Population difference in the association of BDNF promoter methylation with mild cognitive impairment in the Xinjiang Uygur and Han populations

Brain-derived neurotrophic factor (BDNF) epigenomic modifications and brain-related phenotypes in humans: A systematic review

Epigenomic modifications of the brain-derived neurotrophic factor (BDNF) gene have been postulated to underlie the pathogenesis of neurodevelopmental, psychiatric, and neurological conditions. This systematic review summarizes current evidence investigating the association of BDNF epigenomic modifications (DNA methylation, non-coding RNA, histone modifications) with brain-related phenotypes in humans. A novel contribution is our creation of an open access web-based application, the BDNF DNA Methylation Map, to interactively visualize specific positions of CpG sites investigated across all studies for which relevant data were available. Our literature search of four databases through September 27, 2021 returned 1701 articles, of which 153 met inclusion criteria. Our review revealed exceptional heterogeneity in methodological approaches, hindering the identification of clear patterns of robust and/or replicated results. We summarize key findings and provide recommendations for future epigenomic research. The existing literature appears to remain in its infancy and requires additional rigorous research to fulfill its potential to explain BDNF-linked risk for brain-related conditions and improve our understanding of the molecular mechanisms underlying their pathogenesis.

The new mechanism of cognitive decline induced by hypertension: High homocysteine-mediated aberrant DNA methylation

The prevalence and severity of hypertension-induced cognitive impairment increase with the prolonging of hypertension. The mechanisms of cognitive impairment induced by hypertension primarily include cerebral blood flow perfusion imbalance, white and gray matter injury with blood-brain barrier disruption, neuroinflammation and amyloid-beta deposition, genetic polymorphisms and variants, and instability of blood pressure. High homocysteine (HHcy) is an independent risk factor for hypertension that also increases the risk of developing early cognitive impairment. Homocysteine (Hcy) levels increase in patients with cognitive impairment induced by hypertension. This review summarizes a new mechanism whereby HHcy-mediated aberrant DNA methylation and exacerbate hypertension. It involves changes in Hcy-dependent DNA methylation products, such as methionine adenosyltransferase, DNA methyltransferases, S-adenosylmethionine, S-adenosylhomocysteine, and methylenetetrahydrofolate reductase (MTHFR). The mechanism also involves DNA methylation changes in the genes of hypertension patients, such as brain-derived neurotrophic factor, apolipoprotein E4, and estrogen receptor alpha, which contribute to learning, memory, and attention deficits. Studies have shown that methionine (Met) induces hypertension in mice. Moreover, DNA hypermethylation leads to cognitive behavioral changes alongside oligodendroglial and/or myelin deficits in Met-induced mice. Taken together, these studies demonstrate that DNA methylation regulates cognitive dysfunction in patients with hypertension. A better understanding of the function and mechanism underlying the effect of Hcy-dependent DNA methylation on hypertension-induced cognitive impairment will be valuable for early diagnosis, interventions, and prevention of further cognitive defects induced by hypertension.

Epigenetic Peripheral Biomarkers for Early Diagnosis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and represents the leading cause of cognitive impairment and dementia in older individuals throughout the world. The main hallmarks of AD include brain atrophy, extracellular deposition of insoluble amyloid-β (Aβ) plaques, and the intracellular aggregation of protein tau in neurofibrillary tangles. These pathological modifications start many years prior to clinical manifestations of disease and the spectrum of AD progresses along a continuum from preclinical to clinical phases. Therefore, identifying specific biomarkers for detecting AD at early stages greatly improves clinical management. However, stable and non-invasive biomarkers are not currently available for the early detection of the disease. In the search for more reliable biomarkers, epigenetic mechanisms, able to mediate the interaction between the genome and the environment, are emerging as important players in AD pathogenesis. Herein, we discuss altered epigenetic signatures in blood as potential peripheral biomarkers for the early detection of AD in order to help diagnosis and improve therapy.

DNA methylation analyses of the candidate genes identified by a methylome-wide association study revealed common epigenetic alterations in schizophrenia and bipolar disorder

AIM

Schizophrenia (SZ) and bipolar disorder (BD) have been known to share genetic and environmental risk factors, and complex gene-environmental interactions may contribute to their pathophysiology. In contrast to high genetic overlap between SZ and BD, as revealed by genome-wide association studies, the extent of epigenetic overlap remains largely unknown. In the present study, we explored whether SZ and BD share epigenetic risk factors in the same manner as they share genetic components.

