The Interplay Between Enteric Tuft Cell Responses and Giardia Colonization.

BACKGROUND: The chemosensory epithelial tuft cell possesses key roles in the host's response to intestinal infections, including the detection of and response to certain enteric parasites, and aids in parasite clearance (1,2). Limited data indicate that upon activation of tuft cells, downstream tuft and goblet cell hyperplasia may occur concurrently and during the peak of infection (2). The intestinal protozoan Giardia, which is known to cause epithelial barrier dysfunction and is a common cause of diarrheal disease worldwide (3), and the role of tuft cells during this infection has not been investigated.

AIMS: Using Giardia murisas a model, this study aims to uncover novel roles for tuft cells in the pathophysiology of giardiasis by assessing the tuft cell response and measuring the extent of diarrheal disease over the time course of G. murisinfection.

METHODS: Wild type (WT) and tuft cell-deficient (Pou2f3-/- ) C57BL/6 mice (5-7-week-old) were infected with 5x104 G. muris trophozoites or PBS (control) and assessed at days 4, 11 and 21 post-infection. Parasite burden was measured in the duodenum. Immunofluorescence staining for doublecortin-like kinase 1 (DCLK1) and Alcian Blue (AB)/PAS staining was performed in the jejunum for tuft and goblet cell quantification, respectively. Expression of tuft and goblet cell related markers and activation pathway genes were assessed using quantitative PCR (qPCR). Fecal water weight and intestinal motility (fecal count over 60 minutes) were evaluated in stool samples as markers of diarrheal disease.

RESULTS: In WT infected mice, goblet cell counts and Atoh1and Muc2expression were increased at day 4 post-infection, during high parasite burden, while tuft cell numbers and Dclk1expression were increased at clearance phase (day 21), characterized by low parasite burden. The expression of the tuft cell receptor Tas2r was increased at day 21 while Tas1r3 and Sucnr1 remained unchanged. Tuft cell-deficient mice (Pou2f3-/- ) presented with lower parasite burden at days 4 and 11 compared to WT infected mice and Atoh1 and Muc2 expression was not altered in infected Pou2f3-/- mice compared to uninfected controls. At day 11, infected WT mice had increased total fecal counts compared to uninfected controls, while Pou2f3-/- infected mice saw an increase in total fecal counts at day 4. Water stool content was unaltered in infected WT and infected Pou2f3-/- mice, compared to their respective controls.

CONCLUSIONS: The presence of a lower trophozoite burden in tuft cell knockout mice during early Giardiainfection suggests that counterintuitively, tuft cells may facilitate the establishment of Giardia colonization in addition to playing a role during the clearance stage. Tuft and goblet cell increases were not concomitant over the time course of infection, indicating that the tuft cell pathophysiological mechanisms at play during Giardiainfection vary at early and late stages of infection and differ to other parasitic models which engage tuft cell activity. These findings shed light on novel pathways whereby tuft cells may regulate host-microbial interactions in the gut.

REFERENCES: 1. Schneider C, O'Leary CE, Locksley RM. Regulation of immune responses by tuft cells. Nat Rev Immunol. 2019;19(9):584-593. 2. Rajeev S, Sosnowski O, Li S, Allain T, Buret AG, McKay DM. Enteric Tuft Cells in Host-Parasite Interactions. Pathogens. 2021;10(9):1163. 3. Allain T, Amat CB, Motta JP, Manko A, Buret AG. Interactions of Giardia sp. with the intestinal barrier: Epithelium, mucus, and microbiota. Tissue Barriers. 2017;5(1):e1274354.