Food Science and Human Nutrition Department and Center for Nutritional Sciences, College of Agricultural and Life Sciences, University of Florida, Gainesville, Florida.
Food Science and Human Nutrition Department and Center for Nutritional Sciences, College of Agricultural and Life Sciences, University of Florida, Gainesville, Florida
Am J Physiol Gastrointest Liver Physiol. 2015 Feb 1;308(3):G171-8. doi: 10.1152/ajpgi.00021.2014. Epub 2014 Nov 26.
ZIP14 is a zinc transport protein with high expression in the small intestine and liver. Zip14 is upregulated during endotoxemia and leads to increased liver zinc content and transient hypozinemia. Since body zinc status and inflammation are associated with changes in intestinal permeability, we hypothesized that ZIP14 may influence intestinal permeability. Wild-type (WT) and Zip14 knockout (KO) mice were used to determine ZIP14-associated intestinal zinc metabolism and effects on permeability. Fractionation of plasma membranes revealed that ZIP14 is localized to the basolateral membrane of enterocytes. Studies utilizing (65)Zn administered by subcutaneous injection revealed greater zinc accumulation in the SI of Zip14 KO mice compared with WT mice. Isolation of endosomes confirmed the presence of ZIP14. Quantification of endosomal zinc concentration by FluoZin-3AM fluorescence demonstrated that zinc is trapped in endosomes of Zip14 KO mice. Intestinal permeability assessed both by plasma FITC-dextran following gavage and by serum endotoxin content was greater in Zip14 KO mice. Threonine phosphorylation of the tight junction protein occludin, which is necessary for tight junction assembly, was reduced in KO mice. Claudin 1 and 2, known to have an inverse relationship in regards to tight junction integrity, reflected impaired barrier function in KO jejunum. These data suggest involvement of ZIP14 in providing zinc for a regulatory role needed for maintenance of the intestinal barrier. In conclusion, ZIP14 is a basolaterally localized protein in enterocytes and is involved in endosomal trafficking of zinc and is necessary for proper maintenance of intestinal tight junctions.
ZIP14 是一种锌转运蛋白，在小肠和肝脏中表达水平较高。ZIP14 在内毒素血症时上调，导致肝脏锌含量增加和短暂的低锌血症。由于机体锌状态和炎症与肠道通透性变化有关，我们假设 ZIP14 可能影响肠道通透性。使用野生型（WT）和 Zip14 敲除（KO）小鼠来确定 ZIP14 相关的肠道锌代谢和对通透性的影响。质膜的分级分离表明 ZIP14 定位于肠上皮细胞的基底外侧膜。利用皮下注射（65）Zn 的研究表明，与 WT 小鼠相比，Zip14 KO 小鼠的 SI 中锌积累更多。内体的分离证实了 ZIP14 的存在。通过 FluoZin-3AM 荧光对内体锌浓度的定量表明，锌被捕获在 Zip14 KO 小鼠的内体中。通过灌胃后血浆 FITC-右旋糖酐和血清内毒素含量评估的肠道通透性在 Zip14 KO 小鼠中更大。紧密连接蛋白 occludin 的丝氨酸磷酸化减少，这对于紧密连接组装是必需的，在 KO 小鼠中减少。已知紧密连接完整性呈负相关的 Claudin 1 和 2 在 KO 空肠中反映出屏障功能受损。这些数据表明 ZIP14 参与提供锌以发挥维持肠道屏障所需的调节作用。总之，ZIP14 是肠上皮细胞基底外侧定位的蛋白，参与锌的内体运输，是维持肠道紧密连接所必需的。
