Programmed cell death in protists

Metacaspase (Pf MCA-1) as antimalarial drug target: An in silico approach and their biological validation

AIMS

Acquired drug resistance of Plasmodium is a global issue for the treatment of malaria. There are various proteases in the genome of Plasmodium falciparum (P. falciparum) including metacaspase-1 (PfMCA-1) that are essential and are being considered as an attractive drug target. It is aimed to identify novel therapeutics against malaria and their action on PfMCA-1 along with other apoptotic pathway events.

MAIN METHODS

High throughput virtual screening of 55,000 compounds derived from Maybridge library was performed against PfMCA-1. Based on the docking score, sixteen compounds were selected for in vitro antimalarial screening against drug sensitive and resistant strains of P. falciparum using SYBR green-based assay. Subsequently, three lead molecules were selected and subjected to the evaluation of cytotoxicity, caspase like protease activity, mitochondrial membrane potential, ROS generation and DNA fragmentation via TUNEL assay.

KEY FINDINGS

The in silico and in vitro approaches have brought forward some Maybridge library compounds with antiplasmodial activity most likely by enhancing the metacaspase activity. The compound CD11095 has shown better antimalarial efficacy, and KM06591 depicted higher caspase mediated killing, elevated TUNEL positive cells and moderate ROS generation. Mitochondrial membrane depolarization was augmented by RJC0069. Exposure of P. falciparum to CD11095, KM06591 and RJC0069 has ended up in parasite growth arrest via multiple mechanisms.

SIGNIFICANCE

It is proposed that the Maybridge molecules CD11095, KM06591 and RJC0069 have antimalarial activity. Their mechanism of action was found to be by enhancing the metacaspases-like protease activity, mitochondrial depolarization and DNA fragmentation which stipulates significant insights towards promising candidates for drug development.

Autophagy in protists and their hosts: When, how and why?

Pathogenic protists are a group of organisms responsible for causing a variety of human diseases including malaria, sleeping sickness, Chagas disease, leishmaniasis, and toxoplasmosis, among others. These diseases, which affect more than one billion people globally, mainly the poorest populations, are characterized by severe chronic stages and the lack of effective antiparasitic treatment. Parasitic protists display complex life-cycles and go through different cellular transformations in order to adapt to the different hosts they live in. Autophagy, a highly conserved cellular degradation process, has emerged as a key mechanism required for these differentiation processes, as well as other functions that are crucial to parasite fitness. In contrast to yeasts and mammals, protist autophagy is characterized by a modest number of conserved autophagy-related proteins (ATGs) that, even though, can drive the autophagosome formation and degradation. In addition, during their intracellular cycle, the interaction of these pathogens with the host autophagy system plays a crucial role resulting in a beneficial or harmful effect that is important for the outcome of the infection. In this review, we summarize the current state of knowledge on autophagy and other related mechanisms in pathogenic protists and their hosts. We sought to emphasize when, how, and why this process takes place, and the effects it may have on the parasitic cycle. A better understanding of the significance of autophagy for the protist life-cycle will potentially be helpful to design novel anti-parasitic strategies.

Phragmites australis (Cav.) Trin. ex Steud. Extract Induces Apoptosis-like Programmed Cell Death in Acanthamoeba castellanii Trophozoites

Acanthamoeba keratitis (AK) is an infectious ocular disease which is difficult to diagnose correctly and cure. Development of an effective and safe therapeutic drug for AK is needed. Our preliminary screening of more than 200 extracts from wild plants collected in Korea suggested the potential amoebicidal activity of Phragmites australis (Cav.) Trin. ex Steud. extract (PAE) against Acanthamoeba species. Here, we aimed to analyze the amoebicidal activity of PAE on Acanthamoeba and its underlying amoebicidal mechanism. PAE induced amoebicidal activity against both A. castellanii and A. polyphaga trophozoites, while it showed low cytotoxicity in human corneal epithelial cells (HCE-2) and human retinal pigment epithelial cells (ARPE-19). Transmission electron microscopy analysis showed subcellular morphological changes, such as increased granules, abnormal mitochondria, and atypical cyst wall formation, in the PAE-treated A. castellanii. Fluorometric apoptosis assay and TUNEL assay revealed apoptosis-like programmed cell death (PCD) in the PAE-treated A. castellanii. The PAE treatment increased reactive oxygen species production and reduced mitochondrial membrane potential in the amoeba. The enhanced expression of autophagy-associated genes was also detected. These results suggested that PAE exerted a promising amoebicidal effect on A. castellanii trophozoites via the PCD pathway. PAE could be a potential candidate for developing a therapeutic drug for AK.

Is Aging an Inevitable Characteristic of Organic Life or an Evolutionary Adaptation?

Aging is an evolutionary paradox. Several hypotheses have been proposed to explain it, but none fully explains all the biochemical and ecologic data accumulated over decades of research. We suggest that senescence is a primitive immune strategy which acts to protect an individual's kin from chronic infections. Older organisms are exposed to pathogens for a longer period of time and have a higher likelihood of acquiring infectious diseases. Accordingly, the parasitic load in aged individuals is higher than in younger ones. Given that the probability of pathogen transmission is higher within the kin, the inclusive fitness cost of infection might exceed the benefit of living longer. In this case, programmed lifespan termination might be an evolutionarily stable strategy. Here, we discuss the classical evolutionary hypotheses of aging and compare them with the pathogen control hypothesis, discuss the consistency of these hypotheses with existing empirical data, and present a revised conceptual framework to understand the evolution of aging.

Volvox as a Model for Studying Cell Death and Senescence

Abstract

The spherical green alga Volvox consists of several hundred or thousand of somatic cells that undergo terminal differentiation, senescence and death, and a small number of gonidia (asexual reproductive cells) that give rise to the next generation. In the first part of this paper, the ontogenetic diversity of the genus Volvox is briefly considered, as well as the mechanisms of differentiation into the two types of cells mentioned above, which have been thoroughly studied during recent years in Volvox carteri. Then, a detailed critical analysis of the literature and some of my own data on senescence and cell death (mainly in V. carteri and, to a lesser extent, in V. aureus) was carried out, and it was noted that this aspect of Volvox developmental biology has not been sufficiently studied. Some perspectives of further research of the processes of cell death and senescence in representatives of the genus Volvox in a comparative aspect are indicated.

