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

Characterization and functional analysis of the small heat shock protein HSP19.5 in Bombyx mori in response to Nosema bombycis infection

Small heat shock proteins (sHSPs) are molecular chaperones known for their role in maintaining cellular homeostasis and protecting cells from various environmental stresses. This study focuses on the silkworm small heat shock protein HSP19.5 and its potential functions in the context of Nosema bombycis infection, a microsporidian pathogen causing severe disease in the sericulture industry. We cloned and characterized HSP19.5 and revealed its expression patterns in different silkworm tissues and developmental stages. Our results indicate that HSP19.5 expression is significantly up-regulated in response to N. bombycis infection, suggesting a role in the host stress response. Through a series of experiments, including RNA interference and overexpression analyses, we demonstrated that HSP19.5 promotes N. bombycis proliferation, possibly by inhibiting host cell apoptosis and regulating intracellular ROS levels. The cytoplasmic localization of HSP19.5 in silkworm cells is consistent with its function as a molecular chaperone. The results enhance our understanding of the complex host-pathogen interactions between silkworms and N. bombycis, and provides insights that may inform the development of novel strategies to control the pebrine disease.

Host-parasite interplay within a phoronid-microsporidia system: anti-parasitic defense in Lophophorata

Microsporidia (Opisthokonta: Rozellomycota: Microsporidia) are ubiquitous intracellular parasites infecting representatives of all major taxonomic groups of Animalia, from protozoans to mammals, and infecting marine, freshwater, and terrestrial hosts. A representative of the phylum Phoronida was recently added to the list of microsporidian hosts. Only one species Microsporidium phoronidi, a parasite of Phoronis embryolabi, has been recently described. The paper presents further study of this host-parasite system, specifically, the observation of an efficient anti-microsporidial defense reaction in a phoronid host, and a unique mechanism of clearing the host of infection. This defense reaction results in encapsulation of infected cells and subsequent releasing of the capsules through excretory ducts of metanephridia, together with larvae, which regularly leave the mother organism this way. We hypothesize that by encapsulation, phoronids destroy most of parasites, block spread of the infection throughout the body, and prevent horizontal transmission. At the same time, microsporidia that develop in vasoperitoneal tissue that nourish maturing oocytes and embryos, likely overcome the host defense by sporadic or regular infection of embryos. As a result, the parasite secures its persistence in host populations by vertical transmission, which, in turn, benefits evolving less pathogenic forms. Overall, such elaborated and well-balanced phoronid host-microsporidia parasite interactions may suggest long history of co-existence and deserve further studies. New data extend our knowledge about parasite-host interactions and immune response in Lophophorata.

Crotoxin modulates Encephalitozoon cuniculi-infected macrophages toward the M1 microbicidal profile

Crotoxin (CTX), a bioactive extract from the snake Crotalus durissus terrificus, has antibacterial, antitumor, and anti-inflammatory properties. Microsporidia are opportunistic, obligate intracellular fungi that infect vertebrates and invertebrates and are highly resistant to conventional drugs. They can also subvert the microbicidal activity of M1 macrophages to an M2 profile, which is more favorable for the pathogen. Thus, in this study, we evaluated the effects of CTX on the viability of spores of the microsporidium Encephalitozoon cuniculi, as well as on the microbicidal activity of macrophages in vitro. E. cuniculi spores were treated with two concentrations of CTX (2.4 and 4.8 μg/mL) and cultivated in RK-13 cells for viability analysis. Additionally, peritoneal adherent cells (APerC), obtained from peritoneal washes of BALB/c mice, were infected with spores of E. cuniculi for 1 h and treated with CTX for 3 h. The profile of macrophages, cytokine production, viability of macrophages, and proliferative capacity of spores were subsequently evaluated. Treatment of E. cuniculi spores with CTX had no fungicidal or fungistatic effects. Compared to the macrophages in the control group, macrophages infected with E. cuniculi and treated with 2.4 μg/mL CTX presented an increase in the M1 profile, more necrosis, and greater production of the cytokines TNF-α and IL-6, and the spores obtained from these macrophages presented a reduction in proliferative capacity. These results indicated that CTX modulated the M1 profile of macrophages infected with E. cuniculi, resulting in greater production of proinflammatory cytokines and stronger microbicidal activity.

scRNA-seq uncovers the transcriptional dynamics of Encephalitozoon intestinalis parasites in human macrophages

