Basic Study
Copyright ©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Aug 28, 2020; 26(32): 4763-4785
Published online Aug 28, 2020. doi: 10.3748/wjg.v26.i32.4763
Immune and microRNA responses to Helicobacter muridarum infection and indole-3-carbinol during colitis
Rasha Raheem Alkarkoushi, Yvonne Hui, Abbas S Tavakoli, Udai Singh, Prakash Nagarkatti, Mitzi Nagarkatti, Ioulia Chatzistamou, Marpe Bam, Traci L Testerman
Rasha Raheem Alkarkoushi, Yvonne Hui, Prakash Nagarkatti, Mitzi Nagarkatti, Ioulia Chatzistamou, Marpe Bam, Traci L Testerman, Department of Pathology, Microbiology and Immunology, University of South Carolina School of Medicine, Columbia, SC 29209, United States
Abbas S Tavakoli, College of Nursing, University of South Carolina, University of South Carolina, Columbia, SC 29208, United States
Udai Singh, Department of Medicine, Hematology and Oncology, University of Virginia School of Medicine, Charlottesville, VA 22908, United States
Author contributions: Alkarkoushi RR, Hui Y, Tavakoli AS, Testerman TL and Singh U assisted with conceptualization, performed experiments, analyzed data, and drafted the manuscript; Nagarkatti P and Nagarkatti M assisted with conceptualization and funding acquisition; Chatzistamou I performed histopathological analysis; Bam M analyzed microRNA data; Testerman TL conceptualized assisted with funding acquisition, and wrote and edited the manuscript.
Supported by the National Institutes of Health, No. P20GM103641.
Institutional review board statement: This study did not involve human subjects.
Institutional animal care and use committee statement: All experimental procedures were conducted in accordance with the guidelines for the use of experimental animals and were approved by the Institutional Review Committee on Animal Care and Use at the University of South Carolina.
Conflict-of-interest statement: The authors have nothing to disclose.
Data sharing statement: Raw data have been provided as supplemental material.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Corresponding author: Traci L Testerman, PhD, Assistant Professor, Department of Pathology, Microbiology and Immunology, University of South Carolina School of Medicine, 6439 Garners Ferry Road, Columbia, SC 29209, United States.
Received: March 19, 2020
Peer-review started: March 20, 2020
First decision: April 8, 2020
Revised: July 16, 2020
Accepted: August 12, 2020
Article in press: August 12, 2020
Published online: August 28, 2020
Research background

Enterohepatic Helicobacter (EHH) species can infect humans and many animal species. Some of these species are known to cause disease in animals, while others have been described as commensal. In humans, epidemiological evidence suggests that EHH species are associated with inflammatory bowel disease (IBD), but the specific species involved and mechanisms of action are unknown. New treatments being tested for IBD include natural compounds and microRNA (miRNA)-based therapies. MiRNA is also being investigated as a diagnostic tool.

Research motivation

Given the limitations of performing IBD research in humans, an animal model of EHH-mediated pathology is needed. Such a model should reflect the biological changes seen during human IBD. Helicobacter muridarum (H. muridarum) has been referred to as a commensal in mice, yet we previously determined that H. muridarum worsens colitis resulting from dextran sodium sulfate (DSS). This suggested that EHH species could represent environmental factors that cause or worsen IBD in genetically susceptible individuals. It is also important to determine whether phytochemicals being investigated as IBD treatments are influenced by infection with EHH species because there are no commercially available tests for EHH infection in humans.

Research objectives

We sought to determine how the immune and miRNA profiles of H. muridarum-infected wild-type mice compared with DSS-treated mice and with published immune and miRNA profiles of IBD patients. We also determined whether efficacy of a broccoli-derived anti-inflammatory compound, indole-3-carbinol (I3C), was reduced by H. muridarum infection.

Research methods

We measured changes in body weight, stool consistency, and stool blood following H. muridarum infection, DSS treatment, and/or I3C treatment. We then measured cytokine responses in the colon and plasma and histopathological changes in the colon. MiRNA changes and T cell population changes were measured in mesenteric lymph nodes.

Research results

While H. muridarum infection alone did not cause clinical symptoms, it did cause colonic inflammation and induced proinflammatory cytokines. As expected, H. muridarum worsened colitis caused by DSS treatment, but it did not prevent amelioration of colitis by I3C treatment. Both the miRNA changes and cytokine responses to H. muridarum infection were similar to those seen in human IBD and due to DSS treatment. Changes in cytokines and miRNA were consistent with a Th17 response.

Research conclusions

H. muridarum causes subclinical colitis that increases vulnerability to DSS treatment. Since I3C is an aryl hydrocarbon receptor agonist, the efficacy of I3C in the presence of H. muridarum suggests that H. muridarum does not influence the aryl hydrocarbon receptor agonist pathway. The strong similarities between cytokine and miRNA profiles induced by DSS and those induced by H. muridarum suggest that similar mechanisms could be at play and that the mouse model is suitable for studying host interactions with EHH species.

Research perspectives

This research supports the hypothesis that EHH species could contribute to human IBD by exacerbating the response to other inflammatory stimuli. More research is needed on the prevalence of EHH species in humans and the mechanisms underlying EHH-mediated colonic damage.