Turning Back The Clock For Schwann Cells

May 20, 2008

Myelin-making Schwann cells have an ability every aging Hollywood star would envy: they can become young again. According to a study appearing in the May 19 issue of the Journal of Cell Biology, David B. Parkinson (University College London, London, UK) and collogues have pinned down a protein that returns the cells to their youth, a finding that might help researchers understand why myelin production falters in some diseases.

Wrapped around neurons in the peripheral nervous system, Schwann cells can "dedifferentiate" into a state in which they can't manufacture myelin. Reverting to an immature type of cell speeds healing of injured nerves. Researchers knew that the protein Krox-20 pushes immature Schwann cells to specialize and form myelin, but they didn't know what prompts the reversal. One suspect was a protein called c-Jun, which youthful Schwann cells make but Krox-20 blocks.

Parkinson et al. cultured neurons with Schwann cells whose c-Jun gene they could activate. Turning on the gene curbed myelination, suggesting that c-Jun prevents young Schwann cells from growing up. c-Jun also prodded mature Schwann cells to become youthful again, the researchers discovered. Schwann cells that are separated from neurons normally dedifferentiate, but the team found that the cells remained specialized if c-Jun was missing. They suspect that c-Jun works in part by activating Sox-2, as this protein also inhibits myelination.

The researchers now want to investigate whether c-Jun is involved in illnesses where myelin dwindles, such as Charcot-Marie Tooth disease and Guillain-Barre syndrome. The results might also provide clues about multiple sclerosis, in which immune attacks destroy myelin in the central nervous system. Unlike Schwann cells, oligodendrocytes, the myelin makers in the central nervous system, can't revert to an immature state. Whether c-Jun affects oligodendrocyte differentiation isn't known.

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Article adapted by Medical News Today from original press release.
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Parkinson, D.B., et al. 2008. J. Cell Biol. doi:10.1083/jcb.200803013.

Developmental loss of NT-3 in vivo results in reduced levels of myelin-specific proteins

February 01, 2008

Glia. 2008 Feb;56(3):306-17.

Developmental loss of NT-3 in vivo results in reduced levels of myelin-specific proteins, a reduced extent of myelination and increased apoptosis of Schwann cells.

Woolley AG, Tait KJ, Hurren BJ, Fisher L, Sheard PW, Duxson MJ.

Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand.

This work investigates the role of NT-3 in peripheral myelination. Recent articles, based in vitro, propose that NT-3 acting through its high-affinity receptor TrkC may act to inhibit myelin formation by enhancing Schwann cell motility and/or migration. Here, we investigate this hypothesis in vivo by examining myelination formation in NT-3 mutant mice. On the day of birth, soon after the onset of myelination, axons showed normal ensheathment by Schwann cells, no change in the proportion of axons which had begun to myelinate, and no change in either myelin thickness or number of myelin lamellae. However in postnatal day 21 mice, when myelination is substantially complete, we observed an unexpected reduction in mRNA and protein levels for MAG and P(0), and in myelin thickness. This is the opposite result to that predicted from previous in vitro studies, where removal of an inhibitory NT-3 signal would have been expected to enhance myelination. These results suggest that, in vivo, the importance of NT-3 as a major support factor for Schwann cells (Meier et al., (1999) J Neurosci 19:3847-3859) over-rides its potential role as an myelin inhibitor, with the net effect that loss of NT-3 results in degradation of Schwann cell functions, including myelination. In support of this idea, Schwann cells of NT-3 null mutants showed increased expression of activated caspase-3. Finally, we observed significant reduction in width of the Schwann cell periaxonal collar in NT-3 mutant animals suggesting that loss of NT-3 and resulting reduction in MAG levels may alter signaling at the axon-glial interface.

1996 article from New York Times archives explains P0 mutation in Dejerine-Sottas

December 02, 2007

The New York Times recently digitized its pre-Internet archives and opened them to the public, so today I ran a search and found a single mention of Dejerine-Sottas disease. It's an interesting article on the use of x-ray crystallography to shed some light on the proteins created by the P0 mutation, one of the mutations that causes Dejerine-Sottas.

Protein Linked to 3 Nerve Ailments

IN two papers representing the work of 19 researchers, scientists reported last week that they had seen, at a molecular level, the damage to an important protein that is the cause of three genetic nerve disorders. Dr. Thomas Bird, a professor at the University of Washington and chief of neurology at the Veterans Affairs hospital in Seattle, who is not associated with the groups who made the reports, said that the papers are examples of where medicine has arrived: at the molecular detail of human disease.

