Con Pazit, Nitzan Tali, Cnaani Avner
Agricultural Research Organization, Institute of Animal ScienceRishon Letziyon, Israel; Department of Animal Sciences, Faculty of Agriculture, Food and Environment, The Hebrew University of JerusalemRehovot, Israel.
Agricultural Research Organization, Institute of Animal Science Rishon Letziyon, Israel.
Front Physiol. 2017 Jan 23;8:8. doi: 10.3389/fphys.2017.00008. eCollection 2017.
The peptide transporter (PepT) systems are well-known for their importance to protein absorption in all vertebrate species. These symporters use H gradient at the apical membrane of the intestinal epithelial cells to mediate the absorption of small peptides. In fish, the intestine is a multifunctional organ, involved in osmoregulation, acid-base regulation, and nutrient absorption. Therefore, we expected environmental stimuli to affect peptide absorption. We examined the effect of three environmental factors; salinity, pH and feeding, on the expression, activity and localization of three PepT transporters (PepT1a, PepT1b, PepT2) along the intestine of the Mozambique tilapia (). Quantitative real time PCR (qPCR) analysis demonstrated that the two PepT1 variants are typical to the proximal intestinal section while PepT2 is typical to the distal intestinal sections. Immunofluorescence analysis with custom-made antibodies supported the qPCR results, localized both transporters on the apical membrane of enterocytes and provided the first evidence for the participation of PepT2 in nutrient absorption. This first description of segment-specific expression and localization points to a complementary role of the different peptide transporters, corresponding to the changes in nutrient availability along the intestine. Both gene expression and absorption activity assays showed that an increase in water salinity shifted the localization of the PepT genes transcription and activity down along the intestinal tract. Additionally, an unexpected pH effect was found on the absorption of small peptides, with increased activity at higher pH levels. This work emphasizes the relationships between different functions of the fish intestine and how they are affected by environmental conditions.
肽转运体（PepT）系统因其对所有脊椎动物物种蛋白质吸收的重要性而闻名。这些同向转运体利用肠道上皮细胞顶端膜上的H梯度来介导小肽的吸收。在鱼类中，肠道是一个多功能器官，参与渗透压调节、酸碱调节和营养吸收。因此，我们预期环境刺激会影响肽的吸收。我们研究了三个环境因素；盐度、pH值和投喂，对莫桑比克罗非鱼肠道中三种肽转运体（PepT1a、PepT1b、PepT2）的表达、活性和定位的影响。定量实时PCR（qPCR）分析表明，两种PepT1变体是近端肠道段的典型特征，而PepT2是远端肠道段的典型特征。用定制抗体进行的免疫荧光分析支持了qPCR结果，将这两种转运体定位在肠上皮细胞的顶端膜上，并为PepT2参与营养吸收提供了首个证据。这种对段特异性表达和定位的首次描述表明不同肽转运体具有互补作用，这与肠道中营养物质可用性的变化相对应。基因表达和吸收活性测定均表明，水盐度的增加会使PepT基因转录和活性的定位沿肠道向下移动。此外，还发现了一个关于小肽吸收的意外pH效应，即在较高pH水平下活性增加。这项工作强调了鱼类肠道不同功能之间的关系以及它们如何受到环境条件的影响。
