Aβ Generation Research Articles

Not all plaques are created equal: Uncovering a unique molecular signature in Alzheimer's disease.

Although neuritic plaques - comprised of aggregated fibrils of the misfolded protein, amyloid β (Aβ) - have formed a central focus of Alzheimer's disease (AD) research for decades, it is now well understood that plaque burden alone is a poor correlate of cognitive decline. This is highlighted especially when compared against other neuropathological hallmarks, such as synapse loss (the strongest correlate) and hyperphosphorylated protein tau. However, it is known that Familial AD arises due to autosomal dominant mutations directly influencing the generation of Aβ, suggesting that Aβ pathology may play a key upstream role in the disease. Such contrasting lines of evidence have thus raised questions as to why some aged individuals with high plaque burden develop AD while others remain cognitively healthy. In their recent study, published in Analytical Chemistry (June 2024), Enzlein and colleagues aimed to investigate whether differences in the molecular composition of plaques between individuals with sporadic Alzheimer's disease (N = 9) versus age-matched amyloid positive but cognitively unaffected controls (N = 8) could go towards explaining this outstanding question in the field. Using novel methods integrating mass spectrometry imaging with machine learning feature extraction, the authors compared peptide and lipid profiles to a resolving limit of 400 μm2 for >5000 individual plaques. In doing so, a distinct peptide signature was identified in sporadic Alzheimer's disease plaques that was characterised by strongly increased aggregation of the short amyloid β isoform, Aβ1-38 coupled with a lesser co-aggregation of pyroglutamate-modified Aβ3-42pE. Sporadic Alzheimer's disease plaques also demonstrated a robust lipid signature denoted by an increased presence of cell membrane components, GM1 and GM2 gangliosides. Here, we review this work; aiming to place these findings within the context of existing literature and with a view to discussing their importance in developing our current knowledge of Alzheimer's disease.

Systemic Treatment with siRNA Targeting Gamma-Secretase Activating Protein Inhibits Amyloid-β Accumulation in Alzheimer's Disease.

Amyloid-β (Aβ) peptide aggregation in the brain is a key factor in Alzheimer's disease. However, direct inhibition of β-secretase or γ-secretase proves ineffective in reducing Aβ accumulation and improving cognition in Alzheimer's. Recent findings suggest that inhibiting gamma-secretase activating protein (GSAP) can decrease Aβ generation without affecting crucial γ-secretase substrates. Dimerization of Lep9R3LC (diLep9R3LC) was confirmed by Ellman's test. The peptide-small interfering RNA (siRNA) complex ratio, particle size, and surface charge were analyzed using electrophoretic mobility shift assay, and dynamic light scattering, respectively. In a 3xTg mice model of Alzheimer's disease, diLep9R3LC:siRNA complexes were intravenously administered twice a week for 8 weeks. Assessments included gene silencing, protein expression, and behavioral improvement using reverse transcription polymerase chain reaction, quantitative polymerase chain reaction, western blotting, Y-maze, and object recognition tests. The efficacy of Lep9R3LC dimerization was ~80% after a 3-d reaction by Ellman's test. In N2a cells, diLep9R3LC:siGSAP complexes achieved ~70% silencing at 48 h posttransfection. In 7-month-old male 3xTg mice, GSAP knockdown was ~30% in the cortex and ~50% in the hippocampus. The behavior improved in mice treated with diLep9R3LC:siGSAP complexes, showing a 60% increase in entries and an 80% increase object recognition. A novel dipeptide, diLep9R3LC, complexed with siRNA targeting GSAP (siGSAP), efficiently delivers siRNA to the mouse brain, targeting the hippocampus. The treatment inhibits Aβ accumulation, reduces GSK-3β-associated with tau hyperphosphorylation, and improves Alzheimer's behavior. Our findings highlight diLep9R3LC:siGSAP's potential for Alzheimer's and as a siRNA carrier for central nervous system-related diseases.

Active Compounds of Panax ginseng in the Improvement of Alzheimer's Disease and Application of Spatial Metabolomics.

