Fig. 3

Myelin composition and organization. The myelin wrapping around most of the CNS axons includes a large majority of complex lipids and 15–30% of specific proteins. Lipids are essentially made up of cholesterol, galactocerebrosides and phospholipids. This envelope is constantly reshuffled in time and space from the oligodendrocytes that make up the bulk of the glial cells of the CNS. Chronic inflammatory and autoimmune reactions, mutations in certain constituent proteins, attacks by free radicals or ischemic, and metabolic problems related to aging alter the myelin sheath that releases its constituents into the CSF and the bloodstream. In AD, myelin is one of the first bulwarks for the anatomical and functional integrity of the axons it surrounds and undergoes early toxic action of misfolded extracellular toxic proteins or peptides. Abbreviations: AD, Alzheimer’ disease; CNP, C-type natriuretic peptide; CNS, central nervous system; CSF, cerebrospinal fluid; MAG, myelin-associated glycoprotein; MBP, myelin basic protein; MOG, myelin oligodendrocyte glycoprotein; PLP, proteolipid protein