Sialic acid: a sweet swing between mammalian host and Trypanosoma cruzi

Oral infectivity through carnivorism in murine model of Trypanosoma cruzi infection

Introduction

Oral transmission of T. cruzi is probably the most frequent transmission mechanism in wild animals. This observation led to the hypothesis that consuming raw or undercooked meat from animals infected with T. cruzi may be responsible for transmitting the infection. Therefore, the general objective of this study was to investigate host-pathogen interactions between the parasite and gastric mucosa and the role of meat consumption from infected animals in the oral transmission of T. cruzi.

Methods

Cell infectivity assays were performed on AGS cells in the presence or absence of mucin, and the roles of pepsin and acidic pH were determined. Moreover, groups of five female Balb/c mice were fed with muscle tissue obtained from mice in the acute phase of infection by the clone H510 C8C3hvir of T. cruzi, and the infection of the fed mice was monitored by a parasitemia curve. Similarly, we assessed the infective capacity of T. cruzi trypomastigotes and amastigotes by infecting groups of five mice Balb/c females, which were infected orally using a nasogastric probe, and the infection was monitored by a parasitemia curve. Finally, different trypomastigote and amastigote inoculums were used to determine their infective capacities. Adhesion assays of T. cruzi proteins to AGS stomach cells were performed, and the adhered proteins were detected by western blotting using monoclonal or polyclonal antibodies and by LC-MS/MS and bioinformatics analysis.

Results

Trypomastigote migration in the presence of mucin was reduced by approximately 30%, whereas in the presence of mucin and pepsin at pH 3.5, only a small proportion of parasites were able to migrate (∼6%). Similarly, the ability of TCTs to infect AGS cells in the presence of mucin is reduced by approximately 20%. In all cases, 60-100% of the animals were fed meat from mice infected in the acute phase or infected with trypomastigotes or amastigotes developed high parasitemia, and 80% died around day 40 post-infection. The adhesion assay showed that cruzipain is a molecule of trypomastigotes and amastigotes that binds to AGS cells. LC-MS/MS and bioinformatics analysis, also confirmed that transialidase, cysteine proteinases, and gp63 may be involved in TCTs attachment or invasion of human stomach cells because they can potentially interact with different proteins in the human stomach mucosa. In addition, several human gastric mucins have cysteine protease cleavage sites.

Discussion

Then, under our experimental conditions, consuming meat from infected animals in the acute phase allows the T. cruzi infection. Similarly, trypomastigotes and amastigotes could infect mice when administered orally, whereas cysteinyl proteinases and trans-sialidase appear to be relevant molecules in this infective process.

Sialic acid as the potential link between lipid metabolism and inflammation in the pathogenesis of atherosclerosis

In the modern world, cardiovascular diseases have a special place among the most common causes of death. Naturally, this widespread problem cannot escape the attention of scientists and researchers. One of the main conditions preceding the development of fatal cardiovascular diseases is atherosclerosis. Despite extensive research into its pathogenesis and possible prevention and treatment strategies, many gaps remain in our understanding of this disease. For example, the concept of multiple low-density lipoprotein modifications was recently stated, in which desialylation is of special importance. Apart from this, sialic acids are known to be important contributors to processes such as endothelial dysfunction and inflammation, which in turn are major components of atherogenesis. In this review, we have collected information on sialic acid metabolism, analyzed various aspects of its implication in atherosclerosis at different stages, and provided an overview of the role of particular groups of enzymes responsible for sialic acid metabolism in the context of atherosclerosis.