Microsporidia are single-celled intracellular parasites that cause opportunistic diseases in humans. Encephalitozoon intestinalis is a prevalent human-infecting species that invades the small intestine. Macrophages are potential reservoirs of infection, and dissemination to other organ systems is also observed. The macrophage response to infection and the developmental trajectory of the parasite are not well studied. Here we use single cell RNA sequencing to investigate transcriptional changes in both the parasite and the host during E. intestinalis infection of human macrophages in vitro. The parasite undergoes large transcriptional changes throughout the life cycle, providing a blueprint for parasite development. While a small population of infected macrophages mount a response, most remain transcriptionally unchanged, suggesting that the majority of parasites may avoid host detection. The stealthy microsporidian lifestyle likely allows these parasites to harness macrophages for replication. Together, our data provide insights into the host response in primary human macrophages and the E. intestinalis developmental program.

Microsporidian Nosema bombycis secretes serine protease inhibitor to suppress host cell apoptosis via Caspase BmICE

Microsporidia are a group of intracellular pathogens that actively manipulate host cell biological processes to facilitate their intracellular niche. Apoptosis is an important defense mechanism by which host cell control intracellular pathogens. Microsporidia modulating host cell apoptosis has been reported previously, however the molecular mechanism is not yet clear. In this report, we describe that the microsporidia Nosema bombycis inhibits apoptosis of Bombyx mori cells through a secreted protein NbSPN14, which is a serine protease inhibitor (Serpin). An immunofluorescent assay demonstrated that upon infection with N. bombycis, NbSPN14 was initially found in the B. mori cell cytoplasm and then became enriched in the host cell nucleus. Overexpression and RNA-interference (RNAi) of NbSPN14 in B. mori' embryo cell confirmed that NbSPN14 inhibited host cells apoptosis. Immunofluorescent and Co-IP assays verified the co-localization and interaction of NbSPN14 with the BmICE, the Caspase 3 homolog in B. mori. Knocking out of BmICE or mutating the BmICE-interacting P1 site of NbSPN14, eliminated the localization of NbSPN14 into the host nucleus and prevented the apoptosis-inhibiting effect of NbSPN14, which also proved that the interaction between BmICE and NbSPN14 occurred in host cytoplasm and the NbSPN14 translocation into host cell nucleus depends on BmICE. These data elucidate that N. bombycis secretory protein NbSPN14 inhibits host cell apoptosis by directly inhibiting the Caspase protease BmICE, which provides an important insight for understanding pathogen-host interactions and a potential therapeutic target for N. bombycis proliferation.

Microsporidia secretory effectors and their roles in pathogenesis

Microsporidia, a group of unicellular eukaryotic parasites, rely intensely on secretory effectors for successful invasion and proliferation within host cells. This review focuses on the identification, characterization, and functional roles of effectors, including secretory proteins and microRNAs. The adhesion proteins like the Ricin-B-lectin facilitate initial invasion, which binds to the host cell surface. Once inside, microsporidia deploy a range of effectors to modulate host immune responses, such as serpin proteins, and redirect host cell metabolism to meet the parasite's nutritional needs through hexokinase. Some effectors such as microRNAs, alter the host gene expression to create a more favorable intracellular parasitic environment. In conclusion, the secretory effectors of microsporidia play a pivotal role spanning from host cell invasion to intracellular establishment. In the future, more effectors secreted by microsporidia will be studied, which will not only help to elucidate the molecular mechanism of pathogenic manipulation of the host but also help to provide the potential targets for anti-parasitic treatments.

Increased levels of anti-Encephalitozoon intestinalis antibodies in patients with colorectal cancer

BACKGROUND

The prevalence of microsporidiosis in the general population, or within specific groups of individuals/patients, is largely underestimated. The absence of specific seroprevalence tools limits knowledge of the epidemiology of these opportunistic pathogens, although known since the 1980s. Since microsporidia hijack the machinery of its host cell and certain species multiply within intestinal cells, a potential link between the parasite and colorectal cancer (CRC) has been suggested.

METHODOLOGY/PRINCIPAL FINDINGS

To explore a potential epidemiological link between microsporidia and CRC, we evaluated the seroprevalence of Encephalitozoon intestinalis among CRC patients and healthy subjects using ELISA assays based on two recombinant proteins, namely rEiPTP1 and rEiSWP1, targeting polar tube and spore wall proteins. ELISA were performed in 141 CRC patients and 135 healthy controls. Patients with CRC had significantly higher anti-rEiPTP1 IgG levels than subjects in the control group. Anti-rEiPTP1 IgG, anti-rEiSWP1 IgG and anti-rEiPTP1 IgA levels were significantly increased among men with CRC compared to healthy men. Women with CRC who had died had higher rEiSWP1 IgG levels than those who were still alive.

