Altered peripheral BDNF mRNA expression and BDNF protein concentrations in blood of children and adolescents with autism spectrum disorder

Brain-Derived Neurotrophic Factor (BDNF) in Mechanisms of Autistic-like Behavior in BTBR Mice: Crosstalk with the Dopaminergic Brain System

Disturbances in neuroplasticity undoubtedly play an important role in the development of autism spectrum disorders (ASDs). Brain neurotransmitters and brain-derived neurotrophic factor (BDNF) are known as crucial players in cerebral and behavioral plasticity. Such an important neurotransmitter as dopamine (DA) is involved in the behavioral inflexibility of ASD. Additionally, much evidence from human and animal studies implicates BDNF in ASD pathogenesis. Nonetheless, crosstalk between BDNF and the DA system has not been studied in the context of an autistic-like phenotype. For this reason, the aim of our study was to compare the effects of either the acute intracerebroventricular administration of a recombinant BDNF protein or hippocampal adeno-associated-virus-mediated BDNF overexpression on autistic-like behavior and expression of key DA-related and BDNF-related genes in BTBR mice (a widely recognized model of autism). The BDNF administration failed to affect autistic-like behavior but downregulated Comt mRNA in the frontal cortex and hippocampus; however, COMT protein downregulation in the hippocampus and upregulation in the striatum were insignificant. BDNF administration also reduced the receptor TrkB level in the frontal cortex and midbrain and the BDNF/proBDNF ratio in the striatum. In contrast, hippocampal BDNF overexpression significantly diminished stereotypical behavior and anxiety; these alterations were accompanied only by higher hippocampal DA receptor D1 mRNA levels. The results indicate an important role of BDNF in mechanisms underlying anxiety and repetitive behavior in ASDs and implicates BDNF-DA crosstalk in the autistic-like phenotype of BTBR mice.

Prevalence of autistic traits in functional neurological disorder and relationship to alexithymia and psychiatric comorbidity

INTRODUCTION

In a cohort of adults with Functional Neurological Disorder (FND), we aim to: METHODS: 91 patients participating in a FND 5-week outpatient program completed baseline self-report questionnaires for total phobia, somatic symptom severity, attention deficit hyperactivity disorder (ADHD) and dyslexia. Patients were grouped by Autism Spectrum Quotient (AQ-10) score of <6 or ≥ 6 and compared for significant differences in tested variables. This analysis was repeated with patients grouped by alexithymia status. Simple effects were tested using pairwise comparisons. Multistep regression models tested direct relationships between autistic traits and psychiatric comorbidity scores, and mediation by alexithymia.

RESULTS

36 patients (40%) were AQ-10 positive (scoring ≥6 on AQ-10). A further 36 patients (across AQ-10 positive and AQ-10 negative groups) (40%) screened positive for alexithymia. AQ-10 positive patients scored significantly higher for alexithymia, depression, generalised anxiety, social phobia, ADHD, and dyslexia. Alexithymia positive patients scored significantly higher for generalised anxiety, depression, somatic symptoms severity, social phobia, and dyslexia. Alexithymia score was found to mediate the relationship between autistic trait and depression scores.

CONCLUSION

We demonstrate a high proportion of autistic and alexithymic traits, in adults with FND. A higher prevalence of autistic traits may highlight a need for specialised communication approaches in FND management. Mechanistic conclusions are limited. Future research could explore links with interoceptive data.

A Scoping Review on Movement, Neurobiology and Functional Deficits in Dyslexia: Suggestions for a Three-Fold Integrated Perspective

Developmental dyslexia is a common complex neurodevelopmental disorder. Many theories and models tried to explain its symptomatology and find ways to improve poor reading abilities. The aim of this scoping review is to summarize current findings and several approaches and theories, focusing on the interconnectedness between motion, emotion and cognition and their connection to dyslexia. Consequently, we present first a brief overview of the main theories and models regarding dyslexia and its proposed neural correlates, with a particular focus on cerebellar regions and their involvement in this disorder. After examining different types of intervention programs and remedial training, we highlight the effects of a specific structured sensorimotor intervention named Quadrato Motor Training (QMT). QMT utilizes several cognitive and motor functions known to be relevant in developmental dyslexia. We introduce its potential beneficial effects on reading skills, including working memory, coordination and attention. We sum its effects ranging from behavioral to functional, structural and neuroplastic, especially in relation to dyslexia. We report several recent studies that employed this training technique with dyslexic participants, discussing the specific features that distinguish it from other training within the specific framework of the Sphere Model of Consciousness. Finally, we advocate for a new perspective on developmental dyslexia integrating motion, emotion and cognition to fully encompass this complex disorder.

Inflammatory markers, brain-derived neurotrophic factor, and the symptomatic course of adolescent bipolar disorder: A prospective repeated-measures study

BACKGROUND

Numerous studies have found elevated pro-inflammatory markers and reduced brain-derived neurotrophic factor (BDNF) during symptomatic episodes of bipolar disorder (BD) in adults. There is a paucity of research examining these markers in youth with BD, or longitudinally in any BD age group.

METHODS

79 adolescents, ages 13-19 years, were enrolled, including 43 symptomatic adolescents with BD and 36 age-matched healthy controls (HC). Blood samples were collected from all participants at intake, and repeatedly from BD participants at pre-specified intervals over the course of two years. Serum was assayed for levels of pro-inflammatory markers (c-reactive protein [CRP], interleukin [IL]-6, tumor necrosis factor alpha [TNF-α]), BDNF and the anti-inflammatory marker, IL-10. Week-by-week severity of mood symptoms was assessed using semi-structured interviews.

