Cathrin Schnack

The role of TREM2 R47H as a risk factor for Alzheimer's disease, frontotemporal lobar degeneration, amyotrophic lateral sclerosis, and Parkinson's disease

A rare variant in TREM2 (p.R47H, rs75932628) was recently reported to increase the risk of Alzheimers disease (AD) and, subsequently, other neurodegenerative diseases, i.e. frontotemporal lobar degeneration (FTLD), amyotrophic lateral sclerosis (ALS), and Parkinsons disease (PD). Here we comprehensively assessed TREM2 rs75932628 for association with these diseases in a total of 19,940 previously untyped subjects of European descent. These data were combined with those from 28 published data sets by meta‐analysis. Furthermore, we tested whether rs75932628 shows association with amyloid beta (Aβ42) and total‐tau protein levels in the cerebrospinal fluid (CSF) of 828 individuals with AD or mild cognitive impairment. Our data show that rs75932628 is highly significantly associated with the risk of AD across 24,086 AD cases and 148,993 controls of European descent (odds ratio or OR = 2.71, P = 4.67 × 10−25). No consistent evidence for association was found between this marker and the risk of FTLD (OR = 2.24, P = .0113 across 2673 cases/9283 controls), PD (OR = 1.36, P = .0767 across 8311 cases/79,938 controls) and ALS (OR = 1.41, P = .198 across 5544 cases/7072 controls). Furthermore, carriers of the rs75932628 risk allele showed significantly increased levels of CSF‐total‐tau (P = .0110) but not Aβ42 suggesting that TREM2s role in AD may involve tau dysfunction.

The Role of Clusterin, Complement Receptor 1, and Phosphatidylinositol Binding Clathrin Assembly Protein in Alzheimer Disease Risk and Cerebrospinal Fluid Biomarker Levels

CONTEXT Two recent and simultaneously published genome-wide association studies independently implicated clusterin (CLU), complement receptor 1 (CR1), and phosphatidylinositol binding clathrin assembly protein (PICALM) as putative novel Alzheimer disease (AD) risk loci. Despite their strong statistical support, all 3 signals emerged from heterogeneous case-control populations and lack replication in different settings. OBJECTIVE To determine whether genetic variants in CLU, CR1, and PICALM confer risk for AD in independent data sets (n = 4254) and to test the impact of these markers on cerebrospinal fluid (CSF)-Aβ42 and total-tau protein levels (n = 425). DESIGN Genetic association study using family-based and case-control designs. SETTING Ambulatory or hospitalized care. PARTICIPANTS Family samples originate from mostly multiplex pedigrees recruited at different centers in the United States (1245 families, 2654 individuals with AD, and 1175 unaffected relatives). Unrelated case-control subjects originate from 1 clinical center in Germany (214 individuals with AD and 211 controls). All subjects were of European descent. MAIN OUTCOME MEASURES The association between 5 genetic variants in CLU, CR1, and PICALM and risk for AD, and the correlation between these 5 genetic variants and CSF-Aβ42 and tau levels. RESULTS All 3 investigated loci showed significant associations between risk for AD (1-tailed P values ranging from <.001 to .02) and consistent effect sizes and direction. For each locus, the overall evidence of association was substantially strengthened on meta-analysis of all available data (2-tailed P values ranging from 1.1 × 10(-16) to 4.1 × 10⁻⁷). Of all markers tested, only rs541458 in PICALM was shown to have an effect on CSF protein levels, suggesting that the AD risk allele is associated with decreased CSF Aβ42 levels (2-tailed P = .002). CONCLUSIONS This study provides compelling independent evidence that genetic variants in CLU, CR1, and PICALM are genetically associated with risk for AD. Furthermore, the CSF biomarker analyses provide a first insight into the potentially predominant pathogenetic mechanism(s) underlying the association between AD risk and PICALM.

Chitinase enzyme activity in CSF is a powerful biomarker of Alzheimer disease

Objective: DNA damage accumulation in brain is associated with the development of Alzheimer disease (AD), but newly identified protein markers of DNA damage have not been evaluated in the diagnosis of AD and other forms of dementia. Methods: Here, we analyzed the level of novel biomarkers of DNA damage and telomere dysfunction (chitinase activity, N-acetyl-glucosaminidase activity, stathmin, and EF-1α) in CSF of 94 patients with AD, 41 patients with non-AD dementia, and 40 control patients without dementia. Results: Enzymatic activity of chitinase (chitotriosidase activity) and stathmin protein level were significantly increased in CSF of patients with AD and non-AD dementia compared with that of no dementia control patients. As a single marker, chitinase activity was most powerful for distinguishing patients with AD from no dementia patients with an accuracy of 85.8% using a single threshold. Discrimination was even superior to clinically standard CSF markers that showed an accuracy of 78.4% (β-amyloid) and 77.6% (tau). Combined analysis of chitinase with other markers increased the accuracy to a maximum of 91%. The biomarkers of DNA damage were also increased in CSF of patients with non-AD dementia compared with no dementia patients, and the new biomarkers improved the diagnosis of non-AD dementia as well as the discrimination of AD from non-AD dementia. Conclusions: Taken together, the findings in this study provide experimental evidence that DNA damage markers are significantly increased in AD and non-AD dementia. The biomarkers identified outperformed the standard CSF markers for diagnosing AD and non-AD dementia in the cohort investigated.

