Apoptotic induction induces Leishmania aethiopica and L. mexicana spreading in terminally differentiated THP-1 cells

Expression of Network Medicine-Predicted Genes in Human Macrophages Infected with Leishmania major

Leishmania spp. commonly infects phagocytic cells of the immune system, particularly macrophages, employing various immune evasion strategies that enable their survival by altering the intracellular environment. In mammals, these parasites establish persistent infections by modulating gene expression in macrophages, thus interfering with immune signaling and response pathways, ultimately creating a favorable environment for the parasite's survival and reproduction. In this study, our objective was to use data mining and subsequent filtering techniques to identify the genes that play a crucial role in the infection process of Leishmania spp. We aimed to pinpoint genes that have the potential to influence the progression of Leishmania infection. To achieve this, we exploited prior, curated knowledge from major databases and constructed 16 datasets of human molecular information consisting of coding genes and corresponding proteins. We obtained over 400 proteins, identifying approximately 200 genes. The proteins coded by these genes were subsequently used to build a network of protein-protein interactions, which enabled the identification of key players; we named this set Predicted Genes. Then, we selected approximately 10% of Predicted Genes for biological validation. THP-1 cells, a line of human macrophages, were infected with Leishmania major in vitro for the validation process. We observed that L. major has the capacity to impact crucial genes involved in the immune response, resulting in macrophage inactivation and creating a conducive environment for the survival of Leishmania parasites.

Involvement of lipids from Leishmania braziliensis promastigotes and amastigotes in macrophage activation

Leishmania are obligate protozoan parasites responsible for substantial public health problems in tropical and subtropical regions around the world, with L. braziliensis being one of the causative agents of American Tegumentary Leishmaniasis. Macrophages, fundamental cells in the innate inflammatory response against Leishmania, constitute a heterogeneous group with multiple activation phenotypes and functions. The outcome of this infection depends largely on the activation status of macrophages, the first line of mammalian defense and the major target cells for parasite replication. The importance of lipids, the major components of cell membranes, goes beyond their basic structural functions. Lipid bioactive molecules have been described in Leishmania spp., and in the recent years the knowledge about the biological relevance of lipids in particular and their relationship with the immune response is expanding. The present work analyzes the biological effects of L. braziliensis lipids from lysed promastigotes (PRO) to mimic rapid modulatory processes that could occur in the initial steps of infection or the effects of lipids from lysed and incubated promastigotes (PROinc), simulating the parasite lipid degradation processes triggered after parasite lysis that might occur in the mammalian host. To perform these studies, lipid profiles of PRO and PROinc were compared with lipids from amastigotes under similar conditions (AMA and AMAinc), and the effect of these lipid extracts were analyzed on the induction of an inflammatory response in murine peritoneal macrophages: LB induction, COX-2, iNOS and Arginase expression, TNF-α, IL-10 and NO production, Arginase activity and M1/M2 markers mRNA induction.

Leishmania aethiopica cell-to-cell spreading involves caspase-3, AkT, and NF-κB but not PKC-δ activation and involves uptake of LAMP-1-positive bodies containing parasites

Development of human leishmaniasis is dependent on the ability of intracellular Leishmania parasites to spread and enter macrophages. The mechanism through which free promastigotes and amastigotes bind and enter host macrophages has been previously investigated; however, little is known about intracellular trafficking and cell-to-cell spreading. In this study, the mechanism involved in the spreading of Leishmania aethiopica and Leishmania mexicana was investigated. A significant increase in phosphatidylserine (PS) exhibition, cytochrome C release, and active caspase-3 expression was detected (P < 0.05) during L. aethiopica, but not L. mexicana spreading. A decrease (P < 0.05) of protein kinase B (Akt) protein and BCL2-associated agonist of cell death (BAD) phosphorylation was also observed. The nuclear factor kappa-light-chain enhancer of activated B cells (NF-kB) signaling pathway and pro-apoptotic protein protein kinase C delta (PKC-δ) were downregulated while inhibition of caspase-3 activation prevented L. aethiopica spreading. Overall suggesting that L. aethiopica induces host cell's apoptosis during spreading in a caspase-3-dependent manner. The trafficking of amastigotes within macrophages following cell-to-cell spreading differed from that of axenic parasites and involved co-localization with lysosomal-associated membrane protein 1 (LAMP-1) within 10 min postinfection. Interestingly, following infection with axenic amastigotes and promastigotes, co-localization of parasites with LAMP-1-positive structures took place at 1 and 4 h, respectively, suggesting that the membrane coat and LAMP-1 protein were derived from the donor cell. Collectively, these findings indicate that host cell apoptosis, demonstrated by PS exhibition, caspase-3 activation, cytochrome C release, downregulation of Akt, BAD phosphorylation, NF-kB activation, and independent of PKC-δ expression, is involved in L. aethiopica spreading. Moreover, L. aethiopica parasites associate with LAMP-rich structures when taken up by neighboring macrophages.