Neuroprotective role of MMP-9 overexpression in the brain of Alzheimer's 5xFAD mice

Behaviour Hallmarks in Alzheimer's Disease 5xFAD Mouse Model

The 5xFAD transgenic mouse model widely used in Alzheimer's disease (AD) research recapitulates many AD-related phenotypes with a relatively early onset and aggressive age-dependent progression. Besides developing amyloid peptide deposits alongside neuroinflammation by the age of 2 months, as well as exhibiting neuronal decline by the age of 4 months that intensifies by the age of 9 months, these mice manifest a broad spectrum of behavioural impairments. In this review, we present the extensive repertoire of behavioural dysfunctions in 5xFAD mice, organised into four categories: motor skills, sensory function, learning and memory abilities, and neuropsychiatric-like symptoms. The motor problems, associated with agility and reflex movements, as well as balance and coordination, and skeletal muscle function, typically arise by the time mice reach 9 months of age. The sensory function (such as taste, smell, hearing, and vision) starts to deteriorate when amyloid peptide buildups and neuroinflammation spread into related anatomical structures. The cognitive functions, encompassing learning and memory abilities, such as visual recognition, associative, spatial working, reference learning, and memory show signs of decline from 4 to 6 months of age. Concerning neuropsychiatric-like symptoms, comprising apathy, anxiety and depression, and the willingness for exploratory behaviour, it is believed that motivational changes emerge by approximately 6 months of age. Unfortunately, numerous studies from different laboratories are often contradictory on the conclusions drawn and the identification of onset age, making preclinical studies in rodent models not easily translatable to humans. This variability is likely due to a range of factors associated with animals themselves, housing and husbandry conditions, and experimental settings. In the forthcoming studies, greater clarity in experimental details when conducting behavioural testing in 5xFAD transgenic mice could minimise the inconsistencies and could ensure the reliability and the reproducibility of the results.

Single cell RNA sequencing reveals immunomodulatory effects of stem cell factor and granulocyte colony-stimulating factor treatment in the brains of aged APP/PS1 mice

Alzheimers disease leads to progressive neurodegeneration and dementia. Alzheimers disease primarily affects older adults with neuropathological changes including amyloid beta deposition, neuroinflammation, and neurodegeneration. We have previously demonstrated that systemic treatment with combined stem cell factor, SCF, and granulocyte colony stimulating factor, GCSF, reduces amyloid beta load, increases amyloid beta uptake by activated microglia and macrophages, reduces neuroinflammation, and restores dendrites and synapses in the brains of aged APP-PS1 mice. However, the mechanisms underlying SCF-GCSF-enhanced brain repair in aged APP-PS1 mice remain unclear. This study used a transcriptomic approach to identify potential mechanisms by which SCF-GCSF treatment modulates microglia and peripheral myeloid cells to mitigate Alzheimers disease pathology in the aged brain. After injections of SCF-GCSF for 5 consecutive days, single cell RNA sequencing was performed on CD11b positive cells isolated from the brains of 28-month-old APP-PS1 mice. The vast majority of cell clusters aligned with transcriptional profiles of microglia in various activation states. However, SCF-GCSF treatment dramatically increased a cell population showing upregulation of marker genes related to peripheral myeloid cells. Flow cytometry data also revealed an SCF-GCSF-induced increase of cerebral CD45high-CD11b positive active phagocytes. SCF-GCSF treatment robustly increased the transcription of genes implicated in immune cell activation, including gene sets that regulate inflammatory processes and cell migration. Expression of S100a8 and S100a9 were robustly enhanced following SCF-GCSF treatment in all CD11b positive cell clusters. Moreover, the topmost genes differentially expressed with SCF-GCSF treatment were largely upregulated in S100a8-S100a9 positive cells, suggesting a well-conserved transcriptional profile related to SCF-GCSF treatment in resident and peripherally derived CD11b positive immune cells. This S100a8-S100a9-associated transcriptional profile contained notable genes related to proinflammatory and antiinflammatory responses, neuroprotection, and amyloid beta plaque inhibition or clearance. Altogether, this study reveals immunomodulatory effects of SCF-GCSF treatment in the aged brain with Alzheimers disease pathology, which will guide future studies to further uncover the therapeutic mechanisms.

Resveratrol differentially affects MMP-9 release from neurons and glia; implications for therapeutic efficacy

Resveratrol, a naturally occurring polyphenol that activates sirtuin 1 (SIRT1), has been shown to reduce overall levels of matrix metalloprotease-9 (MMP-9) in cerebrospinal fluid (CSF) samples from patients with Alzheimer's dementia (AD). Depending on the site of release, however, MMP-9 has the potential to improve or impair cognition. In particular, its release from microglia or pericytes proximal to the blood brain barrier can damage the basement membrane, while neuronal activity-dependent release of this protease from glutamatergic neurons can instead promote dendritic spine expansion and long-term potentiation of synaptic plasticity. In the present study, we test the hypothesis that resveratrol reduces overall MMP-9 levels in CSF samples from patients with APOE4, an allele associated with increased glial inflammation. We also examine the possibility that resveratrol reduces inflammation-associated MMP release from cultured glia but spares neuronal activity-dependent release from cultured cortical neurons. We observe that resveratrol decreases overall levels of MMP-2 and MMP-9 in CSF samples from AD patients. Resveratrol also reduces CSF levels of tissue inhibitor of metalloproteinases-1 (TIMP-1), glial-derived protein that restricts long-term potentiation of synaptic transmission, in individuals homozygous for APOE4. Consistent with these results, we observe that resveratrol reduces basal and lipopolysaccharide (LPS)-stimulated MMP and TIMP-1 release from cultured microglia and astrocytes. In contrast, however, resveratrol does not inhibit release of MMP-9 from cortical neurons. Overall, these results are consistent with the possibility that while resveratrol reduces potentially maladaptive MMP and TIMP-1 release from activated glia, neuroplasticity-promoting MMP release from neurons is spared. In contrast, resveratrol reduces release of neurocan and brevican, extracellular matrix components that restrict neuroplasticity, from both neurons and glia. These data underscore the diversity of resveratrol's actions with respect to affected cell types and molecular targets and also suggest that further studies may be warranted to determine if its effects on glial MMP release could make it a useful adjunct for AD- and/or anti-amyloid therapy-related damage to the blood brain barrier.

Integrated genomic, proteomic and cognitive assessment in Duchenne Muscular Dystrophy suggest astrocyte centric pathology

Introduction

Documented Duchenne Muscular Dystrophy (DMD) biomarkers are confined to Caucasians and are poor indicators of cognitive difficulties and neuropsychological alterations.

Materials and methods

This study correlates serum protein signatures with cognitive performance in DMD patients of South Asian origin. Study included 25 DMD patients aged 6-16 years. Cognitive profiles were assessed by Wechsler Intelligence Scale for Children. Serum proteome profiling of 1317 proteins was performed in eight DMD patients and eight age-matched healthy volunteers.

