Abnormal Expression and Distribution of MMP2 at Initial Stages of Alzheimer’s Disease-Related Pathology

Tau truncation in the pathogenesis of Alzheimer's disease: a narrative review

ABSTRACT

Alzheimer's disease is characterized by two major neuropathological hallmarks-the extracellular β-amyloid plaques and intracellular neurofibrillary tangles consisting of aggregated and hyperphosphorylated Tau protein. Recent studies suggest that dysregulation of the microtubule-associated protein Tau, especially specific proteolysis, could be a driving force for Alzheimer's disease neurodegeneration. Tau physiologically promotes the assembly and stabilization of microtubules, whereas specific truncated fragments are sufficient to induce abnormal hyperphosphorylation and aggregate into toxic oligomers, resulting in them gaining prion-like characteristics. In addition, Tau truncations cause extensive impairments to neural and glial cell functions and animal cognition and behavior in a fragment-dependent manner. This review summarizes over 60 proteolytic cleavage sites and their corresponding truncated fragments, investigates the role of specific truncations in physiological and pathological states of Alzheimer's disease, and summarizes the latest applications of strategies targeting Tau fragments in the diagnosis and treatment of Alzheimer's disease.

Developing theragnostics for Alzheimer's disease: Insights from cancer treatment

The prevalence of Alzheimer's disease (AD) and its associated economic and societal burdens are on the rise, but there are no curative treatments for AD. Interestingly, this neurodegenerative disease shares several biological and pathophysiological features with cancer, including cell-cycle dysregulation, angiogenesis, mitochondrial dysfunction, protein misfolding, and DNA damage. However, the genetic factors contributing to the overlap in biological processes between cancer and AD have not been actively studied. In this review, we discuss the shared biological features of cancer and AD, the molecular targets of anticancer drugs, and therapeutic approaches. First, we outline the common biological features of cancer and AD. Second, we describe several anticancer drugs, their molecular targets, and their effects on AD pathology. Finally, we discuss how protein-protein interactions (PPIs), receptor inhibition, immunotherapy, and gene therapy can be exploited for the cure and management of both cancer and AD. Collectively, this review provides insights for the development of AD theragnostics based on cancer drugs and molecular targets.

Screening of Active Substances Regulating Alzheimer's Disease in Ginger and Visualization of the Effectiveness on 6-Gingerol Pathway Targets

Ginger has been reported to potentially treat Alzheimer's disease (AD), but the specific compounds responsible for this biological function and their mechanisms are still unknown. In this study, a combination of network pharmacology, molecular docking, and dynamic simulation technology was used to screen active substances that regulate AD and explore their mechanisms. The TCMSP, GeneCards, OMIM, and DisGeNET databases were utilized to obtain 95 cross-targets related to ginger's active ingredients and AD as key targets. A functional enrichment analysis revealed that the pathways in which ginger's active substances may be involved in regulating AD include response to exogenous stimuli, response to oxidative stress, response to toxic substances, and lipid metabolism, among others. Furthermore, a drug-active ingredient-key target interaction network diagram was constructed, highlighting that 6-Gingerol is associated with 16 key targets. Additionally, a protein-protein interaction (PPI) network was mapped for the key targets, and HUB genes (ALB, ACTB, GAPDH, CASP3, and CAT) were identified. Based on the results of network pharmacology and cell experiments, 6-Gingerol was selected as the active ingredient for further investigation. Molecular docking was performed between 6-Gingerol and its 16 key targets, and the top three proteins with the strongest binding affinities (ACHE, MMP2, and PTGS2) were chosen for molecular dynamics analysis together with the CASP3 protein as the HUB gene. The findings indicate that 6-Gingerol exhibits strong binding ability to these disease targets, suggesting its potential role in regulating AD at the molecular level, as well as in abnormal cholinesterase metabolism and cell apoptosis, among other related regulatory pathways. These results provide a solid theoretical foundation for future in vitro experiments using actual cells and animal experiments to further investigate the application of 6-Gingerol.

