RxPG News : Regeneration

Salamanders can regenerate damaged lungs

Sat, 08 Aug 2009 14:19:15 PST

( from http://www.rxpgnews.com ) The salamander is a super hero of regeneration, able to replace lost limbs, damaged lungs, sliced spinal cord - even bits of lopped-off brain.

But it turns out that this remarkable ability isn't so mysterious after all - suggesting that researchers could learn how to replicate it in people.

Scientists had long credited the diminutive amphibious creature's outsized capabilities to 'pluripotent' cells that, like human embryonic stem cells, have the uncanny ability to morph into whatever appendage, organ or tissue happens to be needed or is due for a replacement.

But a team of seven researchers, including a University of Florida - zoologist, debunk that notion.

Based on experiments on genetically modified axolotl salamanders, the researchers have shown that cells from the salamander's different tissues retain the 'memory' of those tissues when they regenerate, contributing with few exceptions only to the same type of tissue from where they came.

Standard mammal stem cells operate the same way, albeit with far less dramatic results - they can heal wounds or knit bone together, but not regenerate a limb or rebuild a spinal cord.

What's exciting about the new findings is they suggest that harnessing the salamander's regenerative wonders is at least within the realm of possibility for human medical science.

Also, the salamanders heal perfectly, without any scars whatsoever, another ability people would like to learn how to mimic, said Malcolm Maden, professor of biology and author of the paper.

Axolotl salamanders, originally native to only one lake in central Mexico, are evolutionary oddities that become sexually reproducing adults while still in their larval stage.

When an axolotl loses, for example, a leg, a small bump called a blastema forms over the injury. It takes only about three weeks for this blastema to transform into a new, fully functioning replacement leg - not long considering these animals can live 12 or more years.

These findings appeared in the Thursday edition of Nature.

Severed nerve fibers in spinal cord can regenerate for long distances

Sat, 19 Aug 2006 21:44:37 PST

( from http://www.rxpgnews.com ) The body's spinal cord is like a super highway of nerves. When an injury occurs, the body's policing defenses put up a roadblock in the form of a scar to prevent further injury, but it stops all neural traffic from moving forward.

Researchers from Case Western Reserve University, Drexel University and the University of Arkansas bypassed this roadblock in the spinal cord. First, the researchers regenerated the severed nerve fibers, also called axons, around the initial large lesion with a segment of peripheral nerve taken from the leg of the same animal that suffered the spinal injury. Next, they jump started neural traffic by allowing many nerve fibers to exit from the end of the bridge. This was accomplished, for the first time, by using an enzyme that stopped growth inhibitory molecules from forming in the small scar that forms at the exit ramp of the bridge, where it is inserted into the spinal cord on the other side of the lesion. This allowed the growing axons to reconnect with the spinal cord.

Jerry Silver, a professor of neurosciences at the Case School of Medicine, was senior author among the researchers reporting in the Journal of Neuroscience article, "Combining an Autologous Peripheral Nervous System 'Bridge' and Matrix Modification by Chondroitinase Allows Robust Functional Regeneration beyond a Hemisection Lesion of the Adult Rat Spinal Cord." The other researchers were John Houle, the lead author, and Veronica Tom (a Case alum) from Drexel University College of Medicine; and Gail Wagoner and Napoleon Phillips from the University of Arkansas.

The researchers employed a combination of two strategies--one old and one new--in efforts to regenerate nerves in the spinal cord and restore movement, said Silver.

For more than 100 years, researchers have used grafts of peripheral nerves from the rib area or parts of the leg. While peripheral nerves can be used successfully as grafts in the limbs, spinal cord injuries put up defenses called inhibitory chondroitin sulfate proteoglycans that create molecular guardrails within scars at the lesion site. These scars act as a barrier to regenerating axons and result in loss of the ability to breathe or move arms or legs, depending upon the injury site.

Silver said the medical community also assumed that the cut axon tips died when they hit the scar wall. In prior research in his lab by his graduate student, Tom, it was discovered that axons are alive and continue to attempt to grow for years. Silver describes them as "trucks stuck in mud going no where." It also explains why some people gain some movement back or come out of comas after many years as the nerve fibers sprout through weakened or remodeled areas of the scar.

About 16 years ago, Silver also made another find that proteoglycans, a sugary protein, is present at the site of spinal cord lesions. He also knew that a particular enzyme from the bacteria Proteus vulgaris, called chondroitinase, might dismantle the proteoglycans by clipping their sugar branches, thereby preventing the scar wall from building.

In a National Institutes of Health-supported animal study, 12 rats had spinal injuries at the cervical level 3 (C3) that resulted in impaired motor functions to their right side limbs. The animals had trouble moving, climbing or grooming.

Combining the old with the new, the researchers grafted a 1.5 centimeter piece of the tibial branch of he sciatic nerve to the C3 area of the spinal cord and allowed the nerve fibers to grow and regenerate over three weeks. .

At approximately two and a half weeks into the new nerve growth, Houle implanted a small pump that delivered a steady dose of chondroitinase to a new incision site near C5 where the researchers hoped to reconnect the other end of the bridge to the spinal cord, but also prevent further scarring. They also primed the newly re-grown axons for rapid regeneration by clipping their ends.

Silver said this method resulted in approximately 20 percent of the nerve fibers leaving the bridge and reconnecting with the spinal cord. It brought about markedly improved mobility for the seven rats given the chondroitinase treatment.

A control group of five rats underwent the same procedure. Instead of the chondroitinase, they were given a saline solution. None showed any nerve growth out of the bridge or improvement in their limbs.

To test whether something other than regeneration was at work in restoring movement, the neural bridges were severed and the rats lost all movement gained from the combination of treatments. This provides the most conclusive evidence to date that severed nerve fibers in the spinal cord can, in fact, regenerate for long distances and establish proper functional connections.

Silver said if the method is perfected and successful with primates, it could go to human trials within a relatively short time.

His next step is a neural bridge that would help quadriplegics, who are unable to breathe without assistance, move their diaphragms on their own. In future animal studies he plans to undertake nerve grafts from the leg to bridge the area of the spinal cord that controls breathing.

"While this was one small step for a rat, it was one giant leap for man," said Silver.

Common brain cells may have stem-cell-like potential

Thu, 17 Aug 2006 16:01:37 PST

( from http://www.rxpgnews.com ) University of Florida researchers have shown ordinary human brain cells may share the prized qualities of self-renewal and adaptability normally associated with stem cells.

Writing online in Development, scientists from UF's McKnight Brain Institute describe how they used mature human brain cells taken from epilepsy patients to generate new brain tissue in mice.

Furthermore, they can coax these pedestrian human cells to produce large amounts of new brain cells in culture, with one cell theoretically able to begin a cycle of cell division that does not stop until the cells number about 10 to the 16th power.

"We can theoretically take a single brain cell out of a human being and - with just this one cell - generate enough brain cells to replace every cell of the donor's brain and conceivably those of 50 million other people," said Dennis Steindler, Ph.D., executive director of UF's McKnight Brain Institute. "This is a completely new source of human brain cells that can potentially be used to fight Parkinson's disease, Alzheimer's disease, stroke and a host of other brain disorders. It would probably only take months to get enough material for a human transplant operation."

