Apolipoprotein E-Mimetics Inhibit Neurodegeneration and Restore Cognitive Functions in a Transgenic Drosophila Model of Alzheimer's Disease

Background

Mutations of the amyloid precursor protein gene (APP) are found in familial forms of Alzheimer''s disease (AD) and some lead to the elevated production of amyloid-β-protein (Aβ). While Aβ has been implicated in the causation of AD, the exact role played by Aβ and its APP precursor are still unclear.

Principal Findings

In our study, Drosophila melanogaster transgenics were established as a model to analyze AD-like pathology caused by APP overexpression. We demonstrated that age related changes in the levels and pattern of synaptic proteins accompanied progressive neurodegeneration and impairment of cognitive functions in APP transgenic flies, but that these changes may be independent from the generation of Aβ. Using novel peptide mimetics of Apolipoprotein-E, COG112 or COG133 proved to be neuroprotective and significantly improved the learning and memory of APP transgenic flies.

Conclusions

The development of neurodegeneration and cognitive deficits was corrected by injections of COG112 or COG133, novel mimetics of apolipoprotein-E (apoE) with neuroprotective activities.     

CCL2 Accelerates Microglia-Mediated Aβ Oligomer Formation and Progression of Neurocognitive Dysfunction

Background

The linkages between neuroinflammation and Alzheimer''s disease (AD) pathogenesis are well established. What is not, however, is how specific immune pathways and proteins affect the disease. To this end, we previously demonstrated that transgenic over-expression of CCL2 enhanced microgliosis and induced diffuse amyloid plaque deposition in Tg2576 mice. This rodent model of AD expresses a Swedish β-amyloid (Aβ) precursor protein mutant.

Methodology/Principal Findings

We now report that CCL2 transgene expression accelerates deficits in spatial and working memory and hippocampal synaptic transmission in β-amyloid precursor protein (APP) mice as early as 2–3 months of age. This is followed by increased numbers of microglia that are seen surrounding Aβ oligomers. CCL2 does not suppress Aβ degradation. Rather, CCL2 and tumor necrosis factor-α directly facilitated Aβ uptake, intracellular Aβ oligomerization, and protein secretion.

Conclusions/Significance

We posit that CCL2 facilitates Aβ oligomer formation in microglia and propose that such events accelerate memory dysfunction by affecting Aβ seeding in the brain.     

APP Intracellular Domain Impairs Adult Neurogenesis in Transgenic Mice by Inducing Neuroinflammation

Background

A devastating aspect of Alzheimer''s disease (AD) is the progressive deterioration of memory due to neuronal loss. Amyloid precursor protein (APP) occupies a central position in AD and APP-derived amyloid-β (Aβ) peptides are thought to play a pivotal role in disease pathogenesis. Nonetheless, it is becoming clear that AD etiology is highly complex and that factors other than Aβ also contribute to AD pathogenesis. APP intracellular domain (AICD) is generated together with Aβ and we recently showed that AICD transgenic mice recapitulate pathological features of AD such as tau hyperphosphorylation, memory deficits and neurodegeneration without increasing the Aβ levels. Since impaired adult neurogenesis is shown to augment memory deficits in AD mouse models, here we examined the status of adult neurogenesis in AICD transgenic mice.

Methodology/Principal Finding

We previously generated transgenic mice co-expressing 59-residue long AICD fragment and its binding partner Fe65. Hippocampal progenitor cell proliferation was determined by BrdU incorporation at 1.5, 3 and 12 months of age. Only male transgenic and their respective wilt type littermate control mice were used. We find age-dependent decrease in BrdU incorporation and doublecortin-positive cells in the dentate gyrus of AICD transgenic mice suggesting impaired adult neurogenesis. This deficit resulted from decreased proliferation and survival, whereas neuronal differentiation remained unaffected. Importantly, this impairment was independent of Aβ since APP-KO mice expressing AICD also exhibit reduced neurogenesis. The defects in adult neurogenesis are prevented by long-term treatment with the non-steroidal anti-inflammatory agents ibuprofen or naproxen suggesting that neuroinflammation is critically involved in impaired adult neurogenesis in AICD transgenic mice.