Histone acetylation in an Alzheimer's disease cell model promotes homeostatic amyloid-reducing pathways

Alzheimer's Disease (AD) is a disorder characterized by cognitive decline, neurodegeneration, and accumulation of amyloid plaques and tau neurofibrillary tangles in the brain. Dysregulation of epigenetic histone modifications may lead to expression of transcriptional programs that play a role either in protecting against disease genesis or in worsening of disease pathology. One such histone modification, acetylation of histone H3 lysine residue 27 (H3K27ac), is primarily localized to genomic enhancer regions and promotes active gene transcription. We previously discovered H3K27ac to be more abundant in AD patient brain tissue compared to the brains of age-matched non-demented controls. In this study, we use iPSC-neurons derived from familial AD patients with an amyloid precursor protein (APP) duplication (APPDup neurons) as a model to study the functional effect of lowering CBP/P300 enzymes that catalyze H3K27ac. We found that homeostatic amyloid-reducing genes were upregulated in the APPDup neurons compared to non-demented controls. We lowered CBP/P300 to reduce H3K27ac, which led to decreased expression of numerous of these homeostatic amyloid-reducing genes, along with increased extracellular secretion of a toxic amyloid-β species, Aβ(1-42). Our findings suggest that epigenomic histone acetylation, including H3K27ac, drives expression of compensatory genetic programs in response to AD-associated insults, specifically those resulting from APP duplication, and thus may play a role in mitigating AD pathology in neurons.

Vitamin A, D, E, and K as Matrix Metalloproteinase-2/9 Regulators That Affect Expression and Enzymatic Activity

Fat-soluble vitamins (vitamin A, D, E, and K) assume a pivotal role in maintaining human homeostasis by virtue of their enzymatic functions. The daily inclusion of these vitamins is imperative to the upkeep of various physiological processes including vision, bone health, immunity, and protection against oxidative stress. Current research highlights fat-soluble vitamins as potential therapeutics for human diseases, especially cancer. Fat-soluble vitamins exert their therapeutic effects through multiple pathways, including regulation of matrix metalloproteinases' (MMPs) expression and enzymatic activity. As MMPs have been reported to be involved in the pathology of various diseases, such as cancers, cardiovascular diseases, and neurological disorders, regulating the expression and/or activity of MMPs could be considered as a potent therapeutic strategy. Here, we summarize the properties of fat-soluble vitamins and their potential as promising candidates capable of effectively modulating MMPs through multiple pathways to treat human diseases.

Sex-specific associations of matrix metalloproteinases in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) can be characterised in vivo by biomarkers reflecting amyloid-β (Aβ) and tau pathology. However, there is a need for biomarkers reflecting additional pathological pathways. Matrix metalloproteinases (MMPs) have recently been highlighted as candidate biomarkers for sex-specific mechanisms and progression in AD.

METHODS

In this cross-sectional study, we investigated nine MMPs and four tissue inhibitors of metalloproteinases (TIMPs) in the cerebrospinal fluid of 256 memory clinic patients with mild cognitive impairment or dementia due to AD and 100 cognitively unimpaired age-matched controls. We studied group differences in MMP/TIMP levels and examined the associations with established markers of Aβ and tau pathology as well as disease progression. Further, we studied sex-specific interactions.

RESULTS

MMP-10 and TIMP-2 levels differed significantly between the memory clinic patients and the cognitively unimpaired controls. Furthermore, MMP- and TIMP-levels were generally strongly associated with tau biomarkers, whereas only MMP-3 and TIMP-4 were associated with Aβ biomarkers; these associations were sex-specific. In terms of progression, we found a trend towards higher MMP-10 at baseline predicting more cognitive and functional decline over time exclusively in women.

CONCLUSION

Our results support the use of MMPs/TIMPs as markers of sex differences and progression in AD. Our findings show sex-specific effects of MMP-3 and TIMP-4 on amyloid pathology. Further, this study highlights that the sex-specific effects of MMP-10 on cognitive and functional decline should be studied further if MMP-10 is to be used as a prognostic biomarker for AD.

