Amyloid beta-degrading cryptidases: insulin degrading enzyme, presequence peptidase, and neprilysin

The role of ACE inhibitors and ARBs in preserving cognitive function via hypertension Management: A critical Update

Hypertension poses a significant risk to cognition-related disorders like dementia. As the global population ages, age-related neurological illnesses such as Alzheimer's disease are becoming increasingly prevalent. The primary hypertension treatments, angiotensin receptor blockers, and angiotensin-converting enzyme inhibitors, exhibit neuroprotective properties. However, observational studies suggest that they may independently contribute to cognitive decline and dementia. Some of these medications have shown promise in reducing cognitive impairment and amyloid buildup in Alzheimer's models. While direct comparisons between the two drug classes are limited, angiotensin receptor blockers have been associated with less brain shrinkage, lower dementia incidence, and slower cognitive decline compared to angiotensin-converting enzyme inhibitors. Both types of medications can influence cognition by passing the blood-brain barrier, with angiotensin receptor blockers potentially offering superior neuroprotective effects due to their selective blockade of the angiotensin type 1 receptor.

Dimerization and dynamics of angiotensin-I converting enzyme revealed by cryoEM and MD simulations

Angiotensin-I converting enzyme (ACE) regulates the levels of disparate bioactive peptides, notably converting angiotensin-I to angiotensin-II and degrading amyloid beta. ACE is a heavily glycosylated dimer, containing 4 analogous catalytic sites, and exists in membrane bound and soluble (sACE) forms. ACE inhibition is a frontline, FDA-approved, therapy for cardiovascular diseases yet is associated with significant side effects, including higher rates of lung cancer. To date, structural studies have been confined to individual domains or partially denatured cryoEM structures. Here we report the cryoEM structure of the full-length, glycosylated, sACE dimer. We resolved four structural states at 2.99 to 3.65 Å resolution which are primarily differentiated by varying degrees of solvent accessibility to the active sites and reveal the full dimerization interface. We also employed all-atom molecular dynamics (MD) simulations and heterogeneity analysis in cryoSPARC, cryoDRGN, and RECOVAR to elucidate the conformational dynamics of sACE and identify key regions mediating conformational change. We identify differences in the mechanisms governing the conformational dynamics of individual domains that have implications for the design of domain-specific sACE modulators.

Characterization and modulation of human insulin degrading enzyme conformational dynamics to control enzyme activity

Insulin degrading enzyme (IDE) is a dimeric 110 kDa M16A zinc metalloprotease that degrades amyloidogenic peptides diverse in shape and sequence, including insulin, amylin, and amyloid-β, to prevent toxic amyloid fibril formation. IDE has a hollow catalytic chamber formed by four homologous subdomains organized into two ~55 kDa N- and C- domains (IDE-N and IDE-C, respectively), in which peptides bind, unfold, and are repositioned for proteolysis. IDE is known to transition between a closed state, poised for catalysis, and an open state, able to release cleavage products and bind new substrate. Here, we present five cryoEM structures of the IDE dimer at 3.0-4.1 Å resolution, obtained in the presence of a sub-saturating concentration of insulin. Analysis of the heterogeneity within the particle populations comprising these structures combined with all-atom molecular dynamics (MD) simulations permitted a comprehensive characterization of IDE conformational dynamics. Our analysis identified the structural basis and key residues for these dynamics that were not revealed by IDE static structures. Notably arginine-668 serves as a molecular latch mediating the open-close transition and facilitates key protein motions through charge-swapping interactions at the IDE-N/C interface. Our size-exclusion chromatography-coupled small-angle X-ray scattering and enzymatic assays of an arginine-668 to alanine mutant indicate a profound alteration of conformational dynamics and catalytic activity. Taken together, this work highlights the power of integrating experimental and computational methodologies to understand protein dynamics, offers the molecular basis of unfoldase activity of IDE, and provides a new path forward towards the development of substrate-specific modulators of IDE activity.

Advances and future trends in the detection of beta-amyloid: A comprehensive review

The neurodegenerative condition known as Alzheimer's disease is typified by the build-up of beta-amyloid plaques within the brain. The timely and precise identification of beta-amyloid is essential for understanding disease progression and developing effective therapeutic interventions. This comprehensive review explores the diverse landscape of beta-amyloid detection methods, ranging from traditional immunoassays to cutting-edge technologies. The review critically examines the strengths and limitations of established techniques such as ELISA, PET, and MRI, providing insights into their roles in research and clinical settings. Emerging technologies, including electrochemical methods, nanotechnology, fluorescence techniques, point-of-care devices, and machine learning integration, are thoroughly discussed, emphasizing recent breakthroughs and their potential for revolutionizing beta-amyloid detection. Furthermore, the review delves into the challenges associated with current detection methods, such as sensitivity, specificity, and accessibility. By amalgamating knowledge from multidisciplinary approaches, this review aims to guide researchers, clinicians, and policymakers in navigating the complex landscape of beta-amyloid detection, ultimately contributing to advancements in Alzheimer's disease diagnostics and therapeutics.

Microglial Lyzl4 Facilitates β-Amyloid Clearance in Alzheimer's Disease

Alzheimer's Disease (AD) is a neurodegenerative condition characterized by the accumulation and deposition of amyloid-β (Aβ) aggregates in the brain. Despite a wealth of research on the toxicity of Aβ and its role in synaptic damage, the mechanisms facilitating Aβ clearance are not yet fully understood. However, microglia, the primary immune cells of the central nervous system, are known to maintain homeostasis through the phagocytic clearance of protein aggregates and cellular debris. In this study, RNA sequencing analysis and live cell functional screens are employed to uncover microglial genetic modifiers related to AD. Lyzl4 is identified, which encodes a c-type lysozyme-like enzyme primarily localized to microglial lysosomes, as a gene significantly upregulated in AD microglia with aging and propose that Lyzl4 upregulation acts as a positive regulator of Aβ clearance. Furthermore, it is found that Lyzl4 overexpression boosts Aβ clearance both in vitro and in vivo, underscoring its potential for mitigating Aβ burden. These novel insights position Lyzl4 as a promising therapeutic target for Alzheimer's disease, paving the way for further exploration into potential AD treatments.

