Association of brain-derived neurotrophic factor DNA methylation and reduced white matter integrity in the anterior corona radiata in major depression

Epigenetic aging in major depressive disorder: Clocks, mechanisms and therapeutic perspectives

Depression, a chronic mental disorder characterized by persistent sadness, loss of interest, and difficulty in daily tasks, impacts millions globally with varying treatment options. Antidepressants, despite their long half-life and minimal effectiveness, leave half of patients undertreated, highlighting the need for new therapies to enhance well-being. Epigenetics, which studies genetic changes in gene expression or cellular phenotype without altering the underlying Deoxyribonucleic Acid (DNA) sequence, is explored in this article. This article delves into the intricate relationship between epigenetic mechanisms and depression, shedding light on how environmental stressors, early-life adversity, and genetic predispositions shape gene expression patterns associated with depression. We have also discussed Histone Deacetylase (HDAC) inhibitors, which enhance cognitive function and mood regulation in depression. Non-coding RNAs, (ncRNAs) such as Long Non-Coding RNAs (lncRNAs) and micro RNA (miRNAs), are highlighted as potential biomarkers for detecting and monitoring major depressive disorder (MDD). This article also emphasizes the reversible nature of epigenetic modifications and their influence on neuronal growth processes, underscoring the dynamic interplay between genetics, environment, and epigenetics in depression development. It explores the therapeutic potential of targeting epigenetic pathways in treating clinical depression. Additionally, it examines clinical findings related to epigenetic clocks and their role in studying depression and biological aging.

Greater methylation of the IL-6 promoter region is associated with decreased integrity of the corpus callosum in schizophrenia

BACKGROUND

Schizophrenia is associated with chronic subclinical inflammation and decreased integrity of the corpus callosum (CC). Our previous study showed associations between peripheral IL-6 levels and the integrity of the CC. Epigenetic studies show associations between methylation of the genes related to immunological processes and integrity of the CC.

AIM

To investigate correlations between methylation status of IL-6 promotor and peripheral IL-6 levels and the integrity of the CC in schizophrenia.

MATERIAL AND METHODS

The participants were 29 chronic schizophrenia patients (SCH) and 29 controls. Decreased integrity of the CC was understood as increased mean diffusivity (MD) and/or decreased fractional anisotropy (FA) in diffusion tensor imaging. Peripheral IL-6 concentrations were measured in serum samples and IL-6 promoter methylation status of 6 CpG sites was analyzed in peripheral leukocytes by pyrosequencing.

RESULTS

Moderate positive correlations were found between CpG1 methylation and the MD of proximal regions of the CC (CCR1-CCR3) and between CpGmean and MD of CCR1 in SCH. Weaker positive correlations were found for CpGmean with CCR2 and CCR3 and negative correlations were found for CpG1 and FA of CCR3 in SCH. Multivariate regression showed that methylation of CpG1, type of antipsychotic treatment, and their interaction were significant independent predictors of MD of CCR1 in SCH. Methylation of CpG2 was negatively correlated with serum IL-6 in SCH.

CONCLUSIONS

The methylation level of the IL-6 promotor region in peripheral leukocytes is associated with the integrity of the CC in schizophrenia and this association may depend on the type of antipsychotic treatment. Further studies are necessary to explain the mechanisms of the observed associations.

Smartphone app for lifestyle improvement improves brain health and boosts the vitality and cognitive function of healthy middle-aged adults

INTRODUCTION

The number of smartphone apps for brain training is increasing, and the number of people who are working on brain training is also increasing. However, researchers disagree about the effectiveness of brain training.

METHODS

Therefore, in this study, we conducted an intervention test with the participation of 70 healthy middle-aged men and women and measured the effect of smartphone apps on lifestyle improvement using brain healthcare quotient calculated from brain imaging data.

RESULTS

As a result, in the intervention group, significant improvements were seen in fractional anisotropy (FA) of the whole brain, corpus callosum, internal capsule, corona radiata, posterior thalamic radiation, external capsule, and superior longitudinal fasciculus. Additionally, in the intervention group, these FA increments correlated with improvements in cognitive function as measured by the trail-making test and vigor as measured by the Profile of Mood States 2nd Edition.

CONCLUSION

The results of this study suggest that improving lifestyle habits through smartphone apps can improve brain health and cognitive and emotional performance of healthy middle-aged adults. This is consistent with previous research that suggests that FA integrity in the limbic-thalamo-cortical pathway influences cognitive function and emotion regulation.

Epigenetic modification impacting brain functions: Effects of physical activity, micronutrients, caffeine, toxins, and addictive substances

Changes in gene expression are involved in many brain functions. Epigenetic processes modulate gene expression by histone modification and DNA methylation or RNA-mediated processes, which is important for brain function. Consequently, epigenetic changes are also a part of brain diseases such as mental illness and addiction. Understanding the role of different factors on the brain epigenome may help us understand the function of the brain. This review discussed the effects of caffeine, lipids, addictive substances, physical activity, and pollutants on the epigenetic changes in the brain and their modulatory effects on brain function.

Epigenetic regulation in major depression and other stress-related disorders: molecular mechanisms, clinical relevance and therapeutic potential

Major depressive disorder (MDD) is a chronic, generally episodic and debilitating disease that affects an estimated 300 million people worldwide, but its pathogenesis is poorly understood. The heritability estimate of MDD is 30-40%, suggesting that genetics alone do not account for most of the risk of major depression. Another factor known to associate with MDD involves environmental stressors such as childhood adversity and recent life stress. Recent studies have emerged to show that the biological impact of environmental factors in MDD and other stress-related disorders is mediated by a variety of epigenetic modifications. These epigenetic modification alterations contribute to abnormal neuroendocrine responses, neuroplasticity impairment, neurotransmission and neuroglia dysfunction, which are involved in the pathophysiology of MDD. Furthermore, epigenetic marks have been associated with the diagnosis and treatment of MDD. The evaluation of epigenetic modifications holds promise for further understanding of the heterogeneous etiology and complex phenotypes of MDD, and may identify new therapeutic targets. Here, we review preclinical and clinical epigenetic findings, including DNA methylation, histone modification, noncoding RNA, RNA modification, and chromatin remodeling factor in MDD. In addition, we elaborate on the contribution of these epigenetic mechanisms to the pathological trait variability in depression and discuss how such mechanisms can be exploited for therapeutic purposes.

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.

Astrocytes as Context for the Involvement of Myelin and Nodes of Ranvier in the Pathophysiology of Depression and Stress-Related Disorders

Astrocytes, despite some shared features as glial cells supporting neuronal function in gray and white matter, participate and adapt their morphology and neurochemistry in a plethora of distinct regulatory tasks in specific neural environments. In the white matter, a large proportion of the processes branching from the astrocytes' cell bodies establish contacts with oligodendrocytes and the myelin they form, while the tips of many astrocyte branches closely associate with nodes of Ranvier. Stability of myelin has been shown to greatly depend on astrocyte-to-oligodendrocyte communication, while the integrity of action potentials that regenerate at nodes of Ranvier has been shown to depend on extracellular matrix components heavily contributed by astrocytes. Several lines of evidence are starting to show that in human subjects with affective disorders and in animal models of chronic stress there are significant changes in myelin components, white matter astrocytes and nodes of Ranvier that have direct relevance to connectivity alterations in those disorders. Some of these changes involve the expression of connexins supporting astrocyte-to-oligodendrocyte gap junctions, extracellular matrix components produced by astrocytes around nodes of Ranvier, specific types of astrocyte glutamate transporters, and neurotrophic factors secreted by astrocytes that are involved in the development and plasticity of myelin. Future studies should further examine the mechanisms responsible for those changes in white matter astrocytes, their putative contribution to pathological connectivity in affective disorders, and the possibility of leveraging that knowledge to design new therapies for psychiatric disorders.

