Focus on mitochondria in schizophrenia research

Despite advances in genomics in recent years, schizophrenia remains one of the most complex challenges of both genetics and neuroscience. The chromosomal abnormality 22q11 deletion syndrome, also known as DiGeorge syndrome, offers a way in, since it is one of the strongest genetic risk factors for schizophrenia.

Out of dozens of genes within the 22q11 deletion, several encode proteins found in mitochondria. A team of Emory scientists, led by cell biologist Victor Faundez, recently analyzed the network of proteins found in human cells, both from individuals affected by 22q11 deletion syndrome and their healthy relatives.

The results are published in Journal of Neuroscience. Note: this is a sprawling paper, involving both proteomics (courtesy of Nick Seyfried, whose Emory epithet is “wizard”) and mutant Drosophila fruit flies. There are four co-first authors: Avanti Gokhale, Cortnie Hartwig, Amanda Freeman and Julia Bassell.

Victor Faundez, PhD

Mitochondrial proteins are important for keeping cells fueled up and in metabolic balance, but how does altering them affect the brain in a way that leads to schizophrenia? That’s the overall question: how do changes in the miniature power plants within the cell affect synapses, the junctions between cells?

The scientists were focusing on one particular mitochondrial protein, SLC25A1, whose corresponding gene is in the 22q11 deletion. Faundez says that SCL25A1 has been largely ignored by other scientists studying 22q11.

“We think SLC25A1 exerts a powerful influence on the neurodevelopmental phenotypes in 22q11,” he says. “Our main focus forward is going to be the function that mitochondria play in synapse biology.” Read more

Posted on March 15, 2019 by Quinn Eastman in Neuro Leave a comment

A life consumed by sleep

Nothing he tried had worked. For Sigurjon Jakobsson, the trip to Atlanta with his family was a last-ditch effort to wake up. He had struggled with sleeping excessively for several years before coming from Iceland to see a visionary neurologist, who might have answers.

In high school, Sigurjon was a decathlete competing as part of Iceland’s national sports team. But at the age of 16, an increasing need for sleep began to encroach upon his life. Sigurjon needed several alarm clocks to get out of bed and was frequently late to school or his job at a construction company. He often slept more than 16 hours in a day.

Sigurjon feeling awake (Atlanta, summer 2018)

When Sigurjon describes his experiences, they sound like depression, although his mood and lack of motivation appear more a consequence of his insatiable desire to sleep. He quit sports. He dropped out of college and became isolated and lost touch with close friends.

“Your will to do things just kinda dies,” he says. “And then you’re always trying and trying again. It just gets worse. You kinda die inside from being tired all the time.”

At the recommendation of a neurologist in Iceland, Sigurjon’s family sought out David Rye, who is known internationally for his research on idiopathic hypersomnia, a poorly understood sleep disorder. Read more

Posted on February 11, 2019 by Quinn Eastman in Neuro Leave a comment

Laughter may be best medicine for brain surgery

Neuroscientists at Emory University School of Medicine have discovered a focal pathway in the brain that when electrically stimulated causes immediate laughter, followed by a sense of calm and happiness, even during awake brain surgery. The effects of stimulation were observed in an epilepsy patient undergoing diagnostic monitoring for seizure diagnosis. These effects were then harnessed to help her complete a separate awake brain surgery two days later.

The behavioral effects of direct electrical stimulation of the cingulum bundle, a white matter tract in the brain, were confirmed in two other epilepsy patients undergoing diagnostic monitoring. The findings are scheduled for publication in the Journal of Clinical Investigation.

Emory neurosurgeons see the technique as a “potentially transformative” way to calm some patients during awake brain surgery, even those who are not especially anxious. For optimal protection of critical brain functions during surgery, patients may need to be awake and not sedated, so that doctors can talk with them, assess their language skills, and detect impairments that may arise from resection. Read more

Posted on February 8, 2019 by Quinn Eastman in Neuro Leave a comment

Probing hyperexcitability in fragile X syndrome

Researchers at Emory University School of Medicine have gained insight into a feature of fragile X syndrome, which is also seen in other neurological and neurodevelopmental disorders.

In a mouse model of fragile X syndrome, homeostatic mechanisms that would normally help brain cells adjust to developmental changes don’t work properly. This helps explain why cortical hyperexcitability, which is linked to sensory sensitivity and seizure susceptibility, gradually appears during brain development.

Studying a model of fragile X syndrome, Emory researchers were looking at neurons displaying single spiking and multi-spiking behavior.

These physiological insights could help guide clinical research and efforts at early intervention, the scientists say. The results were published Feb. 5 by Cell Reports (open access).

Fragile X syndrome is the most common inherited form of intellectual disability and a leading single-gene cause of autism. Individuals with fragile X syndrome often display sensory sensitivity and some — about 15 percent— have seizures.

Scientists’ explanation for these phenomena is cortical hyperexcitability, meaning that the response of the cortex (the outer part of the brain) to sensory input is more than typical. Cortical hyperexcitability has also been observed in the broader category of autism spectrum disorder, as well as migraine or after a stroke.