RESULTS

Adolescents with BD provided an average of 4.6 blood samples, on average every 5.0 months. During the most severe symptomatic interval (i.e., highest sum of mood symptom scores) among BD adolescents, levels of CRP (p = 0.01) and pro- to anti-inflammatory ratios (CRP/IL-10; p < 0.001 and IL-6/IL-10; p = 0.046) were significantly greater, and IL-10 levels (p = 0.004) were significantly lower, vs. HC. There were no differences between BD and HC in IL-6, TNF-α or BDNF. Within BD participants, higher BDNF (p = 0.01) and IL-10 levels (p = 0.001) significantly predicted greater burden of mood symptoms over the subsequent epoch. Moreover, higher CRP levels (p = 0.009) at intake predicted greater time to recovery from the index symptomatic episode.

CONCLUSIONS

In the first repeated-measures study on this topic in adolescents with BD, we found evidence that CRP, an inexpensive and ubiquitous blood test, may be useful in predicting the prospective course of BD symptoms. Future larger studies are warranted.

Elevated levels of cortisol, brain-derived neurotropic factor and tissue plasminogen activator in male children with autism spectrum disorder

Several studies demonstrated biological effects of cortisol, brain-derived neurotrophic factor (BDNF) and tissue plasminogen activator (tPA) on human metabolism and central nervous system. Our study investigated the serum levels of tPA along with BDNF and cortisol in children with autism spectrum disorder (ASD). Thirty three male children with ASD ranging in age from 2 to 15 years were selected for the study group and 27 age-matched healthy male children were selected for the control group. The ASD severity was determined by the score on the Autism Behavior Checklist (ABC). The mean cortisol levels for the study group and the control group were 79.1 ± 30.2 ng/ml and 60.0 ± 25.1 ng/ml, respectively. The mean BDNF levels for the study group and the control group were 5.9 ± 2.8 ng/ml and 3.7 ± 1.8 ng/ml, respectively. The mean tPA levels for the study group and the control group were 32.9 ± 18.5 ng/ml and 25.5 ± 15.1 ng/ml, respectively. Cortisol, BDNF and tPA levels were significantly higher in the study group compared to the control group (p < 0.001). There was no statistically significant effect in terms of age, ABC total and subscale scores on serum cortisol, BDNF and tPA levels in the study group (p > 0.05). It may be suggested that elevations may indicate a role in the pathogenesis of ASD or it may be the case that ASD may alter the levels or pathways of these metabolic factors. LAY SUMMARY: The underlying mechanism or a specific metabolic target relevant to autism spectrum disorder (ASD) has not yet been identified. Cortisol, brain-derived neurotrophic factor (BDNF) and tissue plasminogen activator (tPA) have biological effects on neuroplasticity but little is known about the role of cortisol and tPA-BDNF pathway in ASD. In the present study focused on male children with ASD, we have found higher blood levels of cortisol, BDNF and tPA than their healthy peers. This is the first clinical study to evaluate the serum tPA levels along with BDNF and cortisol in ASD. The results suggest that several neurotrophic and other related markers should be born in mind while examining children with ASD.

Impaired Thiol/Disulfide Homeostasis in Children Diagnosed with Autism: A Case-Control Study

Although genetic factors occupy an important place in the development of autism spectrum disorder (ASD), oxidative stress and exposure to environmental toxicants have also been linked to the condition. The aim of this study was to examine dynamic thiol/disulfide homeostasis in children diagnosed with ASD. Forty-eight children aged 3-12 years diagnosed with ASD and 40 age- and sex-matched healthy children were included in the study. A sociodemographic data form was completed for all the cases, and the Childhood Autism Rating Scale (CARS) was applied to the patients. Thiol/disulfide parameters in serum were measured in all cases and compared between the two groups. Mean native thiol, total thiol concentrations (μmol/L), and median reduced thiol ratios were significantly lower in the ASD group than in the control group (p = 0.001 for all). Median disulfide concentrations (μmol/L), redox potential, and median oxidized thiol ratios were significantly higher in the ASD group than in the control group (p = 0.001, p = 0.001, and p = 0.001, respectively). ROC analysis revealed that area under the curve (AUC) values with "excellent discriminatory potential," for native thiol, total thiol, the reduced thiol ration, the oxidized thiol ratio, and redox potential and with "acceptable discriminatory potential" for disulfide were significantly capable of differentiating individuals with ASD from healthy individuals. No correlation was determined between the severity of autism and laboratory parameters. Impaired dynamic thiol/disulfide homeostasis was observed in children with ASD, suggesting that dynamic thiol/disulfide homeostasis in serum may be of diagnostic value in autism.

