Researchers at Texas Children’s Duncan Neurological Institute (NRI) and Baylor College of Medicine have reported a promising experimental strategy that may ultimately help treat Rett syndrome. Their findings are: scientific translational medicinedescribes methods that may increase levels of key brain proteins that are destroyed in the disease. This research offers early hope for addressing a rare neurodevelopmental disease for which there is currently no treatment.
“Rett syndrome is a rare inherited neurodevelopmental disorder that typically causes developmental regression after 6 to 18 months of normal growth, resulting in severe impairments in motor skills, language, and communication,” said corresponding author Dr. Huda Zoghbi, Duncan NRI Director, Baylor University Distinguished Professor, and Howard Hughes Medical Institute Research Fellow. “This disorder primarily affects girls, affecting approximately 1 in 10,000 live births.”
How MECP2 mutations disrupt brain function
Rett syndrome is caused by loss-of-function mutations in the body. MECP2 gene. This gene plays an important role in the brain because it regulates the activity of many other genes involved in neurological processes. If the gene changes, the resulting MeCP2 protein may be completely lost or unable to function properly. In some cases, mutant forms of MeCP2 may be produced in lower amounts or have reduced DNA-binding ability, which is essential for its role in regulating gene activity.
Experiments in mouse models have shown that the symptoms of Rett syndrome can be reversed under certain conditions. When healthy MeCP2 protein is introduced into the brains of these animals, symptoms improve. The researchers also found that increasing the amount of a partially functional mutant MeCP2 protein could lead to improved survival, movement, and breathing problems in mice.
“This is important because about 65% of Rett syndrome patients have partially functional MeCP2, with reduced DNA binding or lower amounts than normal,” said first author Harini Tirumala, a graduate student in molecular and human genetics in Zoghbi’s lab. “Our studies using mouse models and cells derived from patients with Rett syndrome provide proof of concept that elevated levels of mutant MeCP2 in patients with Rett syndrome may have therapeutic effects.”
Understanding MECP2 protein variants
Developing treatments to modulate MeCP2 levels is difficult because the brain requires the protein to stay within a narrow range. Too little MeCP2 causes Rett syndrome, but too much causes another neurological disease known as MeCP2. MECP2 Duplication syndrome. Achieving the right balance has been a major obstacle to the development of treatments.
“We knew from previous research that the brain normally produces two slightly different versions of the MeCP2 protein, known as E1 and E2,” Zoghbi said. “These versions come from the same gene, which is processed one way to produce E1 and another to produce E2.”
A helpful way to visualize this process is to think of genes as recipes for building proteins. The instruction contains four components: e1, e2, e3, and e4. To create the MeCP2 E1 protein, cells combine e1, e3, and e4. To produce MeCP2 E2, a cell contains all four components. In other words, e2 segments only appear in E2 versions. The brain produces both proteins, but E1 is more abundant.
“We also knew that there were no reports of Rett syndrome patients having mutations in the E2 protein. Only mutations that disrupt the E1 protein cause this condition,” Tirumala said. “Studies in mice support this observation.”
“Overall, we found that MeCP2-E2 differs from MeCP2-E1 in a single component within the gene, is less abundant than E1, is not associated with Rett syndrome, and is not required for MeCP2 function in the brain,” Tirumala said. “This led us to hypothesize that inducing brain cells to skip the e2 component would promote the production of more MeCP2-E1 protein in Rett syndrome patients, improving disease outcome. We tested our hypothesis in mice and cells from Rett syndrome patients.”
Increase MeCP2 protein in experiments
To test this idea, the scientists first removed the e2 segment from the regular segment. Mecp2 They analyzed the genes of the mice to see how this affected protein levels and nerve function. This change significantly increased the production of MeCP2.
“We were pleased to discover that this approach increased MeCP2 protein by 50% to 60% in normal mice,” Tirumala said.
The team then applied the same strategy to cells taken from Rett syndrome patients who had the following symptoms: MECP2 Mutations that reduce protein levels and activity. The researchers evaluated how cells would respond by removing the e2 component from the mutant gene.
“We were excited to see that removing component e2 enhanced MeCP2 production,” Tirumala said. “Importantly, depending on the severity of the mutation, these cells regained some or all of their normal structure, normal electrical activity, and the ability to regulate the levels of other genes.”
Testing possible treatment approaches
The researchers also investigated whether drugs could be used to block the e2 segment and stimulate MeCP2 production.
“We tested the value of morpholinos for enhancing MeCP2 protein production in mice,” Tirumala said. “Morpholinos, in this case, are synthetic molecules designed to prevent the production of the MeCP2-E2 protein by blocking access to the e2 component,” Tirumala said. “We were excited to see that our morpholino significantly increased MeCP2 protein in mice.”
“Our study lays the foundation and provides preclinical evidence for a therapeutic approach for Rett syndrome that increases MeCP2 and results in functional improvement,” Professor Zoghbi said. “Although morpholinos themselves are not an option due to their toxicity, a similar strategy similar to antisense oligonucleotide therapy already used in other conditions could be developed for Rett syndrome.”
Study authors and funding
Other contributors to this study include Li Wang, Yan Li, Sameer S. Bajikar, Ashley G. Anderson, Wei Wang, Alexander J. Trostle, Mahla Zahabiyon, Aleksandar Bajic, Jean J. Kim, Hu Chen, and Zhandong Liu. All were affiliated with Baylor College of Medicine and Duncan NRI during the study, but some have since moved to institutions such as Stanford University, the University of Virginia, and the University of Texas Southwestern Medical Center in Dallas.
This research was supported by the National Institutes of Health (grants 5R01NS057819, P30 CA125123 and S10OD028591), the Howard Hughes Medical Institute, the National Institute of Neurological Disorders and Stroke (F32NS122920), the Henry Engel Foundation, and the Eunice Kennedy Shriver National Institute of Child Health and Human Development. (P50HD103555).
