A Bioinformatics-Based Study on Methylation Alterations of the FBLN1 Gene in Hippocampal Tissue of Alzheimer's Disease Model DKO and DTG Mice.

Alzheimer's disease (AD) is characterized by progressive cognitive decline and late-stage neurobehavioral issues marked by amyloid-beta plaques and Tau protein tangles. This study aims to investigate Fibulin-1(FBLN1) gene expression in the hippocampal tissue of Presenilin-1/Presenilin-2 conditional double-knockout (DKO) and double-transgenic (DTG) mice, using single-cell sequencing and experimental methods to verify abnormal methylation status and correlation with AD. Genomic DNA from DKO and DTG mice was used for genotyping. Reduced Representation Bisulfite Sequencing (RRBS) identified 10 genes with abnormal methylation changes, with protein-protein interaction (PPI) analysis highlighting five core genes, including FBLN1. Single-cell sequencing, RT-PCR, and Western blotting (WB) were used to analyze FBLN1 mRNA and protein levels in the hippocampal tissues of early-stage and mid-stage AD DKO, DTG, and CBAC57 mice. RRBS identified 10 genes with abnormal methylation, with PPI highlighting five core genes. Single-cell sequencing showed significant FBLN1 expression in AD groups. RT-PCR and WB indicated elevated FBLN1 mRNA and protein levels in mid-stage AD DKO and DTG mice compared to CBAC57 mice, with no differences in early-stage AD DKO and CBAC57 mice. RRBS revealed hypomethylation of the FBLN1 gene in mid-stage AD DKO mice. Elevated FBLN1 expression in AD models suggests an age-dependent neurodegenerative mechanism independent of amyloid-beta deposition. This study enhances our understanding of AD's epigenetic mechanisms, which will aid targeted diagnosis, treatment, and prognosis.

Presenilin Deficiency Results in Cellular Cholesterol Accumulation by Impairment of Protein Glycosylation and NPC1 Function.

Presenilin proteins (PS1 and PS2) represent the catalytic subunit of γ-secretase and play a critical role in the generation of the amyloid ß (Aß) peptide and the pathogenesis of Alzheimer disease (AD). However, PS proteins also exert multiple functions beyond Aß generation. In this study, we examine the individual roles of PS1 and PS2 in cellular cholesterol metabolism. Deletion of PS1 or PS2 in mouse models led to cholesterol accumulation in cerebral neurons. Cholesterol accumulation was also observed in the lysosomes of embryonic fibroblasts from Psen1-knockout (PS1-KO) and Psen2-KO (PS2-KO) mice and was associated with decreased expression of the Niemann-Pick type C1 (NPC1) protein involved in intracellular cholesterol transport in late endosomal/lysosomal compartments. Mass spectrometry and complementary biochemical analyses also revealed abnormal N-glycosylation of NPC1 and several other membrane proteins in PS1-KO and PS2-KO cells. Interestingly, pharmacological inhibition of N-glycosylation resulted in intracellular cholesterol accumulation prominently in lysosomes and decreased NPC1, thereby resembling the changes in PS1-KO and PS2-KO cells. In turn, treatment of PS1-KO and PS2-KO mouse embryonic fibroblasts (MEFs) with the chaperone inducer arimoclomol partially normalized NPC1 expression and rescued lysosomal cholesterol accumulation. Additionally, the intracellular cholesterol accumulation in PS1-KO and PS2-KO MEFs was prevented by overexpression of NPC1. Collectively, these data indicate that a loss of PS function results in impaired protein N-glycosylation, which eventually causes decreased expression of NPC1 and intracellular cholesterol accumulation. This mechanism could contribute to the neurodegeneration observed in PS KO mice and potentially to the pathogenesis of AD.

Alzheimer's disease-related presenilins are key to intestinal epithelial cell function and gut immune homoeostasis.