Panax ginseng C.A. Meyer (P. ginseng) is one of the more common traditional Chinese medicines (TCMs). It contains numerous chemical components and exhibits a range of pharmacological effects. An enormous burden is placed on people's health and life by Alzheimer's disease (AD), a neurodegenerative condition. Recent research has shown that P. ginseng's chemical constituents, particularly ginsenosides, have a significant beneficial impact on the prevention and management of neurological disorders. To understand the current status of research on P. ginseng to improve AD, this paper discusses the composition of P. ginseng, its mechanism of action, and its clinical application. The pathogenesis of AD includes amyloid beta protein (Aβ) generation and aggregation, tau protein hyperphosphorylation, oxidant stress, neuroinflammation, mitochondrial damage, and neurotransmitter and gut microbiota disorders. This review presents the key molecular mechanisms and signaling pathways of the active ingredients in P. ginseng involved in improving AD from the perspective of AD pathogenesis. A P. ginseng-related signaling pathway network was constructed to provide effective targets for the treatment of AD. In addition, the application of spatial metabolomics techniques in studying P. ginseng and AD is discussed. In summary, this paper discusses research perspectives for the study of P. ginseng in the treatment of AD, including a systematic and in-depth review of the mechanisms of action of the active substances in P. ginseng, and evaluates the feasibility of applying spatial metabolomics in the study of AD pathogenesis and pharmacological treatment.

HDAC3 inhibition increases the expression levels of the Amyloid Precursor Protein

AbstractBackgroundEpigenetic‐based interventions have recently garnered attention as potential therapies for Alzheimer’s disease (AD). Histone deacetylases (HDACs) represent an interesting target for neurodegenerative diseases therapies, since HDAC inhibitors have been shown to have the ability to reinstate memory even after neuronal loss. Particularly, HDAC3 inhibition has been shown to enhance long‐term memory and reduce amyloid‐β in AD models, although the molecular mechanisms behind these effects are unclear. The aim of this study was to characterise the effects of HDAC3 inhibition on the mechanisms of generation and degradation of Aβ using in vitro and in ex vivo models of ADMethodN2a mouse neuroblastoma cells overexpressing the Swedish mutation (N2asw) as well as organotypic brain cultures (OBCs) of 5XFAD mice were incubated with various concentrations of the HDAC3 selective inhibitor RGFP966 (0.1‐10 μM) for 24h.ResultTreatment with HDAC3 inhibitor RGFP966, led to a 4% increase on Aβ42 levels in N2a cells, associated with elevated levels carboxy‐terminus fragments (CTFs) and APP protein expressions as well as APP mRNA levels. In vitro chromatin immunoprecipitation (ChIP) analysis in N2a cells, revealed enriched HDAC3 binding at APP promoter regions. The increase in APP expression was also detected in OBCs from 5XFAD mice incubated with 1 μM RGFP966, without significant changes in Aβ secretion. In addition, mRNA sequencing in OBCs revealed that HDAC3 inhibition affects neuronal regenerative pathways, in particular linked to neurogenesis, neuronal differentiation, axonogenesis, resulting in an increase in dendritic spine density.ConclusionThese results suggest that the HDAC3 therapeutic role in AD involves the regulation of APP expression and regenerative pathways, leading to increased synaptic connectivity.

Mitigating chronic neuroinflammation in Alzheimer mice by novel immunomodulatory imide drugs (IMiDs) conserves neuroplasticity and cognitive function and also alleviates neurodegeneration‐behavioral impairments in TBI‐challenged mice

AbstractBackgroundNeuroinflammation is an invariable characteristic of chronic neurodegenerative disorders, such as Alzheimer’s disease (AD), and acute ones, epitomized by traumatic brain injury (TBI). However, whether neuroinflammation development drives disease progression or is an epiphenomenon remains unknown.MethodsTo test the hypothesis that, once initiated, AD‐associated chronic neuroinflammation directly drives progressive synaptic/neuronal loss and cognitive decline irrespective of changes in amyloid‐β (Aβ) peptide generation, a new class of immunomodulatory imide drugs (IMiDs) was developed on the backbone of thalidomide/pomalidomide to reduce proinflammatory cytokine generation and resulting inflammation, but lacking action on SALL4 – a key protein implicated in thalidomide teratogenicity. (i) 5xFAD mice, known to develop neuroinflammation consequent to excessive Ab generation, were evaluated over a 4‐month period during which cognitive deficits develop, and (ii) wild type mice subjected to TBI and impacted with motor and cognitive impairments were evaluated to assess whether selective resolution of neuroinflammation by novel IMiDs could mitigate behavioral declines.ResultsPomalidomide (Pom) and the more potent novel analog, 3,6’‐dithioPom (3,6’‐DP), which does not impact SALL4 levels, were administered to reduce microglial cell activation ‐ as confirmed in primary cortical cultures challenged with Aβ and RAW 264.7 cells challenged with lipopolysaccharide (LPS). 3,6’‐DP, in particular, decreased microglial and astrocyte activation in hippocampus and cerebral cortex of 5xFAD mice. This was accompanied by reductions in synaptic and neuronal cell loss, and behavioral impairment in the absence of changes in Aβ plaque or peptide generation. In TBI challenged mice, 3,6’‐DP, likewise, mitigated neuroinflammation and resulted in reduced neuronal loss and behavioral impairments.ConclusionsAD‐associated chronic neuroinflammation directly drives progressive synaptic/neuronal loss and cognitive decline. Pharmacologically mitigating microglial/astrocyte activation without altering Aβ generation provides a means to mitigate AD‐associated cognitive/behavioral impairments, and provides a new drug candidate to alleviate other neurodegenerative disorders, such as TBI.

