Do drugs for bipolar disorder “normalize” brain gene function?

Every day, millions of people with bipolar disorder take medicines that help keep them from swinging into manic or depressed moods. But just how these drugs produce their effects is still a mystery.

Now, a new University of Michigan Medical School study of brain tissue helps reveal what might actually be happening. And further research using stem cells programmed to act like brain cells is already underway.

Using genetic analysis, the new study suggests that certain medications may help “normalize” the activity of a number of genes involved in communication between brain cells. It is published in the current issue of Bipolar Disorders.

The study involved brain tissue from deceased people with and without bipolar disorder, which the U-M team analyzed to see how often certain genes were activated, or expressed. Funding support came from the National Institutes of Health and the Heinz C. Prechter Bipolar Research Fund.

“We found there are hundreds of genes whose activity is adjusted in individuals taking medication – consistent with the fact that there are a number of genes that are potentially amiss in people with bipolar,” says senior author Melvin McInnis, M.D., the U-M psychiatrist, U-M Depression Center member and principal investigator of the Prechter Fund Projects who helped lead the study. “Taking the medications, specifically ones in a class called antipsychotics, seemed to normalize the gene expression pattern in these individuals so that it approached that of a person without bipolar.”

Digging deeper into bipolar genetics

Scientists already know that bipolar disorder’s roots lie in genetic differences in the brain — though they are still searching for the specific gene combinations involved.  

McInnis and his colleagues have now embarked on research developing several a lines of induced pluripotent stem cells derived (iPSC) from volunteers with and without bipolar disorder, which will allow even more in-depth study of the development and genetics of bipolar disorder.

The newly published study looked at the expression, or activity levels, of 2,191 different genes in the brains of 14 people with bipolar disorder, and 12 with no mental health conditions. The brains were all part of a privately funded nonprofit brain bank that collected and stored donated brains, and recorded what medications the individuals were taking at the time of death.

Seven of the brains were from people with bipolar disorder who had been taking one or more antipsychotics when they died. These drugs include clozapine, risperidone, and haloperidol, and are often used to treat bipolar disorder. Most of the 14 brain donors with bipolar disorder were also taking other medications, such as antidepressants, at the time of death.

When the researchers compared the gene activity patterns among the brains of bipolar disorder patients who had been exposed to antipsychotics with patterns among those who weren’t, they saw striking differences.

Then, when they compared the activity patterns of patients who had been taking antipsychotics with those of people without bipolar disorder, they found similar patterns.

The similarities were strongest in the expression of genes involved in the transmission of signals across synapses – the gaps between brain cells that allow cells to ‘talk’ to one another. There were also similarities in the organization of nodes of Ranvier – locations along nerve cells where signals can travel faster.

McInnis, who is the Thomas B. and Nancy Upjohn Woodworth Professor of Bipolar Disorder and Depression in the U-M Department of Psychiatry, worked with U-M scientists Haiming Chen, M.D. and K. Sue O’Shea, Ph.D., of the U-M Department of Cell and Developmental Biology. They also teamed with Johns Hopkins University researcher Christopher Ross, M.D., Ph.D. on the new research; U-M and Johns Hopkins have a long history of collaboration on bipolar disorder research.

The research used brain tissue samples from the Stanley Brain Collection of the Stanley Medical Research Institute in Maryland.

Using “gene chip” analysis to measure the presence of messenger RNA molecules that indicate gene activity, and sophisticated data analysis, they were able to map the expression patterns from the brains and break the results down by bipolar status and medication use. The bipolar and control (non-bipolar) brains were matched by age, gender and other factors.

“In bipolar disorder, it’s not just one gene that’s involved – it’s a whole symphony of them,” says McInnis, who has helped lead U-M’s bipolar genetics research for nearly a decade. “Medications appear to nudge them in a direction that aligns more with the normal expression pattern.”

Among those that were “nudged” were genes that have already been shown to be linked to bipolar disorder, including glycogen synthase kinase 3 beta (GSK3β), FK506 binding protein 5 (FKBP5), and Ankyrin 3 (ANK3).

Going forward, says McInnis, cell culture studies will be critical to studying how medications for bipolar disorder work, and to screen new molecules as potential new medications.

