TREM1 mRNA Expression in Leukocytes and Cognitive Function in Japanese Patients with Alzheimer's Disease.

BACKGROUND: Triggering receptor expressed on myeloid cells 2 (TREM2) activates the innate immune system, promotes phagocytosis by microglia, and is associated with Alzheimer's disease (AD). The possible role of a related molecule, TREM1, in AD remains unknown. OBJECTIVE: We investigated a possible role for TREM1 in AD by determining the gene expression and methylation levels of TREM1 in leukocytes from AD patients. METHODS: Fifty patients with AD and 50 age-matched healthy controls were enrolled. AD patients underwent a battery of neuropsychiatric tests. Peripheral blood samples were obtained from each participant, RNA and DNA were extracted, and samples were assessed for TREM1 mRNA expression and methylation rates at three CpG sites in the TREM1 promoter. RESULTS: TREM1 mRNA expression levels in AD patients were significantly higher than those in controls (p = 0.008). TREM1 mRNA expression levels were not correlated with sex, age, duration of illness, APOE genotype, donepezil treatment, or scores of most neuropsychiatric tests. TREM1 mRNA expression levels in AD patients were correlated with the total score of the Montgomery-Åsberg Depression Rating Scale (p = 0.047, r = - 0.344). Methylation rates at the three CpG sites were significantly lower in AD patients than in controls. We also found a significant correlation between TREM1 mRNA expression and TREM1 DNA methylation rates (p < 0.001). CONCLUSION: TREM1 may be associated with the immune responses in AD, and along with hypomethylation at CpG sites in the TREM1 promoter, may become part of a biomarker panel for AD pathogenesis.

MEF2C mRNA expression and cognitive function in Japanese patients with Alzheimer's disease.

AIM: Despite continuing research into Alzheimer's disease (AD), its pathological mechanisms and modulating factors remain unknown. Several genes influence AD pathogenesis by affecting inflammatory pathways. Myocyte-enhancer factor 2C (MEF2C) is one such candidate gene for AD. METHODS: We examined MEF2C mRNA expression levels and methylation rates of CpG on its promoter region in peripheral leukocytes from Japanese AD patients compared with age- and sex-matched control subjects. RESULTS: In peripheral leukocytes, MEF2C mRNA expression levels in AD subjects were significantly lower than those in control subjects (0.86 ± 0.25 vs 0.99 ± 0.27, respectively, P = 0.007) and were correlated with the Alzheimer's Disease Assessment Scale (r = -0.345, P = 0.049) and the Mini Mental State Examination (r = 0.324, P = 0.02). No significant differences were found in methylation rates between AD and control subjects. CONCLUSION: MEF2C mRNA expression in leukocytes may be a biological marker for cognitive decline in AD.

TOMM40 and APOE Gene Expression and Cognitive Decline in Japanese Alzheimer's Disease Subjects.

BACKGROUND: TOMM40 is located on chromosome 19, is in linkage disequilibrium with apolipoprotein E (APOE), andis reported in several genome-wide association studies to be associated with Alzheimer's disease (AD). OBJECTIVE: Assess APOE and TOM40 and mitochondrial genes as blood biomarkers for AD. METHODS: We examined TOMM40, PTEN-induced putative kinase 1 (PINK1), Parkin RBR E3 ubiquitin protein ligase (PARK2), and APOE mRNA expression in relation to the methylation rates of CpG sites in the upstream region of TOMM40exon 1 in peripheral leukocytes and TOMM40523 polyT genotypes in 60 AD and age- and sex-matched control subjects. RESULTS: TOMM40 mRNA expression was significantly lower in AD subjects (0.87±0.18 versus 1.0±0.23, p = 0.005), and PINK1 mRNA expression was higher in AD subjects (1.5±0.61 versus 1.0±0.52, p < 0.001). TOMM40 mRNA expression was significantly correlated with the Mini-Mental State Examination total score (r = 0.290, p = 0.027). There was no expressional change in peripheral APOE mRNA in either AD or control subjects (p = 0.32). Methylation rates in the upstream region of TOMM40exon 1 were not different between AD and control subjects (average rate: 1.37±0.99 versus 1.39±1.20, p = 0.885), and TOMM40523 polyT genotypes were also not different between AD and control subjects (p = 0.67). CONCLUSION: TOMM40 mRNA expression was lower in AD subjects and was correlated with cognitive decline. Significant changes in both TOMM40 and PINK1 mRNA may be related to mitochondrial dysfunction.

DNA Methylation Changes in Intron 1 of Triggering Receptor Expressed on Myeloid Cell 2 in Japanese Schizophrenia Subjects.