Pharmacological targeting of cognitive impairment in depression: recent developments and challenges in human clinical research

Impaired cognition is often overlooked in the clinical management of depression, despite its association with poor psychosocial functioning and reduced clinical engagement. There is an outstanding need for new treatments to address this unmet clinical need, highlighted by our consultations with individuals with lived experience of depression. Here we consider the evidence to support different pharmacological approaches for the treatment of impaired cognition in individuals with depression, including treatments that influence primary neurotransmission directly as well as novel targets such as neurosteroid modulation. We also consider potential methodological challenges in establishing a strong evidence base in this area, including the need to disentangle direct effects of treatment on cognition from more generalised symptomatic improvement and the identification of sensitive, reliable and objective measures of cognition.

Fractional anisotropy and peripheral cytokine concentrations in outpatients with depressive episode: a diffusion tensor imaging observational study

Over the past few years, evidence of a positive relationship between inflammation and depression has grown steadily. The aim of the current study was to investigate whether such depression-related inflammation could also be associated with altered microstructural changes in the white matter. FA and serum cytokines (IL-1β, IL-6, TNF-α, and IFN-γ) were measured in 25 patients with depression (DE) and 24 healthy controls (HC). Diffusion tensor imaging was performed. Fractional anisotropy (FA) was calculated using the FSL pipeline for Tract-Based Spatial Statistics (TBSS). Both voxelwise and mean whole-brain FA were analyzed using general linear models (GLM). Higher concentrations of IL-1β were associated with lower whole-brain fractional anisotropy, particularly in people with depression (ρ = - 0.67; p < 0.001). TNF-α shared some variance with IL-1β and also showed a negative relationship between TNF-α concentrations and FA in depression (F_1,46 = 11.13, p = 0.002, η²p = 0.21). In detail, the voxelwise analysis showed that the regression slopes of IL-1β on FA were more negative in the DE group than in the HC group, mainly in the corpus callosum (cluster statistics: genu corpus callosum, p = 0.022; splenium of corpus callosum, p = 0.047). Similar effects were not found for the other remaining cytokines. This study clearly demonstrated an association between peripherally measured IL-1β and white matter integrity in depression as assessed by DTI. The results suggest that microstructural changes in the corpus callosum are associated with increased peripheral IL-1β concentrations in depression.

Trait-like white matter abnormalities in current and remitted depression

Microstructural alterations to white matter (WM) have been implicated in the onset and recurrence of major depressive disorder (MDD). The present study aimed to identify trait-like WM abnormality in current and remitted depression, as well as changes to WM that could be specifically related to the state of clinical remission. Diffusion tensor imaging data were collected from 60 patients with medication-naive first episode current depression (cMDD), 41 patients with medication-naive remitted depression (rMDD), and 62 demographically-matched healthy control participants (HCs). Tract-based spatial statistics (TBSS) applied to the whole brain were used to detect microstructural differences of WM among the three groups. TBSS analyses showed that, compared with HCs, both the cMDD and rMDD groups exhibited significantly reduced FA values in the genus and body of the corpus callosum, and superior and anterior corona radiata, with no significant differences between the cMDD and rMDD groups. FA values in the corpus callosum were negatively correlated with the duration of illness in the rMDD group. Reduced WM integrity in the corpus callosum and corona radiata might reflect the trait markers of MDD, and could constitute a neuroanatomical marker of MDD.

Oxytocin receptor genes moderate BDNF epigenetic methylation by childhood trauma

OBJECTIVES

Gene-Environment (G × E) interaction is of increasing importance in understanding the pathophysiology of posttraumatic stress disorder (PTSD). This study investigated the interaction effect of childhood traumatic experience and epigenetic methylation of brain-derived neurotrophic factor (BDNF) and a possible moderating effect of oxytocin receptor (OXTR) gene rs53576.

METHODS

Ninety-nine patients with PTSD and 81 healthy controls (HCs) were recruited. Clinical assessments, including the childhood trauma questionnaire (CTQ) and posttraumatic stress disorder Checklist (PCL) were performed. BDNF methylation and OXTR genotyping (A vs. G allele) were conducted through blood sampling. A two-way multivariate analysis and a moderated regression analysis were conducted to investigate the moderating effect of the OXTR gene on the relationship between CTQ and BDNF methylation.

RESULTS

As for the HC group, the interaction effect of the CTQ and OXTR genotype was significant on BDNF methylation, and the moderation model showed that CTQ and OXTR group are significant predictors of BDNF methylation. In the G-OXTR type, the high CTQ group showed a greater BDNF methylation level. As for the PTSD group, no interaction or moderation effects were found.

LIMITATIONS

The present study did not control the dosage, duration of medications, and different trauma types and the assessment of childhood trauma was based on self-report.

CONCLUSIONS

These results suggested that childhood traumatic experience showed a significant impact on BDNF methylation, and OXTR genes have a moderating effect on this epigenetic mechanism in people who have experienced the childhood traumatic episodes.

White Matter Alterations in Depressive Disorder

Depressive disorder is the most prevalent affective disorder today. Depressive disorder has been linked to changes in the white matter. White matter changes in depressive disorder could be a result of impaired cerebral blood flow (CBF) and CBF self-regulation, impaired blood-brain barrier function, inflammatory factors, genes and environmental factors. Additionally, white matter changes in patients with depression are associated with clinical variables such as differential diagnosis, severity, treatment effect, and efficacy assessment. This review discusses the characteristics, possible mechanisms, clinical relevance, and potential treatment of white matter alterations caused by depressive disorders.

Brain conditions mediate the association between aging and happiness

As the population ages, the realization of a long and happy life is becoming an increasingly important issue in many societies. Therefore, it is important to clarify how happiness and the brain change with aging. In this study, which was conducted with 417 healthy adults in Japan, the analysis showed that fractional anisotropy (FA) correlated with happiness, especially in the internal capsule, corona radiata, posterior thalamic radiation, cingulum, and superior longitudinal fasciculus. According to previous neuroscience studies, these regions are involved in emotional regulation. In psychological studies, emotional regulation has been associated with improvement in happiness. Therefore, this study is the first to show that FA mediates the relationship between age and subjective happiness in a way that bridges these different fields.

Abnormal regional spontaneous brain activities in white matter in patients with autism spectrum disorder

Previous studies have demonstrated patients with autism spectrum disorder (ASD) are accompanied by alterations of spontaneous brain activity in gray matter. However, whether the alterations of spontaneous brain activity exist in white matter remains largely unclear. In this study, 88 ASD patients and 87 typical controls (TCs) were included and regional homogeneity (ReHo) was calculated to characterize spontaneous brain activity in white matter. Voxel-wise two-sample t-tests were performed to investigate ReHo alterations, and cluster-level analyses were conducted to examine structural-functional coupling changes. Compared with TCs, the ASD group showed significantly decreased ReHo in the left superior corona radiata and left posterior limb of internal capsule, and decreased ReHo in the left anterior corona radiata with a trend level of significance. In addition, significantly weaker structural-functional coupling was observed in the left superior corona radiata and left posterior limb of internal capsule in ASD patients. Taken together, these findings highlighted abnormalities of white matter's regional spontaneous brain activity in ASD, which may provide new insights into the pathophysiological mechanisms of this disorder.

Associations between Brain Structural Alterations, Executive Dysfunction, and General Psychopathology in a Healthy and Cross-Diagnostic Adult Patient Sample

BACKGROUND

A general psychopathology 'p' factor captures shared variance across mental disorders in diverse samples and may partly reflect executive dysfunction. Higher p factor scores have been related to structural alterations within the visual association cortex (VAC) and a cerebello-thalamo-cerebrocortical circuit (CTCC), both of which are important for executive control. Here, we tested replicability of these direct associations as well as the indirect role of executive functioning in a sample of healthy and cross-diagnostic adult patients.