Peripheral blood neurotrophic factor levels in children with autism spectrum disorder: a meta-analysis

Increasing evidence suggests that abnormal regulation of neurotrophic factors is involved in the etiology and pathogenesis of Autism Spectrum Disorder (ASD). However, clinical data on neurotrophic factor levels in children with ASD were inconsistent. Therefore, we performed a systematic review of peripheral blood neurotrophic factors levels in children with ASD, and quantitatively summarized the clinical data of peripheral blood neurotrophic factors in ASD children and healthy controls. A systematic search of PubMed and Web of Science identified 31 studies with 2627 ASD children and 4418 healthy controls to be included in the meta-analysis. The results of random effect meta-analysis showed that the peripheral blood levels of brain-derived neurotrophic factor (Hedges’ g = 0.302; 95% CI = 0.014 to 0.591; P = 0.040) , nerve growth factor (Hedges’ g = 0.395; 95% CI = 0.104 to 0.686; P = 0.008) and vascular endothelial growth factor (VEGF) (Hedges’ g = 0.097; 95% CI = 0.018 to 0.175; P = 0.016) in children with ASD were significantly higher than that of healthy controls, whereas blood neurotrophin-3 (Hedges’ g =  − 0.795; 95% CI =  − 1.723 to 0.134; P = 0.093) and neurotrophin-4 (Hedges’ g = 0.182; 95% CI =  − 0.285 to 0.650; P = 0.445) levels did not show significant differences between cases and controls. Taken together, these results clarified circulating neurotrophic factor profile in children with ASD, strengthening clinical evidence of neurotrophic factor aberrations in children with ASD.

Assessment of BDNF serum levels as a diagnostic marker in children with autism spectrum disorder

There has been a significant increase in autism spectrum disorder (ASD) in the last decades that cannot be exclusively attributed to better diagnosis and an increase in the communication of new cases. Patients with ASD often show dysregulation of proteins associated with synaptic plasticity, notably brain-derived neurotrophic factor (BDNF). The objective of the present study was to analyze BDNF serum concentration levels in children with classic forms autism and a healthy control group to determine if there is a correlation between ASD and BDNF serum levels. Forty-nine children with severe classic form of autism, and 37 healthy children were enrolled in the study. Blood samples, from both patients and controls, were collected and BNDF levels from both groups were analyzed. The average BDNF serum concentration level was statistically higher for children with ASD (P < 0.000) compared to the control group. There is little doubt that BDNF plays a role in the pathophysiology of ASD development and evolution, but its brain levels may fluctuate depending on several known and unknown factors. The critical question is not if BDNF levels can be considered a prognostic or diagnostic marker of ASD, but to determine its role in the onset and progression of this disorder.

Epigenetic Effects on Pediatric Traumatic Brain Injury Recovery (EETR): An Observational, Prospective, Longitudinal Concurrent Cohort Study Protocol

Introduction: Unexplained heterogeneity in outcomes following pediatric traumatic brain injury (TBI) is one of the most critical barriers to the development of effective prognostic tools and therapeutics. The addition of personal biological factors to our prediction models may account for a significant portion of unexplained variance and advance the field toward precision rehabilitation medicine. The overarching goal of the Epigenetic Effects on Pediatric Traumatic Brain Injury Recovery (EETR) study is to investigate an epigenetic biomarker involved in both childhood adversity and postinjury neuroplasticity to better understand heterogeneity in neurobehavioral outcomes following pediatric TBI. Our primary hypothesis is that childhood adversity will be associated with worse neurobehavioral recovery in part through an epigenetically mediated reduction in brain-derived neurotrophic factor (BDNF) expression in response to TBI. Methods and analysis: EETR is an observational, prospective, longitudinal concurrent cohort study of children aged 3-18 years with either TBI (n = 200) or orthopedic injury (n = 100), recruited from the UPMC Children's Hospital of Pittsburgh. Participants complete study visits acutely and at 6 and 12 months postinjury. Blood and saliva biosamples are collected at all time points-and cerebrospinal fluid (CSF) when available acutely-for epigenetic and proteomic analysis of BDNF. Additional measures assess injury characteristics, pre- and postinjury child neurobehavioral functioning, childhood adversity, and potential covariates/confounders. Recruitment began in July 2017 and will occur for ~6 years, with data collection complete by mid-2023. Analyses will characterize BDNF DNA methylation and protein levels over the recovery period and investigate this novel biomarker as a potential biological mechanism underlying the known association between childhood adversity and worse neurobehavioral outcomes following pediatric TBI. Ethics and dissemination: The study received ethics approval from the University of Pittsburgh Institutional Review Board. Participants and their parents provide informed consent/assent. Research findings will be disseminated via local and international conference presentations and manuscripts submitted to peer-reviewed journals. Trial Registration: The study is registered with clinicaltrials.org (ClinicalTrials.gov Identifier: NCT04186429).

Systematic Balance Exercises Influence Cortical Activation and Serum BDNF Levels in Older Adults

We sought to investigate whether systematic balance training modulates brain area activity responsible for postural control and influence brain-derived neurotrophic factor (BDNF) mRNA protein expression. Seventy-four older adults were randomly divided into three groups (mean age 65.34 ± 3.79 years, 30 females): Classic balance exercises (CBT), virtual reality balance exercises (VBT), and control (CON). Neuroimaging studies were performed at inclusion and after completion of the training or 12 weeks later (CON). Blood samples were obtained to measure BDNF expression. The study revealed significant interaction of sessions and groups: In the motor imagery (MI) condition for supplementary motor area (SMA) activity (F_{at peak} = 5.25, p < 0.05); in the action observation (AO) condition for left and right supramarginal gyrus/posterior insula (left: F_{at peak} = 6.48, p < 0.05; right: F_{at peak} = 6.92, p < 0.05); in the action observation together with motor imagery (AOMI) condition for the middle occipital gyrus (laterally)/area V5 (left: F_{at peak} = 6.26, p < 0.05; right: F_{at peak} = 8.37, p < 0.05), and in the cerebellum–inferior semilunar lobule/tonsil (F_{at peak} = 5.47, p < 0.05). After the training serum BDNF level has increased in CBT (p < 0.001) and in CBT compared to CON (p < 0.05). Systematic balance training may reverse the age-related cortical over-activations and appear to be a factor mediating neuroplasticity in older adults.

