Novel cholinesterase paralogs of Schistosoma mansoni have perceived roles in cholinergic signaling, glucose scavenging and drug detoxification and are essential for parasite survival

Abstract

Cholinesterase (ChE) function in schistosomes is essential for orchestration of parasite neurotransmission but has been poorly defined with respect to the molecules responsible. Interrogation of the S. mansoni genome has revealed the presence of three ChE domain-containing genes (Smche)s, which we have shown to encode two functional acetylcholinesterases (AChE)s (Smache1 - smp_154600 and Smache3 - smp_136690) and a butyrylcholinesterase (BChE) (Smbche1 - smp_125350). Antibodies to recombinant forms of each SmChE localized the proteins to the tegument and neuromusculature of adults and schistosomula and developmental expression profiling differed among the three molecules, suggestive of functions extending beyond traditional cholinergic signaling. For the first time in schistosomes, we identified ChE enzymatic activity in fluke excretory/secretory (ES) products and, using proteomic approaches, attributed this activity to the presence of SmAChE1 and SmBChE1. To address the hypothesis that tegumental AChE mediates exogenous glucose scavenging by the parasite, we show that RNAi-mediated knockdown of smache1 and smache3, but not smbche1, significantly reduces glucose uptake by schistosomes. Parasite survival in vitro and in vivo was significantly impaired by silencing of each smche, either individually or in combination, attesting to the essential roles of these molecules. Lastly, in the first characterization study of a BChE from helminths, evidence is provided that SmBChE1 may act as a bio-scavenger of AChE inhibitors as the addition of recombinant SmBChE1 to parasite cultures mitigated the effect of the anti-schistosome AChE inhibitor DDVP (DDVP), whereas smbche1-silenced parasites displayed increased sensitivity to DDVP.\n\nAuthor summaryCholinesterases - aceytlcholinesterases (AChE)s and butyrylcholinesterases (BChE)s - are multi-functional enzymes that play a pivotal role in the nervous system of parasites by regulating neurotransmission through acetylcholine hydrolysis. Herein, we provide a detailed characterization of schistosome cholinesterases using molecular, enzymatic and gene-silencing approaches and show evidence for these molecules having roles in glucose scavenging and drug detoxification, in addition to their neuronal function. Further, we demonstrate the importance of these proteins to parasite development and survival through gene knockdown experiments in laboratory animals, providing evidence for the use of these proteins in the development of novel intervention strategies against schistosomiasis.