Involvement of host calpain in the invasion of Cryptosporidium parvum

Role of Host Small GTPases in Apicomplexan Parasite Infection

The Apicomplexa are obligate intracellular parasites responsible for several important human diseases. These protozoan organisms have evolved several strategies to modify the host cell environment to create a favorable niche for their survival. The host cytoskeleton is widely manipulated during all phases of apicomplexan intracellular infection. Moreover, the localization and organization of host organelles are altered in order to scavenge nutrients from the host. Small GTPases are a class of proteins widely involved in intracellular pathways governing different processes, from cytoskeletal and organelle organization to gene transcription and intracellular trafficking. These proteins are already known to be involved in infection by several intracellular pathogens, including viruses, bacteria and protozoan parasites. In this review, we recapitulate the mechanisms by which apicomplexan parasites manipulate the host cell during infection, focusing on the role of host small GTPases. We also discuss the possibility of considering small GTPases as potential targets for the development of novel host-targeted therapies against apicomplexan infections.

Molecular characterization and functional analysis of the Schistosoma mekongi Ca2+-dependent cysteine protease (calpain)

Background

Schistosoma mekongi, which causes schistosomiasis in humans, is an important public health issue in Southeast Asia. Treatment with praziquantel is the primary method of control but emergence of praziquantel resistance requires the development of alternative drugs and vaccines. Calcium-dependent cysteine protease (calpain) is a novel vaccine candidate that has been studied in S. mansoni, S. japonicum, and protozoans including malaria, leishmania and trypanosomes. However, limited information is available on the properties and functions of calpain in other Schistosoma spp., including S. mekongi. In this study, we functionally characterized calpain 1 of S. mekongi (SmeCalp1).

Results

Calpain 1 of S. mekongi was obtained from transcriptomic analysis of S. mekongi; it had the highest expression level of all isoforms tested and was predominantly expressed in the adult male. SmeCalp1 cDNA is 2274 bp long and encodes 758 amino acids, with 85% to 90% homology with calpains in other Schistosoma species. Recombinant SmeCalp1 (rSmeCalp1), with a molecular weight of approximately 86.7 kDa, was expressed in bacteria and stimulated a marked antibody response in mice. Native SmeCalp1 was detected in crude worm extract and excretory-secretory product, and it was mainly localized in the tegument of the adult male; less signal was detected in the adult female worm. Thus, SmeCalp1 may play a role in surface membrane synthesis or host–parasite interaction. We assessed the protease activity of rSmeCalp1 and demonstrated that rSmeCalp1 could cleave the calpain substrate N-succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin, that was inhibited by calpain inhibitors (MDL28170 and E64c). Additionally, rSmeCalp1 could degrade the biological substrates fibronectin (blood clotting protein) and human complement C3, indicating important roles in the intravascular system and in host immune evasion.

Conclusions

SmeCalp1 is expressed on the tegumental surface of the parasite and can cleave host defense molecules; thus, it might participate in growth, development and survival during the entire life-cycle of S. mekongi. Information on the properties and functions of SmeCalp1 reported herein will be advantageous in the development of effective drugs and vaccines against S. mekongi and other schistosomes.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3639-9) contains supplementary material, which is available to authorized users.

Comparative Pathobiology of the Intestinal Protozoan Parasites Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum

Protozoan parasites can infect the human intestinal tract causing serious diseases. In the following article, we focused on the three most prominent intestinal protozoan pathogens, namely, Giardia lamblia, Entamoeba histolytica, and Cryptosporidium parvum. Both C. parvum and G. lamblia colonize the duodenum, jejunum, and ileum and are the most common causative agents of persistent diarrhea (i.e., cryptosporidiosis and giardiasis). Entamoeba histolytica colonizes the colon and, unlike the two former pathogens, may invade the colon wall and disseminate to other organs, mainly the liver, thereby causing life-threatening amebiasis. Here, we present condensed information concerning the pathobiology of these three diseases.

Anti-chlamydial activities of cell-permeable hydrophobic dipeptide-containing derivatives

The obligate intracellular bacteria chlamydia is major human pathogen that causes millions of trachoma, sexually transmitted infections and pneumonia worldwide. We serendipitously found that both calpain inhibitors z-Val-Phe-CHO and z-Leu-Nle-CHO showed marked inhibitory activity against chlamydial growth in human epithelial HeLa cells, whereas other calpain inhibitors not. These peptidomimetic inhibitors consist of N-benzyloxycarbonyl group and hydrophobic dipeptide derivatives. Both compounds strongly restrict the chlamydial growth even addition at the 12 h post infection. Notably, inhibitors-mediated growth inhibition of chlamydia was independent on host calpain activity. Electron microscopic analysis revealed that z-Val-Phe-CHO inhibited chlamydial growth by arresting bacterial cell division and RB-EB re-transition, but not by changing into persistent state. We searched and found that z-Leu-Leu-CHO and z-Phe-Ala-FMK also inhibited chlamydial growth. Neither biotin-hydrophobic dipeptide nor morpholinoureidyl-hydrophobic dipeptide shows inhibitory effects on chlamydial intracellular growth. Our results suggested the possibility of some chemical derivatives based on z-hydrophobic dipeptide group for future therapeutic usage to the chlamydial infectious 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.

