Insights into the physiological function of the β-amyloid precursor protein: beyond Alzheimer's disease

Amyloid Beta Leads to Decreased Acetylcholine Levels and Non-Small Cell Lung Cancer Cell Survival via a Mechanism That Involves p38 Mitogen-Activated Protein Kinase and Protein Kinase C in a p53-Dependent and -Independent Manner

Several studies have shown an inverse correlation between the likelihood of developing a neurodegenerative disorder and cancer. We previously reported that the levels of amyloid beta (Aβ), at the center of Alzheimer's disease pathophysiology, are regulated by acetylcholinesterase (AChE) in non-small cell lung cancer (NSCLC). Here, we examined the effect of Aβ or its fragments on the levels of ACh in A549 (p53 wild-type) and H1299 (p53-null) NSCLC cell media. ACh levels were reduced by cell treatment with Aβ 1-42, Aβ 1-40, Aβ 1-28, and Aβ 25-35. AChE and p53 activities increased upon A549 cell treatment with Aβ, while knockdown of p53 in A549 cells increased ACh levels, decreased AChE activity, and diminished the Aβ effects. Aβ increased the ratio of phospho/total p38 MAPK and decreased the activity of PKC. Inhibiting p38 MAPK reduced the activity of p53 in A549 cells and increased ACh levels in the media of both cell lines, while opposite effects were found upon inhibiting PKC. ACh decreased the activity of p53 in A549 cells, decreased p38 MAPK activity, increased PKC activity, and diminished the effect of Aβ on those activities. Moreover, the negative effect of Aβ on cell viability was diminished by cell co-treatment with ACh.

CNTN4 modulates neural elongation through interplay with APP

The neuronal cell adhesion molecule contactin-4 (CNTN4) is genetically associated with autism spectrum disorder (ASD) and other psychiatric disorders. Cntn4-deficient mouse models have previously shown that CNTN4 plays important roles in axon guidance and synaptic plasticity in the hippocampus. However, the pathogenesis and functional role of CNTN4 in the cortex has not yet been investigated. Our study found a reduction in cortical thickness in the motor cortex of Cntn4 -/- mice, but cortical cell migration and differentiation were unaffected. Significant morphological changes were observed in neurons in the M1 region of the motor cortex, indicating that CNTN4 is also involved in the morphology and spine density of neurons in the motor cortex. Furthermore, mass spectrometry analysis identified an interaction partner for CNTN4, confirming an interaction between CNTN4 and amyloid-precursor protein (APP). Knockout human cells for CNTN4 and/or APP revealed a relationship between CNTN4 and APP. This study demonstrates that CNTN4 contributes to cortical development and that binding and interplay with APP controls neural elongation. This is an important finding for understanding the physiological function of APP, a key protein for Alzheimer's disease. The binding between CNTN4 and APP, which is involved in neurodevelopment, is essential for healthy nerve outgrowth.

Identification and Analysis of Axolotl Homologs for Proteins Implicated in Human Neurodegenerative Proteinopathies

Neurodegenerative proteinopathies such as Alzheimer's Disease are characterized by abnormal protein aggregation and neurodegeneration. Neuroresilience or regenerative strategies to prevent neurodegeneration, preserve function, or restore lost neurons may have the potential to combat human proteinopathies; however, the adult human brain possesses a limited capacity to replace lost neurons. In contrast, axolotls (Ambystoma mexicanum) show robust brain regeneration. To determine whether axolotls may help identify potential neuroresilience or regenerative strategies in humans, we first interrogated whether axolotls express putative proteins homologous to human proteins associated with neurodegenerative diseases. We compared the homology between human and axolotl proteins implicated in human proteinopathies and found that axolotls encode proteins highly similar to human microtubule-binding protein tau (tau), amyloid precursor protein (APP), and β-secretase 1 (BACE1), which are critically involved in human proteinopathies like Alzheimer's Disease. We then tested monoclonal Tau and BACE1 antibodies previously used in human and rodent neurodegenerative disease studies using immunohistochemistry and western blotting to validate the homology for these proteins. These studies suggest that axolotls may prove useful in studying the role of these proteins in disease within the context of neuroresilience and repair.

The role of leptin in regulation of the soluble amyloid precursor protein α (sAPPα) levels in lung cancer cell media

Previously, we found that the levels of soluble amyloid precursor protein α (sAPPα) are regulated, in part, by acetylcholinesterase (AChE) in human A549 (p53 wild-type) and H1299 (p53-null) NSCLC cell lines. In this study, we found regulation of sAPPα levels in the media by leptin, a widely recognized obesity-associated adipokine that has recently been shown to play a possible role in cancer signaling. Increased levels of sAPPα, that were accompanied by lower Aβ40/42 levels in the media of A549 and H1299 cells, were detected upon cell incubation with leptin. Conversely, knockdown of leptin or its receptor led to reduced levels of sAPPα and increased levels of Aβ40/42 in the media of A549 and H1299 cells, suggesting that leptin likely shifts APP processing toward the non-amyloidogenic pathway. A549 cell treatment with leptin increased acetylcholine levels and blocked the activities of AChE and p53. Treatment with leptin resulted in increased activation of PKC, ERK1/2, PI3K, and the levels of sAPPα, effects that were reversed by treatment with kinase inhibitors and/or upon addition of AChE to A549 and H1299 cell media. Cell viability increased by treatment of A549 and H1299 cells with leptin and decreased upon co-treatment with AChE and/or inhibitors targeting PKC, ERK1/2, and PI3K. This study is significant as it provides evidence for a likely carcinogenic role of leptin in NSCLC cells via upregulation of sAPPα levels in the media, and highlights the importance of targeting leptin as a potential therapeutic strategy for NSCLC treatment.

Amyloid Precursor Protein: A Regulatory Hub in Alzheimer's Disease

Decades of research have demonstrated an incontrovertible role of amyloid-β (Aβ) in the etiology of Alzheimer's disease (AD). However, the overemphasis on the pathological impacts of Aβ may obscure the role of its metabolic precursor, amyloid precursor protein (APP), as a significant hub in the occurrence and progression of AD. The complicated enzymatic processing, ubiquitous receptor-like properties, and abundant expression of APP in the brain, as well as its close links with systemic metabolism, mitochondrial function and neuroinflammation, imply that APP plays multifaceted roles in AD. In this review, we briefly describe the evolutionarily conserved biological characteristics of APP, including its structure, functions and enzymatic processing. We also discuss the possible involvement of APP and its enzymatic metabolites in AD, both detrimental and beneficial. Finally, we describe pharmacological agents or genetic approaches with the capability to reduce APP expression or inhibit its cellular internalization, which can ameliorate multiple aspects of AD pathologies and halt disease progression. These approaches provide a basis for further drug development to combat this terrible disease.

Amyloid-β and caspase-1 are indicators of sepsis and organ injury

Background

Sepsis is a life-threatening condition that results from a dysregulated host response to infection, leading to organ dysfunction. Despite the prevalence and associated socioeconomic costs, treatment of sepsis remains limited to antibiotics and supportive care, and a majority of intensive care unit (ICU) survivors develop long-term cognitive complications post-discharge. The present study identifies a novel regulatory relationship between amyloid-β (Aβ) and the inflammasome-caspase-1 axis as key innate immune mediators that define sepsis outcomes.

Methods

Medical ICU patients and healthy individuals were consented for blood and clinical data collection. Plasma cytokine, caspase-1 and Aβ levels were measured. Data were compared against indices of multiorgan injury and other clinical parameters. Additionally, recombinant proteins were tested in vitro to examine the effect of caspase-1 on a functional hallmark of Aβ, namely aggregation.

