Posts tagged proteins
Posts tagged proteins
Scientists are a step closer to understanding how some of the brain’s 100 billion nerve cells co-ordinate their communication. The study is published in the journal Cell Reports.
The University of Bristol research team investigated some of the chemical processes that underpin how brain cells co-ordinate their communication. Defects in this communication are associated with disorders such as epilepsy, autism and schizophrenia, and therefore these findings could lead to the development of novel neurological therapies.
Neurons in the brain communicate with each other using chemicals called neurotransmitters. This release of neurotransmitter from neurons is tightly controlled by many different proteins inside the neuron. These proteins interact with each other to ensure that neurotransmitter is only released when necessary. Although the mechanisms that control this release have been extensively studied, the processes that co-ordinate how and when the component proteins interact is not fully understood.
The School of Biochemistry researchers have now discovered that one of these proteins called ‘RIM1α’ is modified by a small protein named ‘SUMO’ which attaches to a specific region in RIM1α. This process acts as a ‘molecular switch’ which is required for normal neurotransmitter release.
Jeremy Henley, Professor of Molecular Neuroscience in the University’s Faculty of Medical and Veterinary Sciences and the study’s lead author, said: “These findings are important as they show that SUMO modification plays a vital and previously unsuspected role in normal brain function.”
The research builds on the team’s earlier work that identified a group of proteins in the brain responsible for protecting nerve cells from damage and could be used in future for therapies for stroke and other brain diseases.
Why can the symptoms of Parkinson’s disease vary so greatly from one patient to another? A consortium of researchers, headed by a team from the Laboratoire CNRS d’Enzymologie et Biochimie Structurales, is well on the way to providing an explanation. Parkinson’s disease is caused by a protein known as alpha-synuclein, which forms aggregates within neurons, killing them eventually. The researchers have succeeded in characterizing and producing two different types of alpha-synuclein aggregates. Better still, they have shown that one of these two forms is much more toxic than the other and has a greater capacity to invade neurons. This discovery takes account, at the molecular scale, of the existence of alpha-synuclein accumulation profiles that differ from one patient to the next. These results, published on October 10 in Nature Communications, represent a notable advance in our understanding of Parkinson’s disease and pave the way for the development of specific therapies targeting each form of the disease.
Parkinson’s disease, which is the second most frequent neurodegenerative disease after Alzheimer’s, affects some 150,000 people in France. According to those suffering from the disease, it can manifest itself in the form of uncontrollable shaking (in 60% of patients) or by less-localized symptoms such as depression, behavioral and motor disorders. These differences in symptoms point to different forms of Parkinson’s disease.
This condition, for which no curative treatment currently exists, is caused by the aggregation in the form of fibrillar deposits of alpha-synuclein, a protein that is naturally abundant at neuron junctions. These misfolded alpha-synuclein aggregates propagate between neurons. When they invade a new neuron, they are capable of recruiting normal alpha-synuclein and adding it to the deposit. For this reason, many researchers advocate that the alpha-synuclein of the aggregates should be considered as an infectious protein, in other words a prion. Highly toxic, the alpha-synuclein deposits end up by triggering a process of apoptosis, i.e. cell death.
The researchers have shown that there is not just one single type of aggregate. They succeeded in producing two types of aggregate that only differ in how the protein stacks up. At the millionth of a millimeter scale, the first form of aggregate resembles spaghetti, whereas the second form is long and flat, recalling the shape of wider pasta such as linguine. The team of scientists then tried to determine whether these structural differences result in functional differences. To find out, they placed the two types of aggregates in contact with neuronal cells in culture. They discovered that the capacity of the “spaghetti” form to bind to and penetrate cells is notably greater than that of the “linguine” form. The “spaghetti” form is also considerably more toxic and rapidly kills the infected cells. This form has shown itself to be capable of resisting the cell mechanisms responsible for eliminating it, whereas the “linguine” form is, to a certain extent, controlled by the cell.
The researchers are convinced that the existence of at least two forms of alpha-synuclein aggregates explains why doctors are faced with different Parkinson’s diseases depending on the patient. Experiments on mice are currently underway to confirm this hypothesis. Furthermore, the scientists consider that analysis of the type of aggregate could lead to an efficient diagnosis method, which would make it possible in particular to assess the virulence of the disease for each patient. Finally, they hope that by refining the characterization of the structure of the aggregates, it will be possible to develop targeted therapeutic strategies for each variant in order to slow down the propagation of abnormal alpha-synuclein within the brain.
