ADAMs family members as amyloid precursor protein alpha-secretases

Unlocking the therapeutic potential of P2X7 receptor: a comprehensive review of its role in neurodegenerative disorders

The P2X7 receptor (P2X7R), an ATP-gated ion channel, has emerged as a crucial player in neuroinflammation and a promising therapeutic target for neurodegenerative disorders. This review explores the current understanding of P2X7R's structure, activation, and physiological roles, focusing on its expression and function in microglial cells. The article examines the receptor's involvement in calcium signaling, microglial activation, and polarization, as well as its role in the pathogenesis of Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis. The review highlights the complex nature of P2X7R signaling, discussing its potential neuroprotective and neurotoxic effects depending on the disease stage and context. It also addresses the development of P2X7R antagonists and their progress in clinical trials, identifying key research gaps and future perspectives for P2X7R-targeted therapy development. By providing a comprehensive overview of the current state of knowledge and future directions, this review serves as a valuable resource for researchers and clinicians interested in exploring the therapeutic potential of targeting P2X7R for the treatment of neurodegenerative disorders.

A Disintegrin And Metalloprotease 10 expression within the murine central nervous system

A Disintegrin And Metalloprotease 10 (ADAM10), is able to control several important physiopathological processes through the shedding of a large number of protein substrates. Although ADAM10 plays a crucial role in the central nervous system (CNS) development and function, its protein distribution in the CNS has not been fully addressed. Here, we described the regional and cellular ADAM10 protein expression in C57BL/6 mice examined by immunofluorescence 1) throughout the adult mouse brain, cerebellum and spinal cord in vivo and 2) in different cell types as neurons, astrocytes, oligodendrocytes and microglia in vitro. We observed ADAM10 expression through the whole CNS, with a strong expression in the hippocampus, in the hypothalamus and in the cerebral and piriform cortex in the brain, in the Purkinje and in granular cell layers in the cerebellum and in the spinal cord to a lower extent. In vivo, ADAM10 protein expression was mainly found in neurons and in some oligodendroglial cell populations. However, in primary cultures we observed ADAM10 expression in neurons, oligodendrocytes, astrocytes and microglia. Interestingly, ADAM10 was not only found in the membrane but also in cytoplasmic vesicles and in the nucleus of primary cultured cells. Overall, this work highlights a wide distribution of ADAM10 throughout the CNS. The nuclear localization of ADAM10, probably due to its intracellular domain, emphasizes its role in cell signalling in physiological and pathological conditions. Further investigations are required to better elucidate the role of ADAM10 in glial cells.

Role of the prefrontal cortical protease TACE/ADAM17 in neurobehavioral responses to chronic stress during adolescence

INTRODUCTION

Chronic adolescent stress profoundly affects prefrontal cortical networks regulating top-down behavior control. However, the neurobiological pathways contributing to stress-induced alterations in the brain and behavior remain largely unknown. Chronic stress influences brain growth factors and immune responses, which may, in turn, disrupt the maturation and function of prefrontal cortical networks. The tumor necrosis factor alpha-converting enzyme/a disintegrin and metalloproteinase 17 (TACE/ADAM17) is a sheddase with essential functions in brain maturation, behavior, and inflammatory responses. This study aimed to determine the impact of stress on the prefrontal cortex and whether TACE/ADAM17 plays a role in these responses.

METHODS

We used a Lewis rat model that incorporates critical elements of chronic psychosocial stress, such as uncontrollability, unpredictability, lack of social support, and re-experiencing of trauma.

RESULTS

Chronic stress during adolescence reduced the acoustic startle reflex and social interactions while increasing extracellular free water content and TACE/ADAM17 mRNA levels in the medial prefrontal cortex. Chronic stress altered various ethological behavioral domains in the observation home cages (decreased ingestive behaviors and increased walking, grooming, and rearing behaviors). A group of rats was injected intracerebrally either with a novel Accell™ SMARTpool TACE/ADAM17 siRNA or a corresponding siRNA vehicle (control). The RNAscope Multiplex Fluorescent v2 Assay was used to visualize mRNA expression. Automated puncta quantification and analyses demonstrated that TACE/ADAM17 siRNA administration reduced TACE/ADAM17 mRNA levels in the medial prefrontal cortex (59% reduction relative to control). We found that the rats that received prefrontal cortical TACE/ADAM17 siRNA administration exhibited altered eating patterns (e.g., increased food intake and time in the feeding zone during the light cycle).

CONCLUSION

This study supports that the prefrontal cortex is sensitive to adolescent chronic stress and suggests that TACE/ADAM17 may be involved in the brain responses to stress.

Neuroinflammation of Microglial Regulation in Alzheimer's Disease: Therapeutic Approaches

Alzheimer's disease (AD) is a complex degenerative disease of the central nervous system that is clinically characterized by a progressive decline in memory and cognitive function. The pathogenesis of AD is intricate and not yet fully understood. Neuroinflammation, particularly microglial activation-mediated neuroinflammation, is believed to play a crucial role in increasing the risk, triggering the onset, and hastening the progression of AD. Modulating microglial activation and regulating microglial energy metabolic disorder are seen as promising strategies to intervene in AD. The application of anti-inflammatory drugs and the targeting of microglia for the prevention and treatment of AD has emerged as a new area of research interest. This article provides a comprehensive review of the role of neuroinflammation of microglial regulation in the development of AD, exploring the connection between microglial energy metabolic disorder, neuroinflammation, and AD development. Additionally, the advancements in anti-inflammatory and microglia-regulating therapies for AD are discussed.

Exposure to Low-Intensity Blast Increases Clearance of Brain Amyloid Beta

The long-term effects of exposure to blast overpressure are an important health concern in military personnel. Increase in amyloid beta (Aβ) has been documented after non-blast traumatic brain injury (TBI) and may contribute to neuropathology and an increased risk for Alzheimer's disease. We have shown that Aβ levels decrease following exposure to a low-intensity blast overpressure event. To further explore this observation, we examined the effects of a single 37 kPa (5.4 psi) blast exposure on brain Aβ levels, production, and clearance mechanisms in the acute (24 h) and delayed (28 days) phases post-blast exposure in an experimental rat model. Aβ and, notably, the highly neurotoxic detergent soluble Aβ42 form, was reduced at 24 h but not 28 days after blast exposure. This reduction was not associated with changes in the levels of Aβ oligomers, expression levels of amyloid precursor protein (APP), or increase in enzymes involved in the amyloidogenic cleavage of APP, the β- and ϒ-secretases BACE1 and presenilin-1, respectively. The levels of ADAM17 α-secretase (also known as tumor necrosis factor α-converting enzyme) decreased, concomitant with the reduction in brain Aβ. Additionally, significant increases in brain levels of the endothelial transporter, low-density related protein 1 (LRP1), and enhancement in co-localization of aquaporin-4 (AQP4) to perivascular astrocytic end-feet were observed 24 h after blast exposure. These findings suggest that exposure to low-intensity blast may enhance endothelial clearance of Aβ by LRP1-mediated transcytosis and alter AQP4-aided glymphatic clearance. Collectively, the data demonstrate that low-intensity blast alters enzymatic, transvascular, and perivascular clearance of Aβ.