UF McKnight Brain Institute researchers were able to purify and grow highly adaptable cells called adult human neural progenitors from mature human brain tissue. The green marker indicates a support brain cell called an astrocyte and the red marker is an indication of a stem cell, which is highly valued for its ability to transform into any cell type. Blue marks the cell nucleus. Credit: Noah Walton/UF McKnight Brain Institute

The findings document for the first time the ability of common human brain cells to morph into different cell types, a previously unknown characteristic, and are the result of the research team's long-term investigations of adult human stem cells and rodent embryonic stem cells.

Last year, the researchers published details about how they used stem-like brain cells from rodents to duplicate neurogenesis - the process of generating new brain cells - in a dish. The latest findings go further, showing common human brain cells can generate different cell types in cell cultures. In addition, when researchers transplanted these human cells into mice, the cells effectively incorporated in a variety of brain regions.

The human cells were acquired from patients who had undergone surgical treatment for epilepsy and were extracted from support tissue within the gray matter, which is not known for harboring stem cells.

When the donor cells were subjected to a bath of growth agents within cell cultures, a type of cell emerged that behaves like something called a neural progenitor - a cell that is a bit further along in development than a stem cell but shares a stem cell's vaunted ability to divide and transform into different types of brain cells.

Even when the cells from the epilepsy patients were transplanted into mice, bypassing any growth enhancements, they were able to take cues from their surroundings and produce new neurons.

"It was a long and difficult process, but we were able to induce what are basically support cells in the human brain to form beautiful new neurons in a dish," said Noah Walton, a graduate student in the neuroscience department at the UF College of Medicine. "But what we really needed is for these support cells to turn into neurons in the brain, and we found we could get them to do it. Something in the environment in the rodent brain is sufficient to get these cells to become neurons."

Scientists speculate a small amount of existing progenitors may be emerging from the gray matter of the brain and multiplying in torrents, or perhaps the aging clock of the mature cells actually turns backward when the donor cells are in a new environment, returning them to past lives as progenitors or as stem cells.

"It's been shown that the same sorts of tissue from the mouse brain can give rise to rapidly dividing cells, but this shows it is true with human cells," said Ben Barres, M.D., Ph.D., a professor of neurobiology at the Stanford University School of Medicine who was not involved in the research. "That these cells were able to integrate into tissue in an animal model and actually survive - it was extremely important to show that. Now the question is what will these cells do in a human brain? Will they be able to survive for the long term and rebuild circuitry? This work is a first step toward that end."

In addition to using the cells in treatments to repair or replace damaged brain tissue, the ability to massively expand cell populations could prove useful in efforts to test the safety and efficacy of new drugs. It is also possible to genetically modify the cells to produce neurotrophins - substances that help brain tissue survive, researchers said.

Using Embryonic Stem Cells to Awaken Latent Motor Nerve Repair

Sat, 01 Jul 2006 17:22:37 PST

( from http://www.rxpgnews.com ) In a dramatic display of stem cells potential for healing, a team of Johns Hopkins scientists reports that theyve engineered new, completed, fully-working motor neuron circuits -- neurons stretching from spinal cord to target muscles -- in paralyzed adult animals.

The research, in which mouse embryonic stem (ES) cells were injected into rats whose virus-damaged spinal cords model nerve disease, shows that such cells can be made to re-trace complex pathways of nerve development long shut off in adult mammals, the researchers say.

This is proof of the principle that we can recapture what happens in early stages of motor neuron development and use that to repair damaged nervous systems, says Douglas Kerr, M.D., Ph.D., a neurologist who led the Hopkins team.

Its a remarkable advance that can help us understand how stem cells can begin to fulfill their great promise, says Elias A. Zerhouni, director of the National Institutes of Health. Demonstrating restoration of function is an important step forward, though we still have a great distance to go.

The researchers created what amounts to a cookbook recipe to restore lost nerve function, Kerr explains. The approach could one day repair damage from such diseases as ALS (Lou Gehrigs disease), multiple sclerosis or transverse myelitis or from traumatic spinal cord injury, the researchers say. With small adjustments keyed to differences in nervous system targets, Kerr says, the approach may also apply to patients with Parkinson's or Huntingtons disease.

In a report on the study, to be released online June 26 in the Annals of Neurology, the Hopkins team says 11 of the 15 treated rats gained significant, though partial, recovery from paralysis after losing motor neurons to an aggressive infection with Sindbis virus -- one that, in rodents, specifically targets motor neurons and kills them. The animals recovered enough muscle strength to bear weight and step with the previously paralyzed hind leg.

Kerr likens the approach to electrical repair. Paralysis is like turning on a light switch and the light doesnt go on. The connectivity is messed up but you dont know where. Weve asked stem cells to go where needed to fix the circuit.

For a brief period after a nerve dies, it leaves behind whats essentially an empty shell, with some scaffolding and non-nerve substances remaining. But with ES injections at the right time and place, and by adding the right cues, weve learned to restore the biological memory for growing neurons, which is clearly still in place, he added.

The motor circuit engineering combines recent discoveries on stem cell differentiation, a growing understanding of early development of the nervous system, and insights into behavior of the nervous system in traumatic injury, Kerr notes.

As adults, our cells no longer respond to early developmental cues because those cues are usually gone, says Kerr. Thats why we dont recover well from severe injuries. But thats what we believe we have changed. We asked what was there when motor neurons were born, and specifically what let motor neurons extend outward. Then we tried to bring that environment back, in the presence of adaptable, receptive stem cells.

In the study, Kerrs team first pre-treated cultures of mouse embryonic stem cells with growth factors that both increase survival and prompt specialization into motor neurons. Adding retinoic acid and sonic hedgehog protein -- agents that direct cells in the first weeks of life to assume the proper places in the spinal cord -- readied the conditioned ES cells for the motor neuron circuit that starts in the spinal cord. Then, stem cells were fed into the paralyzed rats spinal cords.

Extending new motor neurons in an adult nervous system, however, meant overcoming hurdles. One involved myelin, the fatty material that insulates mature motor neurons. Like the coating on electrical wire, myelin prevents weakening of the traveling electrical impulse and lets it continue long distances. In humans, the myelinated sciatic nerve, for example, exits the spinal cord and extends to the leg muscles it activates, carrying impulses several feet.

Once laid down, however, myelin inhibits further nerve growth -- natures way to discourage excessive wiring in the nervous system. We had to overcome inhibition from myelin lingering in the dead nerve pathways, Kerr explains. Two recently-developed agents, rolipram and dbcAMP enabled that.

The assorted treatments let the new motor neurons survive, grow through the spinal cord and extend slightly into the outlying nervous system. A second hurdle remained in getting the neurons to skeletal muscle targets.

As suggested by earlier work by team member Ahmet Hoke on repair in the outlying, peripheral nervous system, the researchers applied GDNF, a powerful stimulator of neuron growth, to the remains of the newly-dead sciatic nerve at a point near its former leg muscle contacts. GDNF attracted the extending motor neurons, luring them to the muscles. To ensure a continuous supply of GDNF, the researchers relied on injected fetal mouse neural stem cells, a known source of the molecule.

