Immunohistochemical Localization of Fam83h During Fluorosis-induced Mouse Molar Development

The clinical and pathological features of fluorosis are similar to amelogenesis imperfecta (AI) caused by FAM83H mutations, suggesting that excess fluoride could have effects on the expression of Fam83h. Our previous study found that Fam83h was downregulated by fluorosis induction in ameloblasts; the purpose of this study was to underline the importance of understanding the relationship between fluoride administration and Fam83h expression in vivo. A total of 80 healthy female adult Kunming mice were randomly divided into control group or F group that induced the clinical features of fluorosis. Immunohistochemical staining on sections of the embryo mandible regions was performed at different developmental stages. Mouse primary ameloblast-like cells of the two groups at E13.5, E15.5, and E18.5 were cultured and examined for the expression of Fam83h. The expression of Fam83h in the F group was significantly lower than that in the control group; however, Fam83h was observed clearly in the whole enamel organ in the control group. Our findings shed new light on the potential effects of Fam83h in fluorosis using a mouse model and revealed that high fluoride decreased the expression of Fam83h. This may be one of the reasons for the occurrence of fluorosis.

P38/JNK signaling pathway mediates the fluoride-induced down-regulation of Fam83h

BACKGROUND/AIM

The similar clinical and pathological feature in fluorosis and amelogenesis imperfect with FAM83H mutations imply that excess fluoride could have effects on the expression of FAM83H and could elaborate this process by some signal pathways regulation. The present study aims to investigate the effects of fluoride on Fam83h expression and try to explore the molecular signaling regulation between them as well as the association of high concentration fluoride with mineralization in ameloblast lineage cells.

METHODS

Protein expression and signaling pathways of mouse ameloblast-like LS8 cells, exposed to fluoride or MAPK inhibitors, were compared to control cells without exposure. Fam83h, proteins of MAPK signal pathways (ERK, P38 and JNK) were examined by Quantitative real-time PCR and/or Western-blot. ALP activity and ALP staining were used to detect the mineralization in the cells with exposure during 7-day mineralization inducing differentiation.

RESULTS

The results showed that Fam83h protein level in LS8 cells decreased in the presence of fluoride and MAPK inhibitors. Down-regulation of Fam83h by fluoride was related to suppression of JNK and P38 phosphorylation, and the descending degree of P38 was more obvious. Fluoride and MAPK inhibitors treatment significantly decreased the mineralization level in LS8 cells.

CONCLUSION

The findings suggest that JNK and P38 could be key regulatory element for Fam83h expression, and that LS8 cells can respond to fluoride by down-regulating Fam83h expression through the regulation of JNK and p38 signaling pathways.