P2‐083: Age‐related reductions in T‐type calcium channels and their contribution to Alzheimer's disease pathogenesis

Abstract

Over the past 20 years aberrant calcium dysregulation has been consistently implicated in Alzheimer's disease (AD), either in the initiation of AD, the progression of AD-related pathologies, or in mediating the neuronal and synaptic loss resulting from AD pathology. While many studies have implicated high voltage-gated calcium channels in the calcium dyshomeostasis frequently observed in AD, low voltage-gated T-type calcium channels remained to be investigated. We therefore assessed steady state protein levels of CaV 3.1 in 3, 18, and 24 month-old wild-type mice and found that the channels were robustly reduced with age. To understand the effects of reduced T-type channel levels in the aged brain on the pathogenesis of AD, we treated 3xTg-AD mice with a specific T-type channel blocker, NNC-55-0396, to mimic the age-related reductions. Two groups of female 3xTg-AD mice between the ages of 14 and 16 months were injected intraperitoneally every other day for two weeks with either NNC-55-0396 (20 mg/kg) or vehicle and then sacrificed. Despite an experimental period of just two weeks, in mice with established pathology, we found significant increases in soluble levels of Aβ1-42 with T-type channel inhibition. In addition, insoluble levels of Aβ 1-42 trended toward an increase. Accordingly, Western blotting revealed decreases in C83 and the constitutive α -secretase ADAM10, suggesting that blockade of T-type channels downregulates the non-amyloidogenic processing pathway of APP. Notably, no significant changes in tau pathology were observed. However, the cleavage of p35 to p25, which is carried out by calpains, was dramatically reduced with treatment. Further investigation revealed that calpain 1 and 2 protein levels were decreased with drug treatment. Another substrate of calpains, spectrin, was also analyzed in these samples and was found to be similarly decreased in drug-treated mice compared to controls, suggesting that T-type calcium currents contribute substantially to the regulation of calpains. From our results, we conclude that age-related reductions in T-type calcium channels may have the potential to push APP processing toward the amyloidogenic pathway. This could, in turn, predispose the aging brain to develop Alzheimer's disease.