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Producción Científica, Aims/hypothesis Type 2 diabetes is characterised by hyperglucagonaemia and perturbed function of pancreatic glucagon secreting alpha cells but the molecular mechanisms contributing to these phenotypes are poorly understood. Insulin-degrading enzyme (IDE) is present within all islet cells, mostly in alpha cells, in both mice and humans. Furthermore, IDE can degrade glucagon as well as insulin, suggesting that IDE may play an important role in alpha cell function in vivo. Methods We have generated and characterised a novel mouse model with alpha cell-specific deletion of Ide, the A-IDE-KO mouse line. Glucose metabolism and glucagon secretion in vivo was characterised; isolated islets were tested for glucagon and insulin secretion; alpha cell mass, alpha cell proliferation and α-synuclein levels were determined in pancreas sections by immunostaining. Results Targeted deletion of Ide exclusively in alpha cells triggers hyperglucagonaemia and alpha cell hyperplasia, resulting in elevated constitutive glucagon secretion. The hyperglucagonaemia is attributable in part to dysregulation of glucagon secretion, specifically an impaired ability of IDE-deficient alpha cells to suppress glucagon release in the presence of high glucose or insulin. IDE deficiency also leads to α-synuclein aggregation in alpha cells, which may contribute to impaired glucagon secretion via cytoskeletal dysfunction. We showed further that IDE deficiency triggers impairments in cilia formation, inducing alpha cell hyperplasia and possibly also contributing to dysregulated glucagon secretion and hyperglucagonaemia. Conclusions/interpretation We propose that loss of IDE function in alpha cells contributes to hyperglucagonaemia in type 2 diabetes, Ministerio de Economía, Industria y Competitividad (SAF2016-77871-C2-1-R to IC and BFU2016-77125-R to IQ), Ministerio de Ciencia, Innovación y Universidades (PID2019-110496RB-C21 to IC and PID2019-110496RB-C22 to GP), La Caixa Foundation (grant LCF/PR/PR18/51130007 to GP), National Institutes of Health from USA (GM115617), Publicación en abierto financiada por el Consorcio de Bibliotecas Universitarias de Castilla y León (BUCLE), con cargo al Programa Operativo 2014ES16RFOP009 FEDER 2014-2020 DE CASTILLA Y LEÓN, Actuación:20007-CL - Apoyo Consorcio BUCLE

Commonly employed methods for reversibly disrupting gene expression, such as those based on RNAi or CRISPRi, are rarely capable of achieving >80-90% downregulation, making them unsuitable for targeting genes that require more complete disruption to elicit a phenotype. Genetic deletion, on the other hand, while enabling complete disruption of target genes, often produces undesirable irreversible consequences such as cytotoxicity or cell death. Here we describe the design, development and detailed characterization of a dual-function "TRE-Lox" system for effecting either (a) doxycycline (Dox)-mediated downregulation or (b) genetic deletion of cathepsin D (CatD), based on targeted insertion of a tetracycline-response element (TRE) and two LoxP sites into the 5' end of the endogenous gene (CTSD). Using an optimized reverse-tetracycline transrepressor (rtTR) variant fused with the Krüppel-associated box (KRAB) domain, we show that CatD expression can be disrupted by as much as 98% in mouse embryonic fibroblasts (MEFs). This system is highly sensitive to Dox (IC50 = 1.46 ng/mL) and results in rapid (t1/2 = 0.57 d) and titratable downregulation of CatD. Notably, even near-total disruption of CatD expression was completely reversed by withdrawal of Dox. As expected, transient expression of Cre recombinase results in complete deletion of the CTSD gene. The dual functionality of this novel system will facilitate future studies of the involvement of CatD in various diseases, particularly those attributable to partial loss of CatD function. In addition, the TRE-Lox approach should be applicable to the regulation of other target genes requiring more complete disruption than can be achieved by traditional methods.

Inhibition of insulin-degrading enzyme (IDE) has been proposed as a possible therapeutic target for type 2 diabetes treatment. However, many aspects of IDE's role in glucose homeostasis need to be clarified. In light of this, new preclinical models are required to elucidate the specific role of this protease in the main tissues related to insulin handling. To address this, here we generated a novel line of mice with selective deletion of the Ide gene within pancreatic beta-cells, B-IDE-KO mice, which have been characterized in terms of multiple metabolic end points, including blood glucose, plasma C-peptide, and intraperitoneal glucose tolerance tests. In addition, glucose-stimulated insulin secretion was quantified in isolated pancreatic islets and beta-cell differentiation markers and insulin secretion machinery were characterized by RT-PCR. Additionally, IDE was genetically and pharmacologically inhibited in INS-1E cells and rodent and human islets, and insulin secretion was assessed. Our results show that, in vivo, life-long deletion of IDE from beta-cells results in increased plasma C-peptide levels. Corroborating these findings, isolated islets from B-IDE-KO mice showed constitutive insulin secretion, a hallmark of beta-cell functional immaturity. Unexpectedly, we found 60% increase in Glut1 (a high-affinity/low- Km glucose transporter), suggesting increased glucose transport into the beta-cell at low glucose levels, which may be related to constitutive insulin secretion. In parallel, IDE inhibition in INS-1E and islet cells resulted in impaired insulin secretion after glucose challenge. We conclude that IDE is required for glucose-stimulated insulin secretion. When IDE is inhibited, insulin secretion machinery is perturbed, causing either inhibition of insulin release at high glucose concentrations or constitutive secretion.

