Fluoride Alters Klk4 Expression in Maturation Ameloblasts through Androgen and Progesterone Receptor Signaling

Abstract

Fluorosed maturation stage enamel is hypomineralized in part due to a delay in the removal of matrix proteins to inhibit final crystal growth. The delay in protein removal is likely related to reduced expression of kallikrein-related peptidase 4 (KLK4), resulting in a reduced matrix proteinase activity that found in fluorosed enamel. Klk4 transcription is known to be regulated in other cell types by androgen receptor (AR) and progesterone receptors (PR). In this study, we determined the possible role of fluoride in down-regulation of KLK4 expression through changes in AR and PR. Immunohistochemical localization showed that both AR and PR nuclear translocation was suppressed in fluoride exposed mice. However, when AR signaling was silenced in mouse ameloblast-lineage cells (ALCs), expression of both Pgr and Klk4 were increased. Similar to the effect from AR silencing, fluoride also upregulated Pgr in ALCs, but downregulated Klk4. This finding suggests that though suppression of AR transactivation by fluoride increases Prg expression, inhibition of PR transactivation by fluoride has a much greater effect, ultimately resulting in downregulation of Klk4 expression. These findings indicate that in ameloblasts, PR has a dominant role in regulating Klk4 expression. We found that when AR was retained in the cytoplasm in the presence of fluoride, that co-localized with heat shock protein 90 (HSP90), a well-known chaperone for steroid hormone receptors. HSP90 also known to regulate TGF-β signaling. Consistent with the effect of fluoride on AR and HSP90, we found evidence of reduced TGF-β signaling activity in fluorosed ameloblasts as reduced immunolocalization of TGFB1 and TGFBR-2 and a significant increase in Cyclin D1 mRNA expression, which also possibly contributes to the reduced AR signaling activity. In vitro, when serum was removed from the media, aluminum was required for fluoride to inhibit the dissociation of HSP90 from AR. In conclusion, fluoride related downregulation of Klk4 is associated with reduced nuclear translocation of AR and PR, and also reduced TGF-β signaling activity, all of which are regulated by HSP90. We suggest that a common mechanism by which fluoride affects AR, PR, and TGF-β signaling is through inhibiting ATP-dependent conformational cycling of HSP90.

Fluoride exposure and blood cell markers of inflammation in children and adolescents in the United States: NHANES, 2013–2016

“…However, our finding that fluoride was associated specifically with the WBC subtypes of neutrophils and monocytes, while not affecting lymphocytes, eosinophils and basophils, indicates a specific effect of fluoride in enhancing inflammation. In animal models, fluoride in drinking water has been shown to increase activation of NF-kB in cells and organs throughout the body, including ameloblasts [ 34 ] and liver [ 35 ]. NF-kB has a critical role in mediating the inflammatory response [ 36 ], and our report of an association between plasma fluoride concentrations and WBC counts in children suggests that findings of fluoride associated inflammation in animal models, may also be relevant to human populations.…”

Using in vitro bioassays to guide the development of safer bio-based polymers for use in food packaging

“…Sodium fluoride has also been reported to inhibit AR mRNA expression in Sertoli cells in mice, reducing AR protein and gene expression in the testis, therefore, negatively affecting male fertility (Huang et al, 2008). The decrease in AR transcriptional activity observed in the current study may be due to the effect of fluoride on 90-kDa heat-shock protein (HSP90) which may reduce transforming growth factor receptor-2 (TGFR-2) levels, and suppress TGF-β signalling activity, via upregulated cyclins D1 (CCND1) (Knudsen, et al, 1999;Le et al, 2017). Previous studies have also identified that the plastic leachate BPA can directly bind to the AR acting as an antagonist of the AR via inhibiting the actions of endogenous androgens and transcription of AR target genes at concentrations Frontiers in Toxicology frontiersin.org above and below the total daily intake (4 μg/kg body weight/day for a 70 kg person) (Lee et al, 2003;Xu et al, 2005;Sun et al, 2006;Bonefeld-Jørgensen et al, 2007;Teng et al, 2013;Ma et al, 2019).…”

La sphère orale, cible et marqueur de l’exposition environnementale

“…L'exposition au fluor a ainsi été associée à des effets dépassant le cadre buccal et les tissus minéralisés, dont des effets neurotoxiques et une diminution du quotient intellectuel [33,34], des perturbations de l'axe androgénique [35] (le fluor est répertorié comme un PE dans la TEDX List), et une augmentation des processus inflammatoires [36]. L'implication des récepteurs des hormones stéroïdiennes (progestérone et androgènes) dans les mécanismes d'action du fluor sur les améloblastes [37] laisse ainsi suspecter de fortes interactions entre fluor et PE. D'ailleurs, le fluor et le BPA peuvent avoir des effets complémentaires et additionnels comme perturbateurs de l'amélogénèse [38].…”