Neuroimaging: Live from inside the cell

A novel imaging technique provides insights into the role of redox signaling and reactive oxygen species in living neurons, in real time. Scientists of the Technische Universität München (TUM) and the Ludwig-Maximilians-Universität München (LMU) have developed a new optical microscopy technique to unravel the role of “oxidative stress” in healthy as well as injured nervous systems. The work is reported in the latest issue of Nature Medicine.

Reactive oxygen species are important intracellular signaling molecules, but their mode of action is complex: In low concentrations they regulate key aspects of cellular function and behavior, while at high concentrations they can cause “oxidative stress”, which damages organelles, membranes and DNA. To analyze how redox signaling unfolds in single cells and organelles in real-time, an innovative optical microscopy technique has been developed jointly by the teams of LMU Professor Martin Kerschensteiner and TUM Professor Thomas Misgeld, both investigators of the Munich Cluster for Systems Neurology (SyNergy).

“Our new optical approach allows us to visualize the redox state of important cellular organelles, mitochondria, in real time in living tissue” Kerschensteiner says. Mitochondria are the cell’s power plants, which convert nutrients into usable energy. In earlier studies, Kerschensteiner and Misgeld had obtained evidence that oxidative damage of mitochondria might contribute to the destruction of axons in inflammatory diseases such as multiple sclerosis.

The new method allows them to record the oxidation states of individual mitochondria with high spatial and temporal resolution. Kerschensteiner explains the motivation behind the development of the technique: “Redox signals have important physiological functions, but can also cause damage, for example when present in high concentrations around immune cells.”

First surprises
Kerschensteiner and Misgeld used redox-sensitive variants of the Green Fluorescent Protein (GFP) as visualization tools. “By combining these with other biosensors and vital dyes, we were able to establish an approach that permits us to simultaneously monitor redox signals together with mitochondrial calcium currents, as well as changes in the electrical potential and the proton (pH) gradient across the mitochondrial membrane,” says Thomas Misgeld.

The researchers have applied the technique to two experimental models, and have arrived at some unexpected insights. On the one hand, they have been able, for the first time, to study redox signal induction in response to neural damage – in this case, spinal cord injury – in the mammalian nervous system. The observations revealed that severance of an axon results in a wave of oxidation of the mitochondria, which begins at the site of damage and is propagated along the fiber. Furthermore, an influx of calcium at the site of axonal resection was shown to be essential for the ensuing functional damage to mitochondria.

Perhaps the most surprising outcome of the new study was that the study’s first author, graduate student Michael Breckwoldt, was able to image, also for the first time, spontaneous contractions of mitochondria that are accompanied by a rapid shift in the redox state of the organelle. As Misgeld explains, “This appears to be a fail-safe system that is activated in response to stress and temporarily attenuates mitochondrial activity. Under pathological conditions, the contractions are more prolonged and may become irreversible, and this can ultimately result in irreparable damage to the nerve process.”

First brain images of African infants enable research into cognitive effects of nutrition

Brain activity of babies in developing countries could be monitored from birth to reveal the first signs of cognitive dysfunction, using a new technique piloted by a London-based university collaboration.

The cognitive function of infants can be visualised and tracked more quickly, more accurately and more cheaply using the method, called functional near infra-red spectroscopy (fNIRS), compared to the behavioural assessments Western regions have relied upon for decades.

Professor Clare Elwell, Professor of Medical Physics at University College London (UCL), said: “Brain activity soon after birth has barely been studied in low-income countries, because of the lack of transportable brain imaging facilities needed to do this at any reasonable scale. We have high hopes of building on these promising findings to develop functional near infra-red spectroscopy into an assessment tool for investigating cognitive function of infants who may be at risk of malnutrition or childhood diseases associated with low income settings.”

The pioneering study, published this week in Nature Scientific Reports, was performed by a collaboration of researchers from UCL; the London School of Hygiene and Tropical Medicine; the Babylab at Birkbeck, University of London; and the Medical Research Council unit in Gambia. It aimed to investigate the impact of nutrition in resource-poor regions on infant brain development, and was funded by the Bill and Melinda Gates Foundation.

Professor Clare Elwell (UCL Medical Physics & Bioengineering), said: “This is the first use of brain imaging methods to investigate localised brain activity in African infants.

"Until now, much of our understanding of brain development in low income countries has relied upon behavioural assessments which need careful cultural and linguistic translations to ensure they are accurate. Our technology, functional near infrared spectroscopy, can provide a more objective marker of brain activity."

