Molecular Control of Na+ Channel Density and Localization in Myelinated Axons

University Of Michigan At Ann Arbor, Ann Arbor MI

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Abstract

DESCRIPTION (provided by applicant): The long-term goal of this research is to understand the role of Scn1b, encoding voltage-gated Na+ channel ¿1, in CNS myelinating glia. The objective is first, to measure ¿1 expression in wildtype myelin and to characterize myelinating glia-specific Scn1b null mice. This powerful model provides a unique opportunity to study the role of Scn1b in myelination and axo-glial communication. Second, the objective is to determine the signal transduction mechanisms initiated by ¿1-mediated cell-cell adhesion in oligodendrocyte precursor cells (OPCs) or oligodendrocytes (OLs). The overall goal of this proposal is to test the central hypothesis that ¿1 is expressed in OPCs/OLs, in addition to axons, where it contributes to axo-glial communication through cell adhesion and modulation of electrical activity. Two specific aims are proposed: Aim 1. To determine the role of glial-expressed Scn1b in myelination. Preliminary Data demonstrate that mice that lack Scn1b in myelinating glia have movement disorders, dysmyelination, delayed myelination or lack of myelination, and axonal degeneration. These data support the working hypothesis of this aim that Scn1b plays a critical role in OPC development and/or axo-glial communication. Aim 2. To determine the role of Scn1b in OPC/OL signal transduction. The working hypothesis here is that ¿1-¿1 interactions play a key role in recognition of axons by glia and subsequent initiation of myelination via a signaling cascade in glia that involves the CAM contactin as well as fyn kinase activation. Further, it is proposed that ¿1 modulation of Na+ currents plays a role in OPC development, including proliferation, migration, and spacing along axons, and thus may contribute to the initiation of myelination. With respect to expected outcomes, the work proposed in Aims 1 and 2 is expected define a novel role for ¿1 in OPC signaling, including axo-glial communication. These results are expected to have an important positive impact on the fields of demyelinating and hypomyelinating disease. Rapid processing of information in the CNS requires efficient saltatory conduction of action potentials along myelinated axons. Disruptions in myelination result in a range of human neurological diseases, including multiple sclerosis in adults and leukodystrophies in children. While human mutations in SCN1B associated with demyelination, dysmyelination, or hypomyelination have not yet been identified, they have been determined to play a role in other neurological diseases, including severe epilepsy associated with mental retardation. A detailed understanding of the basic mechanisms underlying the role of SCN1B in axo-glial communication is essential to the future development of novel therapeutic regimens for demyelinating disease.