The 245 kb amplified chromosome of Leishmania (V.) braziliensis contains a biopterin transporter gene

A putative role for inosine 5' monophosphate dehydrogenase (IMPDH) in Leishmania amazonensis programmed cell death

Leishmania amazonensis undergoes apoptosis-like programmed cell death (PCD) under heat shock conditions. We identified a potential role for inosine 5' monophosphate dehydrogenase (IMPDH) in L. amazonensis PCD. Trypanosomatids do not have a "de novo" purine synthesis pathway, relying on the salvage pathway for survival. IMPDH, a key enzyme in the purine nucleotide pathway, is related to cell growth and apoptosis. Since guanine nucleotide depletion triggers cell cycle arrest and apoptosis in several organisms we analyzed the correlation between IMPDH and apoptosis-like death in L. amazonensis. The L. amazonensis IMPDH inhibition effect on PCD was evaluated through gene expression analysis, mitochondrial depolarization and detection of Annexin-V labeled parasites. We demonstrated a down-regulation of impdh expression under heat shock treatment, which mimics the natural mammalian host infection. Also, IMPDH inhibitors ribavirin and mycophenolic acid (MPA) prevented cell growth and generated an apoptosis-like phenotype in sub-populations of L. amazonensis promastigotes. Our results are in accordance with previous results showing that a subpopulation of parasites undergoes apoptosis-like cell death in the nutrient poor environment of the vector gut. Here, we suggest the involvement of purine metabolism in previously observed apoptosis-like cell death during Leishmania infection.

Molecular characterization of the MRPA transporter and antimony uptake in four New World Leishmania spp. susceptible and resistant to antimony

•

Level of expression of Pgp is increased in the SbIII-resistant L. guyanensis and L. amazonensis lines.

•

Incorporation of antimony was reduced in the SbIII-resistant L. guyanensis, L. amazonensis and L. braziliensis lines.

•

Down-regulation of AQP1 protein was observed in the SbIII-resistant L. guyanensis and L. amazonensis lines.

•

Rates of SbIII efflux are higher in the SbIII-resistant lines of L. guyanensis and L. braziliensis.

•

Mechanisms of antimony-resistance of the MRPA gene are different among species of Leishmania analyzed.

ATP-binding cassette (ABC) transporters have been associated with drug resistance in various diseases. The MRPA gene, a transporter of ABCC subfamily, is involved in the resistance by sequestering metal-thiol conjugates in intracellular vesicles of Leishmania parasite. In this study, we performed the molecular characterization of the MRPA transporter, analysis of P-glycoprotein (Pgp) and aquaglyceroporin-1 (AQP1) expression, and determination of antimony level in antimony-susceptible and -resistant lines of L. (V.) guyanensis, L. (L.) amazonensis, L. (V.) braziliensis and L. (L.) infantum. PFGE analysis revealed an association of chromosomal amplification of MRPA gene with the drug resistance phenotype in all SbIII-resistant Leishmania lines analyzed. Levels of mRNA from MRPA gene determined by real-time quantitative RT-PCR showed an increased expression of two fold in SbIII-resistant lines of Leishmania guyanensis, Leishmania amazonensis and Leishmania braziliensis. Western blot analysis revealed that Pgp is increased in the SbIII-resistant L. guyanensis and L. amazonensis lines. The intracellular level of antimony quantified by graphite furnace atomic absorption spectrometry showed a reduction in the accumulation of this element in SbIII-resistant L. guyanensis, L. amazonensis and L. braziliensis lines when compared to their susceptible counterparts. Interestingly, a down-regulation of AQP1 protein was observed in the SbIII-resistant L. guyanensis and L. amazonensis lines, contributing for decreasing of SbIII entry in these lines. In addition, efflux experiments revealed that the rates of SbIII efflux are higher in the SbIII-resistant lines of L. guyanensis and L. braziliensis, that may explain also the low SbIII concentration within of these parasites. The BSO, an inhibitor of γ-glutamylcysteine synthetase enzyme, reversed the SbIII-resistance phenotype of L. braziliensis and caused an increasing in the Sb intracellular level in the LbSbR line. Our data indicate that the mechanisms of antimony-resistance are different among species of Leishmania analyzed in this study.

A 245kb mini-chromosome impacts on Leishmania braziliensis infection and survival

Leishmania (V.) braziliensis, the causative agent of mucocutaneous leishmaniasis in the New World, may present an LD1 type genomic amplification that appears as a small 245 kb linear chromosome, and is not clearly associated to the presence of a selection agent. A bt1 gene, codifying for a biopterin transporter protein, was identified in this small chromosome. Leishmania are auxotrophic for pterins and one of the proposed explanations for the appearance of this amplification is the improvement of biopterin capture by the parasite. We analyzed some biological aspects of two lineages of L. braziliensis strain M2903, with and without the small amplified chromosome. We showed differences in infectivity of these lineages, in macrophages and the insect vector Lutzomyia longipalpis, as well as in the uptake and metabolization of intermediates of the Leishmania biopterin salvage pathway. Our results suggest that the genomic amplification favors survival due to improved biopterin capture and at the same time hinders the infective capability, suggesting that within a population different parasites can perform different roles.

Organization of H locus conserved repeats in Leishmania (Viannia) braziliensis correlates with lack of gene amplification and drug resistance

Resistance to antimonials is a major problem when treating visceral leishmaniasis in India and has already been described for New World parasites. Clinical response to meglumine antimoniate in patients infected with parasites of the Viannia sub-genus can be widely variable, suggesting the presence of mechanisms of drug resistance. In this work, we have compared L. major and L. braziliensis mutants selected in different drugs. The cross-resistance profiles of some cell lines resembled those of mutants bearing H locus amplicons. However, amplified episomal molecules were exclusively detected in L. major mutants. The analysis of the L. braziliensis H region revealed a strong conservation of gene synteny. The typical intergenic repeats that are believed to mediate the amplification of the H locus in species of the Leishmania sub-genus are partially conserved in the Viannia species. The conservation of these non-coding elements in equivalent positions in both species is indicative of their relevance within this locus. The absence of amplicons in L. braziliensis suggests that this species may not favour extra-chromosomal gene amplification as a source of phenotypic heterogeneity and fitness maintenance in changing environments.