Division of Rheumatology, Department of Medicine, Medical University of South Carolina (MUSC), Charleston, South Carolina, United States of America.
Mid Atlantic Permanente Medical Group, Mclean, Virginia, United States of America.
PLoS One. 2019 Nov 25;14(11):e0225422. doi: 10.1371/journal.pone.0225422. eCollection 2019.
Type 2 insulin-like growth factor (IGF-II) levels are increased in fibrosing lung diseases such as idiopathic pulmonary fibrosis (IPF) and scleroderma/systemic sclerosis-associated pulmonary fibrosis (SSc). Our goal was to investigate the contribution of IGF receptors to IGF-II-mediated fibrosis in these diseases and identify other potential mechanisms key to the fibrotic process. Cognate receptor gene and protein expression were analyzed with qRT-PCR and immunoblot in primary fibroblasts derived from lung tissues of normal donors (NL) and patients with IPF or SSc. Compared to NL, steady-state receptor gene expression was decreased in SSc but not in IPF. IGF-II stimulation differentially decreased receptor mRNA and protein levels in NL, IPF, and SSc fibroblasts. Neutralizing antibody, siRNA, and receptor inhibition targeting endogenous IGF-II and its primary receptors, type 1 IGF receptor (IGF1R), IGF2R, and insulin receptor (IR) resulted in loss of the IGF-II response. IGF-II tipped the TIMP:MMP balance, promoting a fibrotic environment both intracellularly and extracellularly. Differentiation of fibroblasts into myofibroblasts by IGF-II was blocked with a TGFβ1 receptor inhibitor. IGF-II also increased TGFβ2 and TGFβ3 expression, with subsequent activation of canonical SMAD2/3 signaling. Therefore, IGF-II promoted fibrosis through IGF1R, IR, and IGF1R/IR, differentiated fibroblasts into myofibroblasts, decreased protease production and extracellular matrix degradation, and stimulated expression of two TGFβ isoforms, suggesting that IGF-II exerts pro-fibrotic effects via multiple mechanisms.
2 型胰岛素样生长因子（IGF-II）水平在纤维化性肺疾病中增加，如特发性肺纤维化（IPF）和硬皮病/系统性硬化症相关的肺纤维化（SSc）。我们的目标是研究 IGF 受体在这些疾病中 IGF-II 介导的纤维化中的作用，并确定其他潜在的关键纤维化过程的机制。使用 qRT-PCR 和免疫印迹分析来自正常供体（NL）和 IPF 或 SSc 患者肺组织的原代成纤维细胞中的同源受体基因和蛋白表达。与 NL 相比，SSc 中的稳态受体基因表达降低，但 IPF 中没有。IGF-II 刺激在 NL、IPF 和 SSc 成纤维细胞中差异地下调受体 mRNA 和蛋白水平。针对内源性 IGF-II 及其主要受体，即 1 型 IGF 受体（IGF1R）、IGF2R 和胰岛素受体（IR）的中和抗体、siRNA 和受体抑制导致 IGF-II 反应丧失。IGF-II 使 TIMP:MMP 平衡倾斜，在细胞内和细胞外促进纤维化环境。IGF-II 通过 TGFβ1 受体抑制剂阻止成纤维细胞分化为肌成纤维细胞。IGF-II 还增加了 TGFβ2 和 TGFβ3 的表达，随后激活了经典的 SMAD2/3 信号通路。因此，IGF-II 通过 IGF1R、IR 和 IGF1R/IR 促进纤维化，将成纤维细胞分化为肌成纤维细胞，减少蛋白酶的产生和细胞外基质的降解，并刺激两种 TGFβ 同工型的表达，这表明 IGF-II 通过多种机制发挥促纤维化作用。