Changes in lung sialidases in male and female mice after bleomycin aspiration

Aim of the study: Sialidases, also called neuraminidases, are enzymes that cleave terminal sialic acids from glycoconjugates. In humans and mice, lung fibrosis is associated with desialylation of glycoconjugates and upregulation of sialidases. There are four mammalian sialidases, and it is unclear when the four mammalian sialidases are elevated over the course of inflammatory and fibrotic responses, whether tissue resident and inflammatory cells express different sialidases, and if sialidases are differentially expressed in male and females. Materials and Methods: To determine the time course of sialidase expression and the identity of sialidase expressing cells, we used the bleomycin model of pulmonary fibrosis in mice to examine levels of sialidases during inflammation (days 3 - 10) and fibrosis (days 10 - 21). Results: Bleomycin aspiration increased sialidase NEU1 at days 14 and 21 in male mice and day 10 in female mice. NEU2 levels increased at day 7 in male and day 10 in female mice. NEU3 appears to have a biphasic response in male mice with increased levels at day 7 and then at days 14 and 21, whereas in female mice NEU3 levels increased over 21 days. In control mice, the sialidases were mainly expressed by EpCAM positive epithelial cells, but after bleomycin, epithelial cells, CD45 positive immune cells, and alveolar cells expressed NEU1, NEU2, and NEU3. Sialidase expression was higher in male compared to female mice. There was little expression of NEU4 in murine lung tissue. Conclusions: These results suggest that sialidases are dynamically expressed following bleomycin, that sialidases are differentially expressed in male and females, and that of the four sialidases only NEU3 upregulation is associated with fibrosis in both male and female mice.

The sialidase NEU3 promotes pulmonary fibrosis in mice

BACKGROUND

Sialic acid is often the distal sugar on glycoconjugates, and sialidases are enzymes that remove this sugar. In fibrotic lesions in human and mouse lungs, there is extensive desialylation of glycoconjugates, and upregulation of sialidases including the extracellular sialidase NEU3. In the bleomycin model of pulmonary fibrosis, mice lacking NEU3 (Neu3^-/-) showed strongly attenuated bleomycin-induced weight loss, lung damage, inflammation, and fibrosis. This indicates that NEU3 is necessary for the full spectrum of bleomycin-induced pulmonary fibrosis.

METHODS

To determine if NEU3 is sufficient to induce pulmonary fibrosis, recombinant murine NEU3 and a mutated inactive recombinant murine NEU3 protein were produced. Mice were given recombinant NEU3 proteins by oropharyngeal aspiration, either alone or 10 days after bleomycin challenge. Over the course of 21 days, mice were assessed for weight change, and after euthanasia, bronchoalveolar lavage fluid cells and lung tissue were assessed for inflammation and fibrosis.

RESULTS

Aspiration of recombinant murine NEU3 caused inflammation and fibrosis in the lungs, while inactive NEU3 caused inflammation but not fibrosis. Mice were also treated with recombinant murine NEU3 starting 10 days after bleomycin. In male but not female mice, recombinant murine NEU3 increased inflammation and fibrosis. Inactive NEU3 did not enhance bleomycin-induced lung fibrosis.

CONCLUSION

These results suggest that NEU3 is sufficient to induce fibrosis in the lungs, that aspiration of NEU3 has a greater effect on male mice, and that this effect is mediated by NEU3's enzymic activity.

The thermal proteome stability profile of Trypanosoma cruzi in epimastigote and trypomastigote life stages

Trypanosoma cruzi is a flagellate protozoa being the etiological agent of Chagas disease, a neglected tropical disease, which still poses a public health problem worldwide. The intricate molecular changes during T. cruzi-host interaction have been explored using different largescale omics techniques. However, protein stability is largely unknown. Thermal proteome profiling (TPP) methodology has the potential to characterize proteome-wide stability highlighting key proteins during T. cruzi infection and life stage transition from the invertebrate to the mammalian host. In the present work, T. cruzi epimastigotes and trypomastigotes cell lysates were subjected to TPP workflow and analyzed by quantitative large-scale mass spectrometry-based proteomics to fit a melting profile for each protein. A total of 2884 proteins were identified and associated to 1741 melting curves being 1370 in trypomastigotes (Tm_AVG 53.53 °C) and 1279 in epimastigotes (Tm_AVG 50.89 °C). A total of 453 proteins were identified with statistically different melting profiles between the two life stages. Proteins associated to pathogenesis and intracellular transport had regulated melting temperatures. Membrane and glycosylated proteins had a higher average Tm in trypomastigotes compared to epimastigotes. This study represents the first large-scale comparison of parasite protein stability between life stages. SIGNIFICANCE: Trypanosoma cruzi, a unicellular flagellate parasite, is the etiological agent of Chagas disease, endemic in South America and affecting more that 7 million people worldwide. There is an intense research to identify novel chemotherapeutic and diagnostic targets of Chagas disease. Proteomic approaches have helped in elucidating the quantitative proteome and PTMs changes of T. cruzi during life cycle transition and upon different biotic and abiotic stimuli. However, a comprehensive knowledge of the protein-protein interaction and protein conformation is still missing. In order to fill this gap, this manuscript elucidates the T. cruzi Y strain proteome-wide thermal stability map in the epimastigote and trypomastigote life stages. Comparison between life stages showed a higher average melting temperature stability for trypomastigotes than epimastigotes indicating a host temperature adaptation. Both presented a selective thermal stability shift for cellular compartments, molecular functions and biological processes based on the T. cruzi life stage. Membrane and glycosylated proteins presented a higher thermal stability in trypomastigotes when compared to the epimastigotes.

