Bdnf expression in rat skeletal muscle after acute or repeated exercise

Brain derived growth factor (BDNF) gene of rat has a complex structure: at least four 5' untranslated exons regulated by different promoters and one 3' exon containing the encoding region. BDNF is expressed by skeletal muscles in an activity-dependent manner. In this study, BDNF mRNA was analysed by RT-PCR in the soleus muscle following a single (acute) session of running or a training of five days of running (repetitive exercise). Moreover, the expression of the exons was quantitatively analysed by real time RT-PCR. Finally, muscle BDNF protein level was evaluated by western blotting. BDNF mRNA was found to increase over the second day after acute exercise; on the other hand, two peaks (2 and 24 hours after the last session, respectively) in BDNF mRNA level were found after repetitive exercise, but it was similar to that of controls 6 hours after the last session. BDNF protein level progressively increased also after the mRNA went back to the basal level, so suggesting that it cumulates within the cell after acute exercise, whereas it followed the mRNA level time course after repetitive exercise. These results point to the following conclusions: BDNF mRNA is up-regulated by activity, but this response is delayed to the second day after acute exercise; repetitive exercise transiently depresses the expression of BDNF mRNA, so that the over-expression due to the previous day's exercise completely disappears 6 hours after the last exercise session.     

Huntingtin-associated Protein-1 Interacts with Pro-brain-derived Neurotrophic Factor and Mediates Its Transport and Release

Brain-derived neurotrophic factor (BDNF) plays a pivotal role in brain development and synaptic plasticity. It is synthesized as a precursor (pro-BDNF), sorted into the secretory pathway, transported along dendrites and axons, and released in an activity-dependent manner. Mutant Huntingtin with expanded polyglutamine (polyQ) and the V66M polymorphism of BDNF reduce the dendritic distribution and axonal transport of BDNF. However, the mechanism underlying this defective transport remains unclear. Here, we report that Huntingtin-associated protein-1 (HAP1) interacts with the prodomain of BDNF and that the interaction was reduced in the presence of polyQ-expanded Huntingtin and BDNF V66M. Consistently, there was reduced coimmunoprecipitation of pro-BDNF with HAP1 in the brain homogenate of Huntington disease. Pro-BDNF distribution in the neuronal processes and its accumulation in the proximal and distal segments of crushed sciatic nerve and the activity-dependent release of pro-BDNF were abolished in HAP1^−/− mice. These results suggest that HAP1 may participate in axonal transport and activity-dependent release of pro-BDNF by interacting with the BDNF prodomain. Accordingly, the decreased interaction between HAP1 and pro-BDNF in Huntington disease may reduce the release and transport of BDNF.     

The fragile X syndrome protein represses activity-dependent translation through CYFIP1, a new 4E-BP

Strong evidence indicates that regulated mRNA translation in neuronal dendrites underlies synaptic plasticity and brain development. The fragile X mental retardation protein (FMRP) is involved in this process; here, we show that it acts by inhibiting translation initiation. A binding partner of FMRP, CYFIP1/Sra1, directly binds the translation initiation factor eIF4E through a domain that is structurally related to those present in 4E-BP translational inhibitors. Brain cytoplasmic RNA 1 (BC1), another FMRP binding partner, increases the affinity of FMRP for the CYFIP1-eIF4E complex in the brain. Levels of proteins encoded by known FMRP target mRNAs are increased upon reduction of CYFIP1 in neurons. Translational repression is regulated in an activity-dependent manner because BDNF or DHPG stimulation of neurons causes CYFIP1 to dissociate from eIF4E at synapses, thereby resulting in protein synthesis. Thus, the translational repression activity of FMRP in the brain is mediated, at least in part, by CYFIP1.     

Activity-dependent regulation of BRINP family genes

We previously identified a family of novel developmentally regulated genes: BRINP1, 2, and 3, which are predominantly and widely expressed in the CNS from earlier developmental stages to adulthood. In the present study, we investigated the activity-dependent regulation of BRINP expression in the CNS. Among the three BRINP genes, BRINP1-mRNA was specifically up-regulated in the dentate gyrus of mouse hippocampus by kainic acid treatment. In cultured hippocampal neurons, the induction of BRINP1-mRNA was also observed by the activation of glutamate receptors. Although BDNF-mRNA is up-regulated in a similar activity-dependent manner, BDNF itself did not induce BRINP1-mRNA. From these results, the physiological roles of the activity-dependent induction of BRINP1-mRNA are discussed.     

Identification of brain-derived neurotrophic factor promoter regions mediating tissue-specific, axotomy-, and neuronal activity-induced expression in transgenic mice

The structure of rat brain-derived neurotrophic factor (BDNF) gene is complex; four 5' exons are linked to separate promoters and one 3' exon is encoding the BDNF protein. To analyze the relative importance of the regulatory regions in vivo, we have generated transgenic mice with six different promoter constructs of the BDNF gene fused to the chloramphenicol acetyl transferase reporter gene. High level and neuronal expression of the reporter gene, that in many respects recapitulated BDNF gene expression, was achieved by using 9 kb of genomic sequences covering the promoter regions that lie adjacent to each other in the genome (promoters I and II and promoters III and IV, respectively) and by including sequences of BDNF intron-exon splice junctions and 3' untranslated region in the constructs. The genomic regions responsible for the in vivo upregulation of BDNF expression in the axotomized sciatic nerve and in the brain after kainic acid-induced seizures and KCl-induced spreading depression were mapped. These data show that regulation of the different aspects of BDNF expression is controlled by different regions in vivo, and they suggest that these promoter constructs may be useful for targeted expression of heterologous genes to specific regions of the central and peripheral nervous systems in an inducible manner.     

Beta -amyloid-(1-42) impairs activity-dependent cAMP-response element-binding protein signaling in neurons at concentrations in which cell survival Is not compromised

Cognitive impairment is a major feature of Alzheimer's disease and is accompanied by beta-amyloid (Abeta) deposition. Transgenic animal models that overexpress Abeta exhibit learning and memory impairments, but neuronal degeneration is not a consistent characteristic. We report that levels of Abeta-(1-42), which do not compromise the survival of cortical neurons, may indeed interfere with functions critical for neuronal plasticity. Pretreatment with Abeta-(1-42), at sublethal concentrations, resulted in a suppression of cAMP-response element-binding protein (CREB) phosphorylation, induced by exposure to either 30 mm KCl or 10 microm N-methyl-d-aspartate. The effects of Abeta-(1-42) seem to involve mechanisms unrelated to degenerative changes, since Abeta-(25-35), a toxic fragment of Abeta, at sublethal concentrations did not interfere with activity-dependent CREB phosphorylation. Furthermore, caspase inhibitors failed to counteract the Abeta-(1-42)-evoked suppression of CREB activation. Abeta-(1-42) also interfered with events downstream of activated CREB. The Abeta-(1-42) treatment suppressed the activation of the cAMP response element-containing brain-derived neurotrophic factor (BDNF) exon III promoter and the expression of BDNF exon IIII mRNA induced by neuronal depolarization. In view of the critical role of CREB and BDNF in neuronal plasticity, including learning and memory, the observations indicate a novel pathway through which Abeta may interfere with neuronal functions and contribute to cognitive deficit in Alzheimer's disease before the stage of massive neuronal degeneration.