Escherichia coli Nissle 1917 Protects against Sepsis-Induced Intestinal Damage by Regulating the SCFA/GPRs Signaling Pathway

Abstract

This study explores whether Escherichia coli Nissle 1917 (EcN) can preserve the integrity of the intestinal barrier by modulating the metabolism pathway of short-chain fatty acids (SCFAs) in a C57BL/6J mouse model of lipopolysaccharide (LPS)-induced acute enteritis and a model of a Caco-2 monolayer. The study involved establishing a septic shock model in mice through lipopolysaccharide (LPS) injection. Clinical scores and intestinal permeability were meticulously documented. Immunofluorescence was utilized to localize the tight junction proteins. A quantitative real-time polymerase chain reaction (qRT-PCR) was employed to assess the expression of G protein-coupled receptors (GPRs) signaling. Additionally, the supplement of acetate and butyrate with Caco-2 monolayers to elucidate the potential of EcN in augmenting the intestinal barrier primarily via the modulation of SCFAs and qRT-PCR was performed to detect the expression of tight junction proteins and the activation of the GPRs protein signaling pathway. EcN mitigated the clinical symptoms and reduced intestinal permeability in the colon of LPS-induced mice. It also enhanced the production of SCFAs in the gut and upregulated the expression of SCFA receptor proteins GPR41 and GPR43 in the colon tissue. Our findings reveal that EcN activates the SCFA/GPRs pathway, thereby preserving intestinal barrier function and alleviating inflammation in a mouse sepsis model.

Keywords: Escherichia coli Nissle 1917; G protein-coupled receptors (GPRs); intestinal barrier; short-chain fatty acids.

Figure 1

The detailed animal testing process. i.g., intragastric administration; i.p., intraperitoneal injection.

Figure 2

(A) The clinical status score after modeling. (B) Plasma FITC-dextran 4000 Da (FD-4) concentration. (C,D) Macroscopic pictures of the colon. (E,F) H&E staining of the colon. (G–I) Immunofluorescence of tight junction proteins. DAPI (blue), ZO-1 (green), Occludin (red). Control, control group; LPS, LPS group; EcN, EcN group; EcN + LPS, EcN + LPS group. All data are shown as mean ± SEM (n = 3 for each group). * p < 0.05, ** p < 0.01, LPS versus EcN + LPS.

Figure 3

Effect of EcN on the gut microbiota of mice. Indicators of community diversity Chao1 (A) and Shannon (B). (C) Rank abundance curve in OTU level. (D) PLS-DA analysis in genus level. (E) Phylum abundance and (F) specifies abundance diversity between different groups. Control, control group; LPS, LPS group; EcN, EcN group; EcN + LPS, EcN + LPS group. Data are expressed as the means ± SEM (n = 3 for each group). * p < 0.05, LPS versus Control; # p < 0.05, LPS versus EcN + LPS.

Figure 4

Effect of EcN on the gut microbiota of mice. Differentially abundant microbial taxa identified by LEfSe (A,B) with an LDA score. (C) KEGG pathway analysis based on different abundant microbiota. Control, control group; LPS, LPS group; EcN, EcN group; EcN + LPS, EcN + LPS group.

Figure 5

Effect of EcN on the content of SCFAs and GPRs in mouse feces. (A) acetic acid, (B) propionate acid, (C) isobutyric acid, (D) butyric acid, (E) valeric acid, and (F) isovalent acid. Effect of EcN on the expression of short-chain fatty acid receptor proteins, GPR43 (G) GPR41 (H) in mice colon. EcN, EcN group; EcN + LPS, EcN + LPS group. Data are expressed as the means ± SEM (n = 3 for each group). ns, no statistical significance, * p < 0.05, ** p < 0.01, LPS versus EcN + LPS.

Figure 6

Supplement of acetate and butyrate on the expression of ZO-1 (A), Occludin (B), Claudin-1 (C), GPR43 (D), and GPR41 (E) in the Caco-2 monolayer. Control, control group; LPS, LPS group; Acetate + LPS, Acetate + LPS group Butyrate + LPS, Butyrate + LPS group. Data are expressed as the means ± SEM (n = 3 for each group). * p < 0.05, ** p < 0.01, *** p < 0.01, LPS versus Acetate + LPS. # p < 0.05, ## p < 0.01, ### p < 0.01, LPS versus Butyrate + LPS.