Sporadic Alzheimer's Disease Brains Research Articles

Correlative Chemical Imaging Identifies Amyloid Peptide Signatures of Neuritic Plaques and Dystrophy in Human Sporadic Alzheimer's Disease.

Objective: Alzheimer's disease (AD) is the most common neurodegenerative disease. The predominantly sporadic form of AD is age-related, but the underlying pathogenic mechanisms remain not fully understood. Current efforts to combat the disease focus on the main pathological hallmarks, in particular beta-amyloid (Aβ) plaque pathology. According to the amyloid cascade hypothesis, Aβ is the critical early initiator of AD pathogenesis. Plaque pathology is very heterogeneous, where a subset of plaques, neuritic plaques (NPs), are considered most neurotoxic rendering their in-depth characterization essential to understand Aβ pathogenicity. Methods: To delineate the chemical traits specific to NP types, we investigated senile Aβ pathology in the postmortem, human sporadic AD brain using advanced correlative biochemical imaging based on immunofluorescence (IF) microscopy and mass spectrometry imaging (MSI). Results: Immunostaining-guided MSI identified distinct Aβ signatures of NPs characterized by increased Aβ1-42(ox) and Aβ2-42. Moreover, correlation with a marker of dystrophy (reticulon 3 [RTN3]) identified key Aβ species that both delineate NPs and display association with neuritic dystrophy. Conclusion: Together, these correlative imaging data shed light on the complex biochemical architecture of NPs and associated dystrophic neurites. These in turn are obvious targets for disease-modifying treatment strategies, as well as novel biomarkers of Aβ pathogenicity.

Genome-wide DNA methylation analysis of autosomal dominantly inherited and sporadic Alzheimer disease brains.

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with many biological processes, and molecular changes. The etiology of AD is complex and not specific to a single genetic factor. Epigenetic changes could help explain the missing heritability not capture in GWAS chips and determine functional variants in genome-wide significant loci. Our discovery cohort includes 460 post-mortem brains, 452 AD and 25 controls from Knight-ADRC and Dominantly Inherited Alzheimer Network cohorts. Our study included late-onset (LOAD), but also subjects with Mendelian mutations in APP, PSEN1 and PSEN2 genes (Autosomal Dominant AD; ADAD) and controls. We performed a genome-wide methylation study using DNA from parietal cortex. We used Infinium MethylationEPIC Beadchip arrays (Illumina) to measure DNA methylation. All statistical analyses were adjusted for sex, age at death and neuron proportion. Completion of this project will provide an enhanced characterization of the epigenetic factors associated with AD etiology. This study will enhance the understanding of the molecular dynamics underlying the pathophysiology of AD, and may lead to novel clues for its early detection, prevention and treatment. Epigenetics of AD brains have been previously studied, but this is the first study to analyze both LOAD and ADAD. These results will be presented in the conference.

Citrullination of Amyloid-β Peptides in Alzheimer's Disease.

Protein citrullination (deimination of arginine residue) is a well-known biomarker of inflammation. Elevated protein citrullination has been shown to colocalize with extracellular amyloid plaques in postmortem AD patient brains. Amyloid-β (Aβ) peptides which aggregate and accumulate in the plaques of Alzheimer's disease (AD) have sequential N-terminal truncations and multiple post-translational modifications (PTM) such as isomerization, pyroglutamate formation, phosphorylation, nitration, and dityrosine cross-linking. However, no conclusive biochemical evidence exists whether citrullinated Aβ is present in AD brains. In this study, using high-resolution mass spectrometry, we have identified citrullination of Aβ in sporadic and familial AD brains by characterizing the tandem mass spectra of endogenous N-truncated citrullinated Aβ peptides. Our quantitative estimations demonstrate that ∼ 35% of pyroglutamate3-Aβ pool was citrullinated in plaques in the sporadic AD temporal cortex and ∼ 22% in the detergent-insoluble frontal cortex fractions. Similarly, hypercitrullinated pyroglutamate3-Aβ (∼ 30%) was observed in both the detergent-soluble as well as insoluble Aβ pool in familial AD cases. Our results indicate that a common mechanism for citrullination of Aβ exists in both the sporadic and familial AD. We establish that citrullination of Aβ is a remarkably common PTM, closely associated with pyroglutamate3-Aβ formation and its accumulation in AD. This may have implications for Aβ toxicity, autoantigenicity of Aβ, and may be relevant for the design of diagnostic assays and therapeutic targeting.