OBJECTIVE: Mutations in presenilin genes are the major cause of Alzheimer's disease. However, little is known about their expression and function in the gut. In this study, we identify the presenilins Psen1 and Psen2 as key molecules that maintain intestinal homoeostasis. DESIGN: Human inflammatory bowel disease (IBD) and control samples were analysed for Psen1 expression. Newly generated intestinal epithelium-specific Psen1-deficient, Psen2-deficient and inducible Psen1/Psen2 double-deficient mice were used to dissect the functional role of presenilins in intestinal homoeostasis. RESULTS: Psen1 expression was regulated in experimental gut inflammation and in patients with IBD. Induced deletion of Psen1 and Psen2 in mice caused rapid weight loss and spontaneous development of intestinal inflammation. Mice exhibited epithelial barrier disruption with bacterial translocation and deregulation of key pathways for nutrient uptake. Wasting disease was independent of gut inflammation and dysbiosis, as depletion of microbiota rescued Psen-deficient animals from spontaneous colitis development but not from weight loss. On a molecular level, intestinal epithelial cells lacking Psen showed impaired Notch signalling and dysregulated epithelial differentiation. CONCLUSION: Overall, our study provides evidence that Psen1 and Psen2 are important guardians of intestinal homoeostasis and future targets for barrier-promoting therapeutic strategies in IBD.

Generation and characterization of an iPS cell line (PUMCi006-A) from skin fibroblasts of a patient with an M239T mutation in PSEN2 gene.

Presenilin-2 (PSEN2) mutation is one of the pathogenic factors of autosomal dominant early-onset Alzheimer's disease (EOAD). We generated a human induced pluripotent stem cell (iPSC) line from fibroblasts of an EOAD patient carrying PSEN2 mutation (c.716 T > C) utilizing Sendai reprogramming kit. The resulting iPSC line carried patient-specific point mutation, exhibited typical iPSC morphology, retained a normal karyotype, expressed pluripotency markers, and could form embryoid bodies. Established iPSC line serve as valuable resource for EOAD disease pathogenesis modelling and drug screening.

Presenilin: A Multi-Functional Molecule in the Pathogenesis of Alzheimer's Disease and Other Neurodegenerative Diseases.

Presenilin, a transmembrane protein primarily known for its role in Alzheimer's disease (AD) as part of the γ-secretase complex, has garnered increased attention due to its multifaceted functions in various cellular processes. Recent investigations have unveiled a plethora of functions beyond its amyloidogenic role. This review aims to provide a comprehensive overview of presenilin's diverse roles in AD and other neurodegenerative disorders. It includes a summary of well-known substrates of presenilin, such as its involvement in amyloid precursor protein (APP) processing and Notch signaling, along with other functions. Additionally, it highlights newly discovered functions, such as trafficking function, regulation of ferritin expression, apolipoprotein E (ApoE) secretion, the interaction of ApoE and presenilin, and the Aß42-to-Aß40-converting activity of ACE. This updated perspective underscores the evolving landscape of presenilin research, emphasizing its broader impact beyond established pathways. The incorporation of these novel findings accentuates the dynamic nature of presenilin's involvement in cellular processes, further advancing our comprehension of its multifaceted roles in neurodegenerative disorders. By synthesizing evidence from a range of studies, this review sheds light on the intricate web of presenilin functions and their implications in health and disease.

iPSC-derived PSEN2 (N141I) astrocytes and microglia exhibit a primed inflammatory phenotype.

BACKGROUND: Widescale evidence points to the involvement of glia and immune pathways in the progression of Alzheimer's disease (AD). AD-associated iPSC-derived glial cells show a diverse range of AD-related phenotypic states encompassing cytokine/chemokine release, phagocytosis and morphological profiles, but to date studies are limited to cells derived from PSEN1, APOE and APP mutations or sporadic patients. The aim of the current study was to successfully differentiate iPSC-derived microglia and astrocytes from patients harbouring an AD-causative PSEN2 (N141I) mutation and characterise the inflammatory and morphological profile of these cells. METHODS: iPSCs from three healthy control individuals and three familial AD patients harbouring a heterozygous PSEN2 (N141I) mutation were used to derive astrocytes and microglia-like cells and cell identity and morphology were characterised through immunofluorescent microscopy. Cellular characterisation involved the stimulation of these cells by LPS and Aß42 and analysis of cytokine/chemokine release was conducted through ELISAs and multi-cytokine arrays. The phagocytic capacity of these cells was then indexed by the uptake of fluorescently-labelled fibrillar Aß42. RESULTS: AD-derived astrocytes and microglia-like cells exhibited an atrophied and less complex morphological appearance than healthy controls. AD-derived astrocytes showed increased basal expression of GFAP, S100ß and increased secretion and phagocytosis of Aß42 while AD-derived microglia-like cells showed decreased IL-8 secretion compared to healthy controls. Upon immunological challenge AD-derived astrocytes and microglia-like cells showed exaggerated secretion of the pro-inflammatory IL-6, CXCL1, ICAM-1 and IL-8 from astrocytes and IL-18 and MIF from microglia. CONCLUSION: Our study showed, for the first time, the differentiation and characterisation of iPSC-derived astrocytes and microglia-like cells harbouring a PSEN2 (N141I) mutation. PSEN2 (N141I)-mutant astrocytes and microglia-like cells presented with a 'primed' phenotype characterised by reduced morphological complexity, exaggerated pro-inflammatory cytokine secretion and altered Aß42 production and phagocytosis.

