Concordant association of insulin degrading enzyme gene (IDE) variants with IDE mRNA, Abeta, and Alzheimer's disease

Inhibition of insulin-degrading enzyme in human neurons promotes amyloid-β deposition

Alzheimer's disease (AD) is characterised by the aggregation and deposition of amyloid-β (Aβ) peptides in the human brain. In age-related late-onset AD, deficient degradation and clearance, rather than enhanced production, of Aβ contributes to disease pathology. In the present study, we assessed the contribution of the two key Aβ-degrading zinc metalloproteases, insulin-degrading enzyme (IDE) and neprilysin (NEP), to Aβ degradation in human induced pluripotent stem cell (iPSC)-derived cortical neurons. Using an Aβ fluorescence polarisation assay, inhibition of IDE but not of NEP, blocked the degradation of Aβ by human neurons. When the neurons were grown in a 3D extracellular matrix to visualise Aβ deposition, inhibition of IDE but not NEP, increased the number of Aβ deposits. The resulting Aβ deposits were stained with the conformation-dependent, anti-amyloid antibodies A11 and OC that recognise Aβ aggregates in the human AD brain. Inhibition of the Aβ-forming β-secretase prevented the formation of the IDE-inhibited Aβ deposits. These data indicate that inhibition of IDE in live human neurons grown in a 3D matrix increased the deposition of Aβ derived from the proteolytic cleavage of the amyloid precursor protein. This work has implications for strategies aimed at enhancing IDE activity to promote Aβ degradation in AD.

Insulin-degrading enzyme (IDE) as a modulator of microglial phenotypes in the context of Alzheimer's disease and brain aging

The insulin-degrading enzyme (IDE) is an evolutionarily conserved zinc-dependent metallopeptidase highly expressed in the brain, where its specific functions remain poorly understood. Besides insulin, IDE is able to cleave many substrates in vitro, including amyloid beta peptides, making this enzyme a candidate pathophysiological link between Alzheimer's disease (AD) and type 2 diabetes (T2D). These antecedents led us to address the impact of IDE absence in hippocampus and olfactory bulb. A specific induction of microgliosis was found in the hippocampus of IDE knockout (IDE-KO) mice, without any effects in neither hippocampal volume nor astrogliosis. Performance on hippocampal-dependent memory tests is influenced by IDE gene dose in 12-month-old mice. Furthermore, a comprehensive characterization of the impact of IDE haploinsufficiency and total deletion in metabolic, behavioral, and molecular parameters in the olfactory bulb, a site of high insulin receptor levels, reveals an unambiguous barcode for IDE-KO mice at that age. Using wildtype and IDE-KO primary microglial cultures, we performed a functional analysis at the cellular level. IDE absence alters microglial responses to environmental signals, resulting in impaired modulation of phenotypic states, with only transitory effects on amyloid-β management. Collectively, our results reveal previously unknown physiological functions for IDE in microglia that, due to cell-compartment topological reasons, cannot be explained by its enzymatic activity, but instead modulate their multidimensional response to various damaging conditions relevant to aging and AD conditions.

The Insulin-Degrading Enzyme from Structure to Allosteric Modulation: New Perspectives for Drug Design

The insulin-degrading enzyme (IDE) is a Zn2+ peptidase originally discovered as the main enzyme involved in the degradation of insulin and other amyloidogenic peptides, such as the β-amyloid (Aβ) peptide. Therefore, a role for the IDE in the cure of diabetes and Alzheimer's disease (AD) has been long envisaged. Anyway, its role in degrading amyloidogenic proteins remains not clearly defined and, more recently, novel non-proteolytic functions of the IDE have been proposed. From a structural point of view, the IDE presents an atypical clamshell structure, underscoring unique enigmatic enzymological properties. A better understanding of the structure-function relationship may contribute to solving some existing paradoxes of IDE biology and, in light of its multifunctional activity, might lead to novel therapeutic approaches.

Inhibition of Insulin Degrading Enzyme to Control Diabetes Mellitus and its Applications on some Other Chronic Disease: a Critical Review

PURPOSE

This review aims to provide a precise perceptive of the insulin-degrading enzyme (IDE) and its relationship to type 2 diabetes (T2D), Alzheimer's disease (AD), obesity, and cardiovascular diseases. The purpose of the current study was to provide clear idea of treating prevalent diseases such as T2D, and AD by molecular pharmacological therapeutics rather than conventional medicinal therapy.

METHODS

To achieve the aims, molecular docking was performed using several softwares such as LIGPLOT+, Python, and Protein-Ligand Interaction Profiler with corresponding tools.

RESULTS

The IDE is a large zinc-metalloprotease that breakdown numerous pathophysiologically important extracellular substrates, comprising amyloid β-protein (Aβ) and insulin. Recent studies demonstrated that dysregulation of IDE leads to develop AD and T2D. Specifically, IDE regulates circulating insulin in a variety of organs via a degradation-dependent clearance mechanism. IDE is unique because it was subjected to allosteric activation and mediated via an oligomer structure.

CONCLUSION

In this review, we summarised the factors that modulate insulin reformation by IDE and interaction of IDE and some recent reports on IDE inhibitors against AD and T2D. We also highlighted the latest signs of progress of the function of IDE and challenges in advancing IDE- targetted therapies against T2D and AD.

Genetic Inactivation of Free Fatty Acid Receptor 3 Impedes Behavioral Deficits and Pathological Hallmarks in the APPswe Alzheimer's Disease Mouse Model

The free fatty acid FFA3 receptor (FFA3R) belongs to the superfamily of G-protein-coupled receptors (GPCRs). In the intestine and adipose tissue, it is involved in the regulation of energy metabolism, but its function in the brain is unknown. We aimed, first, to investigate the expression of the receptor in the hippocampus of Alzheimer disease (AD) patients at different stages of the disease and, second, to assess whether genetic inactivation of the Ffar3 gene could affect the phenotypic features of the APP_swe mouse model. The expression of transcripts for FFA receptors in postmortem human hippocampal samples and in the hippocampus of wild-type and transgenic mice was analyzed by RT-qPCR. We generated a double transgenic mouse, FFA3R^−/−/APP_swe, to perform cognition studies and to assess, by immunoblotting Aβ and tau pathologies and the differential expression of synaptic plasticity-related proteins. For the first time, the occurrence of the FFA3R in the human hippocampus and its overexpression, even in the first stages of AD, was demonstrated. Remarkably, FFA3R^−/−/APP_swe mice do not have the characteristic memory impairment of 12-month-old APP_swe mice. Additionally, this newly generated transgenic line does not develop the most important Alzheimer’s disease (AD)-related features, such as amyloid beta (Aβ) brain accumulations and tau hyperphosphorylation. These findings are accompanied by increased levels of the insulin-degrading enzyme (IDE) and lower activity of the tau kinases GSK3β and Cdk5. We conclude that the brain FFA3R is involved in cognitive processes and that its inactivation prevents AD-like cognitive decline and pathological hallmarks.

