Brain-derived Neurotrophic Factor In Astrocytes Research Articles

Noradrenergic stimulation of BDNF synthesis in astrocytes: Mediation via α1- and β1/β2-adrenergic receptors

Brain-derived neurotrophic factor (BDNF) synthesis in astrocytes induced by noradrenaline (NA) is a receptor-mediated process utilizing two parallel adrenergic pathways: β1/β2-adrenergic/cAMP and the novel α1-adrenergic/PKC pathway.BDNF is produced by astrocytes, in addition to neurons, and the noradrenergic system plays a role in controlling BDNF synthesis. Since astrocytes express various subtypes of α- and β-adrenergic receptors that have the potential to be activated by synaptically released NA, we focused our present study on the mediatory role of adrenergic receptors in the noradrenergic up-regulation of BDNF synthesis in cultured neonatal rat cortical astrocytes.NA (1μM) elevates BDNF levels by four-fold after 6h of incubation. Its stimulation was partly inhibited by either the β1-adrenergic antagonist atenolol, the β2-adrenergic antagonist ICI 118,551, or by the α1-adrenergic antagonist prazosin, while the α2-adrenergic antagonist yohimbine showed no effect. BDNF levels in astrocytes were increased by the specific β1-adrenergic agonist dobutamine and the β2-adrenergic agonist salbutamol, as well as by adenylate cyclase activation (by forskolin) and PKA activation (by dBcAMP). However, none of the tested agonists or mediators of the intracellular β-adrenergic pathways were able to reach the level of NA's stimulatory effect. BDNF cellular levels were also elevated by the α1-adrenergic agonist methoxamine, but not by the α2-adrenergic agonist clonidine. The increase in intracellular Ca2+ by ionophore A23187 showed no effect, whereas PKC activation by phorbol 12-myristate 13-acetate (TPA) potently stimulated BDNF levels in the cells. The methoxamine-stimulated BDNF synthesis was inhibited by desensitizing pretreatment with TPA, indicating that the α1-stimulation was mediated via PKC activation. In conclusion, the synthesis of astrocytic BDNF stimulated by noradrenergic neuronal activity is an adaptable process using multiple types (α1 and β1/β2) of adrenergic receptor activation.

Up-regulation of BDNF in Astrocytes by TNF-α: A Case for the Neuroprotective Role of Cytokine

Tumor necrosis factor-alpha (TNF-alpha) is widely known to be involved in physiological and pathophysiological processes of the brain where this proinflammatory cytokine is implicated with regulation of inflammatory and survival components. We report that TNF-alpha up-regulates exon-IV-bdnf mRNA and brain-derived neurotrophic factor (BDNF) protein in primary astrocytes. The BDNF protein was detectable both in cellular lysate and in the extracellular medium. Activation of NF-kappaB by TNF-alpha and inhibition of TNF-alpha-induced BDNF expression by Deltap65 (a dominant-negative mutant) and NEMO-binding domain peptide (an inhibitor of NF-kappaB) suggests that TNF-alpha induces BDNF expression through the activation of NF-kappaB. Similarly, TNF-alpha induced the activation of C/EBPbeta and the expression of BDNF was sensitive to overexpression of DeltaC/EBPbeta (a dominant-negative mutant) and ETO (an inhibitor of C/EBPbeta). Among three MAP kinases, TNF-alpha-induced BDNF up-regulation was sensitive only to inhibitors of ERK MAP kinase. However, the ERK MAP kinase pathway was coupled to activation of C/EBPbeta but not NF-kappaB. Taken together, this study identifies a novel property of TNF-alpha in inducing the expression of BDNF via NF-kappaB and C/EBPbeta in astrocytes that may be responsible for neurotrophic activity of the cytokine.

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.

Brain-Derived Neurotrophic Factor in Astrocytes, Oligodendrocytes, and Microglia/Macrophages after Spinal Cord Injury

Recent studies suggest that the injured adult spinal cord responds to brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT3) with enhanced neuron survival and axon regeneration. Potential neurotrophin sources and cellular localization in spinal cord are largely undefined. We examined glial BDNF localization in normal cord and its temporospatial distribution after injury in vivo. We used dual immunolabeling for BDNF and glial fibrillary acidic protein (GFAP) in astrocytes, adenomatous polyposis coli tumor suppressor protein (APC) for oligodendrocytes or type III CDH receptor (OX42) for microglia/macrophages. In normal cord, small subsets of astrocytes and microglia/macrophages and most oligodendrocytes exhibited BDNF-immunoreactivity. Following injury, the number of BDNF-immunopositive astrocytes and microglia/macrophages increased dramatically at the injury site over time. Most oligodendrocytes contained BDNF 1 day and 1 week following injury, but APC-positive cells were largely absent at the injury site 6 weeks postinjury. Glial BDNF-immunolabeling was also examined 10 and 20 mm from the wound. Ten millimeters from the lesion, astrocyte and microglia/macrophage BDNF-immunolabeling resembled that at the injury at all times examined. Twenty millimeters from injury, BDNF localization in all three glial subtypes resembled controls, regardless of time postlesion. Our findings suggest that in normal adult cord, astrocytes, oligodendrocytes, and microglia/macrophages play roles in local trophin availability and in trophin-mediated injury and healing responses directly within and surrounding the wound site.

Regulation of brain-derived neurotrophic factor and nerve growth factor mRNA in primary cultures of hippocampal neurons and astrocytes

Brain-derived neurotrophic factor (BDNF) and NGF are both expressed by neurons in the hippocampus. In previous studies, it has been demonstrated that both BDNF and NGF mRNA levels are regulated by neuronal activity. Upregulation is predominantly regulated by the glutamate (NMDA and non-NMDA receptors); downregulation, predominantly by the GABA system (Zafra et al., 1990, 1991). In neuronal cultures of the rat hippocampus, potassium depolarization and kainic acid-mediated increases in BDNF and NGF mRNA were eliminated in a dose-dependent manner by the calcium channel blocker nifedipine. Conversely, calcium ionophores (Bay-K8644 and ionomycin) augmented BDNF and NGF mRNA levels by a calmodulin-mediated mechanism. In view of the fact that many potential modulators (conventional transmitters and neuropeptides) of neuronal and astrocytic BDNF and NGF mRNA synthesis may act via the adenylate cyclase system, we studied the effect of forskolin, an activator of adenylate cyclase. Indeed, forskolin enhanced the effects of calcium ionophores and kainic acid on BDNF and NGF mRNA levels. Cytokines, such as interleukin-1 and transforming growth factor-beta 1, which have previously been shown to increase NGF mRNA markedly in astrocytes, were without effect on neuronal BDNF and NGF mRNA levels. In contrast to neuronal cultures, where the regulation of BDNF and NGF mRNA was generally very similar, the regulation in astrocytes was distinctly different. All the cytokines that produce a marked increase in NGF mRNA were without effect on astrocyte BDNF mRNA levels, which under basic conditions were below the detection limit. However, norepinephrine produced a marked elevation of BDNF mRNA in astrocytes, an effect that was further enhanced by glutamate receptor agonists.(ABSTRACT TRUNCATED AT 250 WORDS)