Lights, Chemistry, Action: New Method for Mapping Brain Activity

Building on their history of innovative brain-imaging techniques, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory and collaborators have developed a new way to use light and chemistry to map brain activity in fully-awake, moving animals. The technique employs light-activated proteins to stimulate particular brain cells and positron emission tomography (PET) scans to trace the effects of that site-specific stimulation throughout the entire brain. As described in a paper published online today in the Journal of Neuroscience, the method will allow researchers to map exactly which downstream neurological pathways are activated or deactivated by stimulation of targeted brain regions, and how that brain activity correlates with particular behaviors and/or disease conditions.

"This technique gives us a new way to look at the function of specific brain cells and map which brain circuits are active in a wide range of neuropsychiatric diseases — from depression to Parkinson’s disease, neurodegenerative disorders, and drug addiction — and also to monitor the effects of various treatments," said the paper’s lead author, Panayotis (Peter) Thanos, a neuroscientist and director of the Behavioral Neuropharmacology and Neuroimaging Section — part of the National Institute on Alcohol Abuse and Alcoholism (NIAAA) Laboratory of Neuroimaging at Brookhaven Lab — and a professor at Stony Brook University. "Because the animals are awake and able to move during stimulation, we can also directly study how their behavior correlates with brain activity," he said.

The new brain-mapping method combines very recent advances in a field known as “optogenetics” — the use of optics (light activation) and genetics (genetically coded light-sensitive proteins) to control the activity of individual neurons, or nerve cells — and Brookhaven’s historical development of radioactively labeled chemical tracers to track biological activity with PET scanners. 

The scientists used a modified virus to deliver a light-sensitive protein to particular brain cells in rats. Genetic coding can deliver the protein to specifically targeted brain-cell receptors. Then, after stimulating those proteins with light shone through an optical fiber inserted through a tiny tube called a cannula, they monitored overall brain activity using a radiotracer known as ¹⁸FDG, which serves as a stand-in for glucose, the body’s (and brain’s) main source of energy. 

The unique chemistry of ¹⁸FDG causes it to be temporarily “trapped” inside cells that are hungry for glucose — those activated by the brain stimulation — and remain there long enough for the detectors of a PET scanner to pick up the radioactive signal, even after the animals are anesthetized to ensure they stay still for scanning. But because the animals were awake and moving when the tracer was injected and the brain cells were being stimulated, the scans reveal what parts of the brain were activated (or deactivated) under those conditions, giving scientists important information about how those brain circuits function and correlate with the animals’ behaviors.

"In this paper, we wanted to stimulate the nucleus accumbens, a key part of the brain involved in reward that is very important to understanding drug addiction," Thanos said. "We wanted to activate the cells in that area and see which brain circuits were activated and deactivated in response." 

The scientists used the technique to trace activation and deactivation in number of key pathways, and confirmed their results with other analysis techniques. 

The method can reveal even more precise effects.

"If we want to know more about the role played by specific types of receptors — say the dopamine D1 or D2 receptors involved in processing reward — we could tailor the light-sensitive protein probe to specifically stimulate one or the other to tease out those effects," he said.

Another important aspect is that the technique does not require the scientists to identify in advance the regions of the brain they want to investigate, but instead provides candidate brain regions involved anywhere in the brain – even regions not well understood.

"We look at the whole brain," Thanos said. "We take the PET images and co-register them with anatomical maps produced with magnetic resonance imaging (MRI), and use statistical techniques to do comparisons voxel by voxel. That allows us to identify which areas are more or less activated under the conditions we are exploring without any prior bias about what regions should be showing effects.”

After they see a statistically significant effect, they use the MRI maps to identify the locations of those particular voxels to see what brain regions they are in.

"This opens it up to seeing an effect in any region in the brain — even parts where you would not expect or think to look — which could be a key to new discoveries," he said.

Fatheads: How neurons protect themselves against excess fat

We’re all fatheads. That is, our brain cells are packed with fat molecules, more of them than almost any other cell type. Still, if the brain cells’ fat content gets too high, they’ll be in trouble. In a recent study in mice, researchers at Johns Hopkins pinpointed an enzyme that keeps neurons’ fat levels under control, and may be implicated in human neurological diseases. Their findings are published in the May 2013 issue of Molecular and Cellular Biology.