Coupling hCG-based protease sensors with a commercial pregnancy test strip for simple analyses of protease activities

Proteases play an essential role in many cellular processes, and consequently, abnormalities in their activities are related to various diseases. Methods have been developed to measure the activity of these enzymes, but most involve sophisticated instruments or complicated procedures, which hampers the development of a point-of-care test (POCT). Here, we propose a strategy for developing simple and sensitive methods to analyze protease activity using commercial pregnancy test strips that detect human chorionic gonadotropin (hCG). hCG was engineered to have site-specific conjugated biotin and a peptide sequence, which can be cleaved by a target protease, between hCG and biotin. hCG protein was immobilized on streptavidin-coated beads, resulting in a protease sensor. The hCG-immobilized beads were too large to flow through the membrane of the hCG test strip and yielded only one band in the control line. When the peptide linker was hydrolyzed by the target protease, hCG was released from the beads, and the signal appeared in both the control and test lines. Three protease sensors for matrix metalloproteinase-2, caspase-3, and thrombin were constructed by replacing the protease-cleavable peptide linker. The combination of the protease sensors and a commercial pregnancy strip enabled the specific detection of each protease in the picomolar range, with a 30-min incubation of the hCG-immobilized beads and samples. The modular design of the protease sensor and simple assay procedure will facilitate the development of POCTs for various protease disease markers.

MMP2 rs243866 and rs2285053 Polymorphisms and Alzheimer’s Disease Risk in Slovak Caucasian Population

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder characterised by progressive loss of memory. In the AD brain, matrix metalloproteinases (MMPs) are involved in the disruption of the blood-brain barrier resulting in a neuroinflammatory response. The objective of our investigation was to assess the association of MMP2 rs243866 and rs2285053 polymorphisms with susceptibility to AD, to assess the interaction of MMP2 variants with APOE ε4 risk allele, and to evaluate their influence on the age at disease onset and MoCA score. A total of 215 late-onset AD patients and 373 control subjects from Slovakia were genotyped for MMP2 rs243866 and rs2285053 polymorphisms. The MMP2 association with AD risk and clinical parameters was evaluated by logistic and linear regression analyses. No statistically significant differences in either MMP2 rs243866 and rs2285053 allele or genotype frequencies between AD patients and the control group have been observed (p > 0.05). However, the correlation with clinical findings revealed a higher age at disease onset in MMP2 rs243866 GG carriers in the dominant model as compared to other MMP2 genotype carriers (p = 0.024). Our results suggest that MMP2 rs243866 promoter polymorphism may have an impact on the age at AD onset in the patients.

Metal Complexes as Promising Matrix Metalloproteinases Regulators

Nowadays, cancers and dementia, such as Alzheimer's disease, are the most fatal causes of death. Many studies tried to understand the pathogenesis of those diseases clearly and develop a promising way to treat the diseases. Matrix metalloproteinases (MMPs) have been reported to be involved in the pathology of cancers and AD through tumor cell movement and amyloid degradation. Therefore, control of the levels and actions of MMPs, especially MMP-2 and MMP-9, is necessary to care for and/or cure cancer and AD. Various molecules have been examined for their potential application as regulators of MMPs expression and activity. Among the molecules, multiple metal complexes have shown advantages, including simple synthesis, less toxicity and specificity toward MMPs in cancer cells or in the brain. In this review, we summarize the recent studies and knowledge of metal complexes (e.g., Pt-, Ru-, Au-, Fe-, Cu-, Ni-, Zn-, and Sn-complexes) targeting MMPs and their potentials for treating and/or caring the most fatal human diseases, cancers and AD.

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.

