Crocetin attenuates inflammation and amyloid-β accumulation in APPsw transgenic mice

Background

Crocetin, an agent derived from saffron, has multiple pharmacological properties, such as neuroprotective, anti-oxidant, and anti-inflammatory actions. These properties might benefit the treatment of Alzheimer’s disease (AD). In the present study, we tested whether crocetin attenuates inflammation and amyloid-β (Aβ) accumulation in APPsw transgenic mice, AD mouse models. Cell viability and the levels of Aβ40 and Aβ42 in HeLa cells stably transfected with Swedish mutant APP751 were evaluated. Mice with Swedish mutant APP751 transgene were used as transgenic mouse models of AD, and were orally administrated with crocetin. Aβ protein and inflammatory cytokines were measured with ELISA. NF-κB and P53 were measured with western blot assay. Learning and memory were analyzed with Morris water maze and novel object recognition tests.

Results

Crocetin significantly reduced Aβ40 and Aβ42 secretion in Hela cells without effecting cell viability. In AD transgenic mice, crocetin significantly reduced the pro-inflammatory cytokines and enhanced anti-inflammatory cytokine in plasma, suppressed NF-κB activation and P53 expression in the hippocampus, decreased Aβ in various brain areas, and improved learning and memory deficits.

Conclusion

Crocetin improves Aβ accumulation-induced learning and memory deficit in AD transgenic mice, probably due to its anti-inflammatory and anti-apoptotic functions.

     

Histopathological and molecular heterogeneity among individuals with dementia associated with Presenilin mutations

Background

Mutations in the presenilin (PSEN) genes are associated with early-onset familial Alzheimer's disease (FAD). Biochemical characterizations and comparisons have revealed that many PSEN mutations alter γ-secretase activity to promote accumulation of toxic Aβ42 peptides. In this study, we compared the histopathologic and biochemical profiles of ten FAD cases expressing independent PSEN mutations and determined the degradation patterns of amyloid-β precursor protein (AβPP), Notch, N-cadherin and Erb-B4 by γ-secretase. In addition, the levels of Aβ40/42 peptides were quantified by ELISA.

Results

We observed a wide variation in type, number and distribution of amyloid deposits and neurofibrillary tangles. Four of the ten cases examined exhibited a substantial enrichment in the relative proportions of Aβ40 over Aβ42. The AβPP N-terminal and C-terminal fragments and Tau species, assessed by Western blots and scanning densitometry, also demonstrated a wide variation. The Notch-1 intracellular domain was negligible by Western blotting in seven PSEN cases. There was significant N-cadherin and Erb-B4 peptide heterogeneity among the different PSEN mutations.

Conclusion

These observations imply that missense mutations in PSEN genes can alter a range of key γ-secretase activities to produce an array of subtly different biochemical, neuropathological and clinical manifestations. Beyond the broad common features of dementia, plaques and tangles, the various PSEN mutations resulted in a wide heterogeneity and complexity and differed from sporadic AD.     

Binding of longer Aβ to transmembrane domain 1 of presenilin 1 impacts on Aβ42 generation

Background

Amyloid-β peptide ending at 42nd residue (Aβ42) is believed as a pathogenic peptide for Alzheimer disease. Although γ-secretase is a responsible protease to generate Aβ through a processive cleavage, the proteolytic mechanism of γ-secretase at molecular level is poorly understood.

Results

We found that the transmembrane domain (TMD) 1 of presenilin (PS) 1, a catalytic subunit for the γ-secretase, as a key modulatory domain for Aβ42 production. Aβ42-lowering and -raising γ-secretase modulators (GSMs) directly targeted TMD1 of PS1 and affected its structure. A point mutation in TMD1 caused an aberrant secretion of longer Aβ species including Aβ45 that are the precursor of Aβ42. We further found that the helical surface of TMD1 is involved in the binding of Aβ45/48 and that the binding was altered by GSMs as well as TMD1 mutation.

Conclusions

Binding between PS1 TMD1 and longer Aβ is critical for Aβ42 production.     

