BDNF, proBDNF and IGF-1 serum levels in naïve and medicated subjects with autism

Brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) promote the development and maintenance of neural circuits. Alterations in these factors might contribute to autism spectrum disorder (ASD). We asked whether serum BDNF, proBDNF, and IGF-1 levels are altered in an ASD population compared to controls. We measured serum BDNF, proBDNF, and IGF-1 immunoreactive protein in boys and girls aged 5–15 years old with mild to moderate ASD and non-autistic controls by ELISA. IGF-1 was increased in ASD serum compared to controls and was correlated with age and with CARS scores. Serum BDNF levels did not differ between groups, however, proBDNF serum levels were decreased in subjects with ASD compared to non-autistic controls. Medicated, but not unmedicated, ASD subjects exhibited lower serum proBDNF levels compared to controls, while neither IGF-1 nor BDNF levels differed between treatment groups. These data support the involvement of proBDNF and IGF-1 in the pathogenesis and treatment of autism.

Autism Symptoms in Children and Young Adults With Fragile X Syndrome, Angelman Syndrome, Tuberous Sclerosis Complex, and Neurofibromatosis Type 1: A Cross-Syndrome Comparison

OBJECTIVE

The etiology of autism spectrum disorder (ASD) remains unclear, due to genetic heterogeneity and heterogeneity in symptoms across individuals. This study compares ASD symptomatology between monogenetic syndromes with a high ASD prevalence, in order to reveal syndrome specific vulnerabilities and to clarify how genetic variations affect ASD symptom presentation.

METHODS

We assessed ASD symptom severity in children and young adults (aged 0-28 years) with Fragile X Syndrome (FXS, n = 60), Angelman Syndrome (AS, n = 91), Neurofibromatosis Type 1 (NF1, n = 279) and Tuberous Sclerosis Complex (TSC, n = 110), using the Autism Diagnostic Observation Schedule and Social Responsiveness Scale. Assessments were part of routine clinical care at the ENCORE expertise center in Rotterdam, the Netherlands. First, we compared the syndrome groups on the ASD classification prevalence and ASD severity scores. Then, we compared individuals in our syndrome groups with an ASD classification to a non-syndromic ASD group (nsASD, n = 335), on both ASD severity scores and ASD symptom profiles. Severity scores were compared using MANCOVAs with IQ and gender as covariates.

RESULTS

Overall, ASD severity scores were highest for the FXS group and lowest for the NF1 group. Compared to nsASD, individuals with an ASD classification in our syndrome groups showed less problems on the instruments' social domains. We found a relative strength in the AS group on the social cognition, communication and motivation domains and a relative challenge in creativity; a relative strength of the NF1 group on the restricted interests and repetitive behavior scale; and a relative challenge in the FXS and TSC groups on the restricted interests and repetitive behavior domain.

CONCLUSION

The syndrome-specific strengths and challenges we found provide a frame of reference to evaluate an individual's symptoms relative to the larger syndromic population and to guide treatment decisions. Our findings support the need for personalized care and a dimensional, symptom-based diagnostic approach, in contrast to a dichotomous ASD diagnosis used as a prerequisite for access to healthcare services. Similarities in ASD symptom profiles between AS and FXS, and between NF1 and TSC may reflect similarities in their neurobiology. Deep phenotyping studies are required to link neurobiological markers to ASD symptomatology.

The Presynaptic Scaffold Protein Bassoon in Forebrain Excitatory Neurons Mediates Hippocampal Circuit Maturation: Potential Involvement of TrkB Signalling

A presynaptic active zone organizer protein Bassoon orchestrates numerous important functions at the presynaptic active zone. We previously showed that the absence of Bassoon exclusively in forebrain glutamatergic presynapses (Bsn^Emx1cKO) in mice leads to developmental disturbances in dentate gyrus (DG) affecting synaptic excitability, morphology, neurogenesis and related behaviour during adulthood. Here, we demonstrate that hyperexcitability of the medial perforant path-to-DG (MPP-DG) pathway in Bsn^Emx1cKO mice emerges during adolescence and is sustained during adulthood. We further provide evidence for a potential involvement of tropomyosin-related kinase B (TrkB), the high-affinity receptor for brain-derived neurotrophic factor (BDNF), mediated signalling. We detect elevated TrkB protein levels in the dorsal DG of adult mice (~3–5 months-old) but not in adolescent (~4–5 weeks-old) mice. Electrophysiological analysis reveals increased field-excitatory-postsynaptic-potentials (fEPSPs) in the DG of the adult, but not in adolescent Bsn^Emx1cKO mice. In line with an increased TrkB expression during adulthood in Bsn^Emx1cKO, blockade of TrkB normalizes the increased synaptic excitability in the DG during adulthood, while no such effect was observed in adolescence. Accordingly, neurogenesis, which has previously been found to be increased in adult Bsn^Emx1cKO mice, was unaffected at adolescent age. Our results suggest that Bassoon plays a crucial role in the TrkB-dependent postnatal maturation of the hippocampus.

