from osteoblast dysfunction and dysregulated regulated cell death (RCD). CDKN1A (p21) is a canonical cell-cycle regulator implicated in multiple RCD programs, yet its role in osteoblast injury and apical periodontitis pathogenesis remains undefined. METHODS: Single-cell RNA sequencing (ScRNA) was used to profile osteoblast subpopulations and RCD-related gene expression in human periapical lesions. Porphyromonas gingivalis infection models were established in MG63 and MC3T3-E1 osteoblasts, and DIA proteomics and western blot were used to evaluate RCD-related proteins. The effects of CDKN1A, a disease-associated hub gene screened out in DIA proteomics, on RCD-related proteins were further examined by western blot. Lentiviral silencing and AAV-mediated overexpression were performed in vitro and in rat apical periodontitis models. Bone destruction, RCD activation and osteogenic capacity were assessed by micro-CT, histomorphology and multiplex immunofluorescence. RESULTS: ScRNA data of apical periodontitis showed that osteoblasts in apical lesions exhibited enhanced apoptosis and pyroptosis and reduced ferroptosis. Single-bacteria P. gingivalis infection markedly upregulated CDKN1A, which promoted osteoblast apoptosis and pyroptosis while suppressing necroptosis and ferroptosis. In vivo, CDKN1A expression increased with disease progression and was negatively correlated with the osteogenic marker OPN. CDKN1A overexpression aggravated bone destruction, whereas its knockdown significantly attenuated bone loss and restored osteogenic activity. CONCLUSION: CDKN1A acts as a critical regulator that mediates RCD of osteoblasts, impairs osteogenesis and exacerbates periapical bone destruction in apical periodontitis. Targeting CDKN1A-mediated RCD represents a promising therapeutic strategy to limit bone destruction and promote repair in apical periodontitis.