Better ‘Mini Brains’ Could Help Scientists Identify Treatments for Zika-Related Brain Damage

UCLA researchers develop improved technique for creating brain tissue from stem cells

UCLA researchers have developed an improved technique for creating simplified human brain tissue from stem cells. Because these so-called “mini brain organoids” mimic human brains in how they grow and develop, they’re vital to studying complex neurological diseases.

In a study published in the journal Cell Reports, the researchers used the organoids to better understand how Zika infects and damages fetal brain tissue, which enabled them to identify drugs that could prevent the virus’s damaging effects.

The research, led by senior author Ben Novitch, could lead to new ways to study human neurological and neurodevelopmental disorders, such as epilepsy, autism and schizophrenia.

“Diseases that affect the brain and nervous system are among the most debilitating medical conditions,” said Novitch, UCLA’s Ethel Scheibel Professor of Neurobiology and a member of the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA. “Mini brain organoids provide us with opportunities to examine features of the human brain that are not present in other models, and we anticipate that their similarity to the real human brain will enable us to test how various drugs impact abnormal or diseased brain tissue in far greater detail.”

For about five years, scientists have been using human pluripotent stem cells, which can create any cell type in the body, to develop mini brain organoids. But the organoids they produced have generally been difficult to use for research because they had highly variable structures and inconsistent cellular composition, and because they didn’t correctly mimic the layered structure of the brain and were too small — often no bigger than the head of a pin. They also didn’t survive very long in the laboratory and contained neural tissue that was difficult to classify in relation to real human brain tissue.

The organoids developed by Novitch’s group have a stratified structure that accurately mimics the human brain’s onion-like layers, they survive longer and have a larger and more uniform shape.

To create the brain organoids, Novitch and his team made several modifications to the methods that other scientists used previously: The UCLA investigators used a specific number of stem cells and specialized petri dishes with a modified chemical environment; previous methods used varying amounts of cells and a different type of dish. And they added a growth factor called LIF, which stimulated a cell-signaling pathway that is critical for human brain growth.

The researchers found critical similarities between the organoids they developed and real human brain tissue. Among them: The organoids’ anatomy closely resembled that of the human cortex, the region of the brain associated with thought, speech and decision making; and a diverse array of neural cell types commonly found in the cortex were all present in the organoids, and they exhibited electrical activities and network function, meaning they were capable of communicating with one another much like the neural networks in the human brain do.

The UCLA scientists also found that they could modify their methodology to make other parts of the brain including the basal ganglia, which are involved in the control of movement and are affected by neurodegenerative conditions such as Parkinson’s disease and Huntington’s disease.

“While our organoids are in no way close to being fully functional human brains, they mimic the human brain structure much more consistently than other models,” said Momoko Watanabe, a UCLA postdoctoral fellow and the study’s first author. “Other scientists can use our methods to improve brain research because the data will be more accurate and consistent from experiment to experiment and more comparable to the real human brain.”

When the team exposed the organoids to Zika, they discovered specifically how the virus destroys neural stem cells, the cells from which the brain grows during fetal development. Novitch’s team found that there are four specific molecules, called receptors, on the outer surface of neural stem cells; previous studies have indicated that the Zika virus could bind to these receptors and infect the cells. The researchers then mapped the changes that occur in the neural stem cells after Zika infection, presenting a clearer picture of how the virus infiltrates and harms fetal brain tissue.

Zika is associated with an unusually high incidence of fetal brain damage, so understanding how neural stem cells are affected by the virus could be an important new step toward a treatment.

The researchers tested several drugs on the Zika-infected organoids. They found three that are effective at blocking the virus’s entry into the brain tissue, including two that protected neural stem cells by preventing the interaction between the virus and entry receptors on the neural stem cells. In previous studies by Novitch and other UCLA colleagues, one of those drugs reduced brain damage in fetal mice infected with Zika.

“Many neurological diseases or conditions arise from defects in the way one neuron communicates with another or from the way an external factor, such as a virus, interacts with neural cells,” Novitch said. “If we can focus in at the level of cellular communication, we should be able to model those undesirable cellular interactions and counteract them with drugs or other therapies.”

The team plans to continue using its improved organoids to better understand human brain development and to learn more about autism spectrum disorders, epilepsy and other neurological conditions.

The experimental drugs used in the preclinical study have not been tested in humans or approved by the Food and Drug Administration for treating Zika in humans.

Using DNA to predict schizophrenia and autism

Huntington’s disease, cystic fibrosis, and muscular dystrophy are all diseases that can be traced to a single mutation. Diagnosis in asymptomatic patient for these diseases is relatively easy – You have the mutation? Then you are at risk. Complex diseases, on the other hand, do not have a clear mutational footprint. A new multi-institutional study by Japanese researchers shows a potential rare gene mutation that could act as a predictor for two neurodevelopmental disorders, schizophrenia and autism.

“Aberrant synapse formation is important in the pathogenesis of schizophrenia and autism,” says Osaka University Professor Toshihide Yamashita, one of the authors of the study. “Microglia contribute to the structure and function of synapse connectivities.”