SPIN90 Deficiency Ameliorates Amyloid ß Accumulation by Regulating APP Trafficking in AD Model Mice

AbstractBackgroundAlzheimer’s disease (AD), a common form of dementia, is caused in part by the aggregation and accumulation in the brain of amyloid ß (Aß), a product of the proteolytic cleavage of amyloid precursor protein (APP) in endosomes. Trafficking of APP, such as surface‐intracellular recycling, is an early critical step required for Aβ generation. Less is known, however, about the molecular mechanism regulating APP trafficking. This study investigated the mechanism by which SPIN90, along with Rab11, modulates APP trafficking, Aβ motility and accumulation, and synaptic functionalityMethodThis study utilized live‐imaging technology with molecular, cellular and 5xFAD model mice system.ResultBrain Aβ deposition was lower in the progeny of 5xFAD‐SPIN90KO mice than in 5xFAD‐SPIN90WT mice. Analysis of APP distribution and trafficking showed that the surface fraction of APP was locally distinct in axons and dendrites, with these distributions differing significantly in 5xFAD‐SPIN90WT and 5xFAD‐SPIN90KO mice, and that neural activity‐driven APP trafficking to the surface and intracellular recycling were more actively mobilized in 5xFAD‐SPIN90KO neurons. In addition, SPIN90 was found to be cotrafficked with APP via axons, with ablation of SPIN90 reducing the intracellular accumulation of APP in axons. Finally, synaptic transmission was restored over time in 5xFAD‐SPIN90KO but not in 5xFAD‐SPIN90WT neuronsConclusionThe interaction of SPIN90 and Rab11 is implicated in Aβ production through the regulation of APP trafficking.

ErbB3 Binding Protein 1(EBP1), Novel Modulator of PS2/γ –Secretase, Blocks PS2/ γ –Secretase Cleavage of APP, Reducing Intraneuronal Aβ Generation

AbstractBackgroundErbB3 binding protein 1 (Ebp1) is a multifunctional protein that is involved in various cellular events including cell survival, proliferation, differentiation, and cell cycle progression either in the embryogenesis or human disease. Apart from its roles in brain development, Ebp1 may be involved in neurodegenerative diseases such as Alzheimer’s disease (AD) as its expression was plunged after birth and older brain. AD patients usually have severe synapse and neuron loss, leading to memory decline, which are also occurred in the Ebp1 deficient mice brain. We thus investigated whether alteration of Ebp1 expression affects AD pathology.Methodwe show that in AD patients’ brain and in the 5X‐FAD transgenic mice, Ebp1 level is inversely correlated with Aβ deposition and loss of Ebp1 (Ebp1flox/flox ::CaMKIIa‐Cre) or Ebp1 cleavage by AEP escalates Aβ production in vitro/ex vivo/in vivo studies.ResultForebrain deletion of ErbB3 binding protein 1(Ebp1) in mice model exerted abnormal Aβ deposition and cognitive dysfunction. Ebp1 is greatly reduced, cleaving by asparagine endopeptidase (AEP) in postmortem AD patients and 5X‐FAD mice brains. Besides prominent neuronal death and degeneration, cleaved Ebp1 N84 and N204 fragments notably escalate intraneuronal Aβ generation and aggregates with Aβ in the brain. Whereas Ebp1 associates with APP and presenilin 2 (PS2), a catalytic subunit of γ ‐secretase, protecting APP cleavage by PS2/γ‐secretase in the neuron, AEP‐mediated Ebp1 cleavage liberate blockage of PS2 access to APP in the neurons of 5X‐FAD mice. Accordingly, reinstatement of Ebp1 using AAV2‐ Ebp1 WT or uncleavable mutant expression into brain of 5X‐FAD mice improved behavioral impairment and alleviates Aβ generation.ConclusionEbp1 is a pathological substrate of AEP in AD conditions, eliciting intracellular Aβ production, blocking PS2 access to APP. Targeting APP‐PS2 interaction by non‐cleaved mutant form of Ebp1or elevating intact Ebp1 levels in AD condition may represent a novel intervention opportunity to reduce intracellular Aβ levels.