Are preconceptional stressful experiences crucial elements for the aetiology of autism spectrum disorder? Insights from an animal model

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders characterized by changes in social interactions, impaired language and communication, fear responses and presence of repetitive behaviours. Although the genetic bases of ASD are well documented, the recent increase in clinical cases of idiopathic ASD indicates that several environmental risk factors could play a role in ASD aetiology. Among these, maternal exposure to psychosocial stressors during pregnancy has been hypothesized to affect the risk for ASD in offspring. Here, we tested the hypothesis that preconceptional stressful experiences might also represent crucial elements in the aetiology of ASD. We previously showed that social isolation stress during adolescence results in a marked decrease in the brain and plasma concentrations of progesterone and in the quality of maternal care that these female rats later provide to their young. Here we report that male offspring of socially isolated parents showed decreased agonistic behaviour and social transmission of flavour preference, impairment in reversal learning, increased seizure susceptibility, reduced plasma oxytocin levels, and increased plasma and brain levels of BDNF, all features resembling an ASD-like phenotype. These alterations came with no change in spatial learning, aggression, anxiety and testosterone plasma levels, and were sex-dependent. Altogether, the results suggest that preconceptional stressful experiences should be considered as crucial elements for the aetiology of ASD, and indicate that male offspring of socially isolated parents may be a useful animal model to further study the neurobiological bases of ASD, avoiding the adaptations that may occur in other genetic or pharmacologic experimental models of these disorders.

Brain-derived neurotrophic factor (BDNF) in children with ASD and their parents: a 3-year follow-up

OBJECTIVE

Several lines of evidence point to a probable relationship between brain-derived neurotrophic factor (BDNF) and autism spectrum disorder (ASD), but studies have yielded inconsistent findings on the BDNF serum level in ASD. The study aimed to assess those levels in children with ASD and their families.

METHOD

BDNF serum levels were measured in 45 ASD children without intellectual disability (ID) and allergies, age 30-42 months and age-matched normal controls. BDNF serum levels in the parents of the ASD subjects were compared to normal controls. BDNF serum levels in the ASD subjects were followed up for 3 years and correlated with adaptive functioning changes.

RESULTS

BDNF serum levels were measured to be lower in children with ASD and independent of all the major baseline characteristics of the subjects. Having a child with ASD raises the BDNF levels in parents comparing to controls. Prospectively, no correlation between the change of BDNF variables in time and the change of the Vineland scores was found.

CONCLUSIONS

Our results contradict those from recent published meta-analyses with the age, the presence of ID and allergies being possible contributing factors. The parents' data indeed point to a role of BDNF in the pathophysiology of ASD.

Effect of maternal iron deficiency anemia on fetal neural development

OBJECTIVE

Perinatal iron deficiency may have deleterious consequences on fetal neural development. The present study was conducted to determine the effect of maternal iron deficiency anemia (IDA) on fetal hippocampal morphogenesis and production of brain-derived neurotrophic factor (BDNF).

STUDY DESIGN

Seventy term, singleton neonates born to mothers with IDA (hemoglobin <110g/L and serum ferritin <12 μg/L) formed the study group. Twenty gestational age-matched neonates born to healthy mothers without IDA (hemoglobin ≥110 g/L and serum ferritin >12 μg/L) served as controls. Maternal and fetal inflammatory conditions, infections and neonates with perinatal asphyxia were excluded. Cord blood BDNF concentrations were estimated by enzyme-linked immunosorbent assay. Volumetric analysis of hippocampus (right, left and combined, corrected for total intracranial volume) was done by cranial magnetic resonance imaging on days 3-5 of life.

RESULTS

In the study group, 24 mothers had mild (hemoglobin 100.0-109.0 g/L), 24 had moderate (hemoglobin 70.0-99.0 g/L), and 22 had severe (hemoglobin <70.0 g/L) anemia. Both hippocampal volumes and serum BDNF concentrations of neonates born to iron-deficient mothers were significantly reduced compared to controls. A progressive decline in hippocampal volumes and BDNF concentrations was observed with increasing severity of maternal anemia. Pearson correlation showed significant correlations among maternal and cord blood hemoglobin, iron indices, hippocampal volumes and BDNF concentrations.

CONCLUSIONS

Maternal IDA adversely affects hippocampal morphogenesis and fetal production of BDNF. The degree of affection is proportional to the severity of maternal anemia.

