Trophozoite fitness dictates the intestinal epithelial cell response to Giardia intestinalis infection

Abstract

Giardia intestinalis is a non-invasive, protozoan parasite infecting the upper small intestine of most mammals. Symptomatic infections cause the diarrhoeal disease giardiasis in humans and animals, but at least half of the infections are asymptomatic. However, the molecular underpinnings of these different outcomes of the infection are still poorly defined. Here, we studied the early transcriptional response to G. intestinalis trophozoites, the disease-causing life-cycle stage, in human enteroid-derived, 2-dimensional intestinal epithelial cell (IEC) monolayers. Trophozoites preconditioned in media that maximise parasite fitness triggered only neglectable inflammatory transcription in the IECs during the first hours of co-incubation. By sharp contrast, “non-fit” or lysed trophozoites induced a vigorous IEC transcriptional response, including high up-regulation of many inflammatory cytokines and chemokines. Furthermore, “fit” trophozoites could even suppress the stimulatory effect of lysed trophozoites in mixed infections, suggesting active G. intestinalis suppression of the IEC response. By dual-species RNA-sequencing, we defined the IEC and G. intestinalis gene expression programs associated with these differential outcomes of the infection. Taken together, our results inform on how G. intestinalis infection can lead to such highly variable effects on the host, and pinpoints trophozoite fitness as a key determinant of the IEC response to this common parasite.

The domed architecture ofGiardia’s ventral disc is necessary for attachment and host pathogenesis

“…The recent development of primary organoids derived from small intestinal stem cells [6,36]has opened new avenues for understanding Giardia pathogenesis, particularly considering that inflammation does not necessarily play a significant role in the disease. In brief, 3D organoid cultures are derived from human duodenal biopsy specimens and used to establish a 2-dimensional transwell system known as organoid-derived monolayers (ODMs).…”

“…Giardia colonization and proliferation in the small intestine also disrupts the ecological homeostasis of gastrointestinal commensal microbes [5]. Despite Giardia's significance in global health, the mechanisms of pathogenesis are poorly understood and have been vaguely described as "multifactorial" [1] yet may include parasite metabolism, parasite "fitness" [6], secretion of cysteine proteases [7], or host microbiome dysbiosis [5].…”

“…Disc-mediated attachment of Giardia to the microvilli could directly induce cellular pathology in the host, yet this is perhaps the least explored potential pathogenic mechanism. Early observations of Giardia trophozoites attached to the epithelium showed prominent ventral disc-shaped depressions that remained in the microvilli after parasites had detached [5][6][7] . Disc-and lateral crest-mediated attachment by a single trophozoite would affect roughly 2000 microvilli, and attachment has been proposed to cause both direct and/or indirect host cellular damage that includes shortened microvilli and malabsorption.…”

Equine enteroid-derived monolayers recapitulate key features of parasitic intestinal nematode infection

“…The small 3-D structures of polarized intestinal cells at various stages of differentiation, forming a budding lumen with closed ends, allow studies of enteric infections with a minimal use of experimental animals. To date, most published work on organoid-pathogen interactions involves viruses, bacteria and protozoa [ 6 – 8 ], while the organoid technology has only just begun to be explored for studies of gastrointestinal (GI) nematodes [ 9 – 12 ]. Gastrointestinal nematode infections cause health problems in both human and veterinary medicine that tend to aggravate with the development of anthelminthic resistance as reported for decades [ 13 , 14 ].…”

Equine enteroid-derived monolayers recapitulate key features of parasitic intestinal nematode infection

“…Stem cell-derived intestinal organoid cultures provide unique opportunities for detailed studies of the hostpathogen interplay at the intestinal epithelium of various animal species [1,2]. To date, most published work on organoid-pathogen interactions involves viruses, bacteria and protozoa [3][4][5], while the organoid technology has only just begun to be explored for studies of gastrointestinal (GI) nematodes [6][7][8][9].…”