Conclusion/Significance

Since adult neurogenesis is crucial for spatial memory, which is particularly vulnerable in AD, these findings suggest that AICD can exacerbate memory defects in AD by impairing adult neurogenesis. Our findings further establish that AICD, in addition to Aβ, contributes to AD pathology and that neuroinflammation plays a much broader role in AD pathogenesis than previously thought.     

Dysregulation of the mTOR Pathway Mediates Impairment of Synaptic Plasticity in a Mouse Model of Alzheimer's Disease

Background

The mammalian target of rapamycin (mTOR) is an evolutionarily conserved Ser/Thr protein kinase that plays a pivotal role in multiple fundamental biological processes, including synaptic plasticity. We explored the relationship between the mTOR pathway and β-amyloid (Aβ)-induced synaptic dysfunction, which is considered to be critical in the pathogenesis of Alzheimer''s disease (AD).

Methodology/Principal Findings

We provide evidence that inhibition of mTOR signaling correlates with impairment in synaptic plasticity in hippocampal slices from an AD mouse model and in wild-type slices exposed to exogenous Aβ1-42. Importantly, by up-regulating mTOR signaling, glycogen synthase kinase 3 (GSK3) inhibitors rescued LTP in the AD mouse model, and genetic deletion of FK506-binding protein 12 (FKBP12) prevented Aβ-induced impairment in long-term potentiation (LTP). In addition, confocal microscopy demonstrated co-localization of intraneuronal Aβ42 with mTOR.

Conclusions/Significance

These data support the notion that the mTOR pathway modulates Aβ-related synaptic dysfunction in AD.     

Modeling Alzheimer’s Disease in Mouse without Mutant Protein Overexpression: Cooperative and Independent Effects of Aβ and Tau

Background

Alzheimer’s disease (AD), the most common cause of dementia in the elderly, has two pathological hallmarks: Aβ plaques and aggregation of hyperphosphorylated tau (p-tau). Aβ is a cleavage product of Amyloid Precursor Protein (APP). Presenilin 1 (PS1) and presenilin 2 (PS2) are the catalytic subunit of γ-secretase, which cleaves APP and mediates Aβ production. Genetic mutations in APP, PSEN1 or PSEN2 can lead to early onset of familial AD (FAD). Although mutations in the tau encoding gene MAPT leads to a subtype of frontotemporal dementia and these mutations have been used to model AD tauopathy, no MAPT mutations have been found to be associated with AD.

Results

To model AD pathophysiology in mice without the gross overexpression of mutant transgenes, we created a humanized AD mouse model by crossing the APP and PSEN1 FAD knock-in mice with the htau mice which express wildtype human MAPT genomic DNA on mouse MAPT null background (APP/PS1/htau). The APP/PS1/htau mice displayed mild, age-dependent, Aβ plaques and tau hyperphosphorylation, thus successfully recapitulating the late-onset AD pathological hallmarks. Selected biochemical analyses, including p-tau western blot, γ-secretase activity assay, and Aβ ELISA, were performed to study the interaction between Aβ and p-tau. Subsequent behavioral studies revealed that the APP/PS1/htau mice showed reduced mobility in old ages and exaggerated fear response. Genetic analysis suggested that the fear phenotype is due to a synergic interaction between Aβ and p-tau, and it can be completely abolished by tau deletion.

Conclusion

The APP/PS1/htau model represents a valuable and disease-relevant late-onset pre-clinical AD animal model because it incorporates human AD genetics without mutant protein overexpression. Analysis of the mice revealed both cooperative and independent effects of Aβ and p-tau.     

Prevalence of Alzheimer’s Pathologic Endophenotypes in Asymptomatic and Mildly Impaired First-Degree Relatives

Objective

A positive family history (FH) is a risk factor for late-onset Alzheimer’s disease (AD). Our aim was to examine the effects of FH on pathological and neuronal loss biomarkers across the cognitive spectrum.

Design

Cross-sectional analyses of data from a national biomarker study.

Setting

The Alzheimer’s Disease Neuroimaging Initiative national study.

