TACE/ADAM17-TNF-alpha pathway in rat cortical cultures after exposure to oxygen-glucose deprivation or glutamate.
ABSTRACT The role of the tumor necrosis factor (TNF)-alpha convertase (TACE/ADAM17) in the adult nervous system remains poorly understood. The authors have previously demonstrated that TACE is upregulated in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). They have now used rat mixed cortical cultures exposed to OGD or glutamate to study (1) TACE expression and localization, and (2) the effects of TNF-alpha release on cell viability. OGD-or glutamate-caused TNF-alpha release, an effect that was blocked by the TACE inhibitor BB3103 (BB) (0.1-1 micromol/L; control: 1.67 +/- 0.59; OGD: 6.59 +/- 1.52; glutamate: 3.38 +/- 0.66; OGD +/- BB0.1: 3.23 +/- 0.67; OGD +/- BB1: 1.33 +/- 0.22 pg/mL, n = 6, P < 0.05). Assay of TACE activity as well as Western blot showed that TACE expression is increased in OGD-or glutamate-exposed cells. In control cultures, TACE immunoreactivity was present in some microglial cells, whereas, after OGD or glutamate, TACE immunostaining appeared in most microglial cells and in some astrocytes. Conversely, BB3103 (0.1 micromol/L) caused apoptosis after glutamate exposure as shown by annexin and Hoechst 33342 staining and caspase-3 activity, an effect mimicked by the proteasome inhibitor MG-132 (caspase activity: glutamate: 5.1 +/- 0.1; glutamate + BB: 7.8 +/- 0.8; glutamate + MG: 11.9 +/- 0.5 pmol. min(-1) mg(-1) protein, n = 4, P < 0.05), suggesting that translocation of the transcription factor NF-kappaB mediates TNF-alpha-induced antiapoptotic effect. Taken together, these data demonstrate that, in rat mixed neuronal-glial cortical cultures exposed to OGD or glutamate, (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding, (2) an increase in glial TACE expression contributes to the rise in TNF-alpha, and (3) TNF-alpha release in this setting inhibits apoptosis via activation of the transcription factor NF-kappaB.
- Neuroreport 01/1996; 7(6):1125-1129. · 1.40 Impact Factor
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ABSTRACT: Early events in the signalling of tumor necrosis factor-receptor 1 (TNF-R1), which is the main TNF receptor on most cell types, have been clarified recently. A multimolecular signal transducing complex from which several pathways originate rapidly forms upon TNF-induced aggregation of the receptor. Although fully capable of transducing apoptotic signals, which depend on the adapter Fas-associated death domain protein (FADD) and on the subsequent recruitment/activation of the apoptotic proteases, TNF-R1 usually does not kill cells; this is due to the induction of a complex cytoprotective response that requires TNF-receptor associated factor 2 (TRAF2), a signal transducer that couples TNF-R1 to both nuclear factor kappaB (NFkappaB)-dependent and NFkappaB-independent transcriptional events implicated in induction of genes protecting from TNF cytotoxicity. Although absolutely required for cytoprotection, TNF-receptor associated factor 2 is not sufficient to protect cells from TNF, thus suggesting that it may act in concert with additional TNF-R1 complex components. In this commentary, we will discuss some critical aspects of TNF-R1 signal transduction that are not fully understood: Why do cells not die before the protective protein synthesis has occurred? What are the mechanisms implicated in the termination of each TNF-R1-elicited response? Are there regulatory mechanisms capable of influencing the composition of the TNF-R1 complex and, consequently, the propagation of specific signals?Biochemical Pharmacology 11/1998; 56(8):915-20. · 4.58 Impact Factor
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ABSTRACT: This study was designed to demonstrate the localization of poly-N-acetyl lactosamine residues in postnatal and adult rat brain, visualized by their specific binding to a lectin obtained from Lycopersicon esculentum (tomato). Lectin histochemistry was carried out on cryostat, paraffin, and vibratome sections and was examined by light microscopy. Selected vibratome sections were processed for electron microscopy. Our results showed that tomato lectin histochemistry was found in relation to blood vessels and glial cells in both postnatal and adult rat brain. Since tomato lectin-positive glial cells did not show GFAP immunoreactivity and displayed the same morphological features and overall distribution as nucleoside diphosphatase (NDPase)-positive cells, they were consequently identified as microglial cells. At the electron microscopic level, both ameboid and ramified microglial cells displayed intracytoplasmic and plasma membrane lectin reactivity. In postnatal brain, ameboid microglial cells always showed stronger binding of tomato lectin compared with ramified microglial cells in the adult brain. The putative significance of this decrease in poly-N-acetyl lactosamine from ameboid to ramified microglial cells and the possible role(s) of this sugar residue are discussed.Journal of Histochemistry and Cytochemistry 09/1994; 42(8):1033-41. · 2.26 Impact Factor