Scientists unlock structure of elusive 'stress' protein

Scientists unlock structure of elusive ‘stress’ protein                                                                                                                        Newly discovered structure of the protein receptor that controls our response to stress

Scientists working to design advanced medicines that are perfectly targeted to control the body’s natural receptors have made a major discovery using Diamond’s Microfocus Macromolecular Crystallography beamline (I24). For the first time, they have been able to visualise and study the structure of CRF1, the protein receptor in the brain which controls our response to stress.

Heptares Therapeutics, a leading UK-based drug discovery and development company, was responsible for identifying the 3D structure of the ‘stress’ receptor, and their results are published today in the journal Nature. This discovery will help scientists to develop improved treatments for depression and anxiety. Furthermore, having identified the architecture of CRF1, scientists now have a template that can be used to accelerate research into other protein receptors that are known to be in the same ‘family’, including those that can be targeted to treat Type 2 diabetes and .

Stress-related diseases such as depression and anxiety are now commonplace. 1 in 4 people experience some kind of  in the course of a year. Over 105 million work days are lost to stress each year, costing UK employers £1.2 billion.

The UK also faces a major health challenge from diabetes. In the past 20 years, the number of people in the country suffering from diabetes has more than doubled to 2.9 million. By 2025 it is estimated that 5 million people will have diabetes, and that most of these cases will be Type 2 diabetes.

Heptares is a leader in the development of drugs targeting certain protein receptors, called G protein-coupled receptors. Currently 30% of drugs for a variety of diseases target these receptors, making them the largest and most important family of  in the .

In the past, drug design has been largely the product of trial and error. Drugs would be developed and then tested until they had the desired effect. Because scientists lacked a comprehensive understanding of why and how the drugs were working, this approach could lead to unwanted side-effects.

A new way of making medicines, known as rational drug design, produces drugs that are specifically targeted to protein receptors in the body. By visualising the stress  at the atomic level, they were able, for the first time, to identify a ‘pocket’ in the structure. Computer technology will allow scientists to design a drug to fit precisely into this pocket, inhibiting the response of the ‘stress’ receptor. Such focused targeting will only affect the receptor they are aiming for and reduce the chance of unexpected side effects. The level of detail required for this work could only be achieved using the intense synchrotron light produced at Diamond Light Source, the UK’s synchrotron science facility in Oxfordshire. The synchrotron speeds electrons to near light speed, producing a light 10 billion times brighter than the sun. Around 2,500 scientists a year use this light to study samples, and its intensity allows them to visualise on a scale that is unobtainable in their home laboratories. Heptares is currently the biggest annual industrial user of the synchrotron.

Why do females respond better to stress? New study suggests it’s because of estrogen in the brain ?

he idea that females are more resilient than males in responding to stress is a popular view, and now University at Buffalo researchers have found a scientific explanation. The paper describing their embargoed study will be published July 9 online, in the high-impact journal, Molecular Psychiatry.

“We have examined the  underlying gender-specific effects of stress,” says senior author Zhen Yan, PhD, a professor in the Department of Physiology and Biophysics in the UB School of Medicine and Biomedical Sciences. “Previous studies have found that females are more resilient to , and now our research has found the reason why.”

The research shows that in rats exposed to repeated episodes of stress, females respond better than males because of the protective effect of estrogen. In the UB study, young  exposed to one week of periodic physical restraint stress showed no impairment in their ability to remember and recognize objects they had previously been shown. In contrast, young males exposed to the same stress were impaired in their short-term memory.

An impairment in the ability to correctly remember a familiar object signifies some disturbance in the signaling ability of the  in the prefrontal cortex, the brain region that controls working memory, attention, decision-making, emotion and other high-level “executive” processes. Last year, Yan and UB colleagues published in Neuron a paper showing that repeated stress results in loss of the glutamate receptor in the prefrontal cortex of young males. The current paper shows that the glutamate receptor in the prefrontal cortex of stressed females is intact. The findings provide more support for a growing body of research demonstrating that the glutamate receptor is the molecular target of stress, which mediates the .

The stressors used in the experiments mimic challenging and stressful, but not dangerous, experiences that humans face, such as those causing frustration and feelings of being under pressure, Yan says. By manipulating the amount of estrogen produced in the brain, the UB researchers were able to make the males respond to stress more like females and the females respond more like males.

“When estrogen signaling in the brains of females was blocked, stress exhibited detrimental effects on them,” explains Yan. “When estrogen signaling was activated in males, the detrimental effects of stress were blocked. “We still found the protective effect of estrogen in female rats whose ovaries were removed,” says Yan. “It suggests that it might be estrogen produced in the brain that protects against the detrimental effects of stress.”

In the current study, Yan and her colleagues found that the enzyme aromatase, which produces estradiol, an estrogen hormone, in the brain, is responsible for female stress resilience. They found that aromatase levels are significantly higher in the  of female rats. “If we could find compounds similar to estrogen that could be administered without causing hormonal side effects, they could prove to be a very effective treatment for stress-related problems in males,” she says. She notes that while stress itself is not a psychiatric disorder, it can be a trigger for the development of psychiatric disorders in vulnerable individuals.

New methods to visualize bacterial cell-to-cell communication

Most bacteria are able to communicate with each other by secreting signaling molecules. Once the concentration of signals has reached a critical density (“the Quorum), the bacteria are able to coordinate their behavior. Only when this critical population density has been reached certain genes are activated that lead to, for example, the formation of biofilms or the expression of virulence factors. Bacteria utilize this so-called “Quorum Sensing” (QS) to synchronize their behavior to regulate functions that benefit the entire population.

