Neuroprotective effect of G-CSF requires MEK5/ERK5 signaling.

<p>A–F, Fluorescent microscopic images of mouse primary cortical neuron cultures. A, Untreated neurons. B, Neurons treated with 5 µM oAβ_1–42. C, Neurons treated with 5 µM oAβ_1–42 and 100 ng/ml G-CSF. D, Neurons treated with 5 µM oAβ_1–42, 100 ng/ml G-CSF and 0.3 µM BIX02189. E, Neurons treated with 5 µM oAβ_1–42, 100 ng/ml G-CSF and 3 µM BIX02189. F, Neurons treated with 5 µM oAβ_1–42, 100 ng/ml G-CSF and 30 µM BIX02189. The MEK5/ERK5 inhibitor BIX02189 almost completely suppressed G-CSF–mediated protection against oAβ-induced neurotoxicity. Neurons were stained with anti–MAP-2 antibodies (green), and Aβ was stained with 4G8 antibodies (red). Scale bar: 50 µm. G, Relative neuronal survival. The number of viable neurons (MAP-2–positive neurons) was quantified relative to results observed with untreated neurons. Inhibition of MEK5/ERK5 almost completely ablated the neuroprotective effects of G-CSF. *, <i>p</i><0.001; †, <i>p</i><0.001; ‡, <i>p</i><0.001. Values are means ± SEM (n = 3). H, WST-8 assay. Blocking MEK5/ERK5 almost completely canceled the neuroprotective effects of G-CSF. *, <i>p</i><0.001; †, <i>p</i><0.001; ‡, <i>p</i><0.001. Values are means ± SEM (n = 6).