Manipulation of apoptosis in the host-parasite interaction

Immune response and apoptosis of gibel carp (Carassius auratus gibelio) gills to Chilodonella hexasticha infection: Insights from histopathological and multi-omics analyses

Gibel carp (Carassius auratus gibelio) is an important economically farmed fish in China. Chilodonella hexasticha parasitizes on the gills and fins of host fish, causing disruption to their normal respiration and movement, ultimately resulting in death of the fish. In this study, a combination of histopathological, immunohistochemical, transferase dUTP nick end labeling (TUNEL), multi-omics, and molecular approaches were employed to identify the immune reaction and cell apoptosis in gill tissue in response to C. hexasticha infection. Significant lamellae fusion, hyperplasia, hyperemia, necrosis, and desquamation of infected gibel carp gills were observed. In total, the expression of 3619 genes was higher, and 3143 lower, for gills in the infected group compared to the control group. Furthermore, 76 metabolites were significantly increased and 105 were significantly decreased in the infected group compared with the control group. From the qRT-PCR analysis results, immune system-related genes encoding IL-8, CXCL8a, and CXC11 were significantly up-regulated in infected gibel carp, while ZAP70 was significantly down-regulated. Immunohistochemical results also showed the down-regulated ZAP70 in the infected group. Apoptosis-related genes encoding CASP3 and Mcl-1b were up-regulated in response to C. hexasticha infection. These genes indicate the activation of CASP family-related apoptosis and Bim-mediated mitochondrial apoptotic pathways. TUNEL assays also revealed severe apoptosis in the infected group. Based on this study's results, it can be concluded that C. hexasticha infection leads to histopathological changes in the gills of infected fish, and induces both a significant immune response and apoptosis.

Differential Immune Responses and Underlying Mechanisms of Metabolic Reprogramming in Smooth and Rough Variants of Mycobacterium peregrinum Infections

Mycobacterium peregrinum (Mpgm) is a rapidly growing mycobacteria that is classified as a nontuberculous mycobacterium (NTM) and is commonly found in environmental sources such as soil, water, and animals. Mpgm is considered an opportunistic pathogen that causes infection in immunocompromised individuals or those with underlying medical conditions. Although there have been clinical reports on Mpgm, reports of the immune response and metabolic reprogramming have not been published. Thus, we studied standard Mpgm-ATCC and two clinical strains (Mpgm-S and Mpgm-R) using macrophages and mouse bone marrow-derived cells. Mpgm has two types of colony morphologies: smooth and rough. We grew all strains on the 7H10 agar medium to visually validate the morphology. Cytokine levels were measured via ELISA and real-time PCR. The changes in mitochondrial function and glycolysis in Mpgm-infected macrophages were measured using an extracellular flux analyzer. Mpgm-S-infected macrophages showed elevated levels of inflammatory cytokines, including interleukin (IL)-6, IL-12p40, and tumor necrosis factor (TNF)-α, compared to Mpgm-ATCC- and Mpgm-R-infected macrophages. Additionally, our findings revealed metabolic changes in Mpgm-ATCC and two clinical strains (Mpgm-S and Mpgm-R) during infection; significant changes were observed in the mitochondrial respiration, extracellular acidification, and the oxygen consumption of BMDMs upon Mpgm-S infection. In summary, within the strains examined, Mpgm-S displayed greater virulence, triggered a heightened immune response, and induced more profound shifts in bioenergetic metabolism than Mpgm-ATCC and Mpgm-R. This study is the first to document distinct immune responses and metabolic reorganization following Mpgm infection. These findings lay a crucial foundation for further investigations into the pathogenesis of Mpgm.

Infection by the Parasite Myxobolus bejeranoi (Cnidaria: Myxozoa) Suppresses the Immune System of Hybrid Tilapia

Myxozoa (Cnidaria) is a large group of microscopic obligate endoparasites that can cause emerging diseases, affecting wild fish populations and fisheries. Recently, the myxozoan Myxobolus bejeranoi was found to infect the gills of hybrid tilapia (Nile tilapia (Oreochromis niloticus) × Jordan/blue tilapia (O. aureus)), causing high morbidity and mortality. Here, we used comparative transcriptomics to elucidate the molecular processes occurring in the fish host following infection by M. bejeranoi. Fish were exposed to pond water containing actinospores for 24 h and the effects of minor, intermediate, and severe infections on the sporulation site, the gills, and on the hematopoietic organs, head kidney and spleen, were compared. Enrichment analysis for GO and KEGG pathways indicated immune system activation in gills at severe infection, whereas in the head kidney a broad immune suppression included deactivation of cytokines and GATA3 transcription factor responsible for T helper cell differentiation. In the spleen, the cytotoxic effector proteins perforin and granzyme B were downregulated and insulin, which may function as an immunomodulatory hormone inducing systemic immune suppression, was upregulated. These findings suggest that M. bejeranoi is a highly efficient parasite that disables the defense mechanisms of its fish host hybrid tilapia.

Transcriptomic profiles of Florida pompano (Trachinotus carolinus) gill following infection by the ectoparasite Amyloodiniumocellatum

The dinoflagellate Amyloodinium ocellatum is an important pathogenic parasite infecting cultured marine and brackish water fishes worldwide. This includes cultured Florida pompano (Trachinotus carolinus), which is one of the most desirable marine food fish with high economic value in the USA. A. ocellatum infects fish gills and causes tissue damage, increased respiratory rate, reduced appetite, and mortality, especially in closed aquaculture systems. This study mimicked the natural infection of A. ocellatum in cultured pompano and conducted a transcriptomic comparison of gene expression in the gills of control and A. ocellatum infected fish to explore the molecular mechanisms of infection. RNA-seq data revealed 604 differentially expressed genes in the infected fish gills. The immunoglobulin genes (including IgM/T) augmentation and IL1 inflammation suppression were detected after infection. Genes involved in reactive oxygen species mediating parasite killing were also highly induced. However, excessive oxidants have been linked to oxidative tissue damage and apoptosis. Correspondingly, widespread down-regulation of collagen genes and growth factor deprivation indicated impaired tissue repair, and meanwhile the key executor of apoptosis, caspase-3 was highly expressed (25.02-fold) in infected fish. The infection also influenced the respiratory gas sensing and transport genes and established hypoxic conditions in the gill tissue. Additionally, food intake and lipid metabolism were also affected. Our work provides the transcriptome sequencing of Florida pompano and provides key insights into the acute pathogenesis of A. ocellatum. This information can be utilized for designing optimal disease surveillance strategies, future selection for host resistance, and development of novel therapeutic measures.

Thiazolidine derivatives: In vitro toxicity assessment against promastigote and amastigote forms of Leishmania infantum and ultrastructural study

Neglected diseases, such as Leishmaniasis, constitute a group of communicable diseases that occur mainly in tropical countries. Considered a public health problem with limited treatment. Therefore, there is a need for new therapies. In this sense, our proposal was to evaluate in vitro two series of thiazolidine compounds (7a-7e and 8a-8e) against Leishmania infantum. We performed in vitro evaluations through macrophage cytotoxicity assays (J774) and nitric oxide production, activity against promastigotes and amastigotes, as well as ultrastructural analyzes in promastigotes. In the evaluation of cytotoxicity, the thiazolidine compounds presented CC₅₀ values between 8.52 and 126.83 μM. Regarding the evaluation against the promastigote forms, the IC₅₀ values ranged between 0.42 and 142.43 μM. Compound 7a was the most promising, as it had the lowest IC₅₀. The parasites treated with compound 7a showed several changes, such as cell body shrinkage, shortening and loss of the flagellum, intense mitochondrial edema and cytoplasmic vacuolization, leading the parasite to cell inviability. In assays against the amastigote forms, the compound showed a low IC₅₀ (0.65 μM). These results indicate that compound 7a was efficient for both evolutionary forms of the parasite. In silico studies suggest that the compound has good oral bioavailability. These results show that compound 7a is a potential drug candidate for the treatment of Leishmaniasis.

