Researchers create mini-brains to study autism and test new treatments

Using stem cells taken from patients with a rare and severe form of autism spectrum disorder and intellectual disability, scientists at Scripps Research have developed personalized ‘mini-brains’ (or organoids) to study the disorder in new detail. Thanks to the lab-grown organoids, the team gained new insight into how one genetic mutation leads to autism spectrum disorder. It also showed that an experimental drug called NitroSynapsin reversed some of the brain dysfunction associated with autism in these models.

“Our work shows how this genetic mutation associated with autism disrupts the typical balance of brain cells during development,” said Stuart A. Lipton, MD, PhD, Step Family Foundation Endowed Professor and co-director of the Neurodegeneration New Medicines Center at Scripps Research, a clinical neurologist and senior author of the new study published online in Molecular psychiatry on September 30, 2024. “But we also found that there may be ways to address this imbalance later in life.”

Learning from patients

Autism spectrum disorder (ASD) is a neurological and developmental disorder that affects social interactions, repetitive interests and behavior, and communication. The causes of ASD are only partially known; a number of genetic variants have been linked to the condition, but each explains only a small percentage of cases. For years, studies of ASD have focused on modeling the disorder in mice or studying isolated human brain cells. Neither perfectly mimics the complexity of an interconnected human brain.

Lipton and his colleagues focused on MEF2C haploinsufficiency syndrome (MHS), a rare and severe form of ASD and an intellectual disability caused by a genetic variation in the MEF2C gene. They took skin cells isolated from patients with MHS and used modern stem cell biology techniques to convert those cells into human stem cells, then grew them into tiny millimeter-sized ‘mini brain organoids’ in which the researchers could study how different types of brain cells interact with each other.

We could reproduce essential aspects of patients’ brains to study their electrical activity and other properties. We even brought kids into the lab to see their own mini brains and that was quite emotional for both the kids and the families.”

Stuart A. Lipton, MD, PhD, Step Family Foundation Endowed Professor and Co-Director of the Neurodegeneration New Medicines Center at Scripps Research

In healthy human brains and brain organoids, neural stem cells develop into nerve cells (or neurons), which send and receive messages throughout the brain, as well as into several types of glial cells, supporting cells recently shown to be important in signaling. and in immune function. Healthy brains contain a balance of excitatory neurons that promote electrical signals, and inhibitory neurons that block these signals. Autism causes an excitatory/inhibitory imbalance, often resulting in over-arousal.

In the organoids developed from the cells of children with MHS, the neural stem cells more often developed into glial cells, creating a disproportionately large number of glial cells compared to neurons, Lipton’s group found. Notably, the MHS organoids had fewer inhibitory neurons than normal. This led to excessive electrical signals in the mini-brain, just like many real human brains with ASD.

A role for microRNA

When Lipton’s group investigated exactly how MEF2C mutations could lead to this imbalance between cell types, they found nearly 200 genes that were directly controlled by the MEF2C gene. Three of these genes stood out: instead of encoding DNA that led to messenger (m)RNA and then protein expression, they encoded genes for microRNA molecules.

MicroRNAs (miRNAs) are small RNA molecules that, instead of producing proteins themselves, bind to DNA to control gene expression. This month, two scientists won the 2024 Nobel Prize in Physiology or Medicine for their work describing the discovery of miRNA molecules and how they can influence cell development and behavior.

“In our study, a few specific miRNAs appear to be important in telling developing brain cells whether to become glial cells, excitatory neurons, or inhibitory neurons,” says Lipton. “Mutations in MEFC2 alter the expression of these miRNAs, which in turn prevents the developing brain from making the right nerve cells and the right connections, or synapses, between nerve cells.”

Early developing brain cells from patients with MHS, Lipton’s group found, have lower levels of three specific miRNAs. When the researchers added extra copies of these miRNA molecules to the patient-derived brain organoids, the minibrains developed more normally, with a standard balance of neurons and glial cells.

A potential treatment

Because ASD is generally not diagnosed during fetal brain development, treatments aimed at altering initial development, such as correction of a mutated gene or addition of miRNA molecules to stop the imbalance of cell types, are currently not feasible. However, Lipton was already developing another drug that could help promote the balance between excitatory and inhibitory neurons even after development.

Lipton’s group recently tested such a drug, which he and colleagues invented and patented under the name NitroSynapsin (also known as EM-036), for its ability to restore brain connections in “mini-brains” made of cells that have been affected by Alzheimer’s disease.

In the new article they tested whether the drug could also help treat the MHS form of autism. Using patient-derived brain organoids, Lipton and colleagues showed that in fully developed brain organoids with an imbalance between cell types, NitroSynapsin could partially correct the imbalance, preventing hyperexcitability of the neurons and restoring the excitatory/inhibitory balance in the mini- neurons was restored. brain. This also protected the nerve cell connections or synapses.

More research is needed to show whether the drug improves symptoms in patients with MHS, or affects other forms of autism spectrum disorders that are not caused by mutations in the MEF2C gene. Lipton says he hypothesizes this could be the case because MEF2C is known to affect many other genes linked to autism.

“We continue to test this drug in animal models with the goal of getting it to humans in the near future,” Lipton says. “This is an exciting step in that direction.”