Role and therapeutic targets of P2X7 receptors in neurodegenerative diseases

The P2X7 receptor (P2X7R), a non-selective cation channel modulated by adenosine triphosphate (ATP), localizes to microglia, astrocytes, oligodendrocytes, and neurons in the central nervous system, with the most incredible abundance in microglia. P2X7R partake in various signaling pathways, engaging in the immune response, the release of neurotransmitters, oxidative stress, cell division, and programmed cell death. When neurodegenerative diseases result in neuronal apoptosis and necrosis, ATP activates the P2X7R. This activation induces the release of biologically active molecules such as pro-inflammatory cytokines, chemokines, proteases, reactive oxygen species, and excitotoxic glutamate/ATP. Subsequently, this leads to neuroinflammation, which exacerbates neuronal involvement. The P2X7R is essential in the development of neurodegenerative diseases. This implies that it has potential as a drug target and could be treated using P2X7R antagonists that are able to cross the blood-brain barrier. This review will comprehensively and objectively discuss recent research breakthroughs on P2X7R genes, their structural features, functional properties, signaling pathways, and their roles in neurodegenerative diseases and possible therapies.

Deciphering the Role of Peroxisome Proliferator-activated Receptor α and Phosphodiesterase Type 5 Targets in Alzheimer's Disease

The most prevalent cause of dementia is Alzheimer's disease (AD). Although the global AD rate is on a constant rise, medical research is yet to find a cure for this neurological condition. Current available therapeutic drugs for AD treatment only provide symptomatic alleviation. Therefore, it is essential to establish effective AD treatment strategies in addressing clinical needs. The development of disease-modifying treatments for use in the disease's early stages and the advancement of symptomatic drugs principally used in the disease's later stages are priorities in AD research. Given that the etiology of AD is difficult to comprehend, using a multimodal therapy intervention that targets molecular targets of AD-related degenerative processes is a practical strategy to change the course of AD progression. The current review article discussed PPAR-α (Peroxisome proliferator-activated receptor-α) and PDE5 (Phosphodiesterase type 5) targets with evidence for their preclinical and clinical importance. Furthermore, we support the targets with AD-related processes, functions, and remedial measures. A unique synergistic method for treating AD may involve the beneficial combinatorial targeting of these two receptors. Furthermore, we reviewed different PDE chemical families in this research and identified PDE5 inhibitors as one of the promising AD-related experimental and clinical disease-modifying medications. Lastly, we suggest jointly targeting these two pathways would be more beneficial than monotherapy in AD treatments.

Exploring the efficient natural products for Alzheimer's disease therapy via Drosophila melanogaster (fruit fly) models

Alzheimer's disease (AD) is a grievous neurodegenerative disorder and a major form of senile dementia, which is partially caused by abnormal amyloid-beta peptide deposition and Tau protein phosphorylation. But until now, the exact pathogenesis of AD and its treatment strategy still need to investigate. Fortunately, natural products have shown potential as therapeutic agents for treating symptoms of AD due to their neuroprotective activity. To identify the excellent lead compounds for AD control from natural products of herbal medicines, as well as, detect their modes of action, suitable animal models are required. Drosophila melanogaster (fruit fly) is an important model for studying genetic and cellular biological pathways in complex biological processes. Various Drosophila AD models were broadly used for AD research, especially for the discovery of neuroprotective natural products. This review focused on the research progress of natural products in AD disease based on the fruit fly AD model, which provides a reference for using the invertebrate model in developing novel anti-AD drugs.

Upregulation of endocytic protein expression in the Alzheimer's disease male human brain

Amyloid-beta (Aβ) is produced from amyloid precursor protein (APP) primarily after APP is internalised by endocytosis and clathrin-mediated endocytic processes are altered in Alzheimer's disease (AD). There is also evidence that cholesterol and flotillin affect APP endocytosis. We hypothesised that endocytic protein expression would be altered in the brains of people with AD compared to non-diseased subjects which could be linked to increased Aβ generation. We compared protein expression in frontal cortex samples from men with AD compared to age-matched, non-diseased controls. Soluble and insoluble Aβ40 and Aβ42, the soluble Aβ42/Aβ40 ratio, βCTF, BACE1, presenilin-1 and the ratio of phosphorylated:total GSK3β were significantly increased while the insoluble Aβ42:Aβ40 ratio was significantly decreased in AD brains. Total and phosphorylated tau were markedly increased in AD brains. Significant increases in clathrin, AP2, PICALM isoform 4, Rab-5 and caveolin-1 and 2 were seen in AD brains but BIN1 was decreased. However, using immunohistochemistry, caveolin-1 and 2 were decreased. The results obtained here suggest an overall increase in endocytosis in the AD brain, explaining, at least in part, the increased production of Aβ during AD.

Differential effects of familial Alzheimer's disease-causing mutations on amyloid precursor protein (APP) trafficking, proteolytic conversion, and synaptogenic activity

The amyloid precursor protein (APP) is a key player in Alzheimer`s disease (AD) and the precursor of the Aβ peptide, which is generated by consecutive cleavages of β- and γ-secretases. Familial Alzheimer's disease (FAD) describes a hereditary subgroup of AD that represents a low percentage of AD cases with an early onset of the disease. Different APP FAD mutations are thought to have qualitatively different effects on its proteolytic conversion. However, few studies have explored the pathogenic and putative physiological differences in more detail. Here, we compared different FAD mutations, located at the β- (Swedish), α- (Flemish, Arctic, Iowa) or γ-secretase (Iberian) cleavage sites. We examined heterologous expression of APP WT and FAD mutants in non-neuronal cells and their impact on presynaptic differentiation in contacting axons of co-cultured neurons. To decipher the underlying molecular mechanism, we tested the subcellular localization, the endocytosis rate and the proteolytic processing in detail by immunoprecipitation-mass spectrometry. Interestingly, we found that only the Iberian mutation showed altered synaptogenic function. Furthermore, the APP Iowa mutant shows significantly decreased α-secretase processing which is in line with our results that APP carrying the Iowa mutation was significantly increased in early endosomes. However, most interestingly, immunoprecipitation-mass spectrometry analysis revealed that the amino acid substitutions of APP FAD mutants have a decisive impact on their processing reflected in altered Aβ profiles. Importantly, N-terminally truncated Aβ peptides starting at position 5 were detected preferentially for APP Flemish, Arctic, and Iowa mutants containing amino acid substitutions around the α-secretase cleavage site. The strongest change in the ratio of Aβ40/Aβ42 was observed for the Iberian mutation while APP Swedish showed a substantial increase in Aβ1-17 peptides. Together, our data indicate that familial AD mutations located at the α-, β-, and γ-secretase cleavage sites show considerable differences in the underlying pathogenic mechanisms.

Inhibition of CDK4/6 regulates AD pathology, neuroinflammation and cognitive function through DYRK1A/STAT3 signaling

Repurposing approved drugs is an emerging therapeutic development strategy for Alzheimer's disease (AD). The CDK4/6 inhibitor abemaciclib mesylate is an FDA-approved drug for breast cancer treatment. However, whether abemaciclib mesylate affects Aβ/tau pathology, neuroinflammation, and Aβ/LPS-mediated cognitive impairment is unknown. In this study, we investigated the effects of abemaciclib mesylate on cognitive function and Aβ/tau pathology and found that abemaciclib mesylate improved spatial and recognition memory by regulating the dendritic spine number and neuroinflammatory responses in 5xFAD mice, an Aβ-overexpressing model of AD. Abemaciclib mesylate also inhibited Aβ accumulation by enhancing the activity and protein levels of the Aβ-degrading enzyme neprilysin and the α-secretase ADAM17 and decreasing the protein level of the γ-secretase PS-1 in young and aged 5xFAD mice. Importantly, abemaciclib mesylate suppressed tau phosphorylation in 5xFAD mice and tau-overexpressing PS19 mice by reducing DYRK1A and/or p-GSK3β levels. In wild-type (WT) mice injected with lipopolysaccharide (LPS), abemaciclib mesylate rescued spatial and recognition memory and restored dendritic spine number. In addition, abemaciclib mesylate downregulated LPS-induced microglial/astrocytic activation and proinflammatory cytokine levels in WT mice. In BV2 microglial cells and primary astrocytes, abemaciclib mesylate suppressed LPS-mediated proinflammatory cytokine levels by downregulating AKT/STAT3 signaling. Taken together, our results support repurposing the anticancer drug, CDK4/6 inhibitor abemaciclib mesylate as a multitarget therapeutic for AD pathologies.

