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Scientists unravel how protein impacts intellectual disability

April 25, 2017

JUPITER, FL - April 25, 2017 - Your brain needs just the right balance between excitatory "on" signals and inhibitory "calm down" signals. Now scientists from the Florida campus of The Scripps Research Institute (TSRI) have shown that a protein helps balance nerve cell communication.

The new study, published today online in the journal Cell Reports, could have implications for potential treatments of intellectual disability and other neurodevelopmental disorders.

"This paper adds a new dimension to our understanding of the molecular mechanisms that impact intellectual disability," said Brock Grill, a TSRI associate professor in the Department of Neuroscience. "Our study is the first to identify a defect in neuron communication caused by altering the activity of a gene called HUWE1, which causes intellectual disability, including Juberg-Marsidi-Brooks syndrome."

Studying neuronal communication is important because the brain needs to balance excitatory neurotransmitters (to increase signal transmission) and inhibitory neurotransmitters (to calm nerve cells down). An imbalance in the excitatory/inhibitory ratio is a central feature of many neurodevelopmental disorders--which occurs through gene overexpression or a loss of gene function.

For the study, Grill and his colleagues investigated neuronal communication balance using a simple model circuit in the nematode C. elegans, a small, transparent worm. Despite its small size, this worm shares half its genetic make-up with humans, which makes it an ideal model to study the genetics of neuron function.

The researchers took a close look at GABA, the principal inhibitory neurotransmitter in C. elegans and the human brain. In C. elegans, the protein responsible for regulating GABA transmission is called EEL-1; in humans, the equivalent protein is known as HUWE1.

The researchers studied the function of EEL-1/HUWE1 in the worm motor circuit and found that decreasing or increasing the protein alters GABA transmission, upending the excitatory/inhibitory balance, a shift that leads to impaired locomotion and increased sensitivity to electroshock-induced seizure.

"Using a simple model circuit, we've identified a key player required to achieve a balance of excitation and inhibition," Grill said. "This opens up a new concept for why HUWE1 causes intellectual disability. HUWE1 affects only the release of the GABA neurotransmitter, not the levels or function of the GABA receptor, Grill noted. He said more research is needed into how this actually affects the brain.

"The paper is an important step in understanding how increased or decreased activity of HUWE1 can alter circuit function and lead to intellectual disability," said TSRI Research Assistant Karla Opperman, first author of the study.

The study represents important progress in understanding the molecular underpinnings of intellectual disability. In particular, results from the study show for the first time that mutations that cause Juberg-Marsidi-Brooks syndrome result in loss of HUWE1 function and can impair nerve cell function.
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In addition to Grill and Opperman, other authors of the study, "The HECT Family Ubiquitin Ligase EEL-1 Regulates Neuronal Function and Development," are Andrew Giles and Rayna L. Birnbaum of TSRI; Ben Mulcahy and Mei Zhen of the Lunenfeld-Tannenbaum Research Institute, Mt. Sinai Hospital, Toronto; Monica G. Risley and Ken Dawson-Scully of Florida Atlantic University; and Erik D. Tulgren of the University of Minnesota.

The study was supported by the National Institutes of Health (grant 2R01 NS072129) and the National Science Foundation (grant IOS-1121095). _

About The Scripps Research Institute

The Scripps Research Institute (TSRI) is one of the world's largest independent, not-for-profit organizations focusing on research in the biomedical sciences. TSRI is internationally recognized for its contributions to science and health, including its role in laying the foundation for new treatments for cancer, rheumatoid arthritis, hemophilia, and other diseases. An institution that evolved from the Scripps Metabolic Clinic founded by philanthropist Ellen Browning Scripps in 1924, the institute now employs more than 2,500 people on its campuses in La Jolla, CA, and Jupiter, FL, where its renowned scientists--including two Nobel laureates and 20 members of the National Academies of Science, Engineering or Medicine--work toward their next discoveries. The institute's graduate program, which awards PhD degrees in biology and chemistry, ranks among the top ten of its kind in the nation. In October 2016, TSRI announced a strategic affiliation with the California Institute for Biomedical Research (Calibr), representing a renewed commitment to the discovery and development of new medicines to address unmet medical needs. For more information, see http://www.scripps.edu.

Scripps Research Institute

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