Reduced Sodium Channel Nav1.1 Levels in BACE1-null Mice

Doo Yeon Kim,Manuel T Gersbacher,Perrine Inquimbert,Dora M Kovacs

doi:10.1074/jbc.m110.134692

Doo Yeon Kim, Manuel T Gersbacher + Show 2 more

Open Access

https://doi.org/10.1074/jbc.m110.134692

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Abstract

The Alzheimer BACE1 enzyme cleaves numerous substrates, with largely unknown physiological consequences. We have previously identified the contribution of elevated BACE1 activity to voltage-gated sodium channel Na(v)1.1 density and neuronal function. Here, we analyzed physiological changes in sodium channel metabolism in BACE1-null mice. Mechanistically, we first confirmed that endogenous BACE1 requires its substrate, the β-subunit Na(v)β(2), to regulate levels of the pore-forming α-subunit Na(v)1.1 in cultured primary neurons. Next, we analyzed sodium channel α-subunit levels in brains of BACE1-null mice at 1 and 3 months of age. At both ages, we found that Na(v)1.1 protein levels were significantly decreased in BACE1-null versus wild-type mouse brains, remaining unchanged in BACE1-heterozygous mouse brains. Interestingly, levels of Na(v)1.2 and Na(v)1.6 α-subunits also decreased in 1-month-old BACE1-null mice. In the hippocampus of BACE1-null mice, we found a robust 57% decrease of Na(v)1.1 levels. Next, we performed surface biotinylation studies in acutely dissociated hippocampal slices from BACE1-null mice. Hippocampal surface Na(v)1.1 levels were significantly decreased, but Na(v)1.2 surface levels were increased in BACE1-null mice perhaps as a compensatory mechanism for reduced surface Na(v)1.1. We also found that Na(v)β(2) processing and Na(v)1.1 mRNA levels were significantly decreased in brains of BACE1-null mice. This suggests a mechanism consistent with BACE1 activity regulating mRNA levels of the α-subunit Na(v)1.1 via cleavage of cell-surface Na(v)β(2). Together, our data show that endogenous BACE1 activity regulates total and surface levels of voltage-gated sodium channels in mouse brains. Both decreased Na(v)1.1 and elevated surface Na(v)1.2 may result in a seizure phenotype. Our data caution that therapeutic BACE1 activity inhibition in Alzheimer disease patients may affect Na(v)1 metabolism and alter neuronal membrane excitability in Alzheimer disease patients.

Highlights

Stages of the disease, neuropsychiatric symptoms include depression, aggressiveness, agitation, and generalized anxiety [1]
Nav␤2 Mediates the Effect of by ␤-site APP-cleaving enzyme 1 (BACE1) on Nav1.1 Levels in Primary Neurons—Previously, we found that BACE1 and ␥-secretase sequentially cleave Nav␤2 to release the intracellular domain of Nav␤2 (␤2-ICD)
We found that DR9 treatment decreased Nav1.1 levels up to 50% in a dose-dependent manner (Fig. 1A)

Summary

Introduction

Stages of the disease, neuropsychiatric symptoms include depression, aggressiveness, agitation, and generalized anxiety [1]. We compared total brain Nav1 ␣-subunits levels in 1-monthold BACE1-null and BACE1-heterozygous knock-out with agematched wild-type mice. Hippocampal regions were dissected from the brains of 3-month-old BACE1-null and wild-type control mice, extracted, and analyzed for Nav1 subunits by Western blot analysis.

Results

Conclusion