Patients

257 subjects (ages 55–89), divided into cognitively normal (CN), mild cognitive impairment (MCI), and AD groups, with CSF and FH data.

Outcome Measures

Cerebrospinal fluid (CSF) Aβ42, tau, and tau/Aβ42 ratio, MRI-measured hippocampal volumes.

Statistics

Univariate and multivariate analyses.

Results

In MCI, CSF Aβ42 was lower (p = .005), t-tau was higher (p = 0.02) and t-tau/Aβ42 ratio was higher (p = 0.002) in FH+ than FH− subjects. A significant residual effect of FH on pathologic markers in MCI remained after adjusting for ApoE4 (p<0.05). Among CN, 47% of FH+ exhibited “pathologic signature of AD” (CSF t-tau/Aβ42 ratio >0.39) versus 21% of FH− controls (p = 0.03). The FH effect was not significant in AD subjects. Hippocampal and intracranial volumes did not differ between FH+ and FH− subjects in any group.

Conclusions

A positive family history of late-onset AD is associated with a higher prevalence of an abnormal cerebral beta-amyloid and tau protein phenotype in MCI. The unexplained genetic heritability in family history is about the half the size of the ApoE4 effect. Longitudinal studies are warranted to more definitively examine this issue.     

Dynamin 1 Regulates Amyloid Generation through Modulation of BACE-1

Background

Several lines of investigation support the notion that endocytosis is crucial for Alzheimer’s disease (AD) pathogenesis. Substantial evidence have already been reported regarding the mechanisms underlying amyloid precursor protein (APP) traffic, but the regulation of beta-site APP-Cleaving Enzyme 1 (BACE-1) distribution among endosomes, TGN and plasma membrane remains unclear. Dynamin, an important adaptor protein that controls sorting of many molecules, has recently been associated with AD but its functions remain controversial. Here we studied possible roles for dynamin 1 (dyn1) in Aβ biogenesis.

Principal Findings

We found that genetic perturbation of dyn1 reduces both secreted and intracellular Aβ levels in cell culture. There is a dramatic reduction in BACE-1 cleavage products of APP (sAPPβ and βCTF). Moreover, dyn1 knockdown (KD) leads to BACE-1 redistribution from the Golgi-TGN/endosome to the cell surface. There is an increase in the amount of surface holoAPP upon dyn1 KD, with resultant elevation of α–secretase cleavage products sAPPα and αCTF. But no changes are seen in the amount of nicastrin (NCT) or PS1 N-terminal fragment (NTF) at cell surface with dyn1 KD. Furthermore, treatment with a selective dynamin inhibitor Dynasore leads to similar reduction in βCTF and Aβ levels, comparable to changes with BACE inhibitor treatment. But combined inhibition of BACE-1 and dyn1 does not lead to further reduction in Aβ, suggesting that the Aβ-lowering effects of dynamin inhibition are mainly mediated through regulation of BACE-1 internalization. Aβ levels in dyn1^−/− primary neurons, as well as in 3-month old dyn1 haploinsufficient animals with AD transgenic background are consistently reduced when compared to their wildtype counterparts.

Conclusions

In summary, these data suggest a previously unknown mechanism by which dyn1 affects amyloid generation through regulation of BACE-1 subcellular localization and therefore its enzymatic activities.     

γ-Secretase Dependent Production of Intracellular Domains Is Reduced in Adult Compared to Embryonic Rat Brain Membranes

Background

γ-Secretase is an intramembrane aspartyl protease whose cleavage of the amyloid precursor protein (APP) generates the amyloid β-peptide (Aβ) and the APP intracellular domain. Aβ is widely believed to have a causative role in Alzheimer''s disease pathogenesis, and therefore modulation of γ-secretase activity has become a therapeutic goal. Besides APP, more than 50 substrates of γ-secretase with different cellular functions during embryogenesis as well as adulthood have been revealed. Prior to γ-secretase cleavage, substrates are ectodomain shedded, producing membrane bound C-terminal fragments (CTFs).

