Integrated DNA Methylation/RNA Profiling in Middle Temporal Gyrus of Alzheimer's Disease.

Alzheimer's disease is a neurodegenerative disorder clinically defined by gradual cognitive impairment and alteration in executive function. We conducted an epigenome-wide association study (EWAS) of a clinically and neuropathologically characterized cohort of 296 brains, including Alzheimer's disease (AD) and non-demented controls (ND), exploring the relationship with the RNA expression from matched donors. We detected 5246 CpGs and 832 regions differentially methylated, finding overlap with previous EWAS but also new associations. CpGs previously identified in ANK1, MYOC, and RHBDF2 were differentially methylated, and one of our top hits (GPR56) was not previously detected. ANK1 was differentially methylated at the region level, along with APOE and RHBDF2. Only a small number of genes showed a correlation between DNA methylation and RNA expression statistically significant. Multiblock partial least-squares discriminant analysis showed several CpG sites and RNAs discriminating AD and ND (AUC = 0.908) and strongly correlated with each other. Furthermore, the CpG site cg25038311 was negatively correlated with the expression of 22 genes. Finally, with the functional epigenetic module analysis, we identified a protein-protein network characterized by inverse RNA/DNA methylation correlation and enriched for "Regulation of insulin-like growth factor transport", with IGF1 as the hub gene. Our results confirm and extend the previous EWAS, providing new information about a brain region not previously explored in AD DNA methylation studies. The relationship between DNA methylation and gene expression is not significant for most of the genes in our sample, consistently with the complexities in the gene expression regulation.

Blood RNA transcripts reveal similar and differential alterations in fundamental cellular processes in Alzheimer's disease and other neurodegenerative diseases.

BACKGROUND: Dysfunctional processes in Alzheimer's disease and other neurodegenerative diseases lead to neural degeneration in the central and peripheral nervous system. Research demonstrates that neurodegeneration of any kind is a systemic disease that may even begin outside of the region vulnerable to the disease. Neurodegenerative diseases are defined by the vulnerabilities and pathology occurring in the regions affected. METHOD: A random forest machine learning analysis on whole blood transcriptomes from six neurodegenerative diseases generated unbiased disease-classifying RNA transcripts subsequently subjected to pathway analysis. RESULTS: We report that transcripts of the blood transcriptome selected for each of the neurodegenerative diseases represent fundamental biological cell processes including transcription regulation, degranulation, immune response, protein synthesis, apoptosis, cytoskeletal components, ubiquitylation/proteasome, and mitochondrial complexes that are also affected in the brain and reveal common themes across six neurodegenerative diseases. CONCLUSION: Neurodegenerative diseases share common dysfunctions in fundamental cellular processes. Identifying regional vulnerabilities will reveal unique disease mechanisms. HIGHLIGHTS: Transcriptomics offer information about dysfunctional processes. Comparing multiple diseases will expose unique malfunctions within diseases. Blood RNA can be used ante mortem to track expression changes in neurodegenerative diseases. Protocol standardization will make public datasets compatible.

Oligomeric amyloid ß preferentially targets neuronal and not glial mitochondrial-encoded mRNAs.

INTRODUCTION: Our laboratories have demonstrated that accumulation of oligomeric amyloid ß (OAß) in neurons is an essential step leading to OAß-mediated mitochondrial dysfunction. METHODS: Alzheimer's disease (AD) and matching control hippocampal neurons, astrocytes, and microglia were isolated by laser-captured microdissection from the same subjects, followed by whole-transcriptome sequencing. Complementary in vitro work was performed in OAß-treated differentiated SH-SY5Y, followed by the use of a novel CoQ10 analogue for protection. This compound is believed to be effective both in suppressing reactive oxygen species and also functioning in mitochondrial electron transport. RESULTS: We report decreases in the same mitochondrial-encoded mRNAs in Alzheimer's disease laser-captured CA1 neurons and in OAß-treated SH-SY5Y cells, but not in laser-captured microglia and astrocytes. Pretreatment with a novel CoQ10 analogue, protects neuronal mitochondria from OAß-induced mitochondrial changes. DISCUSSION: Similarity of expression changes in neurons from Alzheimer's disease brain and neuronal cells treated with OAß, and the effect of a CoQ10 analogue on the latter, suggests a pretreatment option to prevent OAß toxicity, long before the damage is apparent.

Nuclear but not mitochondrial-encoded oxidative phosphorylation genes are altered in aging, mild cognitive impairment, and Alzheimer's disease.

