Can Fish Oil Help Preserve Brain Cells?

People with higher levels of the omega-3 fatty acids found in fish oil may also have larger brain volumes in old age equivalent to preserving one to two years of brain health, according to a study published in the January 22, 2014, online issue of Neurology®, the medical journal of the American Academy of Neurology. Shrinking brain volume is a sign of Alzheimer’s disease as well as normal aging.

For the study, the levels of omega-3 fatty acids EPA+DHA in red blood cells were tested in 1,111 women who were part of the Women’s Health Initiative Memory Study. Eight years later, when the women were an average age of 78, MRI scans were taken to measure their brain volume.

Those with higher levels of omega-3s had larger total brain volumes eight years later. Those with twice as high levels of fatty acids (7.5 vs. 3.4 percent) had a 0.7 percent larger brain volume.

“These higher levels of fatty acids can be achieved through diet and the use of supplements, and the results suggest that the effect on brain volume is the equivalent of delaying the normal loss of brain cells that comes with aging by one to two years,” said study author James V. Pottala, PhD, of the University of South Dakota in Sioux Falls and Health Diagnostic Laboratory, Inc., in Richmond, Va.

Those with higher levels of omega-3s also had a 2.7 percent larger volume in the hippocampus area of the brain, which plays an important role in memory. In Alzheimer’s disease, the hippocampus begins to atrophy even before symptoms appear.

Watching Molecules Morph into Memories

In two studies in the January 24 issue of Science (1, 2), researchers at Albert Einstein College of Medicine of Yeshiva University used advanced imaging techniques to provide a window into how the brain makes memories. These insights into the molecular basis of memory were made possible by a technological tour de force never before achieved in animals: a mouse model developed at Einstein in which molecules crucial to making memories were given fluorescent “tags” so they could be observed traveling in real time in living brain cells.

Efforts to discover how neurons make memories have long confronted a major roadblock: Neurons are extremely sensitive to any kind of disruption, yet only by probing their innermost workings can scientists view the molecular processes that culminate in memories. To peer deep into neurons without harming them, Einstein researchers developed a mouse model in which they fluorescently tagged all molecules of messenger RNA (mRNA) that code for beta-actin protein – an essential structural protein found in large amounts in brain neurons and considered a key player in making memories. mRNA is a family of RNA molecules that copy DNA’s genetic information and translate it into the proteins that make life possible.

"It’s noteworthy that we were able to develop this mouse without having to use an artificial gene or other interventions that might have disrupted neurons and called our findings into question," said Robert Singer, Ph.D., the senior author of both papers and professor and co-chair of Einstein’s department of anatomy & structural biology and co-director of the Gruss Lipper Biophotonics Center at Einstein. He also holds the Harold and Muriel Block Chair in Anatomy & Structural Biology at Einstein.

In the research described in the two Science papers, the Einstein researchers stimulated neurons from the mouse’s hippocampus, where memories are made and stored, and then watched fluorescently glowing beta-actin mRNA molecules form in the nuclei of neurons and travel within dendrites, the neuron’s branched projections. They discovered that mRNA in neurons is regulated through a novel process described as “masking” and “unmasking,” which allows beta-actin protein to be synthesized at specific times and places and in specific amounts.

"We know the beta-actin mRNA we observed in these two papers was ‘normal’ RNA, transcribed from the mouse’s naturally occurring beta-actin gene," said Dr. Singer. "And attaching green fluorescent protein to mRNA molecules did not affect the mice, which were healthy and able to reproduce."

Neurons come together at synapses, where slender dendritic “spines” of neurons grasp each other, much as the fingers of one hand bind those of the other. Evidence indicates that repeated neural stimulation increases the strength of synaptic connections by changing the shape of these interlocking dendrite “fingers.” Beta-actin protein appears to strengthen these synaptic connections by altering the shape of dendritic spines. Memories are thought to be encoded when stable, long-lasting synaptic connections form between neurons in contact with each other.

The first paper describes the work of Hye Yoon Park, Ph.D., a postdoctoral student in Dr. Singer’s lab at the time and now an instructor at Einstein. Her research was instrumental in developing the mice containing fluorescent beta-actin mRNA—a process that took about three years.

Dr. Park stimulated individual hippocampal neurons of the mouse and observed newly formed beta-actin mRNA molecules within 10 to 15 minutes, indicating that nerve stimulation had caused rapid transcription of the beta-actin gene. Further observations suggested that these beta-actin mRNA molecules continuously assemble and disassemble into large and small particles, respectively. These mRNA particles were seen traveling to their destinations in dendrites where beta-actin protein would be synthesized.