Exploring the Structural Rearrangements of the Human Insulin-Degrading Enzyme through Molecular Dynamics Simulations

Insulin-degrading enzyme (IDE) is a ubiquitously expressed metallopeptidase that degrades insulin and a large panel of amyloidogenic peptides. IDE is thought to be a potential therapeutic target for type-2 diabetes and neurodegenerative diseases, such as Alzheimer’s disease. IDE catalytic chamber, known as a crypt, is formed, so that peptides can be enclosed and degraded. However, the molecular mechanism of the IDE function and peptide recognition, as well as its conformation changes, remains elusive. Our study elucidates IDE structural changes and explains how IDE conformational dynamics is important to modulate the catalytic cycle of IDE. In this aim, a free-substrate IDE crystallographic structure (PDB ID: 2JG4) was used to model a complete structure of IDE. IDE stability and flexibility were studied through molecular dynamics (MD) simulations to witness IDE conformational dynamics switching from a closed to an open state. The description of IDE structural changes was achieved by analysis of the cavity and its expansion over time. Moreover, the quasi-harmonic analysis of the hinge connecting IDE domains and the angles formed over the simulations gave more insights into IDE shifts. Overall, our results could guide toward the use of different approaches to study IDE with different substrates and inhibitors, while taking into account the conformational states resolved in our study.

Protective Effect of Natural Antioxidant, Curcumin Nanoparticles, and Zinc Oxide Nanoparticles against Type 2 Diabetes-Promoted Hippocampal Neurotoxicity in Rats

Numerous epidemiological findings have repeatedly established associations between Type 2 Diabetes Mellitus (T2DM) and Alzheimer's disease. Targeting different pathways in the brain with T2DM-therapy offers a novel and appealing strategy to treat diabetes-related neuronal alterations. Therefore, here we investigated the capability of a natural compound, curcumin nanoparticle (CurNP), and a biomedical metal, zinc oxide nanoparticle (ZnONP), to alleviate hippocampal modifications in T2DM-induced rats. The diabetes model was induced in male Wistar rats by feeding a high-fat diet (HFD) for eight weeks followed by intraperitoneal injection of streptozotocin (STZ). Then model groups were treated orally with curcumin, zinc sulfate, two doses of CurNP and ZnONP, as well as metformin, for six weeks. HFD/STZ-induced rats exhibited numerous biochemical and molecular changes besides behavioral impairment. Compared with model rats, CurNP and ZnONP boosted learning and memory function, improved redox and inflammation status, lowered Bax, and upregulated Bcl2 expressions in the hippocampus. In addition, the phosphorylation level of the MAPK/ERK pathway was downregulated significantly. The expression of amyloidogenic-related genes and amyloid-beta accumulation, along with tau hyperphosphorylation, were lessened considerably. In addition, both nanoparticles significantly improved histological lesions in the hippocampus. Based on our findings, CurNP and ZnONP appear to be potential neuroprotective agents to mitigate diabetic complications-associated hippocampal toxicity.

Lovastatin attenuates sevoflurane-induced cognitive disorder in aged rats via reducing Aβ accumulation

As a general anesthetic widely used in surgical, sevoflurane has been shown to cause cognitive and memory deficits in the elderly. It's important to find out agents that can counteract sevoflurane-induced cognitive dysfunction. This study is aimed to investigate the effect of lovastatin on sevoflurane-induced cognitive impairment in aged rats and reveal the potential mechanisms. BV-2 cells, rat hippocampal neurons or male aged rats were exposed to 2% sevoflurane for 5 h. The cells were pretreated with 10 μM lovastatin. The rats were intraperitoneally injected with 5 mg/kg/day lovastatin for three days. The results showed that lovastatin enhanced exosomal IDE secretion from sevoflurane-exposed BV-2 cells and promoted Aβ degradation. Lovastatin treatment also inhibited the increased expressions of β-secretase 1 (BACE1) and γ-secretase in hippocampal neurons under sevoflurane exposure in vitro. In animal experiments, the discrimination index in novel object recognition test and percentage of spontaneous alternation in Y-maze test were significantly elevated after lovastatin administration. In addition, Aβ plaque area and contents of soluble Aβ1-40 and Aβ1-42 in the hippocampal tissues were decreased upon lovastatin treatment. Furthermore, lovastatin reversed sevoflurane-induced Aβ accumulation via up-regulating IDE expression, and down-regulating amyloid precursor protein (APP)-related protein expression (β-C-terminal fragment (CTF), BACE1 and γ-secretase). In conclusion, lovastatin alleviates sevoflurane-induced cognitive deficient in aged rats via promoting Aβ degradation and reducing Aβ production. Lovastatin may be beneficial in preventing anesthetic-induced cognitive impairment.

Insulin-degrading enzyme: an ally against metabolic and neurodegenerative diseases

Insulin-degrading enzyme (IDE) function goes far beyond its known proteolytic role as a regulator of insulin levels. IDE has a wide substrate promiscuity, degrading several proteins such as amyloid-β peptide, glucagon, islet amyloid polypeptide (IAPP) and insulin-like growth factors, that have diverse physiological and pathophysiological functions. Importantly, IDE plays other non-proteolytical functions such as a chaperone/dead-end chaperone, an E1-ubiquitin activating enzyme, and a proteasome modulator. It also responds as a heat shock protein, regulating cellular proteostasis. Notably, amyloidogenic proteins such as IAPP, amyloid-β and α-synuclein have been reported as substrates for IDE chaperone activity. This is of utmost importance as failure of IDE may result in increased protein aggregation, a key hallmark in the pathogenesis of beta cells in type 2 diabetes mellitus and of neurons in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. In this review, we focus on the biochemical and biophysical properties of IDE and the regulation of its physiological functions. We further raise the hypothesis that IDE plays a central role in the pathological context of dysmetabolic and neurodegenerative diseases and discuss its potential as a therapeutic target. This article is protected by copyright. All rights reserved.

Effect of lobeglitazone on motor function in rat model of Parkinson's disease with diabetes co-morbidity

Parkinson's disease (PD) and diabetes mellitus share similar pathophysiological characteristics, genetic and environmental factors. It has been reported that people with diabetes mellitus appear to have a remarkable higher incidence of PD than age matched non diabetic individuals. Evidences suggest that use of antidiabetic glitazone is associated with a diminished risk of PD incidence in patients with diabetes. This study examined the effect of lobeglitazone, a member of thiazolidinedione class, in rat model of Parkinson's disease with diabetes co-morbidity. Rats received either rotenone and/or a combination of streptozocin and a high calorie diet for disease induction and they were treated with different doses of lobeglitazone or its vehicle. Behavioral tests comprising rotarod, bar test and rearing test were conducted to evaluate the motor function. Changes in the level tyrosine hydroxylase, TNF-α and NF-κB were analyzed using ELISA. In the same brain regions the possible changes in PPAR-γ receptor level were evaluated. Findings showed that although lobeglitazone tends to reverse the effect of rotenone in animals with diabetes, it was just able to prevent partly the motor defect in rearing test. Furthermore, lobeglitazone (1 mg/kg) reversed, in substantia nigra and striatum, the changes in tyrosine hydroxylase, TNF-α, NF-κB and PPAR-γ receptor content induced by rotenone in rats with diabetic condition. Although other preclinical studies are needed, these findings suggest that lobeglitazone is a promising neuroprotective candidate for clinical trials for PD patients with diabetes co-morbidity.

