Neprilysin: an enzyme candidate to slow the progression of Alzheimer's disease

Association of MME gene polymorphisms with susceptibility to Alzheimer's disease in an Iranian population

Background

the MME gene encodes a membrane metalloendopeptidase, known as neprilysin (NEP). There are no reports on the potential implications of MME gene polymorphisms on the risk of Alzheimer's disease (AD) in the Iranian population. In this study, we studied the potential association of two single nucleotide polymorphisms (SNPs), rs6797911 and rs3736187, in the MME gene and the risk of developing AD in an Iranian population.

Methods

This case-control study comprised 120 AD-diagnosed patients and 120 healthy individuals without any prior family history of AD. The patient and control groups were matched for major demographic and health characteristics. Genotyping was performed by amplification refractory mutation system-polymerase chain reaction (ARMS-PCR).

Results

All patients included in this study were assessed by an experienced neurologist to exclude cases with other forms of dementia based on a brain computed tomography scan and other clinical findings. There were no significant differences in demographic and health characteristics including sex, diabetes, blood pressure, and cigarette smoking status between case and control groups (p > 0.05). However, the age difference appeared significant. Both SNPs were significantly associated with the risk of AD in our study population. The rs3736187 (T > C, 3:155168489) was strongly associated with AD risk under the log-additive model (OR = 1.67, CI = 1.18-2.37, p-value = 0.003). The rs6797911 (T > A, 3:155144601) also showed a significant association with AD risk under the dominant model (TT vs. TA and AA, OR = 3.37, CI = 1.86-6.1, p-value <0.001).

Conclusion

There is a strong association between MME gene polymorphisms and susceptibility to AD in the Iranian population. Amyloid-β (Aβ) can serve as a substrate for the NEP metalloendopeptidase, the product of the MME gene. However, the mechanistic understanding of how these genetic variations affect NEP expression, function, and consequently susceptibility to AD, is poorly understood. Further research is required to fully understand the exact implication of MME gene variations on AD, particularly in a larger, ethnicity-diverse population.

Dual orexin receptor antagonist ameliorates sleep deprivation-induced learning and memory impairment in APP/PS1 mice

Sleep is considered closely related to cognitive function, and cognitive impairment is the main clinical manifestation of Alzheimer's disease (AD). Sleep disturbance in AD patients is more severe than that in healthy elderly individuals. Additionally, sleep deprivation reportedly increases the activity of the hypothalamic orexin system and the risk of AD. To investigate whether intervention with the orexin system can improve sleep disturbance in AD and its impact on AD pathology. In this study, six-month-old amyloid precursor protein/presenilin 1 mice were subjected to six weeks of chronic sleep deprivation and injected intraperitoneally with almorexant, a dual orexin receptor antagonist (DORA), to investigate the effects and mechanisms of sleep deprivation and almorexant intervention on learning and memory in mice with AD. We found that sleep deprivation aggravated learning and memory impairment and increased brain β-amyloid (Aβ) deposition in mice with AD. The application of almorexant can increase the total sleep time of sleep-deprived mice and reduce cognitive impairment and Aβ deposition, which is related to the improvement in Aquaporin-4 polarity. Thus, DORA may be an effective strategy for delaying the progression of AD patients by improving the sleep disturbances.

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

Multi-analyte proteomic analysis identifies blood-based neuroinflammation, cerebrovascular and synaptic biomarkers in preclinical Alzheimer's disease

Background

Blood-based biomarkers are gaining grounds for Alzheimer's disease (AD) detection. However, two key obstacles need to be addressed: the lack of methods for multi-analyte assessments and the need for markers of neuroinflammation, vascular, and synaptic dysfunction. Here, we evaluated a novel multi-analyte biomarker platform, NULISAseq CNS disease panel, a multiplex NUcleic acid-linked Immuno-Sandwich Assay (NULISA) targeting ~120 analytes, including classical AD biomarkers and key proteins defining various disease hallmarks.

Methods

The NULISAseq panel was applied to 176 plasma samples from the MYHAT-NI cohort of cognitively normal participants from an economically underserved region in Western Pennsylvania. Classical AD biomarkers, including p-tau181 p-tau217, p-tau231, GFAP, NEFL, Aβ40, and Aβ42, were also measured using Single Molecule Array (Simoa). Amyloid pathology, tau pathology, and neurodegeneration were evaluated with [11C] PiB PET, [18F]AV-1451 PET, and MRI, respectively. Linear mixed models were used to examine cross-sectional and Wilcoxon rank sum tests for longitudinal associations between NULISA biomarkers and AD pathologies. Spearman correlations were used to compare NULISA and Simoa.

Results

NULISA concurrently measured 116 plasma biomarkers with good technical performance, and good correlation with Simoa measures. Cross-sectionally, p-tau217 was the top hit to identify Aβ pathology, with age, sex, and APOE genotype-adjusted AUC of 0.930 (95%CI: 0.878-0.983). Fourteen markers were significantly decreased in Aβ-PET+ participants, including TIMP3, which regulates brain Aβ production, the neurotrophic factor BDNF, the energy metabolism marker MDH1, and several cytokines. Longitudinally, FGF2, IL4, and IL9 exhibited Aβ PET-dependent yearly increases in Aβ-PET+ participants. Markers with tau PET-dependent longitudinal changes included the microglial activation marker CHIT1, the reactive astrogliosis marker CHI3L1, the synaptic protein NPTX1, and the cerebrovascular markers PGF, PDGFRB, and VEFGA; all previously linked to AD but only reliably measured in cerebrospinal fluid. SQSTM1, the autophagosome cargo protein, exhibited a significant association with neurodegeneration status after adjusting age, sex, and APOE ε4 genotype.

Conclusions

Together, our results demonstrate the feasibility and potential of immunoassay-based multiplexing to provide a comprehensive view of AD-associated proteomic changes. Further validation of the identified inflammation, synaptic, and vascular markers will be important for establishing disease state markers in asymptomatic AD.

Novel Gene Therapy Approaches for Targeting Neurodegenerative Disorders: Focusing on Delivering Neurotrophic Genes

Neurodegenerative illnesses (NDDs) like Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, spinal muscular atrophy, and Huntington's disease have demonstrated considerable potential for gene therapy as a viable therapeutic intervention. NDDs are marked by the decline of neurons, resulting in changes in both behavior and pathology within the body. Strikingly, only symptomatic management is available without a cure for the NDDs. There is an unmet need for a permanent therapeutic approach. Many studies have been going on to target the newer therapeutic molecular targets for NDDs including gene-based therapy. Gene therapy has the potential to provide therapeutic benefits to a large number of patients with NDDs by offering mechanisms including neuroprotection, neuro-restoration, and rectification of pathogenic pathways. Gene therapy is a medical approach that aims to modify the biological characteristics of living cells by controlling the expression of specific genes in certain neurological disorders. Despite being the most complex and well-protected organ in the human body, there is clinical evidence to show that it is possible to specifically target the central nervous system (CNS). This provides hope for the prospective application of gene therapy in treating NDDs in the future. There are several advanced techniques available for using viral or non-viral vectors to deliver the therapeutic gene to the afflicted region. Neurotrophic factors (NTF) in the brain are crucial for the development, differentiation, and survival of neurons in the CNS, making them important in the context of various neurological illnesses. Gene delivery of NTF has the potential to be used as a therapeutic approach for the treatment of neurological problems in the brain. This review primarily focuses on the methodologies employed for delivering the genes of different NTFs to treat neurological disorders. These techniques are currently being explored as a viable therapeutic approach for neurodegenerative diseases. The article exclusively addresses gene delivery approaches and does not cover additional therapy strategies for NDDs. Gene therapy offers a promising alternative treatment for NDDs by stimulating neuronal growth instead of solely relying on symptom relief from drugs and their associated adverse effects. It can serve as a long-lasting and advantageous treatment choice for the management of NDDs. The likelihood of developing NDDs increases with age as a result of neuronal degradation in the brain. Gene therapy is an optimal approach for promoting neuronal growth through the introduction of nerve growth factor genes.