In the second paper, lead author and graduate student Adina Buxbaum of Dr. Singer’s lab showed that neurons may be unique among cells in how they control the synthesis of beta-actin protein.

"Having a long, attenuated structure means that neurons face a logistical problem," said Dr. Singer. "Their beta-actin mRNA molecules must travel throughout the cell, but neurons need to control their mRNA so that it makes beta-actin protein only in certain regions at the base of dendritic spines."

Ms. Buxbaum’s research revealed the novel mechanism by which brain neurons handle this challenge. She found that as soon as beta-actin mRNA molecules form in the nucleus of hippocampal neurons and travel out to the cytoplasm, the mRNAs are packaged into granules and so become inaccessible for making protein. She then saw that stimulating the neuron caused these granules to fall apart, so that mRNA molecules became unmasked and available for synthesizing beta-actin protein.

But that observation raised a question: How do neurons prevent these newly liberated mRNAs from making more beta-actin protein than is desirable? “Ms. Buxbaum made the remarkable observation that mRNA’s availability in neurons is a transient phenomenon,” said Dr. Singer. “She saw that after the mRNA molecules make beta-actin protein for just a few minutes, they suddenly repackage and once again become masked. In other words, the default condition for mRNA in neurons is to be packaged and inaccessible.”

These findings suggest that neurons have developed an ingenious strategy for controlling how memory-making proteins do their job. “This observation that neurons selectively activate protein synthesis and then shut it off fits perfectly with how we think memories are made,” said Dr. Singer. “Frequent stimulation of the neuron would make mRNA available in frequent, controlled bursts, causing beta-actin protein to accumulate precisely where it’s needed to strengthen the synapse.”

To gain further insight into memory’s molecular basis, the Singer lab is developing technologies for imaging neurons in the intact brains of living mice in collaboration with another Einstein faculty member in the same department, Vladislav Verkhusha, Ph.D. Since the hippocampus resides deep in the brain, they hope to develop infrared fluorescent proteins that emit light that can pass through tissue. Another possibility is a fiberoptic device that can be inserted into the brain to observe memory-making hippocampal neurons.

Forget about forgetting – The elderly know more and use it better

What happens to our cognitive abilities as we age? If your think our brains go into a steady decline, research reported this week in the Journal Topics in Cognitive Science may make you think again. The work, headed by Dr. Michael Ramscar of Tübingen University, takes a critical look at the measures usually thought to show that our cognitive abilities decline across adulthood. Instead of finding evidence of decline, the team discovered that most standard cognitive measures, which date back to the early twentieth century, are flawed. “The human brain works slower in old age,” says Ramscar, “but only because we have stored more information over time.”

Computers were trained, like humans, to read a certain amount each day, and to learn new things. When the researchers let a computer “read” only so much, its performance on cognitive tests resembled that of a young adult. But if the same computer was exposed to the experiences we might encounter over a lifetime – with reading simulated over decades – its performance now looked like that of an older adult. Often it was slower, but not because its processing capacity had declined. Rather, increased “experience” had caused the computer’s database to grow, giving it more data to process – which takes time.

Technology now allows researchers to make quantitative estimates of the number of words an adult can be expected to learn across a lifetime, enabling the Tübingen team to separate the challenge that increasing knowledge poses to memory from the actual performance of memory itself. “Imagine someone who knows two people’s birthdays and can recall them almost perfectly. Would you really want to say that person has a better memory than a person who knows the birthdays of 2000 people, but can ‘only’ match the right person to the right birthday nine times out of ten?” asks Ramscar.

The answer appears to be “no.” When Ramscar’s team trained their computer models on huge linguistic datasets, they found that standardized vocabulary tests, which are used to take account of the growth of knowledge in studies of ageing, massively underestimate the size of adult vocabularies. It takes computers longer to search databases of words as their sizes grow, which is hardly surprising but may have important implications for our understanding of age-related slowdowns. The researchers found that to get their computers to replicate human performance in word recognition tests across adulthood, they had to keep their capacities the same. “Forget about forgetting,” explained Tübingen researcher Peter Hendrix, “if I wanted to get the computer to look like an older adult, I had to keep all the words it learned in memory and let them compete for attention.”

