Aβ In Neuronal Cells Research Articles

Mechanism for Scavenging of Amyloid-Β by Hybrid Silica Nanobowls: Diagnostic and Therapeutic Applications for AΒ Pathology

Amyloid beta (Aβ) oligomers are a toxic species implicated in Alzheimer's disease. We report hybrid silica nanoparticles – nanobowls (NB), enveloped in a temperature sensitive lipid-polymer coating, with high affinity (Kd 600nM) for Aβ. Attributed to this, we demonstrate that NB scavenge extracellular and membrane associated Aβ in neuronal cells. Time dependent confocal imaging and fluorescence spectrometry elucidate the mechanism by which NB bind Aβ above the coating's transition temperature. Shedding of the coating to cell membranes is reported as the rate-limiting step for scavenging.

Presynaptic Vesicle Protein SEPTIN5 Regulates the Degradation of APP C-Terminal Fragments and the Levels of Aβ.

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by aberrant amyloid-β (Aβ) and hyperphosphorylated tau aggregation. We have previously investigated the involvement of SEPTIN family members in AD-related cellular processes and discovered a role for SEPTIN8 in the sorting and accumulation of β-secretase. Here, we elucidated the potential role of SEPTIN5, an interaction partner of SEPTIN8, in the cellular processes relevant for AD, including amyloid precursor protein (APP) processing and the generation of Aβ. The in vitro and in vivo studies both revealed that the downregulation of SEPTIN5 reduced the levels of APP C-terminal fragments (APP CTFs) and Aβ in neuronal cells and in the cortex of Septin5 knockout mice. Mechanistic elucidation revealed that the downregulation of SEPTIN5 increased the degradation of APP CTFs, without affecting the secretory pathway-related trafficking or the endocytosis of APP. Furthermore, we found that the APP CTFs were degraded, to a large extent, via the autophagosomal pathway and that the downregulation of SEPTIN5 enhanced autophagosomal activity in neuronal cells as indicated by altered levels of key autophagosomal markers. Collectively, our data suggest that the downregulation of SEPTIN5 increases the autophagy-mediated degradation of APP CTFs, leading to reduced levels of Aβ in neuronal cells.

Liraglutide Suppresses Tau Hyperphosphorylation, Amyloid Beta Accumulation through Regulating Neuronal Insulin Signaling and BACE-1 Activity.

Neuronal insulin resistance is a significant feature of Alzheimer’s disease (AD). Accumulated evidence has revealed the possible neuroprotective mechanisms of antidiabetic drugs in AD. Liraglutide, a glucagon-like peptide-1 (GLP-1) analog and an antidiabetic agent, has a benefit in improving a peripheral insulin resistance. However, the neuronal effect of liraglutide on the model of neuronal insulin resistance with Alzheimer’s formation has not been thoroughly investigated. The present study discovered that liraglutide alleviated neuronal insulin resistance and reduced beta-amyloid formation and tau hyperphosphorylation in a human neuroblostoma cell line, SH-SY5Y. Liraglutide could effectively reverse deleterious effects of insulin overstimulation. In particular, the drug reversed the phosphorylation status of insulin receptors and its major downstream signaling molecules including insulin receptor substrate 1 (IRS-1), protein kinase B (AKT), and glycogen synthase kinase 3 beta (GSK-3β). Moreover, liraglutide reduced the activity of beta secretase 1 (BACE-1) enzyme, which then decreased the formation of beta-amyloid in insulin-resistant cells. This indicated that liraglutide can reverse the defect of phosphorylation status of insulin signal transduction but also inhibit the formation of pathogenic Alzheimer’s proteins like Aβ in neuronal cells. We herein provided the possibility that the liraglutide-based therapy may be able to reduce such deleterious effects caused by insulin resistance. In view of the beneficial effects of liraglutide administration, these findings suggest that the use of liraglutide may be a promising therapy for AD with insulin-resistant condition.

MicroRNA 7 Impairs Insulin Signaling and Regulates Aβ Levels through Posttranscriptional Regulation of the Insulin Receptor Substrate 2, Insulin Receptor, Insulin-Degrading Enzyme, and Liver X Receptor Pathway.

