November 3, 2006
Researchers at USC and Institut de Recherches Cliniques de Montreal (IRCM) have made a key discovery regarding how myelin, the insulating sheath that surrounds neurons, is regulated by the protein Par-3.
At a basic level, our nervous system is like a collection of wires that transmit electrical signals encoding our thoughts, feelings, and actions, both conscious and unconscious. The connections in our brain are formed by neurons that extend to each other and to muscles using long wires called axons. Just as an electrical wire needs insulation, our axons require an insulating sheath (myelin) that helps to propagate the electrical signal and maximize the efficiency and velocity of these signals in our brain and body. It is this property (myelination) that facilitates the long-distance communication in our nervous system across junctions called synapses, such that a thought can result in the movement of a finger or a toe. Diseases and injury that compromise the integrity of myelin such as multiple sclerosis or peripheral neuropathies, have dramatic consequences like paralysis, uncoordinated movements, and neuropathic pain. The discovery reported in this study sheds light on the mechanisms that control how myelin is formed during development of the nerves. The article, which was published in the November 3rd issue of Science, constitutes an important step forward in our understanding of the process of myelination, and opens the way to new research in this field.
More specifically, the study showed that a protein called Par-3 is at the base of the myelination process. This protein becomes localized to one side of the myelin-forming cells called Schwann cells, upon contact with the axon that is to be myelinated. Par-3 acts as a sort of 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 scientists 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 of the cell is in contact with the axon so that they can initiate wrapping and bring essential molecules to this critical interface. These studies open the way to new research, which should help to identify other components that are recruited at the organizing centre set-up by Par-3. Importantly, in cases of demyelination due to disease or injury, it is believed that Schwann cells could be used to re-myelinate axons. But so far this approach has proved to be relatively inefficient. Therefore, these experiments bring about the possibility that manipulating the Par-3 pathway in Schwann cells might allow for more efficient re-myelination of damaged or diseased nerves.The article can be accessed at www.sciencemag.org
Source: Lucette Theriault