A bidirectional link between sulfatide and Alzheimer’s disease

Reduced sulfatide level is found in Alzheimer's disease (AD) patients. Here, we demonstrate that amyloid precursor protein (APP) processing regulates sulfatide synthesis and vice versa. Different cell culture models and transgenic mice models devoid of APP processing or in particular the APP intracellular domain (AICD) reveal that AICD decreases Gal3st1/CST expression and subsequently sulfatide synthesis. In return, sulfatide supplementation decreases Aβ generation by reducing β-secretase (BACE1) and γ-secretase processing of APP. Increased BACE1 lysosomal degradation leads to reduced BACE1 protein level in endosomes. Reduced γ-secretase activity is caused by a direct effect on γ-secretase activity and reduced amounts of γ-secretase components in lipid rafts. Similar changes were observed by analyzing cells and mice brain samples deficient of arylsulfatase A responsible for sulfatide degradation or knocked down in Gal3st1/CST. In line with these findings, addition of sulfatides to brain homogenates of AD patients resulted in reduced γ-secretase activity. Human brain APP level shows a significant negative correlation with GAL3ST1/CST expression underlining the invivo relevance of sulfatide homeostasis in AD.

Comparison of physiological state and conditions imitating the comorbidity of type 2 diabetes with Alzheimer's disease. The impact on: proliferation, H2O2, Aβ42, S100A8, S100B levels, neuronal protrusion and neurogenesis

Abstract Aim: Recent studies demonstrate that individuals with T2DM more likely to develop AD. While, disturbed glucose or insulin homeostasis, are at the forefront of AD research, not much is known about extra- and intracellular interplay between different forms of Aβ and microenviromental fluctuations of glucose or insulin concentrations in neuronal cells. Methods: We create conditions imitating the coexistence of T2DM with AD and compare the results with state where the neuropathological changes are yet not developed. We have investigated the effect of the physiological (Aβ40) and toxic amyloid form (Aβ25–35) and its co-incubation with glucose or insulin on neuronal proliferation, H2O2, Aβ42, S100B, S100A8 protein concentrations, mature neuronal protrusions and neurogenesis. Results: Aβ40 and Aβ25-35 with hyperglycaemia provoked stronger cytotoxic effect comparing to Aβ alone, while hyperinsulinemia dampen this effect. Opposite results were obtained in H2O2 measurement. Insulin stimulated Aβ42 generation when co-incubated with both Aβ forms. Aβ40 and Aβ25-35 caused similar pattern of extracellular S100B protein influx an concomitant cytosolic efflux. Neuronal protrusions and neurogenesis were initiated by co-incubation of Aβ40 with hyperglycaemia while reduced in Aβ25-35 and hyperglycemia or insulinemia. Significance: Our finding suggest that for understanding the biochemical origins of neuropathological amyloid β progression and potential involvement of metabolic disturbances in this process, it’s crucial to gasp preliminary interactions on cellular level. Our data can lead to hypothesis that S100B protein could be a potential modulator as well as indicator of prodromal neuropathological alterations.

Molecular Targets Underlying the Neuroprotective Effects of Boswellic Acid: A Systematic Review.

