Explore the vast range of titles available.

We have investigated and compared the neurotrophic activity of human dental pulp stem cells (hDPSC), human bone marrow-derived mesenchymal stem cells (hBMSC) and human adipose-derived stem cells (hAMSC) on axotomised adult rat retinal ganglion cells (RGC) in vitro in order to evaluate their therapeutic potential for neurodegenerative conditions of RGC. Using the transwell system, RGC survival and length/number of neurites were quantified in coculture with stem cells in the presence or absence of specific Fc-receptor inhibitors to determine the role of NGF, BDNF, NT-3, VEGF, GDNF, PDGF-AA and PDGF-AB/BB in stem cell-mediated RGC neuroprotection and neuritogenesis. Conditioned media, collected from cultured hDPSC/hBMSC/hAMSC, were assayed for the secreted growth factors detailed above using ELISA. PCR array determined the hDPSC, hBMSC and hAMSC expression of genes encoding 84 growth factors and receptors. The results demonstrated that hDPSC promoted significantly more neuroprotection and neuritogenesis of axotomised RGC than either hBMSC or hAMSC, an effect that was neutralized after the addition of specific Fc-receptor inhibitors. hDPSC secreted greater levels of various growth factors including NGF, BDNF and VEGF compared with hBMSC/hAMSC. The PCR array confirmed these findings and identified VGF as a novel potentially therapeutic hDPSC-derived neurotrophic factor (NTF) with significant RGC neuroprotective properties after coculture with axotomised RGC. In conclusion, hDPSC promoted significant multi-factorial paracrine-mediated RGC survival and neurite outgrowth and may be considered a potent and advantageous cell therapy for retinal nerve repair.

Live fluorescent imaging of murine hippocampal slices shows that NMDAR-dependent glutamate signalling leads to postsynaptic BDNF release, with associated signalling of its receptor, TrkB, on the same dendritic spine, suggesting autocrine BDNF signalling. Mechanisms of neuronal plasticity Secreted messenger molecules such as brain-derived neurotrophic factor (BDNF) are known to participate in various forms of neuronal plasticity, such as long-term synaptic potentiation (LTP) and associated changes in dendritic spine morphology, but the exact sites of BDNF release and action remain poorly defined. Two papers from Ryohei Yasuda's lab, published in this issue of Nature , tackle this question. Stephen Harward et al . use live fluorescent imaging of murine hippocampal slices to show that NMDAR-dependent glutamate signalling leads to postsynaptic BDNF release, with associated signalling of its receptor, TrkB, on the same dendritic spine, suggesting autocrine BDNF signalling. In the second study Nathan Hedrick et al . find that the three small GTPases Rac1, RhoA and Cdc42 are differentially involved in structural long-term potentiation of rodent dendritic spines, simultaneously ensuring signal specificity while also priming the system for plasticity. Taken together these results suggest molecular mechanisms for both signal specificity at single spines and synaptic cross-talk, a unique biochemical computation involved in neuronal plasticity and learning. Brain-derived neurotrophic factor (BDNF) and its receptor TrkB are crucial for many forms of neuronal plasticity 1 , 2 , 3 , 4 , 5 , 6 , including structural long-term potentiation (sLTP) 7 , 8 , which is a correlate of an animal’s learning 7 , 9 , 10 , 11 , 12 . However, it is unknown whether BDNF release and TrkB activation occur during sLTP, and if so, when and where. Here, using a fluorescence resonance energy transfer-based sensor for TrkB and two-photon fluorescence lifetime imaging microscopy 13 , 14 , 15 , 16 , we monitor TrkB activity in single dendritic spines of CA1 pyramidal neurons in cultured murine hippocampal slices. In response to sLTP induction 9 , 14 , 15 , 16 , we find fast (onset < 1 min) and sustained (>20 min) activation of TrkB in the stimulated spine that depends on NMDAR ( N -methyl- d -aspartate receptor) and CaMKII signalling and on postsynaptically synthesized BDNF. We confirm the presence of postsynaptic BDNF using electron microscopy to localize endogenous BDNF to dendrites and spines of hippocampal CA1 pyramidal neurons. Consistent with these findings, we also show rapid, glutamate-uncaging-evoked, time-locked BDNF release from single dendritic spines using BDNF fused to superecliptic pHluorin 17 , 18 , 19 . We demonstrate that this postsynaptic BDNF–TrkB signalling pathway is necessary for both structural and functional LTP 20 . Together, these findings reveal a spine-autonomous, autocrine signalling mechanism involving NMDAR–CaMKII-dependent BDNF release from stimulated dendritic spines and subsequent TrkB activation on these same spines that is crucial for structural and functional plasticity.