The role of ADAM17 in cerebrovascular and cognitive function in the APP/PS1 mouse model of Alzheimer's disease

Introduction

The disintegrin and metalloproteinase 17 (ADAM17) exhibits α-secretase activity, whereby it can prevent the production of neurotoxic amyloid precursor protein-α (APP). ADAM17 is abundantly expressed in vascular endothelial cells and may act to regulate vascular homeostatic responses, including vasomotor function, vascular wall morphology, and formation of new blood vessels. The role of vascular ADAM17 in neurodegenerative diseases remains poorly understood. Here, we hypothesized that cerebrovascular ADAM17 plays a role in the pathogenesis of Alzheimer's disease (AD).

Methods and results

We found that 9-10 months old APP/PS1 mice with b-amyloid accumulation and short-term memory and cognitive deficits display a markedly reduced expression of ADAM17 in cerebral microvessels. Systemic delivery and adeno-associated virus (AAV)-mediated re-expression of ADAM17 in APP/PS1 mice improved cognitive functioning, without affecting b-amyloid plaque density. In isolated and pressurized cerebral arteries of APP/PS1 mice the endothelium-dependent dilation to acetylcholine was significantly reduced, whereas the vascular smooth muscle-dependent dilation to the nitric oxide donor, sodium nitroprusside was maintained when compared to WT mice. The impaired endothelium-dependent vasodilation of cerebral arteries in APP/PS1 mice was restored to normal level by ADAM17 re-expression. The cerebral artery biomechanical properties (wall stress and elasticity) and microvascular network density was not affected by ADAM17 re-expression in the APP/PS1 mice. Additionally, proteomic analysis identified several differentially expressed molecules involved in AD neurodegeneration and neuronal repair mechanisms that were reversed by ADAM17 re-expression.

Discussion

Thus, we propose that a reduced ADAM17 expression in cerebral microvessels impairs vasodilator function, which may contribute to the development of cognitive dysfunction in APP/PS1 mice, and that ADAM17 can potentially be targeted for therapeutic intervention in AD.

Treadmill workout activates PPARα in the hippocampus to upregulate ADAM10, decrease plaques and improve cognitive functions in 5XFAD mouse model of Alzheimer's disease

Although liver is rich in peroxisome proliferator-activated receptor α (PPARα), recently we have described the presence of PPARα in hippocampus where it is involved in non-amyloidogenic metabolism of amyloid precursor protein (APP) via ADAM10, decreasing amyloid plaques and improving memory and learning. However, mechanisms to upregulate PPARα in vivo in the hippocampus are poorly understood. Regular exercise has multiple beneficial effects on human health and here, we describe the importance of regular mild treadmill exercise in upregulating PPARα in vivo in the hippocampus of 5XFAD mouse model of Alzheimer's disease. We also demonstrate that treadmill exercise remained unable to stimulate ADAM10, reduce plaque pathology and improve cognitive functions in 5XFADΔPPARα mice (5XFAD mice lacking PPARα). On the other hand, treadmill workout increased ADAM10, decreased plaque pathology and protected memory and learning in 5XFADΔPPARβ mice (5XFAD mice lacking PPARβ). Moreover, the other PPAR (PPARγ) also did not play any role in the transcription of ADAM10 in vivo in the hippocampus of treadmill exercised 5XFAD mice. These results underline an important role of PPARα in which treadmill exercise remains unable to exhibit neuroprotection in the hippocampus in the absence of PPARα.

Interactions between amyloid, amyloid precursor protein, and mitochondria

Mitochondrial dysfunction and Aβ accumulation are hallmarks of Alzheimer's disease (AD). Decades of research describe a relationship between mitochondrial function and Aβ production. Amyloid precursor protein (APP), of which Aβ is generated from, is found within mitochondria. Studies suggest Aβ can be generated in mitochondria and imported into mitochondria. APP and Aβ alter mitochondrial function, while mitochondrial function alters Aβ production from APP. The role these interactions contribute to AD pathology and progression are unknown. Here, we discuss prior research, the rigor of those studies, and the critical knowledge gaps of relationships between APP, Aβ, and mitochondria.

How Can Insulin Resistance Cause Alzheimer's Disease?

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.

Prefrontal cortical protease TACE/ADAM17 is involved in neuroinflammation and stress-related eating alterations

Childhood traumatic stress profoundly affects prefrontal cortical networks regulating top-down control of eating and body weight. However, the neurobiological mechanisms contributing to trauma-induced aberrant eating behaviors remain largely unknown. Traumatic stress influences brain immune responses, which may, in turn, disrupt prefrontal cortical networks and behaviors. The tumor necrosis factor alpha-converting enzyme / a disintegrin and metalloproteinase 17 (TACE/ADAM17) is a sheddase with essential functions in brain maturation, behavior, and neuroinflammation. This study aimed to determine the role of TACE/ADAM17 on traumatic stress-induced disruption of eating patterns. We demonstrate a novel mechanistic connection between prefrontal cortical TACE/ADAM17 and trauma-induced eating behaviors. Fifty-two (52) adolescent Lewis rats (postnatal day, PND, 15) were injected intracerebrally either with a novel Accell™ SMARTpool ADAM17 siRNA or a corresponding siRNA vehicle. The RNAscope Multiplex Fluorescent v2 Assay was used to visualize mRNA expression. Observation cages were used to monitor ethological behaviors in a more naturalistic environment over long periods. We found that traumatic stress blunts startle reactivity and alter eating behaviors (increased intake and disrupted eating patterns). We also found that the rats that received prefrontal cortical TACE/ADAM17 siRNA administration exhibited decreased eating and increased grooming behaviors compared to controls. These changes were associated with decreased AIF-1 expression (a typical marker of microglia and neuroinflammation). This study demonstrates that prefrontal cortical TACE/ADAM17 is involved in neuroinflammation and may play essential roles in regulating feeding patterns under stress conditions. TACE/ADAM17 represents a promising target to ameliorate inflammation-induced brain and behavior alterations.

The Implication of Glial Metabotropic Glutamate Receptors in Alzheimer's Disease

Alzheimer's disease (AD) was first identified more than 100 years ago, yet aspects pertaining to its origin and the mechanisms underlying disease progression are not well known. To this date, there is no therapeutic approach or disease-modifying drug that could halt or at least delay disease progression. Until recently, glial cells were seen as secondary actors in brain homeostasis. Although this view was gradually refuted and the relevance of glial cells for the most diverse brain functions such as synaptic plasticity and neurotransmission was vastly proved, many aspects of its functioning, as well as its role in pathological conditions, remain poorly understood. Metabotropic glutamate receptors (mGluRs) in glial cells were shown to be involved in neuroinflammation and neurotoxicity. Besides its relevance for glial function, glutamatergic receptors are also central in the pathology of AD, and recent studies have shown that glial mGluRs play a role in the establishment and progression of AD. AD-related alterations in Ca2+ signalling, APP processing, and Aβ load, as well as AD-related neurodegeneration, are influenced by glial mGluRs. However, different types of mGluRs play different roles, depending on the cell type and brain region that is being analysed. Therefore, in this review, we focus on the current understanding of glial mGluRs and their implication in AD, providing an insight for future therapeutics and identifying existing research gaps worth investigating.

