Comparative Transcriptomic Exploration Reveals Unique Molecular Adaptations of Neuropathogenic Trichobilharzia to Invade and Parasitize Its Avian Definitive Host

Abstract

To date, most molecular investigations of schistosomatids have focused principally on blood flukes (schistosomes) of humans. Despite the clinical importance of cercarial dermatitis in humans caused by Trichobilharzia regenti and the serious neuropathologic disease that this parasite causes in its permissive avian hosts and accidental mammalian hosts, almost nothing is known about the molecular aspects of how this fluke invades its hosts, migrates in host tissues and how it interacts with its hosts’ immune system. Here, we explored selected aspects using a transcriptomic-bioinformatic approach. To do this, we sequenced, assembled and annotated the transcriptome representing two consecutive life stages (cercariae and schistosomula) of T. regenti involved in the first phases of infection of the avian host. We identified key biological and metabolic pathways specific to each of these two developmental stages and also undertook comparative analyses using data available for taxonomically related blood flukes of the genus Schistosoma. Detailed comparative analyses revealed the unique involvement of carbohydrate metabolism, translation and amino acid metabolism, and calcium in T. regenti cercariae during their invasion and in growth and development, as well as the roles of cell adhesion molecules, microaerobic metabolism (citrate cycle and oxidative phosphorylation), peptidases (cathepsins) and other histolytic and lysozomal proteins in schistosomula during their particular migration in neural tissues of the avian host. In conclusion, the present transcriptomic exploration provides new and significant insights into the molecular biology of T. regenti, which should underpin future genomic and proteomic investigations of T. regenti and, importantly, provides a useful starting point for a range of comparative studies of schistosomatids and other trematodes.

Nitric oxide and cytokine production by glial cells exposed in vitro to neuropathogenic schistosome Trichobilharzia regenti

“…These proteases are highly expressed in migrating schistosomula [50, 51] and can get in contact with the adjacent nervous tissue either when the parasite regurgitates (TrCB1.1 as a digestive enzyme, [18]) or when it struggles through the tissue (TrCB2 as a neurohistolytic enzyme, [13]). In our recent work [17] it remained questionable if secretions of schistosomula may be involved in the CNS pathogenesis, particularly in activation of glial cells.…”

Isoforms of Cathepsin B1 in Neurotropic Schistosomula of Trichobilharzia regenti Differ in Substrate Preferences and a Highly Expressed Catalytically Inactive Paralog Binds Cystatin

“…Therefore, pepsin-processed enzymes were used in most experiments. The asparaginyl endopeptidase (AE, legumain) was confirmed as an endogenous trans-processing enzyme activating other digestive peptidases in human schistosomes (Sajid et al, 2003) and three transcripts coding this enzyme were also found in T. regenti transcriptome (Leontovyč et al, 2016(Leontovyč et al, , 2019. We were able to trans-process the pro-TrCB1 using tick IrAE, obtaining several intermediates during short-time incubations, but this method was not widely used in our experiments, since it provided low yields.…”

“…Cathepsins B also act as potent (carboxy-) exopeptidases (Illy et al, 1997). Several transcripts of cathepsin L and D genes were found also in the transcriptome of T. regenti schistosomula (Leontovyč et al, 2016).…”

“…This was confirmed by incubation with recombinant IrAE (Sojka et al, 2007), which resulted in a single band of ≈30 kDa formed through several intermediates arisen by specific cleavage at sites with Asn and Asp at P1 position. This suggests that the transcripts coding for AE found in the transcriptome of T. regenti (Leontovyč et al, 2016(Leontovyč et al, , 2019 may be involved in the removal of the pro-sequence from pro-TrCB1.6 in vivo. Also, transprocessing of pro-TrCB1.6wt with pepsin-processed active forms pepTrCB1.1 and pepTrCB1.4 resulted in the formation of a major (≈32 kDa) and a minor (≈30 kDa) product in both cases.…”

“…Indeed, both stages require gut-associated peptidases to digest host proteins. In T. regenti, isoforms of the cysteine peptidase cathepsin B1 (TrCB1) are expressed in the gut and represent a subset of a larger group of peptidases that are responsible for digestion (Dvořák et al, 2005;Dolečková et al, 2010;Leontovyč et al, 2016Leontovyč et al, , 2019, much like in human Schistosoma species (Caffrey et al, 2004) and other helminths (Williamson et al, 2003(Williamson et al, , 2004Delcroix et al, 2006;Caffrey et al, 2018). Cathepsin B (IUPAC: EC 3.4.22.1; MEROPS: Clan CA, Family C1) is unique among other papain-like cysteine peptidases due to its ability to act as both an endopeptidase and carboxy-exopeptidase (peptidyl dipeptidase) ( Barrett and Kirschke, 1981).…”