The Role And Mechanism Of CD200 In The Development Of Ovarian Hyperstimulation Syndrome

Ovarian hyperstimulation syndrome(OHSS)is a serious complication associated with the use of human chorionic gonadotropin(hCG)for inducing final oocyte maturation and/or triggering oocyte release.Enlargement of bilateral ovaries and infiltration of blood are two main features of OHSS.In addition to enlarged ovaries,other serious clinical manifestations including ascites,pleural effusion electrolyte abnormalities,low blood volume,oliguria,blood concentration,hypercoagulability,and abnormal liver function can occur in the process of OHSS.In some special cases,respiratory distress syndrome,hypovolemic shock,renal failure and even death may occur.Even though,the pathogenesis of OHSS is not fully understood and there are no special treatments or preventive measures.After using String analysis,we found a significant correlation between CD200 and key proteins associated with OHSS such as VEGF,IL-6 and etc,which suggested that CD200 may play an important biological role in the process of immune anti-inflammatory inhibition of OHSS.CD200(OX-2)is a glycoprotein across the cell surface membrane and is widely expressed in tissues originated from hematopoietic cells and non hematopoietic cells,including thymus cells,the central nervous system(CNS)and retinal nerve cells,glomerular cells,trophoblastic cells,degenerated ovarian cells and blood cells.In addition,CD200 is also expressed in T cells,B cells,dendritic cells(DCs)and endothelial cells in peripheral blood and lymphatic tissue.Previous studies have found that CD200 can exert anti-inflammatory effects by binding to CD200R to inhibit the activation of inflammatory signal pathways ERK,JNK,p38-MAPK and NF-κB.It is well-known that ovulation may be an inflammatory response in the process of ovarian hyperstimulation syndrome(OHSS),and our clinical data showed a negative correlation between the level of CD200 in follicular fluid and both the number of ovulation and the levels of luteinizing hormone,estradiol and progesterone in patients recruited to IVF cycles,but no correlation between serum CD200 and ovulation was found,which indicated that locally produced CD200 may play a more important role in the process of HOSS.Therefore,the purpose of this research was to study whether CD200 plays an anti-inflammatory role in the process of OHSS and its underlying mechanism.In order to clarify whether CD200 played an anti-inflammatory role in the process of OHSS and how to exert these anti-inflammatory effects,we next constructed a rat OHSS model and the results showed that both the expressions of CD200 and its receptor CD200R were decreased in the ovaries of OHSS rats,whereas the expression of inflammatory cytokines such as IL-1β,TNFα were significantly increased,together with the increase of p-NF-κB and p-MAPK signaling molecules that regulate inflammation.The growth factor VEGF and its receptor VEGFR were also significantly increased,which indicated that the vascular permeability of OHSS rats was enhanced.And the expressions of Occludin,ZO-1 and Claudin5 were decreased,which indicated that the vascular connections were destroyed.Taken together,we speculated that the enhancement of vascular permeability in the process of OHSS was due to moderation of anti-inflammatory effect and increase level of inflammatory cytokines which caused by the decrease expression of CD200,and this process was mediated by NF-κB/MAPK signaling pathway.To verify the hypothesis above,we treated granulosa cells with different doses of hCG in vitro to mimic the in vivo OHSS model.We found that the expressions of CD200 and CD200R in granulosa cells were significantly reduced,the expressions of vascular connective proteins were also significantly reduced,while the inflammatory factors and the vascular endothelial growth factor were significantly increased,which were in consistent with our previous animal experiments.Thus we assumed that CD200 in ovarian played an important role in the process of OHSS.In the meanwhile,in order to further prove the anti-inflammatory effect of CD200,we designed a remediation experiment.Exogenous CD200Fc was added to hCG induced granulosa cell culture medium,and the results showed that the expressions of both CD200 and CD200R in granulosa cells were increased,the expressions of inflammatory cytokines were decreased,and the expressions of major proteins p-NF-κB and p-MAPK in the inflammation pathways were down-regulated.We cultured vascular endothelial cells with the same medium used for granulosa cells and the results showed that both the vascular endothelial growth factor VEGF and VEGFR were decreased,the expressions of tight junction proteins in cells showed an increasing tendency,and the vascular connections returned to normal state.Immunofluorescence Dyeing of phalloidin showed that the cytoskeleton was tightly connected and the permeability of cells was improved.In summary,we found that OHSS could increase vascular permeability by inhibiting the expressions of CD200 and by activating NF-κB/MAPK signaling pathway and the expressions of its downstream inflammatory cytokines both in vitro and in vivo.By adding exogenous CD200Fc in vitro,we found that CD200 could inhibit the NF-κB/MAPK signaling pathway and its downstream inflammatory factors to improve vascular permeability.These results indicated that ovarian CD200 played an important role in the process of OHSS,which provided a basis for CD200 as a new target for the treatment of OHSS.