Decreased phosphatidylethanolamine binding protein expression correlates with Aβ accumulation in the Tg2576 mouse model of Alzheimer's disease
Introduction
Alzheimer's disease (AD) is the most common form of diagnosed dementia in the ageing population, accounting for 50–70% of late-onset dementia cases [19], with approximately 10% of individuals over the age of 65, and 40–50% over the age of 75 affected by the disease [20]. AD is clinically characterised by a progressive decline in multiple cognitive functions, with memory impairment and the presence of aphasia, apraxia, agnosia and/or the loss of the ability to plan and organise normal activities [3]. AD is currently classified as either early-onset (<65 years) or late-onset (>65 years) [13]. Early-onset or familial AD (FAD) has been linked with mutations in three key genes that are suggested to be causative. These genes include the amyloid precursor protein (APP) [19], Presenilin 1 (PS1) [48] and Presenilin 2 (PS2) genes [29]. Mutations in these genes are very rare, highly penetrant and transmitted through the family in an autosomal dominant manner. FAD accounts for approximately 10% of all AD cases, with mutations in APP, PS1 and PS2 accounting for ∼30% of this component [52].
At present, no causative genes have been associated with late-onset, or sporadic AD, although a positive correlation between a family history, and development of dementia in later life has been observed [14]. Genetic linkage studies of AD have identified the Apolipoprotein E (Apoe) gene as a risk factor. Studies have shown that inheritance of the Apoe ɛ4 allele may increase the risk of developing AD, while presence of the ɛ2 allele may be protective against developing the disease [12], [45], [50]. In searching for novel AD genes, complete genome screens have been performed to identify regions of genetic linkage that may be involved in its pathogenesis. At present, linkage studies have identified regions on chromosomes 9, 10 and 12 to be of some importance in AD [28], [41]. However, the quest to identify potential genes in these ‘hotspots’ continues.
The use of high-throughput gene expression studies has helped elucidate different pathways of gene expression in humans [10], [16], [33], [40] as well as mouse models of AD [14], [51]. However, the heterogeneity observed between each of the different studies highlights the fact that AD is a genetically complex disease in which the expression of many different genes may play a role in pathogenesis. The current challenge is to identify gene targets that show some homogeneity in their expression amongst patients, as this may help further the understanding of the molecular pathogenesis, particularly in sporadic AD.
The phosphatidylethanolamine binding protein (PEBP) gene has been associated with AD, where decreased mRNA expression was observed in the brain of AD patients, in particular, in the CA1 hippocampal field of patients with late-onset AD [34]. PEBP is also known as Raf kinase inhibitor protein (RKIP), prostatic binding protein, hippocampal cholinergic neurostimulating peptide precursor (HCNPp) and in humans specifically, as neuropolypeptide h3 [47]. PEBP is a small cytosolic protein that was initially purified from bovine brain [5], but was later shown to be expressed in a large range of tissues from mammalian species including humans [23], [47], monkeys [42], rats [17] and mice [2]. PEBP is localised to oligodendrocytes and Schwann cells and was postulated to be involved in membrane biogenesis or lipid transfer [35]. Further studies have shown that PEBP is abundantly distributed throughout the cytoplasm, and its association with plasma membrane suggests that it has a potential role in signalling mechanisms between the membrane and cytoplasm of cells [21], [46]. PEBP is phosphorylated at serine 153 [32], which may be an important feature in its ability to inhibit Raf kinase, and hence, its involvement in regulating the MAP kinase signalling pathway [11].
PEBP is the precursor of the hippocampal cholinergic neurostimulating peptide (HCNP), an 11 amino acid peptide that possesses cholinergic neuronal stimulatory activity. The HCNP is suggested to be able to act independently and also synergistically with nerve growth factor to enhance the production of choline acetyltransferase, which assists in cholinergic development of the medial septal nuclei of the brain [38]. As the cholinergic hypothesis suggests that cognitive decline observed in AD is primarily due to a cholinergic deficit [4], a decrease in overall levels of PEBP and/or HCNP in AD affected patients may help explain why cholinergic impairments are prevalent in the disease.
