Plaques In Alzheimer's Disease Brain Research Articles

Production and characterization of novel monoclonal antibodies against pathological human TDP-43 proteins.

The RNA/DNA-binding protein TDP-43 plays a pivotal role in the ubiquitinated inclusions characteristic of TDP-43 proteinopathies, including most cases of frontotemporal lobar degeneration (FTLD-TDP) and Alzheimer disease (AD). To understand the mechanisms of pathological TDP-43 processing and identify potential biomarkers, we generated novel phosphorylation-independent monoclonal antibodies (MAbs) using bacteria-expressed human full-length recombinant TDP-43. Remarkably, we identified a distinctive MAb, No. 9, targeting an epitope in amino acid (aa) region 311-360 of the C-terminus. This antibody showed preferential reactivity for pathological TDP-43 inclusions, with only mild reactivity for normal nuclear TDP-43. MAb No. 9 revealed more pathology in FTLD-TDP type A and type B brains and in AD brains compared to the commercial p409/410 MAb. Using synthetic phosphorylated peptides, we also obtained MAbs targeting the p409/410 epitope. Interestingly, MAb No. 14 was found to reveal additional pathology in AD compared to the commercial p409/410 MAb, specifically, TDP-43-immunopositive deposits with amyloid plaques in AD brains. These unique immunopositivities observed with MAbs No. 9 and No. 14 are likely attributed to their conformation-dependent binding to TDP-43 inclusions. We expect that this novel set of MAbs will prove valuable as tools for future patient-oriented investigations into TDP-43 proteinopathies.

CERTL reduces C16 ceramide, amyloid-β levels and inflammation in a model of Alzheimer's disease.

Dysregulation of ceramide and sphingomyelin levels have been suggested to contribute to the pathogenesis of Alzheimer's disease (AD). Ceramide transfer proteins (CERTs) are ceramide carriers which are crucial for ceramide and sphingomyelin balance in cells. Extracellular forms of CERTs co-localize with amyloid-β (Aβ) plaques in AD brains. To date, the significance of these observations for the pathophysiology of AD remains uncertain. A plasmid expressing CERTL , the long isoform of CERTs, was used to study the interaction of CERTL with amyloid precursor protein (APP) by co-immunoprecipitation and immunofluorescence in HEK cells. The recombinant CERTL protein was employed to study interaction of CERTL with amyloid-β (Aβ), Aβ aggregation process in presence of CERTL , and the resulting changes in Aβ toxicity in neuroblastoma cells. CERTL was overexpressed in neurons by adeno associated virus (AAV) in a mouse model of familial AD (5xFAD). Ten weeks after transduction, animals were challenged with behavior tests for memory, anxiety and locomotion. At week twelve, brains were investigated for sphingolipid levels by mass spectrometry, plaques and neuroinflammation by immunohistochemistry, gene expression and/or immunoassay. Here, we report that CERTL , binds to APP, modifies Aβ aggregation and reduces Aβ neurotoxicity in vitro. Furthermore, we show that intracortical injection of AAV, mediating the expression of CERTL , decreases levels of ceramide d18:1/16:0 and increases sphingomyelin levels in the brain of male 5xFAD mice. CERTL in vivo over-expression has a mild effect on animal locomotion, decreases Aβ formation and modulates microglia by decreasing their pro-inflammatory phenotype. Our results demonstrate a crucial role of CERTL in regulating ceramide levels in the brain, in amyloid plaque formation and neuroinflammation, thereby opening research avenues for therapeutic targets of AD and other neurodegenerative diseases.

Innate Immunity Protein IFITM3 in Alzheimer's Disease.

Several genes in innate immunity have been implicated in Alzheimer's disease (AD). However, the effect of innate immunity on amyloid β (Aβ) production, which makes amyloid plaques in AD brains, was previously not known. Recently, the antiviral protein interferon-induced transmembrane protein 3 (IFITM3) has been identified as a novel γ-secretase modulatory protein for Aβ production. In this review, the mechanisms of how innate immunity modulates Aβ production via IFITM3-γ-secretase complexes and contributes to AD pathogenesis are discussed.