Of some 4,100 new motor neurons created in the spinal cord, roughly 200 exited the cord and 120 reached skeletal muscle, forming typical nerve-muscle junctions, with appropriate, typical chemical markers. Microscopically, the neurons and their muscle associations appear identical to natural ones in healthy animals.

Fifty of the new neurons were found to carry electrical impulses. (Because such testing is time and labor intensive, only a small area of leg muscle was assayed. The improved ability of treated rats, however, suggests more functional neurons are likely.) The rats gained weight, were more mobile in their cages and measures of muscle strength increased.

Animals treated without even one component of the cocktail experienced no such recovery. Novel ways of tracing the neurons back to their source assured the scientists that they indeed had come from the injected stem cells, not from lingering host neurons.

Understanding how axons find their destinations

Fri, 16 Jun 2006 23:44:37 PST

( from http://www.rxpgnews.com ) During embryonic development, nerve cells hesitantly extend tentacle-like protrusions called axons that sniff their way through a labyrinth of attractive and repulsive chemical cues that guide them to their target.

While several recent studies discovered molecules that repel motor neuron axons from incorrect targets in the limb, scientists at the Salk Institute for Biological Studies have identified a molecule, known as FGF, that actively lures growing axons closer to the right destination.

"The most important aspect of our finding is not necessarily that we finally nailed the growth factor FGF as the molecule that guides a specific subgroup of motor neurons to connect to the muscles that line our spine and neck," says senior author Samuel Pfaff, Ph.D., a professor in the Gene Expression Laboratory, "but that piece by piece, we are uncovering general principles that ensure that the developing nervous system establishes proper neuronal connections."

Understanding how axons find their destinations may help restore movement in people following spinal cord injury, or those with motor neuron diseases such as Lou Gehrig's disease, spinal muscle atrophy, and post-polio syndrome. Failure to establish proper connectivity in the brain may also underlie autism spectrum disorders and mental retardation.

The multitasking members of the FGF growth factor family regulate blood vessel formation, wound repair, lung maturation, and development of skeletal muscle, blood and bone marrow cells. The Salk study adds on more job to an already long list.

"Our study emphasizes that the nervous system does not necessarily rely on an entirely new set of molecules to govern axon navigation, but instead uses growth factors already involved in embryonic development in clever and novel ways," Pfaff says.

Skeletal muscle consists of thousands of muscle fibers, each controlled by one motor neuron whose cell body lies in the brain or spinal cord. Connections between muscle and nerve cells are established embryonically when newborn neurons extend axons to "wire" the appropriate muscle fiber.

The wiring process is highly orchestrated each motor neuron has already pledged allegiance to a particular muscle fiber before it reaches out to connect with its predetermined partner. But until now, scientists could only speculate how the invisible bond was formed.

"The question was how do these motor neurons know where to go," says Pfaff. "It would be a disaster if you wanted to move your arm and instead bent your back."

Earlier studies suggested that muscles lining the spine sent out chemical cues as a siren song for specific motor neurons known as MMCm cells. But when attempts to identify the enticing substance failed, many started to doubt its existence.

After screening numerous candidates, the Pfaff team found not only that FGF is expressed in target muscle, but that FGF "sensors," known as FGF receptors, are expressed in MMCm motor neurons. Furthermore, MMCm axons could not "hear" their muscle partner's call and failed to reach their destination in mouse mutants lacking the sensor molecule.

Finally, using mice engineered to express a fluorescent protein in MMCm neurons, the investigators demonstrated that only the glowing neurons extended axons in the direction of target cells expressing FGF.

"After a lot of hard work, we narrowed it down to FGFs and showed that they were indeed the long sought-after mysterious substance," says Pfaff. Neural stem cells can now be coaxed to develop into motor neurons in a test tube. In that artificial environment, explains Pfaff, "Most external cues that guide immature motor neurons during embryonic development will be missing." Hence the need to identify axon guidance factors. He continues, "It is not enough to make the right cell type, you need to connect them to the right target. Growth factors like FGF may be crucial to persuade and guide them towards the desired destination."

Novel stem cell technology leads to better spinal cord repair

Sun, 30 Apr 2006 19:17:37 PST

( from http://www.rxpgnews.com ) Researchers believe they have identified a new way, using an advance in stem-cell technology, to promote recovery after spinal cord injury of rats, according to a study published in today's Journal of Biology.

Scientists from the New York State Center of Research Excellence in Spinal Cord Injury showed that rats receiving a transplant of a certain type of immature support cell from the central nervous system (generated from stem cells) had more than 60 percent of their sensory nerve fibers regenerate. Just as importantly, the study showed that more than two-thirds of the nerve fibers grew all the way through the injury sites eight days later, a result that is much more promising than previous research. The rats that received the cell transplants also walked normally in two weeks.

The University of Rochester Medical Center, Rochester, N.Y., and Baylor College of Medicine, Houston, collaborated on the work. Researchers believe they made an important advance in stem cell technology by focusing on a new cell type that appears to have the capability of repairing the adult nervous system.

"These studies provide a way to make cells do what we want them to do, instead of simply putting stem cells into the damaged area and hoping the injury will cause the stem cells to turn into the most useful cell types," explains Mark Noble, Ph.D., co-author of the paper, professor of Genetics at the University of Rochester, and a pioneer in the field of stem cell research. "It really changes the way we think about this problem."

The breakthrough is based on many years of stem cell biology research led by Margot Mayer-Proschel, Ph.D., associate professor of Genetics at the University of Rochester. In the laboratory, Mayer-Proschel and colleagues took embryonic glial stem cells and induced them to change into a specific type of support cell called an astrocyte, which is known to be highly supportive of nerve fiber growth. These astrocytes, called glial precursor-derived astrocytes or GDAs, were then transplanted into the injured spinal cords of adult rats. Healing and recovery of the GDA rats was compared to other injured rats that received either no treatment at all or treatment with undifferentiated stem cells.

The rats without the GDA cell transplant did not show any nerve fiber regeneration and still had difficulty walking four weeks after surgery.

"We demonstrated that we can treat these precursor cells, in culture, with signals we know to be important in the development of astrocytes and push these stem cell-like cells down a pathway that supports regeneration of the nervous system," said Stephen Davies, Ph.D., the study's lead investigator and assistant professor of Neurosurgery at Baylor.

"At the heart of stem cell transplantation research is finding the right cell for the right job," Noble added. "In this case the work of this team has identified a cell that provides many more benefits than those seen with other cell types and thus, it gives us hope that we are on a better track."

The GDA cells seem to work by signaling the tissue to repair in several ways, such as by suppressing scar tissue, rescuing motor pathway neurons in the brain and aligning damaged tissue at the injured site. More investigation is needed, however, before the new technology could be used in humans, researchers said.

Myosin-II: A new focus for the mechanism of nerve growth

Sun, 19 Mar 2006 20:22:37 PST

( from http://www.rxpgnews.com ) Researchers at Yale shed new light on the mechanism of nerve cell growth by identifying novel functions for a molecular "motor" protein, myosin-II, according to an article in the March issue of Nature Cell Biology.