Alzheimer disease (AD) is a debilitating neurodegenerative disorder characterized by extracellular deposition of the amyloid β-protein (Aβ) and intraneuronal accumulation of the microtubule-associated protein, tau. Despite a wealth of experimental and genetic evidence implicating both Aβ and tau in the pathogenesis of AD, the precise molecular links between these two pathological hallmarks have remained surprisingly elusive. Here, we review emerging evidence for a critical nexus among Aβ, tau, and the lysosomal protease cathepsin D (CatD) that we hypothesize may play a pivotal role in the etiology of AD. CatD degrades both Aβ and tau in vitro, but the in vivo relevance of this lysosomal protease to these principally extracellular and cytosolic proteins, respectively, had remained undefined for many decades. Recently, however, our group found that genetic deletion of CatD in mice results in dramatic accumulation of Aβ in lysosomes, revealing that Aβ is normally trafficked to lysosomes in substantial quantities. Moreover, emerging evidence suggests that tau is also trafficked to the lysosome via chaperone-mediated autophagy and other trafficking pathways. Thus, Aβ, tau and CatD are colocalized in the lysosome, an organelle that shows dysfunction early in AD pathogenesis, where they can potentially interact. Notably, we discovered that Aβ42-the Aβ species most strongly linked to AD pathogenesis-is a highly potent, low-nanomolar, competitive inhibitor of CatD. Taking these observations together, we hypothesize that Aβ42 may trigger tauopathy by competitive inhibition of CatD-mediated degradation of tau-pathogenic forms of tau, in particular. Herein, we review the evidence supporting this hypothesis and explore the implications for the molecular pathogenesis of AD. Future research into these novel mechanistic links among Aβ, tau and CatD promises to expand our understanding of the etiology of AD and could potentially lead to novel therapeutic approaches for combatting this devastating disease of brain and mind.

Insulin-degrading enzyme (IDE) is a human mononuclear Zn2+-dependent metalloenzyme that is widely regarded as the primary peptidase responsible for insulin degradation. Despite its name, IDE is also critically involved in the hydrolysis of several other disparate peptide hormones, including glucagon, amylin, and the amyloid β-protein. As such, the study of IDE inhibition is highly relevant to deciphering the role of IDE in conditions such as type 2 diabetes mellitus and Alzheimer disease. There have been few reported IDE inhibitors, and of these, inhibitors that directly target the active-site metal ion have yet to be fully explored. In an effort to discover new, metal-binding inhibitors of IDE, a library of ~350 metal-binding pharmacophores was screened against IDE, resulting in the identification of 1-hydroxypyridine-2-thione (1,2-HOPTO) as an effective metal-binding scaffold. Screening of a focused library of HOPTO compounds identified 3-sulfonamide derivatives of 1,2-HOPTO to have good activity against IDE (Ki values of ~50 µM). Further structure-activity relationship studies yielded several thiophene-sulfonamide HOPTO derivatives with good, broad-spectrum activity against IDE that have the potential to be useful pharmacological tools for future studies of IDE.

Producción Científica, Hepatic insulin clearance, a physiological process that in response to nutritional cues clears ~50–80% of circulating insulin, is emerging as an important factor in our understanding of the pathogenesis of type 2 diabetes mellitus (T2DM). Insulin-degrading enzyme (IDE) is a highly conserved Zn2+-metalloprotease that degrades insulin and several other intermediate-size peptides. Both, insulin clearance and IDE activity are reduced in diabetic patients, albeit the cause-effect relationship in humans remains unproven. Because historically IDE has been proposed as the main enzyme involved in insulin degradation, efforts in the development of IDE inhibitors as therapeutics in diabetic patients has attracted attention during the last decades. In this review, we retrace the path from Mirsky’s seminal discovery of IDE to the present, highlighting the pros and cons of the development of IDE inhibitors as a pharmacological approach to treating diabetic patients., Ministerio de Economía, Industria y Competitividad - (grant SAF2016-77871-C2-2-R), Ministerio de Ciencia e Innovación - (grant PID2019-110496RB-C22), Fundación Europea para el Estudio de la Diabetes (Programa Europeo de Investigación de la Diabetes sobre nuevos objetivos para el tipo 2 Diabetes apoyada por MSD-2017), US National Institutes of Health - (GM115617), Fundación “la Caixa" - (grant LCF/PR/PR18/51130007), Junta de Castilla y León y Fondo Social Europeo - ((ORDER EDU/574/2018)

