Biomedical subjects

I Neveu

Publications and source records attributed to I Neveu.

30 records · Page 2Linked to original sources

PubMed1994

Reactive oxygen species influence nerve growth factor synthesis in primary rat astrocytes.

Newborn rat brain astrocytes, cultured in a serum-free medium, were exposed for 30 min to two types of reactive oxygen species. Cells were either treated with the xanthine/xanthine oxidase (X/XOD) system, which generates both H2O2 and the O2.- radical, or to H2O2 alone. Both treatments induced a dose-dependent accumulation of nerve growth factor (NGF) transcripts, 6 h after the exposure. Maximal effect was obtained with 6 mU/ml XOD, or 10(-4) M H2O2. A rapid expression of protooncogenes of the jun and fos families was also noticed in X/XOD- or H2O2-treated cells. This phenomenon was transient in cells exposed to X/XOD. However, in the case of H2O2-treated cells, the accumulation of c-fos or c-jun mRNAs was still pronounced 6 h after the end of the treatment and the levels of cell-secreted NGF appeared relatively reduced, when compared with those obtained after a shock with the X/XOD system. This raised the possibility that H2O2 at 10(-4) M could depress protein synthesis. Measurements of the incorporation of radiolabeled amino acids into trichloroacetic acid-precipitable material supported this assumption. Level of radioactivity associated with cellular material was dramatically reduced in H2O2-treated cells, when it was compared with control or X/XOD-treated cells. Furthermore, treatment of cells with the protein synthesis inhibitor anisomycin had an effect similar to that of H2O2 because it caused an accumulation of c-fos, c-jun, and NGF transcripts after 6 h of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Expression of 25(OH) vitamin D3 24-hydroxylase gene in glial cells.

The expression of the 25(OH) vitamin D3 24-hydroxylase gene was studied in C6 glioma and rat primary glial cell culture. The expression of the 25(OH)D3 24-hydroxylase gene was not detected in C6 glioma or glial cells cultured in a serum-free medium. However, the 25(OH)D3 24-hydroxylase mRNA was induced in a dose-dependent manner in cells treated with 1,25(OH)2D3. These findings provide further evidence for an involvement of vitamin D3 metabolites in brain function.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed1993

NGF deprivation and neuronal degeneration trigger altered beta-amyloid precursor protein gene expression in the rat superior cervical ganglia in vivo and in vitro.

In order to study the expression of beta-amyloid precursor protein (APP) isoforms during neuronal degeneration we have used the rat superior cervical ganglia (SCG) as an experimental model. In the neonate these sympathetic ganglia are nerve growth factor (NGF) dependent and in vivo administration of anti-NGF antiserum results in exaggerated neuronal degeneration. Analysis of APP mRNA transcripts in the SCG, following NGF deprivation, revealed a coincident decrease in APP695 and augmentation of APP751/770. These changes were specific to the SCG and were not seen in sensory ganglia. Subsequent in vitro studies, using primary dissociated cultures of sympathetic or cortical neurones, confirmed these changes in APP gene expression during neuronal degeneration. These observations may have important implications for the generation of beta-amyloid in Alzheimer's disease.

Amyloid beta-Protein Precursor↗

PubMed1993

Enhancement of the synthesis and secretion of nerve growth factor in primary cultures of glial cells by proteases: a possible involvement of thrombin.

Newborn rat brain astrocytes cultured in vitro in a chemically defined medium are shown to secrete enhanced levels of nerve growth factor (NGF) when they are exposed to various types of proteases. Proteolytic enzymes such as alpha-thrombin or collagenase induce a continuous, dose-dependent enhancement of the levels of cell-secreted NGF. Incubation of astrocytes for a 24-h period with 300 ng/ml of alpha-thrombin (approximately 9 nM, or 1 U/ml) results in an increase of the levels of cell-secreted NGF by a factor of three- to fourfold, and at doses 10 times higher, stimulation by a factor of up to four- to fivefold was observed. This phenomenon reflects an enhancement of the cellular pool of NGF mRNA, already noticeable after 3 h of treatment, which is preceded by a temporary activation of protooncogenes encoding transcription factors of the AP-1 family, such as c-fos, c-jun or junB. Trypsin, plasmin, alpha-chymotrypsin, or elastase also enhanced, to different extents, the levels of cell-secreted NGF. However, unlike alpha-thrombin or collagenase, these enzymes cause, above a critical concentration, an extensive cell detachment from the solid support, and this is accompanied by a decrease of their activity on the production of NGF, so that their dose-response curves are bell shaped. Stimulation was maximal at those concentrations that cause a limited loosening of the cell-substratum interactions, as evidenced by a retraction of some cell processes after 24 h of treatment. Studies of the effect of alpha-thrombin indicate that the proteolytic activity itself is required to enhance the production of NGF by astrocytes. Inactivation of alpha-thrombin with D-phenyl-alanyl-L-propyl-L-arginine chloromethyl ketone, phenylmethylsulfonyl fluoride, antithrombin III, or hirudin results in a marked decrease of the stimulatory effect. Furthermore, the prolonged presence of alpha-thrombin is required to elicit a maximal effect on the levels of extracellular NGF, which was observed after 48 h of treatment. It is known that some effects of alpha-thrombin require binding to the cell surface. We found that gamma-thrombin, which still has some proteolytic activity but has lost its ability to bind to the cell surface, is almost as potent as alpha-thrombin in promoting the release of NGF. It is concluded that the effect of thrombin on NGF synthesis is essentially mediated by its proteolytic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1993