The most commonly used signaling molecules are N-Acyl-L-homoserine lactones (AHLs) that are secreted by the bacteria into their surroundings, where they can easily be incorporated by other cells. The AHLs then start binding to specific QS-receptors once a certain density has been reached inside the cell.

New methods to visualize bacterial cell-to-cell communication

Selective labeling of the Burkholderia cenocepacia quorum-sensing receptor CepR.Credit: José Gomes et al.,

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Fluorescent labeling of signaling compound to visualize receptors

The research groups under the leadership of Prof. Karl Gademann (University of Basel) and Prof. Leo Eberl (University of Zurich) have succeeded in visualizing live cell-to-cell communication pathways. The scientists added fluorescents tags to natural AHL signaling molecules and were able to show through tests with bacterial cultures that the modified signaling molecule selectively binds to the Burkholderia cenocepacia QS receptor.

B. cenocepacia is a member of a bacterial group known to form  in the lungs of immunocompromised persons or patients suffering from , causing severe complications such as pneumonia.

The scientists were also able to detect the receptor in a native population of B. cenocepacia. Here, the natural AHL signaling molecule is competing with its artificial analogue for the binding to the receptor. The fluorescent-labeling agent was equally distributed over the live cell, which made it possible to localize the receptor inside the  for the first time.

Broad application possibilities

Using fluorescently labeled AHL analogues represent an operationally simple tool for the imaging of QS receptors in live cells. Thus, this new method could be used for a broad range of applications, such as the fast analysis of QS in various environmental and clinical samples. Furthermore, it might lead to a better understanding of the communication between bacteria and host as well as of the cell-to-cell communication in bacteria populations.

 Explore further: Signaling receptor may provide a target for reducing virulence without antibiotics

Cranial irradiation causes brain degeneration

Cranial irradiation saves the lives of brain cancer patients. It slows cancer progression and increases survival rates. Unfortunately, patients who undergo cranial irradiation often develop problems with cognitive functioning. To determine how radiation affects cognition, Vipan Parihar and Charles Limoli of the University of California, Irvine studied cranial irradiation in mice. They found that exposure to radiation causes degenerative changes to brain architecture similar to those observed in people with neurodegenerative conditions such as Alzheimer’s disease and Huntington’s disease. Their research appears in the Proceedings of the National Academy of Sciences.

Radiation therapy is the routine frontline treatment for almost all forms of pediatric and  cancer because of its ability to forestall tumor growth. While it increases the lifespans of people diagnosed with brain cancer, cranial irradiation can reduce quality of life by causing irreversible cognitive impairment. Central nervous system (CNS) exposure to radiation causes problems with memory, learning, attention, processing speed and executive function.

To understand how reduces cognitive ability, Parihar and Limoli exposed mice to either 1 or 10 Gy of radiation, doses much lower than the maximum dose the CNS can withstand before tissue damage occurs. After 10 or 30 days, the researchers killed the mice and dissected their brains. They then examined the hippocampus, which is associated with learning and memory.

Parihar and Limoli observed dose-dependent reductions in the area, length and branching of dendrites, projections on neurons that send and receive signals to and from other neurons. These reductions persisted after 30 days. The number and density of dendritic spines, bulbous extensions on dendrites, also decreased. Dendritic spines regulate CNS connectivity, are associated with memory storage and play an important role in mediating . There is a positive correlation between number of dendritic spines and synaptic density, which in turn correlates with cognitive ability. The researchers also identified significant changes in levels of pre and post-synaptic proteins.

Reduced dendritic complexity is a characteristic of Alzheimer’s disease, Huntington’s disease, recurrent depressive illness and epilepsy. Dendritic spine abnormalities are associated with Huntington’s disease, temporal lobe epilepsy, AIDS-related dementia, Down syndrome, Rett syndrome and Fragile-X syndrome.

Parihar and Limoli state that the reduction in dendritic spine density and the persistence of degenerative changes after one month is consistent with the irreversible reduction in cognitive functioning experienced by brain cancer survivors who have had cranial radiotherapy.

Cranial irradiation causes brain degeneration

Cranial irradiation is used routinely for the treatment of nearly all brain tumors, but may lead to progressive and debilitating impairments of cognitive function. Changes in synaptic plasticity underlie many neurodegenerative conditions that correlate to specific structural alterations in neurons that are believed to be morphologic determinants of learning and memory. To determine whether changes in dendritic architecture might underlie the neurocognitive sequelae found after irradiation, we investigated the impact of cranial irradiation (1 and 10 Gy) on a range of micromorphometric parameters in mice 10 and 30 d following exposure. Our data revealed significant reductions in dendritic complexity, where dendritic branching, length, and area were routinely reduced (>50%) in a dose-dependent manner. At these same doses and times we found significant reductions in the number (20–35%) and density (40–70%) of dendritic spines on hippocampal neurons of the dentate gyrus. Interestingly, immature filopodia showed the greatest sensitivity to irradiation compared with more mature spine morphologies, with reductions of 43% and 73% found 30 d after 1 and 10 Gy, respectively. Analysis of granule-cell neurons spanning the subfields of the dentate gyrus revealed significant reductions in synaptophysin expression at presynaptic sites in the dentate hilus, and significant increases in postsynaptic density protein (PSD-95) were found along dendrites in the granule cell and molecular layers. These findings are unique in demonstrating dose-responsive changes in dendritic complexity, synaptic protein levels, spine density and morphology, alterations induced in hippocampal neurons by irradiation that persist for at least 1 mo, and that resemble similar types of changes found in many neurodegenerative conditions.