Decreased Deposition of Beta-Amyloid 1-38 and Increased Deposition of Beta-Amyloid 1-42 in Brain Tissue of Presenilin-1 E280A Familial Alzheimer's Disease Patients.

Familial Alzheimer’s Disease (FAD) caused by Presenilin-1 (PS1) mutations is characterized by early onset, cognitive impairment, and dementia. Impaired gamma secretase function favors production of longer beta-amyloid species in PS1 FAD. The PS1 E280A mutation is the largest FAD kindred under study. Here, we studied beta-amyloid deposits in PS1 E280A FAD brains in comparison to sporadic Alzheimer’s disease (SAD). We analyzed cortices and cerebellum from 10 FAD and 10 SAD brains using immunohistochemistry to determine total beta-amyloid, hyperphosphorylated tau (pTau), and specific beta-amyloid peptides 1-38, 1-40, 1-42, and 1-43. Additionally, we studied beta-amyloid subspecies by ELISA, and vessel pathology was detected with beta-amyloid 1-42 and truncated pyroglutamylated beta-amyloid antibodies. There were no significant differences in total beta-amyloid signal between SAD and FAD. Beta-amyloid 1-38 and 1-43 loads were increased, and 1-42 loads were decreased in frontal cortices of SAD when compared to FAD. Beta-amyloid species assessment by ELISA resembled our findings by immunohistochemical analysis. Differences in beta-amyloid 1-38 and 1-42 levels between SAD and FAD were evidenced by using beta-amyloid length-specific antibodies, reflecting a gamma secretase-dependent shift in beta-amyloid processing in FAD cases. The use of beta-amyloid length-specific antibodies for postmortem assessment of beta-amyloid pathology can differentiate between SAD and PS1 FAD cases and it can be useful for identification of SAD cases potentially affected with gamma secretase dysfunction.

Upregulation of the Sarco-Endoplasmic Reticulum Calcium ATPase 1 Truncated Isoform Plays a Pathogenic Role in Alzheimer's Disease.

Dysregulation of the Endoplasmic Reticulum (ER) Ca2+ homeostasis and subsequent ER stress activation occur in Alzheimer Disease (AD). We studied the contribution of the human truncated isoform of the sarco-endoplasmic reticulum Ca2+ ATPase 1 (S1T) to AD. We examined S1T expression in human AD-affected brains and its functional consequences in cellular and transgenic mice AD models. S1T expression is increased in sporadic AD brains and correlates with amyloid β (Aβ) and ER stress chaperone protein levels. Increased S1T expression was also observed in human neuroblastoma cells expressing Swedish-mutated β-amyloid precursor protein (βAPP) or treated with Aβ oligomers. Lentiviral overexpression of S1T enhances in return the production of APP C-terminal fragments and Aβ through specific increases of β-secretase expression and activity, and triggers neuroinflammation. We describe a molecular interplay between S1T-dependent ER Ca2+ leak, ER stress and βAPP-derived fragments that could contribute to AD setting and/or progression.

Bacteroidetes Neurotoxins and Inflammatory Neurodegeneration.

