N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-Q) induces osteoporosis by a mechanism involving CX43-mediated mitochondrial autophagy dysfunction in bone marrow mesenchymal stem cells

As an emerging environmental contaminant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q) poses a potential threat to public health. However, the potential link between 6PPD-Q exposure and bone health remains largely unexplored. This study aims to systematically investigate the toxic effects of 6PPD-Q on bone metabolism and elucidate the underlying mechanisms by integrating transcriptomic sequencing, network toxicology, single-cell RNA, Molecular docking, molecular dynamics with both in vivo and in vitro experiments. Integrative analysis converged on mitophagy as a central mechanism in 6PPD-Q-induced osteoporosis, with single-cell sequencing identifying bone marrow-derived mesenchymal stem cells (BMSCs) as the key cell type and revealing CX43, MMP2, PDGFRB, and FYN as the principal targets. Molecular docking and MD simulations confirmed the targeted binding of 6PPD-Q to CX43. RNA-seq analysis of rat tibiae validated the differential expression of CX43 and the critical role of mitophagy. Both in vivo and in vitro experiments demonstrated that 6PPD-Q-induced bone loss was associated with the downregulation of CX43 and concomitant mitophagy dysregulation. In conclusion, this study elucidates that 6PPD-Q induces bone loss was associated with the downregulation of CX43 and concomitant mitophagy dysregulation. Our work establishes a comprehensive mechanistic framework for 6PPD-Q-induced bone damage and offers novel insights for future research into its bone toxicity. The 1 or 10 mg/kg dose used in this study, although higher than the typical environmental exposure level, is consistent with the effects observed in cadmium exposure and is close to the 8 mg/kg dose used in studies on mouse bone toxicity. Additionally, the 5 ng/mL concentration of 6PPD-Q used in the in vitro experiments is comparable to the concentration detected in freshwater, indicating its environmental relevance.