Notch Signaling Pathway Is Activated by Sulfate Reducing Bacteria.

Sudha B Singh,Matthew G Varga,Cristina N Coffman,Henry C Lin,Amanda Carroll-Portillo

doi:10.3389/fcimb.2021.695299

Abstract

Sulfate Reducing Bacteria (SRB), usually rare residents of the gut, are often found in increased numbers (called a SRB bloom) in inflammatory conditions such as Inflammatory Bowel Disease (IBD), pouchitis, and periodontitis. However, the underlying mechanisms of this association remain largely unknown. Notch signaling, a conserved cell-cell communication pathway, is usually involved in tissue development and differentiation. Dysregulated Notch signaling is observed in inflammatory conditions such as IBD. Lipolysaccharide and pathogens also activate Notch pathway in macrophages. In this study, we tested whether Desulfovibrio, the most dominant SRB genus in the gut, may activate Notch signaling. RAW 264.7 macrophages were infected with Desulfovibrio vulgaris (DSV) and analyzed for the expression of Notch signaling pathway-related proteins. We found that DSV induced protein expression of Notch1 receptor, Notch intracellular domain (NICD) and p21, a downstream Notch target, in a dose-and time-dependent manner. DSV also induced the expression of pro-IL1β, a precursor of IL-1β, and SOCS3, a regulator of cytokine signaling. The gamma secretase inhibitor DAPT or Notch siRNA dampened DSV-induced Notch-related protein expression as well the expression of pro-IL1β and SOCS3. Induction of Notch-related proteins by DSV was not affected by TLR4 -IN -C34(C34), a TLR4 receptor antagonist. Additionally, cell-free supernatant of DSV-infected macrophages induced NICD expression in uninfected macrophages. DSV also activated Notch pathway in the human epithelial cell line HCT116 and in mouse small intestine. Thus, our study uncovers a novel mechanism by which SRB interact with host cells by activating Notch signaling pathway. Our study lays a framework for examining whether the Notch pathway induced by SRB contributes to inflammation in conditions associated with SRB bloom and whether it can be targeted as a therapeutic approach to treat these conditions.

Highlights

Sulfate reducing bacteria (SRB) are anaerobic, gram negative, commensal residents of the colon in humans and other animals (Gibson et al, 1988)
We found that Desulfovibrio vulgaris (DSV) induced Notch1 expression in a dose- dependent manner (Figures 1A, B) with a significant induction observed at multiplicity of infection (MOI) 20 (4.27 ± 0.46.08, p
We report activation of Notch signaling pathway by sulfate reducing bacteria (SRB) as a novel mechanism by which these bacteria communicate with host cells

Summary

Introduction

Sulfate reducing bacteria (SRB) are anaerobic, gram negative, commensal residents of the colon in humans and other animals (Gibson et al, 1988). The localization of SRB in the gut remains largely unexplored. A study showed that Desulfovibrio was mainly localized in the right colon in healthy subjects (Nava et al, 2012). Desulfovibrio species were shown associated with colonic mucin in healthy subjects and in ulcerative colits patients (Earley et al, 2015). A bloom of SRB is found in inflammatory conditions such as inflammatory bowel disease (IBD), colitis, pouchitis and periodontitis (Singh and Lin, 2015). The mechanisms of how SRB interact with host cells remain largely unexplored. Better understanding of interaction of SRB with host cells is critical to unraveling the relationship between SRB bloom and inflammatory diseases and to identify novel targets for treating these conditions

Methods

Results

Conclusion