Apoptosis-Like Cell Death in Leishmania major Treated with HESA-A: An Herbal Marine Compound

Background: The first drug for the treatment of leishmaniasis is pentavalent antimony compounds which have great side effects. Objectives: This study aimed to assess apoptosis induction by HESA-A, an herbal marine compound in Leishmania major promastigotes. Methods: Leishmania major promastigotes were treated with HESA-A in different increasing concentrations ranged 1.625 - 120 µg/mL, and amphotericin B and the phenomenon of apoptosis in the parasite were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, and DNA fragmentation tests. Results: The IC50 value of the compound and amphotericin B at 72 h were estimated at 2.81 µg/mL and 40 µg/mL, respectively. After 72 h of the adjacency of Leishmania major promastigotes with IC50 dose (2.81 µg/mL), the percentage of promastigotes in early and late apoptosis phases in the treated group was 5.4% and 60.4%, respectively. DNA fragmentation of Leishmania major promastigotes treated with 2.81 µg/mL for 72 h was observed. Conclusions: HESA-A, with significant induction of apoptosis in Leishmania major promastigotes, can be plausible in the treatment of cutaneous Leishmaniasis.

Programmed cell death as a black queen in microbial communities

Programmed cell death (PCD) in unicellular organisms is in some instances an altruistic trait. When the beneficiaries are clones or close kin, kin selection theory may be used to explain the evolution of the trait, and when the trait evolves in groups of distantly related individuals, group or multilevel selection theory is invoked. In mixed microbial communities, the benefits are also available to unrelated taxa. But the evolutionary ecology of PCD in communities is poorly understood. Few hypotheses have been offered concerning the community role of PCD despite its far-reaching effects. The hypothesis we consider here is that PCD is a black queen. The Black Queen Hypothesis (BQH) outlines how public goods arising from a leaky function are exploited by other taxa in the community. Black Queen (BQ) traits are essential for community survival, but only some members bear the cost of possessing them, while others lose the trait In addition, BQ traits have been defined in terms of adaptive gene loss, and it is unknown whether this has occurred for PCD. Our conclusion is that PCD fulfils the two most important criteria of a BQ (leakiness and costliness), but that more empirical data are needed for assessing the remaining two criteria. In addition, we hold that for viewing PCD as a BQ, the original BQH needs to include social traits. Thus, despite some empirical and conceptual shortcomings, the BQH provides a helpful avenue for investigating PCD in microbial communities.

De novo Sequencing, Assembly, and Annotation of the Transcriptome for the Free-Living Testate Amoeba Arcella intermedia

Arcella, a diverse understudied genus of testate amoebae is a member of Tubulinea in Amoebozoa group. Transcriptomes are a powerful tool for characterization of these organisms as they are an efficient way of characterizing the protein-coding potential of the genome. In this work, we employed both single-cell and clonal populations transcriptomics to create a reference transcriptome for Arcella. We compared our results with annotations of Dictyostelium discoideum, a model Amoebozoan. We assembled a pool of 38 Arcella intermedia transcriptomes, which after filtering are composed of a total of 14,712 translated proteins. There are GO categories enriched in Arcella including mainly intracellular signal transduction pathways; we also used KEGG to annotate 11,546 contigs, which also have similar distribution to Dictyostelium. A large portion of data is still impossible to assign to a gene family, probably due to a combination of lineage-specific genes, incomplete sequences in the transcriptome and rapidly evolved genes. Some absences in pathways could also be related to low expression of these genes. We provide a reference database for Arcella, and we highlight the emergence of the need for further gene discovery in Arcella.

In vitro activity of 1H-phenalen-1-one derivatives against Leishmania spp. and evidence of programmed cell death

Background

The in vitro activity against Leishmania spp. of a novel group of compounds, phenalenone derivatives, is described in this study. Previous studies have shown that some phenalenones present leishmanicidal activity, and induce a decrease in the mitochondrial membrane potential in L. amazonensis parasites, so in order to elucidate the evidence of programmed cell death occurring inside the promastigote stage, different assays were performed in two different species of Leishmania.

Methods

We focused on the determination of the programmed cell death evidence by detecting the characteristic features of the apoptosis-like process, such as phosphatidylserine exposure, mitochondrial membrane potential, and chromatin condensation among others.

Results

The results showed that four molecules activated the apoptosis-like process in the parasite. All the signals observed were indicative of the death process that the parasites were undergoing.

Conclusions

The present results highlight the potential use of phenalenone derivatives against Leishmania species and further studies should be undertaken to establish them as novel leishmanicidal therapeutic agents.

Characterization of the peroxiredoxin 1 subfamily from Tetrahymena thermophila

Peroxiredoxins are antioxidant enzymes that use redox active Cys residues to reduce H2O2 and various organic hydroperoxides to less reactive products, and thereby protect cells against oxidative stress. In yeasts and mammals, the Prx1 proteins are sensitive to hyperoxidation and consequent loss of their peroxidase activity whereas in most bacteria they are not. In this paper we report the characterization of the Prx1 family in the non-parasitic protist Tetrahymena thermophila. In this organism, four genes potentially encoding Prx1 have been identified. In particular, we show that the mitochondrial Prx1 protein (Prx1m) from T. thermophila is relatively robust to hyperoxidation. This is surprising given that T. thermophila is a eukaryote like yeasts and mammals. In addition, the proliferation of the T. thermophila cells was relatively robust to inhibition by H2O2, cumene hydroperoxide and plant natural products that are known to promote the production of H2O2. In the presence of these agents, the abundance of the T. thermophila Prx1m protein was shown to increase. This suggested that the Prx1m protein may be protecting the cells against oxidative stress. There was no evidence for any increase in Prx1m gene expression in the stressed cells. Thus, increasing protein stability rather than increasing gene expression may explain the increasing Prx1m protein abundance we observed.

