Mechanisms of DNA repair in Trypanosoma cruzi: What do we know so far?

Dissecting the interstrand crosslink DNA repair system of Trypanosoma cruzi

DNA interstrand crosslinks (ICLs) are toxic lesions that can block essential biological processes. Here we show Trypanosoma cruzi, the causative agent of Chagas disease, is susceptible to ICL-inducing compounds including mechlorethamine and novel nitroreductase-activated prodrugs that have potential in treating this infection. To resolve such lesions, cells co-opt enzymes from "classical" DNA repair pathways that alongside dedicated factors operate in replication-dependent and -independent mechanisms. To assess ICL repair in T. cruzi, orthologues of SNM1, MRE11 and CSB were identified and their function assessed. The T. cruzi enzymes could complement the mechlorethamine susceptibility phenotype displayed by corresponding yeast and/or T. brucei null confirming their role as ICL repair factors while GFP-tagged TcSNM1, TcMRE11 and TcCSB were shown to localise to the nuclei of insect and/or intracellular form parasites. Gene disruption demonstrated that while each activity was non-essential for T. cruzi viability, nulls displayed a growth defect in at least one life cycle stage with TcMRE11-deficient trypomastigotes also compromised in mammalian cell infectivity. Phenotyping revealed all nulls were more susceptible to mechlorethamine than controls, a trait complemented by re-expression of the deleted gene. To assess interplay, the gene disruption approach was extended to generate T. cruzi deficient in TcSNM1/TcMRE11 or in TcSNM1/TcCSB. Analysis demonstrated these activities functioned across two ICL repair pathways with TcSNM1 and TcMRE11 postulated to operate in a replication-dependent system while TcCSB helps resolve transcription-blocking lesions. By unravelling how T. cruzi repairs ICL damage, specific inhibitors targeting repair components could be developed and used to increase the potency of trypanocidal ICL-inducing compounds.

Host DNA repair response to oxidative damage is modulated by Trypanosoma cruzi in a strain-dependent manner

The conservation of genomic integrity and stability is essential for cell survival. DNA Damage Responses (DDRs) are considered of paramount importance for all living beings and involve mechanisms of cell cycle regulation and damage-specific DNA repair pathways. Hydrogen peroxide (H₂O₂) is a compound that, in supraphysiological concentrations, damages biomolecules including the DNA, causing base modifications and strand breaks. There is evidence that Trypanosoma cruzi, the protozoan that causes Chagas disease, interferes in the host cell's DNA metabolism. In order to investigate the influence of T. cruzi infection over the host cell capacity to withstand and repair DNA damage, we analyzed L6 cells infected with Berenice, and Colombiana T. cruzi strains according to their viability, proliferation, morphology, DNA degradation, expression of DNA repair, and cell cycle genes following H₂O₂ treatment. It was noted that T. cruzi infection might act as either a stressor or a protective element of host DNA, depending on the strain and H₂O₂ concentration. Cells infected with Berenice strain and treated with 0.8 mM H₂O₂ presented a reduced DNA damage response intensity (e.g., BER and HR). Infection with T. cruzi Colombiana prevented the activation of DNA repair pathways in response to 0.8mM and 1.6mM H₂O₂ (NER and MMR). Nevertheless, since cellular viability was not significantly compromised in Colombiana-infected cells following the oxidative insult, it is possible that the parasite directly influenced the host DNA repair machinery. Our results support the notion that T. cruzi is able to modulate the host cell DNA metabolism in a strain-dependent manner, an event which can be explored in future drug development strategies.