"There are known connections between problems with how the body’s cells process fats and neurodegenerative diseases such as Alzheimer’s, Parkinson’s and amyotrophic lateral sclerosis," says Michael Wolfgang, Ph.D., an assistant professor in the Department of Biological Chemistry at the Johns Hopkins University School of Medicine’s Institute for Basic Biomedical Sciences. "Now we’ve taken a step toward better understanding that connection by identifying an enzyme that lets neurons get rid of excess fat that would otherwise be toxic."

Wolfgang says one clue to the reason for the neurodegeneration/fat-processing connection is that neurons, unlike most cells in the body, seemingly can’t break down fats for energy. Instead, brain cells use fats for tasks such as building cell membranes and communicating information. At the same time, he says, they must prevent the buildup of unneeded fats. Neurons’ fat-loss strategy is rooted in the fact that a fat molecule attached to a chemical group called coenzyme A will be trapped inside the cell, while the coenzyme A-free version can easily cross the cell membrane and escape. With this in mind, Wolfgang, along with colleagues Jessica Ellis, Ph.D., and G. William Wong, Ph.D., focused their study on an enzyme, called ACOT7, which is plentiful in the brain and lops coenzyme A off of certain fat molecules.

The team created mice with a non-working gene for ACOT7 and compared them with normal mice. The scientists saw no obvious differences between the two types of mice as long as they had ready access to food, Wolfgang says. But when food was taken away overnight, so that the mice’s cells would start to break down their fat stores and release fat molecules into the bloodstream for use as energy, ACOT7’s role began to emerge. While the normal fasting mice were merely hungry, the mice lacking ACOT7 had poor coordination, a sign of neurodegeneration. More differences emerged when the researchers dissected the mice; most strikingly, the livers of mice missing ACOT7 were “stark white” with excess fat, Wolfgang says.

Wolfgang cautions that his group’s results are not quite a smoking gun for ACOT7’s involvement in human neurological disease, but says they add to existing circumstantial evidence pointing in that direction. He notes that a special diet that changes the levels of fats and sugars in the bloodstream – the so-called ketogenic diet – can prevent seizures in epileptics; in addition, one study found that patients with epilepsy have less of the ACOT7 enzyme than healthy people.

"We think ACOT7’s purpose is to protect neurons from toxicity and death by allowing excess fat to escape the cells," Ellis says. "Our next step will be to see whether this enzyme does indeed play a role in human neurological disease."

(Image: Courtesy of Sabrina Diano)

Breakthrough in neuroscience could help re-wire appetite control

Researchers at the University of East Anglia (UEA) have made a discovery in neuroscience that could offer a long-lasting solution to eating disorders such as obesity.

It was previously thought that the nerve cells in the brain associated with appetite regulation were generated entirely during an embryo’s development in the womb and therefore their numbers were fixed for life.

But research published today in the Journal of Neuroscience has identified a population of stem cells capable of generating new appetite-regulating neurons in the brains of young and adult rodents.

Obesity has reached epidemic proportions globally. More than 1.4 billion adults worldwide are overweight and more than half a billion are obese. Associated health problems include type 2 diabetes, heart disease, arthritis and cancer. And at least 2.8 million people die each year as a result of being overweight or obese.

The economic burden on the NHS in the UK is estimated to be more than £5 billion annually. In the US, the healthcare cost tops $60 billion.

Scientists at UEA investigated the hypothalamus section of the brain – which regulates sleep and wake cycles, energy expenditure, appetite, thirst, hormone release and many other critical biological functions. The study looked specifically at the nerve cells that regulate appetite.

The researchers used ‘genetic fate mapping’ techniques to make their discovery – a method that tracks the development of stem cells and cells derived from them, at desired time points during the life of an animal.

They established that a population of brain cells called ‘tanycytes’ behave like stem cells and add new neurons to the appetite-regulating circuitry of the mouse brain after birth and into adulthood.

Lead researcher Dr Mohammad K. Hajihosseini, from UEA’s school of Biological Sciences, said: “Unlike dieting, translation of this discovery could eventually offer a permanent solution for tackling obesity.

“Loss or malfunctioning of neurons in the hypothalamus is the prime cause of eating disorders such as obesity.

“Until recently we thought that all of these nerve cells were generated during the embryonic period and so the circuitry that controls appetite was fixed.

“But this study has shown that the neural circuitry that controls appetite is not fixed in number and could possibly be manipulated numerically to tackle eating disorders.

“The next step is to define the group of genes and cellular processes that regulate the behaviour and activity of tanycytes. This information will further our understanding of brain stem cells and could be exploited to develop drugs that can modulate the number or functioning of appetite-regulating neurons.