Immunotherapy in Alzheimer's disease: focusing on the efficacy of gantenerumab on amyloid-β clearance and cognitive decline

Gantenerumab, a human monoclonal antibody (mAb), has been thought of as a potential agent to treat Alzheimer's disease (AD) by specifically targeting regions of the amyloid-β (Aβ) peptide sequence. Aβ protein accumulation in the brain leads to amyloid plaques, causing neuroinflammation, oxidative stress, neuronal damage, and neurotransmitter dysfunction, thereby causing cognitive decline in AD. Gantenerumab involves disrupting Aβ aggregation and promoting the breakdown of larger Aβ aggregates into smaller fragments, which facilitates the action of Aβ-degrading enzymes in the brain, thus slowing down the progression of AD. Moreover, Gantenerumab acts as an opsonin, coating Aβ plaques and enhancing their recognition by immune cells, which, combined with its ability to improve the activity of microglia, makes it an intriguing candidate for promoting Aβ plaque clearance. Indeed, the multifaceted effects of Gantenerumab, including Aβ disaggregation, enhanced immune recognition, and improved microglia activity, may position it as a promising therapeutic approach for AD. Of note, reports suggest that Gantenerumab, albeit its capacity to reduce or eliminate Aβ, has not demonstrated effectiveness in reducing cognitive decline. This review, after providing an overview of immunotherapy approaches that target Aβ in AD, explores the efficacy of Gantenerumab in reducing Aβ levels and cognitive decline.

Insulin-Degrading Enzyme Efficiently Degrades polyQ Peptides but not Expanded polyQ Huntingtin Fragments

Background

Huntington's disease is an inheritable autosomal dominant disorder caused by an expanded CAG trinucleotide repeat within the Huntingtin gene, leading to a polyglutamine (polyQ) expansion in the mutant protein.

Objective

A potential therapeutic approach for delaying or preventing the onset of the disease involves enhancing the degradation of the aggregation-prone polyQ-expanded N-terminal mutant huntingtin (mHTT) exon1 fragment. A few proteases and peptidases have been identified that are able to cleave polyQ fragments with low efficiency. This study aims to identify a potent polyQ-degrading endopeptidase.

Methods

Here we used quenched polyQ peptides to identify a polyQ-degrading endopeptidase. Next we investigated its role on HTT turnover, using purified polyQ-expanded HTT fragments and striatal cells expressing mHTT exon1 peptides.

Results

We identified insulin-degrading enzyme (IDE) as a novel endopeptidase for degrading polyQ peptides. IDE was, however, ineffective in reducing purified polyQ-expanded HTT fragments. Similarly, in striatal cells expressing mHTT exon1 peptides, IDE did not enhance mHTT turnover.

Conclusions

This study shows that despite IDE's efficiency in degrading polyQ peptides, it does not contribute to the direct degradation of polyQ-expanded mHTT fragments.

SGLT2 and DPP4 inhibitors improve Alzheimer's disease-like pathology and cognitive function through distinct mechanisms in a T2D-AD mouse model

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2D) share common features, including insulin resistance. Brain insulin resistance has been implicated as a key factor in the pathogenesis of AD. Recent studies have demonstrated that anti-diabetic drugs sodium-glucose cotransporter-2 inhibitor (SGLT2-i) and dipeptidyl peptidase-4 inhibitor (DPP4-i) improve insulin sensitivity and provide neuroprotection. However, the effects of these two inhibitors on the brain metabolism and insulin resistance remain uninvestigated. We developed a T2D-AD mouse model using a high-fat diet (HFD) for 19 weeks along with a single dose of streptozotocin (100 mg/kg, intraperitoneally) at the fourth week of HFD initiation. Subsequently, the animals were treated with SGLT2-i (empagliflozin, 25 mg/kg/day orally [p.o.]) and DPP4-i (sitagliptin, 100 mg/kg/day p.o.) for 7 weeks. Subsequently, behavioral tests were performed, and the expression of insulin signaling, AD-related, and other signaling pathway proteins in the brain were examined. T2D-AD mice not only showed increased blood glucose levels and body weight but also insulin resistance. SGLT2-i and DPP4-i effectively ameliorated insulin sensitivity and reduced body weight in these mice. Furthermore, SGLT2-i and DPP4-i significantly improved hippocampal-dependent learning, memory, and cognitive functions in the T2D-AD mouse model. Interestingly, SGLT2-i and DPP4-i reduced the hyperphosphorylated tau (pTau) levels and amyloid β (Aβ) accumulation and enhanced brain insulin signaling. SGLT2-i reduced pTau accumulation through the angiotensin converting enzyme-2/angiotensin (1-7)/ mitochondrial assembly receptor axis, whereas DPP4-i reduced Aβ accumulation by increasing insulin-degrading enzyme levels. These findings suggest that SGLT2-i and DPP4-i prevent AD-like pathology and cognitive dysfunction in T2D mice potentially through affecting brain insulin signaling via different mechanisms.

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.

Pharmacogenetics of angiotensin modulators according to APOE-ϵ4 alleles and the ACE insertion/deletion polymorphism in Alzheimer's disease

OBJECTIVE

In Alzheimer's disease (AD), angiotensin II receptor blockers (ARBs) could reduce cerebrovascular dysfunction, while angiotensin-converting enzyme inhibitors (ACEis) might increase brain amyloid-β by suppressing effects of the angiotensin-converting enzyme 1, an amyloid-β-degrading enzyme. However, ACEis could benefit patients with AD by reducing the amyloidogenic processing of the amyloid precursor protein, by central cholinergic and anti-inflammatory mechanisms, and by peripheral modulation of glucose homeostasis. We aimed to investigate whether the ACE insertion/deletion polymorphism is associated with clinical changes in patients with AD, while considering apolipoprotein E (APOE)-ϵ4 carrier status and blood pressure response to angiotensin modulators.

METHODS

Consecutive outpatients with late-onset AD were screened with cognitive tests and anthropometric measurements, while their caregivers were queried for functional and caregiver burden scores. Prospective pharmacogenetic associations were estimated for 1 year, taking APOE-ϵ4 carrier status and genotypes of the ACE insertion/deletion polymorphism into account, along with treatment with ACEis or ARBs.

RESULTS

For 193 patients (67.4% women, 53.4% APOE-ϵ4 carriers), the ACE insertion/deletion polymorphism was in Hardy-Weinberg equilibrium (p = 0.281), while arterial hypertension was prevalent in 80.3% (n = 124 used an ACEi, n = 21 used an ARB). ARBs benefitted mostly APOE-ϵ4 carriers concerning caregiver burden variations, cognitive and functional decline. ACEis benefitted APOE-ϵ4 non-carriers concerning cognitive and functional decline due to improved blood pressure control in addition to possible central mechanisms. The ACE insertion/deletion polymorphism led to variable response to angiotensin modulators concerning neurological outcomes and blood pressure variations.

CONCLUSION

Angiotensin modulators may be disease-modifiers in AD, while genetic stratification of samples is recommended in clinical studies.

