IL-13 Induces YY1 through the AKT Pathway in Lung Fibroblasts

A key feature of lung fibrosis is the accumulation of myofibroblasts. Interleukin 13 (IL-13) is a pro-fibrotic mediator that directly and indirectly influences the activation of myofibroblasts. Transforming growth factor beta (TGF-β) promotes the differentiation of fibroblasts into myofibroblasts, and can be regulated by IL-13. However, IL-13’s downstream signaling pathways are not completely understood. We previously reported that the transcription factor Yin Yang 1 (YY1) is upregulated in fibroblasts treated with TGF-β and in the lungs of mice and patients with pulmonary fibrosis. Moreover, YY1 directly regulates collagen and alpha smooth muscle actin (α-SMA) expression in fibroblasts. However, it is not known if IL-13 regulates fibroblast activation through YY1 expression. We hypothesize that IL-13 up-regulates YY1 expression through regulation of AKT activation, leading to fibroblast activation. In this study we found that YY1 was upregulated by IL-13 in lung fibroblasts in a dose- and time-dependent manner, resulting in increased α-SMA. Conversely, knockdown of YY1 blocked IL-13-induced α-SMA expression in fibroblasts. Furthermore, AKT phosphorylation was increased in fibroblasts treated with IL-13, and AKT overexpression upregulated YY1, whereas blockade of AKT phosphorylation suppressed the induction of YY1 by IL-13 in vitro. In vivo YY1 was upregulated in fibrotic lungs from CC10-IL-13 transgenic mice compared to that from wild-type littermates, which was associated with increased AKT phosphorylation. Taken together, these findings demonstrate that IL-13 is a potent stimulator and activator of fibroblasts, at least in part, through AKT-mediated YY1 activation.肺纤维化的核心特征为肌成纤维细胞蓄积。白细胞介素13（Interleukin 13，IL-13）是一种促纤维化介质，可直接及间接影响肌成纤维细胞的活化。转化生长因子β（Transforming growth factor beta，TGF-β）可促进成纤维细胞向肌成纤维细胞的分化，且其表达可受IL-13调控。然而，IL-13的下游信号通路尚未完全阐明。本课题组既往报道，经TGF-β处理的成纤维细胞以及肺纤维化小鼠与患者的肺组织中，转录因子阴阳1（Yin Yang 1，YY1）的表达均会上调；此外，YY1可直接调控成纤维细胞中胶原蛋白及α平滑肌肌动蛋白（alpha smooth muscle actin，α-SMA）的表达。但目前尚不明确IL-13是否通过调控YY1的表达来介导成纤维细胞活化。本研究提出假说：IL-13可通过调控AKT活化而上调YY1的表达，进而促成成纤维细胞活化。本研究发现，IL-13可呈剂量与时间依赖性方式上调肺成纤维细胞中YY1的表达，进而使α-SMA的表达水平升高。反之，敲低YY1可阻断IL-13诱导的成纤维细胞中α-SMA的表达。进一步实验显示，经IL-13处理的成纤维细胞中AKT磷酸化水平升高；AKT过表达可上调YY1的表达，而阻断AKT磷酸化则可在体外抑制IL-13对YY1的诱导作用。在体内，与野生型同窝仔鼠相比，CC10-IL-13转基因小鼠的纤维化肺组织中YY1表达上调，且该现象与AKT磷酸化水平升高密切相关。综上，本研究结果证实，IL-13是成纤维细胞的强效刺激因子与活化剂，其作用至少部分是通过AKT介导的YY1活化通路实现的。