The green spots above are clumps of protein inside yeast cells that are deficient in both zinc and a protein that prevents clumping. Research by Colin MacDiarmid and David Eide is exploring how a shortage of zinc can contribute to diseases. Photo: Colin MacDiarmid and David Eide/Journal of Biological Chemistry
Scientists at UW-Madison have made a discovery that, if replicated in humans, suggests a shortage of zinc may contribute to diseases like Alzheimer’s and Parkinson’s, which have been linked to defective proteins clumping together in the brain.
With proteins, shape is everything. The correct shape allows some proteins to ferry atoms or molecules about a cell, others to provide essential cellular scaffolding or identify invading bacteria for attack. When proteins lose their shape due to high temperature or chemical damage, they stop working and can clump together — a hallmark of Parkinson’s and Alzheimer’s.
The UW researchers have discovered another stress that decreases protein stability and causes clumping: a shortage of zinc, an essential metal nutrient.
Zinc ions play a key role in creating and holding proteins in the correct shape. In a study just published in the online Journal of Biological Chemistry, Colin MacDiarmid and David Eide show that the gene Tsa1 creates “protein chaperones” that prevent clumping of proteins in cells with a zinc shortage. By holding proteins in solution, Tsa1 prevents damage that can otherwise lead to cell death.
For simplicity, the researchers studied the system in yeast — a single-celled fungus. Yeast can adapt to both shortages and excesses of zinc, says MacDiarmid, an associate scientist. “Zinc is an essential nutrient but if there’s too much, it’s toxic. The issue for the cell is to find enough zinc to grow and support all its functions, while at the same time not accumulating so much that it kills the cell.”
Cells that are low in zinc also produce proteins that counter the resulting stress, including one called Tsa1.
The researchers already knew that Tsa1 could reduce the level of harmful oxidants in cells that are short of zinc. Tsa1, MacDiarmid says, “is really a two-part protein. It can get rid of dangerous reactive oxygen species that damage proteins, but it also has this totally distinct chaperone function that protects proteins from aggregating. We found that the chaperone function was the more important of the two.”
"In yeast, if a cell is deficient in zinc, the proteins can mis-fold, and Tsa1 is needed to keep the proteins intact so they can function," says Eide, a professor of nutritional science. "If you don’t have zinc, and you don’t have Tsa1, the proteins will glom together into big aggregations that are either toxic by themselves, or toxic because the proteins are not doing what they are supposed to do. Either way, you end up killing the cell."
While the medical implications remain to be explored, there are clear similarities between yeast and human cells. “Zinc is needed by all cells, all organisms, it’s not just for steel roofs, nails and trashcans,” Eide says. “The global extent of zinc deficiency is debated, but diets that are high in whole grains and low in meat could lead to deficiency.”
If low zinc supply has the same effect on human cells as on yeast, zinc deficiency might contribute to human diseases that are associated with a build-up of “junked” proteins, such as Parkinson’s and Alzheimer’s. Eide says a similar protective system to Tsa1 also exists in animals, and the research group plans to move ahead by studying that system in human cell culture.
In a landmark discovery, the final piece in the puzzle of understanding how the brain circuitry vital to normal fertility in humans and other mammals operates has been put together by researchers at New Zealand’s University of Otago.
Their new findings, which appear in the leading international journal Nature Communications, will be critical to enabling the design of novel therapies for infertile couples as well as new forms of contraception.
The research team, led by Otago neuroscientist Professor Allan Herbison, have discovered the key cellular location of signalling between a small protein known as kisspeptin* and its receptor, called Gpr54. Kisspeptin had earlier been found to be crucial for fertility in humans, and in a subsequent major breakthrough Professor Herbison showed that this molecule was also vital for ovulation to occur.
In the latest research, Professor Herbison and colleagues at Otago and Heidelberg University, Germany, provide conclusive evidence that the kisspeptin-Gpr54 signalling occurs in a small population of nerve cells in the brain called gonadotropin-releasing hormone (GnRH) neurons.
Using state-of-the-art techniques, the researchers studied mice that lacked Gpr54 receptors in only their GnRH neurons and found that these did not undergo puberty and were infertile. They then showed that infertile mice could be rescued back to completely normal fertility by inserting the Gpr54 gene into just the GnRH neurons.
