Research hints at why stress is more devastating for some

Some people take stress in stride; others are done in by it. New research at Rockefeller University has identified the molecular mechanisms of this so-called stress gap in mice with very similar genetic backgrounds — a finding that could lead researchers to better understand the development of psychiatric disorders such as anxiety and depression.

“Like people, each animal has unique experiences as it goes through its life. And we suspect that these life experiences can alter the expression of genes, and as a result, affect an animal’s susceptibility to stress,” says senior author Bruce McEwen, Alfred E. Mirsky Professor and head of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology. “We have taken an important step toward explaining the molecular origins of this stress gap by showing that inbred mice react differently to stress, with some developing behaviors that resemble anxiety and depression, and others remaining resilient.”

The results, published September 2 in Molecular Psychiatry, point toward potential new markers to aid the diagnosis of stress-related disorders, such as anxiety and depression, and a promising route to the development of new treatments for these devastating disorders.

In experiments, researchers stressed the mice by exposing them to daily, unpredictable bouts of cage tilting, altered dark-light cycles, confinement in tight spaces and other conditions mice dislike with the goal of reproducing the sort of stressful experiences thought to be a primary cause of depression in humans. Afterward, in tests to see if the mice displayed the rodent equivalent of anxiety and depression symptoms, they found about 40 percent showed high levels of behaviors that included a preference for a dark compartment over a brightly lit one, or a loss of interest in sugar water. The remaining 60 percent recovered well from the stress. This distinction between the susceptible mice and the resilient ones was so fundamental that it emerged even before the mice were subjected to stress; some unstressed mice showed an anxiety-like preference for a dark compartment over a lighted one.

The researchers found that the highly stress-susceptible mice had less of an important molecule known as mGlu2 in a stress-involved region of the brain known as the hippocampus. The mGlu2 decrease, they determined, resulted from an epigenetic change, which affects the expression of genes, in this case the gene that codes for mGlu2.

“If you think of the genetic code as words in a book, the book must be opened in order for you to read it. These epigenetic changes, which affect histone proteins associated with DNA, effectively close the book, so the code for mGlu2 cannot be read,” says first author Carla Nasca, a postdoc in the lab and a fellow of the American Foundation for Suicide Prevention. Previously, she and colleagues implicated mGlu2 in depression when they showed that a promising potential treatment known as acetyl carnitine rapidly alleviated depression-like symptoms in rats and mice by reversing these epigenetic changes to mGlu2 and causing its levels to increase.

“Currently, depression is diagnosed only by its symptoms,” Nasca says. “But these results put us on track to discover molecular signatures in humans that may have the potential to serve as markers for certain types of depression. Our work could also lead to a new generation of rapidly acting antidepressants, such as the candidate acetyl carnitine, which would be particularly important to reduce the risk of suicide.”

A reduction in mGlu2 matters because this molecule regulates the neurotransmitter glutamate. While glutamate plays a crucial role relaying messages between neurons as part of many important processes, too much can lead to harmful structural changes in the brain.

“The brain is constantly changing. When stressful experiences lead to anxiety and depressive disorders the brain becomes locked in a state it cannot spontaneously escape,” McEwen says. “Studies like this one are increasingly focusing on the regulation of glutamate as an underlying mechanism in depression and, we hope, opening promising new avenues for the diagnosis and treatment of this devastating disorder.”

(Image caption: Aggressor cells, which have the potential to cause autoimmunity, are targeted by treatment, causing conversion of these cells to protector cells. Gene expression changes gradually at each stage of treatment, as illustrated by the color changes in this series of heat maps. Credit: University of Bristol/Dr. Bronwen Burton)

Scientists discover how to ‘switch off’ autoimmune diseases

Scientists have made an important breakthrough in the fight against debilitating autoimmune diseases such as multiple sclerosis by revealing how to stop cells attacking healthy body tissue.

Rather than the body’s immune system destroying its own tissue by mistake, researchers at the University of Bristol have discovered how cells convert from being aggressive to actually protecting against disease.

The study, funded by the Wellcome Trust, is published in Nature Communications.

It’s hoped this latest insight will lead to the widespread use of antigen-specific immunotherapy as a treatment for many autoimmune disorders, including multiple sclerosis (MS), type 1 diabetes, Graves’ disease and systemic lupus erythematosus (SLE).

MS alone affects around 100,000 people in the UK and 2.5 million people worldwide.

Scientists were able to selectively target the cells that cause autoimmune disease by dampening down their aggression against the body’s own tissues while converting them into cells capable of protecting against disease.

This type of conversion has been previously applied to allergies, known as ‘allergic desensitisation’, but its application to autoimmune diseases has only been appreciated recently.

The Bristol group has now revealed how the administration of fragments of the proteins that are normally the target for attack leads to correction of the autoimmune response.

Most importantly, their work reveals that effective treatment is achieved by gradually increasing the dose of antigenic fragment injected.

In order to figure out how this type of immunotherapy works, the scientists delved inside the immune cells themselves to see which genes and proteins were turned on or off by the treatment.

