Bruno Vellas

Association of Plasma Clusterin Concentration With Severity, Pathology, and Progression in Alzheimer Disease

CONTEXTnBlood-based analytes may be indicators of pathological processes in Alzheimer disease (AD).nnnOBJECTIVEnTo identify plasma proteins associated with AD pathology using a combined proteomic and neuroimaging approach.nnnDESIGNnDiscovery-phase proteomics to identify plasma proteins associated with correlates of AD pathology. Confirmation and validation using immunodetection in a replication set and an animal model.nnnSETTINGnA multicenter European study (AddNeuroMed) and the Baltimore Longitudinal Study of Aging.nnnPARTICIPANTSnPatients with AD, subjects with mild cognitive impairment, and healthy controls with standardized clinical assessments and structural neuroimaging.nnnMAIN OUTCOME MEASURESnAssociation of plasma proteins with brain atrophy, disease severity, and rate of clinical progression. Extension studies in humans and transgenic mice tested the association between plasma proteins and brain amyloid.nnnRESULTSnClusterin/apolipoprotein J was associated with atrophy of the entorhinal cortex, baseline disease severity, and rapid clinical progression in AD. Increased plasma concentration of clusterin was predictive of greater fibrillar amyloid-beta burden in the medial temporal lobe. Subjects with AD had increased clusterin messenger RNA in blood, but there was no effect of single-nucleotide polymorphisms in the gene encoding clusterin with gene or protein expression. APP/PS1 transgenic mice showed increased plasma clusterin, age-dependent increase in brain clusterin, as well as amyloid and clusterin colocalization in plaques.nnnCONCLUSIONSnThese results demonstrate an important role of clusterin in the pathogenesis of AD and suggest that alterations in amyloid chaperone proteins may be a biologically relevant peripheral signature of AD.

Genome-wide association with MRI atrophy measures as a quantitative trait locus for Alzheimer's disease.

Alzheimers disease (AD) is a progressive neurodegenerative disorder with considerable evidence suggesting an initiation of disease in the entorhinal cortex and hippocampus and spreading thereafter to the rest of the brain. In this study, we combine genetics and imaging data obtained from the Alzheimers Disease Neuroimaging Initiative and the AddNeuroMed study. To identify genetic susceptibility loci for AD, we conducted a genome-wide study of atrophy in regions associated with neurodegeneration in this condition. We identified one single-nucleotide polymorphism (SNP) with a disease-specific effect associated with entorhinal cortical volume in an intron of the ZNF292 gene (rs1925690; P-value=2.6 × 10−8; corrected P-value for equivalent number of independent quantitative traits=7.7 × 10−8) and an intergenic SNP, flanking the ARPP-21 gene, with an overall effect on entorhinal cortical thickness (rs11129640; P-value=5.6 × 10−8; corrected P-value=1.7 × 10−7). Gene-wide scoring also highlighted PICALM as the most significant gene associated with entorhinal cortical thickness (P-value=6.7 × 10−6).

Mitochondrial Dysfunction and Immune Activation are Detectable in Early Alzheimer's Disease Blood

Alzheimers disease (AD), like other dementias, is characterized by progressive neuronal loss and neuroinflammation in the brain. The peripheral leukocyte response occurring alongside these brain changes has not been extensively studied, but might inform therapeutic approaches and provide relevant disease biomarkers. Using microarrays, we assessed blood gene expression alterations occurring in people with AD and those with mild cognitive changes at increased risk of developing AD. Of the 2,908 differentially expressed probes identified between the three groups (p < 0.01), a quarter were altered in blood from mild cognitive impairment (MCI) and AD subjects, relative to controls, suggesting a peripheral response to pathology may occur very early. There was strong evidence for mitochondrial dysfunction with decreased expression of many of the respiratory complex I-V genes and subunits of the core mitochondrial ribosome complex. This mirrors changes previously observed in AD brain. A number of genes encoding cell adhesion molecules were increased, along with other immune-related genes. These changes are consistent with leukocyte activation and their increased the transition from circulation into the brain. In addition to expression changes, we also found increased numbers of basophils in people with MCI and AD, and increased monocytes in people with an AD diagnosis. Taken together this study provides both an insight into the functional response of circulating leukocytes during neurodegeneration and also identifies potential targets such as the respiratory chain for designing and monitoring future therapeutic interventions using blood.