Zinc utilization by microglia in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia defined by two key pathological characteristics in the brain, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs) composed of hyperphosphorylated tau. Microglia, the primary innate immune cells of the central nervous system (CNS), provide neuroprotection through Aβ and tau clearance but may also be neurotoxic by promoting neuroinflammation to exacerbate Aβ and tau pathogenesis in AD. Recent studies have demonstrated the importance of microglial utilization of nutrients and trace metals in controlling their activation and effector functions. Trace metals, such as zinc, have essential roles in brain health and immunity, and zinc dyshomeostasis has been implicated in AD pathogenesis. As a result of these advances, the mechanisms by which zinc homeostasis influences microglial-mediated neuroinflammation in AD is a topic of continuing interest since new strategies to treat AD are needed. Here, we review the roles of zinc in AD, including zinc activation of microglia, the associated neuroinflammatory response, and the application of these findings in new therapeutic strategies.

Impact of micronutrients and nutraceuticals on cognitive function and performance in Alzheimer's disease

Alzheimer's disease (AD) is a major global health problem today and is the most common form of dementia. AD is characterized by the formation of β-amyloid (Aβ) plaques and neurofibrillary clusters, leading to decreased brain acetylcholine levels in the brain. Another mechanism underlying the pathogenesis of AD is the abnormal phosphorylation of tau protein that accumulates at the level of neurofibrillary aggregates, and the areas most affected by this pathological process are usually the cholinergic neurons in cortical, subcortical, and hippocampal areas. These effects result in decreased cognitive function, brain atrophy, and neuronal death. Malnutrition and weight loss are the most frequent manifestations of AD, and these are also associated with greater cognitive decline. Several studies have confirmed that a balanced low-calorie diet and proper nutritional intake may be considered important factors in counteracting or slowing the progression of AD, whereas a high-fat or hypercholesterolemic diet predisposes to an increased risk of developing AD. Especially, fruits, vegetables, antioxidants, vitamins, polyunsaturated fatty acids, and micronutrients supplementation exert positive effects on aging-related changes in the brain due to their antioxidant, anti-inflammatory, and radical scavenging properties. The purpose of this review is to summarize some possible nutritional factors that may contribute to the progression or prevention of AD, understand the role that nutrition plays in the formation of Aβ plaques typical of this neurodegenerative disease, to identify some potential therapeutic strategies that may involve some natural compounds, in delaying the progression of the disease.

A comprehensive review of the literature on CD10: its function, clinical application, and prospects

CD10, a zinc-dependent metalloprotease found on the cell surface, plays a pivotal role in an array of physiological and pathological processes including cardiovascular regulation, immune function, fetal development, pain response, oncogenesis, and aging. Recognized as a biomarker for hematopoietic and tissue stem cells, CD10 has garnered attention for its prognostic potential in the progression of leukemia and various solid tumors. Recent studies underscore its regulatory significance and therapeutic promise in combating Alzheimer's disease (AD), and it is noted for its protective role in preventing heart failure (HF), obesity, and type-2 diabetes. Furthermore, CD10/substance P interaction has also been shown to contribute to the pain signaling regulation and immunomodulation in diseases such as complex regional pain syndrome (CRPS) and osteoarthritis (OA). The emergence of COVID-19 has sparked interest in CD10's involvement in the disease's pathogenesis. Given its association with multiple disease states, CD10 is a prime therapeutic target; inhibitors targeting CD10 are now being advanced as therapeutic agents. This review compiles recent and earlier literature on CD10, elucidating its physicochemical attributes, tissue-specific expression, and molecular functions. Furthermore, it details the association of CD10 with various diseases and the clinical advancements of its inhibitors, providing a comprehensive overview of its growing significance in medical research.

miRNA-211-5p inhibition enhances the protective effect of hucMSC-derived exosome in Aβ1-40 -induced SH-SY5Y cells by increasing NEP expression

Exosomes derived from human umbilical cord mesenchymal stem cells (hucMSCs) could alleviate Alzheimer's disease (AD) defects. Additionally, engineered exosomes are more effective in treating diseases. In this study, we established an in vitro model of AD by treating SH-SY5Y cells with Aβ1-40 . We observed that incubation with hucMSC-derived exosomes effectively protected SH-S5Y5 cells from Aβ1-40 -induced damage. Since NEP plays a central role in suppressing AD development, we screened NEP-targeting miRNAs that are differentially expressed in control and AD patients. We identified miR-211-5p as a potent repressor of NEP expression. Exosomes purified from hucMSCs overexpressing miR-211-5p inhibitor exhibited significantly greater efficiency than control exosomes in mitigating the injury caused by Aβ1-40 treatment. However, this enhanced protective effect was nullified by the knockdown of NEP. These observations demonstrate that inhibition of miR-211-5p has the potential to improve the efficacy of hucMSC-derived exosomes in AD treatment by increasing NEP expression.

Inflammation as common link to progressive neurological diseases

Life expectancy has increased immensely over the past decades, bringing new challenges to the health systems as advanced age increases the predisposition for many diseases. One of those is the burden of neurologic disorders. While many hypotheses have been placed to explain aging mechanisms, it has been widely accepted that the increasing pro-inflammatory status with advanced age or "inflammaging" is a main determinant of biological aging. Furthermore, inflammaging is at the cornerstone of many age-related diseases and its involvement in neurologic disorders is an exciting hypothesis. Indeed, aging and neurologic disorders development in the elderly seem to share some basic pathways that fundamentally converge on inflammation. Peripheral inflammation significantly influences brain function and contributes to the development of neurological disorders, including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Understanding the role of inflammation in the pathogenesis of progressive neurological diseases is of crucial importance for developing effective treatments and interventions that can slow down or prevent disease progression, therefore, decreasing its social and economic burden.

Disentangling Accelerated Cognitive Decline from the Normal Aging Process and Unraveling Its Genetic Components: A Neuroimaging-Based Deep Learning Approach

Background

The progressive cognitive decline, an integral component of Alzheimer's disease (AD), unfolds in tandem with the natural aging process. Neuroimaging features have demonstrated the capacity to distinguish cognitive decline changes stemming from typical brain aging and AD between different chronological points.

Objective

To disentangle the normal aging effect from the AD-related accelerated cognitive decline and unravel its genetic components using a neuroimaging-based deep learning approach.

Methods

We developed a deep-learning framework based on a dual-loss Siamese ResNet network to extract fine-grained information from the longitudinal structural magnetic resonance imaging (MRI) data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. We then conducted genome-wide association studies (GWAS) and post-GWAS analyses to reveal the genetic basis of AD-related accelerated cognitive decline.

Results

We used our model to process data from 1,313 individuals, training it on 414 cognitively normal people and predicting cognitive assessment for all participants. In our analysis of accelerated cognitive decline GWAS, we identified two genome-wide significant loci: APOE locus (chromosome 19 p13.32) and rs144614292 (chromosome 11 p15.1). Variant rs144614292 (G > T) has not been reported in previous AD GWA studies. It is within the intronic region of NELL1, which is expressed in neurons and plays a role in controlling cell growth and differentiation. The cell-type-specific enrichment analysis and functional enrichment of GWAS signals highlighted the microglia and immune-response pathways.

Conclusions

Our deep learning model effectively extracted relevant neuroimaging features and predicted individual cognitive decline. We reported a novel variant (rs144614292) within the NELL1 gene.

Towards a Unitary Hypothesis of Alzheimer's Disease Pathogenesis

The "amyloid cascade" hypothesis of Alzheimer's disease (AD) pathogenesis invokes the accumulation in the brain of plaques (containing the amyloid-β protein precursor [AβPP] cleavage product amyloid-β [Aβ]) and tangles (containing hyperphosphorylated tau) as drivers of pathogenesis. However, the poor track record of clinical trials based on this hypothesis suggests that the accumulation of these peptides is not the only cause of AD. Here, an alternative hypothesis is proposed in which the AβPP cleavage product C99, not Aβ, is the main culprit, via its role as a regulator of cholesterol metabolism. C99, which is a cholesterol sensor, promotes the formation of mitochondria-associated endoplasmic reticulum (ER) membranes (MAM), a cholesterol-rich lipid raft-like subdomain of the ER that communicates, both physically and biochemically, with mitochondria. We propose that in early-onset AD (EOAD), MAM-localized C99 is elevated above normal levels, resulting in increased transport of cholesterol from the plasma membrane to membranes of intracellular organelles, such as ER/endosomes, thereby upregulating MAM function and driving pathology. By the same token, late-onset AD (LOAD) is triggered by any genetic variant that increases the accumulation of intracellular cholesterol that, in turn, boosts the levels of C99 and again upregulates MAM function. Thus, the functional cause of AD is upregulated MAM function that, in turn, causes the hallmark disease phenotypes, including the plaques and tangles. Accordingly, the MAM hypothesis invokes two key interrelated elements, C99 and cholesterol, that converge at the MAM to drive AD pathogenesis. From this perspective, AD is, at bottom, a lipid disorder.

