Single-cell RNA sequencing reveals collagen interactions between detached osteoclasts and activated fibroblasts in granulation tissue surrounding sequestra in medication-related osteonecrosis of the jaw

Abstract Objectives Medication-related osteonecrosis of the jaw (MRONJ) is a rare but serious complication of anti-resorptive agents used for osteoporosis and bone metastasis. As the global population ages, the number of patients with MRONJ continues to rise. Resorptive osteoclasts firmly attached to bone surfaces cannot be detected using single-cell RNA-Seq (scRNA-Seq); however, we hypothesized that multinucleated giant and detached osteoclasts (DetOCs) can be detected by this method. This study aimed to characterize DetOCs with scRNA-seq. Materials and Methods scRNA-Seq and immunohistochemistry staining was performed on granulation tissues surrounding sequestra from four patients with MRONJ and radicular cysts, a common odontogenic infectious disease with normal bone metabolism. Results scRNA-Seq and immunohistochemistry staining revealed that DetOCs were detected exclusively in the granulation tissues of MRONJ. These DetOCs expressed well-known osteoclast markers as well as COL27A1 . Subcluster analysis revealed that SPP1 + TREM2 + macrophages differentiated into DetOCs and expressed several types of collagens. Immunostaining confirmed the expression of COL27A1 not only in DetOCs in MRONJ but also in osteoclasts in mandibular cancer. CellChat analysis revealed interactions mediated by collagen signaling pathways between DetOCs, myeloid cells, and activated fibroblasts. Conclusions We successfully characterized DetOCs and identified a distinctive microenvironment involving DetOCs and activated fibroblasts in the granulation tissues surrounding sequestra in MRONJ. Clinical Relevance Identification of DetOCs and their unique interaction with activated fibroblasts in MRONJ lesions provides novel insight into the pathophysiology of sequestrum formation, suggesting potential therapeutic targets to ameliorate MRONJ.