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¹ Graduate School of Comprehensive Human Sciences,
² JST-ERATO Environmental Response Project,
³ Centre for Tsukuba Advanced Research Alliance, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba 305-8577, Japan
⁴ Division of Oral Pathology and Bone Metabolism, Department of Developmental and Reconstructive Medicine, Nagasaki University Graduate School of Biomedical Sciences, 1-7-1 Sakamoto, Nagasaki, 852-8588, Japan
⁵ Department of Oral Anatomy, Showa University School of Dentistry, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8585, Japan

Rodents have brownish-yellow incisors whose colour represents their iron content. Iron is deposited into the mature enamel by ameloblasts that outline enamel surface of the teeth. Nrf2 is a basic region-leucine zipper type transcription factor that regulates expression of a range of cytoprotective genes in response to oxidative and xenobiotic stresses. We found that genetically engineered Nrf2-deficient mice show decolourization of the incisors. While incisors of wild-type mice were brownish yellow, incisors of Nrf2-deficient mice were greyish white in colour. Micro X-ray imaging analysis revealed that the iron content in Nrf2-deficient mouse incisors were significantly decreased compared to that of wild-type mice. We found that iron was aberrantly deposited in the papillary layer cells of enamel organ in Nrf2-deficient mouse, suggesting that the iron transport from blood vessels to ameloblasts was disturbed. We also found that ameloblasts of Nrf2-null mouse show degenerative atrophy at the late maturation stage, which gives rise to the loss of iron deposition to the surface of mature enamel. Our results thus demonstrate that the enamel organ of Nrf2-deficient mouse has a reduced iron transport capacity, which results in both the enamel cell degeneration and disturbance of iron deposition on to the enamel surface.

^* Correspondence: E-mail: masi{at}tara.tsukuba.ac.jp