In vivo localization of human acetylcholinesterase-derived species in a β-sheet conformation at the core of senile plaques in Alzheimer's disease

Many neurodegenerative diseases are characterized by amyloid deposition. In Alzheimer's disease (AD), β-amyloid (Aβ) peptides accumulate extracellularly in senile plaques. The AD amyloid cascade hypothesis proposes that Aβ production or reduced clearance leads to toxicity. In contrast, the cholinergic hypothesis argues for a specific pathology of brain cholinergic pathways. However, neither hypothesis in isolation explains the pattern of AD pathogenesis. Evidence suggests that a connection exists between these two scenarios: the synaptic form of human acetylcholinesterase (hAChE-S) associates with plaques in AD brains; among hAChE variants, only hAChE-S enhances Aβ fibrillization in vitro and Aβ deposition and toxicity in vivo Only hAChE-S contains an amphiphilic C-terminal domain (T40, AChE575-614), with AChE586-599 homologous to Aβ and forming amyloid fibrils, which implicates T40 in AD pathology. We previously showed that the amyloid scavenger, insulin-degrading enzyme (IDE), generates T40-derived amyloidogenic species that, as a peptide mixture, seed Aβ fibrillization. Here, we characterized 11 peptides from a T40-IDE digest for β-sheet conformation, surfactant activity, fibrillization, and seeding capability. We identified residues important for amyloidogenicity and raised polyclonal antibodies against the most amyloidogenic peptide. These new antisera, alongside other specific antibodies, labeled sections from control, hAChE-S, hAPPswe, and hAChE-S/hAPPswe transgenic mice. We observed that hAChE-S β-sheet species co-localized with Aβ in mature plaque cores, surrounded by hAChE-S α-helical species. This observation provides the first in vivo evidence of the conformation of hAChE-S species within plaques. Our results may explain the role of hAChE-S in Aβ deposition and aggregation, as amyloidogenic hAChE-S β-sheet species might seed Aβ aggregation.

The sterol regulatory element-binding protein 2 is dysregulated by tau alterations in Alzheimer disease.

Disturbed neuronal cholesterol homeostasis has been observed in Alzheimer disease (AD) and contributes to the pathogenesis of AD. As the master switch of cholesterol biosynthesis, the sterol regulatory element-binding protein 2 (SREBP-2) translocates to the nucleus after cleavage/activation, but its expression and activation have not been studied in AD which is the focus of the current study. We found both a significant decrease in the nuclear translocation of N-terminal SREBP-2 accompanied by a significant accumulation of C-terminal SREBP-2 in NFT-containing pyramidal neurons in AD. N-terminal- SREBP-2 is also found in dystrophic neurites around plaques in AD brain. Western blot confirmed a significantly reduced nuclear translocation of mature SREBP-2 (mSREBP-2) in AD brain. Interestingly, reduced nuclear mSREBP-2 was only found in animal models of tauopathies such as 3XTg AD mice and P301L Tau Tg mice but not in CRND8 APP transgenic mice, suggesting that tau alterations likely are involved in the changes of mSREBP-2 distribution and activation in AD. Altogether, our study demonstrated disturbed SREBP-2 signaling in AD and related models, and proved for the first time that tau alterations contribute to disturbed cholesterol homeostasis in AD likely through modulation of nuclear mSREBP-2 translocation.

Lipopolysaccharide Associates with Amyloid Plaques, Neurons and Oligodendrocytes in Alzheimer's Disease Brain: A Review.

This review proposes that lipopolysaccharide (LPS, found in the wall of all Gram-negative bacteria) could play a role in causing sporadic Alzheimer’s disease (AD). This is based in part upon recent studies showing that: Gram-negative E. coli bacteria can form extracellular amyloid; bacterial-encoded 16S rRNA is present in all human brains with over 70% being Gram-negative bacteria; ultrastructural analyses have shown microbes in erythrocytes of AD patients; blood LPS levels in AD patients are 3-fold the levels in control; LPS combined with focal cerebral ischemia and hypoxia produced amyloid-like plaques and myelin injury in adult rat cortex. Moreover, Gram-negative bacterial LPS was found in aging control and AD brains, though LPS levels were much higher in AD brains. In addition, LPS co-localized with amyloid plaques, peri-vascular amyloid, neurons, and oligodendrocytes in AD brains. Based upon the postulate LPS caused oligodendrocyte injury, degraded Myelin Basic Protein (dMBP) levels were found to be much higher in AD compared to control brains. Immunofluorescence showed that the dMBP co-localized with β amyloid (Aβ) and LPS in amyloid plaques in AD brain, and dMBP and other myelin molecules were found in the walls of vesicles in periventricular White Matter (WM). These data led to the hypothesis that LPS acts on leukocyte and microglial TLR4-CD14/TLR2 receptors to produce NFkB mediated increases of cytokines which increase Aβ levels, damage oligodendrocytes and produce myelin injury found in AD brain. Since Aβ1–42 is also an agonist for TLR4 receptors, this could produce a vicious cycle that accounts for the relentless progression of AD. Thus, LPS, the TLR4 receptor complex, and Gram-negative bacteria might be treatment or prevention targets for sporadic AD.

