Cryptosporidium parvum activates nuclear factor kappaB in biliary epithelia preventing epithelial cell apoptosis

miR-181d targets BCL2 to regulate HCT-8 cell apoptosis and parasite burden in response to Cryptosporidium parvum infection via the intrinsic apoptosis pathway

Cryptosporidium parvum is an important zoonotic pathogen that is studied worldwide. MicroRNAs (miRNAs) act as post-transcriptional regulators and may play a key role in modulating host epithelial responses following Cryptosporidium infection. Our previous study has shown that C. parvum downregulates the expression of miR-181d through the p50-dependent TLRs/NF-κB pathway. However, the mechanism by which miR-181d regulates host cells in response to C. parvum infection remains unclear. The present study found that miR-181d downregulation inhibited cell apoptosis and increased parasite burden in HCT-8 cells after C. parvum infection. Bioinformatics analysis and luciferase reporter assays have shown that BCL2 was a target gene for miR-181d. Moreover, BCL2 overexpression and miR-181d downregulation had similar results. To further investigate the mechanism by which miR-181d regulated HCT-8 cell apoptosis during C. parvum infection, the expression of molecules involved in the intrinsic apoptosis pathway was detected. Bax, caspase-9, and caspase-3 expression was decreased at 4, 8, 12, and 24 hpi and upregulated at 36 and 48 hpi. Interfering with the expression of miR-181d or BCL2 significantly affected the expression of molecules in the intrinsic apoptosis pathway. These data indicated that miR-181d targeted BCL2 to regulate HCT-8 cell apoptosis and parasite burden in response to C. parvum infection via the intrinsic apoptosis pathway. These results allowed us to further understand the regulatory mechanisms of host miRNAs during Cryptosporidium infection, and provided a theoretical foundation for the design and development of anti-cryptosporidiosis drugs.

Quantitative phosphoproteomic analysis of chicken DF-1 cells infected with Eimeria tenella, using tandem mass tag (TMT) and parallel reaction monitoring (PRM) mass spectrometry

Eimeria tenella is an obligate intracellular parasite which causes great harm to the poultry breeding industry. Protein phosphorylation plays a vital role in host cell-E. tenella interactions. However, no comprehensive phosphoproteomic analyses of host cells at various phases of E. tenella infection have been published. In this study, quantitative phosphoproteomic analysis of chicken embryo DF-1 fibroblasts that were uninfected (UI) or infected with E. tenella for 6 h (PI6, the early invasion phase) or 36 h (PI36, the trophozoite development phase) was conducted. A total of 10,122 phosphopeptides matched to 3,398 host cell phosphoproteins were identified and 13,437 phosphorylation sites were identified. Of these, 491, 1,253, and 275 differentially expressed phosphorylated proteins were identified in the PI6/UI, PI36/UI, and PI36/PI6 comparisons, respectively. KEGG pathway enrichment analysis showed that E. tenella modulated host cell processes through phosphorylation, including focal adhesion, regulation of the actin cytoskeleton, and FoxO signaling to support its early invasion phase, and modulating adherens junctions and the ErbB signaling pathway to favor its trophozoite development. These results enrich the data on the interaction between E. tenella and host cells and facilitate a better understanding of the molecular mechanisms underlying host-parasite relationships.

MiR-4521 affects the propagation of Cryptosporidium parvum in HCT-8 cells through targeting foxm1 by regulating cell apoptosis

Cryptosporidium parvum could regulate the expression of microRNAs of epithelial cells to facilitate its intracellular propagation. MiR-4521 has been reported to play an important role during the development and progression of tumors and infectious diseases by regulating cell proliferation, apoptosis, and autophagy. However, the implication of miR-4521 during C. parvum infection was still unknown. In this study, the expression of miR-4521 was found to be upregulated in HCT-8 cells infected with C. parvum from 8 h post-infection (pi) to 48 hpi, and its upregulation would be related with the TLR/NF-κB signal pathway during C. parvum infection. One potential target of miR-4521, foxm1, was down-regulated in HCT-8 cells from 24 hpi to 48 hpi, and the expression of foxm1 was negatively regulated by miR-4521. The target relationship between miR-4521 and foxm1 was further validated by using dual luciferase reporter assay. Further studies showed that miR-4521 promoted the propagation of C. parvum in HCT-8 cells through targeting foxm1 by regulating BCL2-mediating cell apoptosis. These results contribute to further understanding of the regulatory mechanisms of host miRNAs during Cryptosporidium infection.

Inhibition of Cell Apoptosis by Apicomplexan Protozoa-Host Interaction in the Early Stage of Infection

Apicomplexan protozoa, which are a group of specialized intracellular parasitic protozoa, infect humans and other animals and cause a variety of diseases. The lack of research on the interaction mechanism between Apicomplexan protozoa and their hosts is a key factor restricting the development of new drugs and vaccines. In the early stages of infection, cell apoptosis is inhibited by Apicomplexan protozoa through their interaction with the host cells; thereby, the survival and reproduction of Apicomplexan protozoa in host cells is promoted. In this review, the key virulence proteins and pathways are introduced regarding the inhibition of cell apoptosis by the interaction between the protozoa and their host during the early stage of Apicomplexan protozoa infection. It provides a theoretical basis for the development of drugs or vaccines for protozoal diseases.

A Cryptosporidium parvum vaccine candidate effect on immunohistochemical profiling of CD4+, CD8+, Caspase-3 and NF-κB in mice

BACKGROUND

Cryptosporidium parvum is a protozoan parasite of medical and veterinary importance that causes neonatal diarrhea in many vertebrate hosts. In this study, we evaluated the efficacy of an affinity-purified antigen as a C. parvum vaccine candidate using ileal and liver tissues of experimentally infected neonatal mice by immunohistochemical profiling and immune scoring of CD4+, CD8+, Caspase-3, and nuclear factor kappa B (NF-κB). This vaccine was prepared from the C. parvum oocysts antigen using immune affinity chromatography with cyanogen bromide-activated Sepharose-4B beads.

METHODS

Thirty neonatal mice were divided into three groups (10 mice/group): (1) non-immunized non-infected, (2) non-immunized infected (using gastric tubes with a single dose of 1 × 105 of C. parvum oocysts in 250 µl PBS solution 1 h before a meal) and (3) immunized (twice with 40 µg/kg of purified C. parvum antigen at 2-week intervals and then infected with 1 × 105 C. parvum oocysts simultaneously with the second group). After euthanizing the animals on the 10th day, post-infection, their ileal and liver tissues were collected and prepared for immunohistochemistry (IHC) staining to detect CD4+, CD8+, Caspase-3, and NF-κB levels, which are indicators for T helper cells, cytotoxic T cells, apoptosis, and inflammation, respectively.

RESULTS

The IHC results showed that CD4+, CD8+, Caspase-3, and NF-κB expression varied significantly (P < 0.001) in both organs in all the groups. We also recorded high CD4+ levels and low CD8+ expression in the non-immunized non-infected mice tissues, while the opposite was observed in the non-immunized infected mice tissues. In the immunized infected mice, the CD4+ level was higher than CD8 + in both organs. While the Caspase-3 levels were higher in the ileal tissue of non-immunized infected than immunized infected mice ileal tissues, the reverse was seen in the liver tissues of both groups. Furthermore, NF-κB expression was higher in the liver tissues of non-immunized infected mice than in immunized infected mice tissues. Therefore, the IHC results and immune-scoring program revealed a significant difference (P < 0.001) in the CD4+, CD8+, Caspase-3, and NF-κB expression levels in both ileal and liver tissues of all mice groups, which might be necessary for immunomodulation in these tissues.

CONCLUSIONS

The improvement observed in the immunized infected mice suggests that this vaccine candidate might protect against cryptosporidiosis.

