Epithelial adhesion mediated by pilin SpaC is required for Lactobacillus rhamnosus GG-induced probiotic effects Open Access

Ardita, Courtney St Clair (2014)

Permanent URL: https://etd.library.emory.edu/concern/etds/3f462602c?locale=en


Lactobacilli preparations are marketed for their health benefits and have shown promising efficacy as treatments for intestinal disease. Studies exploring the effect of lactobacilli in the alimentary canals of two common laboratory models, Drosophila and mice, have demonstrated that exposure to lactobacilli positively impacts development, homeostasis, and immune functioning in these systems. However, despite their clinical potential and the existence of laboratory models to investigate them, the nature of the relationship between commensal lactobacilli and host health is poorly characterized. The studies described in this dissertation elucidate some molecular mechanisms behind how probiotic lactobacilli induce salutary effects in the gastrointestinal tracts of flies and mice. Here, we found that Lactobacillus plantarum naturally colonizes laboratory-raised strains of Drosophila and that this bacterium induces cellular reactive oxygen species (ROS) generation in the Drosophila midgut. This cellular ROS generation also activates cell proliferation in the fly midgut. Lactobacilli-induced ROS generation was also shown to occur in cultured mammalian cells, and in the murine intestine. Indeed, Lactobacillus rhamnosus GG (LGG) induces particularly robust ROS generation in mammalian systems. We also established that ROS-generation is dependent on cellular expression of NADPH oxidase (Nox). Lactobacilli-induced ROS generation is significantly diminished in enterocyte specific dNox null Drosophila and in gut epithelial-specific Nox1 null mice. Furthermore, we demonstrated that the LGG pilin adhesion protein, SpaC, is required for LGG-induced ROS generation. An isogenic Lactobacillus rhamnosus GG strain that lacks SpaC (LGGΩspaC) does not adhere to intestinal mucus or murine intestines as well as the wild type strain. SpaC was shown to contribute to the capacity of LGG to induce cellular ROS generation, potentiate ERK MAPK signaling in enterocytes, stimulate cellular proliferation, and protect against radiation-induced injury. Collectively, these data show that commensal lactobacilli found in the alimentary canal lead to beneficial effects in their hosts by inducing cellular ROS generation through a Nox-dependent mechanism. In addition, LGG requires intimate contact with intestinal epithelial cells in order to elicit this ROS induction and its probiotic effects are dependent on bacterial expression of the SpaC pilin protein.

Table of Contents

Chapter 1 Introduction 1

References 30

Chapter 2 Symbiotic lactobacilli stimulate gut epithelial proliferation via Nox-mediated generation of reactive oxygen species 45

Abstract 46

Introduction 46

Materials and Methods 50

Results 55

Discussion 62

References 95

Chapter 3 Epithelial adhesion mediated by pilin SpaC is required for Lactobacillus rhamnosus GG-induced probiotic effects 102

Abstract 103

Introduction 103

Materials and Methods 106

Results 113

Discussion 118

References 133

Chapter 4 Discussion 140

References 144

Appendix 1 Probing the Spatial Organization of Measles Virus Fusion Complexes 145

Abstract 146

Introduction 147

Materials and Methods 151

Results 159

Discussion 169

References 189

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