TNF-alpha Signaling in Silica-Induced Lung Fibrosis

尘肺病是一组因接触各种无机粉尘而引起的肺纤维化疾病。 这些粉尘中的几种，包括二氧化硅，与肺部炎症和随后的肺纤维化的发展有关。 对二氧化硅的炎症反应的特征在于肿瘤坏死因子-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途径，促进NF-κ B和AP-1活化，进而诱导介导二氧化硅促炎（TNF）和促纤维化（胶原蛋白、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，在响应二氧化硅，包括激活ERK 1/2家族的促分裂原活化蛋白激酶（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，保护肺免受二氧化硅诱导的细胞凋亡。我们在体外的初步数据表明，二氧化硅诱导的TNF介导的信号转导的差异与巨噬细胞的生存。 巨噬细胞系RAW 264.7对二氧化硅暴露的反应具有增强的TNF表达。 这种增强的TNF表达促进NF-κ B和ERK 1/2活化。活化的ERK 1/2激酶诱导TNF受体的磷酸化并保护RAW 264.7细胞免受二氧化硅诱导的凋亡。 相比之下，IC-21巨噬细胞系不上调TNF表达响应二氧化硅。 IC-21细胞不激活NF-κ B或ERK激酶响应二氧化硅。 IC- 21细胞不磷酸化TNF受体，并表现出增强的二氧化硅诱导的细胞凋亡。 我们的体内数据表明，个别TNF受体缺陷小鼠的保护，从二氧化硅的纤维化作用。 这种保护作用与二氧化硅敏感（C57 BL/6）小鼠肺中观察到的AP-1活化降低和金属蛋白酶组织抑制剂1（TIMP-1）表达降低相关。 为了进一步理解二氧化硅诱导的肺纤维化的机制，我们的工作假设是，肺中二氧化硅诱导的和TNF受体介导的NF κ B和ERK活化的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）。确定抑制肺泡II型上皮细胞中的NF-κ B活化是否会加重二氧化硅诱导的小鼠肺损伤。2）。确定抑制ERK介导的TNF受体磷酸化是否会加重二氧化硅诱导的肺损伤。3）。目的探讨金属蛋白酶组织抑制因子1（TIMP-1）在小鼠肺组织中的过度表达是否加重二氧化硅所致的肺损伤。

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.