The gram-negative facultative anaerobe Bacteroides fragilis (B. fragilis) constitutes an appreciable proportion of the human gastrointestinal (GI)-tract microbiome. As is typical of most gram-negative bacilli, B. fragilis secretes an unusually complex mixture of neurotoxins including the extremely pro-inflammatory lipopolysaccharide BF-LPS. LPS (i) has recently been shown to associate with the periphery of neuronal nuclei in sporadic Alzheimer's disease (AD) brain and (ii) promotes the generation of the inflammatory transcription factor NF-kB (p50/p65 complex) in human neuronal-glial cells in primary-culture. In turn, the NF-kB (p50/p65 complex) strongly induces the transcription of a small family of pro-inflammatory microRNAs (miRNAs) including miRNA-9, miRNA-34a, miRNA-125b, miRNA-146a, and miRNA-155. These ultimately bind with the 3'-untranslated region (3'-UTR) of several target messenger RNAs (mRNAs) and thereby reduce their expression. Down-regulated mRNAs include those encoding complement factor-H (CFH), an SH3-proline-rich multi-domain-scaffolding protein of the postsynaptic density (SHANK3), and the triggering receptor expressed in myeloid/microglial cells (TREM2), as is observed in sporadic AD brain. Hence, a LPS normally confined to the GI tract is capable of driving a NF-kB-miRNA-mediated deficiency in gene expression that contributes to alterations in synaptic-architecture and synaptic-deficits, amyloidogenesis, innate-immune defects, and progressive inflammatory signaling, all of which are characteristics of AD-type neurodegeneration. This article will review the most recent research which supports the idea that bacterial components of the GI tract microbiome such as BF-LPS can transverse biophysical barriers and contribute to AD-type change. For the first-time, these results indicate that specific GI tract microbiome-derived neurotoxins have a strong pathogenic role in eliciting alterations in NF-kB-miRNA-directed gene expression that drives the AD process.

Altered Expression of Urea Cycle Enzymes in Amyloid-β Protein Precursor Overexpressing PC12 Cells and in Sporadic Alzheimer's Disease Brain.

Urea cycle enzymes may play important yet poorly characterized roles in Alzheimer's disease (AD). Our previous results showed that amyloid-β (Aβ) affects urea cycle enzymes in rat pheochromocytoma (PC12) cells. The aim of the present study was to investigate the changes in arginases, other urea cycle enzymes, and nitric oxide synthases (NOSs) in PC12 cells transfected with AβPP bearing the double 'Swedish' mutation (APPsw, K670M/N671L) and in postmortem sporadic AD brain hippocampus; the mutation intensifies Aβ production and strongly associates with AD neuropathology. mRNA expression was analyzed using real-time PCR in cell cultures and DNA microarrays in hippocampal CA1 area of human AD brains. Arginase activity was measured spectrophotometrically, and arginine, ornithine, and citrulline levels by high-performance liquid chromatography. Our data demonstrated that the expression and activity of arginases (Arg1 and Arg2), as well as the expression of argininosuccinate synthase (Ass) were significantly reduced in APPsw cells compared to control. However, argininosuccinate lyase (Asl) was upregulated in APPsw cells. Real-time PCR analysis revealed significant elevation of neuronal nitric oxide synthase (Nnos) mRNA in APPsw cells, without changes in the endothelial Enos, whereas inducible Inos was undetectable. The changes were found to follow closely those observed in the human hippocampal CA1 region of sporadic AD brains. The changes in enzyme expression were accompanied in APPsw cells by significantly elevated citrulline, ornithine, and arginine. Our findings demonstrate that AβPP/Aβ alters arginine metabolism and induces a shift of cellular homeostasis that may support the oxidative/nitrosative stress observed in AD.

Differential Pattern of Phospholipid Profile in the Temporal Cortex from E280A-Familiar and Sporadic Alzheimer's Disease Brains.

Lipids are considered important factors in the pathogenesis of Alzheimer's disease (AD). In this study, we realized a comparative analysis of the phospholipid profile and phospholipid composition of the temporal cortex from E280A-familiar AD (FAD), sporadic AD (SAD), and healthy human brains. Findings showed a significant decrease of lysophosphatidylcholine and phosphatidylethanolamine formed by low levels of polyunsaturated fatty acids (20 : 4, 22 : 6) in AD brains. However, phosphatidylethanolamine-ceramide and phosphoglycerol were significantly increased in SAD, conformed by high levels of (18 : 0/18 : 1) and (30/32/36 : 0/1/2), respectively. Together, the findings suggest a deficiency in lysophosphacholine and phosphatidylethanolamine, and alteration in the balance between poly- and unsaturated fatty acids in both types of AD, and a differential pattern of phospholipid profile and fatty acid composition between E280A FAD and SAD human brains.