For the studies in the Gambia, babies aged 4–8 months old were played sounds and shown videos of adults performing specific movements, such as playing ‘peek-a-boo’. The fNIRS system monitored changes in blood flow to the baby’s brain and showed that distinct brain regions responded to visual–social prompts, while others responded to auditory-social stimuli. Comparison of the results with those obtained from babies in the UK showed that the responses were similar in both groups.

fNIRS has previously been used to study brain development in UK infants and most recently to investigate early markers of autism during the first few months of life.

Professor Andrew Prentice (Medical Research Council International Nutrition Group, London School of Hygiene and Tropical Medicine) said: “Humans have evolved to survive and succeed on the basis of their large brain and intelligence, but nutritional deficits in early life can limit this success. In order to plan the best interventions to maximise brain function we need tools that can give us an early read out. fNIRS is showing great promise in this respect.”

Scientists Identify Critical New Protein Complex Involved in Learning and Memory

Scientists from the Florida campus of The Scripps Research Institute (TSRI) have identified a protein complex that plays a critical but previously unknown role in learning and memory formation.

The study, which showed a novel role for a protein known as RGS7, was published April 22, 2014 in the journal eLife, a publisher supported by the Howard Hughes Medical Institute, the Max Planck Society and the Wellcome Trust.

“This is a critical building block that regulates a fundamental process—memory,” said Kirill Martemyanov, a TSRI associate professor who led the study. “Now that we know about this important new player, it offers a unique therapeutic window if we can find a way to enhance its function.”

The team looked at RGS7 in the hippocampus, a small part of the brain that helps turn short-term memory in long-term memory.

The scientists found the RGS7 protein works in concert with another protein, R7BP, to regulate a key signaling cascade that is increasingly seen as a critical to cognitive development. The cascade involves the neurotransmitter GABA, which binds to the GABA_b receptor and opens inhibitory channels known as GIRKs in the cell membrane. This process ultimately makes it more difficult for a nerve cell to fire.

This process turned out to be critical to normal functioning, as the research showed mice lacking RGS7 exhibited deficits in learning and memory.

Martemyanov believes the findings could ultimately have broad therapeutic application. “GIRK channels are implicated in a range of neuropsychiatric conditions, including drug addiction and Down’s syndrome, that result from a disproportionate increase in neuronal inhibition as a result of greater mobilization of these channels,” he said. ^“Now that we know the identity of the critical modulator of GIRK channels we can try to find a way to increase its power with the hopes of reducing the inhibitory overdrive, and that might potentially alleviate some of the  disruptions seen in Down’s syndrome. It is possible that similar strategies might apply for dealing with addiction, where adaptations in the GABAb-GIRK pathway play a significant role.”

Targeting the RGS7 protein could allow for better therapeutic outcomes with fewer side effects because it allows for fine tuning of the signaling, according to Olga Ostrovskaya, the first author of the study and a member of Martemyanov’s lab, who sees many ways to follow up on the findings.

“We’re looking into how RGS7 is involved in neural circuitry and functions tied to the striatum, another part of the brain responsible for procedural memory, mood disorders, motivation and addiction,” Ostrovskaya said. “We may uncover the RGS7 regulation of other signaling complexes that may be very different from those in hippocampus.”

Commonly available blood-pressure drug prevents epilepsy after brain injury

Between 10 and 20 percent of all cases of epilepsy result from severe head injury, but a new drug promises to prevent post-traumatic seizures and may forestall further brain damage caused by seizures in those who already have epilepsy.

A team of researchers from UC Berkeley, Ben-Gurion University in Israel and Charité-University Medicine in Germany reports in the current issue of the journal Annals of Neurology that a commonly used hypertension drug prevents a majority of cases of post-traumatic epilepsy in a rodent model of the disease. If independent experiments now underway in rats confirm this finding, human clinical trials could start within a few years.

“This is the first-ever approach in which epilepsy development is stopped, as opposed to common drugs that try to prevent seizures once epilepsy develops,” said coauthor Daniela Kaufer, UC Berkeley associate professor of integrative biology and a member of the Helen Wills Neuroscience Institute. “Those drugs have a very limited success and many side effects, so we are excited about the new approach.”

The team, led by Kaufer; neurosurgeon Alon Friedman, associate professor of physiology and neurobiology at the Ben-Gurion University of the Negev; and Uwe Heinemann of the Charite, provides the first explanation for how brain injury caused by a blow to the head, stroke or infection leads to epilepsy. Based on 10 years of collaborative research, their findings point a finger at the blood-brain barrier – the tight wall of cells lining the veins and arteries in the brain that is breached after trauma.