Organoid-based in vitro systems to model Cryptosporidium parvum infection in 2D and 3D

Typical cancer cell-based culture systems cannot support the full life cycle of Cryptosporidium parvum, despite its monoxenous life cycle which is completed in the small intestine of a single host. There is a block to fertilization and zygote formation in vitro. In this paper, we adapted a 2D organoid derived monolayer system and a 3D inverted enteroid system for use in C. parvum culture. 3D inverted enteroids were successfully infected by C. parvum without the need for microinjection and supported subculture of C. parvum. Using the 2D organoid derived monolayer (ODM) system, the infection can be maintained for at least 3 weeks with new oocyst production throughout. Fertilization was confirmed based on successful mating of two strains of C. parvum. We demonstrated that the apparent block to fertilization in typical cell culture is overcome using ODMs.

MiR-3976 regulates HCT-8 cell apoptosis and parasite burden by targeting BCL2A1 in response to Cryptosporidium parvum infection

BACKGROUND

Cryptosporidium is second only to rotavirus as a cause of moderate-to-severe diarrhea in young children. There are currently no fully effective drug treatments or vaccines for cryptosporidiosis. MicroRNAs (miRNAs) are involved in regulating the innate immune response to Cryptosporidium parvum infection. In this study, we investigated the role and mechanism of miR-3976 in regulating HCT-8 cell apoptosis induced by C. parvum infection.

METHODS

Expression levels of miR-3976 and C. parvum burden were estimated using real-time quantitative polymerase chain reaction (RT-qPCR) and cell apoptosis was detected by flow cytometry. The interaction between miR-3976 and B-cell lymphoma 2-related protein A1 (BCL2A1) was studied by luciferase reporter assay, RT-qPCR, and western blotting.

RESULTS

Expression levels of miR-3976 were decreased at 8 and 12 h post-infection (hpi) but increased at 24 and 48 hpi. Upregulation of miR-3976 promoted cell apoptosis and inhibited the parasite burden in HCT-8 cells after C. parvum infection. Luciferase reporter assay indicated that BCL2A1 was a target gene of miR-3976. Co-transfection with miR-3976 and a BCL2A1 overexpression vector revealed that miR-3976 targeted BCL2A1 and suppressed cell apoptosis and promoted the parasite burden in HCT-8 cells.

CONCLUSIONS

The present data indicated that miR-3976 regulated cell apoptosis and parasite burden in HCT-8 cells by targeting BCL2A1 following C. parvum infection. Future study should determine the role of miR-3976 in hosts' anti-C. parvum immunity in vivo.

Early immune and host cell responses to Cryptosporidium infection

Cryptosporidium spp. are opportunistic protozoan parasites that infect epithelial cells of the small intestine and cause diarrheal illness in both immunocompetent and immunodeficient individuals. These infections may be more severe in immunocompromised individuals and young children, especially in children under 2 in developing countries. The parasite has a global distribution and is an important cause of childhood diarrhea where it may result in cognitive impairment and growth deficits. Current therapies are limited with nitazoxanide being the only FDA-approved drug. However, it is not efficacious in immunocompromised patients. Additionally, there are no vaccines for cryptosporidiosis available. While acquired immunity is needed to clear Cryptosporidium parasites completely, innate immunity and early responses to infection are important in keeping the infection in check so that adaptive responses have time to develop. Infection is localized to the epithelial cells of the gut. Therefore, host cell defenses are important in the early response to infection and may be triggered through toll receptors or inflammasomes which induce a number of signal pathways, interferons, cytokines, and other immune mediators. Chemokines and chemokine receptors are upregulated which recruit immune cells such neutrophils, NK cells, and macrophages to the infection site to help in host cell defense as well as dendritic cells that are an important bridge between innate and adaptive responses. This review will focus on the host cell responses and the immune responses that are important in the early stages of infection.

The role of atypical MAP kinase 4 in the host interaction with Cryptosporidium parvum

Cryptosporidium parvum is an apicomplexan parasite that causes severe zoonotic diarrhea in humans and calves. Since there are no effective treatments or vaccines for infants or immunocompromised patients, it is important to understand the molecular mechanisms of the parasite-host interaction for novel drug discovery. Mitogen-activated protein kinase (MAP kinase) is a key host factor in interactions between host and various pathogens, including parasites. Although the function of conventional MAP kinases against parasite infection has been investigated, that of atypical MAP kinases remains largely unknown. Therefore, we focused on one of the atypical MAP kinases, MAPK4, and its effect on C. parvum infection in human intestinal cells. Here, we report that MAPK4-deficient intestinal cells showed a significant reduction in C. parvum infection. We also show that host MAPK4 has a role in host cell survival from C. parvum infection. In addition, we show that C. parvum requires host MAPK4 for its successful invasion and asexual reproduction. Taken together, our data suggest that MAPK4 is an important host factor contributing to C. parvum infection in human intestinal cells.

Intestinal immune responses to commensal and pathogenic protozoa

The physical barrier of the intestine and associated mucosal immunity maintains a delicate homeostatic balance between the host and the external environment by regulating immune responses to commensals, as well as functioning as the first line of defense against pathogenic microorganisms. Understanding the orchestration and characteristics of the intestinal mucosal immune response during commensal or pathological conditions may provide novel insights into the mechanisms underlying microbe-induced immunological tolerance, protection, and/or pathogenesis. Over the last decade, our knowledge about the interface between the host intestinal mucosa and the gut microbiome has been dominated by studies focused on bacterial communities, helminth parasites, and intestinal viruses. In contrast, specifically how commensal and pathogenic protozoa regulate intestinal immunity is less well studied. In this review, we provide an overview of mucosal immune responses induced by intestinal protozoa, with a major focus on the role of different cell types and immune mediators triggered by commensal (Blastocystis spp. and Tritrichomonas spp.) and pathogenic (Toxoplasma gondii, Giardia intestinalis, Cryptosporidium parvum) protozoa. We will discuss how these various protozoa modulate innate and adaptive immune responses induced in experimental models of infection that benefit or harm the host.

MiR-942-5p targeting the IFI27 gene regulates HCT-8 cell apoptosis via a TRAIL-dependent pathway during the early phase of Cryptosporidium parvum infection

BACKGROUND

MicroRNAs (miRNAs) are involved in the regulation of both the innate and adaptive immune response to Cryptosporidium parvum infection. We previously reported that C. parvum upregulated miR‑942‑5p expression in HCT‑8 cells via TLR2/TLR4‑NF‑κB signaling. In the present study, the role of miRNA-942-5p in the regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated HCT-8 cell apoptosis induced by C. parvum was investigated.

METHODS

Quantitative real-time polymerase chain reaction, western blotting, flow cytometry, and immunofluorescence were used for analysis.

RESULTS

Forced expression of miRNA-942-5p resulted in decreased apoptosis and an increased C. parvum burden in HCT-8 cells. The opposite results were observed using the suppressed expression of miRNA-942-5p. The miRNA-942-5p led to the translational suppression of IFI27 gene through targeting the 3'-untranslated region of the IFI27 gene. Moreover, overexpression of the IFI27 gene produced a high apoptotic ratio and low C. parvum burden. In contrast, a low apoptotic ratio and a high C. parvum burden were observed following downregulation of the IFI27 gene. Both miR-942-5p and the IFI27 gene influenced TRAIL and caspase-8 expression induced by C. parvum in HCT-8 cells. Moreover, TRAIL promoted HCT-8 cell apoptosis in a concentration-dependent manner.

CONCLUSIONS

These data suggested that C. parvum induced the downregulation of IFI27 via relief of miR-942-5p-mediated translational suppression. IFI27 downregulation was affected the burden of C. parvum by regulating HCT-8 cell apoptosis through TRAIL-dependent pathways. Future studies should determine the mechanisms by which C. parvum infection increases miR-942-5p expression and the role of miR-942-5p in hosts' anti-C. parvum immunity in vivo.