Professor Herbison says the findings represent a substantial step forward in enabling new treatments for infertility and new classes of contraceptives to be developed.
"Infertility is a major issue affecting millions of people worldwide. It’s currently estimated that up to 20 per cent of New Zealand couples are infertile, and it is thought that up to one-third of all cases of infertility in women involve disorders in the area of brain circuitry we are studying.
"Our new understanding of the exact mechanism by which kisspeptin acts as a master controller of reproduction is an exciting breakthrough which opens up avenues for tackling what is often a very heart-breaking health issue. Through detailing this mechanism we now have a key chemical switch to which drugs can be precisely targeted," Professor Herbison says.
As well as the findings’ benefits for advancing new therapies for infertility and approaches to controlling fertility, they suggest that targeting kisspeptin may be valuable in treating diseases such as prostate cancer that are influenced by sex steroid hormone levels in the blood, he says.
Professor Herbison noted that the research findings represent a long-standing collaborative effort with the laboratory of Professor Gunther Schutz at Heidelberg University, Germany.
Professor Herbison is Director of the University’s Centre for Neuroendocrinology, which is the world-leading research centre investigating how the brain controls fertility.
"We are delighted to have published this work in one of the top scientific journals and also to be able to maintain the leading role of New Zealand researchers in understanding fertility control," he says.
Scientists at the University of Alabama at Birmingham have identified a molecular pathway that seems to contribute to the ability of malignant glioma cells in a brain tumor to spread and invade previously healthy brain tissue. Researchers said the findings, published Sept. 19, 2013, in the journal PLOS ONE, provide new drug-discovery targets to rein in the ability of these cells to move.
Gliomas account for about a third of brain tumors, and survival rates are poor; only about half of the 10,000 Americans diagnosed with malignant glioma survive the first year, and only about one quarter survive for two years.
“Malignant gliomas are notorious, not only because of their resistance to conventional chemotherapy and radiation therapy, but also for their ability to invade the surrounding brain, thus causing neurological impairment and death,” said Hassan Fathallah-Shaykh, M.D., Ph.D., associate professor in the UAB Department of Neurology. “Brain invasion, a hallmark of gliomas, also helps glioma cells evade therapeutic strategies.”
Fathallah-Shaykh said there is a great deal of interest among scientists in the idea that a low-oxygen environment induces glioma cells to react with aggressive movement, migration and brain invasion. A relatively new cancer strategy to shrink tumors is to cut off the tumor’s blood supply – and thus its oxygen source – through the use of anti-angiogenesis drugs. Angiogenesis is the process of making new blood vessels.
“Stop angiogenesis and you shut off a tumor’s blood and oxygen supply, denying it the components it needs to grow,” said Fathallah-Shaykh. “Drugs that stop angiogenesis are believed to create a kind of killing field. This study identified four glioma cell lines that dramatically increased their motility when subjected to a low-oxygen environment – in effect escaping the killing field to create a new colony elsewhere in the brain.”
Fathallah-Shaykh and his team then identified two proteins that form a pathway linking low oxygen, or hypoxia, to increased motility.
“We identified a signaling protein that is activated by hypoxia called Src,” said Fathallah-Shaykh. “We also identified a downstream protein called neural Wiskott-Aldrich syndrome protein (N-WASP), which is regulated by Src in the cell lines with increased motility.”
The researchers then used protein inhibitors to shut off Src and N-WASP. When either protein was inhibited, low oxygen lost its ability to augment cell movement.
“These findings indicate that Src, N-WASP and the linkage between them – which is something we don’t fully understand yet – are key targets for drugs that would interfere with the ability of a cell to move.” said Fathallah-Shaykh. “If we can stop them from moving, then techniques such as anti-angiogenesis should be much more effective. Anti-motility drugs could be a key component in treating gliomas in the years to come.”
Specific protein found in nearly all high-grade meningiomas
Johns Hopkins researchers say they have found a specific protein in nearly 100 percent of high-grade meningiomas — the most common form of brain tumor — suggesting a new target for therapies for a cancer that does not respond to current chemotherapy.
Importantly, the investigators say, the protein — NY-ESO-1 — is already at the center of a clinical trial underway at the National Cancer Institute. That trial is designed to activate the immune systems of patients with other types of tumors that express the protein, training the body to attack the cancer and eradicate it.
