A study by the University of California, San Diego (UCSD) uses laboratory-grown human brain tissue to identify nerve abnormalities in Pitt-Hopkins syndrome and to test gene therapy tools.
In a study published May 2, 2022 in a journal Nature communication, researchers at the University of California San Diego School of Medicine used human brain organoids to find out how a genetic mutation associated with severe autism disrupts neural development. The use of gene therapy tools to restore gene function has successfully saved nerve structure and function.
Several neurological and neuropsychiatric disorders, including autism spectrum disorders (ASD) and schizophrenia, have been associated with mutations in transcription factor 4 (TCF4), an essential gene in brain development. Transcription factors regulate when other genes are turned on or off, so that their presence or deficiency may have a knock-on effect in the developing embryo. Yet little is known about what happens to the human brain though TCF4 is mutated.
To explore this question, the researchers focused on Pitt-Hopkins syndrome, an ASD specifically caused by mutations in TCF4. Children with a genetic disease have profound cognitive and motor disabilities and are typically nonverbal.
Pitt-Hopkins syndrome (PTHS) is a rare genetic disorder characterized by developmental delay, epilepsy, prominent facial features, and possible intermittent hyperventilation followed by apnea. As more of Pitt-Hopkins emerges, the developmental spectrum of this disorder is expanding to include autism, anxiety, ADHD, and sensory disorders. It is associated with an abnormality in chromosome 18, specifically with inadequate TCF4 gene expression.
Existing mouse models of Pitt-Hopkins syndrome cannot accurately mimic the neural characteristics of patients, so the UCSD team has instead created a human research model for the disorder. Using stem cell technology, they converted patients’ skin cells into stem cells, which were then developed into three-dimensional brain organoids, or “minimozgs.”
Initial observations of brain organoids revealed a number of structural and functional differences between these organoids TCF4 -mutated samples and their controls.
“Even without a microscope, you could find out which brain organoid had the mutation,” said study lead author Alysson R. Muotri, PhD, a professor at 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 -mutated organoids were significantly smaller than normal organoids, and many cells were not actually neurons, but neural progenitors. These simple cells are supposed to multiply and then mature into specialized brain cells, but with mutated organoids, some part of this process has gone wrong.
A number of experiments have revealed that TCF4 the mutation led to downstream dysregulation SOX genes and the Wnt pathway, two important molecular signals that lead embryonic cells to proliferate, mature into neurons, and migrate to the right place in the brain.
Due to this dysregulation, neural progenitors did not multiply efficiently, producing fewer cortical neurons. The cells that matured into the neurons were less exciting than normal, and often clusters remained together instead of arranged in finely tuned nerve circuits.
This atypical cell architecture disrupted the flow of nerve activity in the mutated brain organoid, which, according to the authors, would probably contribute to the deterioration of cognitive and motor functions.
“We were surprised to see such major development problems at all these different scales and let us think about what we could do to solve them,” said first author Fabio Papes, PhD, associate professor at the University of Campinas and visiting scientist at UC. San Diego School of Medicine, who jointly oversaw the work with Muotri. Papes has a relative with Pitt-Hopkins syndrome who motivated him to study TCF4.
The team tested two different gene therapy strategies to restore a functional gene in brain tissue. Both methods have grown effectively TCF4 levels, while correcting the phenotypes of Pitt-Hopkins syndrome at the molecular, cellular and electrophysiological levels.
“The fact that we can repair this one gene and the whole nervous system is restored, even at a functional level, is amazing,” Muotri said.
Muotri notes that these genetic interventions took place in the prenatal stage of brain development, while in a clinical setting, children would be diagnosed and treated several years later. Therefore, clinical trials must first confirm whether later intervention is still safe and effective. The team is currently optimizing its recently licensed gene therapy tools in preparation for a study in which spinal injections of a genetic vector would perhaps restore TCF4 function in the brain.
“For these children and their loved ones, any improvement in motor-cognitive functions and quality of life would be worth a try,” Muotri said.
“The real thing about this job is that these researchers go beyond the lab and work hard to make these findings translatable to the clinic,” said Audrey Davidow, president of the Pitt Hopkins Research Foundation. “This is much more than just stellar academic work; is a real measure of what well-practiced science can achieve to hopefully change people’s lives for the better. ”
Reference: “Loss of transcription factor 4 function is associated with a deficit in progenitor proliferation and cortical neuron 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 and 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 partially funded 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 Joint Department of Genome Institute Energy (DE-AC02-05CH11231).