Presenilin-2 knock-In mice show severe depressive behavior via DVL3 downregulation.

INTRODUCTION: Alzheimer's disease (AD) is the most common form of dementia. Depression is one of the most critical psychiatric complications of AD, and 20%-30% of patients with AD experience symptoms of depression. Phospho-glycogen synthase kinase-3 beta (GSK3ß) is known to be associated with AD and depression. Furthermore, the role of disheveled (DVL) is known to regulate GSK3ß. Moreover, presenilin-2 (PS2) and DVL have cross-talk with each other. Also, it is widely hypothesized that stress leads to hypersecretion of cortisol and is thus associated with depression. Dickkopf WNT signaling pathway inhibitor-1 (DKK-1) is a crucial factor regulating depression and both amyloid beta (Aß) and phosphorylation of tau are widely known as a biomarker of AD. METHODS: To investigate the relationship between AD and depression, and possible pathways connecting the two diseases, we examined memory function and depression-related behavior test results in PS2 knock-in AD mice (PS2 MT). Next, we confirmed that there are relationships between DVL, depression, and cognitive disease through the comparative toxicogenomics database (https://ctdbase.org) and STRING (https://string-db.org) database. RESULTS: PS2 knock-in mice showed much more severe memory impairment and depression than PS2 wild-type mice (PS2 WT). In AD-related behavioral experiments, PS2 MT mice showed more memory dysfunction compared with PS2 WT group mice. Moreover, Aß and phosphorylation of tau showed higher expression in PS2 MT mice than in PS2 WT mice. Depression-related behavioral tests showed that PS2 MT mice exhibited more depressive behaviors than PS2 WT mice. Furthermore, both higher cortisol levels and higher expression of DKK-1 were found in PS2 MT mice relative to PS2 WT mice. The results indicated that there is a relationship between DVL and the release of AD-related mediators and expression of the depression-related glucocorticoid receptor and DKK-1. In the PS2 knock-in group, DVL was significantly decreased compared with the PS2 WT group. CONCLUSION: Depression increases the risk of developing AD and other forms of dementia. Recent evidence indicates that depression symptoms could trigger changes in memory and thinking over time. However, it is recognized that there are no drugs to facilitate a full recovery for both AD and depression. However, our results suggest that AD and depression could be associated, and DVL could be a significant target for the association between AD and depression.

Presenilin2 D439A Mutation Induces Dysfunction of Mitochondrial Fusion/Fission Dynamics and Abnormal Regulation of GTPase Activity.

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disease, and approximately 10% of AD cases are early-onset familial AD (EOFAD), which is mainly linked to point mutations in genes encoding presenilins (PS1 and PS2). Mutations in PS2 are extremely rare and have not received enough attention. Recently, studies have found that Rho GTPase activity is closely related to the pathogenesis of AD. In this study, we used transcriptome sequencing in PS2 siRNA-transfected SH-SY5Y cells and found a group of differentially expressed genes (DEGs) related to the regulation of GTPase activity. Among those DEGs, the most significantly downregulated was Rho guanine nucleotide exchange factor 5 (ARHGEF5). GTPase activity in PS2 siRNA-transfected cells was significantly decreased. Then, we found that the expression of ARHGEF5 and the GTPase activity of Mitochondrial Rho GTPase 2 (Miro2) in PS2 D439A mutant SH-SY5Y cells were significantly decreased. We found for the first time that PS2 can bind to Miro2, and the PS2 D439A mutation reduced the binding between PS2 and Miro2, reduced the expression of Miro2, and resulted in an imbalance in mitochondrial fusion/fission dynamics. In conclusion, PS2 gene knockdown may participate in the pathogenesis of AD through the regulation of GTPase activity. The imbalance in mitochondrial dynamics mediated by the PS2 D439A mutation through regulation of the expression and GTPase activity of Miro2 may be a potential pathogenic mechanism of AD.

