Rebuilding the Brain’s Circuitry

15 12 2011

Neuron transplants have repaired brain circuitry and substantially normalized function in mice with a brain disorder, an advance indicating that key areas of the mammalian brain are more reparable than was widely believed.

Collaborators from Harvard University, Massachusetts General Hospital, Beth Israel Deaconess Medical Center (BIDMC) and Harvard Medical School (HMS) transplanted normally functioning embryonic neurons at a carefully selected stage of their development into the hypothalamus of mice unable to respond to leptin, a hormone that regulates metabolism and controls body weight. These mutant mice usually become morbidly obese, but the neuron transplants repaired defective brain circuits, enabling them to respond to leptin and thus experience substantially less weight gain.

Repair at the cellular-level of the hypothalamus—a critical and complex region of the brain that regulates phenomena such as hunger, metabolism, body temperature, and basic behaviors such as sex and aggression—indicates the possibility of new therapeutic approaches to even higher level conditions such as spinal cord injury, autism, epilepsy, ALS  (Lou Gehrig’s disease), Parkinson’s disease, and Huntington’s disease.

“The next step for us is to ask parallel questions of other parts of the brain and spinal cord, those involved in ALS and with spinal cord injuries. In these cases, can we rebuild circuitry in the mammalian brain? I suspect that we can,” said Jeffrey Macklis. Photo by Matt Craig, Harvard Staff Photographer

“There are only two areas of the brain that are known to normally undergo ongoing large-scale neuronal replacement during adulthood on a cellular level—so-called ‘neurogenesis,’ or the birth of new neurons—the olfactory bulb and the subregion of the hippocampus called the dentate gyrus, with emerging evidence of lower level ongoing neurogenesis in the hypothalamus,” said Jeffrey Macklis, Harvard University professor of stem cell and regenerative biology and HMS professor of neurology at Massachusetts General Hospital, and one of three corresponding authors on the paper. “The neurons that are added during adulthood in both regions are generally smallish and are thought to act a bit like volume controls over specific signaling.  Here we’ve rewired a high-level system of brain circuitry that does not naturally experience neurogenesis, and this restored substantially normal function.”

The two other senior authors on the paper are Jeffrey Flier, dean of Harvard Medical School, and Matthew Anderson, HMS professor of pathology at BIDMC.

The findings are to appear Nov. 25 in Science.

In 2005, Jeffrey Flier, then the George C. Reisman professor of medicine at BIDMC, published a landmark study, also in Science, showing that an experimental drug spurred the addition of new neurons in the hypothalamus and offered a potential treatment for obesity. But while the finding was striking, the researchers were unsure whether the new cells functioned like natural neurons.

Macklis’s laboratory had for several years developed approaches to successfully transplanting developing neurons into circuitry of the cerebral cortex of mice with neurodegeneration or neuronal injury. In a landmark 2000 Nature study, the researchers demonstrated induction of neurogenesis in the cerebral cortex of adult mice, where it does not normally occur. While these and follow-up experiments appeared to rebuild brain circuitry anatomically, the new neurons’ level of function remained uncertain.

To learn more, Flier, an expert in the biology of obesity, teamed up with Macklis, an expert in central nervous system development and repair, and Anderson, an expert in neuronal circuitries and mouse neurological disease models.

The groups used a mouse model in which the brain lacks the ability to respond to leptin. Flier and his lab have long studied this hormone, which is mediated by the hypothalamus. Deaf to leptin’s signaling, these mice become dangerously overweight.

Prior research had suggested that four main classes of neurons enabled the brain to process leptin signaling. Postdocs Artur Czupryn and Maggie Chen, from Macklis’s and Flier’s labs, respectively, transplanted and studied the cellular development and integration of progenitor cells and very immature neurons from normal embryos into the hypothalamus of the mutant mice using multiple types of cellular and molecular analysis. To place the transplanted cells in exactly the correct and microscopic region of the recipient hypothalamus, they used a technique called high-resolution ultrasound microscopy, creating what Macklis called a “chimeric hypothalamus”—like the animals with mixed features from Greek mythology.