Whole-exome sequencing and imaging genetics identify functional variants for rate of change in hippocampal volume in mild cognitive impairment

Whole-exome sequencing of individuals with mild cognitive impairment, combined with genotype imputation, was used to identify coding variants other than the apolipoprotein E (APOE) ɛ4 allele associated with rate of hippocampal volume loss using an extreme trait design. Matched unrelated APOE ɛ3 homozygous male Caucasian participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) were selected at the extremes of the 2-year longitudinal change distribution of hippocampal volume (eight subjects with rapid rates of atrophy and eight with slow/stable rates of atrophy). We identified 57 non-synonymous single nucleotide variants (SNVs) which were found exclusively in at least 4 of 8 subjects in the rapid atrophy group, but not in any of the 8 subjects in the slow atrophy group. Among these SNVs, the variants that accounted for the greatest group difference and were predicted in silico as ‘probably damaging’ missense variants were rs9610775 (CARD10) and rs1136410 (PARP1). To further investigate and extend the exome findings in a larger sample, we conducted quantitative trait analysis including whole-brain search in the remaining ADNI APOE ɛ3/ɛ3 group (N=315). Genetic variation within PARP1 and CARD10 was associated with rate of hippocampal neurodegeneration in APOE ɛ3/ɛ3. Meta-analysis across five independent cross sectional cohorts indicated that rs1136410 is also significantly associated with hippocampal volume in APOE ɛ3/ɛ3 individuals (N=923). Larger sequencing studies and longitudinal follow-up are needed for confirmation. The combination of next-generation sequencing and quantitative imaging phenotypes holds significant promise for discovery of variants involved in neurodegeneration.

A Blood Gene Expression Marker of Early Alzheimer's Disease

A marker of Alzheimers disease (AD) that can accurately diagnose disease at the earliest stage would significantly support efforts to develop treatments for early intervention. We have sought to determine the sensitivity and specificity of peripheral blood gene expression as a diagnostic marker of AD using data generated on HT-12v3 BeadChips. We first developed an AD diagnostic classifier in a training cohort of 78 AD and 78 control blood samples and then tested its performance in a validation group of 26 AD and 26 control and 118 mild cognitive impairment (MCI) subjects who were likely to have an AD-endpoint. A 48 gene classifier achieved an accuracy of 75% in the AD and control validation group. Comparisons were made with a classifier developed using structural MRI measures, where both measures were available in the same individuals. In AD and control subjects, the gene expression classifier achieved an accuracy of 70% compared to 85% using MRI. Bootstrapping validation produced expression and MRI classifiers with mean accuracies of 76% and 82%, respectively, demonstrating better concordance between these two classifiers than achieved in a single validation population. We conclude there is potential for blood expression to be a marker for AD. The classifier also predicts a large number of people with MCI, who are likely to develop AD, are more AD-like than normal with 76% of subjects classified as AD rather than control. Many of these people do not have overt brain atrophy, which is known to emerge around the time of AD diagnosis, suggesting the expression classifier may detect AD earlier in the prodromal phase. However, we accept these results could also represent a marker of diseases sharing common etiology.

Protective variant for hippocampal atrophy identified by whole exome sequencing

We used whole‐exome sequencing to identify variants other than APOE associated with the rate of hippocampal atrophy in amnestic mild cognitive impairment. An in‐silico predicted missense variant in REST (rs3796529) was found exclusively in subjects with slow hippocampal volume loss and validated using unbiased whole‐brain analysis and meta‐analysis across 5 independent cohorts. REST is a master regulator of neurogenesis and neuronal differentiation that has not been previously implicated in Alzheimers disease. These findings nominate REST and its functional pathways as protective and illustrate the potential of combining next‐generation sequencing with neuroimaging to discover novel disease mechanisms and potential therapeutic targets. Ann Neurol 2015;77:547–552

