Gene expression analysis of wild Leishmania major isolates: identification of genes preferentially expressed in amastigotes

New insights to structure and immunological features of Leishmania lipophosphoglycan3

Leishmaniasis is a major public infectious disease caused by the genus Leishmania. No effective drug or vaccination strategy for leishmaniasis has been designed yet. Several intracellular Leishmania antigens have been recognized to serve in vaccination, ensuring long-lasting protection against Leishmania infection. Lipophosphoglican 3 (LPG3) as a member of the heat shock protein 90 family involves in the synthesis of lipophosphoglycan (LPG) and implicates in parasite virulence. Regarding the immunological properties of LPG3 particularly its N-terminal fragment, it would be considered as a favourable adjuvant in Leishmania vaccination.

Evidence of RNA editing in Leishmania braziliensis promastigotes

RNA editing in trypanosomatids is an elaborate form of post-transcriptional processing that inserts and deletes uridines in many mitochondrial pre-mRNAs, providing the genetic information needed to create functional transcripts. The process has been extensively analyzed in Trypanosoma brucei, Crithidia fasciculata, and Leishmania tarentolae. However, few data exist on this mechanism in pathogenic Leishmania species. Here, we show evidence that this process also operates in Leishmania braziliensis, being the first time that RNA editing has been described in a species of the Viannia subgenus. A partially edited transcript corresponding to the NADH dehydrogenase subunit 8 (ND8) gene was identified in L. braziliensis promastigotes. Sequence analysis allowed the identification of the maxicircle-encoded cryptogene, which shows a high degree of sequence conservation with the corresponding cryptogenes in other Leishmania species. Although an edition pattern could be postulated for the ND8 transcripts in L. braziliensis, attempts to isolate completely edited transcripts by RT-PCR were not fruitful; instead, many transcripts with partial and unexpected editing patterns were isolated. This data, together with our inability to detect full-size transcripts by Northern blotting in promastigotes of L. braziliensis, led us to the suggestion that the strain used in this study (M2904) lacks of critical RNA guides for a complete edition of ND8 transcripts.

Oligopeptidase B deficient mutants of Leishmania major

Oligopeptidase B is a clan SC, family S9 serine peptidase found in gram positive bacteria, plants and trypanosomatids. Evidence suggests it is a virulence factor and thus therapeutic target in both Trypanosoma cruzi and T. brucei, but little is known about its function in Leishmania. In this study L. major OPB-deficient mutants (Δopb) were created. These grew normally as promastigotes, had a small deficiency in their ability to undergo differentiation to metacyclic promastigotes, were significantly less able to infect and survive within macrophages in vitro, but were virulent to mice. These data suggest that L. major OPB itself is not an important virulence factor, indicating functional differences between trypanosomes and Leishmania in their interaction with the mammalian host. The possibility that an OPB-like enzyme (designated OPB2) in L. major might compensate for the loss of OPB in Δopb was investigated via by mapping its sequence onto the 1.6Å structure of L. major OPB. This suggested that the residues involved in the S1 and S2 subsites of OPB2 are identical to OPB and hence the substrate specificity would be similar. Consequently there may be redundancy between the two enzymes.

Searching for virulence factors in the non-pathogenic parasite to humans Leishmania tarentolae

Leishmania protozoa are obligate intracellular parasites that reside in the phagolysosome of host macrophages and cause a large spectrum of pathologies to humans known as leishmaniases. The outcome of the disease is highly dependent on the parasite species and on its ascribed virulence factors and the immune status of the host. Characterization of the genome composition of non-pathogenic species could ultimately open new horizons in Leishmania developmental biology and also the disease monitoring. Here, we provide evidence that the lizard non-pathogenic to humans Leishmania tarentolae species expresses an Amastin-like gene, cysteine protease B (CPB), lipophosphoglycan LPG3 and the leishmanolysin GP63, genes well-known for their potential role in the parasite virulence. These genes were expressed at levels comparable to those in L. major and L. infantum both at the level of mRNA and protein. Alignment of the L. tarentolae proteins with their counterparts in the pathogenic species demonstrated that the degree of similarity varied from 59% and 60% for Amastin, 89% for LPG3 and 71% and 68% for CPB, in L. major and L. infantum, respectively. Interestingly, the A2 gene, expressed specifically by the L. donovani complex which promotes visceralization, was absent in L. tarentolae. These findings suggest that the lack of pathogenicity in L. tarentolae is not associated with known virulence genes such as LPG3, CPB, GP63 and Amastin, and that other factors either unique to L. tarentolae or missing from this species may be responsible for the non-pathogenic potential of this lizard parasite.

