HLA-DR4 influences glial activity in Alzheimer's disease hippocampus

Pharmacogenetic and Association Studies on the Influence of HLA Alleles and Rivastigmine on the Iranian Patients with Late-Onset Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting cognitive function. A number of allelic genes from HLA complex have shown variable associations with AD in different populations. In this study, we investigated the association of DQB1*06:00/x, DRB1*04:00/x, DRB1*15:00/x, and B*07:00/x genotypes with AD and their relevance to the efficacy of rivastigmine treatment in the Iranian population. Our findings suggest that DQB1*06:00/x genotype offers strong protection against AD (P = 0.0074), while B*07:00/x genotype imposes a significant susceptibility for sporadic Alzheimer's disease (SAD) (P = 0.009). Interestingly, B*07:00/x genotype does not show any apparent associations with familial Alzheimer's disease (FAD). Our studies also suggest a pharmacogenetic relationship between drug treatment and presence of a particular genotype in the Iranian LOAD patient population. The Clinical Dementia Rating analysis showed that LOAD patients carrying DRB1*04:00/x genotype tend to display a downward trend in the disease severity and symptoms after 2-year follow-up with rivastigmine treatment. Moreover, in our total patient population, the carriers of DQB1*06:00/x and B*07:00/x alleles have better and worse responses to rivastigmine respectively. We also measured the clinical relevance of the testing for these genotypes employing prevalence-corrected positive predictive value (PcPPV) formula. The PcPPV of testing for DQB1*06:00/x in the Iranian LOAD patients was 1.17% which means that people carrying this genotype have half of the probability of the absolute risk for developing LOAD, whereas the PcPPV of testing for B*07:00/x was 4.45% for SAD, which can be interpreted as a doubling chance for developing LOAD among the Iranian population carrying this genotype. These results also suggest that DQβ1 peptide containing positively charged AAs histidine³⁰ and arginine⁵⁵ and HLA class I β chain containing negatively charges aspartic acid¹¹⁴ and glutamic acid^45,152 in their binding groove plays important roles in protection against and susceptibility for LOAD respectively.

The immunogenetics of neurological disease

Genes encoding antigen-presenting molecules within the human major histocompatibility complex (MHC) account for the highest component of genetic risk for many neurological diseases, such as multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. Myriad genetic, immunological and environmental factors may contribute to an individual's susceptibility to neurological disease. Here, we review and discuss the decades long research on the influence of genetic variation at the MHC locus and the role of immunogenetic killer cell immunoglobulin-like receptor (KIR) loci in neurological diseases, including multiple sclerosis, neuromyelitis optica, Parkinson's disease, Alzheimer's disease, schizophrenia, myasthenia gravis and amyotrophic lateral sclerosis. The findings of immunogenetic association studies are consistent with a polygenic model of inheritance in the heterogeneous and multifactorial nature of complex traits in various neurological diseases. Future investigation is highly recommended to evaluate both coding and non-coding variation in immunogenetic loci using high-throughput high-resolution next-generation sequencing technologies in diverse ethnic groups to fully appreciate their role in neurological diseases.

Effects of HLA-DRB1/DQB1 Genetic Variants on Neuroimaging in Healthy, Mild Cognitive Impairment, and Alzheimer's Disease Cohorts

Alzheimer's disease (AD) is the most common form of dementia and exhibits a considerable level of heritability. Previous association studies gave evidence for the associations of HLA-DRB1/DQB1 alleles with AD. However, how and when the gene variants in HLA-DRB1/DQB1 function in AD pathogenesis has yet to be determined. Here, we firstly investigated the association of gene variants in HLA-DRB1/DQB1 alleles and AD related brain structure on magnetic resonance imaging (MRI) in a large sample from the Alzheimer's Disease Neuroimaging Initiative (ADNI). We selected hippocampus, subregion, parahippocampus, posterior cingulate, precuneus, middle temporal, entorhinal cortex, and amygdala as regions of interest (ROIs). Twelve SNPs in HLA-DRB1/DQB1 were identified in the dataset following quality control measures. In the total group hybrid population analysis, our study (rs35445101, rs1130399, and rs28746809) were associated with the smaller baseline volume of the left posterior cingulate and rs2854275 was associated with the larger baseline volume of the left posterior cingulate. Furthermore, we detected the above four associations in mild cognitive impairment (MCI) sub-group analysis, and two risk loci (rs35445101 and rs1130399) were also the smaller baseline volume of the left posterior cingulate in (NC) sub-group analysis. Our study suggested that HLA-DRB1/DQB1 gene variants appeared to modulate the alteration of the left posterior cingulate volume, hence modulating the susceptibility of AD.

N-Substituted carbazolyloxyacetic acids modulate Alzheimer associated gamma-secretase

N-Sulfonylated and N-alkylated carbazolyloxyacetic acids were investigated for the inhibition and modulation of the Alzheimer's disease associated gamma-secretase. The introduction of a lipophilic substituent, which may vary from arylsulfone to alkyl, turned 2-carbazolyloxyacetic acids into potent gamma-secretase modulators. This resulted in the selective reduction of Abeta(42) and an increase of the less aggregatory Abeta(38) fragment by several compounds (e.g., 7d and 8c). Introduction of an electron donating group at position 6 and 8 of N-substituted carbazolyloxyacetic acids either decreased the activity or inversed modulation. The most active compounds displayed activity on amyloid precursor protein (APP) overexpressing cell lines in the low micromolar range and little or no effect on the gamma-secretase cleavage at the epsilon-site.

Histocompatibility antigens, aspirin use and cognitive performance in non-demented elderly subjects

HLA genotype and anti-inflammatory drug use have independently been associated with a lower risk of Alzheimer's disease (AD). We recently reported a negative association between aspirin use and AD. To investigate this further, we performed a cross-sectional study to investigate cognitive performance in 151 non-demented individuals in relation to HLA-DRB1 genotype and aspirin use. Aspirin and HLA-DRB1*01 were positive predictors of performance on logical memory (aspirin, p=0.04) and verbal fluency tests (HLA-DRB1*01, p=0.018), respectively. HLA-DRB1*05 had a negative impact on the Boston naming test (p=0.002). Our results suggest that aspirin use and inflammatory genotype may influence cognition in non-demented subjects.