Determination of critical nucleation number for a single nucleation amyloid-β aggregation model

Aggregates of amyloid-β (Aβ) peptide are known to be the key pathological agents in Alzheimer disease (AD). Aβ aggregates to form large, insoluble fibrils that deposit as senile plaques in AD brains. The process of aggregation is nucleation–dependent in which the formation of a nucleus is the rate–limiting step, and controls the physiochemical fate of the aggregates formed. Therefore, understanding the properties of nucleus and pre-nucleation events will be significant in reducing the existing knowledge–gap in AD pathogenesis. In this report, we have determined the plausible range of critical nucleation number (n*), the number of monomers associated within the nucleus for a homogenous aggregation model with single unique nucleation event, by two independent methods: A reduced-order stability analysis and ordinary differential equation based numerical analysis, supported by experimental biophysics. The results establish that the most likely range of n* is between 7 and 14 and within, this range, n* = 12 closely supports the experimental data. These numbers are in agreement with those previously reported, and importantly, the report establishes a new modeling framework using two independent approaches towards a convergent solution in modeling complex aggregation reactions. Our model also suggests that the formation of large protofibrils is dependent on the nature of n*, further supporting the idea that pre-nucleation events are significant in controlling the fate of larger aggregates formed. This report has re-opened an old problem with a new perspective and holds promise towards revealing the molecular events in amyloid pathologies in the future.

Unfolded Protein Response and PERK Kinase as a New Therapeutic Target in the Pathogenesis of Alzheimer's Disease.

Recent evidence suggests that the development of Alzheimer's disease (AD) and related cognitive loss is due to mutations in the Amyloid Precursor Protein (APP) gene on chromosome 21 and increased activation of eukaryotic translation initiation factor-2α (eIF2α) phosphorylation. The high level of misfolded and unfolded proteins loading in Endoplasmic Reticulum (ER) lumen triggers ER stress and as a result Unfolded Protein Response (UPR) pathways are activated. Stress-dependent activation of the protein kinase RNA-like endoplasmic reticulum kinase (PERK) leads to the significant elevation of phospho-eIF2α. That attenuates general translation and, on the other hand, promotes the preferential synthesis of Activating Transcription Factor 4 (ATF4) and secretase β (BACE1) - a pivotal enzyme responsible for the initiation of the amyloidogenic pathway resulting in the generation of the amyloid β (Aβ) variant with high ability to form toxic senile plaques in AD brains. Moreover, excessive, long-term stress conditions may contribute to inducing neuronal death by apoptosis as a result of the overactivated expression of pro-apoptotic proteins via ATF4. These findings allow to infer that dysregulated translation, increased expression of BACE1 and ATF4, as a result of eIF2α phosphorylation, may be a major contributor to structural and functional neuronal loss resulting in memory impairment. Thus, blocking PERK-dependent eIF2α phosphorylation through specific, small-molecule PERK branch inhibitors seems to be a potential treatment strategy for AD individuals. That may contribute to the restoration of global translation rates and reduction of expression of ATF4 and BACE1. Hence, the treatment strategy can block accelerated β -amyloidogenesis by reduction in APP cleaving via the BACE1-dependent amyloidogenic pathway.

Myelin basic protein associates with AβPP, Aβ1-42, and amyloid plaques in cortex of Alzheimer's disease brain.