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.

Transmembrane BAX inhibitor motif containing 6 suppresses presenilin-2 to preserve mitochondrial integrity after myocardial ischemia-reperfusion injury.

Myocardial ischemia-reperfusion (I/R) damage is characterized by mitochondrial damage in cardiomyocytes. Transmembrane BAX inhibitor motif containing 6 (TMBIM6) and presenilin-2 (PS2) participate in multiple mitochondrial pathways; thus, we investigated the impact of these proteins on mitochondrial homeostasis during an acute reperfusion injury. Myocardial post-ischemic reperfusion stress impaired myocardial function, induced structural abnormalities and promoted cardiomyocyte death by disrupting the mitochondrial integrity in wild-type mice, but not in TMBIM6 transgenic mice. We found that TMBIM6 bound directly to PS2 and promoted its post-transcriptional degradation. Knocking out PS2 in mice reduced I/R injury-induced cardiac dysfunction, inflammatory responses, myocardial swelling and cardiomyocyte death by improving the mitochondrial integrity. These findings demonstrate that sufficient TMBIM6 expression can prevent PS2 accumulation during cardiac I/R injury, thus suppressing reperfusion-induced mitochondrial damage. Therefore, TMBIM6 and PS2 are promising therapeutic targets for the treatment of cardiac reperfusion damage.

Different transmembrane domains determine the specificity and efficiency of the cleavage activity of the γ-secretase subunit presenilin.

The γ-secretase complex catalyzes the intramembrane cleavage of C99, a carboxy-terminal fragment of the amyloid precursor protein. Two paralogs of its catalytic subunit presenilin (PS1 and PS2) are expressed which are autocatalytically cleaved into an N-terminal and a C-terminal fragment during maturation of γ-secretase. In this study, we compared the efficiency and specificity of C99 cleavage by PS1- and PS2-containing γ-secretases. Mass spectrometric analysis of cleavage products obtained in cell-free and cell-based assays revealed that the previously described lower amyloid-ß (Aß)38 generation by PS2 is accompanied by a reciprocal increase in Aß37 production. We further found PS1 and PS2 to show different preferences in the choice of the initial cleavage site of C99. However, the differences in Aß38 and Aß37 generation appear to mainly result from altered subsequent stepwise cleavage of Aß peptides. Apart from these differences in cleavage specificity, we confirmed a lower efficiency of initial C99 cleavage by PS2 using a detergent-solubilized γ-secretase system. By investigating chimeric PS1/2 molecules, we show that the membrane-embedded, nonconserved residues of the N-terminal fragment mainly account for the differential cleavage efficiency and specificity of both presenilins. At the level of individual transmembrane domains (TMDs), TMD3 was identified as a major modulator of initial cleavage site specificity. The efficiency of endoproteolysis strongly depends on nonconserved TMD6 residues at the interface to TMD2, i.e., at a putative gate of substrate entry. Taken together, our results highlight the role of individual presenilin TMDs in the cleavage of C99 and the generation of Aß peptides.

Unraveling Presenilin 2 Functions in a Knockout Zebrafish Line to Shed Light into Alzheimer's Disease Pathogenesis.