The origin and evolution of cell-intrinsic antibacterial defenses in eukaryotes

To survive in a world dominated by bacteria, eukaryotes have evolved numerous self-defense strategies. While some defenses are recent evolutionary innovations, others are ancient, with roots early in eukaryotic history. With a focus on antibacterial immunity, we highlight the evolution of pattern recognition receptors that detect bacteria, where diverse functional classes have been formed from the repeated use and reuse of a small set of protein domains. Next, we discuss core microbicidal strategies shared across eukaryotes, and how these systems may have been co-opted from ancient cellular mechanisms. We propose that studying antibacterial responses across diverse eukaryotes can reveal novel modes of defense, while highlighting the critical innovations that occurred early in the evolution of our own immune systems.

Metacaspases: Potential Drug Target Against Protozoan Parasites

Among the numerous strategies/targets for controlling infectious diseases, parasites-derived proteases receive prime attention due to their essential contribution to parasite growth and development. Parasites produce a broad array of proteases, which are required for parasite entry/invasion, modification/degradation of host proteins for their nourishment, and activation of inflammation that ensures their survival to maintain infection. Presently, extensive research is focused on unique proteases termed as "metacaspases" (MCAs) in relation to their versatile functions in plants and non-metazoans. Such unique MCAs proteases could be considered as a potential drug target against parasites due to their absence in the human host. MCAs are cysteine proteases, having Cys-His catalytic dyad present in fungi, protozoa, and plants. Studies so far indicated that MCAs are broadly associated with apoptosis-like cell death, growth, and stress regulation in different protozoa. The present review comprises the important research outcomes from our group and published literature, showing the variable properties and function of MCAs for therapeutic purpose against infectious diseases.

Meiotic viral attenuation through an ancestral apoptotic pathway

The programmed release of apoptogenic proteins from mitochondria is a core event of apoptosis, although ancestral roles of this phenomenon are not known. In mammals, one such apoptogenic protein is Endonuclease G (EndoG), a conserved mitochondrial nuclease that fragments the DNA of dying cells. In this work, we show that budding yeast executes meiotically programmed mitochondrial release of an EndoG homolog, Nuc1, during sporulation. In contrast to EndoG's ostensible pro-death function during apoptosis, Nuc1 mitochondrial release is pro-survival, attenuating the cytosolic L-A and Killer double-stranded RNA mycoviruses and protecting meiotic progeny from the catastrophic consequences of their derepression. The protective viral attenuation role of this pathway illuminates a primordial role for mitochondrial release of EndoG, and perhaps of apoptosis itself.

Increased ROS generation causes apoptosis-like death: Mechanistic insights into the anti-Leishmania activity of a potent ruthenium(II) complex

Some metallodrugs that exhibit interesting biological activity contain transition metals such as ruthenium, and have been extensively exploited because of their antiparasitic potential. In previous study, we reported the remarkable anti-Leishmania activity of precursor cis-[Ru^IICl₂(dppm)₂], where dppm = bis(diphenylphosphino)methane, and new ruthenium(II) complexes, cis-[Ru^II(η²-O₂CC₁₀H₁₃)(dppm)₂]PF₆ (bbato), cis-[Ru^II(η²-O₂CC₇H₇S)(dppm)²]PF⁶ (mtbato) and cis-[Ru^II(η²-O₂CC₇H₇O₂)(dppm)₂]PF₆ (hmxbato) against some Leishmania species. In view of the promising activity of the hmxbato complex against Leishmania (Leishmania) amazonensis promastigotes, the present work investigated the possible parasite death mechanism involved in the action of this hmxbato and its precursor. We report, for the first time, that hmxbato and precursor promoted an increase in reactive oxygen species production, depolarization of the mitochondrial membrane, DNA fragmentation, formation of a pre-apoptotic peak, alterations in parasite morphology and formation of autophagic vacuoles. Taken together, our results suggest that these ruthenium complexes cause parasite death by apoptosis. Thus, this work provides relevant knowledge on the activity of ruthenium(II) complexes against L. (L.) amazonensis. Such information will be essential for the exploitation of these complexes as future candidates for cutaneous leishmaniasis treatment.

Pumilacidins from the Octocoral-Associated Bacillus sp. DT001 Display Anti-Proliferative Effects in Plasmodium falciparum

Chemical examination of the octocoral-associated Bacillus species (sp.) DT001 led to the isolation of pumilacidins A (1) and C (2). We investigated the effect of these compounds on the viability of Plasmodium falciparum and the mechanism of pumilacidin-induced death. The use of inhibitors of protein kinase C (PKC) and phosphoinositide 3-kinase (PI3K) was able to prevent the effects of pumilacidins A and C. The results indicated also that pumilacidins inhibit parasite growth via mitochondrial dysfunction and decreased cytosolic Ca²⁺.

Molecular and cellular characterization of apoptosis in flat oyster a key mechanisms at the heart of host-parasite interactions

Bonamia ostreae has been associated with the decline of flat oyster Ostrea edulis populations in some European countries. This obligatory intracellular parasite persists and multiplies into hemocytes. Previous in vitro experiments showed that apoptosis is activated in hemocytes between 1 h and 4 h of contact with the parasite. The flat oyster uses the apoptosis pathway to defend against B. ostreae. However, the parasite might be also able to modulate this response in order to survive in its host. In order to investigate this hypothesis the apoptotic response of the host was evaluated using flow cytometry, transmission electron microscopy and by measuring the response of genes involved in the apoptotic pathway after 4 h. In parallel, the parasite response was investigated by measuring the expression of B. ostreae genes involved in different biological functions including cell cycle and cell death. Obtained results allow describing molecular apoptotic pathways in O. edulis and confirm that apoptosis is early activated in hemocytes after a contact with B. ostreae. Interestingly, at cellular and molecular levels this process appeared downregulated after 44 h of contact. Concurrently, parasite gene expression appeared reduced suggesting that the parasite could inhibit its own metabolism to escape the immune response.