Producción Científica, Insulin-degrading enzyme (IDE) is a highly conserved and ubiquitously expressed metalloprotease that degrades insulin and several other intermediate-size peptides. For many decades, IDE had been assumed to be involved primarily in hepatic insulin clearance, a key process that regulates availability of circulating insulin levels for peripheral tissues. Emerging evidence, however, suggests that IDE has several other important physiological functions relevant to glucose and insulin homeostasis, including the regulation of insulin secretion from pancreatic β-cells. Investigation of mice with tissue-specific genetic deletion of Ide in the liver and pancreatic β-cells (L-IDE-KO and B-IDE-KO mice, respectively) has revealed additional roles for IDE in the regulation of hepatic insulin action and sensitivity. In this review, we discuss current knowledge about IDE’s function as a regulator of insulin secretion and hepatic insulin sensitivity, both evaluating the classical view of IDE as an insulin protease and also exploring evidence for several non-proteolytic functions. Insulin proteostasis and insulin sensitivity have both been highlighted as targets controlling blood sugar levels in type 2 diabetes, so a clearer understanding the physiological functions of IDE in pancreas and liver could led to the development of novel therapeutics for the treatment of this disease., Ministerio de Economía, Industria y Competitividad - (grant SAF2016-77871-C2-1-R; SAF2016-77871-C2-2-R), Ministerio de Ciencia e Innovación - (grant PID2019-110496RB-C21; PID2019-110496RB-C22), Fundación Europea para el Estudio de la Diabetes (Programa Europeo de Investigación de la Diabetes sobre nuevos objetivos para el tipo 2 Diabetes apoyada por MSD-2017), US National Institutes of Health - (grant GM115617), Fundación “la Caixa" - (grant LCF/PR/PR18/51130007), Junta de Castilla y León y Fondo Social Europeo - ((ORDER EDU/574/2018 and ORDER EDU/556/2019)

Glucagon is a vital peptide hormone involved in the regulation of blood sugar under fasting conditions. While the processes underlying glucagon production and secretion are well understood, far less is known about its degradation, which could conceivably be manipulated pharmacologically for therapeutic benefit. We describe here the development of novel assays for glucagon degradation, based on a modified glucagon peptide (FBG) labeled with fluorescein and biotin at the N- and C-termini, respectively. Proteolysis at any peptide bond within FBG separates the fluorescent label from the biotin tag, which can be quantified in multiple ways. In one method requiring no specialized equipment, intact FBG is separated from the cleaved fluoresceinated fragments using neutravidin-agarose beads, and hydrolysis is quantified by fluorescence. In an alternative, high-throughput-compatible method, the degree of hydrolysis is quantified using fluorescence polarization after addition of unmodified avidin. Using a known glucagon protease, we confirm that FBG is cleaved at similar sites as unmodified glucagon and utilize both methods to quantify the kinetic parameters of FBG degradation. We show further that the fluorescence polarization-based assay performs exceptionally well (Z’-factor values >0.80) in high-throughput, mix-and-measure format.

The study was partially presented as a poster in the 53rd Annual Meeting of the European Association for the Study of Diabetes, Lisbon 2017., The role of insulin-degrading enzyme (IDE), a metalloprotease with high affinity for insulin, in insulin clearance remains poorly understood. OBJECTIVE: This study aimed to clarify whether IDE is a major mediator of insulin clearance, and to define its role in the etiology of hepatic insulin resistance., [Methods] We generated mice with liver-specific deletion of Ide (L-IDE-KO) and assessed insulin clearance and action., [Results] L-IDE-KO mice exhibited higher (~20%) fasting and non-fasting plasma glucose levels, glucose intolerance and insulin resistance. This phenotype was associated with ~30% lower plasma membrane insulin receptor levels in liver, as well as ~55% reduction in insulin-stimulated phosphorylation of the insulin receptor, and its downstream signaling molecules, AKT1 and AKT2 (reduced by ~40%). In addition, FoxO1 was aberrantly distributed in cellular nuclei, in parallel with up-regulation of the gluconeogenic genes Pck1 and G6pc. Surprisingly, L-IDE-KO mice showed similar plasma insulin levels and hepatic insulin clearance as control mice, despite reduced phosphorylation of the carcinoembryonic antigen-related cell adhesion molecule 1, which upon its insulin-stimulated phosphorylation, promotes receptor-mediated insulin uptake to be degraded., [Conclusion] IDE is not a rate-limiting regulator of plasma insulin levels in vivo., This work was supported by grants from the Ministerio de Economía, Industria y Competitividad: SAF2014-58702-C2-1-R and SAF2016-77871-C2-1-R to ICC; SAF2014-58702-C2-2-R and SAF2016-77871-C2-2-R to GP; supported by the EFSD European Research Programme on New Targets for Type 2 Diabetes supported by an educational research grant from MSD to ICC and GP; the National Institutes of Health: R01-DK054254, R01-DK083850 and RO1-HL-112248 to SMN, and R01-GM115617 to MAL; and the American Diabetes Association: Career Development Award 7-11-CD-13 to MAL.

© 2020 The Authors., The insulin-degrading enzyme (IDE) is a metalloendopeptidase with a high affinity for insulin. Human genetic polymorphisms in Ide have been linked to increased risk for T2DM. In mice, hepatic Ide ablation causes glucose intolerance and insulin resistance when mice are fed a regular diet. [Objective]: These studies were undertaken to further investigate its regulatory role in glucose homeostasis and insulin sensitivity in diet-induced obesity. [Methods]: To this end, we have compared the metabolic effects of loss versus gain of IDE function in mice fed a high-fat diet (HFD). [Results]: We demonstrate that loss of IDE function in liver (L-IDE-KO mouse) exacerbates hyperinsulinemia and insulin resistance without changes in insulin clearance but in parallel to an increase in pancreatic β-cell function. Insulin resistance was associated with increased FoxO1 activation and a ~2-fold increase of GLUT2 protein levels in the liver of HFD-fed mice in response to an intraperitoneal injection of insulin. Conversely, gain of IDE function (adenoviral delivery) improves glucose tolerance and insulin sensitivity, in parallel to a reciprocal ~2-fold reduction in hepatic GLUT2 protein levels. Furthermore, in response to insulin, IDE co-immunoprecipitates with the insulin receptor in liver lysates of mice with adenoviral-mediated liver overexpression of IDE. [Conclusions]: We conclude that IDE regulates hepatic insulin action and whole-body glucose metabolism in diet-induced obesity via insulin receptor levels., This work was supported by grants from the Ministerio de Economía, Industria y Competitividad: SAF2016-77871-C2-1-R to IC; SAF2016-77871-C2-2-R to GP; This work was supported by grants from the Ministerio de Ciencia e Innovación PID2019-110496RB-C21 to IC; PID2019-110496RB-C22 to GP. European Foundation for the Study of Diabetes (European Diabetes Research Programme on New Targets for Type 2 Diabetes supported by MSD-2017) to IC and GP. The project leading to these results has received funding from “la Caixa” Foundation, under agreement LCF/PR/PR18/51130007 to GP. This work was suppoted by grant from NIH GM115617 to ML.