Results

Plasma caspase-1 levels displayed the best predictive value in discriminating ICU patients with sepsis from non-infected ICU patients (area under the receiver operating characteristic curve=0.7080). Plasma caspase-1 and the Aβ isoform Aβx-40 showed a significant positive correlation and Aβx-40 associated with organ injury. Additionally, Aβ plasma levels continued to rise from time of ICU admission to 7 days post-admission. In silico, Aβ harbours a predicted caspase-1 cleavage site, and in vitro studies demonstrated that caspase-1 cleaved Aβ to inhibit its auto-aggregation, suggesting a novel regulatory relationship.

Conclusions

Aβx-40 and caspase-1 are potentially useful early indicators of sepsis and its attendant organ injury. Additionally, Aβx-40 has emerged as a potential culprit in the ensuing development of post-ICU syndrome.

Detection of APP gene recombinant in human blood plasma

The pathogenesis of Alzheimer's disease (AD) is believed to involve the accumulation of amyloid-β in the brain, which is produced by the sequential cleavage of amyloid precursor protein (APP) by β-secretase and γ-secretase. Recently, analysis of genomic DNA and mRNA from postmortem brain neurons has revealed intra-exonic recombinants of APP (gencDNA), which have been implicated in the accumulation of amyloid-β. In this study, we computationally analyzed publicly available sequence data (SRA) using probe sequences we constructed to screen APP gencDNAs. APP gencDNAs were detected in SRAs constructed from both genomic DNA and RNA obtained from the postmortem brain and in the SRA constructed from plasma cell-free mRNA (cf-mRNA). The SRA constructed from plasma cf-mRNA showed a significant difference in the number of APP gencDNA reads between SAD and NCI: the p-value from the Mann-Whitney U test was 5.14 × 10-6. The transcripts were also found in circulating nucleic acids (CNA) from our plasma samples with NGS analysis. These data indicate that transcripts of APP gencDNA can be detected in blood plasma and suggest the possibility of using them as blood biomarkers for Alzheimer's disease.

Evaluation and targeting of amyloid precursor protein (APP)/amyloid beta (Aβ) axis in amyloidogenic and non-amyloidogenic pathways: A time outside the tunnel

In Alzheimer disease (AD), amyloid precursor protein (APP) and production of amyloid beta (Aβ) which is generated by amyloidogenic pathway is implicated in neurotoxicity and neuronal cell deaths. However, physiological Aβ level is essential to improves neuronal survival, attenuates neuronal apoptosis and has neuroprotective effect. In addition, physiological APP level has neurotrophic effect on the central nervous system (CNS). APP has a critical role in the brain growth and development via activation of long-term potentiation (LTP) and acceleration of neurite outgrowth. Moreover, APP is cleaved by α secretase to form a neuroprotective soluble APP alpha (sAPPα) in non-amyloidogenic pathway. Consequently, this mini-review purposes to highlight the possible beneficial role of APP and Aβ. In addition, this mini-review discussed the modulation of APP processing and Aβ production.

Cerebral organoids derived from patients with Alzheimer's disease with PSEN1/2 mutations have defective tissue patterning and altered development

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study human neural development and disease. Especially in the field of Alzheimer's disease (AD), remarkable effort has been put into investigating molecular mechanisms behind this disease. Then, with the advent of 3D neuronal cultures and cerebral organoids (COs), several studies have demonstrated that this model can adequately mimic familial and sporadic AD. Therefore, we created an AD-CO model using iPSCs derived from patients with familial AD forms and explored early events and the progression of AD pathogenesis. Our study demonstrated that COs derived from three AD-iPSC lines with PSEN1(A246E) or PSEN2(N141I) mutations developed the AD-specific markers in vitro, yet they also uncover tissue patterning defects and altered development. These findings are complemented by single-cell sequencing data confirming this observation and uncovering that neurons in AD-COs likely differentiate prematurely.

Spatiotemporal insights of APP function

The amyloid-β precursor protein (APP) is a ubiquitous protein with a strong genetic link to Alzheimer's disease. Although the protein was identified more than forty years ago, its physiological function is still unclear. In recent years, advances in technology have allowed researchers to tackle APP functions in greater depth. In this review, we discuss the latest research pertaining to APP functions from development to aging. We also address the different roles that APP could play in specific types of cells of the central and peripheral nervous system and in other organs of the body. We argue that, until we fully identify the functions of APP in space and time, we will be missing important pieces of the puzzle to solve its pathological implication in Alzheimer's disease and beyond.

Cholesterol-dependent amyloid β production: space for multifarious interactions between amyloid precursor protein, secretases, and cholesterol

Amyloid β is considered a key player in the development and progression of Alzheimer's disease (AD). Many studies investigating the effect of statins on lowering cholesterol suggest that there may be a link between cholesterol levels and AD pathology. Since cholesterol is one of the most abundant lipid molecules, especially in brain tissue, it affects most membrane-related processes, including the formation of the most dangerous form of amyloid β, Aβ42. The entire Aβ production system, which includes the amyloid precursor protein (APP), β-secretase, and the complex of γ-secretase, is highly dependent on membrane cholesterol content. Moreover, cholesterol can affect amyloidogenesis in many ways. Cholesterol influences the stability and activity of secretases, but also dictates their partitioning into specific cellular compartments and cholesterol-enriched lipid rafts, where the amyloidogenic machinery is predominantly localized. The most complicated relationships have been found in the interaction between cholesterol and APP, where cholesterol affects not only APP localization but also the precise character of APP dimerization and APP processing by γ-secretase, which is important for the production of Aβ of different lengths. In this review, we describe the intricate web of interdependence between cellular cholesterol levels, cholesterol membrane distribution, and cholesterol-dependent production of Aβ, the major player in AD.

Investigation of the protective effect of long-term exercise on molecular pathways and behaviours in scopolamine induced alzheimer's disease-like condition

Despite research, the role of exercise in treatment and prevention of neurodegenerative diseases remains unclear. Our study, investigated that protective effect of treadmill exercise on molecular pathways and cognitive behaviours in a scopolamine-induced model of Alzheimer's disease. For that purpose, male Balb/c mice subjected to exercise for 12 weeks. During the last 4 weeks of exercise, mice were given an injection of scopolamine (2 mg/kg). Following injection, open field test and Morris water maze test were used to assess emotional-cognitive behaviour. Hippocampus and prefrontal cortex of mice were isolated, and levels of BDNF, TrkB, and p-GSK3ßSer389 were assessed by western blotting, and levels of APP and Aß-40 were analysed by immunohistochemistry. In our study, scopolamine administration increased anxiety-like behaviour in open field test, while negatively affecting spatial learning and memory in Morris water maze test. We found that exercise had a protective effect against cognitive and emotional decline. Scopolamine decreased levels of p-GSK3ßSer389, BDNF in hippocampus and prefrontal cortex.Whereas TrkB decreased in hippocampus and increased in prefrontal cortex. There was an increase in p-GSK3ßSer389, BDNF, TrkB in the hippocampus, and p-GSK3ßSer389, BDNF in the prefrontal cortex in the exercise + scopolamine group. Immunohistochemical analysis showed that scopolamine administration increased APP and Aß-40 in hippocampus and prefrontal cortex in neuronal and perineuronal areas whereas Aß-40 and APP were reduced in exercise + scopolamine groups. In conclusion, long-term exercise may have a protective effect against scopolamine-induced impairments in cognitive-emotional behaviour. It can be suggested that this protective effect is mediated by increased BDNF levels and GSK3ßSer389 phosphorylation.

