The role of FGF9-mediated TGF-β1/Smad signaling in enamel hypoplasia induced by exposure to fluoride and SO2 in rats

Ying Lv; Yang Wang; Jin Yao; Jiaojiao He; Changhu Lin; Guohui Bai; Chenglong Tu

doi:10.1016/j.ecoenv.2023.115243

The role of FGF9-mediated TGF-β1/Smad signaling in enamel hypoplasia induced by exposure to fluoride and SO₂ in rats

Ecotoxicol Environ Saf. 2023 Sep 15:263:115243. doi: 10.1016/j.ecoenv.2023.115243. Epub 2023 Jul 15.

Authors

Ying Lv¹, Yang Wang², Jin Yao¹, Jiaojiao He¹, Changhu Lin¹, Guohui Bai³, Chenglong Tu⁴

Affiliations

¹ The Key Laboratory of Environmental Pollution Monitoring and Disease Control, Ministry of Education, School of Public Health, Guizhou Medical University, Guiyang 550025, China.
² Infrastructure Construction Department, Guizhou Medical University, Guiyang 550025, China.
³ Key Laboratory of Oral Disease Research, School of Stomatology, Zunyi Medical University, Zunyi, China.
⁴ The Key Laboratory of Environmental Pollution Monitoring and Disease Control, Ministry of Education, School of Public Health, Guizhou Medical University, Guiyang 550025, China. Electronic address: chenglongtu@163.com.

PMID: 37454483
DOI: 10.1016/j.ecoenv.2023.115243

Abstract

Many geographical areas of the world are polluted by both fluoride and sulfur dioxide (SO₂). However, the effects of simultaneous exposure to fluoride and SO₂ on teeth are unknown. Fibroblast growth factor-9 (FGF9) and transforming growth factor-β1 (TGF-β1) are key signaling molecules in enamel development. The purpose of the study was to explore the effects of co-exposure to fluoride and sulfur dioxide on enamel and to investigate the role and mechanism of FGF9 and TGF-β1. First, sodium fluoride (NaF) and SO₂ derivatives were used to construct rat models and evaluate the enamel development of rats. Then, TGF-β1 (cytokine) treatment, SIS3 (inhibitor) treatment and FGF9 gene knockdown were used to explore the mechanism of enamel damage in vitro. The results showed that enamel column crystals in the exposed group were characterized by enamel hypoplasia, as indicated by alterations such as disarrangement of enamel column crystals, space widening and breakage. Ameloblasts also showed pathological changes such as ribosome loss, mitochondrial swelling, nuclear fragmentation and chromatin aggregation. The protein expression of FGF9 was higher and the protein expression of AMBN, TGF-β1 and p-Smad2/3 protein was lower in the groups treated with fluoride and SO₂ individually or in combination compared with the control group. Further studies showed that TGF-β1 significantly upregulated p-Smad2/3 and AMBN protein expression and reduced the inhibitory effects of fluoride and SO₂; furthermore, SISI blocked the effect of TGF-β1. In addition, knockdown of FGF9 upregulated TGF-β1 protein expression, further activated Smad2/3 phosphorylation, eliminated the inhibitory effects of fluoride and SO₂, and increased the protein expression of AMBN. In brief, the study confirms that co-exposure to fluoride and SO₂ can result in enamel hypoplasia in rats and indicates that the underlying mechanism may be closely related to the effect of FGF9 on enamel matrix protein secretion through inhibition of the TGF-β1/Smad signaling pathway.

Keywords: AMBN; Enamel hypoplasia; FGF9; Fluoride; Sulfur dioxide; TGF-β1.

MeSH terms

Animals
Dental Enamel Hypoplasia*
Fluorides / pharmacology
Rats
Signal Transduction
Sulfur Dioxide / pharmacology
Transforming Growth Factor beta1* / genetics
Transforming Growth Factor beta1* / metabolism

Substances

Transforming Growth Factor beta1
Fluorides
Sulfur Dioxide