Integrative multi-omics and causal inference reveal periodontal ligament cell-macrophage crosstalk under orthodontic force.

BACKGROUND: Orthodontic tooth movement requires synchronized mechanoadaptive and osteoimmune interactions, yet molecular pathways linking mechanical forces to immune-mediated bone remodeling remain incompletely characterized. This study aimed to elucidate molecular drivers and dissect cell crosstalk under orthodontic force, with a focus on their immunoregulatory consequences. METHODS: This study combined in vitro compressive loading of human periodontal ligament (PDL) cells with transcriptomic/proteomic profiling, and in vivo single-cell RNA sequencing of alveolar bone macrophages from murine orthodontic models. Mendelian randomization (MR) analysis leveraged genetic instruments from transcriptome-wide (n = 31,684), proteome-wide (n = 35,559), and immune trait genome-wide association studies (n = 3,757). The two-phase framework first identified mechanoresponsive molecular signatures across omics layers, then established causal links to immune cell dynamics through MR. RESULTS: Transcriptomic and proteomic analyses of PDL cells under compressive force revealed LBH upregulation and TGF-β pathway activation and collagen disassembly, evidenced by COL1A1/COL2A1 downregulation. Single-cell RNA sequencing identified Cd40+ macrophages enriched in IL-17 signaling. MR causally linked PDL-derived molecular changes to CD40+ monocyte dynamics: LBH (OR = 0.860, P = 0.019) reduced CD40+ monocyte prevalence, while COL2A1 (OR = 1.115-1.133, P = 0.010) elevated CD40 expression in monocytes. CONCLUSIONS: Orthodontic forces induce transcriptional reprogramming and proteomic remodeling in PDL cells, which drive CD40 signaling in monocytes through mechano-immunological coupling. These adaptations activate Cd40+ macrophages, ultimately redefining orthodontic bone remodeling as a mechano-driven stromal-immune partnership essential for tooth movement.