“Typically there is a lag time before a laboratory finding like this leads to a clear path forward to help patients. But in this case, since there is already a clinical trial underway, we have a chance of helping people sooner rather than later,” says Gregory J. Riggins, M.D., Ph.D., a professor of neurosurgery at the Johns Hopkins University School of Medicine and the senior author of the study published online in the journal Cancer Immunology Research.
In the NCI trial, NY-ESO-1 is found in a much smaller percentage of tumors than Riggins and his team found in high-grade meningioma, suggesting that for the brain cancer, the target would be potentially more significant.
Most low-grade meningiomas located in easy-to-reach locations can be treated successfully with surgery and radiation. But more atypical, higher-grade tumors are much more difficult to eradicate and are deadlier.
Riggins and his colleagues, including Gilson S. Baia, Ph.D., and Otavia L. Caballero, M.D., Ph.D., set out to find cancer antigens in meningioma. Cancer antigens are proteins expressed in tumors but not in healthy cells, making them good targets for chemical or immune system attack. They looked specifically at 37 cancer/testis (CT) genes, which are not found in normal cells in the body except in germ cells and cells cordoned off in the testicles or, in some cases, ovaries.
CT genes are activated, however, in various cancers. While they are seen as “foreign” by the body’s immune system, they are often locked behind the sophisticated defense system that cancers use to evade attack by immune cells. Finding a way to get the immune system to see these protein antigens, however, could allow for the body to recognize the invasion and go after the cancer cells. Various approaches are being used to do that, including vaccines and a system involving removing T-cells from the body and reprogramming them before returning them and setting them loose on the cancer cells.
The Johns Hopkins researchers took tissue from 18 different meningioma samples, removed the genetic material and protein and checked at what levels the 37 different genes were turned on. The gene that is the blueprint for the NY-ESO-1 protein was turned on more frequently than any other, in five of the 18 patient samples.
Then they analyzed NY-ESO-1 expression in a larger group of 110 meningioma tissue samples. They found NY-ESO-1 in 108 of them. The more expression in the sample, they also determined, the higher the tumor grade. The higher levels of NY-ESO-1 expressed also correlated with significantly lower disease-free and overall survival rates in the patients they came from.
The NCI trial originally began in melanoma patients. NY-ESO-1 is expressed in roughly one-third of melanomas as well as approximately one-third of breast, prostate, lung, ovarian, thyroid and bladder cancers, as well as sarcomas. Riggins and his team did not find the protein in glioblastoma, the deadliest form of brain cancer.
He calls the fact that the NCI trial could now include meningioma patients a “stroke of luck.”
“If that therapy did not exist, there would be a lot of work that would have to be done to convince people to pursue this,” Riggins says. “Our goal is to get something that works to the patients. This puts us well on our way.”
Princeton University researchers have created “souped up” versions of the calcium-sensitive proteins that for the past decade or so have given scientists an unparalleled view and understanding of brain-cell communication.
Reported July 18 in the journal Nature Communications, the enhanced proteins developed at Princeton respond more quickly to changes in neuron activity, and can be customized to react to different, faster rates of neuron activity. Together, these characteristics would give scientists a more precise and comprehensive view of neuron activity.
The researchers sought to improve the function of proteins known as green fluorescent protein/calmodulin protein (GCaMP) sensors, an amalgam of various natural proteins that are a popular form of sensor proteins known as genetically encoded calcium indicators, or GECIs. Once introduced into the brain via the bloodstream, GCaMPs react to the various calcium ions involved in cell activity by glowing fluorescent green. Scientists use this fluorescence to trace the path of neural signals throughout the brain as they happen.
GCaMPs and other GECIs have been invaluable to neuroscience, said corresponding author Samuel Wang, a Princeton associate professor of molecular biology and the Princeton Neuroscience Institute. Scientists have used the sensors to observe brain signals in real time, and to delve into previously obscure neural networks such as those in the cerebellum. GECIs are necessary for the BRAIN Initiative President Barack Obama announced in April, Wang said. The estimated $3 billion project to map the activity of every neuron in the human brain cannot be done with traditional methods, such as probes that attach to the surface of the brain. “There is no possible way to complete that project with electrodes, so you have to do it with other tools — GECIs are those tools,” he said.