As nerve cells develop or attempt to recover after damage, they extend growth cones, highly flexible extensions that act as environmental sensors. Growth cones use the information they gather to direct advance of the nerve cells and it has long been known that such advance depends on the coordinated assembly of actin filament networks.

This study implicates the molecular motor, myosin II, as a key part of the process of recycling the actin networks and ultimately sensing and directing nerve growth.

Proteins in the Myosin family function as molecular motors; the most familiar myosins power contraction in heart and skeletal muscles. Myosin II motors are involved in functions such as directed cell movement, cell division and wound closure. While skeletal myosins have been studied in detail, non-muscle myosins are just beginning to be understood and this work identifies a new role for them.

The researchers, led by Paul Forscher, professor of molecular, cellular and developmental biology at Yale used a technique called fluorescent speckle microscopy, or FSM, that let them directly see actin filament assembly, disassembly and movement in living cells. They used FSM to monitor actin dynamics in nerve cells treated with a new drug called blebbistatin, that relaxes non-muscle myosin II and effectively blocks processes such as cell division.

"Past research has focused on how actin structures are assembled at the leading edges of motile cells," said Forscher. "Instead, this paper investigates turnover or recycling of the actin networks. As the complement to actin network assembly, recycling is necessary to prevent actin buildup that could actually impede neuronal advance."

Forscher likened actin networks in the growth cone to a molecular treadmill that is constantly being assembled at the leading edge and moved rearward, powered by a myosin II motor located at its back end. But, the networks making up this actin treadmill are constantly being recycled at the back end, and actin molecules are freed to complete a "virtual belt" cycle and be used again.

"Surprisingly, growth cones of nerve cells rapidly doubled in width when myosin II was blocked by blebbistatin," said Forscher. "FSM see that this was caused by inefficient recycling of actin filaments at the back end of the actin network treadmill."

Recycling of actin bundles at the ends of structures called filopodia was most strongly affected. This is important because filopodia are thought to play a key sensory role in growth cone guidance -- suggesting actin filament recycling and signaling may be intimately related.

The team is now investigating the implications of these findings for control of nerve growth, with particular interest in repair of spinal cord nerves after injury.

Structural remodeling of neurons demonstrated in mature brains

Thu, 29 Dec 2005 15:57:38 PST

( from http://www.rxpgnews.com ) Despite the prevailing belief that adult brain cells don't grow, a researcher at MIT's Picower Institute for Learning and Memory reports in the Dec. 27 issue of Public Library of Science (PLoS) Biology that structural remodeling of neurons does in fact occur in mature brains.

This finding means that it may one day be possible to grow new cells to replace ones damaged by disease or spinal cord injury, such as the one that paralyzed the late actor Christopher Reeve.

"Knowing that neurons are able to grow in the adult brain gives us a chance to enhance the process and explore under what conditions -- genetic, sensory or other -- we can make that happen," said study co-author Elly Nedivi, the Fred and Carole Middleton Assistant Professor of Neurobiology.

While scientists have focused mostly on trying to regenerate the long axons damaged in spinal cord injuries, the new finding suggests targeting a different part of the cell: the dendrite. A dendrite, from the Greek word for tree, is a branched projection of a nerve cell that conducts electrical stimulation to the cell body.

"We do see relatively large-scale growth" in the dendrites, Nedivi said. "Maybe we would get some level of improvement (in spinal cord patients) by embracing dendritic growth." The growth is affected by use, meaning the more the neurons are used, the more likely they are to grow, she said.

The study's co-authors -- Nedivi; Peter T. So, an MIT professor of mechanical and biological engineering; Wei-Chung Allen Lee, an MIT brain and cognitive sciences graduate student; and Hayden Huang, a mechanical engineering research affiliate -- used a method called two-photon imaging to track specific neurons over several weeks in the surface layers of the visual cortex in living mice. While many studies have focused on the pyramidal neurons that promote firing, this work looked at all types of neurons, including interneurons, which inhibit the activity of cortical neurons.

With the help of technology similar to magnetic resonance imaging (MRI), but at a much finer, cellular resolution, the researchers were able to stitch together two-dimensional slices to create the first 3-D reconstruction of entire neurons in the adult cortex. Dendritic branch tips were measured over weeks to evaluate physical changes.

What the researchers saw amazed them.

In 3-D time-lapse images, the brain cells look like plants sprouting together. Some push out tentative tendrils that grow around or retract from contact with neighboring cells. Dendrite tips that look like the thinnest twigs grow longer. Of several dozen branch tips, sometimes only a handful changed; in all, 14 percent showed structural modifications. Sometimes no change for weeks was followed by a growth spurt. There were incremental changes, some as small as seven microns, the largest a dramatic 90 microns.

"The scale of change is much smaller than what goes on during the critical period of development, but the fact that it goes on at all is earth-shattering," Nedivi said. She believes the results will force a change in the way researchers think about how the adult brain is hard-wired.

Nedivi had previously identified 360 genes regulated by activity in the adult brain that she termed candidate plasticity genes or CPGs. Her group found that a surprisingly large number of CPGs encode proteins in charge of structural change. Why are so many of these genes "turned on" in the adult well after the early developmental period of dramatic structural change?

The neuroscience community has long thought that whatever limited plasticity existed in the adult brain did not involve any structural remodeling, mostly because no such remodeling was ever detected in excitatory cells. Yet evidence points to the fact that adult brains can be functionally plastic. In response to the CPG data, Nedivi and Lee revisited this question with the help of So and Huang.

By applying an innovative new imaging technology that allows monitoring of neuronal structural dynamics in the living brain, they found evidence for adult neuronal restructuring in the less-known, less-accessible inhibitory interneurons.

"Maybe the inhibitory network is where the capacity is for large-scale changes," Nedivi said. "What's more, this growth is tied to use, so even as adults, the more we use our minds, the more robust they can be."

How "baby" neurons are integrated into brain

Sun, 25 Dec 2005 00:52:38 PST

( from http://www.rxpgnews.com ) In experiments with mice, scientists from Johns Hopkins' Institute for Cell Engineering have discovered the steps required to integrate new neurons into the brain's existing operations.

For more than a century, scientists thought the adult brain could only lose nerve cells, not gain them, but in fact, new neurons do form during adulthood in all mammals, including humans, and become a working part of the adult brain in mice at the very least.

In the first study to show how these "baby" neurons are integrated into the brain's existing networks, the Johns Hopkins researchers show that a brain chemical called GABA readies baby neurons to make connections to old ones. The discovery is described in the Dec. 11 advance online section of Nature.

"GABA is important during fetal development, but most scientists thought it would have the same role it has with adult neurons, which is to inhibit the cells' signals," says Hongjun Song, Ph.D., an assistant professor in the Neuroregeneration and Repair Program within ICE. "We've shown that GABA instead excites new neurons and that this is the first step toward their integration into the adult brain."

Song added that their discovery might help efforts to increase neuron regeneration in the brain or to make transplanted stem cells form connections more efficiently.