Results

Among the several novel observations we report, better cognitive performance in DMD was associated with increased serum levels of MMP9 and FN1 but decreased Siglec-3, C4b, and C3b. Worse cognitive performance was associated with increased serum levels of LDH-H1 and PDGF-BB but reduced GDF-11, MMP12, TPSB2, and G1B. Secondly, better cognitive performance in Processing Speed (PSI) and Perceptual Reasoning (PRI) domains was associated with intact Dp116, Dp140, and Dp71 dystrophin isoforms while better performance in Verbal Comprehension (VCI) and Working Memory (WMI) domains was associated with intact Dp116 and Dp140 isoforms. Finally, functional pathways shared with Alzheimer's Disease (AD) point towards an astrocyte-centric model for DMD.

Conclusion

Astrocytic dysfunction leading to synaptic dysfunction reported previously in AD may be a common pathogenic mechanism underlying both AD and DMD, linking protein alterations to cognitive impairment. This new insight may pave the path towards novel therapeutic approaches targeting reactive astrocytes.

Matrix disequilibrium in Alzheimer's disease and conditions that increase Alzheimer's disease risk

Alzheimer's Disease (AD) and related dementias are a leading cause of death globally and are predicted to increase in prevalence. Despite this expected increase in the prevalence of AD, we have yet to elucidate the causality of the neurodegeneration observed in AD and we lack effective therapeutics to combat the progressive neuronal loss. Throughout the past 30 years, several non-mutually exclusive hypotheses have arisen to explain the causative pathologies in AD: amyloid cascade, hyper-phosphorylated tau accumulation, cholinergic loss, chronic neuroinflammation, oxidative stress, and mitochondrial and cerebrovascular dysfunction. Published studies in this field have also focused on changes in neuronal extracellular matrix (ECM), which is critical to synaptic formation, function, and stability. Two of the greatest non-modifiable risk factors for development of AD (aside from autosomal dominant familial AD gene mutations) are aging and APOE status, and two of the greatest modifiable risk factors for AD and related dementias are untreated major depressive disorder (MDD) and obesity. Indeed, the risk of developing AD doubles for every 5 years after ≥ 65, and the APOE4 allele increases AD risk with the greatest risk in homozygous APOE4 carriers. In this review, we will describe mechanisms by which excess ECM accumulation may contribute to AD pathology and discuss pathological ECM alterations that occur in AD as well as conditions that increase the AD risk. We will discuss the relationship of AD risk factors to chronic central nervous system and peripheral inflammation and detail ECM changes that may follow. In addition, we will discuss recent data our lab has obtained on ECM components and effectors in APOE4/4 and APOE3/3 expressing murine brain lysates, as well as human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 expressing AD individuals. We will describe the principal molecules that function in ECM turnover as well as abnormalities in these molecular systems that have been observed in AD. Finally, we will communicate therapeutic interventions that have the potential to modulate ECM deposition and turnover in vivo.

The Labyrinthine Landscape of APP Processing: State of the Art and Possible Novel Soluble APP-Related Molecular Players in Traumatic Brain Injury and Neurodegeneration

Amyloid Precursor Protein (APP) and its cleavage processes have been widely investigated in the past, in particular in the context of Alzheimer’s Disease (AD). Evidence of an increased expression of APP and its amyloidogenic-related cleavage enzymes, β-secretase 1 (BACE1) and γ-secretase, at the hit axon terminals following Traumatic Brain Injury (TBI), firstly suggested a correlation between TBI and AD. Indeed, mild and severe TBI have been recognised as influential risk factors for different neurodegenerative diseases, including AD. In the present work, we describe the state of the art of APP proteolytic processing, underlining the different roles of its cleavage fragments in both physiological and pathological contexts. Considering the neuroprotective role of the soluble APP alpha (sAPPα) fragment, we hypothesised that sAPPα could modulate the expression of genes of interest for AD and TBI. Hence, we present preliminary experiments addressing sAPPα-mediated regulation of BACE1, Isthmin 2 (ISM2), Tetraspanin-3 (TSPAN3) and the Vascular Endothelial Growth Factor (VEGFA), each discussed from a biological and pharmacological point of view in AD and TBI. We finally propose a neuroprotective interaction network, in which the Receptor for Activated C Kinase 1 (RACK1) and the signalling cascade of PKCβII/nELAV/VEGF play hub roles, suggesting that vasculogenic-targeting therapies could be a feasible approach for vascular-related brain injuries typical of AD and TBI.

CCR5 deficiency normalizes TIMP levels, working memory, and gamma oscillation power in APOE4 targeted replacement mice

The APOE4 allele increases the risk for Alzheimer's disease (AD) in a dose-dependent manner and is also associated with cognitive decline in non-demented elderly controls. In mice with targeted gene replacement (TR) of murine APOE with human APOE3 or APOE4, the latter show reduced neuronal dendritic complexity and impaired learning. APOE4 TR mice also show reduced gamma oscillation power, a neuronal population activity which is important to learning and memory. Published work has shown that brain extracellular matrix (ECM) can reduce neuroplasticity as well as gamma power, while attenuation of ECM can instead enhance this endpoint. In the present study we examine human cerebrospinal fluid (CSF) samples from APOE3 and APOE4 individuals and brain lysates from APOE3 and APOE4 TR mice for levels of ECM effectors that can increase matrix deposition and restrict neuroplasticity. We find that CCL5, a molecule linked to ECM deposition in liver and kidney, is increased in CSF samples from APOE4 individuals. Levels of tissue inhibitor of metalloproteinases (TIMPs), which inhibit the activity of ECM-degrading enzymes, are also increased in APOE4 CSF as well as astrocyte supernatants brain lysates from APOE4 TR mice. Importantly, as compared to APOE4/wild-type heterozygotes, APOE4/CCR5 knockout heterozygotes show reduced TIMP levels and enhanced EEG gamma power. The latter also show improved learning and memory, suggesting that the CCR5/CCL5 axis could represent a therapeutic target for APOE4 individuals.

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.

CircRNA Samd4 induces cardiac repair after myocardial infarction by blocking mitochondria-derived ROS output

Reactive oxygen species (ROS) derived from oxygen-dependent mitochondrial metabolism are the essential drivers of cardiomyocyte (CM) cell-cycle arrest in adulthood. Mitochondria-localized circular RNAs (circRNAs) play important roles in regulating mitochondria-derived ROS production, but their functions in cardiac regeneration are still unknown. Herein, we investigated the functions and underlying mechanism of mitochondria-localized circSamd4 in cardiac regeneration. We found that circSamd4 was selectively expressed in fetal and neonatal CMs. The transcription factor Nrf2 controlled circSamd4 expression by binding to the promoter of circSamd4 host gene. CircSamd4 overexpression reduced while circSamd4 silenced increased mitochondrial oxidative stress and subsequent oxidative DNA damage. Moreover, circSamd4 overexpression induced CM proliferation and prevented CM apoptosis, which reduced the size of the fibrotic area and improved cardiac function after myocardial infarction (MI). Mechanistically, circSamd4 reduced oxidative stress generation and maintained mitochondrial dynamics by inducing the mitochondrial translocation of the Vcp protein, which downregulated Vdac1 expression and prevented the mitochondrial permeability transition pore (mPTP) from opening. Our findings suggest that circSamd4 is a novel therapeutic target for heart failure after MI.