Many therapeutically important enzymes are present in multiple cellular compartments, where they can carry out markedly different functions, thus there is a need for pharmacological strategies to selectively manipulate distinct pools of target enzymes. Insulin-degrading enzyme (IDE) is a thiol-sensitive zinc-metallopeptidase that hydrolyzes diverse peptide substrates in both the cytosol and the extracellular space, but current genetic and pharmacological approaches are incapable of selectively inhibiting the protease in specific subcellular compartments. Here we describe the discovery, characterization and kinetics-based optimization of potent benzoisothiazolone-based inhibitors that, by virtue of a unique “quasi-irreversible” mode of inhibition, exclusively inhibit extracellular IDE. The mechanism of inhibition involves nucleophilic attack by a specific active-site thiol of the enzyme on the inhibitors, which bear an isothiazolone ring that undergoes irreversible ring opening with the formation of a disulfide bond. Notably, binding of the inhibitors is reversible under reducing conditions, thus restricting inhibition to IDE present in the extracellular space. The identified inhibitors are highly potent (IC(50)(app) = 63 nM), non-toxic at concentrations up to 100 μM and, were found to selectively target a specific cysteine residue within IDE. These novel inhibitors represent powerful new tools for clarifying the physiological and pathophysiological roles of this poorly understood protease, and their unusual mechanism of action should be applicable to other therapeutic targets.

Despite decades of speculation that inhibiting endogenous insulin degradation might treat type-2 diabetes, and the identification of IDE (insulin-degrading enzyme) as a diabetes susceptibility gene, the relationship between the activity of the zinc metalloprotein IDE and glucose homeostasis remains unclear. Although Ide(-/-) mice have elevated insulin levels, they exhibit impaired, rather than improved, glucose tolerance that may arise from compensatory insulin signalling dysfunction. IDE inhibitors that are active in vivo are therefore needed to elucidate IDE's physiological roles and to determine its potential to serve as a target for the treatment of diabetes. Here we report the discovery of a physiologically active IDE inhibitor identified from a DNA-templated macrocycle library. An X-ray structure of the macrocycle bound to IDE reveals that it engages a binding pocket away from the catalytic site, which explains its remarkable selectivity. Treatment of lean and obese mice with this inhibitor shows that IDE regulates the abundance and signalling of glucagon and amylin, in addition to that of insulin. Under physiological conditions that augment insulin and amylin levels, such as oral glucose administration, acute IDE inhibition leads to substantially improved glucose tolerance and slower gastric emptying. These findings demonstrate the feasibility of modulating IDE activity as a new therapeutic strategy to treat type-2 diabetes and expand our understanding of the roles of IDE in glucose and hormone regulation.

The amyloid ß-protein (Aß) is well established to play an indispensible role in the pathogenesis of Alzheimer disease (AD). Aβ is subject to proteolytic degradation by a diverse array of peptidases and proteinases, known collectively as Aβ-degrading proteases (AβDPs). A growing number of AβDPs have been identified, which impact Aß powerfully and in a surprising variety of ways. As such, AßDPs hold considerable therapeutic potential for the treatment and/or prevention of AD. Here we critically review the relative merits of therapeutic strategies targeting AßDPs as compared to current Aß-lowering strategies focused on immunotherapies and pharmacological modulation of Aß-producing enzymes. Several innovative advances have increased considerably the feasibility of delivering AßDPs to the brain or enhancing their activity in a non-invasive manner. We argue that therapies targeting AßDPs offer numerous potential advantages, which should be explored through continued research into this promising field.

Islet amyloid deposition in human type 2 diabetes results in β-cell loss. These amyloid deposits contain the unique amyloidogenic peptide human islet amyloid polypeptide (hIAPP), which is also a known substrate of the protease insulin-degrading enzyme (IDE). Whereas IDE inhibition has recently been demonstrated to improve glucose metabolism in mice, inhibiting it has also been shown to increase cell death when synthetic hIAPP is applied exogenously to a β-cell line. Thus, we wanted to determine whether a similar deleterious effect is observed when hIAPP is endogenously produced and secreted from islets. To address this issue, we cultured hIAPP transgenic mouse islets that have the propensity to form amyloid for 48 and 144 hours in 16.7 mM glucose in the presence and absence of the IDE inhibitor 1. At neither time interval did IDE inhibition increase amyloid formation or β-cell loss. Thus, the inhibition of IDE may represent an approach to improve glucose metabolism in human type 2 diabetes, without inducing amyloid deposition and its deleterious effects.