Complex interactions among second messenger pathways, steroid hormones, and protooncogenes of the Fos and Jun families converge in the regulation of the nerve growth factor gene.

Regulation of the expression of the nerve growth factor (NGF) gene has been reported previously to be mediated via the protooncogene c-fos. Activation of the protein kinase C pathway and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been reported to increase the pool of NGF transcripts in L929 fibroblasts. Here we show that activation of the cyclic AMP second messenger pathway antagonized the effect of phorbol 12-myristate 13-acetate (PMA) or serum on NGF synthesis, whereas it enhanced that of 1,25(OH)2D3. A positive effect was also observed when serum, PMA, and 1,25(OH)2D3 were added together, but dexamethasone reduced this enhancement. There was no close correlation between the increase in c-fos mRNA and that in NGF mRNA, suggesting that expression of the c-fos protooncogene is not necessarily followed by induction of the NGF gene. Rather, these two genes are simultaneously, and not sequentially, induced after forskolin treatment. It appears that regulation of the NGF gene depends on a repertoire of multiple regulatory AP-1 complexes arising from activation of the second messenger pathways. This suggests that NGF gene expression is under the control of a complex interplay among second messenger pathways, protooncogenes, and steroid hormones such as 1,25(OH)2D3 and glucocorticoids.

Animals↗

PubMed1992

Activation of nerve growth factor synthesis in primary glial cells by phorbol 12-myristate 13-acetate: role of protein kinase C.

Phorbol 12-myristate 13-acetate (PMA) induces a dramatic production of nerve growth factor (NGF) in primary cultures of newborn mouse astrocytes maintained in a serum-free medium. This stimulation is dose-dependent and a maximal effect on the levels of cell-secreted factor was observed at a concentration of 10 nM. At this concentration, the promoting effect of PMA appears much more important than that elicited by 10% fetal calf serum (FCS) under the same culture conditions. PMA acts primarily on the accumulation of NGF mRNA, which was detected by northern blot analysis after 6 h of treatment. This accumulation may be totally or partially prevented when PMA-treated glial cells are concomitantly exposed to the protein kinase inhibitors H-7, H-9, and to a lesser degree, HA-1004. The known specificity of these inhibitors agrees with the possibility that protein kinase C (PKC), which constitutes so far the sole known target of PMA, represents a key element involved in the stimulation of NGF gene. The role of PKC is further supported by the observation that alpha phorbol didecanoate, which has no activity on PKC, is depleted of effect on the synthesis of NGF. Likewise, 1,2-dioctanoylglycerol (1,2-DOG) has a weak, but significant promoting action on the production of NGF, unlike the 1,3-isomer which is not active on PKC. Finally, a treatment of 15 min with 100 nM PMA is sufficient to stimulate the cells, suggesting that the activation phase of PKC, rather than its down regulation, constitutes an important trigger leading to an increased expression of the NGF gene.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Pertussis toxin provides evidence for two independent signalling pathways leading to the activation of the nerve growth factor gene.

Increased expression of the nerve growth factor (NGF) gene may be obtained by treating L929 fibroblasts with serum, phorbol 12-myristate 13-acetate (PMA), or 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3). The possible involvement of GTP-binding proteins (G proteins) in these regulatory events was monitored by exposing the cells to pertussis toxin (PT), a compound known to inactivate several types of G proteins by ADP ribosylation. Measurements of the pool of NGF mRNA by Northern blot analysis, and quantification of the factor secreted by the cells with a double-site ELISA assay, indicate that pretreatment with PT decreases by about 60% the effect of serum on the levels of NGF transcript and secreted factor. This effect is accompanied by a corresponding decrease of the expression of c-fos gene, which takes place soon after the addition of serum to the cells. In contrast, PT had no effect on the basal level of NGF mRNA found in cells maintained in serum-free medium or in cells stimulated with PMA or 1,25-(OH)2D3. These results indicate that some serum factor(s) acts via plasma membrane receptors able to interact with PT-sensitive G proteins to modulate NGF gene expression. In contrast, 1,25-(OH)2D3 appears to mediate its action through a different signalling pathway, which is likely to require its cytosolic receptor, and is independent of PT-sensitive G protein and c-fos induction.(ABSTRACT TRUNCATED AT 250 WORDS)

Blotting, Northern↗

PubMed1992

Alteration in the levels of 1,25-(OH)2D3 and corticosterone found in experimental diabetes reduces nerve growth factor (NGF) gene expression in vitro.

