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Claire Marie Vacher

Placental function linked to brain injuries associated with autism

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Claire Marie Vacher

“We saw long-term cerebellar white matter alterations in male experimental models, and behavioral testing revealed social impairments and increased repetitive behaviors, two hallmark features of ASD,” says Claire-Marie Vacher, Ph.D., lead study author.

Allopregnanolone (ALLO), a hormone made by the placenta late in pregnancy, is such a potent neurosteroid that disrupting its steady supply to the developing fetus can leave it vulnerable to brain injuries associated with autism spectrum disorder (ASD), according to Children’s research presented during the Pediatric Academic Societies 2019 Annual Meeting.

In order to more effectively treat vulnerable babies, the Children’s research team first had to tease out what goes wrong in the careful choreography that is pregnancy. According to the Centers for Disease Control and Prevention, about 1 in 10 babies is born preterm, before 37 weeks of gestation. Premature birth is a major risk factor for ASD.

The placenta is an essential and understudied organ that is shared by the developing fetus and the pregnant mother, delivering oxygen, glucose and nutrients and ferrying out waste products. The placenta also delivers ALLO, a progesterone derivative, needed to ready the developing fetal brain for life outside the womb.

ALLO ramps up late in gestation. When babies are born prematurely, their supply of ALLO stops abruptly. That occurs at the same time the cerebellum – a brain region essential for motor coordination, posture, balance and social cognition– typically undergoes a dramatic growth spurt.

“Our experimental model demonstrates that losing placental ALLO alters cerebellar development, including white matter development,” says Anna Penn, M.D., Ph.D., a neonatologist in the divisions of Neonatology and Fetal Medicine, and a developmental neuroscientist at Children’s National. “Cerebellar white matter development occurs primarily after babies are born, so connecting a change in placental function during pregnancy with lingering impacts on later brain development is a particularly striking result.”

The research team created a novel experimental model in which the gene encoding the enzyme responsible for producing ALLO is deleted in the placenta. They compared these preclinical models with a control group and performed whole brain imaging and RNAseq gene expression analyses for both groups.

“We saw long-term cerebellar white matter alterations in male experimental models, and behavioral testing revealed social impairments and increased repetitive behaviors, two hallmark features of ASD,” says Claire-Marie Vacher, Ph.D., lead study author. “These male-specific outcomes parallel the increased risk of brain injury and ASD we see in human babies born prematurely.”

ALLO binds to specific GABA receptors, which control most inhibitory signaling in the nervous system.

“Our findings provide a new way to frame poor placental function: Subtle but significant changes in utero may set in motion neurodevelopmental disorders that children experience later in life,” adds Dr. Penn, the study’s senior author. “Future directions for our research could include identifying new targets in the placenta or brain that could be amenable to hormone supplementation, opening the potential for earlier treatment for high-risk fetuses.”

Pediatric Academic Societies 2019 Annual Meeting presentation

  • “Placental allopregnanolone loss alters postnatal cerebellar development and function.”
    • Sunday, April 28, 2019, 5:15 p.m. to 5:30 p.m. (EST)

Claire-Marie Vacher, Ph.D., lead author; Jackie Salzbank, co-author; Helene Lacaille, co-author; Dana Bakalar, co-author; Jiaqi O’Reilly, co-author; and Anna Penn, M.D., Ph.D., a neonatologist in the divisions of Neonatology and Fetal Medicine, developmental neuroscientist and senior study author.

LCModel output from 32 GA baby

Understanding the long-term consequences of prematurity

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LCModel output from 32 GA baby

Children’s National Health System researchers processed H1-MRS data using LCModel software to calculate absolute metabolite concentrations for N-acetyl-aspartate (NAA), choline (Cho) and creatine (Cr). Preterm infants had significantly lower cerebellar NAA (p=<0.025) and higher Cho (p=<0.001) when compared with healthy term-equivalent infants. The area of the brain within the red box is the cerebellum, the region of interest for this study.

Premature birth, a condition that affects approximately 10 percent of births in the United States, often is accompanied by health problems ranging from difficulties breathing and eating to long-term neurocognitive delays and disabilities. However, the reasons for these problems have been unclear.

In a study published online Aug. 15, 2017 in Scientific Reports, a team of Children’s National Health System clinician-researchers reports that prematurity is associated with altered metabolite profiles in the infants’ cerebellum, the part of the brain that controls coordination and balance. Pre-term infants in the study had significantly lower levels of a chemical marker of nerve cell integrity and significantly higher concentrations of a chemical marker of cellular membrane turnover.