Attaching a Dipeptide to Fullerene as an Antioxidant Hybrid against DNA Oxidation

Emerging evidence has revealed that oxidative damages of DNA correlate with the pathogenesis of some diseases, and numerous investigations have also suggested that supplementation of antioxidants is beneficial for keeping health by rectifying in vivo redox status. Here, we construct antioxidative dipeptides with the Ugi four-component reaction (comprising p-aminobenzyl alcohol, benzaldehyde, or vanillin, a series of antioxidative carboxylic acids and isocyanides as reagents) and then attempt to attach the dipeptides to [60]fullerene by the Bingel reaction. However, this endeavor does not lead to the amelioration of the radical-scavenging property because abilities of fullerenyl dipeptides to trap 2,2'-diphenyl-1-picrylhydrazyl and galvinoxyl radicals are still dependent upon the phenolic hydroxyl group in the dipeptide scaffold rather than upon the fullerenyl group. Alternatively, when the obtained fullerenyl dipeptides are evaluated in a peroxyl radical-induced oxidation of DNA, it is found that introducing a fullerene moiety into dipeptide enables antioxidative effect to be enhanced 20-30% because the fullerene moiety facilitates the corresponding dipeptide to intercalate with DNA strands, and thus, to increase the antioxidative efficacy. Our results suggest that connecting an antioxidative skeleton with the hydrophobic fullerene moiety might lead to a series of novel antioxidant hybrids applied for the inhibition of DNA oxidation.

DNA Double-Strand Breaks: A Double-Edged Sword for Trypanosomatids

For nearly all eukaryotic cells, stochastic DNA double-strand breaks (DSBs) are one of the most deleterious types of DNA lesions. DSB processing and repair can cause sequence deletions, loss of heterozygosity, and chromosome rearrangements resulting in cell death or carcinogenesis. However, trypanosomatids (single-celled eukaryotes parasites) do not seem to follow this premise strictly. Several studies have shown that trypanosomatids depend on DSBs to perform several events of paramount importance during their life cycle. For Trypanosoma brucei, DSBs formation is associated with host immune evasion via antigenic variation. In Trypanosoma cruzi, DSBs play a crucial role in the genetic exchange, a mechanism that is still little explored but appear to be of fundamental importance for generating variability. In Leishmania spp., DSBs are necessary to generate genomic changes by gene copy number variation (CNVs), events that are essential for these organisms to overcome inhospitable conditions. As DSB repair in trypanosomatids is primarily conducted via homologous recombination (HR), most of the events associated with DSBs are HR-dependent. This review will discuss the latest findings on how trypanosomatids balance the benefits and inexorable challenges caused by DSBs.

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.

Dual and Opposite Roles of Reactive Oxygen Species (ROS) in Chagas Disease: Beneficial on the Pathogen and Harmful on the Host

Chagas disease is a neglected tropical disease, which affects an estimate of 6-7 million people worldwide. Chagas disease is caused by Trypanosoma cruzi, which is a eukaryotic flagellate unicellular organism. At the primary infection sites, these parasites are phagocytized by macrophages, which produce reactive oxygen species (ROS) in response to the infection with T. cruzi. The ROS produce damage to the host tissues; however, macrophage-produced ROS is also used as a signal for T. cruzi proliferation. At the later stages of infection, mitochondrial ROS is produced by the infected cardiomyocytes that contribute to the oxidative damage, which persists at the chronic stage of the disease. The oxidative damage leads to a functional impairment of the heart. In this review article, we will discuss the mechanisms by which T. cruzi is able to deal with the oxidative stress and how this helps the parasite growth at the acute phase of infection and how the oxidative stress affects the cardiomyopathy at the chronic stage of the Chagas disease. We will describe the mechanisms used by the parasite to deal with ROS and reactive nitrogen species (RNS) through the trypanothione and the mechanisms used to repair the damaged DNA. Also, a description of the events produced by ROS at the acute and chronic stages of the disease is presented. Lastly, we discuss the benefits of ROS for T. cruzi growth and proliferation and the possible mechanisms involved in this phenomenon. Hypothesis is put forward to explain the molecular mechanisms by which ROS triggers parasite growth and proliferation and how ROS is able to produce a long persisting damage on cardiomyocytes even in the absence of the parasite.