Franck Hansmannel

Increased expression of BIN1 mediates Alzheimer genetic risk by modulating tau pathology

Genome-wide association studies (GWAS) have identified a region upstream the BIN1 gene as the most important genetic susceptibility locus in Alzheimer’s disease (AD) after APOE. We report that BIN1 transcript levels were increased in AD brains and identified a novel 3 bp insertion allele ∼28 kb upstream of BIN1, which increased (i) transcriptional activity in vitro, (ii) BIN1 expression levels in human brain and (iii) AD risk in three independent case-control cohorts (Meta-analysed Odds ratio of 1.20 (1.14–1.26) (P=3.8 × 10−11)). Interestingly, decreased expression of the Drosophila BIN1 ortholog Amph suppressed Tau-mediated neurotoxicity in three different assays. Accordingly, Tau and BIN1 colocalized and interacted in human neuroblastoma cells and in mouse brain. Finally, the 3 bp insertion was associated with Tau but not Amyloid loads in AD brains. We propose that BIN1 mediates AD risk by modulating Tau pathology.

Transcriptomic and genetic studies identify IL-33 as a candidate gene for Alzheimer's disease

The only recognized genetic determinant of the common forms of Alzheimers disease (AD) is the ɛ4 allele of the apolipoprotein E gene (APOE). To identify new candidate genes, we recently performed transcriptomic analysis of 2741 genes in chromosomal regions of interest using brain tissue of AD cases and controls. From 82 differentially expressed genes, 1156 polymorphisms were genotyped in two independent discovery subsamples (n=945). Seventeen genes exhibited at least one polymorphism associated with AD risk, and following correction for multiple testing, we retained the interleukin (IL)-33 gene. We first confirmed that the IL-33 expression was decreased in the brain of AD cases compared with that of controls. Further genetic analysis led us to select three polymorphisms within this gene, which we analyzed in three independent case–control studies. These polymorphisms and a resulting protective haplotype were systematically associated with AD risk in non-APOE ɛ4 carriers. Using a large prospective study, these associations were also detected when analyzing the prevalent and incident AD cases together or the incident AD cases alone. These polymorphisms were also associated with less cerebral amyloid angiopathy (CAA) in the brain of non-APOE ɛ4 AD cases. Immunohistochemistry experiments finally indicated that the IL-33 expression was consistently restricted to vascular capillaries in the brain. Moreover, IL-33 overexpression in cellular models led to a specific decrease in secretion of the Aβ40 peptides, the main CAA component. In conclusion, our data suggest that genetic variants in IL-33 gene may be associated with a decrease in AD risk potentially in modulating CAA formation.

Evidence for induction of the ornithine transcarbamylase expression in Alzheimer's disease

To more rapidly identify candidate genes located within chromosomal regions of interest defined by genome scan studies in Alzheimers disease (AD), we have developed a customized microarray containing all the ORFs (n=2741) located within nine of these regions. Levels of gene expression were assessed in total RNA from brain tissue of 12 controls and 12 AD patients. Of all genes showing differential expression, we focused on the ornithine transcarbamylase (OTC) gene on Xp21.1., a key enzyme of the urea cycle which we found to be expressed in AD brains but not in controls, as confirmed by RT–PCR. We also detected mRNA expression of all the other urea cycle enzymes in AD brains. Immunochemistry experiments revealed that the OTC expression was strictly restricted to vascular endothelial cells in brain. Furthermore, OTC activity was 880% increased in the CSF of probable AD cases compared with controls. We analysed the association of the OTC −389 G/A and −241 A/G promoter polymorphisms with the risk of developing AD. We observed that rare haplotypes may be associated with the risk of AD through a possible modulation of the methylation of the OTC promoter. In conclusion, our results suggest the involvement of a new pathway in AD brains involving the urea cycle.

Is the Urea Cycle Involved in Alzheimer's Disease?

Since previous observations indicated that the urea cycle may have a role in the Alzheimers disease (AD) process, we set out to quantify the expression of each gene involved in the urea cycle in control and AD brains and establish whether these genes could be genetic determinants of AD. We first confirmed that all the urea cycle enzyme genes are expressed in the AD brain. The expression of arginase 2 was greater in the AD brain than in the control brain. The presence of the rare arginase 2 allele rs742869 was associated with an increase in the risk of AD in men and with an earlier age-at-onset for both genders. None of the other genes in the pathway appeared to be differentially expressed in the AD brain or act as genetic determinants of the disease.

A study of the association between the ADAM12 and SH3PXD2A (SH3MD1) genes and Alzheimer's disease

Several observations suggest that neurotoxicity in Alzheimers disease (AD) can be partly attributed to beta-amyloid (Abeta) and senile plaques. Recent work has suggested that the FISH (five SH3 domains) adapter protein and ADAM12 (a disintegrin and metalloprotease) may mediate the neurotoxic effect of Abeta. Both genes are located on chromosome 10, within a region linked to AD (for SH3PXD2A) or nearby (for ADAM12). A recent study reported a statistically significant interaction between 2 variants of these genes (rs3740473 for SH3PXD2A and rs11244787 for ADAM12) with respect to the risk of developing AD. With a view to replicating this observation, we genotyped the two SNPs in four European case-control cohorts of Caucasian origin (1913 cases and 1468 controls) but were unable to confirm the initial results.