An update on Cryptosporidium biology and therapeutic avenues

Cryptosporidium species has been identified as an important pediatric diarrheal pathogen in resource-limited countries, particularly in very young children (0–24 months). However, the only available drug (nitazoxanide) has limited efficacy and can only be prescribed in a medical setting to children older than one year. Many drug development projects have started to investigate new therapeutic avenues. Cryptosporidium’s unique biology is challenging for the traditional drug discovery pipeline and requires novel drug screening approaches. Notably, in recent years, new methods of oocyst generation, in vitro processing, and continuous three-dimensional cultivation capacities have been developed. This has enabled more physiologically pertinent research assays for inhibitor discovery. In a short time, many great strides have been made in the development of anti-Cryptosporidium drugs. These are expected to eventually turn into clinical candidates for cryptosporidiosis treatment in the future. This review describes the latest development in Cryptosporidium biology, genomics, transcriptomics of the parasite, assay development, and new drug discovery.

Is Cryptosporidium a hijacker able to drive cancer cell proliferation?

The pathophysiological mechanisms of Cryptosporidium infection are multifactorial and not completely understood. Some advances achieved recently revealed that the infection by Cryptosporidium parvum induces cytoskeleton remodeling and actin reorganization through the implication of several intracellular signals involving, for example, PI3K, Src, Cdc42 and GTPases. It has also been reported that the infection by C. parvum leads to the activation of NF-κβ, known to induce anti-apoptotic mechanisms and to transmit oncogenic signals to epithelial cells. Despite the growing evidence about the hijacking of cellular pathways, potentially being involved in cancer onset, this information has rarely been linked to the tumorigenic potential of the parasite. However, several evidences support an association between Cryptosporidium infection and the development of digestive neoplasia. To explore the dynamics of Cryptosporidium infection, an animal model of cryptosporidiosis using corticoid dexamethasone-treated adult SCID (severe combined immunodeficiency) mice, orally infected with C. parvum or Cryptosporidium muris oocysts was implemented. C. parvum-infected animals developed digestive adenocarcinoma. When mechanisms involved in this neoplastic process were explored, the pivotal role of the Wnt pathway together with the alteration of the cytoskeleton was confirmed. Recently, a microarray assay allowed the detection of cancer-promoting genes and pathways highly up regulated in the group of C. parvum infected animals when compared to non-infected controls. Moreover, different human cases/control studies reported significant higher prevalence of Cryptosporidium infection among patients with recently diagnosed colon cancer before any treatment when compared to the control group (patients without colon neoplasia but with persistent digestive symptoms). These results suggest that Cryptosporidium is a potential oncogenic agent involved in cancer development beyond the usual suspects. If Cryptosporidium is able to hijack signal transduction, then is very likely that this contributes to transformation of its host cell. More research in the field is required in order to identify mechanisms and molecular factors involved in this process and to develop effective treatment interventions.

The Long Non-Coding RNA Nostrill Regulates Transcription of Irf7 Through Interaction With NF-κB p65 to Enhance Intestinal Epithelial Defense Against Cryptosporidium parvum

The cells of the intestinal epithelium establish the frontline for host defense against pathogens in the gastrointestinal tract and play a vital role in the initiation of the immune response. Increasing evidence supports the role of long non-coding RNAs (lncRNAs) as critical regulators of diverse cellular processes, however, their role in antimicrobial host defense is incompletely understood. In this study, we provide evidence that the lncRNA Nostrill is upregulated in the intestinal epithelium following infection by Cryptosporidium parvum, a globally prevalent apicomplexan parasite that causes significant diarrheal disease and an important opportunistic pathogen in the immunocompromised and AIDS patients. Induction of Nostrill in infected intestinal epithelial cells was triggered by NF-κB signaling and was observed to enhance epithelial defense by decreasing parasitic infection burden. Nostrill participates in the transcriptional regulation of C. parvum-induced Irf7 expression through interactions with NF-κB p65, and induction of Nostrill promotes epigenetic histone modifications and occupancy of RNA polymerase II at the Irf7 promoter. Our data suggest that the induction of Nostrill promotes antiparasitic defense against C. parvum and enhances intestinal epithelial antimicrobial defense through contributions to transcriptional regulation of immune-related genes, such as Irf7.

Persistent Cryptosporidium parvum Infection Leads to the Development of the Tumor Microenvironment in an Experimental Mouse Model: Results of a Microarray Approach

Cryptosporidium spp. are enteric protozoa parasites that infect a variety of vertebrate hosts. These parasites are capable of inducing life-threatening gastrointestinal disease in immunocompromised individuals. With the rising epidemiological evidence of the occurrence of Cryptosporidium infections in humans with digestive cancer, the tumorigenic potential of the parasite has been speculated. In this regard, Cryptosporidium parvum has been reported to induce digestive adenocarcinoma in a rodent model of chronic cryptosporidiosis. However, the processes by which the parasite could induce this carcinogenesis are still unknown. Therefore, the transcriptomes of C. parvum infected ileo-cecal regions of mice developing tumors were analyzed in the current study. For the first time, downregulation of the expression of α-defensin, an anti-microbial target of the parasite in response to C. parvum infection was observed in the transformed tissues. This phenomenon has been speculated to be the result of resistance of C. parvum to the host defense through the upregulated expression of interferon γ-stimulated genes. The inflammatory response generated as result of attenuated expression of anti-microbial peptides highlights the role of immune evasion in the C. parvum-induced tumorigenesis. The study has also succeeded in the characterization of the tumor microenvironment (TME) which is characterized by the presence of cancer associated fibroblasts, myeloid-derived suppressor cells, tumor-associated macrophages and extracellular matrix components. Identification of immune suppressor cells and accumulation of pro-inflammatory mediators speculates that chronic inflammation induced by persistent C. parvum infection assists in development of an immunosuppressive tumor microenvironment.

LncRNA XR_001779380 Primes Epithelial Cells for IFN-γ-Mediated Gene Transcription and Facilitates Age-Dependent Intestinal Antimicrobial Defense

Interferon (IFN) signaling is key to mucosal immunity in the gastrointestinal tract, but cellular regulatory elements that determine interferon gamma (IFN-γ)-mediated antimicrobial defense in intestinal epithelial cells are not fully understood. We report here that a long noncoding RNA (lncRNA), GenBank accession no. XR_001779380, was increased in abundance in murine intestinal epithelial cells following infection by Cryptosporidium, an important opportunistic pathogen in AIDS patients and a common cause of diarrhea in young children. Expression of XR_001779380 in infected intestinal epithelial cells was triggered by TLR4/NF-κB/Cdc42 signaling and epithelial-specific transcription factor Elf3. XR_001779380 primed epithelial cells for IFN-γ-mediated gene transcription through facilitating Stat1/Swi/Snf-associated chromatin remodeling. Interactions between XR_001779380 and Prdm1, which is expressed in neonatal but not adult intestinal epithelium, attenuated Stat1/Swi/Snf-associated chromatin remodeling induced by IFN-γ, contributing to suppression of IFN-γ-mediated epithelial defense in neonatal intestine. Our data demonstrate that XR_001779380 is an important regulator in IFN-γ-mediated gene transcription and age-associated intestinal epithelial antimicrobial defense. IMPORTANCE Epithelial cells along the mucosal surface provide the front line of defense against luminal pathogen infection in the gastrointestinal tract. These epithelial cells represent an integral component of a highly regulated communication network that can transmit essential signals to cells in the underlying intestinal mucosa that, in turn, serve as targets of mucosal immune mediators. LncRNAs are recently identified long noncoding transcripts that can regulate gene transcription through their interactions with other effect molecules. In this study, we demonstrated that lncRNA XR_001779380 was upregulated in murine intestinal epithelial cells following infection by a mucosal protozoan parasite Cryptosporidium. Expression of XR_001779380 in infected cells primed host epithelial cells for IFN-γ-mediated gene transcription, relevant to age-dependent intestinal antimicrobial defense. Our data provide new mechanistic insights into how intestinal epithelial cells orchestrate intestinal mucosal defense against microbial infection.

