There has been increasing concerns over the last 20 years about the potential adverse effects of endocrine disruptors (EDs). Anecdotally, molar incisor hypomineralization (MIH), a recently described enamel pathology, now affecting 1518% of 69 years old children, is increasing concurrently with ED related pathologies. Our previous data show that bisphenol A (BPA) and vinclozolin, two anti-androgenic EDs, impact amelogenesis and enamel mineralization preferentially in male rats and generate similar enamel defects as those described for MIH. The resulting irreversible enamel defects may provide an easily accessible marker for reporting early ED exposure in humans. The aim of the present study was to decipher the mechanism of action of low-dose ED during amelogenesis.
Wistar rats were exposed to low-dose EDs from the first day of gestation to 30 days after birth. Global transcriptomic analysis showed BPA and vinclozolin modulated the expression of a small group of genes directly involved in enamel mineralization, among them the protease KLK4 and the ion-exchanger SLC5A8 which are crucial for amelogenesis. Analysis of the ED putative receptor expression pattern showed that in contrary to estrogen receptor α (ERα) which is mainly expressed by ameloblastic precursors, androgen receptor (AR) was three- to fivefold more expressed in full differentiated ameloblasts responsible of enamel mineralization. In vivo and in vitro analysis carried out on the rat ameloblastic cell line HAT-7 and human androgen-sensitive prostate cancer cells LNCaP showed AR nuclear translocation upon testosterone treatment, and testosterone up-regulation of two enamel specific gene expression (KLK4 and SLC5A8). This induction occurred at the transcriptional level and was inhibited by siRNAs directed against AR as well as by vinclozolin and BPA.
In conclusion, we report that i) dental epithelial cells are sensitive to estrogens and androgens, ii) amelogenesis is modulated by androgens and that iii) two anti-androgenic EDs, BPA and vinclozolin, irreversibly disrupt this process preferentially in male rats by modulating the transcription of enamel specific genes. We thus provide evidence of hormonal influence on amelogenesis and probably on sexual differences of enamel quality.