Hippocampal BDNF overexpression or microR124a silencing reduces anxiety- and autism-like behaviors in rats

MicroRNA124a (miR124a) has emerged recently as a key player for multiple neuropsychiatric disorders including depression, anxiety, alcoholism, and cocaine addiction. Although we have previously reported that miR124a and its target the brain-derived neutrophic factor (BDNF) play an important role in autism-like behaviors, the molecular and behavioral dysfunctions remain unknown. The aim of this study was to understand the effects of sustained decreases in miR124a and increases of BDNF in the dentate gyrus (DG) on neonatal isolation-induced anxiety-and autism like behaviors in rats. Here we report that lentiviral-mediated silencing of miR124a in the adult DG attenuated neonatal isolation-induced anxiety-like behavior in the elevated plus maze (EPM) and open-field (OF) tests. Also, miR124a silencing decreased autism-like phenotype in the marble burying test (MBT), self-grooming (SG), and social interaction tests. Pearson's correlations demonstrated that high levels of BDNF, a direct target of miR124a, were negatively correlated with miR124a expression. Interestingly, viral-mediated BDNF overexpression in the DG also reversed the neonatal isolation-induced anxiety-and autism like phenotypes. Collectively, these findings suggest that miR124a, through its target BDNF, may influence neonatal isolation-induced anxiety-and autism like behaviors. In conclusion, these results do support the hypothesis that miR124a in discrete hippocampal areas contributes to anxiety- and autism-like behaviors and may be involved in the neuroadaptations underlying the development of autism spectrum disorders as a persistent and lasting condition, and therefore provide a clearer mechanistic framework for understanding the physiopathology of such psychiatric illnesses.

Elevated plasma levels of glutamate in children with autism spectrum disorders

Excitatory neurotransmitter signaling through glutamate receptors modulates cognitive functions such as memory and learning, which are usually impaired in autism spectrum disorders (ASD). The aim of this study was to assess the clinical significance of plasma glutamate levels in ASD. Fifty-one children diagnosed with ASD, 51 typically developing children, and 51 children with intellectual disability matched for sex and age were assessed for plasma glutamate at admission. Plasma levels of glutamate were measured by liquid chromatography-tandem mass spectrometry and the severity of ASD was evaluated using the Childhood Autism Rating Scale Score. We found that the mean plasma glutamate levels were significantly (P<0.0001) higher in children with ASD compared with healthy controls and intellectual disability controls [36.1 (SD: 8.3) vs. 23.4 (4.2) vs. 24.7 (4.6) µM; P<0.001, respectively]. Levels of glutamate increased with increasing severity of ASD as defined by the Childhood Autism Rating Scale score. Receiver operating characteristics to diagnose ASD showed areas under the curve of glutamate of 0.92 [95% confidence interval (CI), 0.87-0.96], which was superior to high-sensitivity C-reactive protein [0.64 (95% CI, 0.55-0.75), P<0.001] and homocysteine (area under the curve, 0.72; 95% CI, 0.64-0.81; P<0.000). In multivariate logistic regression analysis, glutamate was an independent diagnosis indicator of ASD with an adjusted odds ratio of 1.362 (95% CI, 1.164-1.512; P<0.0001). The present study shows that autistic children had higher plasma levels of glutamate and elevated plasma glutamate levels may play an important role in the pathogenesis of autism. Further larger studies are required to support our findings.

The role of cord blood BDNF in infant cognitive impairment induced by low-level prenatal manganese exposure: LW birth cohort, China

This study aimed to examine the potential association between low-level prenatal manganese (Mn) exposure and 1-year-old children's neurodevelopment quotient (DQ) by using the Gesell Developmental Inventory (GDI) (motor, adaptive, language, and social domains) and explored the role of brain-derived neurotrophic factor (BDNF) in Mn-induced cognitive impairments. A total of 377 mothers were recruited from a prospective birth cohort in rural northern China. Cord serum concentrations of Mn and BDNF were measured and children's DQ was evaluated. The median serum Mn concentration was 3.4 μg/L. After adjusting for confounding factors, Mn level was significantly associated with gross motor scores (β = -6.0, 95% CI: -11.8 to -0.2, p < 0.05) and personal-social scores (β = -4.2, 95% CI: -8.4 to 0.1, p < 0.05). BDNF level was positively correlated with personal-social score (β = 0.7, 95% CI: 0-1.4, p < 0.05). A significant correlation was found between Mn and BDNF (r = -0.13, 95% CI: -0.23 to -0.03, p < 0.01). Furthermore, the interaction between cord serum Mn and BDNF was significant (p < 0.001). In conclusion, elevated low-level prenatal Mn exposure impaired infant's neurodevelopment, and BDNF plays an important role in cognitive impairment, especially in the personal-social ability.

Peripheral brain-derived neurotrophic factor in autism spectrum disorder: a systematic review and meta-analysis

Brain-derived neurotrophic factor (BDNF) regulates neuronal survival and growth and promotes synaptic plasticity. Recently, researchers have begun to explore the relationship between peripheral BDNF levels and autism spectrum disorder (ASD), but the findings are inconsistent. We undertook the first systematic review and meta-analysis of studies examining peripheral BDNF levels in ASD compared with healthy controls. The PubMed, Embase, and Cochrane Library databases were searched for studies published before February 2016. Fourteen studies involving 2,707 participants and 1,131 incident cases were included. The meta-analysis provided evidence of higher peripheral BDNF levels in ASD compared with controls [standardized mean difference (SMD) = 0.63, 95% confidence interval (95% CI) = 0.18–1.08; P = 0.006]. Subgroup analyses revealed higher BDNF levels in ASD compared with controls for both serum [SMD = 0.58, 95% CI = 0.11–1.04; P = 0.02] and plasma [SMD = 1.27, 95% CI = 0.92–1.61; P < 0.001]. Studies of childhood yielded similar cumulative effect size [SMD = 0.78, 95% CI = 0.31–1.26; P = 0.001], while this was not true for the studies of adulthood [SMD = 0.04, 95% CI = −1.72–1.80; P = 0.97]. This meta-analysis suggests that peripheral BDNF levels are a potential biomarker of ASD.

