Leishmania (Leishmania) amazonensis is an intracellular protozoan parasite responsible for the cutaneous leishmaniasis. The parasite replicates inside mammalian macrophage to establish infection. Host-pathogen interactions result in microRNA-mediated post-transcriptional regulation of host genes involved in inflammatory immune response. We analyzed macrophage miRNA profiles during L. (L.) amazonensis infection. The regulation of macrophage miRNA expression by the parasite correlates with/depends on parasite arginase activity during infection. L. (L.) amazonensis (La-WT) presented significant miRNA profile alteration (27%) compared to L. (L.) amazonensis arginase knockout (La-arg−) (~40%) in relation to uninfected-macrophages. We observed that 78% of the altered miRNAs were up-regulated in La-WT infection, while only 32% were up-regulated in La-arg−-infected macrophages. In contrast to La-WT, the lack of L. (L.) amazonensis arginase led to the inhibition of miR-294 and miR-721 expression. The expression of miR-294 and miR-721 was recovered to levels similar to La-WT in La-arg− addback mutant. The inhibition of miR-294/Nos2 and miR721/Nos2 interactions increased NOS2 expression and NO production, and reduced L. (L.) amazonensis infectivity, confirming Nos2 as target of these miRNAs. The role of miR-294 and miR-721 in the regulation of NOS2 expression during Leishmania replication in infected macrophages pointing these miRNAs as potential new targets for drug development.

In Leishmania, de novo polyamine synthesis is initiated by the cleavage of L-arginine to urea and L-ornithine by the action of arginase (ARG, E.C. 3.5.3.1). Previous studies in L. major and L. mexicana showed that ARG is essential for in vitro growth in the absence of polyamines and needed for full infectivity in animal infections. The ARG protein is normally found within the parasite glycosome, and here we examined whether this localization is required for survival and infectivity. First, the localization of L. amazonensis ARG in the glycosome was confirmed in both the promastigote and amastigote stages. As in other species, arg− L. amazonensis required putrescine for growth and presented an attenuated infectivity. Restoration of a wild type ARG to the arg − mutant restored ARG expression, growth and infectivity. In contrast, restoration of a cytosol-targeted ARG lacking the glycosomal SKL targeting sequence (argΔSKL) restored growth but failed to restore infectivity. Further study showed that the ARGΔSKL protein was found in the cytosol as expected, but at very low levels. Our results indicate that the proper compartmentalization of L. amazonensis arginase in the glycosome is important for enzyme activity and optimal infectivity. Our conjecture is that parasite arginase participates in a complex equilibrium that defines the fate of L-arginine and that its proper subcellular location may be essential for this physiological orchestration.

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Leishmania is a protozoan parasite that alternates its life cycle between the sand fly and the mammalian host macrophages, involving several environmental changes. The parasite responds to these changes by promoting a rapid metabolic adaptation through cellular signaling modifications that lead to transcriptional and post-transcriptional gene expression regulation and morphological modifications. Molecular approaches such as gene expression regulation, next-generation sequencing (NGS), microRNA (miRNA) expression profiling, in cell Western blot analyses and enzymatic activity profiling, have been used to characterize the infection of murine BALB/c and C57BL/6 macrophages, as well as the human monocytic cell-lineage THP-1, with Leishmania amazonensis wild type (La-WT) or arginase knockout (La-arg-). These models are being used to elucidate physiological roles of arginine and polyamines pathways and the importance of arginase for the establishment of the infection. In this review, we will describe the main aspects of Leishmania-host interaction, focusing on the arginine and polyamines pathways and pointing to possible targets to be used for prognosis and/or in the control of the infection. The parasite enzymes, arginase and nitric oxide synthase-like, have essential roles in the parasite survival and in the maintenance of infection. On the other hand, in mammalian macrophages, defense mechanisms are activated inducing alterations in the mRNA, miRNA and enzymatic profiles that lead to the control of infection. Furthermore, the genetic background of both parasite and host are also important to define the fate of infection.