Sex differences in Alzheimer's disease: plasma MMP-9 and markers of disease severity

BACKGROUND

Studies have reported higher plasma matrix metalloproteinase-9 (MMP-9) levels in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Despite evidence that MMP-9 activity and its influence on AD pathophysiology may be modulated by sex hormones, sex differences in the association between MMP-9 and AD biomarkers and cognition have not been explored.

METHODS

Our sample included 238 amyloid-β (Aβ)-positive participants with MCI or AD dementia from the Alzheimer's Disease Neuroimaging Initiative (37.4% women, 74.6 ± 7.3 years). We used linear regression models to examine whether sex modified free and total plasma MMP-9 associations with CSF t-tau, p-tau181, and Aβ₄₂. We used linear mixed effects models to examine whether sex modified total and free plasma MMP-9 associations with cognition, using longitudinal Mini-Mental Status Examination (MMSE) and Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-cog) data.

RESULTS

Total and free MMP-9 levels did not differ by sex, but AD dementia patients had higher total MMP-9 levels than participants with MCI (β = 0.06 [-0.11 to -0.01], p = 0.031). Sex modified the association of CSF t-tau with total (β = 128.68 [55.37 to 201.99], p < 0.001) and free MMP-9 (β = 98.61 [33.61 to 163.62], p = 0.003), whereby higher total and free MMP-9 correlated with higher CSF t-tau in women and lower CSF t-tau in men. Higher free MMP-9 correlated with lower CSF p-tau181 among men (β = -14.98 [-27.37 to -2.58], p = 0.018), but not women. In participants with MCI, higher free MMP-9 levels were associated with higher CSF Aβ₄₂ among men (β = 26.88 [4.03 to 49.73], p = 0.022) but not women. In the overall sample, higher free and total MMP-9 at baseline predicted worsening MMSE scores in women (β = -2.10 [-3.97 to -0.27], p = 0.027 and β = -2.24 [-4.32 to -0.18], p = 0.035) but not men. Higher free MMP-9 correlated with worse ADAS-cog scores (β = 12.34 [3.02 to 21.65], p = 0.011) in women (β = 12.34 [3.02 to 21.65], p = 0.011) but not men with AD dementia cross-sectionally but correlated with worsening ADAS-cog scores longitudinally only in men (β = 8.98 [0.27 to 17.68], p = 0.042).

CONCLUSIONS

MMP-9 may have more detrimental effects on AD-related pathological and cognitive changes in women. If replicated, our findings could help uncover potential mechanisms contributing to women's elevated susceptibility to 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.

Extracellular matrix metalloproteinase-9 (MMP-9) is required in female mice for 17β-estradiol enhancement of hippocampal memory consolidation

Hippocampal plasticity and memory are modulated by the potent estrogen 17β-estradiol (E₂). Research on the molecular mechanisms of hippocampal E₂ signaling has uncovered multiple intracellular pathways that contribute to these effects, but few have questioned the role that extracellular signaling processes may play in E₂ action. Modification of the extracellular matrix (ECM) by proteases like matrix metalloproteinase-9 (MMP-9) is critical for activity-dependent remodeling of synapses, and MMP-9 activity is required for hippocampal learning and memory. Yet little is known about the extent to which E₂ regulates MMP-9 in the hippocampus, and the influence this interaction may have on hippocampal memory. Here, we examined the effects of hippocampal MMP-9 activity on E₂-induced enhancement of spatial and object recognition memory consolidation. Post-training bilateral infusion of an MMP-9 inhibitor into the dorsal hippocampus of ovariectomized female mice blocked the enhancing effects of E₂ on object placement and object recognition memory, supporting a role for MMP-9 in estrogenic regulation of memory consolidation. E₂ also rapidly increased the activity of dorsal hippocampal MMP-9 without influencing its protein expression, providing further insight into hippocampal E₂/MMP-9 interactions. Together, these results provide the first evidence that E₂ regulates MMP-9 to modulate hippocampal memory and highlight the need to further study estrogenic regulation of extracellular modification.

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.

Tau Protein Modulates Perineuronal Extracellular Matrix Expression in the TauP301L-acan Mouse Model

Tau mutations promote the formation of tau oligomers and filaments, which are neuropathological signs of several tau-associated dementias. Types of neurons in the CNS are spared of tau pathology and are surrounded by a specialized form of extracellular matrix; called perineuronal nets (PNs). Aggrecan, the major PN proteoglycans, is suggested to mediate PNs neuroprotective function by forming an external shield preventing the internalization of misfolded tau. We recently demonstrated a correlation between aggrecan amount and the expression and phosphorylation of tau in a TauP310L-acan mouse model, generated by crossbreeding heterozygous aggrecan mice with a significant reduction of aggrecan and homozygous TauP301L mice. Neurodegenerative processes have been associated with changes of PN structure and protein signature. In this study, we hypothesized that the structure and protein expression of PNs in this TauP310L-acan mouse is regulated by tau. Immunohistochemical and biochemical analyses demonstrate that protein levels of PN components differ between TauP301L^HET-acan^WT and TauP301L^HET-acan^HET mice, accompanied by changes in the expression of protein phosphatase 2 A. In addition, tau can modulate PN components such as brevican. Co-immunoprecipitation experiments revealed a physical connection between PN components and tau. These data demonstrate a complex, mutual interrelation of tau and the proteoglycans of the PN.

Harnessing cerebral organoids for Alzheimer's disease research

Alzheimer's disease (AD) is a devastating neurodegenerative disorder affecting the aging population. Despite many studies, there remains an urgent need to identify the root causes of AD, together with potential treatments. Cerebral organoid technology has made it possible to model human neurophysiology and disease with increasing accuracy in patient-derived tissue cultures. Here, we review the most recent advances in modeling AD in organoids and other engineered three-dimensional cell culture systems. Early studies demonstrated that familial AD patient-derived organoids robustly develop disease pathology. Ongoing work has expanded this focus to investigate the genetic and environmental causes of late-onset sporadic AD and harness organoids for high-throughput drug screens. Future organoid models will need to incorporate additional cell types and tissues implicated in disease pathogenesis, including microglia and vasculature. We anticipate the continuation of this rapid progress in developing cerebral organoid technology toward facilitating our understanding of and informing treatment strategies for AD.

