Membrane lipid remodeling modulates γ-secretase processivity.

Imbalances in the amounts of amyloid-ß peptides (Aß) generated by the membrane proteases ß- and γ-secretase are considered as a trigger of Alzheimer's disease (AD). Cell-free studies of γ-secretase have shown that increasing membrane thickness modulates Aß generation but it has remained unclear if these effects are translatable to cells. Here we show that the very long-chain fatty acid erucic acid (EA) triggers acyl chain remodeling in AD cell models, resulting in substantial lipidome alterations which included increased esterification of EA in membrane lipids. Membrane remodeling enhanced γ-secretase processivity, resulting in the increased production of the potentially beneficial Aß37 and/or Aß38 species in multiple cell lines. Unexpectedly, we found that the membrane remodeling stimulated total Aß secretion by cells expressing WT γ-secretase but lowered it for cells expressing an aggressive familial AD mutant γ-secretase. We conclude that EA-mediated modulation of membrane composition is accompanied by complex lipid homeostatic changes that can impact amyloidogenic processing in different ways and elicit distinct γ-secretase responses, providing critical implications for lipid-based AD treatment strategies.

Abnormal amyloid precursor protein processing in periodontal tissue in a murine model of periodontitis induced by Porphyromonas gingivalis.

OBJECTIVE: The study aimed to investigate the change of amyloid precursor protein (APP) processing and amyloid ß (Aß) metabolites in linking periodontitis to Alzheimer's disease (AD). BACKGROUND: Aß is one of the main pathological features of AD, and few studies have discussed changes in its expression in peripheral tissues or analyzed the relationship between the peripheral imbalance of Aß production and clearance. METHODS: A murine model of periodontitis was established by oral infection with Porphyromonas gingivalis (P. gingivalis). Micro-computed tomography (Micro-CT) was used to observe the destruction of the alveolar bone. Nested quantitative polymerase chain reaction (qPCR) was used to measure small quantities of P.gingivalis DNA in different tissues. Behavioral experiments were performed to measure cognitive function in the mice. The mRNA levels of TNF-α, IL-6, IL-8, RANKL, OPG, APP695, APP751, APP770, and BACE1 in the gingival tissues or cortex were detected by RT-PCR. The levels of Aß1-40 and Aß1-42 in gingival crevicular fluid (GCF) and plasma were tested by ELISA. RESULTS: P. gingivalis oral infection was found to cause alveolar bone resorption and impaired learning and memory. P.gingivalis DNA was detected in the gingiva, blood and cortex of the P.gingivalis group by nested qPCR (p < .05). The mRNA expression of TNF-α, IL-6, IL-8, RANKL/OPG, and BACE1 in the gingival tissue was significantly higher than that in the control group (p < .05). Similarly, upregulated mRNA levels of APP695 and APP770 were observed in the gingival tissuses and cortex of the P. gingivalis group (p < .05). The levels of Aß1-40 and Aß1-42 in the GCF and plasma of the P. gingivalis group were significantly higher than those in the control group (p < .05). CONCLUSION: P. gingivalis can directly invade the brain via hematogenous infection. The invasion of P. gingivalis could trigger an immune response and lead to an imbalance between Aß production and clearance in peripheral tissues, which may trigger an abnormal Aß metabolite in the brain, resulting in the occurrence and development of AD.

Amyloid futures in the expanding pathology of brain aging and dementia.

Positron emission tomography (PET) imaging studies of Alzheimer's disease (AD) patients show progressive increases of fibrillar Aß-amyloid. Because current PET ligands underestimate nonfibrillar forms, we assayed soluble Aß in AD and controls. To identify the mechanisms responsible for soluble Aß in AD brains, we examined lipid rafts (LRs), where amyloid precursor protein (APP) is enzymatically processed. Frontal cortex was compared with cerebellum, which has minimal AD pathology. Compared with cognitively normal controls (CTL; Braak 0-1), elevations of soluble Aß40 and Aß42 were similar for intermediate- and later-stage AD (Braak 2-3 and 4-6). Clinical-grade AD showed a greater increase in soluble Aß40 than Aß42 relative to CTL. LR raft yield per gram AD frontal cortex was 20% below that of controls, whereas cerebellar LR did not differ by Braak score. The extensive overlap of soluble Aß levels in controls with AD contrasts with the PET findings on fibrillar Aß. These findings further support fibrillar Aß as a biomarker for AD treatments and show the need for more detailed postmortem analysis of diverse soluble and insoluble Aß aggregates in relation to PET.