“These data suggest that interrupting the developing fetal brain’s usual growth plan during gestation – which can occur through early birth, infection or experiencing brain damage – might trigger a compensatory mechanism. The infant’s brain tries to make up for lost time or heal injured tissue by producing a certain type of cells more quickly than it normally would,” says Catherine Limperopoulos, Ph.D., director of the Developing Brain Research Laboratory at Children’s National and senior study author. “The more sensitive imaging technique that we used also revealed nerve cell damage from brain injuries extends beyond the site of injury, a finding that contrasts with what is found through conventional magnetic resonance imaging (MRI).”

It has long been clear that prematurity – birth before 37 weeks gestation – is accompanied by a number of immediate and long-term complications, from potential problems breathing and feeding at birth to impairments in hearing and sight that can last throughout an individual’s life.

Neurocognitive developmental delays often accompany pre-term birth, many of which can have long-lasting consequences. Studies have shown that children born prematurely are more likely to struggle in school, have documented learning disabilities and experience significant delays in developing gross and fine motor skills compared with children born at full-term.

Several studies have investigated the root cause of these issues in the cerebrum, the structure that takes up the majority of the brain and is responsible for functions including learning and memory, language and communication, sensory processing and movement. However, the cerebellum – a part of the brain that plays an important role in motor control – has not received as much research attention.

In the new study, Limperopoulos and colleagues used a specialized MRI technique that allowed them to parse out differences in which molecules are present in the cerebellum of full-term infants compared with premature infants. Their findings show a variety of differences that could offer clues to explain developmental differences between these two populations – and potentially identify ways to intervene to improve outcomes.

The researchers recruited 59 premature infants, born at 32 or fewer weeks’ gestation, and 61 healthy, full-term infants. Each baby received a special type of MRI known as proton magnetic resonance spectroscopy, or H1-MRS, that measures the concentrations of particular molecules in the brain. The full-term infants had these MRIs shortly after birth; the pre-term infants had them at 39 to 41 weeks gestational age, or around the time that they would have been born had the pregnancy continued to term.

Looking specifically at the cerebellum, the researchers found that the pre-term infants overall had significantly lower concentrations of N-acetyl-aspartate (NAA), a marker of the integrity of nerve cells. They also had significantly higher concentrations of choline, a marker of cell membrane integrity and membrane turnover.

Concentrations of creatine, a marker of stores of cellular energy, were about the same overall between the two groups. However, the researchers found that brain injuries, which affected 35 of the pre-term infants but none of the full-term infants, were associated with significantly lower concentrations of NAA, choline and creatine. Having a neonatal infection, which affected 21 of the pre-term infants but none of the full-term ones, was associated with lower NAA and creatine.

The findings could offer insight into exactly what’s happening in the brain when infants are born pre-term and when these vulnerable babies develop infections or their brains become injured – conditions that convey dramatically higher risks for babies born too early, Limperopoulos says. The differences between the full-term babies and the pre-term ones reflect disturbances these cells are experiencing at a biochemical level, she explains.

Limperopoulos and colleagues note that more research will be necessary to connect these findings to what is already known about developmental problems in pre-term infants. Eventually, she says, scientists might be able to use this knowledge to develop treatments that might be able to change the course of brain development in babies born too early, getting them on track with infants born at term.

“We know that the bodies of pre-term infants demonstrate a remarkable ability to catch up with peers who were born at full-term, in terms of weight and height. Our challenge is to ensure that preemies’ brains also have an opportunity to develop as normally as possible to ensure optimal long-term outcomes,” Limperopoulos says.

Breastfeeding Mom

Breast milk helps white matter in preemies

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Breastfeeding Mom

Critical white matter structures in the brains of babies born prematurely at low birth weight develop more robustly when their mothers breast-feed them, compared with preemies fed formula.

Breast-feeding offers a slew of benefits to infants, including protection against common childhood infections and potentially reducing the risk of chronic health conditions such as asthma, obesity and type 2 diabetes. These benefits are especially important for infants born prematurely, or before 37 weeks gestation – a condition that affects 1 in 10 babies born in the United States, according to the Centers for Disease Control and Prevention. Prematurely born infants are particularly vulnerable to infections and other health problems.

