My Journeys with Three Microbes in the Reproductive Tract

ABSTRACT

Problem: The placenta performs various functions of the lung/GI/GU tract for the developing fetus, while also moderating host defenses of the fetus against infections in utero, and likely educates the developing fetal immune system. It thus has long-term impacts on the health of both the woman and the child. Knowledge is limited about the underlying mechanisms that enable the placenta to serve as a protective barrier for the fetus against infection. The long-term goals of my research program are to, 1) elucidate the normal barriers to infection in the placenta and show how dysfunction in barrier function can lead to adverse maternal-fetal outcomes, 2) define how viral infections impact placental biology, and 3) characterize possible functional roles for the newly described microbiota at the maternal-fetal interface. Method of Study To address the above questions, our research includes the use human placentas, primary human trophoblasts and immune cells derived from term placentas, cultured placental cells, trophoblast organoids, and mousemodels. Results: We found that placentas from women who gave birth prematurely exhibit reduced autophagy activity. Prematurity and reduced autophagy levels were also strongly associated with maternal infection. In a mouse model of pregnancy, we showed that placentas from mice deficient for Atg16L1 were significantly less able to withstand infection, and the deficient mice gave birth prematurely upon an inflammatory stimulus. We have also shown that the autophagy pathway plays a key role in ZIKV vertical transmission from mother to fetus. We demonstrated that hydroxychloroquine (HCQ), an autophagy inhibitor approved for use in pregnant women, can attenuate placental and fetal ZIKV infection and ameliorate adverse placental and fetal outcomes. More recently, we have identified a small molecule inhibitor that targets the NS2B-NS3 protease of ZIKV and inhibits viral replication. It has recently become evident that SARS-CoV-2 infection is also associated with adverse outcomes for pregnant women, including preterm birth, preeclampsia, and fetal growth restriction. We localized SARS-CoV-2 to the placenta and showed that infection alters the Renin Angiotensin System (RAS) that regulates blood pressure, thereby increasing risk for preeclampsia. In new work, we are showing that SARS-CoV-2 non-structural proteins affect autophagy in different ways than in Zika virus. Finally, we have discovered that the maternal fetal interface of the placenta harbors intracellular resident microbes, and functionally demonstrated that they do not induce any inflammatory response or cell death but may promote immune tolerance and support normal pregnancy outcomes. Conclusions: For the past 10 years of my career, I have been working on host microbial interactions at the maternal fetal interface. Our work has led to new insights into viral infections, showing how they co-opt host defenses, and that tolerance may have microbial drivers. We have shown how cellular pathways in the placenta such as autophagy and RAS mechanistically regulate host defenses against pathogens, including ZIKV and SARS-CoV-2. Additionally, our studies provide a foundation for understanding possible 'commensal' microbial- placental interactions and hint at the functional importance of microbes at the fetal maternal interface in maintaining placental health and supporting fetal development.