Sialic Acids as Receptors for Pathogens

Carbohydrates have long been known to mediate intracellular interactions, whether within one organism or between different organisms. Sialic acids (Sias) are carbohydrates that usually occupy the terminal positions in longer carbohydrate chains, which makes them common recognition targets mediating these interactions. In this review, we summarize the knowledge about animal disease-causing agents such as viruses, bacteria and protozoa (including the malaria parasite Plasmodium falciparum) in which Sias play a role in infection biology. While Sias may promote binding of, e.g., influenza viruses and SV40, they act as decoys for betacoronaviruses. The presence of two common forms of Sias, Neu5Ac and Neu5Gc, is species-specific, and in humans, the enzyme converting Neu5Ac to Neu5Gc (CMAH, CMP-Neu5Ac hydroxylase) is lost, most likely due to adaptation to pathogen regimes; we discuss the research about the influence of malaria on this trait. In addition, we present data suggesting the CMAH gene was probably present in the ancestor of animals, shedding light on its glycobiology. We predict that a better understanding of the role of Sias in disease vectors would lead to more effective clinical interventions.

The Role of Sialic Acids in the Establishment of Infections by Pathogens, With Special Focus on Leishmania

Carbohydrates or glycans are ubiquitous components of the cell surface which play crucial biological and structural roles. Sialic acids (Sias) are nine-carbon atoms sugars usually present as terminal residues of glycoproteins and glycolipids on the cell surface or secreted. They have important roles in cellular communication and also in infection and survival of pathogens. More than 20 pathogens can synthesize or capture Sias from their hosts and incorporate them into their own glycoconjugates and derivatives. Sialylation of pathogens’ glycoconjugates may be crucial for survival inside the host for numerous reasons. The role of Sias in protozoa such as Trypanosoma and Leishmania was demonstrated in previous studies. This review highlights the importance of Sias in several pathogenic infections, focusing on Leishmania. We describe in detail the contributions of Sias, Siglecs (sialic acid binding Ig-like lectins) and Neuraminidase 1 (NEU 1) in the course of Leishmania infection. A detailed view on the structural and functional diversity of Leishmania-related Sias and host-cell receptors will be provided, as well as the results of functional studies performed with different Leishmania species.

Utilization of Galectins by Pathogens for Infection

Galectins are glycan-binding proteins which are expressed by many different cell types and secreted extracellularly. These molecules are well-known regulators of immune responses and involved in a broad range of cellular and pathophysiological functions. During infections, host galectins can either avoid or facilitate infections by interacting with host cells- and/or pathogen-derived glycoconjugates and less commonly, with proteins. Some pathogens also express self-produced galectins to interfere with host immune responses. This review summarizes pathogens which take advantage of host- or pathogen-produced galectins to establish the infection.

Alpha-Gal and Cross-Reactive Carbohydrate Determinants in the N-Glycans of Salivary Glands in the Lone Star Tick, Amblyomma americanum