A Circular RNA (circRNA) ciRS‐7 in Alzheimer's disease (AD) targets miRNA‐7 trafficking and promotes deficits in the expression of the ubiquitin conjugase (UBE2A) and the epidermal growth factor receptor (EGFR)

Circular RNAs (circRNAs) represent a recently described category of novel, single stranded ribonucleic acid (ssRNA) abundantly represented in the eukaryotic transcriptome. Non‐polyadenylated and intrinsically resistant to exonucleolytic attack, circRNAs are a highly stable ssRNA species significantly enriched in human brain and retinal tissues. The biological evolution and function of most central nervous system (CNS) circRNAs, however, remains poorly understood. Established methods of ssRNA detection and quantitation that require a free 3′ or 5′ ribonucleotide end may have significantly underestimated circRNA abundance and importance in CNS function in both health and disease. One highly represented circRNA in the human brain and retina is a ~1400 nucleotide (nt) ciRS‐7 that contains about ~70 tandem anti‐miRNA‐7 sequences; ciRS‐7 thereby acts as a kind of endogenous, competing, anti‐complementary miRNA inhibitor or “sponge” to adsorb, and hence quench, the normal function(s) of miRNA‐7 (hsa‐miRNA‐7‐1; 23 nt; chr 9q21.32). Using DNA and miRNA arrays, RNA‐sequencing, enhanced LED‐Northern, ELISA and Western blot hybridization, the circularity‐sensitive probe RNaseR, energy of association (EA) indexing and miRNA‐mRNA bioinformatics algorithms, we here provide initial evidence of a mis‐regulated miRNA‐7‐anti‐miRNA‐7‐circRNA system in sporadic Alzheimer's disease (AD) brain. Deficits in ciRS‐7, and ciRS‐7 “sponging activities” might be expected to increase ambient miRNA‐7 levels in AD‐affected tissues, as is observed, and these ultimately contribute to the down‐regulation of selective miRNA‐7‐sensitive messenger RNA (mRNA) targets. We report here that the up‐regulation of ambient miRNA‐7 in AD brain, due to a deficiency in ciRS‐7 and ciRS‐7‐mediated “sponging” effects, in turn down‐regulates several AD‐relevant mRNA targets and their expression, including the ubiquitin conjugase protein (UBE2A; miRNA‐7‐UBE2A mRNA 3′UTR EA = −22.9 kcal/mol) and the epidermal growth factor receptor (EGFR; miRNA‐7‐EGFR mRNA 3′UTR EA = −23.2 kcal/mol). UBE2A (chr Xq24; ~17kDa), a central effector in the ubiquitination cycle that helps to orchestrate the clearance of amyloid peptides via phagocytosis, is depleted in sporadic AD brain and retina and contributes to amyloidogenesis. Similarly, decreased levels of the transmembrane glycoprotein EGFR (chr 7p11.1; ~134kDa) found in AD appears to be linked to deficits in brain cell proliferation, cytoskeletal rearrangement and angiogenesis. Our conceptual understanding of the highly specialized functions for non‐coding ssRNA such as circRNAs in the human CNS continues to evolve and their presence and activities underscore the increasing complexity of miRNA‐mRNA‐mediated genetic regulatory networks.Support or Funding InformationResearch on miRNA signaling in the Lukiw laboratory involving the innate‐immune response in AD, AMD and in other forms of neurological or retinal disease, amyloidogenesis, ubiquitination, synaptogenesis and brain inflammation was supported through an unrestricted grant to the LSU Eye Center from Research to Prevent Blindness (RPB); the Louisiana Biotechnology Research Network (LBRN) and NIH grants NEI EY006311 and NIA AG038834 (WJL).

