Differential regulation of the nerve growth factor and brain-derived neurotrophic factor genes in L929 mouse fibroblasts

Brain-derived neurotrophic factor and TrkB tyrosine kinase receptor gene expression in zebrafish embryo and larva

The genes that encode the neurotrophin family of secreted polypeptides and the Trk family of high affinity neurotrophin transmembrane protein tyrosine kinase receptors are induced at the time of neurogenesis in mammals and are known to play critical roles in nervous system development. We show here that in contrast to mammals, the genes encoding the neurotrophin brain-derived neurotrophic factor (BDNF) and the neurotrophin receptor TrkB are expressed throughout embryonic development in the zebrafish. At the embryonic stages preceding transcription of endogenous genes all cells contain BDNF transcripts and immunoreactive BDNF and the trkB transcripts lack the region that encodes a kinase domain. As development proceeds, progressively fewer cells contain BDNF transcripts and by the time of neurogenesis the trkB transcripts encode a kinase-domain. In the 4-day-old larva, a small subset of specialized sensory cells on the surface and cells in deeper structures including the gill arches, fin, and cloaca express the BDNF gene at high levels in a promoter-specific fashion. This progressive restriction of BDNF gene expression must involve an extinction of BDNF gene transcription in some and induction of high levels of transcription in a promoter-specific fashion in other cells.

Corticosterone effects on BDNF expression in the hippocampus. Implications for memory formation

The adrenal steroid corticosterone has profound effect on the structure and function of the hippocampus. Probably as a result of that, it modulates memory formation. In this review, the question is addressed if the corticosterone effects on memory processes are mediated by alterations in the expression of the neurotrophin Brain-Derived Neurotrophic Factor (BDNF) in the hippocampus. First, studies are described investigating the effect of corticosterone on BDNF expression in the rat hippocampus. It appears that corticosterone suppresses the BDNF expression at the mRNA and protein level in a subfield-specific way. Second, a model for the mechanism of action is proposed. In this model, activated mineralocorticoid and glucocorticoid receptors repress transcriptional activity of the BDNF promoter site-specifically via interaction with other transcription factors. Third, the implications for learning and memory are discussed. Studies show that during water maze training, corticosterone levels rise significantly, but the BDNF expression is not suppressed in any hippocampal subfield. Furthermore, high BDNF expression levels in specific subfields correlate with a good memory performance. Therefore, we suggest that the resistance of the hippocampal BDNF expression to suppression by corticosterone, as seen after water maze training, may contribute to an optimal memory performance.

Cellular sources of enhanced brain-derived neurotrophic factor production in a mouse model of allergic inflammation

The aim of this study was to investigate production and cellular sources of brain-derived neurotrophic factor (BDNF) production in allergic asthma. For this purpose a mouse model of chronic and severe ovalbumin (OVA)-induced airway inflammation was developed. Allergen-exposed mice developed elevated immunoglobulin E titers; airway inflammation with influx of lymphocytes, monocytes, and eosinophils; and airway hyperresponsiveness. In addition to an influx of inflammatory cells, interleukin (IL)-4 and IL-5 production were enhanced, macrophages showed morphologic signs of activation, and airway epithelium was thickened and displayed a goblet-cell hyperplasia with a marked mucus production. BDNF was detected using in situ hybridization and enzyme-linked immunosorbent assay. Constitutive expression of BDNF messenger RNA (mRNA) was observed in the respiratory epithelium of sensitized and nonsensitized mouse lungs. In addition, BDNF mRNA was detected in airway inflammatory infiltrations and bronchoalveolar lavage fluid (BALF) cells of OVA-sensitized and aerosol-challenged mice. Highest BDNF protein levels were detected in BALF after long-term allergen aerosol exposure. Analysis of BDNF production by isolated lymphocyte subsets revealed T but not B cells as a cellular source of BDNF. In addition, activated alveolar macrophages were identified as BDNF-positive cells. These data indicate that in allergic airway inflammation BDNF production is upregulated and immune cells serve as a source of BDNF.

