Organic cation/carnitine transporter OCTN2 (Slc22a5) is responsible for carnitine transport across apical membranes of small intestinal epithelial cells in mouse
Organic cation/carnitine transporter OCTN2 (Slc22a5) is responsible for carnitine transport across apical membranes of small intestinal epithelial cells in mouse
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DOI：
10.1124/mol.106.024158
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发表时间：
2006-09-01
影响因子：
3.6
通讯作者：
Tsuji, Akira
中科院分区：
文献类型：
--
作者：
Kato, Yukio;Sugiura, Mikihiro;Tsuji, Akira
有机阳离子/肉毒碱转运蛋白 OCTN2 负责肾小管对其内源性底物肉毒碱的重吸收，尽管其在小肠中的生理作用仍存在争议。在这里，我们基于对具有遗传性 octn2 基因缺陷的幼年内脏脂肪变性 (jvs) 小鼠的实验，提出了 OCTN2 在小肠吸收肉碱中起主导作用的直接证据。用尤斯型室系统评估，野生型小鼠小肠顶端表面的肉碱摄取是饱和的，并且高于基底表面的肉碱摄取，而jvs小鼠中几乎不存在具有这些特征的肉碱摄取。在从野生型小鼠获得的分离肠细胞中也证实了肉碱的饱和摄取，并且获得的K-m值（类似于20μM）接近报道的稳定表达小鼠OCTN2（Slc22a5）的人胚胎肾293细胞的肉碱摄取。在各种类型的有机阳离子存在下，肠上皮细胞对肉碱的摄取减少，并且这种抑制谱与小鼠OCTN2的抑制谱相似，而从jvs小鼠获得的肠细胞中肉碱的摄取相当小且不饱和。免疫组织化学和免疫沉淀分析表明 OCTN2 与 PDZK1（一种功能性调节 OCTN2 的衔接蛋白）共定位。免疫电子显微镜观察到吸收性上皮细胞微绒毛中的 OCTN2 和 PDZK1。这些发现表明 OCTN2 主要负责从小鼠小肠上皮细胞顶端表面摄取肉碱，因此它可能是口服 OCTN2 底物治疗剂的有希望的靶标。
The organic cation/carnitine transporter OCTN2 is responsible for renal tubular reabsorption of its endogenous substrate, carnitine, although its physiological role in small intestine remains controversial. Here we present direct evidence for a predominant role of OCTN2 in small intestinal absorption of carnitine based on experiments with juvenile visceral steatosis (jvs) mice, which have a hereditary deficiency of the octn2 gene. Uptake of carnitine, assessed with an Ussing-type chamber system, from the apical surface of the small intestine was saturable and higher than that from the basal surface in wildtype mice, whereas carnitine uptake having these characteristics was almost absent in jvs mice. Saturable uptake of carnitine was also confirmed in isolated enterocytes obtained from wild-type mice, and the K-m value obtained (similar to 20 mu M) was close to that reported for carnitine uptake by human embryonic kidney 293 cells stably expressing mouse OCTN2 ( Slc22a5). The carnitine uptake by enterocytes was decreased in the presence of various types of organic cations, and this inhibition profile was similar to that of mouse OCTN2, whereas uptake of carnitine was quite small and unsaturable in enterocytes obtained from jvs mice. Immunohistochemical and immunoprecipitation analyses suggested colocalization of OCTN2 with PDZK1, an adaptor protein that functionally regulates OCTN2. Immunoelectron microscopy visualized both OCTN2 and PDZK1 in microvilli of absorptive epithelial cells. These findings indicate that OCTN2 is predominantly responsible for the uptake of carnitine from the apical surface of mouse small intestinal epithelial cells, and it may therefore be a promising target for oral delivery of therapeutic agents that are OCTN2 substrates.