Microglial function, INPP5D/SHIP1 signaling, and NLRP3 inflammasome activation: implications for Alzheimer's disease

Recent genetic studies on Alzheimer's disease (AD) have brought microglia under the spotlight, as loci associated with AD risk are enriched in genes expressed in microglia. Several of these genes have been recognized for their central roles in microglial functions. Increasing evidence suggests that SHIP1, the protein encoded by the AD-associated gene INPP5D, is an important regulator of microglial phagocytosis and immune response. A recent study from our group identified SHIP1 as a negative regulator of the NLRP3 inflammasome in human iPSC-derived microglial cells (iMGs). In addition, we found evidence for a connection between SHIP1 activity and inflammasome activation in the AD brain. The NLRP3 inflammasome is a multiprotein complex that induces the secretion of pro-inflammatory cytokines as part of innate immune responses against pathogens and endogenous damage signals. Previously published studies have suggested that the NLRP3 inflammasome is activated in AD and contributes to AD-related pathology. Here, we provide an overview of the current understanding of the microglial NLRP3 inflammasome in the context of AD-related inflammation. We then review the known intracellular functions of SHIP1, including its role in phosphoinositide signaling, interactions with microglial phagocytic receptors such as TREM2 and evidence for its intersection with NLRP3 inflammasome signaling. Through rigorous examination of the intricate connections between microglial signaling pathways across several experimental systems and postmortem analyses, the field will be better equipped to tailor newly emerging therapeutic strategies targeting microglia in neurodegenerative diseases.

Dynamical analysis of a glucose-insulin regulatory system with insulin-degrading enzyme and multiple delays

This paper investigates the dynamics of a glucose-insulin regulatory system model that incorporates: (1) insulin-degrading enzyme in the insulin equation; and (2) discrete time delays respectively in the insulin production term, hepatic glucose production term, and the insulin-degrading enzyme. We provide rigorous results of our model including the asymptotic stability of the equilibrium solution and the existence of Hopf bifurcation. We show that analytically and numerically at a certain value the time delays driven stability or instability occurs when the corresponding model has an interior equilibrium. Moreover, we illustrate the oscillatory regulation and insulin secretion via numerical simulations, which show that the model dynamics exhibit physiological observations and more information by allowing parameters to vary. Our results may provide useful biological insights into diabetes for the glucose-insulin regulatory system model.

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.

Stress induced exacerbation of Alzheimer's disease brain pathology is thwarted by co-administration of nanowired cerebrolysin and monoclonal amyloid beta peptide antibodies with serotonin 5-HT6 receptor antagonist SB-399885

Alzheimer's disease is one of the devastating neurodegenerative diseases affecting mankind worldwide with advancing age mainly above 65 years and above causing great misery of life. About more than 7 millions are affected with Alzheimer's disease in America in 2023 resulting in huge burden on health care system and care givers and support for the family. However, no suitable therapeutic measures are available at the moment to enhance quality of life to these patients. Development of Alzheimer's disease may reflect the stress burden of whole life inculcating the disease processes of these neurodegenerative disorders of the central nervous system. Thus, new strategies using nanodelivery of suitable drug therapy including antibodies are needed in exploring neuroprotection in Alzheimer's disease brain pathology. In this chapter role of stress in exacerbating Alzheimer's disease brain pathology is explored and treatment strategies are examined using nanotechnology based on our own investigation. Our observations clearly show that restraint stress significantly exacerbate Alzheimer's disease brain pathology and nanodelivery of a multimodal drug cerebrolysin together with monoclonal antibodies (mAb) to amyloid beta peptide (AβP) together with a serotonin 5-HT6 receptor antagonist SB399885 significantly thwarted Alzheimer's disease brain pathology exacerbated by restraint stress, not reported earlier. The possible mechanisms and future clinical significance is discussed.

Modulation of the Activity of the Insulin-Degrading Enzyme by Aβ Peptides

The insulin-degrading enzyme (IDE) is an evolutionarily conserved protease implicated in the degradation of insulin and amyloidogenic peptides. Most of the biochemical and biophysical characterization of IDE's catalytic activity has been conducted using solutions containing a single substrate, i.e., insulin or Aβ(1-40). IDE's activity toward a particular substrate, however, is likely to be influenced by the presence of other substrates. Here, we show by a kinetic assay based on insulin's helical circular dichroic signal and MALDI TOF mass spectrometry that Aβ peptides modulate IDE's activity toward insulin in opposing ways. Aβ(1-40) enhances IDE-dependent degradation of insulin, whereas Aβ(pyroE3-42), the most pathogenic pyroglutamate-modified Aβ peptide in AD, inhibits IDE's activity. Intriguingly, Aβ(pyroE3-42) also inhibits IDE's ability to degrade Aβ(1-40). Together, our results implicate Aβ peptides in the abnormal catabolism of IDE's key substrates.

Distinct chemical factors in hydrolytic reactions catalyzed by metalloenzymes and metal complexes

The selective hydrolysis of the extremely stable phosphoester, peptide and ester bonds of molecules by bio-inspired metal-based catalysts (metallohydrolases) is required in a wide range of biological, biotechnological and industrial applications. Despite the impressive advances made in the field, the ultimate goal of designing efficient enzyme mimics for these reactions is still elusive. Its realization will require a deeper understanding of the diverse chemical factors that influence the activities of both natural and synthetic catalysts. They include catalyst-substrate complexation, non-covalent interactions and the electronic nature of the metal ion, ligand environment and nucleophile. Based on our computational studies, their roles are discussed for several mono- and binuclear metallohydrolases and their synthetic analogues. Hydrolysis by natural metallohydrolases is found to be promoted by a ligand environment with low basicity, a metal bound water and a heterobinuclear metal center (in binuclear enzymes). Additionally, peptide and phosphoester hydrolysis is dominated by two competing effects, i.e. nucleophilicity and Lewis acid activation, respectively. In synthetic analogues, hydrolysis is facilitated by the inclusion of a second metal center, hydrophobic effects, a biological metal (Zn, Cu and Co) and a terminal hydroxyl nucleophile. Due to the absence of the protein environment, hydrolysis by these small molecules is exclusively influenced by nucleophile activation. The results gleaned from these studies will enhance the understanding of fundamental principles of multiple hydrolytic reactions. They will also advance the development of computational methods as a predictive tool to design more efficient catalysts for hydrolysis, Diels-Alder reaction, Michael addition, epoxide opening and aldol condensation.