In vitro characterization of fibrillar amyloid, tau deposits, and activated astrocytes in Arctic APP and sporadic Alzheimer's disease brain using, 3H-PIB and 3H-THK5117 and 3H-Deprenyl in comparison to immunostaining

In Vitro Characterization Of Fibrillar Amyloid, Tau Deposits, And Activated Astrocytes In Arctic App And Sporadic Alzheimer's Disease Brain Using, 3H-Pib And 3H-Thk5117 And 3H-Deprenyl In Comparison To Immunostaining

All-trans-retinoic Acid Reduces BACE1 Expression under Inflammatory Conditions via Modulation of Nuclear Factor κB (NFκB) Signaling

Insulin resistance and neuroinflammation have emerged as two likely key contributors in the pathogenesis of Alzheimer disease (AD), especially in those sporadic AD cases compromised by diabetes or cardiovascular disease. Amyloid-β (Aβ) deposition and its associated inflammatory response are hallmarks in sporadic AD brains. Elevated expression and activity of β-secretase 1 (BACE1), the rate-limiting enzyme responsible for the β-cleavage of amyloid precursor proteins to Aβ peptides, are also observed in sporadic AD brains. Previous studies have suggested that there is therapeutic potential for retinoic acid in treating neurodegeneration based on decreased Aβ. Here we discovered that BACE1 expression is elevated in the brains of both Tg2576 transgenic mice and mice on high fat diets. These conditions are associated with a neuroinflammatory response. We found that administration of all-trans-retinoic acid (atRA) down-regulated the expression of BACE1 in the brains of Tg2576 mice and in mice fed a high fat diet. Moreover, in LPS-treated mice and cultured neurons, BACE1 expression was repressed by the addition of atRA, correlating with the anti-inflammatory efficacy of atRA. Mutations of the NFκB binding site in BACE1 promoter abolished the suppressive effect of atRA. Furthermore, atRA disrupted LPS-induced nuclear translocation of NFκB and its binding to BACE1 promoter as well as promoting the recruitment of the corepressor NCoR. Our findings indicate that atRA represses BACE1 gene expression under inflammatory conditions via the modulation of NFκB signaling.

Molecular Pathogenesis of Sporadic Alzheimer's Disease (AD) and Pharmaceutical Research to Develop a Biomarker for AD Diagnosis

Alzheimer's disease (AD) is the most common senile dementia. One of the pathological characteristics of AD is the appearance of senile plaques composed of amyloid-β (Aβ) depositions. Aβ is generated by consecutive cleavages of Aβ precursor protein (APP) by β- and γ-secretases. The common pathogenesis for familial AD (FAD) is believed to involve misprocessing of APP by γ-secretase, resulting in increased Aβ42 peptide deposition. However, little is known about γ-secretase function in sporadic AD (SAD), which is the major type of AD. This may be because Aβ42 peptide has highly aggregative properties; therefore it is not easy to estimate the quantitative alteration of net Aβ42 in SAD patients. Alcadein is a family of neural type I membrane proteins. Processing of Alcadein by APP α- and γ-secretases results in secretion of non-aggregative peptide, p3-Alc, into CSF and blood. The C-terminuses of Aβ and p3-Alc are altered by FAD-linked genetic mutations in catalytic components of γ-secretase, in association with an increase in minor Aβ and p3-Alc species. Thus p3-Alcs are expected to behave as useful indicators of γ-secretase dysfunction in SAD brain. Quantitative and qualitative analyses of p3-Alcs raise the possibility that γ-secretase dysfunction may exist even in the absence of genetic mutations. p3-Alc peptides may be a novel biomarker for AD and an indicator of γ-secretase dysfunction for drug development.

Genomic mosaicism with increased amyloid precursor protein (APP) gene copy number in single neurons from sporadic Alzheimer's disease brains.

Previous reports have shown that individual neurons of the brain can display somatic genomic mosaicism of unknown function. In this study, we report altered genomic mosaicism in single, sporadic Alzheimer's disease (AD) neurons characterized by increases in DNA content and amyloid precursor protein (APP) gene copy number. AD cortical nuclei displayed large variability with average DNA content increases of ~8% over non-diseased controls that were unrelated to trisomy 21. Two independent single-cell copy number analyses identified amplifications at the APP locus. The use of single-cell qPCR identified up to 12 copies of APP in sampled neurons. Peptide nucleic acid (PNA) probes targeting APP, combined with super-resolution microscopy detected primarily single fluorescent signals of variable intensity that paralleled single-cell qPCR analyses. These data identify somatic genomic changes in single neurons, affecting known and unknown loci, which are increased in sporadic AD, and further indicate functionality for genomic mosaicism in the CNS.