The goal of this study was to show that myelin and axons in cortical gray matter are damaged in Alzheimer's disease (AD) brain. Superior temporal gyrus gray matter of AD patients (9 male, 14 female) was compared to cognitively normal controls (8 male, 7 female). Myelin basic protein (MBP) and a degraded myelin basic protein complex (dMBP) were quantified by Western blot. Brain sections were immunostained for MBP, dMBP, axonal neurofilament protein (NF), autophagy marker microtubule-associated proteins 1A/B light chain 3B precursor (LC3B), amyloid-β protein precursor (AβPP), and amyloid markers amyloid β1-42 (Aβ1-42) and FSB. Co-immunoprecipitation and mass spectroscopy evaluated interaction of AβPP/Aβ1-42 with MBP/dMBP. Evidence of axonal injury in AD cortex included appearance of AβPP in NF stained axons, and NF at margins of amyloid plaques. Evidence of myelin injury in AD cortex included (1) increased dMBP in AD gray matter compared to control (p < 0.001); (2) dMBP in AD neurons; and (3) increased LC3B that co-localized with MBP. Evidence of interaction of AβPP/Aβ1-42 with myelin or axonal components included (1) greater binding of dMBP with AβPP in AD brain; (2) MBP at the margins of amyloid plaques; (3) dMBP co-localized with Aβ1-42 in the core of amyloid plaques in AD brains; and (4) interactions between Aβ1-42 and MBP/dMBP by co-immunoprecipitation and mass spectrometry. We conclude that damaged axons may be a source of AβPP. dMBP, MBP, and NF associate with amyloid plaques and dMBP associates with AβPP and Aβ1-42. These molecules could be involved in formation of amyloid plaques.

Autophagy-Related Protein 7 Deficiency in Amyloid β (Aβ) Precursor Protein Transgenic Mice Decreases Aβ in the Multivesicular Bodies and Induces Aβ Accumulation in the Golgi

Alzheimer disease (AD) is biochemically characterized by increased levels of amyloid β (Aβ) peptide, which aggregates into extracellular Aβ plaques in AD brains. Before plaque formation, Aβ accumulates intracellularly in both AD brains and in the brains of AD model mice, which may contribute to disease progression. Autophagy, which is impaired in AD, clears cellular protein aggregates and participates in Aβ metabolism. In addition to a degradative role of autophagy in Aβ metabolism we recently showed that Aβ secretion is inhibited in mice lacking autophagy-related gene 7 (Atg7) in excitatory neurons in the mouse forebrain. This inhibition of Aβ secretion leads to intracellular accumulation of Aβ. Here, we used fluorescence and immunoelectron microscopy to elucidate the subcellular localization of the intracellular Aβ accumulation which accumulates in Aβ precursor protein mice lacking Atg7. Autophagy deficiency causes accumulation of p62(+) aggregates, but these aggregates do not contain Aβ. However, knockdown of Atg7 induced Aβ accumulation in the Golgi and a concomitant reduction of Aβ in the multivesicular bodies. This indicates that Atg7 influences the transport of Aβ possibly derived from Golgi to multivesicular bodies.

Fetzima (levomilnacipran), a drug for major depressive disorder as a dual inhibitor for human serotonin transporters and beta-site amyloid precursor protein cleaving enzyme-1.

Pharmacological management of Major Depressive Disorder includes the use of serotonin reuptake inhibitors which targets serotonin transporters (SERT) to increase the synaptic concentrations of serotonin. Beta-site amyloid precursor protein cleaving enzyme-1 (BACE-1) is responsible for amyloid β plaque formation. Hence it is an interesting target for Alzheimer's disease (AD) therapy. This study describes molecular interactions of a new Food and Drug Administration approved antidepressant drug named 'Fetzima' with BACE-1 and SERT. Fetzima is chemically known as levomilnacipran. The study has explored a possible link between the treatment of Depression and AD. 'Autodock 4.2' was used for docking study. The free energy of binding (ΔG) values for 'levomilnacipran-SERT' interaction and 'levomilnacipran-BACE1' interaction were found to be -7.47 and -8.25 kcal/mol, respectively. Levomilnacipran was found to interact with S438, known to be the most important amino acid residue of serotonin binding site of SERT during 'levomilnacipran-SERT' interaction. In the case of 'levomilnacipran-BACE1' interaction, levomilnacipran interacted with two very crucial aspartic acid residues of BACE-1, namely, D32 and D228. These residues are accountable for the cleavage of amyloid precursor protein and the subsequent formation of amyloid β plaques in AD brain. Hence, Fetzima (levomilnacipran) might act as a potent dual inhibitor of SERT and BACE-1 and expected to form the basis of a future dual therapy against depression and AD. It is an established fact that development of AD is associated with Major Depressive Disorder. Therefore, the design of new BACE-1 inhibitors based on antidepressant drug scaffolds would be particularly beneficial.

