Idiopathic pulmonary fibrosis (IPF) is characterized by a disturbed redox balance and increased production of reactive oxygen species (ROS), which is believed to contribute to epithelial injury and fibrotic lung scarring. The main pulmonary sources of ROS include mitochondria and NADPH oxidases (NOXs), of which the NOX4 isoform has been implicated in IPF. Non-receptor SRC tyrosine kinases (SFK) are important for cellular homeostasis and are often dysregulated in lung diseases. SFK activation by the profibrotic transforming growth factor-β (TGF-β) is thought to contribute to pulmonary fibrosis, but the relevant SFK isoform and its relation to NOX4 and/or mitochondrial ROS in the context of profibrotic TGF-β signaling is not known. Here, we demonstrate that TGF-β1 can rapidly activate the SRC kinase FYN in human bronchial epithelial cells, which subsequently induces mitochondrial ROS (mtROS) production, genetic damage shown by the DNA damage marker γH2AX, and increased expression of profibrotic genes. Moreover, TGF-β1-induced activation of FYN involves initial activation of NOX4 and direct cysteine oxidation of FYN, and both FYN and mtROS contribute to TGF-β-induced induction of NOX4. NOX4 expression in lung tissues of IPF patients is positively correlated with disease severity, although FYN expression is downregulated in IPF and does not correlate with disease severity. Collectively, our findings highlight a critical role for FYN in TGF-β1-induced mtROS production, DNA damage response, and induction of profibrotic genes in bronchial epithelial cells, and suggest that altered expression and activation of NOX4 and FYN may contribute to the pathogenesis of pulmonary fibrosis.

中文翻译：

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促纤维化上皮 TGF-β1 信号传导涉及 NOX4-线粒体串扰和氧化还原介导的酪氨酸激酶 FYN 激活

特发性肺纤维化 (IPF) 的特征是氧化还原平衡紊乱和活性氧 (ROS) 的产生增加，这被认为会导致上皮损伤和纤维化肺瘢痕形成。ROS 的主要肺部来源包括线粒体和 NADPH 氧化酶 (NOX)，其中 NOX4 亚型与 IPF 有关。非受体 SRC 酪氨酸激酶 (SFK) 对细胞稳态很重要，并且在肺部疾病中经常失调。促纤维化转化生长因子-β (TGF-β) 对 SFK 的激活被认为有助于肺纤维化，但在促纤维化 TGF-β 信号传导的背景下，相关的 SFK 同种型及其与 NOX4 和/或线粒体 ROS 的关系尚不清楚. 在这里，我们证明 TGF-β1 可以快速激活人支气管上皮细胞中的 SRC 激酶 FYN，随后诱导线粒体 ROS (mtROS) 产生、DNA 损伤标志物 γH2AX 显示的遗传损伤以及促纤维化基因的表达增加。此外，TGF-β1 诱导的 FYN 活化涉及 NOX4 的初始活化和 FYN 的直接半胱氨酸氧化，FYN 和 mtROS 均有助于 TGF-β 诱导的 NOX4 诱导。IPF 患者肺组织中 NOX4 的表达与疾病严重程度呈正相关，尽管 FYN 表达在 IPF 中下调且与疾病严重程度无关。总的来说，我们的研究结果强调了 FYN 在 TGF-β1 诱导的 mtROS 产生、DNA 损伤反应和支气管上皮细胞中促纤维化基因的诱导中的关键作用，并表明 NOX4 和 FYN 的表达和活化改变可能有助于肺纤维化。