Epigenetic regulation of cell-autonomous type I interferon responses in trophoblast

The placenta is an essential multi-functional organ that supports fetal development. Placental dysfunction has a major impact on both mother and fetus, and is associated with what are known as the great obstetrics syndromes, which include preeclampsia, intrauterine growth restriction and preterm birth. These in turn constitute risk factors for perinatal fetal mortality and morbidity, as well as long-term illness in adulthood. Yet the molecular underpinnings of placental dysfunction remain unclear, requiring research strategies that link basic mechanistic findings with phenotypes and clinical data.

In this proposal we will focus on the regulation of inflammation in the placenta, and how it impacts pregnancy outcomes. Specifically, we will study the regulation of the type I interferon (IFN) response, which constitutes an innate immunity pathway against pathogens such as viruses and bacteria. Notably, type I IFN responses are involved in normal processes in pregnancy such as labour, which presumably occur in sterile conditions. Similarly, dysregulation of type I IFNs is linked to preterm birth, yet this can also seemingly occur in the absence of infection. This suggests that there are cell-intrinsic triggers of inflammation in the placenta.

Indeed, we have found that trophoblast (cells of the placenta) can autonomously display a type I IFN response when cells are depleted of the KAP1 protein. KAP1 is an important accessory protein for epigenetic mechanisms that regulates not only the expression of genes, but also, and arguably most prominently, that of transposable elements (TEs). TEs are repetitive sequences that integrated and replicated within genomes, having expanded to make up approximately half of the human genome. TEs have played important roles in the evolution of the placenta. A key aspect of TE biology relevant to this proposal is that many are derived from ancient retroviruses and can mimic many of their actions, including triggering inflammatory responses within the cell. We therefore hypothesize that epigenetic deregulation of TEs can drive infection-independent type I IFN responses in the placenta, with potential impact for pregnancy outcomes. This is supported by preliminary data in cultured cells and human placentas.

We propose to test this hypothesis by investigating molecular mechanisms in cultured cells, testing phenotypes in animal models, and finally analysing placental samples from appropriate human cohorts. In cell culture models we will deepen our findings on KAP1 and expand it to other TE-regulatory pathways. We will also directly test for a role of TEs in driving type I IFN responses. In mice, we will test the effect of KAP1 and TE deregulation on markers of inflammation, placental development and gestational timing. In humans, we will ask whether sterile type I IFN responses are associated with TE deregulation, both in term and preterm placentas. Through this comprehensive work programme we aim to uncover novel mechanistic and clinical insights into placental inflammation, and its links to normal and pathological pregnancy events.

Human development relies heavily on the correct establishment of a feto-maternal interface, which is essential not only for reproductive success, but also for long-term adult health. The placenta is a key partner in that interface, and placental dysfunction is associated with unfavourable pregnancy outcomes, such as preeclampsia, intrauterine growth restriction and preterm birth.

Type I interferon (IFN) responses in the placenta are associated with term and preterm labour, and can seemingly occur in the absence of infection. One potential cell-intrinsic source of inflammatory triggers are transposable elements (TEs), which in contexts such as cancer and ageing can mimic virally-derived nucleic acids that serve as signals for innate immunity pathways. TEs have made major contributions to the evolution of the placenta, but their potential impact on inflammatory processes therein remains unexplored.

Our preliminary data in trophoblast stem cells and human samples suggest that the epigenetic accessory protein KAP1 silences TEs in trophoblast, suppressing an overt type I IFN response. Here we propose to test a link between epigenetic pathways, TE expression and type I IFN responses in the placenta, going from basic mechanisms to phenotypes and clinical associations. We will manipulate human and mouse trophoblast stem cells to test for roles of KAP1 and other epigenetic regulators in driving cell-intrinsic IFN responses via TEs. We will then test the same mechanisms in vivo using trophoblast-specific KAP1 knockout mice, and assessing its impact on development and gestational timing. Finally, we will transcriptionally profile human placentas where the infection state is known, as well as preterm placentas, to test for an association between TE expression and IFN-stimulated genes.

Our multi-layered approach aims to uncover novel mechanisms of placental inflammation regulation, and translate them into valuable clinical insights into pregnancy health.