Somatic signature of brain-specific single nucleotide variations in sporadic Alzheimer's disease.

Although genome-wide association studies have shown that genetic factors increase the risk of suffering late-onset, sporadic Alzheimer's disease (SAD), the molecular mechanisms responsible remain largely unknown. The aim of the study was to investigate the presence of somatic, brain-specific single nucleotide variations (SNV) in the hippocampus of SAD samples. By using bioinformatic tools, we compared whole exome sequences in paired blood and hippocampal genomic DNAs from 17 SAD patients and from 2 controls and 2 vascular dementia patients. We found a remarkable number of SNVs in SAD brains (~575 per patient) that were not detected in blood. Loci with hippocampus-specific (hs)-SNVs were common to several patients, with 38 genes being present in 6 or more patients out of the 17. While some of these SNVs were in genes previously related to SAD (e.g., CSMD1, LRP2), most hs-SNVs occurred in loci previously unrelated to SAD. The most frequent genes with hs-SNVs were associated with neurotransmission, DNA metabolism, neuronal transport, and muscular function. Interestingly, 19 recurrent hs-SNVs were common to 3 SAD patients. Repetitive loci or hs-SNVs were underrepresented in the hippocampus of control or vascular dementia donors, or in the cerebellum of SAD patients. Our data suggest that adult blood and brain have different DNA genomic variations, and that somatic genetic mosaicism and brain-specific genome reshaping may contribute to SAD pathogenesis and cognitive differences between individuals.

The coexistence of an equal amount of Alzheimer's amyloid‐β 40 and 42 forms structurally stable and toxic oligomers through a distinct pathway

Fibrillar amyloid-β (Aβ) is the major constituent of senile plaques in the brain of patients with Alzheimer's disease (AD). Aβ is a short peptide generated from amyloid precursor protein with two main isoforms, Aβ40 and Aβ42, with the latter having two additional hydrophobic residues at the C-terminus. The two isoforms have distinct characteristics, in which Aβ42 plays a more pathogenic role. Some early-onset familial AD cases possess an elevated Aβ42/Aβ40 level, and biochemical studies show the two species interact with each other. Therefore, understanding structural conversion in the aggregation of mixed Aβ isoforms is essential for elucidating AD pathogenesis. Here, we systematically examined the differences between Aβ42, Aβ40 and various Aβ42/Aβ40 mixtures by monitoring the fibrillization kinetics, epitope changes, assembly, morphology and induced cytotoxicity. We found that the minor Aβ species in different mixing ratios modulated the major aggregation pathway. Size exclusion chromatography, circular dichroism spectroscopy and photo-crosslinking assay showed that soluble Aβ42 oligomers were stabilized after Aβ40 addition, and the equimolar Aβ42/Aβ40 mixture rapidly formed spherical oligomers. These oligomers were the most toxic among those examined as evidenced by neurite degeneration and neuronal toxicity. However, the oligomers were not responsible for intracellular calcium elevation. Overall, our results demonstrated that differently mixed Aβ species repartitioned oligomer intermediates on the major aggregation pathway. Furthermore, the equimolar mixture rapidly formed structurally stable and the most toxic oligomers. These results provided information on the potential pathological mechanisms underlying the elevated Aβ42/Aβ40 ratio in familial AD patients and in the local environment of sporadic AD brains.

