Reprogramming of Uterine Macrophages and Risk of Recurrent Pregnancy Complications

Abstract

Pregnancy loss is a common complication of pregnancy, frequently associated with aberrant inflammation. The risk of subsequent complications, including recurrent pregnancy loss, increases substantially after each miscarriage. Although the mechanisms underlying this increased risk of recurrent pregnancy complications has not been elucidated, aberrant inflammation during pregnancy may cause long-lasting alterations in the uterine immune microenvironment. Macrophages play an important role in inflammatory responses and comprise up to 20% of the uterine leukocytes during early pregnancy. This study therefore assessed whether aberrant inflammation-induced fetal loss alters the function and distribution of uterine macrophage populations and increases the risk of subsequent complications. We established a model of inflammation-induced pregnancy loss using BALB/c female mice mated with C57BL/6 males, administering 20 μg/kg lipopolysaccharide (LPS; i.p.) on gestational day (GD) 10.5, resulting in 71% complete fetal loss. Uterine tissue was collected at the time point corresponding to GD 14.5 or postnatal day 7. Another cohort of mice previously exposed to LPS during the first pregnancy underwent a second pregnancy without LPS to determine whether inflammation-induced complications persist in subsequent pregnancies. Second pregnancies had reduced litter sizes and pup weights. Uterine macrophages were analyzed by flow cytometry. Independent of LPS-treatment, there were increased proportions of recruited macrophages in the first pregnancy and reduced proportions in postpartum uteri. Tissue-resident and tissue-committed subsets remained stable relative to recruited macrophages; however, there were fluctuations the proportions of these cells in response to parity and inflammation exposure. To assess differences in macrophage function, F4/80+ macrophages were isolated from uteri and stimulated with Pam3Cys-LK4. Uterine macrophages of pregnant and postpartum mice displayed heightened cytokine responses to Pam3Cys-LK4 compared with non-pregnant controls, suggesting that pregnancy alone induces a form of innate immune memory within the uterine environment. Overall, maternal inflammation alters uterine macrophage populations, with effects persisting beyond the gestational period. These changes were associated with adverse pregnancy outcomes. This research enhances our understanding of how maternal immunity links pregnancy complications to long-term reproductive health and points to new avenues for therapeutic strategies for preventing recurrent loss.