Abstract
Low-dose fluoride is an effective caries prophylactic, but high-dose fluoride is an environmental health hazard that causes skeletal and dental fluorosis. Treatments to prevent fluorosis and the molecular pathways responsive to fluoride exposure remain to be elucidated. Previously we showed that fluoride activates SIRT1 as an adaptive response to protect cells. Here, we demonstrate that fluoride induced p53 acetylation (Ac-p53) [Lys379], which is a SIRT1 deacetylation target, in ameloblast-derived LS8 cells in vitro and in enamel organ in vivo. Here we assessed SIRT1 function on fluoride-induced Ac-p53 formation using CRISPR/Cas9-mediated Sirt1 knockout (LS8Sirt/KO) cells or CRISPR/dCas9/SAM-mediated Sirt1 overexpressing (LS8Sirt1/over) cells. NaF (5 mM) induced Ac-p53 formation and increased cell cycle arrest via Cdkn1a/p21 expression in Wild-type (WT) cells. However, fluoride-induced Ac-p53 was suppressed by the SIRT1 activator resveratrol (50 µM). Without fluoride, Ac-p53 persisted in LS8Sirt/KO cells, whereas it decreased in LS8Sirt1/over. Fluoride-induced Ac-p53 formation was also suppressed in LS8Sirt1/over cells. Compared to WT cells, fluoride-induced Cdkn1a/p21 expression was elevated in LS8Sirt/KO and these cells were more susceptible to fluoride-induced growth inhibition. In contrast, LS8Sirt1/over cells were significantly more resistant. In addition, fluoride-induced cytochrome-c release and caspase-3 activation were suppressed in LS8Sirt1/over cells. Fluoride induced expression of the DNA double strand break marker γH2AX in WT cells and this was augmented in LS8Sirt1/KO cells, but was attenuated in LS8Sirt1/over cells. Our results suggest that SIRT1 deacetylates Ac-p53 to mitigate fluoride-induced cell growth inhibition, mitochondrial damage, DNA damage and apoptosis. This is the first report implicating Ac-p53 in fluoride toxicity.
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Acknowledgements
We thank Dr. Malcolm L. Snead for generously providing us with LS8 cells, Dr. Atsuko Ogino for her expert advice on CRISPR/Cas9 techniques and Addgene for providing us with vectors. Research reported in this publication was supported by the National Institute of Dental and Craniofacial Research of the National Institutes of Health under award number R01DE018106 (JDB), and was supported by a Seed Grant from The Ohio State University, College of Dentistry under award number 21-100300 (MS).
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MS, contributed to conception, design, data acquisition, analysis, interpretation and draft of the manuscript; AI, contributed to data acquisition, analysis and interpretation; JDB, contributed to design, data interpretation and editing of the manuscript text. All authors critically revised the manuscript, gave final approval and agree to be accountable for all aspects of this work.
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Suzuki, M., Ikeda, A. & Bartlett, J.D. Sirt1 overexpression suppresses fluoride-induced p53 acetylation to alleviate fluoride toxicity in ameloblasts responsible for enamel formation. Arch Toxicol 92, 1283–1293 (2018). https://doi.org/10.1007/s00204-017-2135-2
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DOI: https://doi.org/10.1007/s00204-017-2135-2