Principal Findings

Here, we investigated γ-secretase cleavage of five substrates; APP, Notch1, N-cadherin, ephrinB and p75 neurotrophin receptor (p75-NTR) in membranes isolated from embryonic, young or old adult rat brain by analyzing the release of the corresponding intracellular domains (ICDs) or Aβ40 by western blot analysis and ELISA respectively. The highest levels of all ICDs and Aβ were produced by embryonic membranes. In adult rat brain only cleavage of APP and Notch1 could be detected and the Aβ40 and ICD production from these substrates was similar in young and old adult rat brain. The CTF levels of Notch1, N-cadherin, ephrinB and p75-NTR were also clearly decreased in the adult brain compared to embryonic brain, whereas the APP CTF levels were only slightly decreased.

Conclusions

In summary our data suggests that γ-secretase dependent ICD production is down-regulated in the adult brain compared to embryonic brain. In addition, the present approach may be useful for evaluating the specificity of γ-secretase inhibitors.     

Ginkgo Biloba Extract Ameliorates Oxidative Phosphorylation Performance and Rescues Aβ-Induced Failure

Background

Energy deficiency and mitochondrial failure have been recognized as a prominent, early event in Alzheimer''s disease (AD). Recently, we demonstrated that chronic exposure to amyloid-beta (Aβ) in human neuroblastoma cells over-expressing human wild-type amyloid precursor protein (APP) resulted in (i) activity changes of complexes III and IV of the oxidative phosphorylation system (OXPHOS) and in (ii) a drop of ATP levels which may finally instigate loss of synapses and neuronal cell death in AD. Therefore, the aim of the present study was to investigate whether standardized Ginkgo biloba extract LI 1370 (GBE) is able to rescue Aβ-induced defects in energy metabolism.

Methodology/Principal Findings

We used a high-resolution respiratory protocol to evaluate OXPHOS respiratory capacity under physiological condition in control (stably transfected with the empty vector) and APP cells after treatment with GBE. In addition, oxygen consumption of isolated mitochondria, activities of mitochondrial respiratory enzymes, ATP and reactive oxygen species (ROS) levels as well as mitochondrial membrane mass and mitochondrial DNA content were determined. We observed a general antioxidant effect of GBE leading to an increase of the coupling state of mitochondria as well as energy homeostasis and a reduction of ROS levels in control cells and in APP cells. GBE effect on OXPHOS was even preserved in mitochondria after isolation from treated cells. Moreover, these functional data were paralleled by an up-regulation of mitochondrial DNA. Improvement of the OXPHOS efficiency was stronger in APP cells than in control cells. In APP cells, the GBE-induced amelioration of oxygen consumption most likely arose from the modulation and respective normalization of the Aβ-induced disturbance in the activity of mitochondrial complexes III and IV restoring impaired ATP levels possibly through decreasing Aβ and oxidative stress level.

Conclusions/Significance

Although the underlying molecular mechanisms of the mode of action of GBE remain to be determined, our study clearly highlights the beneficial effect of GBE on the cellular OXPHOS performance and restoration of Aβ-induced mitochondrial dysfunction.     

Longitudinal Study of CSF Biomarkers in Patients with Alzheimer's Disease

Background

The CSF biomarkers tau and Aβ42 can identify patients with AD, even during the preclinical stages. However, previous studies on longitudinal changes of tau and Aβ42 in individual patients with AD and elderly controls report somewhat inconsistent results.

Methodology/Principal Findings

We investigated the levels of tau and Aβ42 at baseline and after 1 year in 100 patients with AD. In a second cohort of 45 AD patients we measured the CSF biomarkers at baseline and after 2 years. Moreover, in 34 healthy elderly controls the CSF biomarkers were followed for 4 years. The baseline levels of tau were increased with >60% in AD patients compared to controls (p<0.001), while baseline Aβ42 levels were decreased with >50% (p<0.001). In the AD group followed for 2 years, tau increased with 16% compared to the baseline levels (p<0.05). However, the levels of tau were stable over 4 years in the controls. The levels of Aβ42 did not change significantly over time in any of the groups. In the patients with AD, tau was moderately associated with worse cognitive performance already at baseline (p<0.05).