Neurodegenerative procedures include a large spectrum of disorders with diverse pathological features and clinical manifestations, such as Alzheimer's Disease (AD), Parkinson's disease (PD), Multiple sclerosis, and Amyotrophic lateral sclerosis (ALS). Neurodegenerative diseases (NDs) are indicated by progressive loss of neurons and cognitive function, which is associated with free radical formation, extra and intercellular accumulation of misfolded proteins, oxidative stress, mitochondrial and neurotrophins dysfunction, bioenergetic impairment, inflammation, and apoptotic cell death. Boswellic acid is a pentacyclic triterpene molecule of plant origin that has been applied for treating several inflammatory disorders. Numerous studies have also investigated its' therapeutic potential against multiple NDs. In this article, we aim to review the neuroprotective effects of boswellic acid on NDs and the related mechanisms of action. The databases of PubMed, Google Scholar, Web of Sciences, and Scopus were searched to find studies that reported the effects of boswellic acid on NDs without time limits. Review articles, letters, editorials, unpublished data, and articles not published in the English language were not included in the study. Overall, 17 studies were included in the present study (8 NDs in general, 5 AD, 3 PD, and 1 ALS). According to the reports, boswellic acid exerts anti-inflammatory, antioxidant, antiapoptotic, and neuromodulatory effects against NDs. Boswellic acid decreases Tau phosphorylation and amyloid-β (Aβ) generation in AD. This substance also protects nigrostriatal dopaminergic neurons and improves motor impairments in PD and modulates neurotransmitters, decreases the demyelination region, and improves behavioral functions in ALS. Due to the significant effects of boswellic acid in NDs, more clinical studies are necessary to evaluate the pharmacokinetics of this substance because it seems that boswellic acid can be used as a complementary or alternative treatment in patients with NDs.

Preferential Regulation of Γ-Secretase-Mediated Cleavage of APP by Ganglioside GM1 Reveals a Potential Therapeutic Target for Alzheimer's Disease.

A hallmark of Alzheimer's disease (AD) is the senile plaque, which contains β-amyloid peptides (Aβ). Ganglioside GM1 is the most common brain ganglioside. However, the mechanism of GM1 in modulating Aβ processing is rarely known. Aβ levels are detected by using Immunohistochemistry (IHC) and enzyme-linked immune-sorbent assay (ELISA). Cryo-electron microscopy (Cryo-EM) is used to determine the structure of γ-secretase supplemented with GM1. The levels of the cleavage of amyloid precursor protein (APP)/Cadherin/Notch1 are detected using Western blot analysis. Y maze, object translocation, and Barnes maze are performed to evaluate cognitive functions. GM1 leads to conformational change of γ-secretase structure and specifically accelerates γ-secretase cleavage of APP without affecting other substrates including Notch1, potentially through its interaction with the N-terminal fragment of presenilin 1 (PS1). Reduction of GM1 levels decreases amyloid plaque deposition and improves cognitive dysfunction. This study reveals the mechanism of GM1 in Aβ generation and provides the evidence that decreasing GM1 levels represents a potential strategy in AD treatment. These results provide insights into the detailed mechanism of the effect of GM1 on PS1, representing a step toward the characterization of its novel role in the modulation of γ-secretase activity and the pathogenesis of AD.

Dapagliflozin improves diabetic cognitive impairment via indirectly modulating the mitochondria homeostasis of hippocampus in diabetic mice.

Cognitive impairment is increasingly recognized as an important comorbidity of diabetes progression; however, the underlying molecular mechanism is unclear. Dapagliflozin, an inhibitor of sodium-glucose co-transporter 2 (SGLT2), has shown promising effects against diabetes in rodent experiments and human clinical assays. This study aimed to determine the underlying mechanism and examine the effect of dapagliflozin on diabetic cognitive impairment. To create an in vivo model of diabetic cognitive impairment, streptozotocin (STZ)-induced diabetic mice were used. Dapagliflozin was administered to mice for 8 weeks. The context fear condition and Morris water maze test was used to evaluate mice's behavioral change. Western blotting was used to evaluate protein expression. Hematoxylin and eosin (HE) and Nissl staining were applied to monitor morphological and structural changes. Congo red staining was performed to identify the formation of senile plaques. Mitochondria morphology was examined using a transmission electron microscope, and blood flow in the mouse cerebral cortex was measured using a laser Doppler imaging assay. Comparison to the diabetes mellitus (DM) group, the dapagliflozin group had lower glucose levels. Behavioral studies have shown that dapagliflozin can restore memory deficits in diabetic mice. The murky cell membrane edges and Nissl bodies more difficult to identify in the DM group were revealed by HE and Nissl staining, which were both improved by dapagliflozin treatment. Dapagliflozin inhibited the progression of Aβ generation and the reduced cerebral blood flow in the DM group was rescued. After dapagliflozin treatment, damaged mitochondria and lack of SGLT2 in the hippocampus and cortex of diabetic mice were repaired. Diabetes-induced cognitive dysfunction was attenuated by dapagliflozin and the effect was indirect rather than direct.

