Conditional deletion of brain-derived neurotrophic factor in the postnatal brain leads to obesity and hyperactivity

Brain-derived neurotrophic factor has been associated previously with the regulation of food intake. To help elucidate the role of this neurotrophin in weight regulation, we have generated conditional mutants in which brain-derived neurotrophic factor has been eliminated from the brain after birth through the use of the cre-loxP recombination system. Brain-derived neurotrophic factor conditional mutants were hyperactive after exposure to stressors and had higher levels of anxiety when evaluated in the light/dark exploration test. They also had mature onset obesity characterized by a dramatic 80-150% increase in body weight, increased linear growth, and elevated serum levels of leptin, insulin, glucose, and cholesterol. In addition, the mutants had an abnormal starvation response and elevated basal levels of POMC, an anorexigenic factor and the precursor for alpha-MSH. Our results demonstrate that brain derived neurotrophic factor has an essential maintenance function in the regulation of anxiety-related behavior and in food intake through central mediators in both the basal and fasted state.     

脑源性神经营养因子研究进展

脑源性神经营养因子是一种小分子二聚体蛋白质,在结构上与神经生长因子相关。对中枢神经系统的多种类型神经元的生长、发育、分化、维护和再生部具有重要作用,对于治疗运动神经元病变以及神经系统迟行性疾病有显疗效。本对其细胞与分子生物学特征、生物学功能进行阐述。     

Alarin-induced antidepressant-like effects and their relationship with hypothalamus–pituitary–adrenal axis activity and brain derived neurotrophic factor levels in mice

Alarin is a newly identified member of the galanin family of peptides. Galanin has been shown to exert regulatory effects on depression. Similar to galanin in distribution, alarin is also expressed in the medial amygdala and hypothalamus, i.e., regions interrelated with depression. However, it remains a puzzle whether alarin is involved in depression. Accordingly, we established the depression-like mouse model using behavioral tests to ascertain the possible involvement of alarin, with fluoxetine as a positive control. With the positive antidepressant-like effects of alarin, we further examined its relationship to HPA axis activity and brain-derived neurotrophic factor (BDNF) levels in different brain areas in a chronic unpredictable mild stress (CUMS) paradigm. In the acute studies, alarin produced a dose-related reduction in the immobility duration in tail suspension test (TST) in mice. In the open-field test, intracerebroventricular (i.c.v.) injection of alarin (1.0 nmol) did not impair locomotion or motor coordination in the treated mice. In the CUMS paradigm, alarin administration (1.0 nmol, i.c.v.) significantly improved murine behaviors (FST and locomotor activity), which was associated with a decrease in corticotropin-releasing hormone (CRH) mRNA levels in the hypothalamus, as well as a decline in serum levels of CRH, adrenocorticotropic hormone (ACTH) and corticosterone (CORT), all of which are key hormones of the HPA axis. Furthermore, alarin upregulated BDNF mRNA levels in the prefrontal cortex and hippocampus. These findings suggest that alarin may potentiate the development of new antidepressants, which would be further secured with the identification of its receptor(s).     

The effect of exercise training modality on serum brain derived neurotrophic factor levels in individuals with type 2 diabetes

Introduction

Brain derived neurotrophic factor (BDNF) has been implicated in memory, learning, and neurodegenerative diseases. However, the relationship of BDNF with cardiometabolic risk factors is unclear, and the effect of exercise training on BDNF has not been previously explored in individuals with type 2 diabetes.

Methods

Men and women (N = 150) with type 2 diabetes were randomized to an aerobic exercise (aerobic), resistance exercise (resistance), or a combination of both (combination) for 9 months. Serum BDNF levels were evaluated at baseline and follow-up from archived blood samples.

Results

Baseline serum BDNF was not associated with fitness, body composition, anthropometry, glucose control, or strength measures (all, p>0.05). Similarly, no significant change in serum BDNF levels was observed following exercise training in the aerobic (−1649.4 pg/ml, CI: −4768.9 to 1470.2), resistance (−2351.2 pg/ml, CI:−5290.7 to 588.3), or combination groups (−827.4 pg/ml, CI: −3533.3 to1878.5) compared to the control group (−2320.0 pg/ml, CI: −5750.8 to 1110.8). However, reductions in waist circumference were directly associated with changes in serum BDNF following training (r = 0.25, p = 0.005).