Management of cell death in parasitic infections

For a long time, host cell death during parasitic infection has been considered a reflection of tissue damage, and often associated with disease pathogenesis. However, during their evolution, protozoan and helminth parasites have developed strategies to interfere with cell death so as to spread and survive in the infected host, thereby ascribing a more intriguing role to infection-associated cell death. In this review, we examine the mechanisms used by intracellular and extracellular parasites to respectively inhibit or trigger programmed cell death. We further dissect the role of the prototypical “eat-me signal” phosphatidylserine (PtdSer) which, by being exposed on the cell surface of damaged host cells as well as on some viable parasites via a process of apoptotic mimicry, leads to their recognition and up-take by the neighboring phagocytes. Although barely dissected so far, the engagement of different PtdSer receptors on macrophages, by shaping the host immune response, affects the overall infection outcome in models of both protozoan and helminth infections. In this scenario, further understanding of the molecular and cellular regulation of the PtdSer exposing cell-macrophage interaction might allow the identification of new therapeutic targets for the management of parasitic infection.

m6A mRNA Methylation Regulates Epithelial Innate Antimicrobial Defense Against Cryptosporidial Infection

Increasing evidence supports that N6-methyladenosine (m⁶A) mRNA modification may play an important role in regulating immune responses. Intestinal epithelial cells orchestrate gastrointestinal mucosal innate defense to microbial infection, but underlying mechanisms are still not fully understood. In this study, we present data demonstrating significant alterations in the topology of host m⁶A mRNA methylome in intestinal epithelial cells following infection by Cryptosporidium parvum, a coccidian parasite that infects the gastrointestinal epithelium and causes a self-limited disease in immunocompetent individuals but a life-threatening diarrheal disease in AIDS patients. Altered m⁶A methylation in mRNAs in intestinal epithelial cells following C. parvum infection is associated with downregulation of alpha-ketoglutarate-dependent dioxygenase alkB homolog 5 and the fat mass and obesity-associated protein with the involvement of NF-кB signaling. Functionally, m⁶A methylation statuses influence intestinal epithelial innate defense against C. parvum infection. Specifically, expression levels of immune-related genes, such as the immunity-related GTPase family M member 2 and interferon gamma induced GTPase, are increased in infected cells with a decreased m⁶A mRNA methylation. Our data support that intestinal epithelial cells display significant alterations in the topology of their m⁶A mRNA methylome in response to C. parvum infection with the involvement of activation of the NF-кB signaling pathway, a process that modulates expression of specific immune-related genes and contributes to fine regulation of epithelial antimicrobial defense.

Circular RNA ciRS-7 affects the propagation of Cryptosporidium parvum in HCT-8 cells by sponging miR-1270 to activate the NF-κB signaling pathway

BACKGROUND

Cryptosporidium is an important zoonotic pathogen responsible for severe enteric diseases in humans and animals. However, the molecular mechanisms underlying host and Cryptosporidium interactions are still not clear.

METHODS

To study the roles of circRNAs in host cells during Cryptosporidium infection, the expression profiles of circRNAs in HCT-8 cells infected with C. parvum were investigated using a microarray assay, and the regulatory role of a significantly upregulated circRNA, ciRS-7, was investigated during C. parvum infection.

RESULTS

C. parvum infection caused notable alterations in the expression profiles of circRNAs in HCT-8 cells, and a total of 178 (including 128 up- and 50 downregulated) circRNAs were significantly differentially expressed following C. parvum infection. Among them, ciRS-7 was significantly upregulated and regulated the NF-κB signaling pathway by sponging miR-1270 during C. parvum infection. Furthermore, the ciRS-7/miR-1270/relA axis markedly affected the propagation of C. parvum in HCT-8 cells.

CONCLUSIONS

Our results revealed that ciRS-7 would promote C. parvum propagation by regulating the miR-1270/relA axis and affecting the NF-κB pathway. To the best of our knowledge, this is the first study to investigate the role of circRNA during Cryptosporidium infection, and the findings provide a novel view for implementing control strategies against Cryptosporidium infection.

Cryptosporidial Infection Suppresses Intestinal Epithelial Cell MAPK Signaling Impairing Host Anti-Parasitic Defense

Cryptosporidium is a genus of protozoan parasites that infect the gastrointestinal epithelium of a variety of vertebrate hosts. Intestinal epithelial cells are the first line of defense and play a critical role in orchestrating host immunity against Cryptosporidium infection. To counteract host defense response, Cryptosporidium has developed strategies of immune evasion to promote parasitic replication and survival within epithelial cells, but the underlying mechanisms are largely unclear. Using various models of intestinal cryptosporidiosis, we found that Cryptosporidium infection caused suppression of mitogen-activated protein kinase (MAPK) signaling in infected murine intestinal epithelial cells. Whereas expression levels of most genes encoding the key components of the MAPK signaling pathway were not changed in infected intestinal epithelial cells, we detected a significant downregulation of p38/Mapk, MAP kinase-activated protein kinase 2 (Mk2), and Mk3 genes in infected host cells. Suppression of MAPK signaling was associated with an impaired intestinal epithelial defense against C. parvum infection. Our data suggest that cryptosporidial infection may suppress intestinal epithelial cell MAPK signaling associated with the evasion of host antimicrobial defense.

Cryptosporidium parvum upregulates miR-942-5p expression in HCT-8 cells via TLR2/TLR4-NF-κB signaling

Background

Micro (mi)RNAs are small noncoding RNA molecules that function in RNA silencing and post-transcriptional regulation of gene expression. This study investigated host miRNA activity in the innate immune response to Cryptosporidium parvum infection.

Methods

In vitro infection model adopts HCT-8 human ileocecal adenocarcinoma cells infected with C. parvum. The expression of miR-942-5p was estimated using quantitative real-time polymerase chain reaction (qPCR). The TLRs-NF-κB signaling was confirmed by qPCR, western blotting, TLR4- and TLR2-specific short-interfering (si)RNA, and NF-κB inhibition.

Results

HCT-8 cells express all known toll-like receptors (TLRs). Cryptosporidium parvum infection of cultured HCT-8 cells upregulated TLR2 and TLR4, and downstream TLR effectors, including NF-κB and suppressed IκBα (nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha). The expression of miR-942-5p was significantly upregulated at 4, 8, 12 and 24 h post-infection, and especially at 8 hpi. The results of TLR4- and TLR2-specific siRNA and NF-κB inhibition showed that upregulation of miR-942-5p was promoted by p65 subunit-dependent TLR2/TLR4-NF-κB pathway signaling.

Conclusions

miR-942-5p of HCT-8 cells was significantly upregulated after C. parvum infection, especially at 8 hpi, in response to a p65-dependent TLR2/TLR4-NF-κB signaling. TLR4 appeared to play a dominant role.

Overview of Poultry Eimeria Life Cycle and Host-Parasite Interactions

Apicomplexan parasites of the genus Eimeria are organisms which invade the intestinal tract, causing coccidiosis, an enteric disease of major economic importance worldwide. The disease causes high morbidity ranging from an acute, bloody enteritis with high mortality, to subclinical disease. However, the presence of intestinal lesions depends on the Eimeria species. The most important poultry Eimeria species are: E. tenella, E. necatrix, E. acervulina, E. maxima, E. brunetti, E. mitis, and E. praecox. Key points to better understanding the behavior of this species are the host-parasite interactions and its life cycle. The present paper reviews the literature available regarding the life cycle and the initial host-parasite interaction. More studies are needed to better understand these interactions in poultry Eimerias, taking into account that almost all the information available was generated from other apicomplexan parasites that generate human disease.