In this paper, we investigated the levels of PEBP at the transcriptional and post-transcriptional levels in hippocampus and cortex of the Tg2576 mouse model of AD, which develop Aβ plaques at approximately 9–12 months of age [24] and non-transgenic littermates. We also studied the cellular distribution of PEBP in the Tg2576 mouse and end-stage sporadic AD.
Section snippets
Tissue samples
For the initial mouse study, 11-month-old female Tg2576 mice (n = 5) and non-transgenic (NTg) littermates (n = 5) were cervically dislocated and brain tissue was collected. For the age study, female Tg2576 mice that were 6 months (n = 5), 11 months (n = 5) and 15 months (n = 4), along with the same number of NTg littermates per group, were asphyxiated with CO2 and the brain removed. Brain tissue taken from the mice was microdissected to obtain hippocampus and cortex for further analysis. Samples were
PEBP expression in Tg2576 mouse hippocampus
To determine the expression of PEBP at transcriptional and post-translational levels, hippocampii from 11 month Tg2576 mice and non-transgenic littermates were dissected for mRNA and protein expression analyses. “Real-time” qRT-PCR, currently one of the more sensitive techniques capable of quantitating gene expression, was used to measure the relative expression of PEBP mRNA in the Tg2576 mouse compared to NTg. The results showed that there was no significant difference in PEBP mRNA expression
Discussion
The aim of this study is to investigate the potential role of PEBP in AD by determining the expression of PEBP at transcriptional and post-transcriptional levels in the Tg2576 mouse model of AD. This model contains the human APP transgene carrying the FAD Swedish (APPsw) double mutations (APP K670N, M671L) identified at the β-cleavage site of APP [37]. The Tg2576 mouse expresses APPsw protein at a high level under the influence of a hamster prion protein (PrP) promoter, which, in the literature
Acknowledgements
We thank Dr. Karen Hsiao for the Tg2576 mouse, Ms. Laura Leone for assisting with immunohistochemistry and Ms. Katrina Laughton for technical assistance. This work was supported by grants from the National Health and Medical Research Council (RMDH, SST, HSS, RC, CLM and QXL). We also thank the National Neural Tissue Resource Centre for the use of the human AD and control fixed brain tissues used in this study.
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2018, Neurochemistry InternationalCitation Excerpt :In the brains of Tg2576 mice, PEBP1 levels decreased with age, starting at 11 months, compared to age-matched control mice (George et al., 2006; Mullan et al., 1992). This is also the time period when amyloid-beta (Aβ) plaques accumulate in the brains of Tg2576 mice (George et al., 2006). Chronic treatment with corticosterone decreases hippocampal PEBP1 expression and impairs cognitive function in rats (Feldmann et al., 2008).
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2014, Neurobiology of AgingCitation Excerpt :The knockdown of RKIP in SH-SY5Y cells has also been demonstrated to affect their differentiation (Hellmann et al., 2010). Moreover, RKIP expression was observed to be reduced in Alzheimer's disease (Maki et al., 2002) and was correlated with amyloid-β plaque formation (George et al., 2006). However, the mechanisms that underlie these phenomena remain poorly understood.
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2013, Biochemical and Biophysical Research CommunicationsCitation Excerpt :It is also necessary to mention the phosphatidylethanolamine-binding protein (PEBP) involved in functioning of cardiovascular system [37], carcinogenesis [38,39], cell apoptosis [40] tumor necrosis [41], protection against bacterial infection [42], and Alzheimer disease [43].
Straightforward isolation of phosphatidyl-ethanolamine-binding protein-1 (PEBP-1) and ubiquitin from bovine testis by hydrophobic-interaction chromatography (HIC)
2011, Journal of Chromatography B: Analytical Technologies in the Biomedical and Life SciencesCitation Excerpt :Indeed, its expression is down-regulated in tumor interstitial fluid from breast cancer patients [12] and it negatively regulates both the MAPK and NFκB pathways that are found hyperactivated in melanomas [13]. Concerning the central nervous system, PEBP-1 has been found down-regulated in the Alzheimer disease model mouse line Tg2576 [14] but, in contrast, it is up-regulated in rat hippocampal progenitor cells which are important for memory formation [15] as well as in the brain of atlantic cod exposed to methylmercury [16]. The isolation of PEBP-1 in a highly purified state was described almost three decades ago but it required a large number of steps [1].