Abstract: Objective To observe changes in proteins of recombination signal-binding protein-J kappa(RBPJ),Jagged 1(Jag1),and hairy and enhancer of split 5(Hes5)in bone tissue of fluorosis rats and to explore the relationship between Notch signaling pathway and skeletal fluorosis.Methods Twenty-four adult Sprague-Dawley rats were randomly divided into 3 groups(a control group,low- and high-fluoride groups;8 rats in each group).The rats of control group were supplied with tap water containing fluoride less than 1 mg/L and those of low- and high-fluoride group were supplied with water containing 50 and 100 mg/L sodium fluoride(NaF).All the rats were sacrificed at 6-month of the treatment.The fluoride contents in urine and bone of the rats were measured with fluoride ion selective electrode method.The bone tissues were stained with hematoxylin-eosin and observed for bone histomorphometric analysis.The protein levels of RBPJ,Jag1,and Hes5 in osteoblasts were detected with immunohistochemistry.The expressions of RBPJ,Jag1,and Hes5 protein and mRNA were detected with Western blot and real-time quantitative PCR.Results Compared with those of the control group,the flouride contents in urine and bone were significantly higher in low- (11.80±1.08 mg/L and 5 974.76±2 036.13 μg/g)and high-fluoride (18.08±1.13 mg/L and 7 996.51±2 669.93 μg/g)group(all P<0.05).Osteosclerosis was observed with optical microscope in the rats of low- and high-fluoride group.The protein expressions of RBPJ in the bones of the low- (4.985±0.913) and high-fluoride group(4.279±1.507) were significantly higher than that of the control group(P<0.05),meanwhile the protein expressions of Jag1 and Hes5 in the bones of the rats of high-fluoride group (0.112±0.024 and 0.128±0.039) were significantly lower than those of the of the control group(both P<0.05).The mRNA expressions of Jag1 and RBPJ (0.005 7±0.005 4 and 0.005 5±0.004 4)in the bones of the rats of high-fluoride group were significantly lower than that of the control group(both P<0.05).Conclusion Excessive fluoride inhibits Notch signaling pathway and therefore reduces the expressions of the downstream target genes,and the changes could enhance osteogenesis and might correlate to the mechanism of skeletal fluorosis.