Distinct Phenotypes Caused by Mutation of MSH2 in Trypanosome Insect and Mammalian Life Cycle Forms Are Associated with Parasite Adaptation to Oxidative Stress.

Santuza M R Teixeira,Carlos R Machado,Priscila C Campos,Jason Bolderson,Alvaro Acosta-Serrano,Julia B Miranda,Ceres L Alves,Richard Mcculloch,Viviane Grazielle-Silva,Tehseen Fatima Zeb

doi:10.1371/journal.pntd.0003870

Abstract

BackgroundDNA repair mechanisms are crucial for maintenance of the genome in all organisms, including parasites where successful infection is dependent both on genomic stability and sequence variation. MSH2 is an early acting, central component of the Mismatch Repair (MMR) pathway, which is responsible for the recognition and correction of base mismatches that occur during DNA replication and recombination. In addition, recent evidence suggests that MSH2 might also play an important, but poorly understood, role in responding to oxidative damage in both African and American trypanosomes.Methodology/Principal FindingsTo investigate the involvement of MMR in the oxidative stress response, null mutants of MSH2 were generated in Trypanosoma brucei procyclic forms and in Trypanosoma cruzi epimastigote forms. Unexpectedly, the MSH2 null mutants showed increased resistance to H2O2 exposure when compared with wild type cells, a phenotype distinct from the previously observed increased sensitivity of T. brucei bloodstream forms MSH2 mutants. Complementation studies indicated that the increased oxidative resistance of procyclic T. brucei was due to adaptation to MSH2 loss. In both parasites, loss of MSH2 was shown to result in increased tolerance to alkylation by MNNG and increased accumulation of 8-oxo-guanine in the nuclear and mitochondrial genomes, indicating impaired MMR. In T. cruzi, loss of MSH2 also increases the parasite capacity to survive within host macrophages.Conclusions/SignificanceTaken together, these results indicate MSH2 displays conserved, dual roles in MMR and in the response to oxidative stress. Loss of the latter function results in life cycle dependent differences in phenotypic outcomes in T. brucei MSH2 mutants, most likely because of the greater burden of oxidative stress in the insect stage of the parasite.

Highlights

Two members of the trypanosomatidae family, Trypanosoma cruzi and Trypanosoma brucei, are important human pathogens, since they cause, respectively, Chagas disease, or American trypanosomiasis, and African Sleeping Sickness, or Human African trypanosomiasis
The high genetic diversity found in the T. cruzi population and the highly diverse repertoire of surface glycoprotein genes found in T. brucei are crucial factors that ensure a successful infection in their hosts
Using knock-out mutants, we showed that, besides acting in the Mismatch Repair (MMR) pathway as a key protein that recognizes and repairs base mismatches, insertions or deletions that can occur after DNA replication, MSH2 has an additional role in the oxidative stress response

Summary

Introduction

Two members of the trypanosomatidae family, Trypanosoma cruzi and Trypanosoma brucei, are important human pathogens, since they cause, respectively, Chagas disease, or American trypanosomiasis, and African Sleeping Sickness, or Human African trypanosomiasis. The life cycles of both these parasites involve two hosts: an invertebrate vector and a mammalian host. Despite being similar in general strategy, the life cycle of T. brucei is different to that of T. cruzi in several key details. In the insect vector BSF cells differentiate into replicative procyclic forms (PCF), which undergo several further differentiation events associated with migration to the fly salivary glands, where non-replicative metacyclic trypomastigotes are formed and can be passed into a new mammalian host through the proboscis when the infected fly is feeding [3]. Irrespective of the detailed differences in the life cycles, differentiation between the mammal-infective and vector-infective forms of both T. cruzi and T. brucei is accompanied by dramatic metabolic changes and morphological alterations [4]. Recent evidence suggests that MSH2 might play an important, but poorly understood, role in responding to oxidative damage in both African and American trypanosomes

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