Mirna Nascimento

Bio: Mirna Nascimento is an academic researcher from McGill University. The author has contributed to research in topics: Leishmania & Amastigote. The author has an hindex of 4, co-authored 4 publications receiving 107 citations.

Intracellular eukaryotic parasites have a distinct unfolded protein response.

Abstract: Insult to the endoplasmic reticulum (ER) activates the Unfolded Protein Response (UPR), a set of signaling pathways that protect the cell from the potential damage caused by improperly folded proteins. Accumulation of misfolded proteins in the ER lumen initiates a series of signal transduction events via activation of three transmembrane ER proteins: Ire1, Atf6 and PERK. Activation of these proteins results in the transcriptional up-regulation of the components of the folding, trafficking and degradation machinery in the ER. PERK further reduces the load on the ER via the phosphorylation of eIF2α, attenuating general protein translation. It is believed that the UPR evolved as a transcriptional response that up-regulates protein folding machinery in the ER and later gained the ability to decrease ER load by attenuating general protein translation in metazoa. However, our in silico analyses of protozoan parasites revealed an absence of proteins involved in the transcriptionally mediated UPR and the presence of both PERK and its target eIF2α. Consistent with these observations, stimulation of the UPR in Leishmania donovani identified an absence of up-regulation of the ER chaperone BiP, the canonical ER chaperone modulated by the UPR in higher eukaryotes, while exhibiting increased phosphorylation of eIF2α which has been shown to attenuate protein translation. We further observed that L. donovani is more sensitive to UPR inducing agents than host macrophages, suggesting that the less evolved stress response could provide a new avenue for therapeutic treatment of parasitic infections.

Heterologous expression of a mammalian protein tyrosine phosphatase gene in Leishmania: effect on differentiation.

Abstract: Leishmania is a protozoan pathogen which is transmitted to humans through the bite of an infected sandfly. This infection results in a spectrum of diseases throughout the developing world, collectively known as leishmaniasis. During its life cycle, Leishmania differentiates from the promastigote stage in the sandfly vector into the amastigote stage in the mammalian host where it multiplies exclusively in macrophage phagolysosomes. Although differentiation of Leishmania is essential for its survival and pathogenesis in the mammalian host, this process is poorly understood. In higher eukaryotic cells, protein tyrosine phosphorylation plays a central role in cell proliferation, differentiation and overall function. We have therefore investigated the role of protein tyrosine phosphorylation in Leishmania differentiation by undertaking complementary approaches to mediate protein tyrosine dephosphorylation in vivo. In the present study, L. donovani were engineered to express a mammalian protein tyrosine phosphatase, or were treated with inhibitors of protein tyrosine kinases, and the resulting phenotype was examined. Both approaches resulted in a partial differentiation from promastigotes to amastigotes including the expression of the amastigote specific A2 protein, morphological change and increased virulence. These data provide support for the involvement of tyrosine phosphorylation in the differentiation of Leishmania.

Targeting the cell stress response of plasmodium falciparum to overcome artemisinin resistance

Abstract: Successful control of falciparum malaria depends greatly on treatment with artemisinin combination therapies. Thus, reports that resistance to artemisinins (ARTs) has emerged, and that the prevalence of this resistance is increasing, are alarming. ART resistance has recently been linked to mutations in the K13 propeller protein. We undertook a detailed kinetic analysis of the drug responses of K13 wild-type and mutant isolates of Plasmodium falciparum sourced from a region in Cambodia (Pailin). We demonstrate that ART treatment induces growth retardation and an accumulation of ubiquitinated proteins, indicative of a cellular stress response that engages the ubiquitin/proteasome system. We show that resistant parasites exhibit lower levels of ubiquitinated proteins and delayed onset of cell death, indicating an enhanced cell stress response. We found that the stress response can be targeted by inhibiting the proteasome. Accordingly, clinically used proteasome inhibitors strongly synergize ART activity against both sensitive and resistant parasites, including isogenic lines expressing mutant or wild-type K13. Synergy is also observed against Plasmodium berghei in vivo. We developed a detailed model of parasite responses that enables us to infer, for the first time, in vivo parasite clearance profiles from in vitro assessments of ART sensitivity. We provide evidence that the clinical marker of resistance (delayed parasite clearance) is an indirect measure of drug efficacy because of the persistence of unviable parasites with unchanged morphology in the circulation, and we suggest alternative approaches for the direct measurement of viability. Our model predicts that extending current three-day ART treatment courses to four days, or splitting the doses, will efficiently clear resistant parasite infections. This work provides a rationale for improving the detection of ART resistance in the field and for treatment strategies that can be employed in areas with ART resistance.

Determinants for the Development of Visceral Leishmaniasis Disease

Abstract: Leishmaniasis is a vector-borne neglected tropical disease associated with a spectrum of clinical manifestations, ranging from self-healing cutaneous lesions to fatal visceral infections. Among the most important questions in Leishmania research is why some species like L. donovani infect visceral organs, whereas other species like L. major remain in the skin. The determinants of visceral leishmaniasis are still poorly understood, although genomic, immunologic, and animal models are beginning to provide important insight into this disease. In this review, we discuss the vector, host, and pathogen factors that mediate the development of visceral leishmaniasis. We examine the progression of the parasite from the initial site of sand fly bite to the visceral organs and its ability to survive there. The identification of visceral disease determinants is required to understand disease evolution, to understand visceral organ survival mechanisms, and potentially to develop better interventions for this largely neglected disease.