Streptococcus oralis and Candida albicans Synergistically Activate μ-Calpain to Degrade E-cadherin From Oral Epithelial Junctions

Streptococcus oralis forms robust mucosal biofilms with Candida albicans that have increased pathogenic potential. In this study, using oral epithelial cultures, organotypic oral mucosal constructs, and a mouse model of oral infection, we demonstrated that S. oralis augmented C. albicans invasion through epithelial junctions. C. albicans and S. oralis decreased epithelial E-cadherin levels by synergistically increasing µ-calpain, a proteolytic enzyme that targets E-cadherin. In the mouse coinfection model this was accompanied by increased fungal kidney dissemination. Coinfection with a secreted aspartyl protease (sap) mutant sap2456 and S. oralis increased μ-calpain and triggered mucosal invasion and systemic dissemination, suggesting that fungal protease activity is not required for invasion during coinfection. We conclude that C. albicans and S. oralis synergize to activate host enzymes that cleave epithelial junction proteins and increase fungal invasion.

Drug Development Against the Major Diarrhea-Causing Parasites of the Small Intestine, Cryptosporidium and Giardia

Diarrheal diseases are among the leading causes of morbidity and mortality in the world, particularly among young children. A limited number of infectious agents account for most of these illnesses, raising the hope that advances in the treatment and prevention of these infections can have global health impact. The two most important parasitic causes of diarrheal disease are Cryptosporidium and Giardia. Both parasites infect predominantly the small intestine and colonize the lumen and epithelial surface, but do not invade deeper mucosal layers. This review discusses the therapeutic challenges, current treatment options, and drug development efforts against cryptosporidiosis and giardiasis. The goals of drug development against Cryptosporidium and Giardia are different. For Cryptosporidium, only one moderately effective drug (nitazoxanide) is available, so novel classes of more effective drugs are a high priority. Furthermore, new genetic technology to identify potential drug targets and better assays for functional evaluation of these targets throughout the parasite life cycle are needed for advancing anticryptosporidial drug design. By comparison, for Giardia, several classes of drugs with good efficacy exist, but dosing regimens are suboptimal and emerging resistance begins to threaten clinical utility. Consequently, improvements in potency and dosing, and the ability to overcome existing and prevent new forms of drug resistance are priorities in antigiardial drug development. Current work on new drugs against both infections has revealed promising strategies and new drug leads. However, the primary challenge for further drug development is the underlying economics, as both parasitic infections are considered Neglected Diseases with low funding priority and limited commercial interest. If a new urgency in medical progress against these infections can be raised at national funding agencies or philanthropic organizations, meaningful and timely progress is possible in treating and possibly preventing cryptosporidiosis and giardiasis.

Cryptosporidiuminfections: molecular advances

Cryptosporidiumhost cell interaction remains fairly obscure compared with other apicomplexans such asPlasmodiumorToxoplasma. The reason for this is probably the inability of this parasite to complete its life cyclein vitroand the lack of a system to genetically modifyCryptosporidium. However, there is a substantial set of data about the molecules involved in attachment and invasion and about the host cell pathways involved in actin arrangement that are altered by the parasite. Here we summarize the recent advances in research on host cell infection regarding the excystation process, attachment and invasion, survival in the cell, egress and the available data on omics.

Calpain-dependent cytoskeletal rearrangement exploited for anthrax toxin endocytosis