Tau Protein Phosphorylated at Threonine-231 is Expressed Abundantly in the Cerebellum in Prion Encephalopathies

Background:

Transmissible spongiform encephalopathies (TSEs) are rare neurodegenerative disorders that affect animals and humans. Bovine spongiform encephalopathy (BSE) in cattle, and Creutzfeld-Jakob Disease (CJD) in humans belong to this group. The causative agent of TSEs is called “prion”, which corresponds to a pathological form (PrP^Sc) of a normal cellular protein (PrP^C) expressed in nerve cells. PrP^Sc is resistant to degradation and can induce abnormal folding of PrP^C, and TSEs are characterized by extensive spongiosis and gliosis and the presence of PrP^Sc amyloid plaques. CJD presents initially with clinical symptoms similar to Alzheimer’s disease (AD). In AD, tau aggregates and amyloid-β protein plaques are associated with memory loss and cognitive impairment in patients.

Objective:

In this work, we study the role of tau and its relationship with PrP^Sc plaques in CJD.

Methods:

Multiple immunostainings with specific antibodies were carried out and analyzed by confocal microscopy.

Results:

We found increased expression of the glial fibrillary acidic protein (GFAP) and matrix metalloproteinase (MMP-9), and an exacerbated apoptosis in the granular layer in cases with prion disease. In these cases, tau protein phosphorylated at Thr-231 was overexpressed in the axons and dendrites of Purkinje cells and the extensions of parallel fibers in the cerebellum.

Conclusion:

We conclude that phosphorylation of tau may be a response to a toxic and inflammatory environment generated by the pathological form of prion.

The interplay between lipid and Aβ amyloid homeostasis in Alzheimer's Disease: risk factors and therapeutic opportunities

Alzheimer's Diseases (AD) is characterized by the accumulation of amyloid deposits of Aβ peptide in the brain. Besides genetic background, the presence of other diseases and an unhealthy lifestyle are known risk factors for AD development. Albeit accumulating clinical evidence suggests that an impaired lipid metabolism is related to Aβ deposition, mechanistic insights on the link between amyloid fibril formation/clearance and aberrant lipid interactions are still unavailable. Recently, many studies have described the key role played by membrane bound Aβ assemblies in neurotoxicity. Moreover, it has been suggested that a derangement of the ubiquitin proteasome pathway and autophagy is significantly correlated with toxic Aβ aggregation and dysregulation of lipid levels. Thus, studies focusing on the role played by lipids in Aβ aggregation and proteostasis could represent a promising area of investigation for the design of valuable treatments. In this review we examine current knowledge concerning the effects of lipids in Aβ aggregation and degradation processes, focusing on the therapeutic opportunities that a comprehensive understanding of all biophysical, biochemical, and biological processes involved may disclose.

MicroRNA-140 silencing represses the incidence of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative condition leading to severe disability from progressive impairments in cognitive functions including memory and learning. Non-coding microRNAs (miRNAs or miRs) have been linked to the pathogenesis of AD. The present study aimed to investigate the clinical significance and biological function of miR-140 in AD. First, we examined the expression of miR-140 and PINK1 in brain tissues of the established AD model rats and neurons cultured with Aβ-derived diffusible ligands (AβDDLs). We identified an interaction between miR-140 and PINK1, and measured spatial learning and memory abilities of the model rats using the Morris water maze (MWM) test. After ectopic expression and depletion experiments in neurons and AD rats, we measured the levels of reactive oxygen species (ROS), and mitochondrial membrane potential (MMP), along with mTOR expression and phosphorylation, and autophagy-related factors. Results showed up-regulation of miR-140 and down-regulation of PINK1 in AD model rats and neurons. PINK1 was verified to be a direct target of miR-140, and silencing of miR-140 suppressed mitochondrial dysfunction, and enhanced autophagy in AD model rats and neurons, as supported by decreased levels of mTOR expression and phosphorylation, β-amyloid p-Tau (Ser396), p-Tau (Thr231), Tau and ROS, and increased MMP levels and expression of Beclin 1 expression and LC3-II/LC3-I. Collectively, functional suppression of miR-140 enhanced autophagy and prevented mitochondrial dysfunction by upregulating PINK1, ultimately suggesting a novel therapeutic target for AD.

Proteolytic cleavage of proBDNF to mBDNF in neuropsychiatric and neurodegenerative diseases

Brain-derived neurotrophic factor (BDNF) is involved in pathophysiological mechanisms in neuropsychiatric diseases, including depression, anxiety, and schizophrenia (SZ), as well as neurodegenerative diseases like Parkinson's disease (PD) and Alzheimer's disease (AD). An imbalance or insufficient pro-brain-derived neurotrophic factor (proBDNF) transformation into mature BDNF (mBDNF) is potentially critical to the disease pathogenesis by impairing neuronal plasticity as suggested by results from many studies. Thus, promoting proBDNF transformation into mBDNF is therefore hypothesized as beneficial for the treatment of neuropsychiatric and neurodegenerative diseases. ProBDNF is proteolytically cleaved into the mBDNF by intracellular furin/proprotein convertases and extracellular proteases (plasmin/matrix metallopeptidases). This article reviews the mechanisms of the conversion of proBDNF to mBDNF and the research status of intracellular/extracellular proteolytic proteases for neuropsychiatric and neurodegenerative disorders.

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 Inhibitors: Potential for the Development of New Therapeutics

The metalloproteinase (MP) family of zinc-dependent proteases, including matrix metalloproteinases (MMPs), a disintegrin and metalloproteases (ADAMs), and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs) plays a crucial role in the extracellular matrix (ECM) remodeling and degradation activities. A wide range of substrates of the MP family includes ECM components, chemokines, cell receptors, and growth factors. Metalloproteinases activities are tightly regulated by proteolytic activation and inhibition via their natural inhibitors, tissue inhibitors of metalloproteinases (TIMPs), and the imbalance of the activation and inhibition is responsible in progression or inhibition of several diseases, e.g., cancer, neurological disorders, and cardiovascular diseases. We provide an overview of the structure, function, and the multifaceted role of MMPs, ADAMs, and TIMPs in several diseases via their cellular functions such as proteolysis of other cell signaling factors, degradation and remodeling of the ECM, and other essential protease-independent interactions in the ECM. The significance of MP inhibitors targeting specific MMP or ADAMs with high selectivity is also discussed. Recent advances and techniques used in developing novel MP inhibitors and MP responsive drug delivery tools are also reviewed.

Metformin Ameliorates Aβ Pathology by Insulin-Degrading Enzyme in a Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease. The accumulation of amyloid beta (Aβ) is the main pathology of AD. Metformin, a well-known antidiabetic drug, has been reported to have AD-protective effect. However, the mechanism is still unclear. In this study, we tried to figure out whether metformin could activate insulin-degrading enzyme (IDE) to ameliorate Aβ-induced pathology. Morris water maze and Y-maze results indicated that metformin could improve the learning and memory ability in APP^swe/PS1^dE9 (APP/PS1) transgenic mice. ¹⁸F-FDG PET-CT result showed that metformin could ameliorate the neural dysfunction in APP/PS1 transgenic mice. PCR analysis showed that metformin could effectively improve the mRNA expression level of nerve and synapse-related genes (Syp, Ngf, and Bdnf) in the brain. Metformin decreased oxidative stress (malondialdehyde and superoxide dismutase) and neuroinflammation (IL-1β and IL-6) in APP/PS1 mice. In addition, metformin obviously reduced the Aβ level in the brain of APP/PS1 mice. Metformin did not affect the enzyme activities and mRNA expression levels of Aβ-related secretases (ADAM10, BACE1, and PS1). Meanwhile, metformin also did not affect the mRNA expression levels of Aβ-related transporters (LRP1 and RAGE). Metformin increased the protein levels of p-AMPK and IDE in the brain of APP/PS1 mice, which might be the key mechanism of metformin on AD. In conclusion, the well-known antidiabetic drug, metformin, could be a promising drug for AD treatment.