The amyloid beta-protein (Abeta), which accumulates abnormally in Alzheimer disease (AD), is degraded by a diverse set of proteolytic enzymes. Abeta-cleaving proteases, largely ignored until only recently, are now known to play a pivotal role in the regulation of cerebral Abeta levels and amyloid plaque formation in animal models, and accumulating evidence suggests that defective Abeta proteolysis may be operative in many AD cases. This review summarizes the growing body of evidence supporting the involvement of specific Abeta-cleaving proteases in the etiology and potential treatment of AD. Recognition of the importance of Abeta degradation to the overall economy of Abeta has revised our thinking about the mechanistic basis of AD pathogenesis and identified a novel class of enzymes that may serve as both therapeutic targets and therapeutic agents.

Perturbations in intracellular Ca 2+ signaling may represent one mechanism underlying Alzheimer's disease (AD). The presenilin-1 gene (PS1), associated with the majority of early onset familial AD cases, has been implicated in this signaling pathway. Here we used the Xenopus oocyte expression system to investigate in greater detail the role of PS1 in intracellular Ca 2+ signaling pathways. Treatment of cells expressing wild-type PS1 with a cell surface receptor agonist to stimulate the phosphoinositide second messenger pathway evoked Ca 2+ -activated Cl - currents that were significantly potentiated relative to controls. To determine which elements of the signal transduction pathway are responsible for the potentiation, we used photolysis of caged inositol 1,4,5-trisphosphate (IP 3 ) and fluorescent Ca 2+ imaging to demonstrate that PS1 potentiates IP 3 -mediated release of Ca 2+ from internal stores. We show that an AD-linked mutation produces a potentiation in Ca 2+ + signaling that is significantly greater than that observed for wild-type PS1 and that cannot be attributed to differences in protein expression levels. Our findings support a role for PS1 in modulating IP 3 -mediated Ca 2+ liberation and suggest that one pathophysiological mechanism by which PS1 mutations contribute to AD neurodegeneration may involve perturbations of this function.

Insulin-degrading enzyme (IDE) is central to the turnover of insulin and degrades amyloid β (Aβ) in the mammalian brain. Biochemical and genetic data support the notion that IDE may play a role in late onset Alzheimer disease (AD), and recent studies suggest an association between AD and diabetes mellitus type 2. Here we show that a natively folded recombinant IDE was capable of forming a stable complex with Aβ that resisted dissociation after treatment with strong denaturants. This interaction was also observed with rat brain IDE and detected in an SDS-soluble fraction from AD cortical tissue. Aβ sequence 17–27, known to be crucial in amyloid assembly, was sufficient to form a stable complex with IDE. Monomeric as opposed to aggregated Aβ was competent to associate irreversibly with IDE following a very slow kinetics (t½ ∼ 45 min). Partial denaturation of IDE as well as preincubation with a 10-fold molar excess of insulin prevented complex formation, suggesting that the irreversible interaction of Aβ takes place with at least part of the substrate binding site of the protease. Limited proteolysis showed that Aβ remained bound to a ∼25-kDa N-terminal fragment of IDE in an SDS-resistant manner. Mass spectrometry after in gel digestion of the IDE ·Aβ complex showed that peptides derived from the region that includes the catalytic site of IDE were recovered with Aβ. Taken together, these results are suggestive of an unprecedented mechanism of conformation-dependent substrate binding that may perturb Aβ clearance, insulin turnover, and promote AD pathogenesis.

Age is the major risk factor for developing Alzheimer’s disease (AD), and modifying age-related factors may help to delay the onset of the disease. The goal of this study was to investigate the relationship between age and the metabolic factors related to the risk of developing AD. The concentrations of insulin, amylin, and amyloid-β peptide (Aβ) in plasma were measured. We further measured the activity of serum Aβ degradation by using fluorescein- and biotin-labeled Aβ40. Apolipoprotein E4 allele (ApoE4) and cognitive impairment were characterized. Subjects were divided into three age groups: 60–70, 70–80, and ≥80 years old. We found that the older the subjects, the lower the concentration of insulin (p = 0.001) and the higher the concentration of Aβ1-40 (p = 0.004) in plasma. However, age was not associated with the concentration of another pancreatic peptide, amylin, and only marginally with Aβ1-42. These relationships remained in the absence of diabetes, cardiovascular disease, and stroke, and regardless of the presence of ApoE4 and cognitive impairment. Both age and ApoE4 were inversely associated with, while insulin was positively associated with, the activities of Aβ degradation in serum. Our study suggested that low concentration of insulin and high concentration of Aβ40 are aging factors related to the risk of AD.

Proteases have long played a central role in the molecular pathogenesis of Alzheimer's disease (AD), yet proteases that degrade the amyloid beta-protein (Abeta) itself were largely ignored until only quite recently. Today, we know that Abeta-degrading proteases are critical regulators of brain Abeta levels in vivo, with evidence accumulating that their dysfunction may play a role in the etiology of AD. This review explores the historical factors that obscured this important aspect of amyloidogenesis, and discusses the many fresh insights it offers into the causes of and potential treatments for AD.

