Dihydrotestosterone enhances growth and infectivity of Leishmania Mexicana.

A strong sex-associated susceptibility towards Leishmania has been reported in males, yet little is known on the effect of hormones in Leishmania physiopathogenicity. Due to the enhanced susceptibility of males to Leishmania mexicana infections, we were interested in analysing the effect exerted by the main androgen produced in males (DHT) on L. mexicana promastigotes. Thus, the aim of this study was to assess the regulation exerted by dihydrotestosterone (DHT) on L. mexicana replication, infectivity, survival and development of tissue lesions. Experiments included growth curves of L. mexicana promastigotes incubated with different doses of DHT, their infection rate, intracellular survival and lesion development in BALB/c mice. Our data show that DHT significantly enhances parasite replication, infection rate and survival in bone marrow-derived macrophages (BMMФ). Promastigotes in the presence of DHT produced significantly larger lesions in BALB/c earlobes. These results suggest that DHT probably plays a critical role during L. mexicana infections, and the higher susceptibility of males possibly relates to benefits gained by the parasite from host-derived hormones. Our data shed new light on the physiopathology of Leishmania infections and are the first attempt to understand the direct interaction between Leishmania and androgens, particularly DHT. Understanding this trans-regulation process employed by parasites to exploit host molecules sheds new light on L. mexicana physiopathogenesis and opens a possible field for studies on drug development.

Leishmania mexicana: promastigotes and amastigotes secrete protein phosphatases and this correlates with the production of inflammatory cytokines in macrophages.

Phosphatase activity of Leishmania spp. has been shown to deregulate the signalling pathways of the host cell. We here show that Leishmania mexicana promastigotes and amastigotes secrete proteins with phosphatase activity to the culture medium, which was higher in the Promastigote Secretion Medium (PSM) as compared with the Amastigote Secretion Medium (ASM) and was not due to cell lysis, since parasite viability was not affected by the secretion process. The biochemical characterization showed that the phosphatase activity present in PSM was higher in dephosphorylating the peptide END (pY) INASL as compared with the peptide RRA (pT)VA. In contrast, the phosphatase activity in ASM showed little dephosphorylating capacity for both peptides. Inhibition assays demonstrated that the phosphatase activity of both PSM and ASM was sensible only to protein tyrosine phosphatases inhibitors. An antibody against a protein phosphatase 2C (PP2C) of Leishmania major cross-reacted with a 44·9 kDa molecule in different cellular fractions of L. mexicana promastigotes and amastigotes, however, in PSM and ASM, the antibody recognized a protein about 70 kDa. By electron microscopy, the PP2C was localized in the flagellar pocket of amastigotes. PSM and ASM induced the production of tumor necrosis factor alpha, IL-1ß, IL-12p70 and IL-10 in human macrophages.

Leishmania mexicana amastigotes inhibit p38 and JNK and activate PI3K/AKT: role in the inhibition of apoptosis of dendritic cells.

Leishmania mexicana is the causal agent of cutaneous leishmaniasis in Mexico. Dendritic cells (DC) are one of the host cells of Leishmania parasites. Intracellular microorganisms inhibit host cell apoptosis as a strategy to ensure their survival in infected cells. We have previously shown that Leishmania mexicana promastigotes and amastigotes inhibit camptothecin-induced apoptosis of monocyte-derived dendritic cells (moDC), but the mechanisms underlying the inhibition of apoptosis of DC by Leishmania have not been established. MAP kinases and PI3K participate in the process of apoptosis and are modulated by different species of Leishmania. As shown in this study, the infection of moDC with L. mexicana amastigotes diminished significantly the phosphorylation of the MAP kinases p38 and JNK. The inhibition of both kinases diminished significantly DNA fragmentation in moDC stimulated with camptothecin. On the other hand, L. mexicana amastigotes were able to activate the anti-apoptotic pathways PI3K and AKT. Our results indicate that L. mexicana amastigotes have the capacity to diminish MAP kinases activation and activate PI3K and AKT, which is probably one of the strategies employed by L. mexicana amastigotes to inhibit apoptosis in the infected moDC.