Drosophila, despite being a useful genetic model of development, have very little DNA methylation on C. What they do have is methylation on A (technically, N6-methyladenine), although little was known about what this modification did for Read more
A recent issue of Emory Health magazine had an article describing the progress of clinical trials for fragile X syndrome, the most common inherited cause of intellectual disability. The article included interviews with the parents of a boy, Samuel McKinnon, who is participating in one of the phase III clinical trials here at Emory.
Last week, results for the phase II study for the same medication were published in Science Translational Medicine. The drug, called STX209 or arbaclofen, is one of the first designed to treat the molecular changes in the brain caused by fragile X syndrome. STX209 shows some promise in its ability to reduce social withdrawal, a key symptom of fragile X syndrome.
In one case, a boy was able to attend his birthday party for the first time in his life. In the past, he had been too shy and couldn’t tolerate hearing people sing Happy Birthday to You, the studyâ€™s lead author Elizabeth Berry-Kravis, MD, PhD from Rush University, told USA Today.
These results have generated excitement among autism researchers and specialists, because a fraction of individuals with fragile X mutations have autism and the same drug strategy may be able to address deficits in other forms of autism.
1. Autism and fragile X are not the same thing.
2. This was a phase II study, the phase III results are yet to come.
3. The study authors are up front about saying that the â€œprimary endpointâ€ (irritability) showed no difference between drug and placebo.
A team led by Emory genetics chair Steve Warren identified the gene responsible for fragile X in 1991, and Emory scientists have been important players in figuring out its effects on the brain.
Warren and colleague Mika Kinoshita are co-authors on a companion paper in STM on treatment of fragile X mice. A thoughtful review piece in the same issue of STM lays out current issues in developing therapies for â€œchildhood disorders of the synapse.â€
If you hear someone talking about a stress hormone, theyâ€™re probably talking about cortisol. Itâ€™s released by the adrenal glands in stressful situations, whether you have to escape a bear or just give a speech. Cortisol is supposed to prepare the body for â€œfight or flight.â€
Kerry Ressler, MD, PhD
Let’s step back a bit, and look at how the brain triggers cortisol production: through a peptide produced in the brain called CRF (corticotropin-releasing factor). CRF is elevated in several disorders such as depression and PTSD, and is also thought to be involved in drug and alcohol dependency.
Neurons that make CRF are found in locations all over the brain, so studying them can be tricky. Kerry Ressler and his colleagues have developed an intriguing tool for studying CRF. In the places where CRF is produced in a mouseâ€™s brain, they can take out the gene of their choice.
Green spots (above) and blue staining (below) indicate where CRF is produced in the mouse brain. PVN = hypothalamus, paraventricular nucleus CeA = central amygdala
In a new paper in PNAS, postdoc Georgette Gafford and Ressler use this tool in a subtle way. They have mice where a gene for a GABA receptor, one of the main inhibitory receptors (brakes) in the nervous system, is deleted, but only in the CRF neurons. This basically has the effect of turning up the volume on CRF production in several parts of the brain. It appears that modulating GABA receptors is something that normally happens to regulate CRF production, but in this case, a restraint on these stress-sensitive cells has been taken off.
â€œThese mice are normal in many ways – normal locomotor and pain responses and no difference in depressive-like behavior or Pavlovian fear conditioning. However, these mutants have increased anxiety-like behavior,â€ Gafford and Ressler write.
They also have â€œimpaired extinction of conditioned fear,â€ meaning that they have trouble becoming NOT afraid of something, like a buzzing sound, to which they have been sensitized by shocks. This is analogous to PTSD in which patients remain afraid and aren’t able to successfully inhibit their prior fear learning, even after the context is now safe.Â [A 2011 paper goes into more detail on this biological aspect of PTSD in a civilian population.]
â€œThese data indicate that disturbance of this specific population of neurons causes increased anxiety and impaired fear extinction, and helps us to further understand mechanisms of fear- and anxiety-related disorders such as PTSD,” Ressler and Gafford write.
Ressler, associate professor of psychiatry and behavioral sciences, is a Howard Hughes Medical Investigator, with a laboratory at the Yerkes National Primate Research Center. He is also co-director of the Grady Trauma Project.
Anyone studying neuroscience will notice that many neurodegenerative diseases seem to have their own sticky, possibly toxic protein.Â This protein tends to aggregate, or clump together, in or near the cells affected by the disease.