Ticks are important ectoparasites and vectors of numerous human and animal pathogens. Ticks secrete saliva that contains various bioactive materials to evade the host defense system, and often facilitates the pathogen transmission. In addition, the Lone star tick saliva is thought to be the sensitizer in red meat allergy that is characterized by an allergic reaction to glycan moieties carrying terminal galactose-alpha-1,3-galactose (aGal). To assess N-glycome of Amblyomma americanum, we examined the N-glycan structures in male and female salivary glands at three different feeding stages and in carcasses of partially fed lone star ticks. We also surveyed the genes involved in the N-glycosylation in the tick species. The aGal epitopes and cross-reactive carbohydrate determinants (CCD) increases over time after the onset of blood feeding in both male and female A. americanum. These CCDs include xylosylation of the core mannose, 1,3-mono and 1,3- and 1,6-difucosylations of the basal GlcNac and mono- or diantennary aGal. Combinations of both xylosylation and aGal and fucosylation and aGal were also found on the N-glycan structures. While the enzymes required for the early steps of the N-glycosylation pathway are quite conserved, the enzymes involved in the later stages of N-glycan maturation in the Golgi apparatus are highly diverged from those of insects. Most of all, we propose that the aGal serves as a molecular mimicry of bioactive proteins during tick feedings on mammalian hosts, while it contributes as a sensitizer of allergy in atypical host human.

Exoproteome profiling of Trypanosoma cruzi during amastigogenesis early stages

Chagas disease is caused by the protozoan Trypanosoma cruzi, affecting around 8 million people worldwide. After host cell invasion, the infective trypomastigote form remains 2–4 hours inside acidic phagolysosomes to differentiate into replicative amastigote form. In vitro acidic-pH-induced axenic amastigogenesis was used here to study this step of the parasite life cycle. After three hours of trypomastigote incubation in amastigogenesis promoting acidic medium (pH 5.0) or control physiological pH (7.4) medium samples were subjected to three rounds of centrifugation followed by ultrafiltration of the supernatants. The resulting exoproteome samples were trypsin digested and analysed by nano flow liquid chromatography coupled to tandem mass spectrometry. Computational protein identification searches yielded 271 and 483 protein groups in the exoproteome at pH 7.4 and pH 5.0, respectively, with 180 common proteins between both conditions. The total amount and diversity of proteins released by parasites almost doubled upon acidic incubation compared to control. Overall, 76.5% of proteins were predicted to be secreted by classical or non-classical pathways and 35.1% of these proteins have predicted transmembrane domains. Classical secretory pathway analysis showed an increased number of mucins and mucin-associated surface proteins after acidic incubation. However, the number of released trans-sialidases and surface GP63 peptidases was higher at pH 7.4. Trans-sialidases and mucins are anchored to the membrane and exhibit an enzyme-substrate relationship. In general, mucins are glycoproteins with immunomodulatory functions in Chagas disease, present mainly in the epimastigote and trypomastigote surfaces and could be enzymatically cleaved and released in the phagolysosome during amastigogenesis. Moreover, evidence for flagella discard during amastigogenesis are addressed. This study provides the first comparative analysis of the exoproteome during amastigogenesis, and the presented data evidence the dynamism of its profile in response to acidic pH-induced differentiation.

Theft and Reception of Host Cell's Sialic Acid: Dynamics of Trypanosoma Cruzi Trans-sialidases and Mucin-Like Molecules on Chagas' Disease Immunomodulation

The last decades have produced a plethora of evidence on the role of glycans, from cell adhesion to signaling pathways. Much of that information pertains to their role on the immune system and their importance on the surface of many human pathogens. A clear example of this is the flagellated protozoan Trypanosoma cruzi, which displays on its surface a great variety of glycoconjugates, including O-glycosylated mucin-like glycoproteins, as well as multiple glycan-binding proteins belonging to the trans-sialidase (TS) family. Among the latter, different and concurrently expressed molecules may present or not TS activity, and are accordingly known as active (aTS) and inactive (iTS) members. Over the last thirty years, it has been well described that T. cruzi is unable to synthesize sialic acid (SIA) on its own, making use of aTS to steal the host's SIA. Although iTS did not show enzymatic activity, it retains a substrate specificity similar to aTS (α-2,3 SIA-containing glycotopes), displaying lectinic properties. It is accepted that aTS members act as virulence factors in mammals coursing the acute phase of the T. cruzi infection. However, recent findings have demonstrated that iTS may also play a pathogenic role during T. cruzi infection, since it modulates events related to adhesion and invasion of the parasite into the host cells. Since both aTS and iTS proteins share structural substrate specificity, it might be plausible to speculate that iTS proteins are able to assuage and/or attenuate biological phenomena depending on the catalytic activity displayed by aTS members. Since SIA-containing glycotopes modulate the host immune system, it should not come as any surprise that changes in the sialylation of parasite's mucin-like molecules, as well as host cell glycoconjugates might disrupt critical physiological events, such as the building of effective immune responses. This review aims to discuss the importance of mucin-like glycoproteins and both aTS and iTS for T. cruzi biology, as well as to present a snapshot of how disturbances in both parasite and host cell sialoglycophenotypes may facilitate the persistence of T. cruzi in the infected mammalian host.

