Up-regulation and increased activity of KV3.4 channels and their accessory subunit MinK-related peptide 2 induced by amyloid peptide are involved in apoptotic neuronal death

The aim of the present study was to investigate whether K_V3.4 channel subunits are involved in neuronal death induced by neurotoxic β-amyloid peptides (Aβ). In particular, to test this hypothesis, three main questions were addressed: 1) whether the Aβ peptide can up-regulate both the transcription/translation and activity of K_V3.4 channel subunit and its accessory subunit, MinK-related peptide 2 (MIRP2); 2) whether the increase in K_V3.4 expression and activity can be mediated by the nuclear factor-κB (NF-κB) family of transcriptional factors; and 3) whether the specific inhibition of K_V3.4 channel subunit reverts the Aβ peptide-induced neurodegeneration in hippocampal neurons and nerve growth factor (NGF)-differentiated PC-12 cells. We found that Aβ_1-42 treatment induced an increase in K_V3.4 and MIRP2 transcripts and proteins, detected by reverse transcription-polymerase chain reaction and Western blot analysis, respectively, in NGF-differentiated PC-12 cells and hippocampal neurons. Patch-clamp experiments performed in whole-cell configuration revealed that the Aβ peptide caused an increase in I_A current amplitude carried by K_V3.4 channel subunits, as revealed by their specific blockade with blood depressing substance-I (BDS-I) in both hippocampal neurons and NGF-differentiated PC-12 cells. The inhibition of NF-κB nuclear translocation with the cell membrane-permeable peptide SN-50 prevented the increase in K_V3.4 protein and transcript expression. In addition, the SN-50 peptide was able to block Aβ_1-42-induced increase in K_V3.4 K⁺ currents and to prevent cell death caused by Aβ_1-42 exposure. Finally, BDS-I produced a similar neuroprotective effect by inhibiting the increase in K_V3.4 expression. As a whole, our data indicate that K_V3.4 channels could be a novel target for Alzheimer's disease pharmacological therapy.