METHODS

We conducted hypothesis-driven (i.e., region-of-interest) and exploratory whole-brain structural neuroimaging analyses using data from the Consortium for Neuropsychiatric Phenomics study of 272 adults who met diagnostic criteria for schizophrenia, bipolar disorder, or attention deficit-hyperactivity disorder or were healthy controls. Using structural equation modeling, we examined direct and indirect relations between structural neural alterations (within regions-of-interest and regions identified from exploratory analyses) and p and executive function factors.

RESULTS

Higher levels of p were associated with decreased executive functioning and VAC grey matter volume, replicating previous research. In contrast, we failed to replicate prior negative relations between the p factor and CTCC structure. A significant indirect relation between VAC grey matter volume and p via executive function also emerged. Whole-brain analyses identified additional structural alterations in supplementary motor area/cingulate cortex, anterior corona radiata, and corpus callosum genu related to the p factor.

CONCLUSIONS

Executive dysfunction may be one mechanism underlying relations between brain structure and general psychopathology. Replication of VAC structural alterations related to p encourages further focus on this brain structure.

Per1 gene polymorphisms influence the relationship between brain white matter microstructure and depression risk

BACKGROUND

Circadian rhythm was involved in the pathogenesis of depression. The detection of circadian genes and white matter (WM) integrity achieved increasing focus for early prediction and diagnosis of major depressive disorder (MDD). This study aimed to explore the effects of PER1 gene polymorphisms (rs7221412), one of the key circadian genes, on the association between depressive level and WM microstructural integrity.

MATERIALS AND METHODS

Diffusion tensor imaging scanning and depression assessment (Beck Depression Inventory, BDI) were performed in 77 healthy college students. Participants also underwent PER1 polymorphism detection and were divided into the AG group and AA group. The effects of PER1 genotypes on the association between the WM characteristics and BDI were analyzed using tract-based spatial statistics method.

RESULTS

Compared with homozygous form of PER1 gene (AA), more individuals with risk allele G of PER1 gene (AG) were in depression state with BDI cutoff of 14 (χ² = 7.37, uncorrected p = 0.007). At the level of brain imaging, the WM integrity in corpus callosum, internal capsule, corona radiata and fornix was poorer in AG group compared with AA group. Furthermore, significant interaction effects of genotype × BDI on WM characteristics were observed in several emotion-related WM tracts. To be specific, the significant relationships between BDI and WM characteristics in corpus callosum, internal capsule, corona radiata, fornix, external capsule and sagittal stratum were only found in AG group, but not in AA group.

CONCLUSION

Our findings suggested that the PER1 genotypes and emotion-related WM microstructure may provide more effective measures of depression risk at an early phase.

DNA Methylation Basis in the Effect of White Matter Integrity Deficits on Cognitive Impairments and Psychopathological Symptoms in Drug-Naive First-Episode Schizophrenia

Background: Mounting evidence from diffusion tensor imaging (DTI) and epigenetic studies, respectively, confirmed the abnormal alterations of brain white matter integrity and DNA methylation (DNAm) in schizophrenia. However, few studies have been carried out in the same sample to simultaneously explore the WM pathology relating to clinical behaviors, as well as the DNA methylation basis underlying the WM deficits. Methods: We performed DTI scans in 42 treatment-naïve first-episode schizophrenia patients and 38 healthy controls. Voxel-based method of fractional anisotropy (FA) derived from DTI was used to assess WM integrity. Participants' peripheral blood genomic DNAm status, quantified by using Infinium® Human Methylation 450K BeadChip, was examined in parallel with DTI scanning. Participants completed Digit Span test and Trail Making test, as well as Positive and Negative Syndrome Scale measurement. We acquired genes that are differentially expressed in the brain regions with abnormal FA values according to the Allen anatomically comprehensive atlas, obtained DNAm levels of the corresponding genes, and then performed Z-test to compare the differential epigenetic-imaging associations (DEIAs) between the two groups. Results: Significant decreases of FA values in the patient group were in the right middle temporal lobe WM, right cuneus WM, right anterior cingulate WM, and right inferior parietal lobe WM, while the significant increases were in the bilateral middle cingulate WM (Ps < 0.01, GRF correction). Abnormal FA values were correlated with patients' clinical symptoms and cognitive impairments. In the DEIAs, patients showed abnormal couple patterns between altered FA and DNAm components, for which the enriched biological processes and pathways could be largely grouped into three biological procedures: the neurocognition, immune, and nervous system. Conclusion: Schizophrenia may not cause widespread neuropathological changes, but subtle alterations affecting local cingulum WM, which may play a critical role in positive symptoms and cognitive impairments. This imaging-epigenetics study revealed for the first time that DNAm of genes enriched in neuronal, immunologic, and cognitive processes may serve as the basis in the effect of WM deficits on clinical behaviors in schizophrenia.

DNA methylations of brain-derived neurotrophic factor exon VI are associated with major depressive disorder and antidepressant-induced remission in females

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been suggested to play important roles in major depressive disorder (MDD) and antidepressant treatment. The main purpose of this study was to evaluate the association of DNA methylation changes in the BDNF gene with MDD and antidepressant treatment.

METHODS

A total of 291 MDD patients and 100 healthy controls were included and followed up for 6 weeks. The Hamilton Depression Rating Scale-17 (HDRS-17) was used to measure treatment improvement. The life events scales (LES) and childhood trauma questionnaire (CTQ) were used to rate recent and early life stress. DNA methylation levels of CpG sites in the BDNF gene were measured.

RESULTS

Two CpG sites in BDNF exon VI (BDNF133 and BDNF134) were demonstrated to have significantly higher methylation in MDD patients than in controls (both FDR-adjusted P = 0.001). A logistics regression model indicated that the interaction between the hypermethylation of BDNF133 and negative subscore of LES was associated to MDD (OR=0.0075, P<0.001). Methylation of BDNF140 at baseline was significantly elevated in remitters (FDR-adjusted P = 0.046) at week 6. In subgroup analyses, these findings could be replicated in females, but not in males.

LIMITATIONS

The methylation status of BDNF after 6 weeks of antidepressant treatment was not measured and the DNA methylation were detected in peripheral blood cells.

CONCLUSIONS

These findings highlight gender-specific alteration of methylation at several CpG sites in BDNF exon VI as a promising candidate indicator of MDD and antidepressant-induced remission.

Elevated serum neurofilament levels in young first-episode and medication-naïve major depressive disorder patients with alterative white matter integrity

The mechanism of white matter (WM) microstructure alteration in major depressive disorder (MDD) is unknown. Serum neurofilament (NF) levels have been identified as promising biomarkers for axonal damage and degeneration in neurological disorders. Furthermore, elevated plasma NF levels were also reported in depressive patients with treatment resistance. The current study investigated the serum NF levels of first-episode, medication-naïve patients with different severities of MDD and assessed their relationships with WM integrity. Diffusion tensor images and serum NF levels of 82 MDD patients and 72 age- and sex-matched healthy controls (HCs) were taken. We found that serum NF levels were significantly higher in patients with MDD than those in HCs. Fractional anisotropy (FA) of six brain WM tracts (the body and genu of the corpus callosum, left superior and posterior corona radiata, and bilateral anterior corona radiata) in patients with MDD were lower than those in the HCs after family-wise error-correction for multiple comparisons. Negative correlations between serum NF levels in the severe group of MDD and the decreased FA of the left anterior corona radiata were found in MDD, which might contribute to an understanding of the pathophysiological mechanism of MDD.

The role of BDNF exon I region methylation in the treatment of depression with sertraline and its clinical diagnostic value

Background

Brain‐derived neurotrophic factor (BDNF) is considered to be one of the best candidate genes for depression. However, whether sertraline treatment affects the methylation level of this gene remains unknown.