Brain insulin resistance is a key pathological feature contributing to obesity, diabetes, and neurodegenerative disorders, including Alzheimer's disease (AD). Besides the classic transcriptional mechanism mediated by hormones, posttranscriptional regulation has recently been shown to regulate a number of signaling pathways that could lead to metabolic diseases. Here, we show that microRNA 7 (miR-7), an abundant microRNA in the brain, targets insulin receptor (INSR), insulin receptor substrate 2 (IRS-2), and insulin-degrading enzyme (IDE), key regulators of insulin homeostatic functions in the central nervous system (CNS) and the pathology of AD. In this study, we found that insulin and liver X receptor (LXR) activators promote the expression of the intronic miR-7-1 in vitro and in vivo, along with its host heterogeneous nuclear ribonucleoprotein K (HNRNPK) gene, encoding an RNA binding protein (RBP) that is involved in insulin action at the posttranscriptional level. Our data show that miR-7 expression is altered in the brains of diet-induced obese mice. Moreover, we found that the levels of miR-7 are also elevated in brains of AD patients; this inversely correlates with the expression of its target genes IRS-2 and IDE. Furthermore, overexpression of miR-7 increased the levels of extracellular Aβ in neuronal cells and impaired the clearance of extracellular Aβ by microglial cells. Taken together, these results represent a novel branch of insulin action through the HNRNPK-miR-7 axis and highlight the possible implication of these posttranscriptional regulators in a range of diseases underlying metabolic dysregulation in the brain, from diabetes to Alzheimer's disease.

1,25(OH)2D3 Protects SH‐SY5Y Human Neuroblastoma Through Decreasing Aβ Toxicity and Reducing Tau Protein Hyperphosphorylation

The accumulation of β amyloid (Aβ) and intracellular tau protein hyperphosphorylation in the brain are the major pathological features of Alzheimer's disease (AD), leading to neuron dysfunctions and brain cell apoptosis. Vit.D has been shown to promote cell survival through increasing the expression of GDNF. In this study, we investigated the preventive effects of 1,25(OH)2D3 on Aβ‐induced toxicity to SH‐SY5Y human neuroblastoma cells. 1,25(OH)2D3 was pre‐treated to the cells at concentrations of 0.1, 1, 10, and 100 nM 24 hours before 24 hours Aβ (1 μM) treatment. It was found that 1,25(OH)2D3 increased GDNF protein expression, activated the phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) pathway and decreased cell tau protein hyperphosphorylation and apoptosis in SH‐SY5Y cells treated with Aβ after the 1,25(OH)2D3 pre‐treatment. In conclusion, 1,25(OH)2D3 showed potentials in protecting the detrimental effects caused by Aβ in neuronal cells.

DPP-4 Inhibitor Linagliptin Attenuates Aβ-induced Cytotoxicity through Activation of AMPK in Neuronal Cells.

SummaryAimIt is now clear that insulin signaling has important roles in regulation of neuronal functions in the brain. Dysregulation of brain insulin signaling has been linked to neurodegenerative disease, particularly Alzheimer's disease (AD). In this regard, there is evidence that improvement of neuronal insulin signaling has neuroprotective activity against amyloid β (Aβ)‐induced neurotoxicity for patients with AD. Linagliptin is an inhibitor of dipeptidylpeptidase‐4 (DPP‐4), which improves impaired insulin secretion and insulin downstream signaling in the in peripheral tissues. However, whether the protective effects of linagliptin involved in Aβ‐mediated neurotoxicity have not yet been investigated.MethodsIn the present study, we evaluated the mechanisms by which linagliptin protects against Aβ‐induced impaired insulin signaling and cytotoxicity in cultured SK‐N‐MC human neuronal cells.ResultsOur results showed that Aβ impairs insulin signaling and causes cell death. However, linagliptin significantly protected against Aβ‐induced cytotoxicity, and prevented the activation of glycogen synthase kinase 3β (GSK3β) and tau hyperphosphorylation by restoring insulin downstream signaling. Furthermore, linagliptin alleviated Aβ‐induced mitochondrial dysfunction and intracellular ROS generation, which may be due to the activation of 5′ AMP‐activated protein kinase (AMPK)‐Sirt1 signaling. This upregulation of Sirt1 expression was also observed in diabetic patients with AD coadministration of linagliptin.ConclusionsTaken together, our findings suggest linagliptin can restore the impaired insulin signaling caused by Aβ in neuronal cells, suggesting DPP‐4 inhibitors may have therapeutic potential for reducing Aβ‐induced impairment of insulin signaling and neurotoxicity in AD pathogenesis.