Read more of Protein Linked to 3 Nerve Ailments

Key Nerve Navigation Pathway Identified

November 27, 2007

Newly launched nerve cells in a growing embryo must chart their course to distant destinations, and many of the means they use to navigate have yet to surface. In a study published in the current issue of the journal Neuron, scientists at the Salk Institute for Biological Studies have recovered a key signal that guides motor neurons -- the nascent cells that extend from the spinal cord and must find their way down the length of limbs such as arms, wings and legs.

The Salk study, led by Samuel Pfaff, Ph.D, a professor in the Gene Expression Laboratory, identifies a mutation they christened Magellan, after the Portuguese mariner whose ship Victoria was first to circumnavigate the globe. The Magellan mutation occurs in a gene that normally pilots motor neurons on the correct course employing a newly discovered mechanism, their results demonstrate.

Read the rest of Key Nerve Navigation Pathway Identified

Critical Knowledge About The Nervous System Uncovered By Rutgers Scientists

November 08, 2007

Uncover the neural communication links involved in myelination, the process of protecting a nerve's axon, and it may become possible to reverse the breakdown of the nervous system's electrical transmissions in such disorders as multiple sclerosis, spinal cord injuries, diabetes and cancers of the nervous system.

With $697,065 in grants from the New Jersey Commission on Spinal Cord Injury and the New Jersey Commission on Brain Injury Research, Haesun Kim of Teaneck, NJ, assistant professor of biological sciences at Rutgers University in Newark, is working on gaining a better understanding of those links.

Specifically, her work focuses on Schwann cells within the peripheral nervous system and their communication links with the axons they myelinate by enwrapping them in myelin. Axons are the long fibrous part of neurons that carry the nerve's electrical signals. A fatty substance, myelin covers those axons both to protect them and to provide a conduit for the fast conduction of electrical signals within the nervous system. Once that myelin is lost,the electrical signal breaks down and eventually the neuron dies -- like a cell phone that loses its signal.

Determining how Schwann cells and axons communicate with one another could lead to an understanding of how to promote remyelination, the rebuilding of myelin, and restoration of that signal. One unique aspect of the communication link between Schwann cells and axons is that they are mutually dependent upon that connection for their existence.

"When Schwann cells are generated during development, axons send out signals to the Schwann cells and tell them, 'You are going to become myelin cells and you are going to myelinate me,'" explains Kim. "The Schwann cells in turn guide the axons to where they need to go and direct the axons to grow."

By pinpointing the sequence and nuances of the communication links involved in myelination, targeted genetic and pharmacological interventions possibly could be developed to restore the loss of myelin. Such an understanding additionally may allow for the effective transplanting of Schwann cells in the central nervous system to promote remyelination and the correction of neurological disorders at that level.

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Article adapted by Medical News Today from original press release.
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The New Jersey Commission on Spinal Cord Injury has provided $397,066 and the New Jersey Commission on Brain Injury Research $299,999 to support Kim's research.

Kim received her M.S. in biology from the University of Toledo, her Ph.D. in cell biology, neurobiology and anatomy from the University of Cincinnati, and performed her post-doctoral work at the Dana-Farber Cancer Institute at Harvard Medical School. She joined the Rutgers-Newark faculty in 2004.

Click here for more information on Dr. Kim's research.

Movies Reveal That the Process of Insulating Nerves Is Surprisingly Dynamic

November 15, 2006

The first time lapse movies of the initial stage of the process that wraps nerve fibers with an outer, insulating layer, published online on Nov. 12 in the journal Nature Neuroscience, are shedding new light on this complex process and should aid in the design of new therapies to promote this protective layer following disease or injury.

An image of the spinal cord of a living zebrafish embryo captures two oligodendrocyte progenitor cells, labeled in red and green fluorescent protein, during the period in development when they are spacing themselves along newly formed axons.

Much like the electrical wiring in your house, the nerves in your body need to be completely covered by a layer of insulation to work properly.

Instead of red, white or black plastic, however, the wiring in the nervous system is protected by layers of an insulating protein called myelin. These layers increase the speed that nerve impulses travel throughout the brain and the body. The critical role they play is dramatically illustrated by the symptoms of multiple sclerosis, which is caused by lesions that destroy myelin. These include: blindness, muscle weakness and paralysis, loss of coordination, stuttering, pain and burning sensations, impotence, memory loss, depression and dementia.