Despite their value, however, the proteins are still limited when it comes to keeping up with the fast-paced, high-voltage ways of brain cells, and various research groups have attempted to address these limitations over the years, Wang said.
“GCaMPs have made significant contributions to neuroscience so far, but there have been some limits and researchers are running up against those limits,” Wang said.
One shortcoming is that GCaMPs are about one-tenth of a second slower than neurons, which can fire hundreds of times per second, Wang said. The proteins activate after neural signals begin, and mark the end of a signal when brain cells have (by neuronal terms) long since moved on to something else, Wang said. A second current limitation is that GCaMPs can only bind to four calcium ions at a time. Higher rates of cell activity cannot be fully explored because GCaMPs fill up quickly on the accompanying rush of calcium.
The Princeton GCaMPs respond more quickly to changes in calcium so that changes in neural activity are seen more immediately, Wang said. By making the sensors a bit more sensitive and fragile — the proteins bond more quickly with calcium and come apart more readily to stop glowing when calcium is removed — the researchers whittled down the roughly 20 millisecond response time of existing GCaMPs to about 10 milliseconds, Wang said.
The researchers also tweaked certain GCaMPs to be sensitive to different types of calcium ion concentrations, meaning that high rates of neural activity can be better explored. “Each probe is sensitive to one range or another, but when we put them together they make a nice choir,” Wang said.
The researchers’ work also revealed the location of a “bottleneck” in GCaMPs that occurs when calcium concentration is high, which poses a third limitation of the existing sensors, Wang said. “Now that we know where that bottle neck is, we think we can design the next generation of proteins to get around it,” Wang said. “We think if we open up that bottleneck, we can get a probe that responds to neuronal signals in one millisecond.”
The faster protein that the Princeton researchers developed could pair with work in other laboratories to improve other areas of GCaMP function, Wang said. For instance, a research group out of the Howard Hughes Medical Institute reported in Nature July 17 that it developed a GCaMP with a brighter fluorescence. Such improvements on existing sensors gradually open up more of the brain to exploration and understanding, said Wang, adding that the Princeton researchers will soon introduce their sensor into fly and mammalian brains.
“At some level, what we’ve done is like taking apart an engine, lubing up the parts and putting it back together. We took what was the best version of the protein at the time and made changes to the letter code of the protein,” Wang said. “We want to watch the whole symphony of thousands of neurons do their thing, and we think this variant of GCaMPs will help us do that better than anyone else has.”
Recycling is not only good for the environment, it’s good for the brain. A study using rat cells indicates that quickly clearing out defective proteins in the brain may prevent loss of brain cells.
Results of a study in Nature Chemical Biology suggest that the speed at which damaged proteins are cleared from neurons may affect cell survival and may explain why some cells are targeted for death in neurodegenerative disorders. The research was supported by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health.
One of the mysteries surrounding neurodegenerative diseases is why some nerve cells are marked for destruction whereas their neighbors are spared. It is especially puzzling because the protein thought to be responsible for cell death is found throughout the brain in many of these diseases, yet only certain brain areas or cell types are affected.
In Huntington’s disease and many other neurodegenerative disorders, proteins that are misfolded (have abnormal shapes), accumulate inside and around neurons and are thought to damage and kill nearby brain cells. Normally, cells sense the presence of malformed proteins and clear them away before they do any damage. This is regulated by a process called proteostasis, which the cell uses to control protein levels and quality.
In the study, Andrey S. Tsvetkov and his colleagues from the University of California, San Francisco (UCSF) and Duke University, Durham, N.C., showed that differences in the rate of proteostasis may be the clue to understanding why certain nerve cells die in Huntington’s, a genetic brain disorder that leads to uncontrolled movements and death.
To measure how quickly proteins are cleared away from cells, the researchers developed a new technique called optical pulse-labeling, allowing them to follow specific proteins in individual living cells. To test the technique, they grew brain cells in a dish and turned on Dendra2, a photoswitchable protein that glows from green to red after being hit by a specific type of light. Both the red and green glow can be followed until the protein is cleared from the cell. In this way, the researchers could track the lifetime of newly produced Dendra2 (which glows green) and older, photoswitched Dendra2 (which glows red) until the protein was cleared away from the cell.