Deletion of insulin-degrading enzyme (IDE) in mice causes accumulation of cerebral amyloid beta-protein (Abeta), hyperinsulinemia, and glucose intolerance. Together with genetic linkage and allelic association of IDE to Alzheimer's disease (AD) and type 2 diabetes mellitus (DM2), these findings suggest that IDE hypofunction could mediate human disease. To date, no coding mutations have been found in the canonical isoform of IDE, suggesting that pathological mutations could exist in undiscovered exons or regulatory regions, including untranslated regions (UTRs). However, neither isoforms arising from alternative splicing nor the UTRs have been described. Here, we systematically characterize human IDE mRNAs, identify a novel splice form, and compare its subcellular distribution, kinetic properties, and ability to degrade Abeta to the known isoform. Six distinct human IDE transcripts were identified, with most of the variance attributable to alternative polyadenylation sites. In the novel spliceoform, an exon we designate "15b" replaces the canonical exon "15a", and the resultant variant is widely expressed. Subcellular fractionation, immunofluorescent confocal microscopy, and immunogold-electron microscopy reveal that the 15b-IDE protein occurs in both cytosol and mitochondria. Organelle targeting of both isoforms is determined by which of two translation start sites is used, and only those isoforms utilizing the second site regulate levels of secreted Abeta. 15b-IDE can exist as a heterodimer with the 15a isoform or as a homodimer. The apparent K(m) values of recombinant 15b-IDE for both insulin and Abeta are significantly higher and the k(cat) and catalytic efficiency markedly lower than those of 15a-IDE. In accord, cells coexpressing beta-amyloid precursor protein (APP) and 15b-IDE accumulated significantly more Abeta in their media than those expressing APP and 15a-IDE. Our results identify a novel, catalytically inefficient form of IDE expressed in brain and non-neural tissues and recommend novel regions of the IDE gene in which to search for mutations predisposing patients to AD and DM2.

Converging evidence suggests that the accumulation of cerebral amyloid beta-protein (Abeta) in Alzheimer's disease (AD) reflects an imbalance between the production and degradation of this self-aggregating peptide. Upregulation of proteases that degrade Abeta thus represents a novel therapeutic approach to lowering steady-state Abeta levels, but the consequences of sustained upregulation in vivo have not been studied. Here we show that transgenic overexpression of insulin-degrading enzyme (IDE) or neprilysin (NEP) in neurons significantly reduces brain Abeta levels, retards or completely prevents amyloid plaque formation and its associated cytopathology, and rescues the premature lethality present in amyloid precursor protein (APP) transgenic mice. Our findings demonstrate that chronic upregulation of Abeta-degrading proteases represents an efficacious therapeutic approach to combating Alzheimer-type pathology in vivo.

Proteases that degrade the amyloid beta-protein (Abeta) are important regulators of brain Abeta levels in health and in Alzheimer's disease, yet few practical methods exist to study their detailed kinetics. Here, we describe robust and quantitative Abeta degradation assays based on the novel substrate, fluorescein-Abeta-(1-40)-Lys-biotin (FAbetaB). Liquid chromatography/mass spectrometric analysis shows that FAbetaB is hydrolyzed at closely similar sites as wild-type Abeta by neprilysin and insulin-degrading enzyme, the two most widely studied Abeta-degrading proteases. The derivatized peptide is an avid substrate and is suitable for use with biological samples and in high throughput compound screening. The assays we have developed are easily implemented and are particularly useful for the generation of quantitative kinetic data, as we demonstrate by determining the kinetic parameters of FAbetaB degradation by several Abeta-degrading proteases, including plasmin, which has not previously been characterized. The use of these assays should yield additional new insights into the biology of Abeta-degrading proteases and facilitate the identification of activators and inhibitors of such enzymes.

Inclusion body myositis (IBM), the most common age-related muscle disease in the elderly population, is an incurable disorder leading to severe disability. Sporadic IBM has an unknown etiology, although affected muscle fibers are characterized by many of the pathobiochemical alterations traditionally associated with neurodegenerative brain disorders such as Alzheimer's disease. Accumulation of the amyloid-beta peptide, which is derived from proteolysis of the larger amyloid-beta precursor protein (betaAPP), seems to be an early pathological event in Alzheimer's disease and also in IBM, where in the latter, it predominantly occurs intracellularly within affected myofibers. To elucidate the possible role of betaAPP mismetabolism in the pathogenesis of IBM, transgenic mice were derived in which we selectively targeted betaAPP overexpression to skeletal muscle by using the muscle creatine kinase promoter. Here we report that older (10 months) transgenic mice exhibit intracellular immunoreactivity to betaAPP and its proteolytic derivatives in skeletal muscle. In this transgenic model, selective overexpression of betaAPP leads to the development of a subset of other histopathological and clinical features characteristic of IBM, including centric nuclei, inflammation, and deficiencies in motor performance. These results are consistent with a pathogenic role for betaAPP mismetabolism in human IBM.

Most cases of autosomal-dominant familial Alzheimer's disease are linked to mutations in the presenilin genes ( PS1 and PS2 ). In addition to modulating β-amyloid production, presenilin mutations also produce highly specific and selective alterations in intracellular calcium signaling. Although the molecular mechanisms underlying these changes are not known, one candidate molecular mediator is calsenilin, a recently identified calcium-binding protein that associates with the C terminus of both PS1 and PS2. In this study, we investigated the effects of calsenilin on calcium signaling in Xenopus oocytes expressing either wild-type or mutant PS1. In this system, mutant PS1 potentiated the amplitude of calcium signals evoked by inositol 1,4,5-trisphosphate and also accelerated their rates of decay. We report that calsenilin coexpression reverses both of these potentially pathogenic effects. Notably, expression of calsenilin alone had no discernable effects on calcium signaling, suggesting that calsenilin modulates these signals by a mechanism independent of simple calcium buffering. Our findings further suggest that the effects of presenilin mutations on calcium signaling are likely mediated through the C-terminal domain, a region that has also been implicated in the modulation of β-amyloid production and cell death.

