sNEP- NSCs do not alter established tangle pathology but increase synaptic density and differentiate primarily into astrocytes. Aged 3xTg-AD mice develop both Aβ plaques and neurofibrillary tangles. We, therefore, examined whether sNEP-NSCs modulate tau pathology in vivo. Immunofluorescent labelling and quantification of phosphorylated tau (AT8 epitope: ser199/202) within the hippocampus revealed no significant differences between sNEP-NSC (A, C-top panel) and control-NSC (B, C-bottom panel) treated sides (n = 5). This finding is in line with previous reports that decreasing Aβ in aged 3xTg-AD mice does not reduce established insoluble tangle pathology. To determine whether sNEP expression leads to a functional effect on neuronal connectivity, we examined synaptophysin immunoreactivity. As shown, sNEP-NSCs increase synaptic density within the subiculum (D) by more than 31% versus control-NSCs (E, P = 0.009, paired t-test). To examine the differentiation of transplanted NSCs, double-labelling for neuronal and glial markers was performed. In agreement with previous studies, very few NSCs (green) transplanted into the aged brain co-express the neuronal marker NeuN (blue, F). In contrast, the great majority of NSCs co-express the astrocytic marker GFAP (red, G-L). Scale Bar = 100 μm in A-B, 15 μm in C, 6 μm in D-E, 15 μm in F, 300 μm in G-I, and 15 μm in J-L. Aβ, beta- amyloid; GFAP, glial fibrillary acidic protein; NSCs, neural stem cells; sNEP, secreted neprilysin.