Folic acid and S-adenosylmethionine reverse Homocysteine-induced Alzheimer's disease-like pathological changes in rat hippocampus by modulating PS1 and PP2A methylation levels.

BACKGROUND: Abnormally elevated homocysteine (Hcy) is recognized as a biomarker and risk factor for Alzheimer's disease (AD). However, the underlying mechanisms by which Hcy affects AD are still unclear. OBJECTIVES: This study aimed to elucidate the effects and mechanisms by which Hcy affects AD-like pathological changes in the hippocampus through in vivo and in vitro experiments, and to investigate whether folic acid (FA) and S-adenosylmethionine (SAM) supplementation could improve neurodegenerative injuries. METHODS: In vitro experiments hippocampal neurons of rat were treated with Hcy, FA or SAM for 24 h; while the hyperhomocysteinemia (HHcy) in Wistar rats was established by intraperitoneal injection of Hcy, and FA was added to feed. The expression of ß-amyloid (Aß), phosphorylated tau protein, presenilin 1 (PS1) at the protein level and the activity of protein phosphatase 2A (PP2A) were detected, the immunopositive cells for Aß and phosphorylated tau protein in the rat hippocampus were also evaluated by immunohistochemical staining. RESULTS: FA and SAM significantly repressed Hcy-induced AD-like pathological changes in the hippocampus, including the increased tau protein phosphorylation at Ser214, Ser396 and the expression of Aß42. In addition, Hcy-induced PS1 expression increased at the protein level and PP2A activity decreased, while FA and SAM were able to retard that. CONCLUSIONS: The increase in PS1 expression and decrease in PP2A activity may be the mechanisms underlying the Hcy-induced AD-like pathology. FA and SAM significantly repressed the Hcy-induced neurodegenerative injury by modulating PS1 and PP2A methylation levels.

Novel insights into presenilin 1 mutation associated with a distinctive dementia phenotype and cotton wool plaques.

BACKGROUND: The mutations in the presenilin 1 gene (PSEN1) are the main cause of familial Alzheimer's disease. PSEN1 mutations affect amyloid-beta peptide production, which accumulates in the brain as senile plaque and cotton wool plaques (CWPs) and relates to other neurodegenerative disorders. Here we report the second case of the PSEN1 G266S mutation, which showed distinctive neuropathological features, including abundant CWPs. Lewy body pathology, and altered amyloid-beta production. METHOD: Using the proband's samples, we performed genetic analysis of the PSEN1, APP, MAPT, and APOE genes, histopathological and immunohistochemical analysis of the brain tissue, and biochemical analysis of Aß production in COS cells transfected with wild-type or mutant PSEN1. RESULTS: The patient presented with memory loss, abnormal behavior, and visual hallucinations. Brain scans showed reduced blood flow, mild atrophy, and white matter lesions. Genetic analysis revealed a heterozygous mutation at codon 266 (G266S) of PSEN1 and polymorphism of MAPT (Q230R). The brain had many CWPs, severe cerebral amyloid angiopathy (CAA), senile plaque, Lewy bodies, and neurites. Electron microscopy displayed myelinated fiber degeneration, mitochondrial damage, and amyloid fibrils in the white matter. The production level of Aß42 in PSEN1 G266S-transfected cells significantly increased. CONCLUSION: Our findings suggest that the PSEN1 G266S mutation may cause a heterogeneous clinical and pathological phenotype, influenced by other genetic or environmental factors.

Ultra-Low-Dose UV-C Photo-stimulation Promotes Neural Stem Cells Differentiation via Presenilin 1 Mediated Notch and ß-Catenin Activation.

Light-based photo-stimulation has demonstrated promising effects on stem cell behavior, particularly in optimizing neurogenesis. However, the precise parameters for achieving optimal results, including the wavelengths, light intensity, radiating energy, and underlying mechanisms, remain incompletely understood. In this study, we focused on utilizing ultraviolet-C (UV-C) at a specific wavelength of 254 nm, with an ultra-low dose at intensity of 330 µW/cm2 and a total energy of 594 mJ/cm2 per day over a period of seven days, to stimulate the proliferation and differentiation of mouse neural stem cells (NSCs). The results revealed that the application of ultra-low-dose UV-C yielded the most significant effect in promoting differentiation when compared to mixed ultraviolet (UV) and ultraviolet-A (UV-A) radiation at equivalent exposure levels. The mechanism exploration elucidated the role of Presenilin 1 in mediating the activation of ß-catenin and Notch 1 by the UV-C treatment, both of which are key factors facilitating NSCs proliferation and differentiation. These findings introduce a novel approach employing ultra-low-dose UV-C for specifically enhancing NSC differentiation, as well as the underlying mechanism. It would contribute valuable insights into brain stimulation and neurogenesis modulation for various diseases, offering potential therapeutic avenues for further exploration.