Picture a glass of milk left in a warm place for several days. Yuck. That is the macro version of the microscopic clumps scientists believe are bothering the brain.Â For many diseases, there is a debate: are the clumps by themselves toxic to neurons, or a byproduct of something else killing the cells?
Parkinsonâ€™s disease has one of the pesky proteins: alpha-synuclein.Â Alzheimerâ€™s disease has two: beta-amyloid outside cells and tau inside.Â ALS (amyotrophic lateral sclerosis) has at least three.*
One of them, TDP-43, is found in protein aggregates in most forms of ALS, both familial and sporadic. Mutations in the TDP-43 gene also account for a small fraction of both familial and sporadic forms of ALS. This suggests that even the normal protein can create problems, but a mutated version can accelerate the disease. In addition, TDP-43 aggregates have been connected with other diseases such as frontotemporal dementia.
Again, it’s not clear whether the aggregates themselves are toxic, or whether it’s more a matter of TDP-43, which appears to regulate RNA processing, is not doing what it’s supposed to in the cell.
TDP-43 protein is mobile within motor neurons.
Emory cell biologists Claudia Fallini and Wilfried Rossoll have been probing the effects of tweaking TDP-43 levels in motor neurons, the cell type vulnerable to degeneration in ALS. They find that motor neurons may be more sensitive to changes in TDP-43 levels than other neurons, which may explain why ALS selectively affects motor neurons.
Fallini was able to obtain aÂ movieÂ of fluorescently-tagged TDP-43 “granules” moving around in live motor neurons. Importantly: this is healthy/functional, not aggregated/ toxic protein. The finding that TDP-43 is mobile implies that it has something to do with transporting RNAs around the cell, rather than only functioning in the nucleus.
“Our data pointÂ to the hypothesis that TDP-43 increased localization in theÂ cytoplasm is the early trigger of toxicity, followed by proteinÂ aggregation,” Fallini says. “Because motor neurons are unique neurons due to their highÂ degree of polarization, we believe they might be more sensitive toÂ alterations in TDP-43 functions in the cytoplasm or the axon.”
In particular, the researchers found that elevated levels of TDP-43 provoke motor neurons to shut down axon outgrowth. They focused on a role for the C-terminal end of TDP-43 in this effect.
â€œNobody had looked at TDP-43 specifically in motor neurons before,â€ she says. â€œOur paper for the first time shows the localization and axonal transport of TDP-43, and the effects of TDP-43 altered levels on motor neuron morphology.â€
*Another ALS protein, SOD1 (superoxide dismutase), apparently forms toxic aggregates when mutated in some cases of familial ALS. At Emory, Terrell Brotherton and Jonathan Glass have been investigating these forms of SOD. The third protein, FUS, has similar properties to TDP-43.
Cell biologist Victor Faundez has been getting someattention for his research on dysbindin, a protein linked to schizophrenia. The information helps to make sense of the complex picture emerging from genetic studies of schizophrenia.
Genetics plays a major role in schizophrenia, but there is no one gene that pulls the trigger. The gene encoding dysbindin was first identified as a potential bad actor in 2002, by researchers studying families with a high rate of schizophrenia. Dysbindin levels are reduced in the brains of schizophrenia patients, and mouse mutants lacking the protein develop normally but have altered signaling in the brain.
Dysbindin is known to be part of a machine that produces vesicles (tiny bubbles containing proteins and neurotransmitters) and transports them around the cell. This machine, found in several tissues besides the brain, has a mouthful of a name: BLOC (Biogenesis of Lysosome-related Organelles Complex).Â Faundezâ€™ lab has shown that defects in BLOC make proteins in neurons â€œmiss the busâ€ that would transport them from the cell body out to the synapse.
The BLOC complex transports vesicles from the cell body out to the synapse. When parts of the complex are missing, neurons appear to develop aberrantly.
The team of Faundez, postdoc Avanti Gokhale and their colleagues set out to define all the parts of the BLOC machine and find other proteins dysbindin comes into contact with. Several of the proteins they found (the results were published in March 2012 in Journal of Neuroscience) are affected by copy number variation in schizophrenia patients.
â€œThis was a surprise,â€ Faundez says. â€œThe genomic studies in schizophrenia identify lots of genes, but looking at them, we donâ€™t know how they relate to each other.â€
Copy number variation means: patients have a deletion or an extra copy of the gene involved. A copy number variation doesnâ€™t mean someone is always going to get schizophrenia, but it may be enough to tip the balance when other risk factors add up.
