Mechanisms of intestinal barrier disruption in acute and chronic liver injury Público

Abstract

Enhanced intestinal permeability is recognized in various liver disease settings. The intestine houses a complex ecosystem of commensal microorganisms. Paramount to intestinal physiology is maintenance of homeostatic compartmentalization of these microbes by forming a tight, yet selectively permeable barrier. The gut barrier is composed of several constituent parts including epithelial, mucus, and immunological components. Compromise of any aspect of this barrier contributes to intestinal leakiness and bacterial translocation. Translocated microbes and their toxins gain immediate access to the liver via the portal circulation where they induce potent inflammatory reactions. Persistent hepatic inflammation driven by gut leakiness is thus thought to be a primary contributor to disease pathogenesis. In this dissertation, we sought characterize underrecognized aspects of intestinal epithelial barrier dysfunction that contribute to chronic and acute liver injury.

We first explored the setting of alcoholic liver disease (ALD), a chronic condition of increasing clinical significance that remains without effective treatments. Using an in vitro system of intestinal epithelial monolayers, we identified the tight junction protein junctional adhesion molecule-A (JAM-A) as a potential target of ethanol-induced gut barrier collapse. Alcohol treatment brought a 30% reduction in JAM-A protein expression and was associated with perturbations in JAM-A signaling targets at earlier time points.

We next examined whether gut permeability contributes to the pathogenesis of acute liver injury using a model of acetaminophen (APAP) overdose. APAP toxicity remains the leading cause of acute liver failure in the western world. We found that intestinal permeability rapidly and markedly increases following APAP intoxication. Gut permeability coincided with marked intestinal apoptosis, which was strikingly limited to cells within the intestinal crypts. With the use of specialized reporter mice, we confirmed that APAP-sensitive cells were predominantly classified as LGR5⁺ stem cells. This suggests that enterotoxicity during APAP intoxication has potentially long-lived consequences.

In summary, this dissertation adds significant knowledge to our understanding of gut barrier physiology by: 1) identifying new molecular targets of ethanol-induced gut barrier disruption; and 2) identifying a novel extrahepatic toxicity following high-dose APAP consumption. Moreover, this work identifies LGR5⁺ stem cell death and dysfunction as a novel potential mechanism of intestinal barrier compromise.

Table of Contents

Chapter 1: Physiology of the gut barrier and its contribution to diseases of the liver and other target organs ---------------------------------------------------------------------------      

1. Introduction ------------------------------------------------------------------------------------1

         2. Components of the gut barrier -----------------------------------------------------------3

                   2.1 Epithelial barrier -------------------------------------------------------------------3

                   2.2 Mucus barrier ----------------------------------------------------------------------19

                   2.3 Immune barrier --------------------------------------------------------------------22

                   2.4 Microbial barrier ------------------------------------------------------------------27

         3. Pathological derangements of gut barrier -----------------------------------------30

         4. Highlights of gut permeability in specific diseases --------------------------------

                   4.1 Alcoholic liver disease ---------------------------------------------------------33

                   4.2 Non-alcoholic fatty liver disease --------------------------------------------34

                   4.3 Drug-induced liver injury ------------------------------------------------------37

                   4.4 Primary sclerosing cholangitis ----------------------------------------------39

                   4.5 Neurological and other disorders ------------------------------------------42

         5. Summary and future directions --------------------------------------------------------44

         6. Conclusion ------------------------------------------------------------------------------------44

         Figures ---------------------------------------------------------------------------------------------46

Chapter 2: Dysregulation of junctional adhesion molecule-A contributes to ethanol-induced barrier disruption in intestinal epithelial cell monolayers --------51

         Abstract -------------------------------------------------------------------------------------------52

         Introduction --------------------------------------------------------------------------------------54

         Materials and methods -----------------------------------------------------------------------56

         Results ---------------------------------------------------------------------------------------------66

         Discussion ---------------------------------------------------------------------------------------72

         Figures ---------------------------------------------------------------------------------------------76

Chapter 3: Acetaminophen intoxication rapidly induces apoptosis of intestinal crypt stem cells and enhances intestinal permeability ------------------------------------91

         Abstract -------------------------------------------------------------------------------------------93

         Introduction --------------------------------------------------------------------------------------94

         Experimental procedures -------------------------------------------------------------------97

         Results -------------------------------------------------------------------------------------------102

         Discussion --------------------------------------------------------------------------------------107

         Figures -------------------------------------------------------------------------------------------111

Chapter 4: Discussion -------------------------------------------------------------------------------120

         Tight junction dysfunction in ALD ------------------------------------------------------121

         Intestinal permeability and intestinal stem cell injury in APAP ALF --------124

         Final Reflections ------------------------------------------------------------------------------127

References -----------------------------------------------------------------------------------------------128

About this Dissertation

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School	Laney Graduate School
Department	Biological and Biomedical Sciences
Subfield / Discipline	Immunology and Molecular Pathogenesis
Degree	Ph.D.
Submission	Dissertation
Language	English
Research Field	Health Sciences, Pathology Health Sciences, Immunology
Palabra Clave	Stem cells Acetaminophen Liver Alcohol Tight Junction Intestine
Committee Chair / Thesis Advisor	Arash Grakoui, Emory University
Committee Members	Brian Evavold, Emory University Joshy Jacob, Emory University Mark Czaja, Emory University Malú Tansey, Emory University

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