Varied research mirrors the complexity of preterm birth
Even when a zygote starts out with a healthy mix of genes, the 40-week journey for a human infant to reach full-term can be thrown off balance in many ways.
Some disruptions occur within days of conception, others happen months into the process. Any can trigger miscarriage and premature birth. Research efforts at Cincinnati Children’s are exploring ways to prevent disruptions and help more pregnancies end in success.
“We are talking about addressing fundamental, unanswered biological questions. What controls the duration of human gestation? Why are human pregnancies supposed to last 270 days, and who controls the timing – the mother? The fetus? Both?” says James Greenberg, MD, Co-Director of the Perinatal Institute at Cincinnati Children’s. “We need to understand the problem of preterm birth in a more granular sense than we do now.”
Getting a Good Start
S.K. Dey, PhD, Director, Division of Reproductive Sciences at Cincinnati Children’s, has devoted years of research to that understanding. Dey focuses on pinning down the molecular mechanisms of embryo implantation. Failed implantation ends a pregnancy within two weeks of fertilization. Not-quite-perfect implantation can lead to a variety of poor outcomes.
In a review article published in December 2012 in Nature Medicine, Dey and colleagues describe a “molecular dialogue” that flows between mother and embryo during implantation. When this cross-talk goes awry, it can lead to problems including preeclampsia, miscarriage and preterm birth.
Their work also shows how defects in specific genes – and the proteins they produce – can prevent successful implantation. It explains previously unknown details of the early stages of development and suggests a potential therapy to rescue some at-risk pregnancies.
In studies of mice, a single low dose of rapamycin (an immune suppressant used in organ transplantation) prevented preterm birth in mice genetically engineered to produce preterm pups. Published online in the October 2011 Proceedings of the National Academy of Sciences (PNAS), the study reports that the mTORC1 signaling pathway plays a critical role in fetal development and that it can be manipulated.
“Implantation is where the process starts. But our knowledge about this stage is lacking. What are the molecular players? How do the transitions work?” Dey asks. “Understanding these molecular signaling networks may lead to approaches to improve the outcome of natural pregnancy and pregnancy conceived through in vitro fertilization techniques.”
Several years of preparatory research must be completed first, Dey says, but the next major step will be to test these mouse model findings in human clinical trials.
Maintaining a Delicate Balance
Other researchers at Cincinnati Children’s are exploring the ways in which the mother’s body tricks its own immune system into accepting the developing fetus rather than attacking it as a foreign invader.
Sing Sing Way, MD, PhD, a pediatrician and researcher in the Division of Infectious Diseases, has published three important recent findings that describe the roles played during pregnancy by an immune suppressive CD4 T-cell subset called regulatory T-cells (T-regs).
First, Way and colleagues reported that pregnancy triggers an accumulation in T-reg levels, which dampens the mother’s immune system to allow the “invasion” of a developing fetus. However, this process also makes the mother more vulnerable to infections. These findings were published in July 2011 in Cell Host Microbe.
Then in a study published August 2012 in Public Library of Science (PLoS) Pathogens, Way and colleagues described how the prenatal pathogen Listeria monocytogenes can override the T-reg levels that maintain the mother’s immune system. This causes her body to attack the fetus and trigger a miscarriage. A similar process occurring later in pregnancy may be the cause of some premature births, Way says.
T-Regs With a Memory
These findings led to a breakthrough study published in October 2012 in Nature reporting that pregnancy does not simply trigger a surge in T-reg cells. Instead, the mother experiences a dramatic increase in T-regs that can “remember” past pregnancies. These T-reg cells recognize paternal antigens so that when the same father impregnates the mother again, the fetus is better protected.
This protective feature increases with multiple pregnancies involving the same father, making future miscarriages less likely. But the effect does not apply to pregnancies involving a new father. If the mother changes partners, Way’s team found that she reacts to a new fetus as if she had never been pregnant before.
Vaccinating Against Miscarriage
This finding supports the possibility of developing a vaccine to protect pregnancy, Way says.