Amyloid-Beta Mediates Homeostatic Synaptic Plasticity.

The physiological role of the amyloid-precursor protein (APP) is insufficiently understood. Recent work has implicated APP in the regulation of synaptic plasticity. Substantial evidence exists for a role of APP and its secreted ectodomain APPsα in Hebbian plasticity. Here, we addressed the relevance of APP in homeostatic synaptic plasticity using organotypic tissue cultures prepared from APP-/- mice of both sexes. In the absence of APP, dentate granule cells failed to strengthen their excitatory synapses homeostatically. Homeostatic plasticity is rescued by amyloid-ß and not by APPsα, and it is neither observed in APP+/+ tissue treated with ß- or γ-secretase inhibitors nor in synaptopodin-deficient cultures lacking the Ca2+-dependent molecular machinery of the spine apparatus. Together, these results suggest a role of APP processing via the amyloidogenic pathway in homeostatic synaptic plasticity, representing a function of relevance for brain physiology as well as for brain states associated with increased amyloid-ß levels.

S327 phosphorylation of the presynaptic protein SEPTIN5 increases in the early stages of neurofibrillary pathology and alters the functionality of SEPTIN5.

Alzheimer's disease (AD) is the most common form of dementia, which is neuropathologically characterized by extracellular senile plaques containing amyloid-ß and intracellular neurofibrillary tangles composed of hyperphosphorylated tau protein. Previous studies have suggested a role for septin (SEPTIN) protein family members in AD-associated cellular processes. Here, we elucidated the potential role of presynaptic SEPTIN5 protein and its post-translational modifications in the molecular pathogenesis of AD. RNA and protein levels of SEPTIN5 showed a significant decrease in human temporal cortex in relation to the increasing degree of AD-related neurofibrillary pathology. Conversely, an increase in the phosphorylation of the functionally relevant SEPTIN5 phosphorylation site S327 was observed already in the early phases of AD-related neurofibrillary pathology, but not in the cerebrospinal fluid of individuals fulfilling the criteria for mild cognitive impairment due to AD. According to the mechanistic assessments, a link between SEPTIN5 S327 phosphorylation status and the effects of SEPTIN5 on amyloid precursor protein processing and markers of autophagy was discovered in mouse primary cortical neurons transduced with lentiviral constructs encoding wild type SEPTIN5 or SEPTIN5 phosphomutants (S327A and S327D). C57BL/6 J mice intrahippocampally injected with lentiviral wild type SEPTIN5 or phosphomutant constructs did not show changes in cognitive performance after five to six weeks from the start of injections. However, SEPTIN5 S327 phosphorylation status was linked to changes in short-term synaptic plasticity ex vivo at the CA3-CA1 synapse. Collectively, these data suggest that SEPTIN5 and its S327 phosphorylation status play a pivotal role in several cellular processes relevant for AD.

Effect of Aß Oligomers on Neuronal APP Triggers a Vicious Cycle Leading to the Propagation of Synaptic Plasticity Alterations to Healthy Neurons.