“This study for the first time offers a new mechanism and an existing, FDA-approved drug to potentially prevent epilepsy in patients after brain injuries or after they develop an abnormal blood-brain barrier,” Friedman said.

The drug, losartan (Cozaar®), prevented seizures in 60 percent of the rats tested, when normally 100 percent of the rats develop seizures after injury. In the 40 percent of rats that did develop seizures, they averaged about one quarter the number of seizures typical for untreated rats. Another experiment showed that administration of losartan for three weeks at the time of injury was enough to prevent most cases of epilepsy in normal lab rats in the following months.

“This is a very exciting result, telling us that the drug worked to prevent the development of epilepsy and not by suppressing the symptoms,” Kaufer said.

Breakdown of the blood-brain barrier

Kaufer and Friedman have been collaboratively investigating the effects of trauma on the brain since Kaufer was a graduate student in Israel 20 years ago. Throughout a postdoctoral position at Stanford University and after joining the UC Berkeley faculty in 2005, she maintained her interest in the blood-brain barrier, which normally protects the brain from potentially damaging chemicals or bacteria in the blood and prevents brain chemicals from leaking into the blood stream.

She and Friedman showed earlier that breaking down the barrier causes inflammation and leads to the development of epilepsy. They pinned the effect to a single protein called albumin, the most common protein in blood serum.

In 2009, they showed that albumin affects astrocytes, the brain’s support cells, by binding to the TGF-β (transforming growth factor-beta) receptor. This initiates a cascade of steps that lead to localized inflammation, which appears to permanently damage the brain’s wiring, leading to the electrical misfiring characteristic of epilepsy. The current paper conclusively demonstrates that blocking the TGF-beta receptor with losartan stops that cascade and prevents the disorder.

Drug’s side effect proves crucial

Coauthor Guy Bar-Klein, a doctoral student at Ben-Gurion University, searched a long list of drugs before discovering losartan, which is approved to treat high blood pressure because it blocks the angiotensin receptor 1, but which incidentally also blocks TGF-β. It worked in the rats when delivered in their drinking water, which means that it somehow gets into the brain through the blood-brain barrier. The experiments suggest that the drug is unable to cross an intact blood-brain barrier, but reaches the brain through a breached barrier when it is most needed, Kaufer said.

Friedman developed a protocol to use MRI to check whether the blood brain barrier has been breached, allowing doctors to give losartan as a preventive treatment, if necessary, after trauma. Kaufer said that the barrier may remain open for only a few weeks after injury, so the drug would not have to be given very long to prevent damage.

“Right now, if someone comes to the emergency room with traumatic brain injury, they have a 10 to 50 percent chance of developing epilepsy, and epilepsy from brain injuries tends to be unresponsive to drugs in many patients.” she said. “I’m very hopeful that our research can spare these patients the added trauma of epilepsy.”

Researchers find link between sleep and immune function in fruit flies

When we get sick it feels natural to try to hasten our recovery by getting some extra shuteye. Researchers from the Perelman School of Medicine at the University of Pennsylvania found that this response has a definite purpose, in fruitflies: enhancing immune system response and recovery to infection. Their findings appear online in two related papers in the journal Sleep, in advance of print editions in May and June.

"It’s an intuitive response to want to sleep when you get sick," notes Center for Sleep and Circadian Neurobiology research associate Julie A. Williams, PhD. "Many studies have used sleep deprivation as a means to understand how sleep contributes to recovery, if it does at all, but there is surprisingly little experimental evidence that supports the notion that more sleep helps us to recover. We used a fruitfly model to answer these questions." Along with post-doctoral fellow, Tzu-Hsing Kuo, PhD, Williams conducted two related studies to directly examine the effects of sleep on recovery from and survival after an infection.

In the first paper, they took a conventional approach by subjecting fruit flies to sleep deprivation before infecting them with either Serratia marcescens or Pseudomonas aeruginosa bacteria. Both the sleep-deprived flies and a non-sleep-deprived control group displayed increased sleep after infection, what the experimenters call an “acute sleep response.”