Postdoc Yu-Dong Zhou, from Anderson’s lab, performed in-depth electrophysiological analysis of the transplanted neurons and their function in the recipient circuitry, taking advantage of the neurons’ glowing green from a fluorescent jellyfish protein carried as a marker.

These nascent neurons survived the transplantation process and developed structurally, molecularly, and electrophysiologically into the four cardinal types of neurons central to leptin signaling. The new neurons integrated functionally into the circuitry, responding to leptin, insulin, and glucose. Treated mice matured and weighed approximately 30 percent less than their untreated siblings or siblings treated in multiple alternate ways.

The researchers then investigated the precise extent to which these new neurons had become wired into the brain’s circuitry using molecular assays, electron microscopy for visualizing the finest details of circuits, and patch-clamp electrophysiology, a technique in which researchers use small electrodes to investigate the characteristics of individual neurons and pairs of neurons in fine detail. Because the new cells were labeled with fluorescent tags, postdocs Czupryn, Zhou, and Chen could easily locate them.

The Zhou and Anderson team found that the newly developed neurons communicated to recipient neurons through normal synaptic contacts, and that the brain, in turn, signaled back. Responding to leptin, insulin and glucose, these neurons had effectively joined the brain’s network and rewired the damaged circuitry.

“It’s interesting to note that these embryonic neurons were wired in with less precision than one might think,” Flier said. “But that didn’t seem to matter. In a sense, these neurons are like antennas that were immediately able to pick up the leptin signal. From an energy-balance perspective, I’m struck that a relatively small number of genetically normal neurons can so efficiently repair the circuitry.”

“The finding that these embryonic cells are so efficient at integrating with the native neuronal circuitry makes us quite excited about the possibility of applying similar techniques to other neurological and psychiatric diseases of particular interest to our laboratory,” said Anderson.

The researchers call their findings a proof of concept for the broader idea that new neurons can integrate specifically to modify complex circuits that are defective in a mammalian brain.

The researchers are interested in further investigating controlled neurogenesis—directing growth of new neurons in the brain from within—the subject of much of Macklis’s research as well as Flier’s 2005 paper, and a potential route to new therapies.

“The next step for us is to ask parallel questions of other parts of the brain and spinal cord, those involved in ALS and with spinal cord injuries,” Macklis said. “In these cases, can we rebuild circuitry in the mammalian brain? I suspect that we can.”

This study was funded by the National Institutes of Health, the Jane and Lee Seidman Fund for Central Nervous System Research, the Emily and Robert Pearlstein Fund for Nervous System Repair, the Picower Foundation, the National Institute of Neurological Disorders and Stroke, Autism Speaks, and the Nancy Lurie Marks Family Foundation.

Hms.harvard.edu [en línea] Boston (USA): hms.harvard.edu, 15 de diciembre de 2011 [ref. 28 de noviembre de 2011] Disponible en Internet:

http://www.focushms.com/features/rebuilding-the-brain%E2%80%99s-circuitry/

 



Transforming Drug Development

17 10 2011

Taking aim at the alarming slowdown in the development of new and lifesaving drugs, Harvard Medical School is launching an  Initiative in Systems Pharmacology, a comprehensive strategy to transform drug discovery by convening biologists, chemists, pharmacologists, physicists, computer scientists and clinicians to explore together how drugs work in complex systems.

“With this Initiative in Systems Pharmacology, Harvard Medical School is reframing classical pharmacology and marshaling its unparalleled intellectual resources to take a novel approach to an urgent problem,” said Jeffrey S. Flier, dean of the Faculty of Medicine at Harvard University, “one that has never been tried either in industry or academia.”

Modern drug discovery has focused on the interaction between a candidate drug and its immediate cellular target. That target is part of a vast and complex biological network, but because studying the drug in the context of a living system is profoundly difficult, scientists have largely avoided this approach.