Shenqi Xingnao Granules ameliorates cognitive impairments and Alzheimer’s disease-like pathologies in APP/PS1 mouse model

Objective

Alzheimer's disease (AD) is along with cognitive decline due to amyloid-β (Aβ) plaques, tau hyperphosphorylation, and neuron loss. Shenqi Xingnao Granules (SQXN), a traditional Chinese medicine, significantly ameliorated the cognitive function and daily living abilities of patients with AD. However, till date, no study has investigated the mechanism of action of SQXN on AD. The present study aimed to verify the effects of SQXN treatment on cognitive impairments and AD-like pathologies in APP/PS1 mice.

Methods

Four-month-old APP/PS1 transgenic (Tg) mice were randomly divided into a model group and SQXN-treated (3.5, 7, 14 g/kg per day) groups. Learning-memory abilities were determined by Morris water maze and object recognition test. All mice were sacrificed and the brain samples were collected after 75 d. The soluble Aβ contents were detected by Elisa kit; The levels of expression of NeuN, APP, phosphorylated tau and related protein were measured by Western blotting; The inflammation factors were detected by the proinflammatory panel kit.

Results

Four-month-old APP/PS1 mice were administered SQXN by oral gavage for 2.5 months. Using the Morris water maze tests and Novel object recognition, we found that SQXN restored behavioral deficits in the experimental group of Tg mice when compared with the controls. SQXN also inhibited neuronal loss (NeuN marker). SQXN treatment decreased soluble Aβ42 through inhibiting the expression of sAPPβ and BACE-1 without regulating full-length amyloid precursor protein (FL APP). Insulin degrading enzyme (IDE), the Aβ degrading enzyme, were increased by SQXN. In addition, SQXN reduced hyperphosphorylated tau protein levels and prevented excessive activation of p-GSK-3β in the brain of APP/PS1 mice. Compared with APP/PS1 transgenic negative mice, IFN-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-12p70, KC/GRO and TNF-α were not obviously changed in the brain of 6.5-month-old APP/PS1 transgenic (Tg) mice. However, SQXN could inhibited the expression of IL-2.

Conclusion

These results demonstrate that SQXN ameliorates the cognitive impairments in APP/PS1 mice. The possible mechanisms involve its inhibition of neuronal loss, soluble Aβ deposition, tau hyperphosphorylation and inflammation.

Shared (epi)genomic background connecting neurodegenerative diseases and type 2 diabetes

The progressive aging of populations has resulted in an increased prevalence of chronic pathologies, especially of metabolic, neurodegenerative and movement disorders. In particular, type 2 diabetes (T2D), Alzheimer’s disease (AD) and Parkinson’s disease (PD) are among the most prevalent age-related, multifactorial pathologies that deserve particular attention, given their dramatic impact on patient quality of life, their economic and social burden as well the etiopathogenetic mechanisms, which may overlap in some cases. Indeed, the existence of common triggering factors reflects the contribution of mutual genetic, epigenetic and environmental features in the etiopathogenetic mechanisms underlying T2D and AD/PD. On this subject, this review will summarize the shared (epi)genomic features that characterize these complex pathologies. In particular, genetic variants and gene expression profiles associated with T2D and AD/PD will be discussed as possible contributors to determine the susceptibility and progression to these disorders. Moreover, potential shared epigenetic modifications and factors among T2D, AD and PD will also be illustrated. Overall, this review shows that findings from genomic studies still deserves further research to evaluate and identify genetic factors that directly contribute to the shared etiopathogenesis. Moreover, a common epigenetic background still needs to be investigated and characterized. The evidences discussed in this review underline the importance of integrating large-scale (epi)genomic data with additional molecular information and clinical and social background in order to finely dissect the complex etiopathogenic networks that build up the “disease interactome” characterizing T2D, AD and PD.

Altered expression of insulin-degrading enzyme and regulator of calcineurin in the rat intracerebral streptozotocin model and human apolipoprotein E-ε4-associated Alzheimer's disease

INTRODUCTION

This study assesses insulin-degrading enzyme (IDE) and regulator of calcineurin 1 (RCAN1) as potential mediators of brain insulin deficiency and neurodegeneration in experimental and human Alzheimer's disease (AD).

METHODS

Temporal lobes from Long Evans rats treated with intracerebral streptozotocin or vehicle and postmortem frontal lobes from humans with normal aging AD (Braak 0-2), moderate (Braak 3-4) AD, or advanced (Braak 5-6) AD were used to measure IDE and RCAN mRNA and protein.

RESULTS

Intracerebral streptozotocin significantly increased IDE and RCAN mRNA and protein. In humans with apolipoprotein E (ApoE) ε3/ε4 or ε4/ε4 and AD, IDE was elevated at Braak 3-4, but at Braak 5-6, IDE expression was significantly reduced. RCAN1 mRNA was similarly reduced in ApoE ε4+ patients with moderate or severe AD, whereas RCAN1 protein declined with the severity of AD and ApoE ε4 dose.

DISCUSSION

The findings suggest that IDE and RCAN1 differentially modulate brain insulin signaling in relation to AD severity and ApoE genotype.

Current and Emerging Pharmacological Targets for the Treatment of Alzheimer's Disease

No cure or disease-modifying therapy for Alzheimer's disease (AD) has yet been realized. However, a multitude of pharmacological targets have been identified for possible engagement to enable drug discovery efforts for AD. Herein, we review these targets comprised around three main therapeutic strategies. First is an approach that targets the main pathological hallmarks of AD: amyloid-β (Aβ) oligomers and hyperphosphorylated tau tangles which primarily focuses on reducing formation and aggregation, and/or inducing their clearance. Second is a strategy that modulates neurotransmitter signaling. Comprising this strategy are the cholinesterase inhibitors and N-methyl-D-aspartate receptor blockade treatments that are clinically approved for the symptomatic treatment of AD. Additional targets that aim to stabilize neuron signaling through modulation of neurotransmitters and their receptors are also discussed. Finally, the third approach comprises a collection of 'sensitive targets' that indirectly influence Aβ or tau accumulation. These targets are proteins that upon Aβ accumulation in the brain or direct Aβ-target interaction, a modification in the target's function is induced. The process occurs early in disease progression, ultimately causing neuronal dysfunction. This strategy aims to restore normal target function to alleviate Aβ-induced toxicity in neurons. Overall, we generally limit our analysis to targets that have emerged in the last decade and targets that have been validated using small molecules in in vitro and/or in vivo models. This review is not an exhaustive list of all possible targets for AD but serves to highlight the most promising and critical targets suitable for small molecule drug intervention.

The core sequence of PIF competes for insulin/amyloid β in insulin degrading enzyme: potential treatment for Alzheimer's disease

The central pathological feature of Alzheimer's disease (AD) is the sequential proteolytic processing of amyloid precursor protein (APP) to amyloid-β peptides (Aβ) agglomeration. The clearance of Aβ may be induced by the large zinc-binding protease insulin degrading enzyme (IDE). IDE is the common link between AD and Type II diabetes as insulin is an IDE target as well. Not surprisingly, the search for safe and effective drugs modulating IDE is ongoing. A new pregnancy derived peptide, PreImplantation Factor (PIF), inhibits neuro-inflammation and crosses the blood-brain-barrier. Importantly, we report that the (R3I4K5P6) core sequence of the PIF peptide modulates IDE function and results in decreased Aβ agglomeration in neuronal cells. Using bioinformatics we show that PIF binds to the IDE complex and sterically competes for the same place as insulin or Aβ. The predicted RIKP sequence and especially the specific I4 and P6 amino acids are essential for hydrophobic interactions with the IDE complex. In terms of potential AD treatment, PIF was successfully tested in neurodegenerative animal models of perinatal brain injury and experimental autoimmune encephalitis. Importantly, sPIF received a FDA Fast Track Approval and orphan drug designation for first-in-human trial in autoimmunity.