CONCLUSIONS/SIGNIFICANCE

These higher antibody levels against microsporidia in patients with CRC suggest a relationship between microsporidia and pathophysiology of CRC.

Microsporidian EnP1 alters host cell H2B monoubiquitination and prevents ferroptosis facilitating microsporidia survival

Microsporidia are intracellular eukaryotic pathogens that pose a substantial threat to immunocompromised hosts. The way these pathogens manipulate host cells during infection remains poorly understood. Using a proximity biotinylation strategy we established that microsporidian EnP1 is a nucleus-targeted effector that modifies the host cell environment. EnP1's translocation to the host nucleus is meditated by nuclear localization signals (NLSs). In the nucleus, EnP1 interacts with host histone H2B. This interaction disrupts H2B monoubiquitination (H2Bub), subsequently impacting p53 expression. Crucially, this inhibition of p53 weakens its control over the downstream target gene SLC7A11, enhancing the host cell's resilience against ferroptosis during microsporidian infection. This favorable condition promotes the proliferation of microsporidia within the host cell. These findings shed light on the molecular mechanisms by which microsporidia modify their host cells to facilitate their survival.

scRNA-seq reveals transcriptional dynamics of Encephalitozoon intestinalis parasites in human macrophages

Microsporidia are single-celled intracellular parasites that cause opportunistic diseases in humans. Encephalitozoon intestinalis is a prevalent human-infecting species that invades the small intestine. Dissemination to other organ systems is also observed, and is potentially facilitated by macrophages. The macrophage response to infection and the developmental trajectory of the parasite are not well studied. Here we use single cell RNA sequencing to investigate transcriptional changes in both the host and parasite during infection. While a small population of infected macrophages mount a response, most remain transcriptionally unchanged, suggesting that the majority of parasites may avoid host detection. The parasite transcriptome reveals large transcriptional changes throughout the life cycle, providing a blueprint for parasite development. The stealthy microsporidian lifestyle likely allows these parasites to harness macrophages for replication and dissemination. Together, our data provide insights into the host response in primary human macrophages and the E. intestinalis developmental program.

Encephalitozoon hellem Infection Promotes Monocytes Extravasation

Background: Microsporidia are a group of obligated intracellular fungus pathogens. Monocytes and the derivative macrophages are among the most important players in host immunity. The invasion of microsporidia may significantly affect the monocytes maturation and extravasation processes. Methods: We utilized a previously established microsporidia infection murine model to investigate the influences of microsporidia Encephalitozoon hellem (E. hellem) infection on monocyte maturation, releasing into the circulation and extravasation to the inflammation site. Flow cytometry and qPCR analysis were used to compare the monocytes and derivative macrophages isolated from bone marrow, peripheral blood and tissues of E. hellem-infected and control mice. Results: The results showed that the pro-inflammatory group of CD11b⁺Ly-6C⁺ monocytes are promoted in E. hellem-infected mice. Interestingly, the percentage of Ly-6C⁺ monocytes from E. hellem-infected mice are significantly lower in peripheral blood while significantly higher in the inflamed small intestine, together with up-regulated ratio of F4/80 macrophage in small intestine as well. Conclusions: Our findings demonstrated that E. hellem infection leads to promoted monocytes maturation in bone marrow, up-regulation of extravasation from peripheral blood to inflammation site and maturation into macrophages. Our study is the first systematic analysis of monocytes maturation and trafficking during microsporidia infection, and will provide better understanding of the pathogen–host interactions.

Microsporidia Promote Host Mitochondrial Fragmentation by Modulating DRP1 Phosphorylation

Microsporidia are obligate intracellular parasites that infect a wide variety of hosts ranging from invertebrates to vertebrates. These parasites have evolved strategies to directly hijack host mitochondria for manipulating host metabolism and immunity. However, the mechanism of microsporidia interacting with host mitochondria is unclear. In the present study, we show that microsporidian Encephalitozoon greatly induce host mitochondrial fragmentation (HMF) in multiple cells. We then reveal that the parasites promote the phosphorylation of dynamin 1-like protein (DRP1) at the 616th serine (Ser616), and dephosphorylation of the 637th serine (Ser637) by highly activating mitochondrial phosphoglycerate mutase 5 (PGAM5). These phosphorylation modifications result in the translocation of DRP1 from cytosol to the mitochondrial outer membrane, and finally lead to HMF. Furthermore, treatment with mitochondrial division inhibitor 1 (Mdivi1) significantly reduced microsporidian proliferation, indicating that the HMF are crucial for microsporidian replication. In summary, our findings reveal the mechanism that microsporidia manipulate HMF and provide references for further understanding the interactions between these ubiquitous pathogens with host mitochondria.