The formation of myelin sheaths during development requires a complex choreography generally considered to be one of nature’s most spectacular examples of the interaction between different kinds of cells. Now, a group of Vanderbilt researchers has successfully produced movies that provide the first direct view of the initial stage of this process: the period when the cells that ultimately produce the myelin sheathing spread throughout the developing nervous system. The results were published online in the journal Nature Neuroscience on Nov. 12 and should aid in the design of new therapies to promote the repair of this protective layer following disease or injury.

“We discovered that this process is far more dynamic than anyone had dreamed,” says Bruce Appel, the associate professor of biological sciences and Kennedy Center investigator who headed up the study.

In the central nervous system, the myelin membranes are produced by cells called oligodendrocytes. These cells must be distributed uniformly along axons – the long, wire-like extensions from neurons that carry nerve impulses – so that the membranes, which wrap the nerve fibers like millions of microscopic pieces of electrician’s tape, can cover the axons completely and uniformly. The wrapping process takes place near the end of fetal development and actually continues for some time after birth.

In order to study this process, Appel and his research group – graduate students Brandon Kirby and Jimann Shin along with post doctoral fellows Norio Takada and Andrew Latimer – created a transgenic zebrafish which incorporates fluorescent proteins in the cells involved in myelination. The zebrafish is a small tropical fish that has become a popular species for studying the process of development in vertebrates (animals with backbones). Because zebrafish embryos are transparent and develop within a few days, they allow biologists to watch developmental processes as they take place: something they cannot do with mice or other mammals. These characteristics allowed the Vanderbilt researchers to obtain images of the cells involved in myelination using a confocal microscope and edit them into time-lapse movies.

The oligodendrocytes that produce the myelin membranes arise from mobile, dividing cells called “oligodentrocyte progenitor cells” or OPCs. OPCs are made in special locations in the brain and spinal cord. These cells seek out axons and spread out along them. Then, at a certain point, a fraction of the OPCs transform themselves into oligodentrocytes and begin wrapping axons. Each cell can wrap portions of several different axons and each axon is wrapped by a large number of oligodentrocytes.

Before the Vanderbilt study, there were a number of different theories about how OPCs space themselves along axons. One was that the axons themselves produce some kind of positional cues that the OPCs follow. Another was that the OPCs sense each other and adjust their position accordingly: a mechanism somewhat similar to that which soldiers on the parade ground use to align a formation by extending their right arm and adjusting their position until their outstretched fingers touch the shoulder of the person on the right.

Previous studies of OPCs grown in tissue culture had seen that they could generate small pseudopods, called filopodia, but no one knew what their purpose might be. So, when the researchers began viewing their movies, they were excited to observe that the cells were continually sending out filopodia in different directions. They found that OPCs not only generate these tiny tentacles, but keep them extending and contracting in a fashion reminiscent of the party noise-makers called blow-outs that unroll when you blow on them and snap back when you stop. They observed that when one of these tiny tentacles touches a neighboring OPC, the cells react by moving in the opposite direction. This caused a surprising amount of movement as the OPCs repeatedly readjusted their positions.

“This could serve as a surveillance mechanism that allows the OPCs to determine the presence or absence of nearby cells of the same type,” says Appel, “and could explain how they distribute themselves along the axons.”

The researchers used the same system to see how the OPCs respond to injuries and conditions like multiple sclerosis. They did so by using a laser to destroy the OPCs along a short length of the embryo’s spine a day before the axon-wrapping stage begins. They found that the OPCs in the vicinity of the gap start dividing to produce additional cells that move into the gap. After a day, the number of OPCs in the gap had grown to 50 percent of normal and after four days it had risen to 70 percent.

“Now that we have a better understanding of OPC and oligodendrocyte behaviors, we are in a much better position to identify and study the genes that are necessary for myelination,” says Appel, “and having these genes in hand should aid in the design of drugs to promote remyelination following disease or injury.”

Video is available by contacting the source.

USC Researchers Closer To Cure For Multiple Sclerosis And Other Myelin-Related Diseases

November 05, 2006

Los Angeles - A breakthrough finding on the mechanism of myelin formation by Jonah Chan, assistant professor of cell and neurobiology at the Keck School of Medicine of the University of Southern California, could have a major impact on the treatment of diseases such as multiple sclerosis and demyelination as a result of spinal cord injuries.

Myelin, the white matter that coats all nerves, allows long-distance communication in the nervous system. "It plays a vital role in the overall health and function of the nervous system, and its degeneration plays a role in a number of diseases, such as multiple sclerosis, peripheral neuropathies, and even in spinal cord injury," Chan explained.