INTRODUCTION: We have comprehensively described the expression profiles of mitochondrial DNA and nuclear DNA genes that encode subunits of the respiratory oxidative phosphorylation (OXPHOS) complexes (I-V) in the hippocampus from young controls, age matched, mild cognitively impaired (MCI), and Alzheimer's disease (AD) subjects. METHODS: Hippocampal tissues from 44 non-AD controls (NC), 10 amnestic MCI, and 18 AD cases were analyzed on Affymetrix Hg-U133 plus 2.0 arrays. RESULTS: The microarray data revealed significant down regulation in OXPHOS genes in AD, particularly those encoded in the nucleus. In contrast, there was up regulation of the same gene(s) in MCI subjects compared to AD and ND cases. No significant differences were observed in mtDNA genes identified in the array between AD, ND, and MCI subjects except one mt-ND6. DISCUSSION: Our findings suggest that restoration of the expression of nuclear-encoded OXPHOS genes in aging could be a viable strategy for blunting AD progression.

Blood Transcript Biomarkers Selected by Machine Learning Algorithm Classify Neurodegenerative Diseases including Alzheimer's Disease.

The clinical diagnosis of neurodegenerative diseases is notoriously inaccurate and current methods are often expensive, time-consuming, or invasive. Simple inexpensive and noninvasive methods of diagnosis could provide valuable support for clinicians when combined with cognitive assessment scores. Biological processes leading to neuropathology progress silently for years and are reflected in both the central nervous system and vascular peripheral system. A blood-based screen to distinguish and classify neurodegenerative diseases is especially interesting having low cost, minimal invasiveness, and accessibility to almost any world clinic. In this study, we set out to discover a small set of blood transcripts that can be used to distinguish healthy individuals from those with Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, Friedreich's ataxia, or frontotemporal dementia. Using existing public datasets, we developed a machine learning algorithm for application on transcripts present in blood and discovered small sets of transcripts that distinguish a number of neurodegenerative diseases with high sensitivity and specificity. We validated the usefulness of blood RNA transcriptomics for the classification of neurodegenerative diseases. Information about features selected for the classification can direct the development of possible treatment strategies.

Increased isoform-specific phosphodiesterase 4D expression is associated with pathology and cognitive impairment in Alzheimer's disease.

Pharmacological phosphodiesterase 4D (PDE4D) inhibition shows therapeutic potential to restore memory function in Alzheimer's disease (AD), but will likely evoke adverse side effects. As PDE4D encodes multiple isoforms, targeting specific isoforms may improve treatment efficacy and safety. Here, we investigated whether PDE4D isoform expression and PDE4D DNA methylation is affected in AD and whether expression changes are associated with severity of pathology and cognitive impairment. In post-mortem temporal lobe brain material from AD patients (n = 42) and age-matched controls (n = 40), we measured PDE4D isoform expression and PDE4D DNA (hydroxy)methylation using quantitative polymerase chain reaction and Illumina 450k Beadarrays, respectively. Linear regression revealed increased PDE4D1, -D3, -D5, and -D8 expression in AD with concurrent (hydroxy)methylation changes in associated promoter regions. Moreover, increased PDE4D1 and -D3 expression was associated with higherplaque and tau pathology levels, higher Braak stages, and progressed cognitive impairment. Future studies should indicate functional roles of specific PDE4D isoforms and the efficacy and safety of their selective inhibition to restore memory function in AD.

Altered sphingolipid function in Alzheimer's disease; a gene regulatory network approach.

Sphingolipids (SLs) are bioactive lipids involved in various important physiological functions. The SL pathway has been shown to be affected in several brain-related disorders, including Alzheimer's disease (AD). Recent evidence suggests that epigenetic dysregulation plays an important role in the pathogenesis of AD as well. Here, we use an integrative approach to better understand the relationship between epigenetic and transcriptomic processes in regulating SL function in the middle temporal gyrus of AD patients. Transcriptomic analysis of 252 SL-related genes, selected based on GO term annotations, from 46 AD patients and 32 healthy age-matched controls, revealed 103 differentially expressed SL-related genes in AD patients. Additionally, methylomic analysis of the same subjects revealed parallel hydroxymethylation changes in PTGIS, GBA, and ITGB2 in AD. Subsequent gene regulatory network-based analysis identified 3 candidate genes, that is, SELPLG, SPHK1 and CAV1 whose alteration holds the potential to revert the gene expression program from a diseased towards a healthy state. Together, this epigenomic and transcriptomic approach highlights the importance of SL-related genes in AD, and may provide novel biomarkers and therapeutic alternatives to traditionally investigated biological pathways in AD.

Genome Sequences of Novel Torque Teno Viruses Identified in Human Brain Tissue.