Methods

Fifty‐three patients with depression and 51 healthy controls were included in the study. The methylation level of BDNF exon I was determined in blood samples from these subjects. The Hamilton Depression Scale was used to evaluate the depression status of patients. Single nucleotide polymorphism detection was used for genotyping, and a receiver operating characteristic (ROC) curve was used to evaluate the predictive value of the methylation level of this locus in patients with depression.

Results

There was a significant difference in the methylation level of BDNF exon I between the control and depression groups. No effect of sertraline monotherapy on BDNF methylation was found in subjects with depression. Moreover, no interaction was found between BDNF genotype and the per cent methylation of BDNF exon I. However, methylation at this site was positively correlated with diurnal variation and retardation scores. Blood homocysteine concentrations were significantly reduced by sertraline treatment. No influence of genotype on serum BDNF concentration was found in subjects with depression. The ROC curve showed that methylation of BDNF exon I may be used to distinguish patients from healthy people, to a certain extent.

Conclusion

Methylation of BDNF exon I may be used as a biomarker of depression and may be a therapeutic target for previously untreated depression.

White Matter Alterations Associated with Pro-inflammatory Cytokines in Patients with Major Depressive Disorder

Objective

Regarding the neuroinflammatory theory of major depressive disorder (MDD), little is known about the effect of pro-inflammatory cytokines on white matter (WM) changes in MDD. We aimed to investigate the relationship between pro-inflammatory cytokines and WM alterations in patients with MDD.

Methods

Twenty-two patients with MDD and 22 healthy controls (HC) were evaluated for brain imaging and pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, IL-8, interferon-γ and tumor necrosis factor (TNF)-α. Tract-based spatial statistics and FreeSurfer were used for brain image analysis.

Results

The levels of TNF-α and IL-8 were significantly higher in the MDD group than in HC. Compared to HC, lower fractional anisotropy (FA), and higher median diffusivity (MD) and radial diffusivity (RD) values were found in the MDD group for several WM regions. Voxel-wise correlation analysis showed that the level of TNF-α was negatively correlated with FA, and positively correlated with MD and RD in the left body and genu of the corpus callosum, left anterior corona radiata, and left superior corona radiata.

Conclusion

Our findings suggest that TNF-α may play an important role in the WM alterations in depression, possibly through demyelination.

Race, Socioeconomic Status, and Cerebellum Cortex Fractional Anisotropy in Pre-Adolescents

Introduction

Cerebellum cortex fractional anisotropy is a proxy of the integrity of the cerebellum cortex. However, less is known about how it is shaped by race and socioeconomic status (SES) indicators such as parental education and household income.

Purpose

In a national sample of American pre-adolescents, this study had two aims: to test the effects of two SES indicators, namely parental education and household income, on cerebellum cortex fractional anisotropy, and to explore racial differences in these effects.

Methods

Using data from the Adolescent Brain Cognitive Development (ABCD) study, we analyzed the diffusion Magnetic Resonance Imaging (dMRI) data of 9565, 9-10-year-old pre-adolescents. The main outcomes were cerebellum cortex fractional anisotropy separately calculated for right and left hemispheres using dMRI. The independent variables were parental education and household income; both treated as categorical variables. Age, sex, ethnicity, and family marital status were the covariates. Race was the moderator. To analyze the data, we used mixed-effects regression models without and with interaction terms. We controlled for propensity score and MRI device.

Results

High parental education and household income were associated with lower right and left cerebellum cortex fractional anisotropy. In the pooled sample, we found significant interactions between race and parental education and household income, suggesting that the effects of parental education and household income on the right and left cerebellum cortex fractional anisotropy are all significantly larger for White than for Black pre-adolescents.

Conclusions

The effects of SES indicators, namely parental education and household income, on pre-adolescents' cerebellum cortex microstructure and integrity are weaker in Black than in White families. This finding is in line with the Marginalization-related Diminished Returns (MDRs), defined as weaker effects of SES indicators for Blacks and other racial and minority groups than for Whites.

Neurotrophic Factor BDNF, Physiological Functions and Therapeutic Potential in Depression, Neurodegeneration and Brain Cancer

Brain-derived neurotrophic factor (BDNF) is one of the most distributed and extensively studied neurotrophins in the mammalian brain. BDNF signals through the tropomycin receptor kinase B (TrkB) and the low affinity p75 neurotrophin receptor (p75NTR). BDNF plays an important role in proper growth, development, and plasticity of glutamatergic and GABAergic synapses and through modulation of neuronal differentiation, it influences serotonergic and dopaminergic neurotransmission. BDNF acts as paracrine and autocrine factor, on both pre-synaptic and post-synaptic target sites. It is crucial in the transformation of synaptic activity into long-term synaptic memories. BDNF is considered an instructive mediator of functional and structural plasticity in the central nervous system (CNS), influencing dendritic spines and, at least in the hippocampus, the adult neurogenesis. Changes in the rate of adult neurogenesis and in spine density can influence several forms of learning and memory and can contribute to depression-like behaviors. The possible roles of BDNF in neuronal plasticity highlighted in this review focus on the effect of antidepressant therapies on BDNF-mediated plasticity. Moreover, we will review data that illustrate the role of BDNF as a potent protective factor that is able to confer protection against neurodegeneration, in particular in Alzheimer's disease. Finally, we will give evidence of how the involvement of BDNF in the pathogenesis of brain glioblastoma has emerged, thus opening new avenues for the treatment of this deadly cancer.

Regionconnect: Rapidly extracting standardized brain connectivity information in voxel-wise neuroimaging studies

Reporting white matter findings in voxel-wise neuroimaging studies typically lacks specificity in terms of brain connectivity. Therefore, the purpose of this work was to develop an approach for rapidly extracting standardized brain connectivity information for white matter regions with significant findings in voxel-wise neuroimaging studies. The new approach was named regionconnect and is based on precalculated average healthy adult brain connectivity information stored in standard space in a fashion that allows fast retrieval and integration. Towards this goal, the present work first generated and evaluated the white matter connectome of the IIT Human Brain Atlas v.5.0. It was demonstrated that the edges of the atlas connectome are representative of those of individual participants of the Human Connectome Project in terms of the spatial organization of streamlines and spatial patterns of track-density. Next, the new white matter connectome was used to develop multi-layer, connectivity-based labels for each white matter voxel of the atlas, consistent with the fact that each voxel may contain axons from multiple connections. The regionconnect algorithm was then developed to rapidly integrate information contained in the multi-layer labels across voxels of a white matter region and to generate a list of the most probable connections traversing that region. Usage of regionconnect does not require high angular resolution diffusion MRI or any MRI data. The regionconnect algorithm as well as the white matter tractogram and connectome, multi-layer, connectivity-based labels, and associated resources developed for the IIT Human Brain Atlas v.5.0 in this work are available at www.nitrc.org/projects/iit. An interactive, online version of regionconnect is also available at www.iit.edu/~mri.

Shape and Volumetric Differences in the Corpus Callosum between Patients with Major Depressive Disorder and Healthy Controls

OBJECTIVE

This study aimed to investigate the morphometric differences in the corpus callosum between patients with major depressive disorder (MDD) and healthy controls and analyze their relationship to gray matter changes.

METHODS

Twenty female MDD patients and 21 healthy controls (HCs) were included in the study. To identify the difference in the regional gray matter concentration (GMC), VBM was performed with T1 magnetic resonance imaging. The shape analysis of the corpus callosum was processed. Diffusion tensor imaging (DTI) fiber-tracking was performed to identify the regional tract pathways in the damaged corpus callosal areas.

RESULTS

In the shape analysis, regional shape contractions in the rostrum and splenium were found in the MDD patients. VBM analysis showed a significantly lower white matter concentration in the genu and splenium, and a significantly lower GMC in the frontal, limbic, insular, and temporal regions of the MDD patients compared to the HCs. In DTI fiber-tracking, the fibers crossing the damaged areas of the genu, rostrum, and splenium were anatomically connected to the areas of lower GMC in MDD patients.