Alterations of excitatory synaptic function are the strongest correlate to the pathologic disturbance of cognitive ability observed in the early stages of Alzheimer's disease (AD). This pathologic feature is driven by amyloid-ß oligomers (Aßos) and propagates from neuron to neuron. Here, we investigated the mechanism by which Aßos affect the function of synapses and how these alterations propagate to surrounding healthy neurons. We used complementary techniques ranging from electrophysiological recordings and molecular biology to confocal microscopy in primary cortical cultures, and from acute hippocampal and cortical slices from male wild-type and amyloid precursor protein (APP) knock-out (KO) mice to assess the effects of Aßos on glutamatergic transmission, synaptic plasticity, and dendritic spine structure. We showed that extracellular application of Aßos reduced glutamatergic synaptic transmission and long-term potentiation. These alterations were not observed in APP KO neurons, suggesting that APP expression is required. We demonstrated that Aßos/APP interaction increases the amyloidogenic processing of APP leading to intracellular accumulation of newly produced Aßos. Intracellular Aßos participate in synaptic dysfunctions as shown by pharmacological inhibition of APP processing or by intraneuronal infusion of an antibody raised against Aßos. Furthermore, we provide evidence that following APP processing, extracellular release of Aßos mediates the propagation of the synaptic pathology characterized by a decreased spine density of neighboring healthy neurons in an APP-dependent manner. Together, our data unveil a complementary role for Aßos in AD, while intracellular Aßos alter synaptic function, extracellular Aßos promote a vicious cycle that propagates synaptic pathology from diseased to healthy neurons.SIGNIFICANCE STATEMENT Here we provide the proof that a vicious cycle between extracellular and intracellular pools of Aß oligomers (Aßos) is required for the spreading of Alzheimer's disease (AD) pathology. We showed that extracellular Aßos propagate excitatory synaptic alterations by promoting amyloid precursor protein (APP) processing. Our results also suggest that subsequent to APP cleavage two pools of Aßos are produced. One pool accumulates inside the cytosol, inducing the loss of synaptic plasticity potential. The other pool is released into the extracellular space and contributes to the propagation of the pathology from diseased to healthy neurons. Pharmacological strategies targeting the proteolytic cleavage of APP disrupt the relationship between extracellular and intracellular Aß, providing a therapeutic approach for the disease.

Activated STAT3 signaling pathway by ligature-induced periodontitis could contribute to neuroinflammation and cognitive impairment in rats.

BACKGROUND: Increasing evidence suggests a causal link between periodontitis and cognitive disorders. Systemic inflammation initiated by periodontitis may mediate the development of cognitive impairment. Our study aims to investigate the effect of ligature-induced periodontitis on cognitive function and the role of signal transducers and activators of transcription 3 (STAT3) in this process. MATERIALS AND METHODS: Ligature-induced periodontitis was established, and the rats were treated intraperitoneally with/without the pSTAT3 inhibitor cryptotanshinone (CTS). Alveolar bone resorption and periodontal inflammation were detected by micro-computed tomography analysis and histopathological evaluation. Locomotor activity and cognitive function were evaluated by the open field test and the Morris water maze test, respectively. The activation of microglia and astrocytes in the hippocampus and cortex was assessed by immunohistochemistry (IHC). The expression of interleukins (IL-1ß, IL-6, IL-8, IL-21) in both the periphery and cortex was evaluated by RT-PCR and ELISA. The expression of TLR/NF-κB and ROS cascades was evaluated by RT-PCR. The expression of pSTAT3 and the activation of the STAT3 signaling pathway (JAK2, STAT3, and pSTAT3) in the periodontal tissue and cortex were assessed by IHC and Western blot. The expression of amyloid precursor protein (APP) and its key secretases was evaluated by RT-PCR. The level of amyloid ß-protein (Aß) and the ratio of Aß1-40/1-42 were measured via ELISA in the plasma and cortex while IHC was used to detect the level of Aß1-42 in the brain. RESULTS: In periodontal ligature rats, significant alveolar bone resorption and local inflammatory cell infiltration were present. Apparent increases in inflammatory cytokines (IL-1ß, IL-6, IL-8, and IL-21) were detected in peripherial blood and brain. Additionally, spatial learning and memory ability was impaired, while locomotor activity was not affected. Activated microglia and astrocytes were found in the cortex and hippocampus, presenting as enlarged cell bodies and irregular protrusions. Levels of TLR/NF-kB, PPAR and ROS were altered. The STAT3 signaling pathway was activated in both the periodontal tissue and cortex, and the processing of APP by ß- and γ-secretases was promoted. The changes mentioned above could be relieved by the pSTAT3 inhibitor CTS. CONCLUSIONS: Ligature-induced periodontitis in rats resulted in systemic inflammation and further abnormal APP processing, leading to cognitive impairments. In this progress, the activation of the STAT3 signaling pathway may play an important role by increasing inflammatory load and promoting neuroinflammation.

NGF and the Amyloid Precursor Protein in Alzheimer's Disease: From Molecular Players to Neuronal Circuits.