Abundant production of brain-derived neurotrophic factor by adult visceral epithelia. Implications for paracrine and target-derived Neurotrophic functions

Brain-derived neurotrophic factor (BDNF) plays a crucial role for the survival of visceral sensory neurons during development. However, the physiological sources and the function of BDNF in the adult viscera are poorly described. We have investigated the cellular sources and the potential role of BDNF in adult murine viscera. We found markedly different amounts of BDNF protein in different organs. Surprisingly, BDNF levels in the urinary bladder, lung, and colon were higher than those found in the brain or skin. In situ hybridization experiments revealed that BDNF mRNA was made by visceral epithelial cells, several types of smooth muscle, and neurons of the myenteric plexus. Epithelia that expressed BDNF lacked both the high- and low-affinity receptors for BDNF, trkB and p75(NTR). In contrast, both receptors were present on neurons of the peripheral nervous system. Studies with BDNF-/-mice demonstrated that epithelial and smooth muscle cells developed normally in the absence of BDNF. These data provide evidence that visceral epithelia are a major source, but not a target, of BDNF in the adult viscera. The abundance of BDNF protein in certain internal organs suggests that this neurotrophin may regulate the function of adult visceral sensory and motor neurons.

Suppression of postischemic hippocampal nerve growth factor expression by a c-fos antisense oligodeoxynucleotide

We examined the uptake and distribution of an antisense phosphorothioated oligodeoxynucleotide (s-ODN) to c-fos, rncfosr115, infused into the left cerebral ventricle of male Long-Evans rats and the effect of this s-ODN on subsequent Fos, NGF, neurotrophin-3 (NT-3), and actin expression. To establish the uptake and turnover of s-ODN in the brain, we studied the copurification of the immunoreactivity of biotin with biotinylated s-ODN that was recovered from different regions of the brain. A time-dependent diffusion and the localization of s-ODN were further demonstrated by labeling the 3'-OH terminus of s-ODN in situ with digoxigenin-dUTP using terminal transferase and detection using anti-digoxigenin IgG-FITC. Cellular uptake of the s-ODN was evident in both the hippocampal and cortical regions, consistent with a gradient originating at the ventricular surface. Degradation of the s-ODN was observed beginning 48 hr after delivery. The effectiveness of c-fos antisense s-ODN was demonstrated by its suppression of postischemic Fos expression, which was accompanied by an inhibition of ischemia-induced NGF mRNA expression in the dentate gyrus. Infusion of saline, the sense s-ODN, or a mismatch antisense s-ODN did not suppress Fos expression. That this effect of c-fos antisense s-ODN was specific to NGF was demonstrated by its lack of effect on the postischemic expression of the NT-3 and beta-actin genes. Our results demonstrate that c-fos antisense s-ODN blocks selected downstream events and support the contention that postischemic Fos regulates the subsequent expression of the NGF gene and that Fos expression may have a functional component in neuroregeneration after focal cerebral ischemia-reperfusion.

Aging in the hippocampus: interrelated actions of neurotrophins and glucocorticoids

Over the past two decades, evidence has been accumulating that diffusible molecules, such as growth factors and steroids hormones, play an important part in neural senescence, particularly in the hippocampus. There is also evidence that these molecules do not act as independent signals, but show interrelated regulation and cooperative control over the aging process. Here, we review some of the changes that occur in the hippocampus with age, and the influence of two classes of signaling substances: glucocorticoids and neurotrophins. We also examine the interactions between these substances and how this could influence the aging process.

Gene expression and apoptosis in the spinal cord neurons after sciatic nerve injury

To demonstrate a dependence of spinal cord motoneurons on the communication with their targets, the expression of immediate early gene c-fos and neurotrophin genes in the lumbar (L3-L6) spinal cord neurons was examined in Sprague-Dawley rats (male > or = 9-weeks-old) with unilateral sciatic nerve transection. Using in situ hybridization, we detected the expression of c-fos mRNA in the motoneurons of the spinal cord segments within 45 min to 3 h of peripheral nerve transection (n = 4 in each time point). The expression of c-fos mRNA was also correlated positively with the expression of Fos antigen using immunohistochemistry, while no change in calbindin and parvalbumin antigens were noted. The expression of BDNF mRNA increased at 90 min after sciatic nerve transection. However, no detectable enhancement in the expression of NGF mRNA was observed. DNA fragmentation in neurons was observed using the incorporation of digoxigenin-dUTP by terminal transferase into 3'-OH terminals of DNA fragments in the ipsilateral section of the spinal cords 48h after nerve injury. Nuclei that exhibited DNA fragmentation were not observed in the spinal cord of the control animals. Lastly, we observed that the majority of astrocytes did not have DNA fragmentation. Because the detection of DNA fragmentation using this assay is one of early detections of apoptosis or programmed cell death, the result suggested we could detect early cell death in spinal cord, and indicated a target dependence of the neurons in the spinal cord after transection of sciatic nerve.