Molecular and Therapeutic Targets for Amyloid-beta Plaques in Alzheimer's Disease: A Review Study

Alzheimer's disease (AD) is characterized by progressive loss of cognition and a gradual decrease in memory. Although AD is considered the most persistent form of dementia and a global concern, no complete cure or agents that can completely halt the progression of AD have been found. In the past years, significant progress has been made in understanding the cellular and molecular changes associated with AD, and numerous drug targets have been identified for the development of drugs for this disease. Amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFT) are the major attributes of AD. Symptomatic relief is the only possible treatment available at present and a disease-modifying drug is of utmost importance. The development of drugs that can inhibit different targets responsible for the formation of plaques is a potential area in AD research. This review is not a complete list of all possible targets for AD but serves to highlight the targets related to Aβ pathology and pathways concerned with the formation of Aβ fragments. This shall serve as a prospect in the identification of Aβ plaque inhibitors and pave the strategies for newer drug treatments. Nevertheless, substantial research is done in this area but to bridle, the clinical difficulty remains a concern.

Exploring cerebral amyloid angiopathy: Insights into pathogenesis, diagnosis, and treatment

Cerebral Amyloid Angiopathy (CAA) is a neurological disorder characterized by the deposition of amyloid plaques in the walls of cerebral blood vessels. This condition poses significant challenges in terms of understanding its underlying mechanisms, accurate diagnosis, and effective treatment strategies. This article aims to shed light on the complexities of CAA by providing insights into its pathogenesis, diagnosis, and treatment options. The pathogenesis of CAA involves the accumulation of amyloid beta (Aβ) peptides in cerebral vessels, leading to vessel damage, impaired blood flow, and subsequent cognitive decline. Various genetic and environmental factors contribute to the development and progression of CAA, and understanding these factors is crucial for targeted interventions. Accurate diagnosis of CAA often requires advanced imaging techniques, such as magnetic resonance imaging (MRI) or positron emission tomography (PET) scans, to detect characteristic amyloid deposits in the brain. Early and accurate diagnosis enables appropriate management and intervention strategies. Treatment of CAA focuses on preventing further deposition of amyloid plaques, managing associated symptoms, and reducing the risk of complications such as cerebral hemorrhage. Currently, there are no disease-modifying therapies specifically approved for CAA. However, several experimental treatments targeting Aβ clearance and anti-inflammatory approaches are being investigated in clinical trials, offering hope for future therapeutic advancements.

Disentangling accelerated cognitive decline from the normal aging process and unraveling its genetic components: A neuroimaging-based deep learning approach

Background

The progressive cognitive decline that is an integral component of AD unfolds in tandem with the natural aging process. Neuroimaging features have demonstrated the capacity to distinguish cognitive decline changes stemming from typical brain aging and Alzheimer's disease between different chronological points.

Methods

We developed a deep-learning framework based on dual-loss Siamese ResNet network to extract fine-grained information from the longitudinal structural magnetic resonance imaging (MRI) data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) study. We then conducted genome-wide association studies (GWAS) and post-GWAS analyses to reveal the genetic basis of AD-related accelerated cognitive decline.

Results

We used our model to process data from 1,313 individuals, training it on 414 cognitively normal people and predicting cognitive assessment for all participants. In our analysis of accelerated cognitive decline GWAS, we identified two genome-wide significant loci: APOE locus (chromosome 19 p13.32) and rs144614292 (chromosome 11 p15.1). Variant rs144614292 (G>T) has not been reported in previous AD GWA studies. It is within the intronic region of NELL1, which is expressed in neuron and plays a role in controlling cell growth and differentiation. In addition, MUC7 and PROL1/OPRPNon chromosome 4 were significant at the gene level. The cell-type-specific enrichment analysis and functional enrichment of GWAS signals highlighted the microglia and immune-response pathways. Furthermore, we found that the cognitive decline slope GWAS was positively correlated with previous AD GWAS.

Conclusion

Our deep learning model was demonstrated effective on extracting relevant neuroimaging features and predicting individual cognitive decline. We reported a novel variant (rs144614292) within the NELL1 gene. Our approach has the potential to disentangle accelerated cognitive decline from the normal aging process and to determine its related genetic factors, leveraging opportunities for early intervention.

Genetically engineered neural stem cells (NSCs) therapy for neurological diseases; state-of-the-art

Neural stem cells (NSCs) are multipotent stem cells with remarkable self-renewal potential and also unique competencies to differentiate into neurons, astrocytes, and oligodendrocytes (ODCs) and improve the cellular microenvironment. In addition, NSCs secret diversity of mediators, including neurotrophic factors (e.g., BDNF, NGF, GDNF, CNTF, and NT-3), pro-angiogenic mediators (e.g., FGF-2 and VEGF), and anti-inflammatory biomolecules. Thereby, NSCs transplantation has become a reasonable and effective treatment for various neurodegenerative disorders by their capacity to induce neurogenesis and vasculogenesis and dampen neuroinflammation and oxidative stress. Nonetheless, various drawbacks such as lower migration and survival and less differential capacity to a particular cell lineage concerning the disease pathogenesis hinder their application. Thus, genetic engineering of NSCs before transplantation is recently regarded as an innovative strategy to bypass these hurdles. Indeed, genetically modified NSCs could bring about more favored therapeutic influences post-transplantation in vivo, making them an excellent option for neurological disease therapy. This review for the first time offers a comprehensive review of the therapeutic capability of genetically modified NSCs rather than naïve NSCs in neurological disease beyond brain tumors and sheds light on the recent progress and prospect in this context.

Advances in Amyloid-β Clearance in the Brain and Periphery: Implications for Neurodegenerative Diseases

This review examines the role of impaired amyloid-β clearance in the accumulation of amyloid-β in the brain and the periphery, which is closely associated with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). The molecular mechanism underlying amyloid-β accumulation is largely unknown, but recent evidence suggests that impaired amyloid-β clearance plays a critical role in its accumulation. The review provides an overview of recent research and proposes strategies for efficient amyloid-β clearance in both the brain and periphery. The clearance of amyloid-β can occur through enzymatic or non-enzymatic pathways in the brain, including neuronal and glial cells, blood-brain barrier, interstitial fluid bulk flow, perivascular drainage, and cerebrospinal fluid absorption-mediated pathways. In the periphery, various mechanisms, including peripheral organs, immunomodulation/immune cells, enzymes, amyloid-β-binding proteins, and amyloid-β-binding cells, are involved in amyloid-β clearance. Although recent findings have shed light on amyloid-β clearance in both regions, opportunities remain in areas where limited data is available. Therefore, future strategies that enhance amyloid-β clearance in the brain and/or periphery, either through central or peripheral clearance approaches or in combination, are highly encouraged. These strategies will provide new insight into the disease pathogenesis at the molecular level and explore new targets for inhibiting amyloid-β deposition, which is central to the pathogenesis of sporadic AD (amyloid-β in parenchyma) and CAA (amyloid-β in blood vessels).