Along with the challenges premature infants face, there is a heightened risk for neurodevelopmental disabilities that often do not fully emerge until the children enter school. A new study by Children’s National Health System researchers shows that breast-feeding might help with this problem. The findings, presented at the 2017 annual meeting of the Pediatric Academic Societies, show that critical white matter structures in the brains of babies born so early that they weigh less than 1,500 grams develop more robustly when their mothers breast-feed them, compared with preemie peers who are fed formula.

The Children’s National research team used sophisticated imaging tools to examine brain development in very low birth weight preemies, who weighed about 3 pounds at birth.

They enrolled 37 babies who were no more than 32 weeks gestational age at birth and were admitted to Children’s neonatal intensive care unit within the first 48 hours of life. Twenty-two of the preemies received formula specifically designed to meet the nutritional needs of infants born preterm, while 15 infants were fed breast milk. The researchers leveraged diffusion tensor imaging – which measures organization of the developing white matter of the brain – and 3-D volumetric magnetic resonance imaging (MRI) to calculate brain volume by region, structure and tissue type, such as cortical gray matter, white matter, deep gray matter and cerebellum.

“We did not find significant differences in the global and regional brain volumes when we conducted MRIs at 40 weeks gestation in both groups of prematurely born infants,” says Catherine Limperopoulos, Ph.D., director of the Developing Brain Research Laboratory and senior author of the paper. “There are striking differences in white matter microstructural organization, however, with greater fractional anisotropy in the left posterior limb of internal capsule and middle cerebellar peduncle, and lower mean diffusivity in the superior cerebellar peduncle.”

White matter lies under the gray matter cortex, makes up about half of the brain’s volume, and is a critical player in human development as well as in neurological disorders. The increased white matter microstructural organization in the cerebral and cerebellar white matter suggests more robust fiber tracts and microarchitecture of the developing white matter which may predict better neurologic outcomes in preterm infants. These critical structures that begin to form in the womb are used for the rest of the person’s life when, for instance, they attempt to master a new skill.

“Previous research has linked early breast milk feeding with increased volumetric brain growth and improved cognitive and behavioral outcomes,” she says. “These very vulnerable preemies already experience a high incidence rate of neurocognitive dysfunction – even if they do not have detectable structural brain injury. Providing them with breast milk early in life holds the potential to lessen those risks.”

The American Academy of Pediatrics endorses breast-feeding because it lowers infants’ chances of suffering from ear infections and diarrhea in the near term and decreases their risks of being obese as children. Limperopoulos says additional studies are needed in a larger group of patients as well as longer-term follow up as growing infants babble, scamper and color to gauge whether there are differences in motor skills, cognition and writing ability between the two groups.

Premature birth may alter critical cerebellar development linked to learning and language

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Diffusion tensor imaging teases out subtle injury to cerebral and cerebellar white matter that is not evident with conventional MRI, allowing researchers to quantify brain tissue microstructure and classify white matter integrity.

Diffusion tensor imaging teases out subtle injury to cerebral and cerebellar white matter that is not evident with conventional MRI, allowing researchers to quantify brain tissue microstructure and classify white matter integrity.

Premature birth can interrupt a key period of brain development that occurs in the third trimester, which has the potential to impact a child’s long-term learning, language, and social skills. A recent case-control study published in The Journal of Pediatrics applied diffusion tensor magnetic resonance imaging (DTI) to zoom in on the microstructures comprising the critical cerebellar neural networks related to learning and language, and found significant differences between preterm and full-term newborns.

“The third trimester, during which many premature births occur, is typically when the developing cerebellum undergoes its most dramatic period of growth. Normally, the cerebellar white matter tracts that connect to the deep nuclei are rich in pathways where nerve fibers cross. Those connections permit information to flow from one part of the brain to another. It is possible that premature birth leads to aberrant development of these critical neural networks,” says Catherine Limperopoulos, Ph.D., director of the Developing Brain Research Laboratory at Children’s National Health System and senior study author.

One in 10 American babies is born prematurely. The brain injury that infants born prematurely experience is associated with a range of neurodevelopmental disabilities, including some whose influence isn’t apparent until years later, when the children begin school. Nearly half of extremely preterm infants go on to experience long-term learning, social, and behavioral impairments.

While conventional magnetic resonance imaging (MRI) can detect many brain abnormalities in newborns, a newer technique called DTI can tease out even subtle injury to cerebral and cerebellar white matter that is not evident with conventional MRI. White matter contains axons, which are nerve fibers that transmit messages. With DTI, researchers can quantify brain tissue microstructure and describe the integrity of white matter.