Medroxyprogesterone Acetate Impairs Amyloid Beta Degradation in a Matrix Metalloproteinase-9 Dependent Manner

Despite the extensive use of hormonal methods as either contraception or menopausal hormone therapy (HT), there is very little known about the potential effects of these compounds on the cellular processes of the brain. Medroxyprogesterone Acetate (MPA) is a progestogen used globally in the hormonal contraceptive, Depo Provera, by women in their reproductive prime and is a major compound found in HT formulations used by menopausal women. MPA promotes changes in the circulating levels of matrix metalloproteinases (MMPs), such as MMP-9, in the endometrium, yet limited literature studying the effects of MPA on neurons and astroglia cells has been conducted. Additionally, the dysregulation of MMPs has been implicated in the pathology of Alzheimer's disease (AD), where inhibiting the secretion of MMP-9 from astroglia reduces the proteolytic degradation of amyloid-beta. Thus, we hypothesize that exposure to MPA disrupts proteolytic degradation of amyloid-beta through the downregulation of MMP-9 expression and subsequent secretion. To assess the effect of progestins on MMP-9 and amyloid-beta, in vitro, C6 rat glial cells were exposed to MPA for 48 h and then the enzymatic, secretory, and amyloid-beta degrading capacity of MMP-9 was assessed from the conditioned culture medium. We found that MPA treatment inhibited transcription of MMP-9, which resulted in a subsequent decrease in the production and secretion of MMP-9 protein, in part through the glucocorticoid receptor. Additionally, we investigated the consequences of amyloid beta-degrading activity and found that MPA treatment decreased proteolytic degradation of amyloid-beta. Our results suggest MPA suppresses amyloid-beta degradation in an MMP-9-dependent manner, in vitro, and potentially compromises the clearance of amyloid-beta in vivo.

Every-other-day feeding exacerbates inflammation and neuronal deficits in 5XFAD mouse model of Alzheimer's disease

Food restriction has been widely associated with beneficial effects on brain aging and age-related neurodegenerative diseases such as Alzheimer's disease. However, previous studies on the effects of food restriction on aging- or pathology-related cognitive decline are controversial, emphasizing the importance of the type, onset and duration of food restriction. In the present study, we assessed the effects of preventive every-other-day (EOD) feeding regimen on neurodegenerative phenotype in 5XFAD transgenic mice, a commonly used mouse model of Alzheimer's disease. EOD feeding regimen was introduced to transgenic female mice at the age of 2 months and the effects on amyloid-β (Aβ) accumulation, gliosis, synaptic plasticity, and blood-brain barrier breakdown were analyzed in cortical tissue of 6-month-old animals. Surprisingly, significant increase of inflammation in the cortex of 5XFAD fed EOD mice was observed, reflected by the expression of microglial and astrocytic markers. This increase in reactivity and/or proliferation of glial cells was accompanied by an increase in proinflammatory cytokine TNF-α, p38 MAPK and EAAT2, and a decrease in GAD67. NMDA receptor subunit 2B, related to glutamate excitotoxicity, was increased in the cortex of 5XFAD-EOD mice indicating additional alterations in glutamatergic signaling. Furthermore, 4 months of EOD feeding regimen had led to synaptic plasticity proteins reduction and neuronal injury in 5XFAD mice. However, EOD feeding regimen did not affect Aβ load and blood-brain barrier permeability in the cortex of 5XFAD mice. Our results demonstrate that EOD feeding regimen exacerbates Alzheimer's disease-like neurodegenerative and neuroinflammatory changes irrespective of Aβ pathology in 5XFAD mice, suggesting that caution should be paid when using food restrictions in the prodromal phase of this neurodegenerative disease.

A transcriptomic analysis of Nsmce1 overexpression in mouse hippocampal neuronal cell by RNA sequencing

Mouse Nsmce1 gene is the homolog of non-structural maintenance of chromosomes element 1 (NSE1) that is mainly involved in maintenance of genome integrity, DNA damage response, and DNA repair. Defective DNA repair may cause neurological disorders such as Alzheimer's disease (AD). So far, there is no direct evidence for the correlation between Nsmce1 and AD. In order to explore the function of Nsmce1 in the regulation of nervous system, we have overexpressed or knocked down Nsmce1 in the mouse hippocampal neuronal cells (MHNCs) HT-22 and detected its regulation of AD marker genes as well as cell proliferation. The results showed that the expression of App, Bace2, and Mapt could be inhibited by Nsmce1 overexpression and activated by the knockdown of Nsmce1. Moreover, the HT-22 cell proliferation ability could be promoted by Nsmce1 overexpression and inhibited by knockdown of Nsmce1. Furthermore, we performed a transcriptomics study by RNA sequencing (RNA-seq) to evaluate and quantify the gene expression profiles in response to the overexpression of Nsmce1 in HT-22 cells. As a result, 224 significantly dysregulated genes including 83 upregulated and 141 downregulated genes were identified by the comparison of Nsmce1 /+ to WT cells, which were significantly enriched in several Gene Ontology (GO) terms and pathways. In addition, the complexity of the alternative splicing (AS) landscape was increased by Nsmce1 overexpression in HT-22 cells. Thousands of AS events were identified to be mainly involved in the pathway of ubiquitin-mediated proteolysis (UMP) as well as 3 neurodegenerative diseases including AD. The protein-protein interaction network was reconstructed to show top 10 essential genes regulated by Nsmce1. Our sequencing data is available in the Gene Expression Omnibus (GEO) database with accession number as GSE113436. These results may provide some evidence of molecular and cellular functions of Nsmce1 in MHNCs.

The role of extracellular matrix metalloproteinase inducer on the action of dihydrotestosterone against the cellular damage induced by Aβ42

Clinical studies have revealed that the risk of Alzheimer's disease (AD) in men is increased by age-related androgen depletion. The level of β-amyloid (Aβ) is elevated in the brains of AD patients, and Aβ is believed to play a critical role in the pathology of AD. Some studies have indicated that androgens affect AD risk by regulating the metabolism of Aβ by an unclear mechanism. In this study, we investigated the role of the extracellular matrix metalloproteinase inducer (CD147) in this action. Initially, we demonstrated that androgens positively regulate the expression of CD147 in adult male rats and SH-SY5Y cells. Furthermore, this regulation may involve androgen receptor (AR). Additionally, interference of CD147 expression decreased the clearance of Aβ in culture medium and reduced cell viability. It also affected the morphology of the cells and the expression of apoptosis-related proteins. Finally, we found that interference of CD147 expression blocked the dihydrotestosterone (DHT)-induced reduction in Aβ and the protection of cells. DHT regulates MMP-2's expression through CD147. Together, these results imply that androgen regulation of Aβ and cell protection may be affected by interfering with the expression of CD147.