"Before this new technique, there was no way to look at individual neurons and their capacity to handle proteins. This method provides a real-time readout of how fast proteins are turned over in neurons and gives us a look at some of the mechanisms involved," said Margaret Sutherland, Ph.D., program director at NINDS.
The researchers followed Dendra2 in a set of striatal neurons, which they obtained from rats. The striatum (where striatal neurons are located) is a brain region involved in a number of brain functions including planning movements and is most heavily affected in Huntington’s disease. They discovered that the mean lifetime of the protein (how long it remained in the cell) varied three- to fourfold, suggesting that rates of proteostasis were different among individual neurons. In other words, some cells may process an identical protein much slower than others.
Then, the researchers investigated how cells deal with different forms of huntingtin, the protein involved in Huntington’s. They fused Dendra2 on the end of a normal or mutant version of huntingtin to track how long the protein remained in cells. The mutant version of huntingtin is longer, and contains three building blocks of the protein repeated an abnormal number of times. These repeats in huntingtin are what cause it to misfold, eventually leading to neuron death and the symptoms of the disease. As predicted, in their experiments, the mutant form of huntingtin caused more rat cells to die than did the normal form of the protein.
The researchers found that the amount of time the mutant protein remained in the cell predicted neuronal survival: shorter mean lifetimes of mutant huntingtin were associated with longer neuronal survival. A shorter mean lifetime indicates that a protein does not remain in the cell for a long time, and that proteostasis is working effectively to clear it away. This suggests that improving proteostasis in Huntington’s brains may improve neuronal survival.
To test this idea, the researchers activated Nrf2, a protein known to regulate protein processing. When Nrf2 was turned on, the mean lifetime of huntingtin was shortened, and the neuron lived longer.
"Nrf2 seems like a potentially exciting therapeutic target. It is profoundly neuroprotective in our Huntington’s model and it accelerates the clearance of mutant huntingtin," said Dr. Steven Finkbeiner, senior author of the paper.
Although both striatal and cortical neurons are affected by mutant huntingtin, striatal neurons are more susceptible to cell death. The investigators found that striatal neurons were not as effective as cortical neurons in recognizing and clearing away the mutant protein.
"One surprising finding from these experiments was the significance of single cells’ ability to clear mutant huntingtin. It turned out that this ability largely predicted their susceptibility, whether that neuron came from the most vulnerable region of the brain – the striatum, or the cortex, which is less vulnerable," said Dr. Finkbeiner. The findings indicate that the toxicity of the damaged proteins may cause neurodegeneration by interfering with the proteostasis system, affecting how quickly they are cleared from neurons.
"The results should remind us that focusing on the disease-causing proteins is only one side of the coin. To understand why some cells die and others are spared, we may need to recognize that there are major, largely unrecognized cell-specific differences in the ways that various types of neurons recognize and dispose of disease-causing proteins," continued Dr. Finkbeiner.
The researchers explored potential mechanisms behind differences in proteostasis. One way that cells normally get rid of proteins is through autophagy — a process in which proteins are packed up into spheres and then broken down. Results in this paper suggested that neurons increased the rate of autophagy when they sensed that the mutant form of huntingtin was accumulating, indicating the autophagy system may be a drug target.
"These findings provide evidence that our brains have powerful coping mechanisms to deal with disease-causing proteins. The fact that some of these diseases don’t cause symptoms we can detect until the fourth or fifth decade of life, even when the gene has been present since birth, suggests that those mechanisms are pretty good," said Dr. Finkbeiner.
Future research is needed to determine why coping mechanisms fail as brain cells age and how neurons in the healthy brain keep the proteostasis system functioning.
"New research methods that help us understand how individual neurons function will increase our understanding of central nervous system disorders and help identify new treatments. It is critical to continue working on the methods such as those described in this paper," said Dr. Sutherland.
A rare, inherited form of mental retardation has led scientists at Washington University School of Medicine in St. Louis to three important “travel agents” at work in the developing brain.
The agents — two individual proteins and a tightly bound cluster of four additional proteins — make it possible for brain neurons to travel from the area where they are born to other brain regions where they will reside permanently and integrate into neuronal circuits. Inhibiting any of these proteins in embryonic mice reduces the ability of neurons, which process and transmit information, to reach their final destinations and, presumably, to hardwire the brain.
