Periodontal ligament cells regulate macrophage polarization via CCL7/CCR1 signaling

Orthodontically induced root resorption (OIRR), a common complication of orthodontic treatment exacerbated by excessive force application, is linked to pro-inflammatory M1 macrophage polarization. This study investigates whether periodontal ligament cells (PDLCs) under heavy compression force regulate macrophage polarization via the CCL7/CCR1 axis to exacerbate OIRR. In the animal experiment, male Wistar rats were subjected to heavy orthodontic force to establish the orthodontic tooth movement model, with the inhibitor group receiving CCR1 antagonist BX471. Histological and immunohistochemical analyses were conducted to assess root resorption and RAW 264.7 polarization in vivo. In the in vitro cell culture study, human PDLCs subjected to heavy compression force were analyzed via RNA-seq, RT-PCR, and Western blot for CCL7 and inflammatory markers. Conditioned media from force-loaded hPDLCs were applied to RAW 264.7 cells, with and without CCR1 inhibition. As a result, heavy compression force significantly increased CCL7 expression in hPDLCs, promoting M1 polarization (TNF-α, iNOS) and inhibiting M2 polarization (Arg-1). CCR1 inhibition reversed this imbalance, restoring the M1/M2 ratio. In vivo, BX471 treatment attenuated root resorption and macrophage polarization. The CCL7/CCR1 signaling pathway mediates the interaction between PDLCs and macrophages, promoting M1 polarization and OIRR under orthodontic force. Targeting CCL7/CCR1 may offer a promising therapeutic approach to mitigate OIRR during orthodontic treatment.