Suppression of progesterone by influenza A virus mediates adverse maternal and fetal outcomes in mice

Influenza A virus during pregnancy disrupts maternal intestinal immunity and fetal cortical development in a dose- and time-dependent manner

Epidemiological studies link exposure to viral infection during pregnancy, including influenza A virus (IAV) infection, with increased incidence of neurodevelopmental disorders (NDDs) in offspring. Models of maternal immune activation (MIA) using viral mimetics demonstrate that activation of maternal intestinal T helper 17 (TH17) cells, which produce effector cytokine interleukin (IL)-17, leads to aberrant fetal brain development, such as neocortical malformations. Fetal microglia and border-associated macrophages (BAMs) also serve as potential cellular mediators of MIA-induced cortical abnormalities. However, neither the inflammation-induced TH17 cell pathway nor fetal brain-resident macrophages have been thoroughly examined in models of live viral infection during pregnancy. Here, we inoculated pregnant mice with two infectious doses of IAV and evaluated peak innate and adaptive immune responses in the dam and fetus. While respiratory IAV infection led to dose-dependent maternal colonic shortening and microbial dysregulation, there was no elevation in intestinal TH17 cells nor IL-17. Systemically, IAV resulted in consistent dose- and time-dependent increases in IL-6 and IFN-γ. Fetal cortical abnormalities and global changes in fetal brain transcripts were observable in the high-but not the moderate-dose IAV group. Profiling of fetal microglia and BAMs revealed dose- and time-dependent differences in the numbers of meningeal but not choroid plexus BAMs, while microglial numbers and proliferative capacity of Iba1+ cells remained constant. Fetal brain-resident macrophages increased phagocytic CD68 expression, also in a dose- and time-dependent fashion. Taken together, our findings indicate that certain features of MIA are conserved between mimetic and live virus models, while others are not. Overall, we provide consistent evidence of an infection severity threshold for downstream maternal inflammation and fetal cortical abnormalities, which recapitulates a key feature of the epidemiological data and further underscores the importance of using live pathogens in NDD modeling to better evaluate the complete immune response and to improve translation to the clinic.

Decoding the molecular pathways governing trophoblast migration and placental development; a literature review

Placental development is a multifaceted process critical for a fruitful pregnancy, reinforced by a complex network of molecular pathways that synchronize trophoblast migration, differentiation, and overall placental function. This review provides an in-depth analysis of the key signaling pathways, such as Wnt, Notch, TGF-β, and VEGF, which play fundamental roles in trophoblast proliferation, invasion, and the complicated process of placental vascular development. For instance, the Wnt signaling pathway is essential to balance trophoblast stem cell proliferation and differentiation, while Notch signaling stimulates cell fate decisions and invasive behavior. TGF-β signaling plays a critical role in trophoblast invasion and differentiation, predominantly in response to the low oxygen environment of early pregnancy, regulated by hypoxia-inducible factors (HIFs). These factors promote trophoblast adaptation, ensure proper placental attachment and vascularization, and facilitate adequate fetal-maternal exchange. Further, we explore the epigenetic and post-transcriptional regulatory mechanisms that regulate trophoblast function, including DNA methylation and the contribution of non-coding RNAs, which contribute to the fine-tuning of gene expression during placental development. Dysregulation of these pathways is associated with severe pregnancy complications, such as preeclampsia, intrauterine growth restriction, and recurrent miscarriage, emphasizing the critical need for targeted therapeutic strategies. Finally, emerging technologies like trophoblast organoids, single-cell RNA sequencing, and placenta-on-chip models are discussed as innovative tools that hold promise for advancing our understanding of placental biology and developing novel interventions to improve pregnancy outcomes. This review emphasizes the importance of understanding these molecular mechanisms to better address placental dysfunctions and associated pregnancy disorders.

Pathogenesis of viral infections during pregnancy

SUMMARYViral infections during pregnancy are associated with significant adverse perinatal and fetal outcomes. Pregnancy is a unique immunologic and physiologic state, which can influence control of virus replication, severity of disease, and vertical transmission. The placenta is the organ of the maternal-fetal interface and provides defense against microbial infection while supporting the semi-allogeneic fetus via tolerogenic immune responses. Some viruses, such as cytomegalovirus, Zika virus, and rubella virus, can breach these defenses, directly infecting the fetus and having long-lasting consequences. Even without direct placental infection, other viruses, including respiratory viruses like influenza viruses and severe acute respiratory syndrome coronavirus 2, still cause placental damage and inflammation. Concentrations of progesterone and estrogens rise during pregnancy and contribute to immunological adaptations, placentation, and placental development and play a pivotal role in creating a tolerogenic environment at the maternal-fetal interface. Animal models, including mice, nonhuman primates, rabbits, and guinea pigs, are instrumental for mechanistic insights into the pathogenesis of viral infections during pregnancy and identification of targetable treatments to improve health outcomes of pregnant individuals and offspring.