Placenta May Protect Unborn Babies from COVID-19 during Pregnancy
Pilot study shows placenta blocks SARS-CoV-2 transmission; results could also have implications for preeclampsia
During pregnancy, the placenta is constantly working to nourish the fetus, bringing it nutrients and oxygen. Now, new research from a Boston University pilot study suggests the temporary organ could also be helping to protect the unborn baby from COVID-19. Researchers found that the placenta may act to block SARS-CoV-2 from traveling from an infected parent to their growing child.
While COVID-19 significantly impacts many pregnant people, the rates of transmission from mother to baby in pregnancy are very low. Researchers from the BU School of Medicine have discovered that the placenta’s ability to control a protein—angiotensin-converting enzyme 2, commonly known as ACE2—that allows SARS-CoV-2 to enter cells may be the secret to its defensive prowess.
In people who had COVID-19 during their pregnancy, ACE2 was present in lower levels in the placenta. The organ was seemingly ditching the protein—which is found all over the body and typically helps manage blood pressure and regulate inflammation—so the virus couldn’t latch on to it.
“We think that when a woman has COVID-19 in pregnancy, the placenta is shedding off ACE2 as a way to block SARS-CoV-2 from being passed to the fetus,” says Elizabeth S. Taglauer, a School of Medicine assistant professor of pediatrics, who helped lead the study. “Our results suggest that the placenta is somehow sensing the mother’s infection and guarding against fetal transmission. If we understand how the placenta is naturally protecting babies from COVID-19, this may provide important information for therapies and strategies to help prevent other SARS-CoV-2 infections from continuing to spread.”
The study involved collecting placentas from two groups of women who delivered at Boston Medical Center (BMC), BU’s primary teaching hospital, from July 2020 through April 2021. The first group was made up of people who had normal pregnancies and no report of SARS-CoV-2 infection. The second group included people who were SARS-CoV-2 positive and had active COVID-19 disease during pregnancy. Researchers observed the ACE2 expression in their placentas under the microscope and by using genetic and protein analysis techniques. The findings appear online in the American Journal of Pathology.
Because the placenta has many similarities in function with the lung—both organs cycle oxygen in and carbon dioxide out—the results may also allow researchers to gain new insights into how COVID-19 impacts the lungs of people who aren’t pregnant.
“The placenta during pregnancy functions as the fetal lung,” says Taglauer, who has studied placental biology and newborn lung biology as a neonatal physician-scientist. “We can’t take lungs out of COVID patients and study them while they’re living, but we can get at the human tissue, the placenta, right away after birth and use it to understand and inform some questions about the lung.”
And there may be implications beyond COVID too. A better understanding of ACE2 regulation, says Taglauer, may help advance treatment for preeclampsia, a serious pregnancy complication.
“ACE2 is also heavily involved in how our blood pressure is regulated and one of the big diseases of pregnancy that I focus on in my work is preeclampsia,” says Taglauer. Preeclampsia is marked by high blood pressure and can lead to organ failure, stroke, or death in pregnant people, and is the cause of 15 percent of premature births in the United States, according to March of Dimes. “Understanding how ACE2 can be regulated by an infection, or how the placenta is shedding it based on its environment, could potentially be important to help us understand how to improve preeclampsia.”
Next for the researchers is scaling up the study to see if its findings hold true in a larger population. After that, Taglauer hopes to examine the mechanism behind the placenta’s ACE2 regulation. In the meantime, she strongly advises all those planning to start a family—or who are already pregnant—to get a COVID vaccine.
“The most important thing for the success of a pregnancy is for the mother to be as healthy as possible. While the babies are being protected from getting the virus, mothers who are pregnant are getting sick, and we know that they have some risks for increased complications in pregnancy,” says Taglauer. “The placenta is a wonderful organ that can protect the babies, but it can only do so much—the mother’s body and health really need to remain stable and that’s why it’s important for them to be vaccinated. We also know through many studies that vaccination is safe for mother and baby during pregnancy.”
The study was coauthored by Elisha Wachman (MED’06), a School of Medicine associate professor of pediatrics and a neonatologist at Boston Medical Center, in collaboration with Ke Yuan, a lung vascular biologist at Boston Children’s Hospital, and Hongpeng Jia, an assistant professor of surgery at Johns Hopkins University. Funding was provided by the Boston University Clinical & Translational Science Institute’s COVID-19 Pilot Grant Program and the National Institutes of Health.