Zika virus targets human trophoblast stem cells and prevents syncytialization in placental trophoblast organoids

An engineered human placental organoid microphysiological system in a vascular niche to model viral infection

The placenta forms the maternal-fetal interface to protect the developing fetus from xenobiotics or pathogens. However, the understanding of complex placental features and responses to pathogens are hindered due to the lack of near-physiological models. Here, we present an engineered human placental organoid microphysiological system (MPS) incorporated with vascular endothelium, which allows to recapitulate early placental features in a vascular niche. The MPS comprises a customized insert-based organ chip and a rocker, enabling in situ differentiation and formation of placental organoids from human trophoblast stem cells under dynamic culture conditions. By incorporating vascular endothelium, trophoblast organoids (TOs) maintain improved cell viability, long-term trophoblast proliferation and differentiation. Moreover, trophoblast organoids cocultured with endothelium (EndTOs) show the activation of innate immune-related signaling pathways and high-level secretion of distinct immunomodulatory factors, including antiviral type I and III interferons and trophoblast-specific factors. We further demonstrate that EndTOs exhibit attenuated susceptibility to Zika virus (ZIKV) than single cultured TOs, indicating the crucial role of vascular niche in enhancing intrinsic antiviral defenses functions of trophoblasts. This bioinspired placental organoid MPS provides a useful platform for studying placental physiology and relevant diseases.

The HAVCR1-centric host factor network drives Zika virus vertical transmission

Zika virus (ZIKV) vertical transmission results in devastating congenital malformations and pregnancy complications; however, the specific receptor and host factors facilitating ZIKV maternal-fetal transmission remain elusive. Here, we employ a genome-wide CRISPR screening and identify multiple placenta-intrinsic factors modulating ZIKV infection. Our study unveils that hepatitis A virus cellular receptor 1 (HAVCR1) serves as a primary receptor governing ZIKV entry in placental trophoblasts. The GATA3-HAVCR1 axis regulates heterogeneous cell tropism in the placenta. Notably, placenta-specific Havcr1 deletion in mice significantly impairs ZIKV transplacental transmission and associated adverse pregnancy outcomes. Mechanistically, the immunoglobulin variable-like domain of HAVCR1 binds to ZIKV via domain III of envelope protein and virion-associated phosphatidylserine. Proteomic profiling and function analyses reveal that AP2S1 cooperates with HAVCR1 for ZIKV internalization through clathrin-mediated endocytosis. Overall, our work underscores the pivotal role of HAVCR1 in mediating ZIKV vertical transmission and highlights a therapeutic target for alleviating congenital Zika syndrome.

The first trimester human placenta responds to Zika virus infection inducing an interferon (IFN) and antiviral interferon stimulated gene (ISG) response

BACKGROUND

Zika virus (ZIKV) is a positive-strand RNA virus of the Flaviviridae family. Maternal ZIKV infection during pregnancy can spread to the placenta and fetus causing severe neurological defects and infants born with microcephaly. Here, we investigated ZIKV infection and the cellular innate antiviral immune response in first trimester human placental explant cultures and isolated primary villus cytotrophoblasts (CTBs).

METHODS

Placentas were obtained with informed consent from women undergoing elective pregnancy termination and either cultured as placental explants or used to isolate primary CTBs. Explants and CTBs were both infected with ZIKV (PRVABC59), and samples evaluated for infection by qRT-PCR, viral plaque and ELISA assays, and immunohistochemical or immunocytochemical staining.

RESULTS

We demonstrate robust infection and production of ZIKV in placental explant and CTB cultures. Both displayed delayed upregulation of interferons (IFN), most notably IFNβ and IFNλ2/3, and a panel of interferon stimulated genes (ISG) (IFI6, IFIT1, IFIT2, IFITM1, ISG15, MX1, RSAD). Stimulation of explants and CTBs with the dsRNA mimic poly(I: C), caused immediate IFN and ISG upregulation, demonstrating the first trimester placenta is innate immune competent. This suggests that either ZIKV blocks the early innate response, or the placental response is inherently hindered.

CONCLUSION

Together these data show that first trimester placenta is susceptible to ZIKV infection which induces a delayed type III IFN antiviral response. This delay likely creates an environment favourable to ZIKV replication and dissemination across the early gestation placenta to fetal tissue, causing pathologies associated with congenital ZIKV syndrome.