β-Amyloid peptide increases levels of iron content and oxidative stress in human cell and Caenorhabditis elegans models of Alzheimer disease

Recent studies indicate that the deposition of β-amyloid peptide (Aβ) is related to the pathogenesis of Alzheimer disease (AD); however, the underlying mechanism is still not clear. The abnormal interactions of Aβ with metal ions such as iron are implicated in the process of Aβ deposition and oxidative stress in AD brains. In this study, we observed that Aβ increased the levels of iron content and oxidative stress in SH-SY5Y cells overexpressing the Swedish mutant form of human β-amyloid precursor protein (APPsw) and in Caenorhabditis elegans Aβ-expressing strain CL2006. Intracellular iron and calcium levels and reactive oxygen species and nitric oxide generation significantly increased in APPsw cells compared to control cells. The activity of superoxide dismutase and the antioxidant levels of APPsw cells were significantly lower than those of control cells. Moreover, iron treatment decreased cell viability and mitochondrial membrane potential and aggravated oxidative stress damage as well as the release of Aβ1-40 from the APPsw cells. The iron homeostasis disruption in APPsw cells is very probably associated with elevated expression of the iron transporter divalent metal transporter 1, but not transferrin receptor. Furthermore, the C. elegans with Aβ-expression had increased iron accumulation. In aggregate, these results demonstrate that Aβ accumulation in neuronal cells correlated with neuronal iron homeostasis disruption and probably contributed to the pathogenesis of AD.     

Neuroprotective effects of blockers for T-type calcium channels

Background

Activation of the liver × receptors (LXRs) by exogenous ligands stimulates the degradation of β-amyloid 1–42 (Aβ42), a peptide that plays a central role in the pathogenesis of Alzheimer's disease (AD). The oxidized cholesterol products (oxysterols), 24-hydroxycholesterol (24-OHC) and 27-hydroxycholesterol (27-OHC), are endogenous activators of LXRs. However, the mechanisms by which these oxysterols may modulate Aβ42 levels are not well known.

Results

We determined the effect of 24-OHC and/or 27-OHC on Aβ generation in SH-SY5Y cells. We found that while 27-OHC increases levels of Aβ42, 24-OHC did not affect levels of this peptide. Increased Aβ42 levels with 27-OHC are associated with increased levels of β-amyloid precursor protein (APP) as well as β-secretase (BACE1), the enzyme that cleaves APP to yield Aβ. Unchanged Aβ42 levels with 24-OHC are associated with increased levels of sAPPα, suggesting that 24-OHC favors the processing of APP to the non-amyloidogenic pathway. Interestingly, 24-OHC, but not 27-OHC, increases levels of the ATP-binding cassette transporters, ABCA1 and ABCG1, which regulate cholesterol transport within and between cells.

Conclusion

These results suggest that cholesterol metabolites are linked to Aβ42 production. 24-OHC may favor the non-amyloidogenic pathway and 27-OHC may enhance production of Aβ42 by upregulating APP and BACE1. Regulation of 24-OHC: 27-OHC ratio could be an important strategy in controlling Aβ42 levels in AD.     

Silibinin: a novel inhibitor of Aβ aggregation

Alzheimer's disease (AD) is characterized by the abnormal aggregation of amyloid β peptide (Aβ) into extracellular fibrillar deposits known as amyloid plaque. Inhibition of Aβ aggregation is therefore viewed as a potential method to halt or slow the progression of AD. It is reported that silibinin (silybin), a flavonoid derived from the herb milk thistle (Silybum marianum), attenuates cognitive deficits induced by Aβ25-35 peptide and methamphetamine. However, it remains unclear whether silibinin interacts with Aβ peptide directly and decreases Aβ peptide-induced neurotoxicity. In the present study, we identified, through employing a ThT assay and electron microscopic imaging that silibinin also appears to act as a novel inhibitor of Aβ aggregation and this effect showed dose-dependency. We also show that silibinin prevented SH-SY5Y cells from injuries caused by Aβ(1-42)-induced oxidative stress by decreasing H(2)O(2) production in Aβ(1-42)-stressed neurons. Taken together, these results indicate that silibinin may be a novel therapeutic agent for the treatment of AD.     