BACE2 deficiency impairs expression and function of endothelial nitric oxide synthase in brain endothelial cells

Beta-site amyloid precursor protein (APP)-cleaving enzyme 2 (BACE2) is highly expressed in cerebrovascular endothelium. Notably, BACE2 is one of the most downregulated genes in cerebrovascular endothelium derived from patients with Alzheimer's disease. The present study was designed to determine the role of BACE2 in control of expression and function of endothelial nitric oxide synthase (eNOS). Genetic downregulation of BACE2 with small interfering RNA (BACE2siRNA) in human brain microvascular endothelial cells (BMECs) significantly decreased expression of eNOS and elevated levels of eNOS phosphorylated at threonine residue Thr495, thus leading to reduced production of nitric oxide (NO). BACE2siRNA also suppressed expression of APP and decreased production and release of soluble APPα (sAPPα). In contrast, adenovirus-mediated overexpression of APP increased expression of eNOS. Consistent with these observations, nanomolar concentrations of sAPPα and APP 17mer peptide (derived from sAPPα) augmented eNOS expression. Further analysis established that γ-aminobutyric acid type B receptor subunit 1 and Krüppel-like factor 2 may function as downstream molecular targets significantly contributing to BACE2/APP/sAPPα-induced up-regulation of eNOS. In agreement with studies on cultured human endothelium, endothelium-dependent relaxations to acetylcholine and basal production of cyclic GMP were impaired in cerebral arteries of BACE2-deficient mice. We propose that in the brain blood vessels, BACE2 may function as a vascular protective protein.

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).

Amyloid Precursor Protein (APP) Regulates Gliogenesis and Neurogenesis of Human Neural Stem Cells by Several Signaling Pathways

Numerous studies have focused on the pathophysiological role of amyloid precursor protein (APP) because the proteolytic processing of APP to β-amyloid (Aβ) peptide is a central event in Alzheimer's disease (AD). However, many authors consider that alterations in the physiological functions of APP are likely to play a key role in AD. Previous studies in our laboratory revealed that APP plays an important role in the differentiation of human neural stem cells (hNSCs), favoring glial differentiation (gliogenesis) and preventing their differentiation toward a neuronal phenotype (neurogenesis). In the present study, we have evaluated the effects of APP overexpression in hNSCs at a global gene level by a transcriptomic analysis using the massive RNA sequencing (RNA-seq) technology. Specifically, we have focused on differentially expressed genes that are related to neuronal and glial differentiation processes, as well as on groups of differentially expressed genes associated with different signaling pathways, in order to find a possible interaction between them and APP. Our data indicate a differential expression in genes related to Notch, Wnt, PI3K-AKT, and JAK-STAT signaling, among others. Knowledge of APP biological functions, as well as the possible signaling pathways that could be related to this protein, are essential to advance our understanding of AD.

O-GalNAc glycosylation determines intracellular trafficking of APP and Aβ production

A primary pathology of Alzheimer's disease (AD) is Aβ deposition in brain parenchyma and blood vessels, the latter being called cerebral amyloid angiopathy (CAA). Parenchymal amyloid plaques presumably originate from neuronal Aβ precursor protein (APP). Although vascular amyloid deposits' origins remain unclear, endothelial APP expression in APP-knock-in mice was recently shown to expand CAA pathology, highlighting endothelial APP's importance. Furthermore, two types of endothelial APP-highly O-glycosylated APP and hypo-O-glycosylated APP-have been biochemically identified, but only the former is cleaved for Aβ production, indicating the critical relationship between APP O-glycosylation and processing. Here, we analyzed APP glycosylation and its intracellular trafficking in neurons and endothelial cells. Although protein glycosylation is generally believed to precede cell surface trafficking, which was true for neuronal APP, we unexpectedly observed that hypo-O-glycosylated APP is externalized to the endothelial cell surface and transported back to the Golgi apparatus, where it then acquires additional O-glycans. Knockdown of genes encoding enzymes initiating APP O-glycosylation significantly reduced Αβ production, suggesting this non-classical glycosylation pathway contributes to CAA pathology and is a novel therapeutic target.

RAGE and its ligand amyloid beta promote retinal ganglion cell loss following ischemia-reperfusion injury

Introduction

Glaucoma is a progressive neurodegenerative disease associated with age. Accumulation of amyloid-beta (Aß) proteins in the ganglion cell layer (GCL) and subsequent retinal ganglion cell (RGC) loss is an established pathological hallmark of the disease. The mechanism through which Aß provokes RGC loss remains unclear. The receptor for the advanced glycation end product (RAGE), and its ligand Aß, have been shown to mediate neuronal loss via internalizing Aß within the neurons. In this study, we investigated whether the RAGE-Aß axis plays a role in RGC loss in experimental glaucoma.

Methods

Retinal ischemia was induced by an acute elevation of intraocular pressure in RAGE^-/- and wild-type (WT) control mice. In a subset of animals, oligomeric Aß was injected directly into the vitreous of both strains. RGC loss was assessed using histology and biochemical assays. Baseline and terminal positive scotopic threshold (pSTR) were also recorded.

Results

Retinal ischemia resulted in 1.9-fold higher RGC loss in WT mice compared to RAGE^-/- mice (36 ± 3% p < 0.0001 vs. 19 ± 2%, p = 0.004). Intravitreal injection of oligomeric Aß resulted in 2.3-fold greater RGC loss in WT mice compared to RAGE^-/- mice, 7-days post-injection (55 ± 4% p = 0.008 vs. 24 ± 2%, p = 0.02). We also found a significant decline in the positive scotopic threshold response (pSTR) amplitude of WT mice compared to RAGE^-/- (36 ± 3% vs. 16 ± 6%).

Discussion

RAGE^-/- mice are protected against RGC loss following retinal ischemia. Intravitreal injection of oligomeric Aß accelerated RGC loss in WT mice but not RAGE^-/-. A co-localization of RAGE and Aß, suggests that RAGE-Aß binding may contribute to RGC loss.

Blood-brain barrier penetrating neprilysin degrades monomeric amyloid-beta in a mouse model of Alzheimer's disease

BACKGROUND

Aggregation of the amyloid-β (Aβ) peptide in the brain is one of the key pathological events in Alzheimer's disease (AD). Reducing Aβ levels in the brain by enhancing its degradation is one possible strategy to develop new therapies for AD. Neprilysin (NEP) is a membrane-bound metallopeptidase and one of the major Aβ-degrading enzymes. The secreted soluble form of NEP (sNEP) has been previously suggested as a potential protein-therapy degrading Aβ in AD. However, similar to other large molecules, peripherally administered sNEP is unable to reach the brain due to the presence of the blood-brain barrier (BBB).

METHODS

To provide transcytosis across the BBB, we recombinantly fused the TfR binding moiety (scFv8D3) to either sNEP or a previously described variant of NEP (muNEP) suggested to have higher degradation efficiency of Aβ compared to other NEP substrates, but not per se to degrade Aβ more efficiently. To provide long blood half-life, an Fc-based antibody fragment (scFc) was added to the designs, forming sNEP-scFc-scFv8D3 and muNEP-scFc-scFv8D3. The ability of the mentioned recombinant proteins to degrade Aβ was first evaluated in vitro using synthetic Aβ peptides followed by sandwich ELISA. For the in vivo studies, a single injection of 125-iodine-labelled sNEP-scFc-scFv8D3 and muNEP-scFc-scFv8D3 was intravenously administered to a tg-ArcSwe mouse model of AD, using scFc-scFv8D3 protein that lacks NEP as a negative control. Different ELISA setups were applied to quantify Aβ concentration of different conformations, both in brain tissues and blood samples.

RESULTS

When tested in vitro, sNEP-scFc-scFv8D3 retained sNEP enzymatic activity in degrading Aβ and both constructs efficiently degraded arctic Aβ. When intravenously injected, sNEP-scFc-scFv8D3 demonstrated 20 times higher brain uptake compared to sNEP. Both scFv8D3-fused NEP proteins significantly reduced aggregated Aβ levels in the blood of tg-ArcSwe mice, a transgenic mouse model of AD, following a single intravenous injection. In the brain, monomeric and oligomeric Aβ were significantly reduced. Both scFv8D3-fused NEP proteins displayed a fast clearance from the brain.