Identification of PS1/gamma-secretase and glutamate transporter GLT-1 interaction sites.

The recently discovered interaction between Presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for generating amyloid-ß peptides, and GLT-1, a major glutamate transporter in the brain (EAAT2), provides a mechanistic link between these two key factors involved in Alzheimer's disease (AD) pathology. Modulating this interaction can be crucial to understand the consequence of such crosstalk in AD context and beyond. However, the interaction sites between these two proteins are unknown. Herein, we utilized an alanine scanning approach coupled with FRET-based fluorescence lifetime imaging microscopy to identify the interaction sites between PS1 and GLT-1 in their native environment within intact cells. We found that GLT-1 residues at position 276 to 279 (TM5) and PS1 residues at position 249 to 252 (TM6) are crucial for GLT-1-PS1 interaction. These results have been cross validated using AlphaFold Multimer prediction. To further investigate whether this interaction of endogenously expressed GLT-1 and PS1 can be prevented in primary neurons, we designed PS1/GLT-1 cell-permeable peptides (CPPs) targeting the PS1 or GLT-1 binding site. We used HIV TAT domain to allow for cell penetration which was assayed in neurons. First, we assessed the toxicity and penetration of CPPs by confocal microscopy. Next, to ensure the efficiency of CPPs, we monitored the modulation of GLT-1-PS1 interaction in intact neurons by fluorescence lifetime imaging microscopy. We saw significantly less interaction between PS1 and GLT-1 with both CPPs. Our study establishes a new tool to study the functional aspect of GLT-1-PS1 interaction and its relevance in normal physiology and AD models.

Efficacy of Sailuotong on neurovascular unit in amyloid precursor protein/presenilin-1 transgenic mice with Alzheimer's disease.

OBJECTIVE: To discuss the influence of Sailuotong (, SLT) on the Neurovascular Unit (NVUs) of amyloid precursor protein (APP)/presenilin-1(PS1) mice and evaluate the role of gas supplementation in activating blood circulation during the progression of Alzheimer's disease (AD). METHODS: The mice were allocated into the following nine groups: (a) the C57 Black (C57BL) sham-operated group (control group), (b) ischaemic treatment in C57BL mice (the C57 ischaemic group), (c) the APP/PS1 sham surgery group (APP/PS1 model group), (d) ischaemic treatment in APP/PS1 mice (APP/PS1 ischaemic group), (e) C57BL mice treated with aspirin following ischaemic treatment (C57BL ischaemic + aspirin group), (f) C57BL mice treated with SLT following ischaemic treatment (C57BL ischaemic + SLT group), (g) APP/PS1 mice treated with SLT (APP/PS1 + SLT group), (h) APP/PS1 mice treated with donepezil hydrochloride following ischaemic treatment (APP/PS1 ischaemic + donepezil hydrochloride group) and (i) APP/PS1 mice treated with SLT following ischaemic treatment (APP/PS1 ischaemic + SLT group). The ischaemic model was established by operating on the bilateral common carotid arteries and creating a microembolism. The Morris water maze and step-down tests were used to detect the spatial behaviour and memory ability of mice. The hippocampus of each mouse was observed by haematoxylin and eosin (HE) and Congo red staining. The ultrastructure of NVUs in each group was observed by electron microscopy, and various biochemical indicators were detected by enzyme-linked immunosorbent assay (ELISA). The protein expression level was detected by Western blot. The mRNA expression was detected by quantitative real-time polymerase chain reaction (qRT-PCR). RESULTS: The results of the Morris water maze and step-down tests showed that ischemia reduced learning and memory in the mice, which were restored by SLT. The results of HE staining showed that SLT restored the pathological changes of the NVUs. The Congo red staining results revealed that SLT also improved the scattered orange-red sediments in the upper cortex and hippocampus of the APP/PS1 and APP/PS1 ischaemic mice. Furthermore, SLT significantly reduced the content of Aß, improved the vascular endothelium and repaired the mitochondrial structures. The ELISA detection, western blot detection and qRT-PCR showed that SLT significantly increased the vascular endothelial growth factor (VEGF), angiopoietin and basic fibroblast growth factor, as well as the levels of gene and protein expression of low-density lipoprotein receptor-related protein-1 (LRP-1) and VEGF in brain tissue. CONCLUSIONS: By increasing the expression of VEGF, SLT can promote vascular proliferation, up-regulate the expression of LRP-1, promote the clearance of Aß and improve the cognitive impairment of APP/PS1 mice. These results confirm that SLT can improve AD by promoting vascular proliferation and Aß clearance to protect the function of NVUs.