Prevalence and Genotyping of Cryptosporidium parvum in Gastrointestinal Cancer Patients

Gastrointestinal cancers are the most commonly occurring malignancies which contributing to over 1/5 of cancer incidences worldwide. Increasing evidences have shown that Cryptosporidium spp., an apicomplexan protozoan, is highly associated with gastrointestinal cancers. However, the prevalence of Cryptosporidium spp. infections among gastrointestinal cancer patients in China has not been estimated yet. We here performed a case-control study to evaluate the occurrences of Cryptosporidium spp. in patients with digestive malignancies before chemotherapy and in control population. Nested PCR amplifying 18S rRNA gene was used to detect the presence of Cryptosporidium spp. in each fecal sample. The results herein confirmed the correlation of Cryptosporidium spp. infection with colorectal and liver cancers, while first identified the high frequencies of Cryptosporidium spp. in esophageal cancer and small intestine cancer. The infection rates of Cryptosporidium spp. in colorectal, esophageal, liver and small intestine cancers were 17.24% (20/116, P<0.001), 6.25% (1/16, P=0.029), 14.29% (1/7, P<0.001) and 40% (2/5, P<0.001), respectively. In addition, molecular characterization indicated that all the Cryptosporidium spp. obtained were Cryptosporidium parvum (C. parvum), and the 18S rRNA sequences were identical to the reference sequences isolated from cattle, suggesting potential zoonotic transmission. Furthermore, subtyping analyses revealed that IIaA15G2R1 and IIaA15G2R2 were the predominant subtypes in colorectal cancer, while IIaA13G2R2 subtype was first named and identified in colorectal and liver cancers. Taken together, for the first time, the prevalence of Cryptosporidium spp. infections in digestive cancer patients has been estimated among Chinese. Our results indicated that C. parvum were highly associated with gastrointestinal cancers, supporting that cryptosporidiosis could be a potential risk factor for these diseases.

Involvement of Cryptosporidium parvum Cdg7_FLc_1000 RNA in the Attenuation of Intestinal Epithelial Cell Migration via Trans-Suppression of Host Cell SMPD3

Intestinal infection by Cryptosporidium parvum causes inhibition of epithelial turnover, but underlying mechanisms are unclear. Previous studies demonstrate that a panel of parasite RNA transcripts of low protein-coding potential are delivered into infected epithelial cells. Using in vitro and in vivo models of intestinal cryptosporidiosis, we report here that host delivery of parasite Cdg7_FLc_1000 RNA results in inhibition of epithelial cell migration through suppression of the gene encoding sphingomyelinase 3 (SMPD3). Delivery of Cdg7_FLc_1000 into infected cells promotes the histone methyltransferase G9a-mediated H3K9 methylation in the SMPD3 locus. The DNA-binding transcriptional repressor, PR domain zinc finger protein 1, is required for the assembly of Cdg7_FLc_1000 into the G9a complex and associated with the enrichment of H3K9 methylation at the gene locus. Pathologically, nuclear transfer of Cryptosporidium parvum Cdg7_FLc_1000 RNA is involved in the attenuation of intestinal epithelial cell migration via trans-suppression of host cell SMPD3.

iTRAQ-based comparative proteomic analysis of cells infected with Eimeria tenella sporozoites

Eimeria tenella is an obligate intracellular parasite that actively invades cecal epithelial cells of chickens. When E. tenella infects a host cell, the host produces a corresponding change to deal with damage caused by this infection. To date, our knowledge on the mechanism of how the host cell responds to E. tenella infection is highly limited at both the molecular and cellular levels. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) coupled with LC-MS/MS was used to screen the differentially expressed proteins (DEPs) in BHK-21 cells infected with E. tenella sporozoites for 24 h post infection. In total, 6139 non-redundant distinct proteins were identified and 195 of these were found to have a fold change ratio ≥1.3 or ≤0.7 and p < 0.05, including 151 up-regulated proteins and 44 down-regulated proteins. The reliability of the proteomic data was further validated with qPCR and western blot. Gene Ontology enrichment indicated that the up-regulated DEPs were mainly involved in binding and catalytic activity, whereas the down-regulated DEPs were catalytic activity and molecular function regulators. Furthermore, KEGG pathway analysis showed that the DEPs participated in the PI3K-Akt, chemokine, Ras, Wnt, and p53 signaling pathways and so on, and the up-regulated and down-regulated DEPs mainly related to the ribosome and mRNA surveillance pathway, respectively. The data in this study provide an important basis to further analyze E. tenella host cell interactions.

Regulation of apoptosis-related genes during interactions between oyster hemocytes and the alveolate parasite Perkinsus marinus

The alveolate Perkinsus marinus is the most devastating parasite of the eastern oyster Crassostrea virginica. The parasite is readily phagocytosed by oyster hemocytes, but instead of intracellular killing and digestion, P. marinus can survive phagocytosis and divide in host cells. This intracellular parasitism is accompanied by a regulation of host cell apoptosis. This study was designed to gain a better understanding of the molecular mechanisms of apoptosis regulation in oyster hemocytes following exposure to P. marinus. Regulation of apoptosis-related genes in C. virginica, and apoptosis-regulatory genes in P. marinus, were investigated via qPCR to assess the possible pathways involved during these interactions. In vitro experiments were also carried out to evaluate the effect of chemical inhibitors of P. marinus antioxidant processes on hemocyte apoptosis. Results indicate the involvement of the mitochondrial pathway (Bcl-2, anamorsin) of apoptosis in C. virginica exposed to P. marinus. In parallel, the antioxidants peroxiredoxin and superoxide dismutase were regulated in P. marinus exposed to C. virginica hemocytes suggesting that apoptosis regulation in infected oysters may be mediated by anti-oxidative processes. Chemical inhibition of P. marinus superoxide dismutase resulted in a marked increase of reactive oxygen species production and apoptosis in infected hemocytes. The implication of oxygen-dependent apoptosis during P. marinus infection and disease development in C. virginica is discussed.

Induction of a Long Noncoding RNA Transcript, NR_045064, Promotes Defense Gene Transcription and Facilitates Intestinal Epithelial Cell Responses against Cryptosporidium Infection

Cryptosporidium is an important opportunistic intestinal pathogen for immunocompromised individuals and a common cause of diarrhea in young children in developing countries. Gastrointestinal epithelial cells play a central role in activating and orchestrating host immune responses against Cryptosporidium infection, but underlying molecular mechanisms are not fully understood. We report in this paper that C. parvum infection causes significant alterations in long noncoding RNA (lncRNA) expression profiles in murine intestinal epithelial cells. Transcription of a panel of lncRNA genes, including NR_045064, in infected cells is controlled by the NF-κB signaling. Functionally, inhibition of NR_045064 induction increases parasite burden in intestinal epithelial cells. Induction of NR_045064 enhances the transcription of selected defense genes in host cells following C. parvum infection. Epigenetic histone modifications are involved in NR_045064-mediated transcription of associated defense genes in infected host cells. Moreover, the p300/MLL-associated chromatin remodeling is involved in NR_045064-mediated transcription of associated defense genes in intestinal epithelial cells following C. parvum infection. Expression of NR_045064 and associated genes is also identified in intestinal epithelium in C57BL/6J mice following phosphorothioate oligodeoxynucleotide or LPS stimulation. Our data demonstrate that lncRNAs, such as NR_045064, play a role in regulating epithelial defense against microbial infection.

Attenuation of Intestinal Epithelial Cell Migration During Cryptosporidium parvum Infection Involves Parasite Cdg7_FLc_1030 RNA-Mediated Induction and Release of Dickkopf-1

Intestinal infection by Cryptosporidium is known to cause epithelial cell migration disorder but the underlying mechanisms are unclear. Previous studies demonstrated that a panel of parasite RNA transcripts of low protein-coding potential are delivered into infected epithelial cells. Using multiple models of intestinal cryptosporidiosis, we report here that C. parvum infection induces expression and release of the dickkopf protein 1 (Dkk1) from intestinal epithelial cells. Delivery of parasite Cdg7_FLc_1030 RNA to intestinal epithelial cells triggers transactivation of host Dkk1 gene during C. parvum infection. Release of Dkk1 is involved in C. parvum-induced inhibition of cell migration of epithelial cells, including noninfected bystander cells. Moreover, Dkk1-mediated suppression of host cell migration during C. parvum infection involves inhibition of Cdc42/Par6 signaling. Our data support the hypothesis that attenuation of intestinal epithelial cell migration during Cryptosporidium infection involves parasite Cdg7_FLc_1030 RNA-mediated induction and release of Dkk1 from infected cells.