Faundez says his teamâ€™s results highlight an approach to examining genes implicated in complex diseases: rather than looking at individual genes, look at circuits in the cell. A strong example: two of the genes that encode dysbindin interaction partners are located within the chromosome 22q11 region. Individuals with a deletion in this region develop schizophrenia at a rate of 30 percent.
Faundezâ€™s team also found that dysbindin interacts with peroxiredoxins, antioxidant enzymes that clean up hydrogen peroxide. They went on to confirm that dysbindin mutant cells have elevated peroxide levels, which hints at a role for altered redox signaling in schizophrenia.
Biomarkers in schizophrenia have been elusive, but Faundez says he thinks his research could lead to identifying a subset of schizophrenia patients where a disturbance of the BLOC system is especially important.
Emory geneticists Andres Moreno-De Luca and Christa Lese-Martin are coauthors on the JN paper.
The fragile X protein — missing in the most common inherited form of intellectual disability — plays a central role in neurons and how they respond to external signals.Â Cell biologist Gary Bassell and his colleagues have been examining how the fragile X protein (FMRP) acts as a “toggle switch.”
Gary Bassell, PhD
FMRP controls the activity of several genes by holding on to the RNAs those genes encode. When neurons get an electrochemical signal from the outside, FMRP releases the RNAs, allowing the RNAs to be made into protein, and facilitating changes in the neurons linked to learning and memory.
The Bassell lab’s new paper in Journal of Neuroscience reveals the role of another player in this process. The first author is postdoctoral fellow Vijay Nalavadi.
The researchers show that neurons modify FMRP with ubiquitin, the cellular equivalent of a tag for trash pickup, after receiving an external signal. In general, cells attach ubiquitin to proteins so that the proteins get eaten up by the proteasome, the cellular trash disposal bin. Here, neurons are temporarily getting rid of FMRP, prolonging the effects of the external signal.
Welcome to what could become a regular feature on the Emory Health Now blog: explaining a word or phrase that is connected with research going on at Emory.
What is the default mode network?
This is a concept that grew out of brain imaging studies, using techniques such as functional magnetic resonance imaging. The default mode network consists of regions of the brain that are active when someone is not doing anything in particular, especially something requiring focused attention. More fancifully: itâ€™s what daydreaming looks like.
The default mode network includes the medial prefrontal cortex (MPFC) and the posterior cingulate cortex (PCC).
Researchers at Emory and elsewhere have been looking at whether the DMNâ€™s activity and its links to other areas of the brain are changed in disorders such as schizophrenia, autism, depression and post-traumatic stress disorder.
At the Atlanta Veterans Affairs Medical Center, Erica Duncan and her colleagues have examined the DMN in people with schizophrenia. They found (as have other groups) that individuals with schizophrenia appear to have difficulty shutting down the DMN and focusing on a task, as well as having a different pattern of connections within the DMN.
Yerkes investigator Lary Walker recently wrote about research connecting metabolic activity in the default mode network with the burden of amyloid in Alzheimerâ€™s disease.
The DMN is made up of several regions of the brain, most prominently the posterior cingulate cortex (PCC) and medial prefrontal cortex (MPFC). Other regions such as the inferior parietal lobule, lateral temporal cortex, and hippocampal formation including parahippocampus are also considered part of the DMN. Note: these regions can also be engaged in other tasks besides daydreaming or introspection.
Dystonia gives sufferers involuntary muscle contractions that cause rigid, twisting movements and abnormal postures. It is the third most common movement disorder, after tremor and Parkinsonâ€™s disease. Neurologists can sometimes use drugs to address the symptoms of dystonia but there is no cure.
A 2008 review by Hess (PDF) concludes that compared with other neurological disorders, â€œour understanding of the biology and potential treatments for dystonia is in its infancy.â€ Still, scientists have known for a while that the cerebellum, a region of the brain that regulates movement, is involved.
â€œWe focused on the cerebellum because studies in patients with dystonia often show that this part of the brain is more active, when examined by MRI,” Hess says. “The abnormal overactivity of the cerebellum is seen in patients with all different types of dystonia, so it seems to be a common hotspot. Our goal was to understand what might be causing the overactivity in mice because if we can stop the overactivity, we might be able to stop the dystonia.”