Methylglyoxal and Glyoxal as Potential Peripheral Markers for MCI Diagnosis and Their Effects on the Expression of Neurotrophic, Inflammatory and Neurodegenerative Factors in Neurons and in Neuronal Derived-Extracellular Vesicles

Methylglyoxal (MG) and glyoxal (GO) are suggested to be associated with the development of neurodegenerative pathologies. However, their peripheral levels in relation to cognitive decline and their effects on key factors in neuronal cells are poorly investigated. The aim of this study was to determine their serum levels in MCI (mild cognitive impairment) and Alzheimer’s disease (AD) patients, to analyze their effects on the neurotrophic and inflammatory factors, on neurodegenerative markers in neuronal cells and in neuronal derived-extracellular vesicles (nEVs). Our results show that MG and GO levels in serum, determined by HPLC, were higher in MCI. ROC (receiver-operating characteristic curves) analysis showed that the levels of MG in serum have higher sensitivity to differentiate MCI from controls but not from AD. Meanwhile, serum GO levels differentiate MCI from control and AD groups. Cells and nEVs levels of BDNF, PRGN, NSE, APP, MMP-9, ANGPTL-4, LCN2, PTX2, S100B, RAGE, Aβ peptide, pTau T181 and alpha-synuclein were quantified by luminex assay. Treatment of neuronal cells with MG or GO reduced the cellular levels of NSE, PRGN, APP, MMP-9 and ANGPTL-4 and the nEVs levels of BDNF, PRGN and LCN2. Our findings suggest that targeting MG and GO may be a promising therapeutic strategy to prevent or delay the progression of AD.

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.

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.

A Role for Matrix Metalloproteases in Antidepressant Efficacy

Major depressive disorder is a debilitating condition that affects approximately 15% of the United States population. Though the neurophysiological mechanisms that underlie this disorder are not completely understood, both human and rodent studies suggest that excitatory/inhibitory (E/I) balance is reduced with the depressive phenotype. In contrast, antidepressant efficacy in responsive individuals correlates with increased excitatory neurotransmission in select brain regions, suggesting that the restoration of E/I balance may improve mood. Enhanced excitatory transmission can occur through mechanisms including increased dendritic arborization and synapse formation in pyramidal neurons. Reduced activity of inhibitory neurons may also contribute to antidepressant efficacy. Consistent with this possibility, the fast-acting antidepressant ketamine may act by selective inhibition of glutamatergic input to GABA releasing parvalbumin (PV)-expressing interneurons. Recent work has also shown that a negative allosteric modulator of the GABA-A receptor α subunit can improve depression-related behavior. PV-expressing interneurons are thought to represent critical pacemakers for synchronous network events. These neurons also represent the predominant GABAergic neuronal population that is enveloped by the perineuronal net (PNN), a lattice-like structure that is thought to stabilize glutamatergic input to this cell type. Disruption of the PNN reduces PV excitability and increases pyramidal cell excitability. Various antidepressant medications increase the expression of matrix metalloproteinases (MMPs), enzymes that can increase pyramidal cell dendritic arborization and spine formation. MMPs can also cleave PNN proteins to reduce PV neuron-mediated inhibition. The present review will focus on mechanisms that may underlie antidepressant efficacy, with a focus on monoamines as facilitators of increased matrix metalloprotease (MMP) expression and activation. Discussion will include MMP-dependent effects on pyramidal cell structure and function, as well as MMP-dependent effects on PV expressing interneurons. We conclude with discussion of antidepressant use for those at risk for Alzheimer’s disease, and we also highlight areas for further study.

Dissociable cognitive impairments in two strains of transgenic Alzheimer's disease mice revealed by a battery of object-based tests

Object recognition tasks detect cognitive deficits in transgenic Alzheimer's disease (AD) mouse models. Object recognition, however, is not a unitary process, and there are many uncharacterized facets of object processing with relevance to AD. We therefore systematically evaluated object processing in 5xFAD and 3xTG AD mice to clarify the nature of object recognition-related deficits. Twelve-month-old male and female 5xFAD and 3xTG mice were assessed on tasks for object identity recognition, spatial recognition, and multisensory object perception. Memory and multisensory perceptual impairments were observed, with interesting dissociations between transgenic AD strains and sex that paralleled neuropathological changes. Overreliance on the widespread "object recognition" task threatens to slow discovery of potentially significant and clinically relevant behavioural effects related to this multifaceted cognitive function. The current results support the use of carefully designed object-based test batteries to clarify the relationship between "object recognition" impairments and specific aspects of AD pathology in rodent models.

Copper and Zinc Dysregulation in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common forms of dementia. Despite a wealth of knowledge on the molecular mechanisms involved in AD, current treatments have mainly focused on targeting amyloid β (Aβ) production, but have failed to show significant effects and efficacy. Therefore, a critical reconsideration of the multifactorial nature of the disease is needed. AD is a complex multifactorial disorder in which, along with Aβ and tau, the convergence of polygenic, epigenetic, environmental, vascular, and metabolic factors increases the global susceptibility to the disease and shapes its course. One of the cofactors converging on AD is the dysregulation of brain metals. In this review, we focus on the role of AD-related neurodegeneration and cognitive decline triggered by the imbalance of two endogenous metals: copper and zinc.

The pharmacological perturbation of brain zinc impairs BDNF-related signaling and the cognitive performances of young mice

Zinc (Zn2+) is a pleiotropic modulator of the neuronal and brain activity. The disruption of intraneuronal Zn2+ levels triggers neurotoxic processes and affects neuronal functioning. In this study, we investigated how the pharmacological modulation of brain Zn2+ affects synaptic plasticity and cognition in wild-type mice. To manipulate brain Zn2+ levels, we employed the Zn2+ (and copper) chelator 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol, CQ). CQ was administered for two weeks to 2.5-month-old (m.o.) mice, and effects studied on BDNF-related signaling, metalloproteinase activity as well as learning and memory performances. CQ treatment was found to negatively affect short- and long-term memory performances. The CQ-driven perturbation of brain Zn2+ was found to reduce levels of BDNF, synaptic plasticity-related proteins and dendritic spine density in vivo. Our study highlights the importance of choosing "when", "where", and "how much" in the modulation of brain Zn2+ levels. Our findings confirm the importance of targeting Zn2+ as a therapeutic approach against neurodegenerative conditions but, at the same time, underscore the potential drawbacks of reducing brain Zn2+ availability upon the early stages of development.

