The genetic influence in fluorosis

DNA sequencing reveals AMELX, ODAM and MMP20 variations in dental fluorosis

OBJECTIVE

Dental fluorosis (DF) is a dental development disorder caused by chronic fluoride overconsumption. There are differences in the susceptibility to and severity of DF in studied populations. The objective of the present study was to determine if single-nucleotide variations (SNVs) in the genes Amelogenin (AMELX), Odontogenic Ameloblast Associated (ODAM) and Matrix Metalloproteinase 20 (MMP20) are associated with DF by evaluating the relationship between variations in these genes and the degree of DF severity.

SUBJECTS AND METHODS

Schoolchildren from two regions of Durango State and Mexico City, Mexico, were studied. The DF phenotype was determined using the Thylstrup and Fejerskov (TF) index. DNA was obtained from the buccal mucosa of each participant, and the presence of the variations rs946252 in AMELX, rs1514392 in ODAM and rs1784418 in MMP20 was determined by bidirectional DNA sequencing.

RESULTS

A total of 180 DNA samples from 30 schoolchildren from 2 areas of Durango State were sequenced and analyzed. Differences in the severity of DF were found between the study areas (p = 0.006). SNVs in theMMP20 gene were present in 76.9 % of the participants in the high fluoride concentration and lower DF severity area.

CONCLUSION

AMELX and ODAM variations was not different between the two populations with respect to DF severity; however, the presence of rs1784418 differed between phenotypes with regard to susceptibility to DF. Therefore, MMP20 might be related to the various phenotypes of DF and may serve as a protective marker.

The Effects of Fluoride on the Gap-Junctional Intercellular Communication of Rats' Osteoblast

The gap junction protein plays an important role in the bone formation and alteration of these proteins leading to cause bone development. Aim to determine the effects of different concentration of fluoride on gap-junctional intercellular communication (GJIC) related genes and proteins in the rats' osteoblast cells. We treated the osteoblast cells with various concentrations (0, 0.01, 0.1, 0.5, and 1.0 mM) NaF for 24 and 72 h. We used the scrape loading and dye transfer technique to research the intracellular connectivity. Moreover, the mRNA expression levels of connexin 43 (Cx43), connexin45 (Cx45), collagen I, and osteocalcin (OCN) were analyzed by qRT-PCR, the protein expression levels of connexin43 (Cx43) were analyzed by western blotting and immunofluorescence. Our results suggested that the osteoblast proliferations were decreased in the 0.5 and 1 mM NaF groups, after 24 and 72 treatments. The scrape loading and dye transfer experiment showed that the GJIC were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In addition, the mRNA expressions of Cx43, Cx45, and OCN, and the protein expressions of Cx43 were increased in the 0.01 mM NaF group and decreased in the 0.5 and 1 mM NaF groups. In summary, these results suggest that the low concentration NaF is good for the GJIC, but the high concentration NaF damages the GJIC.

Aberrant DNA methylation of Cyclind-CDK4-p21 is associated with chronic fluoride poisoning

Endemic fluorosis is a serious problem in public health, affecting thousands of people. Abnormal proliferation and activation of osteoblasts in skeletal fluorosis lesions play a leading role and osteoblast proliferation is finely regulated by the cell cycle. There are a few reports on fluoride-induced DNA methylation. However, the role of DNA methylation of the cyclin/cyclin-dependent kinase (CDK)/cyclin-dependent kinase inhibitor (CKI) regulatory network in skeletal fluorosis has not been investigated. We used a population study and in vitro experiment to explore the relationship between the pathogenesis of skeletal fluorosis and methylation of Cyclin d1/CDK4/p21. The results showed a positive relationship between fluoride exposure and expression of Cyclin d1/CDK4, and a negative relationship between fluoride exposure and expression of P21. Hypermethylation of p21 was found in the fluoride-exposed population, and low expression of p21 attributed to promoter hypermethylation was confirmed in vitro. However, no changes in methylation levels of Cyclin d1 and CDK4 genes were observed in the population exposed to fluoride and NaF-treated osteoblasts. These results show that methylation of p21 gene has a significant impact on the proliferation of osteoblasts during the development of skeletal fluorosis. The present study was a first attempt to link the methylation of the Cyclin d1/CDK4/p21 regulatory network with osteoblast proliferation in skeletal fluorosis.

