Scientists catch brain damage in the act

Scientists have uncovered how inflammation and lack of oxygen conspire to cause brain damage in conditions such as stroke and Alzheimer’s disease.

The discovery, published today in Neuron, brings researchers a step closer to finding potential targets to treat neurodegenerative disorders.

Chronic inflammation and hypoxia, or oxygen deficiency, are hallmarks of several brain diseases, but little was known about how they contribute to symptoms such as memory loss.

The study used state-of-the-art techniques that reveal the movements of microglia, the brain’s resident immune cells. Brain researcher Brian MacVicar had previously captured how they moved to areas of injury to repair brain damage.

The new study shows that the combination of inflammation and hypoxia activates microglia in a way that persistently weakens the connection between neurons. The phenomenon, known as long-term depression, has been shown to contribute to cognitive impairment in Alzheimer’s disease.

“This is a never-before-seen mechanism among three key players in the brain that interact together in neurodegenerative disorders,” says MacVicar with the Djavad Mowafaghian Centre for Brain Health at UBC and Vancouver Coastal Health Research Institute.

“Now we can use this knowledge to start identifying new potential targets for therapy.”

New contender for ‘fat gene’ found

Researchers may have been focusing on the wrong gene.

Scientists studying what they thought was a ‘fat gene’ seem to have been looking in the wrong place, according to research published today in Nature. It suggests instead that the real culprit is another gene that the suspected obesity gene interacts with.

In 2007, several genome studies identified mutations in a gene called FTO that were strongly associated with an increased risk of obesity and type 2 diabetes in humans. Subsequent studies in mice showed a link between the gene and body mass. So researchers, including Marcelo Nóbrega, a geneticist at the University of Chicago, thought that they had found a promising candidate for a gene that helped cause obesity.

The mutations were located in non-coding portions of FTO involved in regulating gene expression. But when Nóbrega looked closer, he found that something was amiss. These regulatory regions contained some elements that are specific for the lungs, one of the few tissues in which FTO is not expressed. “This made us pause,” he says. “Why are there regulatory elements that presumably regulate FTO in the tissue where it isn’t expressed?”

This was not the first red flag. Previous attempts to find a link between the presence of the obesity-associated mutations and the expression levels of FTO had been a “miserable failure”, he says. When Nóbrega presented his new results at meetings, he adds that many people came to him to say ‘I just knew there was something wrong here’.

So Nóbrega’s team cast the net wider, looking for genes in the broader neighbourhood of FTO whose expression matched that of the mutations, and found IRX3, a gene about half a million base pairs away. IRX3 encodes a transcription factor — a type of protein involved in regulating the expression of other genes — and is highly expressed in the brain, consistent with a role in regulating energy metabolism and eating behaviour.

When they examined the looping three-dimensional structure of the chromosome on which both genes sit in mice, zebrafish and human cells, they found that the obesity-associated regions in FTO were physically in contact with the promoter (the initial gene sequence which acts as an on/off switch) of IRX3. So the switches that turn on IRX3 are actually located far away from IRX3 itself, inside another gene. “We think of the genome as a linear thing, but it’s really a complex 3D structure that coils back onto itself,” he says.

Distant genes

IRX3 also appeared to be strongly linked with obesity. People with one of the obesity-associated mutations showed higher expression of IRX3, but not FTO, in brain tissue samples, the team found. Nóbrega and his colleagues also found that mice lacking the gene weighed 25–30% less than mice with a functional IRX3 gene; did not gain weight on a high-fat diet; were resistant to metabolic disorders such as diabetes and had more of the energy-burning cells known as brown fat. The same results were seen in mice in which the expression of IRX3 was blocked in the hypothalamus, a brain region known to regulate feeding behaviour and energy balance.

Inês Barroso, a geneticist at the Wellcome Trust Sanger Institute in Hinxton, UK, says that the work answers some of the questions around the biology of the link found in the genome-wide association studies (GWAS). “That’s always the tricky thing; a GWAS gives you an association, but it’s just a marker on the genome, it doesn’t actually say anything about which gene it’s affecting,” she says. “This strongly suggests that mediation of body mass is going to be through IRX3 rather than FTO.”