Spatial Neurolipidomics at the Single Amyloid-ß Plaque Level in Postmortem Human Alzheimer's Disease Brain.

Lipid dysregulations have been critically implicated in Alzheimer's disease (AD) pathology. Chemical analysis of amyloid-ß (Aß) plaque pathology in transgenic AD mouse models has demonstrated alterations in the microenvironment in the direct proximity of Aß plaque pathology. In mouse studies, differences in lipid patterns linked to structural polymorphism among Aß pathology, such as diffuse, immature, and mature fibrillary aggregates, have also been reported. To date, no comprehensive analysis of neuronal lipid microenvironment changes in human AD tissue has been performed. Here, for the first time, we leverage matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) through a high-speed and spatial resolution commercial time-of-light instrument, as well as a high-mass-resolution in-house-developed orbitrap system to characterize the lipid microenvironment in postmortem human brain tissue from AD patients carrying Presenilin 1 mutations (PSEN1) that lead to familial forms of AD (fAD). Interrogation of the spatially resolved MSI data on a single Aß plaque allowed us to verify nearly 40 sphingolipid and phospholipid species from diverse subclasses being enriched and depleted, in relation to the Aß deposits. This included monosialo-gangliosides (GM), ceramide monohexosides (HexCer), ceramide-1-phosphates (CerP), ceramide phosphoethanolamine conjugates (PE-Cer), sulfatides (ST), as well as phosphatidylinositols (PI), phosphatidylethanolamines (PE), and phosphatidic acid (PA) species (including Lyso-forms). Indeed, many of the sphingolipid species overlap with the species previously seen in transgenic AD mouse models. Interestingly, in comparison to the animal studies, we observed an increased level of localization of PE and PI species containing arachidonic acid (AA). These findings are highly relevant, demonstrating for the first time Aß plaque pathology-related alteration in the lipid microenvironment in humans. They provide a basis for the development of potential lipid biomarkers for AD characterization and insight into human-specific molecular pathway alterations.

Presenilin-1 mutation position influences amyloidosis, small vessel disease, and dementia with disease stage.

INTRODUCTION: Amyloidosis, including cerebral amyloid angiopathy, and markers of small vessel disease (SVD) vary across dominantly inherited Alzheimer's disease (DIAD) presenilin-1 (PSEN1) mutation carriers. We investigated how mutation position relative to codon 200 (pre-/postcodon 200) influences these pathologic features and dementia at different stages. METHODS: Individuals from families with known PSEN1 mutations (n = 393) underwent neuroimaging and clinical assessments. We cross-sectionally evaluated regional Pittsburgh compound B-positron emission tomography uptake, magnetic resonance imaging markers of SVD (diffusion tensor imaging-based white matter injury, white matter hyperintensity volumes, and microhemorrhages), and cognition. RESULTS: Postcodon 200 carriers had lower amyloid burden in all regions but worse markers of SVD and worse Clinical Dementia Rating® scores compared to precodon 200 carriers as a function of estimated years to symptom onset. Markers of SVD partially mediated the mutation position effects on clinical measures. DISCUSSION: We demonstrated the genotypic variability behind spatiotemporal amyloidosis, SVD, and clinical presentation in DIAD, which may inform patient prognosis and clinical trials. HIGHLIGHTS: Mutation position influences Aß burden, SVD, and dementia. PSEN1 pre-200 group had stronger associations between Aß burden and disease stage. PSEN1 post-200 group had stronger associations between SVD markers and disease stage. PSEN1 post-200 group had worse dementia score than pre-200 in late disease stage. Diffusion tensor imaging-based SVD markers mediated mutation position effects on dementia in the late stage.