PLD3 is accumulated on neuritic plaques in Alzheimer's disease brains.

IntroductionRecently, a whole-exome sequencing (WES) study showed that a rare variant rs145999145 composed of p.Val232Met located in exon 7 of the phospholipase D3 (PLD3) gene confers a doubled risk for late-onset Alzheimer’s disease (AD). Knockdown of PLD3 elevates the levels of extracellular amyloid-beta (Aβ), suggesting that PLD3 acts as a negative regulator of Aβ precursor protein (APP) processing. However, the precise cellular location and distribution of PLD3 in AD brains remain largely unknown.MethodsBy quantitative RT-PCR (qPCR), western blot, immunohistochemistry, and bioinformatics analysis, we studied PLD3 expression patterns and levels in a series of AD and control brains, including amyotrophic lateral sclerosis, Parkinson’s disease, multiple system atrophy, and non-neurological cases.ResultsThe levels of PLD3 mRNA and protein expression were reduced modestly in AD brains, compared with those in non-AD brains. In all brains, PLD3 was expressed constitutively in cortical neurons, hippocampal pyramidal and granular neurons but not in glial cells. Notably, PLD3 immunoreactivity was accumulated on neuritic plaques in AD brains. We identified the human granulin (GRN) gene encoding progranulin (PRGN) as one of most significant genes coexpressed with PLD3 by bioinformatics database search. PLD3 was actually coexpressed and interacted with PGRN both in cultured cells in vitro and in AD brains in vivo.ConclusionsWe identified an intense accumulation of PLD3 on neuritic plaques coexpressed with PGRN in AD brains, suggesting that PLD3 plays a key role in the pathological processes of AD.

The effects of impaired cerebral circulation on Alzheimer's disease pathology: evidence from animal studies.

Persistent systemic hypoxia, a direct consequence of alterations in vascular function, can compromise the brain by increasing the risk of developing dementias such as Alzheimer's disease (AD). Vascular contributions to cognitive impairment and AD in aged individuals are common, and several vascular risk factors for AD are linked to hypoxia. Clinical evidence confirms that structural and functional changes characteristic of AD pathology also occur following hypoxic-ischemic events such as stroke and traumatic brain injury. Studies with transgenic and non-transgenic mouse models reliably show that hypoxia increases the levels of amyloid-β peptides that form the characteristic plaques in AD brains. Moreover, some studies suggest that vascular lesions also promote tau phosphorylation, modulate apolipoprotein E expression, and have more profound effects in aged animals, but additional evidence is needed to establish these findings. Although the mechanisms underlying hypoxia-related effects remain unclear, controlled animal studies continue to reveal mechanistic aspects of the relationship between hypoxia and AD pathology that are necessary for therapeutic developments. The present review summarizes evidence from rodent studies regarding the effects of hypoxia on AD-related pathology and evaluates its impact on understanding human disease.

Induction of GADD34 Regulates the Neurotoxicity of Amyloid β.

The possible roles played by growth arrest and DNA damage-inducible gene 34 (GADD34) in Alzheimer's disease (AD) are so far less understood. In this study, we found that GADD34 was increased in the brains of AD transgenic J20 mice. The deposition of β-amyloid (Aβ) peptide is the main component of neurotic plaques in AD brain. Thus, we examined the effect of Aβ in the expression of GADD34 in human SH-SY5Y cells in vitro. Amyloid β (Aβ1-42) treatment led to increased expression of GADD34. Pretreatment with 50 nmol/L of c-Jun N-terminal kinases (JNK) inhibitor SP600125 abolished the upregulation of GADD34. c-Jun silencing by transfection with c-Jun small-interfering RNA abolished the effects of Aβ1-42 on the expression of GADD34. Importantly, chromatin immunoprecipitation studies verified the ability of c-Jun to bind to the GADD34 promoter, and this ability was increased more than 3-fold by Aβ1-42. These data suggest that the induction of GADD34 by Aβ is mediated by JNK/c-Jun pathway. Finally, depletion of GADD34 significantly rescued Aβ-induced cell apoptosis as evidenced by a marked decrease in the number of terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling (TUNEL)-positive cells. Consistently, knockdown of GADD34 attenuated caspase 3 activation induced by Aβ1-42.

