MAPT and Alzheimer disease: To investigate whether released tau is monomeric or remains as larger-order aggregates similar to those found in the neurons from 5M P301S mice (17, 19), tau in the CM was solubilized with SDS (5%), and the preparation was filtered through a 0.2-μm cellulose acetate membrane (presoaked in 5% SDS to eliminate soluble oligomers) under vacuum, a method that traps insoluble tau aggregates from AD brains (20).