Alpha-, Beta-, and Gamma-Secretase, Amyloid Precursor Protein, and Tau Protein Genes in the Hippocampal CA3 Subfield in an Ischemic Model of Alzheimer's Disease with Survival up to 2 Years.

Background: Understanding the phenomena underlying the non-selective susceptibility to ischemia of pyramidal neurons in the CA3 is important from the point of view of elucidating the mechanisms of memory loss and the development of dementia. Objective: The aim of the study was to investigate changes in genes expression of amyloid precursor protein, its cleaving enzymes and tau protein in CA3 post-ischemia with survival of 12-24 months. Methods: We used an ischemic model of Alzheimer's disease to study the above genes using an RT-PCR protocol. Results: The expression of the amyloid precursor protein gene was above the control values at all times post-ischemia. The expression of the α-secretase gene also exceeded the control values post-ischemia. The expression of the ß-secretase gene increased 12 and 24 months post-ischemia, and 18 months was below control values. Presenilin 1 and 2 genes expression was significantly elevated at all times post-ischemia. Also, tau protein gene expression was significantly elevated throughout the observation period, and peak gene expression was present 12 months post-ischemia. Conclusions: The study suggests that the genes studied are involved in the non-amyloidogenic processing of amyloid precursor protein. Additionally data indicate that brain ischemia with long-term survival causes damage and death of pyramidal neurons in the CA3 area of the hippocampus in a modified tau protein-dependent manner. Thus defining a new and important mechanism of pyramidal neuronal death in the CA3 area post-ischemia. In addition expression of tau protein gene modification after brain ischemia is useful in identifying ischemic mechanisms occurring in Alzheimer's disease.

Effectiveness of Novel Drug Delivery System using Curcumin in Alzheimer's Disease.

Alzheimer's disease (AD) is a form of brain degeneration that gradually impairs a person's memory and cognitive skills, eventually making it harder for them to perform everyday activities. Its pathophysiology has been attributed to the deposition of amyloid ß (Aß), neurofibrillary tangles (NFT), and α-synuclein (A-s) in some cases. Presently, 4 drugs have been approved for the treatment. They are Donepezil, Rivastigmine, Galantamine and Memantine. The first three are acetylcholinesterase inhibitors, while memantine is an NMDA receptor antagonist. Even though these medications are successful in treating mild to moderate Alzheimer's disease, they have not been able to reverse the disease or even slow its progression completely. Hence, natural products are gaining more popularity due to the advantage of the multitarget intervention effect. The most investigated spice, Curcuma longa's bioactive component, curcumin, has demonstrated anti-amyloid, anti-NFT, and anti-Lewy body properties and substantial antiinflammatory, antioxidant, and antiapoptotic properties. However, its proven neuroprotective activity is hampered by many factors, such as poor water solubility and bioavailability. Therefore, many novel formulations have been designed to improve its bioavailability with methods such as 1) Micellar Solubilization, 2) Cyclodextrin Complexation, 3) Crystal Modification, and 4) Particle Size Reduction, etc. The current chapter aims to summarize various novel formulations of curcumin and their effectiveness in treating AD.

Neuropathology of patients with preclinical or early clinical Alzheimer's disease with pathogenic PSEN1_p. L392V: Comparison of advanced siblings.

INTRODUCTION: Neuropathological investigation of presymptomatic or early symptomatic presenilin-1 (PSEN1) mutation carriers in familial Alzheimer's disease (AD) is extremely scarce. METHODS: We report the autopsy findings of brothers with familial AD. Case 1 is a 45-year-old man without obvious cognitive impairment, who committed suicide. Case 2 is a 57-year-old older brother of Case 1 with advanced AD symptoms, who died of hypothermia during wondering. RESULTS: In both cases, abundant amyloid plaques positive for amyloid ß (Aß) were found throughout the brain. Progression of neuronal loss and increasing amount and extension of neurofibrillary tangle pathology were evident in Case 2. Genetic investigation revealed a PSEN1_p. L392V mutation in both cases. DISCUSSION: The present study shows a possible neuropathological boundary between symptomatic and preclinical AD with pathogenic PSEN1 mutation. Additional clinicopathological investigation for familial AD-related mutation carriers may be significant to explore the association between familial AD and suicide.