At Emory, graduate student Pernille Bülow forged a collaboration between Peter Wenner, PhD and Gary Bassell, PhD. Wenner, interested in homeostatic plasticity, and Bassell, an expert in fragile X neurobiology, wanted to investigate why a mechanism called homeostatic intrinsic plasticity does not compensate for the changes in the brain brought about in fragile X syndrome. More here.

Posted on February 8, 2019 by Quinn Eastman in Neuro Leave a comment

Nogueira’s trailblazing work on stroke recognized

Neurologist Raul Nogueira’s clinical research on thrombectomy, a life-saving intervention after ischemic stroke, is getting recognition – in non-traditional ways.

A group of Korean neurologists and radiologists recently analyzed the most mentioned neurointervention papers by “altmetrics.” Altmetrics measure the impact a research paper has by looking at online discussion – in international news media, blogs, Wikipedia and social media platforms, as well as attention from post-publication peer-review and patient advocacy groups.

Raul Noguiera, MD

As it turned out, one of Nogueira’s papers was the most mentioned and he was also an author on 12 of the 101 top articles. Nogueira was the first author of a 2018 paper in the New England Journal of Medicine, reporting on results from the DAWN trial. The study was a landmark, extending the time window for thrombectomy to 24 hours. Those treated with thrombectomy in addition to standard care regained significantly more functional independence after 90 days than those who received standard treatment only.

Another recent example that fits within altmetrics: The DAWN study was cited by the American Heart Association as a top research finding in stroke for 2018.

Nogueira is a professor of neurology, neurosurgery and radiology at Emory University School of Medicine and director of endovascular services at Grady Memorial Hospital’s Marcus Stroke & Neuroscience Center. Thrombectomy is the removal of a clot from a blood vessel in the brain – in this case, through a mechanical stent-retriever device.

Posted on February 6, 2019 by Quinn Eastman in Heart, Neuro Leave a comment

Vulnerability to stress – Tet by Tet

Geneticist Peng Jin and colleagues have a paper in Cell Reports this week that is part of a mini-boom in studying the Tet enzymes and their role in the brain. The short way to explain what Tet enzymes do is that they remove DNA methylation by oxidizing it out.

Methylation, a modification of DNA that generally shuts genes off, has been well-studied for decades. The more recent discovery of how cells remove methylation with the Tet enzymes opened up a question of what roles the transition markers have. It’s part of the field of epigenetics: the meaning of these modifications “above” the DNA sequence.

This is my favorite analogy to explain the transition states, such as 5-hydroxymethylcytosine. They’re not really a new letter of the genetic alphabet – they’ve been there all along. We just didn’t see them before.

Imagine that you are an archeologist, studying an ancient civilization. The civilization’s alphabet contains a limited number of characters. However, an initial pass at recently unearthed texts was low-resolution, missing little doodads like the cedilla in French: Ç.

Are words with those marks pronounced differently? Do they have a different meaning?

The new Cell Reports paper shows that it matters what pen writes the little doodads. In mice, removing one Tet enzyme, Tet1, has the opposite effect from removing Tet2, when it comes to response to chronic stress. One perturbation (loss of Tet1) makes the mice more resistant to stress, while the other (loss of Tet2) has them more vulnerable. The researchers also picked up an interaction between Tet1 and HIF1-alpha, critical for regulation of cells’ response to hypoxia. Read more

Posted on December 11, 2018 by Quinn Eastman in Neuro Leave a comment

Circadian rhythms go both ways: in and from retina

In case you missed it, the 2017 Nobel Prize in Medicine marked the arrival of the flourishing circadian rhythm field. Emory Eye Center’s Mike Iuvone teamed up with Gianluca Tosini at Morehouse School of Medicine to probe how a genetic disruption of circadian rhythms affects the retina in mice.

Removal of the Bmal1 gene – an essential part of the body’s internal clock — from the retina in mice was known to disrupt the electrical response to light in the eye. The “master clock” in the body is set by the suprachiasmatic nucleus, part of the hypothalamus, which receives signals from the retina. Peripheral tissues, such as the liver and muscles, have their own clocks. The retina is not so peripheral to circadian rhythm, but its cellular clocks are important too.

What the new paper in PNAS shows is that removal of Bmal1 from the retina accelerates the deterioration of vision that comes with aging, but it also shows developmental effects – see below.

You might think: “OK, the mice have disrupted circadian rhythms for their whole lives, so that’s why their retinas are messed up.” But the Emory/Morehouse experimenters removed the Bmal1 gene from the retina only.

P. Michael Iuvone, PhD, director of vision research at Emory Eye Center

The authors write: “BMAL1 appears to play important roles in both cone development and cone viability during aging… Cones are known to be among the cells with highest metabolism within the body and therefore, alteration of metabolic processes within these cells is likely to affect their health status and viability.”

‘Master key’ microRNA has links to both ASD and schizophrenia

Recent studies of complex brain disorders such as schizophrenia and autism spectrum disorder (ASD) have identified a few “master keys,” risk genes that sit at the center of a network of genes important for brain function. Researchers at Emory and the Chinese Academy of Sciences have created mice partially lacking one of those master keys, called MIR-137, and have used them to identify an angle on potential treatments for ASD.