Plasma Exo-miRNAs Correlated with AD-Related Factors of Chinese Individuals Involved in Aβ Accumulation and Cognition Decline

Numerous studies have investigated the risk factors of Alzheimer’s disease (AD); however, AD-risk factors related miRNAs were rarely reported. In this study, AD-risk factor related miRNAs of 105 Chinese individuals (45 AD patients and 60 cognitively normal controls) were investigated. The results showed that Hsa-miR-185-5p, Hsa-miR-20a-5p, and Hsa-miR-497-5p were related to AD and education, Hsa-miR-185-5p, Hsa-miR-181c-5p, Hsa-miR-664a-3p, Hsa-miR-27a-3p, Hsa-miR-451a, and Hsa-miR-320a were related to AD and depression. Target prediction of above miRNAs showed that these miRNAs were involved in the generation and clearance of amyloid-beta (Aβ), important molecules related to cognition, and disease-activated microglia response to AD. It is worth noting that Hsa-miR-185-5p was related to both education and depression, whose decreased expression pattern in AD patients was alleviated by education and enhanced by depression, and participates in Aβ generation and accumulation. Our results indicated that certain education and depression factors can contribute to AD progression by modulating miRNA expression, implying that preventive interventions might alter AD progression in Chinese patients.

Clinical Features and Potential Mechanisms Relating Neuropathological Biomarkers and Blood-Brain Barrier in Patients With Alzheimer’s Disease and Hearing Loss

Background

The aim of this study was to explore clinical features and potential mechanisms relating neuropathological biomarkers and blood-brain barrier (BBB) in Alzheimer’s disease (AD) and hearing loss (HL).

Materials and Methods

A total of 65 patients with AD were recruited and auditory function was assessed by threshold of pure tone audiometry (PTA). Patients were divided into AD with HL (AD-HL) and AD with no HL (AD-nHL) groups based on the standard of World Health Organization. Clinical symptoms were assessed by multiple rating scales. The levels of neuropathological biomarkers of β amyloid1-42 (Aβ_1–42) and multiple phosphorylated tau (P-tau), and BBB factors of matrix metalloproteinases (MMPs), receptor of advanced glycation end products, glial fibrillary acidic protein, and low-density lipoprotein receptor related protein 1 were measured.

Results

(1) Compared with AD-nHL group, AD-HL group had significantly impaired overall cognitive function and cognitive domains of memory, language, attention, execution, and activities of daily living (ADL) reflected by the scores of rating scales (P < 0.05). PTA threshold was significantly correlated with the impairments of overall cognitive function and cognitive domains of memory and language, and ADL in patients with AD (P < 0.05). (2) P-tau (S199) level was significantly increased in CSF from AD-HL group (P < 0.05), and was significantly and positively correlated with PTA threshold in patients with AD. (3) MMP-3 level was significantly elevated in CSF from AD-HL group (P < 0.05), and was significantly and positively correlated with PTA threshold in patients with AD (P < 0.05). (4) In AD-HL group, P-tau (S199) level was significantly and positively correlated with the levels of MMP-2 and MMP-3 in CSF (P < 0.05).

Conclusion

AD-HL patients have severely compromised overall cognitive function, multiple cognitive domains, and ADL. The potential mechanisms of AD-HL involve elevations of AD neuropathological biomarker of P-tau (S199) and BBB factor of MMP-3, and close correlations between P-tau (S199) and MMP-2/MMP-3 in CSF. Findings from this investigation highly suggest significance of early evaluation of HL for delaying AD progression, and indicate new directions of drug development by inhibiting neuropathological biomarkers of AD and protecting BBB.

The Role of Extracellular Matrix Components in the Spreading of Pathological Protein Aggregates