An Artificial Neural Network Integrated Pipeline for Biomarker Discovery Using Alzheimer's Disease as a Case Study

The field of machine learning has allowed researchers to generate and analyse vast amounts of data using a wide variety of methodologies. Artificial Neural Networks (ANN) are some of the most commonly used statistical models and have been successful in biomarker discovery studies in multiple disease types. This review seeks to explore and evaluate an integrated ANN pipeline for biomarker discovery and validation in Alzheimer's disease, the most common form of dementia worldwide with no proven cause and no available cure. The proposed pipeline consists of analysing public data with a categorical and continuous stepwise algorithm and further examination through network inference to predict gene interactions. This methodology can reliably generate novel markers and further examine known ones and can be used to guide future research in Alzheimer's disease.

Glial Draper Rescues Aβ Toxicity in a Drosophila Model of Alzheimer's Disease

Pathological hallmarks of Alzheimer's disease (AD) include amyloid-β (Aβ) plaques, neurofibrillary tangles, and reactive gliosis. Glial cells offer protection against AD by engulfing extracellular Aβ peptides, but the repertoire of molecules required for glial recognition and destruction of Aβ are still unclear. Here, we show that the highly conserved glial engulfment receptor Draper/MEGF10 provides neuroprotection in an AD model of Drosophila (both sexes). Neuronal expression of human Aβ42^arc in adult flies results in robust Aβ accumulation, neurodegeneration, locomotor dysfunction, and reduced lifespan. Notably, all of these phenotypes are more severe in draper mutant animals, whereas enhanced expression of glial Draper reverses Aβ accumulation, as well as behavioral phenotypes. We also show that the signal transducer and activator of transcription (Stat92E), c-Jun N-terminal kinase (JNK)/AP-1 signaling, and expression of matrix metalloproteinase-1 (Mmp1) are activated downstream of Draper in glia in response to Aβ42^arc exposure. Furthermore, Aβ42-induced upregulation of the phagolysosomal markers Atg8 and p62 was notably reduced in draper mutant flies. Based on our findings, we propose that glia clear neurotoxic Aβ peptides in the AD model Drosophila brain through a Draper/STAT92E/JNK cascade that may be coupled to protein degradation pathways such as autophagy or more traditional phagolysosomal destruction methods.SIGNIFICANCE STATEMENT Alzheimer's disease (AD) and similar dementias are common incurable neurodegenerative disorders in the aging population. As the primary immune responders in the brain, glial cells are implicated as key players in the onset and progression of AD and related disorders. Here we show that the glial engulfment receptor Draper is protective in a Drosophila model of AD, reducing levels of amyloid β (Aβ) peptides, reversing locomotor defects, and extending lifespan. We further show that protein degradation pathways are induced downstream of Draper in AD model flies, supporting a model in which glia engulf and destroy Aβ peptides to reduce amyloid-associated toxicity.

EFAD transgenic mice as a human APOE relevant preclinical model of Alzheimer's disease

Identified in 1993, APOE4 is the greatest genetic risk factor for sporadic Alzheimer's disease (AD), increasing risk up to 15-fold compared with APOE3, with APOE2 decreasing AD risk. However, the functional effects of APOE4 on AD pathology remain unclear and, in some cases, controversial. In vivo progress to understand how the human (h)-APOE genotypes affect AD pathology has been limited by the lack of a tractable familial AD-transgenic (FAD-Tg) mouse model expressing h-APOE rather than mouse (m)-APOE. The disparity between m- and h-apoE is relevant for virtually every AD-relevant pathway, including amyloid-β (Aβ) deposition and clearance, neuroinflammation, tau pathology, neural plasticity and cerebrovascular deficits. EFAD mice were designed as a temporally useful preclinical FAD-Tg-mouse model expressing the h-APOE genotypes for identifying mechanisms underlying APOE-modulated symptoms of AD pathology. From their first description in 2012, EFAD mice have enabled critical basic and therapeutic research. Here we review insights gleaned from the EFAD mice and summarize future directions.

Multifaceted Roles of Metzincins in CNS Physiology and Pathology: From Synaptic Plasticity and Cognition to Neurodegenerative Disorders

The extracellular matrix (ECM) and membrane proteolysis play a key role in structural and functional synaptic plasticity associated with development and learning. A growing body of evidence underscores the multifaceted role of members of the metzincin superfamily, including metalloproteinases (MMPs), A Disintegrin and Metalloproteinases (ADAMs), A Disintegrin and Metalloproteinase with Thrombospondin Motifs (ADAMTSs) and astacins in physiological and pathological processes in the central nervous system (CNS). The expression and activity of metzincins are strictly controlled at different levels (e.g., through the regulation of translation, limited activation in the extracellular space, the binding of endogenous inhibitors and interactions with other proteins). Thus, unsurprising is that the dysregulation of proteolytic activity, especially the greater expression and activation of metzincins, is associated with neurodegenerative disorders that are considered synaptopathies, especially Alzheimer's disease (AD). We review current knowledge of the functions of metzincins in the development of AD, mainly the proteolytic processing of amyloid precursor protein, the degradation of amyloid β (Aβ) peptide and several pathways for Aβ clearance across brain barriers (i.e., blood-brain barrier (BBB) and blood-cerebrospinal fluid barrier (BCSFB)) that contain specific receptors that mediate the uptake of Aβ peptide. Controlling the proteolytic activity of metzincins in Aβ-induced pathological changes in AD patients' brains may be a promising therapeutic strategy.

Overexpression of matrix metalloproteinase-9 (MMP-9) rescues insulin-mediated impairment in the 5XFAD model of Alzheimer's disease

A hallmark of Alzheimer’s disease (AD) is the accumulation of oligomeric amyloid-β (Aβ) peptide, which may be primarily responsible for neuronal dysfunction. Insulin signaling provides a defense mechanism against oligomer-induced neuronal loss. We previously described the neuroprotective role of matrix metalloproteinase 9 (MMP-9) in decreasing the formation of Aβ oligomers. In the present study, we examined the role of MMP-9 on the insulin survival pathway in primary hippocampal cultures and hippocampal cell extracts from 3 month-old wild type, AD (5XFAD), MMP-9-overexpressing (TgMMP-9), and double transgenic mice (5XFAD/TgMMP-9). The data demonstrate that the insulin pathway was compromised in samples from 5XFAD mice, when compared to the wild type and TgMMP-9. This was due to enhanced phosphorylation of IRS1 at Serine 636 (pIRS1-Ser636), which renders IRS1 inactive and prevents insulin-mediated signaling. In 5XFAD/TgMMP-9 samples, the insulin survival pathway was rescued through enhanced activation by phosphorylation of IRS1 at Tyrosine 465 (pIRS1-Tyr465), downstream increased phosphorylation of Akt and GSK-3β, and decreased phosphorylation of JNK kinase. Oligomeric Aβ levels decreased and BDNF levels increased in 5XFAD/TgMMP-9 mice, compared to 5XFAD mice. Our findings indicate that overexpression of MMP-9 rescued insulin survival signaling in vitro and in early stages in the 5XFAD model of AD.

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.