A hypothesis for schizophrenia (SCZ) called the "microglia hypothesis" has been suggested. In SCZ, expression of triggering receptor expressed on myeloid cell 2 (TREM2) mRNA is higher in leukocytes than in healthy individuals. Here, the methylation rates of four CpG sites in TREM2 intron 1 that may bind important transcription factors and the correlation between the methylation rate and mRNA expression were determined. We compared the methylation rates in SCZ patients and age-matched controls (n = 50 each). SCZ patients had significantly lower methylation rates of CpG 2 (17.0 ± 6.7 vs. 20.2 ± 5.0; p = 0.02) and CpG 3 (23.8 ± 8.2 vs. 28.1 ± 6.2; p = 0.01). The average methylation rate (15.3 ± 5.2 vs. 17.6 ± 3.9; p = 0.009) was also lower. A significant negative correlation was found between TREM2 mRNA expression and the methylation rate of CpG 2 (r = -0.252, p = 0.012). SCZ susceptibility markers may include low methylation at TREM2 intron 1 and increased TREM2 mRNA levels. Our pilot study requires validation with higher numbers of participants and with other myeloid cell types.

INPP5D mRNA Expression and Cognitive Decline in Japanese Alzheimer's Disease Subjects.

Microglial dysfunction and inflammation have recently been shown to be related to the development of Alzheimer's disease (AD). Inositol polyphosphate-5-phosphatase (INPP5D) functions broadly as a negative regulator of immune signaling, and its locus was associated with development of AD in a large-scale genome-wide association study. Thus, we examined INPP5D mRNA expression and methylation rates of the CpG sites in the upstream region of INPP5D exon 1 in peripheral leukocytes in 50 AD and age- and sex-matched control subjects. INPP5D mRNA expression in AD subjects was significantly higher than that in control subjects (1.16±0.39 versus 1.0±0.23, p = 0.049) and was correlated with the Mini-Mental State Examination score (p = 0.002, r = 0.426) and the total score of the Alzheimer's Disease Assessment Scale (p < 0.001, r = -0.697). Methylation rates in the upstream region of INPP5D exon 1 were not significantly different between AD and control subjects (average rate: 3.5±3.0 versus 2.8±1.3, p = 0.551). Our results suggested that INPP5D mRNA expression was elevated in the early stage and decreased with cognitive decline in AD. INPP5D mRNA expression in leukocytes may be a useful biomarker for the early stage of AD.

DNA methylation changes at TREM2 intron 1 and TREM2 mRNA expression in patients with Alzheimer's disease.

OBJECTIVES: Recent genome-wide association studies revealed that Triggering receptor expressed on myeloid cells 2 (TREM2) was associated with Alzheimer's disease (AD) and other neurodegenerative diseases. We previously reported that TREM2 mRNA is highly expressed in leukocytes of AD patients compared to those in healthy controls. However, the mechanism of TREM2 expression change is still not known. In this study, we examined the involvement of the DNA methylation status of TREM2 in its high gene expression. MATERIALS AND METHODS: Fifty AD subjects and age- and sex-matched control subjects were recruited (25 males, 25 females; 79.9 ± 5.27 and 79.4 ± 3.92 years old, respectively). TREM2 mRNA expression and the percentage of DNA methylation at four CpG sites in intron 1 of TREM2 were studied using their peripheral leukocytes. RESULTS: We confirmed that TREM2 mRNA expression in leukocytes was significantly higher in AD patients than in controls (p = 0.007). The percentage methylation at three CpG sites in TREM2 intron 1 was significantly lower in AD subjects than in control: CpG1, 9.4 ± 3.2 vs 11.9 ± 4.0 (p = 0.001); CpG2, 15.4 ± 4.9 vs 19.1 ± 4.8 (p = 0.001); CpG3, 20.8 ± 5.5 vs 25.5 ± 5.4 (p < 0.001); and the average percentage methylation of all CpG sites: 13.5 ± 3.7 vs 16.1 ± 3.8 (p = 0.002), respectively. In addition, there were significant negative correlations between TREM2 mRNA expression and the percentage DNA methylation of each of CpG sites (CpG1, r = -0.416, p < 0.001; CpG2, r = -0.510, p < 0.001; CpG3, r = -0.504, p < 0.001; CpG4, r = -0.356, p < 0.001). CONCLUSIONS: Lower DNA methylation at TREM2 intron 1 caused higher TREM2 mRNA expression in the leukocytes of AD subjects versus controls and may be a biomarker for AD.

Gene Expression and Methylation Analysis of ABCA7 in Patients with Alzheimer's Disease.