Nóbrega thinks geneticists should keep in mind this example of unexpected interactions between distant genes when dealing with genetic association studies. “There may be many other cases where people are studying the wrong gene,” he says. “We might be chasing ghosts.”

(Image caption: This image shows a PC12 cell growing onto a randomly textures surface. Note how the cell is spreading out in all directions.)

Surface Characteristics Influence Cellular Growth on Semiconductor Material

Changing the texture and surface characteristics of a semiconductor material at the nanoscale can influence the way that neural cells grow on the material.

The finding stems from a study performed by researchers at North Carolina State University, the University of North Carolina at Chapel Hill and Purdue University, and may have utility for developing future neural implants.

“We wanted to know how a material’s texture and structure can influence cell adhesion and differentiation,” says Lauren Bain, lead author of a paper describing the work and a Ph.D. student in the joint biomedical engineering program at NC State and UNC-Chapel Hill. “Basically, we wanted to know if changing the physical characteristics on the surface of a semiconductor could make it easier for an implant to be integrated into neural tissue – or soft tissue generally.”

The researchers worked with gallium nitride (GaN), because it is one of the most promising semiconductor materials for use in biomedical applications. They also worked with PC12 cells, which are model cells used to mimic the behavior of neurons in lab experiments.

In the study, the researchers grew PC12 cells on GaN squares with four different surface characteristics: some squares were smooth; some had parallel grooves (resembling an irregular corduroy pattern); some were randomly textured (resembling a nanoscale mountain range); and some were covered with nanowires (resembling a nanoscale bed of nails).

Very few PC12 cells adhered to the smooth surface. And those that did adhere grew normally, forming long, narrow extensions. More PC12 cells adhered to the squares with parallel grooves, and these cells also grew normally.

About the same number of PC12 cells adhered to the randomly textured squares as adhered to the parallel grooves. However, these cells did not grow normally. Instead of forming narrow extensions, the cells flattened and spread across the GaN surface in all directions.

More PC12 cells adhered to the nanowire squares than to any of the other surfaces, but only 50 percent of the cells grew normally. The other 50 percent spread in all directions, like the cells on the randomly textured surfaces.

“This tells us that the actual shape of the surface characteristics influences the behavior of the cells,” Bain says. “It’s a non-chemical way of influencing the interaction between the material and the body. That’s something we can explore as we continue working to develop new biomedical technologies.”

Substance in Humans is Effective Fighting Stroke Damage

A molecular substance that occurs naturally in humans and rats was found to “substantially reduce” brain damage after an acute stroke and contribute to a better recovery, according to a newly released animal study by researchers at Henry Ford Hospital.

The study, published online before print in Stroke, the journal of the American Heart Association, was the first ever to show that the peptide AcSDKP provides neurological protection when administered one to four hours after the onset of an ischemic stroke.

This type of stroke occurs when an artery to the brain is blocked by a blood clot, cutting off oxygen and killing brain tissue with crippling or fatal results.

“Stroke is a leading cause of death and disability worldwide,” said Li Zhang, M.D., a researcher at Henry Ford and lead author of the study. “Our data showed that treatment of acute stroke with AcSDKP alone or in combination with tPA substantially reduced neurovascular damage and improved neurological outcome.”

Commonly called a “clot-buster,” tPA, or tissue plasminogen activator, is the only FDA-approved treatment for acute stroke.

However, tPA must be given shortly after the onset of stroke to provide the best results. It also has the potential to cause a brain hemorrhage.

The Henry Ford study found that this narrow “therapeutic window” is extended for up to four hours after stroke and the therapeutic benefit of tPA is amplified when tPA is combined with AcSDKP. Further, the researchers discovered that AcSDKP alone is an effective treatment if given up to one hour after the brain attack.

The researchers tested the actions of both substances on laboratory rats in which acute stroke had been induced. It was already known that the peptide AcSDKP provides anti-inflammatory effects and helps protect the heart when used to treat a variety of cardiovascular diseases. The Henry Ford scientists reasoned that the peptide may have similar neurological benefits.