GABA is a pain Neuropathic pain, one of the most debilitating of all pain states, often arises from injury to a peripheral nerve that depends on activation of a specific cell type known as microglia. This prompts the question, how do the microglia signal to spinal pain neurons? Coull et al . have now identified the biophysical mechanism by which microglia, activated by ATP, cause hyperexcitability of spinal neurons. The microglia release brain-derived neurotrophic factor, which alters chloride ion distribution across the plasma membrane of neurons in lamina I of the spinal cord. This results in the neurotransmitter, GABA, activating (rather than inhibiting) these cells that form part of a major pathway that signals pain. A collection of recent reprints on neuropathic pain, taken from Nature Publishing Group journals is, now available online via tinyurl.com/dzw86. Neuropathic pain that occurs after peripheral nerve injury depends on the hyperexcitability of neurons in the dorsal horn of the spinal cord 1 , 2 , 3 . Spinal microglia stimulated by ATP contribute to tactile allodynia, a highly debilitating symptom of pain induced by nerve injury 4 . Signalling between microglia and neurons is therefore an essential link in neuropathic pain transmission, but how this signalling occurs is unknown. Here we show that ATP-stimulated microglia cause a depolarizing shift in the anion reversal potential ( E anion ) in spinal lamina I neurons. This shift inverts the polarity of currents activated by GABA (γ-amino butyric acid), as has been shown to occur after peripheral nerve injury 5 . Applying brain-derived neurotrophic factor (BDNF) mimics the alteration in E anion . Blocking signalling between BDNF and the receptor TrkB reverses the allodynia and the E anion shift that follows both nerve injury and administration of ATP-stimulated microglia. ATP stimulation evokes the release of BDNF from microglia. Preventing BDNF release from microglia by pretreating them with interfering RNA directed against BDNF before ATP stimulation also inhibits the effects of these cells on the withdrawal threshold and E anion . Our results show that ATP-stimulated microglia signal to lamina I neurons, causing a collapse of their transmembrane anion gradient, and that BDNF is a crucial signalling molecule between microglia and neurons. Blocking this microglia–neuron signalling pathway may represent a therapeutic strategy for treating neuropathic pain.

A common single-nucleotide polymorphism (SNP) in the human brain-derived neurotrophic factor ( BDNF ) gene results in a Val66Met substitution in the BDNF prodomain region. This SNP is associated with alterations in memory and with enhanced risk to develop depression and anxiety disorders in humans. Here we show that the isolated BDNF prodomain is detected in the hippocampus and that it can be secreted from neurons in an activity-dependent manner. Using nuclear magnetic resonance spectroscopy and circular dichroism, we find that the prodomain is intrinsically disordered, and the Val66Met substitution induces structural changes. Surprisingly, application of Met66 (but not Val66) BDNF prodomain induces acute growth cone retraction and a decrease in Rac activity in hippocampal neurons. Expression of p75 NTR and differential engagement of the Met66 prodomain to the SorCS2 receptor are required for this effect. These results identify the Met66 prodomain as a new active ligand, which modulates neuronal morphology. The Val66Met single-nucleotide polymorphism in the BDNF gene is implicated in neuropsychiatric disorders. Anastasia et al. show that this polymorphism results in structural changes in the brain-derived neurotrophic factor prodomain, and growth cone retraction in the hippocampal neurons.