Circulating concentrations of corticosterone and 1,25-(OH)2D3 have been reported to be respectively increased and decreased in the streptozotocin-treated rats. Using the cell line L929 cultured in a steroid-free medium, we show that the alteration in the levels of corticosterone and 1,25-(OH)2D3 found in vivo in experimental diabetes is able to decrease the synthesis of NGF by these cells. This finding raises a possible relationship between the balance in the concentration of these steroids and some aspects of the neuropathic complications found in experimental diabetes.

Animals↗

PubMed1991

MC903, an analogue of 1,25-dihydroxyvitamin D3, increases the synthesis of nerve growth factor.

The effect of MC903, an analogue of 1,25-dihydroxyvitamin D3, on the expression of the nerve growth factor (NGF) gene has been studied in L cells. MC903 induces an increase in both NGF mRNA and protein with a time course similar to that obtained with 1,25-dihydroxyvitamin D3. This finding points to the potential importance of 1,25-dihydroxyvitamin D3 derivatives in the treatment of NGF-sensitive disorders.

Animals↗

PubMed1991

1,25-Dihydroxyvitamin D3 is a potent inducer of nerve growth factor synthesis.

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3), a metabolically active form of vitamin D, is shown to increase in a dose-dependent manner the cellular pool of NGF mRNA in murine L-929 fibroblasts cultured in a serum-free medium. This effect can be detected as early as 3 hours after 1,25-(OH)2D3 addition and persists for at least 28 hours. It is accompanied by an enhancement of the amount of NGF protein secreted in the culture medium. Since the proto-oncogene c-fos appears involved in the regulation of the NGF gene (Mocchetti et al.: Proceedings of the National Academy of Sciences of the United States of America 86: 3871-895, 1989; Hengerer et al: Proceedings of the National Academy of Sciences of the United States of America 87:3899-3903, 1990), the effect of 1,25-(OH)2D3 on c-fos expression was analysed and compared to that elicited by other inducers of the NGF gene, serum (Wion et al: FEBS Letters 189:37-41, 1985) and phorbol 12-myristate 13-acetate (PMA) (Wion et al: FEBS Letters 262:42-44, 1990). Addition of serum or PMA to L-929 cells was rapidly followed by a transient activation of the c-fos gene. In contrast, c-fos transcripts remained undetected in the presence of 1,25-(OH)2D3. The failure to find any evidence of c-fos expression suggests that 1,25-(OH)2D3 could enhance the pool of NGF mRNA by a mechanism independent of the c-fos pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Antagonistic effects of dexamethasone and 1,25-dihydroxyvitamin D3 on the synthesis of nerve growth factor.

Dexamethasone is known to decrease the pool of nerve growth factor (NGF) mRNA in various experimental systems. The negative regulatory effect of the glucocorticoid was first observed in mouse fibroblast-like L929 cells, and was subsequently reported to take place in many experimental systems, including in vivo following sciatic nerve injury. Conversely, another steroid hormone, 1,25-dihydroxy-vitamin D3 (1,25-(OH)2D3) was recently reported to promote NGF synthesis in mouse L929 cells. The present work was undertaken to investigate the effect of the concomitant addition of both steroids to L929 cells. Measurements of NGF mRNA and assays of the mature protein secreted by the cells provide evidence that the negative regulation exerted by dexamethasone may be counteracted in a dose-dependent manner by the positive action of 1,25-(OH)2D3, and vice versa. Therefore, the expression of the NGF gene can be regulated in a subtle way by the balance between the two steroids. It may be expected on the basis of these observations that in tissues that are responsive to both hormones, administration of 1,25-(OH)2D3 should be able to reverse the down-regulation of NGF synthesis elicited by glucocorticoids.

Animals↗

PubMed1990

[Sclerosing cholangitis revealing histiocytosis X].

The case of a 3 year-old boy who presented isolated cholestasis as the initial symptom of histiocytosis X is described. Other symptoms occurred later on. Despite treatment (corticosteroid and Vinblastin), the disease continued to progress and the child died at the age of 4 1/2 years with HIV infection (contaminated blood product) and tuberculosis.

Child, Preschool↗