Creating an atlas of the bone microenvironment during oral inflammatory-related bone disease using single-cell profiling

Abstract

Oral inflammatory diseases such as apical periodontitis are common bacterial infectious diseases that may affect the periapical alveolar bone tissues. A protective process occurs simultaneously with the inflammatory tissue destruction, in which mesenchymal stem cells (MSCs) play a primary role. However, a systematic and precise description of the cellular and molecular composition of the microenvironment of bone affected by inflammation is lacking. In this study, we created a single cell atlas of cell populations that compose alveolar bone in healthy and inflammatory disease states. We investigated changes in expression frequency and patterns related to apical periodontitis, as well as the interactions between MSCs and immunocytes. Our results highlight an enhanced self-supporting network and osteogenic potential within MSCs during apical periodontitis-associated inflammation. MSCs not only differentiated towards osteoblast lineage cells, but also expressed higher levels of osteogenic related markers, including Sparc and Col1a1. This was confirmed by lineage tracing in transgenic mouse models and human samples from oral inflammatory-related alveolar bone lesions. In summary, the current study provides an in-depth description of the microenvironment of MSCs and immunocytes in both healthy and disease states. We also identified key apical periodontitis-associated MSC subclusters and their biomarkers, which could further our understanding of the protective process and the underlying mechanisms of oral inflammatory-related bone disease. Taken together, these results enhance our understanding of heterogeneity and cellular interactions of alveolar bone cells under pathogenic and inflammatory conditions. We provide these data as a tool for investigators not only to better appreciate the repertoire of progenitors that are stress responsive but importantly to help design new therapeutic targets to restore bone lesions caused by apical periodontitis and other inflammatory-related bone diseases.

The neutrophil–osteogenic cell axis promotes bone destruction in periodontitis

“…In addition to OSM, our scRNA-seq data showed that periodontal neutrophils highly expressed IL-1 and TNF, suggesting that neutrophils may act as an important source of osteoclastogenic cytokines in periodontal bone loss. 41,42 Since the marked accumulation of neutrophils was also reported in an apical periodontitis model, 43 the neutrophil-osteogenic cell axis may have a role in bone damage associated with endodontic infection. On the other hand, neutrophils can exert anti-inflammatory and bone-protective functions as evidenced by the fact that the neutrophil depletion delayed bone regeneration in a cranial defect model.…”

Periapical lesion-derived decellularized extracellular matrix as a potential solution for regenerative endodontics

“…Similarly, chronic apical periodontitis is an inflammation-related bone disease resulting from root canal infection, where various immune and non-immune cells interact to balance the inflammatory response and promote tissue restoration [ 28 ]. The osteogenic potential of MSCs increases in the inflammatory state of apical periodontitis [ 27 ]. The periapical lesions analyzed in this study were obtained from teeth that had completed root canal treatment and underwent periapical surgery.…”

“…Different from many reports on the use of DPSCs for pulp regeneration, and considering the difficulties in obtaining homologous MSCs for clinical application, we selected PLDSCs with multi-lineage differentiation ability, which enriches perspective for the source and subsequent application of maxillofacial related stem cells. The single-cell sequencing of apical periodontitis identified PLDSCs as four different subclusters: osteolineage, endothelial, inflammatory and neurological MSCs, indicating more advantageous in angiogenic and neural differentiation to serve as seed cells for tissue regeneration [ 27 , 38 ].…”

“…However, due to the limited availability of seed cells derived from oral and maxillofacial regions, periapical lesion-derived stem cells (PLDSCs) are being considered as a widely available source with mesenchymal stem cell-related antigens, good proliferation ability, and multi-directional differentiation potentials [ 34–37 ]. The mesenchymal stem cells (MSCs) from periapical lesions are prone to differentiate into osteoblast lineage cells under the stimulation of apical periodontitis [ 27 ]. Our research group has also discovered that PLDSCs exhibit less osteogenic/odontoblast differentiation ability compared to DPSCs, but they possess a more vital capability to secrete neurovascular factors and regulate the immune responses, making them potential candidates for tissue engineering of dental pulp [ 38 , 39 ].…”

Nlrp3 inflammasome drives regulatory T cell depletion to accelerate periapical bone erosion

“…The immunosuppression and anti‐osteoclastogenic effect of Treg cells is tightly regulated to maintain bone homeostasis in the presence of inflammation (Huang et al., 2022; Zhu et al., 2020). The human apical papilla and its resident cells from teeth with pulp necrosis and apical periodontitis could survive and retain their stemness in an inflammatory environment, therefore regulating infiltration of cellular elements of adaptive immunity (Chrepa et al., 2017; Fan et al., 2023). We observed that Nlrp3 inflammasome was activated in LPS + ATP treated stem cells from apical papilla (SCAPs), resulting in pyroptosis and release of IL‐1β and IL‐6.…”