Aβ activates RhoA thereby influencing neuron morphology. (A) Western blots showing the activated and total RhoA GTPase in extracts from cultured PC12 nnr5 cells stimulated with NGF (100 ng/ml) for 5 h at the times indicated, or with Aβ (5 μM). Note that in contrast to NGF, Aβ increased the levels of RhoA GTP. The quantification of RhoA GTP in the lower panel is an average from four independent experiments. (B) Representative micrographs of hippocampal neurons cultured for 7 DIV (40,000 cells/cm2), treated with Aβ (5 μM) and/or co-transfected with EGFP and a myc tagged RhoA N19 (a dn form of RhoA) for 16 h. (C, D) Quantification of relative dendrite length (C) and primary dendrite number (D) in the four conditions indicated. Note that the attenuation of RhoA GTPase activity counteracted the effects of Aβ on dendrite length and number. Also note in (C) that the attenuation of RhoA activity increased the length of dendrites per se. (E, F) Quantification of relative dendrite length (E) and primary dendrite number (F) in cultured neurons after addition of CNFy (200 ng/ml: a specific activator of RhoA) for 16 h. (G) 7 DIV neurons in culture were first incubated with C3 ADP rybosyl transferase (1.0 μM) for 18 h, they were stimulated with Aβ (5 μM) for 4 h, lysed and then processed for real time PCR to quantify Hes1 expression. Note that the inhibition of RhoA by C3 prevented the Aβ-induced decrease in Hes1 mRNA.