Clinical applications of human organoids

Organoids are innovative three-dimensional and self-organizing cell cultures of various lineages that can be used to study diverse tissues and organs. Human organoids have dramatically increased our understanding of developmental and disease biology. They provide a patient-specific model to study known diseases, with advantages over animal models, and can also provide insights into emerging and future health threats related to climate change, zoonotic infections, environmental pollutants or even microgravity during space exploration. Furthermore, organoids show potential for regenerative cell therapies and organ transplantation. Still, several challenges for broad clinical application remain, including inefficiencies in initiation and expansion, increasing model complexity and difficulties with upscaling clinical-grade cultures and developing more organ-specific human tissue microenvironments. To achieve the full potential of organoid technology, interdisciplinary efforts are needed, integrating advances from biology, bioengineering, computational science, ethics and clinical research. In this Review, we showcase pivotal achievements in epithelial organoid research and technologies and provide an outlook for the future of organoids in advancing human health and medicine.

Autophagy-Mediated Downregulation of AXL and TIM-1 Promotes Sustained Zika Virus Infection

Zika virus (ZIKV) infection can lead to a variety of clinical outcomes, including severe congenital abnormalities. The phosphatidylserine (PS) receptors AXL and TIM-1 are recognized as critical entry factors for ZIKV in vitro. However, it remains unclear if and how ZIKV regulates these receptors during infection. In this study, we investigated AXL and TIM-1 expression in human alveolar basal epithelial A549 cells, glioblastoma U87 cells, and embryonic stem cells-derived trophoblast following ZIKV infection. We found that both the Asian strain FSS13025 and the African strain MR766 of ZIKV downregulate AXL, with a milder effect on TIM-1. We identified several ZIKV proteins, notably envelope (E), NS2A, NS3, and NS4B, that contribute to this downregulation. Notably, treatment with lysosomal inhibitor NH4Cl or the autophagy inhibitor 3-Methyladenine (3-MA) mitigated the AXL/TIM-1 downregulation, indicating autophagy's involvement in the process. Importantly, this downregulation facilitates sustained viral replication and promotes viral spread by preventing superinfection and limiting cell death, which is also associated with impaired innate immune signaling. Our findings uncover a mechanism by which ZIKV downregulates entry factors to enhance prolonged viral replication and spread.

Teratogenic parasites: disease mechanisms and emerging study models

Congenital infections are a leading preventable cause of pregnancy complications impacting both mother and fetus. Although advancements have been made in understanding various congenital infections, the mechanisms of parasitic infections during pregnancy remain poorly understood. This review covers the global incidence of three parasites capable of congenital transmission - Trypanosoma cruzi, Plasmodium spp., and Toxoplasma gondii - and the state of research into their transplacental transmission strategies. We highlight technological advancements in placental modeling that offer opportunities to reveal how parasites cause gestational pathology. Additionally, we discuss the likelihood that selective adaptation contributed to the evolution of mechanisms that facilitate placental infection. These insights provide a foundation for understanding the progression and pathology of congenital parasitic diseases and identifying future research directions.

SARS-CoV-2 ORF3a Protein Impairs Syncytiotrophoblast Maturation, Alters ZO-1 Localization, and Shifts Autophagic Pathways in Trophoblast Cells and 3D Organoids

SARS-CoV-2 infection poses a significant risk to placental physiology, but its impact on placental homeostasis is not well understood. We and others have previously shown that SARS-CoV-2 can colonize maternal and fetal placental cells, yet the specific mechanisms remain unclear. In this study, we investigate ORF3a, a key accessory protein of SARS-CoV-2 that exhibits continuous mutations. Our findings reveal that ORF3a is present in placental tissue from pregnant women infected with SARS-CoV-2 and disrupts autophagic flux in placental cell lines and 3D stem-cell-derived trophoblast organoids (SC-TOs), impairing syncytiotrophoblast differentiation and trophoblast invasion. This disruption leads to protein aggregation in cytotrophoblasts (CTB) and activates secretory autophagy, increasing CD63+ extracellular vesicle secretion, along with ORF3a itself. ORF3a also compromises CTB barrier integrity by disrupting tight junctions via interaction with ZO-1, mediated by its PDZ-binding motif, SVPL. Co-localization of ORF3a and ZO-1 in SARS-CoV-2-infected human placental tissue supports our in vitro findings. Deleting the PDZ binding motif in the ORF3a protein (ORF3a-noPBM mutant) restored proper ZO-1 localization at the cell junctions in an autophagy-independent manner. Lastly, we demonstrate that constitutive ORF3a expression induces SC-TOs to transition towards a secretory autophagy pathway likely via the PBM motif, as the ORF3a-NoPBM mutants showed a significant lack of CD63 expression. This study demonstrates the functional impact of ORF3a on placental autophagy and reveals a new mechanism for the activation of secretory autophagy, which may lead to increased extracellular vesicle secretion. These findings provide a foundation for exploring therapeutic approaches targeting ORF3a, specifically focusing on its PBM region to block its interactions with host cellular proteins and limiting placental impact.