Unexpectedly, the pre-infection, sleep-deprived flies had a better survival rate. “To our surprise they actually survived longer after the infection than the ones who were not sleep-deprived,” notes Williams. The Penn team found that prior sleep deprivation made the flies sleep for a longer period after infection as compared to the undisturbed controls. They slept longer and they lived longer during the infection. Inducing sleep deprivation after infection rather than before made little difference, as long as the infected flies then got adequate recovery sleep. “We deprived flies of sleep after infection with the idea that if we blocked this sleep, things would get worse in terms of survival,” Williams explains. “Instead they got better, but not until after they had experienced more sleep.”

Sleep deprivation increases activity of an NFkB transcription factor, Relish, which is also needed for fighting infection. Flies without the Relish gene do not experience an acute sleep response and very quickly succumb to infection. But, when these mutants are sleep-deprived before infection, they displayed increased sleep and survival rates after infection. The team then evaluated mutant flies that lacked two varieties of NFkB (Relish and Dif). When flies lacked both types of NFkB genes, sleep deprivation had no effect on the acute sleep response, and the effect on survival was abolished. Flies from both sleep-deprived and undisturbed groups succumbed to infection at equal rates within hours.

"Taken together, all of these data support the idea that post-infection sleep helps to improve survival," Williams says.

In the second study, the researchers manipulated sleep through a genetic approach. They used the drug RU486 to induce expression of ion channels to alter neuronal activity in the mushroom body of the fly brain, and thereby regulate sleep patterns. Compared to a control group, flies that were induced to sleep more, and for longer periods of time for up to two days before infection, showed substantially greater survival rates. The flies with more sleep also showed faster and more efficient rates of clearing the bacteria from their bodies. “Again, increased sleep somehow helps to facilitate the immune response by increasing resistance to infection and survival after infection,” notes Williams.

Because the genetic factors investigated by the Penn team, such as the NFkB pathway, are preserved in mammals, the relative simplicity of the Drosophila model provides an ideal avenue to explore basic functions like sleep. “Investigators have been working on questions about sleep and immunity for more than 40 years, but by narrowing down the questions in the fly we’re now in a good position to identify potentially novel genes and mechanisms that may be involved in this process that are difficult to see in higher animals,” explains Williams.

"These studies provide new evidence of the direct and functional effects of sleep on immune response and of the underlying mechanisms at work. The take-home message from these papers is that when you get sick, you should sleep as much as you can — we now have the data that supports this idea," she concludes.

Unlocking a Mystery of Human Disease … in Space

Huntington’s disease is a grim diagnosis. A hereditary disorder with debilitating physical and cognitive symptoms, the disease usually robs adult patients of their ability to walk, balance, and speak. More than 15 years ago, researchers revealed the disorder’s likely cause—an abnormal version of the protein huntingtin; however, the mutant protein’s mechanism is poorly understood, and the disease remains untreatable.

Now, a new project led by Pamela Bjorkman, Max Delbrück Professor of Biology, will investigate whether the huntingtin protein can form crystals in microgravity aboard the International Space Station (ISS)—crystals that are crucial for understanding the molecular structure of the protein. The experiment was launched from Cape Canaveral in Florida on Friday, April 18 aboard the SpaceX CRS-3 cargo resupply mission to the ISS. On Sunday, April 20 the station’s robotic arm captured the mission’s payload, which included the proteins for Bjorkman’s experiment—which is the first Caltech experiment to take place aboard the ISS.

In the experiment, the researchers hope to grow a crystal of the huntingtin protein—the crystal would be an organized, latticelike arrangement of the protein’s molecules—which is needed to determine the molecular structure of the protein. However, molecules of the huntingtin protein tend to aggregate, or clump together, in Earth’s gravity. And this disordered arrangement makes it incredibly hard to parse the protein’s structure, says Gwen Owens, a graduate student in Bjorkman’s lab and a researcher who helped design the study.

"We need crystals for X-ray crystallography, the technique we use to study the protein, in which we shoot an X-ray through the protein crystal and analyze the organized pattern of radiation that scatters off of it," Owens says. "That pattern is what we depend on to identify the location of every carbon, nitrogen, and sulfur atom within the protein; if we shoot an X-ray beam at a clumped, aggregate protein—like huntingtin often is—we can’t get any data from it," she says.

Researchers have previously studied small fragments of crystallized huntingtin, but because of its large size and propensity to clumping, no one has ever successfully grown a crystal of the full-length protein large enough to analyze with X-ray crystallography. To understand what the protein does—and how defects in it lead to the symptoms of Huntington’s disease—the researchers need to study the full-length protein.

