A study by the University of California, San Diego (UCSD) uses laboratory-grown human brain tissue to identify neurological diseases in Pitt-Hopkins syndrome and test gene therapy devices.
In a study published May 2, 2022 in the journal Nature communication, researchers at the University of California, San Diego School of Medicine used organic matter in the human brain to discover how a genetic mutation associated with severe autism interferes with neurodevelopment. Using a gene therapy device to restore the activity of the gene, nerve structure and function were saved.
Several neuropsychiatric disorders, including autism spectrum disorder (ASD) and schizophrenia, have been linked to mutations in transcription factor 4 (TCF4), an essential gene in brain development. Transcription factors control when other genes are turned on or off, so their presence, or lack thereof, can have a domino effect on the developing embryo. However, little is known about what happens to the human brain and when TCF4 is mutated.
To investigate this question, researchers focused on Pitt-Hopkins syndrome, ASD specifically caused by mutations in TCF4. Children with the genetic disease have profound cognitive and motor disabilities and are usually unprovoked.
Pitt-Hopkins Syndrome (PTHS) is a rare genetic disorder characterized by developmental delays, epilepsy, prominent facial symptoms and possible intermittent hyperventilation followed by respiratory arrest. As more and more of Pitt-Hopkins is discovered, the developmental range of the disorder expands to include autism, anxiety, ADHD, and sensory disturbances. It is linked to an abnormality in chromosome 18, especially inadequate expression of the TCF4 gene.
Current mouse models of Pitt-Hopkins syndrome do not exactly mimic patients’ neurological characteristics, so the UCSD team created a human research model of the disorder instead. Using stem cell technology, they transformed patients’ skin cells into stem cells, which were then developed into three-dimensional brain organs, or “mini-brains”.
Initial examinations of the organs of the brain revealed a large number of structures and differences in function TCF4 -mutated samples and control of them.
“Even without a microscope, you could tell which brain organ mutation had the mutation,” said lead author Alysson R. Muotri, PhD, a professor at the UC San Diego School of Medicine, director of the UC San Diego stem cell program and a member of the Sanford Consortium for Regenerative Medicine.
The TCF4 -mutogenic organic cells were significantly smaller than normal organic cells and many of the cells were not actually neurons, but neurons. These simple cells are supposed to multiply and then develop into specialized brain cells, but in mutated organic cells some part of this process had gone wrong.
A series of experiments revealed that TCF4 mutation led to downstream mismanagement of SOX gene and the Wnt pathway, two important molecular signals that lead embryonic cells to proliferate, develop into neurons, and move to the right place in the brain.
Due to this irregularity, neurons did not multiply efficiently, resulting in fewer neurons in the cerebral cortex. The cells that matured into neurons were less tense than usual and often held together in clusters instead of arranging in fine-tuned nerve channels.
This unconventional cell structure disrupted the flow of neurotransmitters in the mutated brain-organic material, which the authors said would likely contribute to subsequent cognitive and motor impairment.
“We were surprised to see such huge developmental problems on all of these different scales, and it made us wonder what we could do to address them,” said first author Fabio Papes, PhD, associate professor at the University of Campinas and guest researcher at UC. San Diego School of Medicine, which jointly oversaw the work with Muotri. Papes has a relative with Pitt-Hopkins syndrome, who encouraged him to study TCF4.
The team tested two different gene therapy methods to restore the functional gene to brain tissue. Both methods actually increased TCF4 levels, thereby correcting the phenotypes of Pitt-Hopkins syndrome on a molecular, cellular, and electrophysiological scale.
“The fact that we can correct this one gene and the whole nervous system recovers, even at the activity level, is incredible,” said Muotri.
Muotri points out that these genetic interventions took place at the birth stage of brain development, but in a clinical setting, children would receive their diagnosis and treatment a few years later. Thus, clinical trials must first confirm whether subsequent interventions are still safe and effective. The team is now optimizing their newly licensed gene therapy devices in preparation for such a study, as vertebrate injections on the gene pool would hopefully restore TCF4 activity in the brain.
“For these children and their loved ones, any improvement in motor cognitive function and quality of life would be worth trying,” said Muotri.
“What’s really outstanding about this work is that these researchers are going beyond the lab and working hard to make these findings translable to the clinic,” said Audrey Davidow, president of the Pitt Hopkins Research Foundation. “This is so much more than a great academic article; it is a true measure of what science can accomplish to hopefully change people’s lives for the better. “
Reference: “Loss of transcription factor 4 activity is associated with lack of ancestral proliferation and neuronal cortex content” by Fabio Papes, Antonio P. Camargo, Janaina S. de Souza, Vinicius MA Carvalho, Ryan A. Szeto, Erin LaMontagne, José R. Teixeira , Simoni H. Avansini, Sandra M. Sánchez-Sánchez, Thiago S. Nakahara, Carolina N. Santo, Wei Wu, Hang Yao, Barbara MP Araújo, Paulo ENF Velho, Gabriel G. Haddad og Alysson R. Muotri 2 May 2022 , Nature communication.
DOI: 10.1038 / s41467-022-29942-w
Co-authors include: Janaina S. de Souza, Ryan A. Szeto, Erin LaMontagne, Simoni H. Avansini, Sandra M. Sanchez-Sanchez, Wei Wu, Hang Yao and Gabriel Haddad at UC San Diego; Antonio P. Camargo, Vinicius MA Carvalho, Jose R. Teixeira, Thiago S. Nakahara, Carolina N. Santo, Barbara MP Araujo and Paulo ENF Velho at the University of Campinas.
This work was funded in part by the National Institutes of Health (grant R01 MH123828), the Pitt Hopkins Research Foundation, the Sao Paulo Research Foundation (grants 2020 / 11451-7, 2018 / 03613-7, 2018 / 04240-0) and the US Department of Energy Joint Genome Institute (DE-AC02-05CH11231).