Bacillus subtilis ameliorates Escherichia coli-induced endometritis in mice via maintaining endometrial barrier and inhibiting inflammatory response

Intestinal inflammation exacerbates endometritis through succinate production by gut microbiota and SUCNR1-mediated proinflammatory response

Endometritis poses higher health risks to women. Clinical practice has found that gastrointestinal dysfunction is more likely to lead to the occurrence of endometritis. However, the mechanism is unclear. This study explored the influence and mechanism of DSS-induced intestinal inflammation on endometritis. Our findings demonstrate that DSS-induced intestinal inflammation can worsen LPS-induced endometritis in mice, and this effect is dependent on the gut microbiota, as depleting the gut microbiota eliminates this protective effect. Similarly, FMT from DSS-treated mice to recipient mice exacerbates LPS-induced endometritis. In addition, treatment of DSS disrupted an imbalance of succinate-producing and succinate-consuming bacteria and increased the levels of succinate in the gut and uterine tissues. Furthermore, treatment with succinate aggravates LPS-induced endometritis by activating the succinate receptor 1 (SUCNR1), evidenced by inhibition of the activation of SUCNR1 reversed the inflammatory response in uterine tissues induced by succinate during endometritis induced by LPS. Collectively, the results suggested that dysbiosis of the gut microbiota exacerbates LPS-induced endometritis by production and migration of succinate from gut to uterine tissues via the gut-uterus axis, then activates the SUCNR1. This identifies gut-derived succinate as a novel target for treating endometritis, and it indicates that targeting the gut microbiota and its metabolism could be a potential strategy for intervention in endometritis.

Selenomethionine protects against Escherichia coli-induced endometritis by inhibiting inflammation and necroptosis via regulating the PPAR-γ/NF-κB pathway

Endometritis, inflammation of the endometrium, is a major cause of subfertility in women. Selenomethionine (SeMet)is known to exert anti-inflammatory activity. We aimed to verify the protective roles of SeMet on Escherichia coli (E.coli)-induced endometritis. The extent of uterus damage was assessed by detecting histopathology and inflammatory mediators. The results revealed that SeMet significantly prevented E.coli-induced endometritis by attenuating uterine histopathology and inflammatory cytokine production. E.coli-induced MPO activity and MDA content were inhibited by SeMey. E.coli-induced ZO-1 and occludin were upregulated by SeMet. E.coli-induced necroptosis was also inhibited by SeMet. Additionally, E.coli-induced NF-κB activation was alleviated by SeMet. PPAR-γ expression was upregulated by SeMet. Notably, the protective effects of SeMet on endometritis were abolished by a PPAR-γ inhibitor. In conclusion, SeMet inhibits E.coli-induced endometritis by attenuating inflammation and necroptosis, which is mediated by the PPAR-γ/NF-κB signaling pathway.

Subacute Ruminal Acidosis as a Potential Factor that Induces Endometrium Injury in Sheep

The demand for economic benefits has led to an increase in the proportion of high-concentrate (HC) feed in the ruminant diet, resulting in an increased incidence of subacute ruminal acidosis (SARA). During SARA, a high concentration of lipopolysaccharide (LPS) translocated in the rumen induces a systemic inflammatory response. Inflammatory diseases, such as endometritis and mastitis, are often associated with SARA; however, in sheep, the mechanism of the effect of SARA on the endometrium has rarely been reported. Therefore, the aim of this study was to investigate, for the first time, the influence of LPS translocation on endometrial tight junctions (TJs) during SARA in sheep. The results showed that LPS and TNFα levels in the ruminal fluid, serum, and endometrial tissue supernatant during SARA increased, transcription levels of TLR4, NFκB, and TNFα in the endometrium increased, the protein expression level of claudin-1 in the endometrium increased, and the protein expression level of occludin decreased. 17β-estradiol (E₂) inhibits claudin-1 protein expression and promotes occludin expression, and progesterone (P₄) promotes claudin-1 protein expression and inhibits occludin protein expression. E₂ and P₄ regulate claudin-1 and occludin protein expression through their receptor pathways. Here, we found that LPS hindered the regulatory effect of E₂ and P₄ on endometrial TJs by inhibiting their receptor expression. The results of this study indicate that HC feeding can cause SARA-induced LPS translocation in sheep, increase susceptibility to systemic inflammation, induce the endometrial inflammatory response, and cause endometrial epithelial TJ damage directly and/or by obstructing E₂ and P₄ function. LPS translocation caused by SARA has also been suggested to induce an endometrial inflammatory response, resulting in endometrial epithelial barrier damage and physiological dysfunction, which seriously affects ruminant production. Therefore, this study provides new evidence that SARA is a potential factor that induces systemic inflammation in ruminants. It provides theoretical support for research on the prevention of endometritis in ruminants.

Dietary Tryptophan-Mediated Aryl Hydrocarbon Receptor Activation by the Gut Microbiota Alleviates Escherichia coli-Induced Endometritis in Mice

Intestinal microbiota-mediated aryl hydrocarbon receptor (AhR) activation plays an important role in host-microbiota interactions and disease development. However, whether AhR activation mediates infection-induced inflammation in remote organs is not clear. The purpose of this study is to assess the effects and underlying mechanism of AhR activation and gut microbiota-mediated dietary tryptophan (Trp) metabolism on infection-induced inflammation using an Escherichia coli (E. coli)-induced endometritis model in mice. We found that AhR activation by 6-formylindolo (3,2-b) carbazole (Ficz), which is an AhR agonist derived from the photooxidation of Trp, alleviated E. coli-induced endometritis by repairing barrier function and inhibiting inflammatory responses, while inhibition of AhR by CH223191, which is a synthetic AhR antagonist, aggravated E. coli-induced endometritis. Gut dysbiosis damaged AhR activation and exacerbated E. coli-induced endometritis in mice, which responded to the reduced abundance of AhR ligand producers, such as Lactobacillus spp. Supplementation with dietary Trp ameliorated E. coli-induced endometritis in a microbiota-dependent manner, which was associated with the production of AhR ligands. Administration of AhR ligands, including indole and indole aldehyde, but not indole-3-propionic acid, rescued the protective effect of Trp on E. coli-induced endometritis in dysbiotic mice. Moreover, consumption of Lactobacillus reuteri (L. reuteri) containing AhR ligand-producing capability also alleviated E. coli-induced endometritis in mice in an AhR-dependent manner. Our results demonstrate that microbiota-mediated AhR activation is a key factor in fighting pathogen-caused inflammation, which leads to a potential strategy to regulate the gut microbiota and metabolism by dietary Trp or probiotics for the intervention of infectious diseases and reproductive health. IMPORTANCE Infection-induced endometritis is a common and frequently occurring disease in humans and animals. Accumulating evidence suggests an important role of the gut microbiota in the development of infection-induced inflammation. Whether and how gut microbiota-mediated AhR activation regulates the pathogenesis of pathogen-induced endometritis remains unknown. The current study found that AhR activation ameliorated E. coli-induced endometritis, and inhibition of AhR produced negative results. Gut dysbiosis reduced the abundance of AhR ligand producers including Lactobacillus spp., damaged AhR activation, and exacerbated E. coli-induced endometritis. Supplementation with dietary Trp, AhR ligands, and L. reuteri containing AhR ligand-producing capability alleviated E. coli-induced endometritis in mice. Our results suggest an important role of microbiota-mediated AhR activation in the pathogenesis of endometritis and provide potential strategies for the intervention of infectious diseases and reproductive health by regulating the gut microbiota and metabolism.