Complete genome sequences of two novel torque teno viruses (TTVs) were identified in human brain tissue. These sequences are 3,245 nucleotides (nt) and 2,900 nt long and share 68% and 72% open reading frame 1 (ORF1) identity, respectively, with other human TTVs. This report extends the identification of TTV sequences in the brain.

Cell death and survival pathways in Alzheimer's disease: an integrative hypothesis testing approach utilizing -omic data sets.

Whether a cell lives or dies is controlled by an array of intercepting and dynamic molecular pathways. Although there is evidence of neuronal loss in Alzheimer's disease (AD) and multiple programmed cell death (PCD) pathways have been implicated in this process, there has been no comprehensive evaluation of the dominant pathway responsible for cell death in AD. Likewise, the relative dominance of survival and PCD pathways in AD remains unclear. Here, we present the results of hypothesis-driven bioinformatic analysis of PCD and survival pathway activation in paired methylation and expression data from the middle temporal gyrus (MTG) as well as expression from laser-captured cells from the MTG and hippocampus. The results not only indicate activation of cell death pathways in AD-of which apoptosis is responsible for the largest fraction of upregulated genes-but also of cell survival pathways. These results are indicative of a complex balance between survival and death pathways in AD that future studies should work to delineate at a single cell level.

Transcriptome Changes in the Alzheimer's Disease Middle Temporal Gyrus: Importance of RNA Metabolism and Mitochondria-Associated Membrane Genes.

We used Illumina Human HT-12 v4 arrays to compare RNA expression of middle temporal gyrus (MTG; BA21) in Alzheimer's disease (AD = 97) and non-demented controls (ND = 98). A total of 938 transcripts were highly differentially expressed (adj p < 0.01; log2 FC ≥ |0.500|, with 411 overexpressed and 527 underexpressed in AD. Our results correlated with expression profiling in neurons from AD and ND obtained by laser capture microscopy in MTG from an independent dataset (log2 FC correlation: r = 0.504; p = 2.2e-16). Additionally, selected effects were validated by qPCR. ANOVA analysis yielded no difference between genders in response to AD, but some gender specific genes were detected (e.g., IL8 and AGRN in males, and HSPH1 and GRM1 in females). Several transcripts were associated with Braak staging (e.g., AEBP1 and DNALI1), antemortem MMSE (e.g., AEBP1 and GFAP), and tangle density (e.g., RNU1G2, and DNALI1). At the pathway level, we detected enrichment of synaptic vesicle processes and GABAergic transmission genes. Finally, applying the Weighted Correlation Network Analysis, we identified four expression modules enriched for neuronal and synaptic genes, mitochondria-associated membrane, chemical stimulus and olfactory receptor and non-coding RNA metabolism genes. Our results represent an extensive description of MTG mRNA profiling in a large sample of AD and ND. These data provide a list of genes associated with AD, and correlated to neurofibrillary tangles density. In addition, these data emphasize the importance of mitochondrial membranes and transcripts related to olfactory receptors in AD.

Association of AEBP1 and NRN1 RNA expression with Alzheimer's disease and neurofibrillary tangle density in middle temporal gyrus.

We explored RNA expression changes in the middle temporal gyrus (MTG) of Alzheimer's Disease patients (AD) by RNA sequencing the whole transcriptome of 8 AD and 8 Non-Demented (ND) controls. We used three additional expression datasets from related brain regions to validate the findings. The results highlighted the upregulation of AEBP1 and downregulation of NRN1 in AD, as well as their association with Braak staging and neurofibrillary tangles density. Furthermore, more than 400 protein-coding RNAs enriched for "Clathrin-mediated endocytosis" were validated in independent datasets from the same brain region. Finally, using in silico prediction analysis we found a signature of 52 non-protein coding RNAs that perturb key pathways involved in GABAergic transmission and peptide chain elongation. The association of AEBP1 in our data confirmed other published work examining gene expression in the hippocampus of AD patients. NRN1 is involved in neurite outgrowth, and in previous studies it has been shown to reverse synaptic defects and cognitive function impairment in Tg2576 mice. Finally, our results on non-protein coding RNAs suggest a role of these transcripts in altering synaptic and amyloid-ß associated pathways.

Alzheimer's disease-associated (hydroxy)methylomic changes in the brain and blood.