Background Brain-derived neurotrophic factor (BDNF) has been shown to control microglial responses in neuropathic pain. Since adenosine A 2A receptors (A 2A Rs) control neuroinflammation, as well as the production and function of BDNF, we tested to see if A 2A R controls the microglia-dependent secretion of BDNF and the proliferation of microglial cells, a crucial event in neuroinflammation. Methods Murine N9 microglial cells were challenged with lipopolysaccharide (LPS, 100 ng/mL) in the absence or in the presence of the A 2A R antagonist, SCH58261 (50 nM), as well as other modulators of A 2A R signaling. The BDNF cellular content and secretion were quantified by Western blotting and ELISA, A 2A R density was probed by Western blotting and immunocytochemistry and cell proliferation was assessed by BrdU incorporation. Additionally, the A 2A R modulation of LPS-driven cell proliferation was also tested in primary cultures of mouse microglia. Results LPS induced time-dependent changes of the intra- and extracellular levels of BDNF and increased microglial proliferation. The maximal LPS-induced BDNF release was time-coincident with an LPS-induced increase of the A 2A R density. Notably, removing endogenous extracellular adenosine or blocking A 2A R prevented the LPS-mediated increase of both BDNF secretion and proliferation, as well as exogenous BDNF-induced proliferation. Conclusions We conclude that A 2A R activation plays a mandatory role controlling the release of BDNF from activated microglia, as well as the autocrine/paracrine proliferative role of BDNF.

In the past 15 years numerous reports provided strong evidence that brain-derived neurotrophic factor (BDNF) is one of the most important modulators of glutamatergic and GABAergic synapses. Remarkable progress regarding localization, kinetics, and molecular mechanisms of BDNF secretion has been achieved, and a large number of studies provided evidence that continuous extracellular supply of BDNF is important for the proper formation and functional maturation of glutamatergic and GABAergic synapses. BDNF can play a permissive role in shaping synaptic networks, making them more susceptible for the occurrence of plastic changes. In addition, BDNF appears to be also an instructive factor for activity-dependent long-term synaptic plasticity. BDNF release just in response to synaptic stimulation might be a molecular trigger to convert high-frequency synaptic activity into long-term synaptic memories. This review attempts to summarize the current knowledge in synaptic secretion and synaptic action of BDNF, including both permissive and instructive effects of BDNF in synaptic plasticity.

Neurotrophins are growth factors that promote cell survival, differentiation, and cell death. They are synthesized as proforms that can be cleaved intracellularly to release mature, secreted ligands. Although proneurotrophins have been considered inactive precursors, we show here that the proforms of nerve growth factor (NGF) and the proforms of brain derived neurotrophic factor (BDNF) are secreted and cleaved extracellularly by the serine protease plasmin and by selective matrix metalloproteinases (MMPs). ProNGF is a high-affinity ligand for p75NTRwith high affinity and induced p75NTR-dependent apoptosis in cultured neurons with minimal activation of TrkA-mediated differentiation or survival. The biological action of neurotrophins is thus regulated by proteolytic cleavage, with proforms preferentially activating p75NTRto mediate apoptosis and mature forms activating Trk receptors to promote survival.

