What is it about the extra chromosome inherited in Down syndrome—chromosome 21—that alters brain and body development? Researchers at Sanford-Burnham Medical Research Institute (Sanford-Burnham) have new evidence that points to a protein called sorting nexin 27, or SNX27.
SNX27 production is inhibited by a molecule encoded on chromosome 21. The study, published March 24 in Nature Medicine, shows that SNX27 is reduced in human Down syndrome brains. The extra copy of chromosome 21 means a person with Down syndrome produces less SNX27 protein, which in turn disrupts brain function. What's more, the researchers showed that restoring SNX27 in Down syndrome mice improves cognitive function and behavior.
"In the brain, SNX27 keeps certain receptors on the cell surface—receptors that are necessary for neurons to fire properly," said Huaxi Xu, Ph.D., professor in Sanford-Burnham's Del E. Webb Neuroscience, Aging and Stem Cell Research Center and senior author of the study. "So, in Down syndrome, we believe lack of SNX27 is at least partly to blame for developmental and cognitive defects."
SNX27's role in brain function
Xu and colleagues started out working with mice that lack one copy of the snx27 gene. They noticed that the mice were mostly normal, but showed some significant defects in learning and memory. So the team dug deeper to determine why SNX27 would have that effect. They found that SNX27 helps keep glutamate receptors on the cell surface in neurons. Neurons need glutamate receptors in order to function correctly. With less SNX27, these mice had fewer active glutamate receptors and thus impaired learning and memory.
SNX27 levels are low in Down syndrome
Then the team got thinking about Down syndrome. The SNX27-deficient mice shared some characteristics with Down syndrome, so they took a look at human brains with the condition. This confirmed the clinical significance of their laboratory findings—humans with Down syndrome have significantly lower levels of SNX27.
Next, Xu and colleagues wondered how Down syndrome and low SNX27 are connected—could the extra chromosome 21 encode something that affects SNX27 levels? They suspected microRNAs, small pieces of genetic material that don't code for protein, but instead influence the production of other genes. It turns out that chromosome 21 encodes one particular microRNA called miR-155. In human Down syndrome brains, the increase in miR-155 levels correlates almost perfectly with the decrease in SNX27.
Xu and his team concluded that, due to the extra chromosome 21 copy, the brains of people with Down syndrome produce extra miR-155, which by indirect means decreases SNX27 levels, in turn decreasing surface glutamate receptors. Through this mechanism, learning, memory, and behavior are impaired.
Restoring SNX27 function rescues Down syndrome mice
If people with Down syndrome simply have too much miR-155 or not enough SNX27, could that be fixed? The team explored this possibility. They used a noninfectious virus as a delivery vehicle to introduce new human SNX27 in the brains of Down syndrome mice.
"Everything goes back to normal after SNX27 treatment. It's amazing—first we see the glutamate receptors come back, then memory deficit is repaired in our Down syndrome mice," said Xin Wang, a graduate student in Xu's lab and first author of the study. "Gene therapy of this sort hasn't really panned out in humans, however. So we're now screening small molecules to look for some that might increase SNX27 production or function in the brain."
This research was funded by the U.S. National Institutes of Health (National Institute on Aging grants R01AG038710, R01AG021173, R01AG030197, R01AG044420; National Institute of Neurological Disorders and Stroke grants R01NS046673, P30NS076411; Eunice Kennedy Shriver National Institute of Child Health & Human Development grant P01HD29587; National Institute of Environmental Health Sciences grant P01ES016738), Alzheimer's Association, American Health Assistance Foundation, National Natural Science Foundation of China, 973 Prophase Project, Natural Science Funds for Distinguished Young Scholar of Fujian Province, Program for New Century Excellent Talents in Universities, Fundamental Research Funds for the Central Universities, and Fok Ying Tung Education Foundation.
The study was co-authored by Xin Wang, Sanford-Burnham; Yingjun Zhao, Sanford-Burnham and Xiamen University; Xiaofei Zhang, Sanford-Burnham; Hedieh Badie, Sanford-Burnham; Ying Zhou, Sanford-Burnham; Yangling Mu, Salk Institute; Li Shen Loo, Institute of Molecular and Cell Biology, Singapore; Lei Cai, Institute of Molecular and Cell Biology, Singapore; Robert C. Thompson, Sanford-Burnham; Bo Yang, Sanford-Burnham; Yaomin Chen, Sanford-Burnham; Peter F. Johnson, National Cancer Institute-Frederick; Chengbiao Wu, University of California, San Diego; Guojun Bu, Xiamen University; William C. Mobley, University of California, San Diego; Dongxian Zhang, Sanford-Burnham; Fred H. Gage, Salk Institute; Barbara Ranscht, Sanford-Burnham; Yun-wu Zhang, Sanford-Burnham and Xiamen University; Stuart A. Lipton, Sanford-Burnham and University of California, San Diego; Wanjin Hong, Institute of Molecular and Cell Biology, Singapore and Xiamen University; and Huaxi Xu, Sanford-Burnham and Xiamen University.
About Sanford-Burnham Medical Research Institute
Sanford-Burnham Medical Research Institute is dedicated to discovering the fundamental molecular causes of disease and devising the innovative therapies of tomorrow. Sanford-Burnham takes a collaborative approach to medical research with major programs in cancer, neurodegeneration, diabetes, and infectious, inflammatory, and childhood diseases. The Institute is recognized for its National Cancer Institute-designated Cancer Center and expertise in drug discovery technologies. Sanford-Burnham is a nonprofit, independent institute that employs 1,200 scientists and staff in San Diego (La Jolla), California and Orlando (Lake Nona), Florida. For more information, visit us at sanfordburnham.org.
Heather Buschman | EurekAlert!
Further reports about: > Cancer > Gates Foundation > Medical Wellness > Molecular Target > SNX27 > Sanford-Burnham > Xiamen > brain aging > brain function > cell death > cell surface > childhood disease > chromosome 2 > chromosome 21 > glutamate receptor > health services > human brain > synthetic biology
Enduring cold temperatures alters fat cell epigenetics
19.04.2018 | University of Tokyo
Full of hot air and proud of it
18.04.2018 | University of Pittsburgh
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
In an article that appears in the journal “Review of Modern Physics”, researchers at the Laboratory for Attosecond Physics (LAP) assess the current state of the field of ultrafast physics and consider its implications for future technologies.
Physicists can now control light in both time and space with hitherto unimagined precision. This is particularly true for the ability to generate ultrashort...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
19.04.2018 | Materials Sciences
19.04.2018 | Physics and Astronomy
19.04.2018 | Physics and Astronomy