CONCLUSION

A one-time injection of a BBB-penetrating NEP shows the potential to reduce, the likely most toxic, Aβ oligomers in the brain in addition to monomers. Also, Aβ aggregates in the blood were reduced.

Mitogen Activated Protein Kinase (MAPK) Activation, p53, and Autophagy Inhibition Characterize the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Spike Protein Induced Neurotoxicity

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein and prions use common pathogenic pathways to induce toxicity in neurons. Infectious prions rapidly activate the p38 mitogen activated protein kinase (MAPK) pathway, and SARS-CoV-2 spike proteins rapidly activate both the p38 MAPK and c-Jun NH2-terminal kinase (JNK) pathways through toll-like receptor signaling, indicating the potential for similar neurotoxicity, causing prion and prion-like disease. In this review, we analyze the roles of autophagy inhibition, molecular mimicry, elevated intracellular p53 levels and reduced Wild-type p53-induced phosphatase 1 (Wip1) and dual-specificity phosphatase (DUSP) expression in neurons in the disease process. The pathways induced by the spike protein via toll-like receptor activation induce both the upregulation of PrP^C (the normal isoform of the prion protein, PrP) and the expression of β amyloid. Through the spike-protein-dependent elevation of p53 levels via β amyloid metabolism, increased PrP^C expression can lead to PrP misfolding and impaired autophagy, generating prion disease. We conclude that, according to the age of the spike protein-exposed patient and the state of their cellular autophagy activity, excess sustained activity of p53 in neurons may be a catalytic factor in neurodegeneration. An autoimmune reaction via molecular mimicry likely also contributes to neurological symptoms. Overall results suggest that neurodegeneration is in part due to the intensity and duration of spike protein exposure, patient advanced age, cellular autophagy activity, and activation, function and regulation of p53. Finally, the neurologically damaging effects can be cumulatively spike-protein dependent, whether exposure is by natural infection or, more substantially, by repeated mRNA vaccination.

Protofibrillar Amyloid Beta Modulation of Recombinant hCaV2.2 (N-Type) Voltage-Gated Channels

Cav2.2 channels are key regulators of presynaptic Ca²⁺ influx and their dysfunction and/or aberrant regulation has been implicated in many disease states; however, the nature of their involvement in Alzheimer's disease (AD) is less clear. In this short communication, we show that recombinant hCav2.2/b_1b/a₂d₁ channels are modulated by human synthetic AD-related protofibrillar amyloid beta Ab_1-42 peptides. Structural studies revealed a time-dependent increase in protofibril length, with the majority of protofibrils less than 100 nm at 24 h, while at 48 h, the majority were longer than 100 nm. Cav2.2 modulation by Ab_1-42 was different between a 'low' (100 nM) and 'high' (1 µM) concentration in terms of distinct effects on individual biophysical parameters. A concentration of 100 nM Ab_1-42 caused no significant changes in the measured biophysical properties of Cav2.2 currents. In contrast, 1 µM Ab_1-42 caused an inhibitory decrease in the current density (pA/pF) and maximum conductance (Gmax), and a depolarizing shift in the slope factor (k). These data highlight a differential modulation of Cav2.2 channels by the Ab_1-42 peptide. Discrete changes in the presynaptic Ca²⁺ flux have been reported to occur at an early stage of AD; therefore, this study reveals a potential mechanistic link between amyloid accumulation and Ca_v2.2 channel modulation.

Specific Mutations in the Cholesterol-Binding Site of APP Alter Its Processing and Favor the Production of Shorter, Less Toxic Aβ Peptides

Excess brain cholesterol is strongly implicated in the pathogenesis of Alzheimer's disease (AD). Here we evaluated how the presence of a cholesterol-binding site (CBS) in the transmembrane and juxtamembrane regions of the amyloid precursor protein (APP) regulates its processing. We generated nine point mutations in the APP gene, changing the charge and/or hydrophobicity of the amino-acids which were previously shown as part of the CBS. Most mutations triggered a reduction of amyloid-β peptides Aβ40 and Aβ42 secretion from transiently transfected HEK293T cells. Only the mutations at position 28 of Aβ in the APP sequence resulted in a concomitant significant increase in the production of shorter Aβ peptides. Mass spectrometry (MS) confirmed the predominance of Aβx-33 and Aβx-34 with the APPK28A mutant. The enzymatic activity of α-, β-, and γ-secretases remained unchanged in cells expressing all mutants. Similarly, subcellular localization of the mutants in early endosomes did not differ from the APPWT protein. A transient increase of plasma membrane cholesterol enhanced the production of Aβ40 and Aβ42 by APPWT, an effect absent in APPK28A mutant. Finally, WT but not CBS mutant Aβ derived peptides bound to cholesterol-rich exosomes. Collectively, the present data revealed a major role of juxtamembrane amino acids of the APP CBS in modulating the production of toxic Aβ species. More generally, they underpin the role of cholesterol in the pathophysiology of AD.

From Small Peptides to Large Proteins against Alzheimer’sDisease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. The two cardinal neuropathological hallmarks of AD are the senile plaques, which are extracellular deposits mainly constituted by beta-amyloids, and neurofibrillary tangles formed by abnormally phosphorylated Tau (p-Tau) located in the cytoplasm of neurons. Although the research has made relevant progress in the management of the disease, the treatment is still lacking. Only symptomatic medications exist for the disease, and, in the meantime, laboratories worldwide are investigating disease-modifying treatments for AD. In the present review, results centered on the use of peptides of different sizes involved in AD are presented.

Regulation of the Soluble Amyloid Precursor Protein α (sAPPα) Levels by Acetylcholinesterase and Brain-Derived Neurotrophic Factor in Lung Cancer Cell Media

In comparing two human lung cancer cells, we previously found lower levels of acetylcholinesterase (AChE) and intact amyloid-β40/42 (Aβ), and higher levels of mature brain-derived neurotrophic factor (mBDNF) in the media of H1299 cells as compared to A549 cell media. In this study, we hypothesized that the levels of soluble amyloid precursor protein α (sAPPα) are regulated by AChE and mBDNF in A549 and H1299 cell media. The levels of sAPPα were higher in the media of H1299 cells. Knockdown of AChE led to increased sAPPα and mBDNF levels and correlated with decreased levels of intact Aβ40/42 in A549 cell media. AChE and mBDNF had opposite effects on the levels of Aβ and sAPPα and were found to operate through a mechanism involving α-secretase activity. Treatment with AChE decreased sAPPα levels and simultaneously increased the levels of intact Aβ40/42 suggesting a role of the protein in shifting APP processing away from the non-amyloidogenic pathway and toward the amyloidogenic pathway, whereas treatment with mBDNF led to opposite effects on those levels. We also show that the levels of sAPPα are regulated by protein kinase C (PKC), extracellular signal-regulated kinase (ERK)1/2, phosphoinositide 3 Kinase (PI3K), but not by protein kinase A (PKA).

The AICD fragment of APP initiates a FoxO3a mediated response via FANCD2

The amyloid precursor protein (APP) is a cell surface protein of uncertain function that is notable for being the parent protein of beta-amyloid. Research around this protein has focussed heavily on the link to Alzheimer's disease and neurodegeneration. However, there is increasing evidence that APP may be linked to neuronal loss through mechanisms independent of beta-amyloid. FoxO3a is a transcription factor associated with neuronal longevity and apoptosis. In neurons, FoxO3a is associated with cell death through pathways that include BIM, a BCL-2 family member. In this study we have shown that APP overexpression increased the cellular levels and activity of FoxO3a. This increased expression and activity is not a result of decreased phosphorylation but is more likely a result of increased nuclear stability due to increased levels of FANCD2, a binding partner of FoxO3a. The changes caused by APP overexpression were shown to be due to the AICD fragment of APP possibly directly inducing transcription increase in FANCD2. These findings strengthen the link between APP metabolism and FoxO3a neuronal activity. This link may be crucial in better understanding the cellular role of APP and its link to neurodegeneration and aging.

