A novel BDNF polymorphism affects plasma protein levels in interaction with early adversity in rhesus macaques

Genotyping of Macaque Population on the Brain-Derived Neurotrophic Factor Gene Polymorphism by Mismatch Amplification Mutation Assay (MAMA)-PCR

Human rs6265 (196G>A) polymorphism in the BDNF gene is associated with many clinically significant phenotypic manifestations. Rhesus monkey (Macaca mulatta) has a functionally significant rs309950446 ( 136G>A) polymorphism. To determine this polymorphism in macaques, we used mismatch amplification mutation assay (MAMA)-PCR method with non-complementary nucleotide to the template chain at the 3rd position from the 3'-end of the allele-specific primers (mismatch primers), which allowed the best discrimination of the alleles. Genotyping of male rhesus monkeys (n=178) and cynomolgus monkeys (Macaca fascicularis) (n=90) was carried out. The A/A, G/G, and G/A genotypes were found in 16, 34, and 50% rhesus macaques, respectively. In the cynomolgus macaques, the mutant polymorphic allele was not detected. The study results allow considering rhesus macaques as a potential biological model for assessment of the gen-environment interaction of the BDNF gene polymorphism.

Early Life Stress Effects on Glucocorticoid-BDNF Interplay in the Hippocampus

Early life stress (ELS) is implicated in the etiology of multiple psychiatric disorders. Important biological effects of ELS are manifested in stress-susceptible regions of the hippocampus and are partially mediated by long-term effects on glucocorticoid (GC) and/or neurotrophin signaling pathways. GC-signaling mediates the regulation of stress response to maintain homeostasis, while neurotrophin signaling plays a key role in neuronal outgrowth and is crucial for axonal guidance and synaptic integrity. The neurotrophin and GC-signaling pathways co-exist throughout the central nervous system (CNS), particularly in the hippocampus, which has high expression levels of glucocorticoid-receptors (GR) and mineralocorticoid-receptors (MR) as well as brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin-related kinase receptor B (TrkB). This review addresses the effects of ELS paradigms on GC- and BDNF-dependent mechanisms and their crosstalk in the hippocampus, including potential implications for the pathogenesis of common stress-related disorders.

Large-scale polymorphism discovery in macaque G-protein coupled receptors

BACKGROUND

G-protein coupled receptors (GPCRs) play an inordinately large role in human health. Variation in the genes that encode these receptors is associated with numerous disorders across the entire spectrum of disease. GPCRs also represent the single largest class of drug targets and associated pharmacogenetic effects are modulated, in part, by polymorphisms. Recently, non-human primate models have been developed focusing on naturally-occurring, functionally-parallel polymorphisms in candidate genes. This work aims to extend those studies broadly across the roughly 377 non-olfactory GPCRs. Initial efforts include resequencing 44 Indian-origin rhesus macaques (Macaca mulatta), 20 Chinese-origin rhesus macaques, and 32 cynomolgus macaques (M. fascicularis).

RESULTS

Using the Agilent target enrichment system, capture baits were designed for GPCRs off the human and rhesus exonic sequence. Using next generation sequencing technologies, nearly 25,000 SNPs were identified in coding sequences including over 14,000 non-synonymous and more than 9,500 synonymous protein-coding SNPs. As expected, regions showing the least evolutionary constraint show greater rates of polymorphism and greater numbers of higher frequency polymorphisms. While the vast majority of these SNPs are singletons, roughly 1,750 non-synonymous and 2,900 synonymous SNPs were found in multiple individuals.

CONCLUSIONS

In all three populations, polymorphism and divergence is highly concentrated in N-terminal and C-terminal domains and the third intracellular loop region of GPCRs, regions critical to ligand-binding and signaling. SNP frequencies in macaques follow a similar pattern of divergence from humans and new polymorphisms in primates have been identified that may parallel those seen in humans, helping to establish better non-human primate models of disease.

Inflammatory cytokines in depression: neurobiological mechanisms and therapeutic implications

Mounting evidence indicates that inflammatory cytokines contribute to the development of depression in both medically ill and medically healthy individuals. Cytokines are important for development and normal brain function, and have the ability to influence neurocircuitry and neurotransmitter systems to produce behavioral alterations. Acutely, inflammatory cytokine administration or activation of the innate immune system produces adaptive behavioral responses that promote conservation of energy to combat infection or recovery from injury. However, chronic exposure to elevated inflammatory cytokines and persistent alterations in neurotransmitter systems can lead to neuropsychiatric disorders and depression. Mechanisms of cytokine behavioral effects involve activation of inflammatory signaling pathways in the brain that results in changes in monoamine, glutamate, and neuropeptide systems, and decreases in growth factors, such as brain-derived neurotrophic factor. Furthermore, inflammatory cytokines may serve as mediators of both environmental (e.g. childhood trauma, obesity, stress, and poor sleep) and genetic (functional gene polymorphisms) factors that contribute to depression's development. This review explores the idea that specific gene polymorphisms and neurotransmitter systems can confer protection from or vulnerability to specific symptom dimensions of cytokine-related depression. Additionally, potential therapeutic strategies that target inflammatory cytokine signaling or the consequences of cytokines on neurotransmitter systems in the brain to prevent or reverse cytokine effects on behavior are discussed.