Mutations in presenilin 2 (PS2) have been causally linked to the development of inherited Alzheimer's disease (AD). Besides its role as part of the γ-secretase complex, mammalian PS2 is also involved, as an individual protein, in a growing number of cell processes, which result altered in AD. To gain more insight into PS2 (dys)functions, we have generated a presenilin2 (psen2) knockout zebrafish line. We found that the absence of the protein does not markedly influence Notch signaling at early developmental stages, suggesting a Psen2 dispensable role in the γ-secretase-mediated Notch processing. Instead, loss of Psen2 induces an exaggerated locomotor response to stimulation in fish larvae, a reduced number of ER-mitochondria contacts in zebrafish neurons, and an increased basal autophagy. Moreover, the protein is involved in mitochondrial axonal transport, since its acute downregulation reduces in vivo organelle flux in zebrafish sensory neurons. Importantly, the expression of a human AD-linked mutant of the protein increases this vital process. Overall, our results confirm zebrafish as a good model organism for investigating PS2 functions in vivo, representing an alternative tool for the characterization of new AD-linked defective cell pathways and the testing of possible correcting drugs.

Alpha7 nicotinic acetylcholine receptor agonist PHA-543613 improves memory deficits in presenilin 1 and presenilin 2 conditional double knockout mice.

Cholinergic system dysfunction has been considered as a critical feature of neurodegenerative progression in Alzheimer's disease (AD). The α7 nicotinic acetylcholine receptors (α7-nAChRs) are widely expressed in the hippocampus cortex and play an important role in memory formation, considered as potential therapeutic agents targets. However, underlying mechanisms have not been fully elucidated. Here, we combine behavioral, molecular biological methods with in vitro slice and in vivo multichannel electrophysiological recording techniques to investigate the molecular, cellular synaptic and neuronal mechanisms of activating α7-nAChR by PHA-543613 (a selective α7-nAChR agonist), which influences the impaired cognitive function using presenilin 1 (PS1) and presenilin 2 (PS2) conditional double knockout (cDKO) mice. Our results demonstrated that PHA-543613 treatment significantly improved the impaired hippocampus-related memory via recovering the reduced the hippocampal synaptic protein levels of α7-nAChR, NMADAR and AMPAR, thereby restoring the impaired post-tetanic potentiation (PTP), long-term potentiation (LTP), activation of molecular signaling pathway for neuronal protection, theta power and strength of theta-gamma phase-amplitude coupling (PAC) at hippocampus in 6-month-old cDKO mice. For the first time, we systematically reveal the mechanisms by which PHA-543613 improves memory deficits at different levels. Therefore, our findings may be significant for the development of therapeutic strategies for AD.

Presenilin Is Essential for ApoE Secretion, a Novel Role of Presenilin Involved in Alzheimer's Disease Pathogenesis.

Alzheimer's disease (AD) is a debilitating dementia characterized by progressive memory loss and aggregation of amyloid-ß (Aß) protein into amyloid plaques in patient brains. Mutations in presenilin (PS) lead to abnormal generation of Aß, which is the major cause of familial AD (FAD), and apolipoprotein E4 (ApoE4) is the major genetic risk factor for sporadic AD (SAD) onset. However, whether dysfunction of PS is involved in the pathogenesis of SAD is largely unknown. We found that ApoE secretion was completely abolished in PS-deficient cells and markedly decreased by inhibition of γ-secretase activity. Blockade of γ-secretase activity by a γ-secretase inhibitor, DAPT, decreased ApoE secretion, suggesting an important role of γ-secretase activity in ApoE secretion. Reduced ApoE secretion is also observed in nicastrin-deficient cells with reduced γ-secretase activity. PS deficiency enhanced nuclear translocation of ApoE and binding of ApoE to importin α4, a nuclear transport receptor. Moreover, the expression of PS mutants in PS-deficient cells suppressed the restoration effects on ApoE secretion compared with the expression of wild-type PS. Plasma ApoE levels were lower in FAD patients carrying PS1 mutations compared with normal control subjects. Our findings suggest a novel role of PS contributing to the pathogenesis of SAD by regulating ApoE secretion.SIGNIFICANCE STATEMENT Familial AD (FAD) typically results from mutations in the genes encoding amyloid precursor protein, presenilin 1 (PS1), or PS2. Many PS mutants have been found to exert impaired γ-secretase activity and increased amyloid-ß 42 (Aß42)/Aß40 ratio, which induce early amyloid deposition and FAD. On the other hand, apolipoprotein E4 (ApoE4) is the major genetic risk factor for sporadic AD (SAD) and contributes to AD pathogenesis because it has reduced Aß clearance capability compared with ApoE3 and ApoE2. FAD and SAD have long been considered to be caused by these two independent mechanisms; however, for the first time, we demonstrated that PS is essential for ApoE secretion and PS mutants affected ApoE secretion in vitro and in human samples, suggesting a novel mechanism by which PS is also involved in SAD pathogenesis.