Alzheimer's disease (AD), one of the most common causes of dementia in elderly people, is characterized by progressive impairment in cognitive function, early degeneration of basal forebrain cholinergic neurons (BFCNs), abnormal metabolism of the amyloid precursor protein (APP), amyloid beta-peptide (Aß) depositions, and neurofibrillary tangles. According to the cholinergic hypothesis, dysfunction of acetylcholine-containing neurons in the basal forebrain contributes markedly to the cognitive decline observed in AD. In addition, the neurotrophic factor hypothesis posits that the loss nerve growth factor (NGF) signalling in AD may account for the vulnerability to atrophy of BFCNs and consequent impairment of cholinergic functions. Though acetylcholinesterase inhibitors provide only partial and symptomatic relief to AD patients, emerging data from in vivo magnetic resonance imaging (MRI) and positron emission tomography (PET) studies in mild cognitive impairment (MCI) and AD patients highlight the early involvement of BFCNs in MCI and the early phase of AD. These data support the cholinergic and neurotrophic hypotheses of AD and suggest new targets for AD therapy.Different mechanisms account for selective vulnerability of BFCNs to AD pathology, with regard to altered metabolism of APP and tau. In this review, we provide a general overview of the current knowledge of NGF and APP interplay, focusing on the role of APP in regulating NGF receptors trafficking/signalling and on the involvement of NGF in modulating phosphorylation of APP, which in turn controls APP intracellular trafficking and processing. Moreover, we highlight the consequences of APP interaction with p75NTR and TrkA receptor, which share the same binding site within the APP juxta-membrane domain. We underline the importance of insulin dysmetabolism in AD pathology, in the light of our recent data showing that overlapping intracellular signalling pathways stimulated by NGF or insulin can be compensatory. In particular, NGF-based signalling is able to ameliorates deficiencies in insulin signalling in the medial septum of 3×Tg-AD mice. Finally, we present an overview of NGF-regulated microRNAs (miRNAs). These small non-coding RNAs are involved in post-transcriptional regulation of gene expression , and we focus on a subset that are specifically deregulated in AD and thus potentially contribute to its pathology.

Transcriptional repression of the ectodomain sheddase ADAM10 by TBX2 and potential implication for Alzheimer's disease.

BACKGROUND: The ADAM10-mediated cleavage of transmembrane proteins regulates cellular processes such as proliferation or migration. Substrate cleavage by ADAM10 has also been implicated in pathological situations such as cancer or Morbus Alzheimer. Therefore, identifying endogenous molecules, which modulate the amount and consequently the activity of ADAM10, might contribute to a deeper understanding of the enzyme's role in both, physiology and pathology. METHOD: To elucidate the underlying cellular mechanism of the TBX2-mediated repression of ADAM10 gene expression, we performed overexpression, RNAi-mediated knockdown and pharmacological inhibition studies in the human neuroblastoma cell line SH-SY5Y. Expression analysis was conducted by e.g. real-time RT-PCR or western blot techniques. To identify the binding region of TBX2 within the ADAM10 promoter, we used luciferase reporter assay on deletion constructs and EMSA/WEMSA experiments. In addition, we analyzed a TBX2 loss-of-function Drosophila model regarding the expression of ADAM10 orthologs by qPCR. Furthermore, we quantified the mRNA level of TBX2 in post-mortem brain tissue of AD patients. RESULTS: Here, we report TBX2 as a transcriptional repressor of ADAM10 gene expression: both, the DNA-binding domain and the repression domain of TBX2 were necessary to effect transcriptional repression of ADAM10 in neuronal SH-SY5Y cells. This regulatory mechanism required HDAC1 as a co-factor of TBX2. Transcriptional repression was mediated by two functional TBX2 binding sites within the core promoter sequence (- 315 to - 286 bp). Analysis of a TBX2 loss-of-function Drosophila model revealed that kuzbanian and kuzbanian-like, orthologs of ADAM10, were derepressed compared to wild type. Vice versa, analysis of cortical brain samples of AD-patients, which showed reduced ADAM10 mRNA levels, revealed a 2.5-fold elevation of TBX2, while TBX3 and TBX21 levels were not affected. CONCLUSION: Our results characterize TBX2 as a repressor of ADAM10 gene expression and suggest that this regulatory interaction is conserved across tissues and species.

M344 promotes nonamyloidogenic amyloid precursor protein processing while normalizing Alzheimer's disease genes and improving memory.