Larval transcriptomic responses of a stony coral, Acropora tenuis, during initial contact with the native symbiont, Symbiodinium microadriaticum

Although numerous dinoflagellate species (Family Symbiodiniaceae) are present in coral reef environments, Acropora corals tend to select a single species, Symbiodinium microadriaticum, in early life stages, even though this species is rarely found in mature colonies. In order to identify molecular mechanisms involved in initial contact with native symbionts, we analyzed transcriptomic responses of Acropora tenuis larvae at 1, 3, 6, 12, and 24 h after their first contact with S. microadriaticum, as well as with non-native symbionts, including the non-symbiotic S. natans and the occasional symbiont, S. tridacnidorum. Some gene expression changes were detected in larvae inoculated with non-native symbionts at 1 h post-inoculation, but those returned to baseline levels afterward. In contrast, when larvae were exposed to native symbionts, we found that the number of differentially expressed genes gradually increased in relation to inoculation time. As a specific response to native symbionts, upregulation of pattern recognition receptor-like and transporter genes, and suppression of cellular function genes related to immunity and apoptosis, were exclusively observed. These findings indicate that coral larvae recognize differences between symbionts, and when the appropriate symbionts infect, they coordinate gene expression to establish stable mutualism.

Chandipura virus induces cell death in cancer cell lines of human origin and promotes tumor regression in vivo

Chandipura virus (CHPV) is an emerging human pathogen of great clinical significance. In this study, we have investigated the susceptibility pattern of both normal and cancer cell lines of human origin to wild-type (wt) CHPV in order to explore the possibility of developing CHPV as an oncolytic vector (OV). Marked cytopathic effect along with enhanced virus output was observed in cancer cell lines (HeLa, A549, U-138, PC-3, and HepG2) in comparison to normal human adult dermal fibroblast (HADF) cells. At an MOI of 0.1, cancer cell lines were differentially susceptible to CHPV, with cells like HeLa and U-138 having pronounced cell death, while the PC-3 were comparatively resistant. All cell lines used in the study except U-138 restricted CHPV infection to varying degrees with IFN-β pre-treatment and supplementation of interferon (IFN) could neither activate the IFN signaling pathway in U-138 cells. Finally, U-138 tumor xenografts established in non-obese diabetic severe combined immunodeficiency (NOD/SCID) mice showed significant delay in tumor growth in the CHPV-challenged animals. Thus, targeted cytopathic effect in cancer cells at a very low dose with restricted replication in normal cells offers a rationale to exploit CHPV as an oncolytic vector in the future.

Virulence Biomarkers of Bursaphelenchus xylophilus: A Proteomic Approach

The pinewood nematode (PWN), Bursaphelenchus xylophilus, one of the most serious forest pests worldwide, is considered the causal agent of the pine wilt disease (PWD). The main host species belong to the genus Pinus, and a variation in the susceptibility of several pine species to PWN infection is well-known. It is also recognized that there is variation in the virulence among B. xylophilus isolates. In the present study, we applied a quantitative mass spectrometry-based proteomics approach to perform a deep characterization of proteomic changes across two B. xylophilus isolates with different virulence from different hosts and geographical origins. A total of 1,456 proteins were quantified and compared in the two isolates secretomes, and a total of 2,741 proteins were quantified and compared in the nematode proteomes in pine tree extract and fungus stimuli conditions. From the proteomic analyses, a group of proteins was selected and identified as potential virulence biomarkers and shed light on putative most pathogenic proteins of this plant-parasitic nematode. Proteomic data are available via ProteomeXchange with identifier PXD029377.

In vivo and in vitro assessment of host-parasite interaction between the parasitic copepod Brachiella thynni (Copepoda; Lernaeopodidae) and the farmed Atlantic bluefin tuna (Thunnus thynnus)

The Atlantic bluefin tuna (ABFT; Thunnus thynnus) today represents one of the economically most important species for Croatian fisheries industry. Although the most diverse and abundant parasitofauna is usually found in the largest specimens of wild ABFT, the opposite was observed in captivity where parasite populations significantly decline by the end of the farming cycle. Copepod Brachiella thynni, is a skin parasite frequently parasitizing tuna, whose population also decreases in number throughout the rearing process. In order to better understand the immunity mechanisms underlying ABFT reaction to B. thynni infection, we studied expression profiles of immunity related genes; interleukin 1β (il1β), tumour necrosis factors (tnfα1, tnfα2), complement component 4 (c4) and caspase 3 (casp3), in peripheral blood leukocytes (PBLs) during in vitro stimulation by B. thynni protein extracts (i.e. antigens) and in infected tissues at B. thynni parasitation site. Finally, a histopathological analysis of semi-thin and ultra-thin sections of tissues surrounding B. thynii attachment site was performed to evaluate the severity of parasite-induced lesions and identify involved cell lineages. In vitro stimulation of ABFT PBLs with B. thynii antigens caused a dose-depended upregulation of selected genes, among which tnfα1 showed the highest induction by both concentrations of B. thynni protein extract. However, targeted genes were not significantly upregulated in the infected tissue. Also, no significant alterations in ultrastructure of epithelial layers surrounding B. thynii attachment site were noticed, except local tissue erosion, necrosis of squamous epithelium and proliferation of rodlet and goblet cells. Our results suggest that B. thynii has evolved strategies to successfully bypass both innate immune response and the connective-tissue proliferation processes. Therefore, the observed disappearance of this copepod by the end of the rearing process is more likely related to its limited lifespan on the host and its inability to complete the life cycle in the rearing cages, rather than host's reaction.

Identification of variants associated with hard clam, Mercenaria mercenaria, resistance to Quahog Parasite Unknown disease

Severe losses in aquacultured and wild hard clam (Mercenaria mercenaria) stocks have been previously reported in the northeastern United States due to a protistan parasite called QPX (Quahog Parasite Unknown). Previous work demonstrated that clam resistance to QPX is under genetic control. This study identifies single nucleotide polymorphism (SNP) associated with clam survivorship from two geographically segregated populations, both deployed in an enzootic site. The analysis contrasted samples collected before and after undergoing QPX-related mortalities and relied on a robust draft clam genome assembly. ~200 genes displayed significant variant enrichment at each sampling point in both populations, including 18 genes shared between both populations. Markers from both populations were identified in genes related to apoptosis pathways, protein-protein interaction, receptors, and signaling. This research begins to identify genetic markers associated with clam resistance to QPX disease, leading the way for the development of resistant clam stocks through marker-assisted selection.

Proteomic analysis of Ascocotyle longa (Trematoda: Heterophyidae) metacercariae

Ascocotyle longa is parasitic trematode with wide distribution throughout America, Europe, Africa, and Middle East. Despite the fact that this fish-borne pathogen has been considered an agent of human heterophyiasis in Brazil, the molecules involved in the host-parasite interaction remain unknown. The present study reports the proteome profile of A. longa metacercariae collected from the fish Mugil liza from Brazil. This infective stage for humans, mammals and birds was analyzed using nLC-MS/MS approach. We identified a large repertoire of proteins, which are mainly involved in energy metabolism and cell structure. Peptidases and immunogenic proteins were also identified, which might play roles in host-parasite interface. Our data provided unprecedented insights into the biology of A. longa and represent a first step to understand the natural host-parasite interaction. Moreover, as the first proteome characterized in this trematode, it will provide an important resource for future studies.

