Elsevier

Neuroscience Letters

Volume 538, 22 March 2013, Pages 60-65
Neuroscience Letters

The alterations of Ca2+/calmodulin/CaMKII/CaV1.2 signaling in experimental models of Alzheimer's disease and vascular dementia

https://doi.org/10.1016/j.neulet.2013.02.001Get rights and content

Abstract

The two critical forms of dementia are Alzheimer's disease (AD) and vascular dementia (VD). The alterations of Ca2+/calmodulin/CaMKII/CaV1.2 signaling in AD and VD have not been well elucidated. Here we have demonstrated changes in the levels of CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF proteins by Western blot analysis and the co-localization of p-CaMKII/CaV1.2 by double-labeling immunofluorescence in the hippocampus of APP/PS1 mice and VD gerbils. Additionally, expression of these proteins and intracellular calcium levels were examined in cultured neurons treated with Aβ1–42. The expression of CaV1.2 protein was increased in VD gerbils and in cultured neurons but decreased in APP/PS1 mice; the expression of calmodulin protein was increased in APP/PS1 mice and VD gerbils; levels of p-CaMKII, p-CREB and BDNF proteins were decreased in AD and VD models. The number of neurons in which p-CaMKII and CaV1.2 were co-localized, was decreased in the CA1 and CA3 regions in two models. Intracellular calcium was increased in the cultured neurons treated with Aβ1–42. Collectively, our results suggest that the alterations in CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF can be reflective of an involvement in the impairment in memory and cognition in AD and VD models.

Highlights

► CaM was up-regulated in the hippocampus of both APP/PS1 mice and VD gerbils. ► The expression of CaV1.2 protein was increased in VD gerbils and in cultured neurons but decreased in APP/PS1 mice. ► The number of CaMKII and CaV1.2 co-localization positive neurons was decreased in AD and VD models.

Introduction

Progressive impairment in memory and cognition is a key clinical feature of senile dementia and is reflective of degeneration within the central nervous system (CNS). The two major forms of dementia are Alzheimer's disease (AD) and vascular dementia (VD).

Although the exact causative mechanisms of senile dementia remain unknown until now, there is a growing body of evidence supporting the hypothesis that Ca2+ dysregulation contributes in part to AD and VD [3], [4]. The activity of the L-type calcium channel (LTCC) is linked to neuronal survival and death via transduction of calcium-regulated signaling events to the nucleus. The CaV1.2 channel accounts for 80% of the LTCCs in the brain, which is necessary to effectively activate cAMP response element-binding (CREB) and CREB-mediated gene transcription [1].

Calmodulin (CaM), the major intracellular calcium ion binding protein in the mammalian brain [24], has been implicated in many basic neuronal functions [12]. Calcium/calmodulin-dependent protein kinase II (CaMKII) is a Ca2+-activated enzyme, which plays an important role in learning and memory as a modulator of excitation-transcription coupling in neurons [11]. It is also critical for synaptic plasticity and behavioral training that are activated by Ca2+/CaM binding [5], [12]. Additionally, tethering of CaMKII to the COOH terminus of the CaV1.2α subunit is an essential molecular feature of Ca2+-dependent facilitation [7].

Brain-derived neurotrophic factor (BDNF) is a critical protein that supports the development, differentiation, maintenance and plasticity of brain function. The activation of CREB through phosphorylation of Ser133 controls the induction of many genes, including BDNF [18].

However, until now, the changes in Ca2+/calmodulin/CaMKII/CaV1.2 signaling in APP/PS1 mice, in cultured neurons treated with Aβ1–42, and in ischemia-induced VD gerbils, have not been well documented. We hypothesize that these proteins might be involved in the impairment of learning and memory in these models. Thus, the present study was performed to examine the alterations in CaV1.2, CaM, p-CaMKII, p-CREB and BDNF levels and the relationships between p-CaMKII and CaV1.2 in AD and VD models.

Section snippets

Ethical approval

All experimental procedures were conducted in strict accordance with the guidelines established by the Ministry of Health of China and were approved by the Animal Care Committee of China Medical University.

Animal husbandry

Male 9-month-old APP/PS1-Tg mice and age-matched wild-type C57BL/6 mice were obtained from the Jackson Laboratory (West Grove, PA, USA).

Induction of global cerebral ischemia

Transient global ischemia was induced according to the method described previously [20]. Briefly, gerbils were anesthetized with 10% chloral hydrate (350 

Evaluation of dementia models by neuronal cell viability and the Morris water maze

Addition of Aβ1–42 to neuronal cell cultures was found to reduce cell viability in a dose-dependent manner (Fig. 1A). At an Aβ1–42 concentration of 4 μM, neuronal cell viability was 63.51 ± 1.29% compared to the control group. Cultured neurons treated with 4 μM Aβ1–42 for 24 h were used in the subsequent experimental assay as a model group.

The evaluation of the VD model was performed by use of the Morris water maze. The escape latency to reach the platform in the sham and VD groups, was 41.47 ± 4.50

APP/PS1 transgenic mice, neurons treated with Aβ1–42, ischemic gerbils representing AD models in vivo and in vitro and VD models

Our data have shown that ten minutes of global ischemia in gerbils produced learning and memory impairments, which could be considered as constituting an in vivo model of VD. Additionally, a previous study has shown that APP/PS1 mice revealed significant deficits in hippocampal basal synaptic transmission (BST), long-term potentiation (LTP) and memory [15] and the expression of Aβ1–42 is increased in the brain [2]. Thus, we selected 9-month APP/PS1 transgenic mice and neurons treated with 4 μM Aβ

Acknowledgement

This work was supported by Natural Science Foundation of China (81001429, 31071004 and 30270535).

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