Ma Guo-Guang, Shi Bin, Zhang Xue-Peng, Qiu Yue, Tu Guo-Wei, Luo Zhe
Department of Critical Care Medicine, Zhongshan Hospital, Fudan University, Shanghai 200032, China.
Department of Emergency Intensive Care Unit, Yangpu Hospital, Tongji University, Shanghai 200090, China.
Ann Transl Med. 2019 Sep;7(18):473. doi: 10.21037/atm.2019.07.103.
The transcellular transport of muramyl dipeptide (MDP) mediated by peptide transporter (PepT1) involves the translocation into intestinal epithelial cell (IEC) stage and the transport out of IEC stage. However, its mechanism has not been fully understood. This study aimed to investigate the pathways and mechanisms of MDP transcellular transport in enterogenous infection.
Firstly, experimental rats were randomly divided into three groups: sham-operation (sham group), MDP perfusion (MDP group), and PepT1 competitive inhibition (MDP + Gly-Gly group). Then, the overall survival (OS) and intestinal weight were measured in MDP and MDP + Gly-Gly group. HE staining was performed to observe the pathological changes of the small intestine. The levels of IL-6, IL-1b, IL-8, IL-10, TNF-α, and nitric oxide (NO) in rat serum and small intestine were determined by ELISA. To further verify the pathways and mechanisms of MDP transcellular transport from IEC in intestinal inflammatory damage, the NFκB inhibitor, PDTC, was used to treated lamina propria macrophages in small intestinal mucosa in sham, MDP, and MDP + Gly-Gly groups. Finally, the expression of CD80/86 and the antigen presentation of dendritic cells (DCs) were measured by flow cytometry.
MDP infusion was able to induce death, weight loss, and intestinal pathological injury in rats. Competitive binding of Gly-Gly to PepT1 effectively inhibited these effects induced by MDP. As well, competitive of PepT1 by Gly-Gly inhibited inflammation-related cytokines induced by MDP in rat serum and small intestine. Furthermore, we also found that MDP transported by PepT1 contributes to activation of macrophages and antigen presentation of DCs.
PepT1-NFκB signal is pivotal for activation of intestinal inflammatory response and MDP transcellular transport.
肽转运体（PepT1）介导的胞壁酰二肽（MDP）跨细胞转运涉及进入肠上皮细胞（IEC）阶段和从IEC阶段转运出。然而，其机制尚未完全阐明。本研究旨在探讨MDP在肠源性感染中跨细胞转运的途径和机制。
首先，将实验大鼠随机分为三组：假手术组（假手术组）、MDP灌注组（MDP组）和PepT1竞争性抑制组（MDP + 甘氨酰甘氨酸组）。然后，测量MDP组和MDP + 甘氨酰甘氨酸组的总生存期（OS）和肠重量。进行苏木精-伊红（HE）染色以观察小肠的病理变化。通过酶联免疫吸附测定（ELISA）法测定大鼠血清和小肠中白细胞介素-6（IL-6）、白细胞介素-1β（IL-1β）、白细胞介素-8（IL-8）、白细胞介素-10（IL-10）、肿瘤坏死因子-α（TNF-α）和一氧化氮（NO）的水平。为进一步验证MDP在肠道炎症损伤中从IEC跨细胞转运的途径和机制，使用核因子κB（NFκB）抑制剂吡咯烷二硫代氨基甲酸盐（PDTC）处理假手术组、MDP组和MDP + 甘氨酰甘氨酸组小肠黏膜固有层巨噬细胞。最后，通过流式细胞术检测树突状细胞（DCs）的CD80/86表达和抗原呈递。
MDP输注能够诱导大鼠死亡、体重减轻和肠道病理损伤。甘氨酰甘氨酸与PepT1的竞争性结合有效抑制了MDP诱导的这些效应。同样，甘氨酰甘氨酸对PepT1的竞争性抑制也抑制了MDP在大鼠血清和小肠中诱导的炎症相关细胞因子。此外，我们还发现由PepT1转运的MDP有助于巨噬细胞的激活和DCs的抗原呈递。
PepT1-NFκB信号对于激活肠道炎症反应和MDP跨细胞转运至关重要。
