Elsevier

Brain Research Bulletin

Volume 80, Issues 4–5, 28 October 2009, Pages 268-273
Brain Research Bulletin

Research report
miR-34a, a microRNA up-regulated in a double transgenic mouse model of Alzheimer's disease, inhibits bcl2 translation

https://doi.org/10.1016/j.brainresbull.2009.08.006Get rights and content

Abstract

MicroRNAs (miRNAs) are short noncoding regulatory RNA molecules that modulate protein expression by inhibiting mRNA translation or promoting mRNA degradation. However, little is understood about the roles of miRNAs in Alzheimer's disease. During a research for miRNAs that are differentially expressed in cerebral cortex of APPswe/PSΔE9 mice (a model for Alzheimer's disease) and age-matched controls, one candidate miRNA that is relatively highly expressed, miR-34a, was studied further because sequence analysis suggested a likely interaction with the 3′-untranslated region of bcl2 mRNA. We show that the expression of miR-34a is inversely correlated with the protein level of bcl2 in APPswe/PSΔE9 mice and age-matched controls, and miR-34a expression directly inhibits bcl2 translation in SH-SY5Y cells. No effect on bcl2 mRNA level was observed. Western blot analysis of active caspase-3 showed higher levels in APPswe/PSΔE9 mice and stable transfecant cell line of miR-34a than in controls. Consistently, miR-34a knockdown through antisense LNA oligonucleotides increased the level of bcl2 protein in SH-SY5Y cells, which was accompanied by a decrease of active caspase-3. These findings suggested that bcl2 is an important functional target for miR-34a, and the abnormal expression of miR-34a may contribute to the pathogenesis of Alzheimer's disease, at least in part by affecting the expression of bcl2.

Introduction

Alzheimer's disease (AD) is the most prevalent age-associated neurodegenerative disorder, which is characterized by deposition of senile plaque, neurofibrillary tangles (NFTs), and loss of synapses and neurons in the hippocampus and cerebral cortex. It is the major cause of dementia, accounting for 50–70% of the late-onset patients, with 17–20 million affected. The personal, familial, and societal costs of the disease are enormous with chronic symptoms that result in marked functional disability. Although a number of factors have been identified that could be involved in the pathogenesis of AD, such as APP, PS, Tau and BACE1, the mechanism of AD is not very clear yet.

miRNAs are endogenously expressed small ssRNA sequences of ∼22 nucleotides in length which naturally direct gene silencing by suppressing the translation and/or promoting the degradation of target mRNAs by binding to their 3′-untranslated regions(3′-UTR)[11], [21]. miRNAs are abundant in the brain and play an important role in neurodevelopment and synaptic plasticity [13]. Alterations in miRNAs expression in AD have been documented in some studies and suggest that miRNAs critically contribute to the pathogenesis of AD [7], [19], [20], [27]. miR-34a is a member of miR-34 family and this family comprises three processed miRNAs expressed from two separate loci: miR-34a from chromosome 1p36 and the miR-34b/miR-34c cluster from chromosome 11q23. In mice, miR-34a is ubiquitously expressed with the highest expression in brain [18], whereas miR-34b/c is mainly expressed in lung tissues [2]. Reports from several laboratories showed that the up-regulation of miR-34a could reduce apoptosis. Welch et al. [28] reported that ectopic miR-34a induces apoptosis when reintroduced into the neuroblastoma cell lines, which show decreased expression of miR-34a. Chang et al. [5] showed that miR-34a induced apoptosis is at least, in part, dependent on the presence of wild-type p53 indicating that miR-34a may feed back to p53. Furthermore, locked nucleic acids directed against miR-34a protect cells to some extent from the DNA damage-induced apoptosis in wild-type p53-expressing cells [22].

Bcl2 is an anti-apoptotic protein primarily expressed in mitochondria and the outer nuclear membrane, which prevents caspase-9 activation through an interaction with Apaf-1 [15]. It is neuroprotective against apoptotic cell death caused by amyloidogenic peptides [6]. Overexpression of bcl2 could attenuate the processing of APP and tau and reduced the number of NFTs and extracellular deposits of Aβ [23]. However, bcl2 gene expression regulation is not completely understood. Here, we provide data indicating that miR-34a contributes to bcl2 posttranscriptional regulation and that this pathway may be involved in the pathogenesis of AD.

Section snippets

Transgenic mice

The transgenic mice used in this study was produced by co-injection of the APPswe and PS1ΔE9 vectors, and the transgenes were expressed under control of the mouse prion protein promoter, which can drive high protein expression in neurons and astrocytes of the central nervous system [3], [17]. The APPswe transgene encodes a mouse–human hybrid transgene containing the mouse sequence in the extracellular and intracellular regions, and a human sequence within the Aβ domain with Swedish mutations

Differential expression of miRNAs in APPswe/PSΔE9 mice versus control mice

From the 299 distinct miRNAs included on our array, 37 miRNAs were consistently changed in cerebral cortex of APPswe/PSΔE9 mice versus cerebral cortex of age-matched controls (Fig. 1). Of the 37 distinguished miRNAs, 17 were expressed at lower (fold change 0.23–0.90), including mir-20a, miR-29a, miR-125b, miR-128a and miR-106b, which have been linked to AD [4], [9], [10], [19], and 20 at higher (fold change 1.13–2.98) levels than in the age-matched controls. However, the other miRNAs that have

Discussion

miRNAs are small regulatory RNAs that participate in posttranscriptional gene regulation in a sequence-specific manner. miRNAs are abundant in the brain and are essential for efficient brain function [8]. Some researches in mice [12], [24], flies [1], and cultured neurons [12] have suggested that alterations in miRNA networks in the brain contribute to neurodegenerative disease. However, the mechanism of the role of miRNAs in AD is still unclear. Recently, microRNA array has been successfully

Conflicts of interest

There is no conflict of interests among all authors.

Acknowledgments

We thank Wei Tong, Xueli Liu for their excellent technical assistance. We also thank Jiamei Li, Lingling Zhang, Haixia Shi, Xiaoying Li for their kindly help in our research.

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