As a result, predicting the effects of a particular candidate drug in humans is currently all but impossible, and many initially promising drugs have been found to lack efficacy or to have unsupportable levels of toxicity—typically at a late stage of a clinical trial, at a cost of years of effort and up to $1 billion.

“Right now in the world of drug discovery, it’s as if we have a map of a highway system that only contains small pieces extending a few miles here and there, without any connectivity on a large scale,” said Marc Kirschner, the John Franklin Enders University Professor of Systems Biology and chairman of the HMS Department of Systems Biology. “If you try to plan a trip on such fragmentary information, you’ll fail. It’s our inability to develop a coherent picture that has stymied drug discovery for so long.”

As drug makers exhaust the most promising candidate areas, the number of new drugs brought to patients has actually decreased in recent years, even as the cost of discovery has soared.

A better understanding of the whole system of biological molecules that controls medically important biological behavior, and the effects of drugs on that system, will help industry identify the best drug targets and biomarkers. This will help to select earlier the most promising drug candidates, ultimately making drug discovery and development faster, cheaper and more effective.

“Through this new initiative, we will develop large-scale models of biological systems and networks which should more accurately predict drug efficacy,” Kirschner added.

The systems approach

The science of analyzing specific biological processes within the context of an entire living system, called systems biology, is relatively new. Harvard Medical School is a world-leader in this area, having established one of the first department-level programs in 2003.

Building on this success, Harvard’s new effort will apply systems biology’s innovative approaches to the understanding and prediction of drug activity, drawing on the vast range of biomedical expertise available at the medical school and its affiliated teaching hospitals and research institutes.

Led by Kirschner and systems biology professors Peter Sorger and Tim Mitchison, the Initiative in Systems Pharmacology will include faculty from a broad array of disciplines: systems biology, cell biology, genetics, immunology, neurobiology, pharmacology, medicine, physics, computer science and mathematics. The initiative will be fueled by a strong and diverse group of existing faculty and new recruits who will be based in several departments, and will be supported by an ambitious fundraising effort.  New approaches could include use of chemical biology to develop probes of biological pathways and failure analysis on unsuccessful drugs, similar to how the aviation industry scrupulously analyzes accidents to learn what went wrong. Such a practice is not common in today’s pharmaceutical industry.

Other projects currently underway at HMS will be expanded through the new initiative.

For example, Sorger and Mitchison collaborate with Ralph Weissleder, HMS professor of radiology and director of the Center for Systems Biology at Massachusetts General Hospital, to probe the mechanism by which anti-cancer drugs kill tumor cells in patients and thereby make the effects of treatment more predictable.  “What’s amazing is how little we know even about many drugs that work,” Sorger said. “A systems approach could help tailor existing treatments to specific patients, and find new uses for therapies we already have.”

And in the lab of systems biology professor Roy Kishony, scientists research the evolutionary forces that shape the emergence of antibiotic-resistant bacteria, seeking strategies for developing combination therapies to slow or reverse the spread of drug resistance.

The initiative will also include a new educational program, one that develops a new generation of students, postdoctoral fellows and physician-scientists. The goal is to train future leaders in academic and industrial efforts in systems pharmacology and therapeutic discovery.

Transforming therapeutics

The Initiative in Systems Pharmacology is a signature component of an HMS Program in Translational Science and Therapeutics. There are two broad goals: first, to increase significantly our knowledge of human disease mechanisms, the nature of heterogeneity of disease expression in different individuals, and how therapeutics act in the human system; and second—based on this knowledge—to provide more effective translation of ideas to our patients, by improving the quality of drug candidates as they enter the clinical testing and regulatory approval process, aiming to increase the number of efficacious diagnostics and therapies reaching patients.

“Systems pharmacology is the first and a key pillar of Translational Science and Therapeutics at Harvard Medical School,” said William Chin, the Bertarelli Professor of Translational Medical Science, executive dean for research at HMS and former head of research for Eli Lilly & Co.