Nucleic acid drug vectors for diagnosis and treatment of brain diseases

Nucleic acid drugs have the advantages of rich target selection, simple in design, good and enduring effect. They have been demonstrated to have irreplaceable superiority in brain disease treatment, while vectors are a decisive factor in therapeutic efficacy. Strict physiological barriers, such as degradation and clearance in circulation, blood-brain barrier, cellular uptake, endosome/lysosome barriers, release, obstruct the delivery of nucleic acid drugs to the brain by the vectors. Nucleic acid drugs against a single target are inefficient in treating brain diseases of complex pathogenesis. Differences between individual patients lead to severe uncertainties in brain disease treatment with nucleic acid drugs. In this Review, we briefly summarize the classification of nucleic acid drugs. Next, we discuss physiological barriers during drug delivery and universal coping strategies and introduce the application methods of these universal strategies to nucleic acid drug vectors. Subsequently, we explore nucleic acid drug-based multidrug regimens for the combination treatment of brain diseases and the construction of the corresponding vectors. In the following, we address the feasibility of patient stratification and personalized therapy through diagnostic information from medical imaging and the manner of introducing contrast agents into vectors. Finally, we take a perspective on the future feasibility and remaining challenges of vector-based integrated diagnosis and gene therapy for brain diseases.

iTRAQ-Based Proteomic Analysis of APP Transgenic Mouse Urine Exosomes

Alzheimer's disease (AD) is a common dementia disease in the elderly. To get a better understanding of the pathophysiology, we performed a proteomic analysis of the urine exosomes (U-exo) in AD model mice (J20). The polymer precipitation method was used to isolate U-exo from the urine of 3-month-old J20 and wild-type (WT) mice. Neuron-derived exosome (N-exo) was isolated from U-exo by immunoprecipitation. iTRAQ-based MALDI TOF MS/MS was used for proteomic analysis. The results showed that compared to WT, the levels of 61 and 92 proteins were increased in the J20 U-exo and N-exo, respectively. Gene ontology enrichment analysis demonstrated that the sphingolipid catabolic process, ceramide catabolic process, membrane lipid catabolic process, Aβ clearance, and Aβ metabolic process were highly enriched in U-exo and N-exo. Among these, Asah1 was shown to be the key protein in lipid metabolism, and clusterin, ApoE, neprilysin, and ACE were related to Aβ metabolism and clearance. Furthermore, protein-protein interaction analysis identified four protein complexes where clusterin and ApoE participated as partner proteins. Thus, J20 U-exo and N-exo contain proteins related to lipid- and Aβ-metabolism in the early stages of AD, providing a new insight into the underlying pathological mechanism of early AD.

Poly(I:C) promotes neurotoxic amyloid β accumulation through reduced degradation by decreasing neprilysin protein levels in astrocytes

Inflammation associated with viral infection of the nervous system has been involved in the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD) and multiple sclerosis. Polyinosinic:polycytidylic acid (poly[I:C]) is a Toll-like receptor 3 (TLR3) agonist that mimics the inflammatory response to systemic viral infections. Despite growing recognition of the role of glial cells in AD pathology, their involvement in the accumulation and clearance of amyloid β (Aβ) in the brain of patients with AD is poorly understood. Neprilysin (NEP) and insulin-degrading enzyme (IDE) are the main Aβ-degrading enzymes in the brain. This study investigated whether poly(I:C) regulated Aβ degradation and neurotoxicity by modulating NEP and IDE protein levels through TLR3 in astrocytes. To this aim, primary rat primary astrocyte cultures were treated with poly(I:C) and inhibitors of the TLR3 signaling. Protein levels were assessed by Western blot. Aβ toxicity to primary neurons was measured by lactate dehydrogenase release. Poly(I:C) induced a significant decrease in NEP levels on the membrane of astrocytes as well as in the culture medium. The degradation of exogenous Aβ was markedly delayed in poly(I:C)-treated astrocytes. This delay significantly increased the neurotoxicity of exogenous Aβ1-42. Altogether, these results suggest that viral infections induce Aβ neurotoxicity by decreasing NEP levels in astrocytes and consequently preventing Aβ degradation.

Potential Roles of Extracellular Vesicles as Diagnosis Biomarkers and Therapeutic Approaches for Cognitive Impairment in Alzheimer’s Disease

Cognitive dysfunction, the major clinical manifestation of Alzheimer’s disease (AD), is caused by irreversible progressive neurological dysfunction. With the aging of the population, the incidence of AD is increasing year by year. However, there is neither a simple and accurate early diagnosis method, nor an effective method to alleviate or prevent the occurrence and progression of AD. Extracellular vesicles (EVs) are a number of heterogeneous membrane structures that arise from the endosome system or shed from the plasma membrane. In the brain, almost every kind of cell may have EVs, which are related to cell-cell communication and regulate cellular function. At present, an increasing body of evidence suggests that EVs play a crucial role in the pathogenesis of AD, and it is of great significance to use them as specific biomarkers and novel therapeutic targets for cognitive impairment in AD. This article reviews the potential role of EVs as diagnostic biomarkers and treatments for cognitive dysfunction in AD.

Amyloid Beta Dynamics in Biological Fluids-Therapeutic Impact

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

Extracellular Vesicles Released from Neprilysin Gene-Modified Human Umbilical Cord-Derived Mesenchymal Stem Cell Enhance Therapeutic Effects in an Alzheimer's Disease Animal Model

Alzheimer's disease (AD) animal studies have reported that mesenchymal stem cells (MSCs) have therapeutic effects; however, clinical trial results are controversial. Neprilysin (NEP) is the main cleavage enzyme of β-amyloid (Aβ), which plays a major role in the pathology and etiology of AD. We evaluated whether transplantation of MSCs with NEP gene modification enhances the therapeutic effects in an AD animal model and then investigated these pathomechanisms. We manufactured NEP gene-enhanced human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) and intravenously transplanted them in Aβ_1-42-injected AD animal models. We compared the differences in behavioral tests and immunohistochemical assays between four groups: normal, Aβ_1-42 injection, naïve hUC-MSCs, and NEP-enhanced hUC-MSCs. Both naïve and NEP-enhanced hUC-MSC groups showed significant improvements in memory compared to the Aβ_1-42 injection group. There was no significant difference between naïve and NEP-enhanced hUC-MSC groups. There was a significant decrease in Congo red, BACE-1, GFAP, and Iba-1 and a significant increase in BDNF, NeuN, and NEP in both hUC-MSC groups compared to the Aβ_1-42 injection group. Among them, BDNF, NeuN, GFAP, Iba-1, and NEP showed more significant changes in the NEP-enhanced hUC-MSC group than in the naïve group. After stem cell injection, stem cells were not found. Extracellular vesicles (EVs) were equally observed in the hippocampus in the naïve and NEP-enhanced hUC-MSC groups. However, the EVs of NEP-enhanced hUC-MSCs contained higher amounts of NEP as compared to the EVs of naïve hUC-MSCs. Thus, hUC-MSCs affect AD animal models through stem cell-released EVs. Although there was no significant difference in cognitive function between the hUC-MSC groups, NEP-enhanced hUC-MSCs had superior neurogenesis and anti-inflammation properties compared to naïve hUC-MSCs due to increased NEP in the hippocampus by enriched NEP-possessing EVs. NEP gene-modified MSCs that release an increased amount of NEP within EVs may be a promising therapeutic option in AD treatment.

Microbial Infections Are a Risk Factor for Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, comprise a family of disorders characterized by progressive loss of nervous system function. Neuroinflammation is increasingly recognized to be associated with many neurodegenerative diseases but whether it is a cause or consequence of the disease process is unclear. Of growing interest is the role of microbial infections in inciting degenerative neuroinflammatory responses and genetic factors that may regulate those responses. Microbial infections cause inflammation within the central nervous system through activation of brain-resident immune cells and infiltration of peripheral immune cells. These responses are necessary to protect the brain from lethal infections but may also induce neuropathological changes that lead to neurodegeneration. This review discusses the molecular and cellular mechanisms through which microbial infections may increase susceptibility to neurodegenerative diseases. Elucidating these mechanisms is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of neurodegenerative diseases.

Association of Vitamin D Receptor Polymorphisms with Amyloid-β Transporters Expression and Risk of Mild Cognitive Impairment in a Chilean Cohort

Background: Amyloid-β peptide (Aβ) deposition in Alzheimer’s disease (AD) is due to an imbalance in its production/clearance rate. Aβ is transported across the blood-brain barrier by LRP1 and P-gp as efflux transporters and RAGE as influx transporter. Vitamin D deficit and polymorphisms of the vitamin D receptor (VDR) gene are associated with high prevalence of mild cognitive impairment (MCI) and AD. Further, vitamin D promotes the expression of LRP1 and P-gp in AD-animal model brains. Objective: To associate VDR polymorphisms Apa I (rs7975232), Taq I (rs731236), and Fok I (rs2228570) with the risk of developing MCI in a Chilean population, and to evaluate the relationship of these polymorphisms to the expression of VDR and Aβ-transporters in peripheral blood mononuclear cells (PBMCs). Methods: VDR polymorphisms Apa I, Taq I, and Fok I were determined in 128 healthy controls (HC) and 66 MCI patients. mRNA levels of VDR and Aβ-transporters were evaluated in subgroups by qPCR. Results: Alleles A of Apa I and C of Taq I were associated with a lower risk of MCI. HC with the Apa I AA genotype had higher mRNA levels of P-gp and LRP1, while the expression of VDR and RAGE were higher in MCI patients and HC. For Fok I, the TC genotype was associated with lower expression levels of Aβ-transporters in both groups. Conclusion: We propose that the response to vitamin D treatment will depend on VDR polymorphisms, being more efficient in carriers of protective alleles of Apa I polymorphism.