The research team compared imaging from 73 premature infants born before 32 weeks gestation who weighed less than 1,500 grams with 73 healthy newborns born to mothers who delivered at full term after 37 weeks. After the newborns had been fed, swaddled, and fitted with double ear protection, the imaging was performed as they slept. Nurses monitored their heart rates and oxygen saturation. Their brain abnormalities were scored as normal, mild, moderate, or severe.

All of the full-term newborns had normal brain MRIs as did 44 (60.3 percent) of the preemies.

The preemies had significantly higher fractional anisotropy in the cerebellum, the part of the brain that processes incoming information from elsewhere in the brain, permitting coordinated movement as well as modulating learning, language, and social skills. Alterations in cerebellar microarchitecture was associated with markers for illness severe enough to require surgery – such as correcting abnormal blood flow caused by the failure of the ductus arteriosus to close after birth and to remedy a bowel disease known as necrotizing enterocolitis. The risk factors also are associated with compromised cardiorespiratory function and low Apgar score at five minutes, Limperopoulos and co-authors write. The Apgar score is a quick way to gauge, one minute after birth, how well the newborn withstood the rigors of childbirth. It is repeated at five minutes to describe how the newborn is faring outside of the womb.

“In previous studies, we and others have associated cerebellar structural injury in preterm infants with long-term motor, cognitive, and socio-affective impairments. This is one of the first studies to provide a detailed report about these unexpected alterations in cerebellar microstructural organization,” she adds. “We postulate that the combination of premature birth and early exposure of the immature developing cerebellum to the extrauterine environment results in disturbed micro-organization.”

Additional research is warranted in larger groups of patients as well as long-term follow up of this cohort of newborns to determine whether this microstructural disorganization predicts long-term social, behavioral, and learning impairments.

“A large number of these prematurely born newborns had MRI readings in the normal range. Yet, we know that these children are uniquely at risk for developing neurodevelopmental disabilities later in life. With additional study, we hope to identify interventions that could lower those risks,” Limperopoulos says.

Related resources: The Journal of Pediatrics editorial

Every day fetuses remain in utero critical to preserving normal brain development

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preemieimage

If it does not jeopardize the health of the pregnant mother or her fetus, pregnancies should be carried as close to full term as possible to avoid vulnerable preemies experiencing a delay in brain development, study results published October 28 in Pediatrics indicate.

Some 15 million infants around the world – and 1 in 10 American babies – are born prematurely. While researchers have known that preemies’ brain growth is disturbed when compared with infants born at full term, it remained unclear when preemies’ brain development begins to veer off course and how that impairment evolves over time, says Catherine Limperopoulos, Ph.D., Director of the Developing Brain Research Laboratory at Children’s National Health System and senior study author.

A look at the research

In order to shine a spotlight on this critical phase of fetal brain development, Limperopoulos and colleagues studied 75 preterm infants born prior to the 32th gestational week who weighed less than 1,500 grams who had no evidence of structural brain injury. These preemies were matched with 130 fetuses between 27 to 39 weeks gestational age.

The healthy fetal counterparts are part of a growing database that the Children’s National Developing Brain Research Laboratory has assembled. The research lab uses three-dimensional magnetic resonance imaging to carefully record week-by-week development of the normal in utero fetal brains as well as week-by-week characterizations of specific regions of the fetal brain.

The availability of time-lapsed images of normally developing brains offers a chance to reframe research questions in order to identify approaches to prevent injuries to the fetal brain, Limperopoulos says.

“Up until now, we have been focused on examining what is it about being born too early? What is it about those first few hours of life that leaves preemies more vulnerable to brain injury?” she says. “What is really unique about these study results is for the very first time we have an opportunity to better understand the ways in which we care for preemies throughout their hospitalization that optimize brain development and place more emphasis those activities.”

When the research team compared third-trimester brain volumes, preemies showed lower volumes in the cerebrum, cerebellum, brainstem, and intracranial cavity. The cerebrum is the largest part of the brain and controls speech, thoughts, emotions, learning, as well as muscle function. The cerebellum plays a role in learning and social-behavioral functions as well as complex motor functions; it also controls the balance needed to stand up and to walk. The brainstem is like a router, ferrying information between the brain, the cerebellum, and the spinal cord.

“What this study shows us is that every day and every week of in utero development is critical. If at all possible, we need to keep fetuses in utero to protect them from the hazards that can occur in the extra uterine environment,” she says.