Conclusions

Serum BDNF was not associated with fitness, body composition, anthropometry, glucose control, or strength measures at baseline. Likewise, serum BDNF measures were not altered by 9 months of aerobic, resistance, or combination training. However, reductions in waist circumference were associated with decreased serum BDNF levels. Future studies should investigate the relevance of BDNF with measures of cognitive function specifically in individuals with type-2 diabetes.     

The effect of zinc supplementation on brain derived neurotrophic factor: A meta-analysis

BackgroundZinc in one of the most abundant trace minerals in human body which is involved in numerous biological pathways and has variety of roles in the nervous system. It has been assumed that zinc exerts its role in nervous system through increasing brain derived neurotrophic factor (BDNF) concentrations.ObjectivesPresent meta-analysis was aimed to review the effect of zinc supplementation on serum concentrations of BDNF.Methods and materialsFour electronic databases (Pubmed, Scopus, Web of Science, Embase) were searched for identifying studies that examined BDNF levels prior and after zinc supplementation up to May 2020. According to the Cochrane guideline, a meta-analysis was performed to pool the effect size estimate (Hedges’ test) of serum BDNF across studies. Risk of publication bias was assessed using a funnel plot and Egger’s test.ResultsFive studies were eligible and 238 participants were included. These studies enrolled subjects with premenstrual syndrome, diabetic retinopathy, major depression disorder, overweight/obese and obese with mild to moderate depressive disorders. Zinc supplementation failed to increase blood BDNF concentrations with effect size of 0.30 (95 % CI: -0.08, 0.67, P = 0.119). Funnel plot did not suggest publication bias.ConclusionZinc supplementation may not significantly increase BDNF levels. However, the small number of included articles and significant heterogeneity between them can increase the risk of a false negative result; therefore, the results should be interpreted with caution.     

Purification of recombinant brain derived neurotrophic factor using reversed phase displacement chromatography

This work investigates the utility of RPLC displacement chromatography for the purification of recombinant brain derived neurotrophic factor (rHu-BDNF) from its variants and E. coli. protein (ECP) impurities. The closely associated variants (six in total) differ by one amino acid from the native BDNF and thus pose a challenging separation problem. Several operational parameters were investigated to study their effects on the yield of the displacement process. The results indicated that the concentration of trifluoroacetic acid (TFA) in the buffer was a key factor in achieving the desired purification. Displacement chromatography on an analytical scale column resulted in extremely high purity and yield in a single chromatographic step. The process was successfully scaled-up with respect to particle and column diameter. The production rate of a pilot scale RPLC displacement process was shown to be 23 times higher than the combined production rates of the current preparative ion exchange and hydrophobic interaction gradient elution steps that are used to remove variant and ECP impurities, respectively.     

Cyclic amino acid linkers stabilizing key loops of brain derived neurotrophic factor

Based on β-turn-like BDNF loops 2 and 4, involved in receptor interaction, cyclic peptide replicas were designed, synthesized and tested. In addition to the native turn residues, the cyclic peptides include a linker unit between the N- and C-termini, selected by molecular modeling among various non-proteinogenic cyclic amino acids. NMR conformational studies showed that most of the cyclic peptides were able to adopt turn-like structures. Several of the analogues displayed significant inhibition of the BDNF-induced TrkB receptor phosphorylation, and hence could be useful templates for developing improved antagonists for this receptor.     

Single eight-hour shift of light-dark cycle increases brain-derived neurotrophic factor protein levels in the rat hippocampus

We previously reported that an eight hour phase advance in the light-dark (LD) cycle increases sleep in rats. Brain-derived neurotrophic factor (BDNF) is suggested to be one of the sleep and circadian regulating factors. We have therefore observed the responses of BDNF protein in the hippocampus, cerebellum and brainstem under conditions of LD change. BDNF protein was quantitatively measured using an ELISA kit. Under an 8-h LD phase advance, the levels of hippocampal BDNF were significantly increased on the day of the phase change, while the levels in the cerebellum and brainstem remained constant. Plasma corticosterone levels were not largely affected. Thus, a single LD shift acutely affects hippocampal BDNF metabolism with no large stress response.     