Pyroglutamate amyloid β (Aβ) aggravates behavioral deficits in transgenic amyloid mouse model for Alzheimer disease

Pyroglutamate-modified Aβ peptides at amino acid position three (Aβ(pE3-42)) are gaining considerable attention as potential key players in the pathogenesis of Alzheimer disease (AD). Aβ(pE3-42) is abundant in AD brain and has a high aggregation propensity, stability and cellular toxicity. The aim of the present work was to study the direct effect of elevated Aβ(pE3-42) levels on ongoing AD pathology using transgenic mouse models. To this end, we generated a novel mouse model (TBA42) that produces Aβ(pE3-42). TBA42 mice showed age-dependent behavioral deficits and Aβ(pE3-42) accumulation. The Aβ profile of an established AD mouse model, 5XFAD, was characterized using immunoprecipitation followed by mass spectrometry. Brains from 5XFAD mice demonstrated a heterogeneous mixture of full-length, N-terminal truncated, and modified Aβ peptides: Aβ(1-42), Aβ(1-40), Aβ(pE3-40), Aβ(pE3-42), Aβ(3-42), Aβ(4-42), and Aβ(5-42). 5XFAD and TBA42 mice were then crossed to generate transgenic FAD42 mice. At 6 months of age, FAD42 mice showed an aggravated behavioral phenotype compared with single transgenic 5XFAD or TBA42 mice. ELISA and plaque load measurements revealed that Aβ(pE3) levels were elevated in FAD42 mice. No change in Aβ(x)(-42) or other Aβ isoforms was discovered by ELISA and mass spectrometry. These observations argue for a seeding effect of Aβ(pE-42) in FAD42 mice.     

Therapeutic effects of remediating autophagy failure in a mouse model of Alzheimer disease by enhancing lysosomal proteolysis

The extensive autophagic-lysosomal pathology in Alzheimer disease (AD) brain has revealed a major defect

in the proteolytic clearance of autophagy substrates. Autophagy failure contributes on several levels to AD pathogenesis and has become an important therapeutic target for AD and other neurodegenerative diseases. We recently observed broad therapeutic effects of stimulating autophagic-lysosomal proteolysis in the TgCRND8 mouse model of AD that exhibits defective proteolytic clearance of autophagic substrates, robust intralysosomal amyloid-β peptide (Aβ) accumulation, extracellular β-amyloid deposition and cognitive deficits. By genetically deleting the lysosomal cysteine protease inhibitor, cystatin B (CstB), to selectively restore depressed cathepsin activities, we substantially cleared Aβ, ubiquitinated proteins and other autophagic substrates from autolysosomes/lysosomes and rescued autophagic-lysosomal pathology, as well as reduced total Aβ40/42 levels and extracellular amyloid deposition, highlighting the underappreciated importance of the lysosomal system for Aβ clearance. Most importantly, lysosomal remediation prevented the marked learning and memory deficits in TgCRND8 mice. Our findings underscore the pathogenic significance of autophagic-lysosomal dysfunction in AD and demonstrate the value of reversing this dysfunction as an innovative therapeautic strategy for AD.     

The Amazonian herbal Marapuama attenuates cognitive impairment and neuroglial degeneration in a mouse Alzheimer model

Alzheimer's disease (AD) is expected to affect more than 22 million people worldwide by 2025, causing devastating suffering and enormous costs to families and society. AD is a multifactorial disease, with a complex pathological mosaic. In rodents, AD-like dementia can be induced by cerebral microinjection of Aβ peptide, leading to amyloid deposits, amnesia and various features of neurodegeneration. Marapuama (Ptychopetalum olacoides) is regarded as a “brain tonic” in the Amazon region and shows a nootropic profile in rodents.

Aim of the study

Because a specific extract (POEE) of Marapuama was shown to possess promnesic and anti-amnesic properties, the aim of this study was to verify if POEE is also effective against Aβ_1-42-induced cognitive deficit in mice. Additionally, Aβ deposits (Congo red), GFAP immunoreactivity (immunohistochemistry), and neurodegenerative changes in the hippocampal pyramidal layer (Nissl) were examined as measures of Aβ_1-42-induced neurodegeneration.

Materials and methods

CF1 mice were subjected to the experimental Alzheimer model with the Aβ_1-42 i.c.v. administration. The effects of POEE 800 mg/kg were evaluated over 14 consecutive days of treatment.

Results

The data show that 14 days of oral treatment with POEE (800 mg/kg) was effective in preventing Aβ-induced cognitive impairment, without altering the levels of BDNF and with parallel reductions in Aβ deposits and astrogliosis. CA1 hippocampus loss induced by Aβ_1-42 was also diminished in POEE-treated mice.