Conclusions/Significance

Tau and Aβ42 in CSF seem to reflect the underlying disease state in both early and late stages of AD. The slight increase in tau over time observed in the patients with AD is modest when compared to the relatively large difference in absolute tau levels between AD patients and controls. Therefore, these markers maintain their usefulness as state markers over time and might serve as surrogate markers for treatment efficacy in clinical trials.     

The Alzheimer's Disease-Associated Amyloid β-Protein Is an Antimicrobial Peptide

Background

The amyloid β-protein (Aβ) is believed to be the key mediator of Alzheimer''s disease (AD) pathology. Aβ is most often characterized as an incidental catabolic byproduct that lacks a normal physiological role. However, Aβ has been shown to be a specific ligand for a number of different receptors and other molecules, transported by complex trafficking pathways, modulated in response to a variety of environmental stressors, and able to induce pro-inflammatory activities.

Methodology/Principal Findings

Here, we provide data supporting an in vivo function for Aβ as an antimicrobial peptide (AMP). Experiments used established in vitro assays to compare antimicrobial activities of Aβ and LL-37, an archetypical human AMP. Findings reveal that Aβ exerts antimicrobial activity against eight common and clinically relevant microorganisms with a potency equivalent to, and in some cases greater than, LL-37. Furthermore, we show that AD whole brain homogenates have significantly higher antimicrobial activity than aged matched non-AD samples and that AMP action correlates with tissue Aβ levels. Consistent with Aβ-mediated activity, the increased antimicrobial action was ablated by immunodepletion of AD brain homogenates with anti-Aβ antibodies.

Conclusions/Significance

Our findings suggest Aβ is a hitherto unrecognized AMP that may normally function in the innate immune system. This finding stands in stark contrast to current models of Aβ-mediated pathology and has important implications for ongoing and future AD treatment strategies.     

Ginsenoside Rg1 Decreases Aβ1–42 Level by Upregulating PPARγ and IDE Expression in the Hippocampus of a Rat Model of Alzheimer's Disease

Background and Purpose

The present study was designed to examine the effects of ginsenoside Rg1 on expression of peroxisome proliferator-activated receptor γ (PPARγ) and insulin-degrading enzyme (IDE) in the hippocampus of rat model of Alzheimer''s disease (AD) to determine how ginsenoside Rg1 (Rg1) decreases Aβ levels in AD.

Experimental Approach

Experimental AD was induced in rats by a bilateral injection of 10 µg soluble beta-amyloid peptide 1–42 (Aβ_1–42) into the CA1 region of the hippocampus, and the rats were treated with Rg1 (10 mg·kg⁻¹, intraperitoneally) for 28 days. The Morris water maze was used to test spatial learning and memory performance. Hematoxylin-eosin staining was performed to analyze the hippocampal histopathological damage. Immunohistochemistry, western blotting, and real-time PCR were used to detect Aβ_1–42, PPARγ, and insulin-degrading enzyme (IDE) expression in the hippocampus.

Key Results

Injection of soluble Aβ_1–42 into the hippocampus led to significant dysfunction of learning and memory, hippocampal histopathological abnormalities and increased Aβ_1–42 levels in the hippocampus. Rg1 treatment significantly improved learning and memory function, attenuated hippocampal histopathological abnormalities, reduced Aβ_1–42 levels and increased PPARγ and IDE expression in the hippocampus; these effects of Rg1 could be effectively inhibited by GW9662, a PPARγ antagonist.

Conclusions and Implications

Given that PPARγ can upregulate IDE expression and IDE can degrade Aβ_1–42, these results indicate that Rg1 can increase IDE expression in the hippocampus by upregulating PPARγ, leading to decreased Aβ levels, attenuated hippocampal histopathological abnormalities and improved learning and memory in a rat model of AD.     

Low-Density Lipoprotein Receptor-Related Protein 1 (LRP1) Mediates Neuronal Aβ42 Uptake and Lysosomal Trafficking

Background

Alzheimer''s disease (AD) is characterized by the presence of early intraneuronal deposits of amyloid-β 42 (Aβ42) that precede extracellular amyloid deposition in vulnerable brain regions. It has been hypothesized that endosomal/lysosomal dysfunction might be associated with the pathological accumulation of intracellular Aβ42 in the brain. Our previous findings suggest that the LDL receptor-related protein 1 (LRP1), a major receptor for apolipoprotein E, facilitates intraneuronal Aβ42 accumulation in mouse brain. However, direct evidence of neuronal endocytosis of Aβ42 through LRP1 is lacking.

