Signaling pathways involved in environmental sensing in Trypanosoma cruzi
Trypanosoma cruzi is a unicellular parasite and the etiologic agent of Chagas disease. The parasite has a digenetic life cycle alternating between mammalian and insect hosts, where it faces a variety of environmental conditions to which it must adapt in order to survive. The adaptation to these changes is mediated by signaling pathways that coordinate the cellular responses to the new environmental settings. Major environmental changes include temperature, nutrient availability, ionic composition, pH, osmolarity, oxidative stress, contact with host cells and tissues, host immune response, and intracellular life. Some of the signaling pathways and second messengers potentially involved in the response to these changes have been elucidated in recent years and will be the subject of this review.
Noelia Lander, Miguel A. Chiurillo, Roberto Docampo. Mol Microbiol. 2020 Oct 9. doi: 10.1111/mmi.14621.
The mitochondrial Ca2+ uptake in trypanosomatids, which belong to the eukaryotic supergroup Excavata, shares biochemical characteristics with that of animals, which, together with fungi, belong to the supergroup Opisthokonta. However, the composition of the mitochondrial calcium uniporter (MCU) complex in trypanosomatids is quite peculiar, suggesting lineage-specific adaptations. In this work, we used Trypanosoma cruzi to study the role of orthologs for mitochondrial calcium uptake 1 (MICU1) and MICU2 in mitochondrial Ca2+ uptake. T. cruzi MICU1 (TcMICU1) and TcMICU2 have mitochondrial targeting signals, two canonical EF-hand calcium-binding domains, and localize to the mitochondria. Using the CRISPR/Cas9 system (i.e., clustered regularly interspaced short palindromic repeats with Cas9), we generated TcMICU1 and TcMICU2 knockout (-KO) cell lines. Ablation of either TcMICU1 or TcMICU2 showed a significantly reduced mitochondrial Ca2+uptake in permeabilized epimastigotes without dissipation of the mitochondrial membrane potential or effects on the AMP/ATP ratio or citrate synthase activity. However, none of these proteins had a gatekeeper function at low cytosolic Ca2+ concentrations ([Ca2+]cyt), as occurs with their mammalian orthologs. TcMICU1-KO and TcMICU2-KO epimastigotes had a lower growth rate and impaired oxidative metabolism, while infective trypomastigotes have a reduced capacity to invade host cells and to replicate within them as amastigotes. The findings of this work, which is the first to study the role of MICU1 and MICU2 in organisms evolutionarily distant from animals, suggest that, although these components were probably present in the last eukaryotic common ancestor (LECA), they developed different roles during evolution of different eukaryotic supergroups. The work also provides new insights into the adaptations of trypanosomatids to their particular life styles.
Trypanosoma brucei, a protist parasite that causes African trypanosomiasis or sleeping sickness, relies mainly on glycolysis for ATP production when in its mammalian host. Glycolysis occurs within a peroxisome-like organelle named the glycosome. Previous work from our laboratory reported the presence of significant amounts of inorganic polyphosphate (polyP), a polymer of three to hundreds of orthophosphate units, in the glycosomes and nucleoli of T. brucei In this work, we identified and characterized the activity of two Nudix hydrolases, TbNH2 and TbNH4, one located in the glycosomes and the other in the cytosol and nucleus, respectively, that can degrade polyP. We found that TbNH2 is an exopolyphosphatase with higher activity on short chain polyP, while TbNH4 is an endo- and exopolyphosphatase that has similar activity on polyP of various chain sizes. Both enzymes have higher activity at around pH 8.0. We also found that only TbNH2 can dephosphorylate ATP and ADP but with lower affinity than for polyP. Our results suggest that Nudix hydrolases can participate in polyP homeostasis and therefore may help control polyP levels in glycosomes, cytosol and nuclei of T. brucei.