Insulin-Degrading Enzyme Interacts with Mitochondrial Ribosomes and Respiratory Chain Proteins

Insulin-degrading enzyme (IDE) is a highly conserved metalloprotease that is mainly localized in the cytosol. Although IDE can degrade insulin and some other low molecular weight substrates efficiently, its ubiquitous expression suggests additional functions supported by experimental findings, such as a role in stress responses and cellular protein homeostasis. The translation of a long full-length IDE transcript has been reported to result in targeting to mitochondria, but the role of IDE in this compartment is unknown. To obtain initial leads on the function of IDE in mitochondria, we used a proximity biotinylation approach to identify proteins interacting with wild-type and protease-dead IDE targeted to the mitochondrial matrix. We find that IDE interacts with multiple mitochondrial ribosomal proteins as well as with proteins involved in the synthesis and assembly of mitochondrial complex I and IV. The mitochondrial interactomes of wild type and mutant IDE are highly similar and do not reveal any likely proteolytic IDE substrates. We speculate that IDE could adopt similar additional non-proteolytic functions in mitochondria as in the cytosol, acting as a chaperone and contributing to protein homeostasis and stress responses.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Walnut Prevents Cognitive Impairment by Regulating the Synaptic and Mitochondrial Dysfunction via JNK Signaling and Apoptosis Pathway in High-Fat Diet-Induced C57BL/6 Mice

This study was conducted to evaluate the protective effect of Juglans regia (walnut, Gimcheon 1ho cultivar, GC) on high-fat diet (HFD)-induced cognitive dysfunction in C57BL/6 mice. The main physiological compounds of GC were identified as pedunculagin/casuariin isomer, strictinin, tellimagrandin I, ellagic acid-O-pentoside, and ellagic acid were identified using UPLC Q-TOF/MS analysis. To evaluate the neuro-protective effect of GC, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 2′,7′-dichlorodihydrofluorecein diacetate (DCF-DA) analysis were conducted in H₂O₂ and high glucose-induced neuronal PC12 cells and hippocampal HT22 cells. GC presented significant cell viability and inhibition of reactive oxygen species (ROS) production. GC ameliorated behavioral and memory dysfunction through Y-maze, passive avoidance, and Morris water maze tests. In addition, GC reduced white adipose tissue (WAT), liver fat mass, and serum dyslipidemia. To assess the inhibitory effect of antioxidant system deficit, lipid peroxidation, ferric reducing antioxidant power (FRAP), and advanced glycation end products (AGEs) were conducted. Administration of GC protected the antioxidant damage against HFD-induced diabetic oxidative stress. To estimate the ameliorating effect of GC, acetylcholine (ACh) level, acetylcholinesterase (AChE) activity, and expression of AChE and choline acetyltransferase (ChAT) were conducted, and the supplements of GC suppressed the cholinergic system impairment. Furthermore, GC restored mitochondrial dysfunction by regulating the mitochondrial ROS production and mitochondrial membrane potential (MMP) levels in cerebral tissues. Finally, GC ameliorated cerebral damage by synergically regulating the protein expression of the JNK signaling and apoptosis pathway. These findings suggest that GC could provide a potential functional food source to improve diabetic cognitive deficits and neuronal impairments.

Roles of Natriuretic Peptides and the Significance of Neprilysin in Cardiovascular Diseases

Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) activate the guanylyl cyclase A receptor (GC-A), which synthesizes the second messenger cGMP in a wide variety of tissues and cells. C-type natriuretic peptide (CNP) activates the cGMP-producing guanylyl cyclase B receptor (GC-B) in chondrocytes, endothelial cells, and possibly smooth muscle cells, cardiomyocytes, and cardiac fibroblasts. The development of genetically modified mice has helped elucidate the physiological roles of natriuretic peptides via GC-A or GC-B. These include the hormonal effects of ANP/BNP in the vasculature, autocrine effects of ANP/BNP in cardiomyocytes, and paracrine effects of CNP in the vasculature and cardiomyocytes. Neprilysin (NEP) is a transmembrane neutral endopeptidase that degrades the three natriuretic peptides. Recently, mice overexpressing NEP, specifically in cardiomyocytes, revealed that local cardiac NEP plays a vital role in regulating natriuretic peptides in the heart tissue. Since NEP inhibition is a clinically accepted approach for heart failure treatment, the physiological roles of natriuretic peptides have regained attention. This article focuses on the physiological roles of natriuretic peptides elucidated in mice with GC-A or GC-B deletion, the significance of NEP in natriuretic peptide metabolism, and the long-term effects of angiotensin receptor-neprilysin inhibitor (ARNI) on cardiovascular diseases.

Insulin-Degrading Enzyme, an Under-Estimated Potential Target to Treat Cancer?

Insulin-degrading enzyme (IDE) is a multifunctional protease due to the variety of its substrates, its various cellular locations, its conservation between species and its many non-proteolytic functions. Numerous studies have successfully demonstrated its implication in two main therapeutic areas: metabolic and neuronal diseases. In recent years, several reports have underlined the overexpression of this enzyme in different cancers. Still, the exact role of IDE in the physiopathology of cancer remains to be elucidated. Known as the main enzyme responsible for the degradation of insulin, an essential growth factor for healthy cells and cancer cells, IDE has also been shown to behave like a chaperone and interact with the proteasome. The pharmacological modulation of IDE (siRNA, chemical compounds, etc.) has demonstrated interesting results in cancer models. All these results point towards IDE as a potential target in cancer. In this review, we will discuss evidence of links between IDE and cancer development or resistance, IDE's functions, catalytic or non-catalytic, in the context of cell proliferation, cancer development and the impact of the pharmacomodulation of IDE via cancer therapeutics.

Structural basis for the mechanisms of human presequence protease conformational switch and substrate recognition

Presequence protease (PreP), a 117 kDa mitochondrial M16C metalloprotease vital for mitochondrial proteostasis, degrades presequence peptides cleaved off from nuclear-encoded proteins and other aggregation-prone peptides, such as amyloid β (Aβ). PreP structures have only been determined in a closed conformation; thus, the mechanisms of substrate binding and selectivity remain elusive. Here, we leverage advanced vitrification techniques to overcome the preferential denaturation of one of two ~55 kDa homologous domains of PreP caused by air-water interface adsorption. Thereby, we elucidate cryoEM structures of three apo-PreP open states along with Aβ- and citrate synthase presequence-bound PreP at 3.3–4.6 Å resolution. Together with integrative biophysical and pharmacological approaches, these structures reveal the key stages of the PreP catalytic cycle and how the binding of substrates or PreP inhibitor drives a rigid body motion of the protein for substrate binding and catalysis. Together, our studies provide key mechanistic insights into M16C metalloproteases for future therapeutic innovations.

Presequence protease (PreP) is essential to mitochondrial proteostasis. This study leverages advanced vitrification techniques to solve cryoEM structures of apo- and substrate-bound PreP and integrates these data with other analysis to reveal key stages and mechanistic insights of the PreP catalytic cycle.

