The role of IL-17A in the immune microenvironment and bone homeostasis in Porphyromonas gingivalis-induced periodontitis

Abstract

Periodontitis, a widespread chronic inflammatory disease, stems from an imbalance between the oral microbiota and immune responses. Porphyromonas gingivalis (P. gingivalis) is a notable pathogen contributing to its onset. The cytokine interleukin (IL)-17A plays a pivotal role in host defence against microbial organisms and osteo-immunomodulation. Nonetheless, the specific effects of IL-17A on bone remodelling and host–microbe dynamics and the interplay of IL-17A with the complex osteo-immunomodulation network during the progression and recovery phases of live P. gingivalis-induced periodontitis remain inadequately elucidated. Three periodontitis models were established using silk ligature infiltrated with or without heat-killed P. gingivalis (ATCC 33277), or with live P. gingivalis on the bilateral upper molars of wild-type (WT) and IL-17A knockout (KO) mice for 14 days. After ligature removal and periodontal treatment, recovery was monitored for 14 days. The alveolar bone mass was assessed using micron-scale computed tomography. The maxilla specimens underwent staining and real-time quantitative polymerase chain reaction analysis. The oral microbiota was profiled through 16S rRNA sequencing. Subsequently, single-cell RNA sequencing was used for further analysis. Gene set variation analysis and pathway enrichment analysis were conducted on differentially expressed genes and pathway activities. Furthermore, Monocle3 was used for pseudotime analysis, while SCENIC analyzed gene regulatory networks in osteoclasts. CellChat analysis explored osteoclastogenesis involvement in the inflamed periodontal microenvironment. First, IL-17A deficiency exacerbated bone resorption and impaired the recruitment of leukocytes in live P. gingivalis-induced periodontitis. Oral microbiota changes were observed, with the KO mice showing more Proteobacteria and fewer Firmicutes. Excessive P. gingivalis was observed in the KO mice. Second, the analysis revealed six primary cell clusters and 11 distinct immune cell subgroups, with alterations in the abundance of neutrophils, B cells, macrophages, and T cells. Notably, IL-17A was linked to increased neutrophil subclusters, coupled with decreased B cells, dendritic cells, myeloid progenitor cells, natural killer cells, and mast cells. In the case of neutrophils, the KO mice with periodontitis had enhanced angiogenesis, tissue damage, cell proliferation, Notch signalling, and epithelial–mesenchymal transition. The WT mice with periodontitis had enhanced IL-6/JAK/STAT3 signalling and a stronger interferon-alpha response. Furthermore, IL-17A suppressed osteoclast differentiation mediated by CD3+ T cells and osteoblasts by downregulating the RANKL pathway in P. gingivalis-induced periodontitis, with an increased expression of NFATc1 and CTSK in osteoclasts. Our findings indicate a potential association of IL-17A with the progression and recovery phases of live P. gingivalis-induced periodontitis. This association might involve alterations in immune cell composition and function, modulation of inflammatory mediator expression, potential effects on the oral microbiota, and possible contributions to the maintenance of alveolar bone homeostasis. Our in-depth analysis of the interplay between immune and bone cells provides insights into the osteo-immunomodulation network in the pathogenesis of live P. gingivalis-induced periodontitis. These insights provide important considerations for the future clinical use of IL-17A inhibitors in the treatment of periodontitis. In designing future therapeutic strategies for periodontitis resulting from P. gingivalis infection, it might be beneficial to consider enhancing immune cell regulatory capabilities by controlling the IL-17A expression to a certain extent.