They found changes in gene expression that help explain how effective treatment leads to conversion of aggressor into protector cells. The outcome is to reinstate self-tolerance whereby an individual’s immune system ignores its own tissues while remaining fully armed to protect against infection.

By specifically targeting the cells at fault, this immunotherapeutic approach avoids the need for the immune suppressive drugs associated with unacceptable side effects such as infections, development of tumours and disruption of natural regulatory mechanisms.

Professor David Wraith, who led the research, said: “Insight into the molecular basis of antigen-specific immunotherapy opens up exciting new opportunities to enhance the selectivity of the approach while providing valuable markers with which to measure effective treatment. These findings have important implications for the many patients suffering from autoimmune conditions that are currently difficult to treat.”

This treatment approach, which could improve the lives of millions of people worldwide, is currently undergoing clinical development through biotechnology company Apitope, a spin-out from the University of Bristol.

Researchers obtain key insights into how the internal body clock is tuned

Researchers at UT Southwestern Medical Center have found a new way that internal body clocks are regulated by a type of molecule known as long non-coding RNA.

The internal body clocks, called circadian clocks, regulate the daily “rhythms” of many bodily functions, from waking and sleeping to body temperature and hunger. They are largely “tuned” to a 24-hour cycle that is influenced by external cues such as light and temperature.

“Although we know that long non-coding RNAs are abundant in many organisms, what they do in the body, and how they do it, has not been clear so far,” said Dr. Yi Liu, Professor of Physiology. “Our work establishes a role for long non-coding RNAs in ‘tuning’ the circadian clock, but also shows how they control gene expression.”

Determining how circadian clocks work is crucial to understanding several human diseases, including sleep disorders and depression in which the clock malfunctions. The influence of a functional clock is evident in the reduced performance of shift workers and the jet lag felt by long-distance travellers.

Dr. Liu and his team were able to learn more about the circadian rhythms by studying model systems involving the bread mold, Neurospora crassa. The researchers found that the expression of a clock gene named frequency (frq) is controlled by a long non-coding RNA named qrf (frq backwards) − an RNA molecule that is complementary, or antisense, to frq. Unlike normal RNA molecules, qrf does not encode a protein, but it can control whether and how much frq protein is produced.

Specifically, qrf RNA is produced in response to light, and can then interfere with the production of the frq protein. In this way, qrf can “re-set” the circadian clock in a light-dependent way. This regulation works both ways: frq can also block the production of qrf. This mutual inhibition ensures that the frq and qrf RNA molecules are present in opposite “phases” of the clock and allows each RNA to oscillate robustly. Without qrf, normal circadian rhythms are not sustained, indicating that the long non-coding RNA is required for clock functions.

The findings are published online in the journal Nature.

“We anticipate a similar mode of action may operate in other organisms because similar RNAs have been found for clock genes in mice. In addition, such RNAs may also function in other biological processes because of their wide presence in genomes,” said Dr. Liu, who is the Louise W. Kahn Scholar in Biomedical Research.

UT Southwestern investigators are leaders in unraveling the gene networks underlying circadian clocks and have shown that most body organs, such as the pancreas and liver, have their own internal clocks, and that virtually every cell in the human body contains a clock. It now appears that the clocks and clock-related genes – some 20 such genes have been identified – affect virtually all of the cells’ metabolic pathways, from blood sugar regulation to cholesterol production.

Other UT Southwestern researchers involved in the latest findings include Dr. Zhihong Xue, Qiaohong Ye, Dr. Juchen Yang and Dr. Guanghua Xiao. Support for this research included grants from the National Institutes of Health, the Welch Foundation, the Cancer Prevention Research Institute of Texas, and the Biotechnology and Biological Sciences Research Council.

“This study adds to an important body of work that has shown the ubiquity of a circadian clock across species, including humans, and its role in metabolic regulation in cells, organs, and organisms,” said Dr. Michael Sesma, Program Director in the Division of Genetics and Developmental Biology at the of the National Institutes of Health’s National Institute of General Medical Sciences, which partially funded the research. “These new results from Dr. Liu and his colleagues also extend beyond understanding the function of an anti-sense RNA in the fine tuning of a cell’s daily rhythm; they provide an example of the means by which anti-sense transcription likely regulates other key molecular and physiological processes in cells and organisms.”

(Image: Fotolia)

Stress tied to change in children’s gene expression related to emotion regulation, physical health

Children who have been abused or neglected early in life are at risk for developing both emotional and physical health problems. In a new study, scientists have found that maltreatment affects the way genes are activated, which has implications for children’s long-term development. Previous studies focused on how a particular child’s individual characteristics and genetics interacted with that child’s experiences in an effort to understand how health problems emerge. In the new study, researchers were able to measure the degree to which genes were turned “on” or “off” through a biochemical process called methylation. This new technique reveals the ways that nurture changes nature—that is, how our social experiences can change the underlying biology of our genes.

The study, from researchers at the University of Wisconsin, Madison, appears in the journal Child Development. Nearly 1 million children in the United States are neglected or abused every year.

The researchers found an association between the kind of parenting children had and a particular gene (called the glucocorticoid receptor gene) that’s responsible for crucial aspects of social functioning and health. Not all genes are active at all times. DNA methylation is one of several biochemical mechanisms that cells use to control whether genes are turned on or off. The researchers examined DNA methylation in the blood of 56 children ages 11 to 14. Half of the children had been physically abused.

