Effect of fluoride on expression of mRNA and protein of Wnt3a and β-catenin in osteoblast of rats / 中国地方病学杂志

ABSTRACT

Objective To explore the effect of excessive fluoride on expression of mRNA and protein of Wnt3a and β-catenin in rats' osteoblasts and its correlation with pathogenic mechanism of fluorosis.Methods Thirty-six healthy SD rats,weighting 100-120 g and according to body mass,were randomly divided into three groups(twelve in each group).The rats of control were fed wich tap water(fluoride ＜ 1 mg/L) and the experimental rats were exposed to NaF(low-fluoride group5 mg/L,high-fluoride group50 mg/L) added to the drinking water to establish the chronic fluorosis model.After fed for eight morth,all rats were killed and metaphysic of femoral was collected.Rat dental fluorosis was observed and bone fluorine was detected by ashing-fluorin ion selective electrode method.The content of bone alkaline phosphatase (BALP) and tartrate-resistant acid phosphatase 5b(TRACP 5b) in rats' serum was detected by enzyme-linked immunosorbent assay (ELISA).The morphologic changes of the bone were observed by microscopy.The expression of mRNA and protein of Wnt3a and β-catenin in osteoblasts of rats was analyzed with gray scale by hybridization in situ and immunohistochemistry methods,respectively.Results Detection rate of dental fluorosis,fluoride contents of urine and bone were significantly increased [control group0.0％,(1.26 + 0.17)mg/L,(305.58 ± 91.26)mg/kg; low-fluoride group66.7％,(2.06 ± 0.64)mg/L,(632.33 ±123.21)mg/kg; high-fluoride group91.7％,(7.69 ± 1.96)mg/L,(1088.75 ± 156.16) mg/kg] in the rats treated with fluoride,the difference between groups was statistically significant(χ2 =21.6; F =36.57,467.02; all P ＜0.05).The contents of BALP and TRACP-5b in rats' serum were significantly different between groups(F =89.57,7.68; all P ＜ 0.05).Compared with control group[(16.24 + 1.57)U/L],the contents of BALP in rats' serum of the low-fluoride and high-fluoride groups[(31.47 ± 5.30) and (54.61 ± 2.27)U/L] were increased gradually(all P ＜0.05).Compared with the low-fluoride group,the value in the high-fluoride group decreased significantly (P ＜ 0.05).The contents of TRACP-5b in rats' serum of low-fluoride group[(3.45 ± 1.85)U/L] were elevated significantly(all P ＜ 0.05) compared with the control group[(1.26 ± 0.23)U/L] and the high-fluoride group[(2.74 ± 1.85)U/L].The bone cortices were thickened and the bone trabecula was broadened,arranged closely together in chronic fluorosis rats with significant difference compared with the control group.In the low-fluoride and high-fluoride groups,the expression levels of Wnt3a and β-catenin mRNA (low-fluoride group132.87 ± 5.72 and 132.57 ± 9.56; highfluoride group135.60 ± 6.64 and 137.87 ± 9.16) were markedly elevated with significant difference,respectively (F =12.47,5.96; all P ＜ 0.05) compared with those in control groups(119.86 ± 5.04 and 120.58 ± 7.84) by hybridization in situ(P ＜ 0.05),but there was no statistical significance (P ＞ 0.05) of the level of Wnt3a and β-catenin mRNA between low-fluoride and high-fluoride groups.In the low-fluoride and high-fluoride groups,the protein expression of Wnt3a and β-catenin (low-fluoride group137.50 ± 4.32 and 140.85 + 3.54; high-fluoride group142.65 ± 11.84 and 152.52 ± 4.64) were markedly elevated with significant difference,respectively (F =10.07,53.82; all P ＜ 0.05) compared with those in control group (124.01 ± 2.63 and 126.75 ± 4.65) by immunohistochemistry(all P＜ 0.05),Wnt3a protein production in the low-fluoride group was increased without statistical significance compared with the high-fluoride group (P ＞ 0.05).But the protein production of β-catenin in the lowfluoride group was elevated with significant difference compared with the high-fluoride group(P ＜ 0.05).The mRNA and protein production of Wnt3a were positively correlated with the mRNA and protein production of β-catenin (r =0.731,0.658; all P ＜ 0.05).Conclusions Rat bone tissue lesions caused by excessive fluoride may be associated with an increased expression of Wnt3a and β-catenin mRNA and protein in osteoblasts.In chronic fluorosis,fluoride stimulates the overexpression of Wnt3a and β-catenin in the Wnt signal transduction pathway,enhances bone osteogenesis and causes skeletal fluorosis.