Cultured Rat Hippocampal Neurons Exposed to the Mitochondrial Uncoupler Carbonyl Cyanide Chlorophenylhydrazone Undergo a Rapid, Presenilin-Dependent Change in Neuronal Properties.

Presenilin 1 (PS1) is a transmembrane proteolytic subunit of γ-secretase that cleaves amyloid precursor proteins. Mutations in PS1 (mPS1) are associated with early-onset familial Alzheimer's disease (AD). The link between mutated PS1, mitochondrial calcium regulation, and AD has been studied extensively in different test systems. Despite the wide-ranging role of mPS1 in AD, there is a paucity of information on the link between PS1 and neuronal cell death, a hallmark of AD. In the present study, we employed the selective mitochondrial uncoupler carbonyl cyanide chlorophenylhydrazone (CCCP) and compared the reactivity of mPS1-transfected cultured rat hippocampal neurons with PS1 and control neurons in a situation of impaired mitochondrial functions. CCCP causes a slow rise in cytosolic and mitochondrial calcium in all three groups of neurons, with the mPS1 neurons demonstrating a faster rise. Consequently, mPS1 neurons were depolarized by CCCP and measured with TMRM, a mitochondrial voltage indicator, more than the other two groups. Morphologically, CCCP produced more filopodia in mPS1 neurons than in the other two groups, which were similarly affected by the drug. Finally, mPS1 transfected neurons tended to die from prolonged exposure to CCCP sooner than the other groups, indicating an increase in vulnerability associated with a lower ability to regulate excess cytosolic calcium.

Depressive symptoms and hippocampal volume in autosomal dominant Alzheimer's disease.

INTRODUCTION: Depressive symptoms are among early behavioral changes in Alzheimer's disease (AD); however, the relationship between neurodegeneration and depressive symptoms remains inconclusive. To better understand this relationship in preclinical AD, we examined hippocampal volume and depressive symptoms in cognitively unimpaired carriers of the presenilin-1 (PSEN1) E280A mutation for autosomal dominant AD. METHODS: A total of 27 PSEN1 mutation carriers and 26 non-carrier family members were included. Linear regression was used to test the relationship between hippocampal volume and 15-item Geriatric Depression Scale. RESULTS: Carriers and non-carriers did not differ in depressive symptoms or hippocampal volume. Within carriers, lower hippocampal volume was associated with greater depressive symptoms, which remained significant after adjusting for age and cognition. This relationship was not significant in non-carriers. DISCUSSION: Hippocampal neurodegeneration may underlie depressive symptoms in preclinical autosomal dominant AD. These findings provide support for the utility of targeting depressive symptoms in AD prevention. HIGHLIGHTS: We compared unimpaired autosomal dominant Alzheimer's disease (AD) mutation carriers and non-carriers. Carriers and non-carriers did not differ in severity of depressive symptoms. In carriers, hippocampal volume was inversely associated with depressive symptoms. Depressive symptoms may be a useful target in AD prevention.

Huanglian Jiedutang Regulates HIF-1α/VEGF Signaling Pathway to Improve Learning and Memory Abilities of APP/PS1 Transgenic Mice / 中国实验方剂学杂志

ObjectiveTo reveal the effects of Huanglian Jiedutang （HLJDT） on the learning and memory abilities of APP/PS1 transgenic mice via hypoxia-inducible factor-1α （HIF-1α）/vascular endothelial growth factor （VEGF） signaling pathway. MethodForty 5-month-old β-amyloid precursor protein （APP）/presenilin 1（PS1） mice were randomized into the model， donepezil （0.001 g·kg-1·d-1）， and low-， medium-， and high-dose （1.5， 3， 6 g·kg-1·d-1， respectively） HLJDT groups， and 8 C57BL/6 mice were taken as the normal group. After 45 days of continuous administration， Morris water maze test was conducted， and the organ indexes were calculated. The morphological structure of cerebral vascular endothelial cells in mice was observed under a transmission electron microscope. Western blot was employed to measure the protein levels of APP， HIF-1α， VEGF，VEGFA， and brain-derived neurotrophic factor （BDNF） in the hippocampus. The mRNA levels of APP， HIF-1α， and VEGF were determined by real-time fluorescence quantitative polymerase chain reaction （Real-time PCR）. ResultCompared with the normal group， the model group showed prolonged escape latency （P<0.05）， reduced distance and time around the target platform （P<0.05）， decrease brain and spleen indexes （P<0.05）， vascular endothelial cells with karyopyknosis and not abundant cytoplasm， up-regulated protein levels of APP， HIF-1α， VEGF， and VEGFA （P<0.05）， down-regulated protein level of BDNF （P<0.05）， and up-regulated mRNA levels of APP， HIF-1α， and VEGF （P<0.05） in the hippocampus. Compared with the model group， high-dose HLJDT shortened the escape latency （P<0.05）， increased the distance and time around the target platform （P<0.05）， raised the brain and spleen indexes （P<0.05）， repaired the organelles of vascular endothelial cells， down-regulated the protein levels of APP， HIF-1α， VEGF， and VEGFA （P<0.05）， up-regulated the protein level of BDNF （P<0.05）， and down-regulated the mRNA levels of APP， HIF-1α， and VEGF （P<0.05） in the hippocampus. ConclusionHLJDT can improve the learning and memory abilities of mice by reducing the expression of HIF-1α and VEGF， thus protecting the nerves.