“Our long-term goal of course is to translate this work to humans, which could take up to five or 10 years. It could lead to a permanent intervention in infancy for those predisposed to obesity, or later in life as the disease becomes apparent.”

Researchers Develop New System to Study Trigger of Cell Death in Nervous System

Researchers at the University of Arkansas have developed a new model system to study a receptor protein that controls cell death in both humans and fruit flies, a discovery that could lead to a better understanding of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.

Michael Lehmann, an associate professor of biological sciences, uses fruit fly genetics to study the receptor — N-methyl-D-aspartate receptor, known as the NMDA receptor — that triggers programmed cell death in the human nervous system.

With an aging population, neurodegenerative diseases have become a major public health concern, Lehmann said.

“Whenever brain cells die as a result of neurodegenerative disease, or as a consequence of injuries caused by stroke, exposure to alcohol or neurotoxins, this receptor is involved,” he said. “So it’s very important to understand how it functions and how it may be possible to influence it.”

When larvae of Drosophila melanogaster, a common fruit fly, grow from the larval stage into adults, they shed most of their former organs and grow new ones. About 1 ½ years ago, researchers in Lehmann’s laboratory discovered that the NMDA receptor is required for cell death in the system that they had used for several years to study basic mechanisms of programmed cell death in fruit flies.

“Our model system for studying programmed cell death is the salivary glands in the fly larvae, which are comparatively large organs that completely disappear during metamorphosis,” he said. “Disposal of this tissue by programmed cell death provides us with a very nice system to study the genes that are required for the process. We can use it to identify genes that are required for programmed cell death in humans, as well.”

The National Institutes of Health has awarded Lehmann a three-year, $260,530 grant to support the study.

Brandy Ree, a doctoral student in the interdisciplinary graduate program in cell and molecular biology, worked with Lehmann to use a combination of biochemistry and fruit fly genetics in an attempt to define the pathway that leads from activation of the receptor to the cell’s eventual death.

“We developed a new system to study the receptor outside the nervous system in a normal developmental context,” Lehmann said. “Many of the different components involved in cell death are known in this system. There are more than 30,000 publications about this receptor, but there is still very little known about how the receptor causes cell death. We just have to connect the dots and fit the receptor into the pathway to find out how exactly it contributes to the cell’s death.”

A mid-career investigator in the Center for Protein Structure and Function at the University of Arkansas, Lehmann has studied programmed cell death in Drosophila melanogaster for more than a decade.

In 2007, Lehmann’s research group discovered an important mechanism that regulates the destruction of larval fruit fly salivary glands that could point the way to understanding programmed cell death in the human immune system. They published their findings in the Journal of Cell Biology.

(Image: BD Biosciences)

DNA damage occurs as part of normal brain activity

Scientists at the Gladstone Institutes have discovered that a certain type of DNA damage long thought to be particularly detrimental to brain cells can actually be part of a regular, non-harmful process. The team further found that disruptions to this process occur in mouse models of Alzheimer’s disease—and identified two therapeutic strategies that reduce these disruptions.

Scientists have long known that DNA damage occurs in every cell, accumulating as we age. But a particular type of DNA damage, known as a double-strand break, or DSB, has long been considered a major force behind age-related illnesses such as Alzheimer’s. Today, researchers in the laboratory of Gladstone Senior Investigator Lennart Mucke, MD, report in Nature Neuroscience that DSBs in neuronal cells in the brain can also be part of normal brain functions such as learning—as long as the DSBs are tightly controlled and repaired in good time. Further, the accumulation of the amyloid-beta protein in the brain—widely thought to be a major cause of Alzheimer’s disease—increases the number of neurons with DSBs and delays their repair.

"It is both novel and intriguing team’s finding that the accumulation and repair of DSBs may be part of normal learning," said Fred H. Gage, PhD, of the Salk Institute who was not involved in this study. "Their discovery that the Alzheimer’s-like mice exhibited higher baseline DSBs, which weren’t repaired, increases these findings’ relevance and provides new understanding of this deadly disease’s underlying mechanisms."

In laboratory experiments, two groups of mice explored a new environment filled with unfamiliar sights, smells and textures. One group was genetically modified to simulate key aspects of Alzheimer’s, and the other was a healthy, control group. As the mice explored, their neurons became stimulated as they processed new information. After two hours, the mice were returned to their familiar, home environment.

