Genetic analysis of praziquantel response in schistosome parasites implicates a transient receptor potential channel

Abstract

Mass treatment with praziquantel (PZQ) monotherapy is the mainstay for schistosome treatment. This drug shows imperfect cure rates in the field and parasites showing reduced response to PZQ can be selected in the laboratory, but the extent of resistance in Schistosoma mansoni populations is unknown. We examined the genetic basis of variation in PZQ response in a S. mansoni population (SmLE-PZQ-R) selected with PZQ in the laboratory: 35% of these worms survive high dose (73 µg/mL) PZQ treatment. We used genome wide association to map loci underlying PZQ response. The major chr. 3 peak shows recessive inheritance and contains a transient receptor potential (Sm.TRPMPZQ) channel (Smp_246790), activated by nanomoles of PZQ. Marker-assisted selection of parasites at a single Sm.TRPMPZQ SNP enriched populations of PZQ-R and PZQ-S parasites showing >377 fold difference in PZQ response. The PZQ-R parasites survived treatment in rodents better than PZQ-S. Resistant parasites show 2.25-fold lower expression of Sm.TRPMPZQ than sensitive parasites. Specific chemical blockers of Sm.TRPMPZQ enhanced PZQ resistance, while Sm.TRPMPZQ activators increased sensitivity. A single SNP in Sm.TRPMPZQ differentiated PZQ-ER and PZQ-ES lines, but mutagenesis showed this was not involved in PZQ-R, suggesting linked regulatory changes. We surveyed Sm.TRPMPZQ sequence variation in 259 individual parasites from the Newand Old World revealing one nonsense mutation, that results in a truncated protein with no PZQ binding site. Our results demonstrate that Sm.TRPMPZQ underlies variation in PZQ response in S. mansoni and provides an approach for monitoring emerging PZQ-resistance alleles in schistosome elimination programs..

Mechanism of praziquantel action at a parasitic flatworm ion channel

“…Le Clec’h et al . ( 17 ), in the companion article, use genetic approaches to demonstrate how Sm .TRPM PZQ variation modulates PZQ responsiveness in worm populations selected to display differential sensitivity to PZQ. Identification of Sm .TRPM PZQ as a target of PZQ, and resolution of the residues critical for PZQ binding, now enables molecular surveillance approaches to identifying Sm .TRPM PZQ variants that could contribute to lower PZQ efficacy in the field.…”

“…This insight, together with the genetic analyses of Le Clec’h et al . ( 17 ), defines TRPM PZQ as a druggable target for combating diseases caused by parasitic flatworms.…”

Schistosome Sulfotransferases: Mode of Action, Expression and Localization

“…There is some concern that the emergence of PZQ-resistant worms would be inevitable due to the use of mass chemotherapy of PZQ, adding selection pressure to the parasite populations [ 14 ]. Evidence for resistance to PZQ has already been observed in the field and selected for in the laboratory [ 14 , 15 , 16 , 17 , 18 , 19 ]. The efficacy of OXA and PZQ is comparable, although in some cases OXA is more effective against S. mansoni when PZQ drug failure is observed [ 20 ].…”

Genomic analysis of a parasite invasion: Colonization of the Americas by the blood fluke Schistosoma mansoni

“…There are multiple biomedically important traits of interest that vary in S. mansoni populations, including drug susceptibility or resistance, host specificity and cercarial production (Anderson et al, 2018 ). We recently used GWAS for mapping resistance to the first‐line drug (Praziquantel) in laboratory schistosome populations (Le Clec’h et al, 2021 ). Most laboratory S. mansoni populations tested were from South America, where LD decays relatively slowly: these are not ideal for GWAS.…”

“…Single nucleotide variants (SNVs) were called with HaplotypeCaller and GenotypeGVCFs on a contig‐by‐contig basis, combined into a gvcf per individual, and finally merged into a single gvcf for the entire data set. We used high‐quality, SNV data from Le Clec’h et al ( 2021 ) as a training data set for variant recalibration and scored SNV quality using “‐an SOR ‐an MQ ‐an MQRankSum ‐an ReadPosRankSum.” Sensitivity Tranches (‐‐truth‐sensitivity‐tranche) were set at 100, 99.5, 99, 97.5, 95 and 90. We recalibrated SNVs using the 97.5 sensitivity tranche and filtered low‐confidence sites with the following set of filters (‐‐filter‐expression): QD < 2.0, MQ < 30.0, FS > 60.0, SOR > 3.0, MQRankSum < −12.5 and ReadPosRankSum < −8.0."…”