Calcium signaling in intracellular protist parasites

Electrical signaling and coordinated behavior in the closest relative of animals

The transition from simple to complex multicellularity involves division of labor and specialization of cell types. In animals, complex sensory-motor systems are primarily built around specialized cells of muscles and neurons, though the evolutionary origins of these and their integration remain unclear. Here, to investigate sensory-behavior coupling in the closest relatives of animals, we established a line of the choanoflagellate, Salpingoeca rosetta, which stably expresses the calcium indicator RGECO1. Using this, we identify a previously unknown cellular behavior associated with electrical signaling, in which ciliary arrest is coupled with apical-basal contraction of the cell. This behavior and the associated calcium transients are synchronized in the multicellular state and result in coordinated ciliary arrest and colony-wide contraction, suggesting that information is spread among the cells. Our work reveals fundamental insights into how choanoflagellates sense and respond to their environment and enhances our understanding of the integration of cellular and organism-wide behavior in the closest protistan relatives of animals.

Synthesis of a dehydrodieugenol B derivative as a lead compound for visceral leishmaniasis-mechanism of action and in vivo pharmacokinetic studies

Leishmaniasis is a parasitic neglected tropical disease, affecting 12 million people. Available treatments present several limitations, with an increasing number of resistance cases. In the search for new chemotherapies, the natural product dehydrodieugenol B was used as a scaffold for the synthesis of a series of derivatives, resulting in the discovery of the promising analog [4-(4-(5-allyl-3-methoxy-2-((4-methoxybenzyl)oxy)phenoxy)-3-methoxybenzyl)morpholine, 1]. In this work, we investigated the effect of compound 1 on cell signaling in Leishmania (L.) infantum, culminating in cell death, as well as its immunomodulatory effect in the host cell. Additionally, we performed a pharmacokinetic profile study in an animal model. After treatment, compound 1 induced the alkalinization of acidocalcisomes and concomitant Ca2+ release in the parasite. These events may induce depolarization of the mitochondrial potential, with successive collapse of the bioenergetic system, leading to a reduction of ATP and reactive oxygen species (ROS) levels. The analysis of total proteins and protein profile by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) demonstrated that compound 1 also altered the parasite proteins after treatment. Transmission electron microscopy studies revealed ultrastructural damage to mitochondria; together, these data suggest that compound 1 may promote autophagic cell death. Additionally, compound 1 also induced an immunomodulatory effect in host cells, with a reduction of Th1 and Th2 cytokine response, characterizing an anti-inflammatory compound. The obtained pharmacokinetic profile in rats enhances the potential of the compound, with a mean plasma half-life (T1/2) of 21 h. These data reinforce the potential of compound 1 as a new lead for future efficacy studies.

Lethal action of Licarin A derivatives in Leishmania (L.) infantum: Imbalance of calcium and bioenergetic metabolism

Natural metabolites present an extraordinary chemo-diversity and have been used as the inspiration for new drugs. Considering the need for new treatments against the neglected parasitic disease leishmaniasis, three semi-synthetic derivatives of natural neolignane licarin A were prepared: O-acetyl (1a), O-allyl (1b), and 5-allyl (1c). Using an ex vivo assay, compounds 1a, 1b, and 1c showed activity against the intracellular amastigotes of Leishmania (L.) infantum, with IC₅₀ values of 9, 13, and 10 μM, respectively. Despite no induction of hemolytic activity, only compound 1b resulted in mammalian cytotoxicity (CC₅₀ = 64 μM). The most potent compounds (1a and 1c) resulted in selectivity indexes >18. The mechanism of action of compound 1c was evaluated by fluorescent/luminescent based techniques and MALDI-TOF/MS. After a short incubation period, increased levels of the cytosolic calcium were observed in the parasites, with alkalinization of the acidocalcisomes. Compound 1c also induced mitochondrial hyperpolarization, resulting in decreased levels of ATP without altering the reactive oxygen species (ROS). Neither plasma membrane damages nor DNA fragmentation were observed after the treatment, but a reduction in the cellular proliferation was detected. Using MALDI-TOF/MS, mass spectral alterations of promastigote proteins were observed when compared to untreated and miltefosine-treated groups. This chemically modified neolignan induced lethal alterations of the bioenergetic and protein metabolism of Leishmania. Future PKPD and animal efficacy studies are needed to optimize this promising natural-derived compound.

Isolation and identification of sporozoite membrane protein of Cryptosporidium parvum and evaluation of calmodulin-like protein immune protection

Until now, no completely effective parasite-specific drugs or vaccines have been approved for the treatment of cryptosporidiosis. Through the separation and identification of the sporozoite membrane protein of Cryptosporidium parvum (C. parvum), 20 related proteins were obtained. Among them, a calmodulin-like protein (CML) has a similar functional domain-exchange factor hand (EF-hand) motif as calmodulin proteins (CaMs), so it may play a similarly important role in the invasion process. A 663 bp full gene encoding the C. parvum calmodulin-like protein (CpCML) was inserted in pET28a vector and expressed in Escherichia coli. An immunofluorescence assay showed that CpCML was mainly located on the surface of the sporozoites. Three-week-old female BALB/c mice were used for modeling the immunoreactions and immunoprotection of recombinant CpCML (rCpCML) against artificial Cryptosporidium tyzzeri (C. tyzzeri) infections. The results indicated a significantly increased in anti-CpCML antibody response, which was induced by the immunized recombinant protein. Compared to rP23(recombinant P23), GST6P-1(expressed by pGEX-6P-1 transfected E. coli) , GST4T-1(expressed by pGEX-4T-1 transfected E. coli) , glutathione (GSH), adjuvant, and blank control groups, rCpCML-immunized mice produced specific spleen cell proliferation in addition to different production levels of IL-2, IFN-γ, TNF-α, IL-4 and IL-5. Additionally, immunization with rCpCML led to 34.08% reduction of oocyst shedding in C. tyzzeri infected mice faeces which was similart to rP23. These results suggest that CpCML may be developed as a potential vaccine candidate antigen against cryptosporidiosis.

The role of Ca2+ in the injury of host cells during the schizogenic stage of E. tenella

Cecal epithelial cell damage is a key factor in host injure during the development of E. tenella. The intracellular free Ca²⁺ of the host cell is closely related to the invasion, development and proliferation of intracellular parasites, and cell damage. To determine the relationship between Ca²⁺ and host cell damage in the schizogenic stage of E. tenella, we established a chick embryo cecal epithelial cells model of E. tenella infection. Fluorescence staining, flow cytometry, transmission electron microscopy, inhibition and blocking experiments were used to detect the damage effect and mechanism of host cells during the schizogenic stage of E. tenella. The results showed that the host cells cytoskeletal remodeling, cell and organelle structure was destroyed, and apoptosis and necrosis were increased during the schizont stage of E. tenella. Furthermore, the above-mentioned effects of the schizogenic stage of E. tenella on cells can be alleviated by reducing the intracellular Ca²⁺ concentration in the host cells. These observations indicate that the effect of host cell injury was closely related to Ca²⁺ during schizont stage of E. tenella.