The researchers, including postdoctoral fellows Shaoyu Ge and Eyleen Goh, discovered that a constant flood of GABA is required as a first step. Next, the new neuron receives specific connections that communicate using GABA, which shifts the constant barrage of GABA in step one to a pulsed exposure. The third and final step occurs when the new neuron receives connections that communicate via another chemical, the critical excitatory messenger glutamate.

In the adult brain, glutamate is the most prevalent excitatory chemical, and GABA is a major inhibitory chemical. But it turns out that new neurons are excited by GABA, whether they are in the fetal brain or the adult brain, says Song.

"The steps of integration essentially shift the neuron from being a developing neuron to being an adult neuron. Initially it's excited by the flood of GABA, but by the time it's fully integrated, the neuron will respond to GABA and glutamate like other adult neurons," he says.

The researchers' experiments were done on a part of the mouse brain called the dentate gyrus, which is thought to be involved in memory and spatial reasoning, or navigation. It is one of the few parts of the brain where new neurons form throughout life and are integrated into the existing network of cells.

The researchers also figured out why the mouse's new neurons were excited by GABA -- they have greater amounts of chloride ions, making for a different chemical environment. By the time they are fully integrated, their chloride levels have dropped and are similar to other adult neurons.

In the mouse experiments, Goh used a technique to alter the genetics of single cells in order to change new neurons' ability to accumulate chloride ions (and thus to manipulate their response to GABA) and to make them glow with a green protein to ease their identification in the adult brain. Ge measured the electrical output of the neurons to establish whether they had become connected to other neurons.

"Getting new neurons to form connections in other parts of the brain may be helped through the same steps that naturally lead to integration in the dentate gyrus," says Song.

Among the most likely targets for regeneration or replacement efforts are the dopamine-producing neurons that die in Parkinson's disease, muscle-controlling nerves that succumb in diseases like muscular dystrophy and amyotrophic lateral sclerosis, or nerves that are damaged by trauma or injury. In none of these systems are new neurons formed or integrated to any great extent naturally.

Nerve regeneration is possible in spinal cord injuries

Sun, 04 Dec 2005 10:40:38 PST

( from http://www.rxpgnews.com ) A team of scientists at UCSF has made a critical discovery that may help in the development of techniques to promote functional recovery after a spinal cord injury.

By stimulating nerve cells in laboratory rats at the time of the injury and then again one week later, the scientists were able to increase the growth capacity of nerve cells and to sustain that capacity. Both factors are critical for nerve regeneration.

The study, reported in the November 15 issue of the Proceedings of the National Academy of Sciences, builds on earlier findings in which the researchers were able to induce cell growth by manipulating the nervous system before a spinal cord injury, but not after.

Key to the research is an important difference in the properties of the nerve fibers of the central nervous system (CNS), which consists of the brain and spinal cord, and those of the peripheral nervous system (PNS), which is the network of nerve fibers that extends throughout the body.

Nerve cells normally grow when they are young and stop when they are mature. When an injury occurs in CNS cells, the cells are unable to regenerate on their own. In PNS cells, however, an injury can stimulate the cells to regrow. PNS nerve regeneration makes it possible for severed limbs to be surgically reattached to the body and continue to grow and regain function.

Regeneration occurs because PNS cell bodies are sensitive to damage to their nerve processes, and they react by sending out a signal that triggers the nerve fibers to regrow, explains Allan Basbaum, PhD, senior study author and chair of the UCSF Department of Anatomy. "Apparently this communication doesn't take place within the CNS."

Scientists do not yet know the biochemical cause for the difference, he adds.

The traditional scientific approach in efforts to enhance CNS regeneration is to manipulate the biochemical environment of the cells at the site of the spinal cord injury, according to Basbaum. Instead of this type of investigation, Basbaum's team used nervous system manipulation techniques to apply the principles of PNS cell growth capability to CNS cells.

The researchers took advantage of an unusual class of nerve fibers that has both a PNS and a CNS branch. Previously, the researchers had shown in animal studies that an injury made to the peripheral branch prior to a spinal cord injury provided the essential communication signal that enabled the CNS branch to grow. But this only worked if the PNS injury--which served as priming for CNS cell growth--was made at least a week before the CNS injury. "Clearly this would have no utility in clinical situations, where treatments cannot be made in anticipation of spinal cord injury," says Basbaum. Another challenge the researchers faced was stimulating CNS cells to grow beyond the injury site and into healthy tissue, which is essential to help regain function.

"A PNS injury at the time of spinal cord damage will only promote growth of nerve fibers into the spinal cord lesion, but not into the tissue beyond it. This is because growth capacity is enhanced, but it is not sustained," he explains. In the new study, researchers evaluated the effect of two peripheral nerve lesions (injuries) in animals with spinal cord injury. One lesion was made at the time of the cord injury and a second was made a week later. Both lesions were located in the animals' sciatic nerve, which is part of the PNS.

The researchers found that the two "priming lesions" not only promoted significant spinal cord regeneration within the area of the spinal cord injury, but more important, the regenerating axons grew back into normal areas of the spinal cord, where the hope is that functional connections can be reestablished. Axons are the long, fragile, fibers that conduct impulses between nerve cells in the brain, spinal cord and limbs.

"Getting the growth beyond the lesion is key. If we can get those axons to grow even a few centimeters past the lesion, they can start sending signals and developing new circuits throughout the body," says Basbaum. Basbaum adds that timing is critical for successful nerve regeneration. "There is a window of opportunity just after the injury when the potential for growth through and beyond the lesion is greatest. If we wait too long after an injury, the cells revert back to their normal, no-growth state. Plus, scar tissue begins to form, making growth difficult." "These findings give us hope. The nervous system is capable of being modified to a level where we can achieve nerve fiber growth. Ultimately, the goal is to promote growth and sustain it long enough for recovery of movement to occur in spinal cord injury patients," he concludes. Study co-authors include first-author Simona Neumann, PhD, and Kate Skinner, MD, both of UCSF. The research was funded by the Roman Reed Spinal Cord Injury Research Fund of California and the National Institutes of Health.

Silenced smedwi-2 gene shows role in regeneration

Fri, 25 Nov 2005 06:26:38 PST

( from http://www.rxpgnews.com ) Researchers at the University of Utah have discovered that when a gene called smedwi-2 is silenced in the adult stem cells of planarians, the quarter-inch long worm is unable to carry out a biological process that has mystified scientists for centuries: regeneration.

The study published in the Nov. 25 issue of Science was led by Alejandro Sánchez Alvarado, Ph.D., Howard Hughes Medical Institute investigator and professor of neurobiology and anatomy at the U of U School of Medicine, and carried out by members of his laboratory, in particular Helen Hay Whitney Foundation post-doctoral fellow Peter W. Reddien who is now an Associate Member at the Whitehead Institute for Biomedical Research.

Elimination of smedwi-2 not only leads to an inability to mount a regenerative response after amputation, but also to the eventual demise of unamputated animals along a reproducible series of events, that is, regression of the head tip, curling of the body and tissue disintegration. These defects are very similar to what is observed after the planarian stem cells are destroyed by lethal doses of irradiation. The key difference, however, is that the irradiation-like defects observed in animals devoid of smedwi-2 occur even though the stem cells are still present in the organism.

