ABSTRACT
BACKGROUND: Autophagy is implicated in Crohn's disease (CD) pathogenesis. Recent evidence suggests autophagy regulates the microRNA (miRNA)-induced silencing complex (miRISC). Therefore, autophagy may play a novel role in CD by regulating expression of miRISC, thereby altering miRNA silencing. As microbes associated with CD can alter autophagy, we hypothesized that microbial disruption of autophagy affects the critical miRISC component AGO2. METHODS: AGO2 expression was assessed in epithelial and immune cells, and intestinal organoids with disrupted autophagy. Microarray technology was used to determine the expression of downstream miRNAs in cells with defective autophagy. RESULTS: Increased AGO2 was detected in autophagy-deficient ATG5-/- and ATG16-/- mouse embryonic fibroblast cells (MEFs) in comparison with wild-type MEFs. Chemical agents and VacA toxin, which disrupt autophagy, increased AGO2 expression in MEFs, epithelial cells lines, and human monocytes, respectively. Increased AGO2 was also detected in ATG7-/- intestinal organoids, in comparison with wild-type organoids. Five miRNAs were differentially expressed in autophagy-deficient MEFs. Pathway enrichment analysis of the differentially expressed miRNAs implicated signaling pathways previously associated with CD. CONCLUSIONS: Taken together, our results suggest that autophagy is involved in the regulation of the critical miRISC component AGO2 in epithelial and immune cells and primary intestinal epithelial cells. We propose a mechanism by which autophagy alters miRNA expression, which likely impacts the regulation of CD-associated pathways. Furthermore, as enteric microbial products can manipulate autophagy and AGO2, our findings suggest a novel mechanism by which enteric microbes could influence miRNA to promote disease.
Subject(s)
Argonaute Proteins/metabolism , Autophagy/genetics , Bacterial Toxins/metabolism , MicroRNAs/metabolism , Signal Transduction/genetics , Animals , Argonaute Proteins/genetics , Autophagy-Related Protein 5 , Autophagy-Related Protein 7 , Carrier Proteins , Cell Line , Crohn Disease/genetics , Crohn Disease/metabolism , Crohn Disease/microbiology , Epithelial Cells/metabolism , Fibroblasts/metabolism , Humans , Intestinal Mucosa/metabolism , Mice , Mice, Knockout , MicroRNAs/genetics , Microtubule-Associated Proteins/deficiency , Monocytes/metabolism , RNA-Induced Silencing Complex/metabolismABSTRACT
BACKGROUND & AIMS: The Helicobacter pylori toxin vacuolating cytotoxin (VacA) promotes gastric colonization, and its presence (VacA(+)) is associated with more-severe disease. The exact mechanisms by which VacA contributes to infection are unclear. We previously found that limited exposure to VacA induces autophagy of gastric cells, which eliminates the toxin; we investigated whether autophagy serves as a defense mechanism against H pylori infection. METHODS: We investigated the effect of VacA on autophagy in human gastric epithelial cells and primary gastric cells from mice. Expression of p62, a marker of autophagy, was also assessed in gastric tissues from patients infected with toxigenic (VacA(+)) or nontoxigenic strains. We analyzed the effect of VacA on autophagy in peripheral blood monocytes obtained from subjects with different genotypes of ATG16L1, which regulates autophagy. We performed genotyping for ATG16L1 in 2 cohorts of infected and uninfected subjects. RESULTS: Prolonged exposure of human gastric epithelial cells and mouse gastric cells to VacA disrupted induction of autophagy in response to the toxin, because the cells lacked cathepsin D in autophagosomes. Loss of autophagy resulted in the accumulation of p62 and reactive oxygen species. Gastric biopsy samples from patients infected with VacA(+), but not nontoxigenic strains of H pylori, had increased levels of p62. Peripheral blood monocytes isolated from individuals with polymorphisms in ATG16L1 that increase susceptibility to Crohn's disease had reduced induction of autophagy in response to VacA(+) compared to cells from individuals that did not have these polymorphisms. The presence of the ATG16L1 Crohn's disease risk variant increased susceptibility to H pylori infection in 2 separate cohorts. CONCLUSIONS: Autophagy protects against infection with H pylori; the toxin VacA disrupts autophagy to promote infection, which could contribute to inflammation and eventual carcinogenesis.
Subject(s)
Autophagy/physiology , Bacterial Proteins/physiology , Helicobacter Infections/etiology , Helicobacter pylori , Alleles , Animals , Bacterial Proteins/genetics , Cathepsin D/physiology , Crohn Disease/etiology , Crohn Disease/genetics , Genotype , Humans , Immunity, Innate , Mice , Phagosomes/physiologyABSTRACT
PURPOSE OF REVIEW: Helicobacter pylori is implicated in numerous gastric pathologies; however, the prevalence of infection is declining in developed countries. Therefore, it is important to understand the complex mechanism of its interaction with the host and how the changing epidemiology of infection may impact on disease. In this review, we systemically revisit the major novel discoveries of the last year relating to H. pylori disease pathogenesis. RECENT FINDINGS: Novel pathways have been implicated in H. pylori cytotoxin-associated gene (CagA) mediated carcinogenesis, highlighting the aberrant regulation of proliferation and apoptosis. Furthermore, the human microbiome was implicated as having a key role in H. pylori-related disease development. Several studies have begun to delineate the mechanisms behind the epidemiologically inverse correlation of H. pylori infection with asthma and inflammatory bowel disease. SUMMARY: The recent findings enable researchers to focus on novel and previously unsuspected mechanisms in the development of disease, and prompt further research into possible therapeutic approaches. The potential beneficial aspects of H. pylori colonization and the role bacterial flora play in promoting disease have yet to be elucidated, but promise to have a great impact on patient care.