The research shows that studies of the problems older people have with recalling names suffer from a similar blind spot: there is a far greater variety of given names today than there were two generations ago. This cultural shift toward greater name diversity means the number of different names anyone learns over their lifetime has increased dramatically. The work shows how this makes locating a name in memory far harder than it used to be. Even for computers.

Ramscar and his colleagues’ work provides more than an explanation of why, in the light of all the extra information they have to process, we might expect older brains to seem slower and more forgetful than younger brains. Their work also shows how changes in test performance that have been taken as evidence for declining cognitive abilities in fact demonstrates older adults’ greater mastery of the knowledge they have acquired.

Take “paired-associate learning,” a commonly used cognitive test that involves learning to connect words like “up” to “down” or “necktie” to “cracker” in memory. Using Big Data sets to quantify how often different words appear together in English, the Tuebingen team show that younger adults do better when asked to learn to pair “up” with “down” than “necktie” and “cracker” because “up” and “down” appear in close proximity to one another more frequently. However, whereas older adults also understand which words don’t usually go together, young adults notice this less. When the researchers examined performance on this test across a range of word pairs that go together more and less in English, they found older adult’s scores to be far more closely attuned to the actual information in hundreds of millions of words of English than their younger counterparts.

As Prof. Harald Baayen, who heads the Alexander von Humboldt Quantitative Linguistics research group where the work was carried out puts it, “If you think linguistic skill involves something like being able to choose one word given another, younger adults seem to do better in this task. But, of course, proper understanding of language involves more than this. You have also to not put plausible but wrong pairs of words together. The fact that older adults find nonsense pairs – but not connected pairs – harder to learn than young adults simply demonstrates older adults’ much better understanding of language. They have to make more of an effort to learn unrelated word pairs because, unlike the youngsters, they know a lot about which words don’t belong together.”

The Tübingen research conclude that we need different tests for the cognitive abilities of older people – taking into account the nature and amount of information our brains process. “The brains of older people do not get weak,” says Michael Ramscar. “On the contrary, they simply know more.”

[Figure 1: Synaptic signaling occurs when neurotransmitter molecules (glutamate) released by the presynaptic neuron travel through the synaptic cleft to activate glutamate receptors, including NMDA receptors, on the postsynaptic neuron. Image courtesy of the National Institute on Aging]

Amplifying communication between neurons

Neurons send signals to each other across small junctions called synapses. Some of these signals involve the flow of potassium, calcium and sodium ions through channel proteins that are embedded within the membranes of neurons. However, it was unclear whether the flow of potassium ions into the synaptic cleft had a physiological purpose. An international team of researchers including Alexey Semyanov from the RIKEN Brain Science Institute has now revealed that potassium ions that leak out of channel proteins and spill into the synapse augment synaptic signaling between neurons, potentially fulfilling a reinforcement mechanism in learning and memory.

Synaptic communication between neurons begins when calcium ions enter the axon terminal of one neuron—the presynaptic neuron—causing the release of neurotransmitter molecules, such as glutamate, which travel across the synaptic cleft and bind to receptor proteins on the surface of the receiving or postsynaptic neuron (Fig. 1). When the glutamate binds to a receptor known as the NMDA receptor, a channel in the receptor protein opens and calcium flows in, which initiates activation of the postsynaptic neuron.

Semyanov and his colleagues found that the opening of the NMDA receptor channel on the postsynaptic neuron also allows potassium ions to flow out of that neuron and into the synaptic cleft. Blocking the NMDA receptor prevented the rise in potassium ions within the synaptic cleft.

The NMDA receptor is generally blocked by magnesium ions, but these ions can be released from the receptor channel upon repetitive stimulation of the postsynaptic neuron. Through mathematical modeling and subsequent experiments, Semyanov and his colleagues found that potassium levels in the synaptic cleft could increase dramatically on removal of magnesium or during repeated activation of the postsynaptic neuron.

The rise in potassium in the synaptic cleft was shown to increase calcium entry into the presynaptic neuron axon terminal when the postsynaptic neuron was stimulated, and enhanced the probability that the glutamate neurotransmitter would be released from the presynaptic neuron. In this way, repeated activation of a given neuronal network, such as during learning, could augment the strength of communication between neurons, making it more likely that a given stimulus would trigger the activation of postsynaptic neurons.

"New memories are associated with long-term changes in synaptic strength following repetitive activation of the synapse, commonly known as synaptic plasticity," explains Semyanov. "Potassium accumulation and the consequent increase in probability of glutamate release can potentially aid the induction of synaptic plasticity, thus facilitating learning and memory," he says.