Microglia are the only cells in the brain that express the receptor CX3CR1. Mutations in this receptor are known to affect synapse connectivity and cause abnormal social behavior in mice. They have also been associated with neuroinflammatory diseases such as multiple sclerosis, but no study has shown a role in neurodevelopment disorders.

Working with this hypothesis, the researchers conducted a statistical analysis of the CX3CR1 gene in over 7000 schizophrenia and autism patients and healthy subjects, finding one mutant candidate, a single amino acid switch from alanine to threonine, as a candidate marker for prediction.

“Rare variants alter gene function but occur at low frequency in a population. They are of high interest for the study of complex diseases that have no clear mutational cause,” said Yamashita, who added the alanine threonine substitution was a rare variant.

The structure of CX3CR1 includes a domain known as Helix 8, which is important for initiating a signaling cascade. Computer models showed that one amino acid change is enough to compromise the signaling.

“The variant changes the region from hydrophobic to hydrophilic and destabilize Helix 8. We overexpressed the mutation in cells and found Akt signaling was disrupted,” explains Yamashita.

According to Yamashita, the findings are the first to connect a genetic variation in microglia with neurodevelopment disorders. Moreover, he hopes that the discovery could become a basis for predictive diagnostics.

“There is no reliable way to diagnose schizophrenia or autism in asymptomatic patients. Deeper understanding of the genetic risk factors will help us develop preventative measures.”

How Prenatal Maternal Infections May Affect Genetic Factors in Autism Spectrum Disorder

Researchers find activation of maternal immune system during pregnancy disrupts expression of key genes and processes associated with autism and prenatal brain development

For some infections, such as Zika, the virus passes through the placenta and directly attacks the fetus. For others, such as the H1N1 influenza, the virus induces maternal immune activation (MIA) by triggering a woman’s immune system during pregnancy. Both Zika and MIA mechanisms may lead to potentially disastrous neurological repercussions for the unborn child, such as microcephaly (an undersized, underdeveloped brain and head) in the case of Zika or cortical abnormalities with excess numbers of neurons, patches of disorganized cortex, synapse mal-development and early brain overgrowth in some cases of MIA.

Large population-based studies suggest MIA caused by infection during pregnancy are also associated with small increases in risk for psychiatric disorders, including autism spectrum disorder (ASD). In a new study published today in Molecular Psychiatry, researchers at the University of California San Diego School of Medicine, University of Cyprus and Stanford University map the complex biological cascade caused by MIA: the expression of multiple genes involved in autism are turned up or down by MIA, affecting key aspects of prenatal brain development that may increase risk for atypical development later in life.

“We provide novel evidence that supports the link between prenatal infections and biology known to be important in the development of autism,” said senior author Tiziano Pramparo, PhD, associate research scientist at the Autism Center of Excellence at UC San Diego School of Medicine. “There are different routes of importance. We highlight a specific pathway that seems to be key in driving downstream early abnormal brain development.”

“Our work adds to growing evidence that prenatal development is an important window for understanding key biology of relevance to neurodevelopmental conditions like autism,” added lead author Michael Lombardo, PhD, at the University of Cyprus. “MIA is an environmental route of influence on fundamental biological processes important for brain development. The influence it exerts overlaps with key processes known to be important in how the brain in autism develops.”

Pramparo said the effects are not caused by the infectious agents themselves — virus or bacterium — but from the maternal immune response itself. “Although the mechanisms are not entirely known, it has to do with the cascade of altered events regulating production and function of neurons, their synapses and how they arrange themselves in the brain that are triggered when a mother’s immune system is activated.”

For example, increased levels of maternal cytokines (small signaling molecules driven by the immune response) may directly or indirectly alter gene expression in the fetus’ brain.

“These up- and down-regulated genes may lead to an excess or reduction in the normal amounts of proteins required for normal brain development,” Pramparo said. “Importantly, we have found that MIA-induced effects involve both single genes and pathways (many genes working in a coordinated way to serve some dedicated biological purpose) essential for early fetal neurodevelopment.” Among the large number of genes whose activity is altered by the maternal immune response, are a few that, when mutated, are thought to cause more genetic forms of autism in a small subset of all ASD toddlers.

Pramparo suggested the findings have multiple clinical implications.

“In general, the more we know and understand about a disrupted mechanism, the higher the chance of finding amenable targets for potential therapeutic intervention or for informing how to prevent such risk from occurring in the first place.”

Another implication, he said, is the potential to define the effects and clinical phenotypes based upon the underlying mechanisms: genetic, environmental or both.

“The MIA effects are transient but very potent during fetal development and perhaps even more potent than the effects induced by certain types of mutations in single gene forms of autism. Also, depending on when MIA occurs during gestation, the clinical characteristics may vary. The finding of MIA affecting the expression genes known to be important in autism supports the hypothesis that a genetic-by-environment interaction may lead to amplified effects at the clinical level. For example, more severe cases of autism.”