Microsporidiosis in Humans

Microsporidia are obligate intracellular pathogens identified ∼150 years ago as the cause of pébrine, an economically important infection in silkworms. There are about 220 genera and 1,700 species of microsporidia, which are classified based on their ultrastructural features, developmental cycle, host-parasite relationship, and molecular analysis. Phylogenetic analysis suggests that microsporidia are related to the fungi, being grouped with the Cryptomycota as a basal branch or sister group to the fungi. Microsporidia can be transmitted by food and water and are likely zoonotic, as they parasitize a wide range of invertebrate and vertebrate hosts. Infection in humans occurs in both immunocompetent and immunodeficient hosts, e.g., in patients with organ transplantation, patients with advanced human immunodeficiency virus (HIV) infection, and patients receiving immune modulatory therapy such as anti-tumor necrosis factor alpha antibody. Clusters of infections due to latent infection in transplanted organs have also been demonstrated. Gastrointestinal infection is the most common manifestation; however, microsporidia can infect virtually any organ system, and infection has resulted in keratitis, myositis, cholecystitis, sinusitis, and encephalitis. Both albendazole and fumagillin have efficacy for the treatment of various species of microsporidia; however, albendazole has limited efficacy for the treatment of Enterocytozoon bieneusi. In addition, immune restoration can lead to resolution of infection. While the prevalence rate of microsporidiosis in patients with AIDS has fallen in the United States, due to the widespread use of combination antiretroviral therapy (cART), infection continues to occur throughout the world and is still seen in the United States in the setting of cART if a low CD4 count persists.

Encephalitozoon intestinalis Infection Impacts the Expression of Apoptosis-Related Genes in U937 Macrophage Cells

PURPOSE

Encephalitozoon intestinalis affects many physiological processes of host cells to survive, proliferate, and spread to different regions within the body. In this study, the effects of the parasite on host cell apoptosis and proliferation were investigated.

METHODS

To determine the impact of the parasite on the host cell apoptosis, changes in the expression profile of genes were investigated with the qPCR array using the Human Apoptosis Panel in infected and non-infected macrophage cells. Also, the rate of apoptosis in the cells was determined by Giemsa staining method. Cell proliferation was determined by measuring the DNA concentration in infected and non-infected cells.

RESULTS

The thirty-six of apoptosis-related genes were down-regulated, while 20 of apoptosis-related genes were up-regulated in infected cells compared to uninfected cells. However, there were no significant changes detected in 32 analyzed genes between infected and control groups. E. intestinalis was determined to decrease cell proliferation in U937 macrophage cells. Unexpectedly, Giemsa staining showed an increase in the rate of apoptosis in infected cells.

CONCLUSION

Regulated genes after infection are involved in many different biological pathways and various components of the cell. This suggests that the parasite uses highly sophisticated ways to maintain the viability of the cell.

Microsporidia infection upregulates host energy metabolism but maintains ATP homeostasis

Microsporidia are a group of obligate intracellular parasites which lack mitochondria and have highly reduced genomes. Therefore, they are unable to produce ATP via the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. Instead, they have evolved strategies to obtain and manipulate host metabolism to acquire nutrients. However, little is known about how microsporidia modulate host energy metabolisms. Here, we present the first targeted metabolomics study to investigate changes in host energy metabolism as a result of infection by a microsporidian. Metabolites of silkworm embryo cell (BmE) were measured 48 h post infection by Nosema bombycis. Thirty metabolites were detected, nine of which were upregulated and mainly involved in glycolysis (glucose 6-phosphate, fructose 1,6-bisphosphate) and the TCA cycle (succinate, α-ketoglutarate, cis-aconitate, isocitrate, citrate, fumarate). Pathway enrichment analysis suggested that the upregulated metabolites could promote the synthesization of nucleotides, fatty acids, and amino acids by the host. ATP concentration in host cells, however, was not significantly changed by the infection. This ATP homeostasis was also found in Encephalitozoon hellem infected mouse macrophage RAW264.7, human monocytic leukemia THP-1, human embryonic kidney 293, and human foreskin fibroblast cells. These findings suggest that microsporidia have evolved strategies to maintain levels of ATP in the host while stimulating metabolic pathways to provide additional nutrients for the parasite.