A Fundamental Role for Oxidants and Intracellular Calcium Signals in Alzheimer's Pathogenesis-And How a Comprehensive Antioxidant Strategy May Aid Prevention of This Disorder

Oxidative stress and increased cytoplasmic calcium are key mediators of the detrimental effects on neuronal function and survival in Alzheimer's disease (AD). Pathways whereby these perturbations arise, and then prevent dendritic spine formation, promote tau hyperphosphorylation, further amplify amyloid β generation, and induce neuronal apoptosis, are described. A comprehensive program of nutraceutical supplementation, comprised of the NADPH oxidase inhibitor phycocyanobilin, phase two inducers, the mitochondrial antioxidant astaxanthin, and the glutathione precursor N-acetylcysteine, may have important potential for antagonizing the toxic effects of amyloid β on neurons and thereby aiding prevention of AD. Moreover, nutraceutical antioxidant strategies may oppose the adverse impact of amyloid β oligomers on astrocyte clearance of glutamate, and on the ability of brain capillaries to export amyloid β monomers/oligomers from the brain. Antioxidants, docosahexaenoic acid (DHA), and vitamin D, have potential for suppressing microglial production of interleukin-1β, which potentiates the neurotoxicity of amyloid β. Epidemiology suggests that a health-promoting lifestyle, incorporating a prudent diet, regular vigorous exercise, and other feasible measures, can cut the high risk for AD among the elderly by up to 60%. Conceivably, complementing such lifestyle measures with long-term adherence to the sort of nutraceutical regimen outlined here may drive down risk for AD even further.

Gene therapy-mediated enhancement of protective protein expression for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the leading form of dementia but lacks curative treatments. Current understanding of AD aetiology attributes the development of the disease to the misfolding of two proteins; amyloid-β (Aβ) and hyperphosphorylated tau, with their pathological accumulation leading to concomitant oxidative stress, neuroinflammation, and neuronal death. These processes are regulated at multiple levels to maintain homeostasis and avert disease. However, many of the relevant regulatory proteins appear to be downregulated in the AD-afflicted brain. Enhancement/restoration of these 'protective' proteins, therefore, represents an attractive therapeutic avenue. Gene therapy is a desirable means of achieving this because it is not associated with the side-effects linked to systemic protein administration, and sustained protein expression virtually eliminates compliance issues. The current article represents a focused and succinct review of the better established 'protective' protein targets for gene therapy enhancement/restoration rather than being designed as an exhaustive review incorporating less validated protein subjects. In addition, we will discuss how the risks associated with uncontrolled or irreversible gene expression might be mitigated through combining neuronal-specific promoters, inducible expression systems and localised injections. Whilst many of the gene therapy targets reviewed herein are yet to enter clinical trials, preclinical testing has thus far demonstrated encouraging potential for the gene therapy-based treatment of AD.

Type 2 diabetes mellitus-associated transcriptome alterations in cortical neurones and associated neurovascular unit cells in the ageing brain

Type 2 diabetes mellitus (T2D), characterised by peripheral insulin resistance, is a risk factor for dementia. In addition to its contribution to small and large vessel disease, T2D may directly damage cells of the brain neurovascular unit. In this study, we investigated the transcriptomic changes in cortical neurones, and associated astrocytes and endothelial cells of the neurovascular unit, in the ageing brain. Neurone, astrocyte, and endothelial cell-enriched mRNA, obtained by immuno-laser capture microdissection of temporal cortex (Brodmann area 21/22) from 6 cases with self-reported T2D in the Cognitive Function and Ageing Study neuropathology cohort, and an equal number of age and sex-matched controls, was assessed by microarray analysis. Integrated Molecular Pathway Level Analysis was performed using the Kyoto Encyclopaedia of Genes and Genomes database on significantly differentially expressed genes, defined as P < 0.05 and fold-change ± 1.2. Hub genes identified from Weighted Gene Co-expression Network Analysis were validated in neurones using the NanoString nCounter platform. The expression and cellular localisation of proteins encoded by selected candidate genes were confirmed by immunohistochemistry. 912, 2202, and 1227 genes were significantly differentially expressed between cases with self-reported T2D and controls in neurones, astrocytes, and endothelial cells respectively. Changes in cortical neurones included alterations in insulin and other signalling pathways, cell cycle, cellular senescence, inflammatory mediators, and components of the mitochondrial respiratory electron transport chain. Impaired insulin signalling was shared by neurovascular unit cells with, additionally, apoptotic pathway changes in astrocytes and dysregulation of advanced glycation end-product signalling in endothelial cells. Transcriptomic analysis identified changes in key cellular pathways associated with T2D that may contribute to neuronal damage and dysfunction. These effects on brain cells potentially contribute to a diabetic dementia, and may provide novel approaches for therapeutic intervention.

Exercise as Potential Therapeutic Target to Modulate Alzheimer's Disease Pathology in APOE ε4 Carriers: A Systematic Review

Alzheimer's disease (AD) is a progressive neurodegenerative disease for which no effective treatment exists at present. Previous research has found that exercise reduces the risk of AD. Since the apolipoprotein E (APOE) ε4 allele increases the risk of AD and is associated with faster disease progression than the other isoforms, we aimed to highlight the impact of exercise on AD pathology in APOE ε4 carriers. This review focuses on the effect of exercise on cognitive function, dementia risk, amyloid-β (Aβ) metabolism, lipid metabolism, neuroinflammation, neurotrophic factors and vascularization in APOE ε4 carriers. We searched the literature in the PubMed electronic database using the following search terms: physical activity, exercise, aerobic fitness, training, sport, APOE4, Alzheimer's disease, AD and dementia. By cross-referencing, additional publications were identified. Selected studies required older adults to take part in an exercise intervention or to make use of self-reported physical activity questionnaires. All included studies were written and published in English between 2000 and 2020. From these studies, we conclude that exercise is a non-pharmacological treatment option for high-risk APOE ε4 carriers to ameliorate the AD pathological processes including reducing Aβ load, protecting against hippocampal atrophy, improving cognitive function, stabilizing cholesterol levels and lowering pro-inflammatory signals. Variation in study design related to age, cognitive outcomes and the type of intervention explained the differences in study outcomes. However, exercise seems to be effective in delaying the onset of AD and may improve the quality of life of AD patients.

Effects of GrandFusion Diet on Cognitive Impairment in Transgenic Mouse Model of Alzheimer's Disease

Alzheimer’s disease (AD) is the result of the deposition of amyloid β (Aβ) peptide into amyloid fibrils and tau into neurofibrillary tangles. At the present time, there are no possible treatments for the disease. We have recently shown that diets enriched in phytonutrients show protection or limit the extent of damage in a number of neurological disorders. GrandFusion (GF) diets have attenuated the outcomes in animal models of traumatic brain injury, cerebral ischemia, and chronic traumatic encephalopathy. In this study, we investigated the effect of GF diets in a mouse model of AD prior to the development of amyloid plaques to show how this treatment paradigm would alter the accumulation of Aβ peptide and related pathologic changes (i.e., inflammation, cathepsin B, and memory impairment). Administration of GF diets (2–4%) over a period of four months in APP/ΔPS1 double-transgenic mice resulted in attenuation in Aβ peptide levels, reduction of amyloid load, and inflammation, increased cathepsin B expression, and improved spatial orientation. Additionally, treatment with GF diets increased nerve growth factor (NGF) levels in the brain and tempered the memory impairment in the animal model. These data suggest that GF diets may alter the development and progression of the mechanisms associated with the disease process to effectively modify AD pathogenesis.