The study, "The Polarity Protein Par-3 Directly Interacts with p75NTR to Regulate Myelination", appears in the Nov. 3 issue of Science. Chan, who works at the Zilkha Neurogenetic Institute at the Keck School of Medicine of USC, collaborated on the study with Michel Cayouette and researchers at the Institut de Recherches Cliniques de Montreal in Canada.

At a basic level, the nervous system functions like a collection of wires that transmit electrical signals encoding our thoughts, feelings, and actions. Just as an electrical wire needs insulation, myelin is wrapped around axons - the wire-like extensions of neurons that make up nerve fibers. The sheath helps to propagate the electrical signal and maximize the efficiency and velocity of these signals in our brain and body.

Diseases and injuries that compromise the integrity of myelin, such as multiple sclerosis or peripheral neuropathies, have dramatic consequences like paralysis, uncoordinated movements, and neuropathic pain.

Chan's study sheds light on the mechanisms that control how myelin is formed during development of the nerves. The article constitutes an important step forward in understanding the process of myelination and opens the way to new research in this field.

Chan showed that a protein, Par-3, is at the base of the myelination process. This protein becomes localized to one side of the myelin-forming cells, known as Schwann cells, upon contact with the axon that is to be myelinated. Par-3 acts almost as a molecular scaffold to set-up an "organizing centre", which brings together key proteins essential for myelination, in particular a receptor for a molecule secreted by the neurons.

The researchers found that when they disrupted this organizing centre, cells could not form myelin normally. Importantly, their discovery demonstrates that Schwann cells need to become polarized so that they know which side is in contact with the axon to initiate wrapping and to bring essential molecules to this critical interface.

These studies open the way to new research, said Chan, which should help to identify other components that are recruited at the organizing center set-up by Par-3. In multiple sclerosis, or after injury, Schwann cells can re-myelinate axons of the central nervous system to some degree. Therefore, these experiments bring about the possibility that manipulating the Par-3 pathway might allow for more efficient re-myelination of damaged or diseased nerves.

SOURCE: University of Southern California

Researchers Find Protein Determines Nerve's Fate

October 26, 2005

Researchers at the Skirball Institute of Biomolecular Medicine, New York University (NYU) School of Medicine, have found that a protein (neuregulin-1 type III, or NRG1-III) essential for the protective wrapping around a nerve's central wiring, or axons, also determines its fate.

Just as plastic coatings insulate electrical wires, myelin coats nerve fibers. This fatty substance also accelerates message-carrying impulses that travel along the nerve fibers and frees them from interference. For more than a decade, scientists have known that nerve cells make neuregulins, growth proteins that promote glial cell growth. However, the delicate interaction between nerve cells and the glial cells (Schwann cells) that produce them remain a mystery.

It has been shown that growth factor protein NRG1-III triggers glial cells to make myelin. This knowledge should lead researchers to develop more effective treatments for several neurological diseases, including peripheral neuropathy. [Read more]

Developing nervous system sculpted by opposing chemical messengers

June 04, 2005

From Medical News Today: A newborn baby moves, breathes and cries in part because a network of nerves called motor neurons carry signals from the infant's brain and spinal cord to muscles throughout its body.

Thanks to new research by scientists at the Salk Institute for Biological Studies, we are closer to understanding how these complicated network connections are wired up during embryonic development. Salk researchers have discovered that the same chemicals (called neurotransmitters) that are responsible for nerve signals are also involved in the wiring of synapses, the network's crucial contact points between nerves, or between nerves and muscle cells.

The study, published in the May issue of the journal Neuron, showed that as the motor neurons grow from their home base in the spinal cord towards muscles throughout the body, they release two opposing chemical signals. These signals act to preserve synapses that link a motor neuron to its correct muscle cell. 'Spare' sites for potential synapses that fail to team up with a motor neuron are dismantled.

"Our study provides the first evidence in a living animal system that the neurotransmitters themselves are sculpturing the developing nervous system," said Kuo-Fen Lee, Associate Professor at the Salk, who heads the research team reporting its results in Neuron.

Using mice as a model for human biology, Lee and colleagues showed that each long, thin muscle cell in the developing embryo prepares for the arrival of its motor neurons by creating sites for many potential synapses along its length. However, three weeks after conception, all the sites have disappeared, except those that connected with a newly arrived motor neuron and formed a fully functioning synapse. The scientists wanted to know: how does the embryo 'weed out' the potential synapse sites that are not needed? The answer to this question is crucial because it might shine light on how the nervous system could make new connections in medical conditions such as spinal cord injury.

