The mitochondrial calcium uniporter complex in trypanosomes

Abstract

The presence of a conserved mechanism for mitochondrial calcium uptake in trypanosomatids was crucial for the molecular identification of the mitochondrial calcium uniporter (MCU), a long-sought channel present in most eukaryotic organisms. Since then, research efforts to elucidate the role of MCU and its regulatory elements in different biological models have multiplied. MCU is the pore-forming subunit of a multimeric complex (the MCU complex or MCUC) and its predicted structure in trypanosomes is simpler than in mammalian cells, lacking two of its subunits and probably possessing other unidentified components. MCU protein has been characterized in Trypanosoma brucei and Trypanosoma cruzi, the causative agents of African and American trypanosomiasis, respectively. Contrary to its mammalian homolog, TbMCU was found to be essential for cell growth and survival, while its paralog MCUb is an essential protein in T. cruzi. These findings could be further exploited for chemotherapeutic purposes. The emergence of new molecular tools for the genetic manipulation of trypanosomatids has been determinant for the functional characterization of the MCUC components in these organisms. However, further research has to be done to determine the role of each component in intracellular calcium signaling and cell bioenergetics. In this mini-review we summarize the original results on mitochondrial calcium uptake in trypanosomes, how did they contribute to the molecular identification of the MCU, and the functional characterization of the MCUC subunits that has so far been studied in these peculiar eukaryotes.

Functional analysis and importance for host cell infection of the Ca2+-conducting subunits of the mitochondrial calcium uniporter ofTrypanosoma cruzi

“…To investigate the ability of TcMCUc and TcMCUd to transport Ca 2+ , we generated null mutants for these two genes ( TcMCUc -KO and TcMCUd -KO) using the CRISPR/Cas9 method that we adapted to T. cruzi (Figure 2, A–H, and Supplemental Figure S2) (Lander et al , 2015, 2018a; Chiurillo et al , 2017; Cruz-Bustos et al , 2018). As described under Materials and Methods, T. cruzi epimastigotes were transfected with molecular constructs for the constitutive expression of Cas9 nuclease and single guide RNAs (sgRNAs) to target TcMCUc or TcMCUd genes (Figure 2, A and E).…”

“…T. cruzi has a complex life cycle including replicative and nonreplicative stages in the insect vector (epimastigotes and metacyclic trypomastigotes, respectively) and in its mammalian host (intracellular amastigotes, and cell-derived trypomastigotes, respectively). Although they all possess a functional mitochondrial calcium uniporter (MCU) complex, its role in the regulation of mitochondrial metabolism seems more important in the infective stages (Lander et al , 2018a). Infective stages depend more heavily on an aerobic metabolism of fatty acids and amino acids rather than on glycolysis, as is the case of epimastigotes during the exponential growth phase (Barison et al , 2017; Lander et al , 2018a).…”

“…In summary, the MCU complex is essential for maintaining the bioenergetics of the cell and for determining life–death decisions (Cardenas et al , 2010; Huang et al , 2013). The T. cruzi MCU complex has lineage-specific structural and functional differences as compared with the animal complex (Chiurillo et al , 2017; Lander et al , 2018a,b). Selective interference on this pathway in trypanosomes is therefore a valid alternative for drug targeting and its mechanistic study could have important implications for general mitochondrial physiology.…”

Intracellular Ca2+ Signaling in Protozoan Parasites: An Overview with a Focus on Mitochondria

“…Similar to mammals, Trypanosomatids have a well-characterized MCU-mediated Ca 2+ influx mechanism, although some proteins are absent [ 91 , 92 ]. Interference in MCU expression using siRNA or conditional knockdown causes a deficiency in the influx of mitochondrial Ca 2+ .…”

Calcium-sensitive pyruvate dehydrogenase phosphatase is required for energy metabolism, growth, differentiation, and infectivity of Trypanosoma cruzi

“…The finding of MCU activity in trypanosomatids, such as Trypanosoma cruzi (13,14), the agent of Chagas disease, and T. brucei (15), which belongs to the group of parasites that cause sleeping sickness, was important for the discovery of a gene encoding a modulator of the uniporter (mitochondrial calcium uptake 1, or MICU1) (16) and the pore subunit of the channel or MCU (17)(18)(19). After the molecular identification of MCU, other components of the MCU complex were described (20 -23), but only orthologs of MCU, MCUb, MICU1, and MICU2 are present in trypanosomes, whereas MCU regulator (MCUR1) and essential MCU regulator (EMRE) are absent (24,25). Mitochondrial Ca 2ϩ transport in trypanosomes is critical for shaping the dynamics of cytosolic Ca 2ϩ increases, for the bioenergetics of the cells, and for viability and infectivity (26,27).…”