TNF-alpha Signaling in Silica-Induced Lung Fibrosis

尘肺病是由于环境暴露于各种无机粉尘而引起的一组纤维化肺部疾病。其中一些粉尘，包括二氧化硅，与肺部炎症和随后的肺纤维化发展有关。对二氧化硅的炎症反应的特征是肿瘤坏死因子- α (TNF)的表达增加。吸入二氧化硅触发TNF受体介导的信号转导通路，促进NF-kappaB和AP-1的激活，进而诱导介导二氧化硅的促炎（TNF）和促纤维化（胶原、基质金属蛋白酶、TIMP- 1）作用的基因表达。这些TNF介导的信号转导途径，响应于二氧化硅，包括激活ERK1/2家族的丝裂原活化蛋白激酶（MAPK），诱导TNF受体磷酸化。TNF受体磷酸化在矽肺中的重要性尚不清楚。在这里，我们提出TNF受体磷酸化促进细胞存活信号，保护肺部免受二氧化硅诱导的细胞凋亡。我们的体外初步数据显示，二氧化硅诱导的tnf介导的信号转导差异与巨噬细胞存活相关。巨噬细胞系RAW 264.7对二氧化硅暴露有反应，TNF表达增强。这种增强的TNF表达促进NF-kappaB和ERK1/2的激活。活化的ERK1/2激酶诱导TNF受体磷酸化，保护RAW 264.7细胞免受二氧化硅诱导的凋亡。相反，IC-21巨噬细胞系对二氧化硅没有上调TNF的表达。IC-21细胞对二氧化硅的反应不激活nf - κ b或ERK激酶。IC- 21细胞不磷酸化TNF受体，并表现出二氧化硅诱导的细胞凋亡增强。我们的体内数据表明，个体TNF受体缺陷小鼠免受二氧化硅的纤维化作用。这种保护作用与二氧化硅敏感（C57BL/6）小鼠肺中AP-1活性降低和组织金属蛋白酶1 （TIMP-1）表达降低有关。为了进一步了解二氧化硅诱导肺纤维化的机制，我们的工作假设是，二氧化硅诱导的和TNF受体介导的肺中NFkappaB和ERK的激活被破坏将增强肺泡上皮II型细胞的凋亡，从而加重二氧化硅诱导的肺损伤和纤维化。具体目标是：1)；研究抑制肺泡上皮II型细胞NF- kappaB活化是否会加重小鼠二氧化硅诱导的肺损伤。2）. 确定erk介导的TNF受体磷酸化抑制是否会加重二氧化硅诱导的肺损伤。3)。探讨小鼠肺组织金属蛋白酶抑制剂1 （TIMP-1）过表达是否会加重二氧化硅诱导的肺损伤。

The pneumoconioses are a group of fibrotic lung diseases caused by the environmental exposure to a variety of inorganic dusts. Several of these dusts, including silica, are associated with lung inflammation and the subsequent development of lung fibrosis. The inflammatory response to silica is characterized by an increased expression of tumor necrosis factor-alpha (TNF). Inhaled silica triggers TNF receptor-mediated signal transduction pathways promoting NF-kappaB and AP-1 activation which in turn induce the expression of genes mediating the proinflammatory (TNF) and profibrotic (collagen, matrix metalloproteinases, TIMP- 1) effects of silica. These TNF-mediated signal transduction pathways, in response to silica, includes activation of the ERK1/2 family of mitogen-activated protein kinases (MAPK) that induces TNF receptor phosphorylation. The importance of TNF receptor phosphorylation in silicosis is not known. Here we propose that TNF receptor phosphorylation promotes cell survival signals that protect the lungs from silica-induced apoptosis. Our in vitro preliminary data show that differences in the silica-induced-TNF-mediated signal transduction correlate with macrophage cell survival. The macrophage cell line RAW 264.7 reacts to silica exposure with enhanced TNF expression. This enhanced TNF expression promotes NF-kappaB and ERK1/2 activation. Activated ERK1/2 kinases induce phosphorylation of the TNF receptors and protect RAW 264.7 cells from silica-induced apoptosis. In contrast, the IC-21 macrophage cell line does not upregulate TNF expression in response to silica. IC-21 cells do not activate NF-kappaB or ERK kinases in response to silica. IC- 21 cells do not phosphorylate TNF receptors and exhibit enhanced silica-induced apoptosis. Our in vivo data demonstrate that individual TNF receptor deficient mice are protected from the fibrogenic effects of silica. This protection correlates with a decreased AP-1 activation and decreased expression of the Tissue Inhibitor of Metalloproteinase 1 (TIMP-1) observed in the lungs of silica-sensitive (C57BL/6) mice in response to silica. Our working hypothesis to further understand the mechanisms of silica-induced lung fibrosis is that disruption of the silica- induced and TNF receptor-mediated activation of NFkappaB and ERK in the lung will enhance apoptosis in alveolar epithelial type II cells thus aggravating silica-induced lung injury and fibrosis. Specific Aims are: 1). To determine whether inhibition of NF- kappaB activation in alveolar epithelial type II cells will exacerbate silica-induced lung injury in mice. 2). To determine whether inhibition of ERK-mediated phosphorylation of TNF receptors will exacerbate silica-induced lung injury. 3). To determine whether overexpression of Tissue Inhibitor of Metalloproteinase 1 (TIMP-1) in mouse lung exacerbates silica- induced lung injury.