Chronic alcohol ingestion: nerve growth factor gene expression and neurotrophic activity in rat hippocampus

Chronic ethanol treatment induces memory deficits accompanied by anatomical and biochemical changes in basal forebrain and hippocampus. Cholinergic neurons in the septohippocampal pathway are especially vulnerable to alcohol neurotoxicity. Several studies showed that an adequate supply of neurotrophins, such as Nerve Growth Factor and Brain-Derived Neurotrophic Factor, is required for the normal function and survival of cholinergic neurons in basal forebrain and medial septal nuclei. We tested the hypothesis that chronic alcohol ingestion may alter the gene expression level of Nerve Growth Factor in hippocampus, the major source of neurotrophins to the cholinergic neurons in the septohippocampal pathway. We measured Nerve Growth Factor protein and Nerve Growth Factor mRNA contents using sensitive two-site ELISA and Northern analysis. We also tested the endogenous neurotrophic activity, including and excluding Nerve Growth Factor, contained in 5%, 2%, 1%, 0.5% and 0.1% (w/v) hippocampal tissue extracts on sympathetic ganglia neurons. Twenty-eight weeks of chronic ethanol treatment did not reduce Nerve Growth Factor protein, Nerve Growth Factor mRNA, or total neurotrophic activity contained in the rat hippocampus when measured on sympathetic ganglia neurons.

Expression of neurotrophin genes in human fibroblasts: differential regulation of the brain-derived neurotrophic factor gene

Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and neurotrophin-3 (NT-3) are structurally related survival and differentiation factors for distinct sets of peripheral and central neurons. We previously reported that BDNF and NGF gene expression are differentially regulated in mouse L929 fibroblasts. Here we examine expression of these three neurotrophins in human fibroblasts. Northern blots detected BDNF and NT-3 mRNAs in fibroblasts derived from lung (WI-38), calvarium and foreskin. WI-38 cells and foreskin fibroblasts expressed 1.6 kb as well as 4 kb BDNF mRNAs whereas only the smaller BDNF mRNA was detected in calvarium fibroblasts. NGF mRNA was present in foreskin and calvarium but not lung fibroblasts. In WI-38 cells serum treatment increased levels of BDNF mRNA within 2 hr. Cycloheximide did not inhibit the increase. Treatment with 12-O-tetradecanoyl phorbol-13-acetate (TPA) transiently suppressed BDNF mRNA. Treatment with both serum and TPA first stimulated and then transiently suppressed BDNF mRNA. TPA and/or serum did not significantly affect BDNF mRNA in calvarium fibroblasts. These results show that human fibroblasts derived from different tissues express and regulate neurotrophin genes differentially.

An improved method detects differential NGF and BDNF gene expression in response to depolarization in cultured hippocampal neurons

Differential regulation of individual neurotrophins by impulse activity potentially allows transformation of instantaneous signalling into diverse, long-lasting neural alterations. To define the temporal profiles of trophin gene expression we examined nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) mRNAs in dissociated cell cultures of rat hippocampus using an improved solution hybridization technique. Traditional methods lack the precision and sensitivity to detect small changes during brief intervals and the facility to process large sample numbers simultaneously. This improved method has now allowed us to better define the dynamics of depolarization-induced changes in expression of individual trophin genes. Using elevated K+ as a depolarizing stimulus, NGF mRNA increased 40% after 48 h. In contrast, BDNF message rose almost 4-fold within 3 h and attained a maximal 6-fold increase within 6 h. Similar increases in BDNF mRNA levels were exhibited following treatment of cultures with glutamate, an excitatory neurotransmitter. To document the sensitivity of BDNF mRNA to depolarizing conditions, we examined expression after K+ withdrawal. BDNF message began decreasing within one hour post-depolarization, and returned to basal levels after 6 h. Observations indicate that BDNF and NGF mRNAs are induced differentially in response to impulse activity; BDNF message is acutely responsive to ongoing changes, whereas NGF mRNA responds more slowly and sluggishly. The physiological implications of this differential regulation are discussed.