This finding suggests something surprising: the instructions that a daughter stem cell needs to differentiate for regeneration or for maintaining tissue structure begin to be defined at the time of division of its parent cell. "Once the smedwi-2 molecule is eliminated, the animal is destined to die since the functions of the daughter cells are severely compromised" said Sánchez Alvarado.

The study follows a landmark work that he and Reddien published last spring in Developmental Cell, in which, using a method of gene silencing called RNA interference (RNAi), the researchers silenced more than 1,000 planarian genes, some of which they identified as essential for regeneration. The Science study focus on one such gene, smedwi-2, and brings a new level of genetic detail to understanding planarian regeneration.

Planarians long have fascinated biologists with their ability to regenerate. A worm sliced in two forms two new worm s; even a fractional part of a planarian will grow into a new worm. Scientists know that planarian stem cells, called neoblasts, are central to regeneration, but their exact role is only now being learned.

When an animal stem cell divides, two daughter cells are formed: one that is another stem cell and a second one that can differentiate into the cells that form bone, tissue, and other parts of an organism. These second types of cells are essential for regeneration or maintaining the form and function of tissues by replacing cells that die, a process called homeostasis.

By eliminating smedwi-2, the researchers uncovered a role of this protein in regulating the normal differentiation and function of daughter cells.

The researchers postulated three theories why the worms could not regenerate or maintain cells after smedwi-2 was silenced:

# The stem cells were not responding to tissue damage or homeostasis signals.
# The stem cell division progeny failed to migrate to the appropriate tissues.
# The daughter cells didn't know how to differentiate.

The team found that the stem cells were competent to robustly respond to amputation by significantly increasing their proliferation as well as to home to tissues undergoing homeostasis. But the researchers also found that once the daughter cells reach their target tissues, they were unable to properly differentiate.

"The smedwi-2 molecule is doing something early in the specification of stem cell progeny that modulates their ability to differentiate into the proper cell type," Sánchez Alvarado said. How this molecule is modulating stem cells is one of the next steps that he and Reddien are trying to solve. The answer could have far-reaching implications, because genes similar to smedwi-2 are found in plants, animals and human beings.

Novel role for ubiquitin/proteosome in regulation of actin dynamics

Sun, 02 Oct 2005 17:52:38 PST

( from http://www.rxpgnews.com ) In a recent study, Dr. Ingolf Bach and colleagues from the University of Massachusetts Medical School, Worcester and the University of Hamburg (Germany) describe a novel role for the ubiquitin/proteosome protein degradation pathway in the regulation of local actin dynamics in neurons.

The authors are able to show that the ubiquitin ligase Rnf6 polyubiquitinates the kinase LIMK1, targeting it for proteosomal degradation in the growth cones of hippocampal neurons. LIMK1 regulates the dynamics of the actin cytoskeleton primarily via phosphorylation of the actin depolymerization factors ADF/cofilin, with important consequences for cell morphology, cell motility, and the development of neuronal projections. Changes in LIMK1 concentration have an impact in neuronal growth cone actin dynamics and axon formation.

The authors focus on the RING finger protein Rnf6 due to its similarity to the previously identified protein RLIM, which has been shown to bind to nuclear LIM domains and critically regulate the biological activity of LIM-HD transcription factors. The authors find high levels of Rnf6 protein in axonal projections of motor neurons and dorsal root ganglia neurons in mouse embryos at a time in which projections are actively developing, suggesting a role of this protein in the development of these neurons. They are able to show that this is indeed the case by RNAi-mediated knock-down of Rnf6 in primary hippocampal neurons, which stimulate axon outgrowth, and by over-expression of Rnf6 that results in a significant decrease in axon length.

Finding that Rnf6 targets LIMK1 for degradation finally closes this circle of regulation, providing the link between actin dynamics, axonal growth and Rnf6. Importantly, the authors are able to show that changes in axon outgrowth induced by changes in levels of Rnf6 can be restored by compensatory changes in LIMK1 expression, thereby giving Rnf6 a central role in controlling actin dynamics in subcellular structures. Because LIMK1 has been implicated in biological processes such as metastasis and invasion of cancer, Dr. Bach points out that "these results indicate that Rnf6 not only plays an important role in coordinating neuronal development but may be also involved in oncogenesis."

Myosin II involved in guidance of the nerve branches

Fri, 16 Sep 2005 21:23:38 PST

( from http://www.rxpgnews.com ) A protein that helps the ends of growing nerve cells push forward is also involved in guidance of the nerve branches, according to a study by researchers at Washington University School of Medicine in St. Louis.

"We really thought that myosin II was just a motor, but it seems to help steer as well, " says senior investigator Paul C. Bridgman, Ph.D., associate professor of neurobiology. "Better understanding of these guidance systems is essential to efforts to regenerate injured nerves. It's one thing to get nerve cells to grow again, but it's another to actually direct the regenerating nerve to its appropriate target."

Bridgman's lab has been studying cell growth in the peripheral nervous system for more than a decade. Growing branches from peripheral nerves form an enlargement at their tips known as a growth cone.

Bridgman's group was among the first to show that myosin II, which is similar to the myosin proteins found in muscle tissue, contracts to help give the growth cone the traction it needs to crawl forward.

They've also proved that stimulation from the environment affects the direction of a growing axon. Growth cones have a clear preference for laminin type 1, a polypeptide found throughout the body during development but much less common in adults. Mouse nerve cells growing across laminin in the lab will turn away when they encounter other substances and grow along the border of the area containing laminin. In addition, the mouse nerve cells avoid transitions to areas with much lower concentrations of laminin and instead grow along the boundaries of high-concentration regions.

In their newest study, inhibiting myosin II caused growth cones to lose their selectiveness and cross the border between a region containing laminin and a region that had no laminin.

"This proves that myosin II contributes in some way to the growth cone's ability to preferentially select laminin-rich surfaces to grow on," Bridgman says. Scientists know that the nerve growth cone's surface includes receptors that activate kinases.

"There are many different kinases that interact with the type of receptor found on the nerve growth cone, so it's not going to be trivial to figure out which one is important for this function," Bridgman notes.

Gradient guides nerve growth down spinal cord

Tue, 06 Sep 2005 00:29:38 PST

( from http://www.rxpgnews.com ) The same family of chemical signals that attracts developing sensory nerves up the spinal cord toward the brain serves to repel motor nerves, sending them in the opposite direction, down the cord and away from the brain, report researchers at the University of Chicago in the September 2005 issue of Nature Neuroscience (available online August 14). The finding may help physicians restore function to people with paralyzing spinal cord injuries.

Growing nerve cells send out axons, long narrow processes that search out and connect with other nerve cells. Axons are tipped with growth cones, bearing specific receptors, which detect chemical signals and then grow toward or away from the source.

In 2003, University of Chicago researchers reported that a gradient of biochemical signals known as the Wnt proteins acted as a guide for sensory nerves. These nerves have a receptor on the tips of their growth cones, known as Frizzled3, which responds to Wnts.

In this paper, the researchers show that the nerves growing in the opposite direction are driven down the cord, away from the brain, under the guidance of a receptor, known as Ryk, with very different tastes. Ryk sees Wnts as repulsive signals.