Insulin-Degrading Enzyme in the Fight against Alzheimer's Disease

After decades of research and clinical trials there is still no cure for Alzheimer's disease (AD). While impaired clearance of amyloid beta (Aβ) peptides is considered as one of the major causes of AD, it was recently complemented by a potential role of other toxic amyloidogenic species. Insulin-degrading enzyme (IDE) is the proteolytic culprit of various β-forming peptides, both extracellular and intracellular. On the basis of demonstrated allosteric activation of IDE against Aβ, it is possible to propose a new strategy for the targeted IDE-based cleansing of different toxic aggregation-prone peptides. Consequently, specific allosteric activation of IDE coupled with state-of-the-art compound delivery and CRISP-Cas9 technique of transgene insertion can be instrumental in the fight against AD and related neurodegenerative maladies.

Multiple functions of insulin-degrading enzyme: a metabolic crosslight?

Insulin-degrading enzyme (IDE) is a ubiquitous zinc peptidase of the inverzincin family, which has been initially discovered as the enzyme responsible for insulin catabolism; therefore, its involvement in the onset of diabetes has been largely investigated. However, further studies on IDE unraveled its ability to degrade several other polypeptides, such as β-amyloid, amylin, and glucagon, envisaging the possible implication of IDE dys-regulation in the "aggregopathies" and, in particular, in neurodegenerative diseases. Over the last decade, a novel scenario on IDE biology has emerged, pointing out a multi-functional role of this enzyme in several basic cellular processes. In particular, latest advances indicate that IDE behaves as a heat shock protein and modulates the ubiquitin-proteasome system, suggesting a major implication in proteins turnover and cell homeostasis. In addition, recent observations have highlighted that the regulation of glucose metabolism by IDE is not merely based on its largely proposed role in the degradation of insulin in vivo. There is increasing evidence that improper IDE function, regulation, or trafficking might contribute to the etiology of metabolic diseases. In addition, the enzymatic activity of IDE is affected by metals levels, thus suggesting a role also in the metal homeostasis (metallostasis), which is thought to be tightly linked to the malfunction of the "quality control" machinery of the cell. Focusing on the physiological role of IDE, we will address a comprehensive vision of the very complex scenario in which IDE takes part, outlining its crucial role in interconnecting several relevant cellular processes.

Neuroprotective mechanism of Kai Xin San: upregulation of hippocampal insulin-degrading enzyme protein expression and acceleration of amyloid-beta degradation

Kai Xin San is a Chinese herbal formula composed of Radix Ginseng, Poria, Radix Polygalae and Acorus Tatarinowii Rhizome. It has been used in China for many years for treating amnesia. Kai Xin San ameliorates amyloid-β (Aβ)-induced cognitive dysfunction and is neuroprotective in vivo, but its precise mechanism remains unclear. Expression of insulin-degrading enzyme (IDE), which degrades Aβ, is strongly correlated with cognitive function. Here, we injected rats with exogenous Aβ₄₂ (200 μM, 5 μL) into the hippocampus and subsequently administered Kai Xin San (0.54 or 1.08 g/kg/d) intragastrically for 21 consecutive days. Hematoxylin-eosin and Nissl staining revealed that Kai Xin San protected neurons against Aβ-induced damage. Furthermore, enzyme-linked immunosorbent assay, western blot and polymerase chain reaction results showed that Kai Xin San decreased Aβ₄₂ protein levels and increased expression of IDE protein, but not mRNA, in the hippocampus. Our findings reveal that Kai Xin San facilitates hippocampal Aβ degradation and increases IDE expression, which leads, at least in part, to the alleviation of hippocampal neuron injury in rats.

Toward Allosterically Increased Catalytic Activity of Insulin-Degrading Enzyme against Amyloid Peptides

The physiological role of insulin-degrading enzyme (IDE) in the intracytosolic clearance of amyloid β (Aβ) and other amyloid-like peptides supports a hypothesis that human IDE hyperactivation could be therapeutically beneficial for the treatment of late-onset Alzheimer's disease (AD). The major challenge standing in the way of this goal is increasing the specific catalytic activity of IDE against the Aβ substrate. There were previous indications that the allosteric mode of IDE activity regulation could potentially provide a highly specific path toward degradation of amyloid-like peptides, while not dramatically affecting activity against other substrates. Recently developed theoretical concepts are used here to explore potential allosteric modulation of the IDE activity as a result of single-residue mutations. Five candidates are selected for experimental follow-up and allosteric free energy calculations: Ser137Ala, Lys396Ala, Asp426Ala, Phe807Ala, and Lys898Ala. Our experiments show that three mutations (Ser137Ala, Phe807Ala, and Lys898Ala) decrease the K_m of the Aβ substrate. Mutation Lys898Ala results in increased catalytic activity of IDE; on the other hand, Lys364Ala does not change the activity and Asp426Ala diminishes it. Quantifying effects of mutations in terms of allosteric free energy, we show that favorable mutations lead to stabilization of the catalytic sites and other function-relevant distal sites as well as increased dynamics of the IDE-N and IDE-C halves that allow efficient substrate entrance and cleavage. A possibility for intramolecular upregulation of IDE activity against amyloid peptides via allosteric mutations calls for further investigations in this direction. Ultimately, we are hopeful it will lead to the development of IDE-based drugs for the treatment of the late-onset form of AD characterized by an overall impairment of Aβ clearance.

Insulin-degrading enzyme: new therapeutic target for diabetes and Alzheimer's disease?

Insulin-degrading enzyme (IDE) is a major enzyme responsible for insulin degradation. In addition to insulin, IDE degrades many targets including glucagon, atrial natriuretic peptide, and beta-amyloid peptide, regulates proteasomal degradation and other cell functions. IDE represents a pathophysiological link between type 2 diabetes (T2DM) and late onset Alzheimer's disease (AD). Potent and selective modulators of IDE activity are potential drugs for therapies of both diseases. Acute treatment with a novel IDE inhibitor was recently tested in a mouse study as a therapeutic approach for the treatment of T2DM. In contrast, effective IDE activators can be used for the AD treatment. However, because of the pleiotropic IDE action, the sustained treatment with systemic IDE modulators should be carefully tested in animal studies. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets. KEY MESSAGES Insulin-degrading enzyme (IDE) represents a pathophysiological link between type 2 diabetes (T2DM) and Alzheimer's disease (AD). Selective modulators of IDE activity are potential drugs for both T2DM and AD treatment. Development of substrate-selective IDE modulators could overcome possible adverse effects of IDE modulators associated with multiplicity of IDE targets.