CONCLUSION

These findings support that major depressive disorder may be due to disturbances in multiple neuronal circuits, especially those associated with the corpus callosum.

New insights on brain-derived neurotrophic factor epigenetics: from depression to memory extinction

Advances in characterizing molecular profiles provide valuable insights and opportunities for deciphering the neuropathology of depression. Although abnormal brain-derived neurotrophic factor (BDNF) expression in depression has gained much support from preclinical and clinical research, how it mediates behavioral alterations in the depressed state remains largely obscure. Environmental factors contribute significantly to the onset of depression and produce robust epigenetic changes. Epigenetic regulation of BDNF, as one of the most characterized gene loci in epigenetics, has recently emerged as a target in research on memory and psychiatric disorders. Specifically, epigenetic alterations of BDNF exons are heavily involved in mediating memory functions and antidepressant effects. In this review, we discuss key research on stress-induced depression from both preclinical and clinical studies, which revealed that differential epigenetic regulation of specific BDNF exons is associated with depression pathophysiology. Considering that BDNF has a central role in depression, we argue that memory extinction, an adaptive response to fear exposure, is dependent on BDNF modulation and holds promise as a prospective target for alleviating or treating depression and anxiety disorders.

Altered grey matter volume and white matter integrity in individuals with high schizo-obsessive traits, high schizotypal traits and obsessive-compulsive symptoms

Altered brain structures have been found in patients with schizo-obsessive disorder, schizophrenia and obsessive-compulsive disorder in previous studies. However, it is unclear whether similar brain changes are also found in individuals with high schizo-obsessive traits (SOT), high schizotypal traits (SCT) and obsessive-compulsive symptoms (OCS). We examined grey matter volume (GMV) and white matter integrity (WMI, including fractional anisotropy, mean diffusivity, axial diffusivity and radial diffusivity) in 26 individuals with high SOT, 30 individuals with high SCT, 25 individuals with OCS and 30 individuals with low trait scores (LT) in this study. Correlation analysis between GMV, WMI, Schizotypal Personality Questionnaire (SPQ) scores and Obsessive-Compulsive Inventory-Revised (OCI-R) scores in the subclinical groups was also carried out. We found that the SOT group exhibited increased GMV at the right superior occipital gyrus and the left postcentral gyrus compared with the LT group. The SCT group exhibited increased GMV at the right precentral gyrus and the bilateral cuneus compared with the LT group, and decreased fractional anisotropy at the anterior corona radiata compared with the other three groups. The OCS group exhibited increased GMV at the left superior temporal gyrus and decreased GMV at the left pre-supplementary motor area compared with the LT group. These findings highlight specific brain changes in individuals with high SOT, high SCT and OCS, and may thus provide new insights into the neurobiological changes that occur in sub-clinical populations of these disorders.

Abnormal white matter microstructures in Parkinson's disease and comorbid depression: A whole-brain diffusion tensor imaging study

OBJECTIVE

Depressive symptoms are the most common non-motor symptom accompanying Parkinson's disease (PD); however, the neural basis of depression in PD remains unclear. The aim of this study was to characterize possible depression-related white matter microstructural differences in patients with PD and comorbid depression compared with PD patients and healthy controls (HC) without depression.

METHODS

We used diffusion tensor imaging (DTI) to analyze white matter integrity in depressed PD patients (n = 30), non-depressed PD patients (n = 43), and HC (n = 91). Five MRI-derived indices were estimated: fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), and white matter volume (WMV).

RESULTS

Compared with HC and non-depressed PD, depressed PD patients showed significantly increased AD values in the body of corpus callosum, right anterior corona radiate, and left hippocampal part of the cingulum, as well as increased MD values in the left hippocampal part of the cingulum.

CONCLUSIONS

Our results show that frontal and limbic white matter integrity is impaired in depressed PD patients. These findings can be used to better understand potential mechanisms of depression in PD.

DNA methylation and brain structure and function across the life course: A systematic review

MRI has enhanced our capacity to understand variations in brain structure and function conferred by the genome. We identified 60 studies that report associations between DNA methylation (DNAm) and human brain structure/function. Forty-three studies measured candidate loci DNAm; seventeen measured epigenome-wide DNAm. MRI features included region-of-interest and whole-brain structural, diffusion and functional imaging features. The studies report DNAm-MRI associations for: neurodevelopment and neurodevelopmental disorders; major depression and suicidality; alcohol use disorder; schizophrenia and psychosis; ageing, stroke, ataxia and neurodegeneration; post-traumatic stress disorder; and socio-emotional processing. Consistency between MRI features and differential DNAm is modest. Sources of bias: variable inclusion of comparator groups; different surrogate tissues used; variation in DNAm measurement methods; lack of control for genotype and cell-type composition; and variations in image processing. Knowledge of MRI features associated with differential DNAm may improve understanding of the role of DNAm in brain health and disease, but caution is required because conventions for linking DNAm and MRI data are not established, and clinical and methodological heterogeneity in existing literature is substantial.

ENIGMA MDD: seven years of global neuroimaging studies of major depression through worldwide data sharing

A key objective in the field of translational psychiatry over the past few decades has been to identify the brain correlates of major depressive disorder (MDD). Identifying measurable indicators of brain processes associated with MDD could facilitate the detection of individuals at risk, and the development of novel treatments, the monitoring of treatment effects, and predicting who might benefit most from treatments that target specific brain mechanisms. However, despite intensive neuroimaging research towards this effort, underpowered studies and a lack of reproducible findings have hindered progress. Here, we discuss the work of the ENIGMA Major Depressive Disorder (MDD) Consortium, which was established to address issues of poor replication, unreliable results, and overestimation of effect sizes in previous studies. The ENIGMA MDD Consortium currently includes data from 45 MDD study cohorts from 14 countries across six continents. The primary aim of ENIGMA MDD is to identify structural and functional brain alterations associated with MDD that can be reliably detected and replicated across cohorts worldwide. A secondary goal is to investigate how demographic, genetic, clinical, psychological, and environmental factors affect these associations. In this review, we summarize findings of the ENIGMA MDD disease working group to date and discuss future directions. We also highlight the challenges and benefits of large-scale data sharing for mental health research.

White matter disturbances in major depressive disorder: a coordinated analysis across 20 international cohorts in the ENIGMA MDD working group

Alterations in white matter (WM) microstructure have been implicated in the pathophysiology of major depressive disorder (MDD). However, previous findings have been inconsistent, partially due to low statistical power and the heterogeneity of depression. In the largest multi-site study to date, we examined WM anisotropy and diffusivity in 1305 MDD patients and 1602 healthy controls (age range 12-88 years) from 20 samples worldwide, which included both adults and adolescents, within the MDD Working Group of the Enhancing Neuroimaging Genetics through Meta-Analysis (ENIGMA) consortium. Processing of diffusion tensor imaging (DTI) data and statistical analyses were harmonized across sites and effects were meta-analyzed across studies. We observed subtle, but widespread, lower fractional anisotropy (FA) in adult MDD patients compared with controls in 16 out of 25 WM tracts of interest (Cohen's d between 0.12 and 0.26). The largest differences were observed in the corpus callosum and corona radiata. Widespread higher radial diffusivity (RD) was also observed (all Cohen's d between 0.12 and 0.18). Findings appeared to be driven by patients with recurrent MDD and an adult age of onset of depression. White matter microstructural differences in a smaller sample of adolescent MDD patients and controls did not survive correction for multiple testing. In this coordinated and harmonized multisite DTI study, we showed subtle, but widespread differences in WM microstructure in adult MDD, which may suggest structural disconnectivity in MDD.