Lee, along with Salk colleagues Weichun Lin, Bertha Dominguez, Jiefei Yang, Prafulla Aryal, Eugene Brandon and Fred Gage, discovered that the creation of synapses is controlled by the nerves themselves. As they grow towards the muscle cells, the nerve cells release a powerful chemical messenger from their growing ends. Called acetylcholine, this neurotransmitter 'edits out' the potential synapse sites on the muscle cell not destined to connect to a nerve. In mature animals, acetylcholine is a key neurotransmitter responsible for transmitting signals between nerve cells and muscle.

Using a combination of genetic and pharmacological techniques to block the various components of the chemical pathways involved, the Salk researchers painstakingly showed that acetylcholine works in tandem with another chemical produced by nerve cells, called agrin. Where the end of the nerve touches the muscle cell, agrin is concentrated enough to overcome the 'editing' effect of the acetylcholine. Further away from the nerve end, the levels of agrin are not high enough to overcome the more powerful influence of acetylcholine, and the redundant synapse sites are dismantled.

"The result is an interesting mechanism whereby two opposing forces work together to create the crucial synaptic connections between motor neurons and muscle cells," said co-author Prafulla Aryal.

"Although we have suspected for 25 years that something like this was happening, until now no-one has been able to demonstrate it in a living system," said Lee. "It is likely that this process occurs all over the nervous system. If you're going to repair or regenerate nerves in, for example, spinal cord injury you need to know how to form synapses for the right connections to be made."

The Salk Institute for Biological Studies in La Jolla, California, is an independent nonprofit organization dedicated to fundamental discoveries in the life sciences, the improvement of human health and the training of future generations of researchers. Jonas Salk, M.D., whose polio vaccine all but eradicated the crippling disease poliomyelitis in 1955, opened the Institute in 1965 with a gift of land from the City of San Diego and the financial support of the March of Dimes.

The Second National Neuropathy Association Conference

April 19, 2005

A Decade of Dedication

Dr. Zarife Sahenk of Ohio State University will speak on Advances in Nerve Regeneration at the The Second National Neuropathy Association Conference next month.

The Neuropathy Association announces its Second National Conference, May 19-22, 2005 in Bloomington, Minnesota at the Holiday Inn Select. It is in the shadows of the Minneapolis/St. Paul International Airport and the Mall of America.

This year’s theme celebrates The Neuropathy Association’s tenth anniversary, as a "Decade of Dedication." This national event will present the latest developments and future advances by recognized neurology clinicians and researchers attracting both local support group members from a cross section of the country and medical professionals. This is to highlight the extraordinary growth and success of The Neuropathy Association during its first ten years. Today, The Neuropathy Association has a membership of nearly 90,000 and more than 240 support groups.

The meeting is a visible demonstration of the progress made during the last 10 years and the need for additional research uncovering causes and cures for the 10 to 20 million afflicted by neuropathy. Accelerating research programs and growing interest for increasing federal funding by the U.S. Congress are lifting support in the fight to cure this painful and debilitating group of nerve diseases. Come and meet your friends and get all the news at the conference.

New treatment offers better neuropathic pain relief: study

April 02, 2005

A new treatment that uses two old drugs together may offer hope of relief to millions of North Americans who suffer neuropathic pain.

A type of chronic stabbing, burning pain, neuropathic pain is often a mystery to health care workers. But it is a real and debilitating illness for patients who report being unable to work, sleep or concentrate.

The causes are hard to diagnose, but neuropathic pain is sometimes associated with shingles or side effects from diabetes or cancer therapy.

"It was like an electric shock going through my leg. It would come anywhere or any time," said Isabel Abbott, a Beaton, Ont. resident with shingles who suffers from neuropathic pain.

While researchers constantly search for a new ways to treat this condition, a Canadian doctor tried combining two old ones.

"There's a real difference between the combination than with either of these single agents," said Dr. Ian Gilron, an anesthesiologist at Queen's University in Ontario.

Gilron studied using painkillers morphine and gabapentin in patients with diabetes or shingles-related pain.

On their own, each drug reduced pain by about one-quarter or one-third.

Used together, they worked simultaneously on different areas of the brain, and reduced neuropathic pain by 45 per cent.

In addition, patients didn't require as much medication to get an effect.

"You could use less of each drug and get better pain control with lower doses," Gilron said.

The results of Gilron's study will be published Thursday in the New England Journal of Medicine.