Interferon-gamma (IFN-gamma), traditionally associated with a variety of physiological and pathological processes of the immune system, manifests an array of biological effects on cells of the nervous system. Clinical and in vitro studies support a key role for IFN-gamma in the pathogenesis of immune-mediated demyelinating disorders such as multiple sclerosis (MS). To investigate the role of this cytokine within the central nervous system (CNS), transgenic mice were derived in which IFN-gamma transgene expression was selectively targeted to astrocytes, a potentially important cellular source of this cytokine. Here we report that astrocyte-directed expression of IFN-gamma results in regional hypomyelination and selective disruption of brain histogenesis, which included severe cerebellar and hippocampal dysplasia. Transgenic mice were markedly ataxic and the majority died prior to reaching sexual maturity. This study demonstrates that astrocyte-directed expression of IFN-gamma profoundly affects the differentiation and morphogenesis of the brain and provides additional evidence that this cytokine has deleterious consequences on myelin-producing cells, independent of the cellular source.

Interest in the possible role of herpes simplex virus type 1 (HSV1) as a cofactor in the pathogenesis of Alzheimer's disease (AD) has re-emerged following the detection of viral DNA sequences in the central nervous system (CNS). Evidence from 2 independent laboratories indicates that HSV1 may interact with a host-specific factor, the apolipoprotein E epsilon 4 allele, to further augment the risk for AD. In this review, we consider the arguments implicating HSV1 in the pathogenesis of AD. Although further studies are required to confirm a role for HSV1 in AD and to elucidate its underlying molecular basis, implicating a virus in the pathogenesis of this insidious disease clearly offers novel potential treatments.

The identification of the cellular and subcellular regions of the Alzheimer's disease brain to which the presenilin-1 (PS-1) protein localizes is expected to contribute to an understanding of its pathophysiological role. Toward this end, we have derived an affinity-purified antibody to a synthetic PS-1 peptide. In this report, we demonstrate that this antibody, called SW2, specifically recognizes full-length, 47-kDa PS-1 protein from rat primary cortical neurons, from a human neuronal cell line, and from human brain extracts on Western immunoblots. Immunohistochemical analysis of postmortem brain tissue from control and Alzheimer's disease patients using this SW2 antibody indicates an intracellular localization of PS-1 immunoreactivity with prominent perinuclear characteristics in neurons, with staining also detected in neuritic processes. Despite various treatments of the tissue sections, no PS-1 immunoreactivity was observed in neuritic plaques, the hallmark pathological lesions of Alzheimer's disease. In addition, confocal microscopic analysis of immunostained cultured primary neurons revealed a prominent perinuclear pattern of PS-1 immunoreactivity consistent with vesicular localization, as well as punctate staining in neuritic processes.

Insulin-degrading enzyme (IDE) is an atypical zinc-metallopeptidase that degrades insulin and the amyloid ß-protein and is strongly implicated in the pathogenesis of diabetes and Alzheimer’s disease. We recently developed the first effective inhibitors of IDE, peptide hydroxamates that, while highly potent and selective, are relatively large (MW >740) and difficult to synthesize. We present here a facile synthetic route that yields enantiomerically pure derivatives comparable in potency to the parent compounds. Through the generation of truncated variants, we identified a compound with significantly reduced size (MW = 455.5) that nonetheless retains good potency (k(i) = 78 ± 11 nM) and selectivity for IDE. Notably, the potency of these inhibitors was found to vary as much as 60-fold in a substrate-specific manner, an unexpected finding for active-site directed inhibitors. Collectively, our findings demonstrate that potent, small-molecule IDE inhibitors can be developed that, in certain instances, can be highly substrate selective.

Sporadic Alzheimer’s disease (AD) patients have low amyloid-β peptide (Aβ) clearance in the central nervous system (CNS). The peripheral Aβ clearance may also be important but its role in AD remains unclear. We aimed to study the Aβ degrading proteases including insulin degrading enzyme (IDE), angiotensin converting enzyme (ACE) and others in blood. Using the fluorogenic substrate V—a substrate of IDE and other metalloproteases, we showed that human serum degraded the substrate V, and the activity was inhibited by adding increasing dose of Aβ. The existence of IDE activity was demonstrated by the inhibition of insulin, amylin or EDTA, and further confirmed by immunocapture of IDE using monoclonal antibodies. The involvement of ACE was indicated by the ability of the ACE inhibitor, lisinopril, to inhibit the substrate V degradation. To test the variations of substrate V degradation in humans, we used serum samples from a homebound elderly population with cognitive diagnoses. Compared with the elderly who had normal cognition, those with probable AD and amnestic mild cognitive impairment (amnestic MCI) had lower peptidase activities. Probable AD or amnestic MCI as an outcome remained negatively associated with serum substrate V degradation activity after adjusting for the confounders. The elderly with probable AD had lower serum substrate V degradation activity compared with those who had vascular dementia. The blood proteases mediating Aβ degradation may be important for the AD pathogenesis. More studies are needed to specify each Aβ degrading protease in blood as a useful biomarker and a possible treatment target for AD.