Behind Enemy Lines: Immunomodulatory Armamentarium of the Schistosome Parasite

The deeply rooted, intricate relationship between the Schistosoma parasite and the human host has enabled the parasite to successfully survive within the host and surreptitiously evade the host's immune attacks. The parasite has developed a variety of strategies in its immunomodulatory armamentarium to promote infection without getting harmed or killed in the battlefield of immune responses. These include the production of immunomodulatory molecules, alteration of membranes, and the promotion of granuloma formation. Schistosomiasis thus serves as a paradigm for understanding the Th2 immune responses seen in various helminthiases. This review therefore aims to summarize the immunomodulatory mechanisms of the schistosome parasites to survive inside the host. Understanding these immunomodulatory strategies not only provides information on parasite-host interactions, but also forms the basis in the development of novel drugs and vaccines against the schistosome infection, as well as various types of autoimmune and inflammatory conditions.

The influence of selected gastrointestinal parasites on apoptosis in intestinal epithelial cells

Studies on the parasite–host interaction may provide valuable information concerning the modulation of molecular mechanisms as well as of the host immune system during infection. To date, it has been demonstrated that intestinal parasites may affect, among others, the processes of digestion in the gastrointestinal system of the host, thus limiting the elimination of the parasite, the immune response as well as inflammation. However, the most recent studies suggest that intestinal parasites may also affect modulation of the apoptosis pathway of the host. The present paper presents the latest scientific information on the influence of intestinal parasite species (Blastocystis sp., Giardia sp., Cryptosporidium sp., Trichuris sp., Entamoeba histolytica, Nippostrongylus brasiliensis, Heligmosomoides polygyrus) on the molecular mechanisms of apoptosis in intestinal epithelial cells. This paper stresses that the interdependency between the intestinal parasite and the host results from the direct effect of the parasite and the host’s defense reactions, which lead to modulation of the apoptosis pathways (intrinsic and extrinsic). Moreover, the present paper presents the role of proteins involved in the mechanisms of apoptosis as well as the physiological role of apoptosis in the host’s intestinal epithelial cells.

Characterization of Haemonchus contortus Excretory/Secretory Antigen (ES-15) and Its Modulatory Functions on Goat Immune Cells In Vitro

Small size excretory/secretory (ES) antigens of the Haemonchus contortus parasite have intense interest among researchers for understanding the molecular basis of helminths immune regulation in term of control strategies. Immunomodulatory roles of H. contortus ES-15 kDa (HcES-15) on host immune cells during host–parasite interactions are unknown. In this study, the HcES-15 gene was cloned and expression of recombinant protein (rHcES-15) was induced by isopropyl-ß-d-thiogalactopyranoside (IPTG). Binding activity of rHcES-15 to goat peripheral blood mononuclear cells (PBMCs) was confirmed by immunofluorescence assay (IFA) and immunohistochemical analysis showed that H. contortus 15 kDa protein localized in the outer and inner structure of the adult worm, clearly indicated as the parasite’s ES antigen. The immunoregulatory role on cytokines production, cell proliferation, cell migration, nitric oxide (NO) production, apoptosis, and phagocytosis were observed by co-incubation of rHcES-15 with goat PBMCs. The results showed that cytokines IL-4, IL-10, IL-17, the production of nitric oxide (NO), PBMCs apoptosis, and monocytes phagocytosis were all elevated after cells incubated with rHcES-15 at differential protein concentrations. We also found that IFN-γ, TGF-β1, cells proliferation and migration were significantly suppressed with the interaction of rHcES-15 protein. Our findings indicated that low molecular ES antigens of H. contortus possessed discrete immunoregulatory roles, which will help to understand the mechanisms involved in immune evasion by the parasite during host–parasite interactions.

Transcriptome profiling of posterior kidney of brown trout, Salmo trutta, during proliferative kidney disease

BACKGROUND

Tetracapsuloides bryosalmonae is a myxozoan parasite which causes economically important and emerging proliferative kidney disease (PKD) in salmonids. Brown trout, Salmo trutta is a native fish species of Europe, which acts as asymptomatic carriers for T. bryosalmonae. There is only limited information on the molecular mechanism involved in the kidney of brown trout during T. bryosalmonae development. We employed RNA sequencing (RNA-seq) to investigate the global transcriptome changes in the posterior kidney of brown trout during T. bryosalmonae development.

METHODS

Brown trout were exposed to the spores of T. bryosalmonae and posterior kidneys were collected from both exposed and unexposed control fish. cDNA libraries were prepared from the posterior kidney and sequenced. Bioinformatics analysis was performed using standard pipeline of quality control, reference mapping, differential expression analysis, gene ontology, and pathway analysis. Quantitative real time PCR was performed to validate the transcriptional regulation of differentially expressed genes, and their correlation with RNA-seq data was statistically analyzed.

RESULTS

Transcriptome analysis identified 1169 differentially expressed genes in the posterior kidney of brown trout, out of which 864 genes (74%) were upregulated and 305 genes (26%) were downregulated. The upregulated genes were associated with the regulation of immune system process, vesicle-mediated transport, leucocyte activation, and transport, whereas the downregulated genes were associated with endopeptidase regulatory activity, phosphatidylcholine biosynthetic process, connective tissue development, and collagen catabolic process.

CONCLUSION

To our knowledge, this is the first RNA-seq based transcriptome study performed in the posterior kidney of brown trout during active T. bryosalmonae development. Most of the upregulated genes were associated with the immune system process, whereas the downregulated genes were associated with other metabolic functions. The findings of this study provide insights on the immune responses mounted by the brown trout on the developing parasite, and the host molecular machineries modulated by the parasite for its successful multiplication and release.

Differential Sensitivity of Myeloid and Lymphoid Cell Populations to Apoptosis in Peritoneal Cavity of Mice with Model Larval Mesocestoides Vogae Infection

The metacestode stage of the tapeworm Mesocestoides vogae (M. vogae) has the ability of asexual growth in the peritoneal cavity of rodents and other intermediate hosts without restriction. Early immunological events have decisive role in the establishment of infection. In the present study we investigated the kinetic of myeloid and lymphoid cell populations and the proportions of cells undergoing apoptosis in peritoneal cavities of mice within the first month after oral infection with M. vogae larvae. Proportions of cell phenotypes and apoptotic cells were examined by flow cytometry and by microscopical analysis of cells following May/Grünwald staining and fluorescent stain Hoechst 33234, respectively. Total numbers of peritoneal cells increased and their distribution changed towards accumulation of myelo-monocytic cell lineage in the account of reduced proportions of lymphoid cells. CD4+ T cell subpopulations were more abundant than CD8+ and their proportions elevated within two weeks post infection (p.i.) which was followed by a significant decline. Expression level of CD11c marker on myelo-monocytic cells revealed phenotype heterogeneity and proportions of cells with low and medium expression elevated from day 14 p.i. along with concurrent very low presence of CD11c^high phenotype. Lymphoid cell population was highly resistant to apoptosis but elevated proportions of myeloid cells were in early/late stage of apoptosis. Apoptosis was detected in a higher number of adherent cells from day 14 p.i. onwards as evidenced by nuclear fluorescent staining. By contrast, cells adherent to larvae, mostly macrophages and eosinophils, did not have fragmented nuclei. Our data demonstrated that apoptosis did not account for diminished population of peritoneal lymphoid cells and substantial proportions of myeloid cells seem to be more susceptible to apoptotic turnover in peritoneal cavity of mice with ongoing M. vogae infection, suggesting their important role in the host-parasite interactions.

