TAT-pep5 specifically uncouples p75NTR from the RhoA GTPase, and it counteracts the effects of Aβ on dendrite patterning, gene expression and the survival of cultured hippocampal neurons. (A, B and C) E17 hippocampal neurons were plated at a density of 40,000 cells/cm2 and cultured for 7 DIV. Neurons were transfected with pEGFP and then exposed for a further 16 h to TAT-Pep5 (1.0 μM), Aβ (5 μM), or both. The cells were fixed and labelled with the anti-EGFP antibody, and then processed for immunofluorescence. (A) representative micrographs of cultured neurons under the different conditions. The relative dendrite length (B) and primary dendrite numbers (C) was quantified as indicated in the methods section. Note that TAT-pep5 reversed the effects of Aβ on dendrite length and number. (D) Neurons cultured for 7 DIV (40,000 cells/cm2) were first incubated with TAT-Pep5 (1.0 μM) for 18 h, after which they were stimulated with Aβ (5 μM) for 4 h, lysed and then processed for real time PCR to quantify Hes1 expression. Note that TAT-pep5 prevented the Aβ-induced decrease in Hes1 mRNA. (E) 7 DIV cultures (30,000 cells/cm2) were stimulated with TAT-pep5 (1.0 μM) and/or Aβ (5 μM) for 90 h. The neurons were then stained with DAPI and those with intact nuclei were counted. Note that TAT-pep5 rescued around half of the neurons from the deleterious effects of Aβ. (F) Representative micrographs of DAPI stained nuclei in cultured hippocampal neurons treated with Aβ, or with Aβ and TAT-pep5, the latter conferring resistance against Aβ.