HMGB1-induced perturbations in the uterine immune microenvironment and implantation failure in rats

In brief: An excess of extracellular High-Mobility Group Box 1 protein, an alarmin, in the uterine cavity alters the proportion and phenotype of uterine immune cells. These derangements impair decidualization and adversely impact the implantation competence of the endometrium. Abstract Damage-associated molecular patterns or alarmins are endogenous molecules that activate immune cells and drive an inflammatory response. Derangements in damage-associated molecular pattern levels are associated with pregnancy disorders. Our previous study demonstrated that an excess of High-Mobility Group Box 1 (HMGB1), an alarmin, in the uterine cavity leads to implantation failure in rats. The present study investigated whether HMGB1-induced implantation failure was associated with perturbations in the uterine immune microenvironment. Recombinant HMGB1 with/without its inhibitor glycyrrhizin was administered on day 3 post-coitum in Wistar rats. Uterine fluid, uterine horns, and lymph nodes were collected on day 5 post-coitum. HMGB1-associated implantation failure was found to be associated with altered proportions of uterine natural killer cells and regulatory T cells, altered phenotype of macrophages, and impaired decidualization. While total CD68+ macrophage proportion did not change significantly, the proportion of M2 macrophages (CD68+CD163+) was reduced at the implantation sites in the HMGB1-treated uterine horns. The proportion of activated M2 macrophages (CD68+CD163+CD86+MHCIIlow) was also reduced in the HMGB1-treated animals. This was accompanied by a significant increase in Interleukin-1 beta and Interleukin-5 cytokine levels in the uterine fluid. Further, our studies demonstrated that some of these effects, such as a decrease in the uterine natural killer cell proportion and modulation in the macrophage phenotype, result from the direct effect of excess HMGB1 on the endometrium. These effects were not observed in animals receiving both HMGB1 and glycyrrhizin. Thus, an excess of HMGB1 in the uterine cavity alters the proportion/phenotype of uterine immune cells and thereby compromises the implantation competence of the endometrium.