METHODS

We performed DNA methylation analyses of the CpG sites in the top five candidate regions (FAM63B, ARHGAP26, CTAGE11P, TBC1D22A, and intergenic region [IR] on chromosome 16) reported in a previous methylome-wide association study (MWAS) of SZ, using whole blood samples from subjects with BD and controls.

RESULTS

Among the five candidate regions, the CpG sites in FAM63B and IR on chromosome 16 were significantly hypomethylated in the samples from subjects with BD as well as those from subjects with SZ. On the other hand, the CpG sites in TBC1D22A were hypermethylated in the samples from subjects with BD, in contrast to hypomethylation in the samples from subjects with SZ.

CONCLUSION

Hypomethylation of FAM63B and IR on chromosome 16 could be common epigenetic risk factors for SZ and BD. Further comprehensive epigenetic studies for BD, such as MWAS, will uncover the extent of similarity and uniqueness of epigenetic alterations.

Elevation of Peripheral BDNF Promoter Methylation Predicts Conversion from Amnestic Mild Cognitive Impairment to Alzheimer's Disease: A 5-Year Longitudinal Study

Epigenetic aberrations have been identified as biomarkers to predict the risk of Alzheimer's disease (AD). This study aimed to evaluate whether altered DNA methylation status of BDNF promoter could be used as potential epigenetic biomarkers for predicting the progression from amnestic mild cognitive impairment (aMCI) to AD. A total of 506 aMCI patients and 728 cognitively normal controls were recruited in the cross-sectional analyses. Patients (n = 458) from aMCI cohort were classified into two groups after 5-year follow-up: aMCI-stable group (n = 330) and AD-conversion group (n = 128). DNA methylation of BDNF promoter was detected by bisulfite-PCR amplification and pyrosequencing. The DNA methylation levels of CpG1 and CpG2 in promoter I and CpG5 and CpG6 in promoter IV of BDNF gene were significantly higher in the aMCI group than in the control group at baseline and also were increased in the conversion group compared with the non-conversion group at 5-year follow up time point. CpG5 in BDNF promoter IV had the highest AUC of 0.910 (95% CI: 0.817-0.983, p < 0.05). Kaplan-Meier analysis showed a significant AD conversion propensity for aMCI patients with high methylation levels of CpG5 (HR = 1.96, 95% CI: 1.07-2.98, p < 0.001). Multivariate Cox regression analysis revealed elevated methylation status of CpG5 was a significant independent predictor for AD conversion (HR = 3.51, p = 0.013). These results suggest that elevation of peripheral BDNF promoter methylation might be used as potential epigenetic biomarkers for predicting the conversion from aMCI to AD.

DNA Methylation of BDNF Gene in Schizophrenia

Background

Although genetic factors are risk factors for schizophrenia, some environmental factors are thought to be required for the manifestation of disease. Epigenetic mechanisms regulate gene functions without causing a change in the nucleotide sequence of DNA. Brain-derived neurotrophic factor (BDNF) is a neurotrophin that regulates synaptic transmission and plasticity. It has been suggested that BDNF may play a role in the pathophysiology of schizophrenia. It is established that methylation status of the BDNF gene is associated with fear learning, memory, and stressful social interactions. In this study, we aimed to investigate the DNA methylation status of BDNF gene in patients with schizophrenia.

Material/Methods

The study included 49 patients (33 male and 16 female) with schizophrenia and 65 unrelated healthy controls (46 male and 19 female). Determination of methylation pattern of CpG islands was based on the principle that bisulfite treatment of DNA results in conversion of unmethylated cytosine residues into uracil, whereas methylated cytosine residues remain unmodified. Methylation-specific PCR was performed with primers specific for either methylated or unmethylated DNA.

Results

There was no significant difference in methylated or un-methylated status for BDNF promoters between schizophrenia patients and controls. The mean duration of illness was significantly lower in the hemi-methylated group compared to the non-methylated group for BDNF gene CpG island-1 in schizophrenia patients.

Conclusions

Although there were no differences in BDNF gene methylation status between schizophrenia patients and healthy controls, there was an association between duration of illness and DNA methylation.