Erasing traumatic memories

Nearly 8 million Americans suffer from posttraumatic stress disorder (PTSD), a condition marked by severe anxiety stemming from a traumatic event such as a battle or violent attack.

Many patients undergo psychotherapy designed to help them re-experience their traumatic memory in a safe environment so as to help them make sense of the events and overcome their fear. However, such memories can be so entrenched that this therapy doesn’t always work, especially when the traumatic event occurred many years earlier.

MIT neuroscientists have now shown that they can extinguish well-established traumatic memories in mice by giving them a type of drug called an HDAC2 inhibitor, which makes the brain’s memories more malleable, under the right conditions. Giving this type of drug to human patients receiving psychotherapy may be much more effective than psychotherapy alone, says Li-Huei Tsai, director of MIT’s Picower Institute for Learning and Memory.

“By inhibiting HDAC2 activity, we can drive dramatic structural changes in the brain. What happens is the brain becomes more plastic, more capable of forming very strong new memories that will override the old fearful memories,” says Tsai, the senior author of a paper describing the findings in the Jan. 16 issue of Cell.

The new study also reveals the molecular mechanism explaining why older memories are harder to extinguish. Lead authors of the paper are former Picower Institute postdoc Johannes Graff and Nadine Joseph, a technical assistant at the Picower Institute.

Genes and memories

Tsai’s lab has previously shown that when memories are formed, neurons’ chromatin — DNA packaged with proteins — undergoes extensive remodeling. These chromatin modifications make it easier to activate the genes necessary to create new memories.

In this study, the researchers focused on chromatin modifications that occur when previously acquired memories are extinguished. To do this, they first trained mice to fear a particular chamber — by administering a mild foot shock — and then tried to recondition the mice so they no longer feared it, which was done by placing the mice in the chamber where they received the shock, without delivering the shock again.

This training proved successful in mice that had experienced the traumatic event only 24 hours before the reconditioning. However, in mice whose memories were 30 days old, it was impossible to eliminate the fearful memory.

The researchers also found that in the brains of mice with 24-hour-old memories, extensive chromatin remodeling occurred during the reconditioning. For several hours after the mice were placed back in the feared chamber, there was a dramatic increase in histone acetylation of memory-related genes, caused by inactivation of the protein HDAC2. That histone acetylation makes genes more accessible, turning on the processes needed to form new memories or overwrite old ones.

In mice with 30-day-old memories, however, there was no change in histone acetylation. This suggests that re-exposure to a fearful memory opens a window of opportunity during which the memory can be altered, but only if the memory has recently been formed, Tsai says.

“If you do something within this window of time, then you have the possibility of modifying the memory or forming a new trace of memory that actually instructs the animal that this is not such a dangerous place,” she says. “However, the older the memory is, the harder it is to really change that memory.”

Based on this finding, the researchers decided to treat mice with 30-day-old memories with an HDAC2 inhibitor shortly after re-exposure to the feared chamber. Following this treatment, the traumatic memories were extinguished just as easily as in the mice with 24-hour-old memories.

The researchers also found that HDAC2 inhibitor treatment turns on a group of key genes known as immediate early genes, which then activate other genes necessary for memory formation. They also saw an increase in the number of connections among neurons in the hippocampus, where memories are formed, and in the strength of communication among these neurons.

“Our experiments really strongly argue that either the old memories are permanently being modified, or a new much more potent memory is formed that completely overwrites the old memory,” Tsai says.

“This could be a very promising way to bring older memories back, process them in the hippocampus, and then extinguish them with the correct paradigm,” says Jelena Radulovic, a professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine who was not part of the research team.

Treating anxiety

Some HDAC2 inhibitors have been approved to treat cancer, and Tsai says she believes it is worth trying such drugs to treat PTSD. “I hope this will convince people to seriously think about taking this into clinical trials and seeing how well it works,” she says.

Such drugs might also be useful in treating people who suffer from phobias and other anxiety disorders, she adds.

Tsai’s lab is now studying what happens to memory traces when re-exposure to traumatic memories occurs at different times. It is already known that memories are formed in the hippocampus and then transferred to the cortex for longer-term storage. It appears that the HDAC2 inhibitor treatment may somehow restore the memory to the hippocampus so it can be extinguished, Tsai says.

Disease and sleep: Recent studies find new links

One in five U.S. adults shows signs of chronic sleep deprivation, and a shortage of sleep has been linked to health problems as different as diabetes and Alzheimer’s disease. Recent studies have found some interesting connections between illness and what is happening in our brains as we snooze.