Gene and Chromosomal Copy Number Variations as an Adaptive Mechanism Towards a Parasitic Lifestyle in Trypanosomatids

Trypanosomatids are a group of kinetoplastid parasites including some of great public health importance, causing debilitating and life-long lasting diseases that affect more than 24 million people worldwide. Among the trypanosomatids, Trypanosoma cruzi, Trypanosoma brucei and species from the Leishmania genus are the most well studied parasites, due to their high prevalence in human infections. These parasites have an extreme genomic and phenotypic variability, with a massive expansion in the copy number of species-specific multigene families enrolled in host-parasite interactions that mediate cellular invasion and immune evasion processes. As most trypanosomatids are heteroxenous, and therefore their lifecycles involve the transition between different hosts, these parasites have developed several strategies to ensure a rapid adaptation to changing environments. Among these strategies, a rapid shift in the repertoire of expressed genes, genetic variability and genome plasticity are key mechanisms. Trypanosomatid genomes are organized into large directional gene clusters that are transcribed polycistronically, where genes derived from the same polycistron may have very distinct mRNA levels. This particular mode of transcription implies that the control of gene expression operates mainly at post-transcriptional level. In this sense, gene duplications/losses were already associated with changes in mRNA levels in these parasites. Gene duplications also allow the generation of sequence variability, as the newly formed copy can diverge without loss of function of the original copy. Recently, aneuploidies have been shown to occur in several Leishmania species and T. cruzi strains. Although aneuploidies are usually associated with debilitating phenotypes in superior eukaryotes, recent data shows that it could also provide increased fitness in stress conditions and generate drug resistance in unicellular eukaryotes. In this review, we will focus on gene and chromosomal copy number variations and their relevance to the evolution of trypanosomatid parasites.

Sialidase inhibitors attenuate pulmonary fibrosis in a mouse model

Fibrosis involves increasing amounts of scar tissue appearing in a tissue, but what drives this is unclear. In fibrotic lesions in human and mouse lungs, we found extensive desialylation of glycoconjugates, and upregulation of sialidases. The fibrosis-associated cytokine TGF-β1 upregulates sialidases in human airway epithelium cells, lung fibroblasts, and immune system cells. Conversely, addition of sialidases to human peripheral blood mononuclear cells induces accumulation of extracellular TGF-β1, forming what appears to be a sialidase - TGF-β1 - sialidase positive feedback loop. Monocyte-derived cells called fibrocytes also activate fibroblasts, and we found that sialidases potentiate fibrocyte differentiation. A sialylated glycoprotein called serum amyloid P (SAP) inhibits fibrocyte differentiation, and sialidases attenuate SAP function. Injections of the sialidase inhibitors DANA and oseltamivir (Tamiflu) starting either 1 day or 10 days after bleomycin strongly attenuate pulmonary fibrosis in the mouse bleomycin model, and by breaking the feedback loop, cause a downregulation of sialidase and TGF-β1 accumulation. Together, these results suggest that a positive feedback loop involving sialidases potentiates fibrosis, and suggest that sialidase inhibitors could be useful for the treatment of fibrosis.