Reduced fractional anisotropy in depressed patients due to childhood maltreatment rather than diagnosis

Reduced fractional anisotropy (FA) associated with Major Depressive Disorder (MDD) overlaps anatomically with effects of childhood maltreatment experiences. The aim of this study was, therefore, to replicate the negative effect of childhood maltreatment on white matter fiber structure and to demonstrate, that alterations in MDD might be partially attributed to the higher occurrence of childhood maltreatment in MDD. Two independent cohorts (total N = 1 256) were investigated in a diffusion tensor imaging study: The Münster Neuroimaging Cohort (MNC, N = 186 MDD, N = 210 healthy controls, HC) as discovery sample and the Marburg-Münster Affective Disorders Cohort Study (MACS, N = 397 MDD, N = 462 HC) as replication sample. The effects of diagnosis (HC vs. MDD) and Childhood Trauma Questionnaire (CTQ) scores on FA were analyzed. A main effect of diagnosis with higher FA in MDD patients compared with HC was found in the MNC (p_FWE = 0.021), but not in the MACS (p_FWE = 0.52) before correcting for CTQ. A significant negative correlation of FA with CTQ emerged in both cohorts (MNC: p_FWE = 0.006, MACS: p_FWE = 0.012) in several tracts previously described in the literature. No CTQ × diagnosis interaction could be detected. Any main effect of diagnosis was abolished after correcting for CTQ (MNC: p_FWE = 0.562, MACS: p_FWE = 0.115). No differences in FA between MDD and HC could be found after correcting for childhood maltreatment, suggesting that previously reported group differences might be attributed partially to higher levels of maltreatment experiences in MDD rather than diagnosis itself. Furthermore, a well-established finding of reduced FA following childhood maltreatment experiences was replicated.

BDNF genetic variants and methylation: effects on cognition in major depressive disorder

Brain-derived neurotrophic factor (BDNF) gene regulation has been linked to the pathophysiology of major depressive disorder (MDD). MDD patients show cognitive deficits, and altered BDNF regulation has a relevant role in neurocognitive functions. Our goal was to explore the association between BDNF genetic and epigenetic variations with neurocognitive performance in a group of MDD patients and healthy controls considering possible modulating factors. The sample included 134 subjects, 64 MDD patients, and 70 healthy controls. Clinical data, childhood maltreatment, and neurocognitive performance were assessed in all participants. Eleven single nucleotide polymorphisms (SNPs) and two promoter regions in the BDNF gene were selected for genotype and methylation analysis. The role of interactions between BDNF genetic and epigenetic variations with MDD diagnosis, sex, and Childhood Trauma Questionnaire (CTQ) scores was also explored. We observed significant associations between neurocognitive performance and two BDNF SNPs (rs908867 and rs925946), an effect that was significantly mediated by methylation values at specific promoter I sites. We identified significant associations between neurocognitive results and methylation status as well as its interactions with MDD diagnosis, sex, and CTQ scores. Our results support the hypothesis that BDNF gene SNPs and methylation status, as well as their interactions with modulating factors, can influence cognition. Further studies are required to confirm the effect of BDNF variations and cognitive function in larger samples.

White Matter Abnormalities in Major Depression Biotypes Identified by Diffusion Tensor Imaging

Identifying data-driven biotypes of major depressive disorder (MDD) has promise for the clarification of diagnostic heterogeneity. However, few studies have focused on white-matter abnormalities for MDD subtyping. This study included 116 patients with MDD and 118 demographically-matched healthy controls assessed by diffusion tensor imaging and neurocognitive evaluation. Hierarchical clustering was applied to the major fiber tracts, in conjunction with tract-based spatial statistics, to reveal white-matter alterations associated with MDD. Clinical and neurocognitive differences were compared between identified subgroups and healthy controls. With fractional anisotropy extracted from 20 fiber tracts, cluster analysis revealed 3 subgroups based on the patterns of abnormalities. Patients in each subgroup versus healthy controls showed a stepwise pattern of white-matter alterations as follows: subgroup 1 (25.9% of patient sample), widespread white-matter disruption; subgroup 2 (43.1% of patient sample), intermediate and more localized abnormalities in aspects of the corpus callosum and left cingulate; and subgroup 3 (31.0% of patient sample), possible mild alterations, but no statistically significant tract disruption after controlling for family-wise error. The neurocognitive impairment in each subgroup accompanied the white-matter alterations: subgroup 1, deficits in sustained attention and delayed memory; subgroup 2, dysfunction in delayed memory; and subgroup 3, no significant deficits. Three subtypes of white-matter abnormality exist in individuals with major depression, those having widespread abnormalities suffering more neurocognitive impairments, which may provide evidence for parsing the heterogeneity of the disorder and help optimize type-specific treatment approaches.

Altered white matter microstructure in patients with post-stroke depression detected by diffusion kurtosis imaging

The aim of our study is to determine the pathological changes of white matter microstructure in patients with early post-stroke depression (PSD), and to investigate the association between white matter integrity examined by diffusion kurtosis imaging (DKI) and early PSD. Thirty-eight patients with acute cerebral infarction were selected, including 17 patients with depression (PSD group), and 21 patients without depression (N-PSD group). In addition, 20 normal healthy controls (NORM group) were selected. All were taken DKI scans. The white matter of the frontal lobe, temporal lobe, parietal lobe, occipital lobe, anterior limb of internal capsule, and posterior limb of internal capsule, in addition to the genu of corpus callosum and splenium of corpus callosum was selected as a region of interest (ROI). Selected parameters include fractional anisotropy (FA) and mean kurtosis (MK). Compared with N-PSD group and NORM group, FA value of the left frontal lobe and MK value of the bilateral frontal lobe, bilateral temporal lobe, and genu of corpus callosum in PSD group were decreased (P < 0.05). Our results indicated that the early PSD patients had white matter microstructure abnormalities in the frontal lobe, temporal lobe, and genu of corpus callosum. DKI provides a comprehensive brain imaging reference for detecting early microstructural damage of white matter in PSD patients, which can be used as an imaging biomarker to detect early PSD and its progression potentially.

Tryptophan hydroxylase-2 polymorphism is associated with white matter integrity in first-episode, medication-naïve major depressive disorder patients

Considerable evidence suggests that the tryptophan hydroxylase-2 (TPH2) gene is associated with the pathophysiology of major depressive disorder (MDD). In the present study, we investigated alterations of white matter (WM) integrity and the impact of TPH2 polymorphism on WM in a sample of 118 first-episode, medication-naïve, MDD patients and 118 well-matched healthy controls. Whole brain analyses of fractional anisotropy (FA) were performed using tract-based spatial statistics (TBSS). The results showed that the MDD group had significantly reduced FA values for the genu and body of the corpus callosum (CC) and the bilateral anterior corona radiate (ACR). In the MDD patient group, the GG homozygote subgroup exhibited a widespread reduction of FA (uncorrected) and significantly reduced FA in the left retrolenticular portion of the internal capsule and left superior longitudinal fasciculus (SLF) compared with those of the T carriers (GT/TT) (FWE corrected). No significant correlation was found between the FA values in any brain region and the patients' clinical variables. Our findings demonstrate the presence of abnormal white matter integrity in untreated patients with first-episode depression. TPH2-rs4570625 polymorphisms may be involved in the pathological mechanism of WM microarchitecture in patients.

Abnormal Brain-Derived Neurotrophic Factor Exon IX Promoter Methylation, Protein, and mRNA Levels in Patients with Major Depressive Disorder

Brain-derived neurotrophic factor (BDNF) exon IX promoter methylation levels, serum BDNF protein levels, and serum mRNA levels were investigated in patients with major depressive disorder (MDD) and healthy controls. Over two years, 51 patients with MDD and 62 healthy controls were recruited. Peripheral blood was drawn from all participants to analyze the BDNF exon IX promoter methylation levels as well as serum BDNF protein and mRNA levels, at baseline and after four weeks of antidepressant treatment. Methylation sequential analysis showed that patients with MDD (n = 39) had a higher methylation level at CpG site 217 and lower methylation levels at CpG site 327 and CpG site 362. Drug responders (n = 25) had a higher methylation level at CpG site 24 and CpG site 324 than the non-responders (n = 11). Patients with MDD had a lower serum BDNF protein and mRNA levels than the healthy controls. In conclusion, these results showed that BDNF exon IX promoter methylation levels, serum BDNF protein level, and serum BDNF mRNA level could contribute to the pathophysiology of a major depressive disorder.

