Laboratory of Biological Science, Graduate School of Frontier Biosciences and Graduate School of Medicine, Osaka University, Osaka, Japan.
Laboratory of Molecular Function of Food, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, Japan.
Gastroenterology. 2013 Feb;144(2):369-380. doi: 10.1053/j.gastro.2012.10.035. Epub 2012 Oct 23.
BACKGROUND & AIMS: The intestinal symport system moves nutrients across membranes via transporters, and is required for absorption of major nutrients such as glucose, amino acids, and bile acids (which are required for fat absorption). Most of these transporters are regulated by Na(+), but the standard diet does not provide sufficient levels of this ion to the intestinal lumen to support this system. Claudins form paracellular barriers between epithelial cells, and claudin-2 and -15 regulate paracellular ion flow in the intestine. We investigated how cell adherence, tight junction barriers, and claudins regulate the supply of Na(+) to the intestinal lumen in mice.
We created Cldn2(-/-)Cldn15(-/-) (double-knockout) mice and analyzed intestinal tissues by reverse-transcription polymerase chain reaction, immunoblot, immunofluorescence, electron microscopy, and H&E analyses. We also measured paracellular Na(+) flow, luminal Na(+) concentration, and absorption of glucose, amino acids, and fats, which were administered orally to the mice.
Paracellular flow of Na(+) from the intestinal submucosa to the lumen, and therefore the concentration of Na(+) in the lumen, was greatly reduced in intestines of Cldn2(-/-)Cldn15(-/-) mice. Absorption of glucose, amino acids, and fats also decreased in the mice, which died by postnatal day 25 from malnutrition.
The paracellular flow of Na(+) from the intestinal submucosa is regulated by tight junctions that contain claudin-2 and -15. This system is required for the absorption of glucose, amino acids, and fats; disruption of this system in mice leads to infant death as a result of malabsorption.
肠道协同转运系统通过转运蛋白将营养物质穿过细胞膜转运，是吸收葡萄糖、氨基酸和胆汁酸等主要营养物质所必需的（这些物质是脂肪吸收所必需的）。这些转运蛋白大多数受 Na(+)调节，但标准饮食并不能向肠腔提供足够水平的这种离子来支持该系统。 Claudin 蛋白在肠上皮细胞之间形成细胞旁屏障， Claudin-2 和 Claudin-15 调节肠道细胞旁离子流。我们研究了细胞黏附、紧密连接屏障和 Claudin 蛋白如何调节小鼠肠腔中 Na(+)的供应。
我们构建了 Cldn2(-/-)Cldn15(-/-)（双敲除）小鼠，并通过逆转录聚合酶链反应、免疫印迹、免疫荧光、电子显微镜和 H&E 分析分析了肠道组织。我们还测量了细胞旁 Na(+)流、腔 Na(+)浓度以及葡萄糖、氨基酸和脂肪的吸收，这些物质通过口服给予小鼠。
Claudin-2(-/-)Claudin-15(-/-) 小鼠肠组织中，Na(+)从肠黏膜下层向腔的细胞旁流动，因此腔中的 Na(+)浓度大大降低。葡萄糖、氨基酸和脂肪的吸收也减少了，这些小鼠在出生后第 25 天因营养不良而死亡。
Claudin-2 和 Claudin-15 组成的紧密连接调节 Na(+)从肠黏膜下层的细胞旁流动。该系统是葡萄糖、氨基酸和脂肪吸收所必需的；该系统在小鼠中的破坏导致婴儿因吸收不良而死亡。
