The Gut Microbiota-Bile Acids-TGR5 Axis Mediates Eucommia ulmoides Leaf Extract Alleviation of Injury to Colonic Epithelium Integrity.

Zhenya Zhai,Chong Lin,Yichun Liu,Xin Wu,Kai-Min Niu

doi:10.3389/fmicb.2021.727681

Abstract

Eucommia ulmoides leaves (EL) are rich in phenolic acids and flavonoids, showing enhancing intestinal health effects. The intestinal microbiota-bile acid axis plays important roles in the occurrence and recovery of inflammatory bowel disease (IBD). However, whether EL extract (ELE) has regulatory effects on the intestinal microbiota, bile acid metabolism, and IBD is still unclear. To fill this gap, 2% dextran sulfate sodium (DSS)-induced mild IBD in a C57BL/6J mouse model that was treated with 200 or 400 mg/kg (intake dose/body weight) ELE was used. Oral ELE supplementation alleviated DSS-induced shortening of colon and colonic epithelial injury. Compared with the DSS group, ELE supplementation significantly decreased Toll-like receptor 4 (TLR4) and interlukin-6 (IL-6) and increased occludin and claudin-1 mRNA expression level in the colon (p < 0.05). Combined 16S rRNA gene sequencing and targeted metabolomic analyses demonstrated that ELE significantly improved the diversity and richness of the intestinal microbiota, decreased the abundance of Bacteroidaceae, and increased Akkermansiaceae and Ruminococcaceae abundance (p < 0.05) compared with DSS-induced IBD mice. Moreover, ELE significantly increased the serum contents of deoxycholic acid (DCA) and tauroursodeoxycholic acid (TUDCA), which were highly positively correlated with Akkermansia and unidentified_Ruminococccaceae relative to the DSS group. We then found that ELE increased Takeda G-protein coupled receptor 5 (TGR5), claudin-1, and occludin mRNA expression levels in the colon. In the Caco-2 cell model, we confirmed that activation of TGR5 improved the reduction in transepithelial electoral resistance (TEER) and decreased the permeability of FITC-dextran on monolayer cells induced by LPS (p < 0.05). siRNA interference assays showed that the decrease in TGR5 expression led to the decrease in TEER, an increase in FITC-dextran permeability, and a decrease in claudin-1 protein expression in Caco-2 cells. In summary, ELE alleviated IBD by influencing the intestinal microbiota structure and composition of bile acids, which in turn activated the colonic TGR5 gene expression in the colon and promoted the expression of tight junction proteins. These findings provide new insight for using ELE as a functional food with adjuvant therapeutic effects in IBD.

Highlights

In Western countries, the incidence rate of inflammatory bowel disease (IBD) exceeds 0.3%, while in some Asian countries, the incidence of IBD has begun to increase rapidly (Ng et al, 2017)
We found that Eucommia ulmoides leaves (EL) extract (ELE) significantly improved dextran sulfate sodium (DSS)-induced colon epithelial injury and reduced the mRNA expression of TLR4 and IL-6, which might attribute to the enriched phenolic acids, flavonoid, and polysaccharide contents in ELE
Consistent with a previous study, we found that compared with DSS treatment, ELE significantly increased the mRNA expression of TGR5 in the colon of IBD mice

Summary

Introduction

In Western countries, the incidence rate of inflammatory bowel disease (IBD) exceeds 0.3% (more than 2 million people), while in some Asian countries (such as China and Japan), the incidence of IBD has begun to increase rapidly (Ng et al, 2017). The main factor that induces IBD is the disorder of intestinal microbiota and host metabolism caused by high-fat and high-protein “Western diet” (Tang et al, 2019; Sinha et al, 2020). An effective way to prevent and improve IBD is adjusting the diet and increasing the intake of functional food, to improve the intestinal microbiota community and host metabolism. Studies have shown that increase in Bacteroides, Proteobacteria, and Enterobacteriaceae have been found in the intestinal contents and feces of IBD mice and human patients (Zhai Z. et al, 2019). Probiotics such as Akkermansia and Lactobacillus were enriched in mice at the convalescent stage of IBD. Probiotic intervention or fecal bacteria transplantation has been effective in relieving IBD symptoms (Lee and Chang, 2020)

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