“We intend to harness all the strengths of HMS to gain a deeper understanding of the cause and nature of disease, addressing some of the most vexing questions that continue to impede the development of new drugs,” Chin said. “We will focus our strengths and resources to translating such knowledge into new classes of life-saving medicines.”

Focushms.com [en línea] Boston (USA): focushms.com, 17 de octubre de 2011 [ref. 17 de octubre de 2011] Disponible en Internet:

http://www.focushms.com/features/transforming-drug-development/



Cancer’s Secrets Come Into Sharper Focus

29 08 2011

For the last decade cancer research has been guided by a common vision of how a single cell, outcompeting its neighbors, evolves into a malignant tumor.

Through a series of random mutations, genes that encourage cellular division are pushed into overdrive, while genes that normally send growth-restraining signals are taken offline.

With the accelerator floored and the brake lines cut, the cell and its progeny are free to rapidly multiply. More mutations accumulate, allowing the cancer cells to elude other safeguards and to invade neighboring tissue and metastasize.

These basic principles — laid out 11 years ago in a landmark paper, “The Hallmarks of Cancer,” by Douglas Hanahan and Robert A. Weinberg, and revisited in a follow-up article this year — still serve as the reigning paradigm, a kind of Big Bang theory for the field.

But recent discoveries have been complicating the picture with tangles of new detail. Cancer appears to be even more willful and calculating than previously imagined.

Most DNA, for example, was long considered junk — a netherworld of detritus that had no important role in cancer or anything else. Only about 2 percent of the human genome carries the code for making enzymes and other proteins, the cogs and scaffolding of the machinery that a cancer cell turns to its own devices.

These days “junk” DNA is referred to more respectfully as “noncoding” DNA, and researchers are finding clues that “pseudogenes” lurking within this dark region may play a role in cancer.

“We’ve been obsessively focusing our attention on 2 percent of the genome,” said Dr. Pier Paolo Pandolfi, a professor of medicine and pathology at Harvard Medical School. This spring, at the annual meeting of the American Association for Cancer Research in Orlando, Fla., he described a new “biological dimension” in which signals coming from both regions of the genome participate in the delicate balance between normal cellular behavior and malignancy.

As they look beyond the genome, cancer researchers are also awakening to the fact that some 90 percent of the protein-encoding cells in our body are microbes. We evolved with them in a symbiotic relationship, which raises the question of just who is occupying whom.

“We are massively outnumbered,” said Jeremy K. Nicholson, chairman of biological chemistry and head of the department of surgery and cancer at Imperial College London. Altogether, he said, 99 percent of the functional genes in the body are microbial.

In Orlando, he and other researchers described how genes in this microbiome — exchanging messages with genes inside human cells — may be involved with cancers of the colon, stomach, esophagus and other organs.

These shifts in perspective, occurring throughout cellular biology, can seem as dizzying as what happened in cosmology with the discovery that dark matter and dark energy make up most of the universe: Background suddenly becomes foreground and issues once thought settled are up in the air. In cosmology the Big Bang theory emerged from the confusion in a stronger but more convoluted form. The same may be happening with the science of cancer.

Exotic Players

According to the central dogma of molecular biology, information encoded in the DNA of the genome is copied by messenger RNA and then carried to subcellular structures called ribosomes, where the instructions are used to assemble proteins. Lurking behind the scenes, snippets called microRNAs once seemed like little more than molecular noise. But they have been appearing with increasing prominence in theories about cancer.

By binding to a gene’s messenger RNA, microRNA can prevent the instructions from reaching their target — essentially silencing the gene — and may also modulate the signal in other ways. One presentation after another at the Orlando meeting explored how microRNAs are involved in the fine-tuning that distinguishes a healthy cell from a malignant one.