Looking for a solution to this problem, Owens was inspired by a few previous studies of protein formation on space shuttles and the ISS—studies suggesting that proteins can form crystals more readily in a condition of near-weightlessness called microgravity. “The previous studies looked at much simpler proteins, but we thought we could make a pretty good case that huntingtin would be an excellent candidate to study on the ISS,” Owens says.

They proposed such an experiment to the Center for the Advancement of Science in Space (CASIS), which manages U.S. research on the ISS, and it was accepted, becoming part of the first Advancing Research Knowledge, or ARK1, mission.

Because Owens and Bjorkman cannot travel with their proteins, and staff and resources are limited aboard the ISS, the crystal will be grown with a Handheld High-Density Protein Crystal Growth device—an apparatus that will allow astronauts to initiate growth of normal and mutant huntingtin protein crystals from a solution of protein molecules with just the flip of a switch.

As the crystals grow larger over a period of several months, samples will come back to Earth via the SpaceX CRS-4 return mission. The results of the experiment are scheduled to drop into the ocean just off the coast of Southern California—along with the rest of the return cargo—sometime this fall. At that point, Owens will finally be able to analyze the proteins.

"Our ideal result would be to have large crystals of the normal and mutant huntingtin proteins right away—on the first try," she says. After analyzing crystals of the full-length protein with X-ray crystallography, the researchers could finally determine huntingtin’s structure—information that will be crucial to developing treatments for Huntington’s disease.

Physicists push new Parkinson’s treatment toward clinical trials

The most effective way to tackle debilitating diseases is to punch them at the start and keep them from growing.

Research at Michigan State University, published in the Journal of Biological Chemistry, shows that a small “molecular tweezer” keeps proteins from clumping, or aggregating, the first step of neurological disorders such as Parkinson’s disease, Alzheimer’s disease and Huntington’s disease.

The results are pushing the promising molecule toward clinical trials and actually becoming a new drug, said Lisa Lapidus, MSU associate professor of physics and astronomy and co-author of the paper.

“By the time patients show symptoms and go to a doctor, aggregation already has a stronghold in their brains,” she said. “In the lab, however, we can see the first steps, at the very place where the drugs could be the most effective. This could be a strong model for fighting Parkinson’s and other diseases that involve neurotoxic aggregation.”

Lapidus’ lab uses lasers to study the speed of protein reconfiguration before aggregation, a technique Lapidus pioneered. Proteins are chains of amino acids that do most of the work in cells. Scientists understand protein structure, but they don’t know how they are built – a process known as folding.

Lapidus’ lab has shed light on the process by correlating the speed at which an unfolded protein changes shape, or reconfigures, with its tendency to clump or bind with other proteins. If reconfiguration is much faster or slower than the speed at which proteins bump into each other, aggregation is slow, but if reconfiguration is the same speed, aggregation is fast.

Srabasti Acharya, lead author and doctoral candidate in Lapidus’ lab, tested the molecule, CLR01, which was patented jointly by researchers at the University of Duisburg-Essen (Germany) and UCLA. CLR01 binds to the protein and prevents aggregation by speeding up reconfiguration. It’s like a claw that attaches to the amino acid lysine, which is part of the protein.

This work was preceded by Lapidus’ research involving the spice curcumin. While the spice molecules put the researchers on a solid path, the molecules weren’t viable drug candidates because they cannot cross the blood-brain barrier, or BBB, the filter that controls what chemicals reach the brain.

It’s the BBB, in fact, that disproves the notion that people should simply eat more spicy food to stave off Parkinson’s disease.

Spicy misconceptions notwithstanding, CLR01 mimics curcumin molecules’ ability to prevent aggregation. But unlike the spice, CLR01 can crossover the BBB and treat its targeted site. Not only do they go to the right place, but CLR01 molecules also work even better because they speed up reconfiguration even more than curcumin. Additionally Acharya showed that CLR01 slows the first step of aggregation, and the results from the study map out a clear road map for moving the drug to clinical trials.

Hearing about a nontraditional physics lab that was advancing medicine is what brought Acharya to work with Lapidus.

“I knew I wanted to study physics when I came to MSU, but when I heard Dr. Lapidus’ presentation during orientation, I knew this is what I wanted to do,” Acharya said. “We are using physics to better understand biology to help cure actual diseases.”

To help move the research to the next phase, Gal Bitan, co-author and professor at UCLA, is using crowdsourcing to raise funds for the clinical trials. Log on to the indiegogo.com website for more information.