ETAS, an Enzyme-treated Asparagus Extract, Attenuates Amyloid β-Induced Cellular Disorder in PC 12 Cells

One of the pathological characterizations of Alzheimer's disease (AD) is the deposition of amyloid beta peptide (Abeta) in cerebral cortical cells. The deposition of Abeta in neuronal cells leads to an increase in the production of free radicals that are typified by reactive oxygen species (ROS), thereby inducing cell death. A growing body of evidence now suggests that several plant-derived food ingredients are capable of scavenging ROS in mammalian cells. The purpose of the present study was to investigate whether enzyme-treated asparagus extract (ETAS), which is rich in antioxidants, is one of these ingredients. The pre-incubation of differentiated PC 12 cells with ETAS significantly recovered Abeta-induced reduction of cell viability, which was accompanied by reduced levels of ROS. These results suggest that ETAS may be one of the functional food ingredients with anti-oxidative capacity to help prevent AD.

The spirostenol (22 R, 25 R)-20α-spirost-5-en-3β-yl hexanoate blocks mitochondrial uptake of Aβ in neuronal cells and prevents Aβ-induced impairment of mitochondrial function

Aβ 1–42 has been shown to uncouple the mitochondrial respiratory chain and promote the opening of the membrane permeability transition (MPT) pore, leading to cell death. We have previously reported that the spirostenol derivative (22 R, 25 R)-20α-spirost-5-en-3β-yl hexanoate (SP-233) protects neuronal cells against Aβ 1–42 toxicity by binding to and inactivating the peptide. Picomolar concentrations of Aβ 1–42 decreased the mitochondrial respiratory coefficient in mitochondria isolated from the rat forebrain, and this decrease was partially reversed by SP-233. SP-233 abolished the uncoupling of oxidative phosphorylation induced by carbonyl cyanide 3-chlorophenylhydrazone on isolated mitochondria. These results are consistent with a direct effect of SP-233 on the MPT. Moreover, SP-233 displayed a neuroprotective effect on SK-N-AS human neuroblastoma cells treated with the MPT promoter, phenylarsine oxide. Treatment of SK-N-AS cells with Aβ 1–42 resulted in an accumulation of the peptide in the mitochondrial matrix; SP-233 completely scavenged Aβ 1–42 from the matrix. In addition, SP-233 protected the cells against mitochondrial toxins targeting complexes IV and V of the respiratory chain. These results indicate that Aβ 1–42 and SP-233 exert direct effects on mitochondrial function and SP-233 protects neuronal cells against Aβ–induced toxicity by targeting Aβ directly.

Protective melatonin effect on oxidative stress induced by okadaic acid into rat brain.

We studied the effect of melatonin on the oxidative changes produced by the intracerebroventricular (i.c.v.) injection of okadaic acid (200 ng/kg BW) in the Wistar rat. The effects of okadaic acid were evaluated as changes in the quantity of lipid peroxides, reduced glutathione content (GSH) and activity of antioxidative enzymes. Okadaic acid caused lipid peroxidation (5.35 +/- 0.47 micro mol/g tissue in the i.c.v. vehicle group versus 10.14 +/- 0.88 micro mol/g tissue in the okadaic acid group, P < 0.001), GSH consumption (0.115 +/- 0.0065 micro mol/g tissue in the i.c.v. vehicle group versus 0.024 +/- 0.0021 micro mol/g tissue, P < 0.001), and a reduction in the activity of GSH-peroxidase, GSH-reductase and GSH-transferase between 60-80%. All these changes were prevented by pre-injection of 4.5 mg melatonin per kg BW 2 hr before okadaic acid. These findings indicate: (i) okadaic acid induces a status of oxidative stress in the brain, characterized by a high level of lipid peroxidation, decreases in GSH content and diminished activities of antioxidative enzymes, and (ii) melatonin prevents the deleterious effects induced by okadaic acid. In conclusion, the results show the ability of melatonin to modify the neural response to okadaic acid with the protective mechanism likely involving the antioxidative processes of melatonin.