Methodology/Principal Findings

Here we show that LRP1 endocytic function is required for neuronal Aβ42 uptake. Overexpression of a functional LRP1 minireceptor, mLRP4, increases Aβ42 uptake and accumulation in neuronal lysosomes. Conversely, knockdown of LRP1 expression significantly decreases neuronal Aβ42 uptake. Disruptions of LRP1 endocytic function by either clathrin knockdown or by removal of its cytoplasmic tail decreased both uptake and accumulation of Aβ42 in neurons. Finally, we show that LRP1-mediated neuronal accumulation of Aβ42 is associated with increased cellular toxicity.

Conclusions/Significance

These results demonstrate that LRP1 endocytic function plays an important role in the uptake and accumulation of Aβ42 in neuronal lysosomes. These findings emphasize the central function of LRP1 in neuronal Aβ metabolism.     

Allosteric Modulation of PS1/γ-Secretase Conformation Correlates with Amyloid β42/40 Ratio

Background

Presenilin 1(PS1) is the catalytic subunit of γ-secretase, the enzyme responsible for the Aβ C-terminal cleavage site, which results in the production of Aβ peptides of various lengths. Production of longer forms of the Aβ peptide occur in patients with autosomal dominant Alzheimer disease (AD) due to mutations in presenilin. Many modulators of γ-secretase function have been described. We hypothesize that these modulators act by a common mechanism by allosterically modifying the structure of presenilin.

Methodology/Principal Findings

To test this hypothesis we generated a genetically encoded GFP-PS1-RFP (G-PS1-R) FRET probe that allows monitoring of the conformation of the PS1 molecule in its native environment in live cells. We show that G-PS1-R can be incorporated into the γ-secretase complex, reconstituting its activity in PS1/2 deficient cells. Using Förster resonance energy transfer (FRET)-based approaches we show that various pharmacological and genetic manipulations that target either γ-secretase components (PS1, Pen2, Aph1) or γ-secretase substrate (amyloid precursor protein, APP) and are known to change Aβ₄₂ production are associated with a consistent conformational change in PS1.

Conclusions/Significance

These results strongly support the hypothesis that allosteric changes in PS1 conformation underlie changes in the Aβ_42/40 ratio. Direct measurement of physiological and pathological changes in the conformation of PS1/γ-secretase may provide insight into molecular mechanism of Aβ₄₂ generation, which could be exploited therapeutically.     

CXCL1 Contributes to β-Amyloid-Induced Transendothelial Migration of Monocytes in Alzheimer’s Disease

Background

Bone marrow-derived microglia that originates in part from hematopoietic cells, and more particularly from monocytes preferentially attach to amyloid deposition in brains of Alzheimer’s disease (AD). However, the mechanism of monocytes recruited into the amyloid plaques with an accelerated process in AD is unclear.

Methodology/Principal Findings

Here we reported that monocytes from AD patients express significantly higher chemokine (C-X-C motif) ligand 1 (CXCL1) compared to age-matched controls. AD patient’s monocytes or CXCL1-overexpressing THP-1 cells had enhanced ability of β-amyloid (Aβ)-induced transendothelial migration and Aβ-induced transendothelial migration for AD patient’s monocytes or CXCL1-overexpressing THP-1 cells was almost abrogated by anti-CXCL1 antibody. Furthermore, monocytes derived from a transgenic mouse model of AD also expressed significantly higher CXCL1. CD11b⁺CD45^hi population of cells that were recruited from the peripheral blood were markedly bolcked in APP mouse brain by anti-CXCL1 antibody. Accordingly, in response to Aβ, human brain microvascular endothelial cells (HBMEC) significantly up-regulated CXC chemokine receptor 2 (CXCR2) expression, which was the only identified receptor for CXCL1. In addition, a high level expression of CXCR2 in HBMEC significantly promoted the CXCL1-overexpressing THP-1 cells transendothelial migration, which could be was abrogated by anti-CXCR2 antibody. Further examination of possible mechanisms found that CXCL1-overexpressing THP-1 cells induced transendothelial electrical resistance decrease, horseradish peroxidase flux increase, ZO-1 discontinuous and occludin re-distribution from insoluble to soluble fraction through interacting with CXCR2. ROCK inhibitor, Y27632, could block CXCL1-overexpressing THP-1 cells transendothelial migration, whereas other inhibitors had no effects.

