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Ollivier Milhavet

Publications and source records attributed to Ollivier Milhavet.

9 recordsLinked to original sources
PubMed2006

Neural stem cell model for prion propagation.

The study of prion transmission and targeting is a major scientific issue with important consequences for public health. Only a few cell culture systems that are able to convert the cellular isoform of the prion protein into the pathologic scrapie isoform of the prion protein (PrP(Sc)) have been described. We hypothesized that central nervous system neural stem cells (NSCs) could be the basis of a new cell culture model permissive to prion infection. Here, we report that monolayers of differentiated fetal NSCs and adult multipotent progenitor cells isolated from mice were able to propagate prions. We also demonstrated the large influence of neural cell fate on the production of PrP(Sc), allowing the molecular study of prion neuronal targeting in relation with strain differences. This new stem cell-based model, which is applicable to different species and to transgenic mice, will allow thoughtful investigations of the molecular basis of prion diseases, and will open new avenues for diagnostic and therapeutic research.

Animals↗
PubMed2005

Suppression of calcium release from inositol 1,4,5-trisphosphate-sensitive stores mediates the anti-apoptotic function of nuclear factor-kappaB.

The activation of the transcription factor nuclear factor-kappaB (NF-kappaB) by growth factors, cytokines, and cellular stress can prevent apoptosis, but the underlying mechanism is unknown. Here we provide evidence for an action of NF-kappaB on calcium signaling that accounts for its anti-apoptotic function. Embryonic fibroblasts lacking the transactivating subunit of NF-kappaB RelA (p65) exhibit enhanced inositol 1,4,5-trisphosphate (IP(3)) receptor-mediated calcium release and increased sensitivity to apoptosis, which are restored upon re-expression of RelA. The size of the endoplasmic reticulum (ER) calcium pool and the number of IP(3) receptors per cell are decreased in response to stimuli that activate NF-kappaB and are increased when NF-kappaB activity is suppressed. The selective antagonism of IP(3) receptors blocks apoptosis in RelA-deficient cells, whereas activation of NF-kappaB in normal cells leads to decreased levels of the type 1 IP(3) receptor and decreased calcium release. Overexpression of Bcl-2 normalizes ER calcium homeostasis and prevents calcium-mediated apoptosis in RelA-deficient cells. These findings establish an ER calcium channel as a pivotal target for NF-kappaB-mediated cell survival signaling.

Adenosine Triphosphate↗
PubMed2003

Essential role for integrin linked kinase in Akt-mediated integrin survival signaling in hippocampal neurons.

Activation of integrin receptors in neurons can promote cell survival and synaptic plasticity, but the underlying signal transduction pathway(s) is unknown. We report that integrin signaling prevents apoptosis of embryonic hippocampal neurons by a mechanism involving integrin-linked kinase (ILK) that activates Akt kinase. Activation of integrins using a peptide containing the amino acid sequence EIKLLIS derived from the alpha chain of laminin protected hippocampal neurons from apoptosis induced by glutamate or staurosporine, and increased Akt activity in a beta1 integrin-dependent manner. Transfection of neurons with a plasmid encoding dominant negative Akt blocked the protective effect of the integrin-activating peptide, as did a chemical inhibitor of Akt. Although inhibitors of phosphoinositide-3 (PI3) kinase blocked the protective effect of the peptide, we found no increase in PI3 kinase activity following integrin stimulation suggesting that PI3 kinase was necessary for Akt activity but was not sufficient for the increase in Akt activity following integrin activation. Instead, we show a requirement for ILK in integrin receptor-induced Akt activation. ILK was activated following integrin stimulation and dominant negative ILK blocked integrin-mediated Akt activation and cell survival. Activation of ILK and Akt were also required for neuroprotection by substrate-associated laminin. These results establish a novel pathway that signals cell survival in neurons in response to integrin receptor activation.

Animals↗
PubMed2003

RNA interference in biology and medicine.

First discovered in plants the nematode Caenorhabditis elegans, the production of small interfering RNAs (siRNAs) that bind to and induce the degradation of specific endogenous mRNAs is now recognized as a mechanism that is widely employed by eukaryotic cells to inhibit protein production at a post-transcriptional level. The endogenous siRNAs are typically 19- to 23-base double-stranded RNA oligonucleotides, produced from much larger RNAs that upon binding to target mRNAs recruit RNases to a protein complex that degrades the targeted mRNA. Methods for expressing siRNAs in cells in culture and in vivo using viral vectors, and for transfecting cells with synthetic siRNAs, have been developed and are being used to establish the functions of specific proteins in various cell types and organisms. RNA interference methods provide several major advantages over prior methods (antisense DNA or antibody-based techniques) for suppressing gene expression. Recent preclinical studies suggest that RNA interference technology holds promise for the treatment of various diseases. Pharmacologists have long dreamed of the ability to selectively antagonize or eliminate the function of individual proteins--RNAi technology may eventually make that dream a reality.