Interactive effects of genetic polymorphisms and childhood adversity on brain morphologic changes in depression

The etiology of depression is characterized by the interplay of genetic and environmental factors and brain structural alteration. Childhood adversity is a major contributing factor in the development of depression. Interactions between childhood adversity and candidate genes for depression could affect brain morphology via the modulation of neurotrophic factors, serotonergic neurotransmission, or the hypothalamus-pituitary-adrenal (HPA) axis, and this pathway may explain the subsequent onset of depression. Childhood adversity is associated with structural changes in the hippocampus, amygdala, anterior cingulate cortex (ACC), and prefrontal cortex (PFC), as well as white matter tracts such as the corpus callosum, cingulum, and uncinate fasciculus. Childhood adversity showed an interaction with the brain-derived neurotrophic factor (BDNF) gene Val66Met polymorphism, serotonin transporter-linked promoter region (5-HTTLPR), and FK506 binding protein 51 (FKBP5) gene rs1360780 in brain morphologic changes in patients with depression and in a non-clinical population. Individuals with the Met allele of BDNF Val66Met and a history of childhood adversity had reduced volume in the hippocampus and its subfields, amygdala, and PFC and thinner rostral ACC in a study of depressed patients and healthy controls. The S allele of 5-HTTLPR combined with exposure to childhood adversity or a poorer parenting environment was associated with a smaller hippocampal volume and subsequent onset of depression. The FKBP5 gene rs160780 had a significant interaction with childhood adversity in the white matter integrity of brain regions involved in emotion processing. This review identified that imaging genetic studies on childhood adversity may deepen our understanding on the neurobiological background of depression by scrutinizing complicated pathways of genetic factors, early psychosocial environments, and the accompanying morphologic changes in emotion-processing neural circuitry.

The brain-derived neurotrophic factor Val66Met genotype does not influence the grey or white matter structures underlying recognition memory

A single nucleotide polymorphism (SNP) in the gene coding for brain-derived neurotrophic factor (BDNF) has previously been associated with a reduction in recognition memory performance. While previous findings have highlighted that this SNP contributes to recognition memory, little is known about its influence on subprocesses of recognition, familiarity and recollection. Previous research has reported reduced hippocampal volume and decreased fractional anisotropy in carriers of the Met allele across a range of white matter tracts, including those networks that may support recognition memory. Here, in a sample of 61 healthy young adults, we used a source memory task to measure accuracy on each recognition subprocess, in order to determine whether the Val66Met SNP (rs6265) influences these equally. Additionally, we compared grey matter volume between these groups for structures that underpin familiarity and recollection separately. Finally, we used probabilistic tractography to reconstruct tracts that subserve each of these two recognition systems. Behaviourally, we found group differences on the familiarity measure, but not on recollection. However, we did not find any group difference on grey- or white-matter structures. Together, these results suggest a functional influence of the Val66Met SNP that is independent of coarse structural changes, and nuance previous research highlighting the relationship between BDNF, brain structure, and behaviour.

Effects of Uric Acid on the Alterations of White Matter Connectivity in Patients with Major Depression

OBJECTIVE

Uric acid is a non-enzymatic antioxidant associated with depression. Despite its known protective role in other brain disorders, little is known about its influence on the structural characteristics of brains of patients with major depressive disorder (MDD). This study explored the association between uric acid and characteristics of white matter (WM) in patients with MDD.

METHODS

A total of 32 patients with MDD and 23 healthy controls (HCs) were examined. All participants were scored based on the Beck Depression Inventory and Beck Anxiety Inventory at baseline. All patients were also rated with the Hamilton Depression Rating Scale. We collected blood samples from all participants immediately after their enrollment and before the initiation of antidepressants in case of patients. Tract-based spatial statistics were used for all imaging analyses.

RESULTS

Lower fractional anisotropy (FA) and higher radial diffusivity (RD) values were found in the MDD group than in the HC group. Voxelwise correlation analysis revealed that the serum uric acid levels positively correlated with the FA and negatively with the RD in WM regions that previously showed significant group differences in the MDD group. The correlated areas were located in the left anterior corona radiata, left frontal lobe WM, and left anterior cingulate cortex WM.

CONCLUSION

The present study suggests a significant association between altered WM connectivity and serum uric acid levels in patients with MDD, possibly through demyelination.

Neuronal Activity, TGFβ-Signaling and Unpredictable Chronic Stress Modulate Transcription of Gadd45 Family Members and DNA Methylation in the Hippocampus

Neuronal activity is altered in several neurological and psychiatric diseases. Upon depolarization not only neurotransmitters are released but also cytokines and other activators of signaling cascades. Unraveling their complex implication in transcriptional control in receiving cells will contribute to understand specific central nervous system (CNS) pathologies and will be of therapeutically interest. In this study we depolarized mature hippocampal neurons in vitro using KCl and revealed increased release not only of brain-derived neurotrophic factor (BDNF) but also of transforming growth factor beta (TGFB). Neuronal activity together with BDNF and TGFB controls transcription of DNA modifying enzymes specifically members of the DNA-damage-inducible (Gadd) family, Gadd45a, Gadd45b, and Gadd45g. MeDIP followed by massive parallel sequencing and transcriptome analyses revealed less DNA methylation upon KCl treatment. Psychiatric disorder-related genes, namely Tshz1, Foxn3, Jarid2, Per1, Map3k5, and Arc are transcriptionally activated and demethylated upon neuronal activation. To analyze whether misexpression of Gadd45 family members are associated with psychiatric diseases, we applied unpredictable chronic mild stress (UCMS) as established model for depression to mice. UCMS led to reduced expression of Gadd45 family members. Taken together, our data demonstrate that Gadd45 family members are new putative targets for UCMS treatments.

Association between abnormal serum myelin-specific protein levels and white matter integrity in first-episode and drug-naïve patients with major depressive disorder

BACKGROUND

Although the structural abnormalities of white matter (WM) have been described in patients with major depressive disorder (MDD), the neuropathological changes remain unclear. The current study aimed to investigate the myelin oligodendrocyte glycoprotein (MOG) and myelin-associated glycoprotein (MAG) levels and their correlations with WM integrity in first-episode, drug-naïve MDD patients.

METHODS

We obtained diffusion tensor images of 102 first-episode, drug-naïve MDD patients and 81 age- and sex-matched controls. Serum MOG and MAG levels of all participants were measured and compared between the two groups. The correlations between WM integrity and MOG and MAG levels were examined.

RESULTS

MOG and MAG serum levels were significantly higher in MDD patients than in controls. Patients with MDD also showed decreased fractional anisotropy (FA) and axial diffusivity in the WM of the bilateral thalamus, right hippocampus, right temporal lobe, and left pulvinar. At the whole-brain level, no regions showed any correlations of diffusivity parameters with MOG or MAG levels in healthy subjects. However, we observed two-way correlations between the MOG and MAG levels and the FA and mean diffusivity values in the WM of the left middle frontal lobe, right inferior parietal lobe, and right supplementary motor area in MDD patients.

LIMITATIONS

Further investigation with a larger sample size and longitudinal studies are required to better understand the neuropathology of WM integrity in MDD.

CONCLUSIONS

Our findings represent the first evidence of a relationship between abnormal serum myelin-specific protein levels and impaired WM integrity, which may help to better understand the neurobiological mechanisms of MDD.