Genetic factors moderate everyday physical activity effects on executive functions in aging: Evidence from the Victoria Longitudinal Study

OBJECTIVE

Everyday physical activity (EPA) is an important modifiable contributor to age-related variability in executive functioning (EF). However, its role may be moderated by nonmodifiable genetic factors. We tested independent and interactive effects of brain-derived neurotrophic factor (BDNF rs6265) and insulin degrading enzyme (IDE rs6583817) on EF and EPA-EF relationships.

METHOD

The sample consisted of genotyped older adults (N = 577; M age = 70.47 years) over 3 waves (∼9 years) of the Victoria Longitudinal Study. Analyses included (a) confirmatory factor analysis establishing a single latent EF factor from 4 standard EF tasks, (b) latent growth modeling over a 40-year band of aging (ages 53 to 95), and (c) structural regression to investigate the independent and interactive effects of BDNF, IDE, and EPA.

RESULTS

First, higher levels of EPA were associated with better EF performance at the centering age (75 years) and less EF decline. Second, IDE G+ (protective) carriers exhibited better EF performance at Age 75 than their G- (nonprotective) peers. Third, within the IDE G+ carrier group, those with higher EPA exhibited better EF performance and slower decline over time than those with lower EPA. Fourth, for the BDNF homozygote Val group, higher EPA was associated with better EF performance and more gradual EF change; however, this beneficial effect was not seen for Met carriers.

CONCLUSION

The effect of modifiable physical health factors on EF is moderated by biological mechanisms associated with risk-protection genetic polymorphisms.

Treatment with Akebia Saponin D Ameliorates Aβ1–42-Induced Memory Impairment and Neurotoxicity in Rats

Amyloid-β peptide (Aβ) is known to be directly associated with the progressive neuronal death observed in Alzheimer’s disease (AD). However, effective neuroprotective approaches against Aβ neurotoxicity are still unavailable. In the present study, we investigated the protective effects of Akebia saponin D (ASD), a typical compound isolated from the rhizome of Dipsacus asper Wall, on Aβ_1–42-induced impairment of learning and memory formation and explored the probable underlying molecular mechanisms. We found that treatment with ASD (30, 90 or 270 mg/kg) significantly ameliorated impaired spatial learning and memory in intracerebroventricularly (ICV) Aβ_1–42-injected rats, as evidenced by a decrease tendency in escape latency during acquisition trials and improvement in exploratory activities in the probe trial in Morris water maze (MWM). Further study showed that ASD reversed Aβ_1–42-induced accumulation of Aβ_1–42 and Aβ_1–40 in the hippocampus through down-regulating the expression of BACE and Presenilin 2 accompanied with increased the expression of TACE, IDE and LRP-1. Taken together, our findings suggested that ASD exerted therapeutic effects on Aβ-induced cognitive deficits via amyloidogenic pathway.

An Overview of Genome-Wide Association Studies in Alzheimer's Disease

Genome-wide association studies (GWASs) have revealed a plethora of putative susceptibility genes for Alzheimer's disease (AD). With the sole exception of the APOE gene, these AD susceptibility genes have not been unequivocally validated in independent studies. No single novel functional risk genetic variant has been identified. In this review, we evaluate recent GWASs of AD, and discuss their significance, limitations, and challenges in the investigation of the genetic spectrum of AD.

Targeting Insulin-Degrading Enzyme to Treat Type 2 Diabetes Mellitus

Insulin-degrading enzyme (IDE) selectively degrades peptides, such as insulin, amylin, and amyloid β (Aβ) that form toxic aggregates, to maintain proteostasis. IDE defects are linked to the development of type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD). Structural and biochemical analyses revealed the molecular basis for IDE-mediated destruction of amyloidogenic peptides and this information has been exploited to develop promising inhibitors of IDE to improve glucose homeostasis. However, the inhibition of IDE can also lead to glucose intolerance. In this review, I focus on recent advances regarding our understanding of the structure and function of IDE and the discovery of IDE inhibitors, as well as challenges in developing IDE-based therapy for human diseases, particularly T2DM.

Neprilysin Confers Genetic Susceptibility to Alzheimer's Disease in Han Chinese

Alzheimer's disease (AD) is a progressive neurodegenerative disease, with increasing incidence all over the world. Amyloid-β (Aβ) was considered to be the original cause to AD, and many reported pathogenic or risk genes for AD were located in the Aβ generation and degradation pathways. Neprilysin (NEP), insulin-degrading enzyme (IDE), and matrix metalloprotease-9 (MMP-9) are the most important Aβ-degrading proteases. Accumulating genetic evidence suggested that single nucleotide polymorphisms (SNPs) of these genes confer susceptibility to AD in Caucasian populations. In this study, we screened eight SNPs within these three Aβ-degrading protease genes in 1475 individuals of two independent Han Chinese case-control cohorts. SNP rs1816558 of NEP was found to be significantly associated with AD after adjustment for ε4 allele of the apolipoprotein E gene (APOEε4) and the Bonferroni correction. The remaining variants were not associated with risk of AD in Han Chinese sample set. Further data mining revealed that messenger RNA (mRNA) level of NEP substantially increased during the development of AD and was positively correlated with APP expression. The combined results indicated that NEP confers genetic susceptibility to AD in Han Chinese populations.

Alteration in amyloid β42, phosphorylated tau protein, interleukin 6, and acetylcholine during diabetes-accelerated memory dysfunction in diabetic rats: correlation of amyloid β42 with changes in glucose metabolism

Background

Diabetes accelerates memory dysfunction in a continuous, slowly pathological process. Studies suggest that the time course of certain biomarkers can characterize the pathological course of the disease to provide information for early intervention. Thus, there is an urgent need for validated biomarkers to characterize the cognitive impairment induced by DM. We aimed to detect changes in cerebrospinal fluid biomarkers such as amyloid β42, phosphorylated tau protein, interleukin 6, and acetylcholine in diabetic rats over time, and to analyse the relationship between diabetes and cognitive impairment.

Methods

Rats were injected once intraperitoneally with 1% of streptozotocin to establish a diabetic model. Index changes were investigated longitudinally and all were measured at the end of the experiment at day 75. Aβ42, P-tau, IL-6, and ACh levels in CSF, insulin levels in plasma, and Aβ42 levels in plasma and brain tissue were measured by ELISA.

Results

Compared with control, the diabetic model showed ACh in CSF to be decreased by day 15, continuing lower out to day 75. Aβ42 changes in brain and blood showed the same trends but exhibited minima at different time points: day 30 in CSF and day 15 in plasma. After the minimum, Aβ42 in cerebrospinal fluid rose and levelled off lower than in the control group, whereas Aβ42 in plasma rose and went above the controls at day 30, slowly trending upwards for the remainder of the experiment. P-tau protein in CSF in diabetic rats showed an increasing trend, becoming significantly different from the controls at day 60 and day 75. Aβ42 in CSF was strongly negatively correlated with blood glucose at day 15 and was negatively correlated with insulin in serum, particularly at day 45.

Conclusion

Our longitudinal research model suggest that changes in the measured biomarkers appear before learning and memory impairments do. Aβ42 and ACh in the diabetes model group clearly changed from day 0 to day 45, and then P-tau and IL-6 varied significantly from day 45 to day 75. The reduced ACh levels observed possibly correlated with the factors common to changes in Aβ42, P-tau, and IL-6.

