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Expression of mRNAs Regulating Synaptic Function and Neuroplasticity in Incipient AD

ABSTRACT: In Alzheimer’s disease (AD), early deficits in learning and memory are a consequence of synaptic modification which are likely induced by toxic beta-amyloid oligomers (oAβ). To identify molecular targets downstream of oAβ binding we prepared synaptoneurosomes from frontal cortex of control and IAD patients, and isolated mRNAs for comparison of gene expression. This approach elevated synaptic mRNAs above the threshold necessary for expression changes to be discriminated and also reduced other cellular mRNAs. In patients with minimal cognitive impairment (MCI) termed incipient AD (IAD) global measures of cognition declined with increasing levels of dimeric Aβ (dAβ). These patients also showed increased expression of neuroplasticity related genes, many encoding 3' UTR consensus sequences that regulate local translation in the synapse. One such gene, GluR2, displayed elevated mRNA and protein expression in IAD. Other neurotransmitter-related genes were also upregulated. Overexpressed genes may induce compensatory as well as negative effects on cognition and provide targets for intervention to moderate the response to dAβ.

ORGANISM(S): Homo sapiens

PROVIDER: GSE12685 | GEO | 2009/01/10

SECONDARY ACCESSION(S): PRJNA112687

REPOSITORIES: GEO

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Project description:In Alzheimer's disease (AD), early deficits in learning and memory are a consequence of synaptic modification which are likely induced by toxic beta-amyloid oligomers (dAbeta). To identify molecular targets downstream of dAbeta binding we prepared synaptoneurosomes from frontal cortex of control and IAD patients, and isolated mRNAs for comparison of gene expression. This approach elevated synaptic mRNAs above the threshold necessary for expression changes to be discriminated and also reduced other cellular mRNAs. In patients with minimal cognitive impairment (MCI) termed incipient AD (IAD) global measures of cognition declined with increasing levels of dimeric beta (dAbeta). These patients also showed increased expression of neuroplasticity related genes, many encoding 3' UTR consensus sequences that regulate local translation in the synapse. One such gene, GluR2, displayed elevated mRNA and protein expression in IAD. Other neurotransmitter-related genes were also upregulated. Overexpressed genes may induce compensatory as well as negative effects on cognition and provide targets for intervention to moderate the response to dAbeta. Experiment Overall Design: Patient information Experiment Overall Design: CNS tissues were obtained from the USC Alzheimer's Disease Research Center (ADRC) Neuropathology Core, NIA AG05142. Clinical information, including neurological examination, neuropsychological testing such as cognitive assessment, family history, and medications were provided by the USC ADRC Clinical Core. The groups did not differ significantly in age or years of education. Medication histories indicated one IAD patient had used a selective serotonin uptake inhibitor. Post-mortem interval (PMI) ranged from 2 to 9 hours (mean 5.1 hrs.). The study included 8 normal controls and 6 patients with Incipient Alzheimer's Disease. Experiment Overall Design: To augment studies comparing homogenates of control to AD brains, we used synaptoneurosome preparations to enrich for synaptic mRNAs. Synaptoneurosomes were prepared from the prefrontal cortices of control and IAD patients by a simple, rapid, but gentle method using sequential mesh screens.

Project description:s synapse degeneration is an early event in Alzheimer’s disease (AD) pathophysiology, a biofluid marker of synapse loss in living patients could be a surrogate marker of disease prognosis and therefore would be an excellent addition to the AD biomarker arsenal. With direct access to the brain interstitial fluid, the cerebrospinal fluid (CSF) is a potential source of synapse-derived proteins that could be potential biomarkers of underlying synapse degeneration. The aim of this study was to identify, verify and evaluate a set of synaptic proteins as surrogate CSF markers of underlying synapse loss in AD patients. In the Discovery Stage, we combined high-throughput shotgun proteomics of the CSF with an exhaustive search of the literature and public databases for proteomic studies of the CSF and synapse. A thorough characterization of the synaptic component of the CSF identified 210 synaptic proteins that are detectable in human CSF. We selected an initial panel of 22 candidate biomarkers for evaluation. In the Verification Stage, 12 proteins were discarded due to poor detection by targeted mass spectrometry (Selected Reaction Monitoring, SRM). We confirmed the expression of the remaining 10 proteins either directly at (Calsynytenin-1, GluR2, GluR4, Neurexins 2A and 3A, Neuroligin-2, Syntaxin-1B, Thy-1 and Vamp-2), or surrounding (Tenascin-R), the human synapse using Array Tomography microscopy and biochemical fractionation methods. We quantified the synaptic panel by SRM in CSF samples from 2 independent clinical cohorts of cognitively normal controls and all clinical stages of AD (n=140). A set of the panel proteins demonstrated a non-linear profile distinct to that of existing biomarkers whereby the CSF levels were decreased at the earliest preclinical stage of AD, reflecting reduced synaptic density in these asymptomatic individuals and elevated at later symptomatic stages when neurodegeneration is widespread. In conclusion, we have identified a set of novel synapse-specific proteins that could have clinical value for assessing disease progression in individuals at-risk for AD and potentially in other neurological disorders characterized by early synapse loss.

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Expression of mRNAs Regulating Synaptic Function and Neuroplasticity in Incipient AD

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