The Schistosoma mansoni tegumental allergen protein, SmTAL1: Binding to an IQ-motif from a voltage-gated ion channel and effects of praziquantel

Progress interrogating TRPMPZQ as the target of praziquantel

The drug praziquantel (PZQ) has served as the long-standing drug therapy for treatment of infections caused by parasitic flatworms. These encompass diseases caused by parasitic blood, lung, and liver flukes, as well as various tapeworm infections. Despite a history of clinical usage spanning over 4 decades, the parasite target of PZQ has long resisted identification. However, a flatworm transient receptor potential ion channel from the melastatin subfamily (TRPMPZQ) was recently identified as a target for PZQ action. Here, recent experimental progress interrogating TRPMPZQ is evaluated, encompassing biochemical, pharmacological, genetic, and comparative phylogenetic data that highlight the properties of this ion channel. Various lines of evidence that support TRPMPZQ being the therapeutic target of PZQ are presented, together with additional priorities for further research into the mechanism of action of this important clinical drug.

SmTAL-9, a Member of the Schistosoma mansoni Tegument Allergen-Like Family, Is Important for Parasite Survival and a Putative Target for Drug/Vaccine Development

The tegument of Schistosoma mansoni is involved in essential functions for parasite survival and is known to stimulate immune responses in pre-clinical vaccine trials. Smtal-9, a member of the tegument-allergen-like (TAL) family, is one of the components of the tegument of schistosomula recognized by sera from immunized and protected mice. In this work, we assessed the role of Smtal-9 in parasite survival using the RNAi approach. Also, we cloned and expressed a recombinant form of Smtal-9 and evaluated its ability to induce protection in mice. Smtal-9 knockdown did not impact parasite survival in vitro, but significantly decreased schistosomula size. Additionally, significant reduction in both parasite and egg burdens were observed in mice inoculated with Smtal-9-knockdown schistosomula. Immunization using the Smtal-9 as an antigen conferred partial protection against challenge infection. Overall, our results indicate that Smtal-9 is a candidate target for drug and/or vaccine development due to its important role in parasite biology and survival.

Genome-wide insights into adaptive hybridisation across the Schistosoma haematobium group in West and Central Africa

Schistosomiasis remains a public health concern across sub-Saharan Africa; current control programmes rely on accurate mapping and high mass drug administration (MDA) coverage to attempt disease elimination. Inter-species hybridisation can occur between certain species, changing epidemiological dynamics within endemic regions, which has the potential to confound control interventions. The impact of hybridisation on disease dynamics is well illustrated in areas of Cameroon where urogenital schistosomiasis, primarily due to Schistosoma haematobium and hybrid infections, now predominate over intestinal schistosomiasis caused by Schistosoma guineensis. Genetic markers have shown the ability to identify hybrids, however the underlying genomic architecture of divergence and introgression between these species has yet to be established. In this study, restriction site associated DNA sequencing (RADseq) was used on archived adult worms initially identified as; Schistosoma bovis (n = 4), S. haematobium (n = 9), S. guineensis (n = 3) and S. guineensis x S. haematobium hybrids (n = 4) from Mali, Senegal, Niger, São Tomé and Cameroon. Genome-wide evidence supports the existence of S. guineensis and S. haematobium hybrid populations across Cameroon. The hybridisation of S. guineensis x S. haematobium has not been demonstrated on the island of São Tomé, where all samples showed no introgression with S. haematobium. Additionally, all S. haematobium isolates from Nigeria, Mali and Cameroon indicated signatures of genomic introgression from S. bovis. Adaptive loci across the S. haematobium group showed that voltage-gated calcium ion channels (Cav) could play a key role in the ability to increase the survivability of species, particularly in host systems. Where admixture has occurred between S. guineensis and S. haematobium, the excess introgressive influx of tegumental (outer helminth body) and antigenic genes from S. haematobium has increased the adaptive response in hybrids, leading to increased hybrid population fitness and viability.

Praziquantel: An Enigmatic, Yet Effective, Drug

Praziquantel is a remarkably effective drug for the treatment of schistosomiasis. It has few side effects, some of which have been attributed to its inactive enantiomer. Few, if any, verified cases of drug resistance have been reported in a clinical setting. The preponderance of scientific evidence suggests that the drug works by dysregulating calcium homeostasis in the worm. Voltage-gated calcium channels have been proposed as the main pharmacological target of praziquantel, although no direct evidence of interaction with this protein is available. Here, the biochemical pharmacology of praziquantel is briefly reviewed and a hypothesis for its mechanism proposed. This hypothesis suggests that the drug works, in part, by disrupting an interaction between a voltage-gated calcium channel (SmCav1B) and an accessory protein, SmTAL1.