HMGCR is a genetic modifier for risk, age of onset and MCI conversion to Alzheimer's disease in a three cohorts study

Several retrospective epidemiological studies report that utilization of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) inhibitors called statins at mid-life can reduce the risk of developing sporadic Alzheimer's disease (AD) by as much as 70%. Conversely, the administration of these inhibitors in clinically diagnosed subjects with AD confers little or no benefits over time. Here, we investigated the association between AD and HMGCR rs3846662, a polymorphism known to be involved in the regulation of HMGCR exon 13 skipping, in a founder population and in two distinct mixed North American populations of converting mild cognitively impaired (MCI) subjects (Alzheimer's disease Cooperative study (ADCS) and Alzheimer's disease Neuroimaging Initiative (ADNI) cohorts). Targeting more specifically women, the G allele negative (G-) AD subjects exhibit delayed age of onset of AD (P=0.017) and significantly reduced risk of AD (OR: 0.521; P=0.0028), matching the effect size reported by the apolipoprotein E type 2 variant. Stratification for APOE4 in a large sample of MCI patients from the ADCS cohort revealed a significant protective effect of G negative carriers on AD conversion 3 years after MCI diagnosis (odds ratio (OR): 0.554; P=0.041). Conversion rate among APOE4 carriers with the HMGCR's G negative allele was markedly reduced (from 76% to 27%) to levels similar to APOE4 non-carriers (27.14%), which strongly indicate protection. Conversion data from the independent ADNI cohort also showed significantly reduced MCI or AD conversion among APOE4 carriers with the protective A allele (P=0.005). In conclusion, HMGCR rs3846662 acts as a potent genetic modifier for AD risk, age of onset and conversion.

Candidate genes for Alzheimer's disease are associated with individual differences in plasma levels of beta amyloid peptides in adults with Down syndrome

We examined the contribution of candidates genes for Alzheimer's disease (AD) to individual differences in levels of beta amyloid peptides in adults with Down syndrom, a population at high risk for AD. Participants were 254 non-demented adults with Down syndrome, 30-78 years of age. Genomic deoxyribonucleic acid was genotyped using an Illumina GoldenGate custom array. We used linear regression to examine differences in levels of Aβ peptides associated with the number of risk alleles, adjusting for age, sex, level of intellectual disability, race and/or ethnicity, and the presence of the APOE ε4 allele. For Aβ42 levels, the strongest gene-wise association was found for a single nucleotide polymorphism (SNP) on CAHLM1; for Aβ40 levels, the strongest gene-wise associations were found for SNPs in IDE and SOD1, while the strongest gene-wise associations with levels of the Aβ42/Aβ40 ratio were found for SNPs in SORCS1. Broadly classified, variants in these genes may influence amyloid precursor protein processing (CALHM1, IDE), vesicular trafficking (SORCS1), and response to oxidative stress (SOD1).

A genome-wide association meta-analysis of plasma Aβ peptides concentrations in the elderly

Amyloid beta (Aβ) peptides are the major components of senile plaques, one of the main pathological hallmarks of Alzheimer disease (AD). However, Aβ peptides' functions are not fully understood and seem to be highly pleiotropic. We hypothesized that plasma Aβ peptides concentrations could be a suitable endophenotype for a genome-wide association study (GWAS) designed to (i) identify novel genetic factors involved in amyloid precursor protein metabolism and (ii) highlight relevant Aβ-related physiological and pathophysiological processes. Hence, we performed a genome-wide association meta-analysis of four studies totaling 3 528 healthy individuals of European descent and for whom plasma Aβ1-40 and Aβ1-42 peptides levels had been quantified. Although we did not observe any genome-wide significant locus, we identified 18 suggestive loci (P<1 × 10(-)(5)). Enrichment-pathway analyses revealed canonical pathways mainly involved in neuronal functions, for example, axonal guidance signaling. We also assessed the biological impact of the gene most strongly associated with plasma Aβ1-42 levels (cortexin 3, CTXN3) on APP metabolism in vitro and found that the gene protein was able to modulate Aβ1-42 secretion. In conclusion, our study results suggest that plasma Aβ peptides levels are valid endophenotypes in GWASs and can be used to characterize the metabolism and functions of APP and its metabolites.

IDE (rs6583817) polymorphism and pulse pressure are independently and interactively associated with level and change in executive function in older adults

OBJECTIVE

We report a gene × environment (health) study focusing on concurrent performance and longitudinal change in a latent-variable executive function (EF) phenotype. Specifically, we tested the independent and interactive effects of a recently identified insulin degrading enzyme genetic polymorphism (IDE rs6583817) and pulse pressure (PP; one prominent aging-related vascular health indicator) across up to 9 years of EF data in a sample of older adults from the Victoria Longitudinal Study. Both factors vary across a continuum of risk-elevating to risk-reducing and have been recently linked to normal and impaired cognitive aging.

METHOD

We assembled a genotyped and typically aging group of older adults (n = 599, M age = 66 years at baseline), following them for up to 3 longitudinal waves (M interval = 4.4 years). We used confirmatory factor analyses, latent growth modeling, and path analyses to pursue 3 main research goals.

RESULTS

First, the EF single factor model was confirmed comprising 4 executive function tasks and it demonstrated measurement invariance across the waves. Second, older adults with the major IDE G allele exhibited better EF outcomes than homozygotes for the minor A allele at the centering age of 75 years. Adults with higher PP performed more poorly on EF tasks at age 75 years and exhibited greater EF longitudinal decline. Third, gene × health interaction analyses showed that worsening vascular health (higher PP) differentially affected EF performance in older adults with the IDE G allele.

CONCLUSION

Genetic interaction analyses can reveal differential and magnifying effects on cognitive phenotypes in aging. In the present case, pulse pressure is confirmed as a risk factor for concurrent and changing cognitive health in aging, but the effects operate differently across the risk and protective allelic distribution of this IDE gene.

Apolipoprotein E, amyloid-beta, and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the accumulation and deposition of amyloid-beta (Aβ) peptides in the brain. Neuroinflammation occurs in the AD brain and plays a critical role in the neurodegenerative pathology. Particularly, Aβ evokes an inflammatory response that leads to synaptic dysfunction, neuronal death, and neurodegeneration. Apolipoprotein E (ApoE) proteins are involved in cholesterol transport, Aβ binding and clearance, and synaptic functions in the brain. The ApoE4 isoform is a key risk factor for AD, while the ApoE2 isoform has a neuroprotective effect. However, studies have reached different conclusions about the roles of the isoforms; some show that both ApoE3 and ApoE4 have anti-inflammatory effects, while others show that ApoE4 causes a predisposition to inflammation or promotes an inflammatory response following lipopolysaccharide treatment. These discrepancies may result from the differences in models, cell types, experimental conditions, and inflammatory stimuli used. Further, little was known about the role of ApoE isoforms in the Aβ-induced inflammatory response and in the neuroinflammation of AD. Our recent work showed that ApoE isoforms differentially regulate and modify the Aβ-induced inflammatory response in neural cells, with ApoE2 suppressing and ApoE4 promoting the response. In this article, we review the roles, mechanisms, and interrelations among Aβ, ApoE, and neuroinflammation in AD.