Reduced Synaptic STIM2 Expression and Impaired Store-Operated Calcium Entry Cause Destabilization of Mature Spines in Mutant Presenilin Mice

Mushroom dendritic spine structures are essential for memory storage, and the loss of mushroom spines may explain memory defects in Alzheimer's disease (AD). Here we show a significant reduction in the fraction of mushroom spines in hippocampal neurons from the presenilin-1 M146V knockin (KI) mouse model of familial AD (FAD). The stabilization of mushroom spines depends on STIM2-mediated neuronal store-operated calcium influx (nSOC) and continuous activity of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). We demonstrate that STIM2-nSOC-CaMKII pathway is compromised in KI neurons, in aging neurons, and in sporadic AD brains due to downregulation of STIM2 protein. We further establish that overexpression of STIM2 rescues synaptic nSOC, CaMKII activity, and mushroom spine loss in KI neurons. Our results identify STIM2-nSOC-CaMKII synaptic maintenance pathway as a novel potential therapeutic target for treatment of AD and age-related memory decline.

Circular RNA (circRNA) in Alzheimer's disease (AD)

Circular RNAs (circRNAs) are a naturally occurring family of noncoding RNAs (ncRNAs) highly represented in the eukaryotic transcriptome. Recently characterized, traditional methods of RNA detection and analysis requiring a free 5′ or 3′ ribonucleotide terminus may have significantly underestimated circRNA abundance and significance in eukaryotic cells (Salzman et al., 2012; Wilusz and Sharp, 2013; unpublished observations). Intrinsically resistant to exonucleolytic RNA decay, circRNAs appear to be enriched in mammalian brain tissues (Hansen et al., 2013; Memczak et al., 2013). Interestingly, specific ncRNAs such as the evolutionary ancient microRNA-7 (miRNA-7; chr 9q21.32; an important post-transcriptional regulator of human brain gene expression), are not only highly abundant in human brain, but are also associated with a circRNA for miRNA-7 (ciRS-7), in the same tissues; ciRS-7 contains multiple, tandem anti-miRNA-7 sequences (Burmistrova et al., 2007; Hansen et al., 2013; Lukiw et al., 2013). ciRS-7 thereby acts as a kind of endogenous, competing, anti-complementary miRNA “sponge” to adsorb, and hence quench, normal miRNA-7 functions. Using Northern blot hybridization techniques and the circularity-sensitive circRNA probe RNaseR we here provide initial evidence of a mis-regulated miRNA-7-circRNA system in the sporadic Alzheimer's disease (AD) hippocampal CA1 region (Figure ​(Figure1).1). Deficits in ciRS-7, and ciRS-7 “sponging activities” might be expected to increase ambient miRNA-7 levels in AD-affected brain cells, as is observed, to ultimately contribute to the down-regulation of selective miRNA-7-sensitive messenger RNA (mRNA) targets (Cogswell et al., 2008; unpublished observations). The presence of up-regulated miRNA-7, due to a deficiency in ciRS-7 “sponging” effects, has high probability to down-regulate AD-relevant targets, such as, for example, the ubiquitin protein ligase A (UBE2A; miRNA-7-UBE2A mRNA energy of association, EA = −22.86 kcal/mol). UBE2A, an autophagic, phagocytic protein essential in the clearance of amyloid peptides in AD and other progressive inflammatory degenerations of the human CNS, is depleted in AD brain (Bingol and Sheng, 2011; Lonskaya et al., 2013). Such miRNA-mRNA regulatory systems mediated by a family of cell- and/or tissue-enriched circRNAs may represent another important layer of epigenetic control over gene expression in health and disease. Indeed, technological advancement and recent discoveries in the field of ncRNAs continue to challenge our basic doctrines of nucleic acid biochemistry and evolutionary biology. Deficits in other circRNA-mediated “miRNA sponging systems” and ambient up-regulation of specific inducible miRNAs may help explain the widely observed, generalized and progressive down-regulation of gene expression that is characteristic of the sporadic AD brain (Loring et al., 2001; Colangelo et al., 2002; Ginsberg et al., 2012; Lukiw, 2013). Figure 1 (A) Detection of circRNA for miRNA-7 (ciRS-7) in sporadic Alzheimer's disease (AD) and age-matched control hippocampal CA1 [control (C) N = 4; AD (A) N = 6]; the single upper ciRS-7 (~1400 nt) band contains ~70 selectively conserved miRNA-7 binding sites ...

