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

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.

Maintenance of the adult Drosophila intestine: all roads lead to homeostasis

“…Enteroendocrine cells secrete factors [13-15] that promote ISC proliferation [16, 17], influence cell fate choice [18, 19], regulate intestinal peristalsis and defecation [6, 20], and inhibit lipogenesis in enterocytes [21]. Interspersed among the enterocytes and ee cells, along the entire length of the midgut, are intestinal stem cells (ISCs) [22, 23].…”

The Phlebotomus papatasi transcriptomic response to trypanosomatid-contaminated blood is robust but non-specific

“…TrpA1 is more generally associated chemo- and thermo-sensing 22,23 in Drosophila , however a study by Du et al . 2006 links TrpA1 to the expulsion of food-borne pathogens by increased defecation and the DUOX pathway (discussed further below) 24 . Speculatively, reduction in TrpA1 transcripts after L. donovani feeding may hint at modification of host defensive pathways to promote survival.…”

The impact of metagenomic interplay on the mosquito redox homeostasis

“…Usually, commensal bacteria do not release uracil, which may be an evolutionary outcome that adaptive symbionts modify the uracil secretion mechanism to avoid an induction of host ROS production [82]. Interestingly, uracil can modulate Drosophila defecation [87]. This process requires both Duox pathway and transient receptor potential (TRP) channel TRPA1.…”

“…TRPA1 is a HOCl receptor and promotes defecation. Pathogen-derived uracil activates Duox system to generate ROS and HOCl, the latter triggers TRPA1 to promote defecation, resulting in the expulsion of pathogens in parallel to the microbicidal effects of ROS and HOCl [87]. …”