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.

Crystal structures of TTHA1265 and TTHA1264/TTHA1265 complex reveal an intrinsic heterodimeric assembly

Zinc peptidase M16 family members are widely distributed in most prokaryotic and eukaryotic organisms. M16 family has been divided into three subfamilies, M16A, M16B and M16C, based on sequence alignments and subunit connectivity. TTHA1264, an M16B protein found in Thermus thermophiles HB8, possesses an HXXEH motif essential for Zn²⁺ binding and catalytic activity. TTHA1265 is another member of M16B, which lacks the metal-binding motif but with a conserved active-site R/Y pair commonly found in the C-terminal half of M16 enzymes. Sequence analysis showed that two genes coding for TTHA1264 and TTHA1265 assemble into a single operon in the bacterial genome. Here, we report the crystal structure of TTHA1265 and TTHA1264/TTHA1265 complex from T. thermophilus HB8. Interestingly, when TTHA1264 and TTHA1265 are present alone, TTHA1264 forms a monomer, TTHA1265 forms a homodimer, respectively. However, TTHA264 and TTHA1265 assembled into a heterodimeric complex, indicating that they prefer to form heterodimer. Biochemical data further confirmed the heterodimeric assembly indicating intrinsic heterodimeric assembly of TTHA1264 and TTHA1265. This property of TTHA1264 and TTHA1265 is consistent with the characteristics of the M16B family.

Amyloid Beta Dynamics in Biological Fluids-Therapeutic Impact

Despite the significant impact of Alzheimer's disease (AD) at individual and socioeconomic levels and the numerous research studies carried out on this topic over the last decades, the treatments available in daily clinical practice remain less than satisfactory. Among the accepted etiopathogenic hypotheses, the amyloidogenic pathway theory, although intensively studied and even sometimes controversial, is still providing relevant theoretical elements for understanding the etiology of AD and for the further development of possible therapeutic tools. In this sense, this review aims to offer new insights related to beta amyloid (Aβ), an essential biomarker in AD. First the structure and function of Aβ in normal and pathological conditions are presented in detail, followed by a discussion on the dynamics of Aβ at the level of different biological compartments. There is focus on Aβ elimination modalities at central nervous system (CNS) level, and clearance via the blood-brain barrier seems to play a crucial/dominant role. Finally, different theoretical and already-applied therapeutic approaches for CNS Aβ elimination are presented, including the recent "peripheral sink therapeutic strategy" and "cerebrospinal fluid sinks therapeutic strategy". These data outline the need for a multidisciplinary approach designed to deliver a solution to stimulate Aβ clearance in more direct ways, including from the cerebrospinal fluid level.

Aβ31-35 Decreases Neprilysin-Mediated Alzheimer's Amyloid-β Peptide Degradation

Alzheimer's disease is associated with the deposition of extracellular senile plaques, made primarily of amyloid-β (Aβ), particularly peptides Aβ_1-42 and Aβ_1-40. Neprilysin, or neutral endopeptidase (NEP), catalyzes proteolysis of the amyloid peptides (Aβ) and is recognized as one of the major regulators of the levels of these peptides in the brain, preventing Aβ accumulation and plaque formation. Here, we used a combination of techniques to elucidate the mechanism of Aβ binding and cleavage by NEP. Our findings indicate that the Aβ_31-X cleavage products remain bound to the neprilysin active site, reducing proteolytic activity. Interestingly, it was already shown that this Aβ_31-35 sequence is also critical for recognition of Aβ peptides by other targets, such as the serpin-enzyme complex receptor in neuronal cells.

Insulin-Degrading Enzyme: Paradoxes and Possibilities

More than seven decades have passed since the discovery of a proteolytic activity within crude tissue extracts that would become known as insulin-degrading enzyme (IDE). Certainly much has been learned about this atypical zinc-metallopeptidase; at the same time, however, many quite fundamental gaps in our understanding remain. Herein, I outline what I consider to be among the most critical unresolved questions within the field, many presenting as intriguing paradoxes. For instance, where does IDE, a predominantly cytosolic protein with no signal peptide or clearly identified secretion mechanism, interact with insulin and other extracellular substrates? Where precisely is IDE localized within the cell, and what are its functional roles in these compartments? How does IDE, a bowl-shaped protein that completely encapsulates its substrates, manage to avoid getting “clogged” and thus rendered inactive virtually immediately? Although these paradoxes are by definition unresolved, I offer herein my personal insights and informed speculations based on two decades working on the biology and pharmacology of IDE and suggest specific experimental strategies for addressing these conundrums. I also offer what I believe to be especially fruitful avenues for investigation made possible by the development of new technologies and IDE-specific reagents. It is my hope that these thoughts will contribute to continued progress elucidating the physiology and pathophysiology of this important peptidase.

Differential Effects of Polyphenols on Insulin Proteolysis by the Insulin-Degrading Enzyme

The insulin-degrading enzyme (IDE) possesses a strong ability to degrade insulin and Aβ42 that has been linked to the neurodegeneration in Alzheimer's disease (AD). Given this, an attractive IDE-centric strategy for the development of therapeutics for AD is to boost IDE's activity for the clearance of Aβ42 without offsetting insulin proteostasis. Recently, we showed that resveratrol enhances IDE's activity toward Aβ42. In this work, we used a combination of chromatographic and spectroscopic techniques to investigate the effects of resveratrol on IDE's activity toward insulin. For comparison, we also studied epigallocatechin-3-gallate (EGCG). Our results show that the two polyphenols affect the IDE-dependent degradation of insulin in different ways: EGCG inhibits IDE while resveratrol has no effect. These findings suggest that polyphenols provide a path for developing therapeutic strategies that can selectively target IDE substrate specificity.

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.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Toxoplasma gondii Toxolysin 4 Contributes to Efficient Parasite Egress from Host Cells

Egress from host cells is an essential step in the lytic cycle of T. gondii and other apicomplexan parasites; however, only a few parasite secretory proteins are known to affect this process. The putative metalloproteinase toxolysin 4 (TLN4) was previously shown to be an extensively processed microneme protein, but further characterization was impeded by the inability to genetically ablate TLN4. Here, we show that TLN4 has the structural properties of an M16 family metalloproteinase, that it possesses proteolytic activity on a model substrate, and that genetic disruption of TLN4 reduces the efficiency of egress from host cells. Complementation of the knockout strain with the TLN4 coding sequence significantly restored egress competency, affirming that the phenotype of the Δtln4 parasite was due to the absence of TLN4. This work identifies TLN4 as the first metalloproteinase and the second microneme protein to function in T. gondii egress. The study also lays a foundation for future mechanistic studies defining the precise role of TLN4 in parasite exit from host cells. IMPORTANCE After replicating within infected host cells, the single-celled parasite Toxoplasma gondii must rupture out of such cells in a process termed egress. Although it is known that T. gondii egress is an active event that involves disruption of host-derived membranes surrounding the parasite, very few proteins that are released by the parasite are known to facilitate egress. In this study, we identify a parasite secretory protease that is necessary for efficient and timely egress, laying the foundation for understanding precisely how this protease facilitates T. gondii exit from host cells.