2,4-Diacetylphloroglucinol Reduces Beta-Amyloid Production and Secretion by Regulating ADAM10 and Intracellular Trafficking in Cellular and Animal Models of Alzheimer's Disease

There is currently no effective treatment against Alzheimer’s disease (AD), although many strategies have been applied to reduce beta-amyloid (Aβ) levels. Here, we investigated 2,4-diacetylphloroglucinol (DAPG) effects on Aβ levels and mechanisms of action. DAPG was the most effective phloroglucinol derivative for reducing Aβ levels, without being toxic, in various models including HEK293 cells overexpressing Swedish mutant amyloid precursor protein (APP) (293sw), primary astrocytes isolated from APPsw/PS1dE9 transgenic mice, and after intrahippocampal injection of DAPG in APPsw/PS1dE9 transgenic mice. DAPG-mediated Aβ reduction was associated with increased soluble APPα (sAPPα) levels mediated by a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) but not ADAM17. ADAM10 inhibition in DAPG-treated cells prevented the effects on sAPPα but only partly on intracellular and secreted Aβ. To identify regulators of sAPPα and Aβ secretion, various inhibitors of intracellular trafficking were administered with DAPG. Brefeldin A (BFA) reversed DAPG-mediated changes in Aβ secretion in 293sw cells, whereas golgicide A (GCA) and BFA were effective in primary astrocytes, indicating a cell type-specific regulation of the trafficking. Moreover, GCA or BFA effects on sAPPα, but not Aβ, levels in primary astrocytes resembled those of ADAM10 inhibition, indicating at least partly independent trafficking pathways for sAPPα and Aβ. In conclusion, DAPG might be a promising drug candidate against AD regulating ADAM10 and intracellular trafficking, but optimizing DAPG ability to cross the BBB will be needed.

Secreted Amyloid Precursor Protein Alpha, a Neuroprotective Protein in the Brain Has Widespread Effects on the Transcriptome and Proteome of Human Inducible Pluripotent Stem Cell-Derived Glutamatergic Neurons Related to Memory Mechanisms

Secreted amyloid precursor protein alpha (sAPPα) processed from a parent human brain protein, APP, can modulate learning and memory. It has potential for development as a therapy preventing, delaying, or even reversing Alzheimer’s disease. In this study a comprehensive analysis to understand how it affects the transcriptome and proteome of the human neuron was undertaken. Human inducible pluripotent stem cell (iPSC)-derived glutamatergic neurons in culture were exposed to 1 nM sAPPα over a time course and changes in the transcriptome and proteome were identified with RNA sequencing and Sequential Window Acquisition of All THeoretical Fragment Ion Spectra-Mass Spectrometry (SWATH-MS), respectively. A large subset (∼30%) of differentially expressed transcripts and proteins were functionally involved with the molecular biology of learning and memory, consistent with reported links of sAPPα to memory enhancement, as well as neurogenic, neurotrophic, and neuroprotective phenotypes in previous studies. Differentially regulated proteins included those encoded in previously identified Alzheimer’s risk genes, APP processing related proteins, proteins involved in synaptogenesis, neurotransmitters, receptors, synaptic vesicle proteins, cytoskeletal proteins, proteins involved in protein and organelle trafficking, and proteins important for cell signalling, transcriptional splicing, and functions of the proteasome and lysosome. We have identified a complex set of genes affected by sAPPα, which may aid further investigation into the mechanism of how this neuroprotective protein affects memory formation and how it might be used as an Alzheimer’s disease therapy.

Alpha- and Gamma-Tocopherol Modulates the Amyloidogenic Pathway of Amyloid Precursor Protein in an in vitro Model of Alzheimer's Disease: A Transcriptional Study

The amyloid precursor protein (APP) processing pathway was altered in Alzheimer's disease (AD) and contributed to abnormal amyloid-beta (Aβ) production, which forms insoluble interneuron protein aggregates known as amyloid plaques in the brain. Targeting the APP processing pathway is still fundamental for AD modifying therapy. Extensive research has evaluated the protective effects of vitamin E as an antioxidant and as a signaling molecule. The present study aimed to investigate the modulatory effects of different tocopherol isomers on the expression of genes involved in regulating the APP processing pathway in vitro. The screening for the effective tocopherol isomers in reducing APP expression and Aβ-42 was carried out in SH-SY5Y stably overexpressed APP Swedish. Subsequently, quantitative one-step real-time PCR was performed to determine the modulatory effects of selected tocopherol isomers on the expression of genes in SH-SY5Y stably overexpressed three different types of APP (wild-type, APP Swedish, and APP Swedish/Indiana). Our results showed that all tocopherol isomers, especially at higher concentrations (80-100 μM), significantly increased (p < 0.05) the cell viability in all cells group, but only α-tocopherol (ATF) and γ-tocopherol (GTF) significantly decreased (p < 0.05) the APP mRNA level without statistically significant APP protein level, accompanied with a reduced significance (p < 0.05) on the level of Aβ-42 in SH-SY5Y APP Swedish. On the other hand, β- and δ-tocopherol (BTF and DTF) showed no effects on the level of APP expression and Aβ-42. Subsequent results demonstrated that ATF and GTF significantly decreased (p < 0.05) the expression of gene beta-site APP cleaving enzyme (BACE1), APH1B, and Nicastrin (NCSTN), but significantly increased (p < 0.05) the expression of Sirtuin 1 (SIRT1) in SH-SY5Y stably expressed the mutant APP form. These findings suggested that ATF and GTF could modulate altered pathways and may help ameliorate the burden of amyloid load in AD.

Mitigating Effect of Estrogen in Alzheimer’s Disease-Mimicking Cerebral Organoid

Alzheimer’s disease (AD) is the most common condition in patients with dementia and affects a large population worldwide. The incidence of AD is expected to increase in future owing to the rapid expansion of the aged population globally. Researchers have shown that women are twice more likely to be affected by AD than men. This phenomenon has been attributed to the postmenopausal state, during which the level of estrogen declines significantly. Estrogen is known to alleviate neurotoxicity in the brain and protect neurons. While the effects of estrogen have been investigated in AD models, to our knowledge, they have not been investigated in a stem cell-based three-dimensional in vitro system. Here, we designed a new model for AD using induced pluripotent stem cells (iPSCs) in a three-dimensional, in vitro culture system. We used 5xFAD mice to confirm the potential of estrogen in alleviating the effects of AD pathogenesis. Next, we confirmed a similar trend in an AD model developed using iPSC-derived cerebral organoids, in which the key characteristics of AD were recapitulated. The findings emphasized the potential of estrogen as a treatment agent for AD and also showed the suitability of AD-recapitulating cerebral organoids as a reliable platform for disease modeling and drug screening.

Knockdown of Amyloid Precursor Protein: Biological Consequences and Clinical Opportunities

Amyloid precursor protein (APP) and its cleavage fragment Amyloid-β (Aβ) have fundamental roles in Alzheimer's disease (AD). Genetic alterations that either increase the overall dosage of APP or alter its processing to favour the generation of longer, more aggregation prone Aβ species, are directly causative of the disease. People living with one copy of APP are asymptomatic and reducing APP has been shown to lower the relative production of aggregation-prone Aβ species in vitro. For these reasons, reducing APP expression is an attractive approach for AD treatment and prevention. In this review, we will describe the structure and the known functions of APP and go on to discuss the biological consequences of APP knockdown and knockout in model systems. We highlight progress in therapeutic strategies to reverse AD pathology via reducing APP expression. We conclude that new technologies that reduce the dosage of APP expression may allow disease modification and slow clinical progression, delaying or even preventing onset.