Quantitative comparison of presenilin protein expression reveals greater activity of PS2-γ-secretase.

γ-secretase processing of amyloid precursor protein (APP) has long been of interest in the pathological progression of Alzheimer's disease (AD) due to its role in the generation of amyloid-ß. The catalytic component of the enzyme is the presenilins of which there are two homologues, Presenilin-1 (PS1) and Presenilin-2 (PS2). The field has focussed on the PS1 form of this enzyme, as it is typically considered the more active at APP processing. However, much of this work has been completed without appropriate consideration of the specific levels of protein expression of PS1 and PS2. We propose that expression is an important factor in PS1- and PS2-γ-secretase activity, and that when this is considered, PS1 does not have greater activity than PS2. We developed and validated tools for quantitative assessment of PS1 and PS2 protein expression levels to enable the direct comparison of PS in exogenous and endogenous expression systems, in HEK-293 PS1 and/or PS2 knockout cells. We show that exogenous expression of Myc-PS1-NTF is 5.5-times higher than Myc-PS2-NTF. Quantitating endogenous PS protein levels, using a novel PS1/2 fusion standard we developed, showed similar results. When the marked difference in PS1 and PS2 protein levels is considered, we show that compared to PS1-γ-secretase, PS2-γ-secretase has equal or more activity on APP and Notch1. This study has implications for understanding the PS1- and PS2-specific contributions to substrate processing, and their potential influence in AD pathogenesis.

Herpes Simplex Virus 1 Infection Does Not Increase Amyloid-ß Pathology in APP/PS1 Mice.

Using APP/PS1 mice that overproduce amyloid-ß (Aß) peptides, we investigated whether intranasal infection with a neurovirulent clinical strain of herpes simplex virus 1 (HSV-1) before Aß deposition could accelerate or increase Alzheimer's disease-like pathology. After HSV-1 infection, APP/PS1 mice presented a similar disease as wild type animals based on body weight changes, clinical symptoms, and survival rates. The number and volume of Aß plaques, the number of microglia, and the percentages of circulating monocyte subsets were similar in APP/PS1 mice infected or not with HSV-1. Thus, intranasal infection with HSV-1 does not alter Aß pathology in this mouse model.

PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer's disease.

The recently discovered interaction between presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for the generation of amyloid-ß(Aß) peptides, and GLT-1, the major glutamate transporter in the brain (EAAT2 in the human) may provide a mechanistic link between two important pathological aspects of Alzheimer's disease (AD): abnormal Aßoccurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based approach, fluorescence lifetime imaging microscopy (FLIM), to characterize the PS1/GLT-1 interaction in its native environment in the brain tissue of sporadic AD (sAD) patients. There was significantly less interaction between PS1 and GLT-1 in sAD brains, compared to tissue from patients with frontotemporal lobar degeneration (FTLD), or non-demented age-matched controls. Since PS1 has been shown to adopt pathogenic "closed" conformation in sAD but not in FTLD, we assessed the impact of changes in PS1 conformation on the interaction. Familial AD (fAD) PS1 mutations which induce a "closed" PS1 conformation similar to that in sAD brain and gamma-secretase modulators (GSMs) which induce a "relaxed" conformation, reduced and increased the interaction, respectively. This indicates that PS1 conformation seems to have a direct effect on the interaction with GLT-1. Furthermore, using biotinylation/streptavidin pull-down, western blotting, and cycloheximide chase assays, we determined that the presence of PS1 increased GLT-1 cell surface expression and GLT-1 homomultimer formation, but did not impact GLT-1 protein stability. Together, the current findings suggest that the newly described PS1/GLT-1 interaction endows PS1 with chaperone activity, modulating GLT-1 transport to the cell surface and stabilizing the dimeric-trimeric states of the protein. The diminished PS1/GLT-1 interaction suggests that these functions of the interaction may not work properly in AD.

