The pathways and mechanisms of muramyl dipeptide transcellular transport mediated by PepT1 in enterogenous infection

Abstract

Background: 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.Methods: 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.Results: 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.Conclusions: PepT1-NFκB signal is pivotal for activation of intestinal inflammatory response and MDP transcellular transport.

Muramyl Dipeptide Causes Mitochondrial Dysfunction and Intestinal Inflammatory Cytokine Responses in Rats

“…Furthermore, the IL-6 level was significantly higher in the 15 mg/kg MDP+LPS group than in the 1.5 mg/kg MDP+LPS group. The lung microbiome in a sepsis mouse model is enriched with intestine-associated bacteria (23), and the lung tissues of rats collected after enema with MDP have elevated NOD2 protein expression and increased lung injury (9). Therefore, the effects of MDP are not limited to the intestine; they can be elicited through PepT1 in the intestinal epithelium, crossing the intestinal mucosal barrier into the mesenteric lymph nodes and portal system, followed by circulation in the body to distant organs, such as the lungs, where NOD2 recognizes MDP.…”

“…Our previous study showed that the degree of pathological damage was higher in rats infused with MDP in the small intestine than in the control group, as were the expressions of signaling molecules (i.e., NOD2 and RIP2) and inflammatory mediators (i.e., myeloperoxidase, IL-8, and TNF-α). However, competitive inhibition of PepT1 function with short peptide enteral nutrition (SPEN) decreased the degree of MDP-induced intestinal injury, NOD2 and RIP2 mRNA expression, and the levels of inflammatory factors (9). Thus, MDP can cause bacterial product translocation through PepT1 intracellular transport, and SPEN competitively binds PepT1 with MDP, attenuating the intestinal inflammatory response.…”

Dexmedetomidine inhibits mitochondria damage and apoptosis of enteric glial cells in experimental intestinal ischemia/reperfusion injury via SIRT3-dependent PINK1/HDAC3/p53 pathway

“…The subsequent procedures were conducted as per the kit instructions. The optical density (OD) value at a wavelength of 450 nm was measured [ 29 ].…”

Ion channels and transporters regulate nutrient absorption in health and disease

“…Dietary proteins are cleaved into oligopeptides in the lumen and further processed into small peptides (dipeptides and tripeptides) and free amino acids (FAA). Ma GG et al constructed a mouse model, and conducted haematoxylin and eosin (HE) staining, enzyme‐linked immunosorbent assay (ELISA) and other experimental studies to show that PEPT1 (SLC15A1), a high‐capacity/low‐affinity peptide transporter, can achieve proton coupling absorption of more than 8000 different dipeptides and tripeptides, a variety of peptide‐like compounds are also PEPT1 transport substrates, including specific immune stimulants, angiotensin‐converting enzyme inhibitors and β‐lactam antibiotics 14,15 . The peptides in IECs are further hydrolyzed to FAA, and a small part of the absorbed oligopeptides are transported out by the H + ‐dependent peptide transport system on the basement membrane.…”