Date on Master's Thesis/Doctoral Dissertation

5-2022

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Pharmacology and Toxicology

Degree Program

Pharmacology and Toxicology, PhD

Committee Chair

Wenke, Feng

Committee Co-Chair (if applicable)

McClain, Craig

Committee Member

McClain, Craig

Committee Member

Chen, Shao-yu

Committee Member

Siskind, Leah

Committee Member

Deng, Zhongbin

Committee Member

Hood, Joshua

Author's Keywords

Probiotic; ALD; FXR and bile acids

Abstract

Numerous studies have reported the efficacy of probiotics for alcohol-associated liver disease (ALD). These studies indicate a strong interest among the scientific and medical communities in identifying alternative or adjunctive approaches for ALD, for which there is no effective or widely accepted therapeutic option. However, in-depth molecular knowledge on how probiotics render their effects is lacking. Patients with ALD often have increased hepatic bile acids (BAs), which can be toxic and are an important causative factor in liver injury and hepatocyte death. BAs are released into the intestines and serve not only as a “detergent” to promote fat absorption, but also as signal molecules to regulate biological functions through modulation of several receptors, including farnesoid X receptor (FXR). Intestinal FXR activation upregulates fibroblast growth factor (FGF) 15/19 (mouse/human), which is released from the intestine and binds to its receptors, FGFR/β-klotho, in the liver, and activates multiple signaling cascades to suppress BA synthesis and reduce lipogenesis. Activation of intestinal FXR improved ALD in animal models. While FXR activation by BAs is well-studied, its regulation at the transcription level is less clear. The present study demonstrated that microRNA (miR)194 levels were increased in the feces of patients with ALD and in the feces and intestine tissues of mice fed alcohol. miR194 suppressed FXR expression in intestine tissues, ileal organoids, and intestinal epithelial cells. Decreased FXR expression caused by the increased miR194 in the intestine led to a reduction of FGF15 expression and subsequent increased hepatic BA synthesis and lipogenesis in alcohol-fed mice. We further demonstrated that the alcohol increased-miR194 expression was mediated by gut microbiota regulation of taurine metabolism through taurine upregulated gene 1 (Tug1). Importantly, administration of Lactobacillus rhamnosus GG-derived exosome-like nanoparticles (LDNPs) restored gut taurine concentration through altering gut microbiota that led to the suppression of miR194 and activation of FXR-FGF15 pathway, which suppressed BA de novo synthesis and lipogenesis and alcohol-induced liver injury. Indeed, the beneficial effects of LDNPs were eliminated in intestinal FxrΔIECand Fgf15-/- mice. To further investigate the mechanisms of LDNP’s overall beneficial effects in ALD, we performed next-generation RNA sequencing (RNA-seq) in mouse liver and ileum samples. An overarching comparative analysis of differentially regulated genes was conducted. We identified both unique and shared molecular mechanisms and signaling pathways for the treatment of ALD by LDNPs, which can be a basis for future study. In summary, our findings demonstrated that alcohol feeding increases intestinal miR194 through gut microbiota-mediated taurine dysmetabolism resulting in a suppressed Fxr gene expression and a decreased BA-mediated FXR activation, which leads to BA accumulation and increased lipogenesis and injury in the liver, and this can be inhibited by LDNP treatment. Moreover, transcriptomic analysis identifies genes responsive to alcohol and LDNP treatment in the liver and intestine in mice. The present study has shed light on the molecular mechanisms of the intestinal miRNA regulation of hepatic BA synthesis and lipogenesis in ALD and the protective effects of probiotic-derived extracellular vesicles.

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