Ratcheting the complexity a notch higher, Dr. Pandolfi, the Harvard Medical School researcher, laid out an elaborate theory involving microRNAs and pseudogenes. For every pseudogene there is a regular, protein-encoding gene. (Both are believed to be derived from a common ancestral gene, the pseudogene shunted aside in the evolutionary past when it became dysfunctional.) While normal genes express their will by sending signals of messenger RNA, the damaged pseudogenes either are mute or speak in gibberish.

Or so it was generally believed. Little is wasted by evolution, and Dr. Pandolfi hypothesizes that RNA signals from both genes and pseudogenes interact through a language involving microRNAs. (These signals are called ceRNAs, pronounced “sernas,” meaning “competing endogenous RNAs.”)

His lab at Beth Israel Deaconess Medical Center in Boston is studying how this arcane back channel is used by genes called PTEN and KRAS, commonly implicated in cancer, to confer with their pseudotwins. The hypothesis is laid out in more detail this month in an essay in the journal Cell.

Fueled by the free espresso offered by pharmaceutical companies hawking their wares, scientists at the Orlando meeting moved from session to session and browsed corridors of posters, looking for what might have recently been discovered about other exotic players: lincRNA, (for large intervening noncoding), siRNA (small interfering), snoRNA (small nucleolar) and piRNA (Piwi-interacting (short for “P-element induced wimpy testis” (a peculiar term that threatens to pull this sentence into a regress of nested parenthetical explanations))).

In their original “hallmarks” paper — the most cited in the history of Cell — Dr. Hanahan and Dr. Weinberg gathered a bonanza of emerging research and synthesized it into six characteristics. All of them, they proposed, are shared by most and maybe all human cancers. They went on to predict that in 20 years the circuitry of a cancer cell would be mapped and understood as thoroughly as the transistors on a computer chip, making cancer biology more like chemistry or physics — sciences governed by precise, predictable rules.

Now there appear to be transistors inside the transistors. “I still think that the wiring diagram, or at least its outlines, may be laid out within a decade,” Dr. Weinberg said in an e-mail. “MicroRNAs may be more like minitransistors or amplifiers, but however one depicts them, they still must be soldered into the circuit in one way or another.”

In their follow-up paper, “Hallmarks of Cancer: The Next Generation,” he and Dr. Hanahan cited two “emerging hallmarks” that future research may show to be crucial to malignancy — the ability of an aberrant cell to reprogram its metabolism to feed its wildfire growth and to evade destruction by the immune system.

Unwitting Allies

Even if all the lines and boxes for the schematic of the cancer cell can be sketched in, huge complications will remain. Research is increasingly focused on the fact that a tumor is not a homogeneous mass of cancer cells. It also contains healthy cells that have been conscripted into the cause.

Cells called fibroblasts collaborate by secreting proteins the tumor needs to build its supportive scaffolding and expand into surrounding tissues. Immune system cells, maneuvered into behaving as if they were healing a wound, emit growth factors that embolden the tumor and stimulate angiogenesis, the generation of new blood vessels. Endothelial cells, which form the lining of the circulatory system, are also enlisted in the construction of the tumor’s own blood supply.

All these processes are so tightly intertwined that it is difficult to tell where one leaves off and another begins. With so much internal machinery, malignant tumors are now being compared to renegade organs sprouting inside the body.

As the various cells are colluding, they may also be trading information with cells in another realm — the micro-organisms in the mouth, skin, respiratory system, urogenital tract, stomach and digestive system. Each microbe has its own set of genes, which can interact with those in the human body by exchanging molecular signals.

“The signaling these microbes do is dramatically complex,” Dr. Nicholson said in an interview at Imperial College. “They send metabolic signals to each other — and they are sending chemicals out constantly that are stimulating our biological processes.

“It’s astonishing, really. There they are, sitting around and doing stuff, and most of it we don’t really know or understand.”

People in different geographical locales can harbor different microbial ecosystems. Last year scientists reported evidence that the Japanese microbiome has acquired a gene for a seaweed-digesting enzyme from a marine bacterium. The gene, not found in the guts of North Americans, may aid in the digestion of sushi wrappers. The idea that people in different regions of the world have co-evolved with different microbial ecosystems may be a factor — along with diet, lifestyle and other environmental agents — in explaining why they are often subject to different cancers.

