Differential regulation of p75 and trkB mRNA expression after depolarizing stimuli or BDNF treatment in basal forebrain neuron cultures

Counteracting epigenetic mechanisms regulate the structural development of neuronal circuitry in human neurons

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. Genetic findings suggest that there is an overrepresentation of chromatin regulatory genes among the genes associated with ASD. ASH1 like histone lysine methyltransferase (ASH1L) was identified as a major risk factor for ASD. ASH1L methylates Histone H3 on Lysine 36, which is proposed to result primarily in transcriptional activation. However, how mutations in ASH1L lead to deficits in neuronal connectivity associated with ASD pathogenesis is not known. We report that ASH1L regulates neuronal morphogenesis by counteracting the catalytic activity of Polycomb Repressive complex 2 group (PRC2) in stem cell-derived human neurons. Depletion of ASH1L decreases neurite outgrowth and decreases expression of the gene encoding the neurotrophin receptor TrkB whose signaling pathway is linked to neuronal morphogenesis. The neuronal morphogenesis defect is overcome by inhibition of PRC2 activity, indicating that a balance between the Trithorax group protein ASH1L and PRC2 activity determines neuronal morphology. Thus, our work suggests that ASH1L may epigenetically regulate neuronal morphogenesis by modulating pathways like the BDNF-TrkB signaling pathway. Defects in neuronal morphogenesis could potentially impair the establishment of neuronal connections which could contribute to the neurodevelopmental pathogenesis associated with ASD in patients with ASH1L mutations.

Effect of controlled release of brain-derived neurotrophic factor and neurotrophin-3 from collagen gel on neural stem cells

This study aimed to examine the effect of controlled release of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) from collagen gel on rat neural stem cells (NSCs). With three groups of collagen gel, BDNF/collagen gel, and NT-3/collagen gel as controls, BDNF and NT-3 were tested in the BDNF-NT-3/collagen gel group at different time points. The enzyme-linked immunosorbent assay results showed that BDNF and NT-3 were steadily released from collagen gels for 10 days. The cell viability test and the bromodeoxyuridine incorporation assay showed that BDNF-NT-3/collagen gel supported the survival and proliferation of NSCs. The results also showed that the length of processes was markedly longer and differentiation percentage from NSCs into neurons was much higher in the BDNF-NT-3/collagen gel group than those in the collagen gel, BDNF/collagen gel, and NT-3/collagen gel groups. These findings suggest that BDNF-NT-3/collagen gel could significantly improve the ability of NSCs proliferation and differentiation.

Effects of controlled release of brain-derived neurotrophic factor from collagen gel on rat neural stem cells

This study aimed to determine the effects of the controlled release of brain-derived neurotrophic factor (BDNF) from collagen gel on rat neural stem cells (NSCs). With two groups of daily addition of BDNF and collagen gel without BDNF as controls, BDNF was tested using ELISA at different time points. In the BDNF-collagen gel group, BDNF was steadily released from gels for 10 days. The cell viability test and the bromodeoxyuridine incorporation assay showed that the BDNF-collagen gel supported the survival and proliferation of NSCs. Compared with controls, the length of processes was markedly longer and the differentiation percentage from NSCs into neurons was much higher in the BDNF-collagen gel group (P<0.05). These findings suggest that BDNF-collagen gel can significantly reduce the amount of BDNF required for the culture of NSCs and increase the differentiation percentage from NSCs into neurons.

1H-MRS can monitor metabolites changes of lateral intraventricular BDNF infusion into a mouse model of Alzheimer's disease in vivo

Proton magnetic resonance spectroscopy (1H-MRS) can provide noninvasive detection of brain metabolite changes in vivo in Alzheimer's disease (AD). AD is a prevalent neurodegenerative disorder characterized by deposition of β-amyloid peptides (Aβ) in multiple brain regions. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor whose level has been shown to be decreased in AD. BDNF supplementation can offer improvement in AD. However, the means of evaluation are still relatively limited. In the present study, 1H-MRS was applied to evaluate the therapeutic effects of bilateral intraventricular BDNF infusion into APP+PS1 (amyloid precursor protein+presenilin 1) transgenic mice. For comparison to the 1H-MRS changes in the prefrontal cortex, Morris water maze (MWM) test, Fluoro-Jade B staining and immunofluorescence for Aβ, glial fibrillary acidic protein and tropomyosin-related kinase B (TrkB) were also performed. Our results showed that N-acetylaspartate (NAA) levels increased and myo-inositol levels decreased in Tg-BDNF mice compared with Tg-PBS mice. But NAA level in Tg-BDNF mice was still lower than that in wild-type mice at 6weeks after infusion. These changes correlated with increased immunoreactivity of TrkB, reduced compact Aβ peptide and FJB+ neurons in Tg-BDNF mice compared to Tg-PBS mice. However, Tg-BDNF mice did not present obvious changes in behavior in the MWM. Taken together, we suggest that 1H-MRS may be a sensitive means of evaluating metabolic changes in response to therapeutic strategies in AD. Moreover, BDNF, may be a viable means of offering trophic support during disease.

