In conversation with the fetus: Implications of host-microbial bi-directional interactions “eavesdropping” in pregnancy physiology.

Saha Shikha¹, Bittor Jemima², Shehata Emad¹, Beasy Gemma¹, Rodriguez-Cuenca Sergio⁴, Cook Emma², Stephens Katie², Kroon A Paul¹, Lartey Jonathan¹, Smith SC Gordon^{2, 3}, Hayhoe Antonietta¹, and Charnock-Jones D Stephen^{2, 3}, Day-Walsh E Priscilla^{1, 2,3}

¹Quadram Institute Bioscience, Norwich Research Park, Norwich NR4 7UQ, UK

²Department of Obstetrics and Gynaecology, University of Cambridge, School of Clinical Medicine Cambridge, UK,

³The Loke Centre for Trophoblast Research (LCTR), Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK,

⁴Wellcome-MRC Institute of Metabolic Science, University of Cambridge, Cambridge, UK

Abstract Text:

Pregnancy is punctuated by profound physiological changes including but not limited to energy metabolism, immune and endocrine function. Alterations in these processes can lead to adverse pregnancy outcomes which contribute to nearly 5 million infant and maternal deaths annually. Physiological adaptations in pregnancy occur in the presence of large metabolically active commensal microbial communities with an immense capacity to respond to environmental cues and produce bioactive molecules. These bioactive molecules affect key host physiological functions including neuro-endocrine signalling, energy metabolism and immune maturity, the very factors important for pregnancy physiology.  Armed with a diverse protein coding gene pool which is 100-fold higher than that of the human host, the microbiome multiplies the metabolic and signalling capacity of the host. While the maternal microbiome concomitantly changes with maternal physiological adaptations as pregnancy progresses, factors mediating host-microbial interactions in pregnancy are poorly understood.

Using the in-vitro human colon model and LC-MS-MS we show that the microbiome can produce a wide range of bioactive indole-derivatives including tryptamine (tryp) and indole-3-acetic acid (IAA) from tryptophan. Most of these metabolites cross the maternal gut barrier and reach the systemic circulation. With exceptional of tryp, these metabolites were higher in cord than maternal serum suggesting active transport across the placenta to the fetus. The presence of tryp in the maternal serum and placental tissue but not the cord serum suggests possible metabolism within the placenta. Based on structural similarity with serotonin, IAA may also be produced from tryp within the placenta as a non-toxic tryp derivative. Using primary human trophoblast cells, β-hCG immuno assays and Mitostress test, we show that tryp, but not IAA dose dependently reduces trophoblast respiration and differentiation. Forskolin mediates trophoblast differentiation by increasing intracellular cyclic AMP and tryp inhibited the forskolin mediated trophoblast differentiation suggesting effects on cAMP signalling. We further confirm that tryp inhibits cAMP production via inhibitory G-protein Coupled Receptors (GPCRs) with lower concentrations of tryp decreasing cAMP and higher concentrations pharmacologically rather than physiologically increasing cAMP.  Using the POPs transcript database we show that transcripts of proteins which may be involved in tryp transport (TAT1), metabolism (monoamine oxidases (MAOs)) and signalling (adenyl cyclases) are altered in placentas of preeclamptic mothers.

Trophoblast differentiation is pre-requisite to embryo implantation and is crucial for successful pregnancy. We show that the microbial-derived bioactive metabolite tryp but not IAA alter both trophoblast respiration and differentiation. Altered microbial communities may lead to increased tryp production. Tryp detoxification may be mediated by the production of IAA via MAOs. Thus, the placenta must “eavesdrop” on the microbiome and respond to high tryp by modulating its MAO levels and activity to prevent tryp accumulation and continual GPCR signalling. Alterations in the bi-directional eavesdropping and interaction between the host and the microbiome may thus lead to adverse pregnancy outcomes such as preeclampsia and fetal growth restriction.