Conclusions/Significance

The present data indicate that monocytes derived from AD patients overexpressing CXCL1, which is a determinant for Aβ-induced transendothelial migration. CXCL1 expressed by monocytes and CXCR2 on HBMEC is involved in monocytes migrating from blood to brain in AD patients.     

Soluble β-amyloid Precursor Protein Alpha Binds to p75 Neurotrophin Receptor to Promote Neurite Outgrowth

Background

The cleavage of β-amyloid precursor protein (APP) generates multiple proteins: Soluble β-amyloid Precursor Protein Alpha (sAPPα), sAPPβ, and amyloid β (Aβ). Previous studies have shown that sAPPα and sAPPβ possess neurotrophic properties, whereas Aβ is neurotoxic. However, the underlying mechanism of the opposing effects of APP fragments remains poorly understood. In this study, we have investigated the mechanism of sAPPα-mediated neurotrophic effects. sAPPα and sAPPβ interact with p75 neurotrophin receptor (p75^NTR), and sAPPα promotes neurite outgrowth.

Methods and Findings

First, we investigated whether APP fragments interact with p75^NTR, because full-length APP and Aβ have been shown to interact with p75^NTR in vitro. Both sAPPα and sAPPβ were co-immunoprecipitated with p75^NTR and co-localized with p75^NTR on COS-7 cells. The binding affinity of sAPPα and sAPPβ for p75^NTR was confirmed by enzyme-linked immunosorbent assay (ELISA). Next, we investigated the effect of sAPPα on neurite outgrowth in mouse cortical neurons. Neurite outgrowth was promoted by sAPPα, but sAPPα was uneffective in a knockdown of p75^NTR.

Conclusion

We conclude that p75^NTR is the receptor for sAPPα to mediate neurotrophic effects.     

The effect of treadmill exercise on inflammatory responses in rat model of streptozotocin-induced experimental dementia of Alzheimer’s type

[Purpose]

The aim of this study was to investigate the effect of treadmill exercise on inflammatory response in streptozotocin (STZ)-induced animal model of Alzheimer’s disease (AD).

[Methods]

To induce the animal model of AD, Sprague-Dawley rats were injected into intracerebroventricular (ICV) injection with 1.5 mg/kg of STZ. Rats were divided into three groups as Sham-con group (n = 7), STZ-con group (n = 7) and STZ-exe group (n = 7). Exercise group ran on the treadmill for 30 min/day, 5 days/week during 6 weeks.

[Results]

The results of this study were as follows: First, STZ-exe group was improved on cognitive function when compared to STZ-con group in water maze test. Second, STZ-exe group help reduce the expression level of amyloid-beta (Aβ). In addition, Toll-like receptors-4 (TLR4), Nuclear factor-kB (NF-kB), Tumor necrosis factor-α (TNF-α) and Interleukin-1α (IL-1α) level of STZ-exe group was significantly decreased when compared to STZ-con group.

[Conclusion]

These results show that treadmill exercise had positive effect on cognitive function and reduced inflammatory response in STZ-induced animal model of AD.     

Amyloid Precursor Protein Mediated Changes in Intestinal Epithelial Phenotype In Vitro

Background

Although APP and its proteolytic metabolites have been well examined in the central nervous system, there remains limited information of their functions outside of the brain. For example, amyloid precursor protein (APP) and amyloid beta (Aβ) immunoreactivity have both been demonstrated in intestinal epithelial cells. Based upon the critical role of these cells in absorption and secretion, we sought to determine whether APP or its metabolite amyloid β (Aβ), had a definable function in these cells.

