Effects And Mechanism Of Discoid Domain Receptors 1 On Peritoneal Fibrosis In Mice

Objective:To investigate the effects and mechanism of Discoid Domain Receptor 1（DDR1）in peritoneal fibrosis induced by high-glucose peritoneal dialysis solution in mice,and to provide a new idea for the clinical treatments of peritoneal fibrosis.Methods:Male C57/BL normal mice aged 6-8 weeks and male DDR1knockdown mice aged 6-8 weeks were selected and divided into normal control group,peritoneal fibrosis group,DDR1^+/-a group and DDR1^+/-b group,with 5 mice in each group.The mice were kept in a SPF laboratory for 1 week,and the feeding conditions were as follows:standard feed was given to the mice,free water was given to them,the feeding temperature was generally controlled at 18～20℃,the relative humidity was generally controlled at 50%～60%,and the day-night ratio was 12h:12h.Normal control group and DDR1^+/-a group were received a daily intraperitoneal injection of0.9%normal saline,while peritoneal fibrosis group and DDR1^+/-b group were received intraperitoneal injection of 4.25%glucose peritoneal dialysis solution.The injections were kept once a day and the injection dose was 1mL/10g.The period was all for 4 weeks.After the modeling cycle was completed,the peritoneal dialysis ultrafiltration（UF）volume of each group was calculated.The levels of IL-6 and CA125 in peritoneal effusion were detected.The parietal peritoneal tissues of the four groups were collected and stained by HE and Masson to observe the changes of peritoneal morphology.The peritoneal tissues were also used for western blot analyses.,including DDR1,collagenⅠ,epithelial to mesenehymal transition（EMT）markers likeα-SMA and E-cadherin.Results:1.Compared with the control group,the ultrafiltration volume was decreased in the peritoneal fibrosis group and the difference was statistically significant（P<0.01）.Compared with DDR1^+/-a group,ultrafiltration volume in DDR1^+/-b group was decreased,however there was no statistical difference.Compared with the DDR1^+/-b group,the peritoneal dialysis ultrafiltration volume was decreased in the peritoneal fibrosis group,and the difference was statistically significant（P<0.05）.2.Compared with normal control group,the expression of IL-6 in peritoneal effusion was significantly increased in peritoneal fibrosis group.And compared with DDR1^+/-a group,the expression of IL-6 in DDR1^+/-b group also increased（P<0.0001）.Compared with peritoneal fibrosis group,the expression of IL-6 in peritoneal effusion was decreased in DDR1^+/-b group（P<0.01）.3.Compared with normal control group,the expression of CA-125 in peritoneal effusion of mice in peritoneal fibrosis group was significantly decreased（P<0.001）,Compared with DDR1^+/-a group,CA-125 expression in peritoneal effusion of DDR1^+/-b group was decreased.Compared with peritoneal fibrosis group,CA-125expression in peritoneal effusion was increased in DDR1^+/-b group（P<0.05）.4.Then observe mice parietal layer tissue morphological features,HE staining showed that normal control group parietal layer consists of a layer of flattened cells of peritoneal fibrosis group peritoneal thickening,visible surface cells are round,oval,between interstitial inflammatory cell infiltration,DDR1^+/-group a lining peritoneal group compared with normal control group,no significant differences,DDR1^+/-b group compared with group of peritoneal fibrosis,reduced the degree of peritoneal thickening and inflammatory infiltrate.Masson staining showed that the peritoneal tissue in the normal control group was thinner with a certain continuity of distribution,and the peritoneal fibrosis group was significantly thickened with increased collagen deposition.There was no significant difference between the DDR1^+/-a group and the normal control group.The degree of collagen deposition in the DDR1^+/-b group was less than that in the peritoneal fibrosis group.5.The expression of DDR1:The expression of DDR1 in DDR1 knockdown mice(DDR1^+/-a and DDR1^+/-b groups)was lower than that in wild mice（normal control group and peritoneal fibrosis group）.And in peritoneal fibrosis group and DDR1^+/-b group the expression of DDR1were higher than normal control group and DDR1^+/-a).6.The expression of CollagenⅠ:compared with normal control group,in peritoneal fibrosis groups,the expression of CollagenⅠincreased.In DDR1^+/-b group,it’s expression decreased compared with peritoneal fibrosis group.7.EMT markers’（α-SMA and E-cadherin）expression:The expression ofα-SMA was increased in the peritoneal fibrosis group compared with the normal control group,and the expression ofα-SMA was also increased in the DDR1^+/-b group compared with the DDR1^+/-a group.Compared with peritoneal fibrosis group,the expression ofα-SMA in peritoneal tissue of mice in DDR1^+/-b group decreased（P<0.05）.On the contrary,the E-cadherin of expression was decreased in the peritoneal fibrosis group compared with the normal control group;E-cadherin’s expression was also decreased in the DDR1^+/-b group compared with the DDR1^+/-a group;and E-cadherin’s expression was increased in the DDR1^+/-b group compared with the peritoneal fibrosis group,with statistical significance.Conclusion:1.In this study,it was found that DDR1 played a promoting role in peritoneal fibrosis in mice,and inhibition of DDR1 expression could reduce peritoneal fibrosis.2.The promotion of fibrosis by DDR1 could be related to its involvement in regulating EMT.3.Inhibition of DDR1 expression may provide a new idea and research direction for the treatments of fibrosis.