USDA/ARS Children's Nutrition Research Center, Dept. of Pediatrics, Baylor College of Medicine, 1100 Bates St., Houston, TX 77030, USA.
Am J Physiol Endocrinol Metab. 2011 Mar;300(3):E554-63. doi: 10.1152/ajpendo.00620.2010. Epub 2010 Dec 21.
Glucagon-like peptide-2 (GLP-2) is a nutrient-responsive neuropeptide that exerts diverse actions in the gastrointestinal tract, including enhancing mucosal cell survival and proliferation. GLP-2 stimulates mucosal growth in vivo with an increased rate of protein synthesis. However, it was unclear whether GLP-2 can directly stimulate protein synthesis. The objective was to test critically whether GLP-2 receptor (GLP-2R) activation directly stimulates protein synthesis through a PI 3-kinase-dependent Akt-mTOR signaling pathway. HEK 293 cells (transfected with human GLP-2R cDNA) were treated with human GLP-2 with/without pretreatment of PI 3-kinase inhibitor (LY-294002) or mTOR inhibitor (rapamycin). Results show that 1) GLP-2 specifically bound to GLP-2R overexpressed in the HEK cells with K(a) = 0.22 nM and B(max) = 321 fmol/μg protein; 2) GLP-2-stimulated protein synthesis was dependent on the amount of GLP-2R cDNA and the dosage of GLP-2 and reached the plateau among 0.2-2 nM GLP-2; 3) GLP-2-stimulated protein synthesis was abolished by the PI 3-kinase inhibitor and mTOR inhibitor; and 4) GLP-2-mediated stimulation of phosphorylation on Akt and mTOR was dependent on the amount of GLP-2R cDNA transfected and the dosage of GLP-2. In addition, GLP-2-mediated action and signaling in regulation of protein synthesis were confirmed in mouse hippocampal neurons (expressing native GLP-2R). GLP-2 directly stimulated protein synthesis of primary cultured neurons in dosage-dependent, PI 3-kinase-dependent, and rapamycin-sensitive manners, which linked with activation of Akt-mTOR signaling pathway as well. We conclude that GLP-2R activation directly stimulates protein synthesis by activating the PI 3-kinase-dependent Akt-mTOR signaling pathway. GLP-2-stimulated protein synthesis may be physiologically relevant to maintaining neuronal long-term potentiation and providing secondary mediators (namely neuropeptides or growth factors).
胰高血糖素样肽-2（GLP-2）是一种营养感应神经肽，在胃肠道中发挥多种作用，包括增强黏膜细胞的存活和增殖。GLP-2 体内刺激黏膜生长，增加蛋白质合成率。然而，尚不清楚 GLP-2 是否可以直接刺激蛋白质合成。本研究旨在通过 PI3-激酶依赖的 Akt-mTOR 信号通路，严格测试 GLP-2 受体（GLP-2R）激活是否直接刺激蛋白质合成。用/不用 PI3-激酶抑制剂（LY-294002）或 mTOR 抑制剂（rapamycin）预处理，处理转染人 GLP-2R cDNA 的 HEK293 细胞。结果表明：1）GLP-2 特异性结合于过表达的 HEK 细胞中的 GLP-2R，K(a) = 0.22 nM，B(max) = 321 fmol/μg 蛋白；2）GLP-2 刺激的蛋白质合成依赖于 GLP-2R cDNA 的量和 GLP-2 的剂量，在 0.2-2 nM GLP-2 之间达到平台；3）PI3-激酶抑制剂和 mTOR 抑制剂可阻断 GLP-2 刺激的蛋白质合成；4）GLP-2 介导的 Akt 和 mTOR 磷酸化刺激依赖于转染的 GLP-2R cDNA 的量和 GLP-2 的剂量。此外，在表达天然 GLP-2R 的小鼠海马神经元中证实了 GLP-2 调节蛋白质合成的作用和信号传导。GLP-2 以剂量依赖、PI3-激酶依赖和 rapamycin 敏感的方式直接刺激原代培养神经元的蛋白质合成，这也与 Akt-mTOR 信号通路的激活有关。我们的结论是，GLP-2R 激活通过激活 PI3-激酶依赖的 Akt-mTOR 信号通路直接刺激蛋白质合成。GLP-2 刺激的蛋白质合成可能与维持神经元长时程增强和提供二级介质（即神经肽或生长因子）有关。