Several neurodegenerative diseases are characterized by the accumulation of aggregated misfolded proteins. These pathological agents have been suggested to propagate in the brain via mechanisms similar to that observed for the prion protein, where a misfolded variant is transferred from an affected brain region to a healthy one, thereby inducing the misfolding and/or aggregation of correctly folded copies. This process has been characterized for several proteins, such as α-synuclein, tau, amyloid beta (Aβ) and less extensively for huntingtin and TDP-43. α-synuclein, tau, TDP-43 and huntingtin are intracellular proteins, and their aggregates are located in the cytosol or nucleus of neurons. They have been shown to spread between cells and this event occurs, at least partially, via secretion of these protein aggregates in the extracellular space followed by re-uptake. Conversely, Aβ aggregates are found mainly extracellularly, and their spreading occurs in the extracellular space between brain regions. Due to the inherent nature of their spreading modalities, these proteins are exposed to components of the extracellular matrix (ECM), including glycans, proteases and core matrix proteins. These ECM components can interact with or process pathological misfolded proteins, potentially changing their properties and thus regulating their spreading capabilities. Here, we present an overview of the documented roles of ECM components in the spreading of pathological protein aggregates in neurodegenerative diseases with the objective of identifying the current gaps in knowledge and stimulating further research in the field. This could potentially lead to the identification of druggable targets to slow down the spreading and/or progression of these pathologies.

Astrocytes Derived from Familial and Sporadic Alzheimer's Disease iPSCs Show Altered Calcium Signaling and Respond Differently to Misfolded Protein Tau

Astrocytes regulate important functions in the brain, and their dysregulation has been linked to the etiology of neurodegenerative diseases, such as Alzheimer’s disease (AD). The role of astroglia in human AD remains enigmatic, owing to the limitations of animal models, which, while recreating some pathological aspects of the disease, do not fully mirror its course. In addition, the recognition of major structural and functional differences between human and mouse astrocytes has also prompted research into human glial cells. In the current study, astrocytes were generated using human iPSCs from patients with sporadic Alzheimer’s disease (sAD), familial Alzheimer’s disease (fAD) and non-demented controls (NDC). All clones gained astrocyte-specific morphological and proteomic characteristics upon in vitro differentiation, without considerable inter-clonal variances. In comparison to NDC, AD astrocytes displayed aberrant calcium dynamics in response to glutamate. When exposed to monomeric and aggregated tau, AD astrocytes demonstrated hypertrophy and elevated GFAP expression, differential expression of select signaling and receptor proteins, and the enhanced production of metalloproteinases (MMPs). Moreover, astrocytic secretomes were able to degrade tau in both monomeric and pathologically aggregated forms, which was mediated by MMP-2 and -9. The capacity to neutralize tau varied considerably between clones, with fAD astrocytes having the lowest degradability relative to sAD and healthy astrocytes. Importantly, when compared to aggregated tau alone, astrocytic secretome pretreatment of tau differentially reduced its detrimental effects on neurons. Our results show crucial differences in sporadic and familial AD astrocytes and suggests that these cells may play distinctive roles in the pathogenesis of early and late onset Alzheimer’s disease.

Alzheimer’s Disease: An Update and Insights Into Pathophysiology

Alzheimer’s disease (AD) is an irreversible brain disorder associated with slow, progressive loss of brain functions mostly in older people. The disease processes start years before the symptoms are manifested at which point most therapies may not be as effective. In the hippocampus, the key proteins involved in the JAK2/STAT3 signaling pathway, such as p-JAK2-Tyr1007 and p-STAT3-Tyr705 were found to be elevated in various models of AD. In addition to neurons, glial cells such as astrocytes also play a crucial role in the progression of AD. Without having a significant effect on tau and amyloid pathologies, the JAK2/STAT3 pathway in reactive astrocytes exhibits a behavioral impact in the experimental models of AD. Cholinergic atrophy in AD has been traced to a trophic failure in the NGF metabolic pathway, which is essential for the survival and maintenance of basal forebrain cholinergic neurons (BFCN). In AD, there is an alteration in the conversion of the proNGF to mature NGF (mNGF), in addition to an increase in degradation of the biologically active mNGF. Thus, the application of exogenous mNGF in experimental studies was shown to improve the recovery of atrophic BFCN. Furthermore, it is now coming to light that the FGF7/FGFR2/PI3K/Akt signaling pathway mediated by microRNA-107 is also involved in AD pathogenesis. Vascular dysfunction has long been associated with cognitive decline and increased risk of AD. Vascular risk factors are associated with higher tau and cerebral beta-amyloid (Aβ) burden, while synergistically acting with Aβ to induce cognitive decline. The apolipoprotein E4 polymorphism is not just one of the vascular risk factors, but also the most prevalent genetic risk factor of AD. More recently, the research focus on AD shifted toward metabolisms of various neurotransmitters, major and minor nutrients, thus giving rise to metabolomics, the most important “omics” tool for the diagnosis and prognosis of neurodegenerative diseases based on an individual’s metabolome. This review will therefore proffer a better understanding of novel signaling pathways associated with neural and glial mechanisms involved in AD, elaborate potential links between vascular dysfunction and AD, and recent developments in “omics”-based biomarkers in AD.

