Repeat-Driven Generation of Antigenic Diversity in a Major Human Pathogen, Trypanosoma cruzi

Trypanosoma cruzi, a zoonotic kinetoplastid protozoan parasite, is the causative agent of American trypanosomiasis (Chagas disease). Having a very plastic, repetitive and complex genome, the parasite displays a highly diverse repertoire of surface molecules, with pivotal roles in cell invasion, immune evasion and pathogenesis. Before 2016, the complexity of the genomic regions containing these genes impaired the assembly of a genome at chromosomal level, making it impossible to study the structure and function of the several thousand repetitive genes encoding the surface molecules of the parasite. We here describe the genome assembly of the Sylvio X10/1 genome sequence, which since 2016 has been used as a reference genome sequence for T. cruzi clade I (TcI), produced using high coverage PacBio single-molecule sequencing. It was used to analyze deep Illumina sequence data from 34 T. cruzi TcI isolates and clones from different geographic locations, sample sources and clinical outcomes. Resolution of the surface molecule gene distribution showed the unusual duality in the organization of the parasite genome, a synteny of the core genomic region with related protozoa flanked by unique and highly plastic multigene family clusters encoding surface antigens. The presence of abundant interspersed retrotransposons in these multigene family clusters suggests that these elements are involved in a recombination mechanism for the generation of antigenic variation and evasion of the host immune response on these TcI strains. The comparative genomic analysis of the cohort of TcI strains revealed multiple cases of such recombination events involving surface molecule genes and has provided new insights into T. cruzi population structure.

Glutamine metabolism modulates azole susceptibility in Trypanosoma cruzi amastigotes

The mechanisms underlying resistance of the Chagas disease parasite, Trypanosoma cruzi, to current therapies are not well understood, including the role of metabolic heterogeneity. We found that limiting exogenous glutamine protects actively dividing amastigotes from ergosterol biosynthesis inhibitors (azoles), independent of parasite growth rate. The antiparasitic properties of azoles are derived from inhibition of lanosterol 14α-demethylase (CYP51) in the endogenous sterol synthesis pathway. We find that carbons from ¹³C-glutamine feed into amastigote sterols and into metabolic intermediates that accumulate upon CYP51 inhibition. Incorporation of ¹³C-glutamine into endogenously synthesized sterols is increased with BPTES treatment, an inhibitor of host glutamine metabolism that sensitizes amastigotes to azoles. Similarly, amastigotes are re-sensitized to azoles following addition of metabolites upstream of CYP51, raising the possibility that flux through the sterol synthesis pathway is a determinant of sensitivity to azoles and highlighting the potential role for metabolic heterogeneity in recalcitrant T. cruzi infection.

A Novel Antiparasitic Compound Kills Ring-Stage Plasmodium falciparum and Retains Activity Against Artemisinin-Resistant Parasites

Spreading antimalarial resistance threatens effective treatment of malaria, an infectious disease caused by Plasmodium parasites. We identified a compound, BCH070, that inhibits asexual growth of multiple antimalarial-resistant strains of Plasmodium falciparum (half maximal inhibitory concentration [IC50] = 1-2 µM), suggesting that BCH070 acts via a novel mechanism of action. BCH070 preferentially kills early ring-form trophozoites, and, importantly, equally inhibits ring-stage survival of wild-type and artemisinin-resistant parasites harboring the PfKelch13:C580Y mutation. Metabolomic analysis demonstrates that BCH070 likely targets multiple pathways in the parasite. BCH070 is a promising lead compound for development of new antimalarial combination therapy that retains activity against artemisinin-resistant parasites.

Surface-targeted lysosomal membrane glycoprotein-1 (Lamp-1) enhances lysosome exocytosis and cell invasion by Trypanosoma cruzi

To gain entry into non-phagocytic cells, Trypanosoma cruzi trypomastigotes recruit lysosomes to the host cell surface. Lysosome fusion at the site of parasite entry leads to the formation of a parasitophorous vacuole with lysosomal properties. Here, we show that increased expression of the lysosomal membrane glycoprotein Lamp-1 at the cell surface renders CHO cells more susceptible to trypomastigote invasion in a microtubule-dependent fashion. Mutation of critical residues in the lysosome-targeting motif of Lamp-1 abolished the enhancement of T. cruzi invasion. This suggests that interactions dependent on Lamp-1 cytoplasmic tail motifs, and not the surface-exposed luminal domain, modulate T. cruzi entry. Measurements of Ca2+-triggered exocytosis of lysosomes in these cell lines revealed an enhancement of beta-hexosaminidase release in cells expressing wild-type Lamp-1 on the plasma membrane; this effect was not observed in cell lines transfected with Lamp-1 cytoplasmic tail mutants. These results also implicate Ca2+-regulated lysosome exocytosis in cell invasion by T. cruzi and indicate a role for the Lamp-1 cytosolic domain in promoting more efficient fusion of lysosomes with the plasma membrane.

Characterization of a small variable surface glycoprotein from Trypanosoma vivax

Several biochemical properties of a variant surface glycoprotein (VSG) from the parasite Trypanosoma (Duttonella) vivax have been determined. ILDat 2.1 VSG is approximately 40 kDa in size making this the smallest trypanosome VSG described to date. The glycolipid anchor of ILDat 2.1 VSG is resistant to treatment with T. brucei-derived phospholipase C and data based on lectin affinity chromatography, incorporation of radiolabelled sugar and treatment with endoglycosidase H suggest that the T. vivax VSG bears little carbohydrate. cDNA to ILDat 2.1 VSG mRNA has been cloned and the encoded protein sequence includes the N-terminal amino acid peptide sequence derived from native VSG. The molecular weight of the VSG predicted from the translated cDNA sequence is similar to that of the native molecule and in support of the biochemical data it is devoid of sites for N-linked glycosylation. Examination of the deduced ILDat 2.1 VSG protein sequence reveals that it is most similar to T. congolense VSGs in the distribution of Cys residues and like the former it does not contain any of the defined VSG C-terminal domain types. However, unlike T. congolense VSGs it does not readily fit into the currently described VSG N-terminal domain types. Our studies suggest that ILDat 2.1 VSG is distinct from any of the previously characterized VSGs.

Neuropsychological function in borderline personality disorder

To evaluate the possibility of an underlying dimension of organicity in borderline personality disorder (BPD), a carefully diagnosed group of borderline patients was assessed across a wide range of neuropsychological functions and then was compared to an age- and education-matched non-patient control group. The BPD group had significantly lower Verbal, Performance, and Full Scale IQ scores on the WAIS-R. The BPD group also was impaired significantly on motor skills, figural memory, complex visuomotor integration, social or interpersonal intelligence, and on a measure of susceptibility to interference. This pattern of deficits localized to the fronto-temporal regions and became more pronounced when a subgroup analysis was performed. This study suggests that subtle organic factors may be operative in some, but not all, BPD patients.