Intestinal absorption of peptides is vital for the overall health and productivity of dairy cows. This study investigated the regulation, uptake and transport of dipeptides in bovine intestinal epithelial cells (BIECs). We also evaluated the effects of time, pH, concentration of the dipeptides, temperature, presence of diethylpyrocarbonate (DEPC)—an inhibitor of PepT1, and other dipeptides (Met-Met, Lys-Lys or Met-Lys), on the uptake and transport of Gly-Sar-FITC, which was a common fluorophore-labelled dipeptide. Under controlled experiments, BIECs were treated with 25 μM LY294002 (a phosphatidylinositol 3-kinase (PI3K) inhibitor) and 25 μM Perifosine (a protein kinase B (AKT) inhibitor). The subsequent expression of PepT1 in the BIECs was assessed by reverse transcriptase polymerase chain reaction (RT-PCR) and Western blotting. It was found that the uptake and transport of Gly-Sar-FITC were significant high at 37℃ than that at 4℃. The optimal pH for transport and uptake of Gly-Sar-FITC was 6.0–6.5, whereas the two properties decreased significantly in the presence of DEPC, Met-Met, Lys-Lys and Met-Lys (p < 0.05). The apical-to-basolateral transport was also found to be significantly higher than the reverse transport (p < 0.05). PI3K and AKT inhibitors were found to significantly suppress the expression of PepT1, thus impairing uptake and transport of Gly-Sar-FITC. Findings of this study thus suggest that the uptake and transport of Gly-Sar-FITC in BIECs are mediated by PepT1, and the PI3K/AKT signalling pathway regulates the absorption of small peptides.

中文翻译：

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牛肠上皮细胞 Gly-Sar 摄取和转运的特性及调控

肽的肠道吸收对奶牛的整体健康和生产力至关重要。本研究调查了牛肠上皮细胞 (BIEC) 中二肽的调节、摄取和转运。我们还评估了时间、pH、二肽浓度、温度、焦碳酸二乙酯 (DEPC)（一种 PepT1 抑制剂）和其他二肽（Met-Met、Lys-Lys 或 Met-Lys）对摄取和Gly-Sar-FITC 的转运，这是一种常见的荧光团标记的二肽。在对照实验中，用 25 μM LY294002（一种磷脂酰肌醇 3-激酶 (PI3K) 抑制剂）和 25 μM Perifosine（一种蛋白激酶 B (AKT) 抑制剂）处理 BIEC。通过逆转录酶聚合酶链反应 (RT-PCR) 和蛋白质印迹评估 BIECs 中 PepT1 的后续表达。发现37℃时Gly-Sar-FITC的吸收和转运明显高于4℃。Gly-Sar-FITC 转运和摄取的最佳 pH 值为 6.0-6.5，而在 DEPC、Met-Met、Lys-Lys 和 Met-Lys 存在下这两种性质显着降低（p  < 0.05)。还发现从顶端到基底外侧的转运显着高于反向转运（p  < 0.05）。发现 PI3K 和 AKT 抑制剂显着抑制 PepT1 的表达，从而削弱 Gly-Sar-FITC 的摄取和转运。因此，本研究的结果表明，BIECs 中 Gly-Sar-FITC 的摄取和转运是由 PepT1 介导的，而 PI3K/AKT 信号通路调节小肽的吸收。