Alzheimer's disease (AD) comprises multifactorial ailments for which current therapeutic strategies remain insufficient to broadly address the underlying pathophysiology. Epigenetic gene regulation relies upon multifactorial processes that regulate multiple gene and protein pathways, including those involved in AD. We therefore took an epigenetic approach where a single drug would simultaneously affect the expression of a number of defined AD-related targets. We show that the small-molecule histone deacetylase inhibitor M344 reduces beta-amyloid (Aß), reduces tau Ser396 phosphorylation, and decreases both ß-secretase (BACE) and APOEε4 gene expression. M344 increases the expression of AD-relevant genes: BDNF, α-secretase (ADAM10), MINT2, FE65, REST, SIRT1, BIN1, and ABCA7, among others. M344 increases sAPPα and CTFα APP metabolite production, both cleavage products of ADAM10, concordant with increased ADAM10 gene expression. M344 also increases levels of immature APP, supporting an effect on APP trafficking, concurrent with the observed increase in MINT2 and FE65, both shown to increase immature APP in the early secretory pathway. Chronic i.p. treatment of the triple transgenic (APPsw/PS1M146V/TauP301L) mice with M344, at doses as low as 3 mg/kg, significantly prevented cognitive decline evaluated by Y-maze spontaneous alternation, novel object recognition, and Barnes maze spatial memory tests. M344 displays short brain exposure, indicating that brief pulses of daily drug treatment may be sufficient for long-term efficacy. Together, these data show that M344 normalizes several disparate pathogenic pathways related to AD. M344 therefore serves as an example of how a multitargeting compound could be used to address the polygenic nature of multifactorial diseases.

Dimerization leads to changes in APP (amyloid precursor protein) trafficking mediated by LRP1 and SorLA.

Proteolytic cleavage of the amyloid precursor protein (APP) by α-, ß- and γ-secretases is a determining factor in Alzheimer's disease (AD). Imbalances in the activity of all three enzymes can result in alterations towards pathogenic Aß production. Proteolysis of APP is strongly linked to its subcellular localization as the secretases involved are distributed in different cellular compartments. APP has been shown to dimerize in cis-orientation, affecting Aß production. This might be explained by different substrate properties defined by the APP oligomerization state or alternatively by altered APP monomer/dimer localization. We investigated the latter hypothesis using two different APP dimerization systems in HeLa cells. Dimerization caused a decreased localization of APP to the Golgi and at the plasma membrane, whereas the levels in the ER and in endosomes were increased. Furthermore, we observed via live cell imaging and biochemical analyses that APP dimerization affects its interaction with LRP1 and SorLA, suggesting that APP dimerization modulates its interplay with sorting molecules and in turn its localization and processing. Thus, pharmacological approaches targeting APP oligomerization properties might open novel strategies for treatment of AD.

Phosphorylation Signaling in APP Processing in Alzheimer's Disease.

The abnormal accumulation of amyloid-ß (Aß) in the central nervous system is a hallmark of Alzheimer's disease (AD). The regulation of the processing of the single- transmembrane amyloid precursor protein (APP) plays an important role in the generation of Aß in the brain. The phosphorylation of APP and key enzymes involved in the proteolytic processing of APP has been demonstrated to be critical for modulating the generation of Aß by either altering the subcellular localization of APP or changing the enzymatic activities of the secretases responsible for APP processing. In addition, the phosphorylation may also have an impact on the physiological function of these proteins. In this review, we summarize the kinases and signaling pathways that may participate in regulating the phosphorylation of APP and secretases and how this further affects the function and processing of APP and Aß pathology. We also discuss the potential of approaches that modulate these phosphorylation-signaling pathways or kinases as interventions for AD pathology.

Regulation of Synaptic Amyloid-ß Generation through BACE1 Retrograde Transport in a Mouse Model of Alzheimer's Disease.

