The Role of TNF in Hepatotoxicity

TNF 在肝毒性中的作用

• 批准号: 6432285
• 负责人: Dori R Germolec
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF ENVIRONMENTAL HEALTH SCIENCES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6432285
• 关键词: Kupffer's cell; apoptosis; cell growth regulation; dioxins; environmental toxicology; gene expression; hepatotoxin; laboratory mouse; liver toxic disorder; nuclear factor kappa beta; oxidative stress; septic shock; toxin metabolism; tumor necrosis factor alpha

Tumor necrosis factor alpha (TNFalpha) has been demonstrated to be a primary mediator of endotoxin shock. One mechanism of TNF-induced injury is via the activation of NF-kB and the generation of reactive oxygen species. We have hypothesized that 2,3,7,8-tetrachlorodibenzodioxin (TCDD) -induced endotoxin hypersensitivity and subsequent induction of apoptosis may occur through modulation of TNFalpha signaling pathways. Studies using in vivo models of endotoxin hypersensitivity to examine the relationship between TNFalpha signaling and apoptosis are ongoing. We have characterized the kinetics of TCDD-induced hepatic damage in the liver by evaluating serum enzyme levels, quantifying apoptotic cells, and measuring alterations in gene expression at critical time points in B6C3F1 mice exposed to TCDD in the presence or absence of endotoxin. TCDD modulated endotoxin-mediated early expression of Fas, and upregulated expression of caspase 3 (day 10), NFkappaB (day 14), and TNFalpha (days 10 and 14). In addition, combined TCDD/endotoxin altered the kinetics of TCDD-induced hepatoxicity, with peak serum levels occurring 4 days earlier. TNFR1 and TNFR2 gene expression, IkappaBalpha and IkappaBbeta protein expression, and NFkappaB DNA-binding activity did not appear to be modulated by TCDD under the conditions of the study. Previous studies had shown that when rodents are treated with TCDD prior to endotoxin exposure a significant increase in toxicity occurs, and that inhibition of protein synthesis with cycloheximide blocks the TCDD-induced sensitivity to TNF in this model. Overexpression of caspases has been shown to induce apoptosis, and activation of the caspases appears to be necessary for development of the apoptotic phenotype. The protective effects of cycloheximide and alterations in TNFalpha, and NFkappaB gene expression suggest that TCDD treatment may result in alterations in TNF-induced activation of NFkappaB via the TNFalpha/TNFR2/TRAF pathway. The alterations in Fas and Caspase 3 gene expression indicate initiation of apoptosis and suggest involvement of the Fas Ligand/Fas/Caspase pathway.To investigate the mechanism by which TCDD alters NFkappaB expression we are currently examining whether TCDD alters the degradation of the IkappaB/NFkappaB complex at lower doses of endotoxin. In addition, we are attempting to clarify the role of Caspases 1 and 3 by separating and quantifying active and pro-active forms of the protease in treated and untreated animals.

肿瘤坏死因子α（TNF α）已被证明是内毒素休克的主要介质。 TNF诱导的损伤的机制之一是通过NF-kB的活化和活性氧的产生。 我们假设2，3，7，8-四氯二苯并二恶英（TCDD）诱导的内毒素超敏反应和随后诱导的细胞凋亡可能通过调节TNF α信号通路而发生。使用内毒素超敏反应的体内模型来检查TNF α信号传导和细胞凋亡之间的关系的研究正在进行中。 我们的特点是TCDD诱导的肝脏损伤的动力学，通过评估血清酶水平，定量凋亡细胞，并在关键时间点在B6 C3 F1小鼠暴露于TCDD在存在或不存在内毒素的情况下，测量基因表达的变化。 TCDD调节内毒素介导的Fas早期表达，并上调caspase 3（第10天），NF κ B（第14天）和TNF α（第10和14天）的表达。 此外，结合TCDD/内毒素改变了TCDD诱导的肝毒性的动力学，峰值血清水平发生在4天前。 TNFR 1和TNFR 2基因表达、IkappaB α和IkappaB β蛋白表达以及NF κ B DNA结合活性在研究条件下似乎不受TCDD调节。 先前的研究表明，当啮齿动物在内毒素暴露之前用TCDD处理时，毒性显著增加，并且在该模型中用放线菌酮抑制蛋白质合成阻断了TCDD诱导的对TNF的敏感性。 半胱天冬酶的过表达已被证明可诱导细胞凋亡，并且半胱天冬酶的激活似乎是细胞凋亡表型发展所必需的。 放线菌酮的保护作用和TNF α和NF κ B基因表达的改变表明，TCDD治疗可能导致TNF诱导的NF κ B活化通过TNF α/TNFR 2/TRAF途径的改变。 Fas和Caspase 3基因表达的改变表明细胞凋亡的开始，并建议参与Fas配体/Fas/Caspase pathway.To研究TCDD改变NF κ B表达的机制，我们目前正在研究TCDD是否改变在较低剂量的内毒素的IkappaB/NF κ B复合物的降解。 此外，我们正试图通过分离和定量处理和未处理动物中蛋白酶的活性和前活性形式来阐明半胱天冬酶1和3的作用。