Protective effects of luteolin against amyloid beta-induced oxidative stress and mitochondrial impairments through peroxisome proliferator-activated receptor γ-dependent mechanism in Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by the deposition of β-amyloid (Aβ) peptides and dysfunction of mitochondrion, which result in neuronal apoptosis and ultimately cognitive impairment. Inhibiting Aβ generation and repairing mitochondrial damage are prominent strategies in AD therapeutic treatment. Luteolin, a flavonoid compound, exhibits anti-inflammatory neuroprotective properties in AD mice. However, it is still unclear whether luteolin has any effect on Aβ pathology and mitochondrial dysfunction. In this study, the beneficial effect and underlying mechanism of luteolin were investigated in triple transgenic AD (3 × Tg-AD) mice and primary neurons. Our study showed that luteolin supplement significantly ameliorated memory and cognitive impairment of AD mice and exerted neuroprotection by inhibiting Aβ generation, repairing mitochondrial damage and reducing neuronal apoptosis. Further research revealed that luteolin could directly bind with peroxisome proliferator-activated receptor gama (PPARγ) to promote its expression and function. In the culture of hippocampus-derived primary neurons, addition of PPARγ antagonist GW9662 or knockdown of PPARγ with its siRNA could eliminate the effect of luteolin on AD pathologies. In summary, this work revealed for the first time that luteolin effectively improved cognitive deficits of 3 × Tg-AD mice and inhibited Aβ-induced oxidative stress, mitochondrial dysfunction and neuronal apoptosis via PPARγ-dependent mechanism. Hence, luteolin has the potential to serve as a therapeutic agent against AD.

Interplays between different secretases in the generation of Amyloid-[formula omitted] lead to the emergence of ‘Amyloid-[formula omitted] rise’

The abnormal accumulation of Amyloid-β (Aβ) initials the pathological progress of Alzheimer’s disease (AD). γ-secretase, which is a key secretase involving in the formation of Aβ, becomes one of candidate therapeutic targets for preventing the pathological progress of AD. In order to reduce the amount of Aβ in brain, different types of γ-secretase inhibitor were designed to limit the catalytic rate of γ-secretase. However, there is a paradoxical phenomenon called ‘Aβ rise’ can be found in experiment. In this phenomenon, the amount of Aβ will rise as the lower levels of γ-secretase inhibitor is added, which hinders the development of related drugs. In present paper, a mathematical model based on the generation of Aβ is proposed to explore the biological mechanism of ‘Aβ rise’. Through rigorous analysis about the dynamic behavior for this model, we firstly obtain the index for the emergence of ‘Aβ rise’. Furthermore, the analysis results show that both the inhibition of C-terminal fragment (C99) to α-secretase cleavage of amyloid precursor protein (APP) and the lower γ-secretase independent degradation for C99 are contributed to ‘Aβ rise’. Hence, enhancing the intensity of γ-secretase independent degradation of C99 can effectively block the appearance of ‘Aβ rise’. These findings will give new insights on the arise of ‘Aβ rise’ and therapeutic strategies for AD.

Tight control of the APP-Mint1 interaction in regulating amyloid production

Generation of amyloid-β (Aβ) peptides through the proteolytic processing of the amyloid precursor protein (APP) is a pathogenic event in Alzheimer’s disease (AD). APP is a transmembrane protein and endocytosis of APP mediated by the YENPTY motif is a key step in Aβ generation. Mints, a family of cytosolic adaptor proteins, directly bind to the YENPTY motif of APP and facilitate APP trafficking and processing. Here, we generated and examined two Mint1 mutants, Tyr633Ala of Mint1 (Mint1Y633A) that enhanced APP binding, and Tyr549Ala and Phe610Ala mutant (Mint1Y549A/F610A), that reduced APP binding. We investigated how perturbing the APP-Mint1 interaction through these Mint1 mutants alter APP and Mint1 cellular dynamics and Mint1′s interaction with its other binding partners. We found that Mint1Y633A increased binding affinity specifically for APP and presenilin1 (catalytic subunit of γ-secretase), that subsequently enhanced APP endocytosis in primary murine neurons. Conversely, Mint1Y549A/F610A exhibited reduced APP affinity and Aβ secretion. The effect of Mint1Y549A/F610A on Aβ release was greater compared to knocking down all three Mint proteins supporting the APP-Mint1 interaction is a critical factor in Aβ production. Altogether, this study highlights the potential of targeting the APP-Mint1 interaction as a therapeutic strategy for AD.