Amyloid-ß (Aß) peptides play a key role in synaptic damage and memory deficits in the early pathogenesis of Alzheimer's disease (AD). Abnormal accumulation of Aß at nerve terminals leads to synaptic pathology and ultimately to neurodegeneration. ß-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the major neuronal ß-secretase for Aß generation. However, the mechanisms regulating BACE1 distribution in axons and ß cleavage of APP at synapses remain largely unknown. Here, we reveal that dynein-Snapin-mediated retrograde transport regulates BACE1 trafficking in axons and APP processing at presynaptic terminals. BACE1 is predominantly accumulated within late endosomes at the synapses of AD-related mutant human APP (hAPP) transgenic (Tg) mice and patient brains. Defective retrograde transport by genetic ablation of snapin in mice recapitulates late endocytic retention of BACE1 and increased APP processing at presynaptic sites. Conversely, overexpressing Snapin facilitates BACE1 trafficking and reduces synaptic BACE1 accumulation by enhancing the removal of BACE1 from distal AD axons and presynaptic terminals. Moreover, elevated Snapin expression via stereotactic hippocampal injections of adeno-associated virus particles in mutant hAPP Tg mouse brains decreases synaptic Aß levels and ameliorates synapse loss, thus rescuing cognitive impairments associated with hAPP mice. Altogether, our study provides new mechanistic insights into the complex regulation of BACE1 trafficking and presynaptic localization through Snapin-mediated dynein-driven retrograde axonal transport, thereby suggesting a potential approach of modulating Aß levels and attenuating synaptic deficits in AD.SIGNIFICANCE STATEMENT ß-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) trafficking and synaptic localization significantly influence its ß secretase activity and amyloid-ß (Aß) production. In AD brains, BACE1 is accumulated within dystrophic neurites, which is thought to augment Aß-induced synaptotoxicity by Aß overproduction. However, it remains largely unknown whether axonal transport regulates synaptic APP processing. Here, we demonstrate that Snapin-mediated retrograde transport plays a critical role in removing BACE1 from presynaptic terminals toward the soma, thus reducing synaptic Aß production. Adeno-associated virus-mediated Snapin overexpression in the hippocampus of mutant hAPP mice significantly decreases synaptic Aß levels, attenuates synapse loss, and thus rescues cognitive deficits. Our study uncovers a new pathway that controls synaptic APP processing by enhancing axonal BACE1 trafficking, thereby advancing our fundamental knowledge critical for ameliorating Aß-linked synaptic pathology.

Autophagy-mediated Regulation of BACE1 Protein Trafficking and Degradation.

ß-Site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is the major neuronal ß-secretase for amyloid-ß generation and is degraded in lysosomes. The autophagy-lysosomal system plays a key role in the maintenance of cellular homeostasis in neurons. Recent studies established that nascent autophagosomes in distal axons move predominantly in the retrograde direction toward the soma, where mature lysosomes are mainly located. However, it remains unknown whether autophagy plays a critical role in regulation of BACE1 trafficking and degradation. Here, we report that induction of neuronal autophagy enhances BACE1 turnover, which is suppressed by lysosomal inhibition. A significant portion of BACE1 is recruited to the autophagy pathway and co-migrates robustly with autophagic vacuoles along axons. Moreover, we reveal that autophagic vacuole-associated BACE1 is accumulated in the distal axon of Alzheimer's disease-related mutant human APP transgenic neurons and mouse brains. Inducing autophagy in mutant human APP neurons augments autophagic retention of BACE1 in distal axons, leading to enhanced ß-cleavage of APP. This phenotype can be reversed by Snapin-enhanced retrograde transport, which facilitates BACE1 trafficking to lysosomes for degradation. Therefore, our study provides new insights into autophagy-mediated regulation of BACE1 turnover and APP processing, thus building a foundation for future development of potential Alzheimer's disease therapeutic strategies.

Effects of cholesterol transport inhibitor U18666A on APP metabolism in rat primary astrocytes.

Amyloid ß (Aß) peptides generated from the amyloid precursor protein (APP) play an important role in the degeneration of neurons and development of Alzheimer's disease (AD). Current evidence indicates that high levels of cholesterol-which increase the risk of developing AD-can influence Aß production in neurons. However, it remains unclear how altered level/subcellular distribution of cholesterol in astrocytes can influence APP metabolism. In this study, we evaluated the effects of cholesterol transport inhibitor U18666A-a class II amphiphile that triggers redistribution of cholesterol within the endosomal-lysosomal (EL) system-on APP levels and metabolism in rat primary cultured astrocytes. Our results revealed that U18666A increased the levels of the APP holoprotein and its cleaved products (α-/ß-/η-CTFs) in cultured astrocytes, without altering the total levels of cholesterol or cell viability. The cellular levels of Aß1-40 were also found to be markedly increased, while secretory levels of Aß1-40 were decreased in U18666A-treated astrocytes. We further report a corresponding increase in the activity of the enzymes regulating APP processing, such as α-secretase, ß-secretase, and γ-secretase as a consequence of U18666A treatment. Additionally, APP-cleaved products are partly accumulated in the lysosomes following cholesterol sequestration within EL system possibly due to decreased clearance. Interestingly, serum delipidation attenuated enhanced levels of APP and its cleaved products following U18666A treatment. Collectively, these results suggest that cholesterol sequestration within the EL system in astrocytes can influence APP metabolism and the accumulation of APP-cleaved products including Aß peptides, which can contribute to the development of AD pathology.