Fetal MAVS and type I IFN signaling pathways control ZIKV infection in the placenta and maternal decidua

The contribution of placental immune responses to congenital Zika virus (ZIKV) syndrome remains poorly understood. Here, we leveraged a mouse model of ZIKV infection to identify mechanisms of innate immune restriction exclusively in the fetal compartment of the placenta. ZIKV principally infected mononuclear trophoblasts in the junctional zone, which was limited by mitochondrial antiviral-signaling protein (MAVS) and type I interferon (IFN) signaling mechanisms. Single nuclear RNA sequencing revealed MAVS-dependent expression of IFN-stimulated genes (ISGs) in spongiotrophoblasts but not in other placental cells that use alternate pathways to induce ISGs. ZIKV infection of Ifnar1-/- or Mavs-/- placentas was associated with greater infection of the adjacent immunocompetent decidua, and heterozygous Mavs+/- or Ifnar1+/- dams carrying immunodeficient fetuses sustained greater maternal viremia and tissue infection than dams carrying wild-type fetuses. Thus, MAVS-IFN signaling in the fetus restricts ZIKV infection in junctional zone trophoblasts, which modulates dissemination and outcome for both the fetus and the pregnant mother.

Alteration of Trophoblast Syncytialization by Plasmodium falciparum-Infected Erythrocytes

Malaria during pregnancy has been associated with significant risks to both the mother and the fetus, leading to complications such as anemia, low birth weight, and increased infant mortality. The trophoblast cells, a key component of the placenta, are crucial for nutrient and oxygen exchange between mother and fetus. The differentiation of cytotrophoblasts (CTBs) into syncytiotrophoblasts (STBs) is critical for proper pregnancy development. These cells form the bi-stratified epithelium surrounding the placental villi. While previous studies have described an inflammatory activation of STB cells exposed to Plasmodium falciparum-infected erythrocytes (P. falciparum-IE) or components such as hemozoin (HZ), little is known about the direct effect this parasite may have on the epithelial turnover and function of trophoblast cells. This study aims to contribute to understanding mechanisms leading to placental damage during placental malaria using a BeWo cell line as a differentiation model. It was found that P. falciparum-IE interferes with the fusion of BeWo cells, affecting the differentiation process of trophoblast. A reduction in syncytialization could be associated with the adverse effects of infection in fetal health, altering the remodeling of the trophoblast epithelial barrier and reducing their capacity to exchange substances. However, further studies are necessary to assess alterations in the functionality of this epithelium.

Endocytosis at the maternal-fetal interface: balancing nutrient transport and pathogen defense

Endocytosis represents a category of regulated active transport mechanisms. These encompass clathrin-dependent and -independent mechanisms, as well as fluid phase micropinocytosis and macropinocytosis, each demonstrating varying degrees of specificity and capacity. Collectively, these mechanisms facilitate the internalization of cargo into cellular vesicles. Pregnancy is one such physiological state during which endocytosis may play critical roles. A successful pregnancy necessitates ongoing communication between maternal and fetal cells at the maternal-fetal interface to ensure immunologic tolerance for the semi-allogenic fetus whilst providing adequate protection against infection from pathogens, such as viruses and bacteria. It also requires transport of nutrients across the maternal-fetal interface, but restriction of potentially harmful chemicals and drugs to allow fetal development. In this context, trogocytosis, a specific form of endocytosis, plays a crucial role in immunological tolerance and infection prevention. Endocytosis is also thought to play a significant role in nutrient and toxin handling at the maternal-fetal interface, though its mechanisms remain less understood. A comprehensive understanding of endocytosis and its mechanisms not only enhances our knowledge of maternal-fetal interactions but is also essential for identifying the pathogenesis of pregnancy pathologies and providing new avenues for therapeutic intervention.