Glucocorticoid enhances presenilin1-dependent Aβ production at ER’s mitochondrial-associated membrane by downregulating Rer1 in neuronal cells

Stress-induced release of glucocorticoid is an important amyloidogenic factor that upregulates amyloid precursor protein (APP) and β secretase 1 (BACE1) levels. Glucocorticoid also contributes to the pathogenesis of Alzheimer’s disease (AD) by increasing ER-mitochondria connectivity, in which amyloid β (Aβ) processing occurs rigorously because of its lipid raft-rich characteristics. However, the mechanism by which glucocorticoid enhances γ-secretase activity in the mitochondrial-associated membrane of ER (MAM) and subsequent accumulation of mitochondrial Aβ is unclear. In this study, we determined how glucocorticoid enhances Aβ production in MAM using SH-SY5Y cells and ICR mice. First, we observed that cortisol-induced Aβ accumulation in mitochondria preceded its extracellular apposition by enhancing γ-secretase activity, which was the result of increased presenilin 1 (PSEN1) localization in MAM. Screening data revealed that cortisol selectively downregulated the ER retrieval protein Rer1, which triggered its maturation and subsequent entry into the endocytic secretory pathway of PSEN1. Accordingly, overexpression of RER1 reversed the deleterious effects of mitochondrial Aβ on mitochondrial respiratory function and neuronal cell viability. Notably, we found that cortisol guided the glucocorticoid receptor (GR) to bind directly to the RER1 promoter, thus trans-repressing its expression. Inhibiting GR function reduced Aβ accumulation at mitochondria and improved the outcome of a spatial memory task in mice exposed to corticosterone. Taken together, glucocorticoid enhances PSEN1-mediated Aβ generation at MAM by downregulating Rer1, which is a potential target at early stages of AD pathogenesis.

Fingolimod Modulates the Gene Expression of Proteins Engaged in Inflammation and Amyloid-Beta Metabolism and Improves Exploratory and Anxiety-Like Behavior in Obese Mice.

Obesity is considered a risk factor for type 2 diabetes mellitus, which has become one of the most important health problems, and is also linked with memory and executive function decline. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid that regulates cell death/survival and the inflammatory response via its specific receptors (S1PRs). Since the role of S1P and S1PRs in obesity is rather obscure, we examined the effect of fingolimod (an S1PR modulator) on the expression profile of genes encoding S1PRs, sphingosine kinase 1 (Sphk1), proteins engaged in amyloid-beta (Aβ) generation (ADAM10, BACE1, PSEN2), GSK3β, proapoptotic Bax, and proinflammatory cytokines in the cortex and hippocampus of obese/prediabetic mouse brains. In addition, we observed behavioral changes. Our results revealed significantly elevated mRNA levels of Bace1, Psen2, Gsk3b, Sphk1, Bax, and proinflammatory cytokines, which were accompanied by downregulation of S1pr1 and sirtuin 1 in obese mice. Moreover, locomotor activity, spatially guided exploratory behavior, and object recognition were impaired. Simultaneously, fingolimod reversed alterations in the expressions of the cytokines, Bace1, Psen2, and Gsk3b that occurred in the brain, elevated S1pr3 mRNA levels, restored normal cognition-related behavior patterns, and exerted anxiolytic effects. The improvement in episodic and recognition memory observed in this animal model of obesity may suggest a beneficial effect of fingolimod on central nervous system function.

Salvianolic acid B ameliorates retinal deficits in an early-stage Alzheimer's disease mouse model through downregulating BACE1 and Aβ generation.

Alzheimer's disease (AD) is a neurodegenerative disease with subtle onset, early diagnosis remains challenging. Accumulating evidence suggests that the emergence of retinal damage in AD precedes cognitive impairment, and may serve as a critical indicator for early diagnosis and disease progression. Salvianolic acid B (Sal B), a bioactive compound isolated from the traditional Chinese medicinal herb Salvia miltiorrhiza, has been shown promise in treating neurodegenerative diseases, such as AD and Parkinson's disease. In this study we investigated the therapeutic effects of Sal B on retinopathy in early-stage AD. One-month-old transgenic mice carrying five familial AD mutations (5×FAD) were treated with Sal B (20 mg·kg-1·d-1, i.g.) for 3 months. At the end of treatment, retinal function and structure were assessed, cognitive function was evaluated in Morris water maze test. We showed that 4-month-old 5×FAD mice displayed distinct structural and functional deficits in the retinas, which were significantly ameliorated by Sal B treatment. In contrast, untreated, 4-month-old 5×FAD mice did not exhibit cognitive impairment compared to wild-type mice. In SH-SY5Y-APP751 cells, we demonstrated that Sal B (10 μM) significantly decreased BACE1 expression and sorting into the Golgi apparatus, thereby reducing Aβ generation by inhibiting the β-cleavage of APP. Moreover, we found that Sal B effectively attenuated microglial activation and the associated inflammatory cytokine release induced by Aβ plaque deposition in the retinas of 5×FAD mice. Taken together, our results demonstrate that functional impairments in the retina occur before cognitive decline, suggesting that the retina is a valuable reference for early diagnosis of AD. Sal B ameliorates retinal deficits by regulating APP processing and Aβ generation in early AD, which is a potential therapeutic intervention for early AD treatment.