Spatially Resolved Transcriptomes of Mammalian Kidneys Illustrate the Molecular Complexity and Interactions of Functional Nephron Segments

Available transcriptomes of the mammalian kidney provide limited information on the spatial interplay between different functional nephron structures due to the required dissociation of tissue with traditional transcriptome-based methodologies. A deeper understanding of the complexity of functional nephron structures requires a non-dissociative transcriptomics approach, such as spatial transcriptomics sequencing (ST-seq). We hypothesize that the application of ST-seq in normal mammalian kidneys will give transcriptomic insights within and across species of physiology at the functional structure level and cellular communication at the cell level. Here, we applied ST-seq in six mice and four human kidneys that were histologically absent of any overt pathology. We defined the location of specific nephron structures in the captured ST-seq datasets using three lines of evidence: pathologist's annotation, marker gene expression, and integration with public single-cell and/or single-nucleus RNA-sequencing datasets. We compared the mouse and human cortical kidney regions. In the human ST-seq datasets, we further investigated the cellular communication within glomeruli and regions of proximal tubules–peritubular capillaries by screening for co-expression of ligand–receptor gene pairs. Gene expression signatures of distinct nephron structures and microvascular regions were spatially resolved within the mouse and human ST-seq datasets. We identified 7,370 differentially expressed genes (p_adj < 0.05) distinguishing species, suggesting changes in energy production and metabolism in mouse cortical regions relative to human kidneys. Hundreds of potential ligand–receptor interactions were identified within glomeruli and regions of proximal tubules–peritubular capillaries, including known and novel interactions relevant to kidney physiology. Our application of ST-seq to normal human and murine kidneys confirms current knowledge and localization of transcripts within the kidney. Furthermore, the generated ST-seq datasets provide a valuable resource for the kidney community that can be used to inform future research into this complex organ.

Physiology and pharmacology of amyloid precursor protein

Amyloid precursor protein (APP) is an evolutionarily conserved transmembrane protein and a well-characterized precursor protein of amyloid-beta (Aβ) peptides, which accumulate in the brains of individuals with Alzheimer's disease (AD)-related pathologies. Aβ has been extensively investigated since the amyloid hypothesis in AD was proposed. Besides Aβ, previous studies on APP and its proteolytic cleavage products have suggested their diverse pathological and physiological functions. However, their roles still have not been thoroughly understood. In this review, we extensively discuss the evolutionarily-conserved biology of APP, including its structure and processing pathway, as well as recent findings on the physiological roles of APP and its fragments in the central nervous system and peripheral nervous system. We have also elaborated upon the current status of APP-targeted therapeutic approaches for AD treatment by discussing inhibitors of several proteases participating in APP processing, including α-, β-, and γ-secretases. Finally, we have highlighted the future perspectives pertaining to further research and the potential clinical role of APP.

DHA Ameliorates Cognitive Ability, Reduces Amyloid Deposition, and Nerve Fiber Production in Alzheimer’s Disease

Background

The etiology of Alzheimer’s disease (AD) is very complex. Docosahexaenoic acid (DHA) is important in cognitive ability and nervous system development. A limited number of studies have evaluated the efficacy of DHA in the treatment of AD.

Introduction

We detected neurofibrillary tangles (NFT) in the hippocampus and cortex of transgenic mice brain through silver glycine staining. We determined the activity of neurons by staining Nissl bodies, used liquid NMR to detect metabolites in the brain, and functional magnetic resonance imaging results to observe the connection signal value between brain regions.

Materials and Methods

We fed 3-month-old APP/PS1 double transgenic mice with DHA mixed feeds for 4 months to assess the effects of DHA on cognitive ability in AD mice through the Morris water maze and open field tests. To evaluate its effects with AD pathology, continuous feeding was done until the mice reached 9 months of age.

Results

Compared to AD mice, escape latency significantly decreased on the fifth day while swimming speed, target quadrant stay time, and the crossing number of platforms increased by varying degrees after DHA treatment. Brain tissue section staining revealed that DHA significantly reduced Aβ and nerve fibers in the brain of AD mice.

Conclusion

DHA significantly reduced the deposition of Aβ in the brain and inhibited the production of nerve fibers, thereby increasing cognitive abilities in AD mice. In addition, DHA suppressed blood lipid levels, and restored uric acid and urea levels, implying that DHA is a potential therapeutic option for early AD.

Exploring the Role of Ubiquitin-Proteasome System in Parkinson's Disease

Over the last decade, researchers have discovered that  a group of apparently unrelated neurodegenerative disorders, such as Parkinson's disease, have remarkable cellular and molecular biology similarities. Protein misfolding and aggregation are involved in all of the neurodegenerative conditions; as a result, inclusion bodies aggregation starts in the cells. Chaperone proteins and ubiquitin (26S proteasome's proteolysis signal), which aid in refolding misfolded proteins, are frequently found in these aggregates. The discovery of disease-causing gene alterations that code for multiple ubiquitin-proteasome pathway proteins in Parkinson's disease has strengthened the relationship between the ubiquitin-proteasome system and neurodegeneration. The specific molecular linkages between these systems and pathogenesis, on the other hand, are unknown and controversial. We outline the current level of knowledge in this article, focusing on important unanswered problems.

The relationship of early- and late-onset Alzheimer’s disease genes with COVID-19

Individuals with Alzheimer’s disease and other neurodegenerative diseases have been exposed to excess risk by the COVID-19 pandemic. COVID-19’s main manifestations include high body temperature, dry cough, and exhaustion. Nevertheless, some affected individuals may have an atypical presentation at diagnosis but suffer neurological signs and symptoms as the first disease manifestation. These findings collectively show the neurotropic nature of SARS-CoV-2 virus and its ability to involve the central nervous system. In addition, Alzheimer’s disease and COVID-19 has a number of common risk factors and comorbid conditions including age, sex, hypertension, diabetes, and the expression of APOE ε4. Until now, a plethora of studies have examined the COVID-19 disease but only a few studies has yet examined the relationship of COVID-19 and Alzheimer’s disease as risk factors of each other. This review emphasizes the recently published evidence on the role of the genes of early- or late-onset Alzheimer’s disease in the susceptibility of individuals currently suffering or recovered from COVID-19 to Alzheimer’s disease or in the susceptibility of individuals at risk of or with Alzheimer’s disease to COVID-19 or increased COVID-19 severity and mortality. Furthermore, the present review also draws attention to other uninvestigated early- and late-onset Alzheimer’s disease genes to elucidate the relationship between this multifactorial disease and COVID-19.

The positive impact of 12 weeks of dance and balance training on the circulating amyloid precursor protein and serotonin concentration as well as physical and cognitive abilities in elderly women

BACKGROUND

The study aimed to compare the effectiveness of 12-weeks dance training with balance training on fall risk, physical and cognitive functions. The study's second aim was to evaluate the association between physical and cognitive functions with circulating markers of neurodegeneration and cognitive impairments in elders.

MATERIALS AND METHODS

30 older women (aged 73.3 ± 4.5) were randomly assigned into three groups: balance training (BG), dance training (DG) and control group (CG). To assess the study aims Time up and go test (TUG), 6 minute walk test (6MWT), determination test (DT), blood amyloid precursor protein (APP) and serotonin concentration were performed.

