Hypoxia increases fetal hepatic insulin-like growth factor binding protein-1 (IGFBP-1) phosphorylation mediated by mechanistic target of rapamycin (mTOR) inhibition. Whether maternal nutrient restriction (MNR) causes fetal hypoxia remains unclear. We used fetal liver from a baboon (Papio sp.) model of intrauterine growth restriction due to MNR (70% global diet of Control) and liver hepatocellular carcinoma (HepG2) cells as a model for human fetal hepatocytes and tested the hypothesis that mTOR-mediated IGFBP-1 hyperphosphorylation in response to hypoxia requires hypoxia-inducible factor-1α (HIF-1α) and regulated in development and DNA-damage responses-1 (REDD-1) signaling. Western blotting (n = 6) and immunohistochemistry (n = 3) using fetal liver indicated greater expression of HIF-1α, REDD-1 as well as erythropoietin and its receptor, and vascular endothelial growth factor at GD120 (GD185 term) in MNR versus Control. Moreover, treatment of HepG2 cells with hypoxia (1% pO₂) (n = 3) induced REDD-1, inhibited mTOR complex-1 (mTORC1) activity and increased IGFBP-1 secretion/phosphorylation (Ser101/Ser119/Ser169). HIF-1α inhibition by echinomycin or small interfering RNA silencing prevented the hypoxia-mediated inhibition of mTORC1 and induction of IGFBP-1 secretion/phosphorylation. dimethyloxaloylglycine (DMOG) induced HIF-1α and also REDD-1 expression, inhibited mTORC1 and increased IGFBP-1 secretion/phosphorylation. Induction of HIF-1α (DMOG) and REDD-1 by Compound 3 inhibited mTORC1, increased IGFBP-1 secretion/ phosphorylation and protein kinase PKCα expression. Together, our data demonstrate that HIF-1α induction, increased REDD-1 expression and mTORC1 inhibition represent the mechanistic link between hypoxia and increased IGFBP-1 secretion/phosphorylation. We propose that maternal undernutrition limits fetal oxygen delivery, as demonstrated by increased fetal liver expression of hypoxia-responsive proteins in baboon MNR. These findings have important implications for our understanding of the pathophysiology of restricted fetal growth.

中文翻译：

---

宫内生长受限狒狒胎儿和细胞培养中缺氧与胰岛素样生长因子结合蛋白-1磷酸化的相关机制

缺氧会增加雷帕霉素 (mTOR) 抑制机制靶点介导的胎儿肝脏胰岛素样生长因子结合蛋白-1 (IGFBP-1) 磷酸化。母体营养限制 (MNR) 是否会导致胎儿缺氧仍不清楚。我们使用了狒狒的胎肝（狒狒sp.) 由于 MNR（70% 的全球对照饮食）和肝肝细胞癌 (HepG2) 细胞作为人类胎儿肝细胞模型的宫内生长受限模型，并测试了 mTOR 介导的 IGFBP-1 过度磷酸化响应缺氧的假设需要缺氧诱导因子-1α（HIF-1α）并在发育和DNA损伤反应-1（REDD-1）信号传导中受到调节。使用胎儿肝脏的蛋白质印迹 (n = 6) 和免疫组织化学 (n = 3) 表明，在 MNR 中，HIF-1α、REDD-1 以及促红细胞生成素及其受体和血管内皮生长因子在 GD120（GD185 术语）的表达高于 MNR控制。此外，用缺氧 (1% pO ₂) (n = 3) 诱导 REDD-1，抑制 mTOR complex-1 (mTORC1) 活性并增加 IGFBP-1 分泌/磷酸化 (Ser101/Ser119/Ser169)。棘霉素或小干扰 RNA 沉默对 HIF-1α 的抑制阻止了缺氧介导的 mTORC1 抑制和 IGFBP-1 分泌/磷酸化的诱导。二甲基草酰甘氨酸 (DMOG) 诱导 HIF-1α 和 REDD-1 表达，抑制 mTORC1 并增加 IGFBP-1 分泌/磷酸化。化合物 3 对 HIF-1α (DMOG) 和 REDD-1 的诱导抑制了 mTORC1，增加了 IGFBP-1 分泌/磷酸化和蛋白激酶 PKCα 表达。总之，我们的数据表明 HIF-1α 诱导、REDD-1 表达增加和 mTORC1 抑制代表了缺氧和 IGFBP-1 分泌/磷酸化增加之间的机制联系。我们提出母体营养不良会限制胎儿的氧气输送，正如狒狒 MNR 中缺氧反应蛋白的胎儿肝脏表达增加所证明的那样。这些发现对我们理解胎儿生长受限的病理生理学具有重要意义。