title: Sirtuin1 and autophagy protect cells from fluoride-induced cell stress.
abstract: Sirtuin1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase functioning in the regulation of metabolism, cell survival and organismal lifespan. Active SIRT1 regulates autophagy during cell stress, including calorie restriction, endoplasmic reticulum (ER) stress and oxidative stress. Previously, we reported that fluoride induces ER-stress in ameloblasts responsible for enamel formation, suggesting that ER-stress plays a role in dental fluorosis. However, the molecular mechanism of how cells respond to fluoride-induced cell stress is unclear. Here, we demonstrate that fluoride activates SIRT1 and initiates autophagy to protect cells from fluoride exposure. Fluoride treatment of ameloblast-derived cells (LS8) significantly increased Sirt1 expression and induced SIRT1 phosphorylation resulting in the augmentation of SIRT1 deacetylase activity. To demonstrate that fluoride exposure initiates autophagy, we characterized the expression of autophagy related genes (Atg); Atg5, Atg7 and Atg8/LC3 and showed that both their transcript and protein levels were significantly increased following fluoride treatment. To confirm that SIRT1 plays a protective role in fluoride toxicity, we used resveratrol (RES) to augment SIRT1 activity in fluoride treated LS8 cells. RES increased autophagy, inhibited apoptosis, and decreased fluoride cytotoxicity. Rats treated with fluoride (0, 50, 100 and 125ppm) in drinking water for 6weeks had significantly elevated expression levels of Sirt1, Atg5, Atg7 and Atg8/LC3 in their maturation stage enamel organs. Increased protein levels of p-SIRT1, ATG5 and ATG8/LC3 were present in fluoride-treated rat maturation stage ameloblasts. Therefore, the SIRT1/autophagy pathway may play a critical role as a protective response to help prevent dental fluorosis.
authors.affiliation: Department of Mineralized Tissue Biology, The Forsyth Institute, 245 First Street, Cambridge, MA 02142, USA; Harvard School of Dental Medicine, 188 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: Maiko
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Mineralized Tissue Biology, The Forsyth Institute, 245 First Street, Cambridge, MA 02142, USA; Harvard School of Dental Medicine, 188 Longwood Avenue, Boston, MA 02115, USA. Electronic address: jbartlett@forsyth.org.
authors.forename: John D
authors.initials: JD
authors.lastname: Bartlett
mesh_terms: D000565:Ameloblasts / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001343:Autophagy / Q000187:drug effects* / Q000235:genetics; D000071187:Autophagy-Related Protein 5; D000071193:Autophagy-Related Protein 7; D015153:Blotting, Western; D002327:Cariostatic Agents / Q000494:pharmacology; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003743:Dental Enamel / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005459:Fluorides / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D000077185:Resveratrol; D020133:Reverse Transcriptase Polymerase Chain Reaction; D056564:Sirtuin 1 / Q000235:genetics / Q000378:metabolism*; D012969:Sodium Fluoride / Q000494:pharmacology; D013267:Stilbenes / Q000494:pharmacology
chemical_list: C495773:Atg5 protein, mouse; C502661:Atg7 protein, mouse; D000071187:Autophagy-Related Protein 5; D002327:Cariostatic Agents; C480859:Gabarapl1 protein, mouse; D008869:Microtubule-Associated Proteins; D013267:Stilbenes; D012969:Sodium Fluoride; C470545:Sirt1 protein, mouse; C488368:Sirt1 protein, rat; D056564:Sirtuin 1; D000071193:Autophagy-Related Protein 7; D000077185:Resveratrol; D005459:Fluorides
keywords: (NAD(+)); 3-(4,5-dimethylthazol-2-yl)-2,5-di-phenyltetrazolium bromide; AMP-activated protein kinase; AMPK; Ameloblast; Atg; Autophagy; CR; Dental fluorosis; ER; Enamel; Fluoride; HF; JNK1; LS8; MTT; RES; ROS; SIRT1; Sirt1; UPR; ameloblast-derived cells; autophagy related gene; c-Jun N-terminal kinase-1; caloric restriction; eIF2α; endoplasmic reticulum; eukaryotic initiation factor-2, subunit alpha; hydrogen fluoride; inhibitor of mammalian-homolog-target-of-rapamycin; mTOR; nicotinamide adenine dinucleotide; qPCR; quantitative real-time PCR; reactive oxygen species; resveratrol; sirtuin1; unfolded protein response