Dr. Angela Mailis, a pain specialist at Toronto Western Hospital, suggested people with neuropathic pain ask their doctors if this new drug combo might help them.

After four years in pain, Abbott says the treatment has been a godsend. "I walk better," she said, adding, "It's nice not to have to live with the pain."

The next step is to study whether a similar approach can work for other types of chronic pain, such as the types associated with stroke, cancer treatment and back trouble.

Skin biopsies in myelin-related neuropathies: bringing molecular pathology to the bedside

March 19, 2005

Brain. 2005 Mar 17
Li J, Bai Y, Ghandour K, Qin P, Grandis M, Trostinskaia A, Ianakova E, Wu X, Schenone A, Vallat JM, Kupsky WJ, Hatfield J, Shy ME.

Skin biopsy is a minimally invasive procedure and has been used in the evaluation of non-myelinated, but not myelinated nerve fibres, in sensory neuropathies. We therefore evaluated myelinated nerves in skin biopsies from normal controls and patients with Charcot-Marie-Tooth (CMT) disease caused by mutations in myelin proteins. Light microscopy, electron microscopy and immunohistochemistry routinely identified myelinated dermal nerves in glabrous skin that appeared similar to myelinated fibres in sural and sciatic nerve. Myelin abnormalities were observed in all patients with CMT. Moreover, skin biopsies detected potential pathogenic abnormalities in the axolemmal molecular architecture previously undetected in human neuropathies. Finally, myelin gene expression at both mRNA and protein levels was evaluated by real-time PCR and immunoelectron microscopy. Peripheral myelin protein 22 (PMP22) was increased in CMT1A (PMP22 duplication) and decreased in patients with hereditary neuropathy with liability to pressure palsies (PMP22 deletion). Taken together, our data suggest that skin biopsy may in certain circumstances replace the more invasive sural nerve biopsy in the morphological and molecular evaluation of inherited and other demyelinating neuropathies.

Quick update on Vitamin C

October 21, 2004

No vitamin C trials are planned in Germany; researchers from the University of Tuebingen are critical of the success, on the grounds that when taking a high dose of Vitamin C each person will feel more energetic and need less sleep. However, Italian Vitamin C trials begin January 2005, so more information is yet to come.

Ascorbic acid, a first generation medication for Charcot Marie Tooth disease type 1A?

October 17, 2004

From CMTUS comes word of a Med Sci (Paris) article about the effects of ascorbic acid (vitamin C) on CMT1A in mice. Transgenic mice with the disease given ascorbic acid performed significantly better on treadmill and muscle grip tests. Furthermore, nerve biopsies of the sciatic nerve showed remyelination of the nerves with normal-shaped myelin.

Though this study focused on CMT1A, it might have ramifications for Dejerine-Sottas (considered by some to be CMT3) as the gene they focused on was PMP22, which is also affected in Dejerine-Sottas. Please do not take this article as medical advice and self-medicate without consulting your doctor; further studies need to be done.

Click "more" to read the translated article.

Below is the English translation article From Med Sci (Paris). 2004 Oct;20(10):843-844 on Ascorbic Acid/Vitamin C.(with generous thanks to Joyce in Sweden for her outstanding help!) (Thanks too, to Dr. Fontes, for his generosity in sharing his review with us) Footnotes and the Figures from the article are in pdf format along with the original article in the CMTUS Files section. ~ Gretchen

Ascorbic acid; a first generation medication for Charcot Marie Tooth disease type 1A?

by Michel Fontès

(Inserm U. 491 Génétique médicale et développement Faculté de Médécine de la Tirnone, 27, boulevard Jean Moulin, 13385 Marseille Cedex 5, France

Charcot-Marie Tooth (CMT) is the most frequent form of peripheral demyelinating neuropathy and the neuomuscular disorder which affects 1 out of 2,500 persons) [1]. It is characterized by a progressive atrophy of the distal muscles. The first symptoms appear between 20 and 30 years, but about 10% of the cases concerns children or teen-agers. This disease is genetically heterogenous, but half of the patients are affected by the disease type 1A.

It is a demyelinating form which is due to a partial trisomy of a little region of the short arm of the chromosome 17 [2, 3], including the gene PMP22 that is implied in the myelination processes [4]. In order to understand more the physiopathology of CMT and to propose therapeutical solutions, in 1996, along with collaboration with C. Huxley, we have built an animal model of this disease, by inserting a
YAC (yeast artificial chromosome) of 560 kb containing the gene PMP22 human, in the genome murin [3]. This strategy of producing "humanized" mice has been developed in such a manner that the observed abnormalities have the same origin as by the patients, i.e. an abnormality in a human gene.

