Model-guided microarray implicates the retromer complex in Alzheimer's disease
ABSTRACT Although, in principle, gene expression profiling is well suited to isolate pathogenic molecules associated with Alzheimer's disease (AD), techniques such as microarray present unique analytic challenges when applied to disorders of the brain. Here, we addressed these challenges by first constructing a spatiotemporal model, predicting a priori how a molecule underlying AD should behave anatomically and over time. Then, guided by the model, we generated gene expression profiles of the entorhinal cortex and the dentate gyrus, harvested from the brains of AD cases and controls covering a broad age span. Among many expression differences, the retromer trafficking molecule VPS35 best conformed to the spatiotemporal model of AD. Western blotting confirmed the abnormality, establishing that VPS35 levels are reduced in brain regions selectively vulnerable to AD. VPS35 is the core molecule of the retromer trafficking complex and further analysis revealed that VPS26, another member of the complex, is also downregulated in AD. Cell culture studies, using small interfering RNAs or expression vectors, showed that VPS35 regulates Abeta peptide levels, establishing the relevance of the retromer complex to AD. Reviewing our findings in the context of recent studies suggests how downregulation of the retromer complex in AD can regulate local levels of Abeta peptide.
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ABSTRACT: Alzheimer's disease (AD) is characterized by cerebral deposition of β-amyloid (Aβ) peptides, which are generated from amyloid precursor protein (APP) by β- and γ-secretases. APP and the secretases are membrane associated, but whether membrane trafficking controls Aβ levels is unclear. Here, we performed an RNAi screen of all human Rab-GTPases, which regulate membrane trafficking, complemented with a Rab-GTPase-activating protein screen, and present a road map of the membrane-trafficking events regulating Aβ production. We identify Rab11 and Rab3 as key players. Although retromers and retromer-associated proteins control APP recycling, we show that Rab11 controlled β-secretase endosomal recycling to the plasma membrane and thus affected Aβ production. Exome sequencing revealed a significant genetic association of Rab11A with late-onset AD, and network analysis identified Rab11A and Rab11B as components of the late-onset AD risk network, suggesting a causal link between Rab11 and AD. Our results reveal trafficking pathways that regulate Aβ levels and show how systems biology approaches can unravel the molecular complexity underlying AD.
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ABSTRACT: Sortilin, a Golgi sorting protein and a member of the VPS10P family, is the co-receptor for proneurotrophins, regulates protein trafficking, targets proteins to lysosomes and regulates low density lipoprotein metabolism. The aim of this study was to investigate the expression and regulation of sortilin in Alzheimer's disease (AD). A significantly increased level of sortilin was found in human AD brain and in the brains of 6-month-old APPswe/PS1dE9 transgenic mice. Aβ42 enhanced the protein and mRNA expression levels of sortilin in a dose- and time-dependent manner in SH-SY5Y(APP695) cells, but had no effect on sorLA. In addition, proBDNF also significantly increased the protein and mRNA expression of sortilin in these cells. The recombinant extracellular domain of p75(NTR) (P75ECD-FC), or the antibody against the extracellular domain of p75(NTR) , blocked the upregulation of sortilin induced by Aβ, suggesting that Aβ42 increased the expression level of sortilin and mRNA in SH-SY5Y via the p75(NTR) receptor. Inhibition of ROCK, but not JNK, suppressed constitutive and Aβ42 -induced expression of sortilin. In conclusion, this study shows that sortilin expression is increased in the AD brain in human and mice and that Aβ42 oligomer increases sortilin gene and protein expression through p75(NTR) and RhoA signaling pathways, suggesting a potential physiological interaction of Aβ42 and sortilin in Alzheimer's disease. This article is protected by copyright. All rights reserved.Journal of Neurochemistry 07/2013; DOI:10.1111/jnc.12383 · 4.24 Impact Factor
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ABSTRACT: Recent studies indicated sortilin-related receptor 1 (SORL1) to be a risk-gene for late-onset Alzheimer's Disease (AD), although its role in the aetiology and/or progression of this disorder is not fully understood. Here, we report the finding of a novel non-coding (nc) RNA (hereafter referred to as 51A) that maps in antisense (AS) configuration in intron 1 of SORL1 gene. 51A expression drives a splicing shift of SORL1 from the synthesis of the canonical long protein variant 1 to an alternatively spliced protein form. This process, resulting in a decreased synthesis of SORL1 variant 1, is associated with an impaired processing of APP, leading to increase of Aβ formation. Interestingly, we found that 51A is expressed in human brains, being frequently up-regulated in cerebral cortices from Alzheimer's disease patients. Altogether these findings document a novel ncRNA-dependent regulatory pathway that might have relevant implications in neurodegeneration.Disease Models and Mechanisms 03/2013; 6(2):424-433. DOI:10.1242/dmm.009761 · 5.54 Impact Factor