Current Methodological Pitfalls and Caveats in the Assessment of Exercise-Induced Changes in Peripheral Brain-Derived Neurotrophic Factor: How Result Reproducibility Can Be Improved

Neural mechanisms, such as enhanced neuroplasticity within the motor system, underpin exercise-induced motor improvements. Being a key mediator of motor plasticity, brain-derived neurotrophic factor (BDNF) is likely to play an important role in mediating exercise positive effects on motor function. Difficulties in assessing brain BDNF levels in humans have drawn attention to quantification of blood BDNF and raise the question of whether peripheral BDNF contributes to exercise-related motor improvements. Methodological and non-methodological factors influence measurements of blood BDNF introducing a substantial variability that complicates result interpretation and leads to inconsistencies among studies. Here, we discuss methodology-related issues and approaches emerging from current findings to reduce variability and increase result reproducibility.

Effect of non-invasive brain stimulation on behavior and serum brain-derived neurotrophic factor and insulin-like growth factor-1 levels in autistic patients

Aberrant neural connectivity and intra-cortical inhibitory dysfunction are key features of autism. Non-invasive brain stimulation (NIBS) protocols have been proposed that modulate this aberrant plasticity. However, additional investigations are needed to evaluate the impact of this intervention on biological biomarkers of the disease. We recently demonstrated alterations in serum insulin-like growth factor-1 (IGF-1) and brain-derived neurotrophic factor (BDNF) immunoreactivity in subjects with autism compared to controls. The aim of this pilot study was to explore the change in serum levels of the neurotrophic factors BDNF and IGF-1 in patients undergoing NIBS therapy. Sixteen subjects with autism spectrum disorder (ASD) were tested 1 week before and 1 week after NIBS to determine the short-term outcome on behavior using the total score on the autism behavior checklist, autism treatment evaluation checklist, clinical global impression severity and the autism diagnostic interview. ASD subjects younger than 11 years old (n = 11) were treated with transcranial direct current stimulation (tDCS), and those 11 years and older (n = 5) were treated with repetitive transcranial magnetic stimulation (rTMS). Serum levels of BDNF and IGF-1 were evaluated by Enzyme-Linked Immuno-Sorbent Assay before and after the intervention with NIBS. A significant reduction in scores on the clinical behavioral scales was observed in patients treated with NIBS (ABC-T p = .002, CGI-S p = .008, ADI-T and ATEC-T p < .0001). There was a trend towards reduced serum BDNF levels after NIBS (p = .061), while there was no change in IGF-1 levels. These data support further studies on the potential of BDNF as a biomarker to measure the effectiveness of NIBS in autism.

Neuroimmunologic and Neurotrophic Interactions in Autism Spectrum Disorders: Relationship to Neuroinflammation

Autism spectrum disorders (ASD) are the most prevalent set of pediatric neurobiological disorders. The etiology of ASD has both genetic and environmental components including possible dysfunction of the immune system. The relationship of the immune system to aberrant neural circuitry output in the form of altered behaviors and communication characterized by ASD is unknown. Dysregulation of neurotrophins such as BDNF and their signaling pathways have been implicated in ASD. While abnormal cortical formation and autistic behaviors in mouse models of immune activation have been described, no one theory has been described to link activation of the immune system to specific brain signaling pathways aberrant in ASD. In this paper we explore the relationship between neurotrophin signaling, the immune system and ASD. To this effect we hypothesize that an interplay of dysregulated immune system, synaptogenic growth factors and their signaling pathways contribute to the development of ASD phenotypes.

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.