Pro- and mature neurotrophins often elicit opposing biological effects. For example, mature brain-derived neurotrophic factor (mBDNF) is critical for long-term potentiation induced by high-frequency stimulation, whereas proBDNF facilitate long-term depression induced by low-frequency stimulation. Because mBDNF is derived from proBDNF by endoproteolytic cleavage, mechanisms regulating the cleavage of proBDNF may control the direction of BDNF regulation. Using methods that selectively detect proBDNF or mBDNF, we show that low-frequency stimulation induced predominant proBDNF secretion in cultured hippocampal neurons. In contrast, high-frequency stimulation preferentially increased extracellular mBDNF. Inhibition of extracellular, but not intracellular cleavage of proBDNF greatly reduced high-frequency stimulation-induced extracellular mBDNF. Moreover, high-frequency, but not low-frequency stimulation selectively induced the secretion of tissue plasminogen activator, a key protease involved in extracellular proBDNF to mBDNF conversion. Thus, high-frequency neuronal activity controls the ratio of extracellular proBDNF/mBDNF by regulating the secretion of extracellular proteases. Our study demonstrates activity-dependent control of extracellular proteolytic cleavage of a secretory protein, and reveals an important mechanism that controls diametrically opposed functions of BDNF isoforms.

Diabetes is an independent risk factor for stroke. However, the underlying mechanism of how diabetes confers that this risk is not fully understood. We hypothesize that secretion of neurotrophic factors by the cerebral endothelium, such as brain-derived neurotrophic factor (BDNF), is suppressed in diabetes. Consequently, such accrued neuroprotective deficits make neurons more vulnerable to injury. We examined BDNF protein levels in a streptozotocin-induced rat model of diabetes by Western blotting and immunohistochemistry. Levels of total and secreted BDNF protein were quantified in human brain microvascular endothelial cells after exposure to advanced glycation end product (AGE)-BSA by enzyme-linked immunosorbent assay and immunocytochemistry. In media transfer experiments, the neuroprotective efficacy of conditioned media from normal healthy endothelial cells was compared with AGE-treated endothelial cells in an in vitro hypoxic injury model. Cerebrovascular BDNF protein was reduced in the cortical endothelium in 6-month diabetic rats. Immunohistochemical analysis of 6-week diabetic brain sections showed that the reduction of BDNF occurs early after induction of diabetes. Treatment of brain microvascular endothelial cells with AGE caused a similar reduction in BDNF protein and secretion in an extracellular signal-related kinase-dependent manner. In media transfer experiments, conditioned media from AGE-treated endothelial cells were less neuroprotective against hypoxic injury because of a decrease in secreted BDNF. Taken together, our findings suggest that a progressive depletion of microvascular neuroprotection in diabetes elevates the risk of neuronal injury for a variety of central nervous system diseases, including stroke and neurodegeneration.

Apolipoprotein E4 (ApoE4) is a major genetic risk factor for sporadic or late onset Alzheimer’s disease (AD). Brain-derived neurotrophic factor (BDNF) is decreased by 3 to 4-fold in the brains of AD patients at autopsy. ApoE4 mice also have reduced BDNF levels. However, there have been no reports relating the different ApoE isoforms or AD to differential regulation of BDNF. Here we report that in the hippocampal regions of AD patients both prepro-BDNF and pro-BDNF expression showed a 40 and 60% decrease respectively compared to that expression in the hippocampi of age-matched control patients. We further report that ApoE isoforms differentially regulate maturation and secretion of BDNF from primary human astrocytes. After 24 h, ApoE3 treated astrocytes secreted 1.75- fold higher pro-BDNF than ApoE2-treated astrocytes, and ApoE2-treated astrocytes secreted 3-fold more mature-BDNF (m-BDNF) than ApoE3-treated astrocytes. In contrast, ApoE4-treated cells secreted negligible amounts of m-BDNF or pro-BDNF. ApoE2 increased the level of intracellular pre-pro BDNF by 19.04 ± 6.68%, while ApoE4 reduced the pre-pro BDNF by 21.61 ± 5.9% compared to untreated cells. Similar results were also seen in ApoE2, ApoE3 or ApoE4 treated cells at 4 h. Together, these results indicate that an ApoE2 or ApoE3 mediated positive regulation of BDNF may be protective while ApoE4 related defects in BDNF processing could lead to AD pathophysiology. These interactions of the ApoE isoforms with BDNF may help explain the increased risk of AD associated with the ApoE4 isoform.