Wolbachia-induced apoptosis associated with increased fecundity in Laodelphax striatellus (Hemiptera: Delphacidae)

Wolbachia influence the fitness of their invertebrate hosts. They have effects on reproductive incompatibility and egg production. Although the former are well characterized, the mechanistic basis of the latter is unclear. Here, we investigate whether apoptosis, which has been implicated in fecundity in model insects, influences the interaction between fecundity and Wolbachia in the planthopper Laodelphax striatellus. Wolbachia-infected females produced about 30% more eggs than uninfected females. We used the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling staining to visualize apoptosis. Microscopic observations indicated that the Wolbachia strain wStri increased the number of ovarioles that contained apoptotic nurse cells in both young and aged adult females. The frequency of apoptosis was much higher in the infected females. The increased fecundity appeared to be a result of apoptosis of nurse cells, which provide nutrients to the growing oocytes. In addition, cell apoptosis inhibition by caspase messenger RNA interference in Wolbachia-infected L. striatellus markedly decreased egg numbers. Together, these data suggest that wStri might enhance fecundity by increasing the number of apoptotic cells in the ovaries in a caspase-dependent manner. Our findings establish a link between Wolbachia-induced apoptosis and egg production effects mediated by Wolbachia, although the way in which the endosymbiont influences caspase levels remains to be determined.

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Encephalitozoon cuniculi and Vittaforma corneae (Phylum Microsporidia) inhibit staurosporine-induced apoptosis in human THP-1 macrophages in vitro

Obligately intracellular microsporidia regulate their host cell life cycles, including apoptosis, but this has not been evaluated in phagocytic host cells such as macrophages that can facilitate infection but also can be activated to kill microsporidia. We examined two biologically dissimilar human-infecting microsporidia species, Encephalitozoon cuniculi and Vittaforma corneae, for their effects on staurosporine-induced apoptosis in the human macrophage-differentiated cell line, THP1. Apoptosis was measured after exposure of THP-1 cells to live and dead mature organisms via direct fluorometric measurement of Caspase 3, colorimetric and fluorometric TUNEL assays, and mRNA gene expression profiles using Apoptosis RT2 Profiler PCR Array. Both species of microsporidia modulated the intrinsic apoptosis pathway. In particular, live E. cuniculi spores inhibited staurosporine-induced apoptosis as well as suppressed pro-apoptosis genes and upregulated anti-apoptosis genes more broadly than V. corneae. Exposure to dead spores induced an opposite effect. Vittaforma corneae, however, also induced inflammasome activation via Caspases 1 and 4. Of the 84 apoptosis-related genes assayed, 42 (i.e. 23 pro-apoptosis, nine anti-apoptosis, and 10 regulatory) genes were more affected including those encoding members of the Bcl2 family, caspases and their regulators, and members of the tumour necrosis factor (TNF)/TNF receptor R superfamily.

Toxoplasma gondii Histone 4 Affects Some Functions of Murine Ana-1 Macrophages In Vitro

Toxoplasma gondii (T. gondii) is an obligate intracellular protozoan that can infect almost all nucleated cells. Histone proteins and DNA form the nucleosomes, which are the fundamental building blocks of eukaryotic chromatin. Histone 4 is an essential component of a histone octamer. In the present study, T. gondii histone 4 (TgH4) was cloned and the regulatory effect of TgH4 on murine macrophages was characterized. Bioinformatics analysis revealed that TgH4 was highly conserved in structure. Recombinant TgH4 (rTgH4) protein was identified by sera from rats experimentally infected with T. gondii and native TgH4 in the total soluble protein of T. gondii tachyzoites was recognized by polyclonal antibodies against rTgH4, as indicated by immunoblotting analysis. Immunofluorescence assay showed that TgH4 binds to macrophages. Following incubation with rTgH4, the toll-like receptor 4 (TLR4) level of the macrophages was downregulated. Meanwhile, chemotaxis and the proliferation of macrophages were inhibited. However, rTgH4 can promote phagocytosis, apoptosis, and the secretion of nitric oxide, interleukin-6, and tumor necrosis factor-α from macrophages. Just 80 μg/ml rTgH4 can significantly elevate the secretion of interleukin-10 and interleukin-1β (p < 0.05 and p < 0.01). Viewed together, these outcomes indicated that rTgH4 can affect the functions of murine macrophages in vitro.

Excretory-secretory product of third-stage Gnathostoma spinigerum larvae induces apoptosis in human peripheral blood mononuclear cells

Human gnathostomiasis caused by third-stage Gnathostoma spinigerum larvae (G. spinigerum L3) is an important zoonotic disease in tropical areas of the world. The excretory-secretory products (ES) that are excreted by infective larva play a significant role in host immune evasion and tissue destruction. To investigate the poorly understood mechanisms of G. spinigerum L3 pathogenesis, we focused on the potential effect of ES on inducing apoptosis in human immune cells by using human peripheral blood mononuclear cells (PBMCs) as a model. Early and late apoptosis of PBMCs were assessed following the exposure of these cells to G. spinigerum L3 ES (0.1, 0.5, and 1.0 μg/ml) for 6-48 h. The apoptotic cells were identified by flow cytometric staining of PBMC with FITC-annexin V and propidium iodide. The expression of regulatory genes related to apoptosis mechanisms in ES-treated PBMCs was investigated using a Human Apoptosis RT² Profiler™ PCR Array. The results showed significant levels of early phase apoptosis at 18 h and of late phase apoptosis at 24 h. We speculate that this apoptosis in PBMCs occurs via the extrinsic pathway. Apoptosis in the ES-induced PBMCs was observed as quickly as 90 min after exposure, and the highest effect was observed at 18-24 h. Furthermore, ES can trigger apoptosis lasting for 48 h. Our findings expand the understanding of one of the mechanisms involved, immune-evasive strategy mechanism used by G. spinigerum larvae during human gnathostomiasis.

Microsporidia infection impacts the host cell's cycle and reduces host cell apoptosis

Intracellular parasites can alter the cellular machinery of host cells to create a safe haven for their survival. In this regard, microsporidia are obligate intracellular fungal parasites with extremely reduced genomes and hence, they are strongly dependent on their host for energy and resources. To date, there are few studies into host cell manipulation by microsporidia, most of which have focused on morphological aspects. The microsporidia Nosema apis and Nosema ceranae are worldwide parasites of honey bees, infecting their ventricular epithelial cells. In this work, quantitative gene expression and histology were studied to investigate how these two parasites manipulate their host’s cells at the molecular level. Both these microsporidia provoke infection-induced regulation of genes involved in apoptosis and the cell cycle. The up-regulation of buffy (which encodes a pro-survival protein) and BIRC5 (belonging to the Inhibitor Apoptosis protein family) was observed after infection, shedding light on the pathways that these pathogens use to inhibit host cell apoptosis. Curiously, different routes related to cell cycle were modified after infection by each microsporidia. In the case of N. apis, cyclin B1, dacapo and E2F2 were up-regulated, whereas only cyclin E was up-regulated by N. ceranae, in both cases promoting the G1/S phase transition. This is the first report describing molecular pathways related to parasite-host interactions that are probably intended to ensure the parasite’s survival within the cell.

Blue-Print Autophagy: Potential for Cancer Treatment

The marine environment represents a very rich source of biologically active compounds with pharmacological applications. This is due to its chemical richness, which is claiming considerable attention from the health science communities. In this review we give a general overview on the marine natural products involved in stimulation and inhibition of autophagy (a type of programmed cell death) linked to pharmacological and pathological conditions. Autophagy represents a complex multistep cellular process, wherein a double membrane vesicle (the autophagosome) captures organelles and proteins and delivers them to the lysosome. This natural and destructive mechanism allows the cells to degrade and recycle its cellular components, such as amino acids, monosaccharides, and lipids. Autophagy is an important mechanism used by cells to clear pathogenic organism and deal with stresses. Therefore, it has also been implicated in several diseases, predominantly in cancer. In fact, pharmacological stimulation or inhibition of autophagy have been proposed as approaches to develop new therapeutic treatments of cancers. In conclusion, this blue-print autophagy (so defined because it is induced and/or inhibited by marine natural products) represents a new strategy for the future of biomedicine and of biotechnology in cancer treatment.