The composition of the microbiome changes not only geographically but also over time. With improved hygiene, dietary changes and the rising use of antibiotics, levels of the microbe Helicobacter pylori in the human gut have been decreasing in developing countries, and so has stomach cancer. At the same time, however, esophageal cancer has been increasing, leading to speculation that H. pylori provides some kind of protective effect.

At the Orlando meeting, Dr. Zhiheng Pei of New York University suggested that the situation is more complex. Two different types of microbial ecosystems have been identified in the human esophagus. Dr. Pei’s lab has found that people with an inflamed esophagus or with a precancerous condition called Barrett’s esophagus are more likely to harbor what he called the Type II microbiome.

“At present, it is unclear whether the Type II microbiome causes esophageal diseases or gastro-esophageal reflux changes the microbiome from Type I to II,” Dr. Pei wrote in an e-mail. “Either way, chronic exposure of the esophagus to an abnormal microbiome could be an essential step in esophageal damage and, ultimately, cancer.”

Unseen Enemies

At a session in Orlando on the future of cancer research, Dr. Harold Varmus, the director of the National Cancer Institute, described the Provocative Questions initiative, a new effort to seek out mysteries and paradoxes that may be vulnerable to solution.

“In our rush to do the things that are really obvious to do, we’re forgetting to pay attention to many unexplained phenomena,” he said.

Why, for example, does the Epstein-Barr virus cause different cancers in different populations? Why do patients with certain neurological diseases like Parkinson’s, Huntington’s, Alzheimer’s and Fragile X seem to be at a lower risk for most cancers? Why are some tissues more prone than others to developing tumors? Why do some mutations evoke cancerous effects in one type of cell but not in others?

With so many phenomena in search of a biological explanation, “Hallmarks of Cancer: The Next Generation” may conceivably be followed by a second sequel — with twists as unexpected as those in the old “Star Trek” shows. The enemy inside us is every bit as formidable as imagined invaders from beyond. Learning to outwit it is leading science deep into the universe of the living cell.

VALIDADO POR LA SRA. ALBA CALLS.

Nytimes.com [en línea] New York (USA): nytimes.com, 29 de agosto de 2011 [ref. 15 de agosto de 2011] Disponible en Internet:

http://www.nytimes.com/2011/08/16/health/16cancer.html?pagewanted=1&ref=research



New Clue to Parkinson’s

18 08 2011
Shape of key protein surprises researchers

A new study finds that a protein key to Parkinson’s disease has likely been mischaracterized. The protein, alpha-synuclein, appears to have a radically different structure in healthy cells than previously thought, challenging existing disease paradigms and suggesting a new therapeutic approach.

Imagen de previsualización de YouTube

“Our data show that alpha-synuclein was essentially mistakenly characterized as a natively unfolded protein that lacked structure,” said Dennis Selkoe, the Vincent and Stella Coates Professor of Neurologic Diseases at Brigham and Women’s Hospital and Harvard Medical School and senior author of the paper, published online August 14 in the journal Nature. “We think this discovery has fundamental importance for understanding both how alpha-synuclein normally functions and how it becomes altered in Parkinson’s.”

When it comes to proteins, function follows form. A protein consists of a chain of chemical building blocks (amino acids), typically folded into an exquisite three-dimensional structure. Each twist and turn in the chain contributes to the protein’s unique properties and behavior, so it’s critical for scientists to accurately describe the arrangement of folds. But sometimes, they get the entire pattern wrong.

The new study suggests that’s just what happened with alpha-synuclein, the protein that forms clumps called Lewy bodies in the brains of patients with Parkinson’s and certain related disorders. Scientists have long assumed that alpha-synuclein occurs in healthy cells as a single, randomly-coiled chain that resembles a writhing snake. Selkoe’s team has proven, however, that the structure is far more orderly and sophisticated.

