TNF-alpha Signaling in Silica-Induced Lung Fibrosis

尘肺是环境暴露于各种无机粉尘所致的一组纤维性肺部疾病。其中几种粉尘，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以肿瘤坏死因子-α(TNF)表达增加为特征。吸入二氧化硅触发了肿瘤坏死因子受体介导的信号转导通路，促进了核因子-kappaB和AP-1的激活，进而诱导了介导二氧化硅促炎症和促纤维化(胶原、基质金属蛋白酶，TIMP-1)作用的基因的表达。这些由肿瘤坏死因子介导的信号转导通路，包括激活ERK1/2家族的丝裂原活化蛋白激酶(MAPK)，从而诱导肿瘤坏死因子受体的磷酸化。目前尚不清楚肿瘤坏死因子受体磷酸化在矽肺中的重要性。在这里，我们认为，肿瘤坏死因子受体磷酸化促进细胞生存信号，以保护肺免受二氧化硅诱导的细胞凋亡。我们的体外初步数据显示，二氧化硅诱导的肿瘤坏死因子介导的信号转导的差异与巨噬细胞的存活有关。巨噬细胞系RAW 264.7对二氧化硅暴露的反应是肿瘤坏死因子表达增强。这种增强的肿瘤坏死因子表达促进了核因子-kappaB和ERK1/2的激活。活化的ERK1/2激酶诱导肿瘤坏死因子受体的磷酸化，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的反应并不上调肿瘤坏死因子的表达。IC-21细胞对二氧化硅不能激活核因子-kappaB或ERK激酶。IC-21细胞不能磷酸化肿瘤坏死因子受体，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，单个肿瘤坏死因子受体缺陷的小鼠可以免受二氧化硅的纤维化影响。这种保护与二氧化硅敏感(C57BL/6)小鼠肺部对二氧化硅的反应中AP-1活性降低和金属蛋白酶组织抑制物1(TIMP-1)表达减少有关。我们进一步了解二氧化硅诱导的肺纤维化机制的工作假说是，破坏二氧化硅诱导的和肿瘤坏死因子受体介导的肺组织中NFkappaB和ERK的激活将促进肺泡上皮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。具体目标有：1)。目的：探讨抑制肺泡II型上皮细胞中核因子-kappaB的激活是否会加重二氧化硅所致的小鼠肺损伤。2)。目的：确定抑制ERK介导的肿瘤坏死因子受体的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了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.