Elsevier

Neuroscience Letters

Volume 633, 28 October 2016, Pages 40-46
Neuroscience Letters

Research article
Cerebral dopamine neurotrophic factor alleviates Aβ25-35-induced endoplasmic reticulum stress and early synaptotoxicity in rat hippocampal cells

https://doi.org/10.1016/j.neulet.2016.09.008Get rights and content

Highlights

  • ER stress could be triggered by treatment at early stage in primary neurons.

  • CDNF alleviates Aβ-induced early synaptotoxicity.

  • CDNF protects against Aβ-induced ER stress.

Abstract

Alzheimer’s disease (AD) is an age-related progressive neurodegenerative disease, and early stage AD is characterized by synaptic dysfunction generally ascribed to soluble oligomers of amyloid-beta (Aβ). Neurotrophic factors are promising for AD treatment and are integrally involved in neuronal growth, survival and maintenance. Cerebral dopamine neurotrophic factor (CDNF) was recently discovered to have beneficial effects on long-term memory. The present study explored the synaptoprotective effects of CDNF in Aβ-treated primary hippocampal cells. Immunofluorescent analysis of synaptophysin and postsynaptic density protein 95 (PSD95) puncta densities in the group of pretreatment with CDNF before Aβ exposure revealed significant improvements compared to Aβ group. In addition, pretreatment with CDNF reduced the expression levels of endoplasmic reticulum (ER) stress-related proteins, including Bip (also known as GRP78), phosphorylation of eukaryotic translation initiation factor 2 subunit α (peIF2α), phosphorylation of c-Jun N-terminal kinase (pJNK), and cleaved caspase 3, which are increased by Aβ treatment at early stage. Our results revealed protective effects of CDNF on Aβ-induced synaptotoxicity and ER stress, implying that CDNF may protect against Aβ-induced synaptotoxicity through suppression of ER stress. CDNF could be a potential drug candidate for early AD treatment.

Introduction

Alzheimer’s disease (AD), the major cause of dementia, is the most common age-related neurodegenerative disorder. Neuropathological features of AD include extracellular deposits of amyloid-β (Aβ) peptide and intracellular neurofibrillary tangles of hyperphosphorylated tau proteins [1]. Mounting evidence suggests that cognitive deficits in AD begin with subtle alterations of synaptic function before overt neuronal loss is detectable [2]. As the etiology of AD remains unclear, there are currently no effective treatments. Therefore, novel therapies for slowing disease progressions, and particularly those early strategies to prevent synaptic dysfunctions are urgently needed.

Neurotrophic factors (NTF) are a family of growth factors that promote the cell survival, and regulate brain plasticity and neuroregeneration. A new comer of NTF, cerebral dopamine neurotrophic factor (CDNF), which is located in endoplasmic reticulum (ER) and involved in unfolded protein response (UPR) in ER stress [3], [4], displays strong protective and restorative effects in dopaminergic neurons [5], [6]. Recent studies showed overexpression of CDNF could alleviate cell damage and promote nerve regeneration [7], [8]. In addition, gene therapy with CDNF displayed the potential to improve long term memory in APP/PS1 transgenic animals [9]. Although growing body of evidence suggests ER stress is implicated in AD, few are related to Aβ synaptotoxicity [10], [11], [12]. Furthermore, the effects of CDNF on Aβ-induced synaptotoxicity and the related molecular mechanisms remain unclear. Our present report demonstrates the protective effects of CDNF on Aβ-induced synaptotoxicity and ER stress.

Section snippets

Materials

CDNF protein was from R&D (MN, USA). Aβ25-35 was purchased from American Peptide (CA, USA), dissolved in DMSO (Sigma-Aldrich, MO, USA) and stored in −20 °C. Neurobasal A, B27, Dulbecco’s-Modified Eagle Media/F12 (DMEM/F12), fetal bovine serum (FBS), trypsin and PDL were obtained from Gibco (MO, USA). Basic fibroblast growth factor (bFGF) (NY, USA) and Lipofectamine-2000 (CA, USA) were from Invitrogen.

25-35 preparation

25-35 was dissolved in 2 mM DMSO, diluted 1:10 in sterile PBS, vortexed (30 min, room

CDNF expression in rat primary hippocampal cells

Previous studies have indicated that CDNF is expressed in most tissues of brain, especially in hippocampus, but have not confirmed the accurate cell types [5], [8], [17]. The results of immunofluorescence displayed some CDNF-immunolabled cells coexpressed GFAP (marker of astrocytes) or Tuj1 (marker of neurons), suggesting that CDNF was expressed in both astrocytes and neurons (Fig. 2A). In addition, we also verified the expression of CDNF in hippocampal cells using western blot analysis (Fig. 2

Discussion

CDNF is a new member of the novel evolutionary conserved neurotrophic factor family. Currently, most studies on CDNF are mainly in PD disease, and a significant neuroprotective and neurorestorative effect of CDNF has been identified in the mouse PD models [18], [19], which motivated some researchers to investigate its potential therapeutic effect in AD animal models. To our knowledge, only one study so far has addressed the potential of CDNF in AD models [9]. In 2015, Kemppainen reported that

Acknowledgements

The authors are grateful to Prof. Weiming Duan for his kind assistance. This work was supported by the Program for New Century Excellent Talents in University (NCET-10-0015), the Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions (CIT&TCD201304175), Beijing BaiQianWan Talents Program (2015002), Beijing Natural Science Foundation (5152004), National Natural Science Foundation of China (81301100).

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