Significantly, they found that AcSDKP can readily cross the so-called “blood brain barrier” that blocks other neuroprotective substances.

A battery of behavioral tests was given to the lab rats both before and after stroke was induced to measure the effects of AcSDKP administered alone one hour after onset and combined with tPA four hours after stroke.

Besides finding that both methods “robustly” decreased neurological damage associated with stroke, they did so without increasing the incidence of brain hemorrhage or the formation of additional blood clots.

“With the increased use of clot-busting therapy in patients with acute stroke, both the safety and effectiveness of the combined treatment shown in our study should encourage the development of clinical trials of AcSDKP with tPA,” Dr. Zhang says.

Gesturing with hands is a powerful tool for children’s math learning

Children who use their hands to gesture during a math lesson gain a deep understanding of the problems they are taught, according to new research from University of Chicago’s Department of Psychology.

Previous research has found that gestures can help children learn. This study in particular was designed to answer whether abstract gesture can support generalization beyond a particular problem and whether abstract gesture is a more effective teaching tool than concrete action.

“We found that acting gave children a relatively shallow understanding of a novel math concept, whereas gesturing led to deeper and more flexible learning,” explained the study’s lead author, Miriam A. Novack, a PhD student in psychology.

The study, “From action to abstraction: Using the hands to learn math,” is published online by Psychological Science.

The researchers taught third-grade children a strategy for solving one type of mathematical equivalence problem, for example, 4 + 2 + 6 = ____ + 6. They then tested the students on similar mathematical equivalence problems to determine how well they understood the underlying principle.

The researchers randomly assigned 90 children to conditions in which they learned using different kinds of physical interaction with the material. In one group, children picked up magnetic number tiles and put them in the proper place in the formula. For example, for the problem 4 + 2 + 6 = ___ + 6, they picked up the 4 and 2 and placed them on a magnetic whiteboard. Another group mimed that action without actually touching the tiles, and a third group was taught to use abstract gestures with their hands to solve the equations. In the abstract gesture group, children were taught to produce a V-point gesture with their fingers under two of the numbers, metaphorically grouping them, followed by pointing a finger at the blank in the equation.

The children were tested before and after solving each problem in the lesson, including problems that required children to generalize beyond what they had learned in grouping the numbers. For example, they were given problems that were similar to the original one, but had different numbers on both sides of the equation.

Children in all three groups learned the problems they had been taught during the lesson. But only children who gestured during the lesson were successful on the generalization problems.

“Abstract gesture was most effective in encouraging learners to generalize the knowledge they had gained during instruction, action least effective, and concrete gesture somewhere in between,” said senior author Susan Goldin-Meadow, the Beardsley Ruml Distinguished Service Professor in Psychology. “Our findings provide the first evidence that gesture not only supports learning a task at hand but, more importantly, leads to generalization beyond the task. Children appear to learn underlying principles from their actions only insofar as those actions can be interpreted symbolically.”

Researchers Model a Key Breaking Point Involved in Traumatic Brain Injury

Even the mildest form of a traumatic brain injury, better known as a concussion, can deal permanent, irreparable damage. Now, an interdisciplinary team of researchers at the University of Pennsylvania is using mathematical modeling to better understand the mechanisms at play in this kind of injury, with an eye toward protecting the brain from its long-term consequences.

Their recent findings, published in the Biophysical Journal, shed new light on the mechanical properties of a critical brain protein and its role in the elasticity of axons, the long, tendril-like part of brain cells. This protein, known as tau, helps explain the apparent contradiction this elasticity presents. If axons are so stretchy, why do they break under the strain of a traumatic brain injury?    

Tau’s own elastic properties reveal why rapid impacts deal permanent damage to structures within axons, when applying the same force more slowly causes them to safely stretch. This understanding can now be used to make computer models of the brain more realistic and potentially can be applied toward tau-related diseases, such as Alzheimer’s.