Deficiency of Patched 1-induced Gli1 signal transduction results in astrogenesis in Swedish mutated APP transgenic mice

Normally, sonic hedgehog (Shh) signaling induces high levels of Patched 1 (Ptc1) and its associated transcription factor Gli1 with genesis of specific neuronal progeny. But their roles in the neural stem cells (NSCs), including glial precursor cells (GPCs), of Alzheimer's disease (AD) are unclear. Here, we show that Ptc1 and Gli1 are significantly deficits in the hippocampus of an aged AD transgenic mouse mode, whereas these two molecules are highly elevated at young ages. Our similar findings in autopsied AD brains validate the discovery in AD mouse models. To examine whether Aβ peptides, which are a main component of the amyloid plaques in AD brains, affected Ptc1-Gli1 signaling, we treated GPCs with Aβ peptides, we found that high dose of Aβ1-42 but not Aβ1-40 significantly decreased Ptc1-Gli1, while Shh itself was elevated in hippocampal NSCs/GPCs. Furthermore, we found that deficits of Ptc1-Gli1 signaling induced NSCs/GPCs into asymmetric division, which results in an increase in the number of dividing cells including transit-amplifying cells and neuroblasts. These precursor cells commit to apoptosis-like death under the toxic conditions. By this way, adult neural precursor cell pool is exhausted and defective neurogenesis happens in AD brains. Our findings suggest that Ptc1-Gli1 signaling deregulation resulting abnormal loss of GPCs may contribute to a cognition decline in AD brains. The novel findings elucidate a new molecular mechanism of adult NSCs/GPCs on neurogenesis and demonstrate a regulatory role for Ptc1-Gli1 in adult neural circuit integrity of the brain.

Novel radioiodinated 1,3,4-oxadiazole derivatives with improved in vivo properties for SPECT imaging of β-amyloid plaques

We designed and synthesized a novel series of radioiodinated 3-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine (1,3,4-PODP) derivatives for imaging β-amyloid (Aβ) plaques in Alzheimer's disease (AD) brains using single photon emission computed tomography (SPECT). In binding experiments in vitro, 1,3,4-PODP derivatives (3 and 6) displayed high affinity for Aβ(1-42) aggregates (25 and 14 nM, respectively). In experiments in vivo, [123/125I]3 and [123/125I]6 displayed good initial uptake into and rapid washout from the brain in normal mice, and clearly labeled Aβ plaques in Tg2576 mice. Furthermore, specific labeling of Aβ plaques was observed in in vitro autoradiography of postmortem AD brain sections. These results suggested that 1,3,4-PODP derivatives may be useful SPECT probes for detecting Aβ plaques in AD brains.

Clusterin Associates Specifically with Aβ40 in Alzheimer's Disease Brain Tissue

AbstractGenome‐wide association studies have pointed to clusterin (apolipoprotein J) as being linked to the occurrence of Alzheimer's disease (AD); studies have identified the protein as a possible biomarker. The association between clusterin and senile plaques in AD brain is well known, and clusterin levels in AD brain are 40% higher than that in control subjects. The present study investigates, immunohistochemically, the association between clusterin and Aβ peptides in AD and control cortex. A unique and specific association between clusterin and Aβ40 was observed in plaques in the cerebral cortex from AD subjects in that only plaques that contained Aβ40 showed clusterin immunoreactivity, while the many plaques with Aβ42 alone lacked clusterin labeling. Cerebrovascular Aβ in AD brain generally lacked Aβ42 but was positively labeled by both the Aβ40 and the clusterin antibodies. In control subjects, however, Aβ40 was absent from plaques, although very occasional plaques were found to be labeled by both the Aβ42 and the clusterin antibodies. Overall, in AD, but not aged control brain, clusterin was associated specifically with the Aβ40 form of Aβ in the brain. The lack of clusterin in association with Aβ42 may be a significant feature in neuronal loss and neurodegeneration in the disease state.