Revisiting APP secretases: an overview on the holistic effects of retinoic acid receptor stimulation in APP processing

Alzheimer's disease (AD) is the leading cause of dementia worldwide and is characterized by the accumulation of the β-amyloid peptide (Aβ) in the brain, along with profound alterations in phosphorylation-related events and regulatory pathways. The production of the neurotoxic Aβ peptide via amyloid precursor protein (APP) proteolysis is a crucial step in AD development. APP is highly expressed in the brain and is complexly metabolized by a series of sequential secretases, commonly denoted the α-, β-, and γ-cleavages. The toxicity of resulting fragments is a direct consequence of the first cleaving event. β-secretase (BACE1) induces amyloidogenic cleavages, while α-secretases (ADAM10 and ADAM17) result in less pathological peptides. Hence this first cleavage event is a prime therapeutic target for preventing or reverting initial biochemical events involved in AD. The subsequent cleavage by γ-secretase has a reduced impact on Aβ formation but affects the peptides' aggregating capacity. An array of therapeutic strategies are being explored, among them targeting Retinoic Acid (RA) signalling, which has long been associated with neuronal health. Additionally, several studies have described altered RA levels in AD patients, reinforcing RA Receptor (RAR) signalling as a promising therapeutic strategy. In this review we provide a holistic approach focussing on the effects of isoform-specific RAR modulation with respect to APP secretases and discuss its advantages and drawbacks in subcellular AD related events.

Synaptic dysfunction in early phases of Alzheimer's Disease

The synapse is the locus of plasticity where short-term alterations in synaptic strength are converted to long-lasting memories. In addition to the presynaptic terminal and the postsynaptic compartment, a more holistic view of the synapse includes the astrocytes and the extracellular matrix to form a tetrapartite synapse. All these four elements contribute to synapse health and are crucial for synaptic plasticity events and, thereby, for learning and memory processes. Synaptic dysfunction is a common pathogenic trait of several brain disorders. In Alzheimer's Disease, the degeneration of synapses can be detected at the early stages of pathology progression before neuronal degeneration, supporting the hypothesis that synaptic failure is a major determinant of the disease. The synapse is the place where amyloid-β peptides are generated and is the target of the toxic amyloid-β oligomers. All the elements constituting the tetrapartite synapse are altered in Alzheimer's Disease and can synergistically contribute to synaptic dysfunction. Moreover, the two main hallmarks of Alzheimer's Disease, i.e., amyloid-β and tau, act in concert to cause synaptic deficits. Deciphering the mechanisms underlying synaptic dysfunction is relevant for the development of the next-generation therapeutic strategies aimed at modifying the disease progression.

Zinc enzymes in medicinal chemistry

In humans, more than three hundred diverse enzymes that require zinc as an essential cofactor have been identified. These zinc enzymes have demonstrated different and important physiological functions and some of them have been considered as valuable therapeutic targets for drug discovery. Indeed, many drugs targeting a few zinc enzymes have been marketed to treat a variety of diseases. This review discusses drug discovery and drug development based on a dozen of zinc enzymes, including their biological functions and pathogenic roles, their best in class inhibitors (and clinical trial data when available), coordination and binding modes of representative inhibitors, and their implications for further drug design. The opportunities and challenges in developing zinc enzyme inhibitors for the treatment of human disorders are highlighted, too.

Transcriptional activation with Cas9 activator nanocomplexes rescues Alzheimer's disease pathology

CRISPR/Cas9-mediated gene activation is a potential therapeutic strategy that does not induce double-strand break (DSB) DNA damage. However, in vivo gene activation via a Cas9 activator remains a challenge, currently limiting its therapeutic applications. We developed a Cas9 activator nanocomplex that efficiently activates an endogenous gene in the brain in vivo, suggesting its possible application in novel therapeutics. We demonstrated a potential treatment application of the Cas9 activator nanocomplex by activating Adam10 in the mouse brain without introducing insertions and deletions (inDels). Remarkably, in vivo activation of Adam10 with the Cas9 activator nanocomplex improved cognitive deficits in an Alzheimer's disease (AD) mouse model. These results demonstrate the therapeutic potential of Cas9 activator nanocomplexes for a wide range of neurological diseases.

Effect of Global Brain Ischemia on Amyloid Precursor Protein Metabolism and Expression of Amyloid-Degrading Enzymes in Rat Cortex: Role in Pathogenesis of Alzheimer's Disease

The incidence of Alzheimer's disease (AD) increases significantly following chronic stress and brain ischemia which, over the years, cause accumulation of toxic amyloid species and brain damage. The effects of global 15-min ischemia and 120-min reperfusion on the levels of expression of the amyloid precursor protein (APP) and its processing were investigated in the brain cortex (Cx) of male Wistar rats. Additionally, the levels of expression of the amyloid-degrading enzymes neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), and insulin-degrading enzyme (IDE), as well as of some markers of oxidative damage were assessed. It was shown that the APP mRNA and protein levels in the rat Cx were significantly increased after the ischemic insult. Protein levels of the soluble APP fragments, especially of sAPPβ produced by β-secretase, (BACE-1) and the levels of BACE-1 mRNA and protein expression itself were also increased after ischemia. The protein levels of APP and BACE-1 in the Cx returned to the control values after 120-min reperfusion. The levels of NEP and ECE-1 mRNA also decreased after ischemia, which correlated with the decreased protein levels of these enzymes. However, we have not observed any changes in the protein levels of insulin-degrading enzyme. Contents of the markers of oxidative damage (di-tyrosine and lysine conjugates with lipid peroxidation products) were also increased after ischemia. The obtained data suggest that ischemia shifts APP processing towards the amyloidogenic β-secretase pathway and accumulation of the neurotoxic Aβ peptide as well as triggers oxidative stress in the cells. These results are discussed in the context of the role of stress and ischemia in initiation and progression of AD.

Alzheimer's Disease Animal Models: Elucidation of Biomarkers and Therapeutic Approaches for Cognitive Impairment

Alzheimer's disease (AD) is an age-related and progressive neurodegenerative disorder. It is widely accepted that AD is mainly caused by the accumulation of extracellular amyloid β (Aβ) and intracellular neurofibrillary tau tangles. Aβ begins to accumulate years before the onset of cognitive impairment, suggesting that the benefit of currently available interventions would be greater if they were initiated in the early phases of AD. To understand the mechanisms of AD pathogenesis, various transgenic mouse models with an accelerated accumulation of Aβ and tau tangles have been developed. However, none of these models exhibit all pathologies present in human AD. To overcome these undesirable phenotypes, APP knock-in mice, which were presented with touchscreen-based tasks, were developed to better evaluate the efficacy of candidate therapeutics in mouse models of early-stage AD. This review assesses several AD mouse models from the aspect of biomarkers and cognitive impairment and discusses their potential as tools to provide novel AD therapeutic approaches.

Computer-assisted evaluation of plant-derived β-secretase inhibitors in Alzheimer’s disease

Background

Alzheimer’s disease (AD) is a progressive neurodegenerative age-related dementia that results in memory loss of elderly people. Many hypotheses have been formally articulated till now to decipher the pathogenesis of this disease. According to the compelling amyloidogenic hypothesis, β-secretase is a key regulatory enzyme in AD development and is therefore considered as one of the major targets for the development of drugs to treat AD. In this study, 40 plant-derived phytocompounds, proven to have β-secretase inhibitory activity in different laboratory experiments, were evaluated using computational approaches in order to identify the best possible β-secretase inhibitor(s).

Results

Amentoflavone (IFD score: − 7.842 Kcal/mol), Bilobetin (IFD score: − 7.417 Kcal/mol), and Ellagic acid (IFD score: − 6.923 Kcal/mol) showed highest β-secretase inhibitory activities with high binding affinity among all the selected phytocompounds and interacted with key amino acids, i.e., Asp32, Tyr71, and Asp228 in the catalytic site of β-secretase. Moreover, these three molecules exhibited promising results in different drug potential assessment experiments and displayed signs of correlation with significant pharmacological and biological activities.