Toward a Molecular Explanation for Schizophrenia

Surprisingly little is known about schizophrenia. It was only recognized as a medical condition in the past few decades, and its exact causes remain unclear. Since there is no objective test for schizophrenia, its diagnosis is based on an assortment of reported symptoms. The standard treatment, antipsychotic medication, works less than half the time and becomes increasingly ineffective over time.

Now, Prof. Illana Gozes — the Lily and Avraham Gildor Chair for the Investigation of Growth Factors, the director of the Adams Super Center for Brain Studies at the Sackler Faculty of Medicine, and a member of the Sagol School of Neuroscience at Tel Aviv University — has discovered that an important cell-maintenance process called autophagy is reduced in the brains of schizophrenic patients. The findings, published in Nature’s Molecular Psychiatry, advance the understanding of schizophrenia and could enable the development of new diagnostic tests and drug treatments for the disease.

"We discovered a new pathway that plays a part in schizophrenia," said Prof. Gozes. "By identifying and targeting the proteins known to be involved in the pathway, we may be able to diagnose and treat the disease in new and more effective ways."

Graduate students Avia Merenlender-Wagner, Anna Malishkevich, and Zeev Shemer of TAU, Prof. Brian Dean and colleagues of the University of Melbourne, and Prof. Galila Agam and Joseph Levine of Ben Gurion University of the Negev and Beer Sheva’s Psychiatry Research Center and Mental Health Center collaborated on the research.

Mopping up

Autophagy is like the cell’s housekeeping service, cleaning up unnecessary and dysfunctional cellular components. The process — in which a membrane engulfs and consumes the clutter — is essential to maintaining cellular health. But when autophagy is blocked, it can lead to cell death. Several studies have tentatively linked blocked autophagy to the death of brain cells seen in Alzheimer’s disease.

Brain-cell death also occurs in schizophrenics, so Prof. Gozes and her colleagues set out to see if blocked autophagy could be involved in the progression of that condition as well. They found RNA evidence of decreased levels of the protein beclin 1 in the hippocampus of schizophrenia patients, a brain region central to learning and memory. Beclin 1 is central to initiating autophagy — its deficit suggests that the process is indeed blocked in schizophrenia patients. Developing drugs to boost beclin 1 levels and restart autophagy could offer a new way to treat schizophrenia, the researchers say.

"It is all about balance," said Prof Gozes. "Paucity in beclin 1 may lead to decreased autophagy and enhanced cell death. Our research suggests that normalizing beclin 1 levels in schizophrenia patients could restore balance and prevent harmful brain-cell death."

Next, the researchers looked at protein levels in the blood of schizophrenia patients. They found no difference in beclin 1 levels, suggesting that the deficit is limited to the hippocampus. But the researchers also found increased levels of another protein, activity-dependent neuroprotective protein (ADNP), discovered by Prof. Gozes and shown to be essential for brain formation and function, in the patients’ white blood cells. Previous studies have shown that ADNP is also deregulated in the brains of schizophrenia patients.

The researchers think the body may boost ADNP levels to protect the brain when beclin 1 levels fall and autophagy is derailed. ADNP, then, could potentially serve as a biomarker, allowing schizophrenia to be diagnosed with a simple blood test.

An illuminating discovery

To further explore the involvement of ADNP in autophagy, the researchers ran a biochemical test on the brains of mice. The test showed that ADNP interacts with LC3, another key protein regulating autophagy — an interaction predicted by previous studies. In light of the newfound correlation between autophagy and schizophrenia, they believe that this interaction may constitute part of the mechanism by which ADNP protects the brain.

Prof. Gozes discovered ADNP in 1999 and carved a protein fragment, NAP, from it. NAP mimics the protein nerve cell protecting properties. In follow-up studies Prof. Gozes helped develop the drug candidate davunetide (NAP). In Phase II clinical trials, davunetide (NAP) improved the ability of schizophrenic patients to cope with daily life. A recent collaborative effort by Prof. Gozes and Dr. Sandra Cardoso and Dr. Raquel Esteves showed that NAP improved autophagy in cultures of brain-like cells. The current study further shows that NAP facilitates the interaction of ADNP and LC3, possibly accounting for NAP’s results in schizophrenia patients. The researchers hope NAP will be just the first of their many discoveries to improve understanding and treatment of schizophrenia.

(Image: Shutterstock)