Researcher Megan Sheridan

Megan Sheridan

New method leads to discovery of placental cell type

December 20, 2021 By Lauren Hines in Research Tags: placentas, stem cells

Spatial Sequencing — Nathan Bivens, director of the Genomics Technology Core at Bond Life Sciences Center, loads the Chromium 10X Genomics machine as part of the single-cell RNA sequence method. | photo by Lauren Hines, Bond LSC

By Lauren Hines | Bond LSC

During pregnancy, the fetus and mother can talk to each other without saying a word. On a deeper level, a special cell called the syncytiotrophoblast (STB) facilitates this conversation by changing the mother’s physiology based on what the fetus does or does not need.

The Michael Roberts lab at Bond Life Sciences Center knew there had to be other types of this essential cell. However, it wasn’t until postdoctoral fellow Teka Khan recently applied a method to analyze these cells that the lab reported for the first time two kinds of STBs.

“It was, as you can see, a new discovery in the field of placental and developmental biology,” Khan said. “We identified two different kinds of clusters from single nucleus RNA sequence, with a strong resemblance to STBs.”

These cells are responsible for gas exchange between the mother and the fetus — supplying oxygen via the placenta to the baby and disposing of carbon dioxide away from the fetus via circulation. It also produces a range of hormones including HCG, which helps maintain pregnancy. These cells line the placenta and lack many receptors and cell junctions commonly used by viruses to enter the cell, so in theory, they should be impenetrable to viruses.

“Anything that the syncytiotrophoblast is doing correctly or incorrectly could have a major impact on fetal development and then also how the maternal physiology is signaling,” said Megan Sheridan, postdoctoral fellow working with the Roberts lab.

Fully understanding these cells has been difficult due to their large size, fragility, cytoplasm nature and their unusual 5-15 nuclei. Researchers usually use single-cell RNA sequencing (scRNAseq) to understand different cell types in the human placenta since most cells only have one nucleus. However, STBs are least represented by most of these scRNAseq studies, since they are multinucleated, large and fragile.

Instead, Khan implemented a new method called single-nuclei RNA sequencing to analyze each individual nucleus.

“Before that, since people were doing single-cell RNA sequence, the syncytiotrophoblasts were … represented with very little information,” Khan said.

After using this method, Khan found two different nuclei clusters, indicating there were two different types. It was the first-ever attempt of its kind used on trophoblast cell colonies.

The two distinct kinds of STBs have differences in their gene expression profiles, which makes Khan believe they have different functions. However, it’s too early to say what those functions are.

Due to ethical and technical issues, researchers struggle to study the early stages of the human placenta. So, researchers use the BAP model of an early placenta to understand what’s going on in early pregnancy to eventually avoid disorders like miscarriages and preeclampsia. Better understanding this new type of syncytiotrophoblast and other placenta cells can bolster current models of the human placenta.

“Now we are doing the time course experiment using the same snRNAseq technology to see if we can identify how these cell types originate during the differentiation procedure and how they generate different kinds of cells,” Khan said. “This would definitely help us to understand the developmental process of the earliest stages of pregnancy and the placenta, especially the first two to three weeks of the placentation.”

Depending on the function of this new type, researchers could eventually create more targeted treatments.

“If [Khan] can then apply this to our preeclampsia models, then we could find signaling molecules that might be released by STB that is bad versus STB that’s good and see if we could find some sort of marker that would predict if the pregnancy might go wrong,” Sheridan said. “That’s way down the road, but that could be something.”

Now Khan is trying to find the functions of these two types of STBs and how he can apply this to the lab’s current model.

To learn more, read about single-nucleus RNA sequencing in Frontiers in Cell and Developmental Biology or about the BAP model used by the Roberts’ lab.