“That kind of misplacement of brain cells is likely to seriously disrupt mental functions,” said Azad Bonni, MD, PhD, the Edison Professor and chairman of the Department of Anatomy and Neurobiology. “This is just one of many ways that brain development can go awry. To understand intellectual disability and develop treatments, we need to understand the many problems that can arise as the brain develops and its circuitry is established.”
The results appeared June 19 in Neuron.
The new work began as an inquiry into PHF6, a gene that is mutated in patients with Börjeson-Forssman-Lehmann syndrome. This disorder causes mental retardation, developmental delays and skeletal abnormalities. More than a decade ago, scientists identified a link between the condition and PHF6, but they did not know what the gene did in the brain.
Bonni’s laboratory added green fluorescent protein to brain cells to track their development and movement in embryonic mice. Then the researchers inhibited PHF6 in some mice.
In normal mice, as expected, brain neurons migrated from the ventricular zone, where they were born, to the cortical plate, the precursor site of the cerebral cortex. In the mature brain, the cerebral cortex is responsible for higher brain functions such as processing of sensory data, attention and decision-making. In mice whose brain cells lacked PHF6, many brain cells either stayed in the ventricular zone or only completed part of their journey.
In a series of additional experiments, Bonni’s research group showed that the PHF6 protein operates in the nucleus of brain neurons, the command center of the cell. The scientists found that the PHF6 protein interacts with the PAF1 complex, a tightly bound cluster of four proteins that regulates programs of gene expression. This cluster then turns on a cell surface protein called neuroglycan C in brain neurons.
If any of these factors were inhibited, mouse brain neurons were unable to complete their normal migration. The researchers could “rescue” the neurons by restoring the missing protein, allowing the cells to complete their journey.
Disrupting proper brain structure and organization may not be the only problem caused by the PHF6 mutation. A portion of patients with Börjeson-Forssman-Lehmann syndrome also have epilepsy.
In tests in mice, Bonni’s group found that the misplaced brain neurons were more excitable. This might result from changes in the activity of other proteins regulated by PHF6 and could make the brain more susceptible to seizures.
The researchers also learned that increasing the production of neuroglycan C in brain neurons overcomes the harmful effects of PHF6 loss on the migration of neurons.
“Cell surface proteins such as neuroglycan C are in good position to help cells move through their environment,” Bonni said. “The protein’s position on the cell surface of neurons also one day might make it an accessible target for drug treatments for developmental cognitive disorders.”
Bonni suspects there might be additional problems in brain cells that develop without normal PHF6 and that errors in the gene might even impair function in neurons that make it to their final destinations. Further studies are underway.
A new study led by researchers at The Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute (OSUCCC–James) has identified a biochemical pathway in cancer stem cells that is essential for promoting head and neck cancer.
The study shows that a protein called Nanog, which is normally active in embryonic stem cells, promotes the growth of cancer stem cells in head and neck cancer. The findings provide information essential for designing novel targeted drugs that might improve the treatment of head and neck cancer.
Normally, Nanog helps healthy embryonic stem cells maintain their undifferentiated, uncommitted (i.e., pluripotent) state. But recent evidence suggests that Nanog promotes tumor growth by stimulating the proliferation of cancer stem cells.
“This study defines a signaling axis that is essential for head and neck cancer progression, and our findings show that this axis may be disrupted at three key steps,” says principal investigator Quintin Pan, PhD, associate professor of otolaryngology at the OSUCCC – James. “Targeted drugs that are designed to inhibit any or all of these three steps might greatly improve the treatment of head and neck cancer.”
The findings were published in a recent issue of the journal Oncogene.
Specifically, the study shows that an enzyme called “protein kinase C-epsilon” (PKCepsilon) adds energy-packing phosphate groups to the Nanog molecule. This phosphorylation of Nanog stabilizes and activates the molecule.
It also triggers a series of events: Two Nanog molecules bind together, and these are joined by a third “co-activating” molecule called p300. This molecular complex then binds to the promoter region of a gene called Bmi1, an event that increases the expression of the gene. This, in turn, stimulates proliferation of cancer stem cells.
“Our work shows that the PKCepsilon/Nanog/Bmi1 signaling axis is essential to promote head and neck cancer,” Pan says. “And it provides initial evidence that the development of inhibitors that block critical points in this axis might yield a potent collection of targeted anti-cancer therapeutics that could be valuable for the treatment of head and neck cancer.”
(Image: Gray’s Anatomy of the Human Body)