RESULTS

The results showed an improvement in 6MWT (p = 0.0001 for DG and BD), walking speed (p = 0.0001 for DG and BG) and TUG, only for DG (p = 0.0013). The number of correct responses in DT increased in both groups (p = 0.014 and p = 0.005, for DG and BG, respectively). In DG the increase in the total number of reactions was observed (p = 0.013). The improvement in cognitive and physical functions was associated with an increase in APP (p = 0.036 and p = 0.014) and a decrease in serotonin concentrations (p = 0.042 and p = 0.049), respectively in DG and BG.

CONCLUSION

Dance training intervention could have more benefits on elders' physical and cognitive functions. However, both trainings may be important factors modifying the concentration of circulating proteins associated with neurodegenerative and cognitive disorders.

Unconjugated PLGA nanoparticles attenuate temperature-dependent β-amyloid aggregation and protect neurons against toxicity: implications for Alzheimer's disease pathology

Conversion of β-amyloid (Aβ) peptides from soluble random-coil to aggregated protein enriched with β-sheet-rich intermediates has been suggested to play a role in the degeneration of neurons and development of Alzheimer’s disease (AD) pathology. Aggregation of Aβ peptide can be prompted by a variety of environmental factors including temperature which can influence disease pathogenesis. Recently, we reported that FDA-approved unconjugated poly (d,l-lactide-co-glycolide) (PLGA) nanoparticles can have beneficial effects in cellular and animal models of AD by targeting different facets of the Aβ axis. In this study, using biochemical, structural and spectroscopic analyses, we evaluated the effects of native PLGA on temperature-dependent Aβ aggregation and its ability to protect cultured neurons from degeneration. Our results show that the rate of spontaneous Aβ_1–42 aggregation increases with a rise in temperature from 27 to 40 °C and PLGA with 50:50 resomer potently inhibits Aβ aggregation at all temperatures, but the effect is more profound at 27 °C than at 40 °C. It appears that native PLGA, by interacting with the hydrophobic domain of Aβ_1–42, prevents a conformational shift towards β-sheet structure, thus precluding the formation of Aβ aggregates. Additionally, PLGA triggers disassembly of matured Aβ_1–42 fibers at a faster rate at 40 °C than at 27 °C. PLGA-treated Aβ samples can significantly enhance viability of cortical cultured neurons compared to neurons treated with Aβ alone by attenuating phosphorylation of tau protein. Injection of native PLGA is found to influence the breakdown/clearance of Aβ peptide in the brain. Collectively, these results suggest that PLGA nanoparticles can inhibit Aβ aggregation and trigger disassembly of Aβ aggregates at temperatures outside the physiological range and can protect neurons against Aβ-mediated toxicity thus validating its unique therapeutic potential in the treatment of AD pathology.

Human iPSC-Derived Neural Models for Studying Alzheimer's Disease: from Neural Stem Cells to Cerebral Organoids

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study mechanisms of human neural development, disease modeling, and drug discovery in vitro. Especially in the field of Alzheimer’s disease (AD), where this treatment is lacking, tremendous effort has been put into the investigation of molecular mechanisms behind this disease using induced pluripotent stem cell-based models. Numerous of these studies have found either novel regulatory mechanisms that could be exploited to develop relevant drugs for AD treatment or have already tested small molecules on in vitro cultures, directly demonstrating their effect on amelioration of AD-associated pathology. This review thus summarizes currently used differentiation strategies of induced pluripotent stem cells towards neuronal and glial cell types and cerebral organoids and their utilization in modeling AD and potential drug discovery.

The microRNA-455 Null Mouse Has Memory Deficit and Increased Anxiety, Targeting Key Genes Involved in Alzheimer's Disease

The complete molecular mechanisms underlying the pathophysiology of Alzheimer's disease (AD) remain to be elucidated. Recently, microRNA-455-3p has been identified as a circulating biomarker of early AD, with increased expression in post-mortem brain tissue of AD patients. MicroRNA-455-3p also directly targets and down-regulates APP, with the overexpression of miR-455-3p suppressing its toxic effects. Here, we show that miR-455-3p expression decreases with age in the brains of wild-type mice. We generated a miR-455 null mouse utilising CRISPR-Cas9 to explore its function further. Loss of miR-455 resulted in increased weight gain, potentially indicative of metabolic disturbances. Furthermore, performance on the novel object recognition task diminished significantly in miR-455 null mice (p = 0.004), indicating deficits in recognition memory. A slight increase in anxiety was also captured on the open field test. BACE1 and TAU were identified as new direct targets for miR-455-3p, with overexpression of miR-455-3p leading to a reduction in the expression of APP, BACE1 and TAU in neuroblastoma cells. In the hippocampus of miR-455 null mice at 14 months of age, the levels of protein for APP, BACE1 and TAU were all increased. Such findings reinforce the involvement of miR-455 in AD progression and demonstrate its action on cognitive performance.

Sialic Acid Ameliorates Cognitive Deficits by Reducing Amyloid Deposition, Nerve Fiber Production, and Neuronal Apoptosis in a Mice Model of Alzheimer’s Disease

(1) Background: As a natural carbohydrate, sialic acid (SA) is helpful for brain development, cognitive ability, and the nervous system, but there are few reports about the effect of SA on Alzheimer’s disease (AD). (2) Method: The present study evaluated the effect of SA on cognitive ability, neuronal activity, Aβ formation, and tau hyperphosphorylation in a double transgenic AD (2×Tg-AD) mice model. The 2×Tg-AD mice were randomly divided into four groups: the AD control group, 17 mg/kg SA-treated AD group, 84 mg/kg SA-treated AD group, and 420 mg/kg SA-treated AD group. Mice from all four groups were fed to 7 months of age for the behavioral test and to 9 months of age for the pathological factors investigation. (3) Results: In the Morris water maze, the escape latency significantly decreased on the fifth day in the SA-treated groups. The number of rearing and crossing times in the open field test also increased significantly, compared with the control group. SA treatment significantly reduced amyloid β-peptide (Aβ) and nerve fibers and increased the number of Nissl bodies in the brain of AD mice. (4) Conclusions: SA reduced the neuron damage by reducing Aβ and inhibited tau protein hyperphosphorylation, which improved the cognitive ability and mobility of AD mice.

Iron Homeostasis Disorder and Alzheimer's Disease

Iron is an essential trace metal for almost all organisms, including human; however, oxidative stress can easily be caused when iron is in excess, producing toxicity to the human body due to its capability to be both an electron donor and an electron acceptor. Although there is a strict regulation mechanism for iron homeostasis in the human body and brain, it is usually inevitably disturbed by genetic and environmental factors, or disordered with aging, which leads to iron metabolism diseases, including many neurodegenerative diseases such as Alzheimer's disease (AD). AD is one of the most common degenerative diseases of the central nervous system (CNS) threatening human health. However, the precise pathogenesis of AD is still unclear, which seriously restricts the design of interventions and treatment drugs based on the pathogenesis of AD. Many studies have observed abnormal iron accumulation in different regions of the AD brain, resulting in cognitive, memory, motor and other nerve damages. Understanding the metabolic balance mechanism of iron in the brain is crucial for the treatment of AD, which would provide new cures for the disease. This paper reviews the recent progress in the relationship between iron and AD from the aspects of iron absorption in intestinal cells, storage and regulation of iron in cells and organs, especially for the regulation of iron homeostasis in the human brain and prospects the future directions for AD treatments.