Worsening of memory deficit induced by energy-dense diet in a rat model of early-Alzheimer's disease is associated to neurotoxic Aß species and independent of neuroinflammation.

Diet is a modifiable risk factor for Alzheimer's disease (AD), but the mechanisms linking alterations in peripheral metabolism and cognition remain unclear. Since it is especially difficult to study long-term effects of high-energy diet in individuals at risk for AD, we addressed this question by using the McGill-R-Thy1-APP transgenic rat model (Tg(+/-)) that mimics presymptomatic AD. Wild-type and Tg(+/-) rats were exposed during 6months to a standard diet or a Western diet (WD), high in saturated fat and sugar. Results from peripheral and hippocampal biochemical analysis and in situ respirometry showed that WD induced a metabolic syndrome and decreased presynaptic bioenergetic parameters without alterations in hippocampal insulin signaling or lipid composition. Cognitive tests, ELISA multiplex, Western blot, immunohistochemistry and RT-qPCR indicated that WD worsened cognition in Tg(+/-) rats, increased hippocampal levels of monomeric Aß isoforms and oligomeric species, promoted deposits of N-Terminal pyroglutamate-Aß (AßN3(pE)) in CA1 pyramidal neurons and interneurons, decreased transcript levels of genes involved in neuroprotective pathways such as Sirtuin-1 and increased nitrated proteins. Our results support the concept that in the presence of early Aß pathology, diet-induced metabolic dysfunctions may contribute as a "second hit" to impair cognition. Noteworthy, such effect is not mediated by higher microglia activation or disruption of blood brain barrier. However, it may be attributed to increased amyloidogenic processing of amyloid precursor protein, generation of AßN3(pE) and dysregulation of pathways governed by Sirtuin-1. This evidence reinforces the implementation of prophylactic interventions in individuals at risk for AD.

Alzheimer's disease-related amyloid-ß1-42 peptide induces the loss of human sperm function.

Characteristically identified as the main component of senile plaques present in patients suffering from Alzheimer's disease, Aß has been detected in human testis and reproductive fluids, but its effect on spermatozoa has not been addressed. The present study evaluated whether the most toxic and aggregant amyloid precursor protein (APP)-proteolytic product, amyloid-ß1-42 (Aß1-42), was capable of affecting sperm functionality. Normozoospermic samples were either exposed to different Aß1-42 doses or to the untreated and scrambled controls for a maximum of 48 h at 37 °C and 5%CO2, and motility, viability and mitochondrial status were evaluated. Additionally, tyrosine phosphorylation was analyzed by immunocytochemistry and acrosomal integrity through PSA-FITC. A shorter treatment period was used to monitor prompt Ca2+ responses. Aß1-42 peptide decreased motility before inducing mitochondrial impairment (p < 0.05; n = 6). Both outcomes became more pronounced with time, reaching their maximal decrease at 48 h, where even 1 µM produced undesirable effects (p < 0.05; n = 6). Aß1-42 peptide also decreased cell survival (p < 0.05; n = 6). Furthermore, although no effects on tyrosine phosphorylation were observed (p > 0.05; n = 6), reduced acrosomal integrity was detected (p < 0.05; n = 7), which was not correlated with viability loss (p > 0.05). In parallel, all Aß1-42 concentrations elicited a [Ca2+]i rise but a significant difference was only observed at 20 µM (p < 0.05; n = 7) and a tendency was obtained with 10 µM (p = 0.053; n = 7). In conclusion, Aß1-42 peptide oligomers impair sperm function in vitro, although further studies are required to determine the clinical relevance of these findings.

Anti-amyloidogenic effects of glycosphingolipid synthesis inhibitors occur independently of ganglioside alterations.