Meta-Analysis of BDNF Levels in Autism

Brain-derived neurotrophic factor (BDNF) centrally mediates growth, differentiation and survival of neurons, and the synaptic plasticity that underlies learning and memory. Recent meta-analyses have reported significantly lower peripheral BDNF among individuals with schizophrenia, bipolar disorder, and depression, compared with controls. To evaluate the role of BDNF in autism, and to compare autism to psychotic-affective disorders with regard to BDNF, we conducted a meta-analysis of BDNF levels in autism. Inclusion criteria were met by 15 studies, which included 1242 participants. The meta-analysis estimated a significant summary effect size of 0.33 (95 % CI 0.21-0.45, P < 0.001), suggesting higher BDNF in autism than in controls. The studies showed notable heterogeneity, but no evidence of publication biases. Higher peripheral BDNF in autism is concordant with several neurological and psychological theories on the causes and symptoms of this condition, and it contrasts notably with the lower levels of BDNF found in schizophrenia, bipolar disorder, and depression.

Brain-derived neurotrophic factor signaling is altered in the forebrain of Engrailed-2 knockout mice

Engrailed-2 (En2), a homeodomain transcription factor involved in regionalization and patterning of the midbrain and hindbrain regions has been associated to autism spectrum disorders (ASDs). En2 knockout (En2(-/-)) mice show ASD-like features accompanied by a significant loss of GABAergic subpopulations in the hippocampus and neocortex. Brain-derived neurotrophic factor (BDNF) is a crucial factor for the postnatal development of forebrain GABAergic neurons, and altered GABA signaling has been hypothesized to underlie the symptoms of ASD. Here we sought to determine whether interneuron loss in the En2(-/-) forebrain might be related to altered expression of BDNF and its signaling receptors. We first evaluated the expression of different BDNF mRNA isoforms in the neocortex and hippocampus of wild-type (WT) and En2(-/-) mice. Quantitative RT-PCR showed a marked down-regulation of several splicing variants of BDNF mRNA in the neocortex but not hippocampus of adult En2(-/-) mice, as compared to WT controls. Accordingly, levels of mature BDNF protein were lower in the neocortex but not hippocampus of En2(-/-) mice, as compared to WT. Increased levels of phosphorylated TrkB and decreased levels of p75 receptor were also detected in the neocortex of mutant mice. Accordingly, the expression of low density lipoprotein receptor (LDLR) and RhoA, two genes regulated via p75 was significantly altered in forebrain areas of mutant mice. These data indicate that BDNF signaling alterations might be involved in the anatomical changes observed in the En2(-/-) forebrain and suggest a pathogenic role of altered BDNF signaling in this mouse model of ASD.

Association of peripheral BDNF level with cognition, attention and behavior in preschool children

BACKGROUND

Brain-derived neurotrophic factor (BDNF) has been reported to affect development, cognition, attention and behavior. However, few studies have investigated preschool children with regard to these areas. We evaluated the relationship between cognition, attention and peripheral blood concentration of BDNF in preschool children.

METHODS

Twenty-eight children (mean age: 6.16 ± 0.60 years) were recruited. For all subjects, serum and plasma BDNF levels were assessed; intelligence was assessed using the Korean standardisation of the Wechsler Intelligence Scale for Children (KEDI-WISC); attention was assessed using the computerised continuous performance test (CCPT), the children's color trails test (CCTT), the Stroop color-word test for preschool children, and the attention-deficit/hyperactivity disorder rating scale (K-ARS); and finally emotional and behavioral problems were assessed using the child behavior checklist (K-CBCL). We confirmed the previously reported correlations between the various psychometric properties assessed and serum and plasma levels of BDNF in our sample.

RESULTS

Serum BDNF levels were negatively correlated with both KEDI-WISC full scale IQ (FSIQ, r = -0.39, p = 0.04) and verbal IQ (VIQ, r = -0.05, p = 0.01), but not with the performance IQ (PIQ, r = -0.12, p = 0.56). There were no significant relationships between plasma BDNF level and VIQ, PIQ or FSIQ. No correlations were found between either serum or plasma level of BDNF and any of the attentional measures (CCPT, ARS, CCTT or Stroop color word test). The CBCL total behavioral problem and attention problem sections were positively correlated with plasma BDNF level (r = 0.41, p = 0.03), (r = 0.44, p = 0.02), however, no relationship was found between the serum BDNF and any of the composite CBCL measures.

CONCLUSIONS

Our results suggest that high peripheral BDNF may be negatively correlated with intelligence, behavioral problems and clinical symptoms of neuro-developmental disorders such as intellectual disability in preschool children. A high peripheral BDNF concentration may, if these findings are further replicated, prove to be a useful biomarker for such issues in preschool children.