Implications of exosomes derived from cholesterol-accumulated astrocytes in Alzheimer's disease pathology

Amyloid β (Aβ) peptides generated from the amyloid precursor protein (APP) play a critical role in the development of Alzheimer's disease (AD) pathology. Aβ-containing neuronal exosomes, which represent a novel form of intercellular communication, have been shown to influence the function/vulnerability of neurons in AD. Unlike neurons, the significance of exosomes derived from astrocytes remains unclear. In this study, we evaluated the significance of exosomes derived from U18666A-induced cholesterol-accumulated astrocytes in the development of AD pathology. Our results show that cholesterol accumulation decreases exosome secretion, whereas lowering cholesterol increases exosome secretion, from cultured astrocytes. Interestingly, exosomes secreted from U18666A-treated astrocytes contain higher levels of APP, APP-C-terminal fragments, soluble APP, APP secretases and Aβ1-40 than exosomes secreted from control astrocytes. Furthermore, we show that exosomes derived from U18666A-treated astrocytes can lead to neurodegeneration, which is attenuated by decreasing Aβ production or by neutralizing exosomal Aβ peptide with an anti-Aβ antibody. These results, taken together, suggest that exosomes derived from cholesterol-accumulated astrocytes can play an important role in trafficking APP/Aβ peptides and influencing neuronal viability in the affected regions of the AD brain.

Sex-dependent effects of amyloid precursor-like protein 2 in the SOD1-G37R transgenic mouse model of MND

Motor neurone disease (MND) is a neurodegenerative disorder characterised by progressive destruction of motor neurons, muscle paralysis and death. The amyloid precursor protein (APP) is highly expressed in the central nervous system and has been shown to modulate disease outcomes in MND. APP is part of a gene family that includes the amyloid precursor-like protein 1 (APLP1) and 2 (APLP2) genes. In the present study, we investigated the role of APLP2 in MND through the examination of human spinal cord tissue and by crossing APLP2 knockout mice with the superoxide dismutase 1 (SOD1-G37R) transgenic mouse model of MND. We found the expression of APLP2 is elevated in the spinal cord from human cases of MND and that this feature of the human disease is reproduced in SOD1-G37R mice at the End-stage of their MND-like phenotype progression. APLP2 deletion in SOD1-G37R mice significantly delayed disease progression and increased the survival of female SOD1-G37R mice. Molecular and biochemical analysis showed female SOD1-G37R:APLP2-/- mice displayed improved innervation of the neuromuscular junction, ameliorated atrophy of muscle fibres with increased APP protein expression levels in the gastrocnemius muscle. These results indicate a sex-dependent role for APLP2 in mutant SOD1-mediated MND and further support the APP family as a potential target for further investigation into the cause and regulation of MND.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Refining the amyloid β peptide and oligomer fingerprint ambiguities in Alzheimer's disease: Mass spectrometric molecular characterization in brain, cerebrospinal fluid, blood, and plasma

Since its discovery, amyloid-β (Aβ) has been the principal target of investigation of in Alzheimer's disease (AD). Over the years however, no clear correlation was found between the Aβ plaque burden and location, and AD-associated neurodegeneration and cognitive decline. Instead, diagnostic potential of specific Aβ peptides and/or their ratio, was established. For instance, a selective reduction in the concentration of the aggregation-prone 42 amino acid-long Aβ peptide (Aβ42) in cerebrospinal fluid (CSF) was put forward as reflective of Aβ peptide aggregation in the brain. With time, Aβ oligomers-the proposed toxic Aβ intermediates-have emerged as potential drivers of synaptic dysfunction and neurodegeneration in the disease process. Oligomers are commonly agreed upon to come in different shapes and sizes, and are very poorly characterized when it comes to their composition and their "toxic" properties. The concept of structural polymorphism-a diversity in conformational organization of amyloid aggregates-that depends on the Aβ peptide backbone, makes the characterization of Aβ aggregates and their role in AD progression challenging. In this review, we revisit the history of Aβ discovery and initial characterization and highlight the crucial role mass spectrometry (MS) has played in this process. We critically review the common knowledge gaps in the molecular identity of the Aβ peptide, and how MS is aiding the characterization of higher order Aβ assemblies. Finally, we go on to present recent advances in MS approaches for characterization of Aβ as single peptides and oligomers, and convey our optimism, as to how MS holds a promise for paving the way for progress toward a more comprehensive understanding of Aβ in AD research.

Comprehensive analysis of O-glycosylation of amyloid precursor protein (APP) using targeted and multi-fragmentation MS strategy

BACKGROUND

The aberrant proteolytic processing of amyloid precursor protein (APP) into amyloid β peptide (Aβ) in brain is a critical step in the pathogenesis of Alzheimer's disease (AD). As an O-glycosylated protein, O-glycosylation of APP is considered to be related to Aβ generation. Therefore, comprehensive analysis of APP O-glycosylation is important for understanding its functions.

METHODS

We developed a Targeted MS approach with Multi-Fragmentation techniques (TMMF strategy), and successfully characterized O-glycosylation profiling of APP695 expressed in HEK-293 T cells. We calculated relative abundance of glycopeptides with various O-glycosites and O-glycans, and further investigated the alteration of APP O-glycosylation upon TNF-α treatment.

RESULTS

A total of 14 O-glycosites were identified on three glycopeptides of APP, and at least four O-glycans including GalNAc (Tn antigen), core 1, and mono-/di-sialylated core 1 glycans were determinant at the residues of Thr576 and Thr577. We found a dense cluster of truncated O-glycans on the region nearby beginning of E2 domain and high abundance of sialylated O-glycans on the region close to β-cleavage site. Moreover, we also observed that TNF-α could upregulate the expression of APP and the truncated O-glycans on APP in HEK-293 T cell.

CONCLUSION

Our study established an intact O-glycopeptide MS analysis strategy for APP O-glycopeptide identification with enhanced fragmentation efficiency and detection sensitivity. These results provide a comprehensive O-glycosylation map of APP expressed in HEK-293 T cell.

GENERAL SIGNIFICANCE

The accurate O-glycosites and O-glycan structures on APP may lead to a better understanding of the roles O-glycosylation plays in the processing and functions of APP.

Nutraceutical and Probiotic Approaches to Examine Molecular Interactions of the Amyloid Precursor Protein APP in Drosophila Models of Alzheimer's Disease

Studies using animal models have shed light into the molecular and cellular basis for the neuropathology observed in patients with Alzheimer’s disease (AD). In particular, the role of the amyloid precursor protein (APP) plays a crucial role in the formation of senile plaques and aging-dependent degeneration. Here, we focus our review on recent findings using the Drosophila AD model to expand our understanding of APP molecular function and interactions, including insights gained from the fly homolog APP-like (APPL). Finally, as there is still no cure for AD, we review some approaches that have shown promising results in ameliorating AD-associated phenotypes, with special attention on the use of nutraceuticals and their molecular effects, as well as interactions with the gut microbiome. Overall, the phenomena described here are of fundamental significance for understanding network development and degeneration. Given the highly conserved nature of fundamental signaling pathways, the insight gained from animal models such as Drosophila melanogaster will likely advance the understanding of the mammalian brain, and thus be relevant to human health.

Pathobiolgy and Management of Alzheimer's Disease

Amyloid and tau protein abnormalities have been identified as the main causes of Alzheimer's disease but exact mechanisms remain to be revealed. Especially, amyloid beta and tau protein coupling and neuroinflammatory and neurovascular contributions to Alzheimer disease are quite mysterious. Many animal models and basic biological research are trying to solve these puzzles. Known as aging processes, autophagy, mitochondrial degeneration with generation of reactive oxygen species, and age-related epigenetic modifications are also known to be associated with development of Alzheimer's disease. Environmental factors such as bacterial and viral infections, heavy metal ions, diet, sleep, stress, and gut microbiota are also risk factors of Alzheimer's disease. Future development of preventive and therapeutic modalities may be dependent on the pathobiology of Alzheimer's disease.