Conclusion

Amentoflavone, Biolbetin, and Ellagic acid could be investigated further in developing β-secretase-dependent drug for the effective treatment of AD. However, additional in vivo and in vitro experiments might be required to strengthen the findings of this experiment.

Ovariectomy Influences Cognition and Markers of Alzheimer's Disease

Alzheimer's disease (AD) is one of the most devastating and costly diseases, and prevalence of AD increases with age. Furthermore, females are twice as likely to suffer from AD compared to males. The cessation of reproductive steroid hormone production during menopause is hypothesized to cause this difference. Two rodent AD models, APP21 and APP+PS1, and wild type (WT) rats underwent an ovariectomy or sham surgery. Changes in learning and memory, brain histology, amyloid-β (Aβ) deposition, levels of mRNAs involved in Aβ production and clearance, and synaptic and cognitive function were determined. Barnes maze results showed that regardless of ovariectomy status, APP+PS1 rats learned slower and had poor memory retention. Ovariectomy caused learning impairment only in the APP21 rats. High levels of Aβ42 and very low levels of Aβ40 were observed in the brain cortices of APP+PS1 rats indicating limited endogenous PS1. The APP+PS1 rats had 43-fold greater formic acid soluble Aβ42 than Aβ40 at 17 months. Furthermore, levels of formic acid soluble Aβ42 increased 57-fold in ovariectomized APP+PS1 rats between 12 and 17 months of age. The mRNA encoding Grin1 significantly decreased due to ovariectomy whereas levels of Bace1, Chat, and Prkcb all decreased with age. The expression levels of mRNAs involved in Aβ degradation and AβPP cleavage (Neprilysin, Ide, Adam9, and Psenen) were found to be highly correlated with each other as well as hippocampal Aβ deposition. Taken together, these results indicate that both ovariectomy and genotype influence AD markers in a complex manner.

Binding of Cu2+ to Aβ1-29 causes aggregation and toxicity in SH-SY5Y cells

The accumulation and aggregation of amyloid-β (Aβ) are critical factors in the pathogenesis of Alzheimer's disease (AD). Several studies have indicated that metal ions such as Cu²⁺and Zn²⁺ play a key role in the formation and stabilization of neurotoxic Aβ aggregates, however the molecular mechanisms underlying Aβ cytotoxicity have not yet been fully elucidated. Previously, we showed that the Aβ-derived fragment peptide (Aβ-FrP), Aβ1-19, altered conformation in the presence of Cu²⁺, inhibiting its digestion by metalloproteinase-7 (MMP-7). In this study we demonstrated that Aβ1-19 did not form aggregates in the presence of Cu²⁺. Therefore, we synthesized a new Aβ-FrP, Aβ1-29, which displayed Cu²⁺-dependent conformational conversion and aggregate formation. Aβ1-29 was cleaved by MMP-7, however this reaction was inhibited in the presence of Cu²⁺ in a similar way to Aβ1-19. Interestingly, Aβ1-29 showed conformational conversion and aggregate formation in the presence of Zn²⁺, however this did not confer resistance against MMP-7 cleavage. Moreover, Aβ1-29 induced the apoptotic cell death of neural SH-SY5Y cells in the presence of Cu²⁺ but not Zn²⁺. These results suggest that Cu²⁺, unlike Zn²⁺, may play an important role in the aggregation mechanism of Aβ and thus in the pathology of AD.

Structure, regulatory factors and cancer-related physiological effects of ADAM9

The ADAMs family belongs to the transmembrane protein superfamily of zinc-dependent metalloproteases, which consists of multiple domains. These domains have independent but complementary functions that enable them to participate in multiple biological processes. Among them, ADAM9 can not only participate in the degradation of extracellular matrix as a metalloprotease, but also mediate tumor cell adhesion through its deintegrin domain, which is closely related to tumor invasion and metastasis. It is widely expressed in a variety of tumor cells and can affect the proliferation, invasion and metastasis of related cancer cells. We provide our views on current progress, its increasing importance as a strategic treatment goal, and our vision for the future of ADAM9.

The cellular expression and proteolytic processing of the amyloid precursor protein is independent of TDP-43

Alzheimer's disease (AD) is a neurodegenerative condition, of which one of the cardinal pathological hallmarks is the extracellular accumulation of amyloid β (Aβ) peptides. These peptides are generated via proteolysis of the amyloid precursor protein (APP), in a manner dependent on the β-secretase, BACE1 and the multicomponent γ-secretase complex. Recent data also suggest a contributory role in AD of transactive response DNA binding protein 43 (TDP-43). There is little insight into a possible mechanism linking TDP-43 and APP processing. To this end, we used cultured human neuronal cells to investigate the ability of TDP-43 to interact with APP and modulate its proteolytic processing. Immunocytochemistry showed TDP-43 to be spatially segregated from both the extranuclear APP holoprotein and its nuclear C-terminal fragment. The latter (APP intracellular domain) was shown to predominantly localise to nucleoli, from which TDP-43 was excluded. Furthermore, neither overexpression of each of the APP isoforms nor siRNA-mediated knockdown of APP had any effect on TDP-43 expression. Doxycycline-stimulated overexpression of TDP-43 was explored in an inducible cell line. Overexpression of TDP-43 had no effect on expression of the APP holoprotein, nor any of the key proteins involved in its proteolysis. Furthermore, increased TDP-43 expression had no effect on BACE1 enzymatic activity or immunoreactivity of Aβ1-40, Aβ1-42 or the Aβ1-40:Aβ1-42 ratio. Also, siRNA-mediated knockdown of TDP-43 had no effect on BACE1 immunoreactivity. Taken together, these data indicate that TDP-43 function and/or dysfunction in AD is likely independent from dysregulation of APP expression and proteolytic processing and Aβ generation.

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.

Alterations in the Expression of Amyloid Precursor Protein Cleaving Enzymes mRNA in Alzheimer Peripheral Blood

BACKGROUND

Alzheimer's disease (AD) is the most common cause of dementia in elderly populations. Changes in the expression of the Amyloid Precursor Protein (APP)-cleaving enzymes directly affect the formation of Amyloid Beta (Aβ) plaques, a neuropathological hallmark of AD.

OBJECTIVE

We used peripheral blood from AD patients to investigate the expression of genes related to APP-processing [(β-site APP-cleaving enzyme 1 (BACE1), presenilin1 (PSEN1), and a disintegrin and metalloproteinase family 10 (ADAM10) and 17 (ADAM17)] and the epigenetic genes sirtuin (SIRT)1-3, which regulate Aβ production.

METHOD

Real-time polymerase chain reactions were performed to determine the specific mRNA levels in plasma. The mRNA levels in AD patients were compared to those in healthy persons and assessed in relation to the subjects' cognitive performance.

RESULTS

BACE1 mRNA level in AD subjects was significantly higher than those of healthy controls, whereas ADAM10 level was significantly lower in the AD subjects. The SIRT1 level was significantly decreased, while that of SIRT2 was increased in AD subjects and elderly controls compared to levels in healthy young control. In addition, correlations were found between the expression levels of BACE1, ADAM10 and SIRT1 and cognitive performance scores. Total Aβ (Aβ40+Aβ42) levels and the Aβ40/Aβ42 ratio were significantly increased in the AD subjects, whereas decrease in plasma Aβ42 was found in AD subjects. There was a negative correlation between Aβ40 or total Aβ and Thai Mental State Examination (TMSE) while there was no correlation between Aβ40/Aβ42 ratio or Aβ42 and TMSE.

CONCLUSION

The present findings provide evidence and support for the potential roles of these enzymes that drive Aβ synthesis and for epigenetic regulation in AD progression and development, which can possibly be considered peripheral markers of AD.