Platelet Behavior Contributes to Neuropathologies: A Focus on Alzheimer's and Parkinson's Disease

The functions of platelets are broad. Platelets function in hemostasis and thrombosis, inflammation and immune responses, vascular regulation, and host defense against invading pathogens, among others. These actions are achieved through the release of a wide set of coagulative, vascular, inflammatory, and other factors as well as diverse cell surface receptors involved in the same activities. As active participants in these physiological processes, platelets become involved in signaling pathways and pathological reactions that contribute to diseases that are defined by inflammation (including by pathogen-derived stimuli), vascular dysfunction, and coagulation. These diseases include Alzheimer's and Parkinson's disease, the two most common neurodegenerative diseases. Despite their unique pathological and clinical features, significant shared pathological processes exist between these two conditions, particularly relating to a central inflammatory mechanism involving both neuroinflammation and inflammation in the systemic environment, but also neurovascular dysfunction and coagulopathy, processes which also share initiation factors and receptors. This triad of dysfunction-(neuro)inflammation, neurovascular dysfunction, and hypercoagulation-illustrates the important roles platelets play in neuropathology. Although some mechanisms are understudied in Alzheimer's and Parkinson's disease, a strong case can be made for the relevance of platelets in neurodegeneration-related processes.

Potential neurotoxic activity of diverse molecules released by microglia

Microglia are the professional immune cells of the brain, which support numerous physiological processes. One of the defensive functions provided by microglia involves secretion of cytotoxins aimed at destroying invading pathogens. It is also recognized that the adverse activation of microglia in diseased brains may lead to secretion of cytotoxic molecules, which could be damaging to the surrounding cells, including neurons. Several of these toxins, such as reactive oxygen and nitrogen species, L-glutamate, and quinolinic acid, are widely recognized and well-studied. This review is focused on a structurally diverse group of less-established microglia neurotoxins, which were selected by applying the two criteria that these molecules 1) can be released by microglia, and 2) have the potential to be directly harmful to neurons. The following 11 molecules are discussed in detail: amyloid beta peptides (Aβ); cathepsin (Cat)B and CatD; C-X-C motif chemokine ligand (CXCL)10 and CXCL12 (5-67); high mobility group box (HMGB)1; lymphotoxin (LT)-α; matrix metalloproteinase (MMP)-2 and MMP-9; platelet-activating factor (PAF); and prolyl endopeptidase (PEP). Molecular mechanisms of their release by microglia and neurotoxicity, as well as available evidence implicating their involvement in human neuropathologies are summarized. Further studies on several of the above molecules are warranted to confirm either their microglial origin in the brain or direct neurotoxic effects. In addition, investigations into the differential secretion patterns of neurotoxins by microglia in response to diverse stimuli are required. This research could identify novel therapeutic targets for neurological disorders involving adverse microglial activation.

Analysis of the Relationship Between Metalloprotease-9 and Tau Protein in Alzheimer's Disease

BACKGROUND

Neurofibrillary tangles (NFTs) and amyloid plaques are the neuropathological hallmarks in brains with Alzheimer's disease (AD). Post-translational modifications of tau, such as phosphorylation and truncation, have been proposed as initiators in the assembly of the abnormal paired helical filaments that constitute the NFTs. Neurons and NFTs are sites of matrix metalloproteinases (MMPs).