BACKGROUND/OBJECTIVE: The aim of this study was to examine the blood gene expression and methylation of ATP-binding cassette sub-family A member 7 gene (ABCA7) as a biological marker of AD. METHODS: AD subjects (n = 50; 11 males, 77.7±6.05 years old) and age- and sex-matched healthy controls (n = 50) were recruited. A single nucleotide polymorphism in ABCA7 (rs3764650), methylation rates of CpG sites in the ABCA7 promoter region, and ABCA7 mRNA expression levels in peripheral blood were examined. RESULTS: The distribution of the rs3764650 polymorphism in AD subjects was not different from that of controls. Although the methylation rates of AD subjects were not significantly different from those of controls, the ABCA7 mRNA expression level in AD subjects was significantly higher than that in controls. Additionally, the ABCA7 mRNA expression level in AD subjects was significantly correlated with Mini-Mental State Examination recall, the Alzheimer's Disease Assessment Scale total score, and the Clinical Dementia Rating score. We also found a significant correlation between the ABCA7 mRNA expression level and duration of illness. CONCLUSION: The ABCA7 mRNA expression level in peripheral blood may be a marker for early stages of AD and disease progression regardless of rs3764650 and the methylation rate of its promoter.

DNA methylation changes at SNCA intron 1 in patients with dementia with Lewy bodies.

AIM: It is difficult to diagnose dementia with Lewy bodies (DLB) because it exhibits clinical and neuropathological overlap with both Alzheimer's disease and Parkinson's disease. The α-synuclein protein is a major component of Lewy bodies, and accumulation of α-synuclein aggregates causes synaptic dysfunction in DLB. Epigenetic changes at the synuclein alpha ( SNCA ) gene may be involved in DLB pathogenesis. METHODS: We examined DNA methylation rates at 10 CpG sites located in intron 1 of SNCA and SNCA mRNA expression in peripheral leukocytes to compare DLB patients (n = 20; nine men, 11 women; age = 78.8 ± 7.7 years) with healthy controls (n = 20; eight men, 12 women; age = 77.0 ± 6.9 years). RESULTS: The methylation rate at CpG 4 ( P = 0.002) and the overall mean methylation rate at these sites (P < 0.001) were significantly lower in DLB patients than in healthy controls after Bonferroni correction. Although SNCA126 , a partial form of SNCA mRNA expression, was significantly increased in DLB ( P = 0.017), there was no significant difference in total SNCA mRNA expression between DLB patients and healthy controls ( P = 0.165). No correlation was observed between SCNA mRNA expression levels and blood DNA methylation rates in either DLB or healthy controls. CONCLUSION: Our findings indicated that lower methylation rates may be a biomarker for DLB.

Elevated mRNA Expression and Low Methylation of SNCA in Japanese Alzheimer's Disease Subjects.

Despite the continuing debate about the amyloid hypothesis in Alzheimer's disease (AD), the precise pathogenesis is still unclear. Mixed pathology is common and multiple different protein aggregates are seen in human postmortem brains. Aggregates consisting of the alpha-synuclein protein encoded by the Synuclein Alpha gene (SCNA) are common in both dementia with Lewy bodies and AD. We examined SNCA mRNA expression and methylation rates of the CpG island at intron 1 of SNCA in peripheral leukocytes in 50 AD and age- and sex-matched control subjects to verify whether alpha-synuclein pathology affects the AD pathogenesis. SNCA mRNA expression in AD subjects was significantly higher than that in control subjects (1.62±0.73 versus 0.98±0.50, p < 0.001). We found significant differences between AD and control subjects at seven CpG sites (average rate; 8.8±2.7 versus 9.5±2.5, respectively: p = 0.027). The methylation rates tended to be lower in AD subjects at all CpG sites. We conclude that mRNA expression and methylation of SNCA intron 1 are altered in AD, which may be caused by Lewy body pathology in AD.

Association Study and Meta-Analysis of Polymorphisms, Methylation Profiles, and Peripheral mRNA Expression of the Serotonin Transporter Gene in Patients with Alzheimer's Disease.

BACKGROUND/AIM: The aim of this study was to elucidate the relationship between Alzheimer's disease (AD) and the serotonin transporter gene (SLC6A4). METHODS: AD subjects (n = 43) and controls (n = 47) were recruited and evaluated. In leukocytes, we evaluated two polymorphisms in SLC6A4, the serotonin transporter length polymorphic region (5-HTT-LPR) and rs25531, as well as methylation rates of the SLC6A4 promoter region and the SLC6A4 mRNA expression level. We also performed a meta-analysis to examine the relationship between the frequency of the L allele and the risk of AD. RESULTS: The distributions of 5-HTT-LPR and rs25531 polymorphisms in AD subjects were not different from those of controls. Although the methylation rates in AD subjects were not significantly different from those of controls, the expression level in AD subjects was significantly higher than in controls. Additionally, the expression level in AD subjects was significantly correlated with apathy. Meta-analysis revealed that the L/L genotype significantly reduced the risk of AD, but only in the Caucasian population. CONCLUSION: Higher SLC6A4 mRNA expression in leukocytes in AD was associated with apathy regardless of SLC6A4 genotypes and methylation rates of the promoter region. The L/L genotype may reduce the risk of AD in the Caucasian population.