Anti-Apoptotic Effect of Apelin in Human Placenta: Studies on BeWo Cells and Villous Explants from Third-Trimester Human Pregnancy

Previously, we demonstrated the expression of apelin and G-protein-coupled receptor APJ in human placenta cell lines as well as its direct action on placenta cell proliferation and endocrinology. The objective of this study was to examine the effect of apelin on placenta apoptosis in BeWo cells and villous explants from the human third trimester of pregnancy. The BeWo cells and villous explants were incubated with apelin (2 and 20 ng/mL) alone or with staurosporine for 24 to 72 h. First, we analysed the dose- and time-dependent effect of apelin on the expression of apoptotic factors on the mRNA level by real-time PCR and on the protein level using Western blot. Next, we checked caspase 3 and 7 activity by Caspase-Glo 3/7, DNA fragmentation by the Cell Death Detection ELISA kit and oxygen consumption by the MitoXpress-Xtra Oxygen Consumption assay. We found that apelin increased the expression of pro-survival and decreased proapoptotic factors on mRNA and protein levels in both BeWo cells and villous explants. Additionally, apelin inhibited caspase 3 and 7 activity and DNA fragmentation in staurosporine-induced apoptosis as also attenuated oxidative stress by increasing extracellular oxygen consumption. The antiapoptotic effect of apelin in BeWo cells was mediated by the APJ receptor and mitogen-activated protein kinase (ERK1/2/MAP3/1) and protein kinase B (AKT). The obtained results showed the antiapoptotic effect of apelin on trophoblast cells, suggesting its participation in the development of the placenta.

DEVELOPMENT OF MICROSPORIDIOLOGY IN RUSSIA

The study of microsporidia and microsporidioses of wild animals in Russia has been initiated in the 60-s of the past century. In the European part of country, microsporidia, infecting agricultural insect pests (All-Russian Institute of Plant Protection), freshwater arthropods and fishes (State Research Institute of Lake and River Fisheries) and the blood-sucking insects such as horseflies (Biology Institute, Karelian Scientific Center) were studied. In the Western Siberia, microsporidia of blood-sucking mosquitoes were studied (Tomsk University). As a result, by 2000, as many as 118 species and 47 genera of microsporidia were found, including 20 taxa new to science, from 100 animal species. Currently, descriptions of new taxa and taxonomic revision of the previously described taxa are performed using the molecular phylogenetic analysis. The novel data on speciation of microsporidia have been obtained, and the coevolution of parasites and their host insects have been confirmed for microsporidia of blood-sucking mosquitoes. During the study of the structure and physiology of microsporidia, it has been demonstrated, that the secretory proteins of microsporidia migrate into the nucleus of the host cell; the factors of parasites suppressing host cell apoptosis and the presence of specific organelles related to the energy metabolism have been revealed; the mitosomes have been found in the spores and not the prespore stages of microsporidia. The role of the Golgi complex in the formation of the extrusion apparatus, as well as the absence of the vesicular secretory transport in microsporidia, has been shown for the first time. For the first time in Russia, cases of microsporidia infection in HIV-infected patients have been identified. Currently, attention is paid to the development of a new universal taxonomic system of microsporidia combining molecular characteristics with a description of the structural and developmental features of each taxon of the parasites. Microsporidia possess many remarkable structural and functional differences from any other organisms thus substantiating an independent field of biological research: “microsporidiology”.

Innate and Adaptive Immune Responses Against Microsporidia Infection in Mammals

Microsporidia are obligate intracellular and eukaryotic pathogens that can infect immunocompromised and immunocompetent mammals, including humans. Both innate and adaptive immune systems play important roles against microsporidian infection. The innate immune system can partially eliminate the infection by immune cells, such as gamma delta T cell, natural killer cells (NKs), macrophages and dendritic cells (DCs), and present the pathogens to lymphocytes. The innate immune cells can also prime and enhance the adaptive immune response via surface molecules and secreted cytokines. The adaptive immune system is critical to eliminate microsporidian infection by activating cytotoxic T lymphocyte (CTL) and humoral immune responses, and feedback regulation of the innate immune mechanism. In this review, we will discuss the cellular and molecular responses and functions of innate and adaptive immune systems against microsporidian infection.