The results were published this week in Nature Neuroscience.

Mice partially lacking MIR-137 display learning and memory deficits, repetitive behaviors and impaired sociability. MIR-137 encodes a microRNA, which regulates hundreds of other genes, many of which are also connected to schizophrenia and autism spectrum disorder.

By treating mutant mice with papaverine, a vasodilator discovered in the 19th century, scientists could improve the performance of the mice on maze navigation and social behavior tests. Papaverine is an inhibitor of the enzyme Pde10a (phosphodiesterase 10a), which is elevated in mutant mice.

Papaverine is a component of opium, but it has a structure (and effects) that are different from opiates.

Other Pde10a inhibitors have been tested in schizophrenia clinical trials, but the new results suggest this group of compounds could have potential for some individuals with ASD, says senior author Peng Jin, PhD, professor of human genetics at Emory University School of Medicine.

Having just the right level of MIR-137 function is important. Previous studies of people with genetic deletions show that a loss of MIR-137 is connected with intellectual disability and autism spectrum disorder. The reverse situation, in which a genetic variation increases MIR-137 levels, appears to contribute to schizophrenia.

“It’s interesting to think about in the context of precision medicine,” Jin says. “Individuals with a partial loss of MIR137 – either genomic deletions or reduced expression — could potentially be candidates for treatment with Pde10a inhibitors.”

To create the mutant mice, Jin’s lab teamed up with Dahua Chen, PhD and Zhao-Qian Teng, PhD scientists at the State Key Laboratories of Stem Cell and Reproductive Biology and Membrane Biology, part of the Institute of Zoology, Chinese Academy of Sciences in Beijing. Jin says that generating mice with a heritable disruption of MIR-137 was technically challenging, taking several years. Read more

Posted on November 9, 2018 by Quinn Eastman in Neuro Leave a comment

Cells in “little brain” have distinctive metabolic needs

Cells’ metabolic needs are not uniform across the brain, researchers have learned. “Knocking out” an enzyme that regulates mitochondria, cells’ miniature power plants, specifically blocks the development of the mouse cerebellum more than the rest of the brain.

The results were published in Science Advances.

“This finding will be tremendously helpful in understanding the molecular mechanisms underlying developmental disorders, degenerative diseases, and even cancer in the cerebellum,” says lead author Cheng-Kui Qu, MD, PhD, professor of pediatrics at Emory University School of Medicine, Winship Cancer Institute and Aflac Cancer and Blood Disorders Center, Children’s Healthcare of Atlanta.

The cerebellum or “little brain” was long thought to be involved mainly in balance and complex motor functions. More recent research suggests it is important for decision making and emotions. In humans, the cerebellum grows more than the rest of the brain in the first year of life and its development is not complete until around 8 years of age. The most common malignant brain tumor in children, medulloblastoma, arises in the cerebellum.

Qu and his colleagues have been studying an enzyme, PTPMT1, which controls the influx of pyruvate – a source of energy derived from carbohydrates – into mitochondria. They describe pyruvate as “the master fuel” for postnatal cerebellar development.

Cells can get energy by breaking down sugar efficiently, through mitochondria, or more wastefully in a process called glycolysis. Deleting PTPMT1 provides insight into which cells are more sensitive to problems with mitochondrial metabolism. A variety of mitochondrial diseases affect different parts of the body, but the brain is especially greedy for sugar; it never really shuts off metabolically. When someone is at rest, the brain uses a quarter of the body’s blood sugar, despite taking up just 2 percent of body weight in an adult. More here.

Also, see this 2017 item from Stanford on the cerebellum (Nature paper).

Posted on October 24, 2018 by Quinn Eastman in Neuro Leave a comment

Fragile X files — expanded

A genetic disorder caused by silencing of a gene on the X chromosome, fragile X syndrome affects about one child in 5,000, and is more common and more severe in boys. It often causes mild to moderate intellectual disabilities as well as behavioral and learning challenges.

Amy Talboy, MD

The gene responsible for fragile X syndrome, the most common inherited form of intellectual disability, was identified more than 25 years ago. Emory genetics chair Stephen Warren played a major role in achieving that milestone. His work led to insights into the molecular details of learning and memory, and nationwide clinical trials — which have a more complicated story.

Treating the molecular basis of a neurodevelopmental disorder, instead of simply addressing symptoms, is a lofty goal – one that remains unfulfilled. Now a new study, supported by the National Institute of Neurological Disorders and Stroke, is reviving a pharmacological strategy that Warren had a hand in developing.

“This is a very well thought out approach to studying changes in language and learning in children who are difficult to test,” says Amy Talboy, medical director of Emory’s Down Syndrome and Fragile X clinics, who is an investigator in the NINDS study. “It could change how we conduct these types of studies in the future.” Read more

Posted on October 23, 2018 by Quinn Eastman in Neuro Leave a comment

« Previous 1 2 3 4 5 6 7 8 9 10 ... 22 23 Next »