Exploring the role of brain-derived extracellular vesicles in viral infections: from pathological insights to biomarker potential

Extracellular vesicles (EVs) are membrane-bound vesicles secreted by all cell types that play a central role in cell-to-cell communication. Since these vesicles serve as vehicles of cellular content (nucleic acids, proteins and lipids) with the potential to cross biological barriers, they represent a novel attractive window into an otherwise inaccessible organ, such as the brain. The composition of EVs is cell-type specific and mirrors the physiological condition of the cell-of-origin. Consequently, during viral infection, EVs undergo significant changes in their content and morphology, thereby reflecting alterations in the cellular state. Here, we briefly summarize the potential of brain-derived EVs as a lens into viral infection in the central nervous system, thereby: 1) uncovering underlying pathophysiological processes at play and 2) serving as liquid biopsies of the brain, representing a non-invasive source of biomarkers for monitoring disease activity. Although translating the potential of EVs from research to diagnosis poses complexities, characterizing brain-derived EVs in the context of viral infections holds promise to enhance diagnostic and therapeutic strategies, offering new avenues for managing infectious neurological diseases.

Current strategies using 3D organoids to establish in vitro maternal-embryonic interaction

IMPORTANCE

The creation of robust maternal-embryonic interactions and implantation models is important for comprehending the early stages of embryonic development and reproductive disorders. Traditional two-dimensional (2D) cell culture systems often fail to accurately mimic the highly complex in vivo conditions. The employment of three-dimensional (3D) organoids has emerged as a promising strategy to overcome these limitations in recent years. The advancements in the field of organoid technology have opened new avenues for studying the physiology and diseases affecting female reproductive tract.

OBSERVATIONS

This review summarizes the current strategies and advancements in the field of 3D organoids to establish maternal-embryonic interaction and implantation models for use in research and personalized medicine in assisted reproductive technology. The concepts of endometrial organoids, menstrual blood flow organoids, placental trophoblast organoids, stem cell-derived blastoids, and in vitro-generated embryo models are discussed in detail. We show the incorportaion of organoid systems and microfluidic technology to enhance tissue performance and precise management of the cellular surroundings.

CONCLUSIONS AND RELEVANCE

This review provides insights into the future direction of modeling maternal-embryonic interaction research and its combination with other powerful technologies to interfere with this dialogue either by promoting or hindering it for improving fertility or methods for contraception, respectively. The merging of organoid systems with microfluidics facilitates the creation of sophisticated and functional organoid models, enhancing insights into organ development, disease mechanisms, and personalized medical investigations.

Human trophoblast stem cells restrict human cytomegalovirus replication

Placental infection plays a central role in the pathogenesis of congenital human cytomegalovirus (HCMV) infections and is a cause of fetal growth restriction and pregnancy loss. HCMV can replicate in some trophoblast cell types, but it remains unclear how the virus evades antiviral immunity in the placenta and how infection compromises placental development and function. Human trophoblast stem cells (TSCs) can be differentiated into extravillous trophoblasts (EVTs), syncytiotrophoblasts (STBs), and organoids, and this study assessed the utility of TSCs as a model of HCMV infection in the first-trimester placenta. HCMV was found to non-productively infect TSCs, EVTs, and STBs. Immunofluorescence assays and flow cytometry experiments further revealed that infected TSCs frequently only express immediate early viral gene products. Similarly, RNA sequencing found that viral gene expression in TSCs does not follow the kinetic patterns observed during lytic infection in fibroblasts. Canonical antiviral responses were largely not observed in HCMV-infected TSCs and TSC-derived trophoblasts. Rather, infection dysregulated factors involved in cell identity, differentiation, and Wingless/Integrated signaling. Thus, while HCMV does not replicate in TSCs, infection may perturb trophoblast differentiation in ways that could interfere with placental function.

IMPORTANCE

Placental infection plays a central role in human cytomegalovirus (HCMV) pathogenesis during pregnancy, but the species specificity of HCMV and the limited availability and lifespan of primary trophoblasts have been persistent barriers to understanding how infection impacts this vital organ. Human trophoblast stem cells (TSCs) represent a new approach to modeling viral infection early in placental development. This study reveals that TSCs, like other stem cell types, restrict HCMV replication. However, infection perturbs the expression of genes involved in differentiation and cell fate determination, pointing to a mechanism by which HCMV could cause placental injury.