Trans-suppression of defense DEFB1 gene in intestinal epithelial cells following Cryptosporidium parvum infection is associated with host delivery of parasite Cdg7_FLc_1000 RNA

To counteract host immunity, Cryptosporidium parvum has evolved multiple strategies to suppress host antimicrobial defense. One such strategy is to reduce the production of the antimicrobial peptide beta-defensin 1 (DEFB1) by host epithelial cells but the underlying mechanisms remain unclear. Recent studies demonstrate that a panel of parasite RNA transcripts of low protein-coding potential are delivered into infected host cells and may modulate host gene transcription. Using in vitro models of intestinal cryptosporidiosis, in this study, we analyzed the expression profile of host beta-defensin genes in host cells following infection. We found that C. parvum infection caused a significant downregulation of the DEFB1 gene. Interestingly, downregulation of DEFB1 gene was associated with host delivery of Cdg7_FLc_1000 RNA transcript, a C. parvum RNA that has previously demonstrated to be delivered into the nuclei of infected host cells. Knockdown of Cdg7_FLc_1000 in host cells could attenuate the trans-suppression of host DEFB1 gene and decreased the parasite burden. Therefore, our data suggest that trans-suppression of DEFB1 gene in intestinal epithelial cells following C. parvum infection involves host delivery of parasite Cdg7_FLc_1000 RNA, a process that may be relevant to the epithelial defense evasion by C. parvum at the early stage of infection.

Nuclear delivery of parasite Cdg2_FLc_0220 RNA transcript to epithelial cells during Cryptosporidium parvum infection modulates host gene transcription

Intestinal infection by the zoonotic protozoan, Cryptosporidium parvum, causes significant alterations in the gene expression profile in host epithelial cells. The molecular mechanisms of how C. parvum may modulate host cell gene transcription and the pathological significance of such alterations are largely unclear. Previous studies demonstrate that a panel of parasite RNA transcripts are delivered into infected host cells and may modulate host gene transcription. Using in vitro models of intestinal cryptosporidiosis, in this study, we analyzed the impact of host delivery of C. parvum Cdg2_FLc_0220 RNA transcript on host gene expression profile. We found that alterations in host gene expression profile following C. parvum infection were partially associated with the nuclear delivery of Cdg2_FLc_0220. Specifically, we identified a total of 46 overlapping upregulated genes and 8 overlapping downregulated genes in infected cells and cells transfected with Full-Cdg2_FLc_0220. Trans-suppression of the DAZ interacting zinc finger protein 1 like (DZIP1L) gene, the top overlapping downregulated gene in host cells following C. parvum infection and cells transfected with Full-Cdg2_FLc_0220, was mediated by G9a, independent of PRDM1. Cdg2_FLc_0220-mediated trans-suppression of the DZIP1L gene was independent of H3K9 and H3K27 methylation. Data from this study provide additional evidence that delivery of C. parvum Cdg2_FLc_0220 RNA transcript in infected epithelial cells modulates the transcription of host genes, contributing to the alterations in the gene expression profile in host epithelial cells during C. parvum infection.

High association of Cryptosporidium spp. infection with colon adenocarcinoma in Lebanese patients

Background

The association between Cryptosporidium and human colon cancer has been reported in different populations. However, this association has not been well studied. In order to add new strong arguments for a probable link between cryptosporidiosis and colon human cancer, the aim of this study was to determine prevalence and to identify species of Cryptosporidium among Lebanese patients.

Methodology and principal findings

Overall, 218 digestive biopsies were collected in Tripoli, Lebanon, from three groups of patients: (i) patients with recently diagnosed colon intraepithelial neoplasia/adenocarcinoma before any treatment (n = 72); (ii) patients with recently diagnosed stomach intraepithelial neoplasia/adenocarcinoma before any treatment (n = 21); and (iii) patients without digestive intraepithelial neoplasia/adenocarcinoma but with persistent digestive symptoms (n = 125). DNA extraction was performed from paraffin-embedded tissue. The presence of the parasite in tissues was confirmed by PCR, microscopic observation and immunofluorescence analysis. We identified a high rate (21%) of Cryptosporidium presence in biopsies from Lebanese patients with recently diagnosed colonic neoplasia/adenocarcinoma before any treatment. This prevalence was significantly higher compared to 7% of Cryptosporidium prevalence among patients without colon neoplasia but with persistent gastrointestinal symptoms (OR: 4, CI: 1.65–9.6, P = 0.001). When the comparison was done against normal biopsies, the risk of infection increased 11-fold in the group of patients with colon adenocarcinoma (OR: 11.315, CI: 1.44–89.02, P = 0.003).

Conclusions

This is the first study performed in Lebanon reporting the prevalence of Cryptosporidium among patients with digestive cancer. These results show that Cryptosporidium is strongly associated with human colon cancer being maybe a potential etiological agent of this disease.

Potential Sabotage of Host Cell Physiology by Apicomplexan Parasites for Their Survival Benefits

Plasmodium, Toxoplasma, Cryptosporidium, Babesia, and Theileria are the major apicomplexan parasites affecting humans or animals worldwide. These pathogens represent an excellent example of host manipulators who can overturn host signaling pathways for their survival. They infect different types of host cells and take charge of the host machinery to gain nutrients and prevent itself from host attack. The mechanisms by which these pathogens modulate the host signaling pathways are well studied for Plasmodium, Toxoplasma, Cryptosporidium, and Theileria, except for limited studies on Babesia. Theileria is a unique pathogen taking into account the way it modulates host cell transformation, resulting in its clonal expansion. These parasites majorly modulate similar host signaling pathways, however, the disease outcome and effect is different among them. In this review, we discuss the approaches of these apicomplexan to manipulate the host–parasite clearance pathways during infection, invasion, survival, and egress.

Innate immune responses play a key role in controlling infection of the intestinal epithelium by Cryptosporidium

Cryptosporidium infection leads to acute diarrhea worldwide. The development of cryptosporidiosis is closely related to the immune status of its host, affecting primarily young ruminants, infants, and immunocompromised individuals. In recent years, several studies have improved our knowledge on the immune mechanisms responsible for the control of the acute phase of the infection and have highlighted the importance of innate immunity. The parasite develops in the apical side of intestinal epithelial cells, giving these cells a central role, as they are both the exclusive host cell for replication of the parasite and participate in the protective immune response. Epithelial cells signal the infection by producing chemokines, attracting immune cells to the infected area. They also actively participate in host defense by inducing apoptosis and releasing antimicrobial peptides, free or incorporated into luminal exosomes, with parasiticidal activity. The parasite has developed several escape mechanisms to slow down these protective mechanisms. Recent development of several three-dimensional culture models and the ability to genetically manipulate Cryptosporidium will greatly help to further investigate host-pathogen interactions and identify virulence factors. Intestinal epithelial cells require the help of immune cells to clear the infection. Intestinal dendritic cells, well known for their ability to induce and orchestrate adaptive immunity, play a key role in controlling the very early steps of Cryptosporidium parvum infection by acting as immunological sentinels and active effectors. However, inflammatory monocytes, which are quickly and massively recruited to the infected mucosa, seem to participate in the loss of epithelial integrity. In addition to new promising chemotherapies, we must consider stimulating the innate immunity of neonates to strengthen their ability to control Cryptosporidium development. The microbiota plays a fundamental role in the development of intestinal immunity and may be considered to be a third actor in host-pathogen interactions. There is an urgent need to reduce the incidence of this yet poorly controlled disease in the populations of developing countries, and decrease economic losses due to infected livestock.