Evidence has suggested that ganglioside abnormalities may be linked to the proteolytic processing of amyloid precursor protein (APP) in Alzheimer's disease (AD) and that pharmacological inhibition of ganglioside synthesis may reduce amyloid ß-peptide (Aß) production. In this study, we assessed the usefulness of two well-established glycosphingolipid (GSL) synthesis inhibitors, the synthetic ceramide analog D-PDMP (1-phenyl 2-decanoylamino-3-morpholino-1-propanol) and the iminosugar N-butyldeoxynojirimycin (NB-DNJ or miglustat), as anti-amyloidogenic drugs in a human cellular model of AD. We found that both GSL inhibitors were able to markedly inhibit Aß production, although affecting differently the APP cleavage. Surprisingly, the L-enantiomer of PDMP, which promotes ganglioside accumulation, acted similarly to D-PDMP to inhibit Aß production. Concurrently, both D- and L-PDMP strongly and equally reduced the levels of long-chain ceramides. Altogether, our data suggested that the anti-amyloidogenic effects of PDMP agents are independent of the altered cellular ganglioside composition, but may result, at least in part, from their ability to reduce ceramide levels. Moreover, our current study established for the first time that NB-DNJ, a drug already used as a therapeutic for Gaucher disease (a lysosomal storage disorder), was also able to reduce Aß production in our cellular model. Therefore, our study provides novel information regarding the possibilities to target amyloidogenic processing of APP through modulation of sphingolipid metabolism and emphasizes the potential of the iminosugar NB-DNJ as a disease modifying therapy for AD.

Aß-induced Golgi fragmentation in Alzheimer's disease enhances Aß production.

Golgi fragmentation occurs in neurons of patients with Alzheimer's disease (AD), but the underlying molecular mechanism causing the defects and the subsequent effects on disease development remain unknown. In this study, we examined the Golgi structure in APPswe/PS1E9 transgenic mouse and tissue culture models. Our results show that accumulation of amyloid beta peptides (Aß) leads to Golgi fragmentation. Further biochemistry and cell biology studies revealed that Golgi fragmentation in AD is caused by phosphorylation of Golgi structural proteins, such as GRASP65, which is induced by Aß-triggered cyclin-dependent kinase-5 activation. Significantly, both inhibition of cyclin-dependent kinase-5 and expression of nonphosphorylatable GRASP65 mutants rescued the Golgi structure and reduced Aß secretion by elevating α-cleavage of the amyloid precursor protein. Our study demonstrates a molecular mechanism for Golgi fragmentation and its effects on amyloid precursor protein trafficking and processing in AD, suggesting Golgi as a potential drug target for AD treatment.

Spirulina maxima Extract Ameliorates Learning and Memory Impairments via Inhibiting GSK-3ß Phosphorylation Induced by Intracerebroventricular Injection of Amyloid-ß 1-42 in Mice.

Spirulina maxima, a microalga containing high levels of protein and many polyphenols, including chlorophyll a and C-phycocyanin, has antioxidant and anti-inflammatory therapeutic effects. However, the mechanisms where by Spirulina maxima ameliorates cognitive disorders induced by amyloid-ß 1-42 (Aß1-42) are not fully understood. In this study, we investigated whether a 70% ethanol extract of Spirulina maxima (SM70EE) ameliorated cognitive impairments induced by an intracerebroventricular injection of Aß1-42 in mice. SM70EE increased the step-through latency time in the passive avoidance test and decreased the escape latency time in the Morris water maze test in Aß1-42-injected mice. SM70EE reduced hippocampal Aß1-42 levels and inhibited amyloid precursor protein processing-associated factors in Aß1-42-injected mice. Additionally, acetylcholinesterase activity was suppressed by SM70EE in Aß1-42-injected mice. Hippocampal glutathione levels were examined to determine the effects of SM70EE on oxidative stress in Aß1-42-injected mice. SM70EE increased the levels of glutathione and its associated factors that were reduced in Aß1-42-injected mice. SM70EE also promoted activation of the brain-derived neurotrophic factor/phosphatidylinositol-3 kinase/serine/threonine protein kinase signaling pathway and inhibited glycogen synthase kinase-3ß phosphorylation. These findings suggested that SM70EE ameliorated Aß1-42-induced cognitive impairments by inhibiting the increased phosphorylation of glycogen synthase kinase-3ß caused by intracerebroventricular injection of Aß1-42 in mice.