Assessment of fluoride intake from groundwater and intake reduction from delivering bottled water in Chiang Mai Province, Thailand

Fluoride intake from tap water supplied by fluoride-containing groundwater has been the primary cause of fluorosis among the residents of Buak Khang Subdistrict, Chiang Mai Province, Thailand. To reduce fluoride intake, bottled water treated using reverse-osmosis membranes has been made available by community-owned water treatment plants. This study aimed to assess the resultant reduction in fluoride intake from using bottled water for drinking and cooking. Water consumption surveys were conducted by providing bottled water to 183 individuals from 35 randomly selected households and recording the amount of water consumed for drinking and cooking. The mean drinking water consumption was 1.62-1.88 L/capita/day and the cooking water consumption on weekends (5.06 ± 3.04 L/household/day) was higher than that on weekdays (3.80 ± 1.90 L/household/day). The per capita drinking water consumption exhibited a positive correlation with body weight; however, the low-weight subjects consumed more drinking water per kilogram of body weight than the heavy subjects. Although sex and day of the week did not significantly affect drinking water consumption per capita, girls consumed less water in school possibly due to their group mentality. Drinking water consumption per kilogram of body weight was significantly higher among women, children, and the elderly because these groups generally have low body weights. The fluoride intake from using tap water for drinking and cooking was estimated to be 0.18 ± 0.10 mg/kg-body weight/day and 5.55 ± 3.52 mg/capita/day, respectively, whereas using bottled water for drinking and cooking reduced the fluoride intake to 0.002 ± 0.002 mg/kg-body weight/day and 0.07 ± 0.05 mg/capita/day, respectively. Despite the increased cost, 98% and 90% of the subjects selected bottled water over tap water for drinking and cooking, respectively; thus, bottled water delivery services could be used to mitigate fluoride intake in developing countries.

Analysis of the microRNA Profile of Coal-Burning Endemic Fluorosis Using Deep Sequencing and Bioinformatic Approaches

MicroRNAs (miRNAs) differentially expressed in plasma were identified using microRNA sequencing (miRNA-seq), and five miRNAs were selected for validation. Potential target genes of these five miRNAs were predicted using the miRWalk3.0 database, and the overlapping portions were analyzed using the Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. Comparison of the cases and controls revealed 127 known differentially expressed miRNAs. A total of 44 and 83 miRNAs were upregulated and downregulated, respectively. Through target gene prediction of five miRNAs, we obtained 1360 target genes. GO enrichment analysis showed that the target genes of these dysregulated miRNAs were related with secretion, protein binding, and cell growth. The KEGG pathway analysis showed that pathways in cancer, calcium signaling, and rat sarcoma (Ras) signaling, etc. were likely regulated by these five miRNAs. These findings highlight the distinct expression patterns of miRNAs in coal-burning endemic fluorosis.

Trends of SHBG and ABP levels in male farmers: Influences of environmental fluoride exposure and ESR alpha gene polymorphisms

A number of epidemiological studies have reported that chronic exposure to high concentrations of fluoride not only causes dental and skeletal fluorosis but additionally affects serum levels of reproductive hormones. However, possible interaction between fluoride exposure and estrogen receptor alpha (ESRα) gene polymorphisms on sex hormone-binding globulin (SHBG) and androgen binding protein (ABP) of male farmers has not been detailed. Here, we conducted a cross-sectional study including 348 male farmers with different fluoride exposure levels from drinking water in Henan province of China to explore effects of fluoride exposure and ESRα genetic variation on serum SHBG and ABP levels. We found serum SHBG levels in male farmers from the high exposure group to be lower than those of the low exposure group. We also found that concentrations of SHBG affected ABP levels. Furthermore, fluoride exposure and single nucleotide polymorphisms at the XbaI and rs3798577 loci of the ESRα gene affected serum ABP levels. Our findings suggest that chronic fluoride exposure from drinking water is associated with alterations of serum SHBG and ABP concentrations in local male farmers and that the effect of fluoride exposure on ABP levels vary depending on ESRα gene polymorphisms.