"This is remarkable example of the efficiency of nature," said Yimin Zou, PhD, assistant professor of neurobiology, pharmacology, and physiology at the University of Chicago. "The nervous system is using a similar set of chemical signals to regulate axon traffic in both directions along the length of the spinal cord."

It may also prove a boon to clinicians, offering clues about how to grow new connections among neurons to repair or replace damaged nerves. Unlike many other body components, damaged axons in the adult spinal cord cannot adequately repair themselves. An estimated 250,000 people in the United States suffer from permanent spinal cord injuries, with about 11,000 new cases each year.

This study focused on corticospinal neurons, which control voluntary movements and fine-motor skills. These are some of the longest cells in the body. The corticospinal neurons connect to groups of neurons along the length of spinal cord, some of which reach out of the spinal cord. They pass out of the cord between each pair of vertebrae and extend to different parts of the body, for example the hand or foot.

Zou and colleagues studied the guidance system used to assemble this complex network in newborn mice, where corticospinal axon growth is still underway. Before birth, axons grow out from the cell body of a nerve cell in the motor cortex. The axons follow a path back through the brain to the spinal cord.

By the time of birth, the axons are just growing into the cord. During the first week after birth they grow down the cervical and thoracic spinal cord until they reach their proper position, usually after seven to ten days.

From previous studies, Zou and colleagues knew that a gradient of various Wnt proteins, including Wnt4, formed along the spinal cord around the time of birth. Here they show that two other proteins, Wnt1 and Wnt5a are produced at high concentrations at the top of the cord and at consecutively lower levels farther down.

They also found that motor nerves are guided by Wnts through a different receptor, called Ryk, that mediates repulsion by Wnts. Antibodies that blocked the Wnt-Ryk interaction blocked the downward growth of corticospinal axons when injected into the space between the dura and spinal cord in newborn mice.

This knowledge, coupled with emerging stem cell technologies, may provide the most promising current approach to nervous system regeneration. If Wnt proteins could be used to guide transplanted nerve cells--or someday, embryonic stem cells--to restore the connections between the body and the brain, "it could revolutionize treatment of patients with paralyzing injuries to these nerves," Zou suggests.

"Although half the battle is acquiring the right cells to repair the nervous system," he said, "the other half is guiding them to their targets where they can make the right connections."

"Understanding how the brain and the spinal cord are connected during embryonic development could give us clues about how to repair damaged connections in adults with traumatic injury or degenerative disorders," Zou added.

Ephrin-B3 inhibits regrowth of spinal nerve cells

Tue, 12 Jul 2005 13:03:38 PST

( from http://www.rxpgnews.com ) A molecule that helps the body's motor nerve cells grow along proper paths during embryonic development also plays a major role in inhibiting spinal-cord neurons from regenerating after injury, researchers at UT Southwestern Medical Center have found. In cultured cells, the researchers found that a component of myelin a substance that normally insulates and stabilizes long nerve fibers in adult vertebrates chemically blocks the ability of nerve cells to grow through myelin that is released when the spinal cord is damaged. While other myelin components also block nerve growth, a component called ephrin-B3 inhibits such activity as well or better than that of other known blocking agents combined, UT Southwestern researchers report in an upcoming issue of the Proceedings of the National Academy of Sciences.

"I believe that to the extent that overcoming myelin-based inhibition is going to provide some sort of functional recovery for spinal cord injury patients, understanding ephrins is a major step forward," said Dr. Luis Parada, senior author on the paper and director of the Center for Developmental Biology and the Kent Waldrep Center for Basic Research on Nerve Growth and Regeneration at UT Southwestern. A mixture of molecules and proteins, myelin insulates nerve fibers and impedes them from having contact with other nerve cells. After a spinal-cord injury, myelin is released into the tissues. Not only does myelin encourage the growth of scars called glial scars which physically block nerve cells from regrowing in the damaged area, but components of myelin also chemically prevent nerve cells from regrowing there as well.

Considerable research has been done in the past 10 years to identify elements in myelin that chemically inhibit the regeneration of nerve cells, Dr. Parada said. Three individual components the molecules Nogo, MAG and OMgp have been shown to do so in isolation. Developmental biologists at UT Southwestern have been studying how ephrin-B3 helps control how and where nerve fibers grow during early development. They previously showed that the molecule throws up "fences" that repel developing nerves and guide them along the pathways to their appropriate connections to muscles.

In 2002 Dr. Mark Henkemeyer, associate professor in the Center for Developmental Biology and of cell biology and one of the authors of the PNAS study, found that such a "fence" is erected specifically down the middle of the cortical spinal tract, which is damaged during spinal-cord injury.

In the current study, Dr. Parada and his colleagues asked: What is this molecule, whose normal function is to be repellent during embryonic development, doing in the mature system?

"To our surprise, we found that ephrin-B3, which normally is present as a 'wall' down the middle of adult spinal cords, also is found in very high levels in adult myelin," said Dr. Parada.

The researchers knew from previous work that ephrin-B3 interacts with receptors on neurons in the cortical spinal cord. So, in the lab, led by the study's lead author Dr. M. Douglas Benson, a postdoctoral research fellow, they cultured neurons together with isolated ephrin-B3 and confirmed that the molecule activated the neuron's receptors. They then cultured normal myelin together with the neurons and got the same results.

However, when they cultured neurons with myelin from which the ephrin-B3 had been removed, the receptors were not activated. The findings suggest that there is much more to be learned about myelin-based inhibition, Dr. Parada said. "We firmly believe that ephrin-B3 is an important, functional, relevant component of myelin, although there may be other elements that are left to be discovered," he said.

Dr. Parada added that several factors must be overcome before spinal-cord regeneration and recovery from injury can occur in a meaningful way for patients.

"We have to figure out how to dissolve the glial scars or impede their formation," he said. "We also need to get mature neurons to be better at growing, similar to the way they do during embryonic development. And finally, we have to remove myelin-based inhibition. If and when we achieve those three things, then we'll have robust regeneration of injured nerves."

New findings might advance search for new therapies for injured nerve fibers

Thu, 03 Mar 2005 17:26:38 PST

( from http://www.rxpgnews.com ) Long distance messengers star in many heroic tales, perhaps the most famous being the one about the runner who carried the news about the victory of the Greeks over the Persians in the fateful battle of Marathon. A team of researchers at the Weizmann Institute of Science has now discovered how molecular messengers perform a crucial role in the ability of injured nerve cells to heal themselves.

A nerve cell has a cell body and a long extension, called an axon, which in humans can reach up to one meter in length. Nerve cells belonging to the peripheral nervous system can regrow when their axons are damaged. But how does the damaged axon inform the cell body that it must start producing vital proteins for the healing? That's precisely where the molecular messengers, proteins called Erk-1 and Erk-2, enter the picture. When the axon is injured, these proteins bind to molecules of phosphorus. In this phosphorylated state, they can communicate to command centers in the cell, transmitting a message that activates certain genes in the cell body, which then manufactures proteins that are vital for the healing of the injured axon. The problem is that the messengers must transmit their phosphorus message over a great distance along the axon, and in the course of this arduous journey can easily lose their phosphorus en route.