Conclusion

This study offers evidence of functional and neuroprotective effects of two weeks treatment with a Ptychopetalum olacoides extract against Aβ peptide-induced neurotoxicity in mice. Given the multifactorial nature of neurodegeneration, the considerable potential for an AChE inhibitor displaying associated neuroprotective properties such as here reported warrants further clinic evaluation.     

Systemic treatment with liver X receptor agonists raises apolipoprotein E,cholesterol, and amyloid-β peptides in the cerebral spinal fluid of rats

Background

Apolipoprotein E (apoE) is a major cholesterol transport protein found in association with brain amyloid from Alzheimer's disease (AD) patients and the ε4 allele of apoE is a genetic risk factor for AD. Previous studies have shown that apoE forms a stable complex with amyloid β (Aβ) peptides in vitro and that the state of apoE lipidation influences the fate of brain Aβ, i.e., lipid poor apoE promotes Aβ aggregation/deposition while fully lipidated apoE favors Aβ degradation/clearance. In the brain, apoE levels and apoE lipidation are regulated by the liver X receptors (LXRs).

Results

We investigated the hypothesis that increased apoE levels and lipidation induced by LXR agonists facilitates Aβ efflux from the brain to the cerebral spinal fluid (CSF). We also examined if the brain expression of major apoE receptors potentially involved in apoE-mediated Aβ clearance was altered by LXR agonists. ApoE, cholesterol, Aβ40, and Aβ42 levels were all significantly elevated in the CSF of rats after only 3 days of treatment with LXR agonists. A significant reduction in soluble brain Aβ40 levels was also detected after 6 days of LXR agonist treatment.

Conclusions

Our novel findings suggest that central Aβ lowering caused by LXR agonists appears to involve an apoE/cholesterol-mediated transport of Aβ to the CSF and that differences between the apoE isoforms in mediating this clearance pathway may explain why individuals carrying one or two copies of APOE ε4 have increased risk for AD.

     

Structural analysis of the pyroglutamate‐modified isoform of the Alzheimer's disease‐related amyloid‐β using NMR spectroscopy

The aggregation of the Aβ plays a fundamental role in the pathology of AD. Recently, N‐terminally modified Aβ species, pE‐Aβ, have been described as major constituents of Aβ deposits in the brains of AD patients. pE‐Aβ has an increased aggregation propensity and shows increased toxicity compared with Aβ1‐40 and Aβ1‐42. In the present work, high‐resolution NMR spectroscopy was performed to study pE‐Aβ3‐40 in aqueous TFE‐containing solution. Two‐dimensional TOCSY and NOESY experiments were performed. On the basis of NOE and chemical shift data, pE‐Aβ3‐40 was shown to contain two helical regions formed by residues 14–22 and 30–36. This is similar as previously described for Aβ1‐40. However, the secondary chemical shift data indicate decreased helical propensity in pE‐Aβ3‐40 when compared with Aβ1‐40 under exactly the same conditions. This is in agreement with the observation that pE‐Aβ3‐40 shows a drastically increased tendency to form β‐sheet‐rich structures under more physiologic conditions. Structural studies of pE‐Aβ are crucial for better understanding the structural basis of amyloid fibril formation in the brain during development of AD, especially because an increasing number of reports indicate a decisive role of pE‐Aβ for the pathogenesis of AD. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Asymmetric dimethylarginine exacerbates Aβ-induced toxicity and oxidative stress in human cell and Caenorhabditis elegans models of Alzheimer disease

Growing evidence suggests a strong association between cardiovascular risk factors and incidence of Alzheimer disease (AD). Asymmetric dimethylarginine (ADMA), the endogenous nitric oxide synthase inhibitor, has been identified as an independent cardiovascular risk factor and is also increased in plasma of patients with AD. However, whether ADMA is involved in the pathogenesis of AD is unknown. In this study, we found that ADMA content was increased in a transgenic Caenorhabditis elegans β-amyloid (Aβ) overexpression model, strain CL2006, and in human SH-SY5Y cells overexpressing the Swedish mutant form of human Aβ precursor protein (APPsw). Moreover, ADMA treatment exacerbated Aβ-induced paralysis and oxidative stress in CL2006 worms and further elevated oxidative stress and Aβ secretion in APPsw cells. Knockdown of type 1 protein arginine N-methyltransferase to reduce ADMA production failed to show a protective effect against Aβ toxicity, but resulted in more paralysis in CL2006 worms as well as increased oxidative stress and Aβ secretion in APPsw cells. However, overexpression of dimethylarginine dimethylaminohydrolase 1 (DDAH1) to promote ADMA degradation significantly attenuated oxidative stress and Aβ secretion in APPsw cells. Collectively, our data support the hypothesis that elevated ADMA contributes to the pathogenesis of AD. Our findings suggest that strategies to increase DDAH1 activity in neuronal cells may be a novel approach to attenuating AD development.     

