Biomedical subjects

Alessandra Mallei

Publications and source records attributed to Alessandra Mallei.

5 recordsLinked to original sources

PubMed2006

CAAT/enhancer-binding protein delta and cAMP-response element-binding protein mediate inducible expression of the nerve growth factor gene in the central nervous system.

Nerve growth factor (NGF) synthesis in the rat cerebral cortex is induced by the beta2-adrenergic receptor agonist clenbuterol (CLE). Because NGF is a crucial neurotrophic factor for basal forebrain cholinergic neurons, defining the mechanisms that regulate its transcription is important for developing therapeutic strategies to treat pathologies of these neurons. We previously showed that the transcription factor CCAAT/enhancer-binding protein delta (C/EBPdelta) contributes to NGF gene regulation. Here we have further defined the function of C/EBPdelta and identified a role for cAMP response element-binding protein (CREB) in NGF transcription. Inhibition of protein kinase A in C6-2B glioma cells suppressed CLE induction of an NGF promoter-reporter construct, whereas overexpression of protein kinase A increased NGF promoter activity, particularly in combination with C/EBPdelta. A CRE-like site that binds CREB was identified in the proximal NGF promoter, and C/EBPdelta and CREB were found to associate with the NGF promoter in vivo. Deletion of the CRE and/or C/EBP sites reduced CLE responsiveness of the promoter. In addition, ectopic expression of C/EBPdelta in combination with CLE treatment increased endogenous NGF mRNA levels in C6-2B cells. C/EBPdelta null mice showed complete loss of NGF induction in the cerebral cortex following CLE treatment, demonstrating a critical role for C/EBPdelta in regulating beta2-adrenergic receptor-mediated NGF expression in vivo. Thus, our findings demonstrate a critical role for C/EBPdelta in regional expression of NGF in the brain and implicate CREB in CLE-induced NGF gene transcription.

Adrenergic beta-Agonists↗

PubMed2005

The nitrosteroid NCX 1015, a prednisolone derivative, improves recovery of function in rats after spinal cord injury.

Glucocorticoids, given at high-doses, improve recovery of function after spinal cord injury (SCI) in animals. However, side effects combined with a limited efficacy in clinical trials have restricted their usefulness for treatment of SCI patients. Recent studies have shown that incorporation of the nitric oxide releasing moiety into the glucocorticoid structure enhances anti-inflammatory properties and reduces side effects. One compound, a derivative of prednisolone (PRE), (NCX 1015, prednisolone 21 [(4'nitrooxymethyl)benzoate]), has interesting pharmacological properties. Therefore, we investigated its effects on apoptosis and recovery of function in rats after SCI. Rats received subcutaneously vehicle, NCX 1015 or PRE (37 micromol/kg, each) 3.5 h after a standardized thoracic lesion. The treatment was continued once a day for 3 days and the effect of both steroids on apoptosis was examined by immunohistochemistry 24 h after the last injection. NCX 1015 but not PRE reduced TUNEL and activated caspase 3 in both white and ventral gray matter as well as tumor necrosis factor immunoreactivity in ventral horn motorneurons, suggesting that NCX 1015 reduces SCI-induced apoptosis. The effect of NCX 1015 on motor function was then examined by a standard locomotion rating scale (BBB) starting at 1 day after injury and continuing up to 14 days. NCX 1015 improved significantly locomotor activity by 4 days after injury, whereas PRE had an effect equivalent to that of vehicle, thus providing a correlation between the antiapoptotic effect of NCX1015 and its ability to improve recovery of function. The data suggest that NCX 1015 might be a novel experimental therapeutic compound for recovery of function in SCI patients.

Animals↗

PubMed2004

Synergistic effect of dexamethasone and beta-adrenergic receptor agonists on the nerve growth factor gene transcription.