Trypanosoma cruzi reservoir-triatomine vector co-occurrence networks reveal meta-community effects by synanthropic mammals on geographic dispersal

Contemporary patterns of land use and global climate change are modifying regional pools of parasite host species. The impact of host community changes on human disease risk, however, is difficult to assess due to a lack of information about zoonotic parasite host assemblages. We have used a recently developed method to infer parasite-host interactions for Chagas Disease (CD) from vector-host co-occurrence networks. Vector-host networks were constructed to analyze topological characteristics of the network and ecological traits of species’ nodes, which could provide information regarding parasite regional dispersal in Mexico. Twenty-eight triatomine species (vectors) and 396 mammal species (potential hosts) were included using a data-mining approach to develop models to infer most-likely interactions. The final network contained 1,576 links which were analyzed to calculate centrality, connectivity, and modularity. The model predicted links of independently registered Trypanosoma cruzi hosts, which correlated with the degree of parasite-vector co-occurrence. Wiring patterns differed according to node location, while edge density was greater in Neotropical as compared to Nearctic regions. Vectors with greatest public health importance (i.e., Triatoma dimidiata, T. barberi, T. pallidipennis, T. longipennis, etc), did not have stronger links with particular host species, although they had a greater frequency of significant links. In contrast, hosts classified as important based on network properties were synanthropic mammals. The latter were the most common parasite hosts and are likely bridge species between these communities, thereby integrating meta-community scenarios beneficial for long-range parasite dispersal. This was particularly true for rodents, >50% of species are synanthropic and more than 20% have been identified as T. cruzi hosts. In addition to predicting potential host species using the co-occurrence networks, they reveal regions with greater expected parasite mobility. The Neotropical region, which includes the Mexican south and southeast, and the Transvolcanic belt, had greatest potential active T. cruzi dispersal, as well as greatest edge density. This information could be directly applied for stratification of transmission risk and to design and analyze human-infected vector contact intervention efficacy.

Modulation of Cell Sialoglycophenotype: A Stylish Mechanism Adopted by Trypanosoma cruzi to Ensure Its Persistence in the Infected Host

Trypanosoma cruzi, the etiological agent of Chagas disease exhibits multiple mechanisms to guarantee its establishment and persistence in the infected host. It has been well demonstrated that T. cruzi is not able to synthesize sialic acids (Sia). To acquire the monosaccharide, the parasite makes use of a multifunctional enzyme called trans-sialidase (Tc-TS). Since this enzyme has no analogous in the vertebrate host, it has been used as a target in drug therapy development. Tc-TS preferentially catalyzes the transfer of Sia from the host glycoconjugates to the terminal β-galactopyranosyl residues of mucin-like molecules present on the parasite's cell surface. Alternatively, the enzyme can sialylate/re-sialylate glycoconjugates expressed on the surface of host cells. Since its discovery, several studies have shown that T. cruzi employs the Tc-TS activity to modulate the host cell sialoglycophenotype, thus favoring its perpetuation in the infected vertebrate. In this review, we summarize the dynamic of host/parasite sialoglycophenotype modulation, highlighting its role in the subversion of host immune response in order to promote the establishment of persistent chronic infection.

Role of Small RNAs in Trypanosomatid Infections

Trypanosomatid parasites survive and replicate in the host by using mechanisms that aim to establish a successful infection and ensure parasite survival. Evidence points to microRNAs as new players in the host-parasite interplay. MicroRNAs are small non-coding RNAs that control proteins levels via post-transcriptional gene down-regulation, either within the cells where they were produced or in other cells via intercellular transfer. These microRNAs can be modulated in host cells during infection and are among the growing group of small regulatory RNAs, for which many classes have been described, including the transfer RNA-derived small RNAs. Parasites can either manipulate microRNAs to evade host-driven damage and/or transfer small RNAs to host cells. In this mini-review, we present evidence for the involvement of small RNAs, such as microRNAs, in trypanosomatid infections which lack RNA interference. We highlight both microRNA profile alterations in host cells during those infections and the horizontal transfer of small RNAs and proteins from parasites to the host by membrane-derived extracellular vesicles in a cell communication mechanism.

Click chemistry oligomerisation of azido-alkyne-functionalised galactose accesses triazole-linked linear oligomers and macrocycles that inhibit Trypanosoma cruzi macrophage invasion

Reaction of 2-(2-(2-azidoethoxy)ethoxy)ethyl 6-O-(prop-2-ynyl)-β-d-galactopyranoside (7) under CuAAC conditions gives rise to mixed cyclic and linear triazole-linked oligomers, with individual compounds up to d.p. 5 isolable, along with mixed larger oligomers. The linear compounds resolve en bloc from the cyclic materials by RP HPLC, but are separable by gel permeation chromatography. The triazole-linked oligomers—pseudo-galactooligomers—were demonstrated to be acceptor substrates for the multi-copy cell surface trans-sialidase of the human parasite Trypanosoma cruzi. In addition, these multivalent TcTS ligands were able to block macrophage invasion by T. cruzi.

