Abstract: Objective To investigate calpain-1 and caspase-3 protein and mRNA expressions in renal tubular epithelial cells and the impact of the expressions on apoptosis of renal cells in rats with chronic fluorosis.Methods Thirty-six healthy Sprague-Dawley rats were randomly divided into 3 groups(6 males and 6 females in each group):a control group with sodium fluoride of less than 1 mg/L in drinking water,two dose(low and high)groups with sodium fluoride of 5 and 50 mg/L in drinking water.At the end of the 8-month consecutive treatment,the occurrence of dental fluorosis in the rats was observed;the fluorine content in 24-hour urine samples was detected;the expressions of calpain-1 and caspase-3 protein and mRNA were determined with immunohistochemistry and in-situ hybridization(ISH);the apoptosis of renal tubular epithelial cells was detected with terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling(TUNEL)and flow cytometry.Results Dental fluorosis was observed in the rats of low and high fluoride dose groups,with a higher detection rate of dental fluorosis in the high dose group than in the low dose group.Compared to the control group,the rats in fluoride dose groups had a significantly increased urine fluoride content.The expressions of calpain-1 and caspase-3 in renal tubular epithelial cells were increased in the rats of low dose group(77.00±7.60 and 62.33±5.86)and high dose group(83.62±7.78 and 66.65±3.87),with a dose-effect manner;the expression of mRNA in the renal cells was the same as that of the protein.Compared to that of the control group,the apoptosis rate of renal tubular epithelial cells was significantly increased in the rats of low dose group(19.76±2.21%)and high dose group(24.58±2.57%)(P<0.05).There was a correlation between the expressions of calpain-1 and caspase-3 protein and mRNA in renal tubular epithelial cells(r=0.699,P<0.05).Conclusion The apoptosis of renal tubular epithelial cells induced by the increase in the expressions of calpain-1,caspase-3 proteins and mRNA contributes to kidney damage in the rats with chronic fluorosis.