Brain-derived neurotrophic factor serum levels and genotype: association with depression during interferon-α treatment

Depression has been associated with inflammation, and inflammation may both influence and interact with growth factors such as brain-derived neurotrophic factor (BDNF). Both the functional Val66Met BDNF polymorphism (rs6265) and BDNF levels have been associated with depression. It is thus plausible that decreased BDNF could mediate and/or moderate cytokine-induced depression. We therefore prospectively employed the Beck Depression Inventory-II (BDI-II), the Hospital Anxiety and Depression Scale (HADS), and the Montgomery-Asberg Depression Rating Scale (MADRS) in 124 initially euthymic patients during treatment with interferon-alpha (IFN-α), assessing serum BDNF and rs6265. Using mixed-effect repeated measures, lower pretreatment BDNF was associated with higher depression symptoms during IFN-α treatment (F144,17.2=6.8; P<0.0001). However, although the Met allele was associated with lower BDNF levels (F1,83.0=5.0; P=0.03), it was only associated with increased MADRS scores (F4,8.9=20.3; P<0.001), and not the BDI-II or HADS. An exploratory comparison of individual BDI-II items indicated that the Met allele was associated with suicidal ideation, sadness, and worthlessness, but not neurovegetative symptoms. Conversely, the serotonin transporter promoter polymorphism (5-HTTLPR) short allele was associated with neurovegetative symptoms such as insomnia, poor appetite and fatigue, but not sadness, worthlessness, or suicidal ideation. IFN-α therapy further lowered BDNF serum levels (F4,37.7=5.0; P=0.003), but this decrease occurred regardless of depression development. The findings thus do not support the hypothesis that decreasing BDNF is the primary pathway by which IFN-α worsens depression. Nonetheless, the results support the hypothesis that BDNF levels influence resiliency against developing inflammatory cytokine-associated depression, and specifically to a subset of symptoms distinct from those influenced by 5-HTTLPR.

The epigenetic lorax: gene-environment interactions in human health

Over the last decade, we have witnessed an explosion of information on genetic factors underlying common human diseases and disorders. This 'human genomics' information revolution has occurred as a backdrop to a rapid increase in the rates of many human disorders and diseases. For example, obesity, Type 2 diabetes, asthma, autism spectrum disorder and attention deficit hyperactivity disorder have increased at rates that cannot be due to changes in the genetic structure of the population, and are difficult to ascribe to changes in diagnostic criteria or ascertainment. A likely cause of the increased incidence of these disorders is increased exposure to environmental factors that modify gene function. Many environmental factors that have epidemiological association with common human disorders are likely to exert their effects through epigenetic alterations. This general mechanism of gene-environment interaction poses special challenges for individuals, educators, scientists and public policy makers in defining, monitoring and mitigating exposures.

Reprint of: Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

Social deprivation stress is a triggering factor for the emergence of anxiety- and depression-like behaviours and leads to reduced brain BDNF levels in C57BL/6J mice

Stress is a main risk factor that can trigger psychiatric disorders, including anxiety and major depression. Neurotrophins, such as Brain-Derived Neurotrophic Factor (BDNF), have been identified as neuroendocrine effectors involved in the response to stress and in the neurobehavioural changes associated with depression. Aim of this paper was to study the relationship between neuroendocrine activation (circulating corticosterone and brain BDNF levels) and a wide array of depression- and anxiety-like behaviours (anhedonia, behavioural despair, generalised and social anxiety) resulting from exposure to chronic stress. To this end, 3-month-old C57BL/6J male mice were exposed to either chronic disruption of the social structure (SS), to a stable social structure (SG) or to social deprivation (SD), a condition lacking social stimuli. Results show that, despite not developing anhedonia (decreased preference for a sucrose solution), SD mice were characterised by increased emotionality and hypothalamic-pituitary-adrenal axis reactivity in addition to reduced BDNF levels. By contrast, SG and SS mice showed increased anhedonia accompanied by no alterations in the behavioural and neuroendocrine profile. The results here reported indicate that mice exposed to different social housing conditions use different behavioural strategies to cope with external challenges. In addition they suggest that social deprivation might represent a stressful condition triggering the emergence of both anxiety- and depression-like behaviours and clearly indicate BDNF as a main neurobiological variable mediating these responses.

Plasma BDNF is associated with age-related white matter atrophy but not with cognitive function in older, non-demented adults

Brain derived neurotrophic factor (BDNF) seems to be involved in regulation of synaptic plasticity and neurogenesis. BDNF plasma and serum levels have been associated with depression, Alzheimer's disease, and other psychiatric and neurodegenerative disorders. In a community sample, drawn from the Baltimore Longitudinal Study of Aging (BLSA), we examined whether BDNF plasma concentration was associated with rates of age-related change in cognitive performance (n = 429) and regional brain volume (n = 59). Plasma BDNF levels, which were significantly higher in females (p<0.05), were not associated with either concurrent cognitive performance or rates of age-related change in performance across cognitive domains (p's>0.05). Sex differences in the relationship between BDNF and the trajectories of regional brain volume changes were observed for the whole brain and frontal white matter volumes (p<0.05), whereby lower plasma BDNF was associated with steeper volume decline in females but not males. Together, our findings contribute to furthering the understanding of the relationships between plasma BDNF, structural brain integrity and cognition. Potential mechanisms mediating these relationships merit further investigation.

BDNF function as a potential mediator of bipolar disorder and post-traumatic stress disorder comorbidity

Bipolar disorder (BD) and post-traumatic stress disorder (PTSD) frequently co-occur among psychiatric patients, leading to increased morbidity and mortality. Brain-derived neurotrophic factor (BDNF) function is associated with core characteristics of both BD and PTSD. We propose a neurobiological model that underscores the role of reduced BDNF function resulting from several contributing sources, including the met variant of the BDNF val66met (rs6265) single-nucleotide polymorphism, trauma-induced epigenetic regulation and current stress, as a contributor to the onset of both illnesses within the same person. Further studies are needed to evaluate the genetic association between the val66met allele and the BD-PTSD population, along with central/peripheral BDNF levels and epigenetic patterns of BDNF gene regulation within these patients.

Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.