APP-BACE1 Interaction and Intracellular Localization Regulate Aβ Production in iPSC-Derived Cortical Neurons.

Alzheimer's disease (AD) is characterized pathologically by amyloid β (Aβ)-containing plaques. Generation of Aβ from amyloid precursor protein (APP) by two enzymes, β- and γ-secretase, has therefore been in the AD research spotlight for decades. Despite this, how the physical interaction of APP with the secretases influences APP processing is not fully understood. Herein, we compared two genetically identical human iPSC-derived neuronal cell types: low Aβ-secreting neuroprogenitor cells (NPCs) and high Aβ-secreting mature neurons, as models of low versus high Aβ production. We investigated levels of substrate, enzymes and products of APP amyloidogenic processing and correlated them with the proximity of APP to β- and γ-secretase in endo-lysosomal organelles. In mature neurons, increased colocalization of full-length APP with the β-secretase BACE1 correlated with increased β-cleavage product sAPPβ. Increased flAPP/BACE1 colocalization was mainly found in early endosomes. In the same way, increased colocalization of APP-derived C-terminal fragment (CTF) with presenilin-1 (PSEN1), the catalytic subunit of γ-secretase, was seen in neurons as compared to NPCs. Furthermore, most of the interaction of APP with BACE1 in low Aβ-secreting NPCs seemed to derive from CTF, the remaining APP part after BACE1 cleavage, indicating a possible novel product-enzyme inhibition. In conclusion, our results suggest that interaction of APP and APP cleavage products with their secretases can regulate Aβ production both positively and negatively. β- and γ-Secretases are difficult targets for AD treatment due to their ubiquitous nature and wide range of substrates. Therefore, targeting APP-secretase interactions could be a novel treatment strategy for AD. Colocalization of APP species with BACE1 in a novel model of low- versus high-Aβ secretion-Two genetically identical human iPSC-derived neuronal cell types: low Aβ-secreting neuroprogenitor cells (NPCs) and high Aβ secreting mature neurons, were compared. Increased full-length APP (flAPP)/BACE1 colocalization in early endosomes was seen in neurons, while APP-CTF/BACE1 colocalization was much higher than flAPP/BACE1 colocalization in NPCs, although the cellular location was not determined.

Germinated brown rice extract reduces brain lipid peroxidation and Aβ levels via regulations of BACE1, RAGE, IDE and LRP1 expressions in high fat/cholesterol diet-fed rats

A strong association presents between excessive amyloid-β (Aβ) buildup and oxidative stress with Alzheimer’s disease (AD). In view of the multifaceted neuroprotective effects of some dietary elements, the beneficial effect of germinated brown rice was investigated using a high fat/cholesterol diet (HFCD)-induced sporadic rat model of AD. Seven groups, including normal control, HFCD, and HFCD treated with Donepezil, Simvastatin, Probucol, and germinated brown rice ethyl acetate extract (GBR-EA; 100 and 200 mg/kg bw) were included in the present study. Biochemical assays, brain lipid peroxidation, mRNA and protein levels involved in Aβ processing and metabolism pathways were analyzed. HFCD-fed rats exhibited increased brain lipid peroxidation and Aβ levels, as well as altered expressions of proteins involved in Aβ generation, degradation and clearance. GBR-EA treatment groups showed significant reduction in lipid peroxidation and Aβ levels when compared to HFCD group. The effects of GBR-EA on Aβ levels are likely through the modulation of BACE1 and Presenilins, as well as induction of Aβ clearance and degradation. The findings revealed the potential use of germinated brown rice to attenuate HFCD diet-induced neurodegenerative alterations, likely due to reduced brain inflammation, as well as modulation of Aβ processing and metabolism pathways.