Exercise Reverses Amyloid ß-Peptide-Mediated Cognitive Deficits in Alzheimer's Disease Mice Expressing Mutant Presenilin-2.

PURPOSE: The molecular mechanisms by which physical exercise produces beneficial effects on pathologic features and behavioral symptoms of Alzheimer's disease (AD) are not well understood. Herein, we examined whether regular moderate exercise could improve cognitive function and produce transcriptomic responses in the brain. METHODS: Four groups of mice were studied: nontransgenic control, mice expressing the human presenilin-2 wild type, mice expressing the human presenilin-2 with the N141I mutation (Tg-PS2m), and Tg-PS2m that were subjected to treadmill exercise (TE) at a speed of 10 m·min-1 for 50 min·d-1, 5 d·wk-1, for 6 wk (Tg-PS2m/Ex). RESULTS: Tg-PS2m/Ex mice exhibited increased preference in exploring a novel object than Tg-PS2m in the novel object recognition test, whereas differences observed in the water maze test and passive avoidance test were not significant. Western blot and histological analyses using amyloid oligomer (A11) and ß-amyloid (6E10) antibody indicated that amyloid oligomer-reactive bands and plaque deposition in the hippocampus were reduced, although not significantly, after TE. Transcriptomic (RNA-sequencing) analysis and subsequent protein analysis revealed that the cell cycle regulatory gene, Cdc28 protein kinase regulatory subunit 2 (Cks2), was decreased, and the cell cycle- and apoptotic cell death-related factors, including cyclin D1, proliferating cell nuclear antigen, and cleaved caspase-3, were increased in the hippocampus of Tg-PS2m, whereas TE reversed their altered expression. CONCLUSIONS: The results support the hypothesis that the pathologic features and behavioral symptoms of AD caused by accumulation of amyloid ß-peptide in hippocampus, causing aberrant cell cycle reentry and apoptosis, can be reversed by regular exercise.

Conformational Models of APP Processing by Gamma Secretase Based on Analysis of Pathogenic Mutations.

Proteolytic processing of amyloid precursor protein (APP) plays a critical role in the pathogenesis of Alzheimer's disease (AD). Sequential cleavage of APP by ß and γ secretases leads to the generation of Aß40 (non-amyloidogenic) and Aß42 (amyloidogenic) peptides. Presenilin-1 (PS1) or presenilin-2 (PS2) play the role of a catalytic subunit of γ-secretase. Multiple familial AD (FAD) mutations in APP, PS1, or PS2 result in an increased Aß42:Aß40 ratio and the accumulation of toxic Aß42 oligomers and plaques in patient brains. In this study, we perform molecular modeling of the APP complex with γ-secretase and analyze potential effects of FAD mutations in APP and PS1. We noticed that all FAD mutations in the APP transmembrane domain are predicted to cause an increase in the local disorder of its secondary structure. Based on structural analysis of known γ-secretase structures, we propose that APP can form a complex with γ-secretase in 2 potential conformations-M1 and M2. In conformation, the M1 transmembrane domain of APP forms a contact with the perimembrane domain that follows transmembrane domain 6 (TM6) in the PS1 structure. In conformation, the M2 transmembrane domain of APP forms a contact with transmembrane domain 7 (TM7) in the PS1 structure. By analyzing the effects of PS1-FAD mutations on the local protein disorder index, we discovered that these mutations increase the conformational flexibility of M2 and reduce the conformational flexibility of M1. Based on these results, we propose that M2 conformation, but not M1 conformation, of the γ secretase complex with APP leads to the amyloidogenic (Aß42-generating) processing of APP. Our model predicts that APP processing in M1 conformation is favored by curved membranes, such as the membranes of early endosomes. In contrast, APP processing in M2 conformation is likely to be favored by relatively flat membranes, such as membranes of late endosomes and plasma membranes. These predictions are consistent with published biochemical analyses of APP processing at different subcellular locations. Our results also suggest that specific inhibitors of Aß42 production could be potentially developed by selectively targeting the M2 conformation of the γ secretase complex with APP.