“This will open some new therapeutic doors,” said first author Tim Bartels, a postdoctoral researcher in Selkoe’s lab. “Everybody thought the protein was unfolded, so pharmaceutical companies have focused on preventing unfolded alpha-synuclein from aggregating.”

He recommends a new strategy—keeping the folded form of the protein stable.

How did the true structure of alpha-synuclein in healthy cells evade researchers for so long? Scientists knew that alpha-synuclein was abundant in the brain before they made the connection between the protein and Parkinson’s disease in 1997. Experiments in the mid-1990s indicated the protein was stable when exposed to conditions that typically disrupt the structure of most other proteins.

Consider what happens when an egg is boiled: the liquid proteins of the egg white are precipitated by the heat and congeal into a dense white mass. But alpha-synuclein seemed to behave like an egg that remains entirely viscous despite many minutes on the stove. It didn’t precipitate and congeal when boiled. This apparent hardiness made alpha-synuclein easy to work with in the lab. Scientists could boil the protein, even douse it with detergents and other rather harsh chemicals, while ostensibly leaving its structure intact.

Bartels and Selkoe wondered whether labs might be overlooking important aspects of the protein’s natural biology by handling it so roughly, so they designed experiments to probe alpha-synuclein’s behavior using gentler methods. They also bucked a trend by working with protein gathered from human cells rather than from engineered bacteria. The goal was to gain new insight into alpha-synuclein’s clustering behavior.

The initial data took them by surprise. Single, isolated chains of alpha-synuclein—the “monomeric” form of the protein—were absent from their cellular samples.

“I did my PhD on alpha-synuclein, and—like the rest of the world—I assumed that it occurs natively as a monomeric, unfolded protein, so I was shocked,” said Bartels.

Using special gels and other methods that are less disruptive to a protein’s form, the team conducted additional experiments to explore the structure of alpha-synuclein in healthy blood and brain cells. The native protein was exactly four times the predicted weight of a single alpha-synuclein chain, suggesting that cells package four alpha-synuclein chains together as a “tetrameric” unit. Applying sophisticated equipment and techniques, the team validated the molecular weight of the package, confirmed that it consists solely of alpha-synuclein chains and showed that these four chains have orderly twists.

The researchers observed tetrameric alpha-synuclein to be the dominant form of the protein in healthy human cells, and remarkably resistant to aggregation. The tetramers maintained their original structure for 10 days, the entire length of the experiment, while the team monitored their samples for clustering behavior. In stark contrast, alpha-synuclein monomers began to form clusters after a few days and ended up as large aggregates called amyloid fibers. The Lewy bodies that accumulate in the brains of patients with Parkinson’s consist mainly of such amyloid fibers.

“We hypothesize that the folded protein must disassemble into monomers before large pathological aggregates can form,” said Selkoe, who is also co-director of the Center for Neurologic Diseases at Brigham and Women’s Hospital. “If we can keep alpha-synuclein tetrameric and soluble, we might be able to prevent the neuronal degeneration of Parkinson’s disease from progressing—or perhaps from even developing.”

The finding could also prove useful in the quest for new diagnostics. Perhaps ratios of tetrameric protein to monomeric protein in blood cells, serum or spinal fluid will correspond to different propensities or stages of the disease.

Finally, the discovery of the folded tetramers should help labs to uncover the function of alpha-synuclein in healthy cells, which is still much debated. This functional knowledge should, in turn, contribute to researchers’ understanding of Parkinson’s and other diseases characterized by the formation of Lewy bodies rich in aggregated alpha-synuclein.

This research was funded by the National Institute of Neurological Disorders and Stroke.

VALIDADO POR LA SRA. ALBA CALLS.

Focushms.com [en línea] Cambridge (USA): focushms.com, 18 de agosto de 2011 [ref. 14 de agosto de 2011] Disponible en Internet:

http://www.focushms.com/features/new-clue-to-parkinsons/