Presenilin-1 adopts pathogenic conformation in normal aging and in sporadic Alzheimer's disease.

Accumulation of amyloid-β (Aβ) and neurofibrillary tangles in the brain, inflammation and synaptic and neuronal loss are some of the major neuropathological hallmarks of Alzheimer's disease (AD). While genetic mutations in amyloid precursor protein and presenilin-1 and -2 (PS1 and PS2) genes cause early-onset familial AD, the etiology of sporadic AD is not fully understood. Our current study shows that changes in conformation of endogenous wild-type PS1, similar to those found with mutant PS1, occur in sporadic AD brain and during normal aging. Using a mouse model of Alzheimer's disease (Tg2576) that overexpresses the Swedish mutation of amyloid precursor protein but has normal levels of endogenous wild-type presenilin, we report that the percentage of PS1 in a pathogenic conformation increases with age. Importantly, we found that this PS1 conformational shift is associated with amyloid pathology and precedes amyloid-β deposition in the brain. Furthermore, we found that oxidative stress, a common stress characteristic of aging and AD, causes pathogenic PS1 conformational change in neurons in vitro, which is accompanied by increased Aβ42/40 ratio. The results of this study provide important information about the timeline of pathogenic changes in PS1 conformation during aging and suggest that structural changes in PS1/γ-secretase may represent a molecular mechanism by which oxidative stress triggers amyloid-β accumulation in aging and in sporadic AD brain.

Aβ1‐42‐mediated down‐regulation of Uch‐L1 is dependent on NF‐κB activation and impaired BACE1 lysosomal degradation

Amyloid-β 1-42 accumulation is the major pathogenetic event in Alzheimer's disease (AD), believed to be responsible for synaptic dysfunction and neuronal cell death. However, the physiologic activity of Aβ peptides remains elusive: Aβ might not only play a toxic role, but also act as a functional signaling intermediate. We recently reported that Aβ1-42 promotes BACE1 transcription through the activation of the JNK-c-jun pathway. Here, we show that the Aβ1-42-mediated increase in BACE1 expression is accompanied by a decrease in ubiquitin C-terminal hydrolase L1 (Uch-L1) expression and activity in different cellular models such as neuroblastoma SH-SY5Y as well as NT(2) neuronal cells. We also found that the increase in BACE1 and the decrease in Uch-L1 are related events and depend on NF-κB pathway; thus, Aβ1-42 is able to activate NF-κB pathway and the pretreatment with a pharmacological inhibitor, able to block the nuclear translocation of the transactivating unit p65, almost completely prevents both the decrease in Uch-L1 and the increase in BACE1 expression. In addition, the decrease in Uch-L1 activity interferes with the lysosomal degradation of BACE1, as demonstrated by the decrease in Cathepsin D activity and the partial accumulation of BACE1 in lysosomes after Aβ1-42 treatment as well after Uch-L1 inhibition. In support of the in vitro data, we observed low protein levels of Uch-L1 associated with high protein levels of BACE1 in sporadic AD brains. Our data suggest that Uch-L1 could be an attractive target for the development of new therapeutic approaches for AD.

Regulation of β‐site APP‐cleaving enzyme 1 gene expression and its role in Alzheimer’s Disease

Alzheimer's disease (AD) is the most common neurodegenerative disorder leading to dementia. Neuritic plaques are the hallmark neuropathology in AD brains. Proteolytic processing of amyloid-β precursor protein at the β site by beta-site amyloid-β precursor protein-cleaving enzyme 1 (BACE1) is essential to generate Aβ, a central component of the neuritic plaques. BACE1 is increased in some sporadic AD brains, and dysregulation of BACE1 gene expression plays an important role in AD pathogenesis. This review will focus on the regulation of BACE1 gene expression at the transcriptional, post-transcriptional, translation initiation, translational and post-translational levels, and its role in AD pathogenesis. Further studies on BACE1 gene expression regulation will greatly contribute to our understanding of AD pathogenesis and reveal potential novel approaches for AD prevention and drug development.