Loosening ER-Mitochondria Coupling by the Expression of the Presenilin 2 Loop Domain.

Presenilin 2 (PS2), one of the three proteins in which mutations are linked to familial Alzheimer's disease (FAD), exerts different functions within the cell independently of being part of the γ-secretase complex, thus unrelated to toxic amyloid peptide formation. In particular, its enrichment in endoplasmic reticulum (ER) membrane domains close to mitochondria (i.e., mitochondria-associated membranes, MAM) enables PS2 to modulate multiple processes taking place on these signaling hubs, such as Ca2+ handling and lipid synthesis. Importantly, upregulated MAM function appears to be critical in AD pathogenesis. We previously showed that FAD-PS2 mutants reinforce ER-mitochondria tethering, by interfering with the activity of mitofusin 2, favoring their Ca2+ crosstalk. Here, we deepened the molecular mechanism underlying PS2 activity on ER-mitochondria tethering, identifying its protein loop as an essential domain to mediate the reinforced ER-mitochondria connection in FAD-PS2 models. Moreover, we introduced a novel tool, the PS2 loop domain targeted to the outer mitochondrial membrane, Mit-PS2-LOOP, that is able to counteract the activity of FAD-PS2 on organelle tethering, which possibly helps in recovering the FAD-PS2-associated cellular alterations linked to an increased organelle coupling.

Alzheimer's Disease Associated Presenilin 1 and 2 Genes Dysregulation in Neonatal Lymphocytes Following Perinatal Asphyxia.

Perinatal asphyxia is mainly a brain disease leading to the development of neurodegeneration, in which a number of peripheral lesions have been identified; however, little is known about the expression of key genes involved in amyloid production by peripheral cells, such as lymphocytes, during the development of hypoxic-ischemic encephalopathy. We analyzed the gene expression of the amyloid protein precursor, ß-secretase, presenilin 1 and 2 and hypoxia-inducible factor 1-α by RT-PCR in the lymphocytes of post-asphyxia and control neonates. In all examined periods after asphyxia, decreased expression of the genes of the amyloid protein precursor, ß-secretase and hypoxia-inducible factor 1-α was noted in lymphocytes. Conversely, expression of presenilin 1 and 2 genes decreased on days 1-7 and 8-14 but increased after survival for more than 15 days. We believe that the expression of presenilin genes in lymphocytes could be a potential biomarker to determine the severity of the post-asphyxia neurodegeneration or to identify the underlying factors for brain neurodegeneration and get information about the time they occurred. This appears to be the first worldwide data on the role of the presenilin 1 and 2 genes associated with Alzheimer's disease in the dysregulation of neonatal lymphocytes after perinatal asphyxia.

Metals toxicity and its correlation with the gene expression in Alzheimer's disease.

Alzheimer's disease is a common neurodegenerative disease in the elderly population and a leading cause of dementia. Genetics and environmental risk factors were considered to play a major role in the onset of the disease. This study aimed to examine the correlation between different metals levels and the gene expression in Alzheimer's patients with age-matched control subjects. Non- essential metals were measured in the whole blood due to its higher concentration in red blood corpuscles (RBCs) and essential biometals in the serum samples of Alzheimer's disease (AD) by using Inductively coupled plasma optical emission spectroscopy (ICP-OES) that allows the analysis and detection of the different elements at low levels. Gene expression level was performed by quantitative real-time PCR (qRT-PCR). In this study, the levels of Lead and Arsenic metals were not detected in the AD patient samples. Cadmium, Mercury, and Aluminum were found higher in cases as compared to controls with 0.009240 ± 0.0007707 (P = < 0.0001), 0.02332 ± 0.001041 (P = < 0.0001), and 0.09222 ± 0.02804 (P = 0.0087) respectively. Essential biometal like copper was higher 0.1274 ± 0.02453 (P = 0.0254) in cases, while iron 0.1117 ± 0.009599 (P = 0.0304) and zinc 0.03800 ± 0.003462 mg/L were found significantly lower as compared to controls. All targeted genes such as APP, PSEN1, PSEN2, and APOE4 were found up-regulated in AD patients. We concluded that there was no significant correlation between metals dyshomeostasis and gene expressions in this study.