MAPT and tauopathy: To define whether accumulation of pathogenic aggregated tau in microvascular endothelial cells of AD and other tauopathies18 and in models of tauopathy (Fig. 1A) may be a consequence of HSPG-mediated entry of pathogenic soluble aggregated tau into endothelial cells, we incubated human brain microvascular endothelial cells (HBEC) with epitope-tagged recombinant human tau soluble aggregates (Tau-V5) and competitively inhibited tau HSPG binding sites with heparin or treated cells with vehicle33,34 (Fig. 1B).