Activation of beta-adrenergic receptor (betaAR) increases the synthesis of nerve growth factor (NGF) in the brain and in C6-2B glioma cells. However, in the brain, the betaAR-mediated increase in NGF expression appears to require the presence of glucocorticoids, suggesting that NGF promoter may be sensitive to cAMP and glucocorticoid-dependent transcription factors. We tested this hypothesis by exposing C6-2B glioma cells to dexamethasone (DEX) in combination with agents that increase cAMP levels and examining the DNA binding activity of two cAMP-dependent transcription factors that regulate NGF expression: cAMP responsive element binding protein (CREB) and CCAAT/enhancer binding protein delta (C/EBPdelta). Electrophoretic mobility shift assays revealed that the beta(2)AR agonist clenbuterol (CLE) or high levels of cAMP elicited a time-dependent increase in C/EBPdelta binding activity as well as phosphorylated CREB (P-CREB). When DEX, which per se showed little effect on these transcription factors, was combined with CLE, dibutyryl cAMP or isoproterenol, enhanced induction of P-CREB and C/EBP binding activity as well as NGF mRNA was observed. Moreover, the increase in NGF mRNA in the presence of DEX was prolonged compared to that obtained by CLE or other cAMP inducing agents alone. In fact, NGF mRNA levels remained significantly elevated at least for 24 h. These studies suggest that the synergistic effect of DEX on the induction of NGF mRNA may include the ability of this glucocorticoid to potentiate the betaAR-mediated induction of transcription factors.

Adrenergic beta-Agonists↗

PubMed2004

Autocrine regulation of nerve growth factor expression by Trk receptors.

Activation of the neurotrophin receptor Trk induces the release of neurotrophins. However, little is known about the ability of released neurotrophins to modulate their own synthesis in an autocrine manner. As a step towards understanding the role of Trk in regulating the synthesis of neurotrophins, we exposed NIH-3T3 cells expressing TrkA or TrkC receptors to their cognate ligands as well as to GM1, a ganglioside that activates TrkA and TrkC by inducing the release of neurotrophin-3. Nerve growth factor and neurotrophin-3 synthesis were then determined by measuring the relative levels of protein and mRNA. TrkA-expressing cells exposed to human recombinant nerve growth factor exhibited higher levels of nerve growth factor mRNA. Human recombinant neurotrophin-3 evoked an increase in nerve growth factor mRNA in both TrkA and TrkC-expressing cells. GM1 elicited a time-dependent increase in nerve growth factor protein and mRNA in NIH-3T3 cells expressing TrkA or TrkC receptor but not in wild-type cells. Surprisingly, GM1 failed to change neurotrophin-3 levels. The ability of GM1 to increase nerve growth factor mRNA levels was blocked by TrkC-IgG but not by TrkB-IgG receptor body. These data suggest that released neurotrophin-3 may activate a positive autocrine loop of nerve growth factor synthesis by Trk activation.

Analysis of Variance↗

PubMed2002

Antidepressant treatments induce the expression of basic fibroblast growth factor in cortical and hippocampal neurons.

New experimental evidence suggests that the mechanism of action of antidepressants includes the induction of neurotrophic factor synthesis in selected brain areas. The present study is aimed at establishing whether prolonged antidepressant treatments increase the expression of basic fibroblast growth factor (FGF2), a polypeptide growth factor that has a broad neurotrophic activity in the adult central nervous system. Rats received a single dose or long-term (3 weeks) administration of desipramine (DMI), fluoxetine (FLU), and mianserin (MIA), then were sacrificed at 5 and 24 h after the last injection. RNase protection assay and Western blot analysis revealed that all antidepressant drugs elicited an anatomically specific increase in FGF2 mRNA and protein. The increase in FGF2 mRNA after a single injection was seen only at 5 h after the injection and was restricted to the entorhinal cortex, whereas the effect of the long-term treatments lasted up to 24 h and occurred in the entire cortex and hippocampus. Immunohistochemical analysis of FGF2 immunoreactivity was carried out to investigate which cell types responded to the antidepressant treatments. DMI and MIA increased FGF2 proteins predominantly in neurons of layer V throughout the cerebral cortex and in some neurofilament-positive cells of the hippocampus. FLU increased FGF2 immunoreactivity mainly in neurofilament-positive cells of the hippocampus. These findings may explain the therapeutic efficacy of antidepressants in affective disorders.

Animals↗