Fluoride induced chondrocyte extracellular matrix degradation by inhibition of glycolysis by the PHD2/HIF1α signaling pathway.

Studies have shown that fluoride induces cartilage damage, however, the specific mechanism is unknown. In this study, we investigated the effect of fluoride on extracellular matrix metabolism and its molecular regulatory mechanism, using well-established experimental models SW1353 cell line and neonatal rat tibia organ culture. We found that 5 × 10-4 M fluoride reduced proteoglycan synthesis by 20%, significantly downregulated the expression levels of Aggrecan, Collagen Type II and X Alpha 1 Chain, and upregulated various matrix metalloproteinases. Based on RNA sequencing results, we found that differentially expressed genes were significantly enriched in the hypoxia inducible factor 1 (HIF1) signaling pathway, which ranked second in enrichment significance. Further studies demonstrated that fluoride significantly suppressed the expression of glycolysis-related enzymes, the oxygen consumption rate and glycolytic capacity, leading to notably reduced ATP production. Moreover, fluoride decreased both mRNA and protein level of HIF1α by half through increasing prolyl hydroxylase domain 2 expression by twice. Importantly, stabilizing HIF1α with CoCl2 effectively reversed the adverse effects of fluoride. Together, these results suggested that fluoride inhibited glycolytic activity by the PHD2/HIF1α signaling pathway, thereby further disrupting the metabolic balance of the cartilage extracellular matrix.