Zebrafish larvae as a model for investigating dual effects of fluoride on bone development

Long-term excessive ingestion of fluoride is a severe public health threat globally. Skeletal fluorosis, a significant manifestation of prolonged fluoride exposure, is characterized by aberrant bone structure and alterations in bone function. However, there is currently a shortage of an efficient, fast, and easy-to-operate biological model for application in the field of fluorosis research. Zebrafish larvae, with human - like skeletal traits, high reproduction, rapid development, and transparency, are commonly used in bone disease studies. This study evaluates the potential of zebrafish larvae as a novel model for fluoride-induced bone impairment. Results showed dose-dependent differences in cranial and spinal bone mineralization in zebrafish larvae exposed to sodium fluoride (NaF). The detection results of bone formation-related indicators indicated a considerable increase in alkaline phosphatase (ALP) activity in zebrafish larvae at doses of 0.5 and 1 mg/L. Simultaneously, the expression of critical bone formation proteins (BMP2, and β-catenin) was elevated in the 1 and 4 mg/L groups, which is largely consistent with the results of cranial bone mineralization. Fluoride - exposed zebrafish also showed abnormal bone metabolism markers. The total phosphorus (TP) content in the zebrafish larvae of the 100 mg/L group was markedly reduced. The total calcium (TCa) content in the zebrafish of the NaF group zebrafish was slightly decreased, although the tartrate-resistant acid phosphatase (StrACP) activity increased. In conclusion, different fluoride doses cause osteoporosis and osteosclerosis in zebrafish larvae, linked to enhanced osteogenic and osteoclastic activities and abnormal key bone - forming protein expression.