The investigators then examined the neurons of the mice for markers of DSBs. The control group showed an increase in DSBs right after they explored the new environment—but after being returned to their home environment, DSB levels dropped.

"We were initially surprised to find neuronal DSBs in the brains of healthy mice," said Elsa Suberbielle, DVM, PhD, Gladstone postdoctoral fellow and the paper’s lead author. "But the close link between neuronal stimulation and DSBs, and the finding that these DSBs were repaired after the mice returned to their home environment, suggest that DSBs are an integral part of normal brain activity. We think that this damage-and-repair pattern might help the animals learn by facilitating rapid changes in the conversion of neuronal DNA into proteins that are involved in forming memories."

The group of mice modified to simulate Alzheimer’s had higher DSB levels at the start—levels that rose even higher during neuronal stimulation. In addition, the team noticed a substantial delay in the DNA-repair process.

To counteract the accumulation of DSBs, the team first used a therapeutic approach built on two recent studies—one of which was led by Dr. Mucke and his team—that showed the widely used anti-epileptic drug levetiracetam could improve neuronal communication and memory in both mouse models of Alzheimer’s and in humans in the disease’s earliest stages. The mice they treated with the FDA-approved drug had fewer DSBs. In their second strategy, they genetically modified mice to lack the brain protein called tau—another protein implicated in Alzheimer’s. This manipulation, which they had previously found to prevent abnormal brain activity, also prevented the excessive accumulation of DSBs.

The team’s findings suggest that restoring proper neuronal communication is important for staving off the effects of Alzheimer’s—perhaps by maintaining the delicate balance between DNA damage and repair.

"Currently, we have no effective treatments to slow, prevent or halt Alzheimer’s, from which more than 5 million people suffer in the United States alone," said Dr. Mucke, who directs neurological research at Gladstone and is a professor of neuroscience and neurology at the University of California, San Francisco, with which Gladstone is affiliated. "The need to decipher the causes of Alzheimer’s and to find better therapeutic solutions has never been more important—or urgent. Our results suggest that readily available drugs could help protect neurons against some of the damages inflicted by this illness. In the future, we will further explore these therapeutic strategies. We also hope to gain a deeper understanding of the role that DSBs play in learning and memory—and in the disruption of these important brain functions by Alzheimer’s disease."

(Image courtesy: Lulu Qian, Erik Winfree & Jehoshua Bruck | California Institute of Technology)

How two brain areas interact to trigger divergent emotional behaviors

New research from the University of North Carolina School of Medicine for the first time explains exactly how two brain regions interact to promote emotionally motivated behaviors associated with anxiety and reward.

The findings could lead to new mental health therapies for disorders such as addiction, anxiety, and depression. A report of the research was published online by the journal, Nature, on March 20, 2013.

Located deep in the brain’s temporal lobe are tightly packed clusters of brain cells in the almond shaped amygdala that are important for processing memory and emotion. When animals or people are in stressful situations, neurons in an extended portion of the amygdala called the bed nucleus of the stria terminalis, or BNST, become hyperactive.

But, almost paradoxically, neurons in the BNST, which modulate fear and anxiety, reach into a portion of the midbrain that’s involved in behavioral responses to reward, the ventral tegmental area, or VTA.

“For many years it’s been known that dopamine neurons in the VTA are involved in reward processing and motivation. For example, they’re activated during exposure to drugs of abuse and naturally rewarding experiences,” says study senior author Garret Stuber, PhD, assistant professor in the departments of Psychiatry and Cell Biology and Physiology, and the UNC Neuroscience Center.  “On the one hand, you have this area of the brain – the BNST – that’s associated with aversion and anxiety, but it’s in direct communication with a brain reward center. We wanted to figure out exactly how these two brain regions interact to promote different types of behavioral responses related to anxiety and reward.”

In the past, researchers have tried to get a glimpse into the inner workings of the brain using electrical stimulation or drugs, but those techniques couldn’t quickly and specifically change only one type of cell or one type of connection. But optogenetics, a technique that emerged about seven years ago, can.

In the technique, scientists transfer light-sensitive proteins called “opsins” – derived from algae or bacteria that need light to grow – into the mammalian brain cells they wish to study. Then they shine laser beams onto the genetically manipulated brain cells, either exciting or blocking their activity with millisecond precision.