Inhibition of Epithelial-Mesenchymal Transition Maintains Stemness in Human Amniotic Epithelial Cells

Scale-Up of Human Amniotic Epithelial Cells Through Regulation of Epithelial-Mesenchymal Plasticity Under Defined Conditions

Human amniotic epithelial cells (hAECs) have shown excellent efficacy in clinical research and have prospective applications in the treatment of many diseases. However, the properties of the hAECs and their proliferative mechanisms remain unclear. Here, single-cell RNA sequencing (scRNA-seq) is performed on hAECs obtained from amniotic tissues at different gestational ages and passages during in vitro culture. The results showed that the proliferation of hAECs is associated with epithelial-mesenchymal plasticity (EMP) during amniogenesis. Freshly isolated, full-term hAECs are identified as mature epithelial cells. Once cultured in vitro, they are observed to rapidly undergo epithelial-mesenchymal transition (EMT) and enter a partial epithelial-mesenchymal transition (pEMT) state to regain their EMP properties and proliferation capacities. With the continuous development of EMT, hAECs eventually enter a senescent state. The addition of SB431542 and microcarrier screening enabled the effective 3D expansion of hAECs by 50 fold while maintaining the EMP status in hAECs for further proliferation. This study not only elucidated the central proliferation mechanism of hAECs during development and expansion but also optimized the in vitro culture system so that it is sufficient to generate hAECs for 50 patients from a single donor amniotic membrane.

Roles of TGF-β1 in Viral Infection during Pregnancy: Research Update and Perspectives

Transforming growth factor-beta 1 (TGF-β1) is a pleiotropic growth factor playing various roles in the human body including cell growth and development. More functions of TGF-β1 have been discovered, especially its roles in viral infection. TGF-β1 is abundant at the maternal-fetal interface during pregnancy and plays an important function in immune tolerance, an essential key factor for pregnancy success. It plays some critical roles in viral infection in pregnancy, such as its effects on the infection and replication of human cytomegalovirus in syncytiotrophoblasts. Interestingly, its role in the enhancement of Zika virus (ZIKV) infection and replication in first-trimester trophoblasts has recently been reported. The above up-to-date findings have opened one of the promising approaches to studying the mechanisms of viral infection during pregnancy with links to corresponding congenital syndromes. In this article, we review our current and recent advances in understanding the roles of TGF-β1 in viral infection. Our discussion focuses on viral infection during pregnancy, especially in the first trimester. We highlight the mutual roles of viral infection and TGF-β1 in specific contexts and possible functions of the Smad pathway in viral infection, with a special note on ZIKV infection. In addition, we discuss promising approaches to performing further studies on this topic.

TGF-β1 Promotes Zika Virus Infection in Immortalized Human First-Trimester Trophoblasts via the Smad Pathway

The Zika virus (ZIKV) is well known for causing congenital Zika syndrome if the infection occurs during pregnancy; however, the mechanism by which the virus infects and crosses the placenta barrier has not been completely understood. In pregnancy, TGF-β1 is abundant at the maternal–fetal interface. TGF-β1 has been reported to enhance rubella virus binding and infection in human lung epithelial cells. Therefore, in this study, we investigate the role of TGF-β1 in ZIKV infection in the immortalized human first-trimester trophoblasts, i.e., Swan.71. The cells were treated with TGF-β1 (10 ng/mL) for two days before being inoculated with the virus (American strain PRVABC59) at a multiplicity of infection of five. The results showed an enhancement of ZIKV infection, as demonstrated by the immunofluorescent assay and flow cytometry analysis. Such enhanced infection effects were abolished using SB431542 or SB525334, inhibitors of the TGF-β/Smad signaling pathway. An approximately 2-fold increase in the virus binding to the studied trophoblasts was found. In the presence of the Smad inhibitors, virus replication was significantly suppressed. An enhancement in Tyro3 and AXL (receptors for ZIKV) expression induced by TGF-β1 was also noted. The results suggest that TGF-β1 promotes the virus infection via the Smad pathway. Further studies should be carried out to clarify the underlying mechanisms of these findings.

Fetal macrophages assist in the repair of ruptured amnion through the induction of epithelial-mesenchymal transition

The premature rupture of the amniotic sac, a condition referred to as a preterm prelabor rupture of membranes (pPROM), is a leading cause of preterm birth. In some cases, these ruptured membranes heal spontaneously. Here, we investigated repair mechanisms of the amnion, a layer of epithelial cells in the amniotic sac closest to the embryo. Macrophages migrated to and resided at rupture sites in both human and mouse amnion. A process called epithelial-mesenchymal transition (EMT), in which epithelial cells acquire a mesenchymal phenotype and which is implicated in tissue repair, was observed at rupture sites. In dams bearing macrophage-depleted fetuses, the repair of amnion ruptures was compromised, and EMT was rarely detected at rupture sites. The migration of cultured amnion epithelial cells in wound healing assays was mediated by EMT through transforming growth factor-β (TGF-β)-Smad signaling. These findings suggest that fetal macrophages are crucial in amnion repair because of their ability to induce EMT in amnion epithelial cells.