Selective antihypertensive dihydropyridines lower Aβ accumulation by targeting both the production and the clearance of Aβ across the blood-brain barrier

Several large population-based or clinical trial studies have suggested that certain dihydropyridine (DHP) L-type calcium channel blockers (CCBs) used for the treatment of hypertension may confer protection against the development of Alzheimer disease (AD). However, other studies with drugs of the same class have shown no beneficial clinical effects. To determine whether certain DHPs are able to impact underlying disease processes in AD (specifically the accumulation of the Alzheimer Aβ peptide), we investigated the effect of several antihypertensive DHPs and non-DHP CCBs on Aβ production. Among the antihypertensive DHPs tested, a few, including nilvadipine, nitrendipine and amlodipine inhibited Aβ production in vitro, whereas others had no effect or raised Aβ levels. In vivo, nilvadipine and nitrendipine acutely reduced brain Aβ levels in a transgenic mouse model of AD (Tg PS1/APPsw) and improved Aβ clearance across the blood-brain barrier (BBB), whereas amlodipine and nifedipine were ineffective showing that the Aβ-lowering activity of the DHPs is independent of their antihypertensive activity. Chronic oral treatment with nilvadipine decreased Aβ burden in the brains of Tg APPsw (Tg2576) and Tg PS1/APPsw mice, and also improved learning abilities and spatial memory. Our data suggest that the clinical benefit conferred by certain antihypertensive DHPs against AD is unrelated to their antihypertensive activity, but rely on their ability to lower brain Aβ accumulation by affecting both Aβ production and Aβ clearance across the BBB.     

Therapeutic effects of remediating autophagy failure in a mouse model of Alzheimer disease by enhancing lysosomal proteolysis

The extensive autophagic-lysosomal pathology in Alzheimer disease (AD) brain has revealed a major defect: in the proteolytic clearance of autophagy substrates. Autophagy failure contributes on several levels to AD pathogenesis and has become an important therapeutic target for AD and other neurodegenerative diseases. We recently observed broad therapeutic effects of stimulating autophagic-lysosomal proteolysis in the TgCRND8 mouse model of AD that exhibits defective proteolytic clearance of autophagic substrates, robust intralysosomal amyloid-β peptide (Aβ) accumulation, extracellular β-amyloid deposition and cognitive deficits. By genetically deleting the lysosomal cysteine protease inhibitor, cystatin B (CstB), to selectively restore depressed cathepsin activities, we substantially cleared Aβ, ubiquitinated proteins and other autophagic substrates from autolysosomes/lysosomes and rescued autophagic-lysosomal pathology, as well as reduced total Aβ40/42 levels and extracellular amyloid deposition, highlighting the underappreciated importance of the lysosomal system for Aβ clearance. Most importantly, lysosomal remediation prevented the marked learning and memory deficits in TgCRND8 mice. Our findings underscore the pathogenic significance of autophagic-lysosomal dysfunction in AD and demonstrate the value of reversing this dysfunction as an innovative therapeautic strategy for AD.     

TUDCA, a Bile Acid, Attenuates Amyloid Precursor Protein Processing and Amyloid-β Deposition in APP/PS1 Mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by accumulation of amyloid-β (Aβ) peptide in the hippocampus and frontal cortex of the brain, leading to progressive cognitive decline. The endogenous bile acid tauroursodeoxycholic acid (TUDCA) is a strong neuroprotective agent in several experimental models of disease, including neuronal exposure to Aβ. Nevertheless, the therapeutic role of TUDCA in AD pathology has not yet been ascertained. Here we report that feeding APP/PS1 double-transgenic mice with diet containing 0.4 % TUDCA for 6 months reduced accumulation of Aβ deposits in the brain, markedly ameliorating memory deficits. This was accompanied by reduced glial activation and neuronal integrity loss in TUDCA-fed APP/PS1 mice compared to untreated APP/PS1 mice. Furthermore, TUDCA regulated lipid-metabolism mediators involved in Aβ production and accumulation in the brains of transgenic mice. Overall amyloidogenic APP processing was reduced with TUDCA treatment, in association with, but not limited to, modulation of γ-secretase activity. Consequently, a significant decrease in Aβ(1-40) and Aβ(1-42) levels was observed in both hippocampus and frontal cortex of TUDCA-treated APP/PS1 mice, suggesting that chronic feeding of TUDCA interferes with Aβ production, possibly through the regulation of lipid-metabolism mediators associated with APP processing. These results highlight TUDCA as a potential therapeutic strategy for the prevention and treatment of AD.     

