Myeloid integrin α9β1 deficiency protects alveolar bone by remodeling the immune microenvironment of periodontitis

Periodontitis is a chronic inflammatory disease initiated by microbial infection that can lead to periodontal tissue damage and alveolar bone resorption. Macrophages contribute to the regulation of periodontal inflammation and local tissue homeostasis, but the role of integrin α9β1 in these processes remains unclear. Here, we combined analysis of human gingival single-cell transcriptomic data, a mouse model of myeloid cell-specific conditional Itga9 deletion, in vitro experiments with bone marrow-derived macrophages (BMMs), and conditioned-medium experiments in gingival fibroblasts to investigate how α9β1 affects the immune microenvironment and bone destruction in periodontitis. ITGA9 was highly expressed in human gingival macrophages and was further upregulated in periodontitis. Itga9 deletion altered the basal transcriptional state of BMMs and their response to Porphyromonas gingivalis (Pg), with reduced TNF production, downregulation of inflammation-related gene sets, and lower AKT and S6 phosphorylation following Pg stimulation. In vivo, myeloid Itga9 deletion reduced periodontal tissue damage and alveolar bone loss and was accompanied by changes in local immune cell composition and fibroblast-associated communication networks. Gene sets related to skeletal development, ossification, and extracellular matrix (ECM)-receptor interactions were positively enriched in fibroblasts. Further in vitro experiments showed that conditioned medium from Pg-stimulated KO BMMs was less inhibitory to gingival fibroblast mineralization than that from Pg-stimulated Het BMMs, as reflected by higher expression of mineralization-related genes, greater alkaline phosphatase (ALP) activity, and increased mineralized nodule formation. These findings suggest that myeloid integrin α9β1 contributes to the regulation of immune and stromal cell functions in periodontitis and that targeting this receptor may help reduce inflammation-associated bone destruction and support the mineralization potential of gingival fibroblasts.