Extracellular vesicles in parasitic diseases

Parasitic diseases affect billions of people and are considered a major public health issue. Close to 400 species are estimated to parasitize humans, of which around 90 are responsible for great clinical burden and mortality rates. Unfortunately, they are largely neglected as they are mainly endemic to poor regions. Of relevance to this review, there is accumulating evidence of the release of extracellular vesicles (EVs) in parasitic diseases, acting both in parasite–parasite inter-communication as well as in parasite–host interactions. EVs participate in the dissemination of the pathogen and play a role in the regulation of the host immune systems. Production of EVs from parasites or parasitized cells has been described for a number of parasitic infections. In this review, we provide the most relevant findings of the involvement of EVs in intercellular communication, modulation of immune responses, involvement in pathology, and their potential as new diagnostic tools and therapeutic agents in some of the major human parasitic pathogens.

Signalling versatility following self and non-self sensing by myeloid C-type lectin receptors

Among myeloid immune receptors, C-type lectin receptors (CLRs) have a remarkable capacity to sense a variety of self and non-self ligands. The coupling of CLRs to different signal transduction modules is influenced not only by the receptor, but also by the nature, density and architecture of the ligand, which can affect the rate of receptor internalization and trafficking to diverse intracellular compartments. Understanding how the variety of self and non-self ligands triggers differential CLR signalling and function presents a fascinating biological challenge. Non-self ligands usually promote inflammation and immunity, whereas self ligands are frequently involved in communication and tolerance. But pathogens can mimic self-inhibitory signals to escape immune surveillance, and endogenous ligands can contribute to the sensing of pathogens through CLRs. In this review, we survey the complexity and flexibility in functional outcome found in the myeloid CLRs, which is not only based on their differing intracellular motifs, but is also conditioned by the physical nature, affinity and avidity of the ligand.

Bacterial periplasmic sialic acid-binding proteins exhibit a conserved binding site

Sialic acids are a family of related nine-carbon sugar acids that play important roles in both eukaryotes and prokaryotes. These sialic acids are incorporated/decorated onto lipooligosaccharides as terminal sugars in multiple bacteria to evade the host immune system. Many pathogenic bacteria scavenge sialic acids from their host and use them for molecular mimicry. The first step of this process is the transport of sialic acid to the cytoplasm, which often takes place using a tripartite ATP-independent transport system consisting of a periplasmic binding protein and a membrane transporter. In this paper, the structural characterization of periplasmic binding proteins from the pathogenic bacteria Fusobacterium nucleatum, Pasteurella multocida and Vibrio cholerae and their thermodynamic characterization are reported. The binding affinities of several mutations in the Neu5Ac binding site of the Haemophilus influenzae protein are also reported. The structure and the thermodynamics of the binding of sugars suggest that all of these proteins have a very well conserved binding pocket and similar binding affinities. A significant conformational change occurs when these proteins bind the sugar. While the C1 carboxylate has been identified as the primary binding site, a second conserved hydrogen-bonding network is involved in the initiation and stabilization of the conformational states.

Sweet and sour: the impact of differential glycosylation in cancer cells undergoing epithelial-mesenchymal transition

Glycosylation changes are a feature of disease states. One clear example is cancer cells, which commonly express glycans at atypical levels or with different structural attributes than those found in normal cells. Epithelial–mesenchymal transition (EMT) was initially recognized as an important step for morphogenesis during embryonic development, and is now shown to be one of the key steps promoting tumor metastasis. Cancer cells undergoing EMT are characterized by significant changes in glycosylation of the extracellular matrix (ECM) components and cell-surface glycoconjugates. Current scientific methodology enables all hallmarks of EMT to be monitored in vitro and this experimental model has been extensively used in oncology research during the last 10 years. Several studies have shown that cell-surface carbohydrates attached to proteins through the amino acids, serine, or threonine (O-glycans), are involved in tumor progression and metastasis, however, the impact of O-glycans on EMT is poorly understood. Recent studies have demonstrated that transforming growth factor-beta (TGF-β), a known EMT inducer, has the ability to promote the up-regulation of a site-specific O-glycosylation in the IIICS domain of human oncofetal fibronectin, a major ECM component expressed by cancer cells and embryonic tissues. Armed with the knowledge that cell-surface glycoconjugates play a major role in the maintenance of cell homeostasis and that EMT is closely associated with glycosylation changes, we may benefit from understanding how unusual glycans can govern the molecular pathways associated with cancer progression. This review initially focuses on some well-known changes found in O-glycans expressed by cancer cells, and then discusses how these alterations may modulate the EMT process.