Simultaneous gene expression profiling in human macrophages infected with Leishmania major parasites using SAGE

Background

Leishmania (L) are intracellular protozoan parasites that are able to survive and replicate within the harsh and potentially hostile phagolysosomal environment of mammalian mononuclear phagocytes. A complex interplay then takes place between the macrophage (MΦ) striving to eliminate the pathogen and the parasite struggling for its own survival.

To investigate this host-parasite conflict at the transcriptional level, in the context of monocyte-derived human MΦs (MDM) infection by L. major metacyclic promastigotes, the quantitative technique of serial analysis of gene expression (SAGE) was used.

Results

After extracting mRNA from resting human MΦs, Leishmania-infected human MΦs and L. major parasites, three SAGE libraries were constructed and sequenced generating up to 28,173; 57,514 and 33,906 tags respectively (corresponding to 12,946; 23,442 and 9,530 unique tags). Using computational data analysis and direct comparison to 357,888 publicly available experimental human tags, the parasite and the host cell transcriptomes were then simultaneously characterized from the mixed cellular extract, confidently discriminating host from parasite transcripts. This procedure led us to reliably assign 3,814 tags to MΦs' and 3,666 tags to L. major parasites transcripts. We focused on these, showing significant changes in their expression that are likely to be relevant to the pathogenesis of parasite infection: (i) human MΦs genes, belonging to key immune response proteins (e.g., IFNγ pathway, S100 and chemokine families) and (ii) a group of Leishmania genes showing a preferential expression at the parasite's intra-cellular developing stage.

Conclusion

Dual SAGE transcriptome analysis provided a useful, powerful and accurate approach to discriminating genes of human or parasitic origin in Leishmania-infected human MΦs. The findings presented in this work suggest that the Leishmania parasite modulates key transcripts in human MΦs that may be beneficial for its establishment and survival. Furthermore, these results provide an overview of gene expression at two developmental stages of the parasite, namely metacyclic promastigotes and intracellular amastigotes and indicate a broad difference between their transcriptomic profiles. Finally, our reported set of expressed genes will be useful in future rounds of data mining and gene annotation.

Putative markers of infective life stages in Leishmania (Viannia) braziliensis

Gene expression is known to vary significantly during the Leishmania life-cycle. Its monitoring might allow identification of molecular changes associated with the infective stages (metacyclics and amastigotes) and contribute to the understanding of the complex host-parasite relationships. So far, very few studies have been done on Leishmania (Viannia) braziliensis, one of the most pathogenic species. Such studies require, first of all, reference molecular markers. In the present work, we applied differential display analysis (DD analysis) in order to identify transcripts that might be (i) candidate markers of metacyclics and intracellular amastigotes of L. (V.) braziliensis or (ii) potential controls, i.e. constitutively expressed. In total, 48 DNA fragments gave reliable sequencing data, 29 of them being potential markers of infective stages and 12 potential controls. Eight sequences could be identified with reported genes. Validation of the results of DD analysis was done for 4 genes (2 differentially expressed and 2 controls) by quantitative real-time PCR. The infective insect stage-specific protein (meta 1) was more expressed in metacyclic-enriched preparations. The oligopeptidase b showed a higher expression in amastigotes. Two genes, glucose-6-phosphate dehydrogenase and a serine/threonine protein kinase, were found to be similarly expressed in the different biological samples.