TGF-β Promotes Metabolic Reprogramming in Lung Fibroblasts via mTORC1-dependent ATF4 Activation
TGF-β Promotes Metabolic Reprogramming in Lung Fibroblasts via mTORC1-dependent ATF4 Activation
复制标题
DOI：
10.1165/rcmb.2020-0143oc
复制
发表时间：
2020-11-01
影响因子：
6.4
通讯作者：
Hamanaka, Robert B.
中科院分区：
文献类型：
--
作者：
O'Leary, Erin M.;Tian, Yufeng;Hamanaka, Robert B.
特发性肺纤维化是一种致命的间质性肺病，其特征在于肺成纤维细胞向肌成纤维细胞的TGF-β（转化生长因子-β）依赖性分化，这导致胶原蛋白过度沉积和进行性瘢痕形成。我们之前已经证明，肌成纤维细胞合成胶原蛋白需要重新合成甘氨酸，这是胶原蛋白中发现的最丰富的氨基酸。TGF-β上调肺成纤维细胞中丝氨酸-甘氨酸从头合成途径的酶的表达;然而，该途径的转录和信号调节因子仍不完全清楚。在这里，我们证明，TGF-β促进积累的ATF 4（激活转录因子4），这是必需的丝氨酸-甘氨酸合成途径酶的表达增加，以响应TGF-β。我们发现，整合应激反应（ISR）的诱导有助于TGF-β诱导的ATF 4活性;然而，TGF-β下游ATF 4的主要驱动因素是mTOR 1（mTOR复合物1）的激活。TGF-β激活PI 3 K-Akt-mTOR通路，并且抑制PI 3 K防止下游信号传导的激活和ATF 4的诱导。使用一组mTOR抑制剂，我们发现ATF 4激活依赖于mTORC 1，独立于mTORC 2。雷帕霉素，不完全和变构抑制mTORC 1，对TGF-β介导的诱导ATF 4没有影响;然而，Rapalink-1，特异性靶向mTORC 1的激酶结构域，完全抑制ATF 4诱导和TGF-β下游的代谢重编程。我们的研究结果提供了对肌成纤维细胞代谢重编程机制的深入了解，并澄清了关于mTOR抑制在肌成纤维细胞分化中作用的矛盾的已发表研究结果。
Idiopathic pulmonary fibrosis is a fatal interstitial lung disease characterized by the TGF-beta (transforming growth factor-beta)-dependent differentiation of lung fibroblasts into myofibroblasts, which leads to excessive deposition of collagen proteins and progressive scarring. We have previously shown that synthesis of collagen by myofibroblasts requires de novo synthesis of glycine, the most abundant amino acid found in collagen protein. TGF-beta upregulates the expression of the enzymes of the de novo serine-glycine synthesis pathway in lung fibroblasts; however, the transcriptional and signaling regulators of this pathway remain incompletely understood. Here, we demonstrate that TGF-beta promotes accumulation of ATF4 (activating transcription factor 4), which is required for increased expression of the serine-glycine synthesis pathway enzymes in response to TGF-beta. We found that induction of the integrated stress response (ISR) contributes to TGF-beta-induced ATF4 activity; however, the primary driver of ATF4 downstream of TGF-beta is activation of mTORC1 (mTOR Complex 1). TGF-beta activates the PI3K-Akt-mTOR pathway, and inhibition of PI3K prevents activation of downstream signaling and induction of ATF4. Using a panel of mTOR inhibitors, we found that ATF4 activation is dependent on mTORC1, independent of mTORC2. Rapamycin, which incompletely and allosterically inhibits mTORC1, had no effect on TGF-beta-mediated induction of ATF4; however, Rapalink-1, which specifically targets the kinase domain of mTORC1, completely inhibited ATF4 induction and metabolic reprogramming downstream of TGF-beta. Our results provide insight into the mechanisms of metabolic reprogramming in myofibroblasts and clarify contradictory published findings on the role of mTOR inhibition in myofibroblast differentiation.