BACKGROUND: Late-onset Alzheimer's disease (AD) is a complex multifactorial affliction, the pathogenesis of which is thought to involve gene-environment interactions that might be captured in the epigenome. The present study investigated epigenome-wide patterns of DNA methylation (5-methylcytosine, 5mC) and hydroxymethylation (5-hydroxymethylcytosine, 5hmC), as well as the abundance of unmodified cytosine (UC), in relation to AD. RESULTS: We identified epigenetic differences in AD patients (n = 45) as compared to age-matched controls (n = 35) in the middle temporal gyrus, pertaining to genomic regions close to or overlapping with genes such as OXT (- 3.76% 5mC, pSidák = 1.07E-06), CHRNB1 (+ 1.46% 5hmC, pSidák = 4.01E-04), RHBDF2 (- 3.45% UC, pSidák = 4.85E-06), and C3 (- 1.20% UC, pSidák = 1.57E-03). In parallel, in an independent cohort, we compared the blood methylome of converters to AD dementia (n = 54) and non-converters (n = 42), at a preclinical stage. DNA methylation in the same region of the OXT promoter as found in the brain was found to be associated with subsequent conversion to AD dementia in the blood of elderly, non-demented individuals (+ 3.43% 5mC, pSidák = 7.14E-04). CONCLUSIONS: The implication of genome-wide significant differential methylation of OXT, encoding oxytocin, in two independent cohorts indicates it is a promising target for future studies on early biomarkers and novel therapeutic strategies in AD.

Upregulation of histone deacetylase 2 in laser capture nigral microglia in Parkinson's disease.

Histone deacetylase (HDAC) inhibitors have been widely reported to have considerable therapeutic potential in a host of neurodegenerative diseases. However, HDAC inhibitor selectivity and specificity in specific cell classes have been a source of much debate. To address the role of HDAC2 in specific cell classes, and in disease, we examined glial protein and mRNA levels in the substantia nigra (SN) of Parkinson's disease (PD) and normal controls (NCs) by immunohistochemistry and laser captured microdissection followed by quantitative real time polymerase chain reaction. Differential expression analysis in immunohistochemically defined laser capture microglia revealed significant upregulation of HDAC2 in the PD SN compared to NC subjects. Complementary in vivo evidence reveals significant upregulation of HDAC2 protein levels in PD SN microglia compared to NC subjects. Correspondingly, human immortalized telencephalic/mesencephalic microglial cells reveal significant upregulation of HDAC2 in the presence of the potent microglial activator lipopolysaccharide. These data provide evidence that selective inhibition of HDAC2 in PD SN microglia could be a promising approach to treat microglial-initiated nigral dopaminergic neuronal cell loss in PD.

Correction: ANK1 is up-regulated in laser captured microglia in Alzheimer's brain; the importance of addressing cellular heterogeneity.

[This corrects the article DOI: 10.1371/journal.pone.0177814.].

Laser-captured microglia in the Alzheimer's and Parkinson's brain reveal unique regional expression profiles and suggest a potential role for hepatitis B in the Alzheimer's brain.

Expression array data from dozens of laboratories, including our own, show significant changes in expression of many genes in Alzheimer's disease (AD) patients compared with normal controls. These data typically rely on brain homogenates, and information about transcripts specific to microglia and other central nervous system (CNS) cell types, which far outnumber microglia-specific transcripts, is lost. We therefore used single-cell laser capture methods to assess the full range of microglia-specific expression changes that occur in different brain regions (substantia nigra and hippocampus CA1) and disease states (AD, Parkinson's disease, and normal controls). Two novel pathways, neuronal repair and viral processing were identified. Based on KEGG analysis (Kyoto Encyclopedia of Genes and Genomes, a collection of biological pathways), one of the most significant viruses was hepatitis B virus (HBV) (false discovery rate < 0.00000001). Immunohistochemical analysis using HBV-core antibody in HBV-positive control, amnestic mild cognitive impairment, and HBV-positive AD cases show increased HBV immunoreactivity as disease pathology increases. These results are the first, to our knowledge, to show regional differences in human microglia. In addition, these data reveal new functions for microglia and suggest a novel risk factor for AD.

ANK1 is up-regulated in laser captured microglia in Alzheimer's brain; the importance of addressing cellular heterogeneity.

Recent epigenetic association studies have identified a new gene, ANK1, in the pathogenesis of Alzheimer's disease (AD). Although strong associations were observed, brain homogenates were used to generate the data, introducing complications because of the range of cell types analyzed. In order to address the issue of cellular heterogeneity in homogenate samples we isolated microglial, astrocytes and neurons by laser capture microdissection from CA1 of hippocampus in the same individuals with a clinical and pathological diagnosis of AD and matched control cases. Using this unique RNAseq data set, we show that in the hippocampus, ANK1 is significantly (p<0.0001) up-regulated 4-fold in AD microglia, but not in neurons or astrocytes from the same individuals. These data provide evidence that microglia are the source of ANK1 differential expression previously identified in homogenate samples in AD.