Hydroxypyridinethione Inhibitors of Human Insulin-Degrading Enzyme

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 Zn²⁺ ion have yet to be fully explored. In an effort to discover new, zinc-targeting 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 Zn²⁺ -binding scaffold. Screening a focused library of HOPTO compounds identified 3-sulfonamide derivatives of 1,2-HOPTO as inhibitors of IDE (K_i 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.

Structural analysis of Mycobacterium tuberculosis M13 metalloprotease Zmp1 open states

Zinc metalloprotease 1 (Zmp1), a Mycobacterium tuberculosis 75 kDa secreted enzyme, mediates key stages of tuberculosis disease progression. The biological activity of Zmp1 presumably stems from its ability to degrade bacterium- and/or host-derived peptides. The crystal structures of Zmp1 and related M13 metalloproteases, such as neprilysin and endothelin-converting enzyme-1 were determined only in the closed conformation, which cannot capture substrates or release proteolytic products. Thus, the mechanisms of substrate binding and selectivity remain elusive. Here we report two open-state cryo-EM structures of Zmp1, revealed by our SAXS analysis to be the dominant states in solution. Our structural analyses reveal how ligand binding induces a conformational switch in four linker regions to drive the rigid body motion of the D1 and D2 domains, which form the sizable catalytic chamber. Furthermore, they offer insights into the catalytic cycle and mechanism of substrate recognition of M13 metalloproteases for future therapeutic innovations.

Target Enzymes Considered for the Treatment of Alzheimer's Disease and Parkinson's Disease

Various amyloidogenic proteins have been suggested to be involved in the onset and progression of neurodegenerative diseases (ND) such as Alzheimer's disease (AD) and Parkinson's disease (PD). Particularly, the aggregation of misfolded amyloid-β and hyperphosphorylated tau and α-synuclein are linked to the pathogenesis of AD and PD, respectively. In order to care the diseases, multiple small molecules have been developed to regulate the aggregation pathways of these amyloid proteins. In addition to controlling the aggregation of amyloidogenic proteins, maintaining the levels of the proteins in the brain by amyloid degrading enzymes (ADE; neprilysin (NEP), insulin-degrading enzyme (IDE), asparagine endopeptidase (AEP), and ADAM10) is also essential to cure AD and PD. Therefore, numerous biological molecules and chemical agents have been investigated as either inducer or inhibitor against the levels and activities of ADE. Although the side effect of enhancing the activity of ADE could occur, the removal of amyloidogenic proteins could result in a relatively good strategy to treat AD and PD. Furthermore, since the causes of ND are diverse, various multifunctional (multitarget) chemical agents have been designed to control the actions of multiple risk factors of ND, including amyloidogenic proteins, metal ions, and reactive oxygen species. Many of them, however, were invented without considerations of regulating ADE levels and actions. Incorporation of previously created molecules with the chemical agents handling ADE could be a promising way to treat AD and PD. This review introduces the ADE and molecules capable of modulating the activity and expression of ADE.

Anti-Amnesic Effect of Walnut via the Regulation of BBB Function and Neuro-Inflammation in Aβ1-42-Induced Mice

This study was conducted to assess the protective effect of walnut (Juglans regia L.) extract on amyloid beta (Aβ)_1-42-induced institute of cancer research (ICR) mice. By conducting a Y-maze, passive avoidance, and Morris water maze tests with amyloidogenic mice, it was found that walnut extract ameliorated behavioral dysfunction and memory deficit. The walnut extract showed a protective effect on the antioxidant system and cholinergic system by regulating malondialdehyde (MDA) levels, superoxide dismutase (SOD) contents, reduced glutathione (GSH) contents, acetylcholine (ACh) levels, acetylcholinesterase (AChE) activity, and protein expression of AChE and choline acetyltransferase (ChAT). Furthermore, the walnut extract suppressed Aβ-induced abnormality of mitochondrial function by ameliorating reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and ATP contents. Finally, the walnut extract regulated the expression of zonula occludens-1 (ZO-1) and occludin concerned with blood–brain barrier (BBB) function, expression of tumor necrosis factor-alpha (TNF-α), tumor necrosis factor receptor 1 (TNFR1), phosphorylated c-Jun N-terminal kinase (p-JNK), phosphorylated nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor (p-IκB), cyclooxygenase-2 (COX-2), and interleukin 1 beta (IL-1β), related to neuroinflammation and the expression of phosphorylated protein kinase B (p-Akt), caspase-3, hyperphosphorylation of tau (p-tau), and heme oxygenase-1 (HO-1), associated with the Aβ-related Akt pathway.

A novel pectin from Polygala tenuifolia blocks Aβ42 aggregation and production by enhancing insulin-degradation enzyme and neprilysin

More and more evidences show that pectin polysaccharide may have impact on Aβ_42, one important molecule implicated in Alzhemer's disease pathology. We speculate special structural motif of pectin might have better bioactivity on Aβ₄₂. To address this hypothesis, we reported structure and impact of a novel pectin RP02-1 with the molecular weight of 116.0 kDa from roots of Polygala tenuifolia on Aβ₄₂ aggregation and production and the underlying mechanism. Its structure is characterized as a backbone of alternate 1, 2, 4-linked α-Rhap and 1, 4-linked α-GalpA, with branches of terminal (T) -, 1, 3-,1, 4-, 1, 6- and 1, 3, 6-linked β-Galp, T-, 1, 5- and 1, 3, 5-linked α-Araf substituted at C-4 of 1, 2, 4-linked α-Rhap. Bioactivity study shows that this pectin may significantly block the aggregation of Aβ₄₂. We further show that RP02-1 suppresses Aβ₄₂ production with no apparent cytotoxicity in both CHO/APPBACE1 and HEK293-APPsw cells. Mechanism study demonstrates that RP02-1 may enhance the expression of insulin-degradation enzyme (IDE) and neprilysin (NEP), which are the main enzymes involved in Aβ degradation. These results suggest that RP02-1 may be a candidate leading compound for anti-Alzheimer's disease new drug development by attenuating Aβ₄₂ production and inhibiting Aβ₄₂ aggregation.