IDE (rs6583817) polymorphism and type 2 diabetes differentially modify executive function in older adults

We tested independent and interactive contributions of a recently noted and promising insulin degrading enzyme polymorphism (IDE; rs6583817) and type 2 diabetes (T2D) to executive function performance, concurrently and longitudinally. Regarding normal neurocognitive decline and Alzheimer's disease, T2D is a known risk factor and this IDE variant might contribute risk or risk reduction via the minor (A) or major (G) allele. We compared normal aging and T2D groups (baseline n = 574; ages 53-95 years) over 2 longitudinal waves (mean interval = 4.4 years). We used confirmatory factor analysis, latent growth curve modeling, and path analysis. A confirmed single-factor model of 4 executive function tasks established the cognitive phenotype. This IDE variant predicted concurrent group differences and differential change in cognitive performance. Furthermore, the IDE major allele reduced risk of cognitive decline. T2D predicted performance only concurrently. Both IDE and T2D are associated with executive function levels in older adults, but only IDE moderated 2-wave change. Previously linked to Alzheimer's disease, this IDE variant should be further explored for its potential influence on cognitive phenotypes of normal aging.

Linking protective GAB2 variants, increased cortical GAB2 expression and decreased Alzheimer's disease pathology

GRB-associated binding protein 2 (GAB2) represents a compelling genome-wide association signal for late-onset Alzheimer's disease (LOAD) with reported odds ratios (ORs) ranging from 0.75-0.85. We tested eight GAB2 variants in four North American Caucasian case-control series (2,316 LOAD, 2,538 controls) for association with LOAD. Meta-analyses revealed ORs ranging from (0.61-1.20) with no significant association (all p>0.32). Four variants were hetergeneous across the populations (all p<0.02) due to a potentially inflated effect size (OR = 0.61-0.66) only observed in the smallest series (702 LOAD, 209 controls). Despite the lack of association in our series, the previously reported protective association for GAB2 remained after meta-analyses of our data with all available previously published series (11,952-22,253 samples; OR = 0.82-0.88; all p<0.04). Using a freely available database of lymphoblastoid cell lines we found that protective GAB2 variants were associated with increased GAB2 expression (p = 9.5×10(-7)-9.3×10(-6)). We next measured GAB2 mRNA levels in 249 brains and found that decreased neurofibrillary tangle (r = -0.34, p = 0.0006) and senile plaque counts (r = -0.32, p = 0.001) were both good predictors of increased GAB2 mRNA levels albeit that sex (r = -0.28, p = 0.005) may have been a contributing factor. In summary, we hypothesise that GAB2 variants that are protective against LOAD in some populations may act functionally to increase GAB2 mRNA levels (in lymphoblastoid cells) and that increased GAB2 mRNA levels are associated with significantly decreased LOAD pathology. These findings support the hypothesis that Gab2 may protect neurons against LOAD but due to significant population heterogeneity, it is still unclear whether this protection is detectable at the genetic level.

Discovery by the Epistasis Project of an epistatic interaction between the GSTM3 gene and the HHEX/IDE/KIF11 locus in the risk of Alzheimer's disease

Despite recent discoveries in the genetics of sporadic Alzheimer's disease, there remains substantial "hidden heritability." It is thought that some of this missing heritability may be because of gene-gene, i.e., epistatic, interactions. We examined potential epistasis between 110 candidate polymorphisms in 1757 cases of Alzheimer's disease and 6294 control subjects of the Epistasis Project, divided between a discovery and a replication dataset. We found an epistatic interaction, between rs7483 in GSTM3 and rs1111875 in the HHEX/IDE/KIF11 gene cluster, with a closely similar, significant result in both datasets. The synergy factor (SF) in the combined dataset was 1.79, 95% confidence interval [CI], 1.35-2.36; p = 0.00004. Consistent interaction was also found in 7 out of the 8 additional subsets that we examined post hoc: i.e., it was shown in both North Europe and North Spain, in both men and women, in both those with and without the ε4 allele of apolipoprotein E, and in people older than 75 years (SF, 2.27; 95% CI, 1.60-3.20; p < 0.00001), but not in those younger than 75 years (SF, 1.06; 95% CI, 0.59-1.91; p = 0.84). The association with Alzheimer's disease was purely epistatic with neither polymorphism showing an independent effect: odds ratio, 1.0; p ≥ 0.7. Indeed, each factor was associated with protection in the absence of the other factor, but with risk in its presence. In conclusion, this epistatic interaction showed a high degree of consistency when stratifying by sex, the ε4 allele of apolipoprotein E genotype, and geographic region.

Genetic variants influencing human aging from late-onset Alzheimer's disease (LOAD) genome-wide association studies (GWAS)

Genetics plays a crucial role in human aging with up to 30% of those living to the mid-80s being determined by genetic variation. Survival to older ages likely entails an even greater genetic contribution. There is increasing evidence that genes implicated in age-related diseases, such as cancer and neuronal disease, play a role in affecting human life span. We have selected the 10 most promising late-onset Alzheimer's disease (LOAD) susceptibility genes identified through several recent large genome-wide association studies (GWAS). These 10 LOAD genes (APOE, CLU, PICALM, CR1, BIN1, ABCA7, MS4A6A, CD33, CD2AP, and EPHA1) have been tested for association with human aging in our dataset (1385 samples with documented age at death [AAD], age range: 58-108 years; mean age at death: 80.2) using the most significant single nucleotide polymorphisms (SNPs) found in the previous studies. Apart from the APOE locus (rs2075650) which showed compelling evidence of association with risk on human life span (p = 5.27 × 10(-4)), none of the other LOAD gene loci demonstrated significant evidence of association. In addition to examining the known LOAD genes, we carried out analyses using age at death as a quantitative trait. No genome-wide significant SNPs were discovered. Increasing sample size and statistical power will be imperative to detect genuine aging-associated variants in the future. In this report, we also discuss issues relating to the analysis of genome-wide association studies data from different centers and the bioinformatic approach required to distinguish spurious genome-wide significant signals from real SNP associations.

Novel late-onset Alzheimer disease loci variants associate with brain gene expression

OBJECTIVE

Recent genome-wide association studies (GWAS) of late-onset Alzheimer disease (LOAD) identified 9 novel risk loci. Discovery of functional variants within genes at these loci is required to confirm their role in Alzheimer disease (AD). Single nucleotide polymorphisms that influence gene expression (eSNPs) constitute an important class of functional variants. We therefore investigated the influence of the novel LOAD risk loci on human brain gene expression.

METHODS

We measured gene expression levels in the cerebellum and temporal cortex of autopsied AD subjects and those with other brain pathologies (∼400 total subjects). To determine whether any of the novel LOAD risk variants are eSNPs, we tested their cis-association with expression of 6 nearby LOAD candidate genes detectable in human brain (ABCA7, BIN1, CLU, MS4A4A, MS4A6A, PICALM) and an additional 13 genes ±100 kb of these SNPs. To identify additional eSNPs that influence brain gene expression levels of the novel candidate LOAD genes, we identified SNPs ±100 kb of their location and tested for cis-associations.

