Objective: This study was designed to observe the expression of important hedgehog (Hh) signal factors in the bone tissue of rats with chronic fluorosis and cultured osteoblasts in order to investigate the role and significance of the Hh signal in fluoride-induced bone injury.
Methods: Healthy Sprague-Dawley (SD) rats were randomly divided into four groups: the control group, the fluorosis group (F Group), the fluoride + blocker group (F + Cycl group: rats were treated with fluoride + cyclopamine), and the fluoride + blocker control group (F + DMSO group). After 6 months of intervention, the urinary fluoride content of rats in each group was detected. The primary osteoblasts of rats were selected for cell experiment, and the experiment was carried out after the cells were passaged from the second to the fourth generation.
Results: The proliferation rate of primary rat osteoblasts presented time-affected and dose-affected relationships in a short time under treatment with a low dose of sodium fluoride (NaF), but the proliferation of osteoblasts was inhibited by long-term and high-dose NaF exposure. In the F group, the alkaline phosphatase (ALP) activity of osteoblasts increased gradually. The ALP activity was lower in the F + Cycl group than in the F group, and there was no significant difference between the F + DMSO group and F group. With the increase in fluoride exposure, the expression of Hh signal factors and osteogenic-related factor proteins increased gradually. The expressions of Indian hedgehog (Ihh), smoothened (Smo), Glioma-associated oncogene homolog (Gli) 2, and Runt-related transcription factor 2 (Runx2)in the F + Cycl group increased with the dose of fluoride but they were significantly inhibited compared with the F group. Compared with the control group, the content of urinary fluoride in the F group was significantly higher (P < 0.05), but there was no significant change in urinary fluoride content in the F + Cycl group and the F + DMSO group. Compared with the control group, the serum bone alkaline phosphatase (BALP) contents of rats in the other groups increased after 6 months’ intake of fluoride water (P < 0.05). After drug blocking, the serum BALP content in the F + Cycl group was lower than that in the F + DMSO group (P < 0.05). The BALP content in the F + DMSO group was similar to that in the F group: it did not decrease. The mRNA expressions of Ihh, Smo, Gli2, and Runx2 in bone tissue of the F group were significantly higher than those in the control group (P < 0.05). After cyclopamine blocking, the expressions decreased (P < 0.05), but the differences between the F + DMSO group and F group were not statistically significant.
Conclusion: Hh signal plays an important role in fluoride-induced bone injury. The effective inhibition of cyclopamine is expected to be a new target for the treatment of skeletal damage caused by fluorosis.
Keywords: Bone-tissue injury; Fluorosis; Hh signal; Osteoblasts; Skeletal fluorosis.
Endemic fluorosis is a systemic, chronic, toxic disease characterized by skeletal fluorosis and dental fluorosis, which is caused by the long-term intake of fluorine by residents through drinking water, food, air, and other means that exceeds normal physiological needs. It is one of the most widespread and serious endemic diseases in China . After the implementation of prevention and control measures, such as improvements to the water supply and to stoves, the prevalence of endemic fluorosis has been partially controlled. However, due to the complexity of the natural or ecological environment, the pathogenesis of endemic fluorosis is not very clear [2, 3]. Mak et al. found that selective upregulation of the Hh signal in mature osteoblasts could lead to significant increases in osteogenesis and bone resorption ; this is very similar to the pathology of skeletal fluorosis observed in many previous studies. Therefore, we speculate that the hedgehog (Hh) signal may affect the balance of bone remodeling by participating in the differentiation, proliferation, and apoptosis of osteoblasts and accordingly play an important role in the occurrence and development of skeletal fluorosis.
This study was designed to observe the expression of important Hh signal factors in the bone tissue of rats with chronic fluorosis and cultured osteoblasts in order to investigate the role and significance of the Hh signal in fluoride-induced bone injury.
*Abstract and full-text article online at https://josr-online.biomedcentral.com/articles/10.1186/s13018-021-02287-8