TrpA1 Regulates Defecation of Food-Borne Pathogens under the Control of the Duox Pathway.

Eun Jo Du,Young Sik Lee,Youngsoo Jun,Jeong-Ho Park,Kyeongjin Kang,Tong Mook Kang,Sun Hwa Park,Hee Jae Lee,Hyung-Wook Kim,Jae Young Kwon,Ji Hye Lee,Tae Jung Ahn,Ilmin Kwon,Tae Jin Kim,Hana Cho,Irene Miguel-Aliaga

doi:10.1371/journal.pgen.1005773

Abstract

Pathogen expulsion from the gut is an important defense strategy against infection, but little is known about how interaction between the intestinal microbiome and host immunity modulates defecation. In Drosophila melanogaster, dual oxidase (Duox) kills pathogenic microbes by generating the microbicidal reactive oxygen species (ROS), hypochlorous acid (HOCl) in response to bacterially excreted uracil. The physiological function of enzymatically generated HOCl in the gut is, however, unknown aside from its anti-microbial activity. Drosophila TRPA1 is an evolutionarily conserved receptor for reactive chemicals like HOCl, but a role for this molecule in mediating responses to gut microbial content has not been described. Here we identify a molecular mechanism through which bacteria-produced uracil facilitates pathogen-clearing defecation. Ingestion of uracil increases defecation frequency, requiring the Duox pathway and TrpA1. The TrpA1(A) transcript spliced with exon10b (TrpA1(A)10b) that is present in a subset of midgut enteroendocrine cells (EECs) is critical for uracil-dependent defecation. TRPA1(A)10b heterologously expressed in Xenopus oocytes is an excellent HOCl receptor characterized with elevated sensitivity and fast activation kinetics of macroscopic HOCl-evoked currents compared to those of the alternative TRPA1(A)10a isoform. Consistent with TrpA1’s role in defecation, uracil-excreting Erwinia carotovora showed higher persistence in TrpA1-deficient guts. Taken together, our results propose that the uracil/Duox pathway promotes bacteria expulsion from the gut through the HOCl-sensitive receptor, TRPA1(A)10b, thereby minimizing the chances that bacteria adapt to survive host defense systems.

Highlights

Encountering other organisms in nature offers opportunities of benefits or dangers depending on the relationship of the organisms facing each other
Our study reveals that the bleach does not stop there, working further to promote expulsion of the bacteria from the gut through a sensitive bleach detector
In the gut deficient for the bleach detector, the bacteria stayed longer, and opportunistically survived the bleach that they encounter afterwards. This is the first identification of a mechanism illustrating how important it is that gut defense systems control defecation, and helps explain why troubles in the gut cause changes in defecation

Summary

Introduction

Encountering other organisms in nature offers opportunities of benefits or dangers depending on the relationship of the organisms facing each other. Bacterial homeostasis in the Drosophila gut is under the control of two distinct innate immune mechanisms, the imd and Duox pathways [5,6,7]. In the latter, bacteria-originated uracil upregulates Duox activity via G-protein signaling pathways [8,9,10], which are independent of the imd pathway [5,8]. The upregulation of Duox dramatically increases the concentration of highly microbicidal HOCl [8,11] in the gut lumen, as the ROS is enzymatically generated by collaboration of the two cytosolic and extracellular oxidase domains of Duox [12]. The Duox pathway plays a critical role for the control of the gut microbiome homeostasis by responding to bacterially excreted uracil and producing the reactive chlorine oxidant, HOCl

Methods

Results

Conclusion