Glycan Mimetics from Natural Products: New Therapeutic Opportunities for Neurodegenerative Disease

Neurodegenerative diseases (NDs) affect millions of people worldwide. Characterized by the functional loss and death of neurons, NDs lead to symptoms (dementia and seizures) that affect the daily lives of patients. In spite of extensive research into NDs, the number of approved drugs for their treatment remains limited. There is therefore an urgent need to develop new approaches for the prevention and treatment of NDs. Glycans (carbohydrate chains) are ubiquitous, abundant, and structural complex natural biopolymers. Glycans often covalently attach to proteins and lipids to regulate cellular recognition, adhesion, and signaling. The importance of glycans in both the developing and mature nervous system is well characterized. Moreover, glycan dysregulation has been observed in NDs such as Alzheimer's disease (AD), Huntington's disease (HD), Parkinson's disease (PD), multiple sclerosis (MS), and amyotrophic lateral sclerosis (ALS). Therefore, glycans are promising but underexploited therapeutic targets. In this review, we summarize the current understanding of glycans in NDs. We also discuss a number of natural products that functionally mimic glycans to protect neurons, which therefore represent promising new therapeutic approaches for patients with NDs.

Inflammasome-mediated innate immunity in Alzheimer's disease

Historically neurodegenerative diseases, Alzheimer's disease (AD) in particular, have been viewed to be primarily caused and driven by neuronal mechanisms. Very recently, due to experimental, genetic, and epidemiologic evidence, immune mechanisms have entered the central stage and are now believed to contribute significantly to risk, onset, and disease progression of this class of disorders. Although immune activation of microglial cells may over time engage various signal transduction pathways, inflammasome activation, which represents a canonical and initiating pathway, seems to be one of the first responses to extracellular β-amyloid (Aβ) accumulation. Here we review the current understanding of inflammasome activation in AD.-Venegas, C., Heneka, M. T. Inflammasome-mediated innate immunity in Alzheimer's disease.

Crystal structure of peptide-bound neprilysin reveals key binding interactions

Neprilysin (NEP) is a promiscuous zinc metalloprotease with broad substrate specificity and cleaves a remarkable diversity of substrates through endopeptidase action. Two of these - amyloid-β and natriuretic peptides - implicate the enzyme in both Alzheimer's disease and cardiovascular disease, respectively. Here, we report the creation of a catalytically inactive NEP (E584D) to determine the first peptide-bound crystal structure at 2.6 Å resolution. The structure reveals key interactions involved in substrate binding which we have identified to be conserved in other known zinc metalloproteases. In addition, the structure provides evidence for a potential exosite within the central cavity that may play a critical role in substrate positioning. Together, these results contribute to our understanding of the molecular function of NEP.

Alzheimer's disease: pathogenesis, diagnostics, and therapeutics

Currently, 47 million people live with dementia globally, and it is estimated to increase more than threefold (~131 million) by 2050. Alzheimer's disease (AD) is one of the major causative factors to induce progressive dementia. AD is a neurodegenerative disease, and its pathogenesis has been attributed to extracellular aggregates of amyloid β (Aβ) plaques and intracellular neurofibrillary tangles made of hyperphosphorylated τ-protein in cortical and limbic areas of the human brain. It is characterized by memory loss and progressive neurocognitive dysfunction. The anomalous processing of APP by β-secretases and γ-secretases leads to production of Aβ40 and Aβ42 monomers, which further oligomerize and aggregate into senile plaques. The disease also intensifies through infectious agents like HIV. Additionally, during disease pathogenesis, the presence of high concentrations of Aβ peptides in central nervous system initiates microglial infiltration. Upon coming into vicinity of Aβ, microglia get activated, endocytose Aβ, and contribute toward their clearance via TREM2 surface receptors, simultaneously triggering innate immunoresponse against the aggregation. In addition to a detailed report on causative factors leading to AD, the present review also discusses the current state of the art in AD therapeutics and diagnostics, including labeling and imaging techniques employed as contrast agents for better visualization and sensing of the plaques. The review also points to an urgent need for nanotechnology as an efficient therapeutic strategy to increase the bioavailability of drugs in the central nervous system.

A New Perspective in Utilizing MMP-9 as a Therapeutic Target for Alzheimer's Disease and Type 2 Diabetes Mellitus

Matrix metalloprotease 9 (MMP-9) is a 92 kDa type IV collagenase and a member of the family of endopeptidases. MMP-9 is involved in the degradation of extracellular matrix components, tissue remodeling, cellular receptor stripping, and processing of various signaling molecules. In the CNS, the effects of MMP-9 are quite complex, since it exerts beneficial effects including neurogenesis, angiogenesis, myelogenesis, axonal growth, and inhibition of apoptosis, or destructive effects including apoptosis, blood-brain barrier disorder, and demyelination. Likewise, in the periphery, physiological events, as the involvement of MMP-9 in angiogenesis, for instance in wound healing, can be turned into pathological, such as in tumor metastasis, depending on the state of the organism. Alzheimer's disease is a neurodegenerative disorder, characterized by amyloid accumulation and deposition in the brain. Amyloidogenesis, however, also occurs in diseases of the periphery, such as type II diabetes mellitus, where an analogous type of amyloid, is deposited in the pancreas. Interestingly, both diseases exhibit similar pathology and disease progression, with insulin resistance being a major common denominator. Hence, combinatorial strategies searching new or existing molecules to apply for therapeutic use for both diseases are gaining momentum. MMP-9 is extensively studied due to its association with a variety of physiological and pathological processes. Consequently, meticulous design could render MMP-9 into a potential therapeutic target for Alzheimer's disease and type 2 diabetes mellitus; two seemingly unrelated diseases.

Substrate-selective inhibitors that reprogram the activity of insulin-degrading enzyme

Enzymes that act on multiple substrates are common in biology but pose unique challenges as therapeutic targets. The metalloprotease insulin-degrading enzyme (IDE) modulates blood glucose levels by cleaving insulin, a hormone that promotes glucose clearance. However, IDE also degrades glucagon, a hormone that elevates glucose levels and opposes the effect of insulin. IDE inhibitors to treat diabetes therefore should prevent IDE-mediated insulin degradation, but not glucagon degradation, in contrast with traditional modes of enzyme inhibition. Using a high-throughput screen for non-active-site ligands, we discovered potent and highly specific small-molecule inhibitors that alter IDE’s substrate selectivity. X-ray co-crystal structures, including an IDE-ligand-glucagon ternary complex, revealed substrate-dependent interactions that enable these inhibitors to potently block insulin binding while allowing glucagon cleavage, even at saturating inhibitor concentrations. These findings suggest a path for developing IDE-targeting therapeutics, and offer a blueprint for modulating other enzymes in a substrate-selective manner to unlock their therapeutic potential.