Neprilysin expression and functions in development, ageing and disease

Neprilysin (NEP) is an integral membrane-bound metallopeptidase with a wide spectrum of substrates and physiological functions. It plays an important role in proteolytic processes in the kidney, cardiovascular regulation, immune response, cell proliferation, foetal development etc. It is an important neuropeptidase and amyloid-degrading enzyme which makes NEP a therapeutic target in Alzheimer's disease (AD). Moreover, it plays a preventive role in development of cancer, obesity and type-2 diabetes. Recently a role of NEP in COVID-19 pathogenesis has also been suggested. Despite intensive research into NEP structure and functions in different organisms, changes in its expression and regulation during brain development and ageing, especially in age-related pathologies, is still not fully understood. This prevents development of pharmacological treatments from various diseases in which NEP is implicated although recently a dual-acting drug sacubitril-valsartan (LCZ696) combining a NEP inhibitor and angiotensin receptor blocker has been approved for treatment of heart failure. Also, various natural compounds capable of upregulating NEP expression, including green tea (EGCG), have been proposed as a preventive medicine in prostate cancer and AD. This review summarizes the existing literature and our own research on the expression and activity of NEP in normal brain development, ageing and under pathological conditions.

Pharmacological Heart Failure Therapy in Children: Focus on Inotropic Support

Pediatric heart failure is a clinical syndrome, which needs to be distinctly defined and the pathophysiological consequences considered. Pharmacological treatment depends on the disease- and age-specific myocardial characteristics. Acute and chronic low cardiac output is the result of an inadequate heart rate (rhythm), myocardial contractility, preload and afterload, and also ventriculo-ventricular interaction, synchrony, atrio-ventricular and ventricular-arterial coupling. The treatment of choice is curing the cause of heart failure, if possible.Acute HF therapy is still based to the use of catecholamines and inodilators. The cornerstone of chronic HF treatment consists of blocking the endogenous, neuro-humoral axis, in particular the adrenergic and renin-angiotensin-aldosterone system.Before neprilysin inhibitors are used in young children, their potential side-effect for inducing Alzheimer disease needs to be clarified. The focus of the current review is put on the differential use of the inotropic drugs as epinephrine, norepinephrine, dopamine and dobutamine, and also the inodilators milrinone and levosimendan. Considering effects and side-effects of any cardiac stimulating treatment strategy, co-medication with ß-blockers, angiotensin converting inhibitors (ACEIs), angiotensin blockers (ARBs) and mineralocorticoid receptor antagonists (MRAs) is not a contradiction, but a senseful measure, even still during the acute inotropic treatment.Missing sophisticated clinical trials using accurate entry criteria and clinically relevant endpoints, there is especially in cardiovascular diagnosis and treatment of young children a compromise of evidence-based versus pathophysiology-based procedures. But based on the pharmacological and pathophysiological knowledge a hypothesis-driven individualized treatment is already currently possible and therefore indicated.

Traumatic Injury Reduces Amyloid Plaque Burden in the Transgenic 5xFAD Alzheimer's Mouse Spinal Cord

BACKGROUND

Axonal injury has been implicated in the development of amyloid-β in experimental brain injuries and clinical cases. The anatomy of the spinal cord provides a tractable model for examining the effects of trauma on amyloid deposition.

OBJECTIVE

Our goal was to examine the effects of axonal injury on plaque formation and clearance using wild type and 5xFAD transgenic Alzheimer's disease mice.

METHODS

We contused the spinal cord at the T12 spinal level at 10 weeks, an age at which no amyloid plaques spontaneously accumulate in 5xFAD mice. We then explored plaque clearance by impacting spinal cords in 27-week-old 5xFAD mice where amyloid deposition is already well established. We also examined the cellular expression of one of the most prominent amyloid-β degradation enzymes, neprilysin, at the lesion site.

RESULTS

No plaques were found in wild type animals at any time points examined. Injury in 5xFAD prevented plaque deposition rostral and caudal to the lesion when the cords were examined at 2 and 4 months after the impact, whereas age-matched naïve 5xFAD mice showed extensive amyloid plaque deposition. A massive reduction in the number of plaques around the lesion was found as early as 7 days after the impact, preceded by neprilysin upregulation in astrocytes at 3 days after injury. At 7 days after injury, the majority of amyloid was found inside microglia/macrophages.

CONCLUSION

These observations suggest that the efficient amyloid clearance after injury in the cord may be driven by the orchestrated efforts of astroglial and immune cells.

MCF7 Spheroid Development: New Insight about Spatio/Temporal Arrangements of TNTs, Amyloid Fibrils, Cell Connections, and Cellular Bridges

Human breast adenocarcinoma cells (MCF7) grow in three-dimensional culture as spheroids that represent the structural complexity of avascular tumors. Therefore, spheroids offer a powerful tool for studying cancer development, aggressiveness, and drug resistance. Notwithstanding the large amount of data regarding the formation of MCF7 spheroids, a detailed description of the morpho-functional changes during their aggregation and maturation is still lacking. In this study, in addition to the already established role of gap junctions, we show evidence of tunneling nanotube (TNT) formation, amyloid fibril production, and opening of large stable cellular bridges, thus reporting the sequential events leading to MCF7 spheroid formation. The variation in cell phenotypes, sustained by dynamic expression of multiple proteins, leads to complex networking among cells similar to the sequence of morphogenetic steps occurring in embryogenesis/organogenesis. On the basis of the observation that early events in spheroid formation are strictly linked to the redox homeostasis, which in turn regulate amyloidogenesis, we show that the administration of N-acetyl-l-cysteine (NAC), a reactive oxygen species (ROS) scavenger that reduces the capability of cells to produce amyloid fibrils, significantly affects their ability to aggregate. Moreover, cells aggregation events, which exploit the intrinsic adhesiveness of amyloid fibrils, significantly decrease following the administration during the early aggregation phase of neutral endopeptidase (NEP), an amyloid degrading enzyme.

Neuroinflammation drives APOE genotype-dependent differential expression of neprilysin

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by the deposition of amyloid-beta (Aβ) plaques and widespread neuroinflammation. While the cause of AD remains unknown, multiple factors likely contribute to the disease, including heart disease, diabetes, previous head injury, as well as a number of genetic determinants. Inheritance of the apolipoprotein (APOE) ε4 allele represents the strongest genetic risk factor for development of AD, driving pathogenesis and increasing overall disease severity. APOE has long been recognized as a key regulator of cholesterol homeostasis, although a greater appreciation now exists for its role in various innate immune system processes. Indeed, APOE modulates inflammatory environments in brain in large part by altering gene expression profiles in glia, important mediators of immunity in the CNS. While the association between APOE and AD was first observed nearly three decades ago, the mechanism by which APOE ε4 influences the etiology and pathophysiology of AD is not well characterized. Overwhelming data supports the hypothesis that APOE ε4 dysregulates central amyloid metabolism by an undetermined molecular mechanism, thus laying the foundation for disease. A host of amyloid-degrading enzymes (ADEs) regulate Aβ accumulation in brain, and therefore represent valuable therapeutic targets. Neprilysin (NEP), a metalloendopeptidase expressed by activated microglia and astrocytes, is a broad-spectrum ADE able to degrade a variety of Aβ species. Here we describe in vivo and in vitro experiments designed to investigate the potential for APOE genotype to differentially regulate glial NEP in brain under neuroinflammatory conditions. Our results provide a novel mechanism by which APOE genotype-dependent differential expression of NEP by glia during neuroinflammation may contribute to AD pathogenesis.

Protein kinases A and C regulate amyloid-β degradation by modulating protein levels of neprilysin and insulin-degrading enzyme in astrocytes

The pathology of sporadic Alzheimer's disease is hallmarked by altered signal transduction via the neurotransmitter receptor-G-protein-mediated protein kinase A (PKA) and protein kinase C (PKC) pathways. Because the accumulation of amyloid-β (Aβ) depends on its rates of synthesis and clearance, the metabolic pathway of Aβ in the brain and the entire body warrants exploration. The two major enzymes involved in Aβ degradation in the brain are believed to be the neprilysin and insulin-degrading enzyme (IDE). This study investigated whether PKA and PKC regulate the degradation of Aβ by modulating the protein levels of neprilysin and IDE in astrocytes. Activation of PKA induced a significant decrease in neprilysin protein levels in cultured astrocytes, whereas activation of PKC induced a significant decrease in the protein level of neprilysin and an increase in the protein level of IDE. Following activation of PKC, the reduction of neprilysin was achieved by its secretion into the culture media. Moreover, PKA-activated astrocytes significantly delayed the degradation of exogenous Aβ, whereas PKC-activated astrocytes significantly facilitated its degradation. These results suggest that PKA and PKC regulate Aβ degradation in astrocytes through a decrease in the protein level of neprilysin and an increase in neprilysin secretion and protein levels of IDE, respectively.