Histone Deacetylation in the Promoter of p16 Is Involved in Fluoride-Induced Human Osteoblast Activation via the Inhibition of Sp1 Binding

Chronic fluorosis is a systemic condition which principally manifests as defects in the skeleton and teeth. Skeletal fluorosis is characterized by aberrant proliferation and activation of osteoblasts, however, the underlying mechanisms of osteoblast activation induced by fluoride are not fully understood. Therefore, we investigated the pathogenic mechanism of human primary osteoblast proliferation and activation in relation to histone acetylation of the promoter p16, a well-known cell cycle regulation-related gene. The results showed that sodium fluoride (NaF) induced deacetylation and decreased expression of the p16 gene via inhibition of specificity protein 1 (Sp1) binding to its response element, which accounts for NaF increasing cell viability and promoting proliferation in human primary osteoblasts. These results reveal the regulatory mechanism of histone acetylation of the p16 gene on osteoblast activation in skeletal fluorosis.

Role of fluoride induced epigenetic alterations in the development of skeletal fluorosis

Fluoride is an essential trace element required for proper bone and tooth development. Systemic high exposure to fluoride through environmental exposure (drinking water and food) may result in toxicity causing a disorder called fluorosis. In the present study, we investigated the alteration in DNA methylation profile with chronic exposure (30 days) to fluoride (8 mg/l) and its relevance in the development of fluorosis. Whole genome bisulfite sequencing (WGBS) was carried out in human osteosarcoma cells (HOS) exposed to fluoride. Whole genome bisulfite sequencing (WGBS) and functional annotation of differentially methylated genes indicate alterations in methylation status of genes involved in biological processes associated with bone development pathways. Combined analysis of promoter DNA hyper methylation, STRING: functional protein association networks and gene expression analysis revealed epigenetic alterations in BMP1, METAP2, MMP11 and BACH1 genes, which plays a role in the extracellular matrix disassembly, collagen catabolic/organization process, skeletal morphogenesis/development, ossification and osteoblast development. The present study shows that fluoride causes promoter DNA hypermethylation in BMP1, METAP2, MMP11 and BACH1 genes with subsequent down-regulation in their expression level (RNA level). The results implies that fluoride induced DNA hypermethylation of these genes may hamper extracellular matrix deposition, cartilage formation, angiogenesis, vascular system development and porosity of bone, thus promote skeletal fluorosis.

The pathogenesis of endemic fluorosis: Research progress in the last 5 years

Fluorine is one of the trace elements necessary for health. It has many physiological functions, and participates in normal metabolism. However, fluorine has paradoxical effects on the body. Many studies have shown that tissues and organs of humans and animals appear to suffer different degrees of damage after long-term direct or indirect exposure to more fluoride than required to meet the physiological demand. Although the aetiology of endemic fluorosis is clear, its specific pathogenesis is inconclusive. In the past 5 years, many researchers have conducted in-depth studies into the pathogenesis of endemic fluorosis. Research in the areas of fluoride-induced stress pathways, signalling pathways and apoptosis has provided further extensive knowledge at the molecular and genetic level. In this article, we summarize the main results.

Evaluation of genetic polymorphisms in MMP2, MMP9 and MMP20 in Brazilian children with dental fluorosis

Recent studies suggested that genetics contribute to differences in dental fluorosis (DF) susceptibility among individuals having the same environmental exposure. This study evaluated if MMP2, MMP9 and MMP20 are expressed during enamel development and assessed the association between polymorphisms in these genes with DF. Mice susceptible and resistant to DF were used to evaluate if MMPs were candidate genes for DF. The animals received fluoride and their enamels were used for immunohistochemistry. Additionally, 481 subjects from a city with fluoridation of public water supplies were recruited. Genotyping was performed using real time PCR. Allele/genotype frequencies were compared between groups. MMP2, MMP9 and MMP20 immunostaining was detected in both animal groups. DF was observed in 22.4% of the subjects. A borderline association was observed in MMP2 (rs243865), MMP9 (rs17576) and in MMP20 (rs1784418) (p = 0.06, p = 0.08 and p = 0.06 respectively). Briefly, MMPs were expressed during enamel maturation and genetic polymorphisms were not associated with DF.