Hess and her colleagues discovered that drugs that stimulate AMPA receptors induce dystonia when introduced into the mouse cerebellum. Their results suggest that drugs that act in reverse, blocking AMPA receptors, could be used to treat dystonia.
AMPA receptors are a subset of glutamate receptors, a large group of â€œreceiver dishesâ€ for excitatory signals in the brain. Fan performed a variety of experiments to show that AMPA receptor activity plays a specific role in generating dystonia. For example, drugs that affect other types of glutamate receptors did not induce dystonia. AMPA receptor blockers can also reduce dystonia in a genetic model, the â€œtotteringâ€ mouse.
Although pharmaceutical companies have already been testing AMPA receptor blockers as potential antiseizure drugs, caution is in order. AMPA receptor stimulators/ enhancers (or â€œampakinesâ€) have been identified as potential enhancers of learning and memory, so AMPA receptor blockers may interfere with those processes.
â€œOur results suggest that reducing AMPA receptor activity could help alleviate dystonia but we still have a lot of work to do before we know whether blocking AMPA receptor activity in patients will really help,” Hess says. “Since there arenâ€™t many drugs that act at AMPA receptors, one of our goals is to identify drugs that change the â€˜downstreamâ€™ effects of AMPA receptor activation. For example, we may be able to find other drug classes that change neuronal activity in the same way that AMPA receptor blockade changes activity.â€
Geneticist Madhuri Hegde and her colleagues have a paper in the journal Genome Researchthat addresses the question: where do copy number variations come from?
Madhuri Hegde, PhD
Copy number variations (CNVs), which are deletions or duplications of small parts of the genome, have been the subject of genetic research for a long time. But only in the last few years has it become clear that copy number variations are where the action is for complex diseases such as autism and schizophrenia. Geneticists studying these diseases are shifting their focus from short, common mutations (often, single nucleotide polymorphisms or SNPs) to looking at rarer variants such as CNVs. A 2009 discussion of this trend with Steve Warren and Brad Pearce can be found here.
Hegde is the Scientific Director of the Department of Human Geneticsâ€™ clinical laboratory. Postdoctoral fellow Arun Ankala is the first author. In the new paper, Ankala and Hegde examine rearrangements in patientsâ€™ genomes that arose in 62 clinical cases of Duchenneâ€™s muscular dystrophy and several other diseases. Mutations in the DMD gene are responsible for Duchenneâ€™s muscular dystrophy.
The pattern of the rearrangement hints what events took place in the cell beforehand, and hint that a problem took place during replication of the DNA. The signature is a tandem duplication of a short segment next to a large deletion, indicating how the DNA was repaired.
The authors note that the DMD locus is especially prone to these types of problems because it is much larger than other gene loci. The gene is actually the longest human gene known on the DNA level, covering 2.4 megabases (0.08 percent of the genome.)
Replication origins are where the DNA copying machinery in the cell starts unwinding and copying the DNA.Â Bacterial circular chromosomes have just one replication origin. In contrast, humans have thousands of replication origins spread across our chromosomes. In the discussion, the authors suggest that DNA copying problems may also explain duplications and historically embedded rearrangements of the genome.
How much is the development of epilepsy like arthritis?
More than you might expect. Inflammation, or the overactivation of the immune system, appears to be involved in both. In addition, for both diseases, inhibiting the enzyme COX-2 initially looked like a promising approach.
Ray Dingledine, PhD
COX-2 (cyclooxygenase 2) is a target of traditional non-steroid anti-inflammatory drugs like aspirin and ibuprofen, as well as more selective drugs such as Celebrex. With arthritis, selectively inhibiting COX-2 relieves pain and inflammation, but turns out to have the side effect of increasing the risk of heart attack and stroke.
In the development of epilepsy, inhibiting COX-2 turns out to be complicated as well.Â Ray Dingledine, chair of pharmacology at Emory, and colleagues have a new paper showing that COX-2 has both protective and harmful effects in mice after status epilepticus, depending on the timing and what cells the enzyme comes from. Status epilepticus is a period of continuous seizures leading to neurodegeneration, used as a model for the development of epilepsy.
Postdoc Geidy Serrano, now at the Banner Sun Health Research Institute in Arizona, is first author of the paper in Journal of Neuroscience. She and Dingledine were able to dissect COX-2â€™s effects because they engineered mice to have a deletion of the COX-2 gene, but only in some parts of the brain.