DNA methylation in the pathology of Alzheimer's disease: from gene to cognition

Alzheimer's disease (AD) is a debilitating disorder that manifests with amyloid beta plaque deposition, neurofibrillary tangles, neuronal loss, and severe cognitive impairment. Although much effort has been made to decipher the pathogenesis of this disease, the mechanisms causing these detrimental outcomes remain obscure. Over the past few decades, neuroepigenetics has emerged as an important field that, among other things, explores how reversible modifications can change gene expression to control behavior and cognitive abilities. Among epigenetic modifications, DNA methylation requires further elucidation for the conflicting observations from AD research and its pivotal role in learning and memory. In this review, we focus on the essential components of DNA methylation, the effects of aberrant methylation on gene expressions in the amyloidogenic pathway and neurochemical processes, as well as memory epigenetics in Alzheimer's disease.

Tryptophan metabolites modify brain Aβ peptide degradation: A role in Alzheimer's disease?

Among several processes, a decrease in amyloid-beta (Aβ) peptide elimination is thought to be one of the major pathophysiological factors in Alzheimer's disease (AD). Neprilysin (NEP) is a key metalloproteinase controlling the degradation and clearance of Aβ peptides in the brain. NEP is induced by several pharmacological substances, amyloid deposits and somatostatin, but the physiological regulation of its expression remains unclear. This situation hampers the exploitation of NEP regulatory factors/mechanisms to develop effective strategies against Aβ peptide accumulation-induced brain toxicity. Based on recent data aimed at elucidating this major question, the present paper addresses and critically discusses the role of 5-hydroxyindole-acetic acid (5-HIAA) and kynurenic acid (KYNA) in the regulation of NEP activity/expression in the brain. Both 5-HIAA and KYNA are endogenous metabolites of tryptophan, an essential amino-acid obtained through diet and gut microbiome. By interacting with the aryl hydrocarbon receptor, various tryptophan metabolites modulate several metalloproteinases regulating brain Aβ peptide levels under normal and pathological conditions such as AD. In particular, interesting data reviewed here show that 5-HIAA and KYNA stimulate NEP activity/expression to prevent Aβ peptide-induced neurotoxicity. These data open promising perspectives for the development of tryptophan metabolite-based therapies against AD.

Novel Anti-Alzheimer's Therapeutic Molecules Targeting Amyloid Precursor Protein Processing

Alzheimer's disease (AD) is the most common cause of dementia among older people, and the prevalence of this disease is estimated to rise quickly in the upcoming years. Unfortunately, almost all of the drug candidates tested for AD until now have failed to exhibit any efficacy. Henceforth, there is an increased necessity to avert and/or slow down the advancement of AD. It is known that one of the major pathological characteristics of AD is the presence of senile plaques (SPs) in the brain. These SPs are composed of aggregated amyloid beta (Aβ), derived from the amyloid precursor protein (APP). Pharmaceutical companies have conducted a number of studies in order to identify safe and effective anti-Aβ drugs to combat AD. It is known that α-, β-, and γ-secretases are the three proteases that are involved in APP processing. Furthermore, there is a growing interest in these proteases, as they have a contribution to the modulation and production of Aβ. It has been observed that small compounds can be used to target these important proteases. Indeed, these compounds must satisfy the common strict requirements of a drug candidate targeted for brain penetration and selectivity toward different proteases. In this article, we have focused on the auspicious molecules which are under development for targeting APP-processing enzymes. We have also presented several anti-AD molecules targeting Aβ accumulation and phosphorylation signaling in APP processing. This review highlights the structure-activity relationship and other physicochemical features of several pharmacological candidates in order to successfully develop new anti-AD drugs.

Peroxidase activity of heme bound amyloid β peptides associated with Alzheimer's disease

The amyloid cascade hypothesis attributes the neurodegeneration observed in Alzheimer's disease (AD) to the deposition of the amyloid β (Aβ) peptide into plaques and fibrils in the AD brain. The metal ion hypothesis which implicates several metal ions, viz. Zn²⁺, Cu²⁺ and Fe³⁺, in the AD pathology on account of their abnormal accumulation in the Aβ plaques along with an overall dyshomeostasis of these metals in the AD brain was proposed a while back. Metal ion chelators and ionophores, put forward as possible drug candidates for AD, are yet to succeed in clinical trials. Heme, which is widely distributed in the mammalian body as the prosthetic group of several important proteins and enzymes, has been thought to be associated with AD by virtue of its colocalization in the Aβ plaques along with the similarity of several heme deficiency symptoms with those of AD and most importantly, due to its ability to bind Aβ. This feature article illustrates the active site environment of heme-Aβ which resembles those of peroxidases. It also discusses the peroxidase activity of heme-Aβ, its ability to effect oxidative degradation of neurotransmitters like serotonin and also the identification of the highly reactive high-valent intermediate, compound I. The effect of second sphere residues on the formation and peroxidase activity of heme-Aβ along with the generation and decay of compound I is highlighted throughout the article. The reactivities of heme bound Aβ peptides give an alternative theory to understand the possible cause of this disease.

Brain Shuttle Neprilysin reduces central Amyloid-β levels

Reducing Amyloid β (Aβ) in the brain is of fundamental importance for advancing the therapeutics for Alzheimer`s disease. The endogenous metallopeptidase neprilysin (NEP) has been identified as one of the key Aβ-degrading enzymes. Delivery of NEP to the brain by utilizing the Brain Shuttle (BS) transport system offers a promising approach for clearing central Aβ. We fused the extracellular catalytic domain of NEP to an active or inactive BS module. The two BS-NEP constructs were used to investigate the pharmacokinetic/pharmacodynamics relationships in the blood and the cerebrospinal fluid (CSF) in dose-response and multiple dosing. As previously shown, NEP was highly effective at degrading Aβ in blood but not in the CSF compartment after systemic administration. In contrast, the NEP with an active BS module led to a significant CSF exposure of BS-NEP, followed by substantial Aβ reduction in CSF and brain parenchyma. Our data show that a BS module against the transferrin receptor facilitates the transport of an Aβ degrading enzyme across the blood-brain barriers to efficiently reduce Aβ levels in both CSF and brain.

Expression of Neprilysin in Skeletal Muscle by Ultrasound-Mediated Gene Transfer (Sonoporation) Reduces Amyloid Burden for AD

Amyloid β (Aβ) accumulation in the brain is considered to be one of the major pathological changes in the progression of Alzheimer’s disease (AD). Neprilysin (NEP) is a zinc metallopeptidase that efficiently degrades Aβ. However, conventional approaches for increasing NEP levels or inducing its activation via viral-vector gene delivery have been shown to be problematic due to complications involving secondary toxicity, immune responses, and/or low gene transfer efficiency. Thus, in the present study, a physical and tractable NEP gene-delivery system via ultrasound (US) combined with microbubbles was developed for AD therapy. We introduced the plasmid, human NEP (hNEP), into skeletal muscle of 6-month-old amyloid precursor protein/presenilin-1 (APP/PS1) AD mice. Interestingly, we found a significantly reduced Aβ burden in the brain at 1 month after the delivery of overexpressed hNEP into skeletal muscle. Moreover, hNEP-treated AD mice exhibited improved performance in the Morris water maze compared to that of untreated AD mice. In addition, there were no apparent injuries in the injected muscle or in the lungs or kidneys at 1 month after the delivery of hNEP into skeletal muscle. These findings suggest that the introduction of hNEP into skeletal muscle via US represents an effective and safe therapeutic strategy for ameliorating AD-like symptoms in APP/PS1 mice, which may have the potential for clinical applications in the future.

Clinical trials of new drugs for Alzheimer disease

Alzheimer disease (AD) accounts for 60-70% of dementia cases. Given the seriousness of the disease and continual increase in patient numbers, developing effective therapies to treat AD has become urgent. Presently, the drugs available for AD treatment, including cholinesterase inhibitors and an antagonist of the N-methyl-D-aspartate receptor, can only inhibit dementia symptoms for a limited period of time but cannot stop or reverse disease progression. On the basis of the amyloid hypothesis, many global drug companies have conducted many clinical trials on amyloid clearing therapy but without success. Thus, the amyloid hypothesis may not be completely feasible. The number of anti-amyloid trials decreased in 2019, which might be a turning point. An in-depth and comprehensive understanding of the contribution of amyloid beta and other factors of AD is crucial for developing novel pharmacotherapies.In ongoing clinical trials, researchers have developed and are testing several possible interventions aimed at various targets, including anti-amyloid and anti-tau interventions, neurotransmitter modification, anti-neuroinflammation and neuroprotection interventions, and cognitive enhancement, and interventions to relieve behavioral psychological symptoms. In this article, we present the current state of clinical trials for AD at clinicaltrials.gov. We reviewed the underlying mechanisms of these trials, tried to understand the reason why prior clinical trials failed, and analyzed the future trend of AD clinical trials.