Trichomonas vaginalis Macrophage Migration Inhibitory Factor Mediates Parasite Survival during Nutrient Stress

Trichomonas vaginalis is responsible for the most prevalent non-viral sexually transmitted disease worldwide, and yet the mechanisms used by this parasite to establish and maintain infection are poorly understood. We previously identified a T. vaginalis homologue (TvMIF) of a human cytokine, human macrophage migration inhibitory factor (huMIF). TvMIF mimics huMIF’s role in increasing cell growth and inhibiting apoptosis in human host cells. To interrogate a role of TvMIF in parasite survival during infection, we asked whether overexpression of TvMIF (TvMIF-OE) confers an advantage to the parasite under nutrient stress conditions by comparing the survival of TvMIF-OE parasites to that of empty vector (EV) parasites. We found that under conditions of serum starvation, overexpression of TvMIF resulted in increased parasite survival. Serum-starved parasites secrete 2.5-fold more intrinsic TvMIF than unstarved parasites, stimulating autocrine and paracrine signaling. Similarly, we observed that addition of recombinant TvMIF increased the survival of the parasites in the absence of serum. Recombinant huMIF likewise increased the parasite survival in the absence of serum, indicating that the parasite may use this host survival factor to resist its own death. Moreover, TvMIF-OE parasites were found to undergo significantly less apoptosis and reactive oxygen species (ROS) generation under conditions of serum starvation, consistent with increased survival being the result of blocking ROS-induced apoptosis. These studies demonstrated that a parasitic MIF enhances survival under adverse conditions and defined TvMIF and huMIF as conserved survival factors that exhibit cross talk in host-pathogen interactions.

Macrophage migration inhibitory factor (MIF) is a conserved protein found in most eukaryotes which has been well characterized in mammals but poorly studied in other eukaryotes. The limited analyses of MIF proteins found in unicellular eukaryotes have focused exclusively on the effect of parasitic MIF on the mammalian host. This was the first study to assess the function of a parasite MIF in parasite biology. We demonstrate that the Trichomonas vaginalis MIF functions to suppress cell death induced by apoptosis, thereby enhancing parasite survival under adverse conditions. Our research reveals a conserved survival mechanism, shared by a parasite and its host, and indicates a role for a conserved protein in mediating cross talk in host-pathogen interactions.

In vitro activity of 1H-phenalen-1-one derivatives against Acanthamoeba castellanii Neff and their mechanisms of cell death

Acanthamoeba is an opportunistic pathogen which is the causal agent of a sight-threatening ulceration of the cornea known as Acanthamoeba keratitis (AK) and, more rarely, an infection of the central nervous system called "granulomatous amoebic encephalitis" (GAE). The symptoms of AK are non-specific, and so it can be misdiagnosed as a viral, bacterial, or fungal keratitis. Furthermore, current therapeutic measures against AK are arduous, and show limited efficacy against the cyst stage of Acanthamoeba. 1H-Phenalen-1-one (PH) containing compounds have been isolated from plants and fungi, where they play a crucial role in the defense mechanism of plants. Natural as well as synthetic PHs exhibit a diverse range of biological activities against fungi, protozoan parasites or human cancer cells. New synthetic PHs have been tested in this study and they show a potential activity against this protozoa.

Intraspecific chemical communication in microalgae

Contents 516 I. 516 II. 518 III. 518 IV. 521 V. 523 VI. 523 VII. 526 526 References 526 SUMMARY: The relevance of infochemicals in the relationships between organisms is emerging as a fundamental aspect of aquatic ecology. Exchanges of chemical cues are likely to occur not only between organisms of different species, but also between conspecific individuals. Especially intriguing is the investigation of chemical communication in microalgae, because of the relevance of these organisms for global primary production and their key role in trophic webs. Intraspecific communication between algae has been investigated mostly in relation to sexuality and mating. The literature also contains information on other types of intraspecific chemical communication that have not always been explicitly tagged as ways to communicate to conspecifics. However, the proposed role of certain compounds as intraspecific infochemicals appears questionable. In this article, we make use of this plethora of information to describe the various instances of intraspecific chemical communication between conspecific microalgae and to identify the common traits and ecological significance of intraspecific communication. We also discuss the evolutionary implications of intraspecific chemical communication and the mechanisms by which it can be inherited. A special focus is the genetic diversity among conspecific algae, including the possibility that genetic diversity is an absolute requirement for intraspecific chemical communication.

Amoebicidal Activity of Caffeine and Maslinic Acid by the Induction of Programmed Cell Death in Acanthamoeba

Free-living amoebae of the genus Acanthamoeba are the causal agents of a sight-threatening ulceration of the cornea called Acanthamoeba keratitis, as well as the rare but usually fatal disease granulomatous amoebic encephalitis. Although there are many therapeutic options for the treatment of Acanthamoeba infections, they are generally lengthy and/or have limited efficacy. For the best clinical outcome, treatments should target both the trophozoite and the cyst stages, as cysts are known to confer resistance to treatment. In this study, we document the activities of caffeine and maslinic acid against both the trophozoite and the cyst stages of three clinical strains of Acanthamoeba These drugs were chosen because they are reported to inhibit glycogen phosphorylase, which is required for encystation. Maslinic acid is also reported to be an inhibitor of extracellular proteases, which may be relevant since the protease activities of Acanthamoeba species are correlated with their pathogenicity. We also provide evidence for the first time that both drugs exert their anti-amoebal effects through programmed cell death.

The Cytotoxic Effects of Camptothecin and Mastoparan on the Unicellular Green Alga Chlamydomonas reinhardtii

We have recently reported that protease inhibitors affecting the activity of the proteasome cause necrotic cell death in Chlamydomonas reinhardtii instead of inducing apoptosis as shown for some mammalian cell lines. Therefore, we have studied other well-known inducers of apoptosis in mammalian cells for their effects on C. reinhardtii cells. Mastoparan caused rapid cell death without a prominent lag-phase under all growth conditions, whereas the cytotoxic effect of the topoisomerase I inhibitor camptothecin exclusively occurred during the cell-division phase. Essentially no differences between wall-deficient and wild-type cells were observed with respect to dose-response and time-course of camptothecin and mastoparan. In cultures of the wall-deficient strain, cell death was accompanied by swelling and subsequent disruption of the cells, established markers of necrosis. In case of the wild-type strain, camptothecin and mastoparan caused accumulation of apparently intact, but dead cells instead of cell debris due to the presence of the wall. Both in cultures of the wall-deficient and the wild-type strains, cell death was accompanied by an increase of the protein concentration in the culture medium indicating a lytic process like necrosis. Taking together, we have severe doubts on the existence of an apoptotic program in case of C. reinhardtii.