Turning Back the Clock

October 13, 2021 By Lauren Hines in Research Tags: COVID-19, preeclampsia, stem cells

Demonstrated Sample of Stem Cells — Megan Sheridan, a postdoctoral fellow working with the R. Michael Roberts lab, removes the base solution from a demonstrated sample of stem cells that will be grown into placental cells for study of their interaction with the Zika virus. | photo by Phillip Sitter, Bond LSC

By Lauren Hines | Bond LSC

At 24 weeks pregnant, a baby can hear the mother’s lullabies. At 30 weeks, her belly is a little over a foot large. At 40, the hospital bag is already packed and ready to go.

But imagine delivering only two weeks after the bump starts showing.

Preeclampsia makes induced birth necessary as life-threatening symptoms start 20 weeks into pregnancy, and delivery is the only cure. There is a lack of ways to detect it, and it’s difficult to ethically study the early stages of human reproduction. But what if it was possible to rewind the process to see when the source of the disorder took hold?

Different cellular models of the placenta might be that time machine researchers need to study early pregnancy disorders.

The Michael Roberts lab at Bond Life Sciences Center combines the knowledge and practices of three cellular models to learn more about early pregnancy and diseases.

“We can use these different models to study placental infection with viruses like Zika virus and, of course, COVID because there’s still a controversy as to whether COVID is a hazard in early pregnancy,” principal investigator Michael Roberts said. “And my suspicion is it probably is.”

The placenta is the brand-new organ generated by the embryo — the baby — before any of its other organs develop to give the baby nutrients and support as the embryo grows.

Megan Sheridan, postdoctoral fellow working with the Roberts lab, works on a project to combine 2D and 3D models to see how Zika and Dengue virus interact with the placenta and affect early pregnancy.

“[Complications] occur but you don’t necessarily know that until the end of pregnancy when the baby is delivered,” Sheridan said. “We really want to kind of go back in time and try to determine what’s going wrong in early pregnancy.”

Modeling early placental development is vital to see the beginning of disease complications, but the challenge is to get an accurate glimpse while not putting a healthy pregnancy at risk.

“It’s hard to get a good model to do research on that,” said Jie Zhou, postdoctoral fellow in the Roberts lab. “So that’s why we are working on different stem cells and trying to build up the best model to work on.”

So, the Roberts lab uses the BAP model. By working with a hospital, the lab first takes fibroblast cells from discarded umbilical cords after the baby is born. These fibroblast cells can be collected from mothers experiencing a normal pregnancy or pregnancies associated with complications, like preeclampsia. Then, as Sheridan puts it, they add a “cocktail of genes” to turn the cells into induced pluripotent stem cells. From there, the lab adds BAP — a mixture of growth factors and inhibitors that turn the stem cells into trophoblast cells.

Now the lab is back at the beginning of pregnancy except in a Petri dish of cells. In pregnancy, these trophoblast cells line the outside of the embryo.

From here, researchers can see what possibly caused the pregnancy complications in the first place.

“It’s trying to mimic pregnancy in a dish, essentially by using cells that will develop into placental-type cells,” Roberts said.

However, a flat Petri dish is nothing like a real placenta.

“It’s two-dimensional, and we can only culture the cells up to eight days after treatment so if we want to do long-term experiments, we can’t use this model,” Zhou said.

Two alternative models came out in 2018. The first model was by Hiroaki Okae et. al who created a 2D trophoblast cell line where trophoblasts can continually reproduce themselves long past eight days. The second model by Margherita Turco et. al also created a similar cell line, but in three dimensions.

This last model inches even closer to an early placenta. These 3D organoids float around inside a jello-like substance called Matrigel where they self-organize into a placental-like structure.

Together the two models give them a full picture. The 3D model gives a clue into how multiple cell types interact with each other while the 2D model allows researchers to see how a single cell type responds.

Since no model is perfect, the Roberts lab is combining their BAP model with protocols and growth conditions from the other two models to create a foundation for their experiments. Now researchers can start asking deeper questions.

While nothing is quite like a real womb, the Roberts lab will continue working backward.

“All of these models, put together, are really useful because we can kind of use them to their fullest potential and systematically assess which one might represent a certain disease or best answer a certain research question,” Sheridan said.