Unlike typical vaccines, which boost immune response to an invading pathogen, a pregnancy vaccine would help suppress an expectant mother’s immune system. More importantly, vaccines could be tailored to match the father, which would preserve the T-regs with “memory” while suppressing T-regs that could attack a fetus.
If this process translates from mice to humans, the result could be vaccines to boost the chances of full-term birth for couples going through IVF treatments, first-time mothers, or women with a history of miscarriages.
Infection and Pregnancy
Vaginal yeast infections have plagued women worldwide for generations, but only in recent years has science begun to connect vaginal Candida colonization during pregnancy with an increased risk of premature birth.
Margaret Hostetter, MD, Director of the Division of Infectious Diseases, is using a $1 million grant from the Gates Foundation to study why such a common infection can cause such an uncommon outcome.
Candida vaginal infections occur in 22 to 38 percent of pregnant women in the US and in as many as 60 percent of pregnancies in low-resource nations. In many cases, symptoms are so mild that women may not even realize they have been infected.
For some women – experts cannot yet predict which women are most at risk – untreated yeast infections appear to disrupt the delicate balance of T-reg cells that protects the developing fetus from attack by the mother’s immune system.
A Link to Preterm Birth?
Hostetter is leading a three-year project to understand the mechanisms at work during a Candida vaginal infection. She hopes to determine why some infections are associated with premature births, while others are not. Her study was one of only five to be funded from more than 320 applications to the Global Alliance to Prevent Prematurity and Stillbirth, an initiative led by Seattle Children’s Hospital and funded by the Gates Foundation.
“The idea of a link between Candida colonization and premature birth is still debated,” Hostetter says. “But I think we may find that this pathogen is more directly involved than we thought.”
Hostetter’s team hypothesizes that yeast infections trigger a spike in inflammatory Th17 cells, which help attack the infection, but at the expense of T-reg cells needed to protect the fetus. This disruption in the immune system’s balance can lead to fetal wastage and premature birth.
“Preterm birth is the leading cause of death for newborns, affecting rich and poor countries alike,” says Gary Darmstadt, Director of Family Health at the Gates Foundation. “We urgently need to develop new solutions to give every baby a healthy start to life.”
The good news is that inexpensive antifungal treatments are widely available, even in low-resource nations. Results from this study could help identify the best times to screen for Candida and begin treatment.
The longer term goal is to understand how the immune system responds to Candida. It may reveal a pathway that also could be used to prevent pregnancy complications associated with other pathogens, such as E. coli, Trichomonas and Gardnerella bacteria.
The Impact of Stress
Scientists at Cincinnati Children’s also are working to gather hard data on a long-debated question – how much impact does maternal stress play in triggering preterm births?
Some studies suggest that psychological stress by itself plays no significant role in causing premature birth. However, other research clearly shows that stress can synergize with inflammation to cause preterm birth.
Louis Muglia, MD, PhD, Director of the Center for Prevention of Preterm Birth, and Claire Chougnet, PharmD, PhD, a researcher in the Division of Cellular and Molecular Immunology recently received notice that their application was well received by the NIH, and hope to co-lead a multidisciplinary effort to learn more about the connections between stress, infections and the immune response.
“We know that some people cope with stress much better than others. We also know that not every infection during pregnancy leads to preterm birth. So we theorize that there may be a complementary effect,” Chougnet says.
The challenge is how to glean precise data from such hard-to-measure factors. “Proving this theory is very difficult with observational studies in humans. There are too many uncontrollable variables,” Chougnet says.
Her project involves studying rhesus macaques under a variety of carefully controlled laboratory conditions, and will be done in collaboration with the California National Primate Research Center, one of the largest primate centers in the US. The research team involves experts in the physiology of pregnancy, immunology/inflammation, primate behavior and psychology, biostatistics and other fields.
The project will take several years to complete. But if successful, she says, the findings could suggest more effective ways to help anxious, would-be mothers minimize their risk of going into labor too early.