Uncoupling protein-2 is an antioxidant that is up-regulated in the enamel organ of fluoride-treated rats

Abstract

Dental fluorosis is characterized by subsurface hypomineralization and retention of enamel matrix proteins. Fluoride (F−) exposure generates reactive oxygen species (ROS) that can cause endoplasmic reticulum (ER)-stress. We therefore screened oxidative stress arrays to identify genes regulated by F− exposure. Vitamin E is an antioxidant so we asked if a diet high in vitamin E would attenuate dental fluorosis. Maturation stage incisor enamel organs (EO) were harvested from F−-treated rats and mice were assessed to determine if vitamin E ameliorates dental fluorosis. Uncoupling protein-2 (Ucp2) was significantly up-regulated by F− (∼1.5 & 2.0 fold for the 50 or 100 ppm F− treatment groups, respectively). Immunohistochemical results on maturation stage rat incisors demonstrated that UCP2 protein levels increased with F− treatment. UCP2 down-regulates mitochondrial production of ROS, which decreases ATP production. Thus, in addition to reduced protein translation caused by ER-stress, a reduction in ATP production by UCP2 may contribute to the inability of ameloblasts to remove protein from the hardening enamel. Fluoride-treated mouse enamel had significantly higher quantitative fluorescence (QF) than the untreated controls. No significant QF difference was observed between control and vitamin E-enriched diets within a given F− treatment group. Therefore, a diet rich in vitamin E did not attenuate dental fluorosis. We have identified a novel oxidative stress response gene that is up-regulated in vivo by F− and activation of this gene may adversely affect ameloblast function.