Abstract：
Fluoride is a widespread pollutant in the environment. There is a high risk of developing skeletal fluorosis from excessive fluoride exposure. Skeletal fluorosis has different phenotypes (including osteosclerotic, osteoporotic and osteomalacic) under the same fluoride exposure and depends on dietary nutrition. However, the existing mechanistic hypothesis of skeletal fluorosis cannot well explain the condition\'s different pathological manifestations and their logical relation with nutritional factors. Recent studies have shown that DNA methylation is involved in the occurrence and development of skeletal fluorosis. DNA methylation is dynamic throughout life and may be affected by nutrition and environmental factors. We speculated that fluoride exposure leads to the abnormal methylation of genes related to bone homeostasis under different nutritional statuses, resulting in different skeletal fluorosis phenotypes. The mRNA-Seq and target bisulfite sequencing (TBS) result showed differentially methylated genes in rats with different skeletal fluorosis types. The role of the differentially methylated gene Cthrc1 in the formation of different skeletal fluorosis types was explored in vivo and in vitro. Under normal nutritional conditions, fluoride exposure led to hypomethylation and high expression of Cthrc1 in osteoblasts through TET2 demethylase, which promoted osteoblast differentiation by activating Wnt3a/β-catenin signalling pathway, and participated in the occurrence of osteosclerotic skeletal fluorosis. Meanwhile, the high CTHRC1 protein expression also inhibited osteoclast differentiation. Under poor dietary conditions, fluoride exposure led to hypermethylation and low expression of Cthrc1 in osteoblasts through DNMT1 methyltransferase, and increased the RANKL/OPG ratio, which promoted the osteoclast differentiation and participated in the occurrence of osteoporotic/osteomalacic skeletal fluorosis. Our study expands the understanding of the role of DNA methylation in regulating the formation of different skeletal fluorosis types and provides insights into new prevention and treatment strategies for patients with skeletal fluorosis.
摘要：
氟化物是环境中广泛存在的污染物。氟过量暴露导致氟骨症的风险很高。氟骨症具有不同的表型（包括骨硬化性，骨质疏松和骨软化）在相同的氟化物暴露下，并取决于饮食营养。然而,现有的氟骨病机制假说不能很好地解释病情的不同病理表现及其与营养因素的逻辑关系。近年来研究表明,DNA甲基化与氟骨症的发生发展有关。DNA甲基化在整个生命中都是动态的，可能受到营养和环境因素的影响。我们推测在不同的营养状态下，氟暴露会导致骨稳态相关基因的异常甲基化。导致不同的氟骨症表型。mRNA-Seq和靶亚硫酸氢盐测序（TBS）结果显示不同类型的氟骨症大鼠存在差异甲基化基因。在体内和体外探索了差异甲基化基因Cthrc1在不同氟骨症类型形成中的作用。在正常的营养条件下，氟化物暴露导致成骨细胞中Cthrc1的低甲基化和高表达通过TET2去甲基酶，通过激活Wnt3a/β-catenin信号通路促进成骨细胞分化，并参与了骨硬化性氟骨症的发生。同时,高CTHRC1蛋白表达也抑制破骨细胞分化。在恶劣的饮食条件下，氟化物暴露通过DNMT1甲基转移酶导致成骨细胞中Cthrc1的高甲基化和低表达，并增加了RANKL/OPG比率，促进破骨细胞分化，参与骨质疏松/骨软化型氟骨症的发生。我们的研究扩展了对DNA甲基化在调节不同氟骨症类型形成中的作用的理解，并为氟骨症患者的新预防和治疗策略提供了见解。