1H-MRS assessment of the therapeutic effect of bilateral intraventricular BDNF infusion into APP/PS1 double transgenic mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by extracellular accumulation of amyloid deposits. Brain-derived neurotrophic factor (BDNF) is a neurotrophic factor whose levels have been shown to be decreased in AD brains. BDNF supplementation can offer improvement in the course of AD. However, the means of assessment are still relatively limited. In the present study, 1H-MRS was used to evaluate the therapeutic effects of bilateral intraventricular BDNF infusion into Alzheimer's disease APP/PS1 double transgenic mice. For comparison to the 1H-MRS observations, Fluoro-Jade B staining and immunofluorescence for beta amyloid peptides (Aβ), glial fibrillary acidic protein, and tropomyosin-related kinase B (TrkB) were also performed. Our results showed that N-acetylaspartate (NAA) levels increased and myoinositol levels decreased in the BDNF group compared with the PBS group. However, the BDNF group NAA level was still lower than the control group at 6 weeks after infusion. These changes correlated with increased immunoreactivity for TrkB, decreased compact Aβ peptide containing plaques, and decreased Fluoro-Jade B-positive cells in the BDNF-infused mice compared to vehicle controls. These findings demonstrate that 1H-MRS may be a promising means of evaluating the therapeutic effects of BDNF on AD.

Experience-driven axon retraction in the pharmacologically inactivated visual cortex does not require synaptic transmission

BACKGROUND

Experience during early postnatal development plays an important role in the refinement of specific neural connections in the brain. In the mammalian visual system, altered visual experiences induce plastic adaptation of visual cortical responses and guide rearrangements of afferent axons from the lateral geniculate nucleus. Previous studies using visual deprivation demonstrated that the afferents serving an open eye significantly retract when cortical neurons are pharmacologically inhibited by applying a gamma-aminobutyric acid type A receptor agonist, muscimol, whereas those serving a deprived eye are rescued from retraction, suggesting that presynaptic activity can lead to the retraction of geniculocortical axons in the absence of postsynaptic activity. Because muscimol application suppresses the spike activity of cortical neurons leaving transmitter release intact at geniculocortical synapses, local synaptic interaction may underlie the retraction of active axons in the inhibited cortex.

METHOD AND FINDINGS

New studies reported here determined whether experience-driven axon retraction can occur in the visual cortex inactivated by blocking synaptic inputs. We inactivated the primary visual cortex of kittens by suppressing synaptic transmission with cortical injections of botulinum neurotoxin type E, which cleaves a synaptic protein, SNAP-25, and blocks transmitter release, and examined the geniculocortical axon morphology in the animals with normal vision and those deprived of vision binocularly. We found that afferent axons in the animals with normal vision showed a significant retraction in the inactivated cortex, as similarly observed in the muscimol-treated cortex, whereas the axons in the binocularly deprived animals were preserved.

CONCLUSIONS

Therefore, the experience-driven axon retraction in the inactivated cortex can proceed in the absence of synaptic transmission. These results suggest that presynaptic mechanisms play an important role in the experience-driven refinement of geniculocortical axons.

BDNF improves the effects of neural stem cells on the rat model of Alzheimer's disease with unilateral lesion of fimbria-fornix

In this study, neural stem cells (NSCs) were obtained from the hippocampus using the serum-free culturing. NSCs labeled with 5'-bromo-2'-deoxyuridine (BrdU) were transplanted into transected rat basal forebrain followed by the injection of brain-derived neurotrophic factor (BDNF) into the lateral ventricle. Nestin staining and double-labeling immunohistochemistry were used to detect cell survival and neuronal differentiation of the BrdU labeled cells in the basal forebrain and it was observed that labeled NSCs differentiated into neurons and astrocytes in the basal forebrain. Immunohistochemical detection of p75(NGFR) indicated that the number of cholinergic neurons of the combination groups treated by NSCs, BDNF, and NSCs groups had more significant improvement than that of the injured groups in medial septum (MS) and vertical diagonal branch (VDB). Learning and memory abilities were also measured by Y-maze test and the results support that BDNF can enhance the treatment effects of NSCs transplanted into brain lesion model.

Polysialic acid limits choline acetyltransferase activity induced by brain-derived neurotrophic factor

Choline acetyltransferase (ChAT), the enzyme synthesizing acetylcholine, is known to be activated by brain derived neurotrophic factor (BDNF). We found that the specific removal of the carbohydrate polysialic acid (PSA) significantly increased BDNF-induced ChAT-activity in embryonic septal neurons. Using a p75 neurotrophin receptor (p75(NTR)) function-blocking antibody and K252a, a-pan tropomyosin related kinase (Trk) inhibitor, we demonstrate that BDNF-induced ChAT activity requires the stimulation of p75(NTR) and TrkB. PSA removal drastically increased radioactive iodinated ([(125)I])BDNF's maximal binding capacity (Bmax), derived from concentrations of [(125)I]BDNF ranging from 1 pM to 3.2 nM. In the presence of unlabeled nerve growth factor to prevent the binding of [(125)I]BDNF to p75(NTR) sites, the impact of PSA removal on the binding capacity of [(125)I]BDNF was greatly reduced. In conclusion, PSA limits BDNF-induced ChAT activity and BDNF-receptor interactions. BDNF-induced ChAT activity is TrkB and p75(NTR) dependent, and upon PSA removal the additional binding of BDNF to its receptors, especially p75(NTR), likely contributes to the maximal ChAT activity observed. In vivo, the ontogenetic loss of PSA in the postnatal period may allow more interactions between BDNF and its receptors to increase ChAT activity and assure the proper development of the cholinergic septal neurons.