The mTORC1/4EBP1/PPARγ Axis Mediates Insulin-Induced Lipogenesis by Regulating Lipogenic Gene Expression in Bovine Mammary Epithelial Cells
The mTORC1/4EBP1/PPARγ Axis Mediates Insulin-Induced Lipogenesis by Regulating Lipogenic Gene Expression in Bovine Mammary Epithelial Cells
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mTORC1/4EBP1/PPAR γ 轴通过调节牛乳腺上皮细胞中的脂肪生成基因表达来介导胰岛素诱导的脂肪生成
DOI：
10.1021/acs.jafc.9b01411
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发表时间：
2019-05-29
影响因子：
6.1
通讯作者：
Wang, Zhigang
中科院分区：
文献类型：
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作者：
Guo, Zhixin;Cheng, Xiaoou;Wang, Zhigang
4EBP1是mTORC1的主要下游因子，PPARγ是关键的脂肪生成相关转录因子。 mTORC1 和 PPAR gamma 与脂质代谢相关。然而，尚不清楚哪种效应蛋白连接 mTORC1 和 PPAR gamma。本研究调查了 4EBP1 与 PPAR γ 之间的相互作用，作为原代牛乳腺上皮细胞 (pBMEC) 中 mTORC1 调节胰岛素诱导的脂质合成和分泌的潜在机制的一部分。雷帕霉素是 mTORC1 的特异性抑制剂，下调 4EBP1 磷酸化以及 PPAR γ 和以下脂肪生成基因的表达：脂质 1、DGAT1、ACC 和 FAS。雷帕霉素还降低细胞内三酰甘油（TAG）的水平； 10种脂肪酸；以及细胞培养基中TAG、棕榈酸(PA)和硬脂酸(SA)的积累。 shRaptor 或 shRheb 灭活 mTORC1 会减弱 TAG 和 PA 的合成和分泌。相反，Rheb过表达激活mTORC1促进4EBP1磷酸化和PPARγ表达，并上调lipin 1、DGAT1、ACC和FAS的mRNA和蛋白水平，而细胞内和细胞外TAG、PA和SA的水平也升高。此外，4EBP1 直接与 PPAR gamma 相互作用。 shRaptor 使 mTORC1 失活，阻止了 PPAR gamma 的核定位。这些结果表明，mTORC1 通过诱导脂质 1、DGAT1、ACC 和 FAS 的表达来调节脂质合成和分泌，这可能是由 4EBP1/PPAR γ 轴介导的。这一发现构成了 pBMEC 中脂质合成和分泌调节的新机制。
4EBP1 is a chief downstream factor of mTORC1, and PPAR gamma is a key lipogenesis-related transcription factor. mTORC1 and PPAR gamma are associated with lipid metabolism. However, it is unknown which effector protein connects mTORC1 and PPAR gamma. This study investigated the interaction between 4EBP1 with PPAR gamma as part of the underlying mechanism by which insulin-induced lipid synthesis and secretion are regulated by mTORC1 in primary bovine mammary epithelial cells (pBMECs). Rapamycin, a specific inhibitor of mTORC1, downregulated 4EBP1 phosphorylation and the expression of PPAR gamma and the following lipogenic genes: lipin 1, DGAT1, ACC, and FAS. Rapamycin also decreased the levels of intracellular triacylglycerol (TAG); 10 types of fatty acid; and the accumulation of TAG, palmitic acid (PA), and stearic acid (SA) in the cell culture medium. Inactivation of mTORC1 by shRaptor or shRheb attenuated the synthesis and secretion of TAG and PA. In contrast, activation of mTORC1 by Rheb overexpression promoted 4EBP1 phosphorylation and PPAR gamma expression and upregulated the mRNA and protein levels of lipin 1, DGAT1, ACC, and FAS, whereas the levels of intracellular and extracellular TAG, PA, and SA also rose. Further, 4EBP1 interacted directly with PPAR gamma. Inactivation of mTORC1 by shRaptor prevented the nuclear location of PPAR gamma. These results demonstrate that mTORC1 regulates lipid synthesis and secretion by inducing the expression of lipin 1, DGAT1, ACC, and FAS, which is likely mediated by the 4EBP1/PPAR gamma axis. This finding constitutes a novel mechanism by which lipid synthesis and secretion are regulated in pBMECs.