Predicting Autism: Researchers Find Autism Biomarkers in Infancy

By using magnetic resonance imaging (MRI) to study the brains of infants who have older siblings with autism, scientists were able to correctly identify 80 percent of the babies who would be subsequently diagnosed with autism at 2 years of age.

Researchers from the University of Washington were part of a North American effort led by the University of North Carolina to use MRI to measure the brains of “low-risk” infants, with no family history of autism, and “high-risk” infants who had at least one autistic older sibling. A computer algorithm was then used to predict autism before clinically diagnosable behaviors set in. The study was published Feb. 16 in the journal Nature.

This is the first study to show that it is possible to use brain biomarkers to identify which infants in a high-risk pool — that is, those having an older sibling with autism — will be diagnosed with autism spectrum disorder, or ASD, at 24 months of age.

“Typically, the earliest we can reliably diagnose autism in a child is age 2, when there are consistent behavioral symptoms, and due to health access disparities the average age of diagnosis in the U.S. is actually age 4,” said co-author and UW professor of speech and hearing sciences Annette Estes, who is also director of the UW Autism Center and a research affiliate at the UW Center on Human Development and Disability, or CHDD. “But in our study, brain imaging biomarkers at 6 and 12 months were able to identify babies who would be later diagnosed with ASD.”

The predictive power of the team’s findings may inform the development of a diagnostic tool for ASD that could be used in the first year of life, before behavioral symptoms have emerged.

“We don’t have such a tool yet,” said Estes. “But if we did, parents of high-risk infants wouldn’t need to wait for a diagnosis of ASD at 2, 3 or even 4 years and researchers could start developing interventions to prevent these children from falling behind in social and communication skills.”

People with ASD — which includes 3 million people in the United States — have characteristic social communication deficits and demonstrate a range of ritualistic, repetitive and stereotyped behaviors. In the United States, it is estimated that up to one out of 68 babies develops autism. But for infants with an autistic older sibling, the risk may be as high as one out of every five births.

This research project included hundreds of children from across the country and was led by researchers at four clinical sites across the United States: the University of North Carolina-Chapel Hill, UW, Washington University in St. Louis and The Children’s Hospital of Philadelphia. Other key collaborators are at the Montreal Neurological Institute, the University of Alberta and New York University.

“We have wonderful, dedicated families involved in this study,” said Stephen Dager, a UW professor of radiology and associate director of the CHDD, who led the study at the UW. “They have been willing to travel long distances to our research site and then stay up until late at night so we can collect brain imaging data on their sleeping children. The families also return for follow-up visits so we can measure how their child’s brain grows over time. We could not have made these discoveries without their wholehearted participation.”

Researchers obtained MRI scans of children while they were sleeping at 6, 12 and 24 months of age. The study also assessed behavior and intellectual ability at each visit, using criteria developed by Estes and her team. They found that the babies who developed autism experienced a hyper-expansion of brain surface area from 6 to 12 months, as compared to babies who had an older sibling with autism but did not themselves show evidence of autism at 24 months of age. Increased surface area growth rate in the first year of life was linked to increased growth rate of brain volume in the second year of life. Brain overgrowth was tied to the emergence of autistic social deficits in the second year.

The researchers input these data — MRI calculations of brain volume, surface area, and cortical thickness at 6 and 12 months of age, as well as sex of the infants — into a computer program, asking it to classify babies most likely to meet ASD criteria at 24 months of age. The program developed the best algorithm to accomplish this, and the researchers applied the algorithm to a separate set of study participants.

Researchers found that, among infants with an older ASD sibling, the brain differences at 6 and 12 months of age successfully identified 80 percent of those infants who would be clinically diagnosed with autism at 24 months of age.
If these findings could form the basis for a “pre-symptomatic” diagnosis of ASD, health care professionals could intervene even earlier.

“By the time ASD is diagnosed at 2 to 4 years, often children have already fallen behind their peers in terms of social skills, communication and language,” said Estes, who directs behavioral evaluations for the network. “Once you’ve missed those developmental milestones, catching up is a struggle for many and nearly impossible for some.”

Research could then begin to examine interventions on children during a period before the syndrome is present and when the brain is most malleable. Such interventions may have a greater chance of improving outcomes than treatments started after diagnosis.

“Our hope is that early intervention — before age 2 — can change the clinical course of those children whose brain development has gone awry and help them acquire skills that they would otherwise struggle to achieve,” said Dager.

The research team has gathered additional behavioral and brain imaging data on these infants and children — such as changes in blood flow in the brain and the movement of water along white matter networks — to understand how brain connectivity and neural activity may differ between high-risk children who do and don’t develop autism. In a separate study published Jan. 6 in Cerebral Cortex, the researchers identified specific brain regions that may be important for acquiring an early social behavior called joint attention, which is orienting attention toward an object after another person points to it.

“These longitudinal imaging studies, which follow the same infants as they grow older, are really starting to hone in on critical brain developmental processes that can distinguish children who go on to develop ASD and those who do not,” said Dager. “We hope these ongoing efforts will lead to additional biomarkers, which could provide the basis for early, pre-symptomatic diagnosis and serve also to guide individualized interventions to help these kids from falling behind their peers.”