Molecular Insight into the Therapeutic Promise of Flavonoids against Alzheimer's Disease

Alzheimer’s disease (AD) is one of the utmost chronic neurodegenerative disorders, which is characterized from a neuropathological point of view by the aggregates of amyloid beta (Aβ) peptides that are deposited as senile plaques and tau proteins which form neurofibrillary tangles (NFTs). Even though advancement has been observed in order to understand AD pathogenesis, currently available therapeutic methods can only deliver modest symptomatic relief. Interestingly, naturally occurring dietary flavonoids have gained substantial attention due to their antioxidative, anti-inflammatory, and anti-amyloidogenic properties as alternative candidates for AD therapy. Experimental proof provides support to the idea that some flavonoids might protect AD by interfering with the production and aggregation of Aβ peptides and/or decreasing the aggregation of tau. Flavonoids have the ability to promote clearance of Aβ peptides and inhibit tau phosphorylation by the mTOR/autophagy signaling pathway. Moreover, due to their cholinesterase inhibitory potential, flavonoids can represent promising symptomatic anti-Alzheimer agents. Several processes have been suggested for the aptitude of flavonoids to slow down the advancement or to avert the onset of Alzheimer’s pathogenesis. To enhance cognitive performance and to prevent the onset and progress of AD, the interaction of flavonoids with various signaling pathways is proposed to exert their therapeutic potential. Therefore, this review elaborates on the probable therapeutic approaches of flavonoids aimed at averting or slowing the progression of the AD pathogenesis.

Caspr1 Facilitates sAPPα Production by Regulating α-Secretase ADAM9 in Brain Endothelial Cells

The expression of contactin-associated protein 1 (Caspr1) in brain microvascular endothelial cells (BMECs), one of the major cellular components of the neurovascular unit (NVU), has been revealed recently. However, the physiological role of Caspr1 in BMECs remains unclear. We previously reported the nonamyloidogenic processing of amyloid protein precursor (APP) pathway in the human BMECs (HBMECs). In this study, we found Caspr1 depletion reduced the levels of soluble amyloid protein precursor α (sAPPα) in the supernatant of HBMECs, which could be rescued by expression of full-length Caspr1. Our further results showed that ADAM9, the α-secretase essential for processing of APP to generate sAPPα, was decreased in Caspr1-depleted HBMECs. The reduced sAPPα secretion in Caspr1-depleted HBMECs was recovered by expression of exogenous ADAM9. Then, we identified that Caspr1 specifically regulates the expression of ADAM9, but not ADAM10 and ADAM17, at transcriptional level by nuclear factor-κB (NF-κB) signaling pathway. Caspr1 knockout attenuated the activation of NF-κB and prevented the nuclear translocation of p65 in brain endothelial cells, which was reversed by expression of full-length Caspr1. The reduced sAPPα production and ADAM9 expression upon Caspr1 depletion were effectively recovered by NF-κB agonist. The results of luciferase assays indicated that the NF-κB binding sites are located at −859 bp to −571 bp of ADAM9 promoter. Taken together, our results demonstrated that Caspr1 facilitates sAPPα production by transcriptional regulation of α-secretase ADAM9 in brain endothelial cells.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

Role of cyclic nucleotides and their downstream signaling cascades in memory function: Being at the right time at the right spot

A plethora of studies indicate the important role of cAMP and cGMP cascades in neuronal plasticity and memory function. As a result, altered cyclic nucleotide signaling has been implicated in the pathophysiology of mnemonic dysfunction encountered in several diseases. In the present review we provide a wide overview of studies regarding the involvement of cyclic nucleotides, as well as their upstream and downstream molecules, in physiological and pathological mnemonic processes. Next, we discuss the regulation of the intracellular concentration of cyclic nucleotides via phosphodiesterases, the enzymes that degrade cAMP and/or cGMP, and via A-kinase-anchoring proteins that refine signal compartmentalization of cAMP signaling. We also provide an overview of the available data pointing to the existence of specific time windows in cyclic nucleotide signaling during neuroplasticity and memory formation and the significance to target these specific time phases for improving memory formation. Finally, we highlight the importance of emerging imaging tools like Förster resonance energy transfer imaging and optogenetics in detecting, measuring and manipulating the action of cyclic nucleotide signaling cascades.

Degradome of soluble ADAM10 and ADAM17 metalloproteases

Disintegrin and metalloproteinases (ADAMs) 10 and 17 can release the extracellular part of a variety of membrane-bound proteins via ectodomain shedding important for many biological functions. So far, substrate identification focused exclusively on membrane-anchored ADAM10 and ADAM17. However, besides known shedding of ADAM10, we identified ADAM8 as a protease capable of releasing the ADAM17 ectodomain. Therefore, we investigated whether the soluble ectodomains of ADAM10/17 (sADAM10/17) exhibit an altered substrate spectrum compared to their membrane-bound counterparts. A mass spectrometry-based N-terminomics approach identified 134 protein cleavage events in total and 45 common substrates for sADAM10/17 within the secretome of murine cardiomyocytes. Analysis of these cleavage sites confirmed previously identified amino acid preferences. Further in vitro studies verified fibronectin, cystatin C, sN-cadherin, PCPE-1 as well as sAPP as direct substrates of sADAM10 and/or sADAM17. Overall, we present the first degradome study for sADAM10/17, thereby introducing a new mode of proteolytic activity within the protease web.

Histidine 131 in presenilin 1 is the pH-sensitive residue that causes the increase in Aβ42 level in acidic pH

Alzheimer disease (AD) is the most common neurodegenerative disease worldwide. The pathological hallmark of AD is the presence of senile plaques in the brain, which are accumulations of amyloid-β peptide (Aβ) ending at the 42nd residue (i.e. Aβ42), which is produced through multistep cleavage by γ-secretase. Thus, methods to regulate γ-secretase activity to attenuate the production of Aβ42 are in urgent demand towards the development of treatments for AD. We and others have demonstrated that γ-secretase activity is affected by its localization and ambient environment. In particular, an increase in Aβ42 production is correlated with the intracellular transport of γ-secretase and endosomal maturation-dependent luminal acidification. In this study, we focused on the mechanism by which γ-secretase affects Aβ42 production together with alterations in pH. Histidine is known to function as a pH sensor in many proteins, to regulate their activities through the protonation state of the imidazole side chain. Among the histidines facing the luminal side of presenilin (PS) 1, which is the catalytic subunit of γ-secretase, point mutations at H131 had no effect on the Aβ42 production ratio in an acidic environment. We also observed an increase in Aβ42 ratio when histidine was introduced into N137 of PS2, which is the corresponding residue of H131 in PS1. These results indicated that H131 serves as the pH sensor in PS1, which contains γ-secretase, to regulate Aβ42 production depending on the luminal pH. Our findings provide new insights into therapeutic strategies for AD targeting endosomes or the intracellular transport of γ-secretase.

Potential therapeutic roles of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease

All retinoids, which can be natural and synthetic, are chemically related to vitamin A. Both natural and synthetic retinoids use specific nuclear receptors such as retinoic acid receptors and retinoid X receptors to activate specific signaling pathways in the cells. Retinoic acid signaling is extremely important in the central nervous system. Impairment of retinoic acid signaling pathways causes severe pathological processes in the central nervous system, especially in the adult brain. Retinoids have major roles in neural patterning, differentiation, axon outgrowth in normal development, and function of the brain. Impaired retinoic acid signaling results in neuroinflammation, oxidative stress, mitochondrial malfunction, and neurodegeneration leading to progressive Alzheimer's disease, which is pathologically characterized by extra-neuronal accumulation of amyloid plaques (aggregated amyloid-beta) and intra-neurofibrillary tangles (hyperphosphorylated tau protein) in the temporal lobe of the brain. Alzheimer's disease is the most common cause of dementia and loss of memory in old adults. Inactive cholinergic neurotransmission is responsible for cognitive deficits in Alzheimer's disease patients. Deficiency or deprivation of retinoic acid in mice is associated with loss of spatial learning and memory. Retinoids inhibit expression of chemokines and neuroinflammatory cytokines in microglia and astrocytes, which are activated in Alzheimer's disease. Stimulation of retinoic acid receptors and retinoid X receptors slows down accumulation of amyloids, reduces neurodegeneration, and thereby prevents pathogenesis of Alzheimer's disease in mice. In this review, we described chemistry and biochemistry of some natural and synthetic retinoids and potentials of retinoids for prevention of neuroinflammation and neurodegeneration in Alzheimer's disease.

