Mechanism of action of 1,25(OH)_2D_3 in influencing the expression of interleukin-17 and macrophage inflammatory protein-3α and inhibiting the formation of liver fibrosis in rats

Objective To investigate the changes in the expression of interleukin- 17( IL- 17) and macrophage inflammatory protein- 3α( MIP- 3α) in liver tissue and peripheral blood during the formation of liver fibrosis and the mechanism of action of 1,25( OH)2D3in influencing the IL- 17 pathway and inhibiting the formation of liver fibrosis. Methods A total of 48 Sprague- Dawley rats were randomly divided into normal group( olive oil),model group( CCl4 olive oil solution),drug control group( CCl4 olive oil solution + olive oil by gavage),and treatment group( CCl4 olive oil solution + 1,25( OH)2D3olive oil solution by gavage). Eight weeks later the liver tissue was collected for HE staining and Masson staining to determine the pathological staging of fibrosis. ELISA was used to measure the serum level of IL- 17 at different time points after intervention( weeks 4,6,and 8). Immunohistochemistry was used to measure the protein expression of IL- 17 and MIP- 3α in liver tissue at different time points( weeks 4,6,and 8),and real time- PCR was used to measure the mRNA expression of IL- 17 and MIP- 3α in liver tissue at week 8 after intervention. A one- way analysis of variance was used for comparison of continuous data between groups,and the LSD- t test was used for further pairwise comparison. The linear regression analysis was used for correlation analysis. Results At week 8 after intervention,the model group and the drug control group had significant liver fibrosis,and the treatment group had significant alleviation in liver fibrosis. There were significant differences in serum IL- 17 level between the four groups at weeks4,6,and 8( F = 6. 13,5. 79,and 7. 18,all P < 0. 05). The normal group had an extremely low serum level of IL- 17; at each time point,the model group and the drug control group had a significant increase in the serum level of IL- 17 compared with the normal group( all P < 0. 01). At each time point,the treamtent group had significant reductions in the serum level of IL- 17 compared with the model group and the drug control group( all P < 0. 05),and all the groups had the highest level at week 4. Immunohistochemistry and real time-PCR showed that there was almost no expression of IL- 17 and a very low expression level of MIP- 3α in liver tissue in the control group.With the progression of liver fibrosis,serum IL- 17 level decreased gradually,while the IL- 17 level in liver tissue increased gradually( r=- 0. 793,P < 0. 01). There were significant differences in the expression of IL- 17 and MIP- 3α in liver tissue between the four groups at weeks 4,6,and 8( IL- 17: F = 11. 02,9. 61,and 7. 45,all P < 0. 05; MIP- 3α: F = 9. 47,8. 93,and 6. 15,all P < 0. 05). The model group and the drug control group had significant increases in the protein expression of IL- 17 and MIP- 3α in liver tissue compared with the normal group at weeks 4,6,and 8( all P < 0. 01),and the treatment group had significant reductions compared with the drug control group at these time points( all P < 0. 05); all the groups had the highest expression at week 8. At week 8,the model group and the drug control group had significant increases in the mRNA expression of IL- 17 and MIP- 3α compared with the normal group,and the treatment group had significant reductions compared with the drug control group and the model group( FIL- 17= 7. 36,FMIP- 3α= 10. 15,both P < 0.05). Conclusion During the development and progression of liver fibrosis,serum IL- 17 level first increases and then decreases,while the expression of IL- 17 in liver tissue tends to increase gradually,suggesting that in the late stage of liver fibrosis,Th17 cells in serum tend to accumulate in the liver. The 1,25( OH)2D3treatment group had significant reductions in the protein and mRNA expression of IL- 17 and MIP- 3α in the liver compared with the model group and the drug control group,suggesting that the IL- 17 pathway may be one mechanism of action of 1,25( OH)2D3in inhibiting the development and progression of liver fibrosis.