L-type calcium channel subtypes mediating hypothalamic dysfunction caused by amyloid-beta.

Abstract

In Alzheimer's disease (AD), non-cognitive manifestations attributable to hypothalamic dysfunction such as systemic metabolic deficits can occur prior to the cognitive decline (Ishii, M. and Iadecola C., Cell Metabolism 22:761,2015). We previously found in Tg2576 mice overexpressing the Swedish mutation of amyloid precursor protein that amyloid-beta pathology can cause dysfunction in hypothalamic arcuate neuropeptide Y (NPY) neurons, associated with low adiposity and low plasma leptin levels prior to memory decline or plaque formation (Ishii, M. et al., J Neuroscience 34:9096,2014). Furthermore, the hypothalamic arcuate NPY neuronal dysfunction was caused by amyloid-beta modulating low-threshold activated L-type calcium channels (Ishii, M. et al., J Neuroscience 39:8816,2019). However, which of the two major brain L-type calcium channel subtypes Cav 1.2 or Cav 1.3 is involved has not been established. To examine the role of Cav 1.2, we used the Cre-lox system in genetic mouse models to knock-out Cav 1.2 in hypothalamic arcuate NPY neurons (Cav 1.2 cKO). Cav 1.2 cKO mice were bred to NPY-GFP and Tg2576 mice. Two to 3-month-old male or female mice were used for all studies. Voltage-gated L-type calcium currents from hypothalamic slices containing arcuate NPY neurons were recorded using whole-cell voltage-clamp. Cytoplasmic Ca2+ levels were measured ratiometrically by loading Fura-2AM in dissociated arcuate NPY neurons and recording the emitted fluorescence using an inverted fluorescent microscope. Exogenous oligomeric amyloid-β42 caused a significant increase in cytoplasmic Ca2+ levels and L-type calcium currents in arcuate NPY neurons to a similar extent in both Cav 1.2 cKO and wild-type (WT) littermate mice. These effects of amyloid-β42 were reversed by the L-type calcium channel blocker nimodipine. In vivo, Cav 1.2 cKO mice bred to Tg2576 mice had similar body weight deficits compared to Tg2576 mice without deletion of Cav 1.2 in the arcuate NPY neurons. These results suggest that Cav 1.2 does not have a significant role in amyloid-beta mediated dysfunction of hypothalamic arcuate NPY neurons and that Cav 1.3 is likely the major target of amyloid-beta in these neurons. Future studies modulating Cav 1.3 in hypothalamic neurons will help elucidate the mechanisms underlying hypothalamic dysfunction caused by amyloid-beta pathology and its therapeutic potential in AD.