The Osaka FAD mutation E22Δ leads to the formation of a previously unknown type of amyloid β fibrils and modulates Aβ neurotoxicity

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cerebral deposition of amyloid fibrils formed by the amyloid β (Aβ) peptide. Aβ has a length of 39-43 amino acid residues; the predominant Aβ isoforms are Aβ1-40 and Aβ1-42. While the majority of AD cases occur spontaneously, a subset of early-onset familial AD cases is caused by mutations in the genes encoding the Aβ precursor protein or presenilin 1/presenilin 2. Recently, a deletion of glutamic acid at position 22 within the Aβ sequence (E22Δ) was identified in Japanese patients with familial dementia, but the aggregation properties of the deletion variant of Aβ are not well understood. We investigated the aggregation characteristics and neurotoxicity of recombinantly expressed Aβ isoforms 1-40 and 1-42 with and without the E22Δ mutation. We show that the E22Δ mutation strongly accelerates the fibril formation of Aβ1-42 E22Δ compared to Aβ1-42 wild type (wt). In addition, we demonstrate that fibrils of Aβ1-40 E22Δ form a unique quaternary structure characterized by a strong tendency to form fibrillar bundles and a strongly increased thioflavin T binding capacity. Aβ1-40 E22Δ was neurotoxic in rat primary neuron cultures as compared to nontoxic Aβ1-40 wt. Aβ1-42 E22Δ was less toxic than Aβ1-42 wt, but it significantly decreased neurite outgrowth per cell in neuronal primary cultures. Because Aβ1-40 is the major Aβ form in vivo, the gain of toxic function caused by the E22 deletion may explain the development of familial AD in mutation carriers.     

Amyloid-beta42 interacts mainly with insoluble prion protein in the Alzheimer brain

The prion protein (PrP) is best known for its association with prion diseases. However, a controversial new role for PrP in Alzheimer disease (AD) has recently emerged. In vitro studies and mouse models of AD suggest that PrP may be involved in AD pathogenesis through a highly specific interaction with amyloid-β (Aβ42) oligomers. Immobilized recombinant human PrP (huPrP) also exhibited high affinity and specificity for Aβ42 oligomers. Here we report the novel finding that aggregated forms of huPrP and Aβ42 are co-purified from AD brain extracts. Moreover, an anti-PrP antibody and an agent that specifically binds to insoluble PrP (iPrP) co-precipitate insoluble Aβ from human AD brain. Finally, using peptide membrane arrays of 99 13-mer peptides that span the entire sequence of mature huPrP, two distinct types of Aβ binding sites on huPrP are identified in vitro. One specifically binds to Aβ42 and the other binds to both Aβ42 and Aβ40. Notably, Aβ42-specific binding sites are localized predominantly in the octapeptide repeat region, whereas sites that bind both Aβ40 and Aβ42 are mainly in the extreme N-terminal or C-terminal domains of PrP. Our study suggests that iPrP is the major PrP species that interacts with insoluble Aβ42 in vivo. Although this work indicated the interaction of Aβ42 with huPrP in the AD brain, the pathophysiological relevance of the iPrP/Aβ42 interaction remains to be established.     

Expression profiling in APP23 mouse brain: inhibition of Aβ amyloidosis and inflammation in response to LXR agonist treatment

Background

Recent studies demonstrate that in addition to its modulatory effect on APP processing, in vivo application of Liver X Receptor agonist T0901317 (T0) to APP transgenic and non-transgenic mice decreases the level of Aβ_42. Moreover, in young Tg2576 mice T0 completely reversed contextual memory deficits. Compared to other tissues, the regulatory functions of LXRs in brain remain largely unexplored and our knowledge so far is limited to the cholesterol transporters and apoE. In this study we applied T0 to APP23 mice for various times and examined gene and protein expression. We also performed a series of experiments with primary brain cells derived from wild type and LXR knockout mice subjected to various LXR agonist treatments and inflammatory stimuli.

