sirolimus and Leishmaniasis

The mechanistic (or mammalian) target of rapamycin (mTOR) is considered as a critical regulatory enzyme involved in essential signaling pathways affecting cell growth, cell proliferation, protein translation, regulation of cellular metabolism, and cytoskeletal structure. Also, mTOR signaling has crucial roles in cell homeostasis via processes such as autophagy. Autophagy prevents many pathogen infections and is involved on immunosurveillance and pathogenesis. Immune responses and autophagy are therefore key host responses and both are linked by complex mTOR regulatory mechanisms. In recent years, the mTOR pathway has been highlighted in different diseases such as diabetes, cancer, and infectious and parasitic diseases including leishmaniasis, toxoplasmosis, and malaria. The current review underlines the implications of mTOR signals and intricate networks on pathogen infections and the modulation of this master regulator by parasites. Parasitic infections are able to induce dynamic metabolic reprogramming leading to mTOR alterations in spite of many other ways impacting this regulatory network. Accordingly, the identification of parasite effects and interactions over such a complex modulation might reveal novel information regarding the biology of the abovementioned parasites and might allow the development of therapeutic strategies against parasitic diseases. In this sense, the effects of inhibiting the mTOR pathways are also considered in this context in the light of their potential for the prevention and treatment of parasitic diseases.

Topics: Animals; Autophagy; Cell Cycle; Cell Proliferation; Humans; Immunity; Leishmaniasis; Malaria; Parasites; Parasitic Diseases; Phosphorylation; Protein Biosynthesis; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Toxoplasmosis

Recently, autophagy has been implicated as a host defense mechanism against intracellular pathogens. On the other hand, certain intracellular pathogens such as Leishmania can manipulate the host's autophagy to promote their survival. Our recent findings regarding the regulation of autophagy by Leishmania donovani indicate that this pathogen induces non-classical autophagy in infected macrophages, independent of regulation by the mammalian target of rapamycin complex 1. This suggests the fine-tuning of autophagy to optimally promote parasite survival, possibly by the sequestration or modulation of specific autophagosome-associated proteins. To investigate how Leishmania potentially manipulates the composition of host-cell autophagosomes, we undertook a quantitative proteomic study of the human monocytic cell line THP-1 following infection with L. donovani. We used stable isotope labeling by amino acid in cell culture and liquid chromatography-tandem mass spectrometry to compare expression profiles between autophagosomes isolated from THP-1 cells infected with L. donovani or treated with known autophagy inducers. Selected proteomic results were validated by Western blotting. In this study, we showed that L. donovani modulates the composition of macrophage autophagosomes during infection when compared to autophagosomes induced by either rapamycin (selective autophagy) or starvation (non-selective autophagy). Among 1787 proteins detected in Leishmania-induced autophagosomes, 146 were significantly modulated compared to the proteome of rapamycin-induced autophagosomes, while 57 were significantly modulated compared to starvation-induced autophagosomes. Strikingly, 23 Leishmania proteins were also detected in the proteome of Leishmania-induced autophagosomes. Together, our data provide the first comprehensive insight into the proteome dynamics of host autophagosomes in response to Leishmania infection and demonstrate the complex relations between the host and pathogen at the molecular level. A comprehensive analysis of the Leishmania-induced autophagosome proteome will be instrumental in the advancement of understanding leishmaniasis.

Topics: Autophagosomes; Humans; Leishmania donovani; Leishmaniasis; Macrophages; Proteome; Proteomics; Sirolimus

Leishmaniasis is a serious global health problem affecting many people worldwide. While patients with leishmaniasis can be treated with several agents, drug toxicicty and the emergence of resistant strains render available treatments ineffective in the long run. Inhibitors of the mammalian target of rapamycin (mTOR) have been demonstrated to exert anti-pathogen properties. In this study, we tested the therapeutic efficacy of several mTOR inhibitors in controlling infection with Leishmania major. Rapamycin, GSK-2126458 and KU-0063794 were administered to BALB/c mice, which had received an intrafootpad injection of the parasite. Footpad swelling and parasite burden were assessed, and cytokine production by mouse splenocytes and phenotypic changes in draining lymph node cells were evaluated. Treatment with a clinically relevant dose of rapamycin or with GSK-2126458, but not with KU-0063794, dramatically lowered both the footpad swelling and the parasite load in the draining lymph node. Importantly, the employed dose of rapamycin did not kill the promastigotes in vitro as judged by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and electron microscopy. Moreover, the IL-4 production capacity of splenocytes harvested from infected mice that were treated with rapamycin was significantly reduced. Consequently, the IFN-γ:IL-4 production ratio was elevated, suggesting a T helper-type 1 (Th1)-skewed cytokine profile. Finally, the expression level of CD69, an early activation marker, on splenic and lymph node CD4+ and CD8+ T cells was enhanced in rapamycin-treated mice. Taken together, our findings suggest that select mTOR inhibitors may be used in therapeutic settings for the management of leishmaniasis. We propose that the beneficial effects of such inhibitors stem from their immunomodulatory properties. Therefore, the adjuvanticity of mTOR inhibitors may also be considered in vaccination strategies against Leishmania species.

Topics: Animals; Antiprotozoal Agents; Enzyme Inhibitors; Female; Gene Expression Regulation; Inhibitory Concentration 50; Leishmaniasis; Mice; Mice, Inbred BALB C; Morpholines; Pyridazines; Pyrimidines; Quinolines; Sirolimus; Sulfonamides; TOR Serine-Threonine Kinases