They show that deleting COX-2 in the brain reduces the level of inflammatory molecules produced by neurons, but this is the reverse effect of deleting it all over the body or inhibiting the enzyme with drugs.
Four days after status epilepticus, fewer neurons are damaged (bright green) in the neuronal COX-2 knockout mice.
Dingledine identified two take-home messages from the paper:
First, COX-2 itself is probably not a good target for antiepileptic therapy, and it may be better to go downstream, to prostaglandin receptors like EP2.
Second, the timing of intervention will be important, because the same enzyme has opposing actions a few hours after status epilepticus compared to a couple days later.
More of Dingledineâ€™s thinking about inflammation in the development of epilepsy can be found in a recent review.
Biomarkers circulating in the bloodstream may serve as a predictive window for recurrent stroke risk and also help doctors accurately assess what is happening in the brains of patients with acute traumatic brain injury (TBI).
Michael Frankel, MD
Researchers at Emory University School of Medicine, led by principal investigator Michael Frankel, MD, Emory professor of neurology and director of Grady Memorial Hospitalâ€™s Marcus Stroke & Neuroscience Center, are studying biomarkers as part of two ancillary studies of blood samples using two grants from the National Institutes of Health.
In the $1.47 million, four-year grant called â€œBiomarkers of Ischemic Outcomes in Intracranial Stenosisâ€ (BIOSIS), Emory researchers are analyzing blood samples from 451 patients from around the country who were enrolled in a study known as SAMMPRIS (Stenting and Aggressive Medical Management for Preventing Recurrent stroke in Intracranial Stenosis), the first randomized, multicenter clinical trial designed to test whether stenting intracranial arteries would prevent recurrent stroke.
Researchers in the SAMMPRIS study recently published their results in the New England Journal of Medicine, showing that medical management was more effective than stenting in preventing recurrent strokes in these patients. Frankel’s BIOSIS research team is using blood samples from these same patients to continue learning more about the molecular biology of stroke to predict risk of a stroke occurring in the future.
â€œOur goal is to learn more about stroke by studying proteins and cells in the blood that reflect the severity of disease in arteries that leads to stroke. If we can test blood samples for proteins and cells that put patients at high risk for stroke, we can better tailor treatment for those patients,â€ says Frankel.
Patients with narrowed brain arteries, known as intracranial stenosis, have a particularly high risk of disease leading to stroke. At least one in four of the 795,000 Americans who have a stroke each year will have another stroke within their lifetime. Within five years ofÂ a firstÂ stroke,Â the risk for another stroke can increase more than 40 percent. Recurrent strokes often have a higher rate of death and disability because parts of the brain already injured by the original stroke may not be as resilient.
The other study, â€œBiomarkers of Injury and Outcome in ProTECT IIIâ€ (BIO-ProTECT)” is a $2.6 million, five-year NIH grant in which Frankelâ€™s team will use blood to determine what is happening in the brain of patients with acute TBI.Â The blood samples are from patients enrolled in the multicenter clinical trial ProTECT III (Progesterone for Traumatic brain injury, Experimental Clinical Treatment), led by Emory Emergency Medicine Professor, David Wright, MD, to assesses the use of progesterone to treat TBI in 1,140 patients at 17 centers nationwide.
In the BIO-ProTECT study, Emory is collaborating with the Medical University of South Carolina, the University of Pittsburgh, the University of Michigan and Banyan Biomarkers.
TBI is the leading cause of death and disability among young adults in the US and worldwide. According to the Centers for Disease Control and Prevention, approximately 1.4 million Americans sustain a traumatic brain injury each year, leading to 275,000 hospitalizations, 80,000 disabilities, and 52,000 deaths.
Acute TBI leads to a cascade of cellular events set in motion by the initial injury that ultimately lead to cerebral edema (swelling of the brain), cellular disruption and sometimes death. Tissue breakdown leads to the release of proteins into the bloodstream. These proteins may serve as useful biomarkers of the severity of the injury and perhaps provide useful information about response to treatment.
Using the large patient group in the ProTECT III trial, the researchers hope to validate promising TBI biomarkers as predictors of clinical outcome and also evaluate the relationship between progesterone treatment, biomarker levels and outcome.
â€œIf we can better determine the amount of brain injury with blood samples, we can use blood to help doctors better assess prognosis for recovery, and, hopefully whether a patient will respond to treatment with progesterone,â€ says Frankel.