Dr. Michael Fainzilber and graduate students Eran Perlson and Shlomit Hanz of the Weizmann Institute's Biological Chemistry Department found that the Erk messengers, together with their phosphorus message, bind to a special molecule called vimentin, which protects them from dismantling or loss of the phosphorus. Vimentin links up to motor proteins that carry the message along the axon, and thanks to this linkage and protection, the messengers can safely transmit their message, thus bringing the injured axon's call for help to the cell body. The scientists hope that these findings might advance the future search for new therapies for injured nerve fibers.

For the first time scientists have regenerated a damaged optic nerve

Thu, 24 Feb 2005 19:16:38 PST

( from http://www.rxpgnews.com ) Scientists have regenerated a damaged optic nerve for the first time from the eye to the brain in laboratory mice. This feat holds great promise for victims of diseases that destroy the optic nerve, and for sufferers of central nervous system injuries. "For us, this is a dream becoming reality," says Dr. Dong Feng Chen, lead author of the study, assistant scientist at Schepens Eye Research Institute and an assistant professor of ophthalmology at Harvard Medical School. "This is the closest science has come to regenerating so many nerve fibers over a long distance to reach their targets and to repair a nerve previously considered irreparably damaged."

This research, which has been supported in part by grants from the National Institutes of Health, the Department of Defense and the Massachusetts Lions Club, has always been a priority of the institute, but in recent times, urgency around it has increased, according to Dr. Michael Gilmore, director of research at Schepens Eye Research Institute and professor of ophthalmology at Harvard Medical School. In addition to the thousands of Americans blinded by glaucoma and injuries that destroy the optic nerve, and hundreds of thousands disabled by spinal cord injuries, "we were hearing stories of soldiers in the Middle East whose lives were saved by body armor, but who were returning with severe damage to limbs and eyes," he says. "At the same time, we learned of the untimely death of Christopher Reeves. It was, therefore, a priority for us to redouble our efforts to find ways to restore damaged nerves."

According to Senator John Kerry, who supported funding of this important work, "Schepens is doing cutting-edge research that can make a real difference for a new generation of troops returning home with nerve damage. We need to support our troops in actions, not just words, and I am glad that we have been able to get funding for this important work." Adds Congressman Lynch, "Last month, I visited the Walter Reed Army Medical Center in Washington and met with dozens of service men and women who could benefit directly from the good work of the people at Schepens. Their vital research will not only enhance the lives of our soldiers but also gives hope to every American who suffers from diseases of the central nervous system."

Many tissues in the body continually renew themselves if injured. However, this is not true for nerve cells or their fibers (axons) in the Central Nervous System (CNS). The CNS consists of the brain (of which the eye and optic nerve are part) and the spinal cord. For all mammals, including human beings, CNS nerves lose their ability to regenerate after injury at the point in their development when they are fully formed. For example, the optic nerve loses this ability shortly before birth. So for those afflicted by glaucoma, which destroys the optic nerve through excessive internal pressure, or with injuries that sever the optic nerve after that developmental milestone, destruction can be permanent and blinding.

Chen and her research team have dedicated themselves to learning the reasons why CNS tissue stops regenerating and to finding ways to reverse that process, using the optic nerve as their research model. The optic nerve, which connects the eye to the brain, consists of millions of nerve cells, which, when uninjured, transmit visual information from the retina to the brain for interpretation

In earlier research, Chen's team discovered several processes that they believed "locked up" the optic nerve's ability to regenerate. The first lock, they found, was the turning off of a specific gene BCL-2 which, when turned on, activates growth and regeneration. The second lock, they theorized, was a scar on the brain created shortly after birth by "glial" cells. (glial cells have many functions in the brain, one of which is to create this kind of scar tissue). The researchers believed that the scar puts up a physical as well as molecular barrier to regeneration. Although there may be other "locks" to the regeneration door, Chen and her colleagues believed these two were the most important.

In the current research, Dr. Kin-Sang Cho, research associate in Chen's laboratory and the first author of the paper, tested two keys to unlock regeneration. The first key involved the development of a mouse model in which the BCL-2 gene is always turned on (or is overexpressing). The second key was the use of a mouse line carrying mutations of "glial specific genes" that lead to the reduced "glial scar" formation.

By unlocking the regeneration with the first key, for the first time, they observed robust optic nerve regeneration in postnatal mice, which nerves grew rapidly and reached from the eye to the brain in four days. But the regeneration happens only in the younger mice whose brains had not yet formed a "glial scar." In the mice that were slightly older and had developed the "glial scar," regeneration failed again.

Dr. Cho then added the second key by combining BCL-2 overexpresser with the "glial gene" mutation to prevent the development of the "glial scar" in the older transgenic mice. He found that the combination of the turned-on BCL-2 and the mutation of "glial specific genes" caused the optic nerves to return to an embryonic state and stimulated rapid, robust regeneration of the optic nerve--again, as with the younger mice within only a few days.

"We could see that at least 40 percent of the optic nerve had been restored," says Chen, "but we believe that an even higher percentage actually regenerated."

The next step for Chen and her colleagues is to determine if the regenerated optic nerves were functional. In other words, did they cause the mice to see again?

Chen also believes that this combination BCL-2 and scar prevention technique could work to regenerate other Central Nervous System tissue, increasing the possibility that spinal cord patients could walk or move again.

This work has important implications. "The possibility of restoring sight following optic nerve injuries is tremendous. Fifteen percent of all wartime injuries include the eye and those with optic nerve trauma are the most grave. Today's medicine has little effective treatment to offer and blindness is often the end result," says Retired Lieutenant Colonel Robert C. Read of the Clinical Applications Division at the Department of Defense's Telemedicine and Advanced Technology Research Center.

"This outstanding breakthrough by Schepens scientists offers new hope to those who suffer from blinding diseases and injuries, including our returning soldiers. The potential application of this discovery to treatments for other central nervous system injuries is yet another reason why I have been proud to support the Department of Defense's funding of the Center for Excellence in Military Low Vision Research," stated Congressman Mike Capuano.

Adds Congressman Stephen F. Lynch, "This extraordinary breakthrough demonstrates what we can achieve when we support public and private partnerships between the Defense Department and the best researchers and scientists in the field. Because of the decades of work and progress by Dr. Gilmore and Dr. Chen and the entire team at the Schepens Eye Research Institute, the search for a way to repair nerve damage in the human body has taken a giant leap forward."

"I'm so pleased with the work going on at Schepens," Rep. Jim McGovern says. "They are on the frontiers of research that will dramatically improve people's lives. And the Federal Government must continue to be a partner in this vital effort."

A STAT3 Call for Regeneration

Wed, 16 Feb 2005 15:19:38 PST

( from http://www.rxpgnews.com ) Regeneration in the CNS after spinal cord injury is limited because of obstacles such as glial scars and myelin-based inhibitory factors. On the other hand, axons in the PNS are much more resilient. This week, Qiu et al. provide evidence for Janus kinase (JAK)signal transducer and activator of transcription (STAT) signaling downstream of the cytokines. The JAK2STAT3 pathway appears to be growth-promoting after a peripheral nerve injury.