Animals↗
PubMed2002

PrP-dependent cell adhesion in N2a neuroblastoma cells.

The cellular isoform of prion protein (PrP(C)) is a ubiquitous glycoprotein expressed by most tissues and with a biological function yet to be determined. Here, we have used a neuroblastoma cell model to investigate the involvement of PrP in cell adhesion. Incubation of single cell suspension induced cell-cell adhesion and formation of cell aggregates. Interestingly, cells overexpressing PrP exhibit increased cation-independent aggregation. Aggregation was reduced after phosphatidylinositol-specific phospholipase C release of the protein and by pre-incubation of cells with an antibody raised against the N-terminal part of PrP(C). Our paradigm allows the study of the function of PrP as an intercellular adhesion molecule and a cell surface ligand or receptor.

Animals↗
PubMed2002

Oxidative stress and the prion protein in transmissible spongiform encephalopathies.

Transmissible spongiform encephalopathies form a group of fatal neurodegenerative disorders that have the unique property of being infectious, sporadic or genetic in origin. These diseases are believed to be the consequence of the conformational conversion of the prion protein into an abnormal isoform. Their exact pathogenic mechanism remains uncertain, but it is believed that oxidative stress plays a central role. In this article, we will first review in detail the data supporting the latter hypothesis. Subsequently, we will discuss the relationship between the prion protein and the cellular response to oxidative stress, attempting ultimately to link PrP function and neurodegeneration in these disorders.

Animals↗
PubMed2002

Involvement of Gadd153 in the pathogenic action of presenilin-1 mutations.

Mutations in the presenilin-1 (PS1) gene cause early onset familial Alzheimer's disease (FAD) by a mechanism believed to involve perturbed endoplasmic reticulum (ER) function and altered proteolytic processing of the amyloid precursor protein. We investigated the molecular mechanisms underlying cell death and ER dysfunction in cultured cells and knock-in mice expressing FAD PS1 mutations. We report that PS1 mutations cause a marked increase in basal protein levels of the pro-apoptotic transcription factor Gadd153. PS1 mutations increase Gadd153 protein translation without affecting mRNA levels, while decreasing levels of the anti-apoptotic protein Bcl-2. Moreover, an exaggerated Gadd153 response to stress induced by ER stress agents was observed in PS1 mutant cells. Cell death in response to ER stress is enhanced by PS1 mutations, and this endangering effect is attenuated by anti-sense-mediated suppression of Gadd153 production. An abnormality in the translational regulation of Gadd153 may sensitize cells to the detrimental effects of ER stress and contribute to the pathogenic actions of PS1 mutations in FAD.

Alzheimer Disease↗
PubMed2002

Effects of streptozotocin-induced diabetes on markers of skeletal muscle metabolism and monocarboxylate transporter 1 to monocarboxylate transporter 4 transporters.

Diabetes is known to alter both oxidative and glycolytic pathways in a fiber type-dependent manner. In various skeletal muscles of normal rats, monocarboxylate transporter 1 (MCT1) has been found to be highly correlated to lactate uptake, as well as to oxidative capacity, whereas the distribution and characteristics of MCT4 make it a good candidate for the extrusion of lactic acid from glycolytic muscle cells. Since a previous study found decreased sarcolemmal lactate uptake in streptozotocin (STZ)-diabetic rats, we investigated the presence of MCT1 in relation to enzymatic markers of both oxidative and glycolytic pathways, as well as MCT4 content, in STZ-diabetic rats. Soleus (SOL), red tibialis anterior (RTA), extensor digitorus longus (EDL), heart, and preparations of purified sarcolemmal vesicles (SV) from control and STZ-diabetic rats were harvested for MCT1 and MCT4 content, citrate synthase activity (CS), and lactate dehydrogenase (LDH) isozymes. Basal blood lactate concentration was increased by 38% in the diabetic rats (close to 1.91 mmol/L). However, no change was found in either MCT1 or MCT4 content in these rats. The diabetic rats presented fiber type-specific decrease in CS activity. We noted a redistribution in LDH isozymes in diabetic muscles with a general increase in type H-LDH. Regression analyses indicated (1) a strong relationship between LDH-4 and LDH-5 and (2) MCT1 was still correlated with CS activity in diabetic muscles. These results suggest that diabetes-induced hyperlactatemia is not associated with changes in MCT1 or MCT4 expression, but with alterations of oxidative and glycolytic enzymes.

Animals↗