Staphylococcus aureus osteomyelitis drives progressive bone destruction through dysregulated osteoblast–osteoclast crosstalk, yet the role of exosome-mediated circular RNA (circRNA) communication in this process remains poorly understood. This study aimed to determine whether exosomal circRNAs derived from S. aureus-infected osteoblasts orchestrate osteoclast-mediated bone resorption. Exosomes were isolated from hFOB1.19 osteoblasts with or without S. aureus infection, characterized by transmission electron microscopy, nanoparticle tracking analysis, and Western blotting, and their circRNA profiles were screened by RNA sequencing. A murine femoral osteomyelitis model was established via intramedullary S. aureus inoculation followed by tail-vein exosome injection, with bone microarchitecture and osteoclastogenesis assessed by micro-CT, histology, TRAP/ALP staining, qPCR, and Western blotting. The circ_0001843/miR-369-5p/TAFA5 axis was validated by dual-luciferase reporter assays. S. aureus infection markedly upregulated exosomal circ_0001843. In vivo, exosomes from infected osteoblasts aggravated bone destruction, evidenced by decreased BV/TV, increased trabecular separation, enhanced osteoclast activity, and suppressed osteogenic markers. In vitro, circ_0001843 knockdown attenuated RANKL-induced osteoclast differentiation while promoting osteoblast proliferation and mineralization; these protective effects were reversed by exosomes from infected osteoblasts or miR-369-5p inhibition. Mechanistically, circ_0001843 sponged miR-369-5p to derepress TAFA5, thereby disrupting bone remodeling homeostasis. These findings identify exosomal circ_0001843 as a novel mediator of infection-induced bone loss via the miR-369-5p/TAFA5 axis, highlighting a potential therapeutic target for osteomyelitis-associated bone destruction.
The immune response is essential in shaping bone healing outcomes and is of particular interest in mandible fractures, as opposed to other fractures, because of the presence of teeth that are colonised by a multitude of microbes that can cause infection or complicate healing. This study investigated the peripheral blood cell transcriptome during mandibular fracture healing phases with particular focus on immune-related indicators. Blood samples from mandibular fracture patients who had normal healing were collected at the time of injury, then 2 weeks and 6 weeks following the injury, corresponding to the inflammation, repair, and remodelling phases of bone healing, respectively. RNA sequencing was performed for blood cells and analysed using the Ingenuity Pathway Analysis (IPA) software. Data validation was conducted using ELISA for soluble serum factors and blood cell counting using Sysmex. The results indicated distinctive systemic changes between the three healing phases. A significant increase in activity and counts of blood neutrophils and monocytes was noted during the inflammatory and repair phases compared to the remodelling phase. In contrast, a prominent activity and increased quantity of blood lymphocytes were detected in the remodelling phase. Furthermore, increased serum levels and activated signalling of interleukin 10 (IL10) were detected, mainly during the inflammation and repair phases. Interestingly, blood cells were found to express high levels of osteogenesis-related markers during the repair phase, with significantly increased serum levels of Insulin-like growth factor 2 (IGF2). In conclusion, systemic blood cell transcriptomic profiling showed a shift from predominantly innate toward adaptive immune response during mandible healing, with serum IL10 and IGF2 levels indicating the resolution of inflammation and the start of osteogenic repair. Therefore, peripheral blood cells and serum factors could be a promising source of non-invasive biomarkers for monitoring healing trajectories of mandible injuries.
Patients with Alzheimer's disease (AD) often exhibit abnormal bone loss alongside cognitive impairment. However, the mechanisms linking these two conditions remain insufficiently understood. We first employed amyloid precursor protein/presenilin 1 (APP/PS1) mice as the experimental model and demonstrated that they exhibit significant bone loss concurrent with cognitive impairment. Subsequently, we analyzed public datasets for AD and osteoporosis (OP) and identified CXC chemokine ligand 16 (CXCL16) as a shared hub gene between the two diseases. Transcriptomic sequencing further showed increased CXCL16 expression in the femoral tissue of APP/PS1 mice. Immunoblot analysis of brain and bone tissues, together with serum enzyme-linked immunosorbent assay (ELISA), verified the systemic elevation of CXCL16. These findings suggest that CXCL16 may link cognitive impairment with bone loss in APP/PS1 mice. In vitro experiments showed that CXCL16 did not directly affect the differentiation of bone marrow mesenchymal stem cells or bone marrow-derived macrophages. Instead, CXCL16 acted through neutrophils by promoting their migration and potentiating PMA-stimulated neutrophil extracellular trap (NET) formation. Conditioned medium from NET-producing neutrophils inhibited osteogenic differentiation and promoted osteoclastogenesis. In APP/PS1 mice, antagonism of CXCR6, the cognate receptor for CXCL16, with ML339 improved trabecular bone microarchitecture and osteogenic activity and alleviated cognitive impairment. Degradation of NETs with deoxyribonuclease I (DNase I) produced similar effects. Collectively, these results implicate CXCL16-associated enhancement of NET formation in AD-related skeletal deterioration and highlight the CXCL16–NETs pathway as a possible intervention target for maintaining bone homeostasis.