Microarray analysis of cultured rat hippocampal neurons treated with brain derived neurotrophic factor

Brain derived neurotrophic factor (BDNF) has been shown to exert multiple actions on neurons. It plays a role in neuronal growth and maintenance and use-dependent plasticity, such as long-term potentiation and learning. This neurotrophin is believed to regulate neuronal plasticity by modifying neuronal excitability and morphology. There is experimental evidence for both an acute and a long-term effect of BDNF on synaptic transmission and structure but the molecular mechanisms underlying these events have not been completely clarified. In order to study the BDNF-induced molecular changes, the set of genes modulated in cultured hippocampal neurons by BDNF treatment was investigated after subchronic treatment with the neurotrophin. Microarray analysis performed with these cells, revealed increased expression of mRNA encoding the neuropeptides neuropeptide Y and somatostatin, and of the secreted peptide VGF (non acronymic), all of which participate in neurotransmission. In addition, the expression of genes apolipoprotein E (ApoE), delta-6 fatty acid desaturase (Fads2) and matrix metalloproteinase 14 (Mmp14), which play a role in neuronal remodelling, was also enhanced. More studies are needed to investigate and confirm the role of these genes in synaptic plasticity, but the results reported in this paper show that microarray analysis of hippocampal cultures can be used to expand our current knowledge of the molecular events triggered by BDNF in the hippocampus.     

Acute stress induces contrasting changes in AMPA receptor subunit phosphorylation within the prefrontal cortex, amygdala and hippocampus

Exposure to stress causes differential neural modifications in various limbic regions, namely the prefrontal cortex, hippocampus and amygdala. We investigated whether α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) phosphorylation is involved with these stress effects. Using an acute inescapable stress protocol with rats, we found opposite effects on AMPA receptor phosphorylation in the medial prefrontal cortex (mPFC) and dorsal hippocampus (DH) compared to the amygdala and ventral hippocampus (VH). After stress, the phosphorylation of Ser831-GluA1 was markedly decreased in the mPFC and DH, whereas the phosphorylation of Ser845-GluA1 was increased in the amygdala and VH. Stress also modulated the GluA2 subunit with a decrease in the phosphorylation of both Tyr876-GluA2 and Ser880-GluA2 residues in the amygdala, and an increase in the phosphorylation of Ser880-GluA2 in the mPFC. These results demonstrate that exposure to acute stress causes subunit-specific and region-specific changes in glutamatergic transmission, which likely lead to the reduced synaptic efficacy in the mPFC and DH and augmented activity in the amygdala and VH. In addition, these findings suggest that modifications of glutamate receptor phosphorylation could mediate the disruptive effects of stress on cognition. They also provide a means to reconcile the contrasting effects that stress has on synaptic plasticity in these regions. Taken together, the results provide support for a brain region-oriented approach to therapeutics.     

The brain‐derived neurotrophic factor VAL68MET polymorphism modulates how developmental ethanol exposure impacts the hippocampus

Prenatal exposure to alcohol causes a wide range of deficits known as fetal alcohol spectrum disorders (FASDs). Many factors determine vulnerability to developmental alcohol exposure including timing and pattern of exposure, nutrition and genetics. Here, we characterized how a prevalent single nucleotide polymorphism in the human brain‐derived neurotrophic factor (BDNF) gene (val66met) modulates FASDs severity. This polymorphism disrupts BDNF's intracellular trafficking and activity‐dependent secretion, and has been linked to increased incidence of neuropsychiatric disorders such as depression and anxiety. We hypothesized that developmental ethanol (EtOH) exposure more severely affects mice carrying this polymorphism. We used transgenic mice homozygous for either valine (BDNF^val/val) or methionine (BDNF^met/met) in residue 68, equivalent to residue 66 in humans. To model EtOH exposure during the second and third trimesters of human pregnancy, we exposed mice to EtOH in vapor chambers during gestational days 12 to 19 and postnatal days 2 to 9. We found that EtOH exposure reduces cell layer volume in the dentate gyrus and the CA1 hippocampal regions of BDNF^met/met but not BDNF^val/val mice during the juvenile period (postnatal day 15). During adulthood, EtOH exposure reduced anxiety‐like behavior and disrupted trace fear conditioning in BDNF^met/met mice, with most effects observed in males. EtOH exposure reduced adult neurogenesis only in the ventral hippocampus of BDNF^val/val male mice. These studies show that the BDNF val66met polymorphism modulates, in a complex manner, the effects of developmental EtOH exposure, and identify a novel genetic risk factor that may regulate FASDs severity in humans.     