Results

We demonstrate an upregulation of genes related to lipid metabolism/transport, metabolism of xenobiotics and detoxification. Downregulated genes are involved in immune response and inflammation, cell death and apoptosis. Additional treatment experiments demonstrated an increase of soluble apolipoproteins E and A-I and a decrease of insoluble Aβ. In primary LXR^wt but not in LXRα^-/-β^-/- microglia and astrocytes LXR agonists suppressed the inflammatory response induced by LPS or fibrillar Aβ.

Conclusion

The results show that LXR agonists could alleviate AD pathology by acting on amyloid deposition and brain inflammation. An increased understanding of the LXR controlled regulation of Aβ aggregation and clearance systems will lead to the development of more specific and powerful agonists targeting LXR for the treatment of AD.     

Loss of neprilysin alters protein expression in the brain of Alzheimer's disease model mice

Alzheimer's disease (AD) is a neurodegenerative disease displaying extracellular plaques formed by the neurotoxic amyloid β‐peptide (Aβ), and intracellular neurofibrillary tangles consisting of protein tau. However, how these pathologies relate to the massive neuronal death that occurs in AD brains remain elusive. Neprilysin is the major Aβ‐degrading enzyme and a lack thereof increases Aβ levels in the brain twofold. To identify altered protein expression levels induced by increased Aβ levels, we performed a proteomic analysis of the brain of the AD mouse model APPsw and compared it to that of APPsw mice lacking neprilysin. To this end we established an LC‐MS/MS method to analyze brain homogenate, using an ¹⁸O‐labeled internal standard to accurately quantify the protein levels. To distinguish between alterations in protein levels caused by increased Aβ levels and those induced by neprilysin deficiency independently of Aβ, the brain proteome of neprilysin deficient APPsw mice was also compared to that of neprilysin deficient mice. By this approach we identified approximately 600 proteins and the levels of 300 of these were quantified. Pathway analysis showed that many of the proteins with altered expression were involved in neurological disorders, and that tau, presenilin and APP were key regulators in the identified networks. The data have been deposited to the ProteomeXchange Consortium with identifiers PXD000968 and PXD001786 ( http://proteomecentral.proteomexchange.org/dataset/PXD000968 and ( http://proteomecentral.proteomexchange.org/dataset/PXD001786 ). Interestingly, the levels of several proteins, including some not previously reported to be linked to AD, were associated with increased Aβ levels.     

Interactions of amyloid-β peptides on lipid bilayer studied by single molecule imaging and tracking

The amyloid-β peptides (Aβ40 and Aβ42) feature prominently in the synaptic dysfunction and neuronal loss associated with Alzheimer's disease (AD). This has been proposed to be due either to interactions between Aβ and cell surface receptors affecting cell signaling, or to the formation of calcium-permeable channels in the membrane that disrupt calcium homeostasis. In both mechanisms the cell membrane is the primary cellular structure with which Aβ interacts. Aβ concentrations in human bodily fluids are very low (pM-nM) rendering studies of the size, composition, cellular binding sites and mechanism of action of the oligomers formed in vivo very challenging. Most studies, therefore, have utilized Aβ oligomers prepared at micromolar peptide concentrations, where Aβ forms oligomeric species which possess easily observable cell toxicity. Such toxicity has not been observed when nM concentrations of peptide are used in the experiment highlighting the importance of employing physiologically relevant peptide concentrations for the results to be of biological significance. In this paper single-molecule microscopy was used to monitor Aβ oligomer formation and diffusion on a supported lipid bilayer at nanomolar peptide concentrations. Aβ monomers, the dominant species in solution, tightly associate with the membrane and are highly mobile whereas trimers and higher-order oligomers are largely immobile. Aβ dimers exist in a mixture of mobile and immobile states. Oligomer growth on the membrane is more rapid for Aβ40 than for the more amyloidogenic Aβ42 but is largely inhibited for a 1:1 Aβ40:Aβ42 mixture. The mechanism underlying these Aβ40-Aβ42 interactions may feature in Alzheimer's pathology.