Delivery of parasite Cdg7_Flc_0990 RNA transcript into intestinal epithelial cells during Cryptosporidium parvum infection suppresses host cell gene transcription through epigenetic mechanisms

Cryptosporidial infection causes dysregulated transcription of host genes key to intestinal epithelial homeostasis, but the underlying mechanisms remain obscure. Previous studies demonstrate that several Cryptosporidium parvum (C. parvum) RNA transcripts are selectively delivered into epithelial cells during host cell invasion and may modulate gene transcription in infected cells. We report here that C. parvum infection suppresses the transcription of LRP5, SLC7A8, and IL33 genes in infected intestinal epithelium. Trans-suppression of these genes in infected host cells is associated with promoter enrichment of suppressive epigenetic markers (i.e., H3K9me3). Cdg7_FLc_0990, a C. parvum RNA that has previously demonstrated to be delivered into the nuclei of infected epithelial cells, is recruited to the promoter regions of LRP5, SLC7A8, and IL33 genes. Cdg7_FLc_0990 appears to be recruited to their promoter regions together with G9a, a histone methyltransferase for H3K9 methylation. The PR domain zinc finger protein 1, a G9a-interacting protein, is required for the assembly of Cdg7_FLc_0990 to the G9a complex and gene-specific enrichment of H3K9 methylation. Our data demonstrate that cryptosporidial infection induces epigenetic histone methylations in infected cells through nuclear transfer of parasite Cdg7_Flc_0990 RNA transcript, resulting in transcriptional suppression of the LRP5, SLC7A8, and IL33 genes.

Delivery of Parasite RNA Transcripts Into Infected Epithelial Cells During Cryptosporidium Infection and Its Potential Impact on Host Gene Transcription

Cryptosporidium parvum is an important opportunistic parasite pathogen for immunocompromised individuals and a common cause of diarrhea in young children. Previous studies have identified a panel of RNA transcripts of very low protein-coding potential in C. parvum. Using an in vitro model of human intestinal cryptosporidiosis, we report here that some of these C. parvum RNA transcripts were selectively delivered into the nuclei of host epithelial cells during C. parvum infection. Nuclear delivery of several such parasitic RNAs, including Cdg7_FLc_0990, involved heat-shock protein 70-mediated nuclear importing mechanism. Overexpression of Cdg7_FLc_0990 in intestinal epithelial cells resulted in significant changes in expression levels of specific genes, with significant overlapping with alterations in gene expression profile detected in host cells after C. parvum infection. Our data demonstrate that C. parvum transcripts of low protein-coding potential are selectively delivered into epithelial cells during infection and may modulate gene transcription in infected host cells.

Pathogenic Mechanisms of Cryptosporidium and Giardia

Intestinal protozoa are important etiological agents of diarrhea, particularly in children, yet the public health risk they pose is often neglected. Results from the Global Enteric Multicenter Study (GEMS) showed that Cryptosporidium is among the leading causes of moderate to severe diarrhea in children under 2 years. Likewise, Giardia infects approximately 200 million individuals worldwide, and causes acute diarrhea in children under 5 years. Despite this recognized role as pathogens, the question is why and how these parasites cause disease in some individuals but not in others. This review focuses on known pathogenic mechanisms of Cryptosporidium and Giardia, and infection progress towards disease.

Infection Strategies of Intestinal Parasite Pathogens and Host Cell Responses

Giardia lamblia, Cryptosporidium sp., and Entamoeba histolytica are important pathogenic intestinal parasites and are amongst the leading causes worldwide of diarrheal illness in humans. Diseases caused by these organisms, giardiasis, cryptosporidiosis, and amoebiasis, respectively, are characterized by self-limited diarrhea but can evolve to long-term complications. The cellular and molecular mechanisms underlying the pathogenesis of diarrhea associated with these three pathogens are being unraveled, with knowledge of both the strategies explored by the parasites to establish infection and the methods evolved by hosts to avoid it. Special attention is being given to molecules participating in parasite–host interaction and in the mechanisms implicated in the diseases’ pathophysiologic processes. This review focuses on cell mechanisms that are modulated during infection, including gene transcription, cytoskeleton rearrangements, signal transduction pathways, and cell death.

Insights into regulatory molecules of intestinal epithelial cell turnover during experimental infection by Heterophyes heterophyes

Heterophyiasis is an intestinal disease that remains endemic in many parts of the world, particularly the Nile Delta of Egypt and Southeast Asia, yet the populations at risk of infection expand throughout the world. The main histopathological feature of infection is villous atrophy, but the underlying factors are not well understood. Apoptosis of the villous epithelial cells was previously reported to be enhanced during intestinal parasitic infections; however, the role of Heterophyes heterophyes on enterocyte apoptosis was to be explored. Therefore, intestinal sections from mice experimentally infected with H. heterophyes were studied histopathologically and immunohistochemically for caspase-3 and NF-κB and compared to non-infected control mice. Atrophic villi covered by poorly differentiated epithelial cells were observed in the 2nd week post-infection. Also, we noted marked hyperplasia of the intestinal crypts with abundant inflammatory cellular infiltrate in the lamina propria, as well as apoptosis of cells lining the intestinal villi. Both caspase-3 and NF-κB showed positive staining in the intestinal epithelial cells with varying grades of intensity over the length of infection. Caspase-3 expression rose at the 2nd week p.i. then decreased over time, whereas NF-κB expression showed progressive increase throughout the weeks of infection. In conclusion, caspase-3 activation may be an important factor in the apoptotic pathway in early heterophyiasis, and, on the other hand, NF-κB seems to play a role in protecting the intestinal cells from excessive apoptosis. These observations may help open new avenues for tissue protective therapies that avoid or control the deleterious processes of apoptosis in various inflammatory conditions.

Prospects for immunotherapy and vaccines against Cryptosporidium

Cryptosporidium spp is a ubiquitous parasite that has long been recognized as a frequent cause of protozoal diarrhea in humans. While infections in immunocompetent hosts are usually self-limiting, immunocompromised individuals can develop severe, chronic, and life-threatening illness. Vaccine development or immunotherapy that prevents disease or reduces the severity of infection is a relevant option since efficacious drug treatments are lacking. In particular, children in developing countries might benefit the most from a vaccine since cryptosporidiosis in early childhood has been reported to be associated with subsequent impairment in growth, physical fitness, and intellectual capacity. In this review, immunotherapies that have been used clinically are described as well as experimental vaccines and their evaluation in vivo.

Intestinal CD103+ dendritic cells are key players in the innate immune control of Cryptosporidium parvum infection in neonatal mice

Cryptosporidium parvum is a zoonotic protozoan parasite found worldwide, that develops only in the gastrointestinal epithelium and causes profuse diarrhea. Using a mouse model of C. parvum infection, we demonstrated by conditional depletion of CD11c+ cells that these cells are essential for the control of the infection both in neonates and adults. Neonates are highly susceptible to C. parvum but the infection is self-limited, whereas adults are resistant unless immunocompromised. We investigated the contribution of DC to the age-dependent susceptibility to infection. We found that neonates presented a marked deficit in intestinal CD103+ DC during the first weeks of life, before weaning, due to weak production of chemokines by neonatal intestinal epithelial cells (IEC). Increasing the number of intestinal CD103+ DC in neonates by administering FLT3-L significantly reduced susceptibility to the infection. During infections in neonates, the clearance of the parasite was preceded by a rapid recruitment of CD103+ DC mediated by CXCR3-binding chemokines produced by IEC in response to IFNγ. In addition to this key role in CD103+ DC recruitment, IFNγ is known to inhibit intracellular parasite development. We demonstrated that during neonatal infection CD103+ DC produce IL-12 and IFNγ in the lamina propria and the draining lymph nodes. Thus, CD103+DC are key players in the innate immune control of C. parvum infection in the intestinal epithelium. The relative paucity of CD103+ DC in the neonatal intestine contributes to the high susceptibility to intestinal infection.

Innate immune responses against Cryptosporidium parvum infection

Cryptosporidium parvum infects intestinal epithelial cells and is commonly the parasite species involved in mammalian cryptosporidiosis, a major health problem for humans and neonatal livestock. In mice, immunologically mediated elimination of C. parvum requires CD4+ T cells and IFN-γ. However, innate immune responses also have a significant protective role in both adult and neonatal mice. NK cells and IFN-γ have been shown to be important components in immunity in T and B cell-deficient mice, but IFN-γ-dependent resistance has also been demonstrated in alymphocytic mice. Epithelial cells may play a vital role in immunity as once infected these cells have increased expression of inflammatory chemokines and cytokines and demonstrate antimicrobial killing mechanisms, including production of NO and antimicrobial peptides. Toll-like receptors facilitate the establishment of immunity in mice and are involved in the development of inflammatory responses of infected epithelial cells and also dendritic cells.