Sustained lentiviral-mediated overexpression of microRNA124a in the dentate gyrus exacerbates anxiety- and autism-like behaviors associated with neonatal isolation in rats

Autism spectrum disorders (ASD) are highly disabling psychiatric disorders. Despite a strong genetic etiology, there are no efficient therapeutic interventions that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of microRNA (miR) machinery may contribute to the underlying molecular mechanisms involved in ASD. Here, we report a stress model demonstrating that neonatal isolation-induced long-lasting hippocampal elevation of miR124a was associated with reduced expression of its target BDNF mRNA. In addition, we investigated the impact of lentiviral-mediated overexpression of miR124a into the dentate gyrus (DG) on social interaction, repetitive- and anxiety-like behaviors in the neonatal isolation (Iso) model of autism. Rats isolated from the dams on PND 1 to PND 11 were assessed for their social interaction, marble burying test (MBT) and repetitive self-grooming behaviors as adults following miR124a overexpression. Also, anxiety-like behavior and locomotion were evaluated in the elevated plus maze (EPM) and open-field (OF) tests. Results show that, consistent with previously published reports, Iso rats displayed decreased social interaction contacts but increased repetitive- and anxiety-like behaviors. Interestingly, across both autism- and anxiety-like behavioral assays, miR124a overexpression in the DG significantly exacerbated repetitive behaviors, social impairments and anxiety with no effect on locomotor activity. Our novel findings attribute neonatal isolation-inducible cognitive impairments to induction of miR124a and consequently suppressed BDNF mRNA, opening venues for intercepting these miR124a-mediated damages. They also highlight the importance of studying microRNAs in the context of ASD and identify miR124a as a novel potential therapeutic target for improving mood disorders.

Clinical and Neurobiological Relevance of Current Animal Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by social and communication impairments, as well as repetitive and restrictive behaviors. The phenotypic heterogeneity of ASD has made it overwhelmingly difficult to determine the exact etiology and pathophysiology underlying the core symptoms, which are often accompanied by comorbidities such as hyperactivity, seizures, and sensorimotor abnormalities. To our benefit, the advent of animal models has allowed us to assess and test diverse risk factors of ASD, both genetic and environmental, and measure their contribution to the manifestation of autistic symptoms. At a broader scale, rodent models have helped consolidate molecular pathways and unify the neurophysiological mechanisms underlying each one of the various etiologies. This approach will potentially enable the stratification of ASD into clinical, molecular, and neurophenotypic subgroups, further proving their translational utility. It is henceforth paramount to establish a common ground of mechanistic theories from complementing results in preclinical research. In this review, we cluster the ASD animal models into lesion and genetic models and further classify them based on the corresponding environmental, epigenetic and genetic factors. Finally, we summarize the symptoms and neuropathological highlights for each model and make critical comparisons that elucidate their clinical and neurobiological relevance.

Elevated Serum Brain-Derived Neurotrophic Factor (BDNF) but not BDNF Gene Val66Met Polymorphism Is Associated with Autism Spectrum Disorders

The aim of our study was to illuminate the potential role of brain-derived neurotrophic factor (BDNF) in autism spectrum disorder (ASD). We measured the circulating levels of BDNF in serum and BDNF gene (Val66Met) polymorphisms, in which two indicators were then compared between ASD and normal controls. A total of 82 drug-naïve ASD children and 82 age- and gender-matched normal controls were enrolled in the study. Their serum BDNF levels were detected by the ELISA. BDNF Val66Met polymorphism genotyping was conducted as according to the laboratory's standard protocol in laboratory. The ASD severity assessment was mainly determined by the score of the Childhood Autism Rating Scale (CARS). ELISA assay showed that the mean serum BDNF level of children with ASD was significantly (P < 0.0001) higher than that of the control cases (17.75 ± 5.43 vs. 11.49 ± 2.85 ng/ml; t = 9.236). Besides, the serum BDNF levels and CARS scores (P < 0.0001) were positively related. And, the BDNF genotyping results showed that there was no difference between the ASD cases and the control. Among the children with ASD, the mean serum BDNF level of Met/Met group was lower than other groups. According to the ROC curve generated from our clinical data, the optimal cutoff value of serum BDNF levels, an indicator for diagnosis of ASD, was projected to be 12.50 ng/ml. Thus, it yielded a corresponding sensitivity of 81.7 % and the specificity of 66.9 %. Accordingly, area value under the curve was 0.836 (95 % CI, 0.774-0.897); the positive predictive value (PPV) and the negative predictive value (NPV) were 70.1 and 79.1 %, respectively. These results suggested that rather than Val66Met polymorphism, BDNF was more possible to impact the pathogenesis of ASD.

The Role of Epigenetic Change in Autism Spectrum Disorders

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders characterized by problems with social communication, social interaction, and repetitive or restricted behaviors. ASD are comorbid with other disorders including attention deficit hyperactivity disorder, epilepsy, Rett syndrome, and Fragile X syndrome. Neither the genetic nor the environmental components have been characterized well enough to aid diagnosis or treatment of non-syndromic ASD. However, genome-wide association studies have amassed evidence suggesting involvement of hundreds of genes and a variety of associated genetic pathways. Recently, investigators have turned to epigenetics, a prime mediator of environmental effects on genomes and phenotype, to characterize changes in ASD that constitute a molecular level on top of DNA sequence. Though in their infancy, such studies have the potential to increase our understanding of the etiology of ASD and may assist in the development of biomarkers for its prediction, diagnosis, prognosis, and eventually in its prevention and intervention. This review focuses on the first few epigenome-wide association studies of ASD and discusses future directions.