Beta-Amyloid and Tau-Protein: Structure, Interaction, and Prion-Like Properties

During the last twenty years, molecular genetic investigations of Alzheimer's disease (AD) have significantly broadened our knowledge of basic mechanisms of this disorder. However, still no unambiguous concept on the molecular bases of AD pathogenesis has been elaborated, which significantly impedes the development of AD therapy. In this review, we analyze issues concerning processes of generation of two proteins (β-amyloid peptide and Tau-protein) in the cell, which are believed to play the key role in AD genesis. Until recently, these agents were considered independently of each other, but in light of the latest studies, it becomes clear that it is necessary to study their interaction and combined effects. Studies of mechanisms of toxic action of these endogenous compounds, beginning from their interaction with known receptors of main neurotransmitters to specific peculiarities of functioning of signal intracellular pathways upon development of this pathology, open the way to development of new pharmaceutical substances directed concurrently on key mechanisms of interaction of toxic proteins inside the cell and on the pathways of their propagation in the extracellular space.

A Greek Tragedy: The Growing Complexity of Alzheimer Amyloid Precursor Protein Proteolysis

Proteolysis of the amyloid precursor protein (APP) liberates various fragments including the proposed initiator of Alzheimer disease-associated dysfunctions, amyloid-β. However, recent evidence suggests that the accepted view of APP proteolysis by the canonical α-, β-, and γ-secretases is simplistic, with the discovery of a number of novel APP secretases (including δ- and η-secretases, alternative β-secretases) and additional metabolites, some of which may also cause synaptic dysfunction. Furthermore, various proteins have been identified that interact with APP and modulate its cleavage by the secretases. Here, we give an overview of the increasingly complex picture of APP proteolysis.

Therapies for Prevention and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia associated with a progressive neurodegenerative disorder, with a prevalence of 44 million people throughout the world in 2015, and this figure is estimated to double by 2050. This disease is characterized by blood-brain barrier disruption, oxidative stress, mitochondrial impairment, neuroinflammation, and hypometabolism; it is related to amyloid-β peptide accumulation and tau hyperphosphorylation as well as a decrease in acetylcholine levels and a reduction of cerebral blood flow. Obesity is a major risk factor for AD, because it induces adipokine dysregulation, which consists of the release of the proinflammatory adipokines and decreased anti-inflammatory adipokines, among other processes. The pharmacological treatments for AD can be divided into two categories: symptomatic treatments such as acetylcholinesterase inhibitors and N-methyl-D-aspartate (NMDA) receptor antagonists and etiology-based treatments such as secretase inhibitors, amyloid binders, and tau therapies. Strategies for prevention of AD through nonpharmacological treatments are associated with lifestyle interventions such as exercise, mental challenges, and socialization as well as caloric restriction and a healthy diet. AD is an important health issue on which all people should be informed so that prevention strategies that minimize the risk of its development may be implemented.

MMP-9 in translation: from molecule to brain physiology, pathology, and therapy

Matrix metalloproteinase-9 (MMP-9) is a member of the metzincin family of mostly extracellularly operating proteases. Despite the fact that all of these enzymes might be target promiscuous, with largely overlapping catalogs of potential substrates, MMP-9 has recently emerged as a major and apparently unique player in brain physiology and pathology. The specificity of MMP-9 may arise from its very local and time-restricted actions, even when released in the brain from cells of various types, including neurons, glia, and leukocytes. In fact, the quantity of MMP-9 is very low in the naive brain, but it is markedly activated at the levels of enzymatic activity, protein abundance, and gene expression following various physiological stimuli and pathological insults. Neuronal MMP-9 participates in synaptic plasticity by controlling the shape of dendritic spines and function of excitatory synapses, thus playing a pivotal role in learning, memory, and cortical plasticity. When improperly unleashed, MMP-9 contributes to a large variety of brain disorders, including epilepsy, schizophrenia, autism spectrum disorder, brain injury, stroke, neurodegeneration, pain, brain tumors, etc. The foremost mechanism of action of MMP-9 in brain disorders appears to be its involvement in immune/inflammation responses that are related to the enzyme's ability to process and activate various cytokines and chemokines, as well as its contribution to blood-brain barrier disruption, facilitating the extravasation of leukocytes into brain parenchyma. However, another emerging possibility (i.e., the control of MMP-9 over synaptic plasticity) should not be neglected. The translational potential of MMP-9 has already been recognized in both the diagnosis and treatment domains. The most striking translational aspect may be the discovery of MMP-9 up-regulation in a mouse model of Fragile X syndrome, quickly followed by human studies and promising clinical trials that have sought to inhibit MMP-9. With regard to diagnosis, suggestions have been made to use MMP-9 alone or combined with tissue inhibitor of matrix metalloproteinase-1 or brain-derived neurotrophic factor as disease biomarkers. MMP-9, through cleavage of specific target proteins, plays a major role in synaptic plasticity and neuroinflammation, and by those virtues contributes to brain physiology and a host of neurological and psychiatric disorders. This article is part of the 60th Anniversary special issue.

MT5-MMP is a new pro-amyloidogenic proteinase that promotes amyloid pathology and cognitive decline in a transgenic mouse model of Alzheimer's disease

Membrane-type 5-matrix metalloproteinase (MT5-MMP) is a proteinase mainly expressed in the nervous system with emerging roles in brain pathophysiology. The implication of MT5-MMP in Alzheimer's disease (AD), notably its interplay with the amyloidogenic process, remains elusive. Accordingly, we crossed the genetically engineered 5xFAD mouse model of AD with MT5-MMP-deficient mice and examined the impact of MT5-MMP deficiency in bigenic 5xFAD/MT5-MMP(-/-) mice. At early stages (4 months) of the pathology, the levels of amyloid beta peptide (Aβ) and its amyloid precursor protein (APP) C-terminal fragment C99 were largely reduced in the cortex and hippocampus of 5xFAD/MT5-MMP(-/-), compared to 5xFAD mice. Reduced amyloidosis in bigenic mice was concomitant with decreased glial reactivity and interleukin-1β (IL-1β) levels, and the preservation of long-term potentiation (LTP) and spatial learning, without changes in the activity of α-, β- and γ-secretases. The positive impact of MT5-MMP deficiency was still noticeable at 16 months of age, as illustrated by reduced amyloid burden and gliosis, and a better preservation of the cortical neuronal network and synaptophysin levels in bigenic mice. MT5-MMP expressed in HEKswe cells colocalized and co-immunoprecipitated with APP and significantly increased the levels of Aβ and C99. MT5-MMP also promoted the release of a soluble APP fragment of 95 kDa (sAPP95) in HEKswe cells. sAPP95 levels were significantly reduced in brain homogenates of 5xFAD/MT5-MMP(-/-) mice, supporting altogether the idea that MT5-MMP influences APP processing. MT5-MMP emerges as a new pro-amyloidogenic regulator of APP metabolism, whose deficiency alleviates amyloid pathology, neuroinflammation and cognitive decline.