Methodology/Principal Findings

The human colonic epithelial cell line, Caco-2 cells, were cultured to examine APP expression and Aβ secretion, uptake, and stimulation. Similar to human colonic epithelium stains, Caco-2 cells expressed APP. They also secreted Aβ 1-40 and Aβ 1-42, with LPS stimulating higher concentrations of Aβ 1-40 secretion. The cells also responded to Aβ 1-40 stimulation by increasing IL-6 cytokine secretion and decreasing cholesterol uptake. Conversely, stimulation with a sAPP-derived peptide increased cholesterol uptake. APP was associated with CD36 but not FATP4 in co-IP pull down experiments from the Caco-2 cells. Moreover, stimulation of APP with an agonist antibody acutely decreased CD36-mediated cholesterol uptake.

Conclusions/Significance

APP exists as part of a multi-protein complex with CD36 in human colonic epithelial cells where its proteolytic fragments have complex, reciprocal roles in regulating cholesterol uptake. A biologically active peptide fragment from the N-terminal derived, sAPP, potentiated cholesterol uptake while the β secretase generated product, Aβ1-40, attenuated it. These data suggest that APP is important in regulating intestinal cholesterol uptake in a fashion dependent upon specific proteolytic pathways. Moreover, this biology may be applicable to cells beyond the gastrointestinal tract.     

Effects of treadmill exercise on brain insulin signaling and β-amyloid in intracerebroventricular streptozotocin induced-memory impairment in rats

[Purpose]

The purpose of the study is to explore effect of 6 weeks treadmill exercise on brain insulin signaling and β-amyloid(Aβ).

[Methods]

The rat model of Alzheimer’s disease(AD) used in the present study was induced by the intracerebroventricular(ICV) streptozotocin(STZ). To produce the model of animal with AD, STZ(1.5mg/kg) was injected to a cerebral ventricle of both cerebrums of Sprague-Dawley rat(20 weeks). The experimental animals were divided into ICV-Sham(n=7), ICV-STZ CON(n=7), ICV-STZ EXE(n=7). Treadmill exercise was done for 30 min a day, 5 days a week for 6 weeks. Passive avoidance task was carried out before and after treadmill exercise.

[Results]

The results of this study show that treadmill exercise activated Protein kinase B(AKT)/ Glycogen synthase kinase 3α (GSK3α), possibly via activation of insulin receptor(IR) and insulin receptor substrate(IRS) and reduced Aβ in the brain of ICV-STZ rats. More interestingly, treadmill exercise improved cognitive function of ICV-STZ rats. Finally, physical exercise or physical activity gave positive influences on brain insulin signaling pathway.

[Conclusion]

Therefore, treadmill exercise can be applied to improve AD as preventive and therapeutic method.     

The Native Copper- and Zinc- Binding Protein Metallothionein Blocks Copper-Mediated Aβ Aggregation and Toxicity in Rat Cortical Neurons

Background

A major pathological hallmark of AD is the deposition of insoluble extracellular β-amyloid (Aβ) plaques. There are compelling data suggesting that Aβ aggregation is catalysed by reaction with the metals zinc and copper.

Methodology/Principal Findings

We now report that the major human-expressed metallothionein (MT) subtype, MT-2A, is capable of preventing the in vitro copper-mediated aggregation of Aβ_1–40 and Aβ_1–42. This action of MT-2A appears to involve a metal-swap between Zn₇MT-2A and Cu(II)-Aβ, since neither Cu₁₀MT-2A or carboxymethylated MT-2A blocked Cu(II)-Aβ aggregation. Furthermore, Zn₇MT-2A blocked Cu(II)-Aβ induced changes in ionic homeostasis and subsequent neurotoxicity of cultured cortical neurons.

Conclusions/Significance

These results indicate that MTs of the type represented by MT-2A are capable of protecting against Aβ aggregation and toxicity. Given the recent interest in metal-chelation therapies for AD that remove metal from Aβ leaving a metal-free Aβ that can readily bind metals again, we believe that MT-2A might represent a different therapeutic approach as the metal exchange between MT and Aβ leaves the Aβ in a Zn-bound, relatively inert form.