Biomedical subjects

Yoko Tohyama

Publications and source records attributed to Yoko Tohyama.

4 recordsLinked to original sources

PubMed2004

Protein kinase C alpha requirement in the activation of p38 mitogen-activated protein kinase, which is linked to the induction of tumor necrosis factor alpha in lipopolysaccharide-stimulated microglia.

Activated microglia have been suggested to produce a cytotoxic cytokine, tumor necrosis factor alpha (TNF alpha), in many pathological brains. Thus, determining the molecular mechanism of this induction and suppression has been the focus of a great deal of research. Using lipopolysaccharide (LPS) as an experimental inducer of TNF alpha, we investigated the regulatory mechanism by which TNFalpha is induced or suppressed in microglia. We found that LPS-induced TNF alpha is suppressed by pretreatment with the p38 mitogen-activated protein kinase (p38MAPK) inhibitor SB203580. Similar suppression was achieved by pretreatment with specific protein kinase C (PKC) inhibitors, Gö6976, myristoylated pseudosubstrate (20-28), and bisindolylmaleimide. These results suggest that PKC alpha activity as well as p38MAPK activity is associated with TNF alpha induction in LPS-stimulated microglia. The requirement of PKC alpha in LPS-dependent TNFalpha induction was verified in PKC alpha-downregulated microglia which could be induced by phorbol-12-myristate-13-acetate pretreatment. Simultaneously, PKC alpha was found to be requisite for the activation of p38MAPK in LPS-stimulated microglia. In addition, the PKC alpha levels in the LPS-stimulated microglia were observed to decrease in response to the p38MAPK inhibitor, indicating that the PKC alpha levels are regulated by the p38MAPK activity. We therefore concluded that PKC alpha and p38MAPK are interactively linked to the signaling cascade inducing TNFalpha in LPS-stimulated microglia, and that in this cascade, PKC alpha is requisite for the activation of p38MAPK, leading to the induction of TNF alpha.

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PubMed2003

Suppression of lipopolysaccharide-dependent tumor necrosis factor alpha induction in rat microglia, in which protein kinase C alpha is down-regulated.

Microglia are thought to produce a cytotoxic cytokine, tumor necrosis factor alpha (TNF alpha), in the pathological brain. Thus, the mechanism that suppresses the induction of TNF alpha in microglia is of interest. We found that lipopolysaccharide (LPS)-induced TNF alpha is strongly suppressed by pretreatment with specific protein kinase C (PKC) inhibitors, Gö6976 and bisindolylmaleimide, suggesting that PKC alpha plays a role in the signaling cascade of TNF alpha induction. Therefore, the association of PKC alpha with TNF alpha induction was investigated in PKC alpha-deficient microglia prepared by pretreatment with phorbol-12-myristate-13-acetate (PMA). PMA-pretreated microglia strongly decreased the TNF alpha induction in the absence of PKC alpha when activated with LPS. The lack of PKC alpha in the PMA-treated microglia was confirmed by determining conventional PKC activity. Taken together, the present study demonstrated that PKC alpha is a requisite PKC isoform in the signaling cascade of TNF alpha induction in LPS-stimulated microglia.

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PubMed2003

Activation of microglia with lipopolysaccharide leads to the prolonged decrease of conventional protein kinase C activity.

The activation of microglia by lipopolysaccharide (LPS) results in the induction of harmful factors including nitric oxide and tumor necrosis factor alpha (TNFalpha). Such microglial activation was suggested to be mediated by PKC activity based on the results of an inhibitor experiment. To clarify the relationship between microglial activation and PKC activity, conventional PKC (cPKC) activity was measured by enzyme-linked immunosorbent assay (ELISA) in LPS-activated microglia. LPS stimulation caused a time- and dose-dependent decrease (70%) of specific activity of cPKC, ascribed to the decreasing amounts of PKCalpha. However, the remaining PKC activity (30%) was sustained despite longer incubation or higher LPS concentration. Therefore, it is suggested that LPS-stimulated microglia require priming by PKC activation for the induction of harmful factors, while only a part (30%) of original PKC activity is sufficient for durable microglial activation.

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PubMed2002

Ceramide activates microglia to enhance the production/secretion of brain-derived neurotrophic factor (BDNF) without induction of deleterious factors in vitro.

In analyzing the regulation of neurotrophin production/secretion from microglia, C8-ceramide (D-erythro-sphingosine, N-octanoyl-) was found to induce secretion of brain-derived neurotrophic factor (BDNF) from microglia in vitro. In the present study, the action of C8-ceramide in secreting neurotrophic and harmful factors was investigated and compared with the effects of lipopolysaccharide (LPS). C8-ceramide as well as LPS enhanced the production/secretion of BDNF but, different from LPS, did not induce tumor necrosis factor alpha, interleukin-1beta, or nitric oxide. The C8-ceramide-induced BDNF release was significantly suppressed by protein kinase C (PKC) inhibitor, bisindolylmaleimide, which targets PKC isoforms, alpha, beta, gamma, delta and epsilon. However, it was not suppressed by a specific inhibitor of PKCalpha. Furthermore, PKCbeta and gamma were undetected in the microglia. Therefore, PKCdelta and/or epsilon appear to be functioning PKC isoforms. In contrast, none of the mitogen-activated protein kinases (MAPKs) and none of the transcription factors, including the cAMP response element-binding transcription factor (CREB) and nuclear factor kappaB (NFkappaB) were activated in the microglia in response to C8-ceramide. These results indicate that ceramide-induced BDNF release in microglia is mediated by a signaling pathway associated with PKCdelta and/or epsilon, but not with activation of MAPKs, CREB and NFkappaB.

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