Alternative Targets to Fight Alzheimer's Disease: Focus on Astrocytes

The available treatments for patients affected by Alzheimer’s disease (AD) are not curative. Numerous clinical trials have failed during the past decades. Therefore, scientists need to explore new avenues to tackle this disease. In the present review, we briefly summarize the pathological mechanisms of AD known so far, based on which different therapeutic tools have been designed. Then, we focus on a specific approach that is targeting astrocytes. Indeed, these non-neuronal brain cells respond to any insult, injury, or disease of the brain, including AD. The study of astrocytes is complicated by the fact that they exert a plethora of homeostatic functions, and their disease-induced changes could be context-, time-, and disease specific. However, this complex but fervent area of research has produced a large amount of data targeting different astrocytic functions using pharmacological approaches. Here, we review the most recent literature findings that have been published in the last five years to stimulate new hypotheses and ideas to work on, highlighting the peculiar ability of palmitoylethanolamide to modulate astrocytes according to their morpho-functional state, which ultimately suggests a possible potential disease-modifying therapeutic approach for AD.

Chinese herbs and acupuncture to improve cognitive function in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease with a variety of causes. Traditional Chinese medicine (TCM), which includes the two main approaches of acupuncture and herbal medication, views the human body as a self-controlled system network. Fundamental theories, including "qi," the five elements, and the theory of viscera, form the basis for classification. Diseases in humans are considered to be caused by an imbalance of "yang qi" and "yin qi" that lead to the nonhomeostasis of organs. Acupuncture is derived from 12 main meridians and 365 acupuncture points characterized by "blood and qi." Needling of different positions corresponds to specific disease treatments to increase qi. Treatment with Chinese herbal medicines is based on syndrome differentiation characterized as "Zheng" which differs from the cause orientation approach of Western medicine. In this article, we review basic and clinical research studies that describe TCM herbs and acupuncture for the treatment of AD. Moreover, we propose that these two approaches be integrated to improve the outcomes for AD patients.

SHANK2 mutations impair apoptosis, proliferation and neurite outgrowth during early neuronal differentiation in SH-SY5Y cells

SHANK2 mutations have been identified in individuals with neurodevelopmental disorders, including intellectual disability and autism spectrum disorders (ASD). Using CRISPR/Cas9 genome editing, we obtained SH-SY5Y cell lines with frameshift mutations on one or both SHANK2 alleles. We investigated the effects of the different SHANK2 mutations on cell morphology, cell proliferation and differentiation potential during early neuronal differentiation. All mutant cell lines showed impaired neuronal differentiation marker expression. Cells with bi-allelic SHANK2 mutations revealed diminished apoptosis and increased proliferation, as well as decreased neurite outgrowth during early neuronal differentiation. Bi-allelic SHANK2 mutations resulted in an increase in p-AKT levels, suggesting that SHANK2 mutations impair downstream signaling of tyrosine kinase receptors. Additionally, cells with bi-allelic SHANK2 mutations had lower amyloid precursor protein (APP) expression compared to controls, suggesting a molecular link between SHANK2 and APP. Together, we can show that frameshift mutations on one or both SHANK2 alleles lead to an alteration of neuronal differentiation in SH-SY5Y cells, characterized by changes in cell growth and pre- and postsynaptic protein expression. We also provide first evidence that downstream signaling of tyrosine kinase receptors and amyloid precursor protein expression are affected.

MicroRNA-298 reduces levels of human amyloid-β precursor protein (APP), β-site APP-converting enzyme 1 (BACE1) and specific tau protein moieties

Alzheimer's disease (AD) is the most common age-related form of dementia, associated with deposition of intracellular neuronal tangles consisting primarily of hyperphosphorylated microtubule-associated protein tau (p-tau) and extracellular plaques primarily comprising amyloid- β (Aβ) peptide. The p-tau tangle unit is a posttranslational modification of normal tau protein. Aβ is a neurotoxic peptide excised from the amyloid-β precursor protein (APP) by β-site APP-cleaving enzyme 1 (BACE1) and the γ-secretase complex. MicroRNAs (miRNAs) are short, single-stranded RNAs that modulate protein expression as part of the RNA-induced silencing complex (RISC). We identified miR-298 as a repressor of APP, BACE1, and the two primary forms of Aβ (Aβ40 and Aβ42) in a primary human cell culture model. Further, we discovered a novel effect of miR-298 on posttranslational levels of two specific tau moieties. Notably, miR-298 significantly reduced levels of ~55 and 50 kDa forms of the tau protein without significant alterations of total tau or other forms. In vivo overexpression of human miR-298 resulted in nonsignificant reduction of APP, BACE1, and tau in mice. Moreover, we identified two miR-298 SNPs associated with higher cerebrospinal fluid (CSF) p-tau and lower CSF Aβ42 levels in a cohort of human AD patients. Finally, levels of miR-298 varied in postmortem human temporal lobe between AD patients and age-matched non-AD controls. Our results suggest that miR-298 may be a suitable target for AD therapy.

Glycosaminoglycans in Neurodegenerative Diseases

Glycosaminoglycans (GAGs) are linear polysaccharides that consist of alternating disaccharides sequences of uronic acids and/or galactose hexamino sugars most of which are sulfated. GAGs are ubiquitously expressed on the cell surface, in the intracellular milieu and in the extracellular matrix of all animal cells. Thus, GAGs exhibit many essential roles in a variety of physiological and pathological processes. The targets of GAGs are GAG-binding proteins and related proteins that are of significant interest to both the academic community and in the pharmaceutical industry. In this review, the structures of GAGs, their binding proteins, and analogs are presented that further the development of GAGs and their analogs for the treatment of neurodegenerative diseases agents.

From Brain to Heart: Possible Role of Amyloid-β in Ischemic Heart Disease and Ischemia-Reperfusion Injury

Ischemic heart disease (IHD) is among the leading causes of death in developed countries. Its pathological origin is traced back to coronary atherosclerosis, a lipid-driven immuno-inflammatory disease of the arteries that leads to multifocal plaque development. The primary clinical manifestation of IHD is acute myocardial infarction (AMI),) whose prognosis is ameliorated with optimal timing of revascularization. Paradoxically, myocardium re-perfusion can be detrimental because of ischemia-reperfusion injury (IRI), an oxidative-driven process that damages other organs. Amyloid-β (Aβ) plays a physiological role in the central nervous system (CNS). Alterations in its synthesis, concentration and clearance have been connected to several pathologies, such as Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Aβ has been suggested to play a role in the pathogenesis of IHD and cerebral IRI. The purpose of this review is to summarize what is known about the pathological role of Aβ in the CNS; starting from this evidence, we will illustrate the role played by Aβ in the development of coronary atherosclerosis and its possible implications in the pathophysiology of IHD and myocardial IRI. Better elucidation of Aβ's contribution to the molecular pathways underlying IHD and IRI could be of great help in developing new therapeutic strategies.

Amyloid-β Precursor Protein APP Down-Regulation Alters Actin Cytoskeleton-Interacting Proteins in Endothelial Cells

The amyloid-β precursor protein (APP) is a ubiquitous membrane protein often associated with Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA). Despite its role in the development of the pathogenesis, APP exerts several physiological roles that have been mainly investigated in neuronal tissue. To date, the role of APP in vasculature and endothelial cells has not been fully elucidated. In this study, we used molecular and proteomic approaches to identify and investigate major cellular targets of APP down-regulation in endothelial cells. We found that APP is necessary for endothelial cells proliferation, migration and adhesion. The loss of APP alters focal adhesion stability and cell-cell junctions' expression. Moreover, APP is necessary to mediate endothelial response to the VEGF-A growth factor. Finally, we document that APP propagates exogenous stimuli and mediates cellular response in endothelial cells by modulating the Scr/FAK signaling pathway. Thus, the intact expression and processing of APP is required for normal endothelial function. The identification of molecular mechanisms responsible for vasoprotective properties of endothelial APP may have an impact on clinical efforts to preserve and protect healthy vasculature in patients at risk of the development of cerebrovascular disease and dementia including AD and CAA.