DNA analysis of cattle parasitic protozoan Tritrichomonas foetus after photodynamic therapy

Photodynamic therapy (PDT) is a modality of therapy that involves the activation of photosensitive substances and the generation of cytotoxic oxygen species and free radicals to promote the selective destruction of target tissues. This study analyzed the application of PDT to Tritrichomonas foetus, a scourged and etiological agent of bovine trichomoniasis, a sexually transmitted infectious disease. As it is an amitochondrial and aerotolerant protozoan, it produces energy under low O₂ tension via hydrogenosome. T. foetus from an axenic culture was incubated with photosensitizer tetrasulfonated aluminium phthalocyanine and then irradiated with a laser source (InGaAIP) at a density of 4.5Jcm^-2. The DNA integrity of the control and treated group parasites was analyzed by conventional gel electrophoresis and comet assay techniques. In previous results, morphological changes characterized by apoptotic cell death were observed after T. foetus was submitted to PDT treatment. In the treated groups, T. foetus DNA showed a higher concentration of small fragments, about 200pb, in gel electrophoresis after PDT. In the comet assay, the DNA tail percentage was significantly higher in the treated groups. These results demonstrate that PDT leads to DNA fragmentation with changes in nuclear morphology and apoptotic features.

Flat oyster follows the apoptosis pathway to defend against the protozoan parasite Bonamia ostreae

The in vitro model Ostrea edulis hemocyte - Bonamia ostreae is interesting to investigate host-parasite interactions at the cellular level. Indeed, this unicellular parasite infects the flat oyster Ostrea edulis and multiplies within hemocytes, the central effectors of oyster defenses. Apoptosis is a mechanism used by many organisms to eliminate infected cells. In order to study the potential involvement of this mechanism in the oyster response to B. ostreae, in vitro experiments were carried out by exposing hemocytes from the naturally susceptible oyster O. edulis and a resistant oyster species Crassostrea gigas to live and heat-inactivated parasites. Hemocyte apoptotic response was measured using a combination of flow cytometry and microscopy analyses. Whatever the host species was, the parasite was engulfed in hemocytes and induced an increase of apoptotic parameters including intracytoplasmic calcium concentration, mitochondrial membrane potential or phosphatidyl-serine externalization as well as ultrastructural modifications. However, the parasite appears more able to infect flat oyster than cupped oyster hemocytes and the apoptotic response was more important against live than dead parasites in the natural host than in C. gigas. Our results suggest that O. edulis specifically responds to B. ostreae by inducing apoptosis of hemocytes.

Phosphatidylserine is a global immunosuppressive signal in efferocytosis, infectious disease, and cancer

Apoptosis is an evolutionarily conserved and tightly regulated cell death modality. It serves important roles in physiology by sculpting complex tissues during embryogenesis and by removing effete cells that have reached advanced age or whose genomes have been irreparably damaged. Apoptosis culminates in the rapid and decisive removal of cell corpses by efferocytosis, a term used to distinguish the engulfment of apoptotic cells from other phagocytic processes. Over the past decades, the molecular and cell biological events associated with efferocytosis have been rigorously studied, and many eat-me signals and receptors have been identified. The externalization of phosphatidylserine (PS) is arguably the most emblematic eat-me signal that is in turn bound by a large number of serum proteins and opsonins that facilitate efferocytosis. Under physiological conditions, externalized PS functions as a dominant and evolutionarily conserved immunosuppressive signal that promotes tolerance and prevents local and systemic immune activation. Pathologically, the innate immunosuppressive effect of externalized PS has been hijacked by numerous viruses, microorganisms, and parasites to facilitate infection, and in many cases, establish infection latency. PS is also profoundly dysregulated in the tumor microenvironment and antagonizes the development of tumor immunity. In this review, we discuss the biology of PS with respect to its role as a global immunosuppressive signal and how PS is exploited to drive diverse pathological processes such as infection and cancer. Finally, we outline the rationale that agents targeting PS could have significant value in cancer and infectious disease therapeutics.

Deprivation of L-Arginine Induces Oxidative Stress Mediated Apoptosis in Leishmania donovani Promastigotes: Contribution of the Polyamine Pathway

The growth and survival of intracellular parasites depends on the availability of extracellular nutrients. Deprivation of nutrients viz glucose or amino acid alters redox balance in mammalian cells as well as some lower organisms. To further understand the relationship, the mechanistic role of L-arginine in regulation of redox mediated survival of Leishmania donovani promastigotes was investigated. L-arginine deprivation from the culture medium was found to inhibit cell growth, reduce proliferation and increase L-arginine uptake. Relative expression of enzymes, involved in L-arginine metabolism, which leads to polyamine and trypanothione biosynthesis, were downregulated causing decreased production of polyamines in L-arginine deprived parasites and cell death. The resultant increase in reactive oxygen species (ROS), due to L-arginine deprivation, correlated with increased NADP+/NADPH ratio, decreased superoxide dismutase (SOD) level, increased lipid peroxidation and reduced thiol content. A deficiency of L-arginine triggered phosphatidyl serine externalization, a change in mitochondrial membrane potential, release of intracellular calcium and cytochrome-c. This finally led to DNA damage in Leishmania promastigotes. In summary, the growth and survival of Leishmania depends on the availability of extracellular L-arginine. In its absence the parasite undergoes ROS mediated, caspase-independent apoptosis-like cell death. Therefore, L-arginine metabolism pathway could be a probable target for controlling the growth of Leishmania parasites and disease pathogenesis.