The effects of docosahexaenoic acid on glial derived neurotrophic factor and neurturin in bilateral rat model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder marked by cell death in the Substantia nigra (SN). Docosahexaenoic acid (DHA) is the major polyunsaturated fatty acid (PUFA) in the phospholipid fraction of the brain and is required for normal cellular function. Glial cell line derived neurotrophic factor (GDNF) and neurturin (NTN) are very potent trophic factors for PD. The aim of the study was to evaluate the neuroprotective effects of GDNF and NTN by investigating their immunostaining levels after administration of DHA in a model of PD. For this reason we hypothesized that DHA administration of PD might alter GDNF, NTN expression in SN. MPTP neurotoxin that induces dopaminergic neurodegeneration was used to create the experimental Parkinsonism model. Rats were divided into; control, DHA-treated (DHA), MPTP-induced (MPTP), MPTP-induced+DHA-treated (MPTP+DHA) groups. Dopaminergic neuron numbers were clearly decreased in MPTP, but showed an increase in MPTP+DHA group. As a result of this, DHA administration protected dopaminergic neurons as shown by tyrosine hydroxylase immunohistochemistry. In the MPTP+DHA group, GDNF, NTN immunoreactions in dopaminergic neurons were higher than that of the MPTP group. In conclusion, the characterization of GDNF and NTN will certainly help elucidate the mechanism of DHA action, and lead to better strategies for the use of DHA to treat neurodegenerative diseases.     

Cdc42 participates in the regulation of ADF/cofilin and retinal growth cone filopodia by brain derived neurotrophic factor

Rho family GTPases have important roles in mediating the effects of guidance cues and growth factors on the motility of neuronal growth cones. We previously showed that the neurotrophin BDNF regulates filopodial dynamics on growth cones of retinal ganglion cell axons through activation of the actin regulatory proteins ADF and cofilin by inhibiting a RhoA-dependent pathway that phosphorylates (inactivates) ADF/cofilin. The GTPase Cdc42 has also been implicated in mediating the effects of positive guidance cues. In this article we investigated whether Cdc42 is involved in the effects of BDNF on filopodial dynamics. BDNF treatment increases Cdc42 activity in retinal neurons, and neuronal incorporation of constitutively active Cdc42 mimics the increases in filopodial number and length. Furthermore, constitutively active and dominant negative Cdc42 decreased and increased, respectively, the activity of RhoA in retinal growth cones, indicating crosstalk between these GTPases in retinal growth cones. Constitutively active Cdc42 mimicked the activation of ADF/cofilin that resulted from BDNF treatment, while dominant negative Cdc42 blocked the effects of BDNF on filopodia and ADF/cofilin. The inability of dominant negative Cdc42 to block ADF/cofilin activation and stimulation of filopodial dynamics by the ROCK inhibitor Y-27632 indicate interaction between Cdc42 and RhoA occurs upstream of ROCK. Our results demonstrate crosstalk occurs between GTPases in mediating the effects of BDNF on growth cone motility, and Cdc42 activity can promote actin dynamics via activation of ADF/cofilin.     

Galectin-1 induces astrocyte differentiation, which leads to production of brain-derived neurotrophic factor

Brain-derived neurotrophic factor (BDNF) is a neuroprotective polypeptide that is thought to be responsible for neuron proliferation, differentiation, and survival. An agent that enhances production of BDNF is expected to be useful for the treatment of neurodegenerative diseases. Here we report that galectin-1, a member of the family of beta-galactoside binding proteins, induces astrocyte differentiation and strongly inhibits astrocyte proliferation, and then the differentiated astrocytes greatly enhance their production of BDNF. Induction of astrocyte differentiation and BDNF production by an endogenous mammalian lectin may be a new mechanism for preventing neuronal loss after injury.     