Enzyme-digested Colla Corii Asini (E'jiao) prevents hydrogen peroxide-induced cell death and accelerates amyloid beta clearance in neuronal-like PC12 cells

As an aging-associated degenerative disease, Alzheimer’s disease is characterized by the deposition of amyloid beta (Aβ), oxidative stress, inflammation, dysfunction and loss of cholinergic neurons. Colla Corii Asini (CCA) is a traditional Chinese medicine which has been used for feebleness-related diseases and anti-aging. CCA might delay aging-induced degenerative changes in neurons. In the present study, we evaluated antioxidant activity, cytoprotective effects, and Aβ removability of enzyme-digested Colla Corii Asini (CCAD). Oxygen radical absorbance capacity (ORAC) activity assay showed that, as compared to gelatins from the skin of porcine, bovine and cold water fish, CCA exhibited the highest ORAC activity. The ORAC activity of CCA and CCAD was increased gradually by the length of time in storage. Ultrastructure analysis by scanning electron microscopy showed that among CCA manufactured in 2008, 2013, 2017 and gelatin from cold water fish skin, CCA manufactured in 2008 presented the smoothest surface structure. We further tested the protective effects of CCAD (manufactured in 2008) and enzyme-digested gelatin from cold water fish skin (FGD) on hydrogen peroxide (H₂O₂)-induced cell death in nerve growth factor-differentiated neuronal-like PC12 cells. Presto blue assay showed that both FGD and CCAD at 0.5 mg/mL increased cell viability in H₂O₂-treated neuronal-like PC12 cells. The protection of CCAD was significantly superior to that of FGD. Acetylcholinesterase (AchE) assay showed that both FGD and CCAD inhibited AchE activity in nerve growth factor-differentiated neuronal-like PC12 cells to 89.1% and 74.5% of that in non-treated cells, respectively. The data suggest that CCAD might be able to increase the neurotransmitter acetylcholine. Although CCAD inhibited AchE activity in neuronal-like PC12 cells, CCAD prevented H₂O₂-induced abnormal deterioration of AchE. ELISA and neprilysin activity assay results indicated that CCAD reduced amyloid beta accumulation and increased neprilysin activity in Aβ_1–42-treated neuronal-like PC12 cells, suggesting that CCAD can enhance Aβ clearance. Our results suggest that CCA might be useful for preventing and treating Alzheimer’s disease.

Extracellular Vesicles as a Neprilysin Delivery System Memory Improvement in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative brain disorder which has no effective treatment yet due to the blood barrier in the brain that limits the drugs with the potential of disease improvement. Extracellular vesicles (EVs) are biocompatible nanoparticles with a lipid membrane. These vesicles are secreted from various cells such as mesenchymal stem cells (MSCs) and can pass through biological barriers for transfer of information such as signals or be used as carriers for various proteins like Neprilysin (NEP). NEP is an active enzyme in the clearance of abnormal aggregated beta-amyloid sheets in the brain. In the present study, we used EVs to carry NEP for memory improvement in Alzheimer's disease. For this purpose, bone marrow MSCs were isolated from rat femur. Stemness evaluation of established cells was characterized by differentiation potency and specific markers with flowcytometry. EVs were isolated from MSCs supernatant by ultracentrifugation and analyzed by scanning electron microscopy (SEM), dynamic light scattering (DLS) and western blotting. EVs were loaded with NEP by freeze-thaw cycle and then administrated intranasally in a rat model of the AD for 14 days. Our findings showed EV-loaded NEP caused a decrease in IL-1beta and also BAX but an increase in BCL2 expression level in the rat brain. Altogether, these data showed that EV-loaded NEP can improve brain-related behavioural function which may be mediated through the regulation of inflammation and apoptosis. These findings suggest that EV-loaded NEP can be considered as a potential drug delivery system for the improvement of AD.

BHBA treatment improves cognitive function by targeting pleiotropic mechanisms in transgenic mouse model of Alzheimer's disease

Accumulation of amyloid β (Aβ) peptide, inflammation, and oxidative stress contribute to Alzheimer's disease (AD) and trigger complex pathogenesis. The ketone body β-hydroxybutyrate (BHBA) is an endogenous metabolic intermediate that protects against stroke and neurodegenerative diseases, but the underlying mechanisms are unclear. The present study aims to elucidate the protective effects of BHBA in the early stage of AD model and investigate the underlying molecular mechanisms. Three-and-half-month-old double-transgenic mice (5XFAD) overexpressing β-amyloid precursor protein (APP) and presenilin-1 (PS1) were used as the AD model. The 5XFAD mice received 1.5 mmol/kg/d BHBA subcutaneously for 28 days. Morris water maze test, nest construction, and passive avoidance experiments were performed to assess the therapeutic effects on AD prevention in vivo, and brain pathology of 5XFAD mice including amyloid plaque deposition and microglia activation were assessed. Gene expression profiles in the cortexes of 5XFAD- and BHBA-treated 5XFAD mice were performed with high-throughput sequencing and bioinformatic analysis. Mouse HT22 cells were treated with 2 mM BHBA to explore its in vitro protective effects of BHBA on hippocampal neurons against Aβ oligomer toxicity, ATP production, ROS generation, and mitochondrial aerobic respiratory function. APP, BACE1, and neprilysin (NEP) expression levels were evaluated in HT22 cells following treatment with BHBA by measuring the presence or absence of G protein-coupled receptor 109A (GPR109A). BHBA improved cognitive function of 5XFAD mice in Morris water maze test, nesting construction and passive avoidance experiments, and attenuated Aβ accumulation and microglia overactivation in the brain. BHBA also enhanced mitochondrial respiratory function of hippocampal neurons and protected it from Aβ toxicity. The enzymes, APP and NEP were regulated by BHBA via G-protein-coupled receptor 109A (GPR109A). Furthermore, RNA sequencing revealed that BHBA-regulated genes mainly annotated in aging, immune system, nervous system, and neurodegenerative diseases. Our data suggested that BHBA confers protection against the AD-like pathological events in the AD mouse model by targeting multiple aspects of AD and it may become a promising candidate for the prevention and treatment of AD.

The genomes of two parasitic wasps that parasitize the diamondback moth

BACKGROUND

Parasitic insects are well-known biological control agents for arthropod pests worldwide. They are capable of regulating their host's physiology, development and behaviour. However, many of the molecular mechanisms involved in host-parasitoid interaction remain unknown.

RESULTS

We sequenced the genomes of two parasitic wasps (Cotesia vestalis, and Diadromus collaris) that parasitize the diamondback moth Plutella xylostella using Illumina and Pacbio sequencing platforms. Genome assembly using SOAPdenovo produced a 178 Mb draft genome for C. vestalis and a 399 Mb draft genome for D. collaris. A total set that contained 11,278 and 15,328 protein-coding genes for C. vestalis and D. collaris, respectively, were predicted using evidence (homology-based and transcriptome-based) and de novo prediction methodology. Phylogenetic analysis showed that the braconid C. vestalis and the ichneumonid D. collaris diverged approximately 124 million years ago. These two wasps exhibit gene gains and losses that in some cases reflect their shared life history as parasitic wasps and in other cases are unique to particular species. Gene families with functions in development, nutrient acquisition from hosts, and metabolism have expanded in each wasp species, while genes required for biosynthesis of some amino acids and steroids have been lost, since these nutrients can be directly obtained from the host. Both wasp species encode a relative higher number of neprilysins (NEPs) thus far reported in arthropod genomes while several genes encoding immune-related proteins and detoxification enzymes were lost in both wasp genomes.

CONCLUSIONS

We present the annotated genome sequence of two parasitic wasps C. vestalis and D. collaris, which parasitize a common host, the diamondback moth, P. xylostella. These data will provide a fundamental source for studying the mechanism of host control and will be used in parasitoid comparative genomics to study the origin and diversification of the parasitic lifestyle.