Mitochondrial genes are altered in blood early in Alzheimer's disease

Although mitochondrial dysfunction is a consistent feature of Alzheimers disease in the brain and blood, the molecular mechanisms behind these phenomena are unknown. Here we have replicated our previous findings demonstrating reduced expression of nuclear-encoded oxidative phosphorylation (OXPHOS) subunits and subunits required for the translation of mitochondrial-encoded OXPHOS genes in blood from people with Alzheimers disease and mild cognitive impairment. Interestingly this was accompanied by increased expression of some mitochondrial-encoded OXPHOS genes, namely those residing closest to the transcription start site of the polycistronic heavy chain mitochondrial transcript (MT-ND1, MT-ND2, MT-ATP6, MT-CO1, MT-CO2, MT-C03) and MT-ND6 transcribed from the light chain. Further we show that mitochondrial DNA copy number was unchanged suggesting no change in steady-state numbers of mitochondria. We suggest that an imbalance in nuclear and mitochondrial genome-encoded OXPHOS transcripts may drive a negative feedback loop reducing mitochondrial translation and compromising OXPHOS efficiency, which is likely to generate damaging reactive oxygen species.

Identification of functional variants from whole-exome sequencing, combined with neuroimaging genetics

Identification of functional variants from whole-exome sequencing, combined with neuroimaging genetics

No Evidence to Suggest that the Use of Acetylcholinesterase Inhibitors Confounds the Results of Two Blood-Based Biomarker Studies in Alzheimer's Disease

BACKGROUNDnThere is an urgent need to discover Alzheimers disease (AD) biomarkers that are both easily measured and reliable. Research into blood-based biomarkers for AD using transcriptomics and proteomics has been an attractive and promising area of research. However, to date researchers have not looked into the possibility of AD medication being a confounding factor in these studies.nnnOBJECTIVEnThis study explored whether acetylcholinesterase inhibitors (AChEIs), the main class of AD medication, are a confounding factor in AD blood biomarker studies.nnnMETHODSnThe most promising blood transcriptomic and proteomic biomarkers from two recent studies were analyzed to determine if they were differentially expressed between AD subjects on AChEIs and subjects that were not.nnnRESULTSnNone of the gene or protein biomarkers analyzed were found to be significantly altered between subjects in either group.nnnCONCLUSIONnThis study found no evidence that AChEIs are a confounding factor in these published AD blood biomarker studies. Further work is needed to confirm that this is also the case for other proposed biomarkers.

Genome-wide association analysis identifies common variants associated with measures of disease progression in patients with Alzheimer's disease

Background: Alzheimers disease (AD), a leading cause of dementia among the elderly, is a complex neurodegenerative disorder with a strong genetic component. Recent genome-wide association studies (GWAS) have identified loci that alter the risk of AD, but little is known about the genetic risk factors involved with rate of cognitive decline (ROD). Here we report on one of the first GWAS with disease progression in AD patients from the EU funded AddNeuroMed (ANM) project. Methods: Alzheimers patients provided MMSE, CDR and ADAS-cog scores at baseline and for four additional visits over the subsequent year. Rates of decline were calculated over this period using mixed models and the slopes were used as quantitative traits for association analysis. The models included significant covariates such as education and medication. We imputed ∼37 million SNPs from the 1000 Genomes reference panel b37, June 2011 release into the ANM samples using IMPUTEv2. After stringent quality control, 5, 561, 292 SNPs remained for association analysis with ADAS-cog, CDR and MMSE. All analyses were performed under an additive model adjusting for age, sex and APOE4 status using SNPTESTv2 . We corrected for population stratification using principle component analysis (Genomic inflation factors for ADAS-cog, CDR and MMSE were 1.00, 1.02 and 1.01 respectively). Results: We identified 21 novel signals with p<5x10-8: 13 with ADAS-cog, two with CDR and six with MMSE. We also observed nominal association (P <0.05, min-P = 5x10-6) with multiple variants in and around ( ± 250kb) many of the previously identified GWAS AD loci and candidate genes: CLU, ABCA7, CR1, PICALM, CD33, MS4A6A, MS4A4E, BIN1, CD2AP, EXOC3L2, TNF, SORL1, FTO, ACE, MTHFD1L and ATXN1, and with the recently identified GWAS hits for ROD in subjects with mild cognitive impairment (MCI): ACOT11, MYO9A and UBR5. Conclusions: We have identified new loci associated with ROD in AD patients and provide further evidence for known AD/MCI candidate loci with ROD. We will report results of a meta-analysis with the Alzheimers Disease Neuroimaging Initiative (ADNI) cohort.