Multivariate analyses of peripheral blood leukocyte transcripts distinguish Alzheimer's, Parkinson's, control, and those at risk for developing Alzheimer's.

The need for a reliable, simple, and inexpensive blood test for Alzheimer's disease (AD) suitable for use in a primary care setting is widely recognized. This has led to a large number of publications describing blood tests for AD, which have, for the most part, not been replicable. We have chosen to examine transcripts expressed by the cellular, leukocyte compartment of blood. We have used hypothesis-based cDNA arrays and quantitative PCR to quantify the expression of selected sets of genes followed by multivariate analyses in multiple independent samples. Rather than a single study with no replicates, we chose an experimental design in which there were multiple replicates using different platforms and different sample populations. We have divided 177 blood samples and 27 brain samples into multiple replicates to demonstrate the ability to distinguish early clinical AD (Clinical Dementia Rating scale 0.5), Parkinson's disease (PD), and cognitively unimpaired APOE4 homozygotes, as well as to determine persons at risk for future cognitive impairment with significant accuracy. We assess our methods in a training/test set and also show that the variables we use distinguish AD, PD, and control brain. Importantly, we describe the variability of the weights assigned to individual transcripts in multivariate analyses in repeated studies and suggest that the variability we describe may be the cause of inability to repeat many earlier studies. Our data constitute a proof of principle that multivariate analysis of the transcriptome related to cell stress and inflammation of peripheral blood leukocytes has significant potential as a minimally invasive and inexpensive diagnostic tool for diagnosis and early detection of risk for AD.

Novel method to ascertain chromatin accessibility at specific genomic loci from frozen brain homogenates and laser capture microdissected defined cells.

We describe a novel method for assessing the "open" or "closed" state of chromatin at selected locations within the genome. This method combines the use of Benzonase, which can digest DNA in the presence of actin, with qPCR to define digested regions. We demonstrate the application of this method in brain homogenates and laser captured cells. We also demonstrate application to selected sites within more than one gene and multiple sites within one gene. We demonstrate the validity of the method by treating cells with valproate, known to render chromatin more permissive, and by comparison with classical digestion with DNase I in an in vitro preparation. Although we demonstrate the use of this method in brain tissue we also recognize its applicability to other tissue types.

Aberrant intracellular localization of H3k4me3 demonstrates an early epigenetic phenomenon in Alzheimer's disease.

We have previously reported in Alzheimer's disease (AD) the mislocalization of epigenetic molecules between the cell nucleus and the cytoplasm. We have extended our finding to include the aberrant localization of histone 3 trimethylation on lysine 4 (H3k4me3), an epigenetic mark associated with actively transcribing genes as well as those poised for transcription. These findings raise the question of where the ectopic localization of H3k4me3 fits within the cascade of cell biological events in the progression of AD. We, therefore, examined the expression and intracellular location of H3k4me3 as a function of Braak stage and also in relation to a series of tau markers that are indicative of disease state. Both lines of evidence showed that ectopic localization of H3k4me3 is early in the course of disease. Because of the known role of H3k4me3 in the expression of synaptic genes, our data suggest an epigenetic role in synaptic deficits early in the course of AD.

Differential processing of amyloid precursor protein in brain and in peripheral blood leukocytes.

Because amyloid precursor protein (APP) fragments exist in many tissues throughout the body, including the fluid compartments of blood, they have been the focus of numerous investigations into their potential as a biomarker of Alzheimer's disease. Using immunohistochemistry, immunoelectron microscopy, Western blot, and quantitative real-time-polymerase chain reaction (qRT-PCR) analysis we examined whether APP processing in leukocytes is analogous to APP processing in the brain. We show APP immunoreactivity at light and electron microscopic levels in the cytoplasm and nucleus of peripheral blood leukocytes (PBL) yet our Western blot analysis data demonstrated that brain and PBL contain different APP fragments and differentially expressed APP processing enzymes. A Disintegrin and Metalloproteinase domain 10 (ADAM10), nicastrin, and beta-secretase 2 (BACE2) were present in brain but were undetected in PBL. Presenilin 1 and beta-secretase 1 (BACE1) were detected in both tissues but showed different patterns in Western blots. Quantitative PCR results identified Neprilysin as the only processing enzyme we interrogated in which Western and quantitative PCR data coincided. Although our data on differential processing of APP in brain and PBL point to exercising caution when generalizing between blood and brain with regard to mechanisms, they have no implications regarding utility as biomarkers.