Infection pattern and transmission potential of chikungunya virus in two New World laboratory-adapted Aedes aegypti strains

Chikungunya virus (CHIKV) is an emerging mosquito-borne virus belonging to the Togaviridae, which is transmitted to humans by Aedes aegypti and Ae. albopictus. We describe the infection pattern of CHIKV in two New World Ae. aegypti strains, HWE and ORL. Both mosquito strains were susceptible to the virus but showed different infection patterns in midguts and salivary glands. Even though acquisition of a bloodmeal showed moderate levels of apoptosis in midgut tissue, there was no obvious additional CHIKV-induced apoptosis detectable during midgut infection. Analysis of expression of apoptosis-related genes suggested that CHIKV infection dampens rather than promotes apoptosis in the mosquito midgut. In both mosquito strains, the virus was present in saliva within two days post-oral infection. HWE and ORL mosquitoes exhibited no salivary gland infection barrier; however, only 60% (HWE) to 65% (ORL) of the females had released the virus in their saliva at one week post-oral acquisition, suggesting a salivary gland escape barrier. CHIKV induced an apoptotic response in salivary glands of HWE and ORL mosquitoes, demonstrating that the virus caused pathology in its natural vector.

Third-stage Gnathostoma spinigerum larva excretory secretory antigens modulate function of Fc gamma receptor I-mediated monocytes in peripheral blood mononuclear cell culture

Background

Third (infective)-stage Gnathostoma spinigerum larvae (L3) mainly cause human gnathostomiasis. G. spinigerum L3 migrate throughout the subcutaneous tissues, vital organs, and central nervous system and can cause various pathogenesis including sudden death. Interestingly, G. spinigerum L3 can survive and evade host cellular immunity for months or years. The effects of G. spinigerum excretory-secretory (ES) products involved in larval migration and immune-evasive strategies are unknown. Monocytes are innate immune cells that act as phagocytic and antigen-presenting cells and also play roles against helminthic infections via a complex interplay between other immune cells. Fc gamma receptor I (FcγRI) is a high-affinity receptor that is particularly expressed on monocytes, macrophages, and dendritic cells. The cross-linking of FcγRI and antigen-antibody complex initiates signal transduction cascades in phagocytosis, cytokine production, and antibody-dependent cell-mediated cytotoxicity (ADCC). This study investigated whether ES antigen (ESA) from G. spinigerum L3 affects monocyte functions.

Results

Cultures of normal peripheral blood mononuclear cells (PBMC) separated from healthy buffy coats were used as a human immune cell model. ESA was prepared from G. spinigerum L3 culture. Using Real-Time quantitative reverse transcription-polymerase chain reaction (qRT-PCR), the effect of ESA to down-regulate FcγRI mRNA expression in monocytes during 90 min of observation was not well delineated. Flow cytometry analysis revealed a significant phenotypic-decreased FcγRI expression on the monocyte surface at 12 hours (h) of cultivation with the ESA (p = 0.033). Significantly reduced monocyte-mediated phagocytosis capacity was consistently observed after 12 h of ESA pretreatment (p = 0.001).

Conclusions

Our results suggest that G. spinigerum ESA modulates monocyte function via depletion of FcγRI expression. This study provides preliminary information for future in-depth studies to elucidate mechanisms of the immune-evasive strategy of G. spinigerum larvae.

Electronic supplementary material

The online version of this article (doi:10.1186/s41182-016-0005-x) contains supplementary material, which is available to authorized users.

Comparative genomics of Steinernema reveals deeply conserved gene regulatory networks

BACKGROUND

Parasitism is a major ecological niche for a variety of nematodes. Multiple nematode lineages have specialized as pathogens, including deadly parasites of insects that are used in biological control. We have sequenced and analyzed the draft genomes and transcriptomes of the entomopathogenic nematode Steinernema carpocapsae and four congeners (S. scapterisci, S. monticolum, S. feltiae, and S. glaseri).

RESULTS

We used these genomes to establish phylogenetic relationships, explore gene conservation across species, and identify genes uniquely expanded in insect parasites. Protein domain analysis in Steinernema revealed a striking expansion of numerous putative parasitism genes, including certain protease and protease inhibitor families, as well as fatty acid- and retinol-binding proteins. Stage-specific gene expression of some of these expanded families further supports the notion that they are involved in insect parasitism by Steinernema. We show that sets of novel conserved non-coding regulatory motifs are associated with orthologous genes in Steinernema and Caenorhabditis.

CONCLUSIONS

We have identified a set of expanded gene families that are likely to be involved in parasitism. We have also identified a set of non-coding motifs associated with groups of orthologous genes in Steinernema and Caenorhabditis involved in neurogenesis and embryonic development that are likely part of conserved protein-DNA relationships shared between these two genera.

Nosema bombycis (Microsporidia) suppresses apoptosis in BmN cells (Bombyx mori)

Nosema bombycis (N. bombycis, Nb) is a fungus-related and obligate intracellular parasite that causes chronic pebrine disease in the silkworm. After infecting the host, spores obtain energy from host cells and survive for several days. This symbiosis between the pathogen and the host cell suggests that N. bombycis prevents apoptosis and reactive oxygen species (ROS) production of host cells to create the optimal environmental conditions for its growth and development. In this study, different methods were used to prove that N. bombycis suppressed apoptosis in BmN cells. Flow cytometry analysis results showed that spores suppressed apoptosis of BmN cells at 2 and 5 days after infection (P < 0.05). Compared with actinomycin D (ActD) treatment, apoptosis of BmN cells was apparently reduced after spore infection (P < 0.01). Forty-eight hours after infection, the ROS production of BmN cells was down-regulated compared with that after ActD treatment for 6 h. Furthermore, N. bombycis prevented the formation of apoptosomes by down-regulating the expression of apaf-1 and cytochrome C. In addition, N. bombycis also up-regulated the expression of buffy. Western blot analysis demonstrated that spores decreased the level of host cytochrome C at 48 and 98 h post infection. Thus, our results suggested that N. bombycis inhibited the mitochondrial apoptotic pathway of the host cells to create an optimal environment for its own survival.

Expression analysis of the Atlantic bluefin tuna (Thunnus thynnus) pro-inflammatory cytokines, IL-1β, TNFα1 and TNFα2 in response to parasites Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea)

Pro-inflammatory cytokines play an important role in teleost defence against numerous types of pathogens, therefore are often used as biomarkers during various infections. In order to evaluate Atlantic bluefin tuna IL-1β, TNFα1 and TNFα2 induction by PAMPs, we quantified their expression during in vitro stimulation of peripheral blood leukocytes by LPS and Poly I:C. Furthermore, their role in acute and chronic parasitic infection was examined during natural infection of Pseudocycnus appendiculatus (Copepoda) and Didymosulcus katsuwonicola (Digenea), as well as during leukocyte exposure to total protein extracts isolated from two parasite species. Induction of ABT IL-1β and TNFα2 by PAMPs and protein extracts from D. katsuwonicola and P. appendiculatus, as well as during natural infection with two parasites, suggests these cytokines play an important role in inflammation, being engaged in controlling parasite infections, in contrast to ABT TNFα1. Cellular innate response to the digenean D. katsuwonicola showed rather chronic character, resulting with parasite encapsulation in connective tissue. Mast cells, eosinophils, goblet cells, and occasional rodlet cells found at the site of infection, along with the induction of TNFα2, suggest the presence of a moderate inflammatory reaction that fails to seriously endanger digenean existence. In contrast, copepod P. appendiculatus, attached to the gill epithelium by clamping, caused direct tissue disruption with undergoing necrotic or apoptotic processes, and extensive proliferation of rodlet and goblet cells. Differential expression patterns of target cytokines in tissue surrounding two parasites and in vitro PBL model suggest that quality and quantity of tuna immune response is conditioned by parasite adaptive mechanisms and pathogenicity.