Increased Levels of Antigen-Bound β-Amyloid Autoantibodies in Serum and Cerebrospinal Fluid of Alzheimer’s Disease Patients

Recent studies have suggested a protective role of physiological β-amyloid autoantibodies (Aβ-autoantibodies) in Alzheimer’s disease (AD). However, the determination of both free and dissociated Aβ-autoantibodies in serum hitherto has yielded inconsistent results regarding their function and possible biomarker value. Here we report the application of a new sandwich enzyme-linked immunosorbent assay (ELISA) for the determination of antigen-bound Aβ-autoantibodies (intact Aβ-IgG immune complexes) in serum and cerebrospinal fluid (CSF) of a total number of 112 AD patients and age- and gender-matched control subjects. Both serum and CSF levels of Aβ-IgG immune complexes were found to be significantly higher in AD patients compared to control subjects. Moreover, the levels of Aβ-IgG complexes were negatively correlated with the cognitive status across the groups, increasing with declining cognitive test performance of the subjects. Our results suggest a contribution of IgG-type autoantibodies to Aβ clearance in vivo and an increased immune response in AD, which may be associated with deficient Aβ-IgG removal. These findings may contribute to elucidating the role of Aβ-autoantibodies in AD pathophysiology and their potential application in AD diagnosis.

Engulfment adaptor phosphotyrosine-binding-domain-containing 1 (GULP1) is a nucleocytoplasmic shuttling protein and is transactivationally active together with low-density lipoprotein receptor-related protein 1 (LRP1).

APP (amyloid precursor protein) and LRP1 (low-density lipoprotein receptor-related protein 1) have been implicated in the pathogenesis of AD (Alzheimers disease). They are functionally linked by Fe65, a PTB (phosphotyrosine-binding)-domain-containing adaptor protein that binds to intracellular NPxY-motifs of APP and LRP1, thereby influencing expression levels, cellular trafficking and processing. Additionally, Fe65 has been reported to mediate nuclear signalling in combination with intracellular domains of APP and LRP1. We have previously identified another adaptor protein, GULP1 (engulfment adaptor PTB-domain-containing 1). In the present study we characterize and compare nuclear trafficking and transactivation of GULP1 and Fe65 together with APP and LRP1 and report differential nuclear trafficking of adaptors when APP or LRP1 are co-expressed. The observed effects were additionally supported by a reporter-plasmid-based transactivation assay. The results from the present study indicate that Fe65 might have signalling properties together with APP and LRP1, whereas GULP1 only mediates LRP1 transactivation.

Assessment of Alzheimer's disease risk genes with CSF-biomarker levels

Background: Mutations associated with familial early-onset Alzheimer’s disease (AD) were typically found in amyloid precursor protein (APP), and presenilin1 (PSEN1) and presenilin2 (PSEN2). Among them, mutations in PSEN2 are rare, and fewer than 30 different PSEN2 mutations were reported.Methods: 89 dementia patients under 60 years of age were screened for AD mutations. A PCR based genetic analysis was performed on above dementia patients and 128 normal controls. Following segments were amplified: the APP exon 16-17; PSEN1 exon 4-8 and 11; PSEN2 exon 4-7 and 12. Two efficient mutation detection methods were used for screening our samples: single strand conformation polymorphism (SSCP) and heteroduplex analysis with mismatch-specific nuclease. For the identification and confirmation of the specific mutations, the PCR products were sequenced. Results: A missense PSEN2 mutation, a Val->Leu exchange at codon 214, was found in two unrelated patients. Val214Leu is located at the IVth transmembrane domain of presenilin 2 (PS2). PSEN2Val214Leuwas screened in normal controls, but it was not found in them. In silico modeling of PS2with Val and Leu at the position 214 was performed to contribute their molecular structures. The theoretical model (Figure below) revealed that this mutation might result significant structural modifications inside the PS2 protein, leading to overproduction of amyloid beta. Novel PSEN2 Val214Leu mutation at codon was found in two patients from unrelated families. One patient suffered from late-onset dementia without family history. The second patient is a 55-year-old woman whose only daughter has osteogenesis imperfecta. Since PS2 is component of the gamma-secretase complex, it could cleave the osteoblast regulator molecules. The mutation was absent in 128 control patients, supporting PSEN2 Val214Leu as a novel mutation for AD. Since Leu is more hydrophobic than Val, it might be possible, that Val->Leu exchange could result extra disturbances in the interactions between the TMIV helix and the membrane layer. Conclusions:We predicted the structures of presenilin 2 with native Val 214 residue and Leu 214 mutation, and the results revealed significant structural changes in the region. We found a probable novel mutation in the PSEN2 gene in two patients with Alzheimer’s disease from unrelated two families.

Investigation of alternative binding events between the Golgi-localized, gamma ear-containing, ARF-binding (GGA) protein family and BACE1 and its influence on the processing of amyloid precursor protein (APP)

the microarray analysis, we surveyed the binding sites of transcription factors, using the database produced by UCSC Genome Bioinformatics. Results: The increase in the DNA-binding activity of NF-kappa B and AP-1 after exposure to Abeta fibrils was suppressed by PARP-1 inhibitor, 1,5-dihydroxyisoquinoline (DHIQ), and also PARP-1 siRNA. The microarray analysis demonstrated that among 31,042 probes used, 345 and 224 probe sets showed up-regulation and down-regulation, respectively, in the astrocytes after exposure to Abeta fibrils. Furthermore, 87 probe sets showed down-regulation, while only three probe sets showed up-regulation, after addition of DHIQ. Upstream and downstream of the genes detected by these probe sets, the DNA-binding sites of other transcription factors than NF-kappa B and AP-1 were identified. Conclusions: PARP-1 plays an important role in the change of gene expression profile of astrocytes after exposure to A beta fibrils through the activation of a variety of transcription factors. By regulation of these factors, PARP-1 inhibitors could be new therapeutic and/or neuroprotective agents for Alzheimer’s disease.