Differential regulation of ciliary neurotrophic factor and its receptor in the rat hippocampus in response to kainic acid-induced excitotoxicity

We analyzed the changes in expression of ciliary neurotrophic factor (CNTF) and its receptor, ligand-binding subunit a (CNTFRa), in the hippocampus following intraperitoneal administration of a convulsant dose of kainic acid (KA). Immunohistochemistry and immunoblotting showed that CNTF levels rose dramatically between day 1 and day 10, and that the CNTF was located in reactive astrocytes. In contrast, upregulation of CNTFRalpha mRNA, occurred in neurons as well as astrocytes. A rapid, and short-lived (3 h-2 d) increase in CNTFRalpha was also observed in the more resistant granule cells and CA2 pyramidal neurons. The increase in astrocytes was detected by day 1 and was sustained for more than 5 d. These results show that CNTF and CNTFRalpha are differentially regulated in hippocampal neurons and reactive astrocytes following KA injection, indicating that these proteins may be involved in the regulation of astrocyte and neuronal degenerative responses.     

Low‐level laser therapy for traumatic brain injury in mice increases brain derived neurotrophic factor (BDNF) and synaptogenesis

Transcranial low‐level laser (light) therapy (LLLT) is a new non‐invasive approach to treating a range of brain disorders including traumatic brain injury (TBI). We (and others) have shown that applying near‐infrared light to the head of animals that have suffered TBI produces improvement in neurological functioning, lessens the size of the brain lesion, reduces neuroinflammation, and stimulates the formation of new neurons. In the present study we used a controlled cortical impact TBI in mice and treated the mice either once (4 h post‐TBI, 1‐laser), or three daily applications (3‐laser) with 810 nm CW laser 36 J/cm² at 50 mW/cm². Similar to previous studies, the neurological severity score improved in laser‐treated mice compared to untreated TBI mice at day 14 and continued to further improve at days 21 and 28 with 3‐laser being better than 1‐laser. Mice were sacrificed at days 7 and 28 and brains removed for immunofluorescence analysis. Brain‐derived neurotrophic factor (BDNF) was significantly upregulated by laser treatment in the dentate gyrus of the hippocampus (DG) and the subventricular zone (SVZ) but not in the perilesional cortex (lesion) at day 7 but not at day 28. Synapsin‐1 (a marker for synaptogenesis, the formation of new connections between existing neurons) was significantly upregulated in lesion and SVZ but not DG, at 28 days but not 7 days. The data suggest that the benefit of LLLT to the brain is partly mediated by stimulation of BDNF production, which may in turn encourage synaptogenesis. Moreover the pleiotropic benefits of BDNF in the brain suggest LLLT may have wider applications to neurodegenerative and psychiatric disorders.

Neurological Severity Score (NSS) for TBI mice     

Exposure to neonatal separation stress alters exploratory behavior and corticotropin releasing factor expression in neurons in the amygdala and hippocampus

Evidence is accumulating that early emotional experience interferes with the development of the limbic system, which is involved in perception and regulation of emotional behaviors as well as in learning and memory formation. Limbic brain regions, as well as hypothalamic regions and other, nonlimbic areas contain specific neuron subpopulations, which express and release corticotropin releasing factor (CRF). Since these neurons serve to connect limbic function to endocrine, stress-related responses, we proposed that stressful experience during early postnatal brain development should interfere with the development of CRF-containing neurons, particularly in brain regions essential for emotional regulation. Applying neonatal separation stress (daily 1 h separation from the parents and litter mates) as stressor, the number of immunocytochemically identified CRF-expressing neurons/fibers was quantified in the amygdala, hippocampus, paraventricular nucleus of the hypothalamus, piriform cortex, and the somatosensory cortex of 3-week-old stressed and nonstressed Octodon degus, a semi-precocial rodent. Compared to controls neonatally stressed animals showed significantly lower levels of CRF-positive fibers (-60%) in the central amygdala, significantly less CRF-positive neurons in the dentate gyrus (-28%) and the CA1 region (-29%) and significantly lower CRF cell densities in the somatosensory cortex (-26%). On the other hand, we found significantly higher numbers of CRF-immunoreactive neurons in the basolateral amygdaloid complex (+192%) of stressed animals compared to nonstressed controls. No differences in CRF-immunoreactive cell densities were detected in the other regions. Additional behavioral analysis revealed significantly elevated exploratory behavior (+34%) in stressed animals compared to controls, which might indicate reduced anxiety in the stressed animals.