Pro-death activity of a BH3 domain in an aquaporin from the protozoan parasite Leishmania

Cell death in Leishmania

Leishmaniases still represent a global scourge and new therapeutic tools are necessary to replace the current expensive, difficult to administer treatments that induce numerous adverse effects and for which resistance is increasingly worrying. In this context, the particularly original organization of the Leishmania parasite in comparison to higher eukaryotes is a great advantage. It allows for the development of new, very specific, and thus non-cytotoxic treatments. Among these originalities, Leishmania cell death can be cited. Despite a classic pattern of apoptosis, key mammalian apoptotic proteins are not present in Leishmania, such as caspases, cell death receptors, and anti-apoptotic molecules. Recent studies have helped to develop a better understanding of parasite cell death, identifying new proteins or even new apoptotic pathways. This review provides an overview of the current knowledge on Leishmania cell death, describing its physiological roles and its phenotype, and discusses the involvement of various proteins: endonuclease G, metacaspase, aquaporin Li-BH3AQP, calpains, cysteine proteinase C, LmjHYD36 and Lmj.22.0600. From these data, potential apoptotic pathways are suggested. This review also offers tools to identify new Leishmania cell death effectors. Lastly, different approaches to use this knowledge for the development of new therapeutic tools are suggested: either inhibition of Leishmania cell death or activation of cell death for instance by treating cells with proteins or peptides involved in parasite death fused to a cell permeant peptide or encapsulated into a lipidic vector to target intra-macrophagic Leishmania cells.

(De)glutamylation and cell death in Leishmania parasites

Trypanosomatids are flagellated protozoan parasites that are very unusual in terms of cytoskeleton organization but also in terms of cell death. Most of the Trypanosomatid cytoskeleton consists of microtubules, forming different substructures including a subpellicular corset. Oddly, the actin network appears structurally and functionally different from other eukaryotic actins. And Trypanosomatids have an apoptotic phenotype under cell death conditions, but the pathways involved are devoid of key mammal proteins such as caspases or death receptors, and the triggers involved in apoptotic induction remain unknown. In this article, we have studied the role of the post-translational modifications, deglutamylation and polyglutamylation, in Leishmania. We have shown that Leishmania apoptosis was linked to polyglutamylation and hypothesized that the cell survival process autophagy was linked to deglutamylation. A balance seems to be established between polyglutamylation and deglutamylation, with imbalance inducing microtubule or other protein modifications characterizing either cell death if polyglutamylation was prioritized, or the cell survival process of autophagy if deglutamylation was prioritized. This emphasizes the role of post-translational modifications in cell biology, inducing cell death or cell survival of infectious agents.

Leishmania are unique unicellular organisms in terms of cytoskeleton organization and mechanisms of cell death. For example, the major cytoskeletal components of these parasites are microtubules, which form a subpellicular corset. In terms of cell death, an apoptotic phenotype has been characterized in Leishmania but the pathways remain unknown, being devoid of key mammal cell death proteins. In a previous article, we demonstrated that the cytoskeleton of this parasite is extensively glutamylated but, paradoxically, overexpression or inhibition of polyglutamylase expression have limited visible cellular consequences. In this manuscript, we have highlighted the link between polyglutamylation and Leishmania cell death, suggesting the importance of the polyglutamylation/deglutamylation balance in this parasite. Further, we have identified, for the first time in Leishmania, deglutamylases, among which one that, in an original manner, deglutamylates glutamates at branching points but also long glutamate side chains. This work emphasizes the role of post-translational modifications as essential regulators of protein function, not only of mammal cells such as neurons or ciliated/flagellated cells, but also of infectious agents. This work suggests an important and discernible “live or die”—“cell death or autophagy” balance pathway and the conceptual mechanism that is involved in cellular decision making.

Temporal analysis of the autophagic and apoptotic phenotypes in Leishmania parasites

The leishmaniases are worldwide neglected tropical diseases caused by parasitic protozoa of the Leishmania genus. Different stimuli induce Leishmania cell death, but the proteins involved remain poorly understood. Furthermore, confusion often appears between cell death and the cell survival process autophagy, whose phenotype is not clearly defined. In this article, we present a comprehensive and temporal analysis of the cellular events occurring during miltefosine-induced cell death and autophagy in L. major. We also provide a list of features in order to clearly identify apoptotic cells, autophagic cells and to distinguish both processes. Furthermore, we demonstrate that autophagy is followed by apoptosis in the absence of nutrients. Finally, we show that cells treated with the generic kinase inhibitor staurosporine express apoptotic as well as autophagic markers and therefore cannot be used as an apoptosis inducer in Leishmania. These descriptions lead to a better recognition and understanding of apoptosis and autophagy, enabling their targeting in the development of new anti-leishmanial drugs. These researches also make it possible to better understand these processes in general, through the study of an ancestral eukaryote.