Stem cells help identify causes for Angelman's
Researchers used stem cells from patients with Angelman syndrome to identify what cellular defects cause this rare neurogenetic disorder. This important step aids ongoing research looking for a possible cure and treatments now.
Up until now, scientists trying to understand why the brain cells of individuals with Angelman fail to develop properly have relied primarily on mouse models that mimic the disorder. But this study used human stem cells genetically identical to brain cells of Angelman syndrome patients. Angelman stem cells gave researchers a much clearer and more accurate picture of went wrong during development. The study appeared April 24 in Nature Communications.
Angelman syndrome appears in one out of every 15,000 live births. People with Angelman have developmental delays, are prone to seizures, can have trouble walking or balancing, and have limited speech. But they generally present a happy demeanor, frequently laughing and smiling. The disorder occurs when a single gene, known as UBE3A inherited on the mother's chromosome 15, is deleted or made inactive. Occasionally it is due to inheriting two copies of chromosome 15 from a person's father and none from their mother. A father's version is inactivated or "silenced" by genomic imprinting, so no functional version of the gene remains.
"We looked at the electrical activity of these brain cells and their ability to form connections, which is critical to the working circuits in the brain — finding that cells from Angelman patients were impaired. They fail to develop mature electrical activity and didn't form connections readily."
Eric S. Levine PhD, Department of Neuroscience, University of Connecticut School of Medicine, Farmington, Connecticut, USA, and the study's lead author.
The research led by Levine was done in collaboration with another team at the University of Connecticut, Department of Genetics and Genome Sciences, led by developmental geneticist Stormy J. Chamberlain. Chamberlain is investigating the underlying genetic mechanisms causing Angelman and how those mechanisms might be reversed. Levine's team meanwhile is looking at the physiology behind what happens in the brain when the maternal UBE3A gene is missing or fails to work properly.
"What's interesting about this particular study is that Eric captured some of the first electrophysiological differences between Angelman syndrome neurons and typically developing neurons and it appears those primary deficits are setting up all of the other problems that are happening downstream," explains Chamberlain.
The human brain relies on electrical signals to process information. These signals pass between the neurons in our brain via special connections called synapses.
Levine found that around three to five weeks into fetal development, brain cells in unaffected individuals ramp up their electrical activity — while cells from Angelman patients do not. This failure to mature disrupts the ability of Angelman cells to form proper synaptic connections critical for learning, memory, and cognitive development.
"Other researchers haven't seen this deficit in mouse models, but we think it might have some-thing to do with when they are looking," adds Chamberlain, co-author on the current study. "In mouse studies, research has been looking at either adults, juvenile, or early postnatal neurons. Eric is looking at some of the earliest changes in neurons that likely occur during fetal development."
Angelman patients are very active in the ongoing research into their disorder. The induced pluripotent stem cells used in Levine's research were derived from skin and blood cells donated by people with Angelman. These skin and blood cells were reprogrammed back into stem cells, then prompted in the lab to grow into brain cells matching each patient's genetic makeup. This process allowed Levine to closely monitor how cells develop in vitro from the very earliest stages and watch as they begin to differ from control cells of people without the disorder.
To confirm cell defects in Angelman cells were caused by the loss of the UBE3A gene, when Levine edited out the UBE3A gene in control group cells — the same cascading chain of events occurred disrupting synapses.
"In control cells without Angelman, we basically knocked out the gene in order to mimic the Angelman defect. If you do that early enough in development, you see all of the same things go wrong in those cells. Interestingly, if you wait and knock out the gene later in development, you only see a subset of those deficits."
Eric Levine PhD
These results led Levine to believe that delayed electrical activity is one of the driving factors causing defects to occur in brain cells of patients with Angelman. This information is important to the development of possible drugs to combat Angelman. If scientists can stop the initial electrical failure from happening, it might prevent further developmental problems from occuring as well. Chamberlain and Levine are taking their research to the next level. They want to know exactly how loss of the UBE3A gene stops electrical conductivity in early Angelman brain cells.
A secondary benefit of the current study is the stem cell model created by Chamberlain and Levine can now be used to monitor human Angelman brain cells in the lab. This allows for testing any number of compounds to see if it is possible to arrest Angelman defects or perhaps even reverse its cascading damage.
"The Angelman Syndrome Foundation was proud to fund Dr. Levine's research in 2011 and we are thrilled to see the results," says Eileen Braun, executive director of the national nonprofit organization that funds Angelman syndrome research and supports individuals with Angelman and their families.
Angelman syndrome (AS) is a neurogenetic disorder caused by deletion of the maternally inherited UBE3A allele and is characterized by developmental delay, intellectual disability, ataxia, seizures and a happy affect. Here, we explored the underlying pathophysiology using induced pluripotent stem cell-derived neurons from AS patients and unaffected controls. AS-derived neurons showed impaired maturation of resting membrane potential and action potential firing, decreased synaptic activity and reduced synaptic plasticity. These patient-specific differences were mimicked by knocking out UBE3A using CRISPR/Cas9 or by knocking down UBE3A using antisense oligonucleotides. Importantly, these phenotypes could be rescued by pharmacologically unsilencing paternal UBE3A expression. Moreover, selective effects of UBE3A disruption at late stages of in vitro development suggest that changes in action potential firing and synaptic activity may be secondary to altered resting membrane potential. Our findings provide a cellular phenotype for investigating pathogenic mechanisms underlying AS and identifying novel therapeutic strategies.
Other authors: James J. Fink, Tiwanna M. Robinson, Noelle D. Germain, Carissa L. Sirois, Kaitlyn A. Bolduc, Amanda J. Ward, Frank Rigo, Stormy J. Chamberlain & Eric S. Levine
Researchers with Ionis Pharmaceuticals of Carlsbad, California also participated in the study.
Nature Communications 8, Article number: 15038 (2017)
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May 3, 2017 Fetal Timeline Maternal Timeline News News Archive
Actor Collin Farrell's son was born with Angelman Syndome. and
acts as a spokesman for FAST, The Foundation for Angelman Syndrome.
Image Credit: Public Domain