They found that compared to the children who hadn’t been maltreated, the maltreated children had increased methylation on several sites of the glucocorticoid receptor gene, also known as NR3C1, echoing the findings of earlier studies of rodents. In this study, the effect occurred on the section of the gene that’s critical for nerve growth factor, which is an important part of healthy brain development.

There were no differences in the genes that the children were born with, the study found; instead, the differences were seen in the extent to which the genes had been turned on or off. “This link between early life stress and changes in genes may uncover how early childhood experiences get under the skin and confer lifelong risk,” notes Seth D. Pollak, professor of psychology and pediatrics at the University of Wisconsin, Madison, who directed the study.

Previous studies have shown that children who have experienced physical abuse, sexual abuse, and neglect are more likely to develop mood, anxiety, and aggressive disorders, as well as to have problems regulating their emotions. These problems, in turn, can disrupt relationships and affect school performance. Maltreated children are also at risk for chronic health problems such as cardiac disease and cancer. The current study helps explain why these childhood experiences can affect health years later.

The gene identified by the researchers affects the hypothalamic-pituitary-adrenal (HPA) axis in rodents. Disruptions of this system in the brain would make it difficult for people to regulate their emotional behavior and stress levels. Circulating through the body in the blood, this gene affects the immune system, leaving individuals less able to fight off germs and more vulnerable to illnesses.

"Our finding that children who were physically maltreated display a specific change to the glucocorticoid receptor gene could explain why abused children have more emotional difficulties as they age," according to Pollak. "They may have fewer glucocorticoid receptors in their brains, which would impair the brain’s stress-response system and result in problems regulating stress."

The findings have implications for designing more effective interventions for children, especially since studies of animals indicate that the effects of poor parenting on gene methylation may be reversible if caregiving improves. The study also adds to what we know about how child maltreatment relates to changes in the body and mind, findings that were summarized recently in an SRCD Social Policy Report by Sara R. Jaffee and Cindy W. Christian.

The Social Psychology of Nerve Cells

The functional organization of the central nervous system depends upon a precise architecture and connectivity of distinct types of neurons. Multiple cell types are present within any brain structure, but the rules governing their positioning, and the molecular mechanisms mediating those rules, have been relatively unexplored.

A new study by UC Santa Barbara researchers demonstrates that a particular neuron, the cholinergic amacrine cell, creates a “personal space” in much the same way that people distance themselves from one another in an elevator. In addition, the study, published in the Proceedings of the National Academy of Sciences, shows that this feature is heritable and identifies a genetic contributor to it, pituitary tumor-transforming gene 1 (Pttg1).

Patrick Keeley, a postdoctoral scholar in Benjamin Reese’s laboratory at UCSB’s Neuroscience Research Institute, has been using the retina as a model system for exploring such principles of developmental neurobiology. The retina is ideal because this portion of the central nervous system lends itself to such spatial analysis. 

“Populations of neurons in the retina are laid out in single strata within this layered structure, lending themselves to accurate quantitation and statistical analysis,” explained Keeley. “Rather than being distributed as regular lattices of nerve cells, populations in the retina appear to abide by a simple rule, that of minimizing proximity to other cells of the same type. We would like to understand how such populations create and maintain such spacing behavior.”

To address this, Keeley and colleagues quantified the regularity in the population of a particular type of amacrine cell in the mouse retina. They did so in 26 genetically distinct strains of mice and found that every strain exhibited this same self-spacing behavior but that some strains did so more efficiently than others. Amacrine cells are retinal interneurons that form connections between other neurons and regulate bipolar cell output.

“The regularity in the patterning of these amacrine cells showed little variation within each strain, while showing conspicuous variation between the strains, indicating a heritable component to this trait,” said Keeley.

“This itself was something of a surprise, given that the patterning in such populations has an apparently stochastic quality to it,” said Reese, a professor in the Department of Psychological and Brain Sciences. Stochastic systems are random and are analyzed, at least in part, using probability theory.

This strain variation in the regularity of this cellular patterning showed a significant linkage to a location in the genome on chromosome 11, where the researchers identified Pttg1, previously unknown to play any role in the retina.

Working in collaboration with colleagues at the University of Tennessee Health Science Center in Memphis, Keeley’s team demonstrated that the expression of this gene varies across the 26 strains of mice and that there was a positive correlation between gene expression and regularity. They then identified a mutation in this gene that itself correlated with expression levels and with regularity. Working with colleagues at Cedars-Sinai Medical Center in Los Angeles, the team also demonstrated directly that this mutation controlled gene expression.   

“Pttg1 has diverse functions, being an oncogene for pituitary tumors, and is known to have regulatory functions orchestrating gene expression elsewhere in the body,” explained Keeley. “Within this class of retinal neurons, it should be regulating the way in which cells integrate signals from their immediate neighbors, translating that information to position the cell farthest from those neighbors.” Future studies should decipher the genetic network controlled by Pttg1 that mediates such nerve-cell spacing.