Implication of viruses in the etiology of preeclampsia

Preeclampsia is one of the most common disorders that poses threat to both mothers and neonates and a major contributor to perinatal morbidity and mortality worldwide. Viral infection during pregnancy is not typically considered to cause preeclampsia; however, syndromic nature of preeclampsia etiology and the immunomodulatory effects of viral infections suggest that microbes could trigger a subset of preeclampsia. Notably, SARS-CoV-2 infection is associated with an increased risk of preeclampsia. Herein, we review the potential role of viral infections in this great obstetrical syndrome. According to in vitro and in vivo experimental studies, viral infections can cause preeclampsia by introducing poor placentation, syncytiotrophoblast stress, and/or maternal systemic inflammation, which are all known to play a critical role in the development of preeclampsia. Moreover, clinical and experimental investigations have suggested a link between several viruses and the onset of preeclampsia via multiple pathways. However, the results of experimental and clinical research are not always consistent. Therefore, future studies should investigate the causal link between viral infections and preeclampsia to elucidate the mechanism behind this relationship and the etiology of preeclampsia itself.

Endogenous retrovirus HERVH-derived lncRNA UCA1 controls human trophoblast development

Endogenous retroviruses (ERVs) are frequently reactivated in mammalian placenta. It has been proposed that ERVs contribute to shaping the gene regulatory network of mammalian trophoblasts, dominantly acting as species- and placental-specific enhancers. However, whether and how ERVs control human trophoblast development through alternative pathways remains poorly understood. Besides the well-recognized function of human endogenous retrovirus-H (HERVH) in maintaining pluripotency of early human epiblast, here we present a unique role of HERVH on trophoblast lineage development. We found that the LTR7C/HERVH subfamily exhibits an accessible chromatin state in the human trophoblast lineage. Particularly, the LTR7C/HERVH-derived Urothelial Cancer Associated 1 (UCA1), a primate-specific long non-coding RNA (lncRNA), is transcribed in human trophoblasts and promotes the proliferation of human trophoblast stem cells (hTSCs), whereas its ectopic expression compromises human trophoblast syncytialization coinciding with increased interferon signaling pathway. Importantly, UCA1 upregulation is detectable in placental samples from early-onset preeclampsia (EO-PE) patients and the transcriptome of EO-PE placenta exhibits considerable similarities to that of the syncytiotrophoblasts differentiated from UCA1-overexpressing hTSCs, supporting up-regulated UCA1 as a potential biomarker of this disease. Altogether, our data shed light on the versatile regulatory role of HERVH in early human development and provide a unique mechanism whereby ERVs exert a function in human placentation and placental syndromes.

Single-cell RNA sequencing to understand host-virus interactions

Single-cell RNA sequencing (scRNA-seq) has allowed for the profiling of host and virus transcripts and host-virus interactions at single-cell resolution. This review summarizes the existing scRNA-seq technologies together with their strengths and weaknesses. The applications of scRNA-seq in various virological studies are discussed in depth, which broaden the understanding of the immune atlas, host-virus interactions, and immune repertoire. scRNA-seq can be widely used for virology in the near future to better understand the pathogenic mechanisms and discover more effective therapeutic strategies.

Human Trophoblast Stem Cells Restrict Human Cytomegalovirus Replication

Placental infection plays a central role in the pathogenesis of congenital human cytomegalovirus (HCMV) infections and is a cause of fetal growth restriction and pregnancy loss. HCMV can replicate in some trophoblast cell types, but it remains unclear how the virus evades antiviral immunity in the placenta and how infection compromises placental development and function. Human trophoblast stem cells (TSCs) can be differentiated into extravillous trophoblasts (EVTs), syncytiotrophoblasts (STBs), and organoids, and this study assessed the utility of TSCs as a model of HCMV infection in the first trimester placenta. HCMV was found to non-productively infect TSCs, EVTs, and STBs. Immunofluorescence assays and flow cytometry experiments further revealed that infected TSCs frequently only express immediate early viral gene products. Similarly, RNA-sequencing found that viral gene expression in TSCs does not follow the kinetic patterns observed during lytic infection in fibroblasts. Canonical antiviral responses were largely not observed in HCMV-infected TSCs and TSC-derived trophoblasts. Rather, infection dysregulated factors involved in cell identity, differentiation, and WNT signaling. Thus, while HCMV does not replicate in TSCs, infection may perturb trophoblast differentiation in ways that could interfere with placental function.

Importance

Placental infection plays a central role in HCMV pathogenesis during pregnancy, but the species-specificity of HCMV and the limited availability and lifespan of primary trophoblasts have been persistent barriers to understanding how infection impacts this vital organ. Human TSCs represent a new approach to modeling viral infection early in placental development. This study reveals that TSCs, like other stem cell types, restrict HCMV replication. However, infection perturbs the expression of genes involved in differentiation and cell fate determination, pointing to a mechanism by which HCMV could cause placental injury.