In a new study, researchers at the Montreal Neurological Institute (MNI), McGill University, and the Université de Montréal have discovered an essential mechanism for the maintenance of the normal structure of myelin, the protective covering that insulates and supports nerve cells (neurons). Up until now, very little was known about myelin maintenance. This new information provides vital insight into diseases such as Multiple Sclerosis (MS) and other progressive demyelinating diseases in which myelin is destroyed, causing irreversible damage and disrupting the nerve cells' ability to transmit messages. The research, published recently in the Journal of Neuroscience, is the first to identify a role for the protein netrin-1, previously characterized only in the developing nervous system, with this critical function in the adult nervous system. This research was funded by the MS Society of Canada and the Canadian Institutes of Health Research.
Netrin-1, a protein deriving its name from the ancient Indian language, Sanskrit, word for 'one who guides,' is known to guide and direct nerve cell axons to their targets. In the molecular biological studies conducted by the team, they found that blocking the function of netrin-1 and one of its receptors in adult neural tissue causes the disruption of myelin. "We've known for just over 10 years that netrin is essential for normal development of the nervous system, and we also knew that netrin was present in the adult brain, but we didn't know why. It is fascinating that netrin-1 has such a vital role in maintaining the structure of myelin in the adult nervous system," says Dr. Tim Kennedy, a neuroscientist at the MNI and the senior investigator of this study, "continuing to pursue the implications of that are incredibly exciting." "Our mission is to find a cure as quickly as possible and enhance quality of life," says Karen Lee, assistant vice-president of research programs for the MS Society of Canada. "We are pleased to be involved in funding work that supports our mission and feel that this research takes us closer to understanding the players and processes that could aid in remyelination."
The results of this study, a collaboration between Dr. Kennedy's laboratory, clinician-scientists in the Neuroimmunology group at the MNI headed by Dr. Jack Antel, and Dr. Adriana Di Polo's laboratory at the Université de Montréal, are especially significant in Canada which has one of the highest rates of Multiple Sclerosis (MS) in the world with approximately 1,000 new cases of MS diagnosed each year. ''This is an exciting new area of research that could lead to new treatment strategies and ultimately improve the life of the people who suffer from MS. We are proud to be funding this collaborative research between basic and clinician-scientists," said Dr. Rémi Quirion, Scientific Director of the CIHR Institute of Neurosciences, Mental Health and Addiction.
MS is a disease of the central nervous system in which myelin is destroyed. Understanding the factors involved in maintaining myelin and promoting remyelination, offers new therapeutic targets and avenues for the treatment of MS. As described by Dr. Jack Antel, "Current MS therapies aim to block inflammation. In order to protect and restore myelin it is essential to to understand the molecules involved in these processes. This is the new era of the neurobiology of MS." The team is taking the investigation further by teaming up with the MS clinic and doctors at the MNI, providing access to a huge amount of patient data, and enabling them a broader clinical perspective.
Importantly, this newly discovered mechanism implicates a cascade of protein molecules that have not been known to be involved in myelination. The study was carried out in mice and using in vitro cell cultures. The investigators found that myelin develops normally, but then begins to come apart. Interestingly, in some respects this mirrors what happens in some demyelinating diseases like MS, where myelin forms and may be stable for years, but is then disrupted and begins to fail. Specifically, the new findings show that netrin-1 and its receptor are needed to hold paranodal junctions in place, and thereby maintain the structure of myelin. The paranodal junction is a highly specialized region of contact where an oligodendrocyte cell attaches itself to the nerve cell's axon. This juncture acts as a molecular fence, which organizes and segregates the distribution of key proteins along the nerve cells axon and plays an imperative role in the proper conduction of electrical signals along the length of the nerve cell. When the function of netrin-1 and its receptor is disrupted, the organization of this adhesive junction comes apart, disrupting the function of nerve cells in the brain and spinal cord.
This work was supported by grants from the Multiple Sclerosis Society of Canada and Canadian Institutes of Health Research, as well as Multiple Sclerosis Society of Canada studentships, and a Jeanne Timmins Costello Fellowship from the Montreal Neurological Institute. Tim Kennedy is a Killam Trust Scholar and holds a Chercheur Nationaux Award from Fonds de la Recherche en Santé du Québec.
October 2009 marks the 75th anniversary of the MNI. The MNI is a McGill University research and teaching institute, dedicated to the study of the nervous system and neurological diseases. Founded in 1934 by the renowned Dr. Wilder Penfield, the MNI is one of the world's largest institutes of its kind. MNI researchers are world leaders in cellular and molecular neuroscience, brain imaging, cognitive neuroscience and the study and treatment of epilepsy, multiple sclerosis and neuromuscular disorders. The MNI, with its clinical partner, the Montreal Neurological Hospital (MNH), part of the McGill University Health Centre, continues to integrate research, patient care and training, and is recognized as one of the premier neuroscience centres in the world. At the MNI, we believe in investing in the faculty, staff and students who conduct outstanding research, provide advanced, compassionate care of patients and who pave the way for the next generation of medical advances. Highly talented, motivated people are the engine that drives research - the key to progress in medical care. A new building, the North Wing Expansion, is currently under construction and will house state-of-the-art brain imaging facilities. Once the construction is completed and the new building is fully equipped, the scientific community focused on brain imaging research at the MNI will be without equivalent anywhere in the world.
Multiple sclerosis and the Multiple Sclerosis Society of Canada:
Multiple sclerosis is a chronic, often disabling disease of the brain and spinal cord. It is the most common neurological disease of young adults in Canada. Most people with MS are diagnosed between the ages of 15 and 40, and the unpredictable effects of MS last for the rest of their lives. The MS Society provides services to people with MS and their families and funds research to find the cause and cure for this disease. Please visit www.mssociety.ca or call 1-800-268-7582 to make a donation or for more information.
The Canadian Institutes of Health Research (CIHR) is the Government of Canada's agency for health research. CIHR's mission is to create new scientific knowledge and to enable its translation into improved health, more effective health services and products, and a strengthened Canadian health-care system. Composed of 13 Institutes, CIHR provides leadership and support to nearly 12,000 health researchers and trainees across Canada. www.cihr-irsc.gc.ca