RESULTS

CLU rs11136000 (p = 7.81 × 10(-4)) and MS4A4A rs2304933/rs2304935 (p = 1.48 × 10(-4)-1.86 × 10(-4)) significantly influence temporal cortex expression levels of these genes. The LOAD-protective CLU and risky MS4A4A locus alleles associate with higher brain levels of these genes. There are other cis-variants that significantly influence brain expression of CLU and ABCA7 (p = 4.01 × 10(-5)-9.09 × 10(-9)), some of which also associate with AD risk (p = 2.64 × 10(-2)-6.25 × 10(-5)).

CONCLUSIONS

CLU and MS4A4A eSNPs may at least partly explain the LOAD risk association at these loci. CLU and ABCA7 may harbor additional strong eSNPs. These results have implications in the search for functional variants at the novel LOAD risk loci.

Disorder-specific effects of polymorphisms at opposing ends of the Insulin Degrading Enzyme gene

Background

Insulin-degrading enzyme (IDE) is the ubiquitously expressed enzyme responsible for insulin and amyloid beta (Aβ) degradation. IDE gene is located on chromosome region 10q23-q25 and exhibits a well-replicated peak of linkage with Type 2 diabetes mellitus (T2DM). Several genetic association studies examined IDE gene as a susceptibility gene for Alzheimer's disease (AD), however with controversial results.

Methods

We examined associations of three IDE polymorphisms (IDE2, rs4646953; IDE7, rs2251101 and IDE9, rs1887922) with AD, Aβ₄₂ plasma level and T2DM risk in the longitudinal Vienna Transdanube Aging (VITA) study cohort.

Results

The upstream polymorphism IDE2 was found to influence AD risk and to trigger the Aβ₄₂ plasma level, whereas the downstream polymorphism IDE7 modified the T2DM risk; no associations were found for the intronic variant IDE9.

Conclusions

Based on our SNP and haplotype results, we delineate the model that IDE promoter and 3' untranslated region/downstream variation may have different effects on IDE expression, presumably a relevant endophenotype with disorder-specific effects on AD and T2DM susceptibility.

Multiple insulin degrading enzyme variants alter in vitro reporter gene expression

The insulin degrading enzyme (IDE) variant, v311 (rs6583817), is associated with increased post-mortem cerebellar IDE mRNA, decreased plasma β-amyloid (Aβ), decreased risk for Alzheimer's disease (AD) and increased reporter gene expression, suggesting that it is a functional variant driving increased IDE expression. To identify other functional IDE variants, we have tested v685, rs11187061 (associated with decreased cerebellar IDE mRNA) and variants on H6, the haplotype tagged by v311 (v10; rs4646958, v315; rs7895832, v687; rs17107734 and v154; rs4646957), for altered in vitro reporter gene expression. The reporter gene expression levels associated with the second most common haplotype (H2) successfully replicated the post-mortem findings in hepatocytoma (0.89 fold-change, p = 0.04) but not neuroblastoma cells. Successful in vitro replication was achieved for H6 in neuroblastoma cells when the sequence was cloned 5′ to the promoter (1.18 fold-change, p = 0.006) and 3′ to the reporter gene (1.29 fold change, p = 0.003), an effect contributed to by four variants (v10, v315, v154 and v311). Since IDE mediates Aβ degradation, variants that regulate IDE expression could represent good therapeutic targets for AD.

Gene expression endophenotypes: a novel approach for gene discovery in Alzheimer's disease

Uncovering the underlying genetic component of any disease is key to the understanding of its pathophysiology and may open new avenues for development of therapeutic strategies and biomarkers. In the past several years, there has been an explosion of genome-wide association studies (GWAS) resulting in the discovery of novel candidate genes conferring risk for complex diseases, including neurodegenerative diseases. Despite this success, there still remains a substantial genetic component for many complex traits and conditions that is unexplained by the GWAS findings. Additionally, in many cases, the mechanism of action of the newly discovered disease risk variants is not inherently obvious. Furthermore, a genetic region with multiple genes may be identified via GWAS, making it difficult to discern the true disease risk gene. Several alternative approaches are proposed to overcome these potential shortcomings of GWAS, including the use of quantitative, biologically relevant phenotypes. Gene expression levels represent an important class of endophenotypes. Genetic linkage and association studies that utilize gene expression levels as endophenotypes determined that the expression levels of many genes are under genetic influence. This led to the postulate that there may exist many genetic variants that confer disease risk via modifying gene expression levels. Results from the handful of genetic studies which assess gene expression level endophenotypes in conjunction with disease risk suggest that this combined phenotype approach may both increase the power for gene discovery and lead to an enhanced understanding of their mode of action. This review summarizes the evidence in support of gene expression levels as promising endophenotypes in the discovery and characterization of novel candidate genes for complex diseases, which may also represent a novel approach in the genetic studies of Alzheimer's and other neurodegenerative diseases.

Microarray analysis on human neuroblastoma cells exposed to aluminum, β(1-42)-amyloid or the β(1-42)-amyloid aluminum complex

Background

A typical pathological feature of Alzheimer's disease (AD) is the appearance in the brain of senile plaques made up of β-amyloid (Aβ) and neurofibrillary tangles. AD is also associated with an abnormal accumulation of some metal ions, and we have recently shown that one of these, aluminum (Al), plays a relevant role in affecting Aβ aggregation and neurotoxicity.

Methodology

In this study, employing a microarray analysis of 35,129 genes, we investigated the effects induced by the exposure to the Aβ_1–42-Al (Aβ-Al) complex on the gene expression profile of the neuronal-like cell line, SH-SY5Y.

Principal Findings

The microarray assay indicated that, compared to Aβ or Al alone, exposure to Aβ-Al complex produced selective changes in gene expression. Some of the genes selectively over or underexpressed are directly related to AD. A further evaluation performed with Ingenuity Pathway analysis revealed that these genes are nodes of networks and pathways that are involved in the modulation of Ca²⁺ homeostasis as well as in the regulation of glutamatergic transmission and synaptic plasticity.

Conclusions and Significance

Aβ-Al appears to be largely involved in the molecular machinery that regulates neuronal as well as synaptic dysfunction and loss. Aβ-Al seems critical in modulating key AD-related pathways such as glutamatergic transmission, Ca²⁺ homeostasis, oxidative stress, inflammation, and neuronal apoptosis.

Exploration of 16 candidate genes identifies the association of IDE with Alzheimer's disease in Han Chinese

Alzheimer's disease (AD) has a complex pattern of inheritance and many genes have recently been reported to contribute to the disease susceptibility. We selected 106 SNPs within 16 candidate genes and performed a multistage association study using 4 sample sets consisting of 731 AD patients and 738 control subjects to identify genetic factors for AD in Han Chinese. A single nucleotide polymorphism (SNP) in the insulin degrading enzyme gene (IDE), rs3781239, showed a significant association with AD. The C allele increased the risk of AD 1.72-fold than the G allele (odds ratio [OR] = 1.72, 95% confidence interval [CI] = 1.17-2.53, p = 0.006) and CC carriers had a 4.89-fold higher risk for AD than that of the carriers with CG and GG genotypes (odds ratio = 4.89, 95% CI = 1.85-12.91, p = 0.001). Moreover, the CC genotype was significantly associated with earlier age at onset (p = 0.001, hazard ratio [HR] = 2.09, 95% CI = 1.38-3.18). Our data suggest that the polymorphism of IDE is associated with susceptibility to Alzheimer's disease in Han Chinese.