Leishmania donovani, the causative agent of Indian Visceral Leishmaniasis, resides in the gut of the insect vector and the macrophages of their mammalian host and avail nutrients for survival. Nutrient deprivation such as glucose or amino acid alters redox balance in mammalian cells as well as some lower organisms. However, the role of L-arginine, in regulation of redox balance and L. donovani survival yet not properly elucidated. In the present study, we found that L-arginine deprivation from the culture medium hinders growth and proliferation of Leishmania promastigotes. Starvation of L-arginine downregulates the expression of polyamine biosynthetic and thiol metabolic pathway enzymes leading to decreased production of polyamines in Leishmania parasites. Moreover, deprivation of L-arginine alters redox balance in Leishmania promastigotes characterized by the concomitant increase in ROS and decreased antioxidant level. Furthermore, L-arginine deprivation triggered phosphatidyl serine externalization, alteration in mitochondrial membrane potential, release of intraellular calcium and cytochrome-c followed by DNA damage. In summary, the growth and survival of Leishmania depends on the availability of extracellular L-arginine, in absence of which the parasite undergoes ROS mediated, caspase-independent apoptosis-like cell death. Therefore, targeting L-arginine metabolism pathway could be an alternative approach for controlling Leishmania growth and hence disease outcome.

Statins and voriconazole induce programmed cell death in Acanthamoeba castellanii

Members of the genus Acanthamoeba are facultative pathogens of humans, causing a sight-threatening keratitis and a life-threatening encephalitis. In order to treat those infections properly, it is necessary to target the treatment not only to the trophozoite but also to the cyst. Furthermore, it may be advantageous to avoid parasite killing by necrosis, which may induce local inflammation. We must also avoid toxicity of host tissue. Many drugs which target eukaryotes are known to induce programmed cell death (PCD), but this process is poorly characterized in Acanthamoeba. Here, we study the processes of programmed cell death in Acanthamoeba, induced by several drugs, such as statins and voriconazole. We tested atorvastatin, fluvastatin, simvastatin, and voriconazole at the 50% inhibitory concentrations (IC50s) and IC90s that we have previously established. In order to evaluate this phenomenon, we investigated the DNA fragmentation, one of the main characteristics of PCD, with quantitative and qualitative techniques. Also, the changes related to phosphatidylserine exposure on the external cell membrane and cell permeability were studied. Finally, because caspases are key to PCD pathways, caspase activity was evaluated in Acanthamoeba. All the drugs assayed in this study induced PCD in Acanthamoeba. To the best of our knowledge, this is the first study where PCD induced by drugs is described quantitatively and qualitatively in Acanthamoeba.

[From dualism to multiplicity: seeing BCL-2 family proteins and cell death with new eyes]

The concept of cell death has many links to the concept of death itself, defined as the opposite of life. Achievements obtained through research on apoptosis have apparently allowed us to transcend this Manichean view. Death is no longer outside, but rather inside living systems, as a constitutive force at work within the living matter. Whereas the death of cells can be positive and breed "creation" (e.g. during morphogenesis), its dysregulation can also cause or contribute to fatal diseases including cancer. It is tempting to apply this biological discourse to illuminate the relations between life and death, taken in general terms, but does this generalization actually hold? Is this discourse not essentially a metaphor? If cell death is considered as a vital aspect of various biological processes, then are we not faced with some vitalistic conception of death? Are there one or more meanings to the word "death"? Does the power to self-destruct act in opposition to other key features of living entities, or rather in juxtaposition to them? In this article, we first describe how the field of cell death has been developed on the basis of perceived and built dichotomies, mirroring the original opposition between life and death. We detail the limitations of the current paradigm of apoptosis regulation by BCL-2 family proteins, which nicely illustrate the problem of binary thinking in biology. Last, we try to show a way out of this dualistic matrix, by drawing on the notions of multiplicity, complexity, diversity, evolution and contingency.

Interferon-gamma and interlukin-4 patterns in BALB/c mice suffering from cutaneous leishmaniasis treated with cantharidin

Background:

Cutaneous leishmaniasis is a health problem in the world. Lesions should be treated on cosmetically or functionally important sites, such as the face and hands. Cantharidin is a terpenoid compound produced naturally by beetles of Meloidae and Oedemeridae families.

Objectives:

The current study aimed to investigate the effect of cantharidin on Cutaneous Leishmaniasis (CL) lesions and IFN-γ and IL-4 patterns in infected BALB/c mice.

Materials and Methods:

Infected BALB/c mice were divided into five groups as: untreated (control group), eucerin-treated and 0.05%, 0.1% and 0.5% cantharidin-treated. Lesions diameter was measured by Vernier caliper every three days for four weeks. Cytokines levels were measured by enzyme-linked immunosorbent assay (ELISA) using U-CyTech kit.

Results:

The results indicated that treatment with cantharidin exacerbates lesions compared with the controls, except for 0.05% cantharidin dose that restrained lesion growth significantly. Interferon gamma level in cantharidin-treated groups was significantly less than that of the control group. But interlukin-4 level was similar among the groups.

Conclusions:

The current study results indicated that high doses of cantharidin exacerbates leishmaniasis lesion, but low dose of cantharidin inhibits lesion growth.

Redox metabolism in Trypanosoma cruzi. Biochemical characterization of dithiol glutaredoxin dependent cellular pathways

In Trypanosoma cruzi, the modification of thiols by glutathionylation-deglutathionylation and its potential relation to protective, regulatory or signaling functions have been scarcely explored. Herein we characterize a dithiolic glutaredoxin (TcrGrx), a redox protein with deglutathionylating activity, having potential functionality to control intracellular homeostasis of protein and non-protein thiols. The catalytic mechanism followed by TcrGrx was found dependent on thiol concentration. Results suggest that TcrGrx operates as a dithiolic or a monothiolic Grx, depending on GSH concentration. TcrGrx functionality to mediate reduction of protein and non-protein disulfides was studied. TcrGrx showed a preference for glutathionylated substrates respect to protein disulfides. From in vivo assays involving TcrGrx overexpressing parasites, we observed the contribution of the protein to increase the general resistance against oxidative damage and intracellular replication of the amastigote stage. Also, studies performed with epimastigotes overexpressing TcrGrx strongly suggest the involvement of the protein in a cellular pathway connecting an apoptotic stimulus and apoptotic-like cell death. Novel information is presented about the participation of this glutaredoxin not only in redox metabolism but also in redox signaling pathways in T. cruzi. The influence of TcrGrx in several parasite physiological processes suggests novel insights about the protein involvement in redox signaling.