RNA-seq analysis reveals significant transcriptome changes in turbot (Scophthalmus maximus) suffering severe enteromyxosis

Background

Enteromyxosis caused by the intestinal myxozoan parasite Enteromyxum scophthalmi is a serious threat for turbot (Scophthalmus maximus, L.) aquaculture, causing severe catarrhal enteritis leading to a cachectic syndrome, with no therapeutic options available. There are still many aspects of host-parasite interaction and disease pathogenesis that are yet to be elucidated, and to date, no analysis of the transcriptomic changes induced by E. scophthalmi in turbot organs has been conducted. In this study, RNA-seq technology was applied to head kidney, spleen and pyloric caeca of severely infected turbot with the aim of furthering our understanding of the pathogenetic mechanisms and turbot immune response against enteromyxosis.

Results

A huge amount of information was generated with more than 23,000 identified genes in the three organs, amongst which 4,762 were differently expressed (DE) between infected and control fish. Associate gene functions were studied based on gene ontology terms and available literature, and the most interesting DE genes were classified into five categories: 1) immune and defence response; 2) apoptosis and cell proliferation; 3) iron metabolism and erythropoiesis; 4) cytoskeleton and extracellular matrix and 5) metabolism and digestive function. The analysis of down-regulated genes of the first category revealed evidences of a connexion failure between innate and adaptive immune response, especially represented by a high number of DE interferon-related genes in the three organs. Furthermore, we found an intense activation of local immune response at intestinal level that appeared exacerbated, whereas in kidney and spleen genes involved in adaptive immune response were mainly down-regulated. The apoptotic machinery was only clearly activated in pyloric caeca, while kidney and spleen showed a marked depression of genes related to erythropoiesis, probably related to disorders in iron homeostasis. The genetic signature of the causes and consequences of cachexia was also demonstrated by the down-regulation of the genes encoding structural proteins and those involved in the digestive metabolism.

Conclusions

This transcriptomic study has enabled us to gain a better understanding of the pathogenesis of enteromyxosis and identify a large number of DE target genes that bring us closer to the development of strategies designed to effectively combat this pathogen.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1149) contains supplementary material, which is available to authorized users.

Evolution of aging and death: what insights bacteria can provide

Several unresolved issues, paradoxes, and information voids characterize the field of evolution of aging. The recent discovery of aging-like phenomenon in Escherichia coli, marked by asymmetric segregation of damaged components, particularly protein aggregates, has created a number of new possibilities that remain underexplored. Bacterial systems can potentially throw light on issues such as: whether evolution of aging and evolution of death are different phenomena; whether aging is inevitable for life or is an evolved strategy; whether there could be selection for aging or aging is a pleiotropic effect of some other selection; what are the possible mechanisms of antagonistic pleiotropy, if any; and whether there are mechanisms of aging that are conserved throughout the hierarchy of life. Bacterial aging itself is underexplored and least understood as of now, but even scratching the surface appears to reveal things that may compel us to revise some of the classical concepts about evolution of aging. This warrants more focused and innovative inquiry into aging-like processes in bacteria.

Strategies of Echinococcus species responses to immune attacks: implications for therapeutic tool development

Echinococcus species have been studied as a model to investigate parasite-host interactions. Echinococcus spp. can actively communicate dynamically with a host to facilitate infection, growth and proliferation partially via secretion of molecules, especially in terms of harmonization of host immune attacks. This review systematically outlines our current knowledge of how the Echinococcus species have evolved to adapt to their host's microenvironment. This understanding of parasite-host interplay has implications in profound appreciation of parasite plasticity and is informative in designing novel and effective tools including vaccines and drugs for the treatment of echinococcosis and other diseases.

Demyelination initiated by oligodendrocyte apoptosis through enhancing endoplasmic reticulum-mitochondria interactions and Id2 expression after compressed spinal cord injury in rats

BACKGROUND

Demyelination is one of the most important pathological factors of spinal cord injury. Oligodendrocyte apoptosis is involved in triggering demyelination. However, fewer reports on pathological changes and mechanism of demyelination have been presented from compressed spinal cord injury (CSCI). The relative effect of oligodendrocyte apoptosis on CSCI-induced demyelination and the mechanism of apoptosis remain unclear.

AIMS

In this study, a custom-designed model of CSCI was used to determine whether or not demyelination and oligodendrocyte apoptosis occur after CSCI. The pathological changes in axonal myelinated fibers were investigated by osmic acid staining and transmission electron microscopy. Myelin basic protein (MBP), which is used in myelin formation in the central nervous system, was detected by immunofluorescence and Western blot assays. Oligodendrocyte apoptosis was revealed by in situ terminal-deoxytransferase-mediated dUTP nick-end labeling. To analyze the mechanism of oligodendrocyte apoptosis, we detected caspase-12 [a representative of endoplasmic reticulum (ER) stress], cytochrome c (an apoptotic factor and hallmark of mitochondria), and inhibitor of DNA binding 2 (Id2, an oligodendrocyte lineage gene) by immunofluorescence and Western blot assays.

RESULTS

The custom-designed model of CSCI was successfully established. The rats were spastic, paralyzed, and incontinent. The Basso, Beattie, and Bresnahan (BBB) locomotor rating scale scores were decreased as time passed. The compressed spinal cord slices were ischemic. Myelin sheaths became swollen and degenerative; these sheaths were broken down as time passed after CSCI. MBP expression was downregulated after CSCI and consistent with the degree of demyelination. Oligodendrocyte apoptosis occurred at 1 day after CSCI and increased as caspase-12 expression was enhanced and cytochrome c was released. Id2 was distributed widely in the white matter. Id2 expression increased with time after CSCI.

CONCLUSION

Demyelination occurred after CSCI and might be partly caused by oligodendrocyte apoptosis, which was positively correlated with ER-mitochondria interactions and enhanced Id2 expression after CSCI in rats.

Involvement of apoptosis in host-parasite interactions in the zebra mussel

The question of whether cell death by apoptosis plays a biological function during infection is key to understanding host-parasite interactions. We investigated the involvement of apoptosis in several host-parasite systems, using zebra mussels Dreissena polymorpha as test organisms and their micro- and macroparasites. As a stress response associated with parasitism, heat shock proteins (Hsp) can be induced. In this protein family, Hsp70 are known to be apoptosis inhibitors. Mussels were diagnosed for their respective infections by standard histological methods; apoptosis was detected using the TUNEL methods on paraffin sections and Hsp70 by immunohistochemistry on cryosections. Circulating hemocytes were the main cells observed in apoptosis whereas infected tissues displayed no or few apoptotic cells. Parasitism by intracellular bacteria Rickettsiales-like and the trematode Bucephalus polymorphus were associated with the inhibition of apoptosis whereas ciliates Ophryoglena spp. or the trematode Phyllodistomum folium did not involve significant differences in apoptosis. Even if some parasites were able to modulate apoptosis in zebra mussels, we did not see evidence of any involvement of Hsp70 on this mechanism.