OBJECTIVE

The aim of this study was to analyze the relationship of MMP-9 and tau protein in brain samples with AD.

METHODS

This study was performed on brain tissue samples from patients with early, moderate, and late AD. MMPs and tau levels were analyzed by western blot and gelatin-substrate zymography. Immunofluorescence techniques and confocal microscopy were used to analyze the presence of both proteins in NFTs. Further, molecular dynamics simulations (MDS) and protein-protein docking were conducted to predict interaction between MMP-9 and tau protein.

RESULTS

MMP-9 expression was greatest in moderate and late AD, whereas MMP-2 expression was only increased in late-stage AD. Interestingly, confocal microscopy revealed NFTs in which there was co-localization of MMP-9 and tau protein. MDS and protein-protein docking predictions indicate that a high-affinity complex can be formed between MMP-9 and full-length tau protein.

CONCLUSION

These observations provide preliminary evidence of an interaction between these two proteins. Post-translational modifications of tau protein, such as C-terminal truncation or phosphorylation of amino acid residues in the MMP-9 recognition site and conformational changes in the protein, such as folding of the N-terminal sequence over the three-repeat domain, could preclude the interaction between MMP-9 and tau protein during stages of NFT development.

The Causal Role of Lipoxidative Damage in Mitochondrial Bioenergetic Dysfunction Linked to Alzheimer's Disease Pathology

Current shreds of evidence point to the entorhinal cortex (EC) as the origin of the Alzheimer’s disease (AD) pathology in the cerebrum. Compared with other cortical areas, the neurons from this brain region possess an inherent selective vulnerability derived from particular oxidative stress conditions that favor increased mitochondrial molecular damage with early bioenergetic involvement. This alteration of energy metabolism is the starting point for subsequent changes in a multitude of cell mechanisms, leading to neuronal dysfunction and, ultimately, cell death. These events are induced by changes that come with age, creating the substrate for the alteration of several neuronal pathways that will evolve toward neurodegeneration and, consequently, the development of AD pathology. In this context, the present review will focus on description of the biological mechanisms that confer vulnerability specifically to neurons of the entorhinal cortex, the changes induced by the aging process in this brain region, and the alterations at the mitochondrial level as the earliest mechanism for the development of AD pathology. Current findings allow us to propose the existence of an altered allostatic mechanism at the entorhinal cortex whose core is made up of mitochondrial oxidative stress, lipid metabolism, and energy production, and which, in a positive loop, evolves to neurodegeneration, laying the basis for the onset and progression of AD pathology.

Sulfur-containing therapeutics in the treatment of Alzheimer's disease

Sulfur is widely existent in natural products and synthetic organic compounds as organosulfur, which are often associated with a multitude of biological activities. OBenzothiazole, in which benzene ring is fused to the 4,5-positions of the thiazolerganosulfur compounds continue to garner increasing amounts of attention in the field of medicinal chemistry, especially in the development of therapeutic agents for Alzheimer's disease (AD). AD is a fatal neurodegenerative disease and the primary cause of age-related dementia posing severe societal and economic burdens. Unfortunately, there is no cure for AD. A lot of research has been conducted on sulfur-containing compounds in the context of AD due to their innate antioxidant potential and some are currently being evaluated in clinical trials. In this review, we have described emerging trends in the field, particularly the concept of multi-targeting and formulation of disease-modifying strategies. SAR, pharmacological targets, in vitro/vivo ADMET, efficacy in AD animal models, and applications in clinical trials of such sulfur compounds have also been discussed. This article provides a comprehensive review of organosulfur-based AD therapeutic agents and provides insights into their future development.