Background Insulin-degrading enzyme (IDE) is widely recognized as the principal protease responsible for the clearance and inactivation of insulin, but its role in glycemic control in vivo is poorly understood. We present here the first longitudinal characterization, to our knowledge, of glucose regulation in mice with pancellular deletion of the IDE gene (IDE-KO mice). Methodology IDE-KO mice and wild-type (WT) littermates were characterized at 2, 4, and 6 months of age in terms of body weight, basal glucose and insulin levels, and insulin and glucose tolerance. Consistent with a functional role for IDE in insulin clearance, fasting serum insulin levels in IDE-KO mice were found to be ∼3-fold higher than those in wild-type (WT) controls at all ages examined. In agreement with previous observations, 6-mo-old IDE-KO mice exhibited a severe diabetic phenotype characterized by increased body weight and pronounced glucose and insulin intolerance. In marked contrast, 2-mo-old IDE-KO mice exhibited multiple signs of improved glycemic control, including lower fasting glucose levels, lower body mass, and modestly enhanced insulin and glucose tolerance relative to WT controls. Biochemically, the emergence of the diabetic phenotype in IDE-KO mice correlated with age-dependent reductions in insulin receptor (IR) levels in muscle, adipose, and liver tissue. Primary adipocytes harvested from 6-mo-old IDE-KO mice also showed functional impairments in insulin-stimulated glucose uptake. Conclusions Our results indicate that the diabetic phenotype in IDE-KO mice is not a primary consequence of IDE deficiency, but is instead an emergent compensatory response to chronic hyperinsulinemia resulting from complete deletion of IDE in all tissues throughout life. Significantly, our findings provide new evidence to support the idea that partial and/or transient inhibition of IDE may constitute a valid approach to the treatment of diabetes.

2.6 (95% CI: 1.2-5.2), and one copy with a risk ratio of 1.9 (95% CI: 1.1-3.4). Moreover, two adjacent SNPs, rs6163 and rs743572, had similar genotype risk ratios as rs10786712, suggesting that the region flanking rs10786712 may harbor risk variants. Conclusions: We report that the variants at CYP17 decrease age at onset and increase the likelihood of AD in high risk women with DS, independent of BMI, ethnicity, level of intellectual disability, and APOE. We are currently examining the relation between risk SNPs and multiple sex hormone levels to further understand this association.

Background Insulin is a vital peptide hormone that is a central regulator of glucose homeostasis, and impairments in insulin signaling cause diabetes mellitus. In principle, it should be possible to enhance the activity of insulin by inhibiting its catabolism, which is mediated primarily by insulin-degrading enzyme (IDE), a structurally and evolutionarily distinctive zinc-metalloprotease. Despite interest in pharmacological inhibition of IDE as an attractive anti-diabetic approach dating to the 1950s, potent and selective inhibitors of IDE have not yet emerged. Methodology/Principal Findings We used a rational design approach based on analysis of combinatorial peptide mixtures and focused compound libraries to develop novel peptide hydroxamic acid inhibitors of IDE. The resulting compounds are ∼106 times more potent than existing inhibitors, non-toxic, and surprisingly selective for IDE vis-a-vis conventional zinc-metalloproteases. Crystallographic analysis of an IDE-inhibitor complex reveals a novel mode of inhibition based on stabilization of IDE's “closed,” inactive conformation. We show further that pharmacological inhibition of IDE potentiates insulin signaling by a mechanism involving reduced catabolism of internalized insulin. Conclusions/Significance The inhibitors we describe are the first to potently and selectively inhibit IDE or indeed any member of this atypical zinc-metalloprotease superfamily. The distinctive structure of IDE's active site, and the mode of action of our inhibitors, suggests that it may be possible to develop inhibitors that cross-react minimally with conventional zinc-metalloproteases. Significantly, our results reveal that insulin signaling is normally regulated by IDE activity not only extracellularly but also within cells, supporting the longstanding view that IDE inhibitors could hold therapeutic value for the treatment of diabetes.

Background Insulin-degrading enzyme (IDE) is a widely studied zinc-metalloprotease implicated in the pathogenesis of type 2 diabetes mellitus, Alzheimer disease (AD) and varicella zoster virus infection. Despite more than six decades of research on IDE, progress has been hampered by the lack of well-characterized reagents targeting this biomedically important protease. To address this important need, we generated and characterized new mouse monoclonal antibodies (mAbs) targeting natively folded human and rodent IDE. Results Eight monoclonal hybridoma cell lines were derived in house from mice immunized with full-length, natively folded, recombinant human IDE. The mAbs derived from these lines were shown to detect IDE selectively and sensitively by a wide range of methods. Two mAbs in particular—designated 6A1 and 6H9—proved especially selective for IDE in immunocytochemical and immunohistochemical applications. Using a variety of methods, we show that 6A1 selectively detects both human and rodent IDE, while 6H9 selectively detects human, but not rodent, IDE, with both mAbs showing essentially no cross reactivity with other proteins in these applications. Using these novel anti-IDE mAbs, we also developed sensitive and quantitative sandwich ELISAs capable of quantifying IDE levels present in human brain extracts. Conclusion We succeeded in developing novel mAbs that selectively detect rodent and/or human IDE, which we have shown to be suitable for a wide range of applications, including western blotting, immunoprecipitation, immunocytochemistry, immunohistochemistry, and quantitative sandwich ELISAs. These novel anti-IDE mAbs and the assays derived from them constitute important new tools for addressing many unresolved questions about the basic biology of IDE and its role in multiple highly prevalent human diseases.