Host–parasite molecular cross-talk during the manipulative process of a host by its parasite

Many parasite taxa are able to alter a wide range of phenotypic traits of their hosts in ways that seem to improve the parasite’s chance of completing its life cycle. Host behavioural alterations are classically seen as compelling illustrations of the ‘extended phenotype’ concept, which suggests that parasite genes have phenotype effects on the host. The molecular mechanisms and the host–parasite cross-talk involved during the manipulative process of a host by its parasite are still poorly understood. In this Review, the current knowledge on proximate mechanisms related to the ‘parasite manipulation hypothesis’ is presented. Parasite genome sequences do not themselves provide a full explanation of parasite biology nor of the molecular cross-talk involved in host–parasite associations. Recently, first-generation proteomics tools have been employed to unravel some aspects of the parasite manipulation process (i.e. proximate mechanisms and evolutionary convergence) using certain model arthropod-host–parasite associations. The pioneer proteomics results obtained on the manipulative process are here highlighted, along with the many gaps in our knowledge. Candidate genes and biochemical pathways potentially involved in the parasite manipulation are presented. Finally, taking into account the environmental factors, we suggest new avenues and approaches to further explore and understand the proximate mechanisms used by parasite species to alter phenotypic traits of their hosts.

Variation in apoptosis mechanisms employed by malaria parasites: the roles of inducers, dose dependence and parasite stages

Background

Plasmodium berghei ookinetes exhibit an apoptotic phenotype when developing within the mosquito midgut lumen or when cultured in vitro. Markers of apoptosis increase when they are exposed to nitric oxide or reactive oxygen species but high concentrations of hydrogen peroxide cause death without observable signs of apoptosis. Chloroquine and other drugs have been used to induce apoptosis in erythrocytic stages of Plasmodium falciparum and to formulate a putative pathway involving cysteine protease activation and mitochondrial membrane permeabilization; initiated, at least in the case of chloroquine, after its accumulation in the digestive vacuole causes leakage of the vacuole contents. The lack of a digestive vacuole in ookinetes prompted the investigation of the effect of chloroquine and staurosporine on this stage of the life cycle. Finally, the suggestion that apoptosis may have evolved as a strategy employed by ookinetes to increase the fitness of surviving parasites was explored by determining whether increasing the ecological triggers parasite density and nutrient depletion induced apoptosis.

Methods

Ookinetes were grown in culture then either exposed to hydrogen peroxide, chloroquine or staurosporine, or incubated at different densities and in different media. The proportion of ookinetes displaying positive markers for apoptosis in treated samples was compared with controls and results were analyzed using analysis of variance followed by a Turkey’s test, or a Kruskal-Wallis test as appropriate.

Results

Hydrogen peroxide below 50 μM triggered apoptosis but cell membranes were rapidly compromised by higher concentrations, and the mode of death could not be defined. Both chloroquine and staurosporine cause a significant increase in ookinetes with condensed chromatin, caspase-like activity and, in the case of chloroquine, phosphatidylserine translocation and DNA fragmentation (not investigated for staurosporine). However, mitochondrial membrane potential remained intact. No relationship between ookinete density and apoptosis was detected but nutrient depletion significantly increased the proportion of ookinetes with chromatin condensation in four hours.

Conclusions

It is proposed that both a mitochondrial and an amitochondrial apoptotic pathway may be involved, dependent upon the trigger that induces apoptosis, and that pathways may differ between erythrocytic stages and ookinetes, or between rodent and human malaria parasites.

The virulent Wolbachia strain wMelPop increases the frequency of apoptosis in the female germline cells of Drosophila melanogaster

BACKGROUND

Wolbachia are bacterial endosymbionts of many arthropod species in which they manipulate reproductive functions. The distribution of these bacteria in the Drosophila ovarian cells at different stages of oogenesis has been amply described. The pathways along which Wolbachia influences Drosophila oogenesis have been, so far, little studied. It is known that Wolbachia are abundant in the somatic stem cell niche of the Drosophila germarium. A checkpoint, where programmed cell death, or apoptosis, can occur, is located in region 2a/2b of the germarium, which comprises niche cells. Here we address the question whether or not the presence of Wolbachia in germarium cells can affect the frequency of cyst apoptosis in the checkpoint.

RESULTS

Our current fluorescent microscopic observations showed that the wMel and wMelPop strains had different effects on female germline cells of D. melanogaster. The Wolbachia strain wMel did not affect the frequency of apoptosis in cells of the germarium. The presence of the Wolbachia strain wMelPop in the D. melanogasterw1118 ovaries increased the number of germaria where cells underwent apoptosis in the checkpoint. Based on the appearance in the electron microscope, there was no difference in morphological features of apoptotic cystocytes between Wolbachia-infected and uninfected flies. Bacteria with normal ultrastructure and large numbers of degenerating bacteria were found in the dying cyst cells.

CONCLUSIONS

Our current study demonstrated that the Wolbachia strain wMelPop affects the egg chamber formation in the D. melanogaster ovaries. This led to an increase in the number of germaria containing apoptotic cells. It is suggested that Wolbachia can adversely interfere either with the cystocyte differentiation into the oocyte or with the division of somatic stem cells giving rise to follicle cells and, as a consequence, to improper ratio of germline cells to follicle cells and, ultimately, to apoptosis of cysts. There was no similar adverse effect in D. melanogaster Canton S infected with the Wolbachia strain wMel. This was taken to mean that the observed increase in frequency of apoptosis was not the general effect of Wolbachia on germline cells of D. melanogaster, it was rather induced by the virulent Wolbachia strain wMelPop.

Anti-filarial activity of antibiotic therapy is due to extensive apoptosis after Wolbachia depletion from filarial nematodes

Filarial nematodes maintain a mutualistic relationship with the endosymbiont Wolbachia. Depletion of Wolbachia produces profound defects in nematode development, fertility and viability and thus has great promise as a novel approach for treating filarial diseases. However, little is known concerning the basis for this mutualistic relationship. Here we demonstrate using whole mount confocal microscopy that an immediate response to Wolbachia depletion is extensive apoptosis in the adult germline, and in the somatic cells of the embryos, microfilariae and fourth-stage larvae (L4). Surprisingly, apoptosis occurs in the majority of embryonic cells that had not been infected prior to antibiotic treatment. In addition, no apoptosis occurs in the hypodermal chords, which are populated with large numbers of Wolbachia, although disruption of the hypodermal cytoskeleton occurs following their depletion. Thus, the induction of apoptosis upon Wolbachia depletion is non-cell autonomous and suggests the involvement of factors originating from Wolbachia in the hypodermal chords. The pattern of apoptosis correlates closely with the nematode tissues and processes initially perturbed following depletion of Wolbachia, embryogenesis and long-term sterilization, which are sustained for several months until the premature death of the adult worms. Our observations provide a cellular mechanism to account for the sustained reductions in microfilarial loads and interruption of transmission that occurs prior to macrofilaricidal activity following antibiotic therapy of filarial nematodes.

Molecular profiling of the gilthead sea bream (Sparus aurata L.) response to chronic exposure to the myxosporean parasite Enteromyxum leei

The aim of the present work was to investigate the transcriptome response of gilthead sea bream (Sparus aurata) after challenge with the myxosporean Enteromyxum leei, a wide-spread enteric parasite causing heavy economic losses in Mediterranean sparid farms. This parasite causes severe desquamative enteritis which usually leads to death of the fish, and there are no preventative or curative treatments for this enteromyxosis. After 113 days of exposure to parasite-contaminated effluent, fish were classified into three cohorts: control fish not exposed to parasite, those that were exposed and infected, and those that were exposed but not infected. In order to detect target genes that may be candidates for infective status or resistance, a cDNA microarray containing 18,490 cDNA clones enriched in genes differentially expressed after infection was hybridised with head kidney and intestine samples. In infected fish, 371 and 373 genes were differentially regulated at the >1.5-fold level in intestine and head kidney respectively, whereas in non-infected fish 175 and 501 genes were differentially regulated in these tissues, respectively. A global marked gene down-regulation was evident in infected fish, mainly in genes involved in the immune and acute phase response particularly complement and mannose binding lectin. Microarray analysis demonstrated a complex interplay between host and/or parasite derived proteases and protease inhibitors, apoptosis, cell proliferation and antioxidant defence genes in exposed fish. In the head kidney of non-infected fish a marked depression of genes involved in the acute phase response was evident. By contrast, in the intestine of non-infected fish, interferon-stimulated and MHC class II genes involved in antigen processing and presentation were up-regulated, possibly indicating that an active immune response at the local level is important to avoid infection with or proliferation of the parasite.