Current Clinical Applications of Diffusion-Tensor Imaging in Neurological Disorders

Diffusion-tensor imaging (DTI) is a noninvasive medical imaging tool used to investigate the structure of white matter. The signal contrast in DTI is generated by differences in the Brownian motion of the water molecules in brain tissue. Postprocessed DTI scalars can be used to evaluate changes in the brain tissue caused by disease, disease progression, and treatment responses, which has led to an enormous amount of interest in DTI in clinical research. This review article provides insights into DTI scalars and the biological background of DTI as a relatively new neuroimaging modality. Further, it summarizes the clinical role of DTI in various disease processes such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's dementia, epilepsy, ischemic stroke, stroke with motor or language impairment, traumatic brain injury, spinal cord injury, and depression. Valuable DTI postprocessing tools for clinical research are also introduced.

A comprehensive review of genetic and epigenetic mechanisms that regulate BDNF expression and function with relevance to major depressive disorder

Major depressive disorder (MDD) is a mood disorder that affects behavior and impairs cognition. A gene potentially important to this disorder is the brain derived neurotrophic factor (BDNF) as it is involved in processes controlling neuroplasticity. Various mechanisms exist to regulate BDNF's expression level, subcellular localization, and sorting to appropriate secretory pathways. Alterations to these processes by genetic factors and negative stressors can dysregulate its expression, with possible implications for MDD. Here, we review the mechanisms governing the regulation of BDNF expression, and discuss how disease-associated single nucleotide polymorphisms (SNPs) can alter these mechanisms, and influence MDD. As negative stressors increase the likelihood of MDD, we will also discuss the impact of these stressors on BDNF expression, the cellular effect of such a change, and its impact on behavior in animal models of stress. We will also describe epigenetic processes that mediate this change in BDNF expression. Similarities in BDNF expression between animal models of stress and those in MDD will be highlighted. We will also contrast epigenetic patterns at the BDNF locus between animal models of stress, and MDD patients, and address limitations to current clinical studies. Future work should focus on validating current genetic and epigenetic findings in tightly controlled clinical studies. Regions outside of BDNF promoters should also be explored, as should other epigenetic marks, to improve identification of biomarkers for MDD.

Evaluation of reference genes for gene expression studies in mouse and N2a cell ischemic stroke models using quantitative real-time PCR

BACKGROUND

Real-time reverse transcription quantitative polymerase chain reaction (RT-qPCR) is a critical tool for evaluating the levels of mRNA transcribed from genes. Reliable RT-qPCR results largely depend on normalization to suitable reference genes. Middle cerebral artery occlusion (MCAO) and oxygen-glucose deprivation/reoxygenation (OGD/R) are models that are commonly used to study ischemic stroke. However, the proper reference genes for RNA analysis in these two models have not yet been determined.

RESULTS

In this study, we evaluated the expression levels of six candidate housekeeping genes and selected the most suitable reference genes for RT-qPCR analyses of the cortices of MCAO mice and OGD/R-injured N2a cells. Four software programs, geNorm, NormFinder, BestKeeper and RefFinder, were used to validate the stabilities of the candidate reference genes. The results revealed that HPRT and 18S were the most stable reference genes in the cortices of MCAO mice and that β-actin and cyclophilin were the most stable reference genes in the OGD/R-injured N2a cells; in contrast, GAPDH and Sdha were the least stable genes in the cortices of MCAO mice and the OGD/R-injured N2a cells, respectively. Moreover, a combination of HPRT, 18S and cyclophilin was most suitable for normalization in analyses of the cortices of MCAO mice, and a combination of β-actin, cyclophilin, GAPDH, and 18S was most suitable for analyses of the OGD/R-injured N2a cells.

CONCLUSIONS

This study provides appropriate reference genes for further RT-qPCR analyses of in vivo and in vitro ischemic stroke and demonstrates the necessity of validating reference genes for RNA analyses under variable conditions.

Depressive disorders: Processes leading to neurogeneration and potential novel treatments

Mood disorders are wide spread with estimates that one in seven of the population are affected at some time in their life (Kessler et al., 2012). Many of those affected with severe depressive disorders have cognitive deficits which may progress to frank neurodegeneration. There are several peripheral markers shown by patients who have cognitive deficits that could represent causative factors and could potentially serve as guides to the prevention or even treatment of neurodegeneration. Circadian rhythm misalignment, immune dysfunction and oxidative stress are key pathologic processes implicated in neurodegeneration and cognitive dysfunction in depressive disorders. Novel treatments targeting these pathways may therefore potentially improve patient outcomes whereby the primary mechanism of action is outside of the monoaminergic system. Moreover, targeting immune dysfunction, oxidative stress and circadian rhythm misalignment (rather than primarily the monoaminergic system) may hold promise for truly disease modifying treatments that may prevent neurodegeneration rather than simply alleviating symptoms with no curative intent. Further research is required to more comprehensively understand the contributions of these pathways to the pathophysiology of depressive disorders to allow for disease modifying treatments to be discovered.

Antidepressant-Like Effects of Acupuncture-Insights From DNA Methylation and Histone Modifications of Brain-Derived Neurotrophic Factor

Sensitive and stable biomarkers that facilitate depression detection and monitor the antidepressant efficiency are currently unavailable. Thus, the objective is to investigate the potential of DNA methylation and histone modifications of brain-derived neurotrophic factor (BDNF) in monitoring severity and antidepressive effects of acupuncture. The depression rat model was imitated by social isolation and chronic unpredicted mild stress (CUMS). The expression of serum BDNF was detected by enzyme-linked immunosorbent assay (ELISA), the hippocampal BDNF, acetylation levels in histone H3 lysine 9 (acH3K9), and HDAC2 by Western blot, the hippocampal mRNA of BDNF by RT-polymerase chain reaction (PCR). The DNA methylation patterns of the promoter I of BDNF was detected by MS-PCR. We investigated that the expression of BDNF in serum and hippocampus were significantly downregulated compared with controls. The same trend was found in mRNA of BDNF. Notably, acupuncture reversed the downregulation of BDNF in serum and hippocampus and mRNA of BDNF compared with model group. Acupuncture reversed the CUMS-induced downregulation of hippocampal acH3K9. On the contrary, the CUMS-induced upregulation of hippocampal HDAC2 in model group was significantly reversed by acupuncture. Collectively, the antidepressant effect of acupuncture might be mediated by regulating the DNA methylation and histone modifications of BDNF, which may represent novel biomaker for detection of depression and monitoring severity and antidepressive effects.

TESC gene-regulating genetic variant (rs7294919) affects hippocampal subfield volumes and parahippocampal cingulum white matter integrity in major depressive disorder

Two recent genome-wide association studies have suggested that rs7294919 is associated with changes in hippocampal volume. rs7294919 regulates the transcriptional products of the TESC gene, which is involved in neuronal proliferation and differentiation. We investigated the interactive effect of rs7294919 and major depressive disorder (MDD) on the volume of the hippocampal subfields and the integrity of the parahippocampal cingulum (PHC). We also investigated the correlation of these structural changes with the DNA methylation status of rs7294919. A total of 105 patients with MDD and 85 healthy control subjects underwent T1-weighted structural magnetic resonance imaging and diffusion tensor imaging. The rs7294919 was genotyped and its DNA methylation status was assessed in all the participants. We analyzed the hippocampal subfield volumes and PHC integrity using FreeSurfer and the Tracts Constrained by Underlying Anatomy (TRACULA) respectively. Significant interactive effects of rs7294919 and MDD were observed in the volumes of the dentate gyrus and CA4. The patients with MDD had increased methylation in two of the three CpG loci of rs7294919, and the methylation of CpG3 was significantly correlated with right PHC integrity in the MDD group. Our results provide neurobiological evidence for the association of rs7294919 with brain structural changes in MDD.