Dehydroascorbate: a possible surveillance molecule of oxidative stress and programmed cell death in the green alga Chlamydomonas reinhardtii

Chlamydomonas reinhardtii tolerates relatively high H2 O2 levels that induce an array of antioxidant activities. However, rather than rendering the cells more resistant to oxidative stress, the cells become far more sensitive to an additional H2 O2 dose. If H2 O2 is provided 1.5-9 h after an initial dose, it induces programmed cell death (PCD) in the wild-type, but not in the dum1 mutant impaired in the mitochondrial respiratory complex III. This mutant does not exhibit a secondary oxidative burst 4-5 h after the inducing H2 O2 , nor does it activate metacaspase-1 after the second H2 O2 treatment. The intracellular dehydroascorbate level, a product of ascorbate peroxidase, increases under conditions leading to PCD. The addition of dehydroascorbate induces PCD in the wild-type and dum1 cultures, but higher levels are required in dum1 cells, where it is metabolized faster. The application of dehydroascorbate induces the expression of metacaspase-2, which is much stronger than the expression of metacaspase-1. The presence or absence of oxidative stress, in addition to the rise in internal dehydroascorbate, may determine which metacaspase is activated during Chlamydomonas PCD. Cell death is strongly affected by the timing of H2 O2 or dehydroascorbate admission to synchronously grown cultures, suggesting that the cell cycle phase may distinguish cells that perish from those that do not.

Influence of the programmed cell death of lymphocytes on the immunity of patients with atopic bronchial asthma

BACKGROUND

Fairly recent data highlight the role of programmed cell death and autoimmunity, as potentially important factors in the pathogenesis of chronic obstructive airway diseases. The purpose of our research was to determine the influence of apoptotic factors on the immunity of patients with atopic bronchial asthma according to the degree of severity.

METHOD

The study was performed on the peripheral blood of patients with atopic bronchial asthma with different severity. The Immunological aspects were determined with ELISA, the fluorimetric method and the method of precipitation with polyethylene glycol. And the quantification of the parameters of the programmed cell death was performed by the method of flow cytometry and electron microscopy method.

RESULTS

The data obtained from morphological and biochemical parameters show the deregulation of Programmed Death of lymphocytes of patients with atopic bronchial asthma but individual for each group of patients. This dysfunction might induce the secretion of autoantibodies against DNA. This could explain the accumulation of circulating immune complex with average size considered as the most pathogenic in patients with bronchial asthma especially in the patients of serious severity. It should be noted that Patients with bronchial asthma of mild and severe severity had different way and did not have the same degree of deficiency of the immune system.

CONCLUSION

These data suggested that apoptotic factor of lymphocytes may play an important role in controlling immunity of patients with atopic bronchial asthma.

Caspase-like activity during aging and cell death in the toxic dinoflagellate Karenia brevis

The observation of caspase-like activity during cell death has provided a new framework for understanding the evolutionary and ecological contexts of programmed cell death in phytoplankton. However, additional roles for this caspase-like activity, the enzymes responsible, and the targets of this enzyme activity in phytoplankton remain largely undefined. In the present study, the role of caspase-like activity in aging and ROS-mediated cell death were investigated and death programs both dependent on and independent of caspase-like activity were observed in the toxic dinoflagellate, Karenia brevis. The dual use of in situ caspase 3/7 and TUNEL staining identified previously undescribed death-associated morphotypes in K. brevis. In silico motif analysis identified several enzymes with predicted caspase-like activity in the K. brevis transcriptome, although bona fide caspases are absent. Lastly, computational prediction of downstream caspase substrates, using sequence context and predicted secondary structure, identified proteins involved in a wide range of biological processes including regulation of protein turnover, cell cycle progression, lipid metabolism, coenzyme metabolism, apoptotic and autophagic death. To confirm the computational predictions, a short peptide was designed around the predicated caspase cleavage site in a predicted novel K. brevis caspase 3/7-like target, S-adenosylmethionine synthetase (KbAdoMetS). Cleavage of the peptide substrate with recombinant caspase 3 enzyme was determined by MALDI-TOF MS, confirming that KbAdoMetS is indeed a bona fide caspase substrate. These data identify the involvement of caspase-like activity in both aging and cell death in K. brevis and identify novel executioner enzymes and downstream targets that may be important for bloom termination.

The first suicides: a legacy inherited by parasitic protozoans from prokaryote ancestors

It is more than 25 years since the first report that a protozoan parasite could die by a process resulting in a morphological phenotype akin to apoptosis. Since then these phenotypes have been observed in many unicellular parasites, including trypanosomatids and apicomplexans, and experimental evidence concerning the molecular pathways that are involved is growing. These observations support the view that this form of programmed cell death is an ancient one that predates the evolution of multicellularity. Here we review various hypotheses that attempt to explain the origin of apoptosis, and look for support for these hypotheses amongst the parasitic protists as, with the exception of yeast, most of the work on death mechanisms in unicellular organisms has focussed on them. We examine the role that addiction modules may have played in the original eukaryote cell and the part played by mitochondria in the execution of present day cells, looking for examples from Leishmania spp. Trypanosoma spp. and Plasmodium spp. In addition, the expanding knowledge of proteases, nucleases and other molecules acting in protist execution pathways has enabled comparisons to be made with extant Archaea and bacteria and with biochemical pathways that evolved in metazoans. These comparisons lend support to the original sin hypothesis but also suggest that present-day death pathways may have had multifaceted beginnings.