BDNF stimulation of protein synthesis in cortical neurons requires the MAP kinase-interacting kinase MNK1

Although the MAP kinase-interacting kinases (MNKs) have been known for >15 years, their roles in the regulation of protein synthesis have remained obscure. Here, we explore the involvement of the MNKs in brain-derived neurotrophic factor (BDNF)-stimulated protein synthesis in cortical neurons from mice. Using a combination of pharmacological and genetic approaches, we show that BDNF-induced upregulation of protein synthesis requires MEK/ERK signaling and the downstream kinase, MNK1, which phosphorylates eukaryotic initiation factor (eIF) 4E. Translation initiation is mediated by the interaction of eIF4E with the m(7)GTP cap of mRNA and with eIF4G. The latter interaction is inhibited by the interactions of eIF4E with partner proteins, such as CYFIP1, which acts as a translational repressor. We find that BDNF induces the release of CYFIP1 from eIF4E, and that this depends on MNK1. Finally, using a novel combination of BONCAT and SILAC, we identify a subset of proteins whose synthesis is upregulated by BDNF signaling via MNK1 in neurons. Interestingly, this subset of MNK1-sensitive proteins is enriched for functions involved in neurotransmission and synaptic plasticity. Additionally, we find significant overlap between our subset of proteins whose synthesis is regulated by MNK1 and those encoded by known FMRP-binding mRNAs. Together, our data implicate MNK1 as a key component of BDNF-mediated translational regulation in neurons.

Sera from children with autism induce autistic features which can be rescued with a CNTF small peptide mimetic in rats

Autism is a neurodevelopmental disorder characterized clinically by impairments in social interaction and verbal and non-verbal communication skills as well as restricted interests and repetitive behavior. It has been hypothesized that altered brain environment including an imbalance in neurotrophic support during early development contributes to the pathophysiology of autism. Here we report that sera from children with autism which exhibited abnormal levels of various neurotrophic factors induced cell death and oxidative stress in mouse primary cultured cortical neurons. The effects of sera from autistic children were rescued by pre-treatment with a ciliary neurotrophic factor (CNTF) small peptide mimetic, Peptide 6 (P6), which was previously shown to exert its neuroprotective effect by modulating CNTF/JAK/STAT pathway and LIF signaling and by enhancing brain derived neurotrophic factor (BDNF) expression. Similar neurotoxic effects and neuroinflammation were observed in young Wistar rats injected intracerebroventricularly with autism sera within hours after birth. The autism sera injected rats demonstrated developmental delay and deficits in social communication, interaction, and novelty. Both the neurobiological changes and the behavioral autistic phenotype were ameliorated by P6 treatment. These findings implicate the involvement of neurotrophic imbalance during early brain development in the pathophysiology of autism and a proof of principle of P6 as a potential therapeutic strategy for autism.

Neurotrophin blood-based gene expression and social cognition analysis in patients with autism spectrum disorder

Autism spectrum disorders (ASD) comprise neurodevelopmental disorders with clinical onset during the first years of life. The identification of peripheral biomarkers could significantly impact diagnosis and an individualized, early treatment. Although the aetiology of ASD remains poorly understood, there is increasing evidence that neurotrophins and their receptors represent a group of candidate genes for ASD pathophysiology and biomarker research. Total messenger RNA (mRNA) from whole blood was obtained from adolescents and adults diagnosed as ASD (n = 21) according to DSM-IV criteria and confirmed by the Autism Diagnostic Observation Schedule (ADOS) and Autism Diagnostic Interview-Revised (ADI-R) algorithms, as well as healthy controls (n = 10). The mRNA expression of neurotrophins (BDNF, NT3 and NT4) and their receptors (TrkA, TrkB and p75 (NTR) ) was determined by quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, social cognition abilities of ASD patients and controls were determined according to three Theory of Mind (ToM) tests (Reading the Mind in the Eyes, Faux pas, and Happé stories). The NT3 and NT4 mRNA expression in the whole blood was significantly lower in ASD compared to healthy controls, while p75(NTR) was higher (P < 0.005). In addition, lower scores in three of the ToM tests were observed in ASD subjects compared to controls. A significant (P < 0.005) ToM impairment in Happé stories test was demonstrated in ASD. Nevertheless, no correlations were observed between neurotrophins and their receptors expressions and measures of ToM. Given their potential as peripheral blood-based biomarkers, NT3, NT4 and p75 (NTR) mRNA expression patterns may be useful tools for a more personalized diagnostics and therapy in ASD. Further investigations with larger numbers of samples are needed to verify these results.

Serotonin dysregulation in Fragile X Syndrome: implications for treatment

Fragile X Syndrome (FXS) is a trinucleotide repeat disorder that results in the silencing of the Fragile X Mental Retardation 1 gene (FMR1), leading to a lack of the FMR1 protein (FMRP). FMRP is an mRNA-binding protein that regulates the translation of hundreds of mRNAs important for synaptic plasticity. Several of these pathways have been identified and have guided the development of targeted treatments for FXS. Here we present evidence that serotonin is dysregulated in FXS and treatment with the selective serotonin reuptake inhibitor (SSRI) sertraline may be beneficial for individuals with FXS, particularly in early childhood.

Biomarkers in autism

Autism spectrum disorders (ASDs) are complex, heterogeneous disorders caused by an interaction between genetic vulnerability and environmental factors. In an effort to better target the underlying roots of ASD for diagnosis and treatment, efforts to identify reliable biomarkers in genetics, neuroimaging, gene expression, and measures of the body's metabolism are growing. For this article, we review the published studies of potential biomarkers in autism and conclude that while there is increasing promise of finding biomarkers that can help us target treatment, there are none with enough evidence to support routine clinical use unless medical illness is suspected. Promising biomarkers include those for mitochondrial function, oxidative stress, and immune function. Genetic clusters are also suggesting the potential for useful biomarkers.