A Critical Role for the mTORC2 Pathway in Lung Fibrosis

A characteristic of dysregulated wound healing in IPF is fibroblastic-mediated damage to lung epithelial cells within fibroblastic foci. In these foci, TGF-β and other growth factors activate fibroblasts that secrete growth factors and matrix regulatory proteins, which activate a fibrotic cascade. Our studies and those of others have revealed that Akt is activated in IPF fibroblasts and it mediates the activation by TGF-β of pro-fibrotic pathways. Recent studies show that mTORC2, a component of the mTOR pathway, mediates the activation of Akt. In this study we set out to determine if blocking mTORC2 with MLN0128, an active site dual mTOR inhibitor, which blocks both mTORC1 and mTORC2, inhibits lung fibrosis. We examined the effect of MLN0128 on TGF-β-mediated induction of stromal proteins in IPF lung fibroblasts; also, we looked at its effect on TGF-β-mediated epithelial injury using a Transwell co-culture system. Additionally, we assessed MLN0128 in the murine bleomycin lung model. We found that TGF-β induces the Rictor component of mTORC2 in IPF lung fibroblasts, which led to Akt activation, and that MLN0128 exhibited potent anti-fibrotic activity in vitro and in vivo. Also, we observed that Rictor induction is Akt-mediated. MLN0128 displays multiple anti-fibrotic and lung epithelial-protective activities; it (1) inhibited the expression of pro-fibrotic matrix-regulatory proteins in TGF-β-stimulated IPF fibroblasts; (2) inhibited fibrosis in a murine bleomycin lung model; and (3) protected lung epithelial cells from injury caused by TGF-β-stimulated IPF fibroblasts. Our findings support a role for mTORC2 in the pathogenesis of lung fibrosis and for the potential of active site mTOR inhibitors in the treatment of IPF and other fibrotic lung diseases.

特发性肺纤维化（Idiopathic Pulmonary Fibrosis, IPF）中伤口愈合失调的典型特征，是成纤维细胞灶内的肺上皮细胞受到成纤维细胞介导的损伤。在这些病灶中，转化生长因子-β（Transforming Growth Factor-β, TGF-β）与其他生长因子可激活成纤维细胞，后者会分泌生长因子及基质调控蛋白，进而激活纤维化级联反应。本团队及其他研究者的研究均证实，Akt在IPF成纤维细胞中被激活，且其介导了TGF-β对促纤维化通路的激活作用。近期研究表明，mTOR通路的组分mTORC2可介导Akt的激活。本研究旨在探究，采用MLN0128——一种可同时阻断mTORC1与mTORC2的活性位点双重mTOR抑制剂——阻断mTORC2，是否能够抑制肺纤维化。我们检测了MLN0128对TGF-β诱导的IPF肺成纤维细胞中基质蛋白表达的影响；此外，我们采用Transwell共培养体系，观察了其对TGF-β介导的上皮细胞损伤的作用。除此之外，我们在博莱霉素诱导的小鼠肺纤维化模型中评估了MLN0128的药效。研究结果显示，TGF-β可诱导IPF肺成纤维细胞中mTORC2的组分Rictor的表达，进而介导Akt的激活；且MLN0128在体外与体内实验中均展现出强效的抗纤维化活性。我们同时观察到，Rictor的表达上调是由Akt介导的。MLN0128具备多重抗纤维化与肺上皮保护活性：其一，可抑制TGF-β刺激下IPF成纤维细胞中促纤维化基质调控蛋白的表达；其二，可在小鼠博莱霉素肺纤维化模型中抑制纤维化进程；其三，可保护肺上皮细胞免受TGF-β激活的IPF成纤维细胞所介导的损伤。本研究结果证实，mTORC2在肺纤维化的发病机制中发挥关键作用，同时也表明活性位点双重mTOR抑制剂有望用于IPF及其他纤维化性肺疾病的治疗。