The team consists of Vivek Shenoy, professor of materials science and engineering in the School of Engineering and Applied Science, Hossein Ahmadzadeh, a member of Shenoy’s lab, and Douglas Smith, professor of neurosurgery in Penn’s Perelman School of Medicine and director of the Penn Center for Brain Injury and Repair. 

“One of the main things you see in the brains of patients who have died because of a TBI is swellings along the axons,” Shenoy said. “Inside axons are microtubules, which act like tracks for transporting molecular cargo along the axon. When they break, there’s an interruption in the flow of this cargo and it starts to accumulate, which is why you get these swellings.”  

Smith had previously studied the mechanical properties of axons as a whole. By patterning axons in culture in parallel tracts, Smith and his colleagues could apply a stretch to the axons at different forces and speeds and measure how they responded.

“What we saw is that with slow loading rates, axons can stretch up to at least 100 percent with no signs of damage,” Smith said. “But at faster rates, axons start displaying the same swellings you see in the TBI patients. This process occurs even with relatively short stretch at fast rates. So the rate at which stretch is applied is the important component, such as occurs during rapid movement of the brain and stretching of axons due to head impact from a fall, assault or automobile crash.”

This observation still did not explain to researchers why microtubules, the stiffest part of the axon, were the parts that were breaking. To solve that puzzle, the researchers had to delve even deeper into their structure.

Microtubules are closely packed together inside axons, somewhat like a bundle of straws. Binding the individual straws together is the protein tau. Other biophysical modelers had previously accounted for the geometry and elastic properties of the axon during a stretching injury based on Smith’s work but did not have good data for representing tau’s role in the overall behavior of the system when it is loaded with stress over different lengths of time. 

“You need to know the elastic properties of tau,” Shenoy said, “because when you load the microtubules with stress, you load the tau as well. How these two parts distribute the stress between them is going to have major impact on the system as a whole.”

Shenoy and his colleagues had a sense of tau’s elastic properties but did not have hard numbers until a 2011 experiment from a Swiss and German research team physically stretched out lengths of tau by plucking it with the tip of an atomic force microscope.

“This experiment demonstrated that tau is viscoelastic,” Shenoy said. “Like Silly Putty, when you add stress to it slowly, it stretches a lot. But if you add stress to it rapidly, like in an impact, it breaks.”

This behavior is because the strands of tau protein are coiled up and bonded to themselves in different places. Pulled slowly, those bonds can come undone, lengthening the strand without breaking it. 

“The damage in traumatic brain injury occurs when the microtubules stretch but the tau doesn’t, as they can’t stretch as far,” Shenoy said. “If you’re in a situation where the tau doesn’t stretch, such as what happens in fast strain rates, then all the strain will transfer to the microtubules and cause them to break.”

With a comprehensive model of the tau-microtubule system, the researchers were able to boil down the outcome of rapid stress loading to equations with only a handful of variables. This mathematical understanding allowed the researchers to produce a phase diagram that shows the dividing line between strain rates that leave permanent damage versus safe and reversible loading and unloading of stress.

“Predicting what kind of impacts will cause these strain rates is still a complicated problem,” Shenoy said. “I might be able to measure the force of the impact when it hits someone’s head, but that force then has to make its way down to the axons, which depends on a lot of different things.

“You need a multiscale model, and our work will be an input to those models on the smallest scale.”

In the longer term, knowing the parameters that lead to irreversible damage could lead to better understanding of brain injuries and diseases and to new preventive measures. It may even be possible to design drugs that alter microtubule stability and elasticity of axons in traumatic brain injury; Smith’s group has demonstrated that treatment with the microtubule-stabilizing drug taxol reduced the extent of axon swellings and degeneration after stretch injury.    

“Intriguingly, it may be no coincidence that tau is also the same protein that forms neurofibrillary tangles, one of the hallmark brain pathologies of chronic traumatic encephalopathy, or CTE, which is linked to a history of concussions and higher levels of TBI,” said Smith. “Uncovering the role of tau at the time of trauma may provide insight into how it is involved in long-term degenerative processes.”