Natural Marine and Terrestrial Compounds as Modulators of Matrix Metalloproteinases-2 (MMP-2) and MMP-9 in Alzheimer's Disease

Several studies have reported neuroprotective effects by natural products. A wide range of natural compounds have been investigated, and some of these may play a beneficial role in Alzheimer's disease (AD) progression. Matrix metalloproteinases (MMPs), a family of zinc-dependent endopeptidases, have been implicated in AD. In particular, MMP-2 and MMP-9 are able to trigger several neuroinflammatory and neurodegenerative pathways. In this review, we summarize and discuss existing literature on natural marine and terrestrial compounds, as well as their ability to modulate MMP-2 and MMP-9, and we evaluate their potential as therapeutic compounds for neurodegenerative and neuroinflammatory diseases, with a focus on Alzheimer's disease.

Matrix Metalloproteinases as New Targets in Alzheimer's Disease: Opportunities and Challenges

Although matrix metalloproteinases (MMPs) are implicated in the regulation of numerous physiological processes, evidence of their pathological roles have also been obtained in the last decades, making MMPs attractive therapeutic targets for several diseases. Recent discoveries of their involvement in central nervous system (CNS) disorders, and in particular in Alzheimer's disease (AD), have paved the way to consider MMP modulators as promising therapeutic strategies. Over the past few decades, diverse approaches have been undertaken in the design of therapeutic agents targeting MMPs for various purposes, leading, more recently, to encouraging developments. In this article, we will present recent examples of inhibitors ranging from small molecules and peptidomimetics to biologics. We will also discuss the scientific knowledge that has led to the development of emerging tools and techniques to overcome the challenges of selective MMP inhibition.

Metalloproteinases and their tissue inhibitors in Alzheimer's disease and other neurodegenerative disorders

As life expectancy increases worldwide, age-related neurodegenerative diseases will increase in parallel. The lack of effective treatment strategies may soon lead to an unprecedented health, social and economic crisis. Any attempt to halt the progression of these diseases requires a thorough knowledge of the pathophysiological mechanisms involved to facilitate the identification of new targets and the application of innovative therapeutic strategies. The metzincin superfamily of metalloproteinases includes matrix metalloproteinases (MMP), a disintegrin and metalloproteinase (ADAM) and ADAM with thrombospondin motifs (ADAMTS). These multigenic and multifunctional proteinase families regulate the functions of an increasing number of signalling and scaffolding molecules involved in neuroinflammation, blood-brain barrier disruption, protein misfolding, synaptic dysfunction or neuronal death. Metalloproteinases and their physiological inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), are therefore, at the crossroads of molecular and cellular mechanisms that support neurodegenerative processes, and emerge as potential new therapeutic targets. We provide an overview of current knowledge on the role and regulation of metalloproteinases and TIMPs in four major neurodegenerative diseases: Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and Huntington's disease.

Clearance of cerebral Aβ in Alzheimer's disease: reassessing the role of microglia and monocytes

Deficiency in cerebral amyloid β-protein (Aβ) clearance is implicated in the pathogenesis of the common late-onset forms of Alzheimer’s disease (AD). Accumulation of misfolded Aβ in the brain is believed to be a net result of imbalance between its production and removal. This in turn may trigger neuroinflammation, progressive synaptic loss, and ultimately cognitive decline. Clearance of cerebral Aβ is a complex process mediated by various systems and cell types, including vascular transport across the blood–brain barrier, glymphatic drainage, and engulfment and degradation by resident microglia and infiltrating innate immune cells. Recent studies have highlighted a new, unexpected role for peripheral monocytes and macrophages in restricting cerebral Aβ fibrils, and possibly soluble oligomers. In AD transgenic (ADtg) mice, monocyte ablation or inhibition of their migration into the brain exacerbated Aβ pathology, while blood enrichment with monocytes and their increased recruitment to plaque lesion sites greatly diminished Aβ burden. Profound neuroprotective effects in ADtg mice were further achieved through increased cerebral recruitment of myelomonocytes overexpressing Aβ-degrading enzymes. This review summarizes the literature on cellular and molecular mechanisms of cerebral Aβ clearance with an emphasis on the role of peripheral monocytes and macrophages in Aβ removal.