In this case, the therapeutical target is identical by a humanized mouse and by the patients in our study concerning the gene PMP22 human. Many lineages of mice have been obtained and the animals have developed a peripheral neuropathy resembling to CMT1A [6]. We have used essentially the lineage showing the most severe phenotype (lineage C22).

We have used mice CMT C22 as a pre-clinical model in order to test in “clinical mice assays”, a therapeutic approach that could be applicable by the human. Taking into account the difficulties of a genetic therapy approach, we are privileged to use classical pharmacology.

In a prior intention, we researched the bibliography of data concerning molecules “bound” to the myelinisation. Two publications have drawn our attention [7, 8], showing that the ascorbic acid was an absolutely necessary factor to the myelinisation in vitro in the cocultures between axons and Schwann cells. Further research has revealed that persons affected by the disease presented demyelinating peripheral neuropathies.

The toxicity of this molecule being well known, we were able to perform immediate clinical tests of phase II/III. Hence, we carried out with the following experience: animals (males and females) of the lineage C22 transgenic for the gene PMP22 human, have been administrated orally once a week a dose of ascorbic acid corresponding to four grams by the human (no toxicological data exists for larger doses).

On the other arm of the test, the animals were receiving a placebo. The animals’ locomotoric abilities were evaluated at the end of three months by using the well-known test of the rotarod (one measures the time during which an animal is capable of staying on a tread mill turning at a certain speed).

The males (more severely affected than the females) that were treated by a placebo, or those that were not treated, were only able to stay on the tread mill during an average of nine seconds whereas the animals which received the ascorbic acid were able to stay 46 seconds in average. We have carried out a second series of tests: males aged of two months belonging to the same litter, divided into two groups, one treated by a placebo, and the other by ascorbic acid. After three months of treatment, the males that were not treated were not able to stay more than one second on the tread mill (we have chosen litters that were very affected) whereas the animals that were treated stayed 45 seconds (Figure A).

At last, a test concerning the muscular force (grip test) showed us that the treated animals had doubled their muscular force during three months of treatment (Figure 1B) [9]. The total of this data showed an undiscussable therapeutical effect of the ascorbic acid. But what was the mechanism?

In a first period of time, we have helped ourselves with the histologic analysis. Slices of sciatic nerve taken from transgenic animals treated by ascorbic acid have shown a remyelination of fibers that did not exist by non-transgenic animals, or by the transgenic animals treated by a placebo. Furthermore, the gain of myelin found again in a normal shape by the animals treated by the ascorbic acid. At last, the last test concerning the effect of ascorbic acid, the restauration of the duration of a normal life by the animals males of the lineage C22 treated by the ascorbic acid, which is remarkable, because in this lineage, the lethality of the affected males is very important, and this occurs for unknown reasons [9].

The question remains concerning the molecular mechanism leading to the remyelination and to the correction of the phenotype. The hypothesis that came immediately to the mind was an action of the ascorbic acid on the gene PMP22; this one possesses a minimal promoter of 300 pb allowing a specific expression in the Schwann cells. However, this promoter’s activity is repressed if the cells are not stimulated by some dibutyril AMPc or forskolin [10]. However, the ascorbic acid interacts with the pool of AMPc [11].

Hence, we have transfected the Schwann cells by a construction in which the transcription of a (rapporteur) promoter gene is placed under the control of a promoter of PMP22. The cells are incubated with dibutyril AMPc used alone or in association with the ascorbic acid. In these conditions, the ascorbic acid enters in competition with the stimulation of the expression of PMP22 by the AMPc, diminishing it by half. Afterwards we have showed by RT-PCR quantitative in real time that the quantity of transcripts of PMP22 were weaker by the animals treated by ascorbic cid than by those that have received the placebo. The phenotypical correction that is observed by the animals receiving the ascorbic acid is then explained by its action on the expression of the gene PMP22 [9].

In conclusion, the ascorbic acid in a strong dose is capable of correcting the phenotype of animals affected by a disease neighboring that of the CMT1A human. So the road is open for clinical human tests, which we hope that we can carry out with as soon as possible. It is interesting to conclude by underlining that the results of many studies have recently been published, making a reality of similar therapeutical approaches for many genetic diseases.

These works are all based on the same strategy: The use of known molecules, or in development for other applications, in animal models that have genetic diseases. Would the treatments of the first generation for many genetic diseases be based on classical pharmacology?

