Trashing old notions: the significance of small tRNAs in Trichomonas vaginalis extracellular vesicles and implications for host-parasite communication

Abstract

Trichomoniasis is a common sexually transmitted infection caused by the protozoan Trichomonas vaginalis. Extracellular vesicles (EVs) released by this parasite have been shown to play a role in priming host cells for infection. However, the contribution of EV RNA cargo to the infection process remains unclear, which inspired the three experimental chapters of this study. The first chapter compared sRNA-seq data from EVs and their originating cells. The analysis revealed that while cells and EVs had similar RNA biotype abundance, EVs contained smaller RNA fragments. This finding suggested that specific fragment lengths, rather than functional RNA biotypes, were preferentially packaged in the EVs. Additionally, highly abundant fragments contained a known translation inhibitory motif, the terminal oligoguanine (TOG). In the second chapter, quantitative PCR was employed to compare the abundance of selected fragments in cells and EVs of different sizes subjected to stress-free and traditional treatments. The results showed that the conventional treatment exposed the parasites to higher stress, as evidenced by a higher abundance of tRNA fragments (tRFs) in this treatment than in the stress-free one. Furthermore, total fragments were more abundant in EVs exposed to the traditional treatment and in cells exposed to the stress-free treatment, suggesting that the cells exported even more of those fragments in EVs when subjected to stress. The last experimental chapter investigated the inhibitory effect of TOG-containing fragments on translation, both in vitro and in vivo. The results showed that fragments with TOG4 (GGGG) were more inhibitory to in vitro translation (IVT) than TOG3 (GGG) and TOG5 (GGGGG), and tRFs were more inhibitory than tRNA halves. However, some fragments were inhibitory independently of their 5’ sequence, suggesting something other than their 5’end interferes with translation. The analysis of stress granules formation in HeLa cells further corroborated the IVT results. Overall, this study discovered that T. vaginalis packages specific tRNA fragments, including those containing TOGs, in response to stress. These fragments are associated with translation inhibition in human cells. The findings suggest that tRFs, rather than typical miRNAs, are critical small regulatory RNAs produced and packaged by this parasite to modulate the outcome of this infection. Understanding the biology of T. vaginalis and the role of its EV RNA cargo in infection might help the development of alternative and effective treatments for trichomoniasis.