The protective antigen component of Bacillus anthracis toxins can interact with at least three distinct proteins on the host cell surface, capillary morphogenesis gene 2 (CMG2), tumor endothelial marker 8, and β1-integrin, and, with the assistance of other host proteins, enters targeted cells by receptor-mediated endocytosis. Using an antisense-based phenotypic screen, we discovered the role of calpains in this process. We show that functions of a ubiquitous Ca(2+)-dependent cysteine protease, calpain-2, and of the calpain substrate talin-1 are exploited for association of anthrax toxin and its principal receptor, CMG2, with higher-order actin filaments and consequently for toxin entry into host cells. Down-regulated expression of calpain-2 or talin-1, or pharmacological interference with calpain action, did not affect toxin binding but reduced endocytosis and increased the survival of cells exposed to anthrax lethal toxin. Adventitious expression of wild-type talin-1 promoted toxin endocytosis and lethality, whereas expression of a talin-1 mutant (L432G) that is insensitive to calpain cleavage did not. Disruption of talin-1, which links integrin-containing focal adhesion complexes to the actin cytoskeleton, facilitated association of toxin bound to its principal cell-surface receptor, CMG2, with higher-order actin filaments undergoing dynamic disassembly and reassembly during endocytosis. Our results reveal a mechanism by which a bacterial toxin uses constitutively occurring calpain-mediated cytoskeletal rearrangement for internalization.

Interaction of Cryptosporidium parvum with mouse dendritic cells leads to their activation and parasite transportation to mesenteric lymph nodes

Dendritic cells (DCs) are the antigen-presenting cells capable of activating naïve T cells. Although CD4+ T cells are crucial for Cryptosporidium parvum clearance, little is known about the role of DCs in the immune response to this parasite. In this study, the interaction between mouse DCs and C. parvum was investigated both in vitro and in vivo. For in vitro experiments, mouse bone marrow-derived dendritic cells (BMDCs) derived from wild-type C57B1/6 or MyD88-/- or C3H/HeJ mice and DC cell line DC2.4 were pulsed with C. parvum. Active invasion of parasites was demonstrated by parasite colocalization with host cell membranes and actin-plaque formation at the site of attachment. DC activation induced by the parasite invasion was demonstrated by upregulation of costimulatory molecules CD40, CD80, and CD86, as well as inflammatory cytokines IL-12, TNF-α, and IL-6. BMDCs derived from MyD88-/- and C3H/HeJ mice failed to produce IL-12 in response to C. parvum, suggesting the importance of TLR-dependent signaling pathway specially presence of a functional TLR4 pathway, for C. parvum-induced cytokine production. In vivo experiments showed that both parasite antigens and live parasites were transported to mice mesenteric lymph nodes. All together, these data suggest that DCs play a key role in host immune responses to C. parvum and pathogenesis of the disease.

Calpain activation by the Shigella flexneri effector VirA regulates key steps in the formation and life of the bacterium's epithelial niche

The enteropathogen Shigella flexneri invades epithelial cells, leading to inflammation and tissue destruction. We report that Shigella infection of epithelial cells induces an early genotoxic stress, but the resulting p53 response and cell death are impaired due to the bacterium's ability to promote p53 degradation, mainly through calpain protease activation. Calpain activation is promoted by the Shigella virulence effector VirA and dependent on calcium flux and the depletion of the endogenous calpain inhibitor calpastatin. Further, although VirA-induced calpain activity is critical for regulating cytoskeletal events driving bacterial uptake, calpain activation ultimately leads to necrotic cell death, thereby restricting Shigella intracellular growth. Therefore, calpains work at multiple steps in regulating Shigella pathogenesis by disrupting the p53-dependent DNA repair response early during infection and regulating both formation and ultimate death of the Shigella epithelial replicative niche.

Inhibition of calpain blocks the phagosomal escape of Listeria monocytogenes

Listeria monocytogenes is a gram-positive facultative intracellular bacterium responsible for the food borne infection listeriosis, affecting principally the immunocompromised, the old, neonates and pregnant women. Following invasion L. monocytogenes escapes the phagosome and replicates in the cytoplasm. Phagosome escape is central to L. monocytogenes virulence and is required for initiating innate host-defence responses such as the secretion of the cytokine interleukin-1. Phagosome escape of L. monocytogenes is reported to depend upon host proteins such as γ-interferon-inducible lysosomal thiol reductase and the cystic fibrosis transmembrane conductance regulator. The host cytosolic cysteine protease calpain is required in the life cycle of numerous pathogens, and previous research reports an activation of calpain by L. monocytogenes infection. Thus we sought to determine whether host calpain was required for the virulence of L. monocytogenes. Treatment of macrophages with calpain inhibitors blocked escape of L. monocytogenes from the phagosome and consequently its proliferation within the cytosol. This was independent of any direct effect on the production of bacterial virulence factors or of a bactericidal effect. Furthermore, the secretion of interleukin-1β, a host cytokine whose secretion induced by L. monocytogenes depends upon phagosome escape, was also blocked by calpain inhibition. These data indicate that L. monocytogenes co-opts host calpain to facilitate its escape from the phagosome, and more generally, that calpain may represent a cellular Achilles heel exploited by pathogens.