The many roads to parasitism: a tale of convergence

Parasitic organisms account for a large portion of living species. They have arisen on multiple independent occasions in many phyla, and thus encompass a huge biological diversity. This review uses several lines of evidence to argue that this vast diversity can be reduced to a few evolutionary end points that transcend phylogenetic boundaries. These represent peaks in the adaptive landscape reached independently by different lineages undergoing convergent evolution. Among eukaryotic parasites living in or on animals, six basic parasitic strategies are identified based on the number of hosts used per parasite generation, the fitness loss incurred by the host, and the transmission routes used by the parasites. They are parasitoids, parasitic castrators, directly transmitted parasites, trophically transmitted parasites, vector-transmitted parasites and micropredators. These show evidence of convergence in morphology, physiology, reproduction, life cycles and transmission patterns. Parasite-host body size ratios, and the relationship between virulence and intensity of infection, are also associated with the different parasitic strategies, but not consistently so. At the population level, patterns of parasite distribution among hosts are not uniform across all parasitic strategies, but are distinctly different for parasitoids and castrators than for other parasites. To demonstrate that the above six strategies defined for animal parasites are universal, comparisons are made with parasites of plants, in particular, plant-parasitic nematodes and parasitic angiosperms; these are shown to follow the same evolutionary trajectories seen among animal parasites, despite huge physiological and ecological differences between animals and plants. Beyond demonstrating the inevitable convergence of disparate lineages across biological hyperspace towards a limited set of adaptive strategies, this synthesis also provides a unifying framework for the study of parasitism.

Apoptosis stalks Plasmodium falciparum maintained in continuous culture condition

Background

Growth kinetic of Plasmodium falciparum in culture or in the host fall short of expected growth rate considering that there are 4 x 10⁶/µL red blood cell (RBCs) available for invasion and about 16 merozoites growing in each infected RBC. This study determined whether apoptotic machinery is operable to keep the parasite population under check.

Methods

A synchronized culture of P. falciparum (Dd2 strain) was initiated at 0.5% ring stage parasitaemia and kept under conditions not limiting for RBCs and nutrient by adjusting hematocrit to 5% at each schizogony and changing growth media daily. Parasite growth pattern and morphology was evaluated by blood smear microscopy and flow-cytometry using SYBR green. The apoptotic processes were evaluated for evidence of: DNA fragmentation by TUNEL, collapse of mitochondria membrane potential (ΔΨ_m) by TMRE, expression of metacaspse gene by RT-qPCR and by probing parasite proteins with anti-caspase antibodies.

Results

From the seeding parasitaemia of 0.5%, the parasites doubled every 48 hours to a parasitaemia of 4%. Thereafter, the growth stagnated and the culture consistently crashed at about 6% parasitaemia. ΔΨ_m potential collapsed as the parasite density increased and DNA fragmentation increased steadily from 0.2% to ~6%. The expression of metacaspase gene and protein was observed in all stages, but their abundance was variable among the stages.

Conclusion

These findings suggest existence of P. falciparum quorum sensing that keep the parasite population under check.

Targeting caspases in intracellular protozoan infections

Caspases are cysteine aspartases acting either as initiators (caspases 8, 9, and 10) or executioners (caspases 3, 6, and 7) to induce programmed cell death by apoptosis. Parasite infections by certain intracellular protozoans increase host cell life span by targeting caspase activation. Conversely, caspase activation, followed by apoptosis of lymphocytes and other cells, prevents effective immune responses to chronic parasite infection. Here we discuss how pharmacological inhibition of caspases might affect the immunity to protozoan infections, by either blocking or delaying apoptosis.

Apoptosis and S phase of the cell cycle in BeWo trophoblastic and HeLa cells are differentially modulated by Toxoplasma gondii strain types

Transplacental transmission of Toxoplasma gondii causes congenital toxoplasmosis, one of the most severe forms of infection. The ability of the parasite to survive intracellularly largely depends on the blocking of different proapoptotic signaling cascades of the host cells. During pregnancy, however, alterations in the incidence of apoptosis are associated with abnormal placental morphology and function. The aim of this study was to evaluate the incidence of apoptosis and cell proliferation in trophoblastic (BeWo cell line) and uterine cervical (HeLa cell line) cells infected with a highly virulent RH strain or a moderately virulent ME49 strain of T. gondii. BeWo and HeLa cells were infected with RH or ME49 tachyzoites (2:1 and 5:1; parasite:cell) or medium alone (control). After 2 h, 6 h and 12 h of incubation, cells were fixed in 10% formalin and analyzed by immunohistochemistry to determine the apoptosis (expression of cytokeratin 18 neo-epitope--clone M30) and cell in S phase (expression of proliferating cell nuclear antigen--PCNA) indices. RH strain-infected BeWo and HeLa cells showed a lower apoptosis index than non-infected controls, whereas a higher apoptosis index was found in ME49 strain-infected cells compared to controls. In addition, RH-infected cells displayed lower apoptosis index than ME49-infected cells, even though active caspase-3 was detected in both cell types infected with either RH or ME49 strains as well in non-infected cells in all analyzed times of infection. Also, the cell S phase indices were higher in ME49 strain-infected BeWo and HeLa cells as compared to non-infected controls and RH strain-infected cells. These results indicate that RH and ME49 strains of T. gondii possess opposing mechanism of interference in apoptosis and cell cycle S phase of both BeWo and HeLa cells and these differences can be associated to evasion strategies of the parasite to survive inside the host cells.

Cooperation between apoptotic and viable metacyclics enhances the pathogenesis of Leishmaniasis

Mimicking mammalian apoptotic cells by exposing phosphatidylserine (PS) is a strategy used by virus and parasitic protozoa to escape host protective inflammatory responses. With Leishmania amazonensis (La), apoptotic mimicry is a prerogative of the intramacrophagic amastigote form of the parasite and is modulated by the host. Now we show that differently from what happens with amastigotes, promastigotes exposing PS are non-viable, non-infective cells, undergoing apoptotic death. As part of the normal metacyclogenic process occurring in axenic cultures and in the gut of sand fly vectors, a sub-population of metacyclic promastigotes exposes PS. Apoptotic death of the purified PS-positive (PS^POS) sub-population was confirmed by TUNEL staining and DNA laddering. Transmission electron microscopy revealed morphological alterations in PS^POS metacyclics such as DNA condensation, cytoplasm degradation and mitochondrion and kinetoplast destruction, both in in vitro cultures and in sand fly guts. TUNEL^POS promastigotes were detected only in the anterior midgut to foregut boundary of infected sand flies. Interestingly, caspase inhibitors modulated parasite death and PS exposure, when added to parasite cultures in a specific time window. Efficient in vitro macrophage infections and in vivo lesions only occur when PS^POS and PS-negative (PS^NEG) parasites were simultaneously added to the cell culture or inoculated in the mammalian host. The viable PS^NEG promastigote was the infective form, as shown by following the fate of fluorescently labeled parasites, while the PS^POS apoptotic sub-population inhibited host macrophage inflammatory response. PS exposure and macrophage inhibition by a subpopulation of promastigotes is a different mechanism than the one previously described with amastigotes, where the entire population exposes PS. Both mechanisms co-exist and play a role in the transmission and development of the disease in case of infection by La. Since both processes confer selective advantages to the infective microorganism they justify the occurrence of apoptotic features in a unicellular pathogen.