Periodontitis, a chronic immuno-inflammatory disorder, is characterized by progressive destruction of the periodontal attachment apparatus, including cementum, periodontal ligament, and alveolar bone, ultimately leading to tooth exfoliation and systemic sequelae [1,2]. The pathophysiological cascade involves dysbiosis-driven immune dysregulation, disrupting bone remodeling homeostasis through imbalanced osteoclast/osteoblast activity [3]. Notably, the immune-homeostatic niche characterizing healthy periodontium transitions to a pro-inflammatory state during disease progression. This microenvironmental reprogramming impairs antimicrobial defense while promoting selective colonization by pathobionts [4]. Emerging therapeutic paradigms propose immune modulation as a synergistic strategy to enhance stem cell-mediated regenerative approaches in periodontics [5].

Central to the immunopathogenesis of periodontitis is the dynamic interplay between T helper 17 (Th17) cells and Tregs [4,6]. Th17 cells orchestrate osteolytic responses through interleukin-17 (IL-17)-mediated RANKL production, thereby accelerating osteoclastogenesis and subsequent bone resorption [7]. In contrast, Tregs exert immunomodulatory control via IL-10 and TGF-β secretion, while concomitantly regulating bone metabolism through direct cell-cell interactions [8]. Furthermore, Tregs maintain immune homeostasis by suppressing excessive inflammation and have been implicated in bone metabolism regulation [7]. This Th17/Treg axis imbalance, characterized by an increased Th17/Treg ratio, shows a strong correlation with disease severity [8]. Recent studies further indicate that reduced Treg populations contribute to periodontitis progression, providing a potential mechanistic explanation for pregnancy-associated disease exacerbation [9]. Consistent with these findings, our clinical data reveal elevated Th17 and Treg cell levels in periodontitis patients, with a significantly increased Th17/Treg ratio, highlighting the critical role of this imbalance in disease progression.

Tregs, defined by Foxp3+CD25+CD127low immunophenotype, constitute a specialized T lymphocyte subset with dual immunoregulatory and osteogenic functions [10,11]. Beyond their canonical immunosuppressive role, Tregs directly modulate bone remodeling through Wnt10b secretion and OPG/RANKL axis regulation [7,12,13]. Recent studies have expanded the understanding of Tregs in tissue repair and regeneration, including their role in bone remodeling by influencing osteoclast and osteoblast activity [13,14]. Evidence suggests that Tregs promote osteoblast differentiation while inhibiting osteoclastogenesis under conditions of impaired osteogenesis [15]. Moreover, systemic infusion of Tregs (Foxp3+) enhances bone regeneration in calvarial defect modelsby improving the biological properties of bone marrow mesenchymal stromal cells (BMMSCs) [16].

Periodontal ligament stem cells (PDLSCs) have emerged as promising candidates for periodontal remodeling due to their self-renew capacity and ability to differentiate into osteoblasts, which are required for tissue repair [17,18]. However, their osteogenic potential is heavily influenced by the local inflammatory environment and immune cell interactions [19,20]. Building on Tregs’ established role in bone remodeling, we investigated their direct impact on PDLSC-mediated osteogenesis. Previous research has shown that Tregs in the skin can promote epithelial stem cell differentiation by expressing high levels of the Notch ligand Jagged1 [21]. The Notch signaling system, a conserved mechanism for cell-to-cell communication, is crucial in regulating cell fate, including proliferation, differentiation, and apoptosis [22,23]. The function of Notch signaling in dental-related cells has been documented in recent research [[24], [25], [26], [27], [28]]. Numerous developmental processes, especially osteogenesis and ossification, have been demonstrated to depend on Notch signaling pathways, which are activated by ligands like Jagged1 [29]. Additionally, Jagged1 stimulates the osteogenic development of mesenchymal stem cells obtained from various human and murine tissues [[30], [31], [32]].

Tregs' regulatory functions in immune responses and their potential influence on bone metabolism have been previously reported [14,33]. Similar to the role of Notch signaling in stem cell differentiation, the mechanisms by which Tregs modulate osteogenic differentiation of PDLSCs have not been fully explored. In this study, we focused on the impact of Tregs on PDLSC osteogenic development and the underlying mechanisms involving the Notch signaling pathway. Our results reveal that Tregs accumulate in the periodontium of periodontitis patients and significantly enhance PDLSC osteogenesis through Notch signaling, specifically via the upregulation of Jagged1-Notch2 signaling. Inhibition of the Notch pathway reduces this osteogenic potential, highlighting the vital role of Notch signaling in Tregs-mediated osteogenesis. These findings provide a new perspective on the intricate relationship between stem cell development and immune regulation, laying the foundation for potential Treg-based therapeutic strategies for periodontal and bone tissue regeneration.