&amp;#947;-Secretase, Apolipoprotein E and Cellular Cholesterol Metabolism

Genetic studies demonstrate that the 4 allele of the apolipoprotein (apo) E is a risk factor for late onset Alzheimer's disease (AD). Apo E is the major component of lipoprotein particles in the brain that mediate transport of cholesterol and other lipids between neurons and glial cells, indicating an implication of cerebral lipid metabolism in the pathogenesis of AD. In addition, apo E is also involved in the metabolism and aggregation of the amyloid β-peptide (Aβ) that derives from proteolytic processing of the amyloid precursor protein (APP) and is found in plaques of AD brains. The generation of Aβ involves sequential cleavages of APP by proteases called β- and γ-secretase. γ-Secretase is a high molecular weight protein complex containing presenilins as catalytically active subunits. Importantly, mutations in the genes of APP and the two homologous PS proteins are a major cause of familial early onset AD, indicating that the metabolism of APP and generation of Aβ play critical roles in the initiation of the disease. This review focuses on the functional relation of γ-secretase complexes and the metabolism of lipoproteins in the brain. It is hypothesized that γ-secretase activity is critically involved in cellular lipid homeostasis and that impaired lipid metabolism contributes to the pathogenesis of AD.

Association of COL25A1 with Comorbid Antisocial Personality Disorder and Substance Dependence

Antisocial personality disorder (ASPD) is a psychiatric disorder characterized by a long-term pattern of manipulating, exploiting, or violating the rights of others. Subjects ascertained for genetic studies of substance dependence (SD) and diagnosed with ASPD and comorbid SD were included in a two-stage genetic association study. In the discovery stage, 627 single nucleotide polymorphisms (SNPs) located in 179 candidate genes for addiction were analyzed in a case-control cohort and family-based cohort. The significant findings were replicated in an independent case-control cohort. One SNP, rs13134663, in the collagen XXV alpha 1 gene (COL25A1) was significantly associated with ASPD in both African Americans and European Americans (smallest p values were .0002 and .0004, respectively). There was also evidence of association with the same SNP in independent samples of African American and European American cases and control subjects (p = .035 and .033, respectively). Analysis of the combined set of case-control subjects yielded an allelic p value of 9 × 10(-6) with odds ratio (95% confidence interval) of 1.3 (1.16, 1.47) (smallest p = 1 × 10(-7); Bonferroni threshold p = .00012). The COL25A1 gene, located at chromosome 4q25, encodes the collagen-like Alzheimer amyloid plaque component precursor, a type II transmembrane protein specifically expressed in neurons; it co-localizes with amyloid β in senile plaques in Alzheimer disease brains. This SNP maps to the transcription factor binding site and is conserved in 17 vertebrates, including mice and rats. Our findings suggest that COL25A1 may be associated with ASPD, especially in the context of SD.

Changes in Brain β-Amyloid Deposition and Aquaporin 4 Levels in Response to AlteredAgrinExpression in Mice

Conditions that compromise the blood-brain barrier (BBB) have been increasingly implicated in the pathogenesis of Alzheimer disease (AD). AGRIN is a heparan sulfate proteoglycan found abundantly in basement membranes of the cerebral vasculature, where it has been proposed to serve a functional role in the BBB. Furthermore, AGRIN is the major heparan sulfate proteoglycan associated with amyloid plaques in AD brains. To examine the relationship of AGRIN, the BBB, and AD-related pathologies, we generated mice in which the Agrn gene was deleted from either endothelial cells or neurons using gene targeting or was overexpressed using a genomic transgene construct. These mice were combined with a transgenic model of AD that over expresses disease-associated forms of amyloid precursor protein and presenilin 1. In mice lacking endothelial cell expression of Agrn, the BBB remained intact but aquaporin 4 levels were reduced, indicating that the loss of AGRIN affects BBB-associated components. This change in Agrn resulted in an increase in β-amyloid (Aβ) in the brain. Conversely, overexpression of Agrn decreased Aβ deposition, whereas elimination of Agrn from neurons did not change Aβ levels. These results indicate that AGRIN is important for maintaining BBB composition and that changes in Agrn expression (particularly vessel-associated AGRIN) influence Aβ homeostasis in mouse models of AD.