Is the ornithine transcarbamylase gene a genetic determinant of Alzheimer's disease?

Expression of ornithine transcarbamylase (OTC) is strongly induced in the brain of individuals suffering from Alzheimers Disease (AD). Association studies in a population from northern France have revealed that two SNPs -389 G/A (rs5963409) and -241 A/G (rs5963411) located in the promoter of the OTC gene are associated with the risk of developing AD. In the present work, these association studies were extended to a population of 2113 AD cases and 1580 controls from northern France, western France, the United Kingdom and Italy. The rs5963409 minor allele was weakly but significantly associated with an increased risk of developing AD (OR=1.19, p=0.004). This association was independent of age and ApoE status. Our results support that the OTC gene may be a minor genetic determinant of AD.

Association of Ornithine Transcarbamylase Gene Polymorphisms With Hypertension and Coronary Artery Vasomotion

BACKGROUND Previous studies have suggested that the activity of enzymes involved in the urea cycle may modulate nitric oxide (NO) production, arterial vasomotion, and hypertension. Our aim was to determine whether hypertension and coronary vasomotion could be associated with polymorphisms within the ornithine transcarbamylase (OTC) gene, located on chromosome X and coding for a key-enzyme of the urea cycle. METHODS Among 11 OTC polymorphisms that were originally selected from databases, the tag single-nucleotide polymorphism (SNP) rs5963409 and the independent SNP rs1800321 were tested for association with hypertension in two independent population samples recruited in Northern (Multinational MONItoring of trends and determinants in CArdiovascular disease (MONICA) study, n = 1,138) and Western (Etude du Vieillissement Artériel (EVA) study, n = 1,166) France. The vasomotor response of coronary arteries to methylergonovine maleate and isosorbide dinitrate was also evaluated in an independent sample (the vasomotion study, n = 121). RESULTS In males, the frequency of the rs5963409 minor allele was consistently higher in hypertensive (HT) than in normotensive subjects in the MONICA and EVA studies. In the combined sample, the rs5963409 minor allele was associated with an increased risk of hypertension (odds ratio (OR) (95% confidence interval (CI)) = 1.45 (1.10-1.90); P = 0.008). This association was independent of classical confounding factors. Consistently, rs5963409 minor allele was associated with a greater susceptibility to vasoconstriction in response to methylergonovine maleate (P = 0.0072). In contrast, no significant association between rs5963409 and hypertension could be detected in females. CONCLUSION Our results suggest that the OTC rs5963409 polymorphism may be associated with hypertension and coronary vasomotion in males.

Involvement of IL-33 in Alzheimer's disease

tides (Ab) and biometals in the brain represent a major pathogenic pathway in Alzheimer’s disease (AD) and provide the basis for clinical effective disease-modifying therapy (Duce and Bush, 2010; Lannfelt, 2008). Mapping the micro anatomical distribution of essential and trace elements and isotopes in the brain is essential for understanding AD pathobiology and designing new disease-modifying therapies. To date, mapping the brain metallome has been limited by technical barriers. Here we developed a new technique, High-Resolution Metallomic Imaging Mass Spectrometry (HRMIMS), to perform the first high-resolution multi-elemental and isotopic distribution maps of the brain metallome in the Tg2576 transgenic AD mouse model compared to wild-type control mice. Methods: Mice were procured from the Boston University Alzheimer’s Disease Center Transgenic Mouse Facility. Mouse brains were flash frozen and analyzed by metallomic imaging mass spectrometry (MIMS mapping) using a custom cryogenic cell coupled to nanosecond ultraviolet laser ablation (NULA) and hyphenated high-resolution magnetic sector field ICP-MS at the Boston University Center for Biometals & Metallomics, Boston, MA. Laser wavelength, 213 nm; rate, 5-50 mms-1; spot size: 10 micron (high resolution) to 100 micron (scanning resolution). MIMS analysis was conducted on surround to establish elemental background and calibrated with NIST standards. Results: High resolution metallomic maps generated from Tg2576 (Tg) and wild-type (Wt) mouse brain demonstrated unique elemental and isotopic distribution patterns. Zinc (Zn) brain maps revealed a distinctive distribution pattern marked by cortical lamination, prominent allocortical (hippocampus, amygdala) deposition, and isotopic (67Zn, 70Zn). This pattern was progressively disrupted in Tg mice as a function of age with abnormal Zn accumulation co-localizing with amyloid plaque and Timm’s staining. Simultaneous metallomic maps of the same Wt and Tg brains revealed distinctive elemental and isotopic distribution patterns for other important biometals, including copper (Cu), iron (Fe), selenium (Se), molybdenum (Mo), manganese (Mn), and others. Conclusions: We deployed HR-MIMS analysis to generate detailed quantitative high-resolution spatial distribution maps of essential and trace elements and isotopes in Tg2576 transgenic and wild-type mouse brain at 10-100 micron spatial resolution. This study strongly supports a role for zinc in AD-linked brain pathology.