A Study Of The Neurotoxicity Of Myelin Basic Protein(MBP)

Background:Massive demyelination following trauma and neurodegenerative disease in the central nervous system (CNS) not only inhibits neuroregeneration, but also contributes to neuronal damage. Many myelin-associated proteins are released after demyelination. Nogo, myelin-associated glycoprotein, and oligodendrocyte myelin glycoprotein have been identified as inhibitors of neuronal growth by binding to either the Nogo receptor or to a second receptor, PirB. Many studies have revealed that soluble MBP is detectable after demyelination. After destruction of the intact myelin sheath, some MBP dissociates from the plasma membrane and acts in a free, membrane-unbound manner in the extracellular matrix. However, as an abundant myelin associated protein, it is unclear if MBP have a direct effect on neurons.Objective:We found that MBP induced neurotoxicity on cultured neurons. We want to explore the mechanism of this effect. We hope our work deepen knowledge of demyelination and give some clues for related treatments.Methods:DAPI/PI double-staining was used to estimate the death of cultured neurons. To determine whether MBP binds to the neuronal extracellular surface, cultured hippocampal neurons were investigated by surface immunostaining for MBP. Western Blot, electrophysiological techniques, calcium imaging, test of membrane damage and artificial liposome assay were used to investigate the mechanism of the neurotoxicity induced by MBP.Results:We found that MBP specifically bound to the extracellular surface of the neuronal plasma membrane and induces neurotoxicity in vitro. This effect of MBP on neurons was basicity-dependent because the binding was blocked by acidic lipids and competed by other basic proteins. Further studies revealed that MBP induced damage of neuronal membrane integrity and function by depolarizing the resting potential, increasing the permeability to cations and other molecules, and decreasing the membrane fluidity. At last, artificial liposome assay showed that MBP directly disturbed acidic lipid bilayer and resulted in increased membrane permeability.Conclusion:MBP induces neurotoxicity through its direct interaction with acidic components on the extracellular surface of neuronal membrane, which may suggest a possible contribution of MBP to the pathogenesis in the CNS injuries..