Alterations in mitochondria-endoplasmic reticulum connectivity in human brain biopsies from idiopathic normal pressure hydrocephalus patients

Idiopathic normal pressure hydrocephalus (iNPH) is a neuropathology with unknown cause characterised by gait impairment, cognitive decline and ventriculomegaly. These patients often present comorbidity with Alzheimer's disease (AD), including AD pathological hallmarks such as amyloid plaques mainly consisting of amyloid β-peptide and neurofibrillary tangles consisting of hyperphosphorylated tau protein. Even though some of the molecular mechanisms behind AD are well described, little is known about iNPH. Several studies have reported that mitochondria-endoplasmic reticulum contact sites (MERCS) regulate amyloid β-peptide metabolism and conversely that amyloid β-peptide can influence the number of MERCS. MERCS have also been shown to be dysregulated in several neurological pathologies including AD.In this study we have used transmission electron microscopy and show, for the first time, several mitochondria contact sites including MERCS in human brain biopsies. These unique human brain samples were obtained during neurosurgery from 14 patients that suffer from iNPH. Three of these 14 patients presented comorbidities with other dementias: one patient with AD, one with AD and vascular dementia and one patient with Lewy body dementia. Furthermore, we report that the numbers of MERCS are increased in biopsies obtained from patients diagnosed with dementia. Moreover, the presence of both amyloid plaques and neurofibrillary tangles correlates with decreased contact length between endoplasmic reticulum and mitochondria, while amyloid plaques alone do not seem to affect endoplasmic reticulum-mitochondria apposition. Interestingly, we report a significant positive correlation between the number of MERCS and ventricular cerebrospinal fluid amyloid β-peptide levels, as well as with increasing age of iNPH patients.

Anti-amyloidogenic properties of an ethyl acetate fraction from Actinidia arguta in Aβ1-42-induced ICR mice

This study aimed to investigate the ameliorating effect of an ethyl acetate fraction from the fruit Actinidia arguta (EFAA) on amyloid beta (Aβ)-induced neurotoxicity and cognitive deficits in ICR mice. EFAA showed potent protective effects against Aβ-induced neurotoxicity through 2',7'-dichlorofluorescein diacetate (DCF-DA), 2',3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and lactate dehydrogenase (LDH) release into the assay medium. EFAA treatment reduced the intracellular ROS level and lactate dehydrogenase (LDH) release in the mitochondria, and increased cell viability in Aβ-induced neuroblastoma MC-IXC cells. The administration of EFAA significantly attenuated Aβ-induced learning and memory deficits, which were evaluated by Y-maze, passive avoidance, and Morris water maze tests. Furthermore, EFAA showed the ameliorating effect of cholinergic functions by increasing acetylcholine (ACh) levels and decreasing acetylcholinesterase (AChE) activity, and protected antioxidant systems by increasing superoxide dismutase (SOD) and decreasing the oxidized glutathione (GSH)/total GSH and malondialdehyde (MDA) in the brain. Finally, EFAA prevented mitochondrial dysfunction via regulating apoptotic signaling molecules including phosphorylated Akt (p-Akt), phosphorylated tau (p-tau), Bax, and cytochrome c in the brain tissues. Therefore, the present study suggests that EFAA might be a potential source of natural antioxidants with the ability to ameliorate Aβ-induced amnesia.

Exosomes Isolated From Human Umbilical Cord Mesenchymal Stem Cells Alleviate Neuroinflammation and Reduce Amyloid-Beta Deposition by Modulating Microglial Activation in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by excessive accumulation of the amyloid-β peptide (Aβ) in the brain, which has been considered to mediate the neuroinflammation process. Microglial activation is the main component of neuroimmunoregulation. In recent years, exosomes isolated from human umbilical cord mesenchymal stem cells (hucMSC-exosomes) have been demonstrated to mimic the therapeutic effects of hucMSCs in many inflammation-related diseases. In this study, exosomes from the supernatant of hucMSCs were injected into AD mouse models. We observed that hucMSC-exosomes injection could repair cognitive disfunctions and help to clear Aβ deposition in these mice. Moreover, we found that hucMSC-exosomes injection could modulate the activation of microglia in brains of the mice to alleviated neuroinflammation. The levels of pro-inflammatory cytokines in peripheral blood and brains of mice were increased and the levels of anti-inflammatory cytokines were decreased. We also treated BV2 cells with hucMSC-exosomes in culture medium. HucMSC-exosomes also had inflammatory regulating effects to alternatively activate microglia and modulate the levels of inflammatory cytokines in vitro.

Catalytic Mechanism of Amyloid-β Peptide Degradation by Insulin Degrading Enzyme: Insights from Quantum Mechanics and Molecular Mechanics Style Møller-Plesset Second Order Perturbation Theory Calculation

Insulin degrading enzyme (IDE), a metalloprotease that degrades amyloid-β (Aβ) peptides and insulin, is associated with Alzheimer's disease and diabetes. The mechanism of IDE catalyzed degrading of Aβ peptides, which is of fundamental importance in the design of therapeutic methods for Alzheimer's disease, has not been fully understood. In this work, combined quantum mechanics and molecular mechanics (QM/MM) style Møller-Plesset second order perturbation theory (MP2) geometry optimization calculations are performed to investigate the catalytic mechanism of the Aβ40 Phe19-Phe20 peptide bond cleavage by human IDE. The analyses using QM/MM MP2 optimization suggest that a neutral water molecule is at the active site of the enzyme-substrate (ES) complex. The water molecule is in hydrogen bonding with the nearby anionic Glu111 of IDE but not directly bound to the catalytic Zn ion. This is confirmed by QM/MM DFTB3 molecular dynamics simulation. Our studies also reveal that the hydrolysis of the Aβ40 Phe19-Phe20 peptide bond by IDE consists of four key steps. The neutral water is first activated by moving toward and binding to the Zn ion. A gem-diol intermediate is then formed by the activated neutral water molecule attacking the C atom of the Phe19-Phe20 peptide bond. The next is the protonation of the N atom of Phe19-Phe20 peptide bond to form an intermediate with an elongated C-N bond. The final step is the breaking of the Phe19-Phe20 C-N bond. The final step is the rate-determining step with a calculated Gibbs free energy of activation of 17.34 kcal/mol, in good agreement with the experimental value 16.7 kcal/mol. This mechanism provides the basis for the design of biochemical methods to modulate the activity of IDE in humans.