In Silico Structural Analysis Exploring Conformational Folding of Protein Variants in Alzheimer's Disease.

Accurate protein structure prediction using computational methods remains a challenge in molecular biology. Recent advances in AI-powered algorithms provide a transformative effect in solving this problem. Even though AlphaFold's performance has improved since its release, there are still limitations that apply to its efficacy. In this study, a selection of proteins related to the pathology of Alzheimer's disease was modeled, with Presenilin-1 (PSN1) and its mutated variants in the foreground. Their structural predictions were evaluated using the ColabFold implementation of AlphaFold, which utilizes MMseqs2 for the creation of multiple sequence alignments (MSAs). A higher number of recycles than the one used in the AlphaFold DB was selected, and no templates were used. In addition, prediction by RoseTTAFold was also applied to address how structures from the two deep learning frameworks match reality. The resulting conformations were compared with the corresponding experimental structures, providing potential insights into the predictive ability of this approach in this particular group of proteins. Furthermore, a comprehensive examination was performed on features such as predicted regions of disorder and the potential effect of mutations on PSN1. Our findings consist of highly accurate superpositions with little or no deviation from experimentally determined domain-level models.

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 ß-amyloid peptides (Aß). Ganglioside GM1 is the most common brain ganglioside. However, the mechanism of GM1 in modulating Aß processing is rarely known. Aß 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 Aß 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.

Evaluation of the relationship among gene expressions and enzyme activities with antioxidant role and presenilin 1 expression in Alzheimer's disease.

It is known that oxidative stress originating from reactive oxygen species plays a role in the pathogenesis of Alzheimer's disease. In this study, the role of antioxidant status associated with oxidative stress in Alzheimer's disease was investigated. Peripheral blood samples were obtained from 28 healthy individuals (as control) and 28 Alzheimer's patients who met the National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association criteria. Catalase, glutathione S-transferase and paraoxonase 1 enzyme activities in blood plasma and glutathione S-transferase enzyme activities in erythrocytes were determined by spectrophotometer. Catalase, glutathione S-transferase and presenilin 1 gene expressions in leukocytes were determined using qRT-PCR. Data were analysed with SPSS one-way anova, a LSD post hoc test at p < 0.05. The activity of each enzyme was significantly reduced in Alzheimer's patients compared to control. The catalase gene expression level did not change compared to the control. Glutathione S-transferase and presenilin 1 gene expression levels were increased compared to the control.

Perinatal S-Adenosylmethionine Supplementation Represses PSEN1 Expression by the Cellular Epigenetic Memory of CpG and Non-CpG Methylation in Adult TgCRD8 Mice.

DNA methylation, the main epigenetic modification regulating gene expression, plays a role in the pathophysiology of neurodegeneration. Previous evidence indicates that 5'-flanking hypomethylation of PSEN1, a gene involved in the amyloidogenic pathway in Alzheimer's disease (AD), boosts the AD-like phenotype in transgenic TgCRND8 mice. Supplementation with S-adenosylmethionine (SAM), the methyl donor in the DNA methylation reactions, reverts the pathological phenotype. Several studies indicate that epigenetic signatures, driving the shift between normal and diseased aging, can be acquired during the first stages of life, even in utero, and manifest phenotypically later on in life. Therefore, we decided to test whether SAM supplementation during the perinatal period (i.e., supplementing the mothers from mating to weaning) could exert a protective role towards AD-like symptom manifestation. We therefore compared the effect of post-weaning vs. perinatal SAM treatment in TgCRND8 mice by assessing PSEN1 methylation and expression and the development of amyloid plaques. We found that short-term perinatal supplementation was as effective as the longer post-weaning supplementation in repressing PSEN1 expression and amyloid deposition in adult mice. These results highlight the importance of epigenetic memory and methyl donor availability during early life to promote healthy aging and stress the functional role of non-CpG methylation.