Gene therapy reverses autism-associated mutations in organoids
Several neurological and neuropsychiatric diseases, including autism spectrum disorder (ASD) and schizophrenia, are associated with mutations in Transcription Factor 4 (TCF4), a gene essential in the development of Brain.
Transcription factors regulate when other genes are turned on or off, so their presence or absence can induce a domino effect in the developing embryo. However, little is known about what happens to the human brain when TCF4 is mutated.
To explore this question, the researchers focused on Pitt-Hopkins Syndrome, a specific ASD caused by mutations in TCF4. Children with the genetic condition have profound cognitive and motor disabilities and are often unable to speak.
Existing mouse models of Pitt-Hopkins Syndrome do not accurately mimic the neurological features of patients, so the UC San Diego team instead created a human study model of the disorder this.
Using stem cell technology, they converted the patient’s skin cells into stem cells, which were then developed into three-dimensional brain stem cells, or “small brain. “
Initial observations of brain organoids revealed a wide range of structural and functional differences between the TCF4 mutant samples and their controls.
“Even without a microscope, you can still tell which brain organoid has the mutation“, said senior study author Alysson R. Muotri, PhD, professor at UC San Diego School of Medicine, director of the UC San Diego Stem Cell Program and member of the Sanford Society for Regenerative Medicine.
The TCF4 mutant organoids are essentially significantly smaller than the normal organoids, and many of the cells are actually not neurons, but neural reproductive cells. These simple cells are made to multiply and then mature into specialized brain cells, but in mutated organoids, some parts of this process go awry.
A series of experiments showed that TCF4 mutations lead to downregulation of the SOX gene and the Wnt pathway, two key molecular signals that guide embryonic cells to multiply, mature into neurons, and move to the correct location in the brain.
Because of this dysregulation, neural progenitors do not multiply efficiently and, therefore, fewer cortical neurons are produced. Cells that have matured into neurons are less excitable than usual and often cluster together instead of organizing themselves into fine-tuned neural circuits.
This atypical cellular structure disrupted the flow of neural activity in the mutant brain organoid, which the authors say may contribute to impaired cognitive and motor function.
“We are amazed to see such large growing problems of all sizes and it makes us wonder what we can do to solve them.“, first author Fabio Papes, PhD, associate professor at the University of Campinas and visiting scholar at UC San Diego School of Medicine, who has jointly oversaw work with Muotri. Papes is related to Pitt Syndrome -Hopkins, this motivated him to learn TCF4.
The team tested two different gene therapy strategies to restore gene function in brain tissue. Both methods effectively increased TCF4 levels, and in doing so corrected the Pitt-Hopkins Syndrome phenotypes at the molecular, cellular, and electrophysiological scales.
“The fact that we can edit this one gene and the entire nervous system self-healing, even at a functional level, is amazing.“Muotri said.
Muotri notes that these genetic interventions take place in prenatal brain development, while in the clinical setting, children will be diagnosed and treated several years later.
Therefore, clinical trials must first confirm whether a subsequent intervention is still safe and effective. The team is currently optimizing their recently licensed gene therapy tools in preparation for such a trial in which injection of the genetic vector into the spinal cord hopes to restore TCF4 function in Brain.
“For these children and their loved ones, any improvement in motor-cognitive function and quality of life is worth trying.“Muotri said.
“What’s really striking about this study is that these researchers are going beyond the lab and working hard to make these findings translatable to the clinic.“, said Audrey Davidow, president of the Pitt Hopkins Research Foundation.
“This is not just an excellent academic paper; it is a true measure of what well-practiced science can accomplish to hopefully change people’s lives for the better. “