SRC fine-tunes ADAM10 shedding activity to promote pituitary adenoma cell progression

A disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) is a metalloproteinase known to modulate the progression of several types of tumor. However, the role played by ADAM10 in pituitary adenomas is currently unknown, and what factors orchestrate the activation of ADAM10 in this kind of tumor is also unclear. Here, we found that SRC kinase is an ADAM10-interacting partner and that SRC kinase activity is required for this interaction. As a new positive regulator promoting the shedding activity of ADAM10, SRC could compete with calmodulin 1 (CALM1) for ADAM10 binding in a mutually exclusive manner. Strikingly, the interaction between ADAM10 and CALM1 is regulated by SRC activity. Furthermore, we proved that the cytoplasmic region of ADAM10 is required for the shedding activity of ADAM10 upon SRC activation. As a proof-of-concept, we discovered that the combination of ADAM10 and SRC inhibitors can inhibit cell proliferation and migration to a great extent. Thus, our findings shed light on a novel therapeutic strategy to block the tumorigenesis and migration of pituitary adenoma.

Lipid and Lipid Raft Alteration in Aging and Neurodegenerative Diseases: A Window for the Development of New Biomarkers

Lipids in the brain are major components playing structural functions as well as physiological roles in nerve cells, such as neural communication, neurogenesis, synaptic transmission, signal transduction, membrane compartmentalization, and regulation of gene expression. Determination of brain lipid composition may provide not only essential information about normal brain functioning, but also about changes with aging and diseases. Indeed, deregulations of specific lipid classes and lipid homeostasis have been demonstrated in neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). Furthermore, recent studies have shown that membrane microdomains, named lipid rafts, may change their composition in correlation with neuronal impairment. Lipid rafts are key factors for signaling processes for cellular responses. Lipid alteration in these signaling platforms may correlate with abnormal protein distribution and aggregation, toxic cell signaling, and other neuropathological events related with these diseases. This review highlights the manner lipid changes in lipid rafts may participate in the modulation of neuropathological events related to AD and PD. Understanding and characterizing these changes may contribute to the development of novel and specific diagnostic and prognostic biomarkers in routinely clinical practice.

Binding between Prion Protein and Aβ Oligomers Contributes to the Pathogenesis of Alzheimer's Disease

A plethora of evidence suggests that protein misfolding and aggregation are underlying mechanisms of various neurodegenerative diseases, such as prion diseases and Alzheimer's disease (AD). Like prion diseases, AD has been considered as an infectious disease in the past decades as it shows strain specificity and transmission potential. Although it remains elusive how protein aggregation leads to AD, it is becoming clear that cellular prion protein (PrP^C) plays an important role in AD pathogenesis. Here, we briefly reviewed AD pathogenesis and focused on recent progresses how PrP^C contributed to AD development. In addition, we proposed a potential mechanism to explain why infectious agents, such as viruses, conduce AD pathogenesis. Microbe infections cause Aβ deposition and upregulation of PrP^C, which lead to high affinity binding between Aβ oligomers and PrP^C. The interaction between PrP^C and Aβ oligomers in turn activates the Fyn signaling cascade, resulting in neuron death in the central nervous system (CNS). Thus, silencing PrP^C expression may turn out be an effective treatment for PrP^C dependent AD.

Notoginseng Saponin Rg1 Prevents Cognitive Impairment through Modulating APP Processing in Aβ1-42-injected Rats

With the intensification of the aging process of the world, Alzheimer's disease (AD), which is the main type of senile dementia, has become a primary problem in the present society. Lots of strategies have been used to prevent and treat AD in animal models and clinical trials, but most of them ended in failure. Panax notoginseng saponins (PNS) contain a variety of monomer compositions which have been separated and identified. Among of the monomer compositions, notoginseng saponin Rg1 (Rg1) accounts for 20% of the cultivation of panax notoginseng roots. And now PNS have been reported to be widely used to treat cardio-cerebrovascular diseases and have neuroprotective effects to restrain the β-amyloid peptide (Aβ)25-35-mediated apoptosis. Moreover, it is reported that PNS could accelerate the growth of nerve cells, increase the length of axons and promote synaptic plasticity. Whether Rg1 can ameliorate the cognitive impairment and the underlying mechanism has not been elucidated. To study the preventive effect of Rg1 on cognitive impairment and the possible mechanism, we established the cognitive impairment model in rats through Aβ_1-42 (2.6 µg/µL, 5 µL) injection and then treated the rats with Rg1 (25, 50 and 100 mg/kg) administered intragastrically for 4 weeks. We observed that Aβ_1-42 could induce spatial learning and memory deficits in rats. Simultaneously, Aβ_1-42 injection also resulted in the reduced neuron number in cornuammonis 1 (CA1) and dentate gyrus (DG) of hippocampus, as well as the increased level of hyperphosphorylated β-amyloid precursor protein (APP) at Thr668 site with up-regulation of β-APP cleaving enzyme 1 (BACE1) and presenilin 1 (PS1) and down-regulation of a disintegrin and metalloprotease domain-containing protein 10 (ADAM10) and insulin-degrading enzyme (IDE). Administration of Rg1 effectively rescued the cognitive impairment and neuronal loss, and inhibited the β-secretase processing of APP through reducing APP-Thr668 phosphorylation and BACE1/PS1 expression, and increasing the expression of ADAM10 and IDE. We concluded that Rg1 might have neuroprotective effects and could promote learning and memory ability, which might be a viable candidate in AD therapy probably through reducing the generation of Aβ and increasing the degradation of Aβ.

Perinatal Lead (Pb) Exposure and Cortical Neuron-Specific DNA Methylation in Male Mice

: Lead (Pb) exposure is associated with a wide range of neurological deficits. Environmental exposures may impact epigenetic changes, such as DNA methylation, and can affect neurodevelopmental outcomes over the life-course. Mating mice were obtained from a genetically invariant C57BL/6J background agouti viable yellow A^vy strain. Virgin dams (a/a) were randomly assigned 0 ppm (control), 2.1 ppm (low), or 32 ppm (high) Pb-acetate water two weeks prior to mating with male mice (A^vy/a), and this continued through weaning. At age 10 months, cortex neuronal nuclei were separated with NeuN⁺ antibodies in male mice to investigate neuron-specific genome-wide promoter DNA methylation using the Roche NimbleGen Mouse 3x720K CpG Island Promoter Array in nine pooled samples (three per dose). Several probes reached p-value < 10^-5 , all of which were hypomethylated: 12 for high Pb (minimum false discovery rate (FDR) = 0.16, largest intensity ratio difference = -2.1) and 7 for low Pb (minimum FDR = 0.56, largest intensity ratio difference = -2.2). Consistent with previous results in bulk tissue, we observed a weak association between early-life exposure to Pb and DNA hypomethylation, with some affected genes related to neurodevelopment or cognitive function. Although these analyses were limited to males, data indicate that non-dividing cells such as neurons can be carriers of long-term epigenetic changes induced in development.