Evolution of the animal apoptosis network

The number of available eukaryotic genomes has expanded to the point where we can evaluate the complete evolutionary history of many cellular processes. Such analyses for the apoptosis regulatory networks suggest that this network already existed in the ancestor of the entire animal kingdom (Metazoa) in a form more complex than in some popular animal model organisms. This supports the growing realization that regulatory networks do not necessarily evolve from simple to complex and that the relative simplicity of these networks in nematodes and insects does not represent an ancestral state, but is the result of secondary simplifications. Network evolution is not a process of monotonous increase in complexity, but a dynamic process that includes lineage-specific gene losses and expansions, protein domain reshuffling, and emergence/reemergence of similar protein architectures by parallel evolution. Studying the evolution of such networks is a challenging yet interesting subject for research and investigation, and such studies on the apoptosis networks provide us with interesting hints of how these networks, critical in so many human diseases, have developed.

Mastoparan-induced programmed cell death in the unicellular alga Chlamydomonas reinhardtii

BACKGROUND AND AIMS

Under stress-promoting conditions unicellular algae can undergo programmed cell death (PCD) but the mechanisms of algal cellular suicide are still poorly understood. In this work, the involvement of caspase-like proteases, DNA cleavage and the morphological occurrence of cell death in wasp venom mastoparan (MP)-treated Chlamydomonas reinhardtii were studied.

METHODS

Algal cells were exposed to MP and cell death was analysed over time. Specific caspase inhibitors were employed to elucidate the possible role of caspase-like proteases. YVADase activity (presumably a vacuolar processing enzyme) was assayed by using a fluorogenic caspase-1 substrate. DNA breakdown was evaluated by DNA laddering and Comet analysis. Cellular morphology was examined by confocal laser scanning microscopy.

KEY RESULTS

MP-treated C. reinhardtii cells expressed several features of necrosis (protoplast shrinkage) and vacuolar cell death (lytic vesicles, vacuolization, empty cell-walled corpse-containing remains of digested protoplast) sometimes within one single cell and in different individual cells. Nucleus compaction and DNA fragmentation were detected. YVADase activity was rapidly stimulated in response to MP but the early cell death was not inhibited by caspase inhibitors. At later time points, however, the caspase inhibitors were effective in cell-death suppression. Conditioned medium from MP-treated cells offered protection against MP-induced cell death.

CONCLUSIONS

In C. reinhardtii MP triggered PCD of atypical phenotype comprising features of vacuolar and necrotic cell deaths, reminiscent of the modality of hypersensitive response. It was assumed that depending on the physiological state and sensitivity of the cells to MP, the early cell-death phase might be not mediated by caspase-like enzymes, whereas later cell death may involve caspase-like-dependent proteolysis. The findings substantiate the hypothesis that, depending on the mode of induction and sensitivity of the cells, algal PCD may take different forms and proceed through different pathways.

UV-C Exposure Induces an Apoptosis-Like Process in Euglena gracilis

Euglena gracilis is a unicellular, free-living flagellate that inhabits various freshwater environments. Our research shows that exposure to UV-C light can trigger some form of programmed cell death. Cells exposed to UV-C light underwent delayed changes that were strongly reminiscent of apoptosis in mammalian cells, including cell shrinkage and DNA fragmentation that produced the characteristic ladder pattern commonly seen with apoptosis. DNA fragmentation could be inhibited by pretreatment with Z-VAD-FMK and also independently induced by exposure to staurosporine. In addition, Euglena possess proteins that cross-reacted with antibodies raised against human caspases 3 and 9. Given that Euglena are extremely easy to culture and represent a lineage positioned near the base of the eukaryotic tree, they will be an excellent model system for comparative analyses with apoptotic-like death processes in other eukaryotic microbes.

LQB-118, an orally active pterocarpanquinone, induces selective oxidative stress and apoptosis in Leishmania amazonensis

OBJECTIVES

The pterocarpanquinone LQB-118, previously demonstrated to be effective in vivo via oral delivery, was investigated for its mechanism in selective parasite killing.

METHODS

Oxidative stress in Leishmania amazonensis was analysed by evaluating reactive oxygen species (ROS) production (2',7'-dichlorodihydrofluorescein diacetate) and the loss of mitochondrial membrane potential (ΔΨm) using rhodamine, JC-1 and MitoCapture. Ultrastructural analysis was performed using transmission electron microscopy (TEM). DNA fragmentation was evaluated using terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL).

RESULTS

Treatment with LQB-118 induced ROS production in the promastigotes of L. amazonensis in a concentration-dependent manner for the first 4 h and was sustained for 24 h. TEM analysis revealed several alterations typical of apoptosis. Promastigotes presented a reduction of ΔΨm after 24 h of incubation with 2.5 μM (18.7%), 5 μM (63.7%) or 10 μM (70.7%) LQB-118. A sub-G0/G1 cell cycle phenotype was observed in 21%-83% of the promastigotes incubated with 1.25-10 μM LQB-118. Concentration-dependent DNA fragmentation was observed in promastigotes treated with 2.5-10 μM LQB-118, and selective DNA fragmentation was observed in intracellular amastigotes after 72 h with 2.5 μM treatment.

CONCLUSIONS

Our results suggest that LQB-118 selectively induces ROS-triggered and mitochondria-dependent apoptosis in this parasite.

No need for labels: the autofluorescence of Leishmania tarentolae mitochondria and the necessity of negative controls

Background

Fluorescence microscopy is a powerful tool to study the morphology and function of subcellular compartments or to determine the localization of proteins. The method is also regularly used for the analysis of parasitic protists including kinetoplastida.

Results

Here, we report a significant autofluorescence of Leishmania tarentolae mitochondria. The autofluorescence, presumably caused by flavoproteins, was detectable using a variety of cell fixation protocols and had a maximum emission at approximately 538 nm. Stable signals were obtained with xenon lamps as a light source and filter sets that are commonly used for the detection of green fluorescent protein.

Conclusions

On the one hand, we present a methodological approach to examine mitochondrial morphology or to study the colocalization of mitochondrial proteins without additional staining or labeling procedures. On the other hand, under certain experimental conditions, mitochondrial autofluorescence can result in false positive signals, demonstrating the necessity to analyze unlabeled cells as negative controls.