Dejerine-Sottas disease: a case report

January 16, 2004

An article about Dejerine-Sottas from the Sao Paulo Medical Journal has been made available online through SciELO, an electronic virtual library covering a selected collection of Brazilian scientific journals. Abstract available in English and Portuguese, article available in English as a PDF.

MARINHO, Jaqueline Luvisotto, ALONSO NIETO, José Luis and CALORE, Edenilson Eduardo. Dejerine-Sottas disease: a case report. Sao Paulo Med. J. [online]. 2003, vol.121, no.5 [cited 16 January 2004], p.207-209. Available from World Wide Web: <http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-31802003000500006&lng=en&nrm=iso>. ISSN 1516-3180.

Nerve regeneration to be discussed at Given Institute

August 18, 2003

According to this article, those in Aspen, CO on Tue., August 19, can attend a free lecture at the Given Institute on "The Boundless Potential of Peripheral Nerve Regeneration", as part of their summer public lecture series. Though the lecture will focus on carpal-tunnel syndrome, cut nerves, and microvascular surgery breakthroughs, the article also mentions that researchers are finding "faster and better" methods of growing Schwann cells in the laboratory.

Muscle Protein has Role in Nerve Disorders

August 08, 2003

I have so many questions about this article. What do they mean by abnormally folded myelin sheaths, in an "onion bulb" pattern? Does dystroglycan play a role in Dejerine-Sottas? Are nodes of Ranvier affected?

Each Schwann cell envelops a short stretch of axon, and the gaps between each section of the myelin sheath are called nodes of Ranvier. Ions flow through sodium channels at these nodes generating action potentials or nerve impulses. This signal is transmitted down the nerve fiber from one node to the next.

The researchers found that dystroglycan is necessary to form normal myelin sheaths. They also discovered that loss of the protein disrupts the structure of the nodes of Ranvier and affects the nerve?s ability to transmit nerve impulses. The results suggest that disruption of dystroglycan's functions may play a role in various neuropathic disorders.

The UI team developed mice that lacked dystroglycan in their Schwann cells. This specific mutation caused progressive nerve damage in the mice. The mice were less coordinated than normal mice and their sensitivity to heat and pressure was altered. The team also showed that nerve impulses traveled more slowly in these mice.

The researchers examined the peripheral nerve fibers and saw that the myelin sheaths were abnormally folded, indicating that dystroglycan is important for normal myelination of peripheral nerve. This finding was not unexpected, as several earlier studies had suggested that dystroglycan might be involved in myelination.

However, the myelin sheath abnormalities did not seem severe enough to account for the significant reduction in the speed of nerve impulses in the mutant mice. This puzzle led the researchers to another discovery: the absence of dystroglycan appears to disrupt the normal structure of the nodes of Ranvier that are necessary to rapidly transmit nerve impulses along the nerve. In particular, loss of dystroglycan reduces the density of sodium channels that cluster at each node and are critical for normal transmission of nerve impulses.

New article in Journal of Neurology

June 27, 2003

Dejerine-Sottas Neuropathy with Multiple Nerve Roots Enlargement and Hypomyelination Associated with a Missense Mutation of the Transmembrane Domain of MPZ/P0.

Simonati A, Fabrizi G, Taioli F, Polo A, Cerini R, Rizzuto N.

Journal of Neurology 249: 1298-1302, 2002. Reprinted with permission from Dr. Dietrich Steinkopff Verlag.

In a patient affected with a slowly progressive, severe form of Dejerine-Sottas syndrome, symmetric enlargement of cranial nerves and focal hypertrophy of cervical and caudal roots were detected following MRI. Neuropathological features of the sural nerve disclosed a dramatic loss of myelinated fibres, with skewed-to-the-left, unimodal distribution of the few residual fibres, consistent with the diagnosis of congenital hypomyelination neuropathy. Genetic analysis revealed this condition to be associated with a heterozygous G to A transition at codon 167 in the exon 4 of the MPZ/P0 gene causing a Gly138Arg substitution in the transmembrane domain of the mature MPZ/P0 protein. Focal enlargement of the nerve trunks in demyelinating, hereditary motor and sensory neuropathies (HMSN) was previously reported in both asymptomatic and symptomatic cases with root compression, but peculiar to this case is the diffuse involvement of both cranial and spinal nerves. We believe that the relevance of nerve trunk hypertrophy in HMSN is probably underevaluated: therefore MRI investigation of the head and spine should be included in the diagnostic study of selected HMSN patients. Molecular analysis of peripheral myelin genes will help to rule out misdiagnosed cases.