Emerging principles for the therapeutic exploitation of glycosylation

Glycosylation plays a key role in a wide range of biological processes. Specific modification to a glycan's structure can directly modulate its biological function. Glycans are not only essential to glycoprotein folding, cellular homeostasis, and immune regulation but are involved in multiple disease conditions. An increased molecular and structural understanding of the mechanistic role that glycans play in these pathological processes has driven the development of therapeutics and illuminated novel targets for drug design. This knowledge has enabled the treatment of metabolic disorders and the development of antivirals and shaped cancer and viral vaccine strategies. Furthermore, an understanding of glycosylation has led to the development of specific drug glycoforms, for example, monoclonal antibodies, with enhanced potency.

Dendritic cells: a spot on sialic Acid

Glycans decorating cell surface and secreted proteins and lipids occupy the juncture where critical host–host and host-pathogen interactions occur. The role of glycan epitopes in cell–cell and cell-pathogen adhesive events is already well-established, and cell surface glycan structures change rapidly in response to stimulus and inflammatory cues. Despite the wide acceptance that glycans are centrally implicated in immunity, exactly how glycans and their changes contribute to the overall immune response remains poorly defined. Sialic acids are unique sugars that usually occupy the terminal position of the glycan chains and may be modified by external factors, such as pathogens, or upon specific physiological cellular events. At cell surface, sialic acid-modified structures form the key fundamental determinants for a number of receptors with known involvement in cellular adhesiveness and cell trafficking, such as the Selectins and the Siglec families of carbohydrate recognizing receptors. Dendritic cells (DCs) preside over the transition from innate to the adaptive immune repertoires, and no other cell has such relevant role in antigen screening, uptake, and its presentation to lymphocytes, ultimately triggering the adaptive immune response. Interestingly, sialic acid-modified structures are involved in all DC functions, such as antigen uptake, DC migration, and capacity to prime T cell responses. Sialic acid content changes along DC differentiation and activation and, while, not yet fully understood, these changes have important implications in DC functions. This review focuses on the developmental regulation of DC surface sialic acids and how manipulation of DC surface sialic acids can affect immune-critical DC functions by altering antigen endocytosis, pathogen and tumor cell recognition, cell recruitment, and capacity for T cell priming. The existing evidence points to a potential of DC surface sialylation as a therapeutic target to improve and diversify DC-based therapies.

Design of e-pharmacophore models using compound fragments for the trans-sialidase of Trypanosoma cruzi: screening for novel inhibitor scaffolds

Chagas' is a fatal disease that affects millions of people worldwide. The lack of safe and effective treatments for Chagas' highlights the need for the discovery of new drugs to fight the disease. Trypanosoma cruzi, the parasitic cause of Chagas' disease, synthesizes a trans-sialidase (TcTS) enzyme responsible for the transfer of sialic acids from the host cell surface to glycoconjugates on the parasitic cell surface. TcTS has no human analogs and is vital to the life cycle of T. cruzi, making TcTS an important enzyme for drug design against Chagas' disease. We use fragment docking to generate various e-pharmacophore hypotheses depicting protein residues important for ligand binding. Virtual screening of the ZINC Clean Leads database with more than 4 million compounds using the e-pharmacophore models found 82 potential inhibitors of TcTS. Molecular dynamics and free energy of binding calculations were used to rank the compounds based on their affinity for TcTS. Two compounds-ZINC13359679 and ZINC02576132-were found to be the most promising lead candidates for TcTS inhibition, and their binding modes are analyzed in detail.