(Image caption: Researchers have identified a new class of compounds—pharmacologic chaperones—that can stabilize the retromer protein complex (the blue and orange structure shows part of the complex). Retromer plays a vital role in keeping amyloid precursor from being cleaved and producing the toxic byproduct amyloid beta, which contributes to the development of Alzheimer’s. The study found that when the chaperone named R55 (the multicolored molecule) was added to neurons in cell culture, it bound to and stabilized retromer, increasing retromer levels and lowering amyloid-beta levels. Credit: Nature Chemical Biology and lab of Scott A. Small, MD/Columbia University Medical Center.)

“Chaperone” Compounds Offer New Approach to Alzheimer’s Treatment

A team of researchers from Columbia University Medical Center (CUMC), Weill Cornell Medical College, and Brandeis University has devised a wholly new approach to the treatment of Alzheimer’s disease involving the so-called retromer protein complex. Retromer plays a vital role in neurons, steering amyloid precursor protein (APP) away from a region of the cell where APP is cleaved, creating the potentially toxic byproduct amyloid-beta, which is thought to contribute to the development of Alzheimer’s.

Using computer-based virtual screening, the researchers identified a new class of compounds, called pharmacologic chaperones, that can significantly increase retromer levels and decrease amyloid-beta levels in cultured hippocampal neurons, without apparent cell toxicity. The study was published today in the online edition of the journal Nature Chemical Biology.

“Our findings identify a novel class of pharmacologic agents that are designed to treat neurologic disease by targeting a defect in cell biology, rather than a defect in molecular biology,” said Scott Small, MD, the Boris and Rose Katz Professor of Neurology, Director of the Alzheimer’s Disease Research Center in the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain at CUMC, and a senior author of the paper. “This approach may prove to be safer and more effective than conventional treatments for neurologic disease, which typically target single proteins.”

In 2005, Dr. Small and his colleagues showed that retromer is deficient in the brains of patients with Alzheimer’s disease. In cultured neurons, they showed that reducing retromer levels raised amyloid-beta levels, while increasing retromer levels had the opposite effect. Three years later, he showed that reducing retromer had the same effect in animal models, and that these changes led to Alzheimer’s-like symptoms. Retromer abnormalities have also been observed in Parkinson’s disease.

In discussions at a scientific meeting, Dr. Small and co-senior authors Gregory A. Petsko, DPhil, Arthur J. Mahon Professor of Neurology and Neuroscience in the Feil Family Brain and Mind Research Institute and Director of the Helen and Robert Appel Alzheimer’s Disease Research Institute at Weill Cornell Medical College, and Dagmar Ringe, PhD, Harold and Bernice Davis Professor in the Departments of Biochemistry and Chemistry and in the Rosenstiel Basic Medical Sciences Research Center at Brandeis University, began wondering if there was a way to stabilize retromer (that is, prevent it from degrading) and bolster its function. “The idea that it would be beneficial to protect a protein’s structure is one that nature figured out a long time ago,” said Dr. Petsko. “We’re just learning how to do that pharmacologically.”

Other researchers had already determined retromer’s three-dimensional structure. “Our challenge was to find small molecules—or pharmacologic chaperones—that could bind to retromer’s weak point and stabilize the whole protein complex,” said Dr. Ringe.

This was accomplished through computerized virtual, or in silico, screening of known chemical compounds, simulating how the compounds might dock with the retromer protein complex. (In conventional screening, compounds are physically tested to see whether they interact with the intended target, a costlier and lengthier process.) The screening identified 100 potential retromer-stabilizing candidates, 24 of which showed particular promise. Of those, one compound, called R55, was found to significantly increase the stability of retromer when the complex was subjected to heat stress.

The researchers then looked at how R55 affected neurons of the hippocampus, a key brain structure involved in learning and memory. “One concern was that this compound would be toxic,” said Dr. Diego Berman, assistant professor of clinical pathology and cell biology at CUMC and a lead author. “But R55 was found to be relatively non-toxic in mouse neurons in cell culture.”

More important, a subsequent experiment showed that the compound significantly increased retromer levels and decreased amyloid-beta levels in cultured neurons taken from healthy mice and from a mouse model of Alzheimer’s. The researchers are currently testing the clinical effects of R55 in the actual mouse model .

“The odds that this particular compound will pan out are low, but the paper provides a proof of principle for the efficacy of retromer pharmacologic chaperones,” said Dr. Petsko. “While we’re testing R55, we will be developing chemical analogs in the hope of finding compounds that are more effective.”