Heligmosomoides polygyrus antigens inhibit the intrinsic pathway of apoptosis by overexpression of survivin and Bcl-2 protein in CD4 T cells

Many laboratory studies and epidemiological observations confirm that nematodes prevent some immune-mediated diseases. The development of immunologically well-defined laboratory models of intestinal nematode infection has allowed significant advances to be made in understanding the immunological basis of effector mechanisms operating during infection under controlled laboratory conditions. The Heligmosomoides polygyrus- mouse system is used for studies of parasite immunomodulation. H. polygyrus causes a chronic, asymptomatic intestinal infection and effectively maintains both local and systemic tolerance to reduce allergic and autoimmune inflammation. However, exposure of mice to H. polygyrus antigen reduced spontaneous and glucocorticoid-induced apoptosis of CD4- positive T cells in mesenteric lymph node (MLN). In this study we evaluate the proliferation, cytokine secretion, cell cycle progression and expression of apoptosis related genes in MLN CD4 T cells of uninfected and H. polygyrus infected mice ex vivo and in vitro after restimulation with parasite excretory secretory antigen (ESAg), somatic antigen (SAg) and fraction 9 (F9Ag) of somatic antigen. For the first time we explain the influence of H. polygyrus antigens on the intrinsic pathway of apoptosis. We found that the proliferation provoked by fraction 9 and inhibition of apoptosis was dependent on a low Bax/Bcl-2 ratio, dramatical upregulation of survivin, D1 cyclin, P-glycoprotein, and loss of p27Kip1 protein with inhibition of active caspase-3 but not caspase- 8.

Proteasome inhibition of pathologic shedding of enterocytes to defend barrier function requires X-linked inhibitor of apoptosis protein and nuclear factor κB

BACKGROUND & AIMS

Although we are beginning to understand where, when, and how intestinal epithelial cells are shed, physiologically, less is understood about alterations in cell fate during minimally invasive epithelial infections. We used a piglet model of Cryptosporidium parvum infection to determine how elimination of infected enterocytes is balanced with the need to maintain barrier function.

METHODS

We studied the effects of enterocyte shedding by C parvum-infected ileum on barrier function ex vivo with Ussing chambers. The locations and activities of caspase-3, nuclear factor κB (NF-κB), and inhibitor of apoptosis proteins (IAP) were assayed by enzyme-linked immunosorbent assay, immunoblot, and tissue immunoreactivity analyses and using specific pharmacologic inhibitors. The location, specificity, and magnitude of enterocyte shedding were quantified using special stains and light microscopy.

RESULTS

Infection with C parvum activated apoptotic signaling pathways in enterocytes that resulted in cleavage of caspase-3. Despite caspase-3 cleavage, enterocyte shedding was confined to villus tips, coincident with apoptosis, and observed more frequently in infected cells. Epithelial expression of X-linked inhibitor of apoptosis protein (XIAP), activation of NF-κB, and proteasome activity were required for control of cell shedding and barrier function. The proteasome blocked activity of caspase-3; this process was mediated by expression of XIAP, which bound to cleaved caspase-3.

CONCLUSIONS

We have identified a pathway by which villus epithelial cells are maintained during C parvum infection. Loss of barrier function is reduced by active retention of infected enterocytes until they reach the villus tip. These findings might be used to promote clearance of minimally invasive enteropathogens, such as by increasing the rate of migration of epithelial cells from the crypt to the villus tip.

miR-27b targets KSRP to coordinate TLR4-mediated epithelial defense against Cryptosporidium parvum infection

Cryptosporidium is a protozoan parasite that infects the gastrointestinal epithelium and causes a diarrheal disease. Toll-like receptor (TLR)- and NF-κB-mediated immune responses from epithelial cells, such as production of antimicrobial peptides and generation of reactive nitrogen species, are important components of the host's defense against cryptosporidial infection. Here we report data demonstrating a role for miR-27b in the regulation of TLR4/NF-κB-mediated epithelial anti-Cryptosporidium parvum responses. We found that C. parvum infection induced nitric oxide (NO) production in host epithelial cells in a TLR4/NF-κB-dependent manner, with the involvement of the stabilization of inducible NO synthase (iNOS) mRNA. C. parvum infection of epithelial cells activated NF-κB signaling to increase transcription of the miR-27b gene. Meanwhile, downregulation of KH-type splicing regulatory protein (KSRP) was detected in epithelial cells following C. parvum infection. Importantly, miR-27b targeted the 3′-untranslated region of KSRP, resulting in translational suppression. C. parvum infection decreased KSRP expression through upregulating miR-27b. Functional manipulation of KSRP or miR-27b caused reciprocal alterations in iNOS mRNA stability in infected cells. Forced expression of KSRP and inhibition of miR-27b resulted in an increased burden of C. parvum infection. Downregulation of KSRP through upregulating miR-27b was also detected in epithelial cells following LPS stimulation. These data suggest that miR-27b targets KSRP and modulates iNOS mRNA stability following C. parvum infection, a process that may be relevant to the regulation of epithelial anti-microbial defense in general.

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the posttranscriptional level. Accumulating data indicate that miRNAs are an essential part of the complex regulatory networks that control various cellular processes, including host antimicrobial immune responses. Toll-like receptors (TLRs) play an essential role in the activation of innate immunity by recognizing specific patterns of microbial components and activating downstream intracellular signaling pathways, including NF-κB. However, the role of miRNAs in the regulation of TLR/NF-κB-mediated epithelial antimicrobial defense is still unclear. Cryptosporidium is a protozoan parasite that infects the gastrointestinal epithelium in humans. Here, we show that KSRP, an RNA-binding protein and a key mediator of mRNA decay, is a target for miR-27b. Infection by Cryptosporidium parvum activates TLR4/NF-κB signaling and increases miR-27b expression, causing a suppression of KSRP in infected host epithelial cells. Functionally, downregulation of KSRP stabilizes iNOS mRNA and promotes epithelial production of nitric oxide, a molecule with antimicrobial activity. Therefore, miR-27b confers TLR4/NF-κB-mediated epithelial cell anti-Cryptosporidium parvum defense though regulating KSRP. Our study provides a new area of exploration for fine-tuning TLR/NF-κB-mediated host reactions in response to microbial challenge.

Cryptosporidiosis: host immune responses and the prospects for effective immunotherapies

Cryptosporidium spp. that develop in intestinal epithelial cells are responsible for the diarrhoeal disease cryptosporidiosis, which is common in humans of all ages and in neonatal livestock. Following infection, parasite reproduction increases for a number of days before it is blunted and then impeded by innate and adaptive immune responses. Immunocompromised hosts often cannot establish strong immunity and develop chronic infections that can lead to death. Few drugs consistently inhibit parasite reproduction in the host, and chemotherapy might be ineffective in immunodeficient hosts. Future options for prevention or treatment of cryptosporidiosis might include vaccines or recombinant immunological molecules, but this will probably require a better understanding of both the mucosal immune system and intestinal immune responses to the parasite.

Parasites and malignancies, a review, with emphasis on digestive cancer induced by Cryptosporidium parvum (Alveolata: Apicomplexa)

The International Agency for Research on Cancer (IARC) identifies ten infectious agents (viruses, bacteria, parasites) able to induce cancer disease in humans. Among parasites, a carcinogenic role is currently recognized to the digenetic trematodes Schistosoma haematobium, leading to bladder cancer, and to Clonorchis sinensis or Opisthorchis viverrini, which cause cholangiocarcinoma. Furthermore, several reports suspected the potential association of other parasitic infections (due to Protozoan or Metazoan parasites) with the development of neoplastic changes in the host tissues. The present work shortly reviewed available data on the involvement of parasites in neoplastic processes in humans or animals, and especially focused on the carcinogenic power of Cryptosporidium parvum infection. On the whole, infection seems to play a crucial role in the etiology of cancer.