HMGB1 induces macrophage pyroptosis and serves as a promising diagnostic marker for chronic endometritis

Abstract

Background Chronic endometritis (CE) reflects the local imbalance of endometrial immune microenvironment after inflammation. High mobility group box 1 (HMGB1) is highly involved in both immunity and inflammation. The purpose of this study was to explore the effects of HMGB1 on the endometrium of CE.Methods In the pilot study, the expression level of pyroptosis-associated marker GSDMD-NT and its co-localization with macrophages in endometrial tissues collected from CEs and controls were detected by qRT-PCR, western blot (WB), immunohistochemical (IHC) and immunofluorescence (IF) staining. Next, the roles of HMGB1 as a driver of macrophage pyroptosis was investigated in vitro using human THP-1 cells. To evaluate whether HMGB1 could be served as a target for treatment of CE, CE mouse model was established by LPS intrauterine perfusion, and treatment with glycyrrhizic acid, an inhibitor of HMGB1, was given. Lastly, receiver operating characteristic (ROC) curves of endometrium and uterine fluid HMGB1 were constructed to assess the predictive values in a cohort study including 154 patients.Results In the pilot study, we found that pyroptosis-associated marker GSDMD-NT was significantly increased in the CE endometrium(P < 0.05), and co-localization of GSDMD-NT and macrophages were detected by IF staining. In vitro experiments demonstrated that HMGB1 induced pyroptosis in human THP-1 derived macrophage. HMGB1 expression was induced in a dose-dependent manner under LPS stimulation in both cytoplasm and cell supernatant of HESCs. Treatment with HMGB1 inhibitor (glycyrrhizic acid) significantly suppressed endometrium inflammation in LPS-induced CE mouse model. In the cohort study, we confirmed that HMGB1 mRNA level dramatically increased in the CE group (n = 83) compared with those of control (n = 71, 21.04 ± 14.92 vs. 8.89 ± 6.91, P < 0.001). Correspondingly, the expression of HMGB1 in uterine fluid of CE (n = 19) was significantly higher than control [n = 46, 1415pg/ml (616–3656) vs. 638.2pg/ml (318.9–1124), P < 0.001]. Positive correlation was observed between HMGB1 and the number of CD138 (rs = 0.592, P < 0.011). Area under the curve (AUC) for the prediction of CE by HMGB1 levels of the endometrium or uterine fluid were 0.830 (95%CI 0.769 to 0.892) and 0.756 (95%CI 0.614 to 0.898) respectively.Conclusions HMGB1 effectively induces macrophages pyroptosis in human endometrium, and HMGB1 level of endometrium or uterine fluid can be served as a promising diagnostic marker for CE.