The Role Of EP2/EP4 Receptor In PGE2 Promoting Acute Liver Regeneration In Mice

Objective:To investigate the role of E-type prostaglandin receptor 2（EP2）and E-type prostaglandin receptor 4（EP4）in prostaglandin E2（PGE2）promoting liver regeneration in mice by using the acute liver regeneration model of 2/3 partial hepatectomy（PH）.Methods:Immunohistochemistry,Western blotting and qRT-PCR were used to detect the mRNA and protein expression of EP2 and EP4 in the regenerating liver of mice on the 1st,2nd and 7th day after PH operation,and to determine whether EP2 or EP4 participate in the liver regeneration after pH operation.Using SW033291 inhibitor intervention,immunohistochemistry was used to detect the expression levels of BrdU and Cyclin D1 in liver cells of mice on the 2nd day after PH operation to verify the promotion of PGE2 on liver regeneration in mice.TG4-155（EP2 selective antagonist）and L-161982（EP4 selective antagonist）were used to co-interfere with sw033291 inhibitor.The expression level of BrdU and cyclin D1 in liver cells of mice on the 2nd day after pH operation was detected by Immunohistochemistry,and whether EP2 or EP4 mediate the promotion of PGE2 on liver regeneration was determined.The expression of BrdU and cyclin D1 in EP4 hepatocyte conditional knockout mice were detected by immunohistochemistry on the 2nd day after pH operation,to verify whether PGE2 can directly acts on EP4 of hepatocytes to promote liver regeneration.Results:（1）Compared with the sham operation group,the expression of EP2 mRNA in the liver of PH group was up-regulated on the 1st day（3.273±1.524%vs 0.978±0.200%）and 2nd day（3.543±1.447%vs 1.006±0.218%）after operation,the difference was statistically significant（P<0.01）.The expression level of EP2 protein in PH group was up-regulated on the 1st day（0.908±0.152%vs 0.040±0.010%）,2nd day（1.496±0.160%vs 0.046±0.016%）and7th day（0.570±0.134%vs 0.121±0.050%）after operation,and the difference was statistically significant（P<0.01）.The expression of EP4 mRNA in PH group was up-regulated on the 1st day（4.178±1.337%vs 1.092±0.333%）and 2nd day（4.479±1.969%vs 0.937±0.281%）after operation,the difference was statistically significant（P<0.01）.The expression of EP4 protein in PH group was up-regulated on the 1st day（1.196±0.210%vs 0.505±0.124%）,2nd day（1.901±0.153%vs 0.499±0.077%）and7th day（0.758±0.168%vs 0.452±0.123%）after operation,the difference was statistically significant（P<0.01）.（2）On the 2nd day after PH operation,compared with PH group,the BrdU positive cell rate of liver in PH+SW033291 group was higher（37.983±5.909%vs 11.451±2.994%）,the difference was statistically significant（P<0.01）.The positive rate of Cyclin D1 cells in liver was higher（52.496±4.647%vs 32.923±5.258%）,the difference was statistically significant（P<0.01）.（3）On the 2nd day after PH operation,compared with the SW033291 group,the BrdU positive cell rate in the liver of SW033291+TG4-155 group（13.522±3.953%vs 37.983±5.909%）and the SW033291+L-161982 group（10.996±1.571%vs 37.983±5.909%）decreased,the difference was statistically significant（P<0.01）.The Cyclin D1 positive cell rate in the liver of SW033291+TG4-155 group（28.518±4.836%vs 52.496±4.647%）and the SW033291+L-161982 group（28.171±4.861%vs 52.496±4.647%）decreased,the difference was statistically significant（P<0.01）.（4）On the 2nd day after PH operation,compared with the EP4^f/f/f control group,the BrdU positive cell rate（9.321±0.974%vs12.283±1.871%）of the liver in the EP4_Alb^-/-knockout group was slightly lower,with no significant difference.Compared with the EP4^f/f mice treated with SW033291,the rate of BrdU positive cells in the liver of EP4_Alb^-/-knockout mice treated with SW033291（15.691±2.040%vs 28.896±5.397%）decreased,the difference was statistically significant（P<0.01）.Compared with the EP4^f/f/f control group,the Cyclin D1 positive cell rate（34.012±5.377%vs 38.557±6.568%）of the liver in the EP4_Alb^-/-knockout group was slightly lower,with no significant difference.Compared with the EP4^f/f mice treated with SW033291,the rate of Cyclin D1 positive cells in the liver of EP4_Alb^-/-knockout mice treated with SW033291（37.720±4.228%vs 51.097±4.389%）decreased obviously,the difference was statistically significant（P<0.01）.Conclusion:This study demonstrated that both EP2 and EP4 participate in the process of acute liver regeneration in mice and both EP2 and EP4 mediate the process of PGE2 promoting acute liver regeneration in mice.