Supplementary Material for: The E280A Presenilin Mutation Reduces Voltage-Gated Sodium Channel Levels in Neuronal Cells

Background: Familial Alzheimer's disease (FAD) mutations in presenilin (PS) modulate PS/γ-secretase activity and therefore contribute to AD pathogenesis. Previously, we found that PS/γ-secretase cleaves voltage-gated sodium channel β₂-subunits (Na_vβ₂), releases the intracellular domain of Na_vβ₂ (β₂-ICD), and thereby, increases intracellular sodium channel α-subunit Na_v1.1 levels. Here, we tested whether FAD-linked PS1 mutations modulate Na_vβ₂ cleavages and Na_v1.1 levels. Objective: It was the aim of this study to analyze the effects of PS1-linked FAD mutations on Na_vβ₂ processing and Na_v1.1 levels in neuronal cells. Methods: We first generated B104 rat neuroblastoma cells stably expressing Na_vβ₂ and wild-type PS1 (wtPS1), PS1 with one of three FAD mutations (E280A, M146L or ΔE9), or PS1 with a non-FAD mutation (D333G). Na_vβ₂ processing and Na_v1.1 protein and mRNA levels were then analyzed by Western blot and real-time RT-PCR, respectively. Results: The FAD-linked E280A mutation significantly decreased PS/γ-secretase-mediated processing of Na_vβ₂ as compared to wtPS1 controls, both in cells and in a cell-free system. Na_v1.1 mRNA and protein levels, as well as the surface levels of Na_v channel α-subunits, were also significantly reduced in PS1(E280A) cells. Conclusion: Our data indicate that the FAD-linked PS1(E280A) mutation decreases Na_v channel levels by partially inhibiting the PS/γ-secretase-mediated cleavage of Na_vβ₂ in neuronal cells.