Department of Nutrition, Food Science, Physiology and Toxicology, University of Navarra, Pamplona, Spain.
Acta Physiol (Oxf). 2012 May;205(1):82-91. doi: 10.1111/j.1748-1716.2012.02412.x. Epub 2012 Feb 10.
Studies in rodents have shown that leptin controls sugars and glutamine entry in the enterocytes by regulating membrane transporters. Here, we have examined the effect of leptin on sugar and amino acids absorption in the human model of intestinal cells Caco-2 and investigated the transporters involved.
Substrate uptake experiments were performed in Caco-2 cells, grown on plates, in the presence and the absence of leptin, and the expression of the different transporters in brush border membrane vesicles was analysed by Western blot.
Leptin inhibited 0.1 mm α-methyl-D-glucoside uptake after 5 or 30 min treatment and decreased SGLT1 protein abundance in the apical membrane. Uptake of 20 μm glutamine and 0.1 mm phenylalanine was also inhibited by leptin, indicating sensitivity to the hormone of the Na(+) -dependent neutral amino acid transporters ASCT2 and B(0) AT1. This inhibition was accompanied by a reduction in the transporters expression at the brush border membrane. Leptin also inhibited 1 mm proline and β-alanine uptake in Na(+) medium at pH 6, conditions for optimal activity of the H(+) -dependent neutral amino acid transporter PAT1. In this case, abundance of PAT1 in the brush border membrane after leptin treatment was not modified. Interestingly, leptin inhibitory effect on β-alanine uptake was reversed by the PKA inhibitor H-89 suggesting involvement of PKA pathway in leptin's regulation of PAT1 activity.
These data show in human intestinal cells that leptin can rapidly control the activity of physiologically relevant transporters for rich-energy molecules, that is, D-glucose (SGLT1) and amino acids (ASCT2, B(0) AT1 and PAT1).
啮齿动物研究表明，瘦素通过调节膜转运体来控制肠细胞中的糖和谷氨酰胺进入。在此，我们研究了瘦素对人肠细胞 Caco-2 模型中糖和氨基酸吸收的影响，并探讨了涉及的转运体。
在存在和不存在瘦素的情况下，通过平板培养的 Caco-2 细胞进行底物摄取实验，并通过 Western blot 分析刷状缘膜囊泡中不同转运体的表达。
瘦素处理 5 或 30 分钟后，抑制 0.1 mM α-甲基-D-吡喃葡萄糖摄取，并减少顶膜上 SGLT1 蛋白丰度。瘦素还抑制了 20 μm 谷氨酰胺和 0.1 mM 苯丙氨酸的摄取，表明其对 Na(+) 依赖性中性氨基酸转运体 ASCT2 和 B(0) AT1 敏感。这种抑制伴随着刷状缘膜上转运体表达的减少。瘦素还抑制了 pH 6 下 Na(+) 介质中 1 mM 脯氨酸和 β-丙氨酸的摄取，这是 H(+) 依赖性中性氨基酸转运体 PAT1 的最佳活性条件。在这种情况下，瘦素处理后 PAT1 在刷状缘膜中的丰度没有改变。有趣的是，PAT1 对 β-丙氨酸摄取的抑制作用被 PKA 抑制剂 H-89 逆转，这表明 PKA 途径参与了瘦素对 PAT1 